JPH10292289A - Thin porous paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin porous paper thin and excellent in piercing strength, small in maximum pore diameter and hardly causing a pin hall. SOLUTION: This thin porous paper comprises a para-aramid pulp having 20-250 ml freeness, a para-aramid short fiber having 0.8-3 d fiber size and 3-15 mm fiber length, and a heat hardenable resin, and has <=35 μm thickness. The proportion of the para-aramid short fiber is 15-60 parts weight based on 100 parts weight total of the para-aramid fiber and the para-aramid pulp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous paper having excellent heat resistance, chemical resistance, piercing strength and few pinholes, and has a wide range of industrial applications such as filter paper and battery separator paper. Suitable for.

[0002]

2. Description of the Related Art Conventionally, synthetic paper using aramid fiber has been manufactured as paper having excellent strength, heat resistance and dimensional stability. Among para-aramid fibers, para-aramid fibers are particularly excellent in heat resistance, chemical resistance and the like, and their use in printed wiring boards, honeycomb structures and the like has been studied.

[0003] With respect to the production of sheets using aramid fibers, as disclosed in Japanese Patent Application Laid-Open No. 7-3693, short fibers, staples, pulp and granular polymer of para-aromatic polyamide swollen with water are disclosed. And drying under pressure to obtain a paper comprising only para-aramid, or as disclosed in JP-A-5-106191, an aromatic polyamide short fiber and an aromatic fiber having a fiber diameter of 0.7 μm or less. Techniques such as heat-resistant paper in which two components consisting of polyamide microfibrils or a pulp-like aromatic polyamide having a fiber diameter of more than 0.7 μm have been proposed have been proposed. It was difficult to obtain paper having excellent strength and few pinholes.

On the other hand, in the fields of battery separators, heat-resistant filters, etc., in order to obtain higher performance, ultra-thin, heat-resistant and chemical-resistant microporous structures having high piercing strength are required. There is a need for a porous sheet.

[0005] These characteristics are effective, for example, in battery separators to prevent short-circuits due to dendrites generated from the electrodes, and in filter paper, they are effective in preventing rupture of dust particles during filtration. Although a para-aramid fiber is promising as a material satisfying such requirements, it has been extremely difficult to maintain high piercing strength in thin paper.

[0006]

The blending of para-aramid short fibers generally has the effect of increasing the strength, but since the fiber diameter is larger than that of fibrillated pulp, the pore diameter is increased and pinholes are liable to occur. As described above, the piercing strength and the maximum hole diameter (the frequency of occurrence of pinholes) tend to be contradictory, and the technique disclosed above has not solved this difficulty.

[0007]

In view of this situation, the present inventors have studied the blending of para-aramid pulp having various freenesses and para-aramid short fibers having various fiber diameters and fiber lengths. Even in the specifications, thin-leaf perforated paper having sufficient piercing strength and having very few pinholes was obtained.

That is, the present invention provides a freeness of 20 to 25.
It is a paper having a thickness of 35 μm or less, which is composed of 0 ml of para-aramid pulp, a fiber diameter of 0.8 to 3 denier, para-aramid short fiber having a fiber length of 3 to 15 mm, and a thermosetting resin. The present invention relates to a thin-leaf perforated paper characterized in that the ratio of the para-aramid short fibers is 15 to 60 parts by weight as 100 parts by weight.

[0009] The second invention of the present invention relates to the thin porous paper of the above invention, having a maximum pore diameter of 20 µm or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, para-aramid pulp is obtained by beating para-aramid fibers so that the freeness becomes 20 to 250 ml. Thereby, aramid pulp will contain a large amount of fine fibers having a fiber diameter of 1 μm or less,
A network with a fine pore size is formed.

When the aramid pulp freeness exceeds 250 ml, the fiber diameter of the aramid pulp becomes large, so that it becomes impossible to maintain a fine pore diameter and it is difficult to form a thin sheet. If the aramid pulp freeness is less than 20 ml, excessive microfibrillation occurs, which is disadvantageous in strength and wet papermaking.

In the present invention, it is possible to use para-aramid pulp having a freeness of 250 ml or more as needed. Refining equipment,
A beater or the like can be used. Combining para-aramid pulp and para-aramid short fibers obtained by beating,
Improves piercing strength.

