JPH03258532A - Multi-layered semibaked substance of polytetra-fluoroethylene - Google Patents

Abstract

PURPOSE:To obtain a PTFE multilayered and semibaked substance having a specific crystal invert ratio and an excellent drawing property by heating the multilayered and unbaked substance of two or more polytetrafluoroethylene (PTFE) layers at a temperature of the melting point or higher of a PTFE baked substance. CONSTITUTION:A PTFE multilayered and semibaked substance is formed by heating a multilayered and unbaked substance consisting at least of two or more PTFE layers to the melting point or higher of the PTFE. Each layer of the PTFE multi-layered and semibaked substance obtained herein is characterized such that the each layer has a distinct peak of heat of melting in the range of 332-348 on the crystal melting curves by an indicating scanning calorimeter and has a value of 0.10-0.85 in a crystal invert ratio defined by heat of melting of a unbaked substance, a semibaked substance, and a baked substance. At least one of PTFE fine powders 1,2,3 constituting each layer of PTFE is preferable to contain a nonfibrous substance therein.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to polytetrafluoroethylene (hereinafter referred to as PTF).
The present invention relates to a multilayer semi-fired body (referred to as E), and more specifically relates to a PTFE multilayer semi-fired body with excellent stretchability.

[Conventional technology]

PTFE is a plastic with excellent heat resistance and chemical resistance, and its porous membrane is widely used as a filter for corrosive gases and liquids, an electrolytic diaphragm, and an electrolytic diaphragm. In particular, its use as a precision filtration filter for various gases and liquids used in the semiconductor industry has become an extremely important field of application.

In order to be an excellent filtration filter, it is necessary to have a sharp pore size distribution and a large amount of permeation per unit time when fluid is permeated at a constant pressure.
It is known that when the porosity and pore size are constant, the amount of fluid permeation increases as the film thickness becomes thinner. However, when the membrane thickness is reduced, the pressure during filtration deforms the porous membrane.
The pore size may change or, in some cases, it may break, causing it to no longer function as a filter. In addition, a thin porous membrane is extremely difficult to handle, and there are problems such as damage when processing it into a filter module or setting it in a filter holder.

In order to solve these problems, a PTFE multilayer porous membrane has been proposed, which is composed of a thin PTFE porous membrane having micropores and another PTFE porous membrane supporting the thin PTFE porous membrane.

The manufacturing method involves layering multiple paste-extruded PTFE sheets while still containing liquid lubricant, rolling or pressing them with calendar rolls to obtain an integrated PTFE multilayer green body, and then removing the liquid lubricant. A method is known in which a PTFE multilayer porous membrane is obtained by stretching in at least one direction (Japanese Unexamined Patent Publication No. 5'1-131236).

[Problem that the invention seeks to solve]

However, the PTFE multilayer green body used in this manufacturing method has poor stretchability. For example, when stretched at a high magnification, the resulting multilayer porous membrane has an uneven pore size distribution, making it difficult to use as a precision filtration filter. was not performing its functions adequately.

[Means to solve the problem]

The present inventors have repeatedly researched the manufacturing method of PTFE multilayer porous membrane, and found that the PTFE multilayer semi-fired body has excellent stretchability.
In particular, it is possible to produce a multilayer porous membrane with a uniform pore size distribution even when stretched at a high magnification, and it is
The present invention was completed based on the discovery that when a PTFE multilayer semi-fired body made of E-fine powder is stretched, each layer becomes fiberized independently, resulting in a PTFE multilayer porous membrane consisting of layers with different average pore diameters. I ended up doing it.

That is, the gist of the present invention is that a multilayer unfired body consisting of at least two or more polytetrafluoroethylene layers is manufactured by heating to a temperature equal to or higher than the melting point of the fired polytetrafluoroethylene body, and each layer has a differential scanning calorific value. It has a clear heat of fusion peak in the range of 332 to 348°C on the crystal melting curve measured by a meter, and the crystal conversion rate defined by the heat of fusion of the green, semi-fired, and fired products is 0.10 to 0.85. A polytetrafluoroethylene multilayer semi-fired body characterized by:

Here, "PTFE" refers not only to a homopolymer of tetrafluoroethylene, but also to a homopolymer of tetrafluoroethylene and
Also included are copolymers with other copolymerizable monomers of not more than 1% by weight, in particular 1% by weight.

