JPH07243189A - Production of porous formed material of aramid - Google Patents

Abstract

PURPOSE:To obtain a porous formed material of aramid having excellent impregnating properties, fluid permeability, heat resistance and mechanical characteristics by mixing aramid paper pulp with non-aramid fiber and making the mixture into paper. CONSTITUTION:Aramid fibrid is mixed with aramid short fibers in the weight ratio of 85/15-15/85, and made into aramid paper, which is ground to give aramid paper pulp which comprises 70-20wt.% based on the whole weight of pulp not passing through 12 mesh by a sieving test in running water and 50-10wt.% based on the whole weight of pulp passing through 12 mesh but not 80 mesh and has 300-800ml Canadian standard freeness. Aramid paper pulp treated at >= the glass transition temperature of aramid is used as part of the pulp. The pulp is mixed with thermop-lastic fibers having 200-280 deg.C thermally softening temperature such as polyethylene terephthalate in the weight ratio of 90/10-10/900, made into a sheetlike state, heated and pressurized at >=the thermally softening temperature and formed into a given shape. Carbon fibers, silicon carbide fibers and mineral fibers are usable as the non-aramid fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous aramid molding having excellent impregnating property and fluid permeability. More specifically, it has a high air permeability that was difficult to manufacture by the conventional wet papermaking method, and has not only excellent impregnability and fluid permeability but also good heat resistance as an aramid molded product, and mechanical properties, The present invention relates to a novel method for producing a sheet-like porous aramid molding useful as an insulating board, a filter, various structural materials, etc. at low cost.

[0002]

2. Description of the Related Art Aramid paper obtained by wet-paper-making aramid fibrids and aramid short fibers to form a sheet, and further heat-pressing (calendering) processing as necessary,
Sheet-shaped heat-resistant molded articles made of aramid such as aramid board are widely used in electrical insulating materials, structural materials, heat-resistant food containers, and other industrial fields.

Of these various applications, when used by impregnating resin, insulating oil, etc., or as a breathable structural material, the aramid molded article has good heat resistance,
It is required to maintain mechanical properties and have high air permeability.

However, in the conventional method of wet-making a sheet of aramid fibrid and aramid fiber into a sheet,
For products with a high basis weight (for example, a basis weight of 200 g / m ² ), it is quite possible to manufacture an aramid molded product having a high degree of porosity such that the Gurley air permeability is less than 10 minutes / 100 ml air. It was difficult.

Therefore, in order to produce an aramid sheet which is required to have high air permeability, a dense aramid sheet-like molded article once produced by wet papermaking is mechanically provided with a large number of fine apertures. It is conceivable to carry out processing such as processing or papermaking by adding an additive for making it porous, and then performing porosification processing, but the process is complicated,
Not only the production cost becomes high, but also the quality of the product is deteriorated, and it cannot be put to practical use.

Therefore, conventionally, it has been considered difficult to industrially produce a porous aramid molded product having high air permeability and good quality by wet papermaking.

[0007]

The main object of the present invention is to produce a sheet-like porous aramid-like molded article having a high air permeability, which is conventionally difficult to produce by wet papermaking, at low cost by using wet papermaking. It is to provide a method of manufacturing. In other words, the present invention not only has a high air permeability that is not available in the past, but is excellent in impregnability and fluid permeability, and also has good heat resistance as an aramid molded product, mechanical properties, an insulating board, a filter, The main object of the present invention is to provide a method for producing a sheet-shaped porous aramid molded article useful as various structural materials by wet papermaking.

[0008]

Means for Solving the Problems The present inventors have earnestly studied a method for producing a porous sheet-like molded article made of aramid having a high air permeability by wet papermaking, and as a result, have been used in a conventional method. Instead of aramid fibrids, aramid paper pulp obtained by crushing aramid paper, particularly by heat-processing aramid paper pulp having a size and drainage in a specific range, by wet papermaking, cannot be realized by conventional methods at all. It is now possible to manufacture aramid porous sheet moldings with a high degree of air permeability at low cost, and effectively recycle the waste paper from the aramid paper manufacturing process that had to be discarded. They have found that they can also be used, and have reached the present invention.

