TW201818979A - Water absorbing sheet - Google Patents

Abstract

A water-absorbing sheet has a water-containing photocuring film of a water-containing acrylic monomer film that contains a water-soluble acrylic monomer component and water. The water-soluble acrylic monomer component exhibits transparency when mixed with 18 mass% or more of water at 23 DEG C. More specifically, transparency with a haze of 8% or less. It is preferable that all of the water-soluble acrylic monomers that constitute part of the water-soluble acrylic monomer component exhibit transparency even when mixed with 18 mass% or more of water at 23 DEG C. Examples of such water-soluble acrylic monomers include hydroxy-group-containing acrylic monomers, and in particular, 4-hydroxybutyl acrylate, 2-hydroxypropyl acrylate, or 2-hydroxyethyl methacrylate.

Description

   Absorbent sheet   

The present invention relates to a water-absorbent sheet having high transparency.

As a water-absorbent sheet such as a paper diaper or a pet sheet that requires high water-absorbency, an acrylic polymer particle is dispersed on a base material and fixed with a bonding material (Patent Document 1).

Patent Document 1: Japanese Unexamined Patent Publication No. 11-170414

However, as a new application of the water-absorbent sheet, it is considered to be applied to a window glass or a transparent display. In this case, the practical transparency of the water-absorbent sheet is required, that is, the haze does not exceed 8%, or the manufacturing cost is not due to the application. Over a relatively large area. However, even if the prior water-absorbent sheet used a transparent material as a base material or a coating bonding material, the acrylate polymer particles that can be obtained at a relatively low cost have a particle size that is relatively larger than the wavelength of visible light, so they appear cloudy. Or the appearance of the polymer can be seen, and there is a problem that the desired transparency cannot be obtained.

An object of the present invention is to solve the above problems of the prior art, and to provide a water-absorbent sheet which has high transparency before and after water absorption and can be manufactured at low cost.

The present inventors have found that a water-absorbent sheet obtained by photo-hardening a water-containing acrylic monomer film while maintaining its water-containing state unexpectedly achieves both good transparency and water absorption, thereby completing the present invention. The water-containing acrylic monomer film is formed by forming a water-containing composition, and the water-containing composition is obtained by mixing water with a water-soluble acrylic monomer component that exhibits transparency under prescribed water-containing conditions.

That is, the present invention provides a water-absorbent sheet having an aqueous photocurable film containing an aqueous acrylic monomer film, wherein the aqueous acrylic monomer film contains a water-soluble acrylic monomer component and water, and a water-soluble acrylic acid. The monomer component is transparent when mixed with water of 18% by mass or more at 23 ° C.

In addition, the present invention provides a method for producing a water-absorbent sheet having a water-containing photocurable film containing an aqueous acrylic monomer film, wherein the aqueous acrylic monomer film contains a water-soluble acrylic monomer component and water. The production method includes the steps of forming a water-containing photocurable acrylic monomer composition on a base film to form a water-containing acrylic monomer film, wherein the water-containing photocurable acrylic monomer composition is contained in 23 A water-soluble acrylic monomer component, a photopolymerization initiator, a cross-linking agent, and water that exhibits transparency when mixed with water of 18% by mass or more; a transparent release film is laminated on an aqueous acrylic monomer film; The acrylic monomer film is irradiated with ultraviolet rays from the transparent release film or the base film side, thereby forming a water-containing photocurable film while maintaining the water content of the water-containing acrylic monomer film.

The water-absorbent sheet of the present invention has a water-containing photocuring film containing a water-containing acrylic monomer film. The water-containing acrylic monomer film contains a water-soluble acrylic monomer component and water, and is used for mixing at 23 ° C. with 18% by mass or more of water. Those that exhibit transparency at times are used as the water-soluble acrylic monomer component. Such a water-soluble acrylic monomer component is composed of at least a water-soluble acrylic monomer that exhibits transparency when mixed with water of 18% by mass or more at 23 ° C, and can be obtained relatively easily and at low cost. Therefore, the water-absorbent sheet of the present invention can achieve both good water absorption and transparency.

Hereinafter, the water-absorbent sheet of the present invention will be described in detail.

