WO2001094101A1

WO2001094101A1 - Polytetrafluoroethylene molded article and method for its production

Info

Publication number: WO2001094101A1
Application number: PCT/JP2001/004159
Authority: WO
Inventors: Osamu Shirasaki; Takashi Inaoka; Shuji Tagashira; Yasuhiko Sawada
Original assignee: Daikin Industries, Ltd.
Priority date: 2000-06-06
Filing date: 2001-05-18
Publication date: 2001-12-13
Also published as: JP2001341138A

Abstract

A method for producing fired polytetraferuoroethylene molded article having a cylindrical form wherein a polytetraferuoroethylene powder is subjected to a compression molding to prepare a pre-compression molded material having a cylindrical form, a mandrel is placed through the central hole of the pre-compression molded material, and the pre-compression molded material is suspended in a horizontal position by supporting the mandrel and then fired, characterized in that the mandrel used has an outer diameter (Dm) which is the same as or greater than the central hole diameter (cD) of the pre-compression molded material after the firing; a large fired porous polytetraferuoroethylene molded article and a wide fired porous polytetraferuoroethylene sheet; and a gas-permeable film and a cushion sheet comprising the above sheet. The method has allowed the firing of a large polytetraferuoroethylene molded article to be carried out while suppressing the deformation of the article and also allowed the firing of a large porous polytetraferuoroethylene molded article which has been difficult to be fired by a conventional method.

Description

Akira Itoda Polytetrafluoroethylene molded body and its manufacturing method Technical field

The present invention relates to a method for producing a large, thick calcined polytetrafluoroethylene (PTFE) molded body, particularly having a length of 400 mm or more. According to the production method of the present invention, a porous sintered body or a solid body of PTFE with low distortion can be produced, and a large-sized porous sheet obtained by cutting and cutting can be produced. It is useful as a material for permeable membranes and shock absorbing sheets. Background art

Sintered PTFE molded products are used in various products by utilizing their excellent heat resistance, chemical resistance, electrical insulation, high-frequency properties, non-adhesion, and low friction. .

Since PTFE has the property that it cannot be melted, it is preformed by compression molding or paste extrusion and then fired to obtain a fired molded body. ing . In the case of the paste extrusion method, sheet-shaped or small-diameter rod-shaped or tube-shaped objects cannot be formed, and large-sized compacts can be obtained exclusively by compression molding. Manufactured from preformed molded products.

Preforming and firing by the conventional compression preforming method are performed as follows.

First, PTFE powder is uniformly filled in the annular space of a mold having an annular space, and then pressed from above to obtain a compression-molded body. A cylindrical pre-compression molded body is obtained. Place the preform in a heating furnace and place it at 350-380 ° C. By calcining for 3 to 80 hours, a calcined PTFE molded body is manufactured.

The obtained cylindrical fired PTFE molded body is processed into a sheet by a scribing machine. Cutting is performed by inserting the core rod of a cutting machine into the center hole of the cylindrical fired molded body, and cutting it to a desired thickness from the outside with a byte. Yes.

If a large-sized molded body is to be manufactured and processed by this method, it is necessary to first heat it for a long time in order to achieve uniform firing. Then, the PTFE preform formed during the heating and sintering is thermally deformed by its own weight, and the lower part expands. Since this deformation hinders the cutting process, it must be cut off until the surface becomes straight, which is wasteful. In addition, since the center hole of the fired compact also deforms, it is necessary to adjust the hole diameter before applying to the cutting machine.

In consideration of these problems, in the W098 / 41386 and WOOOZ16968 pan fret, the pre-compacted body is placed horizontally and rotated. A method has been proposed in which firing is carried out in a short time so that the firing is uniform and the deformation is reduced. The concrete method is as follows: (1) Put a pre-compression molded body inside a large metal pipe, and make a pipe so that the cylindrical pre-formed body rolls inside the pipe. (2) passing the shaft through the center hole of the pre-compressed molded body, and firing while rotating the shaft. The method is described.

