JP4846533B2 - Method for producing polytetrafluoroethylene porous body - Google Patents

Description

  The present invention relates to a method for producing a polytetrafluoroethylene porous body.

  As a typical product of a polytetrafluoroethylene (PTFE) porous body, there is a PTFE porous film used for an air filter or a bag filter.

PTFE does not dissolve in most solvents except for special solvents, and its melt viscosity is as high as 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.

  The PTFE porous membrane is generally produced by a method called paste extrusion method as disclosed in Patent Document 1 below. In the paste extrusion method, an organic solvent such as oil is added as a forming aid to PTFE fine powder to form a rod shape, and then the rod-shaped molded body is paste-extruded by an extruder to form a sheet-shaped molded body. This is rolled with a roll before the forming aid is volatilized. The rolled sheet-like molded body becomes a PTFE porous film by performing steps such as drying, biaxial stretching, and firing.

  However, in the above paste extrusion method, the fine powder and the molding aid are blended with each other. Therefore, aging for a long time (for example, a dozen hours) is indispensable before applying the rod-shaped molded body to the extruder. This hinders productivity improvement. Furthermore, since an organic solvent is used as a molding aid, there is an environmental problem. Under such circumstances, today, there is an urgent need to develop a production method that does not use an organic solvent and is excellent in productivity.

As a promising candidate, a method of producing a porous PTFE material using an aqueous dispersion of PTFE as a starting material can be considered. For example, a method called a casting method is known as a method for obtaining a PTFE sheet by coating an aqueous dispersion of PTFE particles on a support such as a metal plate, drying and baking the coating, and then peeling the coating from the support. However, it is not widely used industrially because it is inferior to the paste extrusion method in terms of productivity and cost.
Japanese Patent Laid-Open No. 10-30031

  In view of the above problems, an object of the present invention is to provide a method for producing a porous PTFE body, which uses an aqueous dispersion of PTFE as a starting material, is excellent in productivity, and can be expected to reduce costs.

That is, the present invention
(i) The force of the polytetrafluoroethylene particles approaching or coming into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding an agglomerate of polytetrafluoroethylene particles encapsulating water, a surfactant and a foaming agent,
(ii) forming an aggregate;
(iii) a step of reducing the amount of water contained in the formed body of aggregates;
The manufacturing method of the polytetrafluoroethylene porous body containing this is provided.

In another aspect, the present invention provides:
(i) by applying a force for the polytetrafluoroethylene particles to approach or come into contact with each other to a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, and water as a dispersion medium, Obtaining an aggregate of polytetrafluoroethylene particles encapsulating water and a surfactant;
(ii) Sub-step A for forming an aggregate into a rod shape, Sub-step B for obtaining a pellet by cutting the rod-shaped formed body made of the aggregate in a direction crossing the length direction, and a sheet by compressing the pellet A step of forming an agglomerate, comprising sub-step C of forming into a shape;
(iii) a step of reducing the amount of water contained in the formed body of aggregates;
The manufacturing method of the polytetrafluoroethylene porous body containing this is provided.

  According to the production method of the present invention, a moldable aggregate can be obtained directly from a dispersion of PTFE particles. That is, it is possible to continuously produce a PTFE porous material using an aqueous dispersion of PTFE particles as a starting material, and productivity and cost reduction equivalent to or higher than those of a conventional paste extrusion method can be expected. Moreover, since it is not necessary to use an organic solvent, an environmental load is also small.

  Further, according to the former of the production method of the present invention, the aggregate of PTFE particles obtained in the step (i) includes a foaming agent. Therefore, the molded body can be efficiently made porous. When a foaming agent is used in the conventional paste extrusion method, dispersion of the foaming agent in the paste becomes insufficient, and the shape of the molded product after foaming the foaming agent tends to be non-uniform. However, as in the present invention, when an aqueous dispersion is used as a starting material, it is possible to sufficiently and uniformly disperse the foaming agent in the aggregate of PTFE particles, and there is a problem of uneven shape of the molded body. Hard to occur. In addition, when a PTFE porous membrane is produced by applying the production method of the present invention, it is possible to omit the stretching step that is essential in the conventional paste extrusion method.

  In the latter of the production methods of the present invention, as the step of forming the aggregate, a step of forming an aggregate of PTFE particles into a rod shape, a step of cutting the rod-shaped formed body to obtain a pellet, Compressing and forming into a sheet. Since moldable aggregates can be produced continuously, these processes can be performed on a consistent production line, and as a result, high productivity and low cost can be expected.

  According to the production method of the present invention, agglomerates of PTFE particles (hereinafter also simply referred to as “aggregates”) containing water and a surfactant (in the former of the present invention, a foaming agent is further added). ) Can be formed. Such an aggregate cannot be obtained as an intermediate product by the conventional method for producing a PTFE molded product. 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 while the PTFE particles are dispersed. Therefore, an aggregate containing water and a surfactant is not formed.

