JP2000044705A - Preparation of ion-exchange sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent problems such as discoloration, cracking, tear and odor which occur in an ion-exchange sheet obtained by a wet papermaking method and to provide a method of preparing an ion-exchange sheet having sufficient ion-exchanging properties. SOLUTION: A polyvinyl alcohol-based salt-type ion-exchange fiber, e.g. an Na-type ion-exchange fiber and a binder fiber are mixed and dispersed, subjected to wet papermaking to obtain a sheet. After drying, the fibers are heat-fused and the obtained dry sheet is immersed in an acidic or alkaline aqueous solution, washed with pure water and dehydrated to obtain an ion- exchange fiber sheet.

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 sheet having an ion-exchange function, and more particularly to a method for producing an ion-exchange sheet in which salt type exchange fibers are formed into a sheet by wet papermaking.

[0002]

2. Description of the Related Art In recent years, demands for pure water and atmosphere free of ionic impurities have been increasing in the semiconductor industry. In particular, semiconductor factories and medical sites require clean rooms with high cleanliness. In such clean rooms, there is an increasing demand for high-level cleanliness using filters that remove not only dust but also ions in the atmosphere. As a filter material, a nonwoven fabric such as polypropylene is irradiated with an electron beam or the like to introduce an ion-exchange group, an ion-exchange group is introduced by adding a chemical to an activated carbon fiber sheet,
It is known that fibers having an ion exchange function are formed into a nonwoven fabric by a dry method or a wet method. Examples of the ion-exchange fiber include a sulfonated polystyrene and polypropylene composite fiber having a sea-island cross-section, a fiber obtained by mixing a polystyrene sulfonic acid with a polyvinyl alcohol (PVA) base material, and then dry-spinning the fiber, and the like. It has been known.

[0003] Ion exchange fibers based on PVA have advantages such as a high adsorption rate and a high ion exchange capacity.
However, when forming into a non-woven fabric, the heat added in the heat melting process using a binder causes deterioration and deterioration of the ion exchange fiber, and causes problems such as discoloration, cracking, and tearing after forming the sheet. As for the problem of discoloration, there is a possibility that the discolored (blackened) sheet may be recovered to some extent by controlling the humidity, but the problem of the appearance such as cracks remains. Further, as another conventional technique, a filter using an amine as an anion exchange fiber has been proposed, but there is a problem that an amine odor is generated by heating in a manufacturing process.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an ion exchange sheet free from problems such as discoloration, cracks, tears and odors by wet papermaking.

[0005]

The present inventors have conducted intensive studies in view of the above problems. As a result, the use of a H-type strongly acidic cation-exchange fiber or an OH-type strongly basic cation-exchange fiber and a binder fiber results in a heat melting process. The heat added causes deterioration and deterioration of the ion-exchange fiber, and causes problems such as discoloration, cracking, and tearing after being formed into a sheet, whereas these problems do not occur when a salt-type ion-exchange fiber is used. The inventors have found that the present invention has been completed. The present invention is to wet-process the salt-type ion-exchange fiber and the binder fiber into a sheet, form a sheet, heat and fix the fibers together, and then subject the sheet to an acid or alkali treatment, followed by washing and dewatering. This is a method for producing an ion exchange sheet characterized by the following.

The salt type ion exchange fiber used in the production method of the present invention is preferably a fiber obtained by mixing a salt type polymer having sufficient ion exchange capacity with PVA or the like and dry spinning the fiber. It is preferable that the ion exchange activity is low because the ion exchange activity is easily deteriorated. That is, the fiber is made of P
Fibers having a high ion exchange capacity in a salt form and having a low ion exchange activity in VA are preferred. A fiber obtained by directly spinning a fiber having the above characteristics is preferable, but a fiber which has been subjected to a treatment for reducing the activity of H-type fiber having high ionic activity is also preferable. For example, there is a cation exchange fiber having a sulfonic acid salt. The fibers are prepared by mixing PVA and sodium polystyrene sulfonate, adding water, heating and melting, and then dry spinning. The fibers at this stage have low activity and can be used. Further, a highly active fiber obtained by acetalizing the obtained yarn with a mixed solution of sulfuric acid, sodium sulfate, and glutaraldehyde is commercially available, but since the fiber has high activity, it is immersed in an aqueous solution of sodium hydrogen carbonate. It is also possible to reduce the activity by performing the treatment described above.

