JPS63239019A - Tetrafluoroethylene polymer molded item - Google Patents

Abstract

PURPOSE:To improve the resistance to creep and enhance the resostance to crushing, mechanical strength and corrosion-resisting sealing properties by a method wherein the material draw ratio, specific gravity and orientation release stress of an ultrahigh molecular-weight tetrafluoroethylene polymer molded item, which is stretched at least biaxially and has specified number-average molecular weight, are set to specified values. CONSTITUTION:The molded item concerned is a tetrafluoroethylene polymer (PTFE) highly oriented molded item, wherein the number-average molecular weight is 1,000,000 or more, the material draw ratio D is 3 fold or more, the specific gravity is 1.8 or more and the orientation release stress at 200 deg.C exceeds 5 kg/cm<2>. PTFE is a homopolymer of tetrafluoroethylene (TFE) or a copolymer containing 70 mol. % or more of TFE and a blending polymer threrof. As the monomer component to copolymerize with TFE, perfluoroalkyvinylether or the like is empolyed. PTFE is mainly empolyed as the matrix resin component of the item. Further, PTFE containing filler, which is blended with 50 wt% or less of reinforcing material such as glass fiber, carbon fiber or the like, is also empolyed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Due to its outstanding properties, tetrafluoroethylene polymer (hereinafter abbreviated as PTFE) is currently one of the important industrial materials. Especially in the field of sealing materials and lining materials such as gaskets and packing materials, PTFE is used for its chemical resistance, heat resistance, cold resistance, low friction, non-staining properties,
It is widely used as molded products in various shapes due to its excellent properties such as non-adhesiveness and electrical insulation.

The present invention is applicable to corrosion-resistant materials such as sealing materials and lining materials, bridges,
This invention relates to PTFE molded products suitable for use as support plates, sliding pads, etc. for heavy objects such as outdoor tanks and factory frames.

[Prior art] The melt viscosity of a normal thermoplastic resin at the molding temperature is 10
3 to 104 poise, but the melting point of PTFE (327°C
) Even at 380° C., the viscosity is as high as 10 days poise, making it difficult to mold using molding methods such as melt extrusion or injection molding. Therefore, PTFE molded products are generally produced by a method in which PTFE powder is preformed by compression, etc., and then heated and incinerated above its melting point (compression molding method).

(ram extrusion method, paste extrusion method, etc.), or further cutting of the PTFE substrate formed in this process, cutting from the cut product, punching, stretching (roll rolling method, etc.)
It is manufactured by the tensile stretching method).

Furthermore, in the field of gasket materials, PTFE containing fillers such as glass fiber, graphite, carbon fiber, and zirconium oxide is also manufactured.

[Problems to be solved by the present invention] The heat resistance temperature of PTFH is generally 260°C,
When used as a sealing material for gaskets and the like, compression resistance and mechanical strength to withstand external forces are required, and the limit temperature at which it can be used is considerably lower than 260°C, depending on the structure, shape, and purpose. This is due to the wood-like property of PTFE, which tends to creep under load, and of course, the higher the temperature, the more likely it is to creep.

In the field of corrosion-resistant gasket materials, in order to improve compression creep resistance, fillers are added and materials with low creep properties and PT are used.
Improvements have been made, such as structurally combining FE or filled PTFE, but both have problems such as insufficient compression creep resistance at high temperatures and low chemical resistance. In addition, sealing materials other than gaskets, such as valve seals (pole valve seats, gate valve seats, etc.) and other interlocking sealing materials (gerande seals,
PTFE is also used in cases where corrosion resistance is required (U packing, ■ packing, etc.), but improvement in compression creep resistance is similarly desired.

The Ikh stretched long sheet made by stretching and forming PTFE using the roll rolling method also has improved compression creep resistance, but the roll rolling method only allows uniaxial stretching in one stretching process, so it cannot be stretched at high temperatures of 100°C or higher. When a compressive force is applied to a region, it contracts in the direction of the stretching axis in a plane perpendicular to the compressive force and stretches in a direction perpendicular thereto, resulting in a substantial dimensional change. Further, in a tensile stretching method that does not involve rolling, porous PTFE is obtained.

On the other hand, PTFE is also important as a corrosion-resistant lining material, but it is prone to blistering, which may cause problems in its reliability as a corrosion-resistant lining. Blistering is a phenomenon observed in gas-phase fluid piping, and there is a desire to improve the blister resistance.

The problems to be solved by the present invention are, firstly, PTFIJ
The purpose is to improve the creep resistance of shaped products.

The PTFE molded article of the present invention provides a PTFE molded article suitable for use in situations where compression resistance (especially compression creep resistance) and mechanical strength are required. In particular, the present invention provides a PTFE molded product suitable as a corrosion-resistant sealing material. Second, the present invention aims to improve the gas barrier properties of the PTFE molded product.As a result, the present invention provides a PTFE molded product that has improved blister resistance and is suitable as a highly reliable lining material.

[Means and effects for solving the problems] As a result of repeated studies by the present inventors to develop a PTFE molded product with excellent creep resistance and gas barrier properties, the inventors have found that a highly biaxially oriented PTFE molded product has been developed. The present invention was based on the discovery that it has extremely excellent compression creep resistance and gas barrier properties. That is, the present invention.

