JPH0132054B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in compression stretch molding or extrusion stretch molding of thermoplastic resins.

The objects of the present invention are to improve the moldability of resins such as ultra-high molecular weight resins that are difficult to extrude and stretch mold due to their high viscosity, and to improve the extrusion and stretch molding of easily heat decomposable resins such as polyvinylidene chloride. Improvements in the method of forming biaxially oriented sheets or pipes by biaxially stretching in an extrusion die in a high viscosity state, improvements in the method of forming biaxially oriented sheets by compressing thermoplastic resin in a compression mold, etc. The object of the present invention is to provide a stretch forming method that achieves the following.

In order to improve resin flow within the die during extrusion stretch molding or compression stretch molding of thermoplastic resins,
It is known to coat the inner surface of the die with a lubricant (e.g. USP2597553, USP2688153,
USP3504075 etc.)

Coating the inner surface of the die with a lubricant significantly improves the flow of the thermoplastic resin within the die, allowing molding to be performed at low pressure.

However, there are various problems with lubricant coating on the inner surface of the die.

The biggest problem is that it is difficult for the lubricant to leak uniformly over a certain height on the inner surface of the die, and the resin flows faster in areas covered with more lubricant than in other areas. , which makes it difficult to achieve uniform molding. Roughening the inner surface of the die makes it easier to coat the lubricant uniformly on the inner surface of the die.
Although it is described in USP4087222, this is insufficient. Furthermore, it is necessary to clean the lubricant adhering to the molded product, and there are problems such as there being no easy cleaning method. The present invention is a molding method that improves these problems.

In compression stretch molding or extrusion stretch molding, in which a heated thermoplastic resin is stretched by compression or extrusion in a die, the inner surface of the die is coated with a lubricant, and the resin is heated. The plastic resin has at least three layers, the surface layer resin has a lower viscosity than the inner core resin during molding, the surface layer resin and the inner core resin are non-adhesive and can be easily peeled off after molding, and the thickness of the surface layer is the same as the thickness of the inner core layer. This is a thermoplastic resin stretch molding method characterized by a thickness of 1/10 or less. In other words, a thin layer with good fluidity is provided on the surface layer of the thermoplastic resin, and the surface layer with good fluidity compensates for poor flow due to unevenness or thinness of the lubricant on the inner surface of the die, and improves the inner core layer of the resin. It is made to flow.

The viscosity of the surface resin during molding is preferably 1/2 or less of the viscosity of the core resin, and the surface resin is preferably a soft resin with a low glass transition temperature such as polyethylene or polypropylene, particularly polyolefin.

The present invention will be explained with reference to the drawings.

FIG. 1 is an explanatory diagram showing the flow state of resin and polymer in the die.

FIG. 2 is a graph showing the relationship between temperature and viscosity of various thermoplastic resins or polymers.

FIG. 3 is an explanatory view showing the process of forming a biaxially oriented sheet by a compression stretch forming method.

FIGS. 4 and 7 are cross-sectional diagrams showing an apparatus for forming biaxially oriented sheets by extrusion stretch molding.

FIG. 5 is an explanatory diagram showing an enlarged stretching portion for forming a biaxially oriented sheet using the apparatus shown in FIG. 4.

FIG. 6 is a cross-sectional view showing an apparatus for forming biaxially oriented pipes by extrusion stretch molding.

FIG. 1 shows the velocity at each position when the thermoplastic resin or thermoplastic resin and polymer flows through the die. When the thermoplastic resin is flowed through the die at a low speed, a speed 1 and a speed curve 2 shown in 1-1 are shown. When flowing at high speed, a velocity curve 3 shown in 1-2 is shown. In 1-1 and 1-2, shearing force acts in the resin, and as a result, flow resistance becomes significantly large when high-viscosity resin flows in the die.
Further, the in-die flow of the resin shown in 1-1 and 1-2 is not suitable for biaxial stretching in the die.

When the inner surface of the die is uniformly and sufficiently coated with lubricant, the resin slides on the die surface, resulting in a so-called plug flow state 1-3. However, it is difficult to uniformly coat the inner surface of the die with the lubricant, and if the lubricant becomes non-uniform, the flow becomes a mixed flow of 1-1 or 1-2 and 1-3, resulting in large turbulence.

