JP2944129B2 - Film-shaped superabsorbent sheet and method for producing the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a film-like superabsorbent sheet and a method for producing the same, and more specifically, it consists essentially of only a superabsorbent substance, has sufficient strength as a single film, and The present invention relates to a film-like high water-absorbing sheet having high water-absorbing ability, especially excellent ion-absorbing water-absorbing ability, and a method for producing the same.

2. Description of the Related Art Generally, a superabsorbent sheet is used in a form in which a superabsorbent substance is bonded to a base material such as paper or nonwoven fabric. On the other hand, there are almost no sheets made of a superabsorbent material alone, and a small number of existing ones are of a type obtained by crosslinking a water-soluble polymer, and have sufficient water absorbing ability or practical strength of a film. Absent. As a deformation of a single sheet, there is a sheet in which a highly water-absorbing substance is dispersed in a non-water-absorbing component matrix of a synthetic resin or rubber, but the water absorbing ability is not sufficient.

Therefore, the present inventors have repeatedly studied to obtain a highly water-absorbing sheet substantially consisting only of a highly water-absorbing substance and having both sufficient water-absorbing ability and film strength. In the method of obtaining a sheet, a polymer produced by irradiation curing selects acrylic acid and acrylate as monomers exhibiting high water absorption ability, and a water-soluble polymer which cross-links to this during curing to exhibit film strength It has been found that the above-mentioned object can be achieved by applying an aqueous solution containing the compound to the substrate, and curing the coating film directly on the substrate by electron beam irradiation. No. 63-171818).

This highly water-absorbent sheet is a useful sheet excellent in both film strength and water absorbing ability. The present inventors have further continued intensive research to impart excellent water absorption to ionic water, especially seawater, to this sheet. By selecting the concentration in a specific range and further adding a specific amount of a bifunctional monomer to the coating solution, it was unexpectedly found that the water absorbing ability was improved, and the present invention was completed. Was.

Means for Solving the Problems The present invention provides: (a) a total of 5 to 70 parts by weight of acrylic acid and acrylate in a molar ratio of 90:10 to 10:90; (b) 95 to 30 parts by weight of polyethylene oxide; And (c) a seawater-resistant film-like high water absorption having a water absorption capacity 30 times or more that of a physiological saline solution comprising an electron beam cured film of a composition containing 0.01 to 5 parts by weight of a water-soluble bifunctional monomer. And a method for producing the same.

The seawater-resistant film-like superabsorbent sheet of the present invention is a cured product of electron beam irradiation of a blend of three essential components.

The first essential component of the formulation is acrylic acid and acrylate, a combination of both of which are known as starting monomers to obtain superabsorbent polymer resins. Examples of the acrylate include a salt with an alkali metal or a salt with an alkaline earth metal, and a salt with an alkali metal such as sodium, lithium and potassium is particularly preferred.

The ratio of acrylic acid and acrylate is important in determining the water absorbing ability, and in the present invention, the ratio of both is in the range of 90:10 to 10:90 by molar ratio. When the proportion of acrylic acid is smaller than the range, the reactivity at the time of electron beam irradiation is reduced, and only a water-soluble polymer is obtained.
If the ratio of acrylic acid is larger than the above range, the water absorbing ability is lowered, which is not suitable.

The second essential component is polyethylene oxide. This component is for imparting sufficient strength to the formed film. Since this polyethylene oxide exhibits a certain degree of water absorption due to cross-linking, in the present invention, a film substantially consisting only of the superabsorbent material is obtained.

The third essential component is a water-soluble bifunctional monomer which is a crosslinking agent. This time, it was found that by using this cross-linking agent as an essential component, the ability to absorb ionic water such as seawater was improved. Examples of water-soluble bifunctional monomers include polyethylene glycol diacrylate, N, N'-methylenebisacrylamide, polyethylene glycol methacrylate, N, N'-dihydroxyethylenebisacrylamide and the like. Polyethylene glycol diacrylamide from the viewpoint of improving the water resistance and seawater resistance.
N, N'-methylenebisacrylamide is preferred.

In the present invention, the ratio between these three components is important. First, the ratio of the total of acrylic acid and acrylate to polyethylene oxide is 5 to 70 parts by weight: 95 to 3 parts by weight.
0 parts by weight. If the ratio of acrylic acid and the acid salt is smaller than the above range, the water absorption capacity of the resulting film is not sufficient,
On the other hand, if it exceeds the above range, the strength of the film will not be sufficient.

Further, the ratio of the crosslinking agent is 0.1 part by weight based on the two components.
01 to 5 parts by weight. Outside of these ranges, seawater resistance is not sufficient. If the amount is less than 0.01 part by weight, the crosslinking of the water-soluble polymer becomes insufficient, and it becomes difficult to obtain a well-balanced and homogenous polymer. This is not suitable because a functional product cannot be obtained.

The film-like sheet of the present invention can be obtained for the first time by electron beam irradiation curing of a composition in the form of an aqueous solution in which the above three components are blended at a specific ratio and concentration.

In order to produce the superabsorbent sheet of the present invention, first, a composition comprising the above three components in the above ratio is prepared. These components themselves are easily available, and the order of addition of the components in the formulation is not particularly limited, and can be easily carried out according to a conventional method.

For example, acrylic acid and acrylate may be separately prepared, or a part of acrylic acid may be neutralized and prepared as a mixture of acrylic acid and acrylate.

For mixing with polyethylene oxide, polyethylene oxide may be directly added to a mixed aqueous solution of acrylic acid and acrylate, or an aqueous solution of polyethylene oxide may be added.

