JPH07237257A - See-through member - Google Patents

Abstract

PURPOSE:To provide a see-through member which can he molded under an ordinary molding condition, does not cause a trouble such as contamination by eluate and is comprised of a PFA composition and superior in clearness of an image. CONSTITUTION:A see-through member is a molten molded product of a tetrafluoroethylene/fluoroalkoxytrifluoroethylene copolymer composition containing polytetrafluoroethylene possessing a crystallization temperature of at least 305 deg.C and a crystallization heat of at least 50J/g. It is preferable that polytetrafluoroethylene contained in the copolymer composition is at least 0.01wt.% and not exceeding 4wt.%. Then it is preferable that a recrystallized mean spherulite diameter of the molded product does not exceed 15 microns.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a see-through member obtained by melt-extruding a tetrafluoroethylene / fluoroalkoxytrifluoroethylene copolymer composition having excellent image definition.

[0002]

2. Description of the Related Art Conventionally, fluororesins such as polychlorotrifluoroethylene have been used as see-through members for peep windows and liquid level gauges for storage tanks and the like which are required to have heat resistance and chemical resistance. However, the melt-formable tetrafluoroethylene / fluoroalkoxytrifluoroethylene copolymer (known as PFA), which has the best heat resistance and chemical resistance among fluororesins, is used to observe objects through molded products. when doing,
Since the image definition is low, it is difficult to see the details of the object, and the material is not suitable as a see-through member.

The reason why the image clarity of the PFA molded product is low as described above is that coarse spherulites reaching a diameter of 20 to 150 microns are formed during crystallization of PFA which is a crystalline resin. Generally, the size of spherulites can be reduced by increasing the number of spherulite nuclei, and various inorganic or organic crystal nucleating agents have been added to crystalline resins for this purpose. In the case of fluororesins as well, in the case of polychlorotrifluoroethylene, metal sulfates (Japanese Patent Application Laid-Open No. Sho 4
9-5153), for polyvinylidene fluoride, inorganic substances such as alkali metal salts (Japanese Patent Publication No. 49-17015) and organic cyclic compounds (Japanese Patent Publication No. 48-33983) have been proposed. However, no crystal nucleating agent suitable for PFA has been proposed. Also, adding a crystal nucleating agent of the kind described above to PFA causes contamination due to elution of the nucleating agent, and
It is not preferable because it will impair the advantages of FA. On the other hand, it is possible to suppress the growth of spherulites by rapidly cooling the resin from a molten state by means of water cooling or the like, but this is a practically difficult method and the distortion of the molded product becomes large. Problems also arise.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a transparent member which can be molded under normal molding conditions and which is made of a PFA composition which does not cause problems such as contamination by eluates and which has excellent image clarity. To provide.

The present inventors have studied to achieve the above-mentioned object, and as a result, by adding a small amount of a specific polytetrafluoroethylene (PTFE) to PFA, the spherulites are refined and PFA The present invention has been completed by finding that the image sharpness of a melt-molded product can be significantly improved without impairing the properties.

[0006]

A transparent member according to the present invention is a tetrafluoroethylene / fluoroalkoxytrifluoroethylene containing polytetrafluoroethylene having a crystallization temperature of 305 ° C. or higher and a heat of crystallization of 50 J / g or higher. It is a melt-molded product of the copolymer composition. This see-through member is a transparent molded article for observing a substance through see-through without directly exposing the naked eye to the substance.

As will be seen in Examples and Comparative Examples described below, the image clarity of the molded product and the molded product (a test piece obtained by cutting off a part of the molded product) are melted and the melt is heated to 10 ° C. Average spherulite diameter (hereinafter referred to as recrystallized average spherulite diameter) or maximum spherulite diameter (hereinafter referred to as recrystallized maximum spherulite diameter) formed when recrystallized by cooling at a cooling rate of 1 / min. ), The smaller the recrystallized average spherulite diameter (or the recrystallized maximum spherulite diameter), the higher the image clarity of the molded article under the same molding conditions. The transparent member of the present invention has a recrystallized average spherulite diameter of 15
When the particle size is not more than 10 μm, preferably not more than 10 μm, the image definition becomes excellent.