The present invention will be explained in detail below.

The PTFE multilayer semi-fired body of the present invention can be manufactured through the steps shown below.

(1) Molding process of PTFE multilayer unfired body This process consists of PTFE
This is carried out in accordance with the paste extrusion method and calender rolling method, which are conventionally known as methods for manufacturing unfired FE sheets and the like.

First, a multilayer preform 7 is produced according to the procedure shown in FIG. For example, this multilayer preform 7 is shown in FIG.
), three PTFE fine powders 1
．． 2 and 3, a second layer 5, and a third layer 6 (this figure is an example of a flat three-layer structure, and is not limited to this), and each of these layers 4~
No. 6 is obtained by adding a liquid lubricant such as solvent naphtha or white oil to a fine powder produced by coagulating a PTFE emulsion polymerized aqueous dispersion with an average particle size of 0.2 to 0.4 μm. It will be done. The amount of this liquid lubricant used varies depending on its type, molding conditions, etc., and is usually used in the range of 20 to 35 parts by weight per 100 parts by weight of fine powder. Moreover, a coloring agent etc. can also be further added to this. First, as shown in FIG. 1(a), a PTF to obtain the first layer 4 is placed in a box-shaped mold 8.
Place the E-fine powder 1 in a layer on the lower mold 9''2, and then move the upper mold 10 with the arrow 1 as shown in Figure 1 (1)).
Press in direction 1. The first layer 4 is thus compressed.

Next, the upper mold 10 is removed, and as shown in FIG. 1(C), PTFE fine powder 2 is put in to form the second layer 5, and the same procedure as in FIG. 1(b) is carried out. Compression is performed using the upper mold 10 to form the second layer 5 on the first layer 4 as shown in FIG. 1(d). After that, add PTFE fine powder 3 for the third layer 6,
It is pressed by the upper mold lO.

In this way, it finally has the first layer 4, second layer 5 and third layer 6 as shown in FIG. 1(e), and is placed in the cylinder 12 of the paste extrusion mold shown in FIG. A multilayer preform 7 is obtained which is shaped to a size that allows it to be snugly housed.

Next, this preformed body 7 is placed in a cylinder part 12 of a paste extrusion apparatus shown in FIG. 2, and then pressed by a ram 14. Cylinder part 1 of the mold shown in Fig. 2
2, for example, the cross section in the direction perpendicular to the axis is 50 mm x 100 m
m rectangle, and part 12 of the cylinder at the exit part 13 of the mold.
It consists of a 50mm x 5mm nozzle with one end narrowed.

In this way, the first layer 4, the second layer 5, and the third layer 6 are completely integrated, and each layer has a uniform thickness in the paste extruded sheet 1.
5 is molded. It was confirmed using a stereoscopic microscope that the thickness composition ratio of each layer of this paste extrusion sheet 15 was the same as the thickness composition ratio of each layer of the multilayer preform. By forming the preformed body 7 in advance in this way, the thickness can be freely selected, making it extremely thin.
Furthermore, even layers with low strength can be easily multilayered.

Next, if necessary, the paste extruded sheet is rolled according to a normal rolling method. The paste extrusion sheet is cut into appropriate lengths and rolled with a rolling roll in the same direction or in a direction perpendicular to the extrusion direction to obtain a multilayer molded product having a thickness of, for example, 100 μm. Thereafter, the liquid lubricant is removed from this multilayer molded body by extraction and/or drying (for example, heating and drying in an oven at 250° C. for 20 seconds) to form a PTFE multilayer green body.

Moreover, the PTFE multilayer green body can also be obtained by a conventionally known manufacturing method.