That is, depending on the position as shown in 1-4,
The velocity distribution becomes as shown in 4, 5, and 6, and the resin flow becomes turbulent. As in the present invention, on the surface layer of the resin layer,
When a thin, well-flowing layer 8 is provided, the inner core layer 7 exhibits a flow close to a stable plug flow, resulting in a preferred velocity distribution 9 1-5.

The present invention will be explained in more detail in Sections 1-6.

Even if the inner surface of the die is coated with a lubricant, there is frictional resistance, and the flow rate of the resin layer in contact with the inner surface of the die is slow. However, when the surface layer is made of a low-viscosity resin, the flow of the low-viscosity resin layer becomes faster, canceling the frictional resistance with the die and stabilizing the flow of the resin inner core layer. As a result, the resin inner core layer exhibits a velocity distribution 10 close to a plug flow. It is preferable that the portion 11 with the highest flow rate exists in the surface layer. Even if the frictional resistance between the die inner surface and the resin layer is uneven due to uneven lubricant coating, the inner core resin exhibits a velocity distribution close to plug flow due to the presence of the low viscosity resin layer on the surface. .

Figure 2 shows the relationship between temperature and viscosity of various resins.

In Figure 2, PMMA (MW4400000) is polymethyl methacrylate with a weight average molecular weight of 4.4 million formed by cell cast polymerization, PMMA
(MW150000) is a methyl methacrylate copolymer containing 3% by weight of methyl acrylate with a weight average molecular weight of 150,000, ABS #301 is an ABS resin, Stylac #301 (manufactured by Asahi Kasei Corporation), PS #666 is a polystyrene resin, Styron #666 (manufactured by Asahi Kasei Industries, Ltd.), PP
(MI0.5) and PP (MI4) are melt index
PE M6520, an improved polypropylene obtained by randomly copolymerizing 2% by weight of ethylene with 0.5 and 4, is low density polyethylene M6520 (manufactured by Asahi Kasei Corporation).

In molding PMMA, PS, and ABS, PP and PE can be well used as the surface layer of the resin. Polyolefins such as PP and PE have the property of slipping easily inside the die, making them good as surface layer resins.

In general, the coefficient of dynamic friction between the steel (S45C) that makes up the die and various resins is the following value. (lubrication, 11 , 12
(1966) 485) Polymethyl methacrylate 0.568 Polystyrene 0.368 ABS resin 0.366 Polyvinyl chloride 0.219 Polypropylene 0.300 High-density polyethylene 0.139 Resins with a small coefficient of dynamic friction, such as PP and PE, easily slide inside the die and are suitable as surface resins. be. In particular, PP or
When PE is used as the surface layer, the effect is noticeable.

In order to make the inside of the die more slippery, it is preferable to add an additive having excellent lubricity to the surface resin.
As additives with excellent lubricity, resin acid salts such as calcium stearate, silicone oils such as polydimethylsiloxane, or low-molecular compounds that bleed more easily than the surface resin are used.

Next, a case will be described in which biaxially oriented molding of a thermoplastic resin is performed using the present invention.

FIG. 3 shows the process of forming a biaxially oriented sheet by compression stretch forming.

A thick-walled base material 14 heated to a temperature above the glass transition temperature and below the melting point of the thermoplastic resin is placed in the excessively heated compression molding die 13 3-1. Compression molding die 1
The inner surface of 3 is coated with a lubricant. The thick-walled base material 14 consists of an inner core 15 and a surface layer 16 of thermoplastic resin, the viscosity of the surface resin at the molding temperature is lower than the viscosity of the inner core resin, and the thickness of the surface layer is 1/10 or less of the thickness of the inner core layer. be.

In this state, when a compression force is applied to the compression molding die 13 to compress the thick-walled base material 14, the thick-walled base material 14 is biaxially oriented 3-2. After the compression molding die 13 is cooled and the molded article 17 is cooled and solidified, it is taken out from the die and the surface resin is peeled off from the molded article to obtain a biaxially oriented molded article with a good thermoplastic resin inner core layer.

