JP2008144137A - Method for producing polytetrafluoroethylene-containing solid material having hole and method for producing polytetrafluoroethylene molded article having hole - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method superior in productivity to conventional ones for producing a polytetrafluoroethylene-molded article having holes. <P>SOLUTION: The polytetrafluoroethylene-molded article having holes is produced by giving force to a PTFE particle dispersion, that contains a PTFE particle, a surface active agent, and water as a dispersant and to which is introduced air bubbles, so that the particles gather or come into contact with each other and a PTFE-containing solid material having holes originated in the bubble is obtained, and the solid material is properly dried and baked to form the PTFE-molded article. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a PTFE molded article using a dispersion of polytetrafluoroethylene (PTFE) particles as a starting material.

  Polytetrafluoroethylene (PTFE) has characteristics such as high chemical resistance and low dielectric constant, and has a high melting point and excellent heat resistance. Therefore, it is used in a wide range of applications mainly in the chemical and electrical fields. Yes. Further, it is widely used for mechanical applications such as a member used for a non-lubricated sliding portion by utilizing a characteristic with a small coefficient of friction and surface tension.

On the other hand, PTFE does not dissolve in most solvents except for special solvents, and its melt viscosity is as high as about 10 ¹⁰ to 10 ¹¹ Pa · s (10 ¹¹ to 10 ¹² P) at 380 ° C. For this reason, it is difficult to apply various molding methods (extrusion molding, injection molding, etc.) used for molding a general thermoplastic resin to manufacture a PTFE molded body. In these molding methods, the melt viscosity of the resin during molding is usually about 10 ² to 10 ³ Pa · s.

  Conventionally, as a method for producing a PTFE molded body, a method called a sintering molding method is generally used. In the sintering molding method, powdery PTFE particles are used as a starting material, and after preforming at room temperature (a molding aid may be added if necessary), the formed preform is converted into PTFE. The whole is sintered (fired) by heating to a melting point (327 ° C.) or higher to obtain a PTFE molded product.

  The details of the steps in the sintering molding method may be appropriately selected according to the shape of the molded body to be obtained. For example, when obtaining a sheet-like PTFE molded body (PTFE sheet), a cylindrical PTFE molded body (PTFE block) ) May be formed by preforming and firing, and the outer peripheral portion of the formed block may be cut (cutting method). According to this method, a sheet having a relatively large thickness (for example, 25 μm or more) can be obtained, but in order to efficiently manufacture the sheet, it is necessary to increase the size of the block. In order to suppress the occurrence of cracks and the like, a long time (approximately 2 to 5 days, depending on the size of the block) is required for preforming and firing. In addition, the sintering method including the cutting method is basically a batch production method, and it is difficult to continuously produce a PTFE molded body from a starting material.

  Apart from the cutting method, a casting method is known as a method for producing a PTFE sheet. In the casting method, a dispersion of PTFE particles (PTFE dispersion) as a starting material is applied onto a support such as a metal plate, dried and fired, and then peeled from the support to obtain a PTFE sheet. According to this method, a PTFE sheet that is thinner and has no distortion can be obtained as compared with the case where the sintering molding method is used. However, the thickness of the sheet obtained by one application, drying and firing is limited to about 20 μm in order to suppress a minute defect called a mud crack, and in order to obtain a sheet having a thickness exceeding 20 μm. It is necessary to repeat the application and baking of the dispersion several times. Moreover, in the casting method, it is difficult to form a molded body having a shape other than the sheet shape.

  For example, Non-Patent Document 1 (pages 141 to 142 for the cutting method and page 130 for the casting method) describes the cutting method and the casting method and other methods for producing a PTFE molded body.

By the way, as with other resins, PTFE may be required to have a molded body having pores inside. The PTFE molded body having pores is useful as a cable insulating material or the like. Conventionally, a PTFE molded body having pores is typically produced by using a foaming agent (for example, Patent Document 1).
Fluorine resin handbook, edited by Takaomi Satokawa, published by Nikkan Kogyo Shimbun, 1990 JP-T-2004-500026

  In the conventional method for producing a PTFE molded product, there is a limit to improvement in productivity, and the shape of the molded product obtained is also limited. In particular, in order to obtain a molded body having pores therein, an additional raw material represented by a foaming agent and a special process are required.

  Therefore, the present invention has a higher productivity than the conventional manufacturing method, and a method for manufacturing a PTFE molded body having a high degree of freedom in the shape of the obtained molded body. Furthermore, a PTFE molded body is manufactured based on this manufacturing method. An object of the present invention is to provide a method for producing an intermediate product (hereinafter referred to as “PTFE-containing solid”).