However, the method (1) required a heating furnace large enough to accommodate a large metal pipe, and the preform rolled inside the pipe. The surface of the molded body after firing may be altered. The method of penetrating the shaft of (2) is specifically described in Example 1 of the W098Z41386 pan fret, and the center hole of the preliminary compression-molded article is described. (25 cm in diameter) through a shaft with an outer diameter of 23 cm and sintering while rotating the shaft to obtain a fired molded body with a core hole diameter of 25 cm. According to this description, the outer diameter of the shaft during firing is smaller than the diameter of the core hole of the molded product, and the shaft is always rotated in a state of line contact with the inner surface of the core hole. Therefore, it is smaller than the center hole diameter of the molded body after firing.

If the baking is continued for a long time while rotating by line contact in this way, the deformation due to heat occurs, although not as in the above-described baking method of standing. There are times when you do.

At this time, it is not described in the International Publication, and in the description of Example 1, the center pore diameter of the PTFE molded body before and after firing does not change, but generally, If the compression ratio during preforming is increased, the PTFE preform may shrink due to firing. This phenomenon is conspicuous when the porous compact is fired. The inventors of the present invention have noticed this shrinkage phenomenon and, by taking the shrinkage phenomenon into account, actively utilize the shrinkage phenomenon, thereby obtaining a sintered PTFE compact with little deformation even if it is large. This led to the completion of the present invention.

An object of the present invention is to provide a large-sized calcined PTFE compact having little deformation during sintering.

The present invention also provides a large-sized porous fired PTFE molded body that could not be produced conventionally, and a wide porous PTFE sheet obtained by cutting the same. aimed to . Disclosure of invention

The present invention provides a cylindrical pre-pressurizing method by compressing PTFE powder. A pre-compression molded body is produced, and a mandrel is passed through a center hole of the obtained pre-compression molded body, and the pre-compression molded body is supported by supporting the mandrel. In the method of manufacturing a cylindrical fired polytetrafluoroethylene molded body that is suspended horizontally and fired, the same as the core diameter cD after firing of the pre-compression molded body is used. The present invention relates to a manufacturing method characterized by using a mandrel having a large outer diameter Dm.

The outer diameter of the mandrel to be used must be the same as or larger than the core hole diameter of the pre-compressed compact after firing as described above. Further, from the viewpoint of the core hole diameter of the pre-compression molded body before firing, although it differs depending on the solid or porous body, the center hole diameter of the pre-compression molded body before firing is 90 to 110%. %, Especially 95 to 105%.

In the firing, the pre-compression molded body may be hung horizontally while being suspended by a mandrel, and may be calcined. Alternatively, the horizontally hung mandrel may be rotated. The pre-compression molded body may be fired. According to the present invention, it is possible to produce a fired molded body with little deformation without rotating the molded body.

In the case of producing a porous fired PTFE molded body, it is preferable to use, as a raw material, a PTFE powder, a powder obtained by a suspension polymerization method, which has been fired and then ground. In the case of producing a solid calcined PTFE compact, it is preferable to use a powder obtained by a suspension polymerization method as a raw material PTFE powder and pulverized. Sile .

According to the manufacturing method of the present invention, the length Lp of the pre-compression molded body is 400 mm or more, or the ratio LpZ Dp of the length Lp of the pre-compression molded body to the outer diameter Dp is 1 or more. Large PTFE moldings can be manufactured. Further, according to the production method of the present invention, it is a porous cylindrical member having a length L of 400 mm or more, and a cylindrical wall thickness H of 50 mm or more. On the other hand, it is possible to produce a large-sized new calcined PTFE porous compact having a ratio L / H of length to wall thickness H of 1 or more.

The present invention also relates to a fired PTFE porous molded article obtained by cutting and cutting the new fired porous PTFE molded article, particularly to a width of 400 mm or more and further to a thickness force of 0 mm. Also for porous PTFE porous sheet of 1mm or more.

