JPH06278237A - Water absorption sheet - Google Patents

Abstract

PURPOSE:To prevent lowering of freshness and, moreover, provide a water absorption sheet with high strength by absorbing moisture that emanates or evaporates from itself in the case of wrapping goods containing moisture and high humidity therein such as fresh foods or the like. CONSTITUTION:A water absorption sheet is obtained that consists of two sheets of paper base materials and an intermediate layer being laid therebetween, and the intermediate layer is arranged in a manner being adjacent to the inner surface of the paper base material 1, in which the sheet has water absorptive sections 4 consisting of a mixture of high water absorption polymer and binder, and also has a waterproofing adhesive part 5 having water absorbing sections 4 buried therein and being in contact with the inner surface of both the paper base materials.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to packaging of flowers, vegetables, fresh foods, processed foods, etc. which contain water or have a high humidity atmosphere, or a sheet used for transporting them to obtain water-absorbing materials. More specifically, the present invention relates to a water-absorbent sheet that can prevent the freshness from being deteriorated by absorbing condensed water such as water or steam that is leached or evaporated from itself when the fresh material as described above is packaged.

[0002]

2. Description of the Related Art In recent years, superabsorbent polymers which absorb hundreds of times their own weight of water have been developed, and water absorbent sheets used in the food field and the like have been developed using the superabsorbent polymers. (See Japanese Patent Application Laid-Open No. 2-8048 and Japanese Patent Application Laid-Open No. 3-59196) These water-absorbent sheets are used for directly packaging flowers, vegetables, fruits, and other fresh foods, or for packaging in cardboard boxes for transportation. , Absorbs water or water vapor released from these items to be packaged, keeps the inside of the package clean,
It is effectively used as a packaging material to prevent contamination and spoilage.

[0003]

In such a conventional water absorbent sheet, as shown in FIG. 3, a layer 12 containing a super absorbent polymer is formed on the lower surface of a paper substrate 11 to form a uniform layer on the entire surface. In addition, since the support 13 such as a plastic layer is further provided, the superabsorbent polymer swelled when absorbing the water swells out from the end face in the thickness direction of the sheet to the outside. However, there is a problem that it adheres to food items and other items to be packaged. Further, since the paper base material 11 on the layer containing the superabsorbent polymer and protecting the superabsorbent polymer has a weak water resistance, it is possible to prevent the permeation of fresh food or the like during packaging and transportation. There has been a problem that the water-absorbent polymer which absorbs water released from foods and the like and is rubbed against the foods and the like is broken and the superabsorbent polymer inside is adhered to and contaminated with the foods and the like. The present invention is intended to solve such problems, and perishes fresh foods or the like that release water or water vapor, in the usual packaging method or in the packaging for transportation. It is an object of the present invention to provide a packaging material that can sufficiently maintain the freshness of.

[0004]

The present invention comprises a first paper base and a second paper base, and an intermediate layer between the two paper bases, the intermediate layer being the first paper base. Of a water-absorbent section which is arranged so as to be in contact with the inner surface of the sheet and which is composed of a mixture of a super-water-absorbent polymer and a binder, and a water-resistant adhesive portion which embeds the water-absorbent section and bonds the inner surfaces of both paper base materials. It is a sex sheet. With such a structure, if fresh food or the like is packaged so that the surface of the first paper base material is in contact with the surface of the first paper base, the moisture from the fresh food or the like absorbs water from the superabsorbent polymer and the binder. Permeates and is retained here. This water-absorbing section is in contact with the first paper base material, but is embedded and covered in the water-resistant adhesive in all three other directions, and is exposed to the outside even in the plane direction of the paper base material. Since there is no such thing, it will be in a state of having enough water.

Materials used in the present invention will be described below. Examples of the super absorbent polymer include acrylic acid-sodium acrylate copolymer, vinyl alcohol-acrylic acid copolymer, starch-acrylic acid copolymer and the like.
Further, the super absorbent polymer is preferably used in a powder form, and a particle size of 150 μm or less is preferable because it has a large surface area and can exhibit a sufficiently rapid water absorbing action and is easy to handle. When the particle size is larger than 150 μm, the stability of the paint when dispersed in a solution of a hydrophilic binder to form a paint, and the water-absorbent section formed by coating are good. The coated surface cannot be obtained.