  The present invention includes PTFE particles, a surfactant, and water as a dispersion medium, and applies a force that allows the particles to approach or contact each other to a dispersion of PTFE particles into which bubbles are introduced. And a method for producing a PTFE-containing solid material having pores, which obtains a PTFE-containing solid material containing pores derived from the bubbles and containing the surfactant.

  Moreover, this invention is a manufacturing method of the PTFE molded object which has a void | hole including the process of obtaining the PTFE containing solid substance which has a void | hole by the said manufacturing method, and the process of reducing the quantity of the water contained in the said solid substance. I will provide a.

  According to the present invention, the PTFE molded body can be manufactured with higher productivity than the conventional PTFE molded body manufacturing method, and the degree of freedom of the shape of the obtained molded body can be increased. In particular, according to the present invention, it is possible to produce a PTFE molded article having pores without using a foaming agent and without requiring heating to a high temperature for foaming.

  According to the present invention, a PTFE-containing solid material containing water as a dispersion medium and a surfactant can be obtained. As apparent from the manufacturing method, this solid is an aggregate formed by binding of PTFE particles. Such agglomerates cannot be obtained as an intermediate product by the conventional production method. For example, as in the production method of the present invention, in a casting method using a dispersion of PTFE particles (hereinafter also simply referred to as “dispersion”) as a starting material, water is removed by drying in a state where PTFE particles are dispersed. In addition, an aggregate containing water and a surfactant is not formed. Further, unlike the particle aggregate obtained by simply precipitating the PTFE particles in the dispersion, the PTFE-containing solid obtained by the present invention does not return to the particles again even after the water is removed by drying. .

  According to the production method of the present invention, the PTFE particles are aggregated to such an extent that the imparted shape is retained (has self-shape retaining property), and the shape is deformable (has deformability). A PTFE-containing solid material containing water can be obtained. This solid can basically be deformed into an arbitrary shape until it is dried or fired, for example, by transforming the obtained solid into a sheet and then drying and / or firing. A PTFE sheet can be obtained. The PTFE-containing solid material according to the present invention is also characterized by a large range that can be deformed without breaking.

  The reason why such a PTFE-containing solid is obtained by the production method of the present invention is not clear, but probably a structure in which the PTFE phase and the aqueous phase are mixed with each other by the action of the surfactant in the dispersion. It is thought to be formed. Elucidation of the detailed structure of the PTFE-containing solid matter requires further investigation, but the mechanism in which the solid shape retention property of the solid matter is manifested by the PTFE phase formed by joining the PTFE particles to each other to some extent. Can be considered. In some cases, a stronger binding structure may be formed between the PTFE particles, or a part of the PTFE particles may be fibrillated to form a PTFE network structure. In addition, a mechanism in which the deformability of the solid material is expressed by the presence of a stable aqueous phase via a surfactant between the hydrophobic PTFE phase is conceivable.

  Examples of a method for applying a force that allows PTFE particles to approach or come into contact with each other in the dispersion include a method in which the dispersion is supplied to the chamber or the tube and the force is applied in the chamber or the tube.

  A method for applying the above force to the dispersion is exemplified below.

Method A: Method of supplying the dispersion liquid to the chamber and applying the force in the chamber Method B: Method of applying the force by spraying the dispersion liquid onto the target Method C: Tubular body serving as a flow path for the dispersion liquid A method of applying the force by bringing the dispersion into contact with a barrier that blocks the flow of the dispersion disposed in Method A. In Method A, the pressure generated in the chamber as the dispersion is supplied is brought closer to the PTFE particles. It can utilize for the force made to contact and can connect the pipe body (1st pipe body) which discharges the PTFE containing solid substance formed in the chamber so that it may mention later.

  In Method A, the dispersion liquid supplied to the chamber may be sprayed in the chamber (Method A1) or passed through a constriction provided in the chamber (Method A2).

  In the method A1, the dispersion may be sprayed, for example, toward the inner wall of the chamber or a member disposed in the chamber. When the dispersion collides with the inner wall or member, a force is applied so that the PTFE particles approach or come into contact with each other.

  In the method A1, depending on the structure and shape of the chamber, the spraying condition of the dispersion liquid, the PTFE particles can be collided with each other, and the dispersion liquid and the PTFE-containing solid material formed in the chamber are collided. It is also possible to apply a force that the PTFE particles approach or come into contact with each other.