In the present invention, tetrafluoroethylene /
Fluoroalkoxytrifluoroethylene copolymer (P
FA) is a crystalline copolymer of tetrafluoroethylene and fluoroalkoxytrifluoroethylene represented by Formula 1 or Formula 2, and the content of fluoroalkoxytrifluoroethylene in the copolymer is 1 to 10% by weight. belongs to. This copolymer can be melt-molded by melt extrusion molding, injection molding, etc., and is 0.5 to 500 g / 10 minutes at 372 ° C. ± 1 ° C., preferably 0.5 to 50 g.
It has a melt flow rate (MFR) of / 10 minutes. Examples of the fluoroalkoxytrifluoroethylene include perfluoro (methyl vinyl ether), perfluoro (propyl vinyl ether), perfluoro (isobutyl vinyl ether) and the like.

[0009]

[Chemical 1]

[0010]

[Chemical 2]

In the present invention, the above-mentioned P is used for refining spherulites.
Polytetrafluoroethylene (PTF) contained in FA
E) is a modification containing a homopolymer of tetrafluoroethylene (TFE) or a modifier such as a trace amount of less than 1% by weight of hexafluoropropylene (HFP), fluoroalkoxytrifluoroethylene, fluoroalkylethylene or chlorotrifluoroethylene. It is PTFE and satisfies the two conditions that the crystallization temperature measured by a differential scanning calorimeter (DSC) by the method described below is 305 ° C. or higher and the heat of crystallization is 50 J / g or higher.

There is a correlation between the crystallization temperature of PTFE contained in PFA and the effect of refining spherulites, and the higher the crystallization temperature, the smaller the content of spherulites can be. The crystallization temperature of PTFE needs to be 305 ° C. or higher, and is preferably 310 ° C. or higher.

Further, even if the crystallization temperature is 305 ° C. or higher, in the PTFE having a heat of crystallization of less than 50 J / g, the PFA powder and the PTFE fine particles having an average particle size of 0.05 to 1 micron are higher than the melting temperature of PTFE. When a composition uniformly mixed at a low temperature is molded under a condition that the shearing action on the molten composition is small, such as melt compression molding or melt piston extrusion, fine spherulites can be obtained. However, the spherulite refining effect tends to be lost under conditions in which a large shearing action is exerted on the molten composition during screw kneading or extrusion during screw kneading or the like.

It is known that the crystallization temperature and heat of crystallization of PTFE are affected by two factors, the modifier content and the molecular weight. P molded by compression preforming / firing method
While the “molding powder” of TFE and the “fine powder” of PTFE formed by the paste extrusion / firing method each have a number average molecular weight of several million or more, the above-mentioned PTFE suitable for the purpose of the present invention. Has a lower molecular weight and higher crystallinity. Such PTFE is used in the known production method of low molecular weight PTFE such as TFE polymerization in the presence of a chain transfer agent, “molding powder”, “fine powder” or thermal decomposition or radiolysis of these molded products. It can be obtained by selecting the condition in consideration of two factors. Since such PTFE has low molecular weight and high crystallinity, it lacks in mechanical strength, and unlike "molding powder" and "fine powder", it is not used by itself for molding purposes, but the purpose of the present invention is to It has been found that the minor additions achieved do not have any adverse effect on the mechanical properties of PFA.

By incorporating PTFE satisfying the above-mentioned conditions into PFA, the spherulite diameter sharply decreases. Regarding the lower limit of the content, as the crystallization temperature of the PTFE to be contained increases as described above, it is difficult to limit the numerical values because the spherulites can be made finer with a smaller content, but it is difficult to limit the composition from the molten state to 10 ° C / It is desirable to include an effective amount to provide a recrystallized average spherulite size of 15 microns or less, preferably 10 microns or less when crystallized at a cooling rate of minutes. As shown in Examples described later, when PTFE having a crystallization temperature Tc of 314 ° C. (heat of crystallization Hc of 60 J / g) was contained, the recrystallized average spherulite diameter was 0.01% by weight. Is 13 microns, so 0.01% by weight is a guideline for the lower limit of the content.