  According to the step (i) of the production method of the present invention, the PTFE particles are aggregated to such an extent that the imparted shape is retained (having self-shape retention), and the shape is deformable (deformability). It is possible to obtain an aggregate containing water to the extent that This agglomerate can basically be transformed into any shape until dried or fired. For example, after the obtained aggregate is formed into a sheet or a rod (step (ii)), it is dried and / or fired to reduce the amount of water to promote porosity (step (iii)), A PTFE porous body can be obtained.

  Hereafter, each process (i) (ii) (iii) mentioned above is demonstrated in detail.

  The reason why such an agglomerate is obtained in step (i) is not necessarily clear, but probably a structure in which the PTFE phase and the aqueous phase are mixed with each other is formed by the action of the surfactant in the dispersion. This is probably because of this. Although elucidation of the detailed structure of the agglomerates requires further study, a mechanism is considered that the self-shape-retaining property of the agglomerates is manifested by the PTFE phase formed by joining PTFE particles to each other to some extent. It is done. 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 aggregate is expressed by the presence of a stable aqueous phase via a surfactant between the hydrophobic PTFE phase is conceivable.

There is no particular limitation on the method for applying a force that allows PTFE particles to approach or come into contact with each other in the dispersion. For example, the following method may be used.
A. The dispersion is supplied to the chamber, and the above force is applied in the chamber.
B. The force is applied by spraying the dispersion onto the target.
C. The force is applied by bringing the dispersion into contact with a barrier arranged in the flow path of the dispersion to prevent the dispersion from flowing.

  In the method A, the pressure generated in the chamber as the dispersion is supplied can be used as a force for bringing the PTFE particles closer to or in contact with each other, and the aggregate formed in the chamber is discharged as described later. A tubular body (first tubular body) can be connected.

  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, PTFE particles can collide with each other depending on the structure and shape of the chamber, the injection condition of the dispersion liquid, and the PTFE particles are collided with the aggregate formed in the chamber. It is also possible to apply forces that approach or contact 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. Although the target in method B can be set freely, the target is disposed in order to suppress the dispersion of the sprayed dispersion and to increase the ratio of the amount of aggregate obtained to the amount of the sprayed dispersion. A higher degree of sealing of the space is preferable.

  The injection pressure of the dispersion may be freely set depending on the content of PTFE particles in the dispersion, the content of the surfactant, the shape of the chamber, the internal volume, etc. If the injection pressure is too low, It may be difficult to obtain. Therefore, the injection pressure of the dispersion liquid may be set to, for example, 40 MPa or more, preferably 100 MPa or more, more preferably 150 MPa or more.

  According to the knowledge of the present inventors, the formation of aggregates can be started immediately by setting a relatively high injection pressure, for example, 100 MPa or more at the initial stage of aggregation of PTFE particles. After the aggregates are generated in the chamber, even if the injection pressure is reduced to less than 100 MPa, for example, 40 MPa to 50 MPa, the aggregates are stably and continuously formed by spraying the dispersion liquid onto the generated aggregates. Can be generated. As described above, the spray pressure of the dispersion liquid can be made different between the time when the generation of the aggregate is started and the time when the aggregate is continuously generated after a certain time has elapsed from the start time. Specifically, the former injection pressure can be increased and the latter injection pressure can be decreased, so that unnecessary energy is not consumed.

  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. When the dispersion liquid passes through the barrier disposed in the flow path (second tube), the flow of the dispersion liquid is disturbed, or the dispersion liquid partially stays in the dispersion liquid. A pressure imbalance occurs and a force is applied that causes the PTFE particles to approach or contact each other.

  For example, the barrier may be disposed inside the second tubular body. The barrier may be a bent portion or a narrowed portion of the second tubular body. In this case, the method C supplies the dispersion liquid to the second tubular body having the bent portion or the narrowed portion, and the bent portion. It can also be said that this is a method of applying a force for the PTFE particles to approach or come into contact with each other in the region or the constriction.

  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 causes the PTFE particles to approach or come into contact with each other by colliding the dispersion and the aggregate 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 internal volume is not particularly limited, but a commercially available device such as an optimizer manufactured by Sugino Machine may be applied. The optimizer is originally a pulverization / dispersion device that pulverizes and atomizes various materials such as pigments, fillers, and catalysts, and the present inventors have found an application for obtaining an aggregate of PTFE particles. .

  An example of the chamber is shown in FIG. The chamber 1A 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 3a and 3b via supply paths 6a and 6b formed inside the structure 5 of the chamber 1A. A discharge port 8 for discharging aggregates formed in the chamber 1A (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 1A 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 performed). 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 (wall surface of the internal space 2) of the chamber 1A (method A1 can be implemented). It is preferable that the injection directions of the nozzles 3a and 3b are variable because such operations can be performed freely.