It is an ultra-high molecular weight PTFE molded product with a number average molecular weight of 100 degrees or more stretched in at least two axial directions, an actual stretching ratio of 3 times or more, a specific gravity of 1.8 or more, and an orientation release stress ( (hereinafter abbreviated as ORS)
Highly oriented PTF with a weight of 5 kg/cm2 or more
This is an E-oriented molded product.

The molded products described in the present invention refer to relatively simple-shaped products such as films, sheets, plates, disk-shaped products, and processed products and deformed products obtained by machining and molding of the products, such as monospherical, It is a ring-shaped, plate-shaped, etc. molded product.

The wall thickness of these molded products is arbitrarily determined depending on the purpose, but is preferably 0.1 mm or more, more preferably 0.25t+++ or more and 20 mm or less.

PTFE mentioned in the present invention is a homopolymer of tetrafluoroethylene (hereinafter abbreviated as TFE) or TFE.
A copolymer containing 70 mol% or more, preferably 90 mol% or more, and a blend polymer consisting of them, and a number average molecular weight of 106 to 10B, preferably 2
X 106 to 108, more preferably 5 X 106
It is an ultra-high molecular weight substance of ~5×107.

Particularly preferred is an ultra-high molecular weight homopolymer of TFE.

As the monomer component to be copolymerized with TFE, perfluoroalkyl vinyl ether, hexafluoropropylene, ethylene, chlorotrifluoroethylene, etc. are preferable.

Generally, the standard specific gravity of molded products (hereinafter abbreviated as S, S, G) is used as a standard for the molecular weight of PTFE. S, S, G, PTFE ASTN 11-1457
This refers to the specific gravity of a sample molded under certain heat treatment conditions shown in .

PTFE (7) S, S, G, and number average molecular weight (F7I
There is a certain relationship between (R, D, mouth oban)
et al, :Meeting of the
Am, Ghers, Sac,, At1antic
Git2 (1956)), expressed by the following formula ("Fluororesin", Nikkan Kogyo Shimbun).

S, S, G, = -0,0579 Rag @n + 2
．． 6123 In the same manner, the number average molecular weight can be determined from the oriented molded product of the present invention or the PTFE base material before stretching. In other words, oriented molded products or PTF
The specific gravity of the sample obtained by heat-treating the E substrate under the thermal conditions shown in ASTM D-1457 is made to correspond to S, S, G, and the number average molecular weight can be determined from the above relationship.

In addition, the above PTFE is used as the main matrix resin component, and reinforcing materials such as glass fiber, carbon fiber, graphite, carbon, molybdenum disulfide, bronze, zirconium oxide, zirconium silicate, etc. ! A! Filled PTFE in which 60% by weight or less of at least one of a ji-based filler and an organic filler such as aromatic polyamide mM1 or slightly aromatic polyester fiber is blended is also referred to as PTF in the present invention.
It shall be included in H. Further, other thermoplastic resins and various compounding agents can be added to the PTFE in an amount of 10 parts by weight or less, if necessary.

The PTFE oriented molded product of the present invention is made of the above-mentioned ultra-high molecular weight PTF.
After pressing E, the sintered base material is molded with at least biaxial orientation. PTFE ultra-high molecular weight material is generally a powder, which is compacted under high pressure by pressure molding at room temperature, and then heated to a high temperature (generally above the melting point of PTFH,
The molded product is sintered at a temperature (preferably in the range of 340 to 400°C), and has a specific gravity of 1.8 or more, preferably 2 or more, and is used as a base material and oriented in at least two axes.

The oriented PTFE molded article of the present invention is oriented at least biaxially. The present invention will be explained below using a sheet-like molded product as an example.

There are three types of sheet stretching: uniaxial stretching, biaxial stretching, and multiaxial stretching.
Although there are various embodiments, the oriented PTFE sheet of the present invention is subjected to two-wheel stretching or multiaxial stretching. - Axial stretching is generally done by pulling in one direction or by rolling;
- Molecular orientation occurs in the axial direction. Biaxial stretching is performed by stretching in two directions perpendicular to each other, and molecules are mainly oriented in the two directions of the tensile force. Multiaxial stretching is performed by the forming method of the present invention described later, and is almost uniformly oriented in all directions (360°C). In the present invention, multiaxial stretching is particularly preferred. - Even axially stretched sheets can be compressed. Creep resistance is improved, but substantial dimensional changes occur, making it impractical.
In biaxially oriented sheets and multiaxially oriented sheets, such anisotropic dimensional changes are small and practically unnoticeable, especially in the case of multiaxially oriented sheets, there is no problem at all.

In biaxial stretching, the ratio of stretching ratios in the orthogonal stretching axis directions within the stretching plane (hereinafter abbreviated as "vertical and horizontal" for convenience) can be set arbitrarily, but the oriented PTFE sheet of the present invention The ratio of the longitudinal and transverse stretching ratios is preferably 1:3 to 1:1, particularly preferably 1:1.5 to 1:1.