The spherulite diameter tends to decrease with an increase in the PTFE content, but when the content is 1 to 2% by weight or more, the degree of decrease of the spherulite diameter with the increase of the content is small, and the spherulite diameter is small. Is almost constant. The upper limit of the PTFE content varies depending on the MFR of PFA, the use conditions of the molded product, etc., but generally the crystallinity of the composition tends to increase as the PTFE content increases, and the content of 2 to 4% by weight or more With the amount, the image sharpness and the mechanical properties tend to deteriorate. For this reason, the content of PTFE is usually 4% by weight or less, preferably 2% by weight or less.

As a method of incorporating PTFE into PFA, known methods such as a melt-kneading method, a dry blending method of PFA pellets or powder and PTFE powder, a wet blending method of PFA dispersion liquid and PTFE powder or PTFE dispersion liquid, etc. Both can be used. The PTFE used in the present invention has an extremely high compatibility with PFA in the molten state, so that it is easy to perform PF at the time of melt kneading or melt extrusion.
Disperse in A to give a very homogeneous composition. Therefore,
The form of PTFE to be added is not particularly limited, and powders of several microns to several tens of microns are usually used in consideration of workability.

There are no particular restrictions on the molding conditions for obtaining the see-through member of the present invention, and the conditions such as extrusion molding, injection molding, transfer molding and compression molding that have been conventionally applied to PFA can be used as they are. . Further, JP-A-62-104822 and JP-A-2-1632
The method using a fluorine gas described in 128 can also stabilize the polymer end groups of the obtained composition or molded article.

The present invention will be described in detail below with reference to Examples and Comparative Examples. As PFA, tetrafluoroethylene / perfluoropropyl vinyl ether (P
PVE) copolymer, PPVE content; melt flow rate (MFR); melting temperature, crystallization temperature, heat of crystallization; recrystallization average spherulite diameter; recrystallization maximum spherulite diameter; tensile strength , Elongation; MIT bending life and perspective distance were measured by the following methods.

PPVE content: Absorbance ratio was determined from the infrared absorption spectrum (nitrogen atmosphere) of a film having a thickness of about 50 μm obtained by compressing sample PFA at 350 ° C. and then water cooling, and previously containing PPVE. The PPVE content of the sample was determined using a calibration curve obtained with a standard film of known amount.

[0021]

[Equation 1]

Melt flow rate (MFR): Using a melt indexer manufactured by Toyo Seiki Co., Ltd., a 5 g sample was measured at 372 ° C.
After filling into a cylinder with an inner diameter of 9.53 mm held at ± 1 ° C and holding it for 5 minutes, push it out through an orifice with an inner diameter of 2.1 mm and a length of 8 mm under a load of 5 kg (piston and weight), and the extrusion speed at this time (G / 10 minutes) was determined as MFR.

Melting temperature, crystallization temperature, heat of crystallization: A differential scanning calorimeter DSC7 type manufactured by Perkin Elmer was used.
A 5 mg sample is weighed, placed in a dedicated aluminum pan, crimped by a dedicated crimper, and then stored in the DSC body to start heating. The temperature was raised from 200 ° C to 380 ° C at 10 ° C / min, and the melting peak temperature was determined as the melting temperature (Tm1: ° C) from the melting curve obtained at this time. Sample at 380 ° C
The temperature was lowered to 200 ° C. at 10 ° C./min, and the crystallization peak temperature was determined as the crystallization temperature (Tc, ° C.) from the crystallization curve obtained at this time. Heat of crystallization (H
c: J / g) was determined according to a conventional method from the peak area determined by connecting a point where the curve deviates from the baseline and a point where it returns to the baseline with a straight line before and after the crystallization peak. Hold the sample at 200 ℃ for 1 minute, then again to 380 ℃ 10 ℃
The temperature was raised at a heating rate of / min, and the melting peak temperature was determined as the melting temperature (Tm2: ° C) from the melting curve obtained at this time. Each numerical value was obtained to the first decimal place and rounded by the method of JIS Z8401.