The salt type anion exchange fiber is, for example, a fiber obtained by mixing polyethylene imine with PVA or the like, dry-spinning, treating with ethylene glycol diglycidyl ether, or quaternary aminating with chlorohydroxypropyltrimethylammonium chloride or the like. and so on. These four
Grade ammonium salt type fibers are preferred because of their low activity,
It is also possible to use the OH type salt fiber having a high ionic activity with a reduced activity by a treatment such as immersion in an aqueous sodium chloride solution.

The salt type ion exchange fibers include alkali metal salts, alkaline earth metal salts, NR ₄ X (R is hydrogen, an alkyl group or alkylene group having 12 or less carbon atoms,
X is a halogen atom) and the like. The salt type ion exchange fiber is preferably of low activity, for example, low activity Na salt type ion exchange fiber, low activity Ca salt type ion exchange fiber, low activity K salt type ion exchange fiber and the like.
The low activity Na salt type ion exchange fiber can be obtained, for example, by immersing the H type strongly acidic cation exchange fiber in an aqueous sodium hydrogen carbonate solution.

As the binder fiber, for example, polyethylene, polypropylene or the like is used. An ethylene-vinyl alcohol copolymer core-sheath fiber having polyethylene or polypropylene as a core is preferable because it can be fused at a relatively low temperature and does not deteriorate with acid and / or alkali.

When the salt type ion exchange sheet is wet-formed, the salt type ion exchange fiber and the binder fiber are mixed in a weight ratio of 8%.
After mixing at a ratio of 0:20 to 65:35 and dispersing in water, a fiber layer is formed using a wire or the like, and dried with a dryer to form a sheet. If necessary, shaking is performed on the wire to improve the uniformity of the sheet. At this time, the salt-type ion exchange fiber has a fiber length of 2 to 10 mm, preferably 3 to 8 mm. If the fiber length is shorter than 2 mm, there are problems such as deterioration of air permeability, high pressure loss, detachment from the fiber sheet, and the like. On the other hand, if the length is longer than 10 mm, the dispersion of the fibers deteriorates, and there is a problem such as occurrence of aggregation. , Fiber thickness is 6-9
Denier, preferably about 7 to 8.5 denier.
The binder fiber length is 3 to 7 mm, preferably 4 to 7 mm.
6 mm, fiber thickness is 1-3 denier, preferably 1.
It is about 5 to 2.5 denier. The water dispersion preferably has a basis weight of about 130 to 150 g / m ^{2 in} absolute weight.

Next, the fibers of the wet-laid paper of the ion-exchange sheet made into a non-woven fabric are heated to be melted by heat. The heating temperature is usually 110 to 140 ° C, preferably 120 to 130 ° C.
° C, especially 124-126 ° C. The heating time varies depending on the heating temperature, but is preferably about 30 to 1500 seconds. Usually, an ion-exchange sheet is obtained by passing through a dryer at this ambient temperature, for example, a Yankee dryer for 140 to 300 seconds. The ion exchange sheet obtained by wet papermaking is preferably pleated if necessary. Pleating includes reciprocating method, rotary method, etc., the surface area per unit area increases,
It is preferable because the ion exchange efficiency is improved. After treating the ion exchange sheet thus obtained with acid or alkali,
After washing and dehydration, an ion exchange sheet is obtained. Specifically, it is preferable to use hydrochloric acid or the like for a sheet containing cation exchange fibers, and to use sodium hydroxide or the like for a sheet containing anion exchange fibers.

After the acid or alkali treatment, the ion exchange sheet is washed with pure water and dehydrated. Dehydration is preferably performed at a temperature of 50 ° C. or less under reduced pressure in order to prevent discoloration and odor of the sheet. It is preferable to carry out drying at 50 ° C. or lower, if necessary, to completely remove water, and more preferably a vacuum drying method at 50 ° C. or lower. The activity of the ion-exchange sheet is reduced by prolonged use. In this case, the acid or alkali treatment having the function of increasing the activity of the ion exchange group can be performed to increase the activity and regenerate. The acid or alkali described above can be used for this regeneration.