Furthermore, in the case of multiaxial stretching, it is preferable to use a multiaxially oriented sheet in which the stretching ratio is substantially uniform in all directions.The multiaxially oriented sheet described here has a ratio of the minimum value to the maximum value of the stretching ratio in each direction, l:
1-1:2. Preferably 1:1-1:1.5,
More preferably, the ratio is 1:1 to 1:1.2. When the ratio of the stretching ratio exceeds 1:5, it approaches uniaxial stretching and 100
``When a pressure exceeding 100 kg/ctm' is applied in a temperature range exceeding 0, an anisotropic dimensional change occurs even though the compression set itself shows a small value.This phenomenon is particularly noticeable in the field of sealing materials. Undesirable.

The PTFE oriented molded product of the present invention has a substantial stretching ratio of 3 times or more.

Biaxial stretching or multiaxial stretching of ultra-high polymer zptFE improves compression creep resistance. As a result of a detailed study on the relationship between actual stretch ratio and compression creep resistance, it was discovered that molded products with an actual stretch ratio of 3 times or more have significantly superior compression creep resistance, leading to the present invention. A more preferable range is that the actual stretching ratio is 4 times or more. In the range of the actual stretch ratio of 5 times or less, the compression creep resistance improves in proportion to the actual stretch ratio, and the larger the actual stretch ratio is, the better it is, and for practical purposes, a material with an actual stretch ratio of 3 times or more is good. This is the range that can be used. On the other hand, the actual stretching ratio is 5
．． When it exceeds 0, not only the compression creep resistance in the low temperature range but also the dependence of the compression creep resistance on the actual stretching ratio in the high temperature range of 200°C or higher and under high compressive force conditions of about 500 kg/cm2 decreases. , the stability of compression creep resistance increases,
Further, if an attempt is made to stretch the film to an actual stretching ratio of more than 20, breakage tends to occur, and stretching is essentially impossible. When considering stretching processability, the actual stretching ratio is 3≦D
≦20, further 4<D≦15, especially 5.0<D≦10
A range of 1 is preferred.

The actual stretching ratio D described in the present invention, the stretching ratio in the stretching axis direction,
The ratio of longitudinal and transverse stretching ratios and multiaxial stretching will be explained using FIGS. 4 and 5.

On the left side of FIGS. 4 and 5 are test pieces cut out from the oriented PTFE sheet of the present invention, and on the right side are ASTM
The test piece is schematically shown after the test piece was heat-treated under the thermal conditions shown in No. 0-1457. A.I.

Bl, ..., Hl indicate the positions of AO, BO, -, HO after heat treatment.

A test piece cut out from the oriented PTFE sheet of the present invention (
For example, 110mm x 110mm x Toss thickness)
On the plane of the radius do as shown in the figure (for example, do = 50
Draw a circle (mm) at room temperature, and draw it according to ASTM D-14
When heat-treated according to No. 57, the oriented state of the oriented sheet is released, and the PTFE is almost restored to the state before stretching. Naturally, the circle drawn on the plane also shrinks in accordance with the orientation state.

When reduced to an elliptical shape as shown in FIG. 4, the major axis direction is the vertical stretching axis, and the minor axis direction is the horizontal stretching axis. The longitudinal and transverse stretching ratios are the ratio of the lengths on each stretching axis before and after recovery,
That is, they are expressed as OCo/DC+ (or 0GO10G+ or GoGo/C+G+) and 0Ao10A+ (or 0Eo10E+ or AoEo/A+E+). Also.

The ratio of vertical and horizontal stretching ratios is expressed as (vertical stretching ratio)=(horizontal stretching ratio), with the vertical stretching ratio being 1.

As shown in FIG. 5, it is preferable for the oriented PTFE sheet of the present invention that the stretching ratios are approximately equal in all directions in a plane. Specifically, each stretching ratio (OA oloA + ).

0Bo10B+, 0Co10C+, 00010[l
l, 0EO10EI, 0FO10F+.

The standard deviation σ of 0Go10G+, 0Fo10F+) is σ
≦0.9 is preferable. The multiaxial stretching referred to in the present invention is considered to be a special aspect of two-wheel stretching, and the standard deviation σ of the stretching ratio is σ≦0.5, preferably σ≦0. .2.

The actual stretching ratio in the present invention refers to the thickness ratio before and after heat treatment in FIGS. 4 and 5. That is, D = T,
/T.

The oriented PTFE molded product of the present invention is a solid body with substantially no voids, and has a specific gravity of 1.8 or more, preferably 2.0 or more, and more preferably 2.1 or more.

Specific gravity is measured according to ASTM D-792.

The PTFE molded article of the present invention is drawn in a state in which ultra-high molecular weight PTFE is entangled with each other, and when the molded article is heated, OR9, which indicates the degree of orientation, occurs. PT of the present invention
OR3 of FE molded product at 200℃ is 5 kg/crs2
The above is preferable, more preferably 7 kg/cm2 or more, especially 40 kg/cm2 or more and 40 kg/c+s2 or less. If the ORS at 200°C is less than 5 kg/cm2, the improvement in compression creep resistance is generally insufficient. The ORS described here is based on ASTM D-150
4, and the detailed measurement method is described in Section 9.
Shown in the figure.