By this compression stretch molding method, a biaxially oriented sheet having a thickness of 1 to 10 mm and a stretching ratio of 1.5 to 7 times in terms of area ratio can be favorably molded. This compression stretch molding method is particularly suitable for molding biaxially oriented sheets with a thickness of 1 mm or more. In order to form a biaxially oriented sheet with a thickness of 1 mm or more using the method of the present invention, a high compressive force is required.

On the other hand, when a biaxially oriented sheet with a thickness of 10 mm or more is molded by the method of the present invention, molding stability is lacking. The most suitable example of molding by this compression method is a thick sheet of ultra-high molecular weight polymethyl methacrylate molded by the cell cast method, with a sheet of polyolefin pasted on the surface as a so-called masking material. This is a method of molding using a compression molding die in which a lubricant is present.

The most preferable surface layer resin used in the compression stretch molding method is one in which the viscosity of the resin changes gradually due to temperature by partially crosslinking a soft polyolefin such as PE or PP. The slower the change in resin viscosity due to temperature, the wider the range of suitability for molding, which is preferable. Further, in the compression stretch molding method, it is preferable to mold the thick-walled base material in a state in which the entire surface of the thick-walled base material is covered with the surface layer resin. For example, the entire thick-walled material is made of PE,
A method of covering with a shrink sheet such as PP can be used. More preferably, the inside of the covering sheet is evacuated by vacuum packaging and then the shrink packaging is applied to achieve good molding.

FIG. 4 shows an apparatus for forming biaxially oriented sheets by extrusion stretch molding according to the present invention.

In FIG. 4, the thermoplastic resin for the inner core layer that has been heat-plasticized by the first extruder 18 is press-fitted into a die 19 in the form of a sheet. The thermoplastic resin for the surface layer heat-plasticized by the second extruder 20 is press-fitted into the die 19 to become the surface layer of the thermoplastic resin, and is formed into a three-layer sheet-like thick-walled molded product at the A portion of the die 19. die 19
Part A is cooled, and here the three-layer sheet-like thick-walled molded body is cooled to a temperature above the glass transition temperature and below the melting point of the thermoplastic resin. Portion A requires a length to cool the resin almost uniformly, and after cooling, it may be heated slightly to make the temperature uniform, if necessary.

Further, in the middle of part A, there is a series of devices for oozing lubricant in order to apply lubricant to the interface between the surface of the thick-walled molded body and the die surface. The high-pressure lubricant is guided from the lubricant introduction path 21 to a plurality of seepage ports 22, seeps out onto the surface of the resin molded article, and applies the lubricant to the interface between the molded article surface and the die surface.

The lubricant seepage port 22 has a small slit shape.
Alternatively, it is made of a material such as sintered metal that has fine communicating pores, and the lubricant seeps out from the fine pores.

When a resin molded body is cooled to a temperature above the glass transition temperature and below the melting point temperature and whose surface is uniformly coated with a lubricant, the core resin flows at approximately the same speed within the die, resulting in a so-called plug flow.

Next, in part B of the die, the plug flow molded body is rolled and biaxially oriented. Portion B of the die has a structure in which the thickness of the resin is reduced. Figure 5 shows the change in flow of the molded product in part B. The molded body is simultaneously rolled biaxially in the flow direction and in a direction perpendicular to the flow direction while maintaining the plug flow, and is biaxially oriented. The force for rolling the molded body is the force for extruding it from an extrusion molding machine.

The biaxially oriented compact is further cooled in the C section of the die, preferably to below the glass transition temperature before exiting the die 19. Cold water 2 as needed
3, it is further cooled and passed through a rubber roll 24 to become a biaxially oriented sheet.

In order to make the sheet uniform from the die 19, it is also effective to provide resistance to the rotation of the rubber roll 24 to prevent the sheet from coming out.

When the surface layer of the sheet that has come out of the rubber roll is peeled off, a biaxially oriented sheet of thermoplastic core resin is obtained.