<Water-absorbent sheet>

The water-absorbent sheet of the present invention has a water-containing photocurable film containing a water-soluble acrylic monomer component and water-containing acrylic monomer film. The water-absorbent sheet of the present invention may have a single-layer structure of the water-containing photocurable film. In addition, a structure in which a water-based photo-hardening film is laminated on the base film may be used. The base film may be transparent. In addition, it is also possible to have a structure in which the surface area layer of the water-containing photocurable film on the opposite side of the base film has a release film that is transparent and also serves as a protective sheet. In the present invention, the term "acrylic" includes "methacrylic".

(Water-soluble acrylic monomer component)

In the present invention, the water-soluble acrylic monomer component exhibits transparency when mixed with water of 18% by mass or more at 23 ° C. Therefore, when the aqueous acrylic monomer film is light-cured to form an aqueous light-curable film, good transparency can be achieved. In addition, the evaluation temperature is "23 ° C" because the ambient temperature in the general manufacturing process is 23 ° C, and the mixing amount of water is "18% by mass or more" as an indicator of the following degree: Even after the water-containing acrylic monomer film is irradiated with ultraviolet rays, the photocuring component (polymer) does not dissolve from water, and transparency can be maintained.

In the present invention, "water-soluble" of the water-soluble acrylic monomer component means that the monomer component is not separated into layers and the like, and is mixed with water at an arbitrary ratio. This measurement can be performed by a "mixing experiment", which is a method of gradually increasing the amount of water-soluble acrylic monomer component added to water and confirming it at the same time. The "transparency" of the water-soluble acrylic monomer component means that the haze (opacity) measured in accordance with JIS K7136 is 8% or less, and preferably 5% or less.

When the water-soluble acrylic monomer component contains more than one type of water-soluble acrylic monomer, that is, a plurality of water-soluble acrylic monomer components, all of these water-soluble acrylic monomer components are at 23 ° C and As described above, 18% by mass or more of water exhibits transparency when mixed, and it is preferable in terms of maintaining transparency even after irradiation with ultraviolet rays.

(Water-soluble acrylic monomer)

As such a water-soluble acrylic monomer, a well-known water-soluble acrylic monomer which has a carboxyl group, an amine group, a hydroxyl group, a polyether group, etc. which are hydrophilic groups is used.

Specific examples of such a water-soluble acrylic monomer include 4-hydroxybutyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxyethyl methyl in terms of transparency of a water-containing photocurable film. A hydroxyl group-containing acrylic monomer such as acrylate. These may be used in combination or may be used alone.

In addition, as long as the water-soluble acrylic monomer component exhibits transparency when mixed with water of 18% by mass or more at 23 ° C, it may be various hydrophilic monomers in addition to the above-mentioned hydroxyl-containing acrylic monomer. Specific examples of the various hydrophilic monomers include vinyl alcohol, vinyl acetate, (meth) acrylic acid, (meth) acrylate, (meth) acrylamide, and the like. These hydrophilic monomers may be bonded to a hydrophilic group such as a hydroxyl group, a carboxyl group, or a polyether group, if necessary. Among them, preferred examples include hydroxyethylpropenamide and acrylic acid. When hydroxyethyl acrylamide or acrylic acid is used as the hydrophilic monomer, the hardness of the sheet of the water-absorbent sheet can be adjusted, and the viscosity can be weakened. As a result, a water-absorbent sheet can be manufactured roll-to-roll.

A (meth) acrylamidonium-based quaternary ammonium salt monomer of the following formula (1) may be used as the hydrophilic monomer. When this monomer is used, the water-absorbent polymer sheet of the present invention can be provided with high water-absorption property, and the viscosity of the water-absorbent sheet in which the water-containing state is maintained can be suppressed or adjusted.