For example, PTFE fine powders 1 and 2.3 are each individually pasted and extruded to obtain a sheet, and a plurality of these sheets are stacked and rolled with a calendar roll or compressed by a press to form an integrated PTFE multilayer green body. You can also get In addition, this molding process is all performed using PT.
It is carried out at a temperature below about 327° C., which is the melting point of the FE fired body, most commonly around room temperature.

(2) Heat treatment process In this step, the PTFE multilayer unfired body obtained in the above molding process is heated at a temperature higher than the melting point of the PTFE fired body, so that each layer is There is a clear peak in the range of 332 to 348°C on the crystal melting curve according to
This is a step of obtaining a semi-fired multi-layer semi-fired body having a particle size of 85 or less.

The multilayer semi-fired body in this process is a multilayer unfired body made of PTF.
It can be obtained by heating at a temperature higher than the melting point of the E-sintered body, preferably higher than the melting point of the PTFE fired body, and lower than the maximum melting point of the powder used to obtain the multilayer green body. It can also be obtained by heating a multilayer green body for a very short time at a temperature higher than the melting point of the PTFE green body, but even in that case, the crystal conversion ratio after heating is within the above-mentioned range. It is necessary to be within. However, no matter how long a multilayer green body is heated at a temperature lower than the melting point of the PTFE fired body, a multilayer semi-fired body cannot be obtained.

It is difficult to determine the heating time required for the heat treatment in this step, depending on the heating temperature, film thickness of the heated material, and other conditions, but in general, the higher the heating temperature, the shorter the heating time. Also, the thicker the film, the longer the heating time. As a result, treatment conditions can be experimentally determined in practice so that a crystal conversion rate falling within the above range can be obtained.

In this process, whether or not each layer of the multilayer green body has been semi-fired can be determined by a crystal melting curve of 332 to 34 by DSC.
It can be determined by having a clear heat of fusion peak in the range of 8℃, and a crystal conversion rate defined by the heat of fusion of unfired, semi-fired, and fired bodies of 0.10-0°85. .

Crystal melting curves were determined by D SC (Perkin-Blem
Recording is performed using a DSC-7 model (manufactured by Er Corporation).

First, a sample of a PTFE green body is placed in a DSC aluminum pan, and the heat of fusion of the green body and the heat of fusion of the fired body are measured in the following steps.

Step 1 A sample of the PTFE unfired body (PTFE fine powder raw material for forming each layer) was heated at a heating rate of 50°C/min for 25 minutes.
Heat to 0°C, then 250°C at a heating rate of 10°C/min.
Heat from °C to 380 °C.

An example of a crystal melting curve recorded in this heating step is shown in FIG. The position of the heat of fusion curve that appears in this step is defined as the melting point of the rPTFE green body or the melting point of the PTFE fine powder.

Step 2 Immediately after heating to 380°C, the sample is cooled to 250'C at a cooling rate of 10'C/min.

Step 3 Heat the sample again to 380'C at a heating rate of 10°C/min.

An example of a crystal melting curve recorded in Step 3 is shown in FIG. The position of the heat of fusion curve that appears in step 3 is
rPTFE sintered body's melting point.

The heat of fusion of a PTFE green or fired body is proportional to the area between the endothermic curve and the baseline, and is
In the E1mer DS (-7 type), it is automatically calculated by setting the analysis temperature.

Subsequently, a sample is taken from the semi-sintered PTFE semi-sintered body layer made of this PTFE'7 ein powder raw material after the heat treatment in this step, and the crystal melting curve of this sample is recorded according to procedure 1. An example of the curve 1 line in this case is shown in FIG. PT semi-fired in this process
The FE semi-fired body has a crystal melting curve of 332 to 34
It has a clear heat of fusion peak in the 8°C range.

Therefore, the crystal conversion rate is calculated by the following formula: Crystal conversion rate - (ΔH1 - ΔH3) / (△H2 - ΔH2) where △H1 is the heat of fusion of the PTFE green body (see Figure 3). ΔH2 is the heat of fusion of the PTFE fired body (see FIG. 4), and ΔH3 is the heat of fusion of the PTFE semi-fired body (see FIG. 5). Therefore, if the crystal conversion rate of each layer measured after the heat treatment in this step is, for example, 0, it is still an unfired body, and if the crystal conversion rate is 1, it can be said that it is a completely fired fired body.

