JPH042408B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to polytetrafluoroethylene polymer molded articles. More specifically, the present invention provides an ultra-high molecular weight polytetrafluoroethylene system having characteristic values for specific gravity, orientation release stress, contraction start temperature, average maximum expansion ratio, and maximum contraction ratio in the direction of minimum maximum contraction. Regarding polymer molded products. The molded article of the present invention has excellent creep resistance and gas barrier properties, as well as excellent dimensional stability and impact resistance. Therefore, the molded products of the present invention can be used as sealing materials such as gaskets and packings, lining materials, supporting plates for heavy objects such as factory frames, sliding members such as sliding pads, shaft sleeves, bearings, piston rings, etc. suitable. In particular, the molded product of the present invention is suitable for packing such as automobile parts that require dimensional stability and impact resistance at high temperatures.
Suitable for gaskets and bearings. [Prior Art] Due to its outstanding properties, polytetrafluoroethylene is currently one of the important industrial materials. In particular, polytetrafluoroethylene is used in the field of sealing materials and lining materials for gaskets, packings, etc. due to its chemical resistance, heat resistance, cold resistance, low friction, non-contamination, non-adhesiveness, electrical insulation, etc. Due to its excellent properties, it is widely used as molded products of various shapes. The melt viscosity of ordinary thermoplastic resins such as polystyrene, polyethylene, polyamide, and acrylic resins at the molding temperature is approximately 10 ³ to 10 ⁴ poise.
Polytetrafluoroethylene has a high viscosity of approximately 10 ^{to 11} poise even at 380°C, which is above its melting point (327°C).
It is difficult to mold using the above-mentioned normal thermoplastic resin molding methods such as melt extrusion and injection molding. Therefore, polytetrafluoroethylene molded products are generally produced using a unique method (compression molding method, ram extrusion method, (paste extrusion method, etc.). Details of these methods are given, for example, in "Fluororesin", pages 53-54, published by Nikkan Kogyo Shimbunsha (April 1976). The polytetrafluoroethylene molded product formed by the above method can be further processed into a molded product with a more complex shape by cutting, cutting out the cut product, punching, stretching (roll rolling method, tension stretching method), etc. can do. The heat resistance temperature of polytetrafluoroethylene is generally 260°C under no load, but when used as a sealing material for gaskets, etc., it is required to have compression resistance and mechanical strength to withstand the load, and the structure and The maximum usable temperature varies depending on the shape and application.
It is much lower than 260℃. This is due to the fact that polytetrafluoroethylene has the property of being prone to creep under load, particularly at high temperatures. Conventionally, in the field of corrosion-resistant gasket materials, the following two measures have been mainly taken to deal with the creep characteristics of polytetrafluoroethylene. One is gas fiber, graphite,
This is the addition of fillers such as carbon fiber and zirconium oxide, and the other is the structural combination of less creeping materials such as jacket-type or spiral-wound gaskets with polytetrafluoroethylene or filled polytetrafluoroethylene. It is. However, filled polytetrafluoroethylene also has insufficient compression creep resistance at high temperatures and, depending on the type of filler, has reduced chemical resistance. Jacket-type gaskets and spiral-wound gaskets have problems such as chemical resistance, the need for high tightening pressure, and the inability to manufacture special shapes. As mentioned above, polytetrafluoroethylene gaskets are important as corrosion-resistant gasket materials.
It is strongly desired to improve the compression creep resistance of polytetrafluoroethylene. In addition, when corrosion resistance is required for sealing materials other than gaskets, such as valve seals (ball valve seats, gate valve seats, etc.) and other dynamic sealing materials (grand packing, U packing, V packing, etc.) Polytetrafluoroethylene is used for this purpose, but it is also desired to improve its compression creep resistance. A uniaxially oriented long sheet made by stretching polytetrafluoroethylene using a roll rolling method also has improved compression creep resistance;
Because only uniaxial orientation is possible in the stretching process, 100
When compressive force is applied in a high temperature region of .degree. C. or higher, the material contracts in the direction of the orientation axis in a plane perpendicular to the compressive force and expands in the direction perpendicular thereto, resulting in a substantial dimensional change. In addition, a tensile stretching method that does not involve rolling results in porous polytetrafluoroethylene, and the molded product that is the object of the present invention cannot be obtained. The following proposal has recently been made as a means to overcome the above-mentioned drawbacks of polytetrafluoroethylene molded articles.
The proposal can be found in US Pat. No. 4,388,259 and USSR Pat. No. 4,057,32. In particular, the method disclosed in the above US patent for improving the creep resistance properties of gaskets made of polytetrafluoroethylene includes the steps of (1) heating a polytetrafluoroethylene sheet of a predetermined thickness to a temperature at which the polymer enters a gel state; The method includes the steps of 2) compressing the heated sheet until it has a thickness equal to or less than the above thickness, (3) cooling the sheet in the compressed state, and (4) cutting it into a gasket shape. However, this method still does not provide sufficient improvement in creep resistance. Among the two embodiments shown in the above-mentioned Soviet patent, Embodiment 2 includes a polytetrafluoroethylene preform.
It has been described that an annular packing can be formed by compressing it by 1.2 times or more, but with the method described in this example, it is possible to compress it by at most 2 times, and it is possible to mold highly oriented polytetrafluoroethylene. It is difficult to mold the product. Furthermore, Example 1 shows that polytetrafluoroethylene is oriented by roll rolling, but roll rolling is a method used for forming a uniaxially stretched elongated sheet as described above, and It is necessary to carry out roll rolling with a tensile force applied to the material, cool it, and then release the tensile force, and it is difficult to achieve a high degree of orientation in more than two axes. In any case, even with the method disclosed in the above-mentioned Soviet patent, the desired improvement in creep resistance cannot be achieved. On the other hand, although polytetrafluoroethylene is important as a corrosion-resistant lining material, it is prone to blister phenomenon, which may cause problems in its reliability as a corrosion-resistant lining material. The blister phenomenon is a phenomenon especially seen in gas-phase fluid piping.
Improvement in blister resistance is desired. Blister resistance is closely related to the gas barrier properties of the molded product, and generally, as gas barrier properties improve, blister resistance tends to improve, and conversely, as gas barrier properties decrease, blister resistance tends to worsen. It is in. Furthermore, when polytetrafluoroethylene is used as a gasket material or lining material, unexpected damage or mechanical action from the outside, such as impact, may cause cracking or breakage, so improvement in impact resistance is desired. [Problems to be solved by the present invention] The problems to be solved by the present invention are firstly to improve the creep resistance of polytetrafluoroethylene polymer molded articles, and to improve the compression resistance (especially The object of the present invention is to provide polytetrafluoroethylene polymer molded products such as sealing materials suitable for use in situations where high compression creep resistance and mechanical strength are required. Second, the gas barrier properties of polytetrafluoroethylene polymer molded articles are improved, and as a result, the blister resistance is improved, making polytetrafluoroethylene polymers suitable as highly reliable lining materials. Our goal is to provide molded products. The third object is to provide a polytetrafluoroethylene polymer molded article having excellent dimensional stability. A fourth object is to provide a polytetrafluoroethylene polymer molded article having excellent impact resistance. [Means and effects for solving the problems] The present inventors have worked diligently to develop polytetrafluoroethylene polymer molded products with excellent creep resistance, gas barrier properties, dimensional stability, and impact resistance. After much consideration. As a result, it was found that polytetrafluoroethylene polymer molded products with excellent creep resistance, gas barrier properties, etc. can be obtained by compression molding or ram extrusion molding of polytetrafluoroethylene polymers under specific conditions. did. However, it was found that the dimensional stability and impact resistance of this molded article were still insufficiently improved. Therefore, the present inventors conducted further intensive research. As a result, the present inventors surprisingly found that polytetrafluoroethylene polymer molded articles having an average maximum expansion ratio of 2.0 or more, which will be described later, usually have an orientation release stress (200°C) value of 5 Kg/cm ² or more. is shown, but
It has been found that this molded article is further heat-shrinked under specific conditions and has an orientation release stress value of less than 5 kg/cm ² which has excellent dimensional stability. In addition, through the above-mentioned shrinkage treatment, polytetrafluoroethylene has been made to have specific gravity, shrinkage start temperature, orientation release stress, average maximum expansion ratio, and maximum shrinkage ratio in the direction of minimum contraction as described below. It has been found that molded articles made from this type of polymer have excellent impact resistance. Based on these findings, the present invention has been completed. That is, according to the present invention, the number average molecular weight is approximately