Recrystallized average spherulite diameter: A slice having a thickness of about 0.2 mm obtained by slicing the melt-molded product was placed as a sample on a slide glass and attached to a METTLER FP82HT type hot stage. The sample was melted by raising the temperature to 360 ° C. at 40 ° C./min, held at 360 ° C. for 3 minutes, and then cooled to 200 ° C. at 10 ° C./min for recrystallization. After the temperature of the sample portion reached 200 ° C., the slide glass on which the sample was placed was removed from the hot stage, and the surface of the sample was observed with an optical microscope magnification of 100 and 400 times while confirming the spherulite structure by polarization. The diameter of 200 consecutive spherulites observed on the sample surface was measured, and the average value was defined as the recrystallized average spherulite diameter. In addition, the largest one was defined as the recrystallized maximum spherulite diameter. Since the spherulites are observed as distorted polygons due to collision with adjacently grown spherulites, the major axis diameter is defined as the diameter. For recrystallized samples with an average spherulite diameter of 5 microns or less, a scanning electron microscope (3000 magnification and 5
000 times) was also used to measure the spherulite diameter. In the following examples and comparative examples, the extruded product during MFR measurement was sliced in the direction perpendicular to the extruded direction and used as a sample.

Tensile strength, elongation: The sample was filled in a mold heated to 350 ° C. on a hot press, heated for 20 minutes, and then pressed at a pressure of about 5 kgf / cm ² for about 1 minute, and then the mold was opened. Transfer to a room temperature press and transfer about 30 kgf / cm ²
And press for 20 minutes to cool. ASTMD14 from a sheet with a thickness of about 1.5 mm created in this way
According to 57-83, 5 test pieces were cut out, and a tensile test was performed at an initial gripping interval of 22.2 mm and a pulling speed of 50 mm / min to determine the strength and elongation at break (average value of 5 test pieces).

MIT Flex Life: After heating the sample in a mold heated to 350 ° C. on a hot press for 15 minutes, P
30 to 60 kgf / c, depending on FA MFR
Press at a pressure of m ² for about 1 to 4 minutes, then move the mold to a room temperature press and press to about 50 kgf / cm ² ,
Leave to cool for a minute. Approximately 110 m in length from a film having a thickness of 0.19-0.21 mm created in this way
m, 15 mm wide test piece cut out, ASTM D-21
It is attached to a MIT massage and fatigue tester manufactured by Toyo Seiki according to the standard of 76, and at a load of 1 kg, at an angle of 135 degrees to the left and right, 1
The number of times of reciprocal bending (average value for 3 test pieces) until the test piece is bent at a speed of 75 times / min is M
The IT bending life was used.

Permeation limit distance: 4 g of the sample was filled in a cylindrical mold having an inner diameter of 28 mm, heated for 30 minutes on a hot press heated to 370 ° C., and then transferred to a room temperature press for 50 kgf / cm ^2. Let it cool for 20 minutes while pressurizing. The disc-shaped test piece having a thickness of 3 mm thus obtained was attached to the tip of a cylinder having an inner diameter of 29 mm and a length of 30 mm, and a black line having a width of 1 mm was drawn at 1 mm intervals through the test piece from the other end of the cylinder. The white plate is visually observed under an illumination of 500 lux. The maximum distance from the test piece where the distance between the black line and the black line can be discriminated to the white plate was measured and used as the perspective limit distance, which was used as a measure of image clarity.

[0028]

Examples 1 to 6, Comparative Examples 1 to 3 PPVE content 3.0
% By weight, MFR 2.0 g / 10 minutes, recrystallized average spherulite diameter 44 microns, recrystallized maximum spherulite diameter 68 micron PF
99 parts by weight of melt-extruded pellets of A and 1 part by weight of 8 kinds of PTFE powders of A to H (average particle size 2 to 20 microns) having the characteristics shown in Table 1 were mixed with a roller mixer (R-60H type manufactured by Toyo Seiki Co., Ltd., Mixer capacity approx. 60 cc, kneading material: Hastelloy C276), and kneading part set temperature 3
50 ° C., resin temperature 345 to 352 ° C., roller rotation number 1
It was melt-kneaded at 5 rpm for 10 minutes to obtain a PFA composition containing 1% by weight of PTFE. For comparison, PTFE was not added and only PFA was melt-kneaded under the same conditions. Each composition was melt-kneaded and then cut into pellets of 3 to 5 mm square to prepare samples for molding. The properties of each composition and the test pieces molded from the composition are shown in Table 2. The results of measuring the recrystallized average spherulite diameter and the recrystallized maximum spherulite diameter of the test piece used for measuring the perspective limit distance were the same as those shown in Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