That is, the present invention is a method for producing a porous sheet-shaped molded product, which comprises mixing aramid paper pulp obtained by crushing aramid paper and non-aramid fibers into a sheet to prepare a sheet.

The "aramid paper pulp" which is one of the raw materials in the method of the present invention is a pulp-like material obtained by crushing aramid paper so that it can be made into paper. The "aramid paper" referred to here is a generic name for sheet-like materials such as paper and boards which are substantially wet-processed of aramid fibrids and aramid short fibers, and may be shaped into a specific shape by secondary processing. .

The aramid constituting the aramid fibrids may be of any kind as long as it is a wholly aromatic polyamide obtained by the reaction of an aromatic diamine and an aromatic dicarboxylic acid chloride. Among them, poly (meta-phenylene isophthalate) is particularly preferable. Among the aramids industrially produced, the meta-aramid represented by amide) has excellent heat resistance and moldability,
In addition, it is preferably used because it has heat fusion property.

The aramid constituting the aramid short fiber may be any wholly aromatic polyamide obtained by the reaction of an aromatic diamine and an aromatic dicarboxylic acid chloride, but poly (meta-phenylene isophthalamide) is particularly preferable. is there. However, even if the aramid fiber is a poly (para-phenylene terephthalamide) fiber or a fiber of a copolymerized para aramid composed of a terephthalic acid component and a diamine component composed of 3,4′-diaminodiphenyl ether and para-phenylenediamine, Well, it may also be a mixture of these with poly (meta-phenylene isophthalamide) fibers. The length of short fibers (fiber length) is 0.1 to 10
The range of mm is preferable.

This aramid paper has a weight ratio of aramid fibrids and aramid short fibers of 15/85 to 85 /
It is preferable that a large amount of materials are mixed and wet-fabricated at a mixing ratio of 15, particularly 70/30 to 70/30, because they are easily produced and easily obtained.

In addition to the above components, this aramid paper contains
It may contain a small amount of fillers and additives. Further, as the aramid paper, either paper which has not been subjected to heat treatment other than substantially dry (uncalendered paper) or paper which has been subjected to heat and pressure treatment after or simultaneously with drying (calendar paper) can be used. Further, this aramid paper is not limited to a normal paper-like product, and may be a board-like product obtained by laminating a plurality of sheets, so-called aramid board is also included in the category of aramid paper in the present invention.

In the method of the present invention, as the raw aramid paper,
It is better to use waste paper generated in the process of manufacturing or processing aramid paper, and using such waste paper not only reduces costs, but also enables reuse of waste and effective use of resources. .

The aramid paper pulp used in the method of the present invention is a pulp-like material obtained by crushing the aramid paper as described above so that it can be made into paper. According to the research conducted by the present inventors, this aramid paper pulp is used. In a sieving test in running water, the 12-mesh non-passage is 70 to 20% by weight (preferably 60 to 30 wt%) of the total weight, and the 12-mesh pass is 80 mesh non-passage of the total weight is 50 to 10%. weight%
(Preferably 40 to 20% by weight), the rest is 80 mesh, and the Canadian standard freeness (Canadian Standard Freeness) is 300 to 80.
It was found that when 0 ml of aramid paper pulp was used, a good sheet having good paper-making property and sufficiently high air permeability was obtained.

Here, the sieving test and the measurement of Canadian standard freeness are carried out by the following methods. (1) Sieving test Aramid paper pulp slurries adjusted to have a net solid content of 10 g are sieved in running water with wire meshes having different opening sizes (large mesh size to small mesh size are arranged in this order). To do. The wire mesh used is four kinds of 12 mesh / 24 mesh / 48 mesh / 80 mesh. The dry weight of aramid paper pulp captured by each wire net is expressed as a ratio to the total solid content. (2) Measurement of Canadian standard freeness The aramid paper pulp slurry adjusted to have a net solid content of 3 g is supplied to a Canadian standard freeness meter, and the amount of drainage (ml) discharged from the side pipe is measured. To do.