The compression creep resistance of the PTFE oriented molded product of the present invention improves in proportion to the actual stretching ratio when the actual stretching ratio is 5 times or less. The strain S falls within the range shown by the following equation.

S($)=-14D+(83±10) A more preferable range is S($)=-140+(83±8).

In the range of the actual stretching ratio of 5 times or more, the compression set S
is generally 15% or less, more preferably 12% or less, and most preferably 10% or less.

The compression set S (%) not only represents the compression creep of the oriented PTFE sheet under the conditions, but also indicates the reliability of the compression creep resistance under conditions milder than the conditions, as well as the reliability of the compression creep resistance under conditions more severe than the conditions. This serves as an indicator of compression creep resistance.

The stretching method is not particularly specified, but any method may be used as long as a product that satisfies the requirements of the present invention can be produced by stretching or by accompanying processing before and after stretching. As a stretching method, roll rolling method and tension stretching method are conventionally common, but the roll rolling method produces a preferable range of simultaneously biaxially stretched sheet and multiaxially stretched sheet among the PTFE oriented sheets of the present invention. Also, the tensile stretching method is not suitable for PTFH.
As used for making porous materials, the generation and increase of voids during stretching is unavoidable.

The present inventors have discovered that PT
After studying the forming method for stretching the FE material, we developed the PTF of the present invention.
An E-oriented sheet was obtained. The stretching method includes PTF heated to a temperature of 150°C or higher, preferably 170°C to 340°C.
P, which is characterized by stretching the base material of E under pressure in a guide.
This is a method for stretching TFH. In particular, in order to obtain a highly oriented molded article of the present invention with a stretching ratio of 5 times or more,
The PTFE substrate heated to a high temperature of ~340°C is stretched under pressure.

An outline will be explained below.

Stretching under pressure in a gouer means stretching the PTFE base material in a compression die or an extrusion die in compression molding or extrusion molding by causing a plug flow due to compression force or extrusion force. Here, the love-lug flow includes a state close to it. Also, in order to make the plug flow, at least the inner surface of the goo or PTF! Preferably, a lubricant is present on the surface of the substrate.

A PTFE base is a molded product made from PTFE molding powder through the general process of pre-compression molding, firing, and cooling, and particularly refers to a relatively thick sheet-like product. PTFE
Prior to stretching, the substrate is preheated to 150° C. or higher.

A preferable preheating temperature is 170 to 340°C, more preferably 200 to 327°C.

The temperature may be uniform throughout, but it may be hotter on the surface side and colder on the center side, or only the surface layer may be made of PTF.
It is also possible to have a distribution such that the temperature is above the melting point of E and the inside is below the melting point.

The temperature of the goo is at least the temperature of the inner surface of the goo (PTFE
Temperature of the surface layer of the substrate - 100) "0 or more, preferably P
It can be arbitrarily selected in consideration of stretch formability and productivity within the range of the temperature of the surface layer of the TFE layer to 400°C.

When stretching under pressure, a high pressure of 10 kg/cs 2 or more, preferably 50 kg/cm 2 or more, more preferably 80 kg/cm 2 or more and 2000 kg/cm 2 or less is applied to the PTFE substrate.

In order to have a lubricant present on the inner surface of the gou, in the case of compression molding, it is generally applied before molding, and in the case of extrusion molding, it is either 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.

It is extremely important to cause plug flow when stretching under pressure in the throat FE receipt guide of the present invention. In order to cause plug flow, it is preferable to perform at least one of the following operations during molding.

■Lubricant is present on the inner surface of the goo.

■ Laminating and coating other thermoplastic resins on the surface of the PTFE base. The thermoplastic resin has a melting point lower than that of PTFE and/or has a melting point lower than that of PTFE under the temperature conditions during stretching.
Those with lower viscoelasticity are preferred.

Coating the surface of the PτFE substrate with a thin sheet of thermoplastic resin not only improves the plug flow properties of the PTFE substrate, but also prevents the lubricant from adhering to the stretched sheet when it is present on the inner surface of the die. There is an effect that can be achieved by peeling off the laminated sheet to remove the lubricant. In order to remove the lubricant, the surface of the PTFE substrate may be coated with a thin sheet or film of the same quality.PTFE is non-adhesive to each other and can be heated at temperatures below the melting point of PTFH. It can be easily peeled off even if pressure is applied. Various resins can be used as the laminated coating sheet to improve plug flow properties and/or remove lubricant, but ultra-high molecular weight polyethylene, ultra-high molecular weight polyethylene,
Poly-4-methylpentene-1, PTFE, etc. are most preferably used.

If the PTFE is stretched by continuing pressurization without plug flow, the PTFE will undergo melt fracture or brittle fracture. In addition, if stretching is carried out under conditions where it becomes difficult for the bar to plug flow, non-uniform orientation will remain, resulting in strength weaknesses within the oriented sheet. Not suitable as a sealing material.