This extrusion stretch forming method is particularly effective for forming thick biaxially oriented sheets with a thickness of 1 mm or more at a stretching ratio of 1.5 to 7 times in terms of area ratio.
Suitable for axially oriented sheets.

The formed biaxially oriented sheet can subsequently be further formed into a corrugated sheet, if desired. Such corrugated sheets are also included in the sheet of the present invention.

FIG. 6 shows how to form a biaxially oriented pipe by a similar method.

In FIG. 6, the thermoplastic resin for the inner core that has been heat-plasticized by the first extruder 25 is press-fitted into a die 26 in the form of a pipe. The thermoplastic resin for the surface layer extruded by the second extruder 27 is press-fitted into the die 26 and becomes the front and back layers of the thermoplastic resin pipe, resulting in a pipe with a three-layer structure.

The pipe becomes a pipe with a constant thickness at the D portion of the die 26, and is cooled to a temperature above the glass transition temperature and below the melting point temperature. The D portion of the die 26 needs to be long enough for the resin to be sufficiently cooled. In order to cool uniformly, it is preferable to appropriately provide a cooling section and a heating section in the D section.

Furthermore, in the middle of section D, there is a series of devices that ooze out lubricant in order to apply lubricant to the interface between the surface of the thick-walled pipe and the die surface. Also apply lubricant. The lubricant is guided from the high-pressure lubricant introduction path 28 to a plurality of seepage ports 29 on the outer and inner surfaces of the pipe, seeps out onto the pipe surface, and is applied to the interface between the pipe and the die surface. Ru.

A thick-walled pipe that is cold-poled to a temperature above the glass transition temperature and below the melting point and whose surface is uniformly coated with lubricant has a so-called plug flow in which the inner core flows at approximately the same speed within the die.

Next, in the E section of the die, the diameter of the plug flow pipe is enlarged, the wall thickness is reduced, and the pipe is biaxially oriented. The diameter of the thick-walled pipe is expanded and rolled by the extrusion pressure from the extrusion molding machine while maintaining plug flow, and the pipe is biaxially oriented simultaneously in the flow direction and the diameter direction. The biaxially oriented pipe is further cooled in the F section of the die, preferably below the glass transition temperature, before exiting the die 26.

If necessary, it is further cooled with cold water 30 and passed through a rubber roll 31 to form a biaxially oriented pipe. In order to uniformly extrude the pipe, it is effective to apply resistance to the rotation of the rubber roll 31 and apply a counter pressure to the pipe coming out of the die 26.

In the present invention, a molded article having three or more layers can be molded as necessary. FIG. 7 shows oriented molding of a five-layer structure made of three types of resins using a method similar to that shown in FIGS. 4 and 5.

In FIG. 7, a first resin heat-plasticized by a first extruder 32 is press-fitted into a die 35, and a second resin heat-plasticized by a second extruder 33 is fed into a die 35. It is press-fitted and becomes the surface layer of the first resin, forming a three-layer structure. Furthermore, the third resin is heated and plasticized in the third extruder 34 and press-fitted into the die 35 to become the outermost layer body,
It becomes a 5-layer body.

The outermost layer formed of the third resin has a lower viscosity during molding than the inner core layer formed of the first and second resins, and the thickness of each outermost layer is 1/10 or less of the thickness of the inner core layer. The outermost layer and inner core layer are non-adhesive and can be easily peeled off after molding.

Next, as in FIGS. 4 and 5, the inner surface layer of the die is coated with a lubricant, cooled, biaxially stretched, further cooled, and exited from the die 35. The surface layer 36 is peeled off from the five-layer biaxially stretched sheet to obtain a good three-layer biaxially stretched sheet 37 to which no lubricant is attached.

Forming a 5-layer biaxially oriented sheet and peeling off the outermost layer to form a 3-layer biaxially oriented sheet can also be performed in the same manner using the compression stretch molding method. When forming a five-layer biaxially stretched sheet by extrusion stretch molding or compression stretch molding, the resin in the innermost core layer (third layer) has a softening temperature lower than that of the resin in the inner surface layers (second and fourth layers). It is preferable that the viscosity at the time of molding is high or high. That is, it is preferable to use a resin for the innermost core layer (third layer) that has a higher molecular weight or a higher softening temperature and is more heat resistant than the resin for the inner core layer (second and fourth layers). .