_{CH 2 = C (R 1)} CON (R 2) -AN + (R 3) (R 4) (R 5) ‧X - (1)

In Formula (1), R ₁ and R ₂ are each independently a hydrogen atom or a lower alkyl group. R ₃ and R ₄ are lower alkyl, R ₅ is lower alkyl, lower alkenyl, or benzyl, A is lower alkylene group, and X ^- is a halogen anion or perchlorate ion. Among these substituents, examples of the lower alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl, pentyl, and hexyl. Among them, methyl is preferred. Examples of the lower alkenyl include vinyl, 1 or 2-propenyl, 1,2 or 3-butenyl, 1,2,3 or 4-pentenyl, 1,2,3,4 or 5- Hexenyl and the like. Examples of the lower alkylene group include methylene, ethylene, propyl, butyl, pentyl, and hexyl. Examples of the halogen anion include a chloride anion, a bromine anion, and an iodine anion.

Preferred R ₁ is a hydrogen atom, preferred R ₂ is a methyl group, preferred R ₃ , R ₄ and R ₅ are methyl groups, preferred A is propylene, and preferred X ^- is a chloride anion.

On the other hand, as specific examples of the cation part of the (meth) acrylamidoamine-based quaternary ammonium salt monomer, acrylaminoaminomethyltrimethylammonium and acrylaminoaminomethyltriethyl Ammonium, allylaminomethyltripropylammonium, allylaminoethyltrimethylammonium, allylaminopropylpropyltrimethylammonium, allylaminopropylpropylmethyldiethyl Ammonium, propenylaminopropylethyldimethylammonium, propenylaminopropylmethyldipropylammonium, propenylaminopropylpropyltriethylammonium, propenylaminopropylpropyl Acrylamidines such as tripropylammonium, acrylamidoaminoethyldimethylbenzylammonium, acrylamidoaminopropyldimethylbenzylammonium, acrylamidoaminopropylpropyldiethylbenzylammonium Department of quaternary ammonium cation. Among these, from the viewpoint of easy availability of inexpensive industrial raw materials, acrylamidoaminopropyltrimethylammonium and acrylamidoaminopropyldimethylbenzylammonium are preferred. Particularly preferred is acrylamidoaminopropyltrimethylammonium.

Therefore, as the (meth) acrylamidoamine-based quaternary ammonium salt monomer of the preferred formula (1), acrylaminoaminopropyltrimethylammonium chloride may be mentioned, in other words, dimethylaminopropyl Acrylamide chloride methyl salt.

(Aqueous acrylic monomer film)

Such an aqueous acrylic monomer film containing a water-soluble acrylic monomer component and water will be described later, and the water-containing acrylic monomer component containing at least the water-soluble acrylic monomer component and water is hardened by a conventional method such as a calender method. It is obtained by forming a film of an acryl-based monomer composition. The film thickness varies depending on the purpose of the water-absorbent sheet, but it is usually 10 to 1000 μm, and preferably 50 to 500 μm.

Since the water content in such a water-containing acrylic monomer film is substantially the same as the water content of a water-containing photocurable film to be described later, it is adjusted from the viewpoint of the mechanical strength required for the water-absorbent sheet or the rationality in the manufacturing steps. This water content is preferably in the range of 5 to 50% by mass. Within this range, not only the water-soluble acrylic monomer component exhibits miscibility with water of 18% by mass or more, but also the effect of "reliably reducing the haze of the water-containing photocurable film after ultraviolet irradiation" can be obtained. As the water, distilled water and ion-exchanged water can be preferably used. The measurement of the water content can be performed by measuring the change in weight using the "heating scale".

(Photopolymerization initiator, crosslinking agent)

In the present invention, the water-containing acrylic monomer film usually contains a photopolymerization initiator. The purpose is to promote the hardening of the monomer film. The water-containing acrylic monomer film preferably further contains a crosslinking agent. In order to increase the water holding power of the water-containing photocurable film, the water-based photocurable film is given a mechanical strength of "a roll-to-roll water-containing photocurable film can be wound".