[0013]

Example 1 (Preparation of low activity Na salt type ion exchange fiber) High activity H
Type copolymer acidic cation exchange fiber (manufactured by Nichibi, trade name: MP-IEF-SC (H) GA-HG, fiber length 5m)
m, 8 deniers) in 1% aqueous sodium hydrogen carbonate solution.
After immersion treatment for a period of time, the resultant was washed with pure water and dried under reduced pressure to obtain a low-activity Na salt type cation exchange fiber. (Preparation of ion exchange sheet) 70 parts by weight of the Na salt type ion exchange fiber and 30 parts by weight of ethylene vinyl alcohol core-sheath fiber (produced by Daiwabo Co., Ltd., fiber length: 5 mm, 2 denier) having polypropylene as a binder were dispersed in water. Thus, a dispersion was obtained. The dispersion was wet-laid with an inclined wire. Next, the sheet was dried through a Yankee dryer at 125 ° C. to obtain a sheet having a basis weight of 140 g / m ² .
The sheet was immersed in a 1% hydrochloric acid aqueous solution, washed with pure water, and dried at 25 ° C. under reduced pressure to obtain an H-type ion-exchange fiber sheet according to the production method of the present invention.

Example 2 (Preparation of low activity Cl salt type ion exchange fiber) High activity O
H-type copolymer acidic cation exchange fiber (manufactured by Nichibi, trade name: IEF-SC (OH) PEI-HG, fiber length 5 m
m, 8 denier) in a 1% aqueous solution of sodium chloride for 1 hour, then wash with pure water, dry under reduced pressure
An anion exchange fiber (salt structure: RN ₄ Cl) was obtained. (Preparation of ion exchange sheet) 70 parts by weight of the Cl salt type ion exchange fiber and 30 parts by weight of an ethylene vinyl alcohol core-sheath fiber (produced by Daiwabo Co., Ltd., fiber length 5 mm, 2 denier) having polypropylene as a binder were dispersed in water. Thus, a dispersion was obtained. The dispersion was wet-laid with an inclined wire. Next, the sheet was dried through a Yankee dryer at 125 ° C. to obtain a sheet having a basis weight of 140 g / m ² .
The sheet was immersed in a 4% aqueous sodium hydroxide solution, washed with pure water and dried at 25 ° C. under reduced pressure to obtain an OH type anion exchange fiber sheet according to the production method of the present invention.

Example 3 (Preparation of low activity Na salt type ion exchange fiber) Na type ion exchange fiber (fiber length 5 mm) was prepared by mixing PVA and sodium polystyrene sulfonate, adding water, heating and melting, and then dry-spinning. , 8 deniers) and ethylene vinyl alcohol core-sheath fiber (produced by Daiwabo Co., Ltd., fiber length 5 mm,
(Denier) 30 parts by weight was dispersed in water to obtain a dispersion.
The dispersion was wet-laid with an inclined wire. Then 12
Dry through a 5 ° C Yankee dryer and weigh 14
A sheet of 0 g / m ² was obtained. The sheet was immersed in a 1% hydrochloric acid aqueous solution, washed with pure water, and dried at 25 ° C. under reduced pressure to obtain an H-type ion-exchange fiber sheet according to the production method of the present invention.

Example 4 (Preparation of low activity K salt type ion exchange fiber) High activity H type copolymer acidic cation exchange fiber (trade name, manufactured by Nichibi Co., Ltd.)
MP-IEF-SC (H) GA-HG, fiber length 5 mm,
8 denier) was immersed in an aqueous solution of potassium hydrogen carbonate for 1 hour, washed with pure water and dried under reduced pressure to obtain a K salt type cation exchange fiber. Preparation of ion exchange sheet is Example 1
In the same manner as in the above, an H-type cation exchange sheet was obtained by the production method of the present invention.

