JPH09279496A - Water-absorbing sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a water-absorbing sheet having a high dry and wet strengths and insolubility in hot water by carrying out the crosslinking treatment of a web sheet comprising cellulosic fibers and a polyvinyl alcohol fibrous binder. SOLUTION: This water-absorbing sheet is formed by mixing bulky cellulosic fibers such as a crosslinked pulp, a mercerized pulp or a crosslinked and mercerized pulp with a polyvinyl alcohol fibrous binder at (80/20) to (99.5/0.5) weight ratio, then forming a web sheet having >=10g/m<2> , preferably >=15g/m<2> basis weight, subsequently spraying and applying a treating liquid containing a crosslinking agent such as a polycarboxylic acid onto the web sheet, heat- treating the resultant sheet, performing the crosslinking treatment of the polyvinyl alcohol fibrous binder and making the sheet insoluble in hot water without deteriorating the water absorptivity thereof.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a water-absorbent sheet comprising a web sheet formed of cellulose fibers and a polyvinyl alcohol (hereinafter abbreviated as “PVA”) fibrous binder, and a method for producing the same, more specifically, cellulose. A fiber and a PVA fibrous binder are dispersed in water, papermaking is performed to form a wet state / or a dried state of the PVA fibrous binder, and the PVA fibrous binder is formed of a web sheet crosslinked with a crosslinking agent. Characteristic, without losing water absorption, express hot water insolubility,
The present invention also relates to a water-absorbent sheet capable of significantly improving dry strength and wet strength and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in order to improve the strength of a water absorbent sheet such as paper or non-woven fabric containing cellulose fiber as a main fiber, PVA, polyester,
Attempts have been made to incorporate fibers such as polyamide into cellulose fibers. As a method for producing such a water-absorbent sheet, especially paper, cellulose fibers and water-soluble PVA fibers as a binder are generally dispersed in water, and after papermaking, fibers are bonded to each other through a heating roll at about 110 ° C. in a wet state. And then dried. However, it is insufficient to improve the strength of the paper obtained by this method, particularly the strength when wet.

On the other hand, there are many reports and technical data on the method of crosslinking PVA. PVA has hitherto been known as a typical water-soluble polymer.
It is used in a wide range of industrial applications such as emulsifiers. In these applications, it is often necessary to improve strength and water resistance, and many methods relating to these have been proposed. For example, regarding water resistance and insolubilization, Nagano, Yamane and Toyoshima, "Poval" (revised new edition), Polymer Publishing Society (1981), pages 256 to 2.
It is reviewed on page 61.

Such a conventional technique, that is, a method of mixing PVA fibrous binder with cellulose fiber and making paper,
Although a technique for increasing the strength and improving the water resistance of a PVA film by cross-linking a VA binder is known, P
None of the water-absorbent sheets composed of the VA fibrous binder and the cellulose fibers showed high strength even when dried and when wet. Further, there was no hot water-insoluble water-absorbent sheet having a water-absorbent or hydrophilic function.

Therefore, it is an object of the present invention to provide a water-absorbent sheet having high dry strength and wet strength without impairing water absorbency and having insolubility in hot water, and a method for producing the same.

[0006]

The present inventors can achieve the above object by forming a web sheet from a cellulose fiber and a PVA fibrous binder, and then adding a cross-linking agent to effect cross-linking. I found out.

The present invention has been made on the basis of the above findings, and is characterized by comprising a web sheet formed of cellulose fibers and PVA fibrous binder, and the PVA fibrous binder being cross-linked by a cross-linking agent. A water absorbent sheet is provided.

In the present invention, as a preferred method for producing the water absorbent sheet, a web sheet is formed from cellulose fibers and PVA fibrous binder, and then the PVA fibrous binder in the web sheet is cross-linked with a cross-linking agent. The present invention provides a method for producing a water absorbent sheet, which is characterized by the above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The water-absorbent sheet and the method for producing the same of the present invention will be described in detail below mainly based on the method for producing the water-absorbent sheet.

