WO2000052112A1

WO2000052112A1 - Cold-storage material with excellent shape stability and process for producing the same

Info

Publication number: WO2000052112A1
Application number: PCT/JP2000/001445
Authority: WO
Inventors: Katsuyoshi Watanabe; Seio Sato
Original assignee: Toyo Eizai Kabushiki Kaisha
Priority date: 1999-03-15
Filing date: 2000-03-10
Publication date: 2000-09-08
Also published as: AU2940400A

Abstract

A cold-storage material with excellent shape stability which is obtained by freezing a composition comprising: 100 parts by weight of a highly water-absorbing resin in which water has been absorbed in an amount of 40 to 150 times by weight the amount of the highly water-absorbing resin on a dry basis; and at least 25 parts by weight of an aqueous polyvinyl alcohol solution having a concentration of 10 wt.% or higher. The process comprises causing a highly water-absorbing resin to absorb water in an amount of 40 to 150 times by weight the amount of the highly water-absorbing resin on a dry basis, separately preparing an aqueous polyvinyl alcohol solution having a concentration of 10 wt.% or higher, subsequently mixing the water-absorbing resin containing water absorbed therein with the aqueous solution to produce a composition for a cold-storage material, and then freezing the resultant composition.

Description

Description Cold storage material with excellent shape stability and method for producing the same

Technical field

The present invention relates to a cold storage material having excellent shape stability, for example, a cold storage material that can be used by hanging it on a wall of a cold storage box. Background art

Conventionally, the most common cold storage material is ice. It has been used for cold storage of fresh foods, ice sacs, ice pillows, etc. for a long time, but its use is limited because it becomes just water after thawing. For this reason, a plastic film bag or the like, which is filled with water and frozen, or a gel formed by using a water-absorbent resin together with water is used. Further, a regenerator material having a configuration in which water droplets are contained in an oily polymer constituting a gel layer is also known. However, these regenerator materials retain their shape when frozen, but only become amorphous after thawing. By the way, considering the cooling system, after cooling by the cooling system in an air-tight and insulated cold storage car or refrigerator, the cooling system may be operated for a long time while cooling is required. In this case, the cooling system is stopped or separated from the cooling system, and the low temperature is maintained by relying on the airtightness and heat insulation of the cool box and cool car. This is due to the cost of maintaining the cooling system.

From this point of view, attempts have been made to use cold storage materials together with cold storage vehicles and cool storages in order to maintain a low temperature with cold storage materials after shutting down the cooling system. The cold storage material used for such applications is thin in order to increase heat transfer efficiency and surface area. It is desirably a meat rectangular shape (it may be a square shape, hereinafter represented by “rectangular shape”).

However, in the case of the above-mentioned conventional cold storage material, the shape after defrosting is indefinite, so that a thin rectangular cold storage material must be placed horizontally and the floor space is limited. In such cases, there was a problem of taking up too much space.

From such a viewpoint, it is desired to develop a cool storage material that can be hung on the wall of a cool box or a cool car, but as described above, the conventional cool storage material has no shape stability. Therefore, the development of a regenerative material with excellent shape stability that can withstand a suspended state even during thawing has been desired.

The present invention has been made in view of the above-mentioned problems of the prior art, and provides a cold storage material having excellent shape stability, for example, capable of maintaining a thin rectangular shape even in a suspended state at the time of thawing. Raised as an issue. Another object is to provide a suitable method for producing such a cold storage material. Disclosure of the invention

The regenerator material of the present invention has a concentration of 10% by mass or more with respect to 100 parts by mass of the superabsorbent resin that has absorbed 40 to 150 times by mass of the weight of the superabsorbent resin at the time of drying. The gist lies in that the composition for a cold storage material containing a vinyl alcohol aqueous solution in a proportion of 25 parts by mass or more is a frozen product. Since the cold storage material of this configuration retains a rectangular shape even after defrosting, it is most suitable as a cold storage material for cold storage and cold storage vehicles. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view for explaining a method of measuring “hip strength”, FIG. 2 is a side sectional view of a refrigerator, and FIG. 3 is a sectional view taken along line AA of FIG. FIG. BEST MODE FOR CARRYING OUT THE INVENTION

The regenerator material of the present invention is a composition for a regenerator material comprising, as essential components, a superabsorbent resin that has absorbed water at a high magnification and an aqueous solution of polyvinyl alcohol (hereinafter abbreviated as PVA) capable of forming a gel by freezing. It is obtained by freezing things. The most important feature of the present invention is that the amount and concentration of the superabsorbent resin, which is an essential component for exhibiting the cool storage effect, and the amount and concentration of the PVA aqueous solution for ensuring the gel strength and shape stability are in the optimal range. It has been decided to.