The crystal conversion rate of the PTFE semi-fired body of the layer heat-treated in this step is 0.10 to 0.85, preferably 0.15 to 0.85.
Must be 75.

The PTFE multilayer semi-fired body obtained through the molding step (1) and the heat treatment step (2) may have a usual shape, such as a film, sheet, tube, or rod.

The PTFE multilayer semi-fired body of the present invention is useful in itself. For example, a PTFE multilayer semi-fired tape can be used as an insulating material for flat cables. P
A flat cable made of TFE is usually obtained by sandwiching a cable wire between two unfired tapes, crimping them with a roll, and then firing them to fuse the two unfired tapes together.

However, unfired tapes undergo large dimensional changes during firing, requiring process control due to dimensional changes, and also have poor fusion properties. One side of the multilayer semi-fired body of the present invention is made of, for example, PTF containing perfluorovinyl ether.
If it is composed of E, it has good heat fusion properties, and dimensional changes during firing are small (and process control can be reduced).

Furthermore, the PTFE multilayer semi-fired body of the present invention can be stretched to form a PTFE multilayer porous membrane.

Stretching of a PTFE multilayer semi-fired body is generally carried out using a tenter device between rolls having different rotational speeds or in an oven. It is appropriate that the stretching temperature is lower than the melting point of the PTFE fired body.

The stretching rate can be determined depending on the purpose, and stretching can be carried out in the -axial direction or in the biaxial direction. Normally, for industrial production, stretching is carried out in the following manner.

(a) In the case of stretching in the axial direction, the multilayer semi-fired body is stretched in the same direction as the extrusion direction or in a direction perpendicular to the extrusion direction.

(iv) In the case of biaxial stretching, the multilayer semi-fired body is first stretched in a uniaxial direction as in (a), and then stretched in a direction perpendicular to this direction.

By this stretching, each layer of the multilayer semi-fired body becomes a porous structure in which micropores are uniformly distributed throughout, and finally a PTFE multilayer porous membrane in which each layer has micropores is obtained.

Further, the obtained multilayer porous membrane is heated at a temperature higher than the melting point of the PTFE fired body, or at a temperature higher than the stretching temperature, if necessary. This heating eliminates dimensional changes in the multilayer porous body and increases its mechanical strength.

Here, the average pore diameter of each layer of the multilayer porous membrane is 1.2.3 m--
--- Determined by the variety and composition. That is, the present inventors have proposed that each layer of a PTFE multilayer semi-fired body consists of at least two or more types of PTFE fine powder 1, 2.3 as a means for obtaining a multilayer porous membrane consisting of at least two or more layers having different average pore diameters. − It was found that it must be composed of

The reason why PTFE Fine Powder 1,2.3-.

The DSC crystal melting curve of PTFE fine powder can vary depending on the manufacturing conditions, so it is difficult to classify it unconditionally, but it is generally divided into the following two types. In other words, a type ■ that has a sharp heat of fusion peak at 341 to 348°C on the high temperature side and no clear heat of fusion peak below that temperature (Figure 6 shows a type 1 of this type
There are 5 examples). There is also type (1) (an example of this type is shown in Fig. 9) which has a heat of fusion peak at 337-348°C and a peak at low temperature at 333-342°C. However, in the case of type (2), one of these two heat of fusion peaks does not show a clear peak and may be observed as a shoulder. (An example is shown in Fig. 12) Generally, when a multilayer unfired body made of a combination of type ■ PTFE fine powder and type ■ PTFE fine powder is heat-treated at a temperature higher than the melting point of the PTFE fired body, type ■ A layer made of PTFE fine powder has a small crystal conversion rate, and a layer made of type PTFE fine powder has a large crystal conversion rate. If the layer of type (1) has a small crystal conversion rate when stretched in the direction, that is, the layer of type (2) has a large average pore diameter, and has a large conversion rate of crystal, that is, the layer of type (2) becomes a multilayer porous membrane that has a small average pore size. . Therefore, when selecting the PTF6 E fine powder to constitute each layer of the multilayer semi-fired body, it is sufficient to select the PTF6 E fine powder so that each layer of the multi-layer semi-fired body has a different crystal conversion rate. In addition to combinations of PTFE fine powders, for example, combinations of type (2) and combinations of type (2) are substantially possible.