As the photopolymerization initiator, a known radical type photopolymerization initiator can be used. Specific examples include benzoin such as benzoin, benzoin methyl ether, benzoin ether, benzoin isopropyl ether, benzoin isobutyl ether, anisole methyl ether, 4- (2-hydroxyethoxy) Phenyl (2-hydroxy-2-propyl) ketone (Darocure-2959; BASF Japan Co., Ltd.), α-hydroxy-α, α'-dimethylacetophenone (Darocure-1173; BASF Japan Co., Ltd. ), Methoxyacetophenone, 2,2'-dimethoxy-2-phenylacetophenone (Irgacure-651; BASF Japan Co., Ltd.), 2-hydroxy-2-cyclohexylacetophenone ( Irgacure-184; BASF Japan Co., Ltd.), 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenylketone, 4 -Acetophenones such as phenoxydichloroacetophenone, 4-tert-butyl-dichloroacetophenone, 2-hydroxy-2-methylphenylacetone, 2-hydroxy-4'-isopropyl- Phenylacetone such as 2-methylphenylacetone, benzophenone, methylbenzophenone, p-chlorobenzophenone, p-dimethylaminobenzophenone and other benzophenones, 9-oxysulfur (thioxanthone), 2-chloro9-oxysulfur 2-ethyl 9-oxysulfur , 2-isopropyl 9-oxysulfur , 2,4-dichloro 9-oxysulfur , 2,4-diethyl 9-oxysulfur 2,4-diisopropyl 9-oxysulfur Dodecyl 9-oxysulfur 9-oxysulfur Class, bis (2,4,6-trimethylbenzylidene) -phenylphosphine oxide, 2,4,6-trimethylbenzylidene diphenylphosphine oxide, bis (2,4 , 6-trimethylbenzyl) -2,4-di-n-butoxyphenylphosphine oxide, bis (2,6-dimethoxybenzyl) -2,4,4-tri Fluorenylphosphine oxides such as methylpentylphenylphosphine oxide, diphenylethylene dione, dibenzocycloheptanone, α-fluorenyl oxime ester, and the like.

Moreover, as a crosslinking agent, a well-known crosslinking agent can be used, It is preferable to use a polyfunctional acrylate type crosslinking agent. Specific examples include tripropylene glycol diacrylate, neopentaerythritol triacrylate, trimethylolpropane triacrylate, isotricyanic acid EO modified di and triacrylate, and trimethylolpropane. EO modified triacrylate, dipentaerythritol penta and hexaacrylate, ditrimethylolpropane tetraacrylate, etc.

The blending amount of the photopolymerization initiator in the aqueous acrylic monomer film is preferably 0.01 to 1 part by mass, and more preferably 0.1 to 0.5 part by mass relative to 100 parts by mass of the water-soluble acrylic monomer component described above. . Within this range, good film-forming properties can be achieved. The blending amount of the cross-linking agent in the aqueous acrylic monomer film is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 1 part by mass relative to 100 parts by mass of the water-soluble acrylic monomer component described above. . Within this range, good water absorption and solubility resistance can be achieved.

(Water-containing light hardening film)

The water-absorbent sheet of the present invention contains an aqueous photocurable film derived from the aforementioned aqueous acrylic monomer film. The photo-curing of the aqueous acrylic monomer film can be performed by irradiating ultraviolet rays to the aqueous acrylic monomer film, as described later. The film thickness varies depending on the purpose of the water-absorbent sheet, but it is usually 10 to 1000 μm, and preferably 50 to 500 μm.

The water content of the water-containing photocurable film depends on the water content of the water-containing acrylic monomer film, but is preferably 5 to 50% by mass, and more preferably 10 to 30% by mass. Within this range, good film-forming properties can be achieved. The measurement of the water content of the water-containing photocurable film can be performed by the same method as that of the water-containing acrylic monomer film.

The haze of the water-containing photocurable film according to JIS K7136 is preferably 8% or less, and more preferably 5% or less. Within this range, good transparency can be achieved.

The water absorption of the water-containing photocurable film is preferably 10% by mass or more, and more preferably 50% by mass or more with respect to the weight thereof. Within this range, "prevention of condensation" and the like can be realized.

(Other ingredients)

The water-containing light-hardening film of the water-absorbent sheet of the present invention may contain a transparent thermoplastic resin or antioxidant, a light stabilizer, a polymerization inhibitor, and a silane coupling agent that are compatible with the water-based light-hardening film within a range that does not impair the effects of the present invention. , Dyes, etc.