The present invention further relates to the gas permeable membrane or the buffer sheet, which is the above-mentioned fired PTFE porous sheet. Brief description of the drawing

FIG. 1 is a schematic side view showing a suspended state of a pre-compression-molded article produced by the production method of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

The greatest feature of the present invention is that a pre-compressed PTFE compact shrinks during sintering, and a mandrel with a specific outer diameter is placed in the center hole of the pre-compressed compact. As a result, at least after firing, the core hole of the fired molded body and the mandrel are brought into close contact with each other.

When such a mandrel is used and the pre-compression molded body is suspended horizontally and fired, the pre-formed body shrinks during firing and embraces the mandrel. As a result, deformation of the molded body due to heating can be suppressed.

Therefore, the outer diameter of the mandrel to be used is the same as the diameter of the core hole after shrinkage generated by firing the pre-compression molded body. Or something big is needed. The outer diameter of the mandrel is determined experimentally by measuring the shrinkage rate of the pre-compression molded body to be fired by firing in advance.

The shrinkage rate of the core hole due to the firing of the pre-compression molded body depends on whether the target molded body is solid or porous, whether the pre-compression molded body Reference, compression ratio, pressure, compression speed, compression time, properties of PTFE powder used (particle size, particle size distribution, molecular weight of PTFE, whether PTFE has been modified, Or fired powder, unfired powder, granulated or not), and the cooling rate during firing, etc., 0 to: 15%, usually 0.1 to 10%. Therefore, it is usually sufficient to use a mandrel having an outer diameter of 90% or more, preferably 95% or more of the center hole diameter of the pre-compression molded body before firing.

The upper limit of the outer diameter of the mandrel is determined by whether it can be inserted into the pre-compression molded body. Since the pre-compression molded body expands thermally by heating, it is preferably heated to about 50 to 250 ° C, or expanded mechanically if necessary. In addition, a mandrel having an outer diameter of up to 110%, preferably up to 105% of the core hole diameter at the time of preforming of the pre-compression molded body can be used. The reason for introducing a larger mandrel up to the extension may be found in the aforementioned W098Z16696 panfret. This is to accommodate the case of a pre-compression molded body that hardly shrinks during sintering. If a mandrel with an excessively large outer diameter is forcibly inserted, the residual stress in the portion near the mandrel of the molded body increases due to firing, and the density becomes non-uniform. Cracks may occur.

The material of the mandrel is a material that can withstand the firing temperature. There is no particular limitation, but usually stainless steel, nickel-plated iron, chrome-plated iron, etc. are preferred. Can be used. If necessary, the mandrel may be a cutting core used in the subsequent cutting process. In this case, the cutting operation can be performed without pulling out the mandrel after firing.

Even if the PTFE used in the present invention is a homopolymer of tetrafluoroethylene (TFE), it is modified by up to about 5 mol% with other monomers. Even if it is PTFE (hereinafter, unless otherwise specified, PTFE includes modified PTFE). Specifically, a perfluorovinyl ether such as that described in the W〇98 Z 41386 pamphlet is preferred. The polymerization method may be either a suspension polymerization method or an emulsion polymerization method, but a so-called molding powder obtained by pulverizing particles obtained by suspension polymerization is used. I like it. The particle size of the PTFE powder is a number average particle size of 5 to 600 m, preferably 10 to 150 μιη.

The PTFE powder used in the present invention may be an unfired product or a fired product (including a semi-fired product). However, when producing a porous compact, it is preferable to use calcined PTFE powder, and when producing a solid compact, it is preferable to use unfired PTFE powder.