As a result, it is intended to provide a cold storage material with excellent shape stability in a configuration in which a soft super absorbent resin swelled by absorbing water at a high magnification is held in a solid three-dimensional network of PVA gel. Was completed. The regenerative material of the present invention has shape stability such that it can be hung without any other member (eg, a bag or the like) for stabilizing the shape. In addition, since the water in the superabsorbent resin and the water contained in the PVA gel that have sufficiently absorbed water are frozen, a cold storage effect is exhibited more than conventional cold storage materials. Furthermore, even if a part of water evaporates due to freezing, it can be re-absorbed and re-frozen, and the shape stability of the cold storage material itself can be maintained. It can now be used.

The composition in which the concentration of the aqueous polyvinyl alcohol solution in the composition for cold storage material is 11 to 20% by mass, and the ratio of the aqueous solution of polyvinyl alcohol in the composition for cold storage material is 100 parts by mass of the water-absorbing superabsorbent resin. On the other hand, a configuration of 100 parts by mass or less is a preferred embodiment from the viewpoint of improving the gel strength. When the water absorption of the superabsorbent resin in the composition for a cold storage material is 70 to 120 times the weight of its own weight, the balance between the cold storage effect and the gel strength is optimized.

The composition for a cold storage material may contain 2 to 8 parts by mass of pulp fiber based on 100 parts by mass of the superabsorbent resin that has absorbed water. Shape stability is further improved. In addition, the frozen body of the composition for a cold storage material is covered with one or more sheets. Can be adopted. As the sheet, a metal foil and a Z or breathable material are preferred. With the configuration covered with the metal foil, the shape stability can be improved without losing water during freezing and thawing. On the other hand, if the cold storage material is covered with a breathable material, a material that hinders the heat transfer effect is not used, so that the air storage medium can exhibit the cold storage effect more effectively. Even if the sheet is made of a breathable material, the surface of the superabsorbent resin that has absorbed water is completely or partially covered by the substance that has gelled by freezing. Lose less. By adopting a configuration that is covered with a breathable material such as non-woven fabric and covered with metal foil, the shape retention is enhanced.

The cold storage material comprising the pulp-free type cold storage material composition of the present invention is capable of absorbing water in an amount of 40 to 150 mass times the weight of the superabsorbent resin at the time of drying by the superabsorbent resin, and separately An aqueous solution of polyvinyl alcohol having a concentration of 10% by mass or more is prepared, and then the water-absorbing superabsorbent resin and the aqueous solution of polyvinyl alcohol are mixed to form a composition for a cold storage material. Thereafter, the composition for a cold storage material is frozen. It is preferable to manufacture by carrying out.

In the case of pulp-containing type, prepare pulp fiber dispersion water in which a predetermined amount of pulp fiber is dispersed in a predetermined amount of water, and add water-absorbent superabsorbent resin to this pulp fiber dispersion water to absorb water. Depending on the weight of the superabsorbent resin at the time of drying, between 40 and 150 mass times the weight of the superabsorbent resin, and between 2 and 8 mass per 100 mass parts of the superabsorbent resin after water absorption. Of a pulp fiber in a ratio of 10 parts by mass, and a mixture of the mixture and a separately prepared aqueous solution of polyvinyl alcohol having a concentration of 10% by mass or more were mixed to form a composition for a cold storage material. It is preferable to employ a method of freezing the composition. Hereinafter, the present invention will be described in more detail.

The first essential component of the composition for a cold storage material used to obtain the cold storage material of the present invention is a superabsorbent resin that has absorbed water. Higher water absorption than PVA gel alone This is because the combination of resin and PVA gel has a high cooling effect. The latent heat of fusion of water is about 80 kca 1 / kg, which has a large cold storage effect. The latent heat of cold storage material is more than 60 kca 1 / kg, which is close to the latent heat of water.