PTF so that the crystal conversion rate of each layer of the multilayer semi-fired body is different.
When E fine powder is combined, the difference between the maximum and minimum crystal conversion rates of each layer of the multilayer semi-fired body is 0.1.
It is preferable to set it as above.

Next, another condition for PTFE Fine Powder 12.3 to be different from two or more types is that at least one of PTFE Fine Powders 1 and 2.3 °°°' contains a non-fibrous material. Can be mentioned.

In general, PTFE fine powder has the property that fibers are easily formed from powder particles in processes where the processed material is subjected to shearing force, such as a paste extrusion process, a rolling process, and a stretching process. On the other hand, particles of polymers such as PTFE low molecular weight polymer, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), etc.
No fibers are formed during the two-layer processing process. Therefore, a layer of fine powder containing non-fibrous material such as polymer particles that do not form fibers has a small number of fibers formed in each of the above steps, resulting in a large average pore diameter, and a layer consisting only of fine powder. will have a smaller average pore size.

Therefore, it is preferable that the non-fibrous material is contained in a layer having a low crystal conversion rate. Polymer particles that do not form fibers are
It does not fall off easily because it is incorporated into the tangles of the fine powder's fibers, but in order to completely prevent it from falling off, it must be heated at a temperature higher than the melting point of the polymer particles that do not form fibers. Therefore, it is effective to weld the fibers.

The mixing ratio of non-fibrous polymer particles is 5 to 120 parts by weight, preferably 20 to 100 parts by weight, per 100 parts by weight of fine powder.

If it is less than 5 parts by weight, there is no mixing effect, and if it is more than 120 parts by weight, there is a problem that the strength of the multilayer porous membrane becomes weak.

In addition, these non-fibrous materials are not limited to the above-mentioned fluororesin, but also include particles of inorganic substances such as carbon, graphite, titanium oxide, iron oxide, silica, glass fiber, and glass peas, and organic polymers. These objectives can also be achieved by mixing particles of polyimide, polyamideimide, polyphenylene sulfide, aromatic polyester, polyether ether kedone, etc. as molecules.

As explained above, the PTFE multilayer semi-fired body of the present invention consists of at least two layers having different average pore diameters.
E It is useful as a material for obtaining multilayer porous membranes.

Examples are shown below, and various physical properties in the examples were measured by the following methods.

(1) Film thickness ■ Film thickness meter 9 made by Mitutoyo (LD-110MH type) Measured using.

(2) Porosity The weight (W, g) and absolute dry weight (Wo, g) of a membrane whose pores were filled with pure water using the ethanol replacement method, and its volume (
V, car) was measured and calculated using the following formula.

(W-Wo)
Set it in a 15cm2 filter holder and set it at 0.
．． It was pressurized with nitrogen gas at 639 bar and the amount of nitrogen gas permeated was measured using a mass flow meter.

From this measured value, effective transmission area - square centimeter (c
Permeation amount (unit, l/Cm) per hour per m2)
2 ・time) was calculated.

(4) Average pore size Coulter Porometer
The mean flow pore size (MFP) measured with the ER Electronics Co., Ltd. (USA) was defined as the 0 average pore size. It was confirmed through the following model experiment that the actually measured average pore diameter of the multilayer porous membrane of the present invention almost corresponds to the pore diameter of the layer with the smallest pore diameter of the multilayer porous membrane.