By the extrusion stretch molding of the present invention, uniaxially oriented molding can also be performed in the same manner. Uniaxially oriented round bars and the like can be formed well. A strong linear body can be obtained by forming a uniaxially oriented round bar of polyoxymethylene, nylon, polyethylene terephthalate, etc. by the method of the present invention, and then superstretching the round bar by a tensile method.

Next, another application example of the present invention will be described.

Molded products made of ultra-high molecular weight polyethylene with a weight average molecular weight of 1 million or more have excellent wear resistance, lubricity, impact resistance, chemical resistance, sound absorption, etc. However, the stretch-molding processability is poor, and a satisfactory stretch-molded product has not been obtained to date. For example, it is molded by powder compression molding, ram extrusion molding, calender molding, etc. The extrusion stretch molding method of the present invention enables extrusion stretch molding of a resin in a high viscosity state, and can satisfactorily extrude stretch mold a highly viscous body of ultra-high molecular weight polyethylene. The molding method of the present invention can be applied to polyethylene, polypropylene, which has been difficult to mold in the past.
Suitable for stretch molding of various ultra-high molecular weight materials including ABS resin.

Trying to flow ultra-high molecular weight polymers in a laminar flow through an extrusion die requires extremely high extrusion pressure, and when high extrusion pressure is applied, melt fractures occur, making it difficult to obtain good extrusion and stretch-molded products. It is often not possible to obtain it.

The method of the present invention, that is, the inner surface of the die is coated with a lubricant during molding, and the ultra-high molecular weight material is used as the inner core,
By performing extrusion stretch molding using a low-viscosity resin as the surface layer, the ultra-high molecular weight material can be made to flow in the die in a plug flow state, resulting in a significant reduction in extrusion pressure, resulting in good molding. Goods can be obtained. According to the present invention, it is also possible to extrude sheets, pipes, irregularly shaped products, etc. of ultra-high molecular weight polymers, which have been difficult to mold up to now.

Heat-decomposable resins that easily undergo thermal decomposition, such as polyvinyl chloride and polyvinylidene chloride, are required to be molded at as low a temperature as possible. Until now, these resins have been molded at low temperatures by adding large amounts of heat stabilizers, plasticizers, etc. to lower the viscosity and improve moldability.
The method of the present invention allows molding in a high viscosity state, and allows stretch molding at low temperatures by reducing the amount of stabilizers, plasticizers, etc. added.

The surface layer thickness of the surface layer resin of the present invention is 1/10 or less of the inner core layer thickness of the inner core resin, and the thickness is 0.01 mm ~
The thickness is about 2 mm, preferably 0.05 mm to 1 mm. If it becomes too thin, the effect of improving resin flow is lost, and if it is too thick, it is not economical to peel off the surface layer resin after molding and use only the core resin. It is preferable that the surface layer be thin as long as the flow improvement effect is sufficiently recognized.

The thickness at which the flow improvement effect is observed varies depending on the viscosity of the surface layer resin, and is appropriately determined depending on the purpose of use. By peeling the surface resin layer from the molded body after molding, the lubricant adhering to the molded body can also be removed at the same time. It is of course possible to use the method of the present invention only for removing lubricant adhering to a molded article, but in this case, it is economically preferable for the surface layer to be thin.

The lubricants mentioned in the present invention include liquid paraffin,
Various silicone oils such as polydimethylsiloxane,
In addition to stearic acid, various fatty acids and their metal salts such as stearic acid metal salts, various surfactants, and mixtures of these fluids, commonly used lubricants can be used.

The viscosity during molding described in the present invention is the viscosity when biaxially oriented in biaxially oriented molding, for example,
In biaxial orientation by extrusion molding, the viscosity at part B in FIG. 4 is the most important viscosity during molding.