Comparative Example 1 H-type strongly acidic cation exchange fiber (manufactured by Nichibi, trade name: M
P-IEF-SC (H) GA-HG, fiber length 5 mm, 8
(Denier) 70 parts by weight and 30 parts by weight of ethylene vinyl alcohol core-sheath fiber (produced by Daiwabo Co., Ltd., fiber length 5 mm, 2 denier) having polypropylene as a core were dispersed in water to obtain a dispersion. The dispersion was wet-laid with an inclined wire. Then, it was dried through a Yankee dryer at 125 ° C. to obtain a cation exchange sheet having a basis weight of 140 g / m ² and turned black for comparison.

Comparative Example 2 OH type strongly basic anion exchange fiber (trade name: IEF-SC (OH) PEI-HG, manufactured by Nichibi Co., Ltd., fiber length 5 m)
m, 8 deniers) 70 parts by weight and an ethylene vinyl alcohol core-sheath fiber having polypropylene as a core (manufactured by Daiwabo Co., Ltd., fiber length 5 mm, 2 deniers) 3
0 parts by weight was dispersed in water to obtain a dispersion. The dispersion was wet-laid with an inclined wire. Then, it was dried through a Yankee dryer at 125 ° C. to obtain an anion exchange sheet having a basis weight of 140 g / m ² and turned yellow for comparison. In addition, an amine odor was felt immediately before the end of drying.

(Change in color tone) The color tone of the raw material fiber and the color tone of the obtained ion exchange sheet were visually observed, and the change in color tone is shown in Table 1. (Evaluation of Crack Resistance of Ion Exchange Sheet) A V-shaped block was prepared, the ion exchange sheet was placed on a concave shape, and the convex shape was placed on the sheet, and a pressure of ² kgf / cm ² was applied. The extracted ion exchange sheet was visually observed, and the results are shown in Table 1.
It was shown to. Those with no abnormal appearance were marked with a circle.

(Neutral salt resolution) Cation exchange sheet neutral salt resolution: dried sample
0 g is precisely weighed, and 500 ml of a 0.1N sodium chloride solution.
After immersion for 24 hours, the produced hydrogen chloride was subjected to neutralization titration with sodium hydroxide to determine the neutral salt resolution. Neutral salt resolution of anion exchange sheet: dried sample
0 g is precisely weighed, and 500 ml of a 0.1N sodium chloride solution.
After immersion for 24 hours, the sodium hydroxide formed was neutralized and titrated with hydrogen chloride to determine the neutral salt resolution. The neutral salt resolution obtained is shown in Table 1.

[0021]

[Table 1]

No discoloration was observed with the ion exchange sheet obtained by the production method of the present invention and the heat applied during the production, no cracking or cracking occurred in the cracking resistance test, and the neutral salt resolution was the same as that of the conventional product. It was confirmed that it was equal to or more than a comparative example. On the other hand, in the ion exchange sheet of the comparative example, discoloration occurred due to heat during production, and cracking or cracking occurred in the crack resistance test. In Comparative Example 2, an amine odor was felt immediately before the end of drying.

[0023]

According to the production method of the present invention, the discoloration and odor of the ion exchange sheet can be prevented by the heat applied during the production in order to enhance the ion exchange activity after the wet papermaking of the ion exchange sheet. An ion exchange sheet having an excellent ion exchange capacity can be obtained.

Claims (3)

[Claims] The present invention is characterized in that the salt type ion exchange fiber and the binder fiber are formed into a sheet by wet papermaking, heated to fix the fibers together, and then the sheet is subjected to an acid or alkali treatment, followed by washing and dehydration. A method for producing an ion exchange sheet. 2. The salt of the salt type ion exchange fiber is an alkali metal salt, an alkaline earth metal salt or NR ₄ X (R is hydrogen, an alkyl group or alkylene group having 12 or less carbon atoms,
2. The method for producing an ion-exchange sheet according to claim 1, wherein the ion-exchange sheet comprises at least one of the salts represented by (X is a halogen atom). 3. The method for producing an ion exchange sheet according to claim 1, wherein the dehydration step is performed at 50 ° C. or lower.