The binder in which the superabsorbent polymer powder is dispersed is a hydrophilic binder having a hydrophilic polar group, but it is soluble in water as well as in a solvent other than water. Is. Therefore, the water absorbing section can be easily formed by coating the coating material dissolved in water or other solvent by printing or the like. When a water-absorbing layer is formed by mixing the above water-absorbing polymer with a hydrophobic binder, the water-absorbing performance is inferior, and especially the initial water-absorbing speed is remarkably lowered.
When the water-soluble binder is mixed and dispersed with the superabsorbent polymer, the superabsorbent polymer may absorb and swell water as a solvent, resulting in poor coating properties.
From the above points, as the binder used in the present invention,
Although it is hydrophilic in nature, it is preferable that it is soluble in a solvent other than water, for example, toluene, methanol, ethanol or the like in the state of the coating liquid when forming the water absorbing layer. Specific examples include polyethylene oxide, polyethyloxazoline, polyvinylpyrrolidone, and the like. In addition,
The content of the binder is preferably 50% by weight or less with respect to the superabsorbent polymer so that the water absorbency of the superabsorbent polymer is not significantly impaired.

The coating amount of the mixture of the superabsorbent polymer and the binder constituting the water-absorbing section is appropriately determined depending on the type of fresh food or the like to be packaged, but generally 1 to 50 g / m ² ( (Solid content) is preferred. The two paper base materials used in the present invention constitute a layer that protects the water-absorbing section. The water-absorbing layer absorbs water released from foods or the like as soon as possible, or absorbs water. The water absorbing section has a function of preventing the water absorbing section from adhering to an article to be packaged such as food. Therefore, it is necessary to absorb and permeate moisture and water vapor as quickly as possible, and to have a strength that does not break even when rubbed with food or the like while absorbing moisture and being wet. As such a paper substrate, one having a Steckigt sizing degree of 1 second or less according to JIS P 8122 to a wet strength of 0.5 Kgf / 15 mm or more according to JIS P 8135 is preferable. When the Steckigt sizing degree is 1 second or more, the absorption rate of water released from food becomes slow and the water easily accumulates on the paper substrate. Also, when the wet strength is less than 0.5 Kgf / 15 mm, when a fresh food is transported, when a portion in contact with the food is rubbed while being wet with the moisture released from the food, the portion is broken and the super absorbent polymer in Easily attaches to food.

The water-resistant adhesive used for forming the intermediate layer in the present invention is adhered to two paper base materials sandwiching the water-absorbing section, and even when the water-absorbing section absorbs water and swells. It has the functions of suppressing the peeling of paper base materials, preventing the water-absorbing section from protruding to the outside, and preventing the absorbed water from leaking to the outside. Therefore, the binder needs to be water resistant, and specific examples thereof include acrylic binders and polyurethane binders.

In the structure of the water absorbent sheet of the present invention, for example, as shown in FIG. 1, the water absorbent section 4 is partly contacted with the inner surface of the first paper base material 1 and is not exposed to the outside in cross section. The first paper base material 1 and the second paper base material 2 are joined together by a water-resistant adhesive portion 5 and laminated so that the intermediate layer 3 is formed. ing. The reason why the water-absorbing section 4 is provided inside the end surface of the paper substrate is that the periphery of the sheet is covered and adhered with a water-resistant adhesive portion, thereby absorbing water and swelling. This is to prevent the polymer from leaking out and leaking water. FIG. 2 is a plan view of the water absorbent sheet of the present invention, showing a state in which the water absorbent section 4 is provided on the back surface of the first paper substrate 1.

As one example of the method for producing a water-absorbent sheet of the present invention, the above super-absorbent polymer is mixed and dispersed in a binder prepared by dissolving it in an organic solvent such as toluene or methanol by a disperser such as Disper. After the coating liquid for the water-absorbent section is prepared, the coating liquid is applied to the first paper base material 1 so as to provide the water-absorbent section 4 by a coating method such as a gravure roll having a plate formed in a desired shape. dry. In this case, the shape of the water-absorbing sections is cylindrical and arranged in parallel in this case, but instead of this, it may be random, grid-shaped or strip-shaped. In short, it is necessary that the water absorption section is not exposed on the end face. Further, the emulsion paint or solution type paint of the water-resistant adhesive is applied onto the second paper base material 2 and the surface of the water absorbing section 4 of the first paper base material 1 in the state where the applied surface is undried. They are opposed to each other and pasted with a nip roll or the like, and then dried by hot air to adhere them. Then, the water-absorbent sheet of the present invention can be obtained by cutting with a sheet cutter or the like so that the water-absorbent section 4 does not extend beyond the end surface of the sheet.

Embodiments of the present invention will be described below. Example 1 A binder used in the water absorbing section was prepared with the following formulation. -Binder 10 parts by weight (polyethylene oxide, trade name Alcox R-150 manufactured by Meisei Chemical Industry Co., Ltd.)-Toluene 45 parts by weight-Methanol 45 parts by weight While stirring the above composition at 50 ° C for 30 minutes, the binder A 10% solution of Next, a coating material for the water-absorbing section was prepared by using the 10% binder solution obtained above and the following formulation. -Super absorbent polymer 60 parts by weight (acrylic acid-sodium acrylate copolymer, trade name Aqualserve AP-300SS manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)-Binder 10% solution 100 parts by weight