The thermoplastic resin mentioned in the present invention can be any thermoplastic resin that is generally used for extrusion stretch molding or compression stretch molding, and can further be a thermoplastic resin that can be thermoplasticized in an extrusion molding machine. For example, polystyrene, styrene-acrylonitrile copolymer, ABS resin, polyvinyl chloride, polymethyl methacrylate, polycarbonate, polyester, nylon, polyoxymethylene, polyphenylene ether, or blends of these resins,
Copolymers, etc.

The surface layer resin described in the present invention is particularly preferably a polyolefin having a low glass transition temperature, such as polyethylene, polypropylene, various modified polypropylenes, etc., but a wide variety of resins having a viscosity within the range described in the present invention can be used.

The biaxial stretching temperature described in the present invention, which is higher than the glass transition temperature and lower than the melting point temperature, is generally a temperature suitable for orienting a synthetic resin, and the preferable temperature range differs depending on the resin. For crystalline resins, the temperature is preferably higher than the temperature at which crystallization occurs and lower than the temperature at which the crystals melt. For non-crystalline resins, the temperature is below the molding temperature of general injection molding, extrusion molding, etc., preferably below (the molding temperature -30°C) and above (glass transition temperature +10°C).

The method of the present invention is suitable for thick-walled molded products, preferably 1 mm.
It is suitable for molding products with a thickness of 1.5 or more, preferably 1.5 or more. It is particularly suitable for forming biaxially oriented molded products such as thick sheets and pipes.

By the method of the present invention, an oriented molded product with any stretching ratio can be obtained, but a stretching ratio of 1.5 to 10 times (thickness ratio) is preferable due to the effects of stretching.

The present invention facilitates the molding of thermoplastic resins in a high viscosity state, making it possible to perform biaxially oriented molding, stretch molding of ultra-high molecular weight materials, stretch molding of easily thermally decomposable resins, etc., and its economic effects are big.

Example 1 A 20 mm thick sheet preformed product (1) of polymethyl methacrylate with a weight average molecular weight of 4 million, and a 0.5 mm thick MI0.5 having the viscosity curve shown in FIG. 2 on the front and back of the preformed product. A biaxially oriented sheet was formed by compression molding using a three-layer preform (2) to which a sheet of improved polypropylene was attached. Using the molding apparatus shown in Figure 3, the inner surface of the compression die was coated with a lubricant, polydimethylsiloxane, and the die and preform were heated to 150°C. A sheet was formed by compressing it to a thickness and stretching it to a thickness ratio of 5 times. Biaxially oriented sheet 1
The minimum required compressive force per cm ² is for preforms (1):
It was 110Kg/cm ² , and 70Kg/cm ² for the preformed product (2). By providing the surface layer with MI4 modified polypropylene having a thickness of 0.5 mm and a viscosity curve shown in Figure 2, the flow inside the die is significantly improved, and as a result, larger molded parts can be formed with low compression force. It became possible. By peeling off the surface layer of polypropylene from the biaxially oriented sheet after molding, a biaxially oriented sheet of polymethyl methacrylate to which no lubricant was attached was obtained.

Example 2 A biaxially oriented sheet was molded by extrusion using the molding apparatus shown in FIG. The inner core resin is a copolymer acrylic resin of methyl methacrylate and methyl acrylate (5% by weight of methyl acrylate, weight average molecular weight 150,000), the surface resin is MI4 improved polypropylene with the viscosity curve shown in Figure 2, and the lubricant is polydimethylsiloxane was used. The first extruder and the second extruder extrude the surface resin and the inner core resin, and the inner core is
mm, the front and back layers are 1 mm thick, and the temperature is further increased to 150℃.
Cooled to . The lubricant was allowed to seep out from the middle of part A to the interface between the surface of the thick three-layer body and the inner surface of the die. Biaxial orientation was performed 5 times in the B part of the die, and cooled in the C part to obtain a biaxially oriented three-layer sheet with a thickness of 4 mm. After molding, the polypropylene surface layer was peeled off to obtain a good biaxially oriented acrylic sheet to which no lubricant was attached. Similar biaxial orientation was performed using a single-layer acrylic resin without polypropylene on the surface layer, but the flow within the die was unstable, and flow irregularities due to poor flow were observed on the surface of the resulting biaxially oriented sheet. A uniform biaxially oriented sheet could not be obtained, and further cleaning of the lubricant on the surface was required.