  The chamber 1A preferably has a structure that allows the internal space 2 to be a pressurized atmosphere. That is, the chamber 1A may be capable of forming aggregates in an atmosphere having a pressure higher than atmospheric pressure. For example, a pressure adjusting mechanism for adjusting the pressure in the internal space 2 can be provided in the chamber 1A. By pressurizing the inside of the chamber 1A, the force that the PTFE particles approach or come into contact with each other can be more efficiently applied to the dispersion. Even when the pressure adjusting mechanism is not provided, conditions such as the cross-sectional area of the discharge port 8 and the length and number of pipes connected to the discharge port 8 are appropriately adjusted, and the dispersion liquid is supplied from the nozzles 3a and 3b. Can be made a pressurized atmosphere in the chamber 1A. The same applies to the chambers 1B, 1C, 1D, and 1E 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 1B 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 1B shown in FIG. 2, the dispersion liquid is supplied to the mixing valve 9 via the supply port 7 and the supply paths 6a and 6b, and the pressurized water 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 1C shown in FIG. 3, a freely rotatable sphere 10 is disposed at one end of the internal space 2, and a nozzle 3 for injecting the dispersion liquid is disposed at the other end thereof. 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 1C. The wall surface between the nozzle 3 and the sphere 10 in the internal space 2 is formed with a discharge port 8 for discharging the aggregate formed in the chamber 1C (inside the internal space 2) to the outside of the chamber 1C. .

  In the chamber 1C shown in FIG. 3, by supplying the pressurized dispersion liquid to the nozzle 3 via the supply port 7 and the supply path 6, the dispersion liquid is sprayed into the internal space 2 and arranged in the chamber 1C. It can be made to collide with the spherical body 10 which is the member (method A1 can be implemented). At this time, by arranging 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 aggregate from the discharge port 8. Can be efficiently discharged.

  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 </ b> D 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. The core 12b is formed with a discharge path 14 that passes from the center of the upper surface 13b through the core 12b to the outside of the chamber 1D. The core 12a is supported by the outer peripheral body 11 via a support member (not shown).

  By adjusting the position 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 1D 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 as an aggregate of PTFE particles from the discharge port 8 of the chamber 1D.

  The pressure of the dispersion to be supplied (supply pressure) may be set freely depending on the shape and internal volume of the chamber, the size of the interval d, the amount of the dispersion to be supplied, and the like. It may be difficult to obtain things.

  In each of the chambers 1A to 1D shown in FIGS. 1 to 4, a tube (first tube) is connected to the discharge port 8, and aggregates are brought into contact with 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. Aggregates with improved properties can be obtained. Further, such an aggregate 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. As a cause of improving the strength of the aggregate and the molded body, it is considered that a skin layer in which PTFE particles are more firmly bonded to each other is formed on the surface of the aggregate and the molded body by passing through the first tubular body. It is done. It is also conceivable that a shear force is generated inside the aggregate due to the frictional force generated between the first tubular body and the surface of the aggregate, and further binding and joining of the PTFE particles are promoted. In order to discharge the aggregate while making contact with the entire inner wall of the tube, the shape and diameter of the discharge port 8, the shape, inner diameter and length of the tube may be selected.

  The shape, inner diameter, length, etc. of the first tube to be connected are not particularly limited, and can be freely set according to the shape and inner volume of the chambers 1A to 1D, the amount of the dispersion supplied to the chambers 1A to 1D, and the like. it can. 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 processing speed of the dispersion is about 0.1 to 0.5 L / min, the inner diameter of the tube connected to the chambers 1A to 1D is in the range of about 1 mm to 10 mm, and the length of the tube is 1 mm to 5000 mm. A range of the degree may be used. In the chamber 1 </ b> D shown in FIG. 4, depending on the shape of the discharge path 14, the discharge path 14 can also serve as the tube body.

  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.

  Further, a chamber 1E as shown in FIG. 5 can also be used to apply a force for the PTFE particles to approach or contact each other. A chamber 1E shown in FIG. 5 has a structure 5 (chamber body) in which a nozzle 3 is arranged, one end connected to the structure 5, the other end forms a discharge port 8 for a dispersion, and is ejected from the nozzle 3. And an adapter 18 having a wall surface on which the dispersion liquid can collide. The adapter 18 can be a bent tube 18 (L-shaped tube). The ejection direction 4 of the nozzle 3 is adjusted so that the sprayed dispersion liquid collides with the inner wall surface of the bent tube 18, more precisely, the inner wall surface of the bent portion 18a. Such a bent tube 18 can be connected to the chambers 1A to 1D shown in FIGS.

