JPH0262211A - Method for forming orientated formed item - Google Patents

Abstract

PURPOSE:To orientate stock by a method wherein the stock is plug-flowed by compressive force in a die or between rolls at the temperature higher than the glass transition temperature of the stock under the condition that resin sheets, the frictional force of which against the stock is larger than that between the stocks each other, are respectively pinched between the stocks made of polytetrafluoroethylene (PTFE) or of its copolymer. CONSTITUTION:PTFE stock is preheated up to 150 deg.C or higher and preferably to 200 - 327 deg.C. The temperature of a die or of rolls is selected within the range from the temperature at the surface layer part of the stock minus 100 deg.C to 400 deg.C. In order to plug-flow the stock by compressive force or the like, lubricant such as silicone oil or the like is applied onto the inner surface of the die or onto the surface of the stock. As the resin sheet, which develops large frictional force, a sheet made of PTFE blended with 5wt% or more, especially 10wt% or more of glass fibers or the like is preferable. If forming is done under the condition that three plies of the stock 5 are laminated to each other, slippage occurs between respective stocks and the stocks 6 in forming process shift each other positionally. When the stocks 5 are compressed so as to be orientated and formed under the condition that the resin sheets 7, which develop large frictional force, are placed between the stocks 5, no positional shifting of the stocks 8 occurs during forming process. The resin sheet 7 must be stretched together with the stock 8 as shown by one represented by the numeral 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Due to its outstanding properties, polytetrafluoroethylene is currently one of the important industrial materials. Particularly in the field of sealing materials and lining materials such as gaskets and packing materials, PTFE has excellent properties such as chemical resistance, heat resistance, cold resistance, low friction, non-contamination, non-adhesiveness, and electrical insulation. It is widely used as molded products of various shapes.

The present invention is applicable to corrosion-resistant materials such as sealing materials and lining materials, bridges,
The present invention relates to a good method for forming a dense PTFE stretched sheet that can be used well for supporting plates, sliding pads, etc. of heavy objects such as outdoor tanks and industrial frames.

[Conventional technology]

The melt viscosity of normal thermoplastic resin at molding temperature is 10
Polytetrafluoroethylene has a high viscosity of 3 to 10' voids even at 380° C., which is higher than its melting point (327° C.), and is difficult to mold using molding methods such as melt extrusion or injection molding.

Therefore, in terms of -C, the molded product can be produced by a method (compression molding method, ram extrusion method, paste extrusion method, etc.) in which the powder is preformed by compression etc. and then heated to a temperature above the melting point, or by the process It is manufactured by further cutting the molded base material, cutting out the cut product, punching, stretching (roll rolling method, tension stretching method), etc.

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

The heat resistance temperature of polytetrafluoroethylene is generally 260
°C, but when used as a sealing material such as a gasket, compression resistance and mechanical strength to withstand external forces are required, and the maximum usable temperature is 260 °C depending on the structure, shape, and purpose. It is much colder than that. This is due to the inherent property of polytetrafluoroethylene that it 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, improvements have been made to improve compression creep resistance, such as adding fillers or structurally combining low-creep materials with polytetrafluoroethylene or filled polytetrafluoroethylene. However, all of them 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 (ball valve seats, gate valve seats, etc.) and other dynamic sealing materials (grand packing, U packing,
Polytetrafluoroethylene is also used in cases where corrosion resistance is required (packing, etc.), but it is also desired to improve compression creep resistance.

On the other hand, polytetrafluoroethylene is important as a corrosion-resistant lining material, but it tends to cause 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.

We have proposed the superiority of biaxially oriented polytetrafluoroethylene sheets as improvements to these problems in Japanese Patent Applications No. 62-61302 and No. 62-71370.
I proposed it in the issue. The present invention is a molding method that can favorably mold these biaxially oriented sheets, especially thin biaxially oriented sheets.

[Problems to be solved by the present invention]

The method for forming the biaxially oriented sheet was also described in detail in the specification of the application, but as the method for forming the thin oriented sheet,
A preferred method is to stretch the substrates after laminating them, and to separate the oriented molded products one inch apart from each other after stretching.

However, the problem with this method is that polytetrafluoroethylene has a small frictional force, so it easily slips on each other, and the laminated state collapses during orientation molding, resulting in a significantly low yield.

[Means and effects for solving the problems] The present invention is a molding method that can satisfactorily mold a thin biaxially oriented sheet. That is, the present invention is applicable to stretching polytetrafluoroethylene or a copolymer mainly composed of tetrafluoroethylene (abbreviated as PTFE) under pressure within a die or between rolls. or more PTFs
Place the E substrates one on top of the other, (2) Place a resin sheet between the substrates that provides a greater frictional force against the substrates than the frictional force between the PTFE substrates, (3) Inside the die. The surface or the interface between the roll surface and the base material is lubricated, (4) the base material is oriented by compressive force or extrusion force at a temperature higher than the glass transition temperature of the PTFE base material ((5) after orientation, from inside the die Provided is a method for molding an oriented molded product of PTFE, characterized in that the oriented molded product formed from each substrate is peeled off from each other.