  The dispersion liquid may be ejected from a nozzle having an ejection port, and the structure and shape of the nozzle, for example, the shape of the ejection port can be freely set.

  Similarly, in the method B, the dispersion may be ejected from a nozzle having an ejection port. The target in Method B is not limited as long as it is an object having a strength that can withstand the spray pressure of the dispersion. In order to suppress scattering of the sprayed dispersion and increase the ratio of the amount of the obtained PTFE-containing solid to the amount of the sprayed dispersion, it is preferable that the space in which the target is disposed has a high degree of sealing.

  The injection pressure of the dispersion may be set freely depending on the content of PTFE particles in the dispersion, the content of the surfactant, the shape of the chamber and the internal volume, etc., but if the injection pressure is too low, the PTFE-containing solid It may be difficult to obtain things.

  In the method A2, the shape of the constriction part through which the dispersion liquid passes is not particularly limited, and may be, for example, a slit shape. As the dispersion passes through the slit, a force is applied that causes the PTFE particles to approach or contact each other.

  The above-mentioned force may be applied to the dispersion liquid by supplying the dispersion liquid to the chamber via two or more supply paths and causing the dispersion liquid supplied from the two or more supply paths to collide with each other in the chamber. (Method A3). In the method A3, PTFE particles can be collided with each other depending on the structure and shape of the chamber, the colliding method, and the like.

  In order to cause the dispersion liquid to collide with each other in the chamber, for example, the dispersion liquid may be sprayed from a nozzle disposed at each end of the two or more supply paths. At this time, by disposing at least two nozzles in the chamber so that the respective injection directions intersect, the dispersions can collide with each other more efficiently.

  In the method C, the dispersion may be supplied to, for example, a tubular body (second tubular body) having the barrier and the force may be applied. The barrier disturbs the flow of the dispersion liquid or partially retains the dispersion liquid, creating a pressure imbalance in the dispersion liquid and applying a force for the PTFE particles to approach or contact each other.

  The barrier may be, for example, a plate-like member disposed so as to narrow the flow path inside the second tubular body. The barrier can also be formed by bending the second tube or partially reducing its inner diameter. That is, the barrier may be a bent portion or a narrowed portion of the second tubular body. In this case, Method C can be said to be a method in which the dispersion liquid is supplied to the second tubular body having the bent portion or the narrowed portion, and a force is applied so that the PTFE particles approach or come into contact with each other in the bent portion or the narrowed portion. .

  When supplying the dispersion liquid to the second tube body, the dispersion liquid may be supplied by being sprayed from a nozzle. In this case, the force can be efficiently applied to the PTFE particles. The nozzle used for spraying may be the same as in method A1, and the spray pressure of the dispersion liquid can be freely set depending on the content of PTFE particles in the dispersion, the content of surfactant, the shape of the second tubular body, and the like. That's fine.

  In Method C, the PTFE particles can collide with each other depending on the structure and shape of the second tubular body, the supply condition of the dispersion, and the like. It is also possible to apply a force that the PTFE particles approach or come into contact with each other by colliding the dispersion and the PTFE-containing solid material formed in the second tube.

  The shape, the inner diameter, the length of the second tubular body, the shapes of the bent portion and the narrowed portion, etc. are not particularly limited.

  Method A1 to A3, Method B, and Method C are examples of a method of applying a force for the PTFE particles contained in the dispersion to approach or contact each other to the dispersion of the PTFE particles. It is not limited to the case where the method shown in the example is used.

  The configuration of the chamber for applying the force to the dispersion liquid including the shape and the internal volume is not particularly limited, but a commercially available device (for example, an optimizer manufactured by Sugino Machine) may be applied. The optimizer is originally a pulverizing / dispersing device that pulverizes and atomizes various materials such as pigments, fillers, and catalysts, and the present inventors have found an application for obtaining a PTFE-containing solid.

  An example of the chamber is shown in FIG. The chamber 1 shown in FIG. 1 has a substantially conical shape in which the inner space 2 is cut off at the periphery near the bottom surface, and a pair of nozzles 3a and 3b for injecting a dispersion liquid are provided on the periphery. The injection port is arranged so as to face the internal space 2. The nozzles 3a and 3b are in a positional relationship where the respective injection directions 4a and 4b intersect each other. The dispersion liquid can be supplied from the supply port 7 to the nozzles 3 a and 3 b via supply paths 6 a and 6 b formed inside the structure 5 of the chamber 1. A discharge port 8 for discharging the PTFE-containing solid material formed in the chamber 1 (inside the internal space 2) is formed near the apex of the internal space 2 that is substantially conical. The shape of the discharge port 8 is not particularly limited, and may be, for example, a circular shape.