(Manufacturing method of water-absorbent sheet)

The water-absorbent sheet of the present invention having a water-containing photocurable film containing a water-based acrylic monomer film can be produced by a production method having the following steps (A) to (C). The water-containing acrylic monomer film contains water-soluble Acrylic monomer component and water.

(Step A)

First, a water-containing photocurable acrylic monomer composition is formed on a base film to form a water-containing acrylic monomer film. The formation of this aqueous acrylic monomer film can be formed by a known method. For example, a water-based photocurable acrylic monomer composition can be applied to a base film such as a polyethylene terephthalate film subjected to a peeling treatment by a known method such as a calendar method or a bar coating method. The base film is preferably transparent (ultraviolet-transmitting) so that ultraviolet irradiation in step C described later can be performed.

The water-containing photocurable acrylic monomer composition contains a water-soluble acrylic monomer component, a photopolymerization initiator, a crosslinking agent, and water. Regarding the types or blending ratios of these ingredients, as described in the water-absorbent sheet of the present invention.

That is, as the water-soluble acrylic monomer component, it is used when it is transparent when mixed with water of 18% by mass or more at 23 ° C. Specifically, it is used in which the haze according to JIS K7136 is 8% or less. The purpose is to achieve good transparency when the aqueous acrylic monomer film is light-cured into an aqueous light-curable film.

In addition, the aqueous photocurable acrylic monomer composition may contain a transparent thermoplastic resin or an antioxidant, a light stabilizer, a polymerization inhibitor, a silane coupling agent, a dye, and the like, which are compatible with the aqueous photocurable film after being photocured.

(Step B)

Next, a transparent release film was laminated on the water-containing acrylic monomer film. By laminating this film, it is possible to photo-harden the water-containing acrylic monomer film in the following step C while maintaining the water content of the water-containing acrylic monomer film. As a transparent peeling film, a well-known transparent peeling film can be used, For example, a commercially available peeled polyethylene terephthalate film etc. can be used. In addition, the "transparency" of the transparent release film means that the ultraviolet rays used in step C described later will be transmitted.

(Step C)

By irradiating the water-containing acrylic monomer film with ultraviolet rays from the transparent release film or the base film side, a water-containing photocurable film is formed while maintaining the water content of the water-containing acrylic monomer film. Irradiation of ultraviolet rays can be performed by a known ultraviolet irradiation technique. For example, the water-containing acrylic monomer film can be irradiated with ultraviolet rays emitted from a chemical lamp, a high-pressure mercury lamp, or the like from a transparent release film or a base film side, thereby performing the operation. As an example of ultraviolet irradiation conditions, a chemical lamp adjusted to 0.5 to 1.5 mW / cm ^{2 may} be irradiated with ultraviolet rays for 5 to 10 minutes, and then a high-pressure mercury lamp may be irradiated at a light amount of 1000 to 1500 mJ / cm ² . In addition, "under the condition that the water content of the water-containing acrylic monomer film is maintained" means that the water content of the water-containing acrylic monomer film before ultraviolet irradiation and the water content of the water-based photocurable film after ultraviolet irradiation are substantially the same. In addition, whether or not the water content of the water-containing acrylic monomer film is maintained can be evaluated by the same method as a known measurement method of the water content of the water-containing acrylic monomer film.

The water-absorbent sheet having a water-containing light-curable film produced in this manner can be preferably used by being adhered to an adherend such as a transparent display after removing the transparent release film.

Examples

Hereinafter, the present invention will be specifically described with experimental examples and examples.

Experimental example (mixing test of acrylic monomer and water)

The state of the mixed solution when the acrylic monomer and water were uniformly mixed at 23 ° C in various ratios was visually observed. The colorless and transparent case was evaluated as good "○", and the case of white turbidity was evaluated as "x". The obtained results are shown in Table 1. In addition, the evaluations of "good" and "bad" are based on the haze according to JIS K7136, which respectively meet the conditions of "less than 8%" and "more than 8%".

It can be seen from Table 1 that 2-hydroxybutyl acrylate will become cloudy if mixed with 18 parts by mass or more of water at 23 ° C, and other acrylate monomers will not be mixed even when mixed with 18 parts by mass or more of water at 23 ° C. Cloudy. Therefore, when the acrylic monomer composition is light-cured in a water-containing state, it is understood that at least a water-soluble acrylic monomer that does not become cloudy even when mixed with water at 18 parts by mass or more at 23 ° C should be used.