Also, the frozen regenerator material of the above composition and a gel (4.5 cm X 3.0 cm X 2 to 2.5 cm each) obtained from a 15% aqueous PVA solution were mixed at 29.5 °. When the temperature change inside these was measured under an atmosphere of C, the time required from 15 ° C to + 5 ° C was longer for the cold storage material of the present invention (142 minutes), The PVA single gel reached +5 in about 80% of the time (111 minutes) of the cold storage material of the present invention. That is, the cold storage effect of the superabsorbent resin was confirmed. The melting point (solidification point) of the cold storage material of the present invention was 0 ° C. If the freezing point is too low, disadvantages such as a long freezing time may occur depending on the performance of the freezer. However, since the cold storage material of the present invention does not have a low freezing point, it can be frozen even in a home freezer. Is high.

In the present invention, as the superabsorbent resin, any of a crushed body, a powder, a fiber and the like can be used, but in consideration of a water absorption ratio and shape retention in a gel, the superabsorbent resin powder (crushed) (Including body shape) is preferred.

The amount of water to be absorbed by the superabsorbent resin is 40 to 150 times the mass of the superabsorbent resin when dried (self-weight). If the water absorption is less than 40 times, a suitable cold storage effect is not exhibited. In addition, since the water absorption is small, the swelling degree of the highly water-absorbent resin is low and it remains in a fine powder form. However, it is difficult to obtain a uniform mixture. On the other hand, if it exceeds 150 times, the strength of the gel body becomes weak, which is not preferable. This is because the strength of the swollen superabsorbent resin itself is weak, free water exists around the swollen superabsorbent resin, weakens the adhesion with PVA, and the adhesive force between the superabsorbent resins increases. Is thought to be due to You. On the other hand, if it exceeds 150 times, water is gradually released from the superabsorbent resin due to repeated freeze-thaw cycles, which is not preferable. A more preferable lower limit of the water absorption capacity is 70 times, and a more preferable upper limit is 120 times.

If water (free water) that can move freely is present on the surface of the swelling particles after absorbing water, even if the mixture (composition) with the PVA aqueous solution is frozen, the PVA gel and the swelling particles may be frozen. Since the adhesive strength is hardly developed, it is preferable to absorb water to a level where free water does not exist even in the above range of water absorption, in consideration of the water absorption limit of the superabsorbent resin.

Specific examples of the superabsorbent resin include a cross-linked polyacrylic acid partially neutralized product, a self-cross-linked sodium polyacrylate, a starch-acrylonitrile graft copolymer or a neutralized product thereof, and a starch-acrylic acid graft copolymer. Or a neutralized product thereof, a vinyl acetate-acrylate copolymer copolymer, an acrylonitrile copolymer or a hydrolyzate or cross-linked product of an acrylamide copolymer, and maleic acid and α-one-year-old olefin copolymer. Can be Among them, easily available general-purpose crosslinked products of partially neutralized polyacrylic acid, self-crosslinked sodium polyacrylate, and starch-acrylic acid graft copolymer can be preferably used.

In the present invention, an aqueous solution of polyvinyl alcohol (PVA) is selected as the second essential component of the composition for a cold storage material, as it has a shape stability that can be gelled by freezing and can be suspended only by a frozen product. did. As a gelling substance, agar, gelatin, lactogenin, agarose, pectin, sodium alginate, carboxymethylcellulose, dextran, konjac mannan, rubbers and the like are known. These can be used alone or cross-linked with aldehydes such as formaldehyde, daltaraldehyde, terephthalaldehyde, amines such as hexamethylenediamine, hydroxyl-containing compounds such as phenol, boric acid, and various polyvalent metal ion-containing compounds. By adding the agent, it gels when cooled. However, the resulting gel is brittle and crosslinked for safety. The use of agents is also not preferred.

On the other hand, the PVA aqueous solution gels by freezing, and forms a gel with very good shape stability that does not break down even when thawed. Therefore, in the present invention, PVA was selected as the gelling substance. If the degree of degradation of PVA is low, a gel having shape stability cannot be obtained. Therefore, it is preferable to select a gel having a degree of degradation of 96% or more. It is more preferably at least 98%, most preferably a completely modified type. It is preferable to select a polymerization degree of 100 or more from the viewpoint of gel shape stability.