Ultra-high molecular weight polytetrafluoroethylene polymer molded products with a weight of 1,000,000 or more and a specific gravity of 1.8 or more, 200
Orientation release stress at ℃5
Kg/cm ² or less, the shrinkage start temperature measured using Thermomechanical Analysis is 80°C or higher, and heating at a temperature higher than the shrinkage start temperature substantially eliminates the mutual interaction within the molded article. It has a heat shrinkage characteristic of contracting in a plane parallel to and expanding in a direction perpendicular to the plane,
In this case, the polytetra has an average maximum expansion ratio of 2 times or more and 10 times or less in a direction perpendicular to the plane, and a maximum contraction ratio of 0.71 or less in the direction in which the maximum contraction in the plane is minimum. A fluoroethylene polymer molded article is provided. According to the present invention, the shape of the molded product can be arbitrarily selected and is not limited. However, usually it is in sheet form. The term "sheet-like" used in the present invention has the broadest meaning, and is a general term that includes all wide and thin materials such as "film" and "plate." The sheet-like molded product of the present invention can be planar or curved. Examples of the planar shape include a disk shape, a ring shape, and the like. Examples of the curved surface include a cylindrical shape, a cylindrical shape, a dish shape, and a pipe shape. Both the planar molded product and the curved molded product of the present invention can be molded by the same method. For example, it can be manufactured by compression molding or extrusion molding a preformed product under the conditions described below and subjecting the molded product to compression treatment. During the above compression molding or extrusion molding, a flat mold can be used to obtain a flat molded product, and a curved mold can be used to obtain a curved molded product. . The molded product obtained by the above method can be made into a complicated shape by machining such as cutting. The wall thickness of the molded article according to the present invention can be arbitrarily determined depending on the purpose. The wall thickness is preferably 0.05 mm or more, more preferably 0.1 mm or more and 25 mm or less. The polytetrafluoroethylene polymer used in the present invention is a homopolymer of tetrafluoroethylene, a copolymer containing 70 mol% or more, preferably 90 mol% or more of tetrafluoroethylene, and a blend polymer thereof. , and has a number average molecular weight of 10 ⁶ to 10 ⁸ , preferably 2×10 ⁶ to 10 ⁸ , more preferably 5×10 ⁶ to 5×10 ⁷ as measured by standard specific gravity method. In particular, ultrahigh molecular weight homopolymers of tetrafluoroethylene are preferred. Monomer components to be copolymerized with tetrafluoroethylene include perfluoroalkyl vinyl ether, hexafluoropropylene, ethylene, chlorotrifluoroethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, perfluorobutadiene, perfluoroolefin, and perfluorobutadiene. Preferred are alkyl acrylates, propylene, and the like. In addition, the above polytetrafluoroethylene polymer is used as the main matrix resin component, and reinforcing materials such as glass fiber, carbon fiber, graphite, carbon black, molybdenum disulfide, bronze, zirconium oxide, zirconium silicate, boron whiskers, etc. Inorganic fillers and organic fillers such as aromatic polyamide fibers, aromatic polyester fibers, polyphenylene sulfide, polysulfone, polyethersulfone, polyamideimide, aromatic polyimide, polyetherimide, polyetheretherketone, polyetherketone, etc. A filled polytetrafluoroethylene polymer containing 60% by weight or less of at least one filler is also included in the polytetrafluoroethylene polymer referred to in the present invention. In addition, if necessary, the above polytetrafluoroethylene polymer may contain polymethyl methacrylate, polypropylene, ABS resin, poly-4-methylpentene, etc. within a range of 10 parts by weight or less.
1. Other thermoplastic resins such as polycarbonate, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, polyethylene terephthalate, plasticizers, dyes, and other compounding agents can be added. The polytetrafluoroethylene polymer molded article of the present invention is preferably at least biaxially oriented. At least biaxially oriented according to the present invention,
Biaxial or multiaxial orientation is meant. Biaxial orientation is formed by stretching in two directions perpendicular to each other, and the molecules are mainly oriented in the two directions of the tension. The multiaxial orientation is formed by a molding method used in the present invention, which will be described later, and is almost uniformly oriented in all directions (360°).
Uniaxially oriented sheets also improve compression creep properties, but when compressive force is applied at high temperatures of 100°C or higher,
shrinks in the direction of the stretching axis in the plane perpendicular to the compressive force,
Since it stretches in a direction perpendicular to this, a substantial dimensional change occurs, which is undesirable. In biaxially oriented sheets and other axially oriented sheets, such anisotropic dimensional changes are small and do not pose a practical problem. Particularly in the case of multiaxially oriented sheets, there is no problem at all. The polytetrafluoroethylene polymer molded article according to the present invention can be obtained by thermomechanical analysis (abbreviated TMA) as described below.
The shrinkage start temperature measured using a molded article is 80°C or higher, and heating at a temperature higher than the shrinkage start temperature causes the molded product to shrink in substantially mutually parallel planes and perpendicular to the plane. It has heat-shrinkable properties that allow it to expand in different directions. The molded article according to the present invention has an average maximum expansion factor of 2 times or more and 10 times or less in the direction perpendicular to the above plane, and a direction in which the maximum shrinkage in the above plane is the minimum (hereinafter often simply referred to as the "minimum shrinkage direction"). It is characterized by a maximum shrinkage ratio of 0.71 or less. The average maximum expansion ratio and the maximum contraction ratio in the minimum contraction direction as used in the present invention will be explained. The left side of FIGS. 4 and 5 shows a test piece cut out parallel to the orientation direction from the polytetrafluoroethylene polymer molded product of the present invention. Draw a circle with radius r, for example 50 mm, on the test piece at room temperature with point O as the center, divide the circumference into 45° increments, and divide the circumference into 8
Determine points A ₀ , B ₀ , ..., H ₀ . Next, A ₀ , B ₀ ,
..., H ₀ at 8 points, and the average value T ₀ is taken as the thickness of this test piece. This test piece is heated to 380°C, uniformly heated to 380°C inside, and then heated to 380°C for an additional 5 hours. This heat treatment releases the orientation state of the molded product, and the molded product recovers to the state before stretching. That is, it contracts (maximum contraction) in planes that are substantially parallel to each other within the specimen, and expands (maximum expansion) in a direction perpendicular to the plane. Naturally, the circle drawn on the plane also shrinks in accordance with the alignment state. The reduced test piece was placed in the fourth
It is shown on the right side of FIG. A ₁ , B ₁ , ..., H ₁
corresponds to A ₀ , B ₀ , ..., H ₀ and indicates their positions after reduction. The thicknesses at A ₁ , B ₁ , ..., H ₁ are determined, and the average value T ₁ is determined. Further, for the test piece after heat treatment, the point _M1 having the maximum distance from the origin O to the circumference is determined, and the length ( ₁ ) of the line segment _OM1 is determined. The average maximum expansion factor is defined as T ₁ /T ₀ ,
The maximum shrinkage factor in the direction of minimum shrinkage is defined as ₁ /r. The molded article of the present invention needs to have a maximum shrinkage ratio of less than 0.71 measured in the direction in which the maximum shrinkage within the plane is minimum. If the maximum shrinkage ratio measured in the direction in which the maximum shrinkage in the above-mentioned plane is minimum exceeds 0.71, it approaches uniaxial orientation or non-orientation, which is not preferable. With biaxial orientation, the ratio of the maximum shrinkage ratios in the orthogonal directions of the orientation axes within the orientation plane can be set arbitrarily, but in the molded sheet of the present invention, the ratio of the maximum shrinkage ratios in both axes is 3:1. The ratio is preferably 1:1 to 1:1, particularly 1.5:1 to 1:1. When the ratio of maximum shrinkage ratio exceeds 3:1, it approaches uniaxial orientation,
If a pressure exceeding 100 Kg/cm ² is applied in a temperature range exceeding 100°C, an anisotropic dimensional change will occur even though the compression set S itself shows a small value. This phenomenon is particularly undesirable in the field of sealants. Furthermore, in the case of multiaxial orientation, a multiaxially oriented sheet whose maximum shrinkage ratio is substantially uniform in all directions is preferred. The multiaxially oriented sheet described herein has a ratio of the minimum value to the maximum value of the maximum shrinkage ratio in each direction of 1:1 to 1:2, preferably 1:1 to 1:1.5, and more preferably 1:1.
The ratio is 1 to 1:1.2. As shown in FIG. 5, it is preferable for the polytetrafluoroethylene polymer molded article of the present invention that the maximum shrinkage ratio is approximately equal in all plane directions. Specifically, the maximum shrinkage ratio measured in each direction (OA ₁ /
r, OB ₁ /r, OC ₁ /r, OD ₁ /r, OE ₁ /r,
