JPS61141529A - Forming of fluorine resin - Google Patents

Abstract

PURPOSE:To provide the forming method of biaxially oriented sheet, improved in mechanical properties, electrical properties, transparency and the like, by a method wherein the preform of fluorine resin, heated to a temperature near the melting point thereof, is oriented in a lubricated die under pressure. CONSTITUTION:Lubricating agent is coated on the inner surface 2 of the compression die 1, which is heated to a temperature substantially equal to the temperature of the mass of fluorine plastic. The fluorine resin mass 3, heated to a temperature near the melting point thereof, is put in the die 1 as shown by the diagram (1-1), the mass 3 is compressed to effect biaxially orientation through plug flow as shown by the diagram (1-2), the mass 3 is stabilized by cooling as it is or by keeping a temperature optimum for the crystalization thereof, and, thereafter, the biaxially oriented sheet 4 is taken out of the die 1. According to this forming method, the orientation of fluorine resin such as PTFE, which is hard to work, may be effect economically and the dense oriented sheet, prominent in mechanical properties, electrical properties, transparency or the like and few in void, may be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for molding fluororesin mainly made of tetrafluoroethylene (hereinafter abbreviated as TFE) such as polytetrafluoroethylene (hereinafter abbreviated as PTFE). It depends. More specifically, the present invention relates to a method of stretching a fluororesin such as PTF[E to form a sheet with excellent electrical and mechanical properties.

[Conventional technology]

Until now, PTPE sheets have generally been manufactured by cutting a flat or cylindrical product formed by molding PTFH molding powder through three basic steps: preforming (compression molding) → firing → cooling. This PTFI! It is known that the electrical properties, mechanical properties, and other properties of a cut sheet vary significantly depending on the raw material PTFH molding powder and the molding conditions.The reason for this is that PTFI! has a significantly high melt viscosity, resulting in voids in the cutting sheet.
It is said that this is because the

Currently, the conventional method of improving the electrical insulation properties and tensile strength of cut sheets is to use fine powder for PTPE molding as a raw material to make molded products as dense as possible (Japanese Patent Publication No. 34-10177). This is what is cut.

If even higher electrical insulation and tensile strength are expected, a method is used in which the cut sheet is rolled using rolls to reduce voids (Japanese Patent Publication No. 44-16287.
JP-A-54-61259, etc.).

[Problem that the invention seeks to solve]

However, in the rolling process using rolls, the surface conditions of the rolls, such as fine scratches and distortions, directly affect the surface condition and thickness non-uniformity of the sheet, which in turn affects the electrical and mechanical properties of the film and reduces the product yield. Therefore, it is essential to use expensive special rolls with high processing precision, and even then, the yield is low and it is economically disadvantageous. In addition, when the rolling rate is increased to obtain a particularly thin sheet, the sheet is likely to break, and when rolling is performed at high temperatures to prevent rolling breakage, the rolling roll expands and distortion occurs on the roll surface. However, there is a drawback that the thickness of the sheet becomes non-uniform, and it is difficult to form an ultra-thin sheet with a good surface condition by a rolling method.

The present invention utilizes commonly used PTPI! The object of the present invention is to provide a method for forming a biaxially stretched sheet with improved mechanical properties, electrical properties, transparency, etc.

[Means for solving problems]

The present invention is a fluororesin molding method characterized by stretching a fluororesin preform heated to near its melting point temperature in a lubricated die under pressure.

The sheet mentioned in the present invention is a general term for so-called sheets and films, and the present invention is a method suitable for forming a sheet having a thickness of about 1 to 10 days, preferably a sheet having a thickness of 10 to 5 inches.

The fluororesin mentioned in the present invention is PTFI! Or TF
It is a copolymer mainly composed of B, and the copolymer has a TFE content of 90% by weight or more, more preferably 95% by weight or more. Copolymerization components include hexafluoropropylene, perfluoroalkyl vinyl ether, and ethylene. However, a particularly preferred fluororesin in the present invention is PT
FI! It is a homopolymer or a copolymer containing 98% by weight or more of TPB, and these PTFH are ultra-high molecular weight materials having a weight average molecular weight of 1 million or more.

A fluororesin preform is a pressurized and fused molded product of the above fluororesin, and is mainly a flat preform.
It has a shape suitable for biaxial stretching.