(Model experiment) Average pore diameter measured with Coulter Poromer 0.20 μm 1 thickness 47 μm (Porous membrane A
), average pore diameter 0.98 μm, thickness 69 μm (porous membrane B)
A single-layer porous PTFE membrane was prepared. Next, we measured the average pore diameter using a Coulter porometer of a porous membrane consisting of two layers simply stacking porous membrane A and porous membrane B, and a porous membrane consisting of three layers with porous membrane A as an intermediate layer and sandwiched between porous membranes B. was 0.19 μm, and the latter was 0°18 μm, and these average pore diameters were values that almost matched the average pore diameter of porous membrane A.

〔Example〕

In the examples and comparative examples of the present invention, the following PTFE fine powder was used.

The above-mentioned PTFE fine powders 1 to 4 are coagulated powders of PTFE emulsion polymerized aqueous dispersions having an average primary particle size of about 0.2 to 0.4 μm.

*Method for producing PTFE fine powder 4 Average particle diameter of approximately 0.2 to 0.4 with the heat of fusion peak shown in Figure 6
A mixture consisting of 100 parts by weight of an aqueous dispersion of PTFE emulsion polymerization of μm and an aqueous dispersion of PTFE low molecular weight polymer particles (manufactured by Daikin Industries, Ltd., trade name: Lubron L-5) as a non-fibrous material was prepared. do. When this mixture is stirred in a stirring tank, the respective -order molecules are uniformly mixed to form secondary agglomerated particles having a size of about 200 μm to 1000 μm. The secondary agglomerated particles were heated to 150°C.
PTFE Fine Powder 3
I got it.

Example 1 Using PTFE fine powder 1 (having a heat of fusion peak shown in FIG. 6) and PTFE fine powder 2 (having a heat of fusion peak shown in FIG. 9), a liquid lubricant (manufactured by Exxon, Inc.,
After blending 23 parts by weight (trade name: Isopar M), the first
A multilayer preform in which the thickness composition ratio of each layer was 1:1 was produced by the procedure shown in the figure. Next, this multilayer preform was placed in a cylinder 12 of a paste extrusion mold shown in FIG. 2, and extruded by a ram 14 to obtain a sheet.

Furthermore, the obtained sheet was cut into lengths of about 100 mm, rolled in a direction perpendicular to the extrusion direction, and then
The liquid lubricant was removed by heating and drying in an oven at 0.degree. C. for 20 seconds to obtain a multilayer green body with a thickness of 100 .mu.3 m.

Here, a multi-layer unfired body identical to the above-mentioned multi-layer unfired body was prepared using powder of the − layer that had been colored with a pigment in advance, and its thickness cross section was observed using a stereomicroscope. It was confirmed that the thickness composition ratio was 1:1, which is the same as the thickness composition ratio of each layer of the multilayer preform.

Next, this multilayer green body was placed in an oven at 338°C for 320°C.
A multilayer semi-fired body was obtained by heat treatment for seconds.

A sample was collected by scraping the surface of the layer made of fine powder 1 of this multilayer semi-fired body, and the heat of fusion peak on the crystal melting curve was measured by DSC. The results are shown in Figure 7. The results of measuring the heat of fusion peak of the layer shown in FIG. 10 are shown in FIG.

Further, the results of measuring the heat of fusion peak on the crystal melting curve of the fired body of Fine Powder 1 by DSC are shown in FIG. 8, and the results of measuring the heat of fusion peak of the fired body of Fine Powder 2 are shown in FIG.

From FIGS. 6, 7, and 8, the crystal conversion rate of the layer made of fine powder 1 of the obtained multi-layer semi-fired body was 0.58, and FIGS. 9, 10, and 11 From the figure, the crystal conversion rate of the layer consisting of Fine Powder 2 of the obtained multilayer semi-fired body was 0.75.

Next, this multilayer semi-fired body was stretched 3 times at 400%/sec in the same direction as the rolling direction in an oven at about 300°C, and further stretched 5 times in the direction perpendicular to the rolling direction to increase the thickness. Sa4
A multilayer porous membrane of 5 μm was obtained.