In the method for producing a water absorbent sheet of the present invention, as described above, a web sheet is formed from cellulose fibers and a PVA fibrous binder, and then the PVA fibrous binder in the web sheet is crosslinked with a crosslinking agent. It is characterized by

Examples of the cellulose fibers used in the production method of the present invention include natural cellulose fibers such as wood pulp and cotton, regenerated cellulose fibers such as rayon and cupra, crosslinked pulp, mercerized pulp, crosslinked mercerized pulp. Bulky cellulose fibers and the like are listed, and among them, bulky cellulose fibers, especially crosslinked pulp, mercerized pulp or crosslinked mercerized pulp are preferably used.
These cellulose fibers may be used alone or in combination of two or more.

The PVA fibrous binder used in the production method of the present invention is a thermoplastic PVA fibrous binder having a melting temperature in water of 50 ° C to 90 ° C. The fiber diameter of the PVA fibrous binder is preferably 0.3 to 5 denier (hereinafter, denier is abbreviated as "d"), more preferably 0.5 to 3 d, and fiber length is preferable. Is from 0.5
It is 10 mm, more preferably 1 to 7 mm.

In the production method of the present invention, the weight ratio (the former / the latter) of the amount of the cellulose fiber used and the amount of the PVA fibrous binder used when forming the web sheet is preferably from 80/20. It is 99.5 / 0.5, and more preferably 85/15 to 99/1. When the above weight ratio is less than 80/20 (that is, when the cellulose fiber is less than 80 parts by weight and the PVA fibrous binder is more than 20 parts by weight), the water-absorbing sheet obtained may have a water-absorbing property or hydrophilic property. Not only the properties are lost, but also the flexibility may be deteriorated, and the above weight ratio is 99.
When it exceeds 5 / 0.5 (that is, when the cellulose fiber is 9
Over 9.5 parts by weight, 0.5% PVA fibrous binder
If the amount is less than 1 part by weight), the strength of the resulting water-absorbent sheet may be low and it may be difficult to withstand use.

In the production method of the present invention, when forming the web sheet, polyolefin fibers such as polyethylene and polypropylene, synthetic fibers such as polyester and polyamide fibers, and composite fibers thereof and hydrophilic fine particles are used. Fibers, etc., such as the above cellulose fibers and the above PVA
It can be used in combination with a fibrous binder.

As a forming method for forming the above web sheet, a wet paper making method and a dry paper making method are generally used, but the forming method is not limited to these.

The web sheet has a basis weight of 1
It is preferably formed so as to have a weight of 0 to 200 g / m ² . The web sheet has a water content (relative to solid content) of 50 when it is formed by the wet papermaking method.
It is preferable to form it in an amount of ˜500% by weight, and when it is formed by the dry papermaking method, it is 0 to 50% by weight.
It is preferable to form so that

In the manufacturing method of the present invention, after forming the web sheet, the PVA in the web sheet is formed.
The cross-linking agent that cross-links the fibrous binder is not particularly limited as long as it can cross-link the PVA fibrous binder, and examples thereof include aldehydes such as glyoxal, dialdehyde starch, polyacrolein, and N-
Methylol urea, N-methylol melamine and other methylol compounds, divinyl sulfone and other activated vinyl compounds,
Epoxy compounds such as epichlorohydrin, tartaric acid, citric acid, malic acid, maleic acid, fumaric acid, succinic acid, tricarballylic acid, butanetetracarboxylic acid, polymaleic acid, polyacrylic acid, polyacrylic acid-maleic acid copolymers, etc. Polycarboxylic acid, diisocyanate compound,
Inorganic cross-linking agents such as Cu, B, Al, Ti, Zr, Sn, V and Cr can be used.

Among the above-mentioned crosslinking agents,
Polycarboxylic acid is preferably used because it does not accompany generation of formalin or harmful gas and does not leave heavy metals. The polycarboxylic acid may be neutralized with an alkali component such as sodium hydroxide or ammonia, if necessary.

As a method for crosslinking the PVA fibrous binder with the crosslinking agent, a known crosslinking method is generally used and is not particularly limited. For example, an aqueous solution of the crosslinking agent (concentration is preferably 0. 5-10
(% By weight), followed by heat treatment by applying hot air having a temperature of 100 to 170 ° C. for 4 seconds to 10 minutes, or an aqueous solution of the cross-linking agent for the web sheet (concentration is preferably 0.5 to 1).
0% by weight), and then apply a predetermined amount of cross-linking agent with mangle or the like, and then hot air at a temperature of 100 to 170 ° C. for 4 seconds to
Examples include a method of applying heat for 10 minutes and heat treatment.