In this way, the PtoFE oriented sheet stretched under pressure in the die loses its orientation even at relatively low temperatures below 100°C, and for example, when left at 80°C for 20 hours, the orientation returns by 3%.
In some cases, a certain degree of dimensional change (the length decreases) occurs.

In order to have dimensional stability in such a low temperature range, it is preferable to heat-treat this PTFE oriented sheet with shrinkage at a temperature range of about 70°C to 150°C, preferably 80°C to 120°C. . Among the oriented PTFE sheets after the heat treatment, those satisfying the requirements for the oriented PTFE sheet of the present invention are also included in the present invention. The oriented PTFE sheet of the present invention has improved dimensional stability in the low temperature range.
The shrinkage rate at 12 hours at ℃ is preferably 1.5% or less, more preferably 1% or less, particularly preferably 0.6% or less. This shrinkage rate is the average value of the length shrinkage rates in each direction on the plane of the oriented sheet, and is the value obtained when the oriented sheet is placed on a smooth solid and allowed to shrink freely.

Generally, the maximum temperature during transportation and storage is approximately 80℃,
If the shrinkage rate at 0℃ for 12 hours is 1.5% or less,
Can be used generally.

The PTFE oriented sheet of the present invention can be formed by stretching a PTFE base under pressure in a gouge, but the oriented sheet can be further punched and cut into final products such as gaskets and packing. When the substrate is stretched under pressure in a gooey, it can also be simultaneously stretched and formed into the shape of a final product such as a gasket. In this case, PTF
E It is necessary that the base material be stretched uniformly, and it is necessary to take sufficient measures such as coating the inner surface of the goo with a lubricant. Therefore, in the present invention, it is easier to obtain a uniformly oriented molded product by molding a large sheet and processing and molding from the sheet when molding a gasket or the like.

This will be explained below with reference to the drawings.

FIG. 1 shows the progress of stretching a PTFE substrate by compression molding.

FIG. 2 shows a PTFE substrate laminated with PTFE before stretching.

FIG. 3 is a schematic diagram showing the structure of a compression die suitable for carrying out the present invention.

FIGS. 4 and 5 show a method for determining the actual stretching ratio D, stretching ratio, etc. of the oriented PTFE sheet.

6 and 7 show stretching by ram extrusion.

FIG. 8 shows a Δ11 constant device for compression set S.

FIG. 9 shows a measuring device for OR9, and FIG. 1θ shows the relationship between the actual stretching ratio and the compression set S.

In FIG. 1, at least the inner surface 2 of the compression die l is heated in advance to an arbitrary temperature of (surface layer temperature of the PTFE substrate - 100)"C or higher.
i < (1
-1) At this time, it is preferable to have a lubricant present on the inner surface 2t of the compression die.
Plug flow the FE substrate 3 and stretch it 1-2),
After cooling to about 100° C. or lower while applying compressive force, the die 1 is opened and the stretched PTFE 4 is taken out.

Used as a PTFE base when manufacturing thin-walled expanded PTFE, when manufacturing multiple sheets of expanded PTFE in one press to improve productivity, or when wanting to easily remove lubricant adhering to molded products after pressing. As shown in FIG. 2, it is preferable to take the form of a laminate of PTFE and/or other thermoplastic resins. In the case of a laminated PTFE base, each layer is peeled off after stretch forming. PTF
The laminated interface between E is.

If the temperature of the PTFE base is below its melting point, it can be easily peeled off after stretching. Peeling at the laminated interface with other thermoplastic resins will not be a problem at all if the temperature of the laminated PTFE substrate during stretch molding is below the melting point of the thermoplastic resin, preferably below (melting point -30)°C. If the thermoplastic resin is a resin such as ultra-high molecular weight polyethylene whose viscosity decreases little even when the melting point is exceeded, it can be used satisfactorily even above the melting point.

In Fig. 3, a cold/heat die plate 11 is fixed to the die plate 10 of the compression press via a heat insulating material 13, and the cold/heat die plate 11 has cold/heat medium holes 12 through which the cold/heat medium flows. The temperature is constantly regulated. Die on the cold/heat die plate 11! 4 is installed. die 1
4 is before molding (surface oil temperature of PTFE base -100
) "Heated to any temperature above 0. PTF
The temperature of the E substrate 17 is also 150°C or higher, preferably 170-3
It is preheated to a temperature of 40°C.

In addition, it is preferable to apply lubricant to the inner surface of the die in advance, and compress the PTFE element J'l! l! 17 is stretched. At this time, the thickness during molding is adjusted using spacers 15 so that the actual stretching ratio is 2 to 5 times. Further, after cooling in the compressed state, the oriented sheet is taken out, and the cooling rate at this time is adjusted by the heat insulating plate 18 and the cold/hot die plate 11.

In FIG. 3, the die 14 and the cold/hot die plate) 11
If it has 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 PTFE sheet of the present invention. In FIG. The FE base material is put in and extruded into the die 27 while being heated by the ram 25. As a PTFE base,
In addition to a single layer of PTFE, a laminated PTFE substrate as shown in FIG. 2 can be used in the same manner as in compression molding and stretch molding. In the middle of part A of the die 27, a series of lubricant seeping devices are provided in order to apply the lubricant to the interface between the surface of the PTFE substrate and the die surface. The high-pressure lubricant is guided from the lubricant introduction path 28 to a plurality of seepage ports 29, and the PT
The lubricant oozes onto the surface of the FE base material and coats 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 fine communicating hole such as sintered metal, and the lubricant seeps out from the fine hole.