It is preferable that the standard deviation σ of OF ₁ /r, OG ₁ /r, OH ₁ /r) satisfies σ≦0.20. Multiaxial orientation in the present invention is considered to be at least a special aspect of biaxial orientation, and refers to the case where the standard deviation of the maximum shrinkage ratio σ is σ≦0.15, preferably σ≦0.10. be. The polytetrafluoroethylene polymer molded article of the present invention has an average maximum expansion ratio D of 2 times or more and 10 times or less. If the ultra-high molecular weight polytetrafluoroethylene polymer is biaxially or multiaxially oriented, the compression creep resistance will be improved. Average maximum expansion factor D
As a result of a detailed study on the relationship between the average maximum expansion ratio and compression creep resistance, it was found that molded products with an average maximum expansion ratio of 2 times or more have significantly superior compression creep resistance. A more preferable range is the average maximum expansion ratio D
is more than three times as large. In the range of 5 times or less, the compression creep resistance improves in proportion to D, and the larger D is, the better, and the range where D is 2 times or more can be used satisfactorily. On the other hand, when D exceeds 5.0, the stability of compression creep resistance increases not only in a low temperature range but also in a high temperature range of 200° C. or higher and under high compressive force conditions of about 500 Kg/cm ² . Furthermore, if an attempt is made to orient the material to an average maximum expansion ratio D of more than 10, breakage tends to occur, making orientation virtually impossible. In consideration of workability, the average maximum expansion ratio D is preferably in the range of 3≦D≦7. The polytetrafluoroethylene polymer molded article of the present invention is a substantially void-free solid body, and has a specific gravity of 1.8 or more, preferably 2.0 or more, and more preferably 2.1 or more. ASIT D-792 is used to measure specific gravity.
This shall be done in accordance with. Polytetrafluoroethylene polymer oriented molded products with an average maximum expansion ratio of 3.0 times or more, obtained by stretching a polytetrafluoroethylene polymer base (preformed product) under pressure, have excellent creep resistance and gas Has blocking properties. however,
The molded article may be heated particularly at high temperatures, e.g. 70 to 100°C.
At , a return of orientation occurs. For example, heating the molded article at 80 DEG C. for 20 hours in air results in an undesirable dimensional change of about 3% as a result of reorientation. The present inventors surprisingly found that polytetrafluoroethylene polymer molded articles with an average maximum expansion ratio of 2.0 or more usually exhibit an orientation release stress (200°C) value of 5 Kg/cm ² or more.
It has been found that this molded article is further heat-shrinked under specific conditions and has an orientation release stress value of less than 5 kg/cm ² which has excellent dimensional stability. In the present invention, the contraction start temperature measured using thermomechanical analysis (abbreviation TMA) is the state in which the sample expands as the temperature increases, when the dimensional change of the sample is measured while heating under the measurement conditions described below. This is the temperature at which the sample contracts as the temperature increases. The polytetrafluoroethylene polymer molded article of the present invention has a shrinkage onset temperature of 80°C as measured using TMA.
It is necessary that it is above. Molded products having a shrinkage start temperature of less than 80°C are undesirable because of their poor dimensional stability. Preferably, the molded article has a shrinkage start temperature of 125°C or higher, particularly preferably a molded product that has a shrinkage start temperature of 150°C or higher. Normally, in polytetrafluoroethylene polymer molded products oriented in at least two axes, the shrinkage onset temperature measured using TMA is less than 80°C, so by applying the heat treatment that causes shrinkage as described above, It is necessary to set the shrinkage start temperature to 80°C or higher. The oriented polytetrafluoroethylene polymer molded product of the present invention has excellent impact resistance. For the oriented molded product of the present invention, the Izot impact strength Y (Kg cm/cm) at 23°C is preferably determined by the formula Y≧4.0D+I ₀ (I ₀ is the temperature at 23°C of the polytetrafluoroethylene polymer base used). Notched Izo impact strength Y (Kg·cm/cm), D represents the average maximum expansion ratio). I ₀ varies depending on the polytetrafluoroethylene polymer powder used. Particularly preferably, the relationship is as follows: Y≧4.0D+I ₀ +2. Izotsu impact strength is ASTM-
Measured according to D256. The polytetrafluoroethylene polymer molded article according to the present invention is produced by forming what is generally called a base (or preform) by a known method from an ultra-high molecular weight polytetrafluoroethylene polymer having a number average molecular weight of about 1 million or more. It can be manufactured by manufacturing, orienting this by compression molding, ram extrusion molding, etc., and subjecting the oriented molded product to heat shrink treatment. The polytetrafluoroethylene polymer base is
A known method, for example, compression molding the moldable powder of the polymer at room temperature at about 100 to 1000 kg/cm ² and molding the resulting compression molded product at a temperature higher than the gelation temperature, preferably 327°C or higher, more preferably can be produced by sintering at a temperature of 340 to 400°C and cooling after sintering. The specific gravity of the above substrate is preferably
It is 1.8 or more, more preferably 2 or more. The method for orienting the polytetrafluoroethylene polymer substrate is not particularly limited, as long as it satisfies the requirements of the present invention and can be produced by orientation or by accompanying processing before and after orientation. Conventionally, roll rolling and tension stretching methods have been commonly used as orientation methods, but in the roll rolling method, biaxially oriented sheets and multiaxially oriented sheets within the preferred range of the polytetrafluoroethylene polymer molded products of the present invention are used. It is not possible to produce oriented sheets. Further, in the tensile stretching method, as is used for making polytetrafluoroethylene polymers porous, the generation and increase of voids during stretching is unavoidable. The present inventors investigated a molding method for orienting a polytetrafluoroethylene polymer base while suppressing the generation and increase of voids, and found that the molding method is 150°C or higher, preferably 170°C to 340°C, and more preferably 250°C or higher. 340°C, even more preferably
We have discovered a method for orienting a polytetrafluoroethylene polymer, which is characterized by orienting a polytetrafluoroethylene polymer base in a die under pressure at a temperature of 300°C to 327°C. In particular, in order to obtain the highly oriented molded article of the present invention with an average maximum expansion ratio of 5 times or more, a polytetrafluoroethylene polymer base heated to a high temperature of 250°C to 340°C is oriented under pressure. It is preferable. Orientation under pressure in a die means to orient the polytetrafluoroethylene polymer base by causing a plug flow in a compression die or an extrusion die by compression force or extrusion force in compression molding or extrusion molding. Further, in order to cause plug flow, it is preferable that a lubricant be present at least on the inner surface of the die or on the surface of the polytetrafluoroethylene polymer base. Prior to orientation, the polytetrafluoroethylene polymer base is preheated to 150°C or higher. Preferable preheating temperature is 170°C to 340°C, more preferably 200 to 327°C. The temperature for orientation may be uniform over the entire surface, but it may be higher on the surface layer side and lower temperature on the center side, or only the surface layer may be higher than the melting point of the polytetrafluoroethylene polymer and the inner part may be lower. They can also be distributed, such that they are all below the melting point. The temperature of the die can be arbitrarily selected within the range of the temperature of the inner surface of the die from room temperature to 400° C., taking into account the form of growth and productivity.
In particular, when the temperature of the inner surface of the die is less than (temperature of the surface layer of the polytetrafluoroethylene polymer base - 50) °C, especially less than (temperature of the surface layer of the polytetrafluoroethylene polymer base - 100) °C, If the inner surface of the die and the entire lower surface of the polymer substrate come into direct contact after the polytetrafluoroethylene polymer substrate is placed on the die prior to molding and until it is oriented under pressure, only the lower surface will be rapidly cooled. Since the temperature difference between the top and bottom surfaces of the ethylene polymer matrix becomes large and it becomes difficult to orient the top and bottom surfaces evenly, a method is needed to reduce the temperature difference. This method includes, for example, a method in which the polytetrafluoroethylene polymer base 3 is curved during preheating as shown in FIG. 12a, and a method in which projections 5 are provided on the die surface 1 as shown in FIG. 12b. Method of placing polytetrafluoroethylene polymer matrix 3 on top, 1st