As a method for producing the above-mentioned aramid paper pulp, a method of pulverizing aramid paper, for example, waste aramid paper, by a dry method, a wet method or both means is used. The dry method is a method in which a shredder, a crusher, a kneader or the like is used, and the aramid paper is impacted and decomposed into fine particles without substantially interposing water.
The wet method is a method in which an aramid paper is impacted in an aqueous medium to reduce the particle size. Examples of equipment for efficiently performing such wet pulverization include a high-speed disintegrator, a refiner, and a beater. In the method of the present invention, when producing aramid paper pulp, after pulverizing by a dry method, pulverizing by a wet method, and further performing a sieving treatment if necessary, the above size, drainage This is preferable because it is easy to obtain aramid paper pulp.

In the method of the present invention, at least a part of the aramid paper pulp used has a glass transition temperature (Tg).
Those subjected to heat treatment at the above temperature are preferable. This heat treatment may be performed at the manufacturing stage of aramid paper pulp,
It may be carried out during the production or processing stage of the raw aramid paper. That is, when using aramid paper (uncalendered paper) which has not been subjected to a heat treatment other than a drying operation substantially as it is formed by wet papermaking from aramid fibrid and aramid short fiber as a raw material, aramid paper is crushed by crushing treatment. Before or after conversion into paper pulp, it may be heat-treated at least once at a temperature not lower than the glass transition point of the aramid paper, and at the glass transition point or higher for the purpose of improving mechanical properties of the paper at the stage of manufacturing and processing the aramid paper. When the aramid paper (calendar paper) which has been subjected to the heating and pressurizing treatment (calendering) at the above temperature is used, it can be crushed as it is and used as a heat-treated aramid paper pulp.

When the aramid is poly (meta-phenylene isophthalamide), the glass transition temperature (Tg) of the aramid varies depending on its molecular weight, molecular weight distribution, crystallinity, orientation degree, degree of plasticization and the like. , Usually 270 ℃
It is the temperature in the vicinity. The heat treatment is preferably carried out until the aramid paper pulp shows substantially no heat-sealing property. For example, at 270 ° C., 1 second or more is preferable.

The proportion of the aramid paper pulp used in the above heat treatment is preferably 10% by weight or more of the whole, and 10 to 100% by weight of the whole aramid paper pulp is heat-treated at a temperature not lower than the glass transition point. By setting the above, a sufficiently porous molded product can be obtained.

In the method of the present invention, the above-mentioned aramid paper pulp and non-aramid fiber are mixed and wet-formed into a sheet. Here, the non-aramid fiber refers to a fiber composed of a component (material) that is chemically different from the fibrid and the short fiber constituting the aramid paper pulp, and examples of such a fiber include polyethylene terephthalate, polybutylene terephthalate, and nylon. 6, fibers from general-purpose thermoplastic polymers such as nylon 66, polyacrylonitrile, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, etc., fibers from heat-resistant polymers such as liquid crystal polyarylate, polyether ketone, polyphenylene sulfide, carbon, graphite, Inorganic fibers such as silicon carbide and natural fibers such as cotton and linter can be exemplified.

Above all, the heat fusion temperature is 200 to 280 ° C.
The thermoplastic synthetic fiber (1) is suitable because a good molded product can be obtained, and particularly, polyethylene terephthalate fiber and polybutylene terephthalate fiber are most suitable.

The thermal fusion temperature referred to here is such that when the cotton-like fiber mass is subjected to a load (50 kg / cm ² ) and gradually heated, the fusion between the fibers substantially begins. Refers to temperature.

As this non-aramid fiber, only one kind may be used, but two or more kinds may be used in combination. The fiber thickness (fineness) is preferably in the range of 0.1 to 50 deniers. If the fibers are thinner than 0.1 de, the entanglement between the fibers becomes remarkable during mixed papermaking, and the texture of the obtained sheet may be impaired. If it is thicker than 50 de, the mechanical properties of the obtained sheet and molded article tend to be deteriorated.
The fiber length (fiber length) is preferably in the range of 1 to 30 mm in order to realize good paper-making properties and mechanical properties of the sheet or the molded product.