  In the chamber 1 shown in FIG. 1, the pressurized dispersion liquid is supplied to the nozzles 3a and 3b via the supply port 7 and the supply paths 6a and 6b, so that the dispersion liquid is injected into the internal space 2 and collides with each other. (Method A3 can be realized). Further, by using the chamber 1 having the same structure, the number of nozzles to be arranged is one, or by controlling the injection directions 4a and 4b of the nozzles 3a and 3b, the dispersion liquid is injected into the internal space 2, It can be made to collide with the inner wall of the chamber 1 (the wall surface of the inner space 2) (method A1 can be realized).

  The chamber 1 preferably has a sealable structure, and the force can be applied to the dispersion more efficiently by sealing the chamber 1 as necessary. The chamber 1 may be provided with a pressure adjusting port for adjusting the pressure in the internal space 2 as necessary. For example, a pressure adjusting valve may be disposed in the pressure adjusting port. . The same applies to the chamber 1 shown in FIGS.

  A method for supplying the pressurized dispersion liquid to the nozzles 3 a and 3 b is not particularly limited. For example, the dispersion liquid pressurized by a high-pressure pump may be supplied from the supply port 7. Using the chamber 1 as shown in FIG. 2, the dispersion and the water pressurized by the pump (pressurized water) are supplied to the mixing valve 9 provided immediately before the nozzles 3a and 3b via mutually different supply paths. And after mixing both with the mixing valve 9, you may supply to nozzle 3a, 3b. In the chamber 1 shown in FIG. 2, pressurized water is supplied to the mixing valve 9 via the supply port 7 and the supply paths 6a and 6b, and the dispersion is supplied to the mixing valve 9 via the supply ports 17a and 17b and the supply paths 16a and 16b. .

  Another example of the chamber is shown in FIG. In the chamber 1 shown in FIG. 3, a freely rotatable sphere 10 is arranged at one end of the internal space 2, and a nozzle 3 for injecting the dispersion liquid is provided at the other end of the injection port. Are arranged so as to face the internal space 2. The nozzle 3 and the sphere 10 are in a positional relationship where the injection direction 4 of the nozzle 3 intersects the sphere 10. The dispersion liquid can be supplied to the nozzle 3 from the supply port 7 via the supply path 6 formed inside the structure 5 of the chamber 1. A discharge port 8 for discharging the PTFE-containing solid material formed in the chamber 1 (inside the internal space 2) is formed on the wall surface between the nozzle 3 and the sphere 10 in the internal space 2.

  In the chamber 1 shown in FIG. 3, by supplying the pressurized dispersion liquid to the nozzle 3 through the supply port 7 and the supply path 6, the dispersion liquid is sprayed into the internal space 2 and disposed in the chamber 1. It can be made to collide with the spherical body 10 which is the member (method A1 is realizable). At this time, by disposing the nozzle 3 and the sphere 10 so that the injection direction 4 of the nozzle 3 deviates from the center of the sphere 10, the sphere 10 can be rotated by the dispersion liquid injection, and the chamber 1 due to the collision of the dispersion liquid. Internal wear can be suppressed.

  The sphere 10 is preferably made of a material that does not deform due to the collision of the dispersion liquid. For example, the sphere 10 may be made of ceramic, metal (preferably alloys having high hardness), diamond, or the like.

  Another example of the chamber is shown in FIG. In the chamber 1 shown in FIG. 4, a pair of cores 12 a and 12 b are accommodated inside a cylindrical outer peripheral body 11. Each of the cores 12a and 12b has a shape in which a truncated cone is joined to one end surface of the cylindrical body, and the upper surfaces 13a and 13b of the truncated cones in each of the cores are spaced apart by a certain distance d. It arrange | positions so that it may mutually oppose. The central axes of the outer peripheral body 11 and the cores 12a and 12b are substantially the same. A supply port 7 for supplying the dispersion liquid is formed at one end of the outer peripheral body 11. The outer diameter of the core 12 a close to the supply port 7 is smaller than the inner diameter of the outer peripheral body 11 and is far from the supply port 7. The outer diameter of the child 12 b is the same as the inner diameter of the outer peripheral body 11. Further, the core 12 b is formed with a discharge path 14 that passes from the center of the upper surface 13 b to the inside of the core 12 b and communicates with the outside of the chamber 1. The core 12a is supported by the outer peripheral body 11 via a support member (not shown).