As shown in Figure 2c, the entire lower surface of the polytetrafluoroethylene polymer base 3 is held by using a jig, such as a metal thread 51, to hold the polytetrafluoroethylene polymer base 3 in a floating state. There is a method of directly contacting the inner surface of the die to prevent only the bottom surface from cooling rapidly. When the orientation is performed as shown in FIG. 12, the surface of the polytetrafluoroethylene polymer substrate 3 is laminated and coated with a thin sheet or film 6 of thermoplastic resin or polytetrafluoroethylene polymer. This is preferable because the lubricant that adheres in layers can be easily removed. When orienting under pressure, the polytetrafluoroethylene polymer substrate is subjected to a pressure of 300 Kg/cm ² or more, preferably 500 Kg/cm ² or more, more preferably 1000 Kg/cm ² or more and 4000 Kg/cm ² or less. Orient by applying high pressure. In order to have a lubricant on the inner surface of the die, in the case of compression molding, it is generally applied before molding, and in the case of extrusion molding, it can be press-fitted into the extrusion die from the outside or applied before molding. is common. As the lubricant, silicone oil with excellent heat resistance is suitable. In the present invention, it is extremely important to cause a plug flow when the polytetrafluoroethylene polymer matrix is oriented under pressure in a die. In order to cause plug flow, it is preferable to perform at least one of the following operations during molding. A lubricant is present on the inner surface of the die. The surface of the polytetrafluoroethylene polymer base is laminated and coated with another thermoplastic resin. The thermoplastic resin preferably has a melting point lower than that of the polytetrafluoroethylene polymer and/or has a lower viscoelasticity than the polytetrafluoroethylene polymer under the temperature conditions during orientation. Coating the surface of the polytetrafluoroethylene polymer base with a thin sheet of thermoplastic resin not only improves the plug flow properties of the polytetrafluoroethylene polymer base, but also allows lubricant to be applied to the inner surface of the die. When the lubricant is present on the orientation sheet, removing the lubricant that adheres to the orientation sheet can be achieved by peeling off the laminated seal. In order to remove the lubricant, the surface of the polytetrafluoroethylene polymer substrate may be laminated and coated with a thin sheet or film of the same polytetrafluoroethylene polymer. Polytetrafluoroethylene polymers are non-adhesive to each other, and can be easily peeled off even when heated and pressed at temperatures around the melting point of the polytetrafluoroethylene polymer or lower. Various resins can be used as the laminated sheet to improve plug flow properties and/or remove lubricant, but ultra-high molecular weight polyethylene, poly-4-methylpentene-1, and polytetrafluoroethylene polymers are used. etc. are best used. If an attempt is made to orient the polytetrafluoroethylene polymer by continuing pressurization without plug flow, the polytetrafluoroethylene polymer will undergo melt fracture or brittle fracture. In addition, if orientation is performed under conditions where plug flow becomes difficult, an uneven orientation state will remain, resulting in weak points in the orientation sheet. Not suitable as a sealing material. A more detailed explanation will be given below with reference to the drawings. In FIG. 1, at least the inner surface 2 of the compression die 1 is heated in advance to an arbitrary temperature above room temperature and below 400°C. The polytetrafluoroethylene polymer base 3 adjusted to the above temperature is placed between the heated compression die 1-1. At this time, it is preferable that a lubricant be present on the inner surface 2 of the compression die. However, if the temperature of the inner surface of the die is less than (temperature of the surface layer of the polytetrafluoroethylene polymer base - 50°C), only the bottom surface of the polytetrafluoroethylene polymer base described above will be prevented from cooling rapidly. take a method. The polytetrafluoroethylene polymer base material 3 is compressed and oriented with a plug flow, and after cooling to about 100°C or less by applying the compressive force, the die 1 is opened and the oriented polytetrafluoroethylene polymer base material 3 is Take out the combined molded product 4. When manufacturing thin-walled oriented polytetrafluoroethylene polymer molded products, when manufacturing multiple oriented polytetrafluoroethylene polymer molded products in one press to improve productivity, or after pressing. When it is desired to easily remove the lubricant adhering to the molded product, the polytetrafluoroethylene polymer matrix 3 is coated with polytetrafluoroethylene polymers and/or as shown in FIG.
Alternatively, it is preferable to form a laminate with another thermoplastic resin 6. For a laminated polytetrafluoroethylene polymer base, each layer is peeled off after molding. The laminated interface between polytetrafluoroethylene polymers can be easily peeled off after molding if the temperature of the polytetrafluoroethylene polymer base is below the melting point. Peeling at the laminated interface with other thermoplastic resins can be prevented even if the temperature of the laminated polytetrafluoroethylene polymer substrate during molding is below the melting point of the thermoplastic resin, preferably below (melting point - 30)°C. There is no problem at all. If the thermoplastic resin is a resin such as ultra-high molecular weight polymethylene whose viscosity decreases little even when the melting point is exceeded, it can be used satisfactorily even above the melting point. In FIG. 3, the die plate 10 of the compression press
The cold/heat die plate 11 is connected via the heat insulating material 13 to
is fixed, and the cold/heat die plate 11 is provided with cold/heat medium holes 12 through which cold/heat medium flows, and the temperature is constantly regulated. A die 1 is attached to a cold/hot die plate 11. Prior to molding, the die 1 is heated to an arbitrary temperature above room temperature and below 400°C.
The substrate 3 is also preheated to a temperature above 150°C, preferably between 170 and 340°C. Further, it is preferable to apply a lubricant to the inner surface of the die in advance. The polytetrafluoroethylene polymer matrix 3 is oriented by compression. At this time, the thickness during molding is adjusted using spacers 15 so that a predetermined average maximum expansion ratio is obtained. Further, after cooling in the compressed state, the oriented sheet is taken out. The cooling rate at this time is adjusted by the heat insulating plate 18 and the cold/hot die plate 11. In FIG. 3, if the die 1 and the cold/hot die plate 11 have a curved shape such as a spherical shape, the molded product will also have a curved shape accordingly. FIG. 6 shows an apparatus for extrusion molding a polytetrafluoroethylene polymer sheet. In FIG. 6, a polytetrafluoroethylene polymer base material is put into a ram extrusion molding machine 26 consisting of a prismatic heating cylinder 24 with a square cross section and a square ram 25, and is heated by the ram 25 while being heated by a die. 27. As the polytetrafluoroethylene polymer substrate, not only a single layer polytetrafluoroethylene polymer substrate but also a laminated polytetrafluoroethylene polymer substrate as shown in Fig. 2, as in the case of compression molding, can be used. Can be used.
In the middle of part A of the die 27, a series of devices for oozing lubricant is provided in order to apply the lubricant to the interface between the surface of the polytetrafluoroethylene polymer matrix and the die surface. The high-pressure lubricant is guided from the lubricant introduction path 28 to the plurality of seepage ports 29, and seeps out onto the surface of the polytetrafluoroethylene polymer substrate.
Apply lubricant to the interface between the molded body surface and the die surface. The lubricant seepage port 29 is made of a material having a small slit shape or a material such as sintered metal having fine communicating holes, and the lubricant seeps out from the fine holes.
Alternatively, it is also possible to apply a lubricant to the inner surface of the die by spraying or the like before molding. The polytetrafluoroethylene polymer matrix having the surface uniformly coated with the lubricant undergoes a so-called plug flow in which the surface layer and center of the polytetrafluoroethylene polymer flow at approximately the same speed in the die 27. Next, in part B of the die 27, the plug flow polytetrafluoroethylene polymer base is oriented. The B portion of the die 27 has a structure in which the thickness of the polytetrafluoroethylene polymer base is reduced. The flow change of the polytetrafluoroethylene type polymer of the B part when biaxially oriented is explained in the seventh section.
Shown in the figure. The polytetrafluoroethylene polymer matrix is simultaneously extruded biaxially in the flow direction and in a direction perpendicular to the flow direction while maintaining plug flow, and is multiaxially oriented. The force for orienting the polytetrafluoroethylene polymer matrix is exerted by the extrusion force from the ram extruder 26. The multiaxially oriented polytetrafluoroethylene polymer molded article is cooled in the C portion of the die and exits the die 27. The multiaxially oriented polytetrafluoroethylene polymer molded product is taken up by a roll 30. When a laminated polytetrafluoroethylene polymer base is used as the polytetrafluoroethylene polymer base, the polytetrafluoroethylene polymer base of the present invention can be prepared by peeling off the laminated polytetrafluoroethylene polymer sheet extruded from the die 27. A fluoroethylene polymer oriented sheet is obtained. The polytetrafluoroethylene polymer sheet oriented under pressure in the die undergoes thermal contraction in a relatively high temperature range of 100° C. or lower. The above polymer sheet is preferable for use under conditions where only creep resistance and blister resistance are required, but is not preferable under conditions where dimensional stability is additionally required. The polytetrafluoroethylene polymer molded article of the present invention must have an ORS of less than 5 kg/cm ² at 200°C. Usually, in a polytetrafluoroethylene polymer molded product oriented in at least two axes so that the average maximum expansion ratio is 2 times or more, the ORS at 200°C is 5 Kg/cm ² or more. In order to provide dimensional stability to such molded products, this polytetrafluoroethylene polymer molded product is heat treated to cause shrinkage, and
It is necessary that the ORS value at °C be less than 5 kg/cm ² . Therefore, the polytetrafluoroethylene polymer oriented molded product oriented under pressure in a die is further subjected to shrinkage treatment to obtain the final product of the present invention. The temperature of the shrinkage treatment is generally 150°C to the melting point of the polymer,