The ratio of the above-mentioned aramid paper pulp and non-aramid fibers to be mixed and paper-formed is 90/10 to 10/90, especially 8 in terms of the weight ratio of aramid paper pulp / non-aramid fibers.
It is preferably 8/12 to 50/50. When the proportion of aramid paper pulp is more than 90% by weight, not only the strength of wet paper during wet mixing and papermaking becomes low and the handleability is deteriorated, but also the porosity performance of the obtained molding tends to be insufficiently exhibited. . On the other hand, if the proportion of aramid paper pulp is less than 10% by weight, the strength of wet paper tends to be low.

In the method of the present invention, the above-mentioned aramid paper pulp and non-aramid fibers are mixed in water, and the obtained aqueous dispersion is formed into a sheet by ordinary wet papermaking. Wet papermaking can be carried out using a general paper machine such as a Fourdrinier paper machine and a cylinder paper machine. At this time, if necessary, suitable additives may be added to the aqueous dispersion.

The basis weight of the sheet produced is 20 to 100.
It is preferably set in the range of 0 g / m ² . If the basis weight of the sheet is too small, it will be difficult to handle the wet paper, and if it is too large, non-uniform parts such as swelling and deviation in the sheet surface will easily occur if the drainage time during papermaking becomes long. Without
Productivity is also reduced.

The sheet-like molded product obtained by the wet papermaking can be further improved in mechanical properties, surface smoothness and the like by subjecting it to heating and pressing.

In the heat and pressure processing, a usual method such as a method of passing a sheet-shaped molded product between a pair of heated metal rolls or a method of using a flat plate press can be adopted.

As the processing temperature, a temperature range is selected in which at least one of aramid paper pulp and non-aramid fiber, which is a material forming the sheet, is thermally softened and fused. For example, when the non-aramid fiber is polyethylene terephthalate fiber, a temperature of 230 ° C or higher, particularly 240 ° C or higher and lower than the melting point of the polyester is preferable. If the heat-sealing component is aramid paper pulp that has not been heat-treated, a temperature above the glass transition point of the aramid component is a preferable processing temperature.

The pressurizing condition varies depending on the processing temperature,
When heating and pressing between a pair of metal rolls, a linear pressure of 10
kg / cm or more is suitable, and 5kg / mm ^{2 for} flat plate press
Is the preferred pressure.

As described above, the aramid paper pulp, which is preferably partially or wholly subjected to the heat treatment at a temperature of the glass transition point or more, and the non-aramid fiber are mixed at a predetermined ratio, and wet papermaking is performed. A useful porous aramid sheet can be obtained by heating and pressing the sheet-shaped material. This sheet is not necessarily a flat sheet, but may be a deformed sheet or a sheet having a change in thickness.

[0034]

As described above, according to the method of the present invention, the aramid sheet once produced, for example, the waste aramid paper which is inevitably generated in the production process, is effectively used, and air, water, etc. are obtained by wet papermaking. It is possible to manufacture a porous aramid molded article having extremely good fluid permeability of at a low cost.

Various methods can be used to evaluate the porosity of the molded product. The product of the method of the present invention has, for example, a basis weight of 200 g / m ² and a Gurley air permeability of 1
It shows a high degree of air permeability of seconds to 200 seconds / 100 ml air (a smaller value means better air permeability). Sheet-like moldings (aramid paper) made from ordinary aramid fibrids and aramid fibers have low air permeability and it is practically difficult to measure Gurley air permeability at the same basis weight. From this it can be seen that the product according to the invention has a very good porosity.

[0036]

EXAMPLES The present invention will now be described in detail with reference to examples, but these are for explaining the present invention and the present invention is not limited to these examples.

The air permeability in the examples is indicated by the time required for 100 ml of air to pass through the molded product by a Gurley type densometer.

[Examples 1 to 6] (Production of aramid fibrids and aramid fibers) Poly (meta-) having an intrinsic viscosity of 1.35 obtained by a known two-step interfacial polymerization method (see Japanese Patent Publication No. 47-10867). (Phenyleneisophthalamide) was dissolved in N-methylpyrrolidone to prepare a dope.