Examples 1 to 3 and Comparative Example 1

Using a rotary wing mixer (SANY Motor, New East Scientific Co., Ltd.), 88 parts by mass of acrylic monomers, 12 parts by mass of water, and a photopolymerization initiator (Darocure 1173, BASF Japan Co., Ltd.) shown in Table 2 were used. ) 0.3 parts by mass and 0.3 parts by mass of a cross-linking agent (M-400, Toa Synthesis Co., Ltd.) were uniformly mixed to prepare a water-containing photocurable acrylic monomer composition. Using a bar coater, this aqueous photocurable acrylic monomer composition was applied to a peeling polyethylene terephthalate film in a thickness of 200 μm, and another peeling polyethylene terephthalate was placed thereon. Diester film. The water-containing photocurable acrylic monomer composition film (that is, the water-containing acrylic monomer film) sandwiched between two peeling-treated polyethylene terephthalate films was irradiated with a chemical adjusted to 1 mW / cm ² The ultraviolet light (dominant wavelength 365nm) of the lamp was 5 minutes, and then the ultraviolet light (dominant wavelength 365nm) from a high-pressure mercury lamp was irradiated so as to become a cumulative amount of light of 1000mJ / cm ² to produce a water-containing light-hardened film which was peeled off and treated with polyethylene terephthalate. Absorbent sheet held by diester. In addition, the water content of the water-containing photocurable acrylic monomer composition film in the water-absorbing sheets of Examples 1 to 3 and Comparative Example 1 and the water content of the cured water-containing photocurable film were both approximately 12% (mass Benchmark), no substantial difference.

<Evaluation>

The "transparency" of the water-containing photocurable acrylic monomer composition was evaluated as described below, and the "water absorption" of the obtained water-absorbent sheet was tested for "water absorption" as described below and evaluated. The "transparency" of the water-absorbent sheet (a water-containing photocurable film) is measured and evaluated as described below. The obtained results are shown in Table 2.

(Transparency of water-containing photocurable acrylic monomer composition)

The state of the composition was visually observed, and the case of colorless and transparent was evaluated as good "○", and the case of white and cloudy was evaluated as bad "×".

(Water absorption of water-absorbent sheet)

The water-absorbent sheet was cut 1 cm square, and the polyethylene terephthalate film that had been peeled off from both sides was immersed in 30 ml of purified water for 24 hours. The mass after immersion is set to W1), and the water absorption rate is calculated according to the formula "water absorption (%) = [(W1-W0) / W0] x 100".

(Transparency of water-absorbing sheet (light-curing film))

The haze of the water-absorbent sheet of the polyethylene terephthalate film after peeling off the double-sided peeling treatment was measured in accordance with JIS K7136, and evaluated according to the following evaluation criteria.

Evaluation benchmark

○: When the haze is below 8%

△: When the haze exceeds 8% and is less than 10%

×: When the haze exceeds 10%

As can be seen from Table 2, the water-absorbent sheets of Examples 1 to 3 were excellent in transparency and exhibited good water-absorbency. In particular, it was learned that by changing the type of water-soluble acrylic monomer, the water absorption of the water-absorbent sheet can be controlled.

In contrast, the water-absorbent sheet of Comparative Example 1 is shown in Table 1. Since 2-hydroxybutyl acrylate, which becomes cloudy when mixed with 18 parts by mass or more of water at 23 ° C., was used as a water-soluble acrylic monomer, Therefore, the transparency of the water-absorbent sheet causes a problem.

Industrial availability

The water-absorbent sheet of the present invention exhibits good water absorption and exhibits good transparency (specifically, a haze of 8% or less). Therefore, it is suitable as a water-absorptive material applied to a window glass, a transparent display, or the like.