Stretching under pressure in a lubricated die as described in the present invention refers to stretching the resin base material by causing a plug flow using compressive force or extrusion force in a compression die or extrusion die in which a lubricant is present on the inner surface of the die. It is. Compression molding and extrusion molding can be favorably used as a method of pressure molding within a die. In compression molding, a PTFE preform heated to around its melting point is compressed and stretched by plug flow, the oriented molded product is stabilized as it is under pressure, and then the molded product is taken out from the die and stabilized. "To crystallize" means to cool and solidify the material, or to maintain it at a temperature suitable for crystallization, and to take it out after sufficiently crystallizing it. In extrusion molding, PTFI is heated near its melting point! The preform is caused to plug flow in the extrusion die by extrusion pressure. PTFI into the extrusion die, which has a shape with increased width and reduced thickness! It can be stretched by extruding.

Under pressure described in the present invention means under a pressure of 10 kg/- or more,
Preferably 50kg/cj or more, more preferably 80k
It is stretched under high pressure of not less than g/cIA and not more than 2000 ksr/d. When molding is performed using the method of the present invention by compression molding or extrusion molding, as the thickness of the molded product becomes thinner, the pressure required for molding increases significantly (and this makes stable plug flow molding difficult. In this case, it is preferable to laminate two or more layers of preforms and then peel each layer after molding. It is necessary to laminate the preforms in such a way that they can be easily peeled off after molding. It is preferable to place a release sheet or apply a release agent on the interface of the molded product.As the release sheet, a sheet of a different resin that does not adhere to the fluororesin when heated is used. It is preferable that the viscosity is close to that of the fluororesin, and in general, a sheet of a different resin with a large molecular weight and a high melting point can be used successfully.As a release agent, silicone oil, metal soap, etc., which can fuse the fluororesins together, can be used. liquid that can prevent
Solids can be used.

The inner surface of the die must be smooth enough to allow the resin base to flow smoothly, and a die with sudden changes in flow is not preferred.

The inner surface of the die can be brought into a lubricated state by applying a lubricant to the inner surface of the die or by providing a sheet containing a lubricant at the interface between the inner surface of the die and the substrate. can.

Applying lubricant is the most common.

The lubricant described in the present invention has a viscosity of 50% during molding.
00 voids or less, preferably 1000 voids or less, such as liquid paraffin, various silicone oils such as polydimethylsiloxane, various fatty acid metal salts such as stearic acid metal salts, various surfactants, polyethylene glycol, low molecular weight polyethylene, In addition to mixtures of these fluids, commonly used lubricants can be used.

The vicinity of the melting point temperature described in the present invention refers to the melting point (1
), and a range higher than ('11-40°C) < lower than ('l1i-60°C) can be used satisfactorily. ('f!+-40℃) At lower temperatures, PTF
The viscosity of B is large and stretching is difficult (~, ('&+60℃)
), PTFE begins to decompose. The most preferable forming temperature in the present invention is a temperature in the range of 1 to 1+50° C.), and it is most preferable to rapidly cool the PTFE under high pressure and stretch it in this range, with the degree of crystallinity of the PTFE being low.

Stretching described in the present invention refers to uniaxial stretching or biaxial stretching, preferably biaxial stretching, in which the longitudinal and lateral stretching ratios are equal. The stretching ratio can be appropriately selected as required, but an area ratio of about 1.1 times to 320 times can be used satisfactorily. More preferably, it is 2 to 15 times.

In the present invention, after stretching at around the melting point temperature, it is cooled to room temperature to solidify and taken out from the die, or it is cooled to a temperature that promotes crystallization and held at that temperature to promote crystallization and stabilize. It can then be removed from the die. 2
An axially stretched sheet is completely stable if the temperature is below the glass transition temperature of the fluororesin, but if it is crystallized after biaxial stretching, it will be stabilized by crystallization and no shrinkage will occur even above the glass transition temperature.

[Mechanism of action of the present invention]

The molecular weight of PTPE is generally large, with a weight average molecular weight of 1
0,000,000 or more, and ultra-high molecular weight materials having a molecular weight of around 10,000,000 are also used. Also, PTFB chains are very rigid.

For this reason, PTFI! The melt viscosity of is very high, and even if it exceeds the melting point temperature, it becomes only about IQII voids.