This PTFE powder is then preformed by compression molding. Compression molding can be carried out under the same molding conditions using the same mold as before. Specifically, when producing a porous molded body, the calcined PTFE powder having a number average particle diameter of 10 to 150 μm is molded into a mold having an annular space (cavity). It is filled and compressed at a compression pressure of 10 to 100 MPa to a compression ratio of 3 to 6, preferably 4 to 5. When manufacturing solid compacts, number average Unfired PTFE powder having a particle size of 10 to 700 μm is filled into a mold having an annular space (cavity), and a compression ratio of 2 to 8 at a compression pressure of 10 to 50 MPa is preferable. Compression to 3-6.

The mold is not particularly limited as long as it can produce a cylindrical preform having a center hole, but is not limited to the mold according to the production method of the present invention. For example, a large-sized fired molded body can be manufactured. The large (preliminary or fired) compacts of the present invention have a length L of 4 OO mm or more, and the longest depends on the size of the mold and firing furnace. It is about 2000mm. In particular, the ratio LpZ between the length Lp and the outer diameter (diameter) Dp is 1 or more, especially those having a length of 2 to 20 and more particularly the length Lp and the wall thickness Hp (outside diameter Dp It can be manufactured with a relatively thin wall thickness ratio of Lp / Hp of 1 or more, especially 4 to 10 (difference in center hole diameter (diameter) cDp).

The diameter of the core hole of the pre-compression molded body differs depending on the size (length, outer diameter) of the pre-molded body, etc., but it is usually appropriately selected in the range of 10 to 500 mm.

The mandrel described above is passed through the center hole of the pre-compressed molded body thus obtained, and is suspended horizontally in a firing furnace. This condition is shown in Figure 1 (schematic side view).

In FIG. 1, 1 is a pre-compression molded body, 2 is a mandrel, and both ends of the mandrel 2 are supported by a suspension base 3. The pre-compression molded body 1 is separated from the floor 4 of the firing furnace.

The production method of the present invention may be fired in the state of horizontal suspension as shown in Fig. 1 or described in the W098 / 41386 Nom fret. In this way, firing may be performed while rotating with a rotating mechanism (not shown in FIG. 1).

The sintering is performed at the melting point (pre-sintering) 337 to 347 ° C for baked products, 322 to 332 ° C for baked products), preferably 10 to 60 ° C, preferably 15 to 50 ° C. This can be done by heating for ~ 200 hours.

When firing while rotating the preform (while rotating the mandrel), the rotation speed depends on the firing temperature, firing time, size of the preform, and the like. It may be appropriately selected according to the conditions, but it is usually 1 to 300 rotations Z time, preferably 10 to 100 rotations Z time. According to the present invention, the rotation can be performed smoothly, at least during firing, because the preform is in a state of embracing (adhering to) the mandrel. In addition, uniform sintering can be achieved, and the amount of deformation can be reduced.

According to the production method of the present invention, it is possible to obtain a fired PTFE molded article having a small amount of deformation and uniformly fired. The fired PTFE molded body may be a solid body (specific gravity 2.10 to 2.2) or a porous body (specific gravity 0.8 to 1.8). Solid large molded articles can also be obtained by the methods described in the respective non-flats of the aforementioned WO98Z41386 and WO00 / 16968, but the production method of the present invention According to the method, a material having a smaller deformation amount and being able to be used immediately in a post-process cutting process can be obtained.

On the other hand, a large-sized porous fired PTFE molded article was obtained for the first time by the manufacturing method of the present invention. Since the pre-compression molded body for a porous body has low mechanical strength, the amount of deformation is too large in the conventional standing firing method, and it is excessive even in the rotary firing method. When the shaft is in line contact with the shaft, the load concentrates and the deformation becomes large. Therefore, a large-scale porous fired molded product at a practical level cannot be manufactured. I didn't.

Therefore, the length L is 400 mm or more and the wall thickness H is 50 mm or less. Above, a cylindrical porous fired PTFE molded article having a ratio L / H of length L to wall thickness H of 1 or more is a novel material.