The amount of the cross-linking agent used is preferably 1 to 30 with respect to 100 parts by weight of the PVA fibrous binder.
It is 0 parts by weight, and more preferably 2 to 200 parts by weight. When the amount of the cross-linking agent used is less than 1 part by weight, the cross-linking effect is not exhibited and the strength of the resulting water absorbent sheet is low.
It may be difficult to withstand use, and if it exceeds 300 parts by weight, a large amount of the cross-linking agent component may remain in the resulting water-absorbent sheet or it may cause deterioration of flexibility, so the content should be within the above range. Is preferred.

In the production method of the present invention, a catalyst can be used for the purpose of smoothly promoting the reaction (esterification reaction) of crosslinking the PVA fibrous binder with the crosslinking agent. Examples of the catalyst include phosphoric acid, sodium hypophosphite, potassium dihydrogen phosphate, phosphoric acid compounds such as sodium phosphate, inorganic acids such as sulfuric acid and hydrochloric acid, sodium carbonate, sodium acetate, titanium compounds and the like. Among them, a phosphoric acid compound is preferably used.

The amount of the catalyst used is preferably 5 to 100 parts by weight, more preferably 5 to 70 parts by weight, based on 100 parts by weight of the crosslinking agent.

In the production method of the present invention, a paper strengthening agent generally used in the production of paper, if necessary,
A wet paper strengthening agent, a sizing agent and the like, an additive for the purpose of imparting flexibility to the sheet, and a fiber dispersibility improving agent for the purpose of increasing the uniformity of the sheet may be used.

Further, in the manufacturing method of the present invention, a drying treatment can be carried out if necessary. In this case, after forming the web sheet, the drying treatment and the crosslinking with the crosslinking agent may be performed at the same time. Further, after forming the web sheet, a drying treatment is performed, and then a heat treatment is performed with the crosslinking agent. You may crosslink by. Here, the drying treatment can be performed, for example, by hot air having a temperature of 50 to 170 ° C.

When the above PVA fibrous binder is cross-linked in advance and then wet papermaking or the like is performed, the PVA fibrous binder cannot be melted by heat in the drying step, so that the binder effect is lost. The strength of the water absorbent sheet is extremely low and is not included in the scope of the present invention.

Further, when a bulky and highly crosslinked cellulose fiber is used as the cellulose fiber, a large amount of the PVA fibrous binder is required in order to achieve high strength. Hydrophilicity may be impaired. In such a case, by increasing the amount of the PVA fibrous binder to be used for crosslinking, it is possible to increase the strength without impairing the water absorbency and hydrophilicity, and reduce the bonding points between the fibers. Therefore, it also has excellent flexibility.

Specific examples of the method for producing the water absorbent sheet of the present invention include, but are not limited to, the following. When the wet papermaking method is used as the method for forming the web sheet, cellulose fibers and PVA fibrous binder are mixed and disintegrated, and then papermaking is performed. Next, a method of obtaining a water absorbent sheet by spraying a predetermined amount of an aqueous solution of a cross-linking agent, followed by drying and cross-linking. A web sheet is previously formed from the cellulose fibers and the PVA fibrous binder by the above wet papermaking method. Then, the obtained sheet is dipped in an aqueous solution of a cross-linking agent, a predetermined amount of the cross-linking agent is applied with mangle or the like, and then cross-linked by heat treatment or the like to obtain a water absorbent sheet. When the dry papermaking method is used as the method for forming the web sheet, cellulose fibers and PVA fibrous binder are mixed and laminated fibers. A method of obtaining a water-absorbent sheet by spraying a predetermined amount of an aqueous solution of a cross-linking agent on the sheet obtained by drying and then performing cross-linking by a method such as heat treatment.

According to the production method of the present invention, a hot-water-insoluble water-absorbent sheet having both water absorbency, hydrophilicity and flexibility, and greatly improved dry strength and wet strength can be easily prepared.
And it becomes possible to manufacture at low cost. Further, according to the present invention, it is possible to manufacture a water absorbent sheet in a paper making process which has been conventionally performed.

According to the manufacturing method of the present invention, the dry strength is 2
More than 00g / 25mm, wet strength is 30g / 25
A water-absorbent sheet having a size of mm or more can be easily obtained.

