JPS5953960B2 - Acid- and alkali-resistant paper with breathability and liquid permeability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides, for example, appropriate ventilation and
This paper relates to acid- and alkali-resistant paper that has liquid permeability.

BACKGROUND ART In recent years, the uses of paper have expanded, and paper is now widely used in various industrial applications, such as industrial filters.

As is well known, papers used in filters and the like are required to have appropriate air permeability and liquid permeability, unlike general films, and in recent years, the required properties have gradually become higher. .

For example, filter characteristics such as paper thickness density, size and number of holes penetrating the paper layer are strictly defined, and a filter that satisfies these requirements is required. In addition, waste acid and waste alkali treated filter paper, battery separator paper, etc. are required to have strong acidity or strong alkalinity, which hardly dissolves even when used in strong acid or strong alkaline solutions. However, conventional papers such as spunbond paper, dry nonwoven fabric, and wet nonwoven fabric have strong acid resistance and alkali resistance, as well as breathability and liquid permeability, and they also have hole sizes that can be adjusted according to customer requirements. We have not been able to find anything that allows us to freely and easily control the size, number, etc. during manufacturing.

That is, in general, in the wet papermaking method, from the viewpoint of wet web strength, it is extremely difficult to make paper using synthetic fibers with high chemical resistance, such as polyolefin fibers, alone or mixed with different types of olefin fibers due to the low wet web strength. Even if paper can be made, it is extremely bulky and has poor paper strength, especially when wet.

In addition, when heat-pressed, it becomes film-like, allowing ventilation,
Liquid permeability cannot be satisfied. In order to modify this, wet strong resin processing and thermal processing are generally used, but additive processing within the resin does not solve the problem of bulkiness, and post-processing such as impregnation processing reduces the degree of processing. It was inappropriate because there was a trade-off between chemical resistance, ventilation, and liquid permeability. On the other hand, in dry papermaking, the fibers used are generally longer and bulkier than in wet papermaking, which significantly weakens the strength of straight and loose paper, so treatments such as resin impregnation are generally applied. As mentioned above in the resin processing of wet papermaking, it has been impossible to easily and freely control ventilation and liquid permeability due to the trade-off relationship between chemical resistance and air permeability and liquid permeability. This invention was made in view of the above circumstances.
This paper proposes an acid- and alkali-resistant paper that can easily and freely control the size, number, etc. of holes within a given paper thickness range to have appropriate air permeability and liquid permeability. .

In this invention, the strong acid-soluble fibers can be ordinary cellulose pulp made of softwood, hardwood, etc., having fiber length and diameter appropriate depending on the purpose, Manila hemp pulp, linter pulp, bagasse pulp, etc.
Further, as the strong acid- and strong alkali-insoluble fibers, polyolefin fibers such as polyethylene and polypropylene, polyvinylidene chloride fibers, polyvinyl chloride fibers, etc. can be used.

The above-mentioned strong acid-soluble fibers and strong acid- and strong alkali-insoluble fibers are mixed in a range of 0.5 to 90 parts by weight, 10 to 99.5 parts by weight, and paper is made using a normal papermaking method, and the resulting paper sheets are heat-treated. After applying this process, the paper sheet is treated with a strong acid to dissolve and remove the strong acid-soluble fibers in the paper sheet, thereby forming holes or grooves of an appropriate size in the paper sheet.

The size of the holes formed in the paper sheets is controlled by the size of the strong acid-soluble fibers mixed into paper, and the number of holes is controlled by the blending ratio of the strong acid-soluble fibers.

For example, temperate softwood pulp, a type of cellulose fiber, has an average fiber length of 2.7 to 3.6 mm and an average diameter of 32 to 43 mm.
μ, and that of temperate hardwood pulp is 0.7 to 1
．． 6 mm and 20 to 40 μm, but by using these appropriately, it is possible to easily and freely form holes in micron units, etc. while controlling the size.

Further, by appropriately selecting the blending ratio of the strong acid-soluble fiber within the range of 0.5 to 90 parts by weight, it is possible to appropriately control the number of holes.

If the blending ratio of strong acid-soluble fibers is less than 0.5 parts by weight, the hole-forming effect will generally be almost lost, and if the blending ratio of strong acid- and strong alkali-insoluble fibers is less than 10 parts by weight, the network after strong acid treatment will generally become weak. is difficult to form. The strong acid treatment can be carried out, for example, by immersing the mixed paper in a 75% (by weight) sulfuric acid bath, and after the concentrated sulfuric acid treatment, the sulfuric acid can be removed by washing with water and neutralizing it.

Furthermore, after washing with sulfuric acid, a network or film of strong acid- and strong alkali-insoluble fibers made of polyolefin fibers etc. will not be compatible with water due to the nature of the fibers, but in this case, a surfactant may be used depending on the purpose. In short, according to the present invention, the size and number of holes can be controlled by appropriately selecting and blending the size and blending ratio of strong acid-soluble fibers. Since it can be easily and freely controlled, it is possible to produce acid- and alkali-resistant paper sheets with appropriate ventilation and liquid permeability.

Note that a mixed paper of strong acid-soluble fibers such as cellulose pulp and strong acid- and strong alkali-insoluble fibers is heat-treated, and before the acid treatment, a general staining solution for cellulose-based pulp identification, such as Sel.
When dyed with leger staining solution, it can be easily distinguished from olefin fibers, which are made of net-like or film-like fibers by dyeing only cellulose pulp.

When this is treated with acid, the cellulose pulp is removed,
Holes or grooves approximately the same size as the pulp fibers are observed under the microscope in the traces. Therefore, according to the above method, the size, number, etc. of holes formed by strong acid treatment can be confirmed in advance. Examples of this invention will be shown below.

Example 1 85% (by weight) polyolefin fiber (trade name SWPE-400, Mitsui Zerapack) and 15% bleached hardwood pulp
(weight) was made into paper using a hand sheet machine with a concentration of 0.02% and a target basis weight of 30 g/m.

Next, the paper sheets obtained by drying with a cylindrical dryer at 105°C were hot pressed with a cylindrical dryer at 120 to 130°C. This is placed in a 75% sulfuric acid bath, left for 60 seconds, and then washed with water to remove the sulfuric acid, thereby obtaining the desired acid- and alkali-resistant paper.

The properties of this paper were as follows.

Note 1 Measured by the method described in JISP8124 Note 2 JI
Measured by the method described in SP8118 Note 3 JISP81
Measured by the method described in 18 Note 4 Measured by the method described in JISP8117 Note 5
Time Soaking Note 6 Soaking in 75% H2S04 solution at 20°C for 1 hour Example 2 40% (weight) of polyolefin fiber (polypropylene fiber for general paper making, 2 d x 10 mm) and 60% (weight) of bleached softwood pulp were mixed using a cylinder paper machine. The paper was made with a target basis weight of 55 g/m.

This paper was heat-treated by pressing it with two heated rolls at about 165°C, then immersed in 75% concentrated sulfuric acid for 3 minutes, and then washed with water to remove the sulfuric acid. The obtained paper had a rough mesh shape and had excellent acid resistance and alkali resistance. The properties of this paper were as follows. Note that the paper quality test method was the same as in Example 1.

Claims (1)

[Claims] 1. Making paper by mixing 0.5 to 90 parts by weight of strong acid-soluble fibers and 10 to 99.5 parts by weight of strong acid- and strong alkali-insoluble fibers,
After further heat treatment, a strong acid is applied to dissolve and remove the strong acid-soluble fibers to produce acid- and alkali-resistant paper with air permeability and liquid permeability.