The temperature is preferably 180°C to 300°C, and the time varies depending on the dimensions of the molded product, but is generally 1 second to 1000 hours, preferably 1 minute to 10 hours. In the shrinking treatment, it is preferable to perform free shrinkage without applying pressure. This shrinkage treatment slightly reduces the average maximum expansion ratio of the oriented molded product. For example, when shrinking an oriented molded product at 220°C for 2 hours, the average maximum expansion ratio of the oriented molded product is 4.63.
3.31, 4.03 to 3.11, 3.41 to 2.71
, the one of 2.44 drops to 2.06. Therefore, in order to obtain an oriented molded product according to the present invention, the orientation conditions of the substrate and the heat shrinkage treatment conditions of the oriented molded product are set in consideration of the change in the average maximum expansion ratio due to this shrinkage treatment. In addition, as a method for easily performing the above-mentioned shrinkage treatment, a polytetrafluoroethylene polymer molded article oriented in at least two axes is heated at a temperature of 150°C or higher. Melting point or below, preferably 180℃ or above 300℃
In this method, the material is taken out of the molding machine at the following temperature and cooled while allowing free shrinkage. Furthermore, as a simple method for performing shrinkage treatment, a polytetrafluoroethylene polymer sheet formed by extrusion molding is
When extrusion molding is carried out at a temperature of 180°C or higher and lower than the melting point of the polytetrafluoroethylene polymer, preferably 180°C or higher and 300°C or lower, the multiaxially oriented polytetrafluoroethylene polymer base material will adhere to the C of the die.
The temperature is controlled at the part, and it exits the C part of the die in a softened state, and is then cooled while freely shrinking.
ORS is less than 5Kg/ ^cm2 without further heat treatment,
This is preferable because the polytetrafluoroethylene polymer sheet of the present invention having a shrinkage onset temperature measured using TMA of 80° C. or higher can be obtained. The polytetrafluoroethylene polymer molded article of the present invention can be molded by orienting the polytetrafluoroethylene polymer base in a die under pressure and performing a shrinkage treatment as described above. The sheet can be further processed into final products such as gaskets, packings, sealing materials, lining materials, etc. by machining such as cutting, typified by punching and slicing. Further, when the polytetrafluoroethylene polymer base is oriented under pressure in a die, it can be simultaneously formed into the shape of a final product such as a gasket. In this case, it is necessary to take sufficient measures to ensure that the polytetrafluoroethylene polymer base is uniformly oriented. Also,
It is necessary to consider the shrinkage rate when performing heat shrinkage treatment to reduce ORS when molding. However, in the present invention, a method in which a large sheet is molded and the sheet is punched, cut, etc. into a final product is preferred since it is possible to obtain a uniformly oriented gasket. [Effects of the Invention] In the present invention, the polytetrafluoroethylene polymer is preferably at least biaxially oriented, more preferably multiaxially oriented so as to exhibit a predetermined average maximum expansion ratio and maximum contraction ratio, and is further oriented at 200°C. The biggest problem with conventional polytetrafluoroethylene polymer molded products is solved by heating and shrinking ^so that the ORS at To provide a polytetrafluoroethylene polymer molded article which has significantly improved compression creep resistance, which was one of the aspects, and which has higher compressive strength, excellent impact resistance, and maintains dimensional stability. . Furthermore, the polytetrafluoroethylene polymer molded article of the present invention has significantly improved gas barrier properties, tensile strength, and the like. The reason for the improvement in compression creep resistance is not clear, but it is thought to be as follows. The molecules of polytetrafluoroethylene polymers have ultra-high molecular weight, relatively high rigidity, and long chains, which are intricately intertwined. When this is highly oriented, the molecular chains involved in the entanglement become highly tense, and each molecular chain reaches a state of approximately equal tension. It is assumed that the external force acting on the oriented sheet in this state is evenly distributed to each molecular chain, and that the slippage phenomenon of molecular chains at entanglement points is less likely to occur, resulting in a marked improvement in compression creep resistance. . In the method of orienting the polytetrafluoroethylene polymer molded article under pressure in a die, which is a preferred method for producing the polytetrafluoroethylene polymer molded article of the present invention, the void content does not increase due to orientation, as determined from the specific gravity before and after molding. In any case, it is presumed that the gas barrier properties are improved by changes in morphology due to orientation. The reason for the improvement in dimensional stability is not clear, but it is believed that heat treatment relaxes the orientation of the parts that cause molecular movement in the oriented polytetrafluoroethylene polymer molded product to some extent. It will be done. The reason for the improvement in impact resistance is not clear, but
This is thought to be because the orientation of the oriented polytetrafluoroethylene polymer molded article was relaxed to some extent by heat treatment, and a portion exhibiting gum elasticity was generated. The polytetrafluoroethylene polymer molded article of the present invention, which has excellent compression creep resistance, blister resistance, dimensional stability, and impact resistance, has the inherent property of polytetrafluoroethylene polymer, that is, chemical resistance. Requires properties such as durability, corrosion resistance, low friction, non-adhesiveness, and heat resistance, as well as compression resistance, mechanical strength, impact resistance, and dimensional stability that can withstand external forces that are applied during use. It is particularly suitable for use in various situations. For example, it is suitable as a sealing material for gaskets and packings, and for sliding members such as bearings and piston rings. Many of the polytetrafluoroethylene polymer molded products of the present invention have better compression creep resistance than conventional filled polytetrafluoroethylene polymer molded products even if they do not contain fillers. . It has excellent compression creep resistance, especially in high temperature ranges. Therefore, the range of usable conditions (temperature, seal internal pressure, etc.) as a gasket material without fillers can be greatly expanded.
In addition, we also offer sealing materials other than gaskets, such as V-packs, U-packs, etc. used for gland seals of low-speed/low-pressure stirrers, valves, pumps, etc.
It is also suitable for packings such as O-rings, diagonal packings, and square packings. Moreover, it is suitable as a substitute for the polytetrafluoroethylene polymer part used in conventional combination type sealing materials. Examples include the polytetrafluoroethylene polymer part in a polytetrafluoroethylene polymer jacket-type gasket and spiral gasket, and back-up springs and slipper seals. Also, diaphragms and valves are used as valve parts.
The problem with Peroz is that it is weak in strength,
The sheet of the present invention can also be suitably used here. It is also suitable for polytetrafluoroethylene polymer balls used as check valves in liquid transport devices. It is also suitable for ball valve seats in Beauli valves, gate valve seats in gate valves, and valve discs. The shape and dimensions of the polytetrafluoroethylene polymer sheet of the present invention used in the above-mentioned sealing material are arbitrarily determined depending on what is used. However, as a flat gasket, it is often used in the form of a sheet with a thickness of 0.2 mm to 5 mm, preferably 0.5 mm to 4 mm. In the field of bearings, conventional polytetrafluoroethylene polymers are used under low load and low sliding speed conditions due to large compression creep, but the polytetrafluoroethylene polymer sheet of the present invention has high compression creep. Suitable for use conditions that require dimensional stability under heavy loads and high temperatures. It is particularly suitable for use as support plates and sliding pads for heavy objects such as bridges, outdoor tanks, and factory structures, as well as packings, gaskets, and bearings for automobile parts, and can improve their durability. Among the polytetrafluoroethylene polymer molded articles of the present invention, those containing fillers have increased dimensional stability at high temperatures, and further improved compression creep resistance and impact resistance. In addition, because wear resistance is improved, molded products of the present invention containing fillers may be preferable to molded products containing no fillers, depending on usage conditions. . As described above, the molded article of the present invention can be used in applications for polytetrafluoroethylene polymers, which have conventionally been used under limited usage conditions due to problems such as compression creep and gas permeation. The range of use can be greatly expanded. Furthermore, since it has both the properties improved by orientation and the excellent properties inherent to polytetrafluoroethylene polymers, new uses for polytetrafluoroethylene polymers can be developed. In addition, the polytetrafluoroethylene polymer sheet of the present invention has various properties required as a cryogenic material, especially excellent impact resistance at cryogenic temperatures and excellent compression creep resistance. Various chemicals, oils, solvents and mixtures thereof, especially
Sealing materials for containers of LNG, liquefied oxygen, liquefied nitrogen, liquefied ammonia, etc., sealing materials for refrigerant containers used in superconducting coils, superconducting cables, etc., piping flanges, pumps, autoclaves, valve bonnets, manholes, various measuring instruments, etc. It is suitable as a material for sealing parts. For these uses, among the molded articles of the present invention, those having a notched Izot impact strength at -196°C of 10 Kg·cm/cm or more, particularly 15 Kg·cm/cm or more are preferably used. [Example] The present invention will be described below with reference to Examples. In the Examples and Comparative Examples of the present invention, the properties of the polymers and molded articles were measured by the following methods. 1 Measurement of the average maximum expansion ratio and maximum contraction ratio in the minimum contraction direction Samples of oriented molded products (for large dimensions, e.g. 100 cm in length, 100 cm in width, 10 cm in height) 10cm, width 10cm, height 3