Next, the water-absorbent sheet of the present invention will be described. The water-absorbent sheet of the present invention is preferably obtained by the above-mentioned production method of the present invention, and comprises cellulose fiber and polyvinyl alcohol fibrous binder. It is characterized in that it is formed and comprises a web sheet in which the polyvinyl alcohol fibrous binder is cross-linked by a cross-linking agent. In addition, what is not specifically described in the water absorbent sheet of the present invention is the same as that described in the manufacturing method of the present invention described above.

The water-absorbent sheet of the present invention is obtained in a weight ratio of the amount of the above-mentioned cellulose fiber and the amount of the above-mentioned polyvinyl alcohol fibrous binder used.
That is, the weight ratio (former / latter) of the cellulose fibers and the polyvinyl alcohol fibrous binder in the water absorbent sheet of the present invention is preferably 80/20 to 99.
5 / 0.5, and more preferably 85/15 to 99 /
It is one.

The basis weight of the water absorbent sheet of the present invention is generally preferably 10 g / m ² or more, more preferably 15 g / m ² or more. The basis weight is 10 g /
If it is less than m ² , the shape retention of the sheet may be poor and it may be difficult to withstand use.

Further, the water-absorbent sheet of the present invention has high performance and is used for various purposes. Specifically, since it has a paper dust prevention effect and high surface strength, it can be applied to various types of paper. In addition, because it has high wet strength, it is used for sanitary materials such as napkins and household miscellaneous goods such as disposable tissues, wet tissues, paper towels, wipers, etc., and also for various applications where paper and non-woven fabrics have been conventionally applied. Used.

[0034]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Examples 1 to 4] VPB105-1 [PV
A fibrous binder, made by Kuraray Co., Ltd.] and HBA / S
[Cellulose fiber (cross-linked pulp), Wafer (WEYE
RHAUSER Co.)]] and the usage amount shown in [Table 1] below,
After disintegrating with 300 ml of water with a mixer for 1 minute, using a square sheet machine [manufactured by Kumagai Riki Kogyo Co., Ltd.], the basis weight was 45 g / m ² , the thickness was 0.6 mm, the size was 25 cm, and the water content was 100%. A wet web sheet was obtained. As the cross-linking agent composition, a cross-linking agent of the type and the amount used shown in [Table 1] below is dissolved in 6 g of ion-exchanged water, and if necessary, the catalyst and the neutralization of the type and the use amount shown in [Table 1] below are used. After adding the agent, it is sprayed on the above web sheet and dried with a 120 ° C dryer [heating roll, manufactured by Kumagai Riki Kogyo Co., Ltd.].
Drying and crosslinking of the VPB105-1 were simultaneously performed for 0 seconds to obtain a water absorbent sheet (basis weight: 45.5 g / m ² ).

Example 5 0.06 g of VPB105-1 [PVA fibrous binder, manufactured by Kuraray Co., Ltd.], POROSANIER-J [cellulose fiber (mercerized pulp), manufactured by ITT RAYONIER INC.] ] 2.35 g
And NBKP [cellulose fiber (uncrosslinked pulp), softwood] 0.59 g together with 300 ml of water in a mixer 1
After disintegrating for a minute, a basis weight of 45
g / m ² , thickness 0.5 mm, 25 cm square, water content 110
% Wet web sheet was obtained and this web sheet was dried. Separately from this, as a cross-linking agent composition, maleic acid 0.013 as a cross-linking agent is added to 10 g of ion-exchanged water.
g was dissolved, and 0.001 g of phosphoric acid was further added as a catalyst to obtain a crosslinking agent solution. Then, the web sheet was dipped in the crosslinking agent solution, and then the VPB105-1 was cross-linked with a 120 ° C. dryer for 30 seconds to obtain a water absorbent sheet (basis weight 45.2 g / m ² ).

Comparative Example 1 By the same operation as in Example 1, V
PB105-1; 0.15g and HBA · S; 2.85g
Was disintegrated with 300 ml of water with a mixer for 1 minute, and then a square sheet machine was used to obtain a wet web sheet having a basis weight of 45 g / m ² , a thickness of 0.6 mm, a 25 cm square, and a water content of 100%. . The obtained web sheet was dried for 20 seconds by a 120 ° C. dryer without spraying the cross-linking agent to obtain a water absorbent sheet (basis weight 45 g / m ² ).