In short, it is only necessary to prepare a uniform aqueous solution in which the above-mentioned three components are consequently mixed in the above-mentioned ratio. Uniformity is considered to have been achieved if the liquid is transparent or nearly transparent. Making the aqueous solution uniform is required from the viewpoint of accelerating the reaction and improving the film strength.

This time, the total amount of the three essential components is 25-
It was found that when the content was in the range of 65% by weight, the water absorption capacity of the obtained film for ionic water was improved.

In addition, a coloring agent or a filler for coloring a film or the like, or a thickener or a surfactant for improving liquid properties such as a viscosity of a coating solution can be appropriately added.

The coating liquid thus prepared is cast on a substrate, and a coating liquid film is formed on the substrate. Casting is generally performed by a coating method, for example, knife coating,
Both roll coating and gravure coating are possible. The substrate to be used is not particularly limited, and any of film, paper, woven fabric, and nonwoven fabric can be used.

After the coating film is formed, the coating film is cured by irradiating an electron beam.

Irradiation atmosphere may be in air or inert gas,
Irradiation conditions are irradiation voltage of 100 to 2000 KV, preferably 150 to 10
00KV, dose 1-20Mrad, preferably 2-10Mrad.

The irradiation of the electron beam causes the polymerizable monomers acrylic acid and acrylate to polymerize, causing the polyethylene oxide and a small amount of a cross-linking agent to cross-link and cure the compound.

It is considered that the reaction by electron beam irradiation is easy to control, so that the controllability of the reaction is excellent, and that polymerization and cross-linking occur in a well-balanced manner. For this reason, a film having excellent water absorption capacity may be obtained.

After irradiation with an electron beam, if necessary, the film is dried, and the formed film is peeled off from the substrate to obtain the highly water-absorbing film-like sheet of the present invention.

The film-like sheet of the present invention thus obtained has a water absorption capacity of about 30 to 80 times that of ionic water and is excellent in seawater resistance. Therefore, it can be suitably used not only for conventional non-ionized water applications such as sheet-shaped and tape-shaped water-stopping materials and cold insulators, but also for ionic water applications such as water-stopping in submarine cable coating systems. it can. It should be noted that the film-like superabsorbent sheet of the present invention can be used not only as a single substance but also in a state where a base material is attached.

Examples Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 (1) Preparation of coating solution Aqueous solution 1 containing 8.9 g of acrylic acid and 4.8 g of potassium hydroxide
1.1 g was added dropwise under cooling and stirring to obtain a mixed solution having a molar ratio of acrylic acid: acrylate = 30: 70. 20 g of polyethylene oxide (PEO-1 manufactured by Iron and Steel Chemical Co., Ltd.) was added to 20 g of this solution.
79.8 g of an aqueous solution was added, and 0.2 g of polyethylene glycol diacrylate was further added and mixed to obtain a uniform coating liquid.

The weight ratio of (acrylic acid + acrylate): polyethylene oxide: polyethylene glycol diacrylate in this solution is 42.6: 56.7: 0.7.

(2) Casting onto a base material The above coating solution was cast at a thickness of 0.2 mm onto a polyester film (Lumirror manufactured by Toray Industries, Ltd.) base material having a thickness of 0.1 mm using a knife coater.

(3) Curing by electron beam Immediately after coating, irradiate with an electron beam under irradiation conditions of irradiation voltage of 200 KV, dose of 6 Mrad, atmosphere in the atmosphere, dry at 105 ° C for 10 minutes, and peel off the polyester film substrate. The film-like superabsorbent sheet of the invention was obtained.

When the water absorbing ability of this super absorbent sheet with respect to physiological saline (0.9% saline) was measured, it showed a water absorbing ability with a swelling degree of 70 times.

Comparative Example 1 A coating liquid was prepared in exactly the same manner as in Example 1 except that only polyethylene glycol diacrylate was not added in the preparation of the coating liquid (1).
(3) A film-like water-absorbent sheet was obtained in exactly the same manner as in Example 1 with respect to curing by electron beams.

The water-absorbing capacity of this solution was measured, and it was partially dissolved, and the water-absorbing capacity was as low as about 20 times, which was not satisfactory as a highly water-absorbent sheet.

Effects of the Invention According to the present invention, a film-like high water-absorbing sheet having good water-absorbing ability even with ion water and having sufficient strength is provided.

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁶ Identification symbol FI // C08L 33/02 C08L 33/02 (56) References JP-A-2-138307 (JP, A) JP-A-64-65108 (JP, a) JP Akira 63-251401 (JP, a) JP Akira 57-167307 (JP, a) JP Akira 56-91837 (JP, a) (58 ) investigated the field (Int.Cl. ⁶ , DB name) C08F 2/54 C08F 2/44 C08F 220/06 C08J 5/18 C08L 33/02 B01J 20/26

Claims (2)

(57) [Claims] 1. A total of 5 to 70 parts by weight of acrylic acid and acrylate in a molar ratio of 90:10 to 10:90; (b) 95 to 30 parts by weight of polyethylene oxide; and (c) water solubility. A highly water-absorbent sheet in the form of a seawater-resistant film having a water absorption capacity 30 times or more that of a physiological saline solution comprising an electron beam cured film of a composition containing 0.01 to 5 parts by weight of a bifunctional monomer. 2. A composition comprising: (a) a total of 5 to 70 parts by weight of acrylic acid and acrylate in a molar ratio of 90:10 to 10:90; (b) 95 to 30 parts by weight of polyethylene oxide; (C) An aqueous solution containing 0.01 to 5 parts by weight of a water-soluble bifunctional monomer in a total water concentration of 25 to 65% by weight is cast, and then the cast is cured by irradiating with an electron beam. A method for producing a seawater-resistant film-like superabsorbent sheet having a water absorption capacity of at least 30 times that of physiological saline, characterized in that the formed cured film is peeled off from the substrate.