  As shown in FIG. 6, by injecting the dispersion P onto the bent portion 18a of the bent tube 18, the formation of the aggregate 19 starts at the bent portion 18a (step S1). Then, by continuing to spray the dispersion P onto the aggregate 19 that has started to be generated in the bent tube 18, the aggregate 19 gradually grows and fills the inside of the bent tube 18 (step S2). Eventually, the aggregate 19 is discharged from the outlet 8 of the bent tube 18 to the outside of the chamber 1E (step S3). As described above, according to the chamber 1E in FIG. 5, the dispersion liquid collides with the bent portion 18a when the formation of the aggregate is started, and the aggregate present in the bent portion 18a is formed after an appropriate amount of aggregate is formed. By causing the dispersion to collide with itself, it is possible to apply a force that the PTFE particles approach or come into contact with each other. In this way, aggregates can be generated continuously.

  The adapter 18 is not limited to the bent tube 18 as long as the adapter 18 includes a wall on which the dispersion liquid ejected from the nozzle 3 collides and a discharge port through which aggregates generated by the collision are discharged. However, it is preferable that the portion where the aggregate is pushed forward as in the bent tube 18 is sufficiently long, because the above-described skin layer is formed because the aggregate receives shearing force while traveling through the portion.

  Further, the injection direction 4 of the nozzle 3 is not limited to the above. For example, the injection direction of the nozzle 3 can be adjusted such that the injected dispersion liquid collides with the inner wall surface 5 p of the structure 5. In that case, the inner wall surface 5p of the structure 5 is preferably a tapered surface that is smoothly inclined toward the connection portion between the nozzle 3 and the structure 5. In this way, the aggregate formed in the structure 5 moves smoothly toward the bent tube 18.

  The temperature of the chambers 1A to 1E shown in FIGS. 1 to 5 and the temperature of the dispersion liquid supplied to the chambers 1A to 1E (treatment temperature) are usually in the range of 0 ° C. to 100 ° C., and 25 ° C. to 80 ° C. The range of 25 degreeC-50 degreeC is more preferable. In order to maintain the processing temperature at the above temperature, the chambers 1A to 1E may be provided with a temperature adjustment mechanism as necessary. In particular, in the case of the chambers 1A to 1E for injecting the dispersion liquid to the internal space 2 or the bent portion 18a of the bent tube 18, the temperature of the system rises due to the injection, and therefore it is preferable to include a cooling mechanism. If the temperature of the system is too high, the water contained in the aggregates may evaporate, and it may be difficult to obtain aggregates having sufficient flexibility and self-supporting properties. However, in terms of ease of aggregation of PTFE particles, a moderately high temperature is superior, so that not only a cooling mechanism but also a heating mechanism should be provided so that all temperature conditions can be realized.

  Next, the step (ii) of forming the aggregate can be performed according to the shape of the porous body to be produced. For example, when the porous body to be manufactured is a porous film, step (ii) is a step of forming the aggregate into a sheet. The method for forming the aggregate into a sheet shape is not particularly limited, and examples thereof include a method by passing a channel having a square or slit-like cross section, for example, a T-die. In this case, a sheet-like molded body having a cross-sectional shape corresponding to the cross-sectional shape of the flow path can be obtained. Further, according to this method, in combination with the step (i) described above, it is possible to easily obtain a long sheet-like molded body. In addition, the cross-sectional shape of a flow path here means the cross section of the direction orthogonal to the advancing direction of an aggregate.

  Next, step (iii) for reducing the amount of water contained in the sheet-like molded body is performed. This step (iii) may include a step of drying the sheet-like molded body in a temperature range below the melting point of PTFE. The specific method of a drying process is not specifically limited, For example, a sheet-like molded object should just be heated up to 50 to 200 degreeC, and should just hold | maintain about 1 minute-60 minutes. In some cases, the sheet-like molded body may be air-dried.

  When a sheet-like molded object contains a foaming agent, in the said drying process, a foaming agent can be foamed, reducing the quantity of the water contained in a molded object. That is, the sheet-like molded body is dried in a temperature range below the melting point of PTFE and the foaming agent foams. If it does in this way, reduction of the quantity of water and foaming of a foaming agent will combine, and porosity will advance efficiently. An appropriate drying temperature range is, for example, 130 ° C. to 200 ° C., depending on the type of foaming agent. Such an effect can be obtained in the same manner for molded articles having other shapes containing a foaming agent.

  In addition, the aggregate obtained by injecting a dispersion liquid from a nozzle usually has a temperature exceeding room temperature. If the temperature of the aggregate at this time is about 80 ° C., for example, it is preferable because the foaming agent contained in the aggregate hardly foams.