A scanning electron micrograph of the surface of the layer made of fine powder 1 and an SEM photograph of the surface of the layer made of fine powder 2 of this multilayer porous membrane were taken and observed.
It was found that a multilayer porous membrane was formed in which the layer made of Fine Powder 1 had a large average pore size and the layer made of Fine Powder 2 had a small average pore size.

The porosity of this multilayer porous membrane is 83%, and the average pore diameter is 0.24.
μm, and the gas permeation rate was 280β/cm2 hours.

Example 2 PTFE fine powder 1 and 2 used in Example 1
was extruded, rolled, and heat treated in the same manner as in Example 1, except that the thickness composition ratio of the layer consisting of Fine Powder 1 and the layer consisting of Fine Powder 2 was set to 4:1, and the thickness was 100.
A multilayer semi-fired body of μm was obtained.

Next, this multilayer semi-fired body was stretched six times in the same direction as the rolling direction at 100%/sec in an oven at about 300°C to obtain a multilayer porous film with a thickness of 59 μm.

As in Example 1, observation of the SEM photographs revealed that the layer made of Fine Powder 1 had a large average pore diameter, and the layer made of Fine Powder 2 had a small average pore diameter.

The porosity of this multilayer porous membrane is 63%, and the average pore diameter is 0.08.
μm, and the gas permeation amount was 13.5 A/cm 2 ·hr.

Example 3 A multilayer semi-fired body was stretched 3 times at 400%/sec in the same direction as the rolling direction in an oven at about 300°C, and further stretched 5 times in the direction perpendicular to the rolling direction. In the same manner as in Example 2, a multilayer porous membrane with a thickness of 43 μm was obtained.

It was found from the SEM photographs that the layer made of Fine Powder 1 had a large average pore diameter, and the layer made of Fine Powder 2 had a small average pore diameter.

The porosity of this multilayer porous membrane is 82%, and the average pore diameter is 0.25.
μm, gas permeation amount is 345. g/cm” hour.

Example 4 As an example of a combination of fine powders whose heat of fusion peaks on the crystal melting curve by DSC both belong to type 2, first fine powder 2 containing 23 parts by weight of liquid lubricant (heat of fusion peak shown in Figure 9) was used. Using Fine Powder 3 (which has a heat of fusion peak shown in FIG. 12 and is also a copolymer with 0.01 wt% perfluorovinyl ether) containing 22 parts by weight of a liquid lubricant and Extrusion and rolling were carried out in accordance with Example 2 to obtain a multilayer green body having a thickness of 100 μm and a thickness ratio of 4:1 of the layer consisting of fine powder 2 and the layer consisting of fine powder 3. Next, this multilayer unfired body was heat-treated in an oven at 338° C. for 150 seconds to obtain a multilayer semi-fired body. When the crystal conversion rate of the layer consisting of fine powder 2 and the crystal conversion rate of the layer consisting of fine powder 3 of the obtained multilayer semi-fired body were measured in the same manner as in Example 1, they were each 0.55.0. It was .73. Next, the multilayer semi-fired body was biaxially stretched in the same manner as in Example 1, and the thickness was 42 μm.
A multilayer porous membrane of m was obtained.

As a result of observing the SEM photographs, it was found that the layer consisting of Fine Powder 2 had a large average pore diameter, and the layer consisting of Fine Powder 3 had a small average pore diameter.

The porosity of this multilayer porous membrane is 80%, and the average pore diameter is 0.19.
The gas permeation amount per μm1 was 1291/cm2 hour.

Example 5 10 of PTFE fine powder l used in Example 1
A mixture of 0 parts by weight and 100 parts by weight of PTFE low molecular weight polymer 8 particles was used as PTFE fine powder 4, and using this PTFE fine powder 4 and the PTFE fine powder 2 used in Example 1,
Extrusion, rolling, heat treatment, and stretching were carried out in the same manner as in Example 1, except that the thickness composition ratio of the layer consisting of fine powder 4 and the layer consisting of fine powder 2 was 4:1 to obtain a multilayer porous membrane with a thickness of 49 μm. Ta.