Using this dope, aramid fibers were produced by a wet spinning-drawing heat treatment method. The denier of this aramid fiber is 2 de, the strength is 4.6 g / de and the elongation is 3
It was 7%. This aramid fiber was cut into a length of 6 mm and supplied to the next step.

On the other hand, an aramid fibrid was produced by using a dope of poly (meta-phenylene isophthalamide) prepared separately by a precipitation device equipped with a stator and a rotor (see Japanese Patent Publication No. 52-161621). This fibrid was adjusted to a Canadian standard freeness of 105 ml by beating in a water dispersion (slurry) state by disc refinery and by a high-speed disintegrator. (Production of aramid paper) The aramid fibers (slurry) dispersed in water and the aramid fibrids (slurry) dispersed in water were mixed to prepare a paper stock. An aramid sheet (uncalendered paper) having a basis weight of 40 g / m ^{2 is} obtained by introducing this paper material to a Fourdrinier paper machine, making it at a paper making speed of 40 m / min, and drying it.
[I] was produced. (Manufacture of aramid paper pulp) An aramid sheet (uncalendered paper) [I] immediately after paper making was crushed with a dot-type shredder, and a product passing through a sieve having an opening diameter of 3.5 mm was collected,
Aramid pulp was obtained.

The aramid paper pulp immediately after crushing was subjected to a sieving test, and it was found that the 12-mesh non-passage was 64 of the total weight.
% By weight, 24 mesh non-passage is 1 when 12 mesh passes
1% by weight, 7% by weight of 48-mesh non-passage after 24 mesh passage, 2% by weight of 80-mesh non-passage after 48-mesh passage, and 16% by weight of 80-meshew passage.

This was dispersed in water to give a concentration of 0.5% by weight.
Of aramid paper pulp slurry (A) was prepared. This slurry (A) was beaten with a disc refiner (made by Kumagai Kogyo Co., Ltd.) to adjust the Canadian standard freeness to 630 ml. The result of the sieving test of the aramid paper pulp after the disc refiner treatment shows that 12-mesh non-passage is 40 wt% of the total weight, 12-mesh pass is 24 mesh non-passage is 13 wt%, and 24-mesh pass is 48-mesh pass. The passing amount was 5% by weight, the passing amount of 48 mesh was 80%, and the passing amount was 3% by weight, and the passing amount of 80 mesh was 21% by weight.

A part of this slurry was taken out, dehydrated and dried, and then heat-treated at a temperature of 300 ° C. for 1 hour to obtain a heat-treated aramid paper pulp slurry (B). (Production of Porous Aramid Molded Product) The above aramid paper pulp slurry (A), the above heat treated aramid paper pulp slurry (B) and polyethylene terephthalate (PET) fibers (fineness 1.5 de, fiber length 6 mm) are dispersed in water. The resulting slurry was mixed in a ratio of each constituent (solid content) as shown in Table 1 below.

The solid content concentration of this slurry was about 0.2% by weight. Wet paper making by supplying slurry to Fourdrinier paper machine,
It was dried and made into a sheet.

This was heat-pressed using a flat plate press at a temperature of 300 ° C. and a pressure of 25 kg / cm ² .

Table 1 shows various properties of the obtained aramid molded product.

[0047]

[Table 1]

[Examples 7 to 9] (Production of aramid sheet) An aramid sheet (uncalendered paper) immediately after paper making produced in the same manner as in Examples 1 to 5
A part of [I] was taken out and subjected to heating and pressure processing (calendering) under a condition of a linear pressure of 100 kg / cm between a pair of steel rolls having a surface temperature of 300 ° C.

The obtained paper-like sheet (calendar paper) [I
I] had a basis weight of 40 g / m ² and had improved mechanical strength, surface smoothness, and electrical insulation. (Production of aramid paper pulp) The above aramid sheet (calender paper) [II] (fiber / fibrid = 40/6)
0, basis weight 40 g / m ² ) was crushed by the same method as in Examples 1 to 6 and beaten to obtain aramid paper pulp.