The obtained cylindrical calcined PTFE molded body is subjected to a scribing U (scube) process in the same manner as in the prior art, and is formed into a sheet shape. Since the sintered compact produced by the conventional manufacturing method has a large amount of deformation during firing, a considerable amount (thickness) is cut out before cutting out a sheet to be a product. In addition, it was necessary to correct the shape of the core hole to a perfect circle according to the core rod of the cutting machine. However, since the solid and porous fired PTFE molded articles obtained by the present invention have a small amount of deformation, the amount to be cut off first can be reduced. Since the center hole is round along the shape of the mandrel where the center hole is round, the cutting machine can be left alone or with a small force [1]. I can do it.

A porous fired PTFE sheet obtained by cutting from a large fired PTFE molded body with a length of 400 mm or more has a width of 400 mni or more, and such a wide porous hole is used. High quality fired PTFE sheets have not been obtained in the past. In addition, the thickness of the sheet can be adjusted by cutting, and a porous fired PTFE sheet having a thickness of 0.1 mm or more, for example, 0.1 to 1 Omm can be easily obtained. be able to .

These calcined PTFE sheets can be used for various purposes. For example, in the case of a solid sheet, heat-resistant insulating tapes such as heat-resistant electric wires, motor vehicles, and generators; corrosion-resistant linings such as chemical plants; piping gaskets. It can be used for molds, mold release films, etc.

In addition, the porous sheet is a gas permeable membrane utilizing the property of transmitting gas such as a gas-liquid separation membrane, a filter, a gas removal membrane, and a gas generation membrane. Packs, cushions, and various seals It can be used for cushioning sheets that use the buffering properties of materials, gaskets, etc .; soundproof covering materials, heat-proofing materials, and polishing pads.

Hereinafter, the present invention will be described based on embodiments, but the present invention is not limited to only the embodiments.

Example 1

Modified PTFE unmodified PTFE (Perfluoro (propylene vinyl ether) manufactured by suspension polymerization method), apparent density 0.42 g / cc, melting point 341 (° C) at 350 to 360 ° C, and then pulverized to an average particle size of 125 m to obtain a calcined PTFE powder.

710 g of the calcined PTFE powder was filled in a mold having an annular cavity with an outer diameter of 100 mm and an inner diameter of 5 Omm. The packing (apparent) density at this time was 0.45 g / cc. Then, compression was performed at a compression molding pressure of 49.6 MPa (500 kgf / cm ² ) for 10 minutes to produce a pre-compression molded body. The size of the product removed from the mold and left for 1 hour is shown below.

Length Lp: 67.5 mm

Outer diameter Dp: 100.65mm

Lp / Dp: 0.67

Center hole diameter c D p: 50mm

Wall thickness Hp: 25mm

Lp / Hp: 2.68

Specific gravity: 1.75 ~: L.76

The same operation was repeated to produce a total of five pre-compacted compacts (Apl to Ap5) of the same size.

First, the preformed body Ap 1 has a stainless steel (SUS) pipe with an outer diameter of 48.5 mm (97% of the core hole diameter cDp). After passing through a mandrel (length 300 mm), a pre-formed body Ap2 is passed through a SUS mandrel with an outer diameter of 50. Omm (100% of cDp). 3 was passed through a SUS mandrel with an outer diameter of 50.5 mm (101% of cDp), and the preform Ap 4 was passed through an outer diameter of 51.0 mm (102% of cDp). I passed. The preforms Ap3 and AP4 were inserted while heating the preform at 200 ° C. Nothing was inserted into the preformed body Ap5.

The preforms Ap:! ~ Ap4 with mandrels inserted were suspended horizontally between two suspension stands placed in the firing furnace. The preformed body Ap5 was set up in the firing furnace as it was. In this state, the inside of the baking furnace is heated up to 360 ° C at a heating rate of 50 ° CZ for 50 hours, and fired at 360 ° C for 6 hours, and then cooled at a rate of 50 ° CZ. The temperature was lowered to 80 ° C in the furnace, removed from the furnace, and moved to a constant temperature room at 25 ° C.