As a result of observing the SEM photographs, it was found that a multilayer porous membrane was formed in which the layer made of Fine Powder 4 had a large average pore diameter, and the layer made of Fine Powder 2 had a small average pore diameter.

The porosity of this multilayer porous membrane is 84%, and the average pore diameter is 0.25.
The gas permeation rate per μm1 was 523 n/cm2 hours.

Example 6 Using PTFE Fine Powder 4 used in Example 4 and PTFE Fine Powder 2 used in Example 1,
A multilayer preform consisting of three layers in which a layer of fine powder 2 is sandwiched between a layer of fine powder 4 and a thickness composition ratio of 2:1:2 was prepared, and it was extruded, rolled, and heat treated according to Example 1. , and stretched to obtain a multilayer porous membrane with a thickness of 48 μm.

The pore diameter of this multilayer porous membrane is 83%, and the average pore diameter is 0.24.
．． czm, gas permeation amount was 4351/Cm2 hours.

Example 7 In order to examine the stretchability of the multi-layer semi-fired body obtained in Example 1, this multi-layer semi-fired body was stretched at 500%/sec in the same direction as the rolling direction in an oven at about 300°C. Stretched 5 times,
Furthermore, it was stretched 5 times in the direction perpendicular to the rolling direction.

The obtained porous membrane had a thickness of 39 μm, a porosity of 83%, and a gas permeation rate of 300. &/cm2 · time, and the average pore diameter was uniform at 0.26 μm.

Comparative Example 1 For comparison with Example 7, the multilayer green body obtained in Example 1 was stretched in the same manner as in Example 7 while remaining unfired.

However, the obtained porous membrane was partially thick and thin, and the pore size
The amount of gas permeation was also non-uniform.

In the porous membranes obtained in Example 7 and Comparative Example 1, three locations were randomly sampled, and various physical property values of these locations were measured. The results are shown in Table 1.

Table 1 From these measurement results, it can be seen that the multilayer semi-fired body of the present invention has excellent stretchability.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a procedure for manufacturing a multilayer preform. FIG. 2 is a sectional view showing a state in which paste extrusion molding is performed. FIG. 3, FIG. 4, and FIG. 5 show examples of crystal melting curves measured by differential scanning calorimetry of PTFE green bodies, fired bodies, and semi-fired bodies, respectively. 6, 7, and 8 show crystal melting curves measured by differential scanning calorimetry of the unfired, semi-fired, and fired PTFE fine powders used in Example 1, respectively. FIG. 9, FIG. 1O, and FIG. 11 show crystal melting curves of the unfired, semi-fired, and fired PTFE fine powders 2 used in Example 1, respectively, measured by differential scanning calorimetry. FIG. 12 shows the crystal melting curve of the green body of PTFE Fine Powder 3 used in Example 4, measured by differential scanning calorimetry. Mold, 9 Lower mold, 10 Upper mold 2 Cylinder 3 Outlet part, 4 Ram and above

Claims (1)

[Scope of Claims] 1. Manufactured by heating a multilayer unfired body consisting of at least two or more layers of polytetrafluoroethylene to a temperature equal to or higher than the melting point of the fired polytetrafluoroethylene body, each layer having a differential scanning calorific value. 332 on the crystal melting curve by meter
A polytetra characterized by having a clear heat of fusion peak in the range of ~348°C and a crystal conversion rate defined by the heat of fusion of green, semi-fired and fired bodies of 0.10 to 0.85. Fluoroethylene multilayer semi-fired body. 2. Polytetrafluoroethylene fine powder 1 that should constitute each layer of polytetrafluoroethylene
, 2, 3..., wherein at least one of them has a heat of fusion peak on a crystal melting curve measured by a differential scanning calorimeter that is different from the others. Ethylene multilayer semi-fired body. 3. Polytetrafluoroethylene fine powder 1 to constitute each layer of polytetrafluoroethylene
The polytetrafluoroethylene multilayer semi-fired product according to claim 1, wherein at least one of , 2, 3, . . . contains a non-fibrous material.