When PFA does not contain PTFE (Comparative Example 1), the heat of crystallization (Hc) of the contained PTFE (A) is 50.
When it is less than J / g (Comparative Example 2) and contained PTFE
When the crystallization temperature (Tc) of (H) was less than 305 ° C. (Comparative Example 3), the recrystallized average spherulite diameter of the melt-molded product was 24 μm or more (the recrystallized maximum spherulite diameter was 35 μm). Above), while the see-through limit distance is 5 cm, it is 30
In each of Examples 1 to 6 containing 1% by weight of PTFE (B to G) having a crystallization temperature (Tc) of 5 ° C. or higher and a heat of crystallization (Hc) of 50 J / g or higher, recrystallization of the melt-molded product was performed. The average spherulite diameter is 15 microns or less (the maximum recrystallized spherulite diameter is 20 microns or less), and the perspective limit distance is 75 cm or more. Further, comparing Examples 1, 3 and 5, PTFE (D) having a highest crystallization temperature (Tc) of 316 ° C.
Containing PTFE (B) having the smallest recrystallized average spherulite diameter of 2 μm (recrystallized maximum spherulite diameter of 4 μm) and a crystallization temperature of 314 ° C. Recrystallization average spherulite diameter of 3 micron (recrystallization maximum spherulite diameter of 5 micron) followed by recrystallization of Example 5 containing 308 ° C PTFE (F), which has the lowest crystallization temperature. The average spherulite diameter is 12 microns (the maximum recrystallized spherulite diameter is 18 microns), which is the largest in the examples, and the perspective limit distance is the smallest in the examples.

[0032]

[Comparative Example 4] A fine powder obtained by aggregating an aqueous dispersion of PTFE has a melting peak temperature Tm1 of 337 ° C, Tm2 of 327 ° C, and a crystallization temperature of 3.
14 ° C, crystallization heat is 34 J / g, average particle size is about 0.2
An aqueous dispersion of micron PTFE with an average particle size of about 0.
2 micron, PPVE content of 3.0% by weight, melting temperature (Tm2) of 309 ° C. to an aqueous dispersion of PFA, added so that the weight ratio of PFA resin component and PTFE resin component is 99: 1, and stirred. While nitric acid was added to break the emulsion, trichlorotrifluoroethane was added, and the mixture was granulated by stirring. The granulated powder thus obtained was washed with water and then dried and heat-treated at 290 ° C. for 15 hours to obtain a powder composition having an average particle size of about 450 μm. The composition had an MFR of 1.7 g / 10 minutes, a melt indexer extrudate had an average recrystallized spherulite diameter of 2 microns, a maximum recrystallized spherulite diameter of 3 microns, and a perspective limit distance of 50 cm. However, when this powder composition was put into a roller mixer and melt-kneaded in the same manner as in Example 1, MFR after melt-kneading
Was 1.7 g / 10 minutes, the melt-indexer extrudate had a recrystallized average spherulite diameter of 33 microns, a recrystallized maximum spherulite diameter of 45 microns, and a perspective distance of 5 cm. The PFA powder obtained in the same manner without adding PTFE had an MFR of 2.4 g / 10 minutes and a recrystallized average spherulite diameter of 5
6 micron, recrystallized maximum spherulite diameter is 70 micron, MFR after melt-kneading is 2.3 g / 10 minutes, melt indexer extrudate recrystallized average spherulite diameter is 35 micron, recrystallized maximum The spherulite diameter was 45 μm, and the see-through limit distance was 5 cm. The above results show that the heat of crystallization is 34 J /
In the PFA powder added with PTFE of this comparative example of g, the recrystallization average spherulite diameter is 2 μm and the recrystallization maximum spherulite diameter is 3 μm, which is extremely small in the melt indexer extrudate having a small shearing action. , The spherulite refining effect is lost when kneading is performed under shearing action during melting, and the image clarity is reduced.