Generally, stretching of thermoplastic resin is carried out at a temperature above the glass transition temperature and below the melting point of the resin.
Alternatively, since it has a high viscosity even above the melting point, it can be stretched near or above the melting point. In order to achieve better stretching, it is preferable to conduct the stretching in a state with a low degree of crystallinity, but since PTFE tends to crystallize, in order to stretch it in an amorphous state, it is preferable to conduct the stretching at a temperature near or above the melting point of PTFE. PTFI heated above the point
I! The molding method of the present invention involves stretching a preform under pressure.
This is a very preferable method in view of the high viscosity and high crystallinity of TFE.

Furthermore, by performing the stretching in a die under high pressure, microvoids that tend to occur in molded products can be reduced, and a stretched sheet with excellent performance can be obtained. In contrast to conventional stretching of PTFH, which was carried out under atmospheric pressure or by rolling with rolls, in the present invention, PTFH is stretched in a high viscosity state under pressure in a compression die or an extrusion die. , good results are obtained.

[Explanation with drawings]

In FIG. 1, a lubricant is applied to the inner surface 2 of a compression die 1, and the inner surface of the compression die is heated to a temperature equal to that of the fluororesin base material. The fluororesin base material 3 heated to around the melting point temperature is placed in the die 1 (l-1), compressed to cause the base material 3 to plug flow and become biaxially oriented (1-2), and then cooled or After stabilizing the temperature by maintaining it at a temperature suitable for crystallization, the biaxially oriented sheet 4 is taken out from inside the die 1. The compressive force required to form the biaxially oriented sheet 4 varies depending on the type of resin, stretching temperature, stretching ratio, thickness of the biaxially oriented sheet, etc. As the resin base becomes thinner, the force required to compress it and achieve biaxial orientation increases, making molding difficult.

In FIG. 2, after applying a lubricant to the inner surface 6 of the compression die 5, a non-adhesive film 8 is placed on each interface and both surfaces of the four fluororesin substrates 7, and the material is placed inside the compression die. Place <
(2-1). After heating to a temperature near the melting point of the substrate 7, the substrate 7 is compressed to cause a plug flow to form four 2° axis-oriented sheets 9 (2-2), and then cooled under pressure. Alternatively, the four biaxially oriented sheets 9 are held under pressure at a temperature suitable for crystallization and taken out from the compression die 5 (2-3), and then each biaxially oriented sheet is peeled off to form a non-adhesive film. is peeled from the oriented sheet to obtain a thin biaxially oriented sheet 10 (2-4).

In FIG. 3, (3-1) indicates each interface 1 of the resin base 11.
Method of applying lubricant or mold release agent to 2, (3-2)
(3-3) is a method in which a non-adhesive resin film 13 is placed on each interface and surface of the resin base 11, and (3-3) is a method in which a non-adhesive resin film 13 is placed on each interface of the resin base 11, and the entire stacked base is non-adhesive. Method of vacuum packaging with plastic film 14 (
3-4) is a method in which two types of non-adhesive resins 15 and 16 are alternately stacked on each other.

This lamination molding allows thin oriented sheets to be formed well, and furthermore, a plurality of oriented sheets can be formed by one compression molding or extrusion molding, which has a large economic effect.

In FIG. 4, a cooling die plate 22 is fixed to a die plate 20 of the compression press via a heat insulating material 21, and the cooling die plate 22 is provided with refrigerant holes 23 through which a refrigerant flows, and is constantly cooled. A die 24 is attached to the cooling die plate 22. When no compressive force is applied to the die plate 20, that is, when the mold is open, the die 24 is brought into a non-contact state with the cooling die plate by the pins 25 pressed by the push springs 26 attached to the cooling die plate 22. Become. Bolts 27 are attached at regular intervals to maintain a non-contact state. die 24
A thin heat insulating layer 2 is provided on the back side of the die 24 to adjust the heating rate of the die 24 when the die 24 contacts the cooling die plate 22.
8 is provided.

In FIG. 5, which shows the process of molding according to the present invention using the die shown in FIG. The die 24 and the heating plate 29 are brought into contact with each other, and the die 24 is heated (5-B). At this time,
The die 24 is kept out of contact with the cooling plate 22,
Only die 24 is heated. The heating plate 29 has a cartridge heater built therein and is constantly heated. When the die 24 is heated to a certain temperature by the heating plate 29, the heating plate 29 retreats and instead inserts the frame plate 31 and the heated fluororesin base 32 between the dies 24. The die 24 is oriented on the cooling plate 2.
2, the oriented plate-shaped molded product is also cooled. (5-D) The molded product 33 oriented and sufficiently fixed in the die is opened and the frame plate 31
<5-E).