(cut to cm), measure and record each dimension at room temperature. Next, this sample is heated at an ambient temperature of 380°C, and the temperature is evenly heated to 380°C inside, and then heated at the same temperature for 5 hours. This heating causes contraction in successive substantially mutually parallel planes within the sample and expansion in a direction perpendicular to this plane. Cool the sample to room temperature, measure the dimensions again, and compare the dimensions recorded above to determine the direction in which the dimensions increase the most. This direction of maximum dimension increase can be considered to correspond to the direction of expansion. A test piece of constant thickness (for example, 110 mm
mm, width 110mm, thickness 10mm). Using this test piece, the method described earlier (text
(see pages 16-17), draw a circle and set the circumference at 45°.
The average maximum expansion ratio and the maximum contraction ratio in the direction of minimum contraction are determined by dividing the specimen into sections, measuring the thickness, heat-treating at 380°C for 5 hours, and cooling. 2 Measurement of number average molecular weight A sample of any shape is taken out from a polytetrafluoroethylene polymer or a molded product thereof.
This sample is heat treated under certain heat treatment conditions specified in ASTM D-1457. After heat treatment, measure the specific gravity of the sample. This specific gravity is standard specific gravity (hereinafter referred to as S.
(abbreviated as SG). There is a certain relationship between SSG and number average molecular weight (Mn) [RD
Doban et al.: Meeting of the Am.Chem.
Soc., Atlantic City (1956)], and is expressed by the following formula ("Fluorine Resin", Nikkan Kogyo Shimbun). SSG=−0.0579log Mn+22.6113 By using the above formula, the number average molecular weight can be determined from SSG. 3 Measurement of compression set S (%) Compression set S at 200℃・500Kg/ ^cm2・1 hour
The measurement of (%) will be explained below using FIG. The test piece 34 was prepared from the polytetrafluoroethylene polymer sheet of the present invention or a comparative sample by the same method as in item 1 above.
It was cut out to 50mm x 50mm x 2mm or 3mm thick. Place this on a smooth tempered glass plate 33 (160mm x
160mm x 5mm thick). Clean the surface of the glass plate and test piece. Furthermore, one side has a mirror finish (surface roughness 0.1S to 0.6SJIS).
B0601) Stainless steel plate 32 (220mm x 220
mm x 6 mm thick) between mirror surfaces. The laminate is sandwiched between hot press plates 31 (400 mm x 400 mm x 60 mm thick) whose temperature has been adjusted to 200°C in advance,
A compressive force corresponding to a pressure of 500 kg/cm ² was applied to the test piece 34. Without considering the increase in area due to deformation of the test piece 34 during the test, the initial compressive force was maintained and heating and pressurization was continued for 1 hour, then the heater power of the hot press plate 31 was turned off and water was passed through the hot press plate. It was then cooled to room temperature over about 30 minutes and taken out. The compressive force was maintained even during cooling. At least 5 locations within one specimen, the thickness before and after the compression test (t ₀ ,
t ₁ ) using a micrometer (JIS B7503 1st grade product)
The compression set at each position is (t ₀ − t ₁ ) t ₀
×1002, and the arithmetic mean was taken as the compression set S (%) described in the present invention. However, if the entire structure is destroyed, the compression set S
(%) is not calculated. Measurement is basically ASTM
Followed D621. 4. Measurement of orientation release stress (ORS) (Kg/cm ² ) A tensile tester modified as shown in Figure 9 was used. Test piece 39 has a length of 80 mm and a width of 10 mm.
A strip (thickness is arbitrary) is cut out along the orientation axis in the same manner as in Section 1 above. Set the test piece 39 on the grip 37. The distance between the grips at this time is 50 mm. After this, 200
The oil bath 41 heated to .degree. C. is raised so that the top of the grip 37 is immersed in oil. The contractile force of the sample is detected by a load cell 40 and recorded on a recorder (not shown). Oriented polytetrafluoroethylene polymer molded product
The shrinkage force at 200°C had an equilibrium value about 5 minutes after immersion. After immersing the sample in oil, read the equilibrium value of the shrinkage force, and convert it to stress by dividing it by the cross-sectional area of the ampoule (thickness x width). The stress values in each orientation axis direction were numerically averaged, and this was defined as the ORS at 200° C. in the present invention. Measurement is ASTM
Followed D1504. 5 Measurement of specific gravity According to ASTM D792. 6 Water vapor transmission rate (g/cm ² ·24 hr) Measured according to ASTM F372 at 38°C and 90% relative humidity. 7 Oxygen permeability (ml/m ² ·day · atm) Measured at 30°C according to ASTM D1434. 8. Measurement of Shrinkage Start Temperature by TMA The dimensional change of the polytetrafluoroethylene polymer oriented under the following conditions was measured when the temperature was increased. The test piece was cut out along the orientation axis using a microtome in the same manner as in Section 1 above. Measuring device Seiko Electronics Co., Ltd. TMA-10 Measuring temperature 30°C to 300°C Measuring conditions Heating rate 5°C/min Tensile stress acting on sample 5 g/mm ² Sample width 3 mm Sample thickness 0.2 mm Distance between chucks 10 mm Dimensions As for the change value, a positive direction means expansion of the sample, and a negative direction means contraction. Attach the sample to the chuck at room temperature and heat it.
When the temperature is raised, the sample of oriented polytetrafluoroethylene polymer usually expands as the temperature increases, as shown in FIG. 10, but when it reaches a certain temperature, it stops elongating, and when the temperature is raised further, it begins to shrink. The temperature at which this elongation changes to contraction is the contraction start temperature in the present invention. If the sample continues to shrink without elongating when the sample is attached and heating/temperature raising is started, the shrinkage start temperature is 30°C or lower. In addition, in the case of unoriented polytetrafluoroethylene, 30℃
In the range of ~300°C, it only elongates without shrinking. 9 Measurement of dimensional change rate Measurement of dimensional change rate will be explained using FIG. 11. As shown on the left side of FIG. 11, points A ₀ , B ₀ , . . . H ₀ that divide the circumference by 45° are placed on the polytetrafluoroethylene polymer sheet before heating. Here, the distance _{0 0} between points A ₀ and E ₀ is L ₁ , and similarly _{0 0} is
Let L ₂ , _{0 0} be L ₃ , _{and 0 0} be L ₄ . Then 200℃
A polytetrafluoroethylene polymer sheet is placed in a constant temperature bath and heated. After 10 hours, the polytetrafluoroethylene polymer sheet is removed from the thermostatic chamber and left until the temperature of the sheet reaches room temperature. The distance _{0 0} between points A ₀ and E ₀ after heating is l ₁ ,
Similarly, let _{0 0} be l ₂ , _{0 0} be l ₃ , and _{0 0} be l ₄ .
The dimensional change rate αn (n=1 to 4) is defined as αn (%)=ln−Ln/Ln×100. The average α αn (%) of the four dimensional changes obtained in this way=α ₁ +α ₂ +α ₃ +α ₄ /4 is defined as the dimensional change rate in this example. Furthermore, the maximum value of αn is set as αmax, the minimum value as αmin, and R defined as R=αmax−αmin was also determined. 10 Measurement of Izot Impact Strength Test pieces were cut out along the orientation axis by the same method as in Section 1 above, and measurements were carried out at 23°C and -196°C in accordance with ASTM D256. Example 1 and Comparative Examples 1 to 4 "Fluororesin" (Nikkan Kogyo Shimbun, 1975, 4)
14 mm thick made of homopolymer of tetrafluoroethylene (TFE) manufactured by the free baking method shown in (Published in May, pp. 58-65) etc.
An unoriented polytetrafluoroethylene sheet (manufactured by Nippon Valqua Industries Co., Ltd., VALFLON R No. 7000, specific gravity 2.16, number average molecular weight approximately 1 x 10 ⁷ ) was used as a polytetrafluoroethylene base material, and this was pressed into the press shown in Figure 3. Orientation was performed by compression molding using a molding machine to obtain an oriented polytetrafluoroethylene sheet (about 3 mm thick) with an average maximum expansion ratio of 4.6.
(Comparative Example 2). During the molding, permeated silicone (KF965, 10000 cs) was used as a lubricant, and a 0.1 mm thick polytetrafluoroethylene film was placed between the die 1 and the polytetrafluoroethylene base 3 and oriented. Further, the cold/hot die plate 11 was set at room temperature. Next, the polytetrafluoroethylene sheet of Comparative Example 2 thus obtained was subjected to free shrinkage by heating at 220° C. for 2 hours to obtain a product of the present invention (Example 1). Comparative Examples 3 and 4 were obtained by subjecting the polytetrafluoroethylene sheet of Comparative Example 2 to free shrinkage under heating at 80°C and 150°C for 2 hours, respectively, and Comparative Example 1 was an unoriented polytetrafluoroethylene sheet. be. Table 1 shows the orientation temperature, heating free shrinkage temperature, average maximum expansion ratio D, maximum shrinkage ratio in the direction of minimum contraction, ORS at 200℃, shrinkage start temperature by TMA, dimensional change rate at 200℃, compression set S ,
Izot impact strength and specific gravity are shown. FIG. 10 shows the dimensional changes of the molded products of Example 1 and Comparative Examples 1 and 2 due to TMA. The above results show that the oriented molded product of the present invention has excellent compression creep resistance, dimensional stability, and impact resistance.