The concentration of the PVA aqueous solution is an important factor that affects gel strength. However, those having the above-mentioned high degree of polymerization and high degree of polymerization have a high viscosity when converted into an aqueous solution, so that from the viewpoint of workability, the concentration cannot be too high. In the present invention, in consideration of gel strength and workability, it is necessary to use a PVA aqueous solution having a concentration of 10% by mass or more, and if it is thinner than 10% by mass, a highly swollen superabsorbent resin is retained. It cannot be used as a cold storage material with strong gel strength that can be hung for a long time. As the concentration increases, the gel strength increases. However, from the viewpoint of workability, it is preferable to use one having a mass of 20% by mass or less, and most preferably a 11 to 15% by mass aqueous PVA solution.

The ratio of the superabsorbent resin to the aqueous PVA solution in the composition for a cold storage material must be not less than 25 parts by mass of the aqueous PVA solution based on 100 parts by mass of the superabsorbent resin after absorbing water. If the amount is less than 25 parts by mass, the shape stability effect of the PVA gel cannot be sufficiently obtained, and if water is absorbed again after thawing, the swollen superabsorbent resin may fall apart. In order to obtain a strong gel which can be hung for a long time, the amount is preferably at least 30 parts by mass, more preferably at least 40 parts by mass.

The more PVA aqueous solution, the better the gel strength. However, considering the cold storage effect of the highly water-absorbing resin, the amount of cold storage per unit mass of cold storage material decreases as the amount of PVA gel increases with respect to the amount of superabsorbent resin after water absorption. become. Therefore, the amount of the PVA aqueous solution is preferably 100 parts by mass or less based on 100 parts by mass of the superabsorbent resin after water absorption. More preferably 8 0 parts by mass or less, more preferably 70 parts by mass or less.

Further, when a highly water-absorbent resin having a low water absorption outside the scope of the present invention and a low-concentration PVA aqueous solution are mixed and allowed to stand, the superabsorbent resin absorbs water from the PVA aqueous solution and falls within the range of the present invention. Although it is conceivable that the amount of water absorption may be ensured, the water transfer between the PVA aqueous solution and the superabsorbent resin is not so large, and the desired gel strength cannot be obtained.

The composition for a cold storage material before freezing may contain relatively long fibers and the like in order to obtain further shape stability in addition to the superabsorbent resin and the aqueous solution of PVA. In particular, a water-absorbing fiber having a fiber length of 1 mm or more is preferable. Since the PVA gel and the fibers are entangled with each other to hold the superabsorbent resin, a stronger gel network is obtained. However, it is extremely difficult to uniformly disperse fibers having a long fiber length in a viscous cold storage material composition from the viewpoint of workability. Therefore, fibers with a fiber length of at most 4 mm should be selected. Although ground pulp can be used, defibrated pulp obtained by defibrating a pulp board is preferable. If pulp fibers are added, the amount is preferably 2 to 8 parts by mass based on 100 parts by mass of the water-absorbing superabsorbent resin. If the amount is less than 2 parts by mass, the effect of improving the shape stability by adding pulp fibers is small, and if the amount is more than 8 parts by mass, the workability of the production process of the composition for a cold storage material is extremely poor, which is not preferable. It is more preferably at most 6 parts by mass.

The regenerator material of the present invention has an excellent regenerative effect because the superabsorbent resin that has absorbed water is retained in the gel formed by the freezing of the PVA aqueous solution, and the gel network is maintained even after the frozen matter is thawed. Therefore, it has shape stability that can be suspended. Therefore, it can be used as a cold storage material in the form of a gel. However, considering the ease of handling during manufacturing and use, it is recommended to use a cold storage material covered with a sheet. It is not necessary to cover the entire surface of the cold storage material with the sheet. As the sheet, a gas-permeable material such as a metal foil and / or a non-woven fabric having good heat conductivity is used. In the case of metal foil, the cold storage material does not lose moisture during freezing or thawing. Also, good shape stability is obtained. Since the cold storage material of the present invention has good shape stability, it is not necessary to increase the thickness of the metal foil. If it is too thick, the cooling effect is reduced. Therefore, it is recommended to use those having a size of 100 zm or less, preferably 50 / zm or less. The material of the metal foil is not particularly limited, but an easily available aluminum foil is inexpensive and preferable. Acrylic resin, urethane resin, polyolefin, polyvinyl chloride resin, epoxy resin, etc. are used to increase the durability (such as heat resistance) of aluminum foil, or to provide heat resistance and fingerprint resistance. Coated, laminated or baked aluminum foil may be used.