  Moreover, you may further bak the sheet-like molded object which passed through the drying process (baking process). That is, step (iii) may include a drying step and a firing step. The specific method of a baking process is not specifically limited, For example, the sheet-like molded object which passed through the drying process is accommodated in an electric furnace, and the temperature (327 degreeC-about 400 degreeC, Preferably it is 360 degreeC more than melting | fusing point of PTFE). To about 380 ° C. and hold for about 1 to 60 minutes. In addition, what is necessary is just to set the time of drying and baking suitably according to the thickness etc. of a sheet-like molded object.

  However, when the molded body contains a foaming agent and the foaming agent is of a type that remains in the porous PTFE membrane in the form of microcapsules, the foaming agent may disappear or leave by heating. Therefore, when there is a possibility that the foaming agent may disappear or leave, it is preferable not to perform the firing step.

  Moreover, it can also implement without distinguishing a drying process and a baking process. For example, the drying process performed below the melting point of PTFE and the firing process performed above the melting point of PTFE can be continuously performed by changing the atmospheric temperature of the furnace containing the sheet-like molded body over time. By removing water from the molded body in a temperature range lower than the melting point of PTFE, the porous body of the molded body can be promoted. Thus, a PTFE porous film having sufficient air permeability and strength can be obtained by drying and firing the sheet-like molded body.

  The sheet-like molded body formed through the drying step or the drying and firing steps may be used as a product (PTFE porous membrane) as it is, or may be further subjected to steps such as rolling and stretching as necessary. . However, a sheet-like molded body in which the amount of water has been reduced through the drying step, particularly one containing a foaming agent, can be a sufficiently porous film without being stretched.

  Further, the step (ii) of forming the aggregate may be a step of forming the aggregate into a rod shape. The rod-shaped molded body can be obtained by passing the aggregate through a flow path such as the bent tube 18 described in FIG. And a sheet-like molded object can be obtained by rolling the rod-shaped molded object with a roller. By drying the sheet-like molded product thus obtained, or drying and firing, a PTFE porous membrane having sufficient ventilation performance and mechanical strength can be obtained.

  Furthermore, a sheet-like molded body can be obtained from a rod-shaped molded body by the method shown in FIG. In the method shown in FIG. 7, first, the aggregate is formed into a rod shape by passing through a flow path such as the bent pipe 18 described in FIG. 6 to obtain a rod-shaped formed body 19 made of the aggregate (sub-process A). ). Next, the rod-shaped molded body 19 is cut in a direction crossing the length direction (preferably a direction orthogonal) to obtain a large number of pellets 191 (sub-process B). Next, the pellet 191 is pressed and hardened in a direction orthogonal to the cross section by the press machine 21 and formed into a sheet (sub process C). Furthermore, the obtained sheet-like molded body 193 is dried in the electric furnace 23, and the step (iii) of reducing the amount of water contained therein is performed. This step (iii) may be a drying step, or may include a drying step and a firing step.

As explained above, the degree of freedom of the shape of the aggregate obtained in step (i) is large. Therefore, the rod-shaped molded body 19 having a large cross-sectional area can be easily obtained. Although depending on conditions such as the composition of the dispersion and the injection pressure, for example, a rod-shaped molded body 19 having a cross-sectional area of 7 mm ^{2 to} 7900 mm ² (3 mm to 100 mm in the case of a round bar shape) can be obtained. And if this rod-shaped molded object 19 is cut into round pieces, the pellet 191 for manufacturing the porous membrane 195 can be prepared. The thickness of the pellet 191 can be adjusted according to the thickness required for the porous film 195 to be manufactured. For example, when a porous membrane 195 having a thickness of 0.5 mm to 3 mm is to be manufactured, a pellet 191 having a thickness of 1 mm to 6 mm is suitable. By compression-molding the pellet 191, a sheet-like molded body 193 having a thickness smaller than that of the pellet 191 is obtained. Furthermore, the PTFE porous film 195 having a thickness smaller than that of the sheet-shaped molded body 193 is obtained by drying the sheet-shaped molded body 193 or drying and firing.

  For example, when a circular PTFE porous membrane is cut from a long PTFE porous membrane manufactured by a conventional paste extrusion method, it is inevitable that a discard margin is generated. On the other hand, according to the present embodiment shown in FIG. 7, the PTFE porous membrane 195 can be manufactured with almost no discarding allowance and in some cases with no occurrence, so that the material cost can be reduced. Contribute to

  In addition, a PTFE porous membrane produced by a conventional paste extrusion method using an organic solvent has a high porosity and a high collection performance, but has a dense structure in which the PTFE particles are bound to the inside. Therefore, the film thickness becomes very thin in order to ensure a constant air flow rate as a filter. That is, it is difficult to apply a PTFE porous membrane manufactured by a paste extrusion method to a use that requires a thickness while having a large pore diameter and high ventilation. In addition, a PTFE porous membrane produced by a paste extrusion method, particularly a PTFE porous membrane made porous by biaxial stretching, is very thin, so that it is difficult to handle and it is difficult to improve the yield.