[0033]

Example 7: PPVE content 3.0% by weight, MFR 1.
9 g / 10 minutes, recrystallized average spherulite diameter 55 micron, recrystallized maximum spherulite diameter 77 micron PFA melt-extruded pellets and PTFE powder B (Tc = 3) used in Example 1
14 ° C., Hc = 60 J / g) with the content shown in Table 3,
Melt kneading was carried out in the same manner as in Example 1. Table 3 shows the properties of the obtained composition and the test pieces molded from the composition. In this example, when a MIT flex life test piece was prepared, a pressure of 60 kgf / cm ² for about 4 minutes was adopted as a pressurizing condition before transferring the die to a room temperature press.

[0034]

[Table 3]

The results shown in Table 3 show that even if the PTFE content is 0.1% by weight, the average recrystallized spherulite diameter is 44 to 13 microns when the content is not, and the maximum recrystallized spherulite diameter is If the content is not contained, it will be drastically reduced from 63 microns to 20 microns.
To improve. If it is contained in an amount of 1% by weight, the recrystallized average spherulite diameter is 4 microns and the recrystallized maximum spherulite diameter is 5 microns.
If it is contained by weight, the average recrystallized spherulite diameter is 3 microns,
The maximum recrystallized spherulite diameter is reduced to 4 microns and the transillumination limit distance is increased to 90 cm. However, even if contained in an amount of 2% by weight or more, the recrystallized average spherulite diameter and the recrystallized maximum spherulite diameter do not decrease further and become almost constant, and the perspective limit distance tends to decrease. Further, it can be seen that when the content is 4% by weight or less, there is no adverse effect on the tensile strength, elongation and bending life.

[0036]

Example 8 PPVE content 3.4% by weight, MFR1
5.0 g / 10 minutes, recrystallized average spherulite diameter 49 microns,
Recrystallized PFA melt-extruded pellets with a maximum spherulite diameter of 62 microns and the PTFE powder B (T
c = 314 ° C., Hc = 60 J / g) at the contents shown in Table 4 were melt-kneaded in the same manner as in Example 1. The properties of the resulting composition and test pieces molded from the composition are shown in Table 4.
Shown in. In this example, when a MIT flex life test piece was prepared, a pressure of 30 kgf / cm ² for about 1 minute was adopted as the pressurizing condition before transferring the mold to a room temperature press.

[0037]

[Table 4]

From the results shown in Table 4, the recrystallized average spherulite diameter is 38 to 13 microns when the PTFE content is 0.01% by weight, and the recrystallized maximum spherulite diameter is the same. It is drastically reduced from 50 microns to 18 microns in the case of no inclusion, and the perspective limit distance is improved from 5 cm to 65 cm. However, it can be seen that the inclusion of 4 wt% or more does not significantly improve the perspective limit distance.

[0039]

The transparent member made of the PFA composition of the present invention is superior in heat resistance and chemical resistance as compared with the conventional transparent member made of polychlorotrifluoroethylene, etc. Suitable for windows, liquid level gauges, windows for monitoring reaction vessels used at high temperatures, etc. Since PTFE used as an additive has the same heat resistance and chemical resistance as PFA, the problem of contamination by eluates does not occur.

Claims (5)

[Claims] 1. A crystallization temperature of 305 ° C. or higher and 50 J / g
A transparent member, which is a melt-molded product of a tetrafluoroethylene / fluoroalkoxytrifluoroethylene copolymer composition containing polytetrafluoroethylene having the above heat of crystallization. 2. The see-through member according to claim 1, wherein the polytetrafluoroethylene contained in the tetrafluoroethylene / fluoroalkoxytrifluoroethylene copolymer composition is 0.01% by weight or more. 3. The see-through member according to claim 2, wherein the polytetrafluoroethylene contained in the tetrafluoroethylene / fluoroalkoxytrifluoroethylene copolymer composition is 4% by weight or less. 4. A crystallization temperature of 305 ° C. or higher and 50 J / g.
A melt-molded article of a tetrafluoroethylene / fluoroalkoxytrifluoroethylene copolymer composition containing polytetrafluoroethylene having the above heat of crystallization,
A transparent member having a recrystallized average spherulite diameter of 15 microns or less. 5. The see-through member according to claim 4, wherein the recrystallized average spherulite diameter is 10 microns or less.