In FIGS. 4 and 5, if the die 24 and the cooling die plate 22 have a curved shape such as a spherical shape, the molded product will also have a curved shape accordingly.

In the molding method shown in FIGS. 4 and 5, the resin base heated to around the melting point temperature can be cooled and compressed and biaxially oriented. The most preferred method of the present invention is to heat the fluororesin to around its melting point to reduce its crystallinity, rapidly cool it, and then stretch it.

FIG. 6 shows an apparatus for extruding biaxially oriented sheets according to the method of the present invention. In FIG. 6, the fluororesin is heated and plasticized in an extrusion molding machine 41 and is formed into a molded body with a constant thickness in a portion A of a die 42. As shown in FIG. In the middle of part A, there is a series of lubricant oozing devices 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 43 to the plurality of seepage ports 44, 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 44 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 through the fine pores.

A resin molded body whose surface is uniformly coated with a lubricant exhibits a so-called plug flow in which the surface layer and inner core of the molded body flow at the same speed within the die. Next, in part B of the die, the plug flow molded body is biaxially oriented.

Portion B of the die has a structure in which the thickness of the resin is reduced.

FIG. 7 shows the change in flow of the molded product in part B. The molded body is simultaneously extruded in two directions in the plug flow direction and in the direction perpendicular to the flow direction, 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 cooled in the C section of the die and exits the die 2. If necessary, it is further cooled with cold water 45 or the like, and taken up with a take-up roll 46 to become a biaxially oriented sheet.

When the fluorine resin is a difficult-to-process resin such as a PTFE homopolymer, the ram extrusion shown in FIG. 8 is used as necessary.

In FIG. 9, the fluororesin that has been heat-plasticized in an extruder 41 is shaped into a constant thick-walled pipe in a D portion of a die 47.

In the middle of section D, there is a series of lubricant seeping devices for applying lubricant to the interface between the thick-walled pipe surface and the die surface. Apply lubricant to both the outside and inside surfaces of the pipe. The high-pressure lubricant is led from the lubricant introduction path 48 to a plurality of seepage ports 49 on the outer and inner surfaces of the pipe, seeps out onto the pipe surface, and applies the lubricant to the interface between the pipe and the die surface. . A thick-walled pipe that is cooled to a temperature above the glass transition temperature and below the melting point temperature and whose surface is uniformly coated with lubricant has a so-called plug flow in which the resin surface layer and inner core flow at approximately the same speed in the die. . Next, in the 8th part of the die, the diameter of the plug flow pipe is expanded, the wall thickness is reduced, and the pipe is biaxially oriented. The diameter of the thick-walled pipe is expanded and oriented by the extrusion pressure from the extrusion molding machine during plug flow.
It is simultaneously biaxially oriented in the flow direction and diametrical direction. The biaxially oriented pipe is further cooled in the F section of the die and passes through the die 47.
exit.

If necessary, it is further cooled with cold water 50 or the like, and the take-up roll 5
1 and becomes a biaxially oriented pipe.

〔Effect of the invention〕

By the molding method of the present invention, it is possible to economically stretch a difficult-to-process fluororesin such as PTFE, and a dense stretched sheet with few voids and excellent mechanical properties, electrical properties, transparency, etc. can be obtained. .

The most suitable applications for fluororesin include electrical insulation sheets and printed wiring boards.
Electrical properties such as high dielectric breakdown voltage, low dielectric constant, and low dielectric loss tangent are required, and mechanical properties such as tensile strength are also required. The sheet formed by the method of the present invention has fewer voids, becomes a dense sheet, has improved electrical properties, and also has improved mechanical properties due to the stretching effect.

Example (PTFE preformed sheet) PTFE molding fine powder with an average particle size of 35 μm was preformed in a cylindrical mold at a molding pressure of 175 kg/c+J, and the sheet had a diameter of 100 μm.
Obtained a cylindrical crane body. The above cylindrical body was fired in an electric furnace at 370°C for 15 hours. A sheet of 0.1 inch and 1 inch was cut from the fired body using a lathe to form a preformed product of the present invention and a comparative sample.

[Biaxial stretching by compression molding] Using the compression molding method shown in Figures 4 and 5, PTFE
The preform was subjected to biaxial stretching.