Alternatively, it is also possible to apply a lubricant to the inner surface of the goo by spraying or the like before molding.

The P7FE base coated with lubricant evenly coated on the surface has a PTFE surface layer and an inner core flowing at approximately the same speed in the die 27.
The plug-flow PTFE substrate is stretched in the B section of the zero-order die 27, which is a so-called plug flow.

The B portion of the die 27 has a structure in which the thickness of the PTFE substrate is reduced. FIG. 7 shows the change in flow of PTFE in part B during biaxial stretching. The PTFE base material is simultaneously extruded biaxially in the flow direction and in the direction perpendicular to the flow direction while maintaining the plug flow, and is multiaxially stretched. The force for stretching the PTFE substrate is exerted by the extrusion force from the ram extruder 26. The polyaxially stretched PTFE green body is cooled in the C section of the die and exits the die 27.

The biaxially stretched PTFE is taken off by a roll 30. When a laminated PTFE base is used as the PTFE base, the PTFE sheet of the present invention can be obtained by peeling off the i-MPTFE stretched sheet extruded from the die 27.

From the PTFE oriented sheet of the present invention formed by compression molding or extrusion molding, the P of the present invention
Molded products of TFE oriented sheets, especially sealing materials and lining materials, are obtained.

[Effects of the Invention] The present invention is made of PTFE which is biaxially stretched to a predetermined actual stretching ratio, preferably multiaxially stretched.

Conventional PT can be
The present invention provides an oriented PTFE sheet that significantly improves compression creep resistance, which has been one of the biggest problems in FE sheets, and has even higher compressive strength.

Furthermore, the oriented PTFE sheet of the present invention has significantly improved gas barrier properties, tensile strength, etc.

1. The reason for the improvement in compression creep resistance is not clear, but it is thought to be as follows. The molecules of PTFE are ultra-high molecular weight, relatively rigid and long chains, which are intricately intertwined. When this is stretched to a high degree, the molecular chains between the entanglement points become highly tensed, and each molecular chain reaches a state of approximately equal tension.

It is assumed that the external force acting on the stretched sheet in this state is evenly distributed to each molecular chain, and that the slippage of molecular chains at the entanglement points is less likely to occur, resulting in a marked improvement in compression creep resistance. be done.

In the method of stretching the PTFE sheet under pressure in a gou, which is the preferred manufacturing method of the present invention, there is no significant increase in void content based on the specific gravity before and after stretching.In any case, there is no change in morphology due to stretching. It is estimated that the gas barrier property is improved by this.

PTFE of the present invention with significantly improved compression creep resistance
The sheet is required to have the original properties of PTFE, that is, chemical resistance, corrosion resistance, low friction, non-adhesion, and heat resistance.
In addition, it is particularly suitable for use in situations where external force acts upon it and requires compression resistance and mechanical strength to withstand the external force.For example, it is used as a sealing material for gaskets and packings, and for bearings Suitable for sliding members such as piston rings.

Even if the PTFE sheet of the present invention does not contain fillers, it has better compression creep resistance than conventional filled PTFE sheets. There is. Therefore, the range of usable conditions (temperature, seal internal pressure, etc.) as a PTFE gasket material with no filler added can be greatly expanded. It is also suitable for sealing materials other than gaskets, such as V-packets, U-packets, O-rings, diagonal packings, square-shaped packings, etc. used for gland seals of low-speed/low-pressure stirrers, valves, pumps, etc. . It is also suitable as a substitute for the PTFE part used in conventional combination type sealing materials.
These include the PTFE part in PTFE jacket type gaskets and spiral gaskets, backup rings, slipper seals, etc. In addition, the strength of diaphragms and bellows as valve parts is weak, which is a problem.
The sheet of the present invention can also be suitably used here. In addition, PT is used as a check valve in liquid transport equipment.
It is also suitable for FE poles. It is also suitable for use as a pole valve seat in a pole valve, a gate valve seat in a gate valve, or a valve disc.

The shape and dimensions of the PTFE sheet of the present invention used for 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 1,2++s to 5 layers, preferably 0.5mm to 4cm thick.

In the field of bearings, conventional PTFE is used under low load and low sliding speed conditions due to its large compression creep.
The PTFE sheet of the present invention is suitable for use under high load conditions. It is particularly suitable for use as support plates and sliding pads for heavy objects such as bridges, outdoor tanks, and factory structures, and can improve their durability.

Among the PTFE sheets of the present invention, those containing filler have increased dimensional stability at high temperatures and further improved compression creep resistance. In addition, since wear resistance is improved,
Depending on the conditions of use, the PTFE sheet of the present invention containing a filler may be preferable.

As described above, the PTFE sheet of the present invention can be used in PTFH applications, which have conventionally been used under limited usage conditions due to problems such as compression creep and gas permeation.
Its range of use can be greatly expanded. In addition, it combines properties improved by stretching with the original excellent properties of PTFE.