On the other hand, when a breathable material is used as the sheet, the frozen body can come into contact with the surrounding air without any hindrance, so that the cold storage effect can be effectively exhibited. However, when the composition for a cold storage material is frozen by coating with a breathable material, it freezes and freezes, and when dried, loses some water. However, the loss of moisture is far less than when used as a cold storage material while absorbing water with the superabsorbent resin. This is because the surface of the superabsorbent resin that has absorbed water is entirely or partially covered by the PVA gel. If the cool storage material is used repeatedly, it is advisable to replenish and absorb the water in the thawed cool storage material after use. By reabsorbing water, it can be returned to almost the original mass of the cold storage material. Examples of the breathable material include nonwoven fabrics, fine meshes made of woven fabric, paper, metal, synthetic resin, and the like. In addition, if the gel is coated with such a gas-permeable material and frozen, the gel is entangled with the openings of the gas-permeable material (the gaps between fibers such as non-woven fabric and the mesh of a mesh-like material), thereby improving the shape stability of the gel. .

By selecting the shape of the cold storage material, it is possible to obtain a cold storage material that is rigid enough to stand alone after thawing. Since the cold storage material of the present invention has good adhesion to metal foil, it is possible to produce a large (for example, 40 cm square or more) cold storage material. When using the cold storage material for a long period of time, cover it with a breathable material and then cover it with a bag of non-breathable material such as metal foil. The use of an inverted configuration is recommended. A cold storage material that is large, has good shape stability and easy handling, and has no water loss.

The regenerator material of the present invention includes a good thermal conductive material such as metal powder and metal fiber; an inorganic or organic antibacterial agent such as silver-based, copper-based, and imidazole-based; a fungicide; a preservative; a wood powder, a diatomaceous earth, and a clay. A filler such as kaolin, bentonite, and talc may be added as appropriate. In the present invention, the fibrous superabsorbent resin is not excluded, and any superabsorbent fiber capable of achieving the water absorption ratio specified in the present invention can be used. Since the pattern for freezing the composition for a cold storage material containing an aqueous solution is the most preferable in terms of water absorption, price, etc., the following is a preferred method for producing the composition for a cold storage material and the cold storage material having this pattern. Will be described. There are two types of the above-mentioned composition for cold storage materials: a pulp fiber-free type and a pulp fiber-containing type.

In the case of the pulp fiber-free type, it is not necessary to consider the step of dispersing the pulp fiber, so that the powdery superabsorbent resin absorbs a predetermined amount of water within the range specified in the present invention. A polyvinyl alcohol aqueous solution having a high concentration is prepared, then the water-absorbing superabsorbent resin is mixed with the aqueous polyvinyl alcohol solution, and then the mixture is frozen to produce the cold storage material of the present invention. .

"Mixing" means that the superabsorbent resin after water absorption is embedded in the continuous layer of the PVA aqueous solution. Specifically, a method of mixing and stirring the water-absorbing superabsorbent resin and the PVA aqueous solution in a container, loading the water-absorbing superabsorbent resin into a flat container such as a shallow tray, etc. There is a method of pouring an aqueous solution to integrate the two.

When mixing the water-absorbing superabsorbent resin and the PVA aqueous solution with a beaker or the like, it is preferable to stir the mixture so that bubbles do not enter. Bubbles may enter, but if it is in an appropriate amount, shape stability is not significantly affected, so that it may be frozen as it is, or a known defoaming means may be employed. Make the resulting mixture into a shallow tray, etc. When loaded and frozen, a thin regenerator material is obtained. Alternatively, the mixture may be loaded into a bag-like container made of a metal foil and / or a non-woven fabric and then frozen.

When covering the cold storage material with a sheet-like body, spread the sheet-like body on a tray or the like, load the mixture, and then place the sheet-like body on the tray as an integral part or a separate member for the upper covering part The top surface of the loaded mixture can be covered, and the contents can be taken out of the tray as a tray or as a sheet, and only this can be frozen. When using a breathable material as the sheet-like body, and loading the superabsorbent resin after absorbing water into a tray, etc., and then pouring the PVA aqueous solution, use a nonwoven fabric or other such material spread on a tray. After loading the superabsorbent resin after absorbing water and coating the surface with a breathable material for top coating, pour the PVA aqueous solution uniformly over it and then take it out of the tray together with the breathable material and turn it over It is preferable that the bottom side is used as the front side, and the PVA aqueous solution is poured again from above the air-permeable material on this side to make the mixing state of the two uniform.