Five 1 m thick PTFE preforms were laminated, and a 0.3 fl thick polypropylene sheet was placed at each interface to form a preform. The cooling die plate 22 was heated to 20°C, and the die 24 coated with lubricant (polydimethylsiloxane) was heated to PT.
It was heated to around the melting point temperature of FE. PT with separate heating device
A PTFE preform heated to around the melting point temperature of FH is placed in the above-mentioned heated die 24, compressed with high compression force (120 kg/cffl per oriented sheet after molding), rapidly cooled, and compressed with an area ratio of 10 It was biaxially stretched twice.

The high-temperature die 24 was rapidly cooled by contacting the cooling die plate 22 at 20° C. due to compression, and the fluororesin was also stretched while being cooled. The stretching time was approximately 7 seconds, during which time the surface temperature of the die 24 decreased by approximately 100°C. After cooling sufficiently while applying a high compressive force, it was taken out from the die and each layer was peeled off. The performance of the obtained PTFE sheet is shown in the following table. The biaxially stretched sheets (B, C) formed by the method of the present invention are
It was more transparent than the unstretched cut sheet (A), and had excellent dielectric breakdown voltage and tensile strength.

Margin below

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention by compression molding, Fig. 2 is a schematic diagram showing another embodiment, and Fig. 3 is a compression molding in which a plurality of resin substrates are stacked on top of each other in a non-adhered state. FIG. 4 is a schematic diagram showing various embodiments, FIG. 4 is a sectional view showing essential parts of the compression molding machine used in the present invention, and FIG. 5 is a diagram showing the present invention using the compression molding machine shown in FIG. 4. 6 is a cross-sectional view showing the main part of an embodiment of the present invention by extrusion molding, and FIG. FIG. 8 is a sectional view showing the main parts of an embodiment using extrusion molding using a ram extruder, and FIG. 9 is a sectional view showing the main parts of an embodiment in which pipes are formed by extrusion molding. be. Patent Applicant Asahi Kasei Kogyo Co., Ltd. Figure 5 U0 jlE5 Procedure Amendment (Voluntary) February 28, 1985 Manabu Shiga, Commissioner of the Patent Office1, Indication of Case Patent Application No. 262949 of 19882, Name of the invention, resin molding method 3, relationship with the case of the person making the amendment Patent applicant 1-2-6-4 Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture, ``Detailed description of the invention'' in the specification to be amended ” column 5, contents of amendment (1) Page 4, line 6, “Polymer” is corrected to “Difficult-to-process resin such as polymer”. (2) Page 6, line 6, “different resin sheet” is “sheet”
I am corrected. (3) Add the following sentence to page 6, line 12. ``Also, by taking advantage of the fact that PTF [!] is difficult to adhere to each other,
If the preforms are heated separately, laminated, and immediately compression molded, they can be easily peeled off after molding. ” (4) Page 7 No. 1
Correct line 1 "r(T, -60°C)" to "(T. +60°C)". (5) Page 7, line 14 r PTFI! Before J.
Add "over time." (6) Page 8, line 3, change “1.1 times or 320 times” to “1.1
"From 20 times to 20 times," he corrected. Procedural amendment (voluntary) March 6, 1985 Manabu Shiga, Commissioner of the Patent Office1, Indication of the case 1982 Patent Application No. 2629492, Name of the invention Method for molding fluororesin3, Person making the amendment Case Relationship with Patent applicant 1-2-6-4 Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture, "Detailed description of the invention" column 5 of the specification subject to amendment, Contents of amendment (1), page 11, line 6 Add the following sentence after . "Alternatively, the substrates 11 are heated separately and then laminated immediately before compression molding, or the substrates 11 are heated to a slightly lower temperature than the T. Even if it is laminated and compressed, it can be easily peeled off after molding.'' (2)
) On page 16, line 20, "Example" is corrected to "Example 1." (3) Add the following sentence after page 18, line 9. “Example 2 Ten PTPB preforms of IM thickness used in Example 1 were prepared, and after heating the preforms separately to 370°C,
The layers were laminated and immediately biaxially stretched in the same manner as in Example 1 using the compression molding method shown in FIGS. 4 and 5. Set the die temperature to 37
It was compressed at 0° C. and then biaxially stretched to an area ratio of 10 times while being rapidly cooled. After cooling, each biaxially stretched layer can be easily peeled off, with a thickness of 0.1
■Thick transparent biaxially stretched PTF [! Ten sheets were obtained. The performance of each sheet was similar to B in the table of Example 1. ”

Claims (1)

[Claims] A fluororesin molding method characterized by stretching a fluororesin preform heated to a temperature close to or above its melting point under pressure in a lubricated die.