The fiber diameter of the para-aramid short fibers used in the present invention is suitably 0.8 to 3 denier. If the fiber diameter exceeds 3 denier, the formation of contact points between the fibers decreases, and it becomes difficult to form a thin sheet. In addition, the retention of the fine para-aramid pulp during papermaking deteriorates, and pinholes also occur. On the other hand, if it is less than 0.8 denier, the fiber diameter is too small to maintain a sufficient piercing strength. on the other hand,
The fiber length is suitably 3 to 15 mm. If the fiber length is less than 3 mm, the effect of improving the piercing strength cannot be obtained, and
If it exceeds m, the uniformity of the sheet is lost, which is not preferable.

The mixing ratio of the para-aramid short fibers is preferably 15 to 60 parts by weight based on 100 parts by weight of the total of the para-aramid short fibers and the para-aramid pulp. Mixing ratio is 6
If the amount exceeds 0 parts by weight, pinholes are generated, and a uniform sheet cannot be obtained. If the amount is less than 15 parts by weight, the piercing strength is not improved.

[0015] The sheet of the present invention requires a thermosetting resin as a binder.
Thermosetting resins such as phenolic resins, melamine resins, polyimide resins, and furan resins are suitable, and other thermosetting resins may be used.

The thermosetting resin is added in an amount of 5 to 50 parts by weight based on 100 parts by weight of the total of the para-aramid short fibers and the para-aramid pulp. The method of adding the thermosetting resin, the place of addition is not limited, and for example, a method of forming a slurry of para-aramid pulp and para-aramid short fibers before papermaking, a method of forming the resin powder or resin fibers, or a method after papermaking or A method of impregnating an emulsion, an aqueous solution, a solvent varnish, or the like at the time of processing the subsequent sheet, or adding a spray may be used.

By subjecting the sheet formed under the above conditions to a heat calendering treatment, the strength is further increased. It is also effective to increase the degree of curing of the binder with a hot air dryer or the like. Although the temperature of the heat calendering treatment varies depending on the melting and curing characteristics of the binder, it is generally 150 ° C.
° C. If necessary, curing can be performed by impregnating with a thermosetting resin after the thermal calendering. In addition, if the heat calender alone is insufficient for curing, additional curing may be performed by any method.

According to a second aspect of the present invention, the maximum pore size is set to 20 μm.
m below. If the maximum pore size is larger than 20 μm, pinholes occur, which causes problems in the use of porous paper.

[0019]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. The content of the present invention is not limited to the examples.

The maximum pore size shown in the following Examples and Comparative Examples was measured using a Coulter porometer 2 in accordance with ASTMF-316-80. The piercing strength is based on Japanese Agriculture and Forestry Standards for retort pouch food (April 25, 1988)
According to the Ministry of Agriculture, Forestry and Fisheries Notification No. 540), the diameter is 1.0 mm,
A needle having a tip shape of 0.5 mmR was pierced at a speed of 50 ± 5 mm / min, and the strength when the needle penetrated was measured.

Example 1 Para-aramid pulp (Kevlar pulp manufactured by DuPont) was dispersed in water so as to have a slurry concentration of 3%, dispersed with a pulper and beaten with a disk refiner to reduce the freeness to 5%.
The volume was 0 ml. Water is added to this slurry to a concentration of 0.3%
Was prepared as a para-aramid pulp slurry.

<Dispersion and papermaking of para-aramid short fibers> In water, para-aramid short fibers (Kevlar 2 manufactured by DuPont)
9, a fiber length of 6 mm) was added to a slurry concentration of 0.3%, and the mixture was stirred and dispersed by a stirrer. Then, the above-mentioned para-aramid pulp slurry was added to this para-aramid short fiber slurry, followed by stirring and mixing. The mixing ratio is solid content of para-aramid short fiber 1
5 parts by weight and 85 parts by weight of para-aramid pulp were used. The obtained slurry was used to make thin paper of 24 g / m ² tsubo using a TAPPI hand-making machine, and an acrylic thermosetting resin emulsion (Kanebo NSC Iodosol AD57) was obtained as a binder. After the addition of 10% solids, the mixture was dried with hot air at 140 ° C.

The obtained sheet was heated and pressed at a linear pressure of 180 kg / cm by a chilled / chilled calender having a roll temperature of 200 ° C. About the obtained thin paper, rice tsubo, thickness,
The maximum pore diameter and piercing strength were measured. Table 1 shows the results.