The molded products mentioned in the present invention are molded products of relatively simple shapes such as films, sea I., disc-shaped products, and the like.

The wall thickness of these molded products is arbitrarily determined depending on the purpose, but is preferably 2 mm or less, more preferably 0.05 mm or more and 1 mmff or less.

PTFE referred to in the present invention refers to tetrafluoroethylene (
A homopolymer of TFE (hereinafter abbreviated as TFE), or a copolymer mainly composed of TFE, that is, a copolymer containing 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more of TFE, or A blend polymer consisting of these, preferably having a number average molecular weight of 10
It is an ultra-high molecular weight material of 6 to 10''. Particularly preferred is an ultra-high molecular weight material of TFE homopolymer.

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

In addition, the above PTFE is used as the main matrix resin component, and the reinforcing materials are carbon fiber, graphite, carbon, molybdenum disulfide, bronze, zirconium oxide,
Filled P containing 60% by weight or less of at least one of inorganic fillers such as zirconium silicate and organic fillers such as aromatic polyamide fibers and aromatic polyester fibers.
TFE composition, and if necessary, the above-mentioned PTFE (T
The technical scope of the present invention also includes compositions in which other thermoplastic resins and various compounding agents are added in an amount of 10 parts by weight or less per 100 parts by weight of FE homopolymer or copolymer.

Ultrahigh molecular weight PTFE can be used particularly well in the molding method of the present invention. This material is generally a powder, which is compacted under high pressure by compression molding at room temperature and then heated to a high temperature (generally above the melting point temperature of PTFH, preferably in the range of 340 to 400°C in the case of polytetrafluoroethylene). A molded product having a specific gravity of preferably 1.8 or more, more preferably 2 or more is obtained by sintering the product, and the molded product is used as a PTFE base and oriented in at least two axes.

The oriented PTFE molded product of the present invention is oriented in at least one axis. 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, a particularly preferred orientation among the oriented PTFE sheets of the present invention is biaxial stretching or multiaxial stretching.

The molding method of the present invention is suitable for molding a sheet having an area ratio stretching ratio of 2 times or more of the oriented PTFE molded product.

Biaxial stretching or multiaxial stretching of ultra-high polymer 1PTFE improves compression creep resistance. As a result of a detailed study on the relationship between stretch ratio and compression creep resistance, we found that at a stretch ratio of 2.
Molded products that are more than double the size have significantly superior compression creep resistance.

Stretching under pressure in a die 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. The term "plug flow" here includes states similar to that. Further, in order to cause plug flow, it is necessary to have a lubricant present at least on the inner surface of the die or on the surface of the PTFE substrate.

In the case of ultra-high molecular weight PTFE, the PTFE base refers to a molded product made through a general process of pre-compression molding → firing → cooling of molding powder.

In the method of the present invention, there are two or more P inside the die or between the rolls.
The TFE substrates are placed one on top of the other, and a resin sheet that provides a greater frictional force against the substrate than the PTFE substrate-to-substrate force is placed between the substrates. The frictional force mentioned here is the frictional force during stretch molding, and is the frictional force in a heated and pressurized state. Further, the larger value of the static frictional force and the dynamic frictional force is used here. Various sheets can be used as the resin sheet that provides a large frictional force, but a particularly preferred sheet is a sheet made of PTFE mixed with various fillers to increase the frictional force.

In particular, when PTFE contains 5% by weight or more, preferably 10% by weight or more of glass fiber, asbestos, rock wool, etc., the filler gets caught in the heated and pressurized state, resulting in a large frictional force. Although a resin sheet other than PTFE can be used, it is necessary to use it at a temperature below the melting point of the resin sheet. In the present invention, due to the frictional force between the PTFE substrate,
More than double 11! It is preferable to use a resin sheet that provides frictional force.

When the PTFE base material is oriented, it is necessary to stretch the resin sheet together with the stretching of the base material, and for this reason, the viscosity of the resin sheet during molding and the PTFE
Preferably, the viscosity of the substrates is similar. For this reason as well, a sheet in which a large amount of filler is blended with PTFE to increase the frictional force is preferable as the resin sheet of the present invention. Naturally, the resin sheet needs to be able to be peeled off from the oriented molded product after molding.

Prior to stretching, the PTFE substrate is preheated to 150°C or higher. Preferable preheating temperature is 170-340'C
, more preferably 200 to 327°C.