【table】

[Table] Examples 2 to 4 and Comparative Examples 5 and 6 Using a polytetrafluoroethylene sheet with a thickness of 12 mm as a polytetrafluoroethylene base, a polytetrafluoroethylene sheet with an average maximum expansion ratio of 4.1 was prepared in the same manner as in Comparative Example 2. (Comparative Example 5). Next, the polytetrafluoroethylene sheet of Comparative Example 5 thus obtained was heated at 150°C, 220°C, and 300°C.
The present invention was obtained by free shrinking by heating at ℃ for 2 hours (Examples 2, 3, and 4). Comparative example 6 is 80% of comparative example 5.
It was obtained by free shrinkage under heating at ℃ for 1 hour. Examples 5 to 8 and Comparative Examples 7 to 10 Same as Comparative Example 2, average maximum expansion ratio 3.4
(Comparative Example 7) and polytetrafluoroethylene sheets having an average maximum expansion ratio of 2.4 (Comparative Example 9) were obtained. Next, the sheet of Comparative Example 7 obtained in this way was heated at 80℃ and 150℃.
Comparative Example 8 was heated at 220°C for 2 hours to shrink freely.
Polytetrafluoroethylene sheets of Examples 5 and 6 were obtained. Further, from Comparative Example 9, polytetrafluoroethylene sheets of Comparative Example 10 and Examples 7 and 8 were obtained. Example 9 and Comparative Example 11 Same as Comparative Example 2, average maximum expansion ratio 5.7
A polytetrafluoroethylene sheet was obtained (Comparative Example 11). Next, the sheet of Comparative Example 11 obtained in this way was
The polytetrafluoroethylene sheet of Example 9 was obtained by heating and freely shrinking at 300° C. for 2 hours. Table 2 shows the measurement results of Examples 2 to 9 and Comparative Examples 5 to 11. From the results in Table 2, it can be seen that the molded articles of the present invention have excellent compression creep resistance, dimensional stability, and impact resistance. From FIG. 13, it can be seen that the product of the present invention obtained by free shrinking under heat has significantly improved impact resistance compared to unoriented polytetrafluoroethylene and oriented polytetrafluoroethylene sheets that have not been free shrinked under heat. Recognize.

【table】

[Table] Examples 10 to 13, Comparative Examples 12 to 19 The orientation temperature was changed to 300°C, and the average maximum expansion ratio was 5.1 in the same manner as in Examples 1 to 9 and Comparative Examples 1 to 11.
(Comparative Example 12), average maximum expansion ratio 4.2 (Comparative Example 15),
A polytetrafluoroethylene sheet with an average maximum expansion ratio of 3.1 (Comparative Example 18) was obtained. Then add these to 80
℃, 150℃, 220℃ for 2 hours by heating and free shrinking, Comparative Examples 12, Comparative Examples 13, 14 and Examples
10. Polytetrafluoroethylene sheets of Examples 16 and 17 and Example 11 were obtained from Comparative Example 15, and Comparative Example 19 and Examples 12 and 13 were obtained from Comparative Example 18. Table 3 shows the results of Examples 10-13 and Comparative Examples 12-19. From the results in Table 3, it can be seen that the polytetrafluoroethylene molded article of the present invention has excellent compression creep resistance and dimensional stability.

【table】

[Table] Example 14 A 12 mm thick polytetrafluoroethylene sheet made of a tetrafluoroethylene homopolymer (VALFLON R sheet No. 7000, manufactured by Nippon Valqua Industries Co., Ltd.) was press-formed as shown in Figure 3. Using a machine, the cold/hot die plate 11 is set at 220°C for orientation by compression molding.Then, the molded product is taken out at a temperature of 220°C, and left to cool while allowing free shrinkage. Expansion magnification 3.8 times,
A polytetrafluoroethylene oriented sheet of the present invention having a thickness of 3.1 mm was obtained. Table 4 shows the results. From the results in Table 4, the polytetrafluoroethylene sheet of the present invention obtained by the method of Example 14 is as follows:
It can be seen that the dimensional stability and impact resistance are improved while maintaining excellent compression creep resistance.

【table】

[Table] Example 15 15 mm thick polytetrafluoroethylene sheet made of tetrafluoroethylene mophopolymer (Nippon Valqua Industries Co., Ltd., VALFLON R sheet)
No. 7000), this is oriented by compression molding using the press molding machine shown in Fig. 3, with the cold/hot die plate 11 set at 260°C, and then the cold/hot die sheet 11 is cooled to 220°C. , the temperature of the molded product was set to 220℃, the molded product was taken out from the molding machine, and left to cool while allowing free shrinkage, and the average maximum expansion ratio was 5.8.
A polytetrafluoroethylene sheet of the present invention having a thickness of 2.6 mm was obtained. Table 5 shows the results. From the results in Table 5, it can be seen that the product of the present invention obtained by the method of Example 15 has improved dimensional stability and impact resistance while maintaining excellent compression creep resistance.

【table】

[Table] Example 16, Comparative Examples 20, 21 Thirty polytetrafluoroethylene sheets (manufactured by Nippon Valqua Industries Co., Ltd., VALFLON R cutting tape No. 7900) with a thickness of 0.33 mm made of a tetrafluoroethylene homopolymer were It was used as a polytetrafluoroethylene sheet for laminated substrates, and in the same manner as in Example 1, it was multiaxially oriented about 5 times using the press molding machine shown in Fig. The physical properties of the polytetrafluoroethylene sheet of the present invention having an expansion ratio of 3.3 and a thickness of 0.1 mm were measured (Example 16). In Comparative Example 20, a laminated polytetrafluoroethylene sheet similar to that in Example 16 was oriented 3.3 times to obtain a sheet with a thickness of 0.1 mm, and the physical properties were measured without free shrinkage under heat.
Comparative Example 21 is a commercially available unoriented polytetrafluoroethylene sheet with a thickness of 0.1 mm (Nippon Valqua Industries Co., Ltd.).
VALFLON R cutting tape No. 7900 (manufactured by Kawasaki Co., Ltd.) was used as is. For the above three types of sheets, orientation conditions, 200
ORS, water vapor permeability, and oxygen permeability at ℃
Shown in the table. From the results in Table 6, it can be seen that the polytetrafluoroethylene sheet of the present invention has a
It can be seen that the blister resistance is improved to the same extent as the oriented sheet without the oriented sheet.