Example 2 Thin paper was obtained in the same manner as in Example 1 except that the freeness of para-aramid pulp was changed to 100 ml. The properties are shown in Table 1.

Example 3 Tissue paper was obtained in the same manner as in Example 1, except that the mixing ratio of the para-aramid short fibers was 60 parts by weight based on 100 parts by weight of the total of the para-aramid short fibers and the para-aramid pulp. The properties are shown in Table 1.

Example 4 Thin paper was obtained in the same manner as in Example 1 except that the fiber length of the para-aramid short fibers was 3 mm. The properties are shown in Table 1.

Example 5 Thin paper was obtained in the same manner as in Example 1 except that the freeness of para-aramid pulp was changed to 250 ml. The properties are shown in Table 1.

EXAMPLE 6 Para-aramid short fibers were prepared with the exception that the fiber diameter was 3 denier.
Thin paper was obtained in the same manner as in Example 1. The properties are shown in Table 1.

Example 7 Example 1 was repeated except that the fiber diameter of the para-aramid short fibers was 0.8 denier and the blending ratio was 60 parts by weight based on 100 parts by weight of the total of the para-aramid short fibers and the para-aramid pulp.
Thin paper was obtained in the same manner as described above. The properties are shown in Table 1.

Comparative Example 1 Thin paper was produced in the same manner as in Example 1 except that the freeness of para-aramid pulp was 100 ml and the amount of para-aramid short fibers was 0. Table 2 shows the physical properties.

Comparative Example 2 Thin paper was produced in the same manner as in Example 1 except that the freeness of para-aramid pulp was changed to 10 ml. Table 2 shows the physical properties.

Comparative Example 3 Thin paper was produced in the same manner as in Example 1 except that the mixing ratio of para-aramid short fibers was changed to 10 parts by weight with respect to 100 parts by weight of the total of para-aramid short fibers and para-aramid pulp. Table 2 shows the physical properties.

Comparative Example 4 Thin paper was manufactured in the same manner as in Example 1 except that the fiber length of the para-aramid short fibers was changed to 1 mm. Table 2 shows the physical properties.

Comparative Example 5 Thin paper was produced in the same manner as in Example 1, except that the freeness of para-aramid pulp was changed to 300 ml. Table 2 shows the physical properties.

Comparative Example 6 Example 1 was repeated except that the fiber diameter of the para-aramid short fibers was 0.5 denier and the blending ratio was 60 parts by weight based on 100 parts by weight of the total of the para-aramid short fibers and the para-aramid pulp.
Thin paper was obtained in the same manner as described above. Table 2 shows the physical properties.

Comparative Example 7 The para-aramid short fiber had a fiber diameter of 5 deniers.
Thin paper was obtained in the same manner as in Example 1. Table 2 shows the physical properties.

[0037]

[Table 1]

[0038]

[Table 2]

Examples 1 to 5 all have a maximum pore diameter of 20 μm.
m or less, a thin-leaf porous paper having a good piercing strength of 35 μm or less in thickness was obtained. However, Comparative Examples 1, 3, and 4
In each case, the piercing strength is inferior to that of the example, and in Comparative Example 2, although the piercing strength is excellent, the maximum pore diameter is large. Further, in Comparative Example 5, the thickness exceeds 35 μm, and the intended ultrathin thin-leaf porous paper cannot be obtained.

[0040]

According to the present invention, it is possible to obtain a thin-leaf porous paper which has not been obtained until now and which is thin, has a small tsubo, and has excellent piercing strength. Further, it is possible to obtain a thin-leaf porous paper having a small maximum pore diameter and little pinholes.

Claims (2)

[Claims] 1. Freeness 20-250 ml of para-aramid pulp, fiber diameter 0.8-3 denier, fiber length 3-15
mm paper having a thickness of 35 μm or less, comprising para-aramid short fibers and a thermosetting resin, wherein the total ratio of the para-aramid short fibers and the para-aramid pulp is 100 parts by weight, and the ratio of the para-aramid short fibers is 15 to 60 parts by weight. Thin paper perforated paper characterized by the following. 2. The thin paper perforated paper according to claim 1, wherein the maximum pore diameter is 20 μm or less.