After being left for 24 hours, the size of each fired PTFE molded body was measured. Table 1 shows the results.

The size was measured by the following method.

Outer diameter: Five points are measured at equal intervals in the longitudinal direction of the fired molded body, and the average value is determined.

Core hole diameter: Measure at two points at both ends and calculate the average value.

Also, in Table 1, the outer diameter shrinkage ratio indicates the shrinkage ratio of the outer diameter of the preformed body to the outer diameter Dp of the preformed body. the shrinkage of Kokoroana径in the fired shaped body against the middle Kokoroana diameter _c D p it is Table Wa. However, when hugging occurred, contraction could not be measured. Further, the expansion coefficient in the longitudinal direction represents the expansion coefficient of the length in the longitudinal direction of the fired molded body with respect to the length Lp in the longitudinal direction of the preformed body. table 1

As shown in Table 1, the diameter of the pre-compressed compact was smaller than the core hole diameter.

When a mandrel with an outer diameter smaller than 3% is used (Ap1), the mandrel does not become entangled even after firing (shrinkage rate of core hole) : 1.4%), and the outer diameter of the obtained fired molded article was slightly elliptical. In addition, when the porcelain was vertically baked (Ap5), the contraction rate of the medial foramen was 4.2%, but it was 1.

The reason that the center hole did not shrink by only 4% was that the core was fired with both ends free, so that the expansion in the long-hand direction became large, It is considered that the contraction in the hole direction (radial direction) was suppressed. On the other hand, when a mandrel having an outer diameter equal to or larger than the core hole diameter of the pre-compression molded body is used (Ap 2 to 4), the mandrel is caught after firing. As a result, the fired molded body maintained a substantially perfect circle. In the case of vertical firing, which is the conventional firing method (Ap 5), the outer diameter of the lower part of the fired molded body is about 1.5% larger than that of the upper part and becomes a trapezoidal shape. The whole was elliptical.

Then, the porous fired PTFE molded body (Ap 2 to 4) in which the mandrel was entangled was subjected to cutting to obtain a 0.5 mm thick porous fired PTFE sheet. The sheet is prepared, and its pore size (using POROMETER manufactured by Coulter Electric), hardness (AS KER. C) and tensile strength in the width direction of the cutting sheet and tensile elongation (based on JIS K 6891) ) Was measured. The results are also shown in Table 1.

As shown in Table 1, each of the porous fired PTFE sheets has sufficient mechanical properties.

Example 2

Unfired PTFE (modified PTFE modified with perfluoro (propyl vinyl ether) manufactured by suspension polymerization method) Apparent density 0.42 g / cc, melting point 341 ° C) at 350 to 360 ° C, and then pulverized to an average particle size of 125 m to obtain a calcined PTFE powder.

This calcined PTFE powder (18,400 g) was filled in a mold having a ring-shaped cavity having an outer diameter of 174 mm and an inner diameter of 50 mm. The packing (apparent) density at this time was 0.45 g Zcc. Then, pre-compression molding was prepared by compressing at a compression molding pressure of 49.6 MPa (500 kgf / cm ² ) for 60 minutes. The size of the product removed from the mold and left for 1 hour is shown below. Length Lp: 453mm

Outer diameter Dp: 174mm

Lp / Dp: 2.6

Center hole diameter c D p: 50mm

Wall thickness Hp: 62mm

Lp / Hp: 7.3

Specific gravity: 1.8 to 1.85

A mandrel (length: 50 mm) of stainless steel (SUS) with an outer diameter of 50 mm (100% of center hole diameter cDp) LOOOmm), and suspended horizontally between two suspension stands placed in the firing furnace. In this state, the temperature was raised to 360 ° C in 13 hours, calcined at 360 ° C for 13 hours, lowered to room temperature in 10 hours, and removed from the furnace. It was removed and moved into a constant temperature room at 25 ° C.