The temperature may be uniform throughout, but it can also be distributed such that the surface layer is higher in temperature and the center is lower in temperature.

The die temperature or roll surface temperature is at least the temperature of the inner surface of the die (temperature of the surface layer of the PTFE base - 100).
It can be arbitrarily selected in consideration of stretch formability and productivity, preferably in the range of 400°C or higher, above the temperature of the surface layer of the PTFE base.

When stretching under pressure, a high pressure of 10 Kg/cmz or more, preferably 50 Kg/cm2 or more, more preferably 80 Kg/am'' or more is applied to the PTFE substrate.

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

Stretching under pressure within a die or between rolls as described in the present invention refers to compression and stretching in a compression die, extrusion and stretching in an extrusion die, compression and stretching between rolls, etc. This will be explained next using the diagram.

Figures 1 to 3 show the case where stretch molding is performed by compression molding. Figures 4 and 5 show the case where stretch molding is performed by extrusion molding. FIG. 6 shows the case where stretch forming is performed by roll rolling.

In FIG. 1, at least the inner surface 2 of the compression die 1 is heated in advance to a constant temperature. A PTFE substrate adjusted to a constant temperature is placed between the heated compression die I.
1-1). At this time, a lubricant is made to exist on the inner surface 2 of the compression die. The PTFE base material 3 is compressed and stretched by plug flow (1-2). After applying compression force and cooling to a certain temperature or lower, the die 1 is opened and the stretched PTF
Take out E4.

FIG. 2 shows the method shown in FIG.
It shows the movement of PTFE when unevenly laminated and molded, and when only the PTFE base is laminated and compression-stretched,
Since TFE has a small coefficient of friction, slippage occurs at the interface of each substrate, and the positions of the PTFE substrates 6 shift from each other during the forming process (2
-1). The purpose of the present invention is to prevent slippage at the interface of each substrate, as shown in (2-2). That is, in the present invention, the PTFE substrates 5 are overlapped, and the p T F E
When a resin sheet 7 that produces a frictional force greater than the frictional force between the substrates 5 is placed between the substrates and compression-stretch molded, the frictional force increasing effect of the resin sheet 7 reduces P during the forming process.
The positions of the TFE substrates 8 do not shift with respect to each other (2-2). The resin sheet 9 that increases the frictional force needs to be stretched in parallel with the stretching of the PTFE base 8.

FIG. 3 shows the process of forming a biaxially oriented sheet by compression molding using the method of the present invention. In Fig. 3, lubricant is applied to the inner surface 2 of the compression die l, and PTF
E substrates 5 are laminated, and resin sheets 7 that provide a large frictional force are placed on each interface of the substrates 5 (3-1). After heating to a certain temperature, it is compressed and the entire laminate of the PTFE substrate 5 and resin sheet 7 is caused to plug flow and become oriented (3 to 3).
2), Cool it and take it out from the die 3-3
), mold the biaxially oriented PTFE sheet 10, and then peel off the biaxially oriented PTFE sheet 10 and the resin seam 1 to obtain the desired biaxially oriented PTFE sheet (3-4)
.

The method of the present invention has very low frictional force even under heat and pressure.
This solves the slippery phenomenon inherent in PTFE molding, and is completely unnecessary when laminating and molding materials such as methacrylic resin.

That is, the present invention can only be discovered by carrying out lamination molding of PTFE.

FIG. 4 shows an extrusion apparatus in which the method of the invention can be used. In FIG. 4, the laminated PTFE substrate according to the present invention is put into a ram extrusion molding machine 14 consisting of a prismatic heating cylinder 12 with a square cross section and a square ram 13, and is heated by the ram 13. It is extruded into the die 15. In the middle of part A of the die 15, there is a series of lubricant seeping devices 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 in the lubricant introduction path 16.
The lubricant is further guided to a plurality of infiltration ports 17, oozes out onto the surface of the PTFE base material, and applies a lubricant to the interface between the surface of the molded body and the surface of the die. The lubricant seepage port 17 is made of a material with fine communication holes, such as a small slint or sintered metal.
The lubricant seeps out from the micropores. Alternatively, it is also possible to apply a lubricant to the inner surface of the die by spraying or the like before molding.

The PTFE base material whose surface is uniformly coated with lubricant exhibits a so-called plug flow in which the entire PTFE base material flows at approximately the same speed within the die 15. Next, in the B part of die 15,
Stretch the PTFEi material of Plug Flow. B of die 15
The portion has a structure in which the thickness of the PTFE substrate is reduced.

The flow change of PTFE in part B during biaxial stretching is shown in the fifth figure.
Shown in the figure. 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 ram extruder 1.
This is done by pushing out force from 4. Biaxially stretched PTF
The E substrate is cooled in the C section of the die and exits the die 15.