[0038]

[Table 1]

Next, the physical properties of the water-absorbent sheets obtained in Examples 1 to 5 and Comparative Example 1 were evaluated according to the following [Physical property evaluation method]. The results are shown in Table 2 below.

[Physical property evaluation method] <Dry strength> 25 mm wide and 75 m long from the water absorbent sheet
Cut a sample for evaluation of m
After being stored in a constant temperature and humidity room at 60 ° C. and 60% RH for 24 hours, the tensile breaking strength was measured using Tensilon (manufactured by Toyo Seiki Co., Ltd.), and the obtained measured value was defined as the dry strength. In addition, as a measurement condition of the tensile breaking strength, the distance between chucks is 5
The pulling speed was 300 mm / min.

<Wet strength> 25 m wide from the water absorbent sheet
A sample for evaluation having a length of m and a length of 75 mm was cut out, and this sample was stored in a constant temperature and humidity room at 25 ° C. and 60% RH for one day and then immersed in ion-exchanged water for 30 minutes. Then, the tensile strength at break when wet was measured in the same manner as the above dry strength measuring method, and the obtained measured value was defined as the wet strength.

<Water Absorption> A 5 cm square sample for evaluation was cut out from the water absorbent sheet, and 1 cc of ion-exchanged water was quickly dropped on this sample. At this time, the water absorption rate of the sample was evaluated in the following four stages. A: Absorbs the entire amount instantly. ○: Absorb the entire amount within 1 second. Δ: The entire amount is absorbed within 3 seconds. X: It takes 3 seconds or more to absorb the whole amount.

<Hot water insoluble> A 5 cm square sample for evaluation was cut out from the water absorbent sheet, immersed in boiling water and boiled for 2 minutes. Next, this was put into cold water to cool, and then dried with a hot air dryer at 120 ° C. for 1 hour. The sample after drying was visually evaluated in the following four stages. A: There is no change. ◯: There is a slightly dissolved portion. Δ: About half the amount of the shape is destroyed. X: The shape is not retained.

<Flexibility> A 10 cm square sample for evaluation was cut out from the water absorbent sheet, and this sample was evaluated by touch with fingers, and the degree of flexibility was evaluated according to the following four grades. A: Very soft. ：: Soft. Δ: There is some elasticity. X: Hard.

[0045]

[Table 2]

As is clear from the above results, according to the manufacturing method of the present invention, there is little breakage or settling of the sheet when water is absorbed, and stable water absorption can be maintained.
Since hot water insolubility is exhibited, it is possible to easily manufacture a water absorbent sheet that can also retain water such as hot water (Examples 1 to 5).

[0047]

The water-absorbent sheet of the present invention has high dry strength and wet strength without impairing water absorbability and is insoluble in hot water. Further, according to the manufacturing method of the present invention, it is possible to easily obtain the water absorbent sheet having the above-mentioned performance.

Claims (8)

[Claims] 1. A water-absorbent sheet comprising a web sheet formed of cellulose fibers and a polyvinyl alcohol fibrous binder, the polyvinyl alcohol fibrous binder being cross-linked by a cross-linking agent. 2. A weight ratio of the cellulose fiber and the polyvinyl alcohol fibrous binder (former / latter).
Is 80/20 to 99.5 / 0.5, The water absorbent sheet according to claim 1, wherein 3. The water absorbent sheet according to claim 1, wherein the cellulose fibers are bulky cellulose fibers. 4. The water absorbent sheet according to claim 1, wherein the bulky cellulose fibers are crosslinked pulp, mercerized pulp or crosslinked mercerized pulp. 5. A method for producing a water absorbent sheet, which comprises forming a web sheet from cellulose fibers and a polyvinyl alcohol fibrous binder, and then crosslinking the polyvinyl alcohol fibrous binder in the web sheet with a crosslinking agent. 6. The weight ratio (the former / the latter) of the amount of the cellulose fiber used and the amount of the polyvinyl alcohol fibrous binder used in forming the web sheet is 8
It is 0 / 20-99.5 / 0.5, The manufacturing method of the water absorbent sheet of Claim 5 characterized by the above-mentioned. 7. The method for producing a water absorbent sheet according to claim 5, wherein the cellulose fibers are bulky cellulose fibers. 8. The method for producing a water absorbent sheet according to claim 5, wherein the crosslinking agent is a polycarboxylic acid.