After standing for 24 hours, the size of the porous fired PTFE molded body was measured.

^ d L: 585mm

Outer diameter D: 162. lmm

Center hole diameter c D ： 50mm

Wall thickness H: 56.0 mm

Shrinkage (%): Outer diameter 6.8%

Expansion rate (%): 29% in the longitudinal direction

Specific gravity: 1.68

Enclosure of mandrel: Yes (Free center diameter shrinkage 0.65% in case of free)

Change in external shape: Although shrinkage occurred, the shape remained almost circular, and no change in wall thickness in the longitudinal direction was observed.

Example 3 Unsintered PTFE (modified PTFE modified with perfluoro (propylene ether) manufactured by suspension polymerization method) Apparent density 0.42 g / 1075 g of cc, melting point of 341 ° C., average particle diameter of 33 μm) was filled in a mold having an annular cavity with an outer diameter of 100 mm and an inner diameter of 50 mm. The packing (apparent) density at this time was 0.45 g Zcc. Then, compression was performed at a compression molding pressure of 29.4 MPa (300 kgfXcm ² ) for 10 minutes to produce a pre-compression molded body. The size of the product removed from the mold and left for 1 hour is shown below.

Length p: 84.5 mm

Outer diameter Dp: 99.8mm

Lp / Dp: 0.84

Center hole diameter cDp: 50mm

Wall thickness Hp: 24.9mm

Lp / Hp: 3.39

Specific gravity: 2.169 to 2.171

The same operation was repeated to produce a total of four pre-compressed compacts (Ap6 to Ap9) of the same size.

First, the preformed body Ap 6 has a mandrel (length) of stainless steel (SUS) pipe with an outer diameter of 48.5 mm (97% of the center hole diameter cDp). Through the preformed body Ap7, through a SUS mandrel with an outer diameter of 50.Omm (100% of cDp), and through the preformed body Ap8 with an outer diameter of 50.5 mm ( (101% of cDp) passed through a SUS mandrel. The preform Ap 8 was inserted while heating the preform at 100 ° C. Nothing was inserted into the preform Ap9.

The preforms Ap 6 to Ap 8 passed through the mandrel were suspended horizontally between two suspension stands placed in a firing furnace. Reserve The molded body Ap9 was kept standing in the sintering furnace as it was. In this state, the inside of the sintering furnace is heated up to 360 t at a heating rate of 50 Z hours to 360 t, and is held at 360 ° C for 6 hours, followed by sintering, and then a cooling rate of 50 ° CZ time The temperature was lowered to 80 ° C by heating and removed from the furnace and moved into a constant temperature room at 25 ° C.

After leaving for 24 hours, the size of each solid calcined PTFE molded body was measured. The results are shown in Table 2.

Table 2

As shown in Table 2, all of the pre-compressed compacts (Ap 6 to 8) had mandrels entangled after firing (Fri). The contraction rate of the median pore diameter of Ap 9 was 4.8%), and the solid sintered compact maintained almost a perfect circle. Standing, which is the conventional firing method When firing is performed (Ap 9), the outer diameter of the lower portion of the solid fired molded body becomes approximately 0.35% larger than that of the upper portion to form a trapezoid, and the entire shape becomes an ellipse. It was.

Example 4

Unmodified PTFE modified with PTFE (Propyl vinyl ether) manufactured by suspension polymerization, apparent density 0.42 g / cc (Melting point: 342 ° C.) 138 kg was filled in a mold having an annular cavity with an outside diameter of 418 mm and an inside diameter of 150 mm. The packing (apparent) density at this time was 0.67 g / cc. Then, compression was performed at a compression molding pressure of 19.6 MPa (200 kgf / cm ² ) for 60 minutes to produce a pre-compression molded body. The size of the sample removed from the mold and left for 1 hour is shown below.