The biaxially stretched PTFE is taken off by rolls 18. When a laminated PTFE base is used as the PTFE base, a molded article is obtained by peeling off the laminated PTFE stretched sheet extruded from the die 15.

FIG. 6 shows a roll rolling method in which the method of the invention can be used. In FIG. 6, a lubricant 20 is applied to the surfaces of two heated compression rolls 19, and heated sheets having a laminated structure shown in the present invention (top sheet 21, PTFE base material 22, larger friction force A laminate consisting of resin sheets 23 that yields the following properties is indented and compression rolled, taken off by a take-up roll 24, and then each layer is divided into 7 layers.

In the molding method shown in Figure 3, a release film is placed between the resin bases in order to prevent the resin bases from adhering to each other and being unable to be peeled off after molding when the resin bases are laminated and molded. It has been done to put PT on resin base
When using FE, all the conventional ideas do not hold,
PTFE is self-non-adhesive, and not only does it not require a release film, but it also easily peels off from each other, causing the problem that the laminated layer collapses during molding, making it extremely difficult to place a resin film as shown in the present invention. It was found to be effective.

[Effects of the Invention] The present invention is a method for effectively and economically forming a stretched PTFE sheet, particularly a thin stretched PTFE sheet. In particular, this method is suitable for forming biaxially oriented PTFE sheets, which are very economically useful.

PTFE biaxially stretched sheets are required to have the original properties of PTFE, that is, chemical resistance, corrosion resistance, low friction, non-adhesion, and heat resistance, as well as compression resistance and resistance to external forces that are applied during use. It is particularly suitable for use in situations where mechanical strength and dimensional stability are required. For example, it is suitable as a sealing material for gaskets and packings, and for sliding members such as bearings and piston rings.

A polytetrafluoroethylene sheet made of a homopolymer of TFE produced by the free-haking method shown in Example "Fluororesin" (Nikkan Kogyo Shimbun, published in April 1976, pp. 58-65). (Number average molecular weight approximately 1
xlo') was used as the PTFE matrix.

A polytetrafluoroethylene sheet containing 20% by weight of glass fiber was used as a resin sheet and a skin sheet that produced a friction force greater than the friction force between the PTFE substrates.
It was manufactured and used in the same manner as base E. Using these materials, an oriented PTFE sheet was obtained by the compression molding method shown in FIG.

The laminated PTFE base material to be compressed had the following configuration.

Skin sheet 0.3 mm thick PTFE sheet 4 〃〃 Resin sheet QJ // //PTFE sheet 4 〃〃 Resin sheet 0.3 //// PTFE sheet 4 〃〃 Skin sheet 0.3〃〃 Lubricating during stretch molding Shin-Etsu Silicone (KF) is used as an agent.
965.10000 cs) was applied to the inner surface 2 of the compressed die.

The compression die temperature was set at 240'C. Laminated PTF
The E substrate was preheated to 300''C using a preheating press provided separately.The laminated substrate preheated to 300℃ was compressed using a compression die at 240℃, plug-flowed, stretched, and left to stand under pressure for 10 minutes. After that, it was taken out.The laminate was evenly coated with 2
The laminate did not collapse during axial stretching. The laminate was biaxially stretched to four times the area ratio, and by peeling it off from each other, three PTFE stretched sheets with a thickness of 1 mm and four stretched sheets with a thickness of 0.075 mm were obtained. Since the laminate did not collapse during compression and stretching, the yield of the stretched sheet was good and it could be molded well.

Comparative Example The laminated PTFE base material to be compressed was formed by laminating only three 4 mm thick tetrafluoroethylene sheets, and the rest was molded in exactly the same manner as in the example. The laminate collapsed during compression and stretching, and uniform plug flow was not possible.

[Brief explanation of the drawing]

The drawings show compression molding, extrusion molding, and roll rolling methods in which the method of the present invention can be successfully used. 1 to 3 show stretch forming by compression molding, FIGS. 4 to 5 show stretch forming by extrusion molding, and FIG. 6 shows stretch forming by roll rolling. Patent applicant: Asahi Kasei Kogyo Co., Ltd. (+-2)

Claims (1)

[Claims] When stretching polytetrafluoroethylene or a copolymer mainly composed of tetrafluoroethylene (abbreviated as PTFE) under pressure within a die or between rolls, (1) within the die or between the rolls; (2) place a resin sheet between the two substrates, which produces a greater frictional force against the substrate than the frictional force between the PTFE substrates; (3) ) PTFE oriented molding characterized in that the interface between the inner surface of the die or the roll surface and the base material is lubricated, and (4) the base material is oriented by compressive force or extrusion force at a temperature higher than the glass transition temperature of the base material. Product molding method