  On the other hand, according to the production method of the present invention, a PTFE porous membrane having a structure in which PTFE particles are densely bound in the surface layer portion and the binding is coarser in the inside than in the surface layer portion can be obtained. That is, according to the production method of the present invention, a PTFE porous membrane having a large thickness (for example, 0.5 mm or more) and a sufficient strength while having a high air permeability can be produced easily and with high productivity. . And the further improvement of ventilation performance can be anticipated by addition of a foaming agent.

  Moreover, the shape of the rod-shaped molded object 19 is not limited to the round bar shape as shown in FIG. That is, the aggregate can be formed into a rod shape by passing through a flow path having a circular, rectangular, or polygonal cross section that is connected to the chambers 1A to 1E or that the chambers 1A to 1E have. it can. As described above, according to the present embodiment, it is possible to reduce waste of materials as much as possible regardless of the shape of the PTFE porous membrane to be manufactured.

  The method shown in FIG. 7 for producing the PTFE porous membrane 195 via the rod-shaped molded body 19 can be applied to the case where a dispersion liquid containing no foaming agent is used. However, the PTFE porous membrane 195 having higher ventilation performance is used. In order to obtain, the use of a dispersion containing a blowing agent is recommended.

  In the production method of the present invention, an agglomerate 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. For example, the dispersion may be continuously supplied to the chambers 1A to 1E shown in FIGS. 1 to 5 and the aggregates may be continuously discharged from the chambers 1A to 1E. At this time, depending on the configuration of the chambers 1A to 1E, the mass of the dispersion supplied to the chambers 1A to 1E and the mass of the aggregates discharged from the chambers 1A to 1E can be made substantially the same. .

  For example, by continuously supplying the dispersion liquid to the chamber 1E shown in FIG. 5, the aggregate formed into a rod shape is continuously discharged from the flow path such as the bent tube 18. At this time, depending on the configuration of the flow path 18, the mass of the dispersion supplied to the bent tube 18 and the mass of the aggregate discharged from the bent tube 18 can be made substantially the same. An aggregate of PTFE particles can be obtained with a high yield, and thus a rod-shaped molded body can be obtained.

  Moreover, in the example of FIG. 7, the process (iii) which reduces the quantity of water is implemented after the sub process C which compresses and forms the pellet 191. However, in the step (iii), if it is limited to the time of carrying out the drying step, it is not limited to the example of FIG. 7 and is carried out in an arbitrary period after the sub-step A for forming the aggregate into a rod shape. Can do. Specifically, a drying process can be implemented in the following period. That is, you may dry the rod-shaped molded object or pellet which is a preform for obtaining a sheet-shaped molded object. When the drying step is performed in the state of the rod-shaped molded body 19, there is an advantage that cutting for making the pellet 191 is easy.

A period between the sub-step A in which the aggregate is formed into a rod shape in the step (ii) and the sub-step B in which the rod-shaped formed body 19 is cut to form a pellet 191. The rod shape in the step (ii) A period between the sub-process B for cutting the molded body 19 to form the pellet 191 and the sub-process C for compressing the pellet 191 to obtain the sheet-shaped molded body 193

  Next, the dispersion liquid will be described.

  The content of PTFE particles in the dispersion is not particularly limited, but in order to obtain an agglomerate having an excellent balance between self-shape retention and deformability, the content can be in the range of 40% by mass to 70% by mass. A preferable lower limit of the content of PTFE particles is 50% by mass, and more preferably 55% by mass. A preferable upper limit of the content of PTFE particles is 65% by mass. Although depending on the method of applying force to the dispersion and the conditions, basically, as the content of PTFE particles in the dispersion increases, the self-shape retention of the resulting aggregate improves and the content of PTFE particles As the value decreases, the deformability of the resulting aggregate tends to improve.

  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 content of the surfactant in the dispersion is not particularly limited, but in order to obtain an agglomerate having an excellent balance between self-shape retention and deformability, a range of 0.01% by mass to 15% by mass is preferable. More preferable in the order of 1 mass% to 10 mass%, 1 mass% to 9 mass%, and 2 mass% to 7 mass%. When the surfactant content is too low, the PTFE phase and the aqueous phase are separated, and it is difficult to obtain an aggregate that uniformly contains water, the surfactant, and the foaming agent. When the content of the surfactant is excessive, the aggregating action when PTFE particles collide with each other decreases, and it becomes difficult to form the PTFE phase itself.

  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 lower than the melting point of PTFE (for example, 100 ° C. or higher and a melting point or lower). In this case, the surfactant is decomposed when the obtained agglomerates are fired, and formed by firing. Further, the amount of the surfactant remaining in the PTFE molded product 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. An appropriate amount of a foaming agent can be mixed into these PTFE dispersions and used in the present invention.