When this was subjected to a sieving test, Examples 1 to 1
The result was almost the same as that of 6, and the Canadian standard freeness was 730 ml.

This aramid paper pulp was dispersed in water to obtain a slurry (C). This slurry (C) and Example 1
The same polyethylene terephthalate fiber slurries as Nos. 6 to 6 were mixed at the constituent (solid content) ratios shown in Table 2 below, wet-processed, and then dried to obtain a sheet.

This was heated and pressed under the same conditions as in Examples 1 to 6. Table 2 shows various properties of the obtained aramid molded product (sheet).

[0053]

[Table 2]

[Examples 10 to 11 and Comparative Examples 1 and 2] Wet papermaking, drying, and heating and pressing were carried out in the same manner as in Example 1 except that the amount of polyethylene terephthalate fiber added was changed. And made a sheet. Table 3 shows the properties of the obtained aramid molded products (sheets).

Further, when no polyethylene terephthalate fiber was added at all (Comparative Example 1) and when the proportion of polyethylene terephthalate fiber was 95% by weight (Comparative Example 2), an aramid molded article was similarly prepared and its characteristics were measured. did. The respective results are shown in Table 3.

[0056]

[Table 3]

In each of the experiments shown in Table 3, when the polyethylene terephthalate fiber was not contained (Comparative Example 1), the air permeability was poor and the object of the present invention was not achieved. Further, when the polyethylene terephthalate fiber content was 95% by weight (Comparative Example 2), the strength of the wet paper was extremely low and the handling was very difficult. Moreover, the barely obtained aramid molded product also had extremely poor formation and was not practical.

[Examples 12 to 13] In Example 1,
An aramid molded product was prepared in the same manner except that carbon fiber or silicon carbide fiber was used instead of polyethylene terephthalate fiber, and its characteristics were measured.

The respective results are shown in Table 4.

[0060]

[Table 4]

Claims (8)

[Claims] 1. A porous aramid molded article produced by mixing and forming aramid paper pulp obtained by crushing aramid paper and non-aramid fibers at a weight ratio of 90/10 to 10/90 to form a sheet. Method. 2. As an aramid paper pulp obtained by crushing aramid paper, in a sieving test in running water, 12 mesh non-passage is 70 to 20% by weight of the total weight, and 12 mesh non-passage is 80 mesh non-passage. 50 to 10% by weight
The method for producing a porous aramid molded article according to claim 1, wherein the aramid paper pulp having a Canadian standard freeness of 300 to 800 ml is used. 3. Aramid fibrid and aramid short fibers 85/15 to 15/85 as aramid paper pulp.
The method for producing a porous aramid molded product according to claim 1 or 2, characterized in that aramid paper obtained by mixing and making papers in a weight ratio of is crushed and used. 4. The porous aramid molded product according to claim 1, wherein the aramid paper pulp which is heat-treated at a temperature not lower than the glass transition point of aramid is used as at least a part of the aramid paper pulp. Production method. 5. The porous aramid molded product according to claim 4, wherein a thermoplastic synthetic fiber having a heat softening temperature of 200 to 280 ° C. is used as the non-aramid fiber mixed with the aramid paper pulp for papermaking. Manufacturing method. 6. The method for producing a porous aramid molded product according to claim 4, wherein carbon fiber, silicon carbide fiber or mineral fiber is used as the non-aramid fiber mixed with aramid paper pulp for papermaking. 7. The porous aramid according to claim 5, wherein aramid paper pulp obtained by crushing aramid paper is mixed with non-aramid fibers to form a paper, and heated and pressed at a thermal softening temperature or higher of the thermoplastic synthetic fiber. Method for manufacturing molded article. 8. An aramid paper pulp obtained by crushing aramid paper is mixed with a non-aramid fiber, and paper-making is carried out at the same time as heating or pressurizing at a temperature not lower than the heat softening temperature of the thermoplastic synthetic fiber, or after pressurizing and shaping into a predetermined shape. The method for producing a porous porous aramid molded article according to claim 7, wherein