In the case of pulp fiber-containing compositions for cold storage materials, it is necessary to disperse pulp fibers with a long fiber length in a viscous mixture, so the following method is recommended. First, the pulp fiber is dispersed in water in excess of a predetermined amount to be absorbed by the superabsorbent resin. This is because pulp fibers are easily entangled and are difficult to disperse unless water is at least 30 times the weight of the pulp fibers. In addition, pulp fibers that have been defibrated in advance may be added to water, or a predetermined amount of pulp board (plate pulp) may be added to water and stirred with a mixer or the like. When the pulp fiber dispersion water containing an excessive amount of water is obtained, a part of the water is removed until the amount of water to be absorbed by the superabsorbent resin reaches a predetermined amount (the mass may be checked). I do. To this, add superabsorbent resin powder that has not absorbed water, stir appropriately with a mixer, etc., and then leave it to absorb water. As a result, a mixture of the superabsorbent resin and the pulp fiber that has absorbed a predetermined amount of water can be obtained. Pulp fiber also has water absorption, and absorbs a small amount of water. Since the water absorption capacity of fat is overwhelmingly large, it does not significantly affect the water absorption capacity of the superabsorbent resin.

Subsequently, a composition for a cold storage material can be obtained by mixing a mixture of pulp fiber and a superabsorbent resin that has absorbed water with a separately prepared aqueous solution of PVA. Since the pulp fiber is contained, the pulp fiber cannot be mixed well without stirring in a container such as a beaker. Therefore, the above-described mixing method of pouring the PVA solution is not suitable for the pulp fiber-containing type. The composition for a cold storage material of the present invention is a mixture of a relatively high-concentration PVA solution and a highly water-absorbent resin that has absorbed water at a high magnification, so that the composition is viscous regardless of the presence or absence of pulp fibers. In addition, the composition has thixotropic properties. Therefore, as described above, unless the water absorption capacity and the amount of the superabsorbent resin and the PVA solution concentration and the amount are controlled within the ranges specified in the present invention, the production efficiency, the shape stability and the cool storage effect are good. Can not be.

The regenerator material of the present invention can be obtained by freezing the composition for a regenerator material at a temperature of not more than freezing point, preferably not more than 110 ° C. In order to quickly exert the cold storage effect, the thickness is preferably as thin as about 3 mm to 30 mm. However, if it is necessary to exert the cold storage effect for a long time, the thickness may be further increased. The size of one cold storage material is not particularly limited. The design can be changed as appropriate according to the size of various cool boxes (including ice boxes, etc.).

Since the regenerator material of the present invention has shape stability that does not collapse even after thawing, it can be used not only when it is used horizontally but also when suspended. In order to use it suspended, for example, it may be suspended in a gel form, or by using a part of a gas-permeable sheet covered with the gel form, or the gel form or its covering may be further suspended. It is possible to adopt a mode of wrapping with metal foil and attaching it to a wall with a mechanical hook-and-loop fastener or an adhesive tape. It is also possible to use a method in which a plurality of cold storage materials are attached to a panel made of FRP, foamed plastic plate, plastic step pole, etc., suspended, and put in a cold storage tank. Also, if you add pulp fiber, Since it can exhibit rigidity to a level that allows it to be self-supporting, it can be obtained by covering it with a breathable material or loading it into a package with a shape like a standing vouch to obtain a self-sustaining cold storage material. It can also be used on the floor. Of course, such a self-sustaining cold storage material can also be used hanging. Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples, and all modifications within the scope of the present invention are included in the present invention. . In Examples, “parts” and “%” mean “parts by mass” and “% by mass”.