Length Lp: 560.2 mm

Outer diameter Dp: 18mm

Lp / Dp: 1.34

Medium Shiso diameter cDp: 150mm

Wall thickness Hp: 134mm

Lp / Hp: 4.18

Specific gravity: 2.06

A mandrel (length) of a stainless steel (SUS) pipe with an outer diameter of 146 mm (97.26% of the center hole diameter cDp) (1000 mm), and suspended horizontally between two suspension tables placed in the firing furnace. In this state, raise the temperature to 360 ° C in 22.5 hours, hold at 360 ° C for 25 hours, calcine, then lower to room temperature in 25 hours, and place in a furnace. Was taken out and moved into a constant temperature room at 25 ° C.

After standing for 24 hours, the resulting large solid fired PTF E The size of the molded body was measured.

Length: 597.5 mm

Outer diameter D: 400.7 mm

Center hole diameter c D: 146mm

Wall thickness H: 127.3 mm

Shrinkage (%): Outer diameter 4.14%

Expansion rate (%): 6.7% in the longitudinal direction

Specific gravity: 2.169 to 2.171

Mandrel embrace: Yes (4 to 7% core hole diameter shrinkage when free)

Change in external shape: Shrinkage occurred, but almost a perfect circle was maintained, and no change in wall thickness in the longitudinal direction was observed. Industrial applicability

According to the present invention, the firing of a large-sized PTFE molded body can be performed while suppressing deformation. In particular, it is possible to fire a large-sized porous PTFE molded body, which has conventionally been difficult to fire, and it is possible to provide a wide porous fired PTFE sheet. .

Claims

The range of the wording is as follows: Polytetrafluoroethylene powder is compression-molded to produce a cylindrical pre-compression molded body, and a mandrel is inserted into a center hole of the pre-compression molded body. The pre-compressed body is suspended horizontally by passing through the rail and supporting this mandrel, and calcining is performed. This is a method of manufacturing an ethylene molded body, and uses a mandrel Dm with the same diameter or a large outer diameter as the core hole diameter c D after firing of the pre-compressed molded body. A manufacturing method characterized by this.

2. The method according to claim 1, wherein the pre-compressed body is calcined while being horizontally hung by a mandrel, allowed to stand, and fired.

The method according to claim 1, wherein the pre-compression molded body is fired while rotating the mandrel suspended horizontally.

Polytetrafluoroethylene powder is obtained by a suspension polymerization method, and is a powder that has been calcined and then pulverized, and the obtained molded body is a porous molded body. The production method according to any one of claims 1 to 3, which is a claim.

Claims in which the polytetrafluoroethylene powder is obtained by a suspension polymerization method, is a pulverized powder, and the obtained molded body is a solid molded body. The production method according to any one of Items 1 to 3.

The production method according to any one of claims 1 to 5, wherein the length Lp of the pre-compression molded body is 400 mm or more.

The method according to any one of claims 1 to 6, wherein the ratio Lp / Dp of the length Lp and the outer diameter Dp of the pre-compressed body is 1 or more.

It is porous and has a cylindrical shape with a length L of at least 400 mm. A calcined polytetrafluoroethylene porous molded article having a cylindrical wall thickness H of 50 mm or more.

9. The porous molded article according to claim 8, wherein a ratio L / H of the length L to the thickness H is 1 or more.

10. A fired porous tetrafluoroethylene porous molded article obtained by cutting the fired porous molded body according to claim 8 or 9.

11. The porous molded article according to claim 10, wherein the porous molded article is a fired polytetrafluoroethylene mouth porous sheet having a width of 400 mm or more.

12. The porous molded article according to claim 11, which is a sheet having a thickness of 0.1 mm or more.

13. A gas permeable membrane made of the fired porphyra tetrafluoroethylene porous sheet according to claim 11 or claim 12.

14. A buffering screen made of the fired porphyra tetrafluoroethylene porous sheet according to claim 11 or 12.