  As the foaming agent, for example, H750D, H755, H770D manufactured by Dainichi Seika Kogyo Co., Ltd. can be used. Since these foaming agents can be foamed at 100 ° C. to 200 ° C., they can be suitably used in the present invention. In addition, thermally expandable microspheres that expand by heating are preferable as a foaming agent because they have a high porosity effect.

  Although the content rate of the foaming agent in a dispersion liquid is not specifically limited, For example, it can be set as the range of 5 mass%-35 mass%, Preferably it is the range of 10 mass%-20 mass%. If the amount of the foaming agent is too large, molding may become unstable, and if the amount is too small, foaming may be insufficient.

  The dispersion may contain a substance other than PTFE particles, water, a surfactant, and a foaming agent, for example, a filler made of an inorganic material such as glass, carbon, metal, and ceramic.

  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.

Example 1
First, with respect to AD938 manufactured by Asahi Glass Co., Ltd. (PTFE particle content: 60% by mass), which is a commercially available PTFE dispersion, H750D manufactured by Dainichi Seika Kogyo Co., Ltd. is added as a foaming agent so that the content is 13% by mass. An aqueous dispersion as a starting material was prepared.

In order to obtain an aggregate of PTFE particles from the prepared dispersion, a chamber 1E shown in FIG. 5 was used. The volume of the internal space 2 of the chamber body 5 was 30 cm ^3, and the nozzle 3 having a circular injection port (0.15 mmφ) was disposed in the chamber body 5. As the bending tube 18, a cylindrical L-shaped tube (inner diameter φ7 mm, length 200 mm (bending portion 18 a is approximately the center)) was used.

  The dispersion liquid was supplied to the chamber 1E, the spray pressure was set to 230 MPa, and the dispersion liquid was sprayed from the nozzle 3. The spray amount of the dispersion was about 0.5 liter / min.

  About 20 seconds after the start of injection, a rod-shaped aggregate (diameter 7 mm) made of a round bar-shaped aggregate, that is, an aggregate of PTFE particles, started to be discharged from the tip of the bending tube 18. By analysis, it was confirmed that the rod-shaped molded body contained water, a surfactant and a foaming agent.

  Next, the obtained rod-shaped molded body was dried in a furnace set at 130 ° C. for 30 minutes. Furthermore, as explained in FIG. 7, the rod-shaped molded body was cut into round pieces to obtain pellets. Next, this pellet was compression-molded with a press machine to obtain a total of five PTFE sheets having a diameter of 20 mm and a thickness of 2 mm. An SEM image of the surface of the obtained PTFE sheet is shown in FIG. A spherical object is a foaming agent, and a thick fibrous portion is formed by binding PTFE particles. A state where the foaming agent is dispersed so as to spread between the fibers can be confirmed.

(Example 2)
A PTFE sheet was produced in the same manner as in Example 1 except that a dispersion containing no foaming agent (AD938 manufactured by Asahi Glass Co., Ltd.) was used.

(Comparative example)
To a commercially available PTFE fine powder (Daikin Kogyo Co., Ltd., Polyflon Fine Powder F104), n-dodecane was added and kneaded as a molding aid so as to have a content of 20% by mass. A paste containing was obtained. After aging the paste for 12 hours, the paste was poured into a reduced flow die (preliminary tube inner diameter 77 mm, outlet inner diameter 6.1 mm) having a cross-sectional area attenuation of 40 to obtain a rod-shaped molded body having a diameter of 5 mm. The rod-shaped shaped body was cut into round pellets having a thickness of 3 mm, and the pellets were compression-molded and dried to obtain a total of five PTFE sheets having a thickness of 0.28 mm.

(Air permeability measurement)
The air permeability of the PTFE sheets of Examples and Comparative Examples was measured with an automatic Gurley type densometer by the method defined in JIS P 8117 (1998). As a result of the measurement, the PTFE sheet of Example 1 (including the foaming agent) was 1 to 5 seconds, the PTFE sheet of Example 2 (not including the foaming agent) was 15 to 50 seconds, and the PTFE sheet of the comparative example was 95. Second to 240 seconds. Although the PTFE sheets of Examples 1 and 2 were thicker than the PTFE sheets of Comparative Examples, the air permeability was high.

FIG. 1 is a schematic view showing a first specific example of a chamber that can be used in the method for producing a PTFE porous body of the present invention. FIG. 2 is a schematic view showing a second specific example of a chamber that can be used in the method for producing a PTFE porous body of the present invention. FIG. 3 is a schematic view showing a third specific example of a chamber that can be used in the method for producing a PTFE porous body of the present invention. FIG. 4 is a schematic view showing a fourth specific example of a chamber that can be used in the method for producing a PTFE porous body of the present invention. FIG. 4 is a schematic view showing a fifth specific example of a chamber that can be used in the method for producing a porous PTFE material of the present invention. FIG. 6 is a schematic view continuously showing how aggregates are generated in the chamber shown in FIG. FIG. 7 is a process diagram for explaining the steps until a PTFE porous membrane is obtained from a rod-shaped molded body. FIG. 8 is an SEM image of a PTFE sheet produced by the method of the present invention.