  By adjusting the positions of the cores 12a and 12b and appropriately controlling the value of the distance d, the gap 15 between the upper surfaces 13a and 13b can be made into a slit-like constriction, and a pressurized dispersion liquid is supplied. By supplying to the chamber 1 from the port 7, the dispersion liquid can be passed through the narrowed portion (gap 15) disposed in the chamber (method A2 can be realized). The dispersion liquid passes through the gap 15 and then flows into the discharge path 14 and is discharged from the discharge port 8 of the chamber 1 as PTFE-containing solid matter.

  The pressure of the dispersion liquid to be supplied (supply pressure) may be freely set depending on the shape and internal volume of the chamber, the size of the interval d, the amount of the dispersion liquid to be supplied, etc. If the supply pressure is too low, PTFE It may be difficult to obtain contained solids.

  In each chamber 1 shown in FIGS. 1 to 4, a PTFE-containing solid material is connected to the discharge port 8 while a tube (first tube) is connected to the entire inner wall of the tube from the connected tube. Is preferably discharged. When the aggregate discharged from the discharge port 8 passes through the first tubular body, it is possible to further apply a force for bringing the PTFE particles closer to or in contact with each other. A solid having improved properties can be obtained. Further, such a solid material can be formed into a molded body having improved mechanical properties such as strength. For example, by selecting the shape, inner diameter, length, etc. of the first tubular body, A molded body having a tensile strength in the MD direction (flow direction: in this case, the direction of discharging from the tube) of 1 MPa or more, and in some cases 2 MPa or more, or 2.5 MPa or more can be obtained. The reason why the strength of the PTFE-containing solid material and the molded body obtained from the solid material is improved is that a skin layer in which PTFE particles are more firmly bonded to each other is formed on the surface of the solid material by passing through the first tubular body. It is thought that it is done. It is also conceivable that the frictional force generated between the first tubular body and the surface of the solid material generates a shearing force inside the aggregate and promotes further binding and joining of the PTFE particles. In order to discharge the solid matter while making contact with the entire inner wall of the tube, the shape and diameter of the discharge port 8, the shape, inner diameter, length, and the like of the tube may be selected.

  The shape, inner diameter, length, and the like of the first tubular body to be connected are not particularly limited, and can be freely set according to the shape and inner volume of the chamber 1, the amount of the dispersion liquid supplied to the chamber 1, and the like. Basically, the longer the tubular body, the better the self-shape retaining property and mechanical properties of the obtained aggregates. Therefore, the length of the tubular body is preferably larger than the minimum inner diameter of the tubular body. As an example, when the treatment speed of the dispersion is about 0.1 to 0.5 L / min, the inner diameter of the tube connected to the chamber 1 is in the range of about 1 mm to 10 mm, and the length of the tube is about 1 mm to 5000 mm. It may be a range. In the chamber 1 shown in FIG. 4, depending on the shape of the discharge path 14, the discharge path 14 can also serve as the tube.

  In order to apply force to the aggregate more efficiently, it is preferable that the minimum inner diameter of the first tubular body is equal to or smaller than the diameter of the discharge port 8. Further, it may be a tubular body whose inner diameter gradually changes as it moves away from the discharge port 8 (that is, the inner surface is tapered). In this case, it is preferable that the inner diameter gradually decreases as it moves away from the discharge port 8.

  The temperature of the chamber 1 and the temperature of the dispersion liquid supplied to the chamber 1 (treatment temperature) are usually in the range of 0 ° C to 100 ° C, preferably in the range of 25 ° C to 80 ° C, and preferably in the range of 25 ° C to 50 ° C. A range is more preferred. In order to keep the processing temperature within the above temperature range, the chamber 1 may include a cooling mechanism as necessary. In particular, in the case of the chamber 1 for injecting the dispersion liquid into the internal space 2, it is preferable to provide a cooling mechanism because the temperature of the system rises due to the injection.

  The PTFE-containing solid material obtained by the production method of the present invention, for example, the PTFE-containing solid material discharged from the discharge port 8 shown in FIGS. 1 to 4 may be further deformed. The shape of the deformation and the method of deforming are not particularly limited. For example, a string-like solid can be obtained by passing the first tubular body, and a sheet-like solid can be obtained by passing the slit. Alternatively, the solid material may be passed through various dies (die) used for extrusion molding, and by selecting the shape of the die, solid material having various shapes such as a string shape and a sheet shape can be obtained. . For example, the solid material deformed into a string shape or a sheet shape may be further deformed by rolling or the like.

  Similarly to the above, the solid matter discharged from the second tubular body used in the method C may be further modified.