Example 3 A three-layer biaxially oriented sheet was molded by extrusion molding as described in the specification using the molding apparatus shown in FIG. In Figure 7, a first extruder extruded polycarbonate, a second extruder extruded polymethyl methacrylate, and a third extruder extruded modified polypropylene. The inner surface of the die was coated with polydimethylsiloxane. Inside the die, the polycarbonate core is 10 mm thick, the polymethyl methacrylate layers on both surfaces are 5 mm thick, and the polypropylene layer is 1 mm thick. The extruded biaxially oriented sheet was a 4 mm thick 5x stretched sheet. After molding, by peeling off the outermost polypropylene layer, a good sheet with no lubricant attached was obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the flow state of resin and polymer in the die. FIG. 2 is a graph showing the relationship between temperature and viscosity of various thermoplastic resins or polymers. FIG. 3 is an explanatory view showing the process of forming a biaxially oriented sheet by an extrusion stretch molding method. FIGS. 4 and 7 are cross-sectional diagrams showing an apparatus for forming biaxially oriented sheets by extrusion stretch molding. FIG. 5 is an explanatory diagram showing an enlarged stretching portion for forming a biaxially oriented sheet using the apparatus shown in FIG. 4. FIG. 6 is a cross-sectional view showing an apparatus for forming biaxially oriented pipes by extrusion stretch molding. 1...Speed, 2, 3, 4, 5, 6, 9, 10,
12... Velocity distribution (velocity curve), 7... Inner core layer,
8... Thin layer with good fluidity, 11... Portion with the highest flow rate, 13... Compression molding die, 14... Thick wall base, 15... Inner core, 16... Surface layer, 17... Molded product, 19 ,26,36...Die,18,20,
25, 27, 32, 33, 34...extruder, 2
1, 28... Lubricant introduction path, 22, 29... Seepage port, 23, 30... Cold water, 24, 31... Rubber roll, 36... Surface layer, 37... Biaxially stretched sheet.

Claims (1)

[Claims] 1. In compression stretch molding or extrusion stretch molding in which a heated thermoplastic resin is stretched by compression or extrusion in a die, the inner surface of the die is coated with a lubricant, In addition, the thermoplastic resin has at least three layers, the surface layer resin has a lower viscosity during molding than the inner core resin, the surface layer resin and the inner core resin are non-adhesive so that they can be easily peeled off after molding, and the thickness of the surface layer is less than that of the inner core resin. A thermoplastic resin stretch molding method characterized by having a thickness of 1/10 or less of the layer thickness. 2. The molding method according to claim 1, wherein the viscosity of the surface resin during molding is 1/2 or less of the viscosity of the inner core resin. 3. The molding method according to claim 1 or 2, wherein the surface layer resin is a soft resin. 4. The molding method according to any one of claims 1 to 3, wherein the surface resin is polyolefin. 5 Compression stretch molding involves heating a preformed thermoplastic resin to a temperature above the glass transition temperature and below the melting point of the core resin, and then compressing it in a die heated to approximately the same temperature to achieve biaxial orientation. , cooled to a thickness of 1~
The molding method according to any one of claims 1 to 4, which is carried out by taking out a 10 mm biaxially oriented sheet. 6 In extrusion stretch molding, the temperature of the extruded thermoplastic resin is controlled to be above the glass transition temperature and below the melting point temperature of the core resin, and then it is biaxially oriented in a die by extrusion pressure to form a resin with a thickness of 1 to 10 mm. The molding method according to any one of claims 1 to 4, which is carried out by taking out a biaxially oriented sheet. 7. The method for molding an extrusion molded product according to any one of claims 1 to 4, wherein the inner core resin is an ultra-high molecular weight material having a weight average molecular weight of 1 million or more. 8. The molding method according to any one of claims 1 to 4, wherein the inner core resin is an easily thermally decomposable resin.