Claims (18)

    A water-absorbent sheet having a water-based photocurable film having a water-containing acrylic monomer film, wherein the water-containing acrylic monomer film contains water-soluble acrylic monomer components and water, and the water-soluble acrylic monomer components are at 23 ° C. and 18 ° C. When mixed with water of more than mass%, it is transparent.         For example, the water-absorbent sheet according to item 1 of the patent application scope, wherein the transparency of the water-soluble acrylic monomer component when mixed with water of 18% by mass or more at 23 ° C is 8% or less of haze.         For example, the water-absorbent sheet according to item 1 or 2 of the patent application scope, in which all the water-soluble acrylic monomers constituting the water-soluble acrylic monomer component are transparent even when mixed with water of 18% by mass or more at 23 ° C.         For example, the water-absorbent sheet according to item 3 of the application, wherein the water-soluble acrylic monomer is an acrylic monomer containing a hydroxyl group.         For example, the water-absorbent sheet according to item 4 of the application, wherein the acrylic monomer containing a hydroxyl group is 4-hydroxybutyl acrylate, 2-hydroxypropyl acrylate, or 2-hydroxyethyl methacrylate.         The water-absorbent sheet according to any one of claims 1 to 5, wherein the water-containing acrylic monomer film contains a photopolymerization initiator and a crosslinking agent.         For example, the water-absorbent sheet according to item 6 of the patent application, wherein the water-containing acrylic monomer film contains a photopolymerization initiator in an amount of 0.01 to 1 part by mass relative to 100 parts by mass of the water-soluble acrylic monomer component, and the content is 0.01. The proportion of ~ 5 parts by mass contains a crosslinking agent.         For example, the water-absorbent sheet according to any one of claims 1 to 7, wherein the water content of the water-containing light-curing film is 5 to 50% by mass.         For example, the water-absorbent sheet according to any one of claims 1 to 8, wherein the haze of the water-containing light-hardening film is 8% or less.         For example, the water-absorbent sheet according to any one of claims 1 to 9, wherein the water absorption of the water-containing photocurable film is 10% by mass or more relative to its weight.         A manufacturing method of a water-absorbent sheet having a water-containing photocurable film of a water-containing acrylic monomer film, wherein the water-containing acrylic monomer film contains a water-soluble acrylic monomer component and water, and the manufacturing method has the following Step: forming a water-containing photocurable acrylic monomer composition on a base film to form a water-containing acrylic monomer film, wherein the water-containing photocurable acrylic monomer composition is contained at 23 ° C. and 18% by mass Water-soluble acrylic monomer components, photopolymerization initiators, cross-linking agents, and water that exhibit transparency when mixed with the above water; laminated transparent release films on aqueous acrylic monomer films; and aqueous acrylic monomer films By irradiating ultraviolet rays from the transparent release film or the base film side, a water-containing photocurable film is formed while the water content of the water-containing acrylic monomer film is maintained.         For example, the manufacturing method according to item 11 of the patent application range, wherein the transparency of the water-soluble acrylic monomer component when mixed with water of 18% by mass or more at 23 ° C is 8% or less of haze.         For example, the manufacturing method of the scope of patent application No. 11 or 12 uses all water-soluble acrylic monomers constituting a water-soluble acrylic monomer component that exhibits transparency even when mixed with water of 18% by mass or more at 23 ° C.         For example, the manufacturing method according to item 13 of the patent application scope uses a hydroxyl-containing acrylic monomer as a water-soluble acrylic monomer.         For example, the manufacturing method according to item 14 of the patent application range uses 4-hydroxybutyl acrylate, 2-hydroxypropyl acrylate, or 2-hydroxyethyl methacrylate as a hydroxyl-containing acrylic monomer.         For example, the manufacturing method according to any one of claims 11 to 15, wherein the water content in the water-containing acrylic monomer film is 5 to 50% by mass.         The manufacturing method according to any one of claims 11 to 16, wherein the aqueous acrylic monomer film contains a photopolymerization initiator and a crosslinking agent.         For example, the manufacturing method according to item 17 of the patent application scope, wherein the water-containing acrylic monomer film contains a photopolymerization initiator in an amount of 0.01 to 1 part by mass relative to 100 parts by mass of the water-soluble acrylic monomer component, and the content is 0.01 to 1 part by mass. A cross-linking agent is contained in a proportion of 5 parts by mass.