[Table] Example 17, Comparative Examples 22, 23 Glass fiber-containing polytetrafluoroethylene sheet (Nihon Valqua Kogyo Co., Ltd.) was prepared in the same manner as in Example 1.
VALFLON R No. 7000-2NO (manufactured by VALFLON R No. 7000-2NO, containing 20% by weight of glass fiber) was multiaxially oriented about 5 times using the press molding machine shown in Figure 3, and then 220
The polytetrafluoroethylene sheet of the present invention was obtained by free shrinking by heating at °C. (Example 17). Comparative example 22
was obtained without heating free shrinkage at the same average maximum expansion ratio as in Example 17, and in Comparative Example 23.
is a polytetrafluoroethylene sheet with unoriented glass fibers. The results are shown in Table 7. From the results in Table 7, the polytetrafluoroethylene sheet of the present invention maintains excellent compression creep resistance even when containing glass fiber, and
It can also be seen that the dimensional stability is improved.

【table】

[Table] Example 18 and Comparative Examples 24 to 30 Unoriented polytetrafluoroethylene sheets of various thicknesses (manufactured by Nippon Valqua Industries Co., Ltd., VALFLON)
R No.7000, specific gravity 2.16, number average molecular weight approximately 1×10 ⁷ )
is used as a polytetrafluoroethylene base,
This was oriented by compression molding using the press molding machine shown in Figure 3, and polytetrafluoroethylene oriented sheets (with a thickness of about 2
mm) was obtained. During molding, Shin-Etsu silicone (KF965, 10000cs) was used as a lubricant, and 0.1mm
A thick polytetrafluoroethylene film was oriented between the die 1 and the polytetrafluoroethylene substrate 3. In addition, cold/heat die plate 1
1 was set to room temperature. Next, the thus obtained polytetrafluoroethylene sheet was subjected to free shrinkage under heating to obtain a product of the present invention. Table 8 shows the orientation temperature, heating free shrinkage temperature, average maximum expansion ratio D, ORS at 200°C, compression set S, dimensional change rate, and specific gravity. Below, the product of the present invention will be explained in detail using the drawings. Figure 14 shows the average maximum expansion magnification of each sample and
The ORS at 200℃ is shown. Comparative Example 24 is an unoriented polytetrafluoroethylene sheet. As the average maximum expansion magnification D is increased, as shown by arrow (1)
ORS increased (Comparative Examples 24 to 28). Next, each of the two samples obtained in Comparative Example 28
Freely shrink by heating at 80℃ and 150℃ for 2 hours, then 200℃
When the ORS was measured, hysteresis was drawn as shown by arrow (2) (Comparative Examples 29 and 30). Furthermore, the sample obtained in Comparative Example 28 was heated to 220°C.
When subjected to free shrinkage under heating for a period of time, the ORS was 0 even though the average maximum expansion ratio D was greater than 1.
Thus, a product of the present invention was obtained (Example 18). Figure 15 shows 200% of Example 18 and Comparative Examples 25 to 30.
℃, dimensional change rate in 10 hours and ORS at 200℃
showed the relationship between The product of the present invention had a dimensional change rate of 0 and had excellent dimensional stability. Figure 16 shows Example 18 and Comparative Examples 24 to 30.
Dimensional change rate at 200℃ for 10 hours and 500℃ at 200℃
The relationship between Kg/cm ² and compression set S in 1 hour is shown. From the above results, it can be seen that the molded article of the present invention has excellent compression creep resistance and dimensional stability.

[Table] Examples 19 to 24 Various oriented polytetrafluoroethylene sheets were obtained in the same manner as in Example 18. The result is the 9th
Shown in the table. Comparative Examples 31-35 Oriented polytetrafluoroethylene sheets were obtained in the same manner as in Comparative Examples 24-30. The results are shown in Table 9. From the results in Table 9, it can be seen that the molded products of the present invention have excellent compression creep resistance and dimensional stability.

[Table] Example 25 A 13 mm thick polytetrafluoroethylene sheet made of a tetrafluoroethylene homopolymer (VALFLON R sheet No. 7000, manufactured by Nippon Valqua Industries, Ltd.) was press-formed as shown in Figure 3. Using a machine, the cold/hot die plate 11 is set at 220°C to perform orientation by compression molding.Then, the molded product is taken out at a temperature of 220°C, and allowed to cool while allowing free shrinkage to reach the average maximum expansion. Magnification 3.3x,
A polytetrafluoroethylene sheet of the present invention having a thickness of 3.9 mm was obtained. Table 10 shows the results. From the results in Table 10, the polytetrafluoroethylene sheet of the present invention obtained by the method of Example 25 is as follows:
It can be seen that the dimensional stability is improved while maintaining excellent compression creep resistance.

【table】 [Brief explanation of drawings]

FIG. 1 shows the progress of orienting a polytetrafluoroethylene polymer by compression molding. 1... Compression die, 2... Inner surface, 3... Polytetrafluoroethylene polymer base, 4... Oriented polytetrafluoroethylene polymer Figure 2 shows lamination of polytetrafluoroethylene polymers. The figure shows the base material before molding. 3...Single layer substrate of polytetrafluoroethylene polymer, 6...Other thermoplastic resin film or polytetrafluoroethylene polymer film,
7...Laminated base of polytetrafluoroethylene polymer FIG. 3 is a schematic diagram showing the structure of a compression die suitable for carrying out the present invention. 2...Die inner surface, 3...Polytetrafluoroethylene polymer base, 10...Die plate,
11...Cold/heat die plate, 13, 18...Insulating material, 14...Die, 15...Spacer for setting thickness Figures 4 and 5 show the average maximum expansion of polytetrafluoroethylene polymer. We will show you how to find the maximum contraction magnification measured in the direction where the maximum contraction is the minimum. Figures 6 and 7 show orientation by ram extrusion. 24...Prismatic heating cylinder, 25...Square ram, 26...Ram extrusion molding machine, 27...Die, 28...Lubricant introduction path, 29...Bleeding port, 3
0...Roll Figure 8 shows a compression set S measuring device. 31... Hot press plate, 32... Stainless steel plate, 33... Tempered glass plate, 34... Test piece Figure 9 shows the ORS measuring device. 35...Tensile testing machine, 36...Crosshead (fixed), 37...Gripper, 38...Gripper fixing jig, 39...Test sample, 40...Load cell, 41...Oil bath, 42... Lifter (for raising and lowering oil bath) Figure 10 shows the dimensional change and shrinkage start temperature during heating of the oriented polytetrafluoroethylene polymer measured using TMA. FIG. 11 shows a method for determining the dimensional change rate. FIG. 12 shows a method for placing a polytetrafluoroethylene polymer base in a die when the temperature of the inner surface of the die is less than (surface layer temperature of the polytetrafluoroethylene polymer base −50°C). 1... Compression die, 3... Polytetrafluoroethylene polymer base, 6... Thermoplastic resin film or polytetrafluoroethylene polymer film, 50... Projections, 51... Polytetrafluoroethylene polymer base Jig for holding the union in space FIG. 13 shows the relationship between the average maximum expansion ratio D and the Izod impact strength. The fourteenth shows the relationship between the average maximum expansion magnification D and the ORS. Figure 15 shows
The relationship between dimensional change rate and ORS is shown. Figure 16 shows
The relationship between dimensional change rate and compression set S is shown.

Claims (1)

[Claims] 1 Ultra-high molecular weight polytetrafluoroethylene polymer molded product with a number average molecular weight of approximately 1 million or more, a specific gravity of 1.8 or more, an orientation release stress of less than 5 kg/cm ² at 200°C, and a thermomechanical analysis ( Thermomechanical
Shrinkage start temperature measured using analysis) is 80
℃ or higher and higher than the shrinkage start temperature, the molded article has a heat shrinkage characteristic of shrinking in substantially mutually parallel planes and expanding in a direction perpendicular to the plane. In this case, the average maximum expansion ratio in the direction perpendicular to the plane is 2 times or more and 10 times or less, and the maximum contraction ratio in the direction in which the maximum contraction in the plane is minimum is 0.71 or less. Polytetrafluoroethylene polymer molded product.