New uses for PTFH can be developed.

[Example] The present invention will be explained below with reference to Examples.

First, methods for measuring compression set S, ORS, specific gravity, etc. described in the present invention will be explained.

1. Measurement of compression set S (200° C., 500 kg/c+s2, 1 hour) The measurement of compression set S (%) will be explained below using FIG. 8. The test piece 30 is made from the PTFE oriented sheet of the present invention or a comparative sample, measuring 5hm x 50mm x 1 to 3a.
It was cut out into mt. This is a smooth tempered glass plate 33 (1
60a+m x 160m+* x 5mmL) The surfaces of the tempered glass plate and the test piece, which are to be sandwiched between the two, are cleaned in advance with acetone or ethanol. Furthermore, one side has a mirror finish (surface roughness 0.IS -0,6
SJIS B 011i01) stainless steel plate 32
The laminate is sandwiched between mirror surfaces of (220 I x 220 mm x 6 amt) and heated press plate 31 (400 mm x 400 mm) whose temperature has been adjusted in advance to 200°C.
x 60 mmt), and a compressive force equivalent to a pressure of 500 kg/cm2 was applied to the test piece 30. Without considering the increase in area due to deformation of the test piece 30 during the test, heating and pressurization was continued for 1 hour while maintaining the initial compressive force, and then the heater power of the hot press plate 31 was turned off and water was passed through the hot press plate. The mixture was cooled to room temperature over about 30 minutes and then taken out. The compressive force was maintained even during cooling.

At least 5 positions in one test piece, the thickness before and after the compression test (to, t+) was measured with a buchromometer (JIS B 7503 1st grade product), and the compression set was measured at each position (to-t+). ) Calculated by x 100 t.

The compression set S (%) described in the present invention was determined by taking the arithmetic average of the results.However, if the entire structure is destroyed, the compression set S (%) is not calculated. ASTM D 621 was basically followed. Measurement of specific gravity followed ASTM D 792.

2. A modified ORS tensile testing machine as shown in Figure 9 was used. The test piece is a strip of length 80 mm + width 10 layers (thickness is arbitrary) cut out along two orthogonal stretching axes, and the test piece is set in a grip. The distance between the grips at this time is 5 Otm layer. Thereafter, the oil bath heated to 200° C. is raised so that the top of the grip is immersed in the oil. The contractile force of the sample is detected by a load cell and recorded on a recorder. Stretched PTFE 2
The shrinkage force at 00°C had an equilibrium value. The shrinkage force or equilibrium value of the shrinkage force is read 5 minutes after immersing the sample in oil, and this is divided by the cross-sectional area of the sample (thickness x width) to convert it into stress. The stress values in each stretching axis direction were numerically averaged, and this was defined as the heat shrinkage stress at 200° C. in the present invention. Measurements followed ASTM D 1504.

3. Measurement of specific gravity was in accordance with ASTM 0792.

4. Water vapor transmission rate (g/cm2・24hr) 38℃, 9
Measured according to ASTM F 372 at 0% relative humidity.

5. Tensile strength at break and tensile elongation at break Measured according to ASTM D 638 and ASTM 08B2.

6. Oxygen permeability (mjJ#+2・day-atm) 30
Measured according to ASTM D 1434 at °C.

7. Total light transmittance and haze Measured according to AsTM 01003.

Example 1 and Comparative Example 1 PTFE of various thicknesses molded by free baking method
Base material (manufactured by Nippon Valka Industry, Palflon sheet No.
, 7000. Specific gravity 2.1G, number average molecular weight approximately 1X10
7) were preheated to the temperatures shown in Table 1, and compressed using the compression press shown in FIG. 3 at the temperatures shown in Table 1 to obtain an expanded PTFE sheet (sample No. 101-1).
07), each stretched sheet had the actual stretching ratio D shown in Table 1, OR9 at 200°C, 200°C-500k
It has a compression set (S) in g/cm2. PTF
E Before compression molding the substrate, apply silicone oil (KF 965, manufactured by Shin-Etsu Silicon ■) to the inner surface of the compression die.
A viscosity of 10,000 cps at room temperature was applied. Further, a 0.1-inch thick PTFE film was placed between the goo and the PTFE substrate and stretched. Cold/thermal die play [was at room temperature.

A sheet having an actual stretching ratio of 3 times or less was formed using substantially the same method as above, and sample No. 201. No. 20
I got 2.

(The following is a blank space) The relationship between the compression set S and the actual stretching ratio is shown in FIG. The following was confirmed from Figure 10.

(i) 2≦D≦5 S=-140+ (83±10) (%) (ii) D>5 S≦15 (%) Example 2 10 mm of PTFH containing about 20% by weight of glass fiber
Thick sheet (manufactured by Nihon Valcar Co., Ltd., Parflon No.,
7010. Specific gravity: 2.3) was molded in the same manner as in Example 1 to obtain a stretched sheet with an actual stretching ratio of 6.5 times. Table 1 shows the molding conditions and measurement results. The sheet has excellent compression creep resistance.