  Thus, according to the production method of the present invention, the degree of freedom of the shape of the obtained PTFE-containing solid material can be increased. For example, the minimum thickness of the obtained solid material is 20 μm or more, and depending on the production conditions, 20 μm can be reduced. 1 mm or more, or 2 cm or more. Conversely, the maximum thickness of the obtained PTFE-containing solid material can be 5 cm or less. The thickness of the PTFE-containing solid material indicates, for example, the diameter when the solid material is a string or the like, and the thickness when the solid material is a sheet.

  The minimum thickness and the maximum thickness of the obtained PTFE-containing solid matter are the diameter of the discharge port 8, the (minimum) inner diameter of the first tube connected to the discharge port 8, and the (minimum) of the second tube. It can be controlled by selecting the inner diameter, the shape of a die for deforming the agglomerates, and the like. For example, by connecting a first tubular body having a minimum inner diameter exceeding 20 μm to the discharge port 8, a solid material having a maximum thickness (maximum diameter) exceeding 20 μm can be obtained.

  In the production method of the present invention, a PTFE-containing solid can be continuously obtained by continuously applying the above force to the dispersion. That is, not a batch production method but a continuous production method. Specifically, the dispersion liquid may be continuously supplied to the chamber or the pipe body, the above force may be applied in the chamber or the pipe body, and the PTFE-containing solid material may be continuously discharged from the chamber or the pipe body.

  In this case, if the chamber or tube has a structure other than the supply port and the discharge port, there is no opening through which substances enter and exit, and the mass of the dispersion supplied to the chamber or tube and the chamber or tube are discharged from the chamber or tube. The mass of the PTFE-containing solid material can be made substantially the same. In such an initial stage of continuous production, liquid may be discharged from the chamber or the like, probably because sufficient force is not applied to the dispersion. However, once the initial stage is reached and a stable state in which a sufficient force is applied to the dispersion is achieved, the entire amount of the dispersion is then changed to a PTFE-containing solid. Thereafter, except for a small amount of water lost by evaporation from the discharged PTFE-containing solid material, the supplied dispersion and the obtained PTFE-containing solid material have the same mass. As described above, according to the production method of the present invention, substantially all of the liquid phase raw material (dispersion) containing the solid content can be changed to a solid phase single phase intermediate (PTFE-containing solid). it can.

  In the production method of the present invention, the dispersion may be continuously supplied to the second tube used in Method C, and the aggregates may be continuously discharged from the second tube. Also in this case, as described above, depending on the configuration of the second tubular body, the mass of the dispersion supplied to the second tubular body and the mass of the PTFE-containing solid matter discharged from the second tubular body Can be substantially the same.

  The content of PTFE particles in the dispersion is not particularly limited, but in order to obtain a PTFE-containing solid material having an excellent balance between self-shape retention and deformability, a range of 40% by mass to 70% by mass is preferable, and 50% by mass. The range of% -70 mass% is more preferable, and the range of 55 mass% -70 mass% is further more preferable. Although depending on the method and conditions for applying force to the dispersion, basically, as the content of PTFE particles in the dispersion increases, the self-shape retention of the resulting solid improves, and the content of PTFE particles As the value becomes smaller, the deformability of the obtained solid matter tends to be improved.

  The average particle diameter of the PTFE particles is usually in the range of 0.1 μm to 40 μm, and preferably in the range of 0.2 μm to 1 μm.

  The surfactant content in the dispersion is not particularly limited, but in order to obtain a PTFE-containing solid having an excellent balance between self-shape retention and deformability, a range of 0.01% by mass to 15% by mass is preferable. The range of 0.1% by mass to 10% by mass, the range of 1% by mass to 9% by mass, and the range of 2% by mass to 7% by mass are more preferable. If the content of the surfactant is within a preferable range, it becomes easy to obtain a PTFE-containing solid while suppressing the separation of the PTFE phase and the aqueous phase.

  The type of the surfactant is not particularly limited. For example, an anionic surfactant such as a carboxylate having a hydrocarbon skeleton, a nonionic surfactant such as a fluorosurfactant, a silicone surfactant, and the like. Use it. It is preferable to use a surfactant that decomposes at a temperature below the melting point of PTFE. In this case, the surfactant is decomposed when the obtained PTFE-containing solid is fired, and the PTFE molded body formed by firing is decomposed. The amount of the remaining surfactant can be reduced.