The above mixture was dispersed and mixed for 15 minutes at a rotation speed of 1000 rpm using a high speed disperser. The above dispersion was used, with a Steckigt size degree of 0 seconds and a wet tensile strength of 0.7K.
gf / 15mm unsized neutral paper (basis weight 50g /
m ² ), on a first paper substrate of 8 mm in diameter and 1 in depth
Spots of 50 μm were applied in the same manner as in FIG. 2 using a gravure plate roll having a circular pattern with a pitch of 3 mm to form a water-absorbing section, and then at 110 ° C. for 1 hour.
It was dried with hot air for a minute. The solid coating amount is 6.8 g / m ²
Met. Next, a 45% aqueous emulsion of acrylic acid ester resin (trade name: Polysol AT-13, manufactured by Showa High Polymer Co., Ltd.) was formed on a second paper substrate of the same quality as the first paper substrate.
The water-resistant adhesive consisting of 0) has a solid content of 2 with a wire bar.
The adhesive coating layer was applied evenly to 0 g / m ² , and the adhesive coating layer was attached to the side provided with the spot-shaped water-absorbing section in an undried state. After that 130 ℃ 2
It was dried with hot air for a minute. Furthermore, the water absorbent sheet of the present invention was obtained by cutting into a shape in which a binder coating portion was left around 20 mm from the outermost spot portion of the patterned water absorbent section.

Example 2 Polyethyloxazoline (manufactured by Somar, trade name PEOX-0 as a binder for forming a water-absorbing section)
A water absorbent sheet of the present invention was obtained in the same manner as in Example 1 except that the 10% methanol solution of 5) was used.

Example 3 Polyvinylpyrrolidone (manufactured by GAF, trade name PVP K-90) as a binder for forming a water-absorbing section
A water-absorbent sheet of the present invention was obtained in the same manner as in Example 1 except that the 10% methanol solution of 1 was used.

Comparative Example 1 As in Example 1, the coating for the water-absorbing section was uniformly applied to the entire inner surface of the first paper base material using a wire bar, and the water-absorbing section was applied to the end surface of the sheet. A comparative water-absorbent sheet was obtained in the same manner as in Example 1 except that it was cut into pieces.

A water absorption test was conducted on the above Examples and Comparative Examples. As the water absorption test method, the sheet was immersed in water and the amount of water absorbed was measured over time. or,
At that time, the degree of protrusion of the super absorbent polymer from the sheet end surface was also observed. The results are shown in Table 1.

[0017]

[Table 1]

Further, the water-absorbent sheets of Examples 1 to 3 were actually laid on a corrugated cardboard box to carry out a transport test of lettuce to which water was attached. The water-absorbent sheet after the transportation test had a good absorbency of water released from the lettuce, no breakage of the sheet, and no protrusion of the superabsorbent polymer.
The condition of lettuce was good without any damage.

[0019]

The water-absorbent sheet of the present invention has a water-permeable and water-resistant two paper base materials,
It has a water-absorbing section containing a superabsorbent polymer that comes into contact with the inner surface of the one paper substrate, and a water-resistant adhesive is used to cover the water-absorbing section. Since it is provided so as to be embedded in the water resistant adhesive so as to be more inward, and the water absorbing section is adhered so as not to protrude or be exposed to the outside even in the end face in the thickness direction. In addition, when packaging foods or the like that release water or water vapor, or when used during transportation, it is possible to quickly absorb the water generated from the foods and the like without breaking the sheet and protruding the superabsorbent polymer, and thus the freshness. It has an excellent effect of not impairing

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a water absorbent sheet of the present invention.

FIG. 2 Same as above

FIG. 3 is a sectional view showing an example of a conventional water absorbent sheet.

[Explanation of symbols]

 1 First Paper Base Material 2 Second Paper Base Material 3 Intermediate Layer 4 Water Absorbing Section 5 Water Resistant Adhesive Part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08L 33/00 LHR 7921-4J 39/06 LJY 7921-4J 71/02 LQA 9167-4J 79/02 LQZ 9285-4J // A23B 7/00 9281-4B

Claims (3)

[Claims] 1. A first paper base material and a second paper base material, and an intermediate layer between the two paper base materials, wherein the intermediate layer is arranged so as to contact the inner surface of the first paper base material. And a water-absorbent sheet consisting of a mixture of a super-water-absorbent polymer and a binder, and a water-resistant adhesive part that covers the water-absorbent section by embedding it and joins the inner surfaces of both paper substrates. . 2. The binder is polyethylene oxide,
The water absorbent sheet according to claim 1, which is polyethyloxazoline or polyvinylpyrrolidone. 3. The paper substrate has a Steckigt sizing degree according to JIS P 8122 of 1 second or less, and JIS P 8122.
Wet tensile strength based on 8135 is 0.5 Kgf / 15
The water absorbent sheet according to claim 1, which has a thickness of at least mm.