Example 1

First, the amount of tap water shown in Table 1 was placed in a beaker, a superabsorbent resin powder (“AQUALIC CA”: manufactured by Nippon Shokubai Co., Ltd.) was added, and the mixture was swollen with water while stirring. At first, absorb water with good agitation so that free water does not exist. As the water absorption and swelling progressed, air bubbles began to enter due to the stirring. The stirring was stopped, and the mixture was allowed to stand for at least 10 minutes to allow sufficient water absorption. Then, a separately prepared 10% aqueous solution of PVA (“Kuraray Povar PVA—117H”: degree of polymerization: 170,000, degree of oxidation: 99.6 mol%: manufactured by Kuraray) was added. A predetermined amount shown in Table 1 was added to a beaker containing the superabsorbent resin having absorbed water. The mixture was gently stirred as little as possible so that air bubbles did not enter, and the water-absorbing and swollen superabsorbent resin was mixed with a PVA aqueous solution to obtain a composition for a cold storage material.

Acrylic resin container (inner size: 205 mm x 94 mm: height: 20 mm) and aluminum foil (thickness: 30; m: 244 mm x 133 mm, four corners cut into squares of 20 mm x 20 mm) ), And the composition for cold storage material (mixture of superabsorbent resin and PVA aqueous solution) was loaded evenly. 200 mm x 90 mm aluminum foil is placed on top, and the composition for the cold storage material together with the metal foil from the acryl resin container Take out the object, place it upside down on a flat plate, and place the flat plate on top of it to freeze the cold storage material flat, and put it in a freezer (-17 to-22 ° C).

Frozen for 24 hours. The frozen regenerator material was removed from the freezer, thawed to remove the aluminum foil, and the shape stability of the gel and the retention of the superabsorbent resin were evaluated based on the following criteria.

• Shape stability (after one freeze / thaw)

◎: Can be hung by picking with two fingers

〇 ··· Can be hung by picking with four fingers

△: Can be hung if sandwiched between both hands

X: If you try to hang it with both hands, the gel collapses and you cannot hang it. • Retention of super water absorbent resin (after freezing and thawing once)

〇: Even if the surface of the gel is rubbed with a fingertip, the superabsorbent resin cannot be removed from the gel.

X: When the surface of the gel is rubbed with a fingertip, the superabsorbent resin comes off the gel. table 1

Ρ V につれて As the amount of aqueous solution decreases, gel shape stability and resin retention It turns out that it is inferior. In the experiment No. 7 in which the water absorption ratio was 200 times, it was found that the extremely swelled superabsorbent resin particles could not be retained by the PVA gel, resulting in poor shape stability and poor resin retention.

Example 2

Instead of aluminum foil, a non-woven fabric (made of polypropylene: basis weight 20 gZm ² ) was used as the sheet. 0.50 g of the water-absorbent resin powder was placed in 50.0 g of tap water, stirred, and allowed to absorb water for 10 minutes or more. A 14 cm x 14 cm non-woven fabric was laid in a frame with an inner size of 10 cm x 10 cm square, and the water-swollen resin was put on the non-woven fabric to make it flat. A nonwoven fabric (9 cm × 9 cm) was placed on the nonwoven fabric, the four-sided extension of the lower nonwoven fabric was folded, and then a 10% aqueous PVA solution was poured over the 10 g nonwoven fabric. The PVA aqueous solution easily permeated from the nonwoven fabric to the swelling resin side. The frame was removed, inverted, and 10 g of a 10% aqueous PVA solution was poured over the nonwoven fabric again. — 17 to 1 22 t: Freezer for 1 day. The obtained regenerator material showed shape stability enough to be suspended with a finger even after thawing. In addition, this regenerator material was able to return its mass to the level before freezing when water was reabsorbed.

The mass loss of the cold storage material of this example during freezing was small. When left in the freezer for 1 day, the mass decreased by 2 to 3 g, but thereafter, it decreased only by 0.5 gZ day. As a comparison, when only the water-absorbing superabsorbent resin was frozen without pouring the PVA aqueous solution, the mass decreased by 2 to 3 g on the first day. Thereafter, the mass continued to decrease by 1.4 gZ days.

Example 3

A composition for a cold storage material having the composition shown in Table 2 was prepared in the same manner as in Example 1. The obtained composition for a cold storage material was directly loaded into the acryl resin box used in Example 1 as flatly as possible to level the surface, and the entire box was covered with a wrap film to cover the periphery. It was left to freeze in a freezer at 22 ° C for 1 day. Mixing and stirring After thawing, the gel was taken out of the box and evaluated according to the following criteria in order to evaluate the workability during loading and loading, and to evaluate properties such as the strength of the gel. The shape stability and the resin retention were evaluated according to the same criteria as in