  A commercially available PTFE dispersion may be used as the dispersion. Examples of commercially available PTFE dispersions include AD series such as AD938, AD911, AD912, AD1, AD639, and AD936 manufactured by Asahi Glass Co., Ltd. (former Asahi Glass Fluoropolymers Co., Ltd.), D1, D2, and D3 manufactured by Daikin Industries, Ltd. A series may be used. These commercially available PTFE dispersions usually contain a surfactant.

  The dispersion may contain substances other than PTFE particles, water, and a surfactant.

  The PTFE-containing solid obtained by the production method of the present invention has pores derived from bubbles in the dispersion. Bubbles can be introduced into the dispersion by the release of gas into the dispersion. The type of gas is not particularly limited, but air is sufficient. The gas may be released, for example, by disposing a bubbler (foam) connected to a pump for pumping the gas in the dispersion. The ratio of pores in the PTFE-containing solid can be adjusted by the amount of bubbles introduced into the dispersion, and the amount of bubbles can be easily adjusted by the amount of gas supplied to the bubbler. The introduction of pores by bubbles is superior to the introduction of pores by using a foaming agent in that the ratio of the pores in the PTFE-containing solid can be easily controlled.

  Another advantage of introducing voids by bubbles is that high porosity can be easily achieved. According to the production method of the present invention, a PTFE-containing solid material having a porosity of more than 30%, preferably 50% or more, and more preferably 70% or more can be obtained. Even a conventional manufacturing method can achieve a somewhat high porosity. However, in the conventional manufacturing method, heating is required for causing the foaming agent to act, and the water evaporates by this heating in exchange for realizing a high porosity. For this reason, it is not possible to obtain a PTFE-containing solid having a porosity of more than 30% while containing water or containing water and a surfactant.

  According to the production method of the present invention, it is possible to obtain a wide variety of PTFE-containing solids and PTFE molded bodies. According to the present invention, PTFE-containing solids having a minimum thickness of more than 20 μm while having pores, in particular, PTFE containing a porosity of more than 30% while having a minimum thickness of more than 20 μm Solids can also be produced. An example of the PTFE-containing solid material that can be produced according to the present invention is a solid material that has a thread shape, a string shape, or a column shape, and has a porosity of more than 30%. The solid material that can be produced according to the present invention may be, for example, cylindrical. Another example of the PTFE-containing solid material that can be produced by the present invention is a solid material that is cylindrical and has a porosity of more than 30%.

  According to the production method of the present invention, unlike the original properties of PTFE, a PTFE-containing solid material having a surface having a high affinity with water can also be obtained. It is considered that the hydrophilicity of the surface of the solid material is expressed by the action of a surfactant contained in the solid material. The surface of the PTFE molded body obtained from the PTFE-containing solid material can also be made hydrophilic. In the present specification, a surface having a water contact angle of 45 ° or less when a water droplet of about 2 μL is dropped is defined as hydrophilic.

  The method for producing a PTFE molded product of the present invention includes a step (drying step) of reducing the amount of water contained in the PTFE-containing solid obtained by the above method. The specific method of a drying process is not specifically limited, For example, the obtained solid substance should just be heated up to the temperature of 50 to 200 degreeC, and should be hold | maintained about 1 minute-60 minutes. However, when it is necessary to continuously develop the hydrophilicity of the PTFE-containing solid on the surface of the PTFE molded product, the heating temperature for drying (removing water) is set to a temperature at which the surfactant is not decomposed. The temperature is preferably 250 ° C. or lower. When the surfactant is decomposed and removed, the PTFE molded product exhibits the inherent hydrophobicity of PTFE.

  In this production method, the PTFE-containing solid material that has undergone the drying step may be further baked (baking step). The specific method of a baking process is not specifically limited, For example, the solid substance which passed through the drying process is accommodated, for example in an electric furnace, and the temperature more than melting | fusing point of PTFE (327 degreeC-about 400 degreeC, Preferably it is 360 degreeC- 380 ° C.) and held for about 1 to 60 minutes. The drying and firing time may be set as appropriate according to the thickness of the aggregate.

  The internal structure of the PTFE molded product obtained by the present invention may be affected by drying or the like. However, it is possible to obtain a PTFE molded product in which the minimum thickness and shape described above are maintained for the PTFE-containing solid material, and it is also possible to obtain a PTFE molded product having a porosity as high as the above.

  The PTFE molded body formed through the drying step or the drying and firing steps may be used as a product as it is, and steps such as rolling and stretching may be further added as necessary. In this way, a PTFE molded body having pores is produced.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below.