Explanation of symbols

1A, 1B, 1C, 1D, 1E Chamber 3, 3a, 3b Nozzle 19 Aggregate P Dispersion

Claims (17)

(i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Only including,
A method for producing a polytetrafluoroethylene porous body, wherein the dispersion is supplied to a chamber and the force is applied in the chamber . The dispersion, by spraying toward the inner wall or member disposed within the chamber of the chamber, the manufacturing method of the polytetrafluoroethylene porous body according to claim 1, applying said force. (i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Including
A method for producing a polytetrafluoroethylene porous body , wherein the force is applied to the aggregate by injecting the dispersion. The method for producing a porous polytetrafluoroethylene according to claim 2 or 3 , wherein the dispersion is sprayed from a nozzle. Supplying the dispersion to the chamber via two or more supply channels;
The two or more the dispersion liquid supplied from the supply path, by impinging one another in the chamber, the manufacturing method of the polytetrafluoroethylene porous body according to claim 1, applying said force. The method for producing a porous polytetrafluoroethylene according to claim 5 , wherein the dispersion liquid is ejected from nozzles arranged at respective ends of the two or more supply paths and collides with each other in the chamber. (i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Including
The step (iii) is a method for producing a polytetrafluoroethylene porous body , which is a step of drying the molded body made of the aggregate in a temperature range below the melting point of polytetrafluoroethylene and the foaming agent foams. (i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Including
The step (ii) is a step of forming the aggregate into a rod shape,
The step (iii) is a method for producing a polytetrafluoroethylene porous body, comprising the step of drying the rod-shaped molded body made of the aggregate in a temperature range below the melting point of polytetrafluoroethylene. (i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Including
The step (ii) includes a sub-step A for forming the aggregate into a rod shape, and a sub-step B for obtaining a pellet by cutting the rod-shaped formed body made of the aggregate in a direction crossing the length direction, and compressing the pellets comprises a sub step C of forming into a sheet, a manufacturing method of a polytetrafluoroethylene porous body. The step (iii) is a step of drying the formed body of the aggregate in a temperature range below the melting point of polytetrafluoroethylene,
The method for producing a porous polytetrafluoroethylene according to claim 9 , wherein the step (iii) is performed after the sub-step A in the step (ii). Supplying the dispersion to the chamber and applying the force in the chamber;
The aggregate according to claim 8 or 9 , wherein the aggregate is formed into a rod shape by passing through a flow path having a circular, rectangular, or polygonal cross section connected to the chamber or included in the chamber itself. A method for producing a polytetrafluoroethylene porous body. The method for producing a porous polytetrafluoroethylene according to claim 11 , wherein the aggregate having substantially the same mass as the dispersion supplied to the chamber is discharged from the flow path. The method for producing a porous polytetrafluoroethylene according to claim 11 , wherein the dispersion is continuously supplied to the chamber, and the aggregate formed into a rod shape is continuously discharged from the flow path. (i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Including
The content of the polytetrafluoroethylene particles is in the range of 40% to 70% by weight, the production method of the porous polytetrafluoroethylene material in the dispersion. (i) Force that the polytetrafluoroethylene particles approach or come into contact with each other in a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, a foaming agent, and water as a dispersion medium. Adding the water, the surfactant and the foaming agent to obtain an aggregate of the polytetrafluoroethylene particles,
(ii) forming the agglomerates;
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
Including
The polytetrafluoroethylene porous body is more thick 0.5mm polytetrafluoroethylene porous membrane, method for producing a polytetrafluoroethylene porous material to be produced. (i) by applying a force for the polytetrafluoroethylene particles to approach or contact each other to a dispersion of polytetrafluoroethylene particles containing polytetrafluoroethylene particles, a surfactant, and water as a dispersion medium. Obtaining the aggregate of the polytetrafluoroethylene particles encapsulating the water and the surfactant;
(ii) Sub-step A for forming the aggregate into a rod shape, Sub-step B for obtaining a pellet by cutting the rod-shaped formed body made of the aggregate in a direction crossing the length direction, and compressing the pellet And sub-step C for forming into a sheet, and forming the agglomerates,
(iii) a step of reducing the amount of the water contained in the molded body comprising the aggregates;
The manufacturing method of the polytetrafluoroethylene porous body containing this. The method for producing a porous polytetrafluoroethylene according to claim 16 , wherein the dispersion further contains a foaming agent.