Comparative Example 2 Two types of PTFE commercially available and used as sealing materials for gaskets etc. (Sample No. 203°N
o, 204) was measured and shown in Table 1.

Sample no.

203 PTFH homopolymer 2m thick sheet (
Parflon No. 7000, manufactured by Nippon Halca Industry ■
．． Specific gravity 2.1) 204 PTF filled with approximately 20% by weight of glass fiber
H homopolymer 2mmmm-to [manufactured by Nihon Valka Co., Ltd., Parflon [glass included] No. 7010
．． Specific gravity 2.3] Example 3 PTF with a thickness of 0.5 cm made of a homopolymer of PTFH
E-sheet (manufactured by Nippon Valka Industry, Parflon cutting tape No. 7900) 4 sheets and 4mm thickness + 7) PT
Two FE sheets (manufactured by Nippon Valka Co., Ltd., Parflon Sheet No. 7000) were used as PTFE sheets for the laminated substrate. Each sheet was heated in a hot air circulation oven at 350° C. for about 1 hour. Each sheet became translucent as the crystals melted. Remove each sheet from the oven 4mm 10.5mm 10.5mm 10.5 m10
．． The layers were quickly laminated to a layer configuration of 5 mm/4 mm to form a laminated PTFE base. When laminating, at least only the outermost layer of each sheet is crystallized in order to separate each layer after stretching. The laminated PTFE base material was multiaxially stretched to an actual stretching ratio of about 5 times by the compression molding method shown in FIG.
A TFE sheet was obtained (sample No., 301° specific gravity 2
．． 0). The heat shrinkage stress of sample No. 301 at 200° C. was 15 kg/c112. Oxygen permeability is 1
? GOmI! /m2day-atm. Also,
A commercially available PTFE sheet consisting of a homopolymer of PTFH0. III thickness (Palflon made by Megi Valcar Industries v4) ■
The oxygen permeability of cutting tape No. 7900 is 7600.
Otori f/m"day-atm.

Example 4 and Comparative Example 3 A laminated PTFE base having the same layer structure as Example 3 was sandwiched between press plates heated to 200°C, heated for 19 minutes, and then compressed to about The PTFE sheets of the present invention having a thickness of approximately 0.1 and 0.8 were obtained by stretching to an actual stretching ratio of 5 times (sample No. 401).
.

The sheet had an OR9 of 15 kg/cm2 at 200°C and a specific gravity of 2.1. Similarly, after preheating the laminated PTFE substrate to 300°C, it was molded in the same manner (sample No. 402), and the sheet had an OR9 of 15 kg/cm2 and a specific gravity of 2.1. ■Peng thickness and 0.8■Peng thickness, stretching magnification 5 times,
200℃ (7) ORS is 15kg/cm2, specific gravity is 2
．． There was 0te.

Table 2 shows the water vapor permeability of the 0.1 m thick sheets of samples No. 401 and No. 402.

・, [bottom ξ white) Reference example Tensile breaking strength and tensile breaking elongation Sample No. 104
．． 108.110.201.301.401.402.
403 was measured and shown in Table 3.

Further, the total light transmittance and haze were measured for No. 301.401°402 and 403 and are shown in Table 3. As is clear from Table 3, the sheet of the present invention is excellent in tensile strength, total light transmittance, and haze.

(Margin below)

[Brief explanation of the drawing]

Fig. 1 is a process explanatory diagram showing the progress of stretching PTFE by compression molding, Fig. 2 is an explanatory diagram showing a base material with m layers of PTFE before stretching, and Fig. 3 is a compression molding suitable for carrying out the present invention. Schematic diagrams showing the structure of the die, Figures 4 and 5 are PTF
An explanatory diagram showing the method of determining the actual stretching ratio, stretching ratio, etc. of an E-oriented sheet, Figures 6 and 7 are explanatory diagrams showing stretching by ram extrusion molding, and Figure 8 is an explanatory diagram showing the method for measuring compression set. FIG. 9 is an explanatory diagram to show the method for measuring OR9, and FIG. 10 is an explanatory diagram to show the relationship between the real stretching ratio and compression set.

Claims (4)

[Claims] (1) Ultra-high molecular weight tetrafluoroethylene polymer molded product with a number average molecular weight of 1 million or more, stretched in at least two axial directions, with an effective stretching ratio D of 3 times or more, a specific gravity of 1.8 or more, and further at 200°C. A highly oriented tetrafluoroethylene polymer molded product with an orientation release stress of 5 kg/cm^2 or more. (2) The molded article according to claim 1, which contains 60% by weight or less of a filler. (3) Ultra-high molecular weight tetrafluoroethylene polymer molded product with a number average molecular weight of 1 million or more, stretched in at least two axial directions, with an effective stretching ratio D of 3 times or more, a specific gravity of 1.8 or more, and further at 200°C. A tetrafluoroethylene polymer molded product that is highly oriented with an orientation release stress of 5 kg/cm^2 or more and has a shrinkage rate of 1.5% or less at 80°C for 12 hours. (4) The molded article according to claim 3, which contains 60% by weight or less of a filler.