  As a dispersion, AD938 manufactured by Asahi Glass Co., Ltd. (PTFE particle content: 60 mass%, surfactant content: 5 mass%, PTFE particle average particle diameter: 0.25 μm), which is a commercially available PTFE dispersion, was prepared. A chamber having the structure shown in FIG. 3 was prepared.

The internal volume of the chamber was 12.3 cm ^3, and a nozzle having a circular injection port (0.15 mmφ) was arranged in the chamber. A tube having an inner diameter of 1.6 mm and a length of 200 mm having a circular cross section was connected to the discharge port (circular, diameter: 12.7 mm).

  The dispersion liquid pressurized to 200 MPa was supplied to the chamber. The supply amount of the dispersion was about 0.5 L / min, and the treatment temperature was 25 ° C. While being supplied to the chamber, the dispersion was bubbled with air, and bubbles were introduced into the dispersion. The supply amount of air was about 0.5 L / min.

  Several seconds after the supply of the dispersion, the string-like PTFE-containing solid matter was discharged from the tip of the tube. Thereafter, only the PTFE-containing solid matter continued to be discharged as a string-like continuum from the tip of the tube. The total amount of water and surfactant in the supplied dispersion is included in the PTFE-containing solid. The outer diameter of the PTFE-containing solid was about 2.2 mm.

  The PTFE-containing solid material thus obtained was dried at 80 ° C. for about 60 minutes to obtain a PTFE molded product having an outer shape of about 2 mm. The cross section was observed with a scanning electron microscope. The results are shown in FIG.

  Moreover, when the porosity was measured about the PTFE containing solid substance and the PTFE molded object, both were about 80%. The porosity was determined from the specific gravity of the molded body and the specific gravity of PTFE.

  INDUSTRIAL APPLICABILITY The present invention provides a method for producing a PTFE molded body having pores with high productivity using a dispersion of PTFE particles as a starting material, and has utility value in each field that uses a fluororesin having pores. high.

It is a schematic diagram which shows an example of the chamber which can be used for implementation of this invention. It is a schematic diagram which shows another example of the chamber which can be used for implementation of this invention. It is a schematic diagram which shows another example of the chamber which can be used for implementation of this invention. It is a schematic diagram which shows another example of the chamber which can be used for implementation of this invention. It is a scanning electron micrograph of the cross section of the PTFE molded object produced in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Internal space 3, 3a, 3b Nozzle 4, 4a, 4b Injection direction 5 Structure 6, 6a, 6b Supply path 7 Supply port 8 Discharge port 9 Mixing valve 10 Sphere 11 Outer body 12a, 12b Core 13a, 13b Upper surface 14 Discharge path 15 Gap 16a, 16b Supply path 17a, 17b Supply port

Claims (10)

  The polytetrafluoroethylene particles, a surfactant, and water as a dispersion medium are added to the dispersion of the polytetrafluoroethylene particles into which bubbles are introduced, by applying a force that the particles approach or contact each other, A method for producing a polytetrafluoroethylene-containing solid having pores, which comprises the water and the surfactant and obtains a polytetrafluoroethylene-containing solid having pores derived from the bubbles.   2. The method for producing a polytetrafluoroethylene-containing solid material having pores according to claim 1, wherein the bubbles are introduced into the dispersion liquid by releasing a gas into the dispersion liquid.   The method for producing a solid material containing polytetrafluoroethylene having pores according to claim 1, wherein the dispersion is supplied to a chamber or a tube, and the force is applied in the chamber or the tube.   The production of polytetrafluoroethylene-containing solid material having pores according to claim 3, wherein the dispersion liquid is continuously supplied to the chamber or tube body, and the solid material is continuously discharged from the chamber or tube body. Method.   The method for producing a polytetrafluoroethylene-containing solid having pores according to claim 4, wherein the solid having substantially the same mass as that of the supplied dispersion is discharged.   The method for producing a polytetrafluoroethylene-containing solid having pores according to claim 1, wherein the minimum thickness of the solid exceeds 20 μm.   The method for producing a polytetrafluoroethylene-containing solid having pores according to claim 6, wherein the porosity of the solid exceeds 30%.   The method for producing a polytetrafluoroethylene-containing solid having pores according to claim 1, further comprising a step of deforming the solid. Obtaining a polytetrafluoroethylene-containing solid having pores by the method according to claim 1;
A step of reducing the amount of water contained in the solid matter, and a method for producing a polytetrafluoroethylene molded article having pores. The method for producing a polytetrafluoroethylene molded article having pores according to claim 9, further comprising a step of heating the molded article to a temperature equal to or higher than the melting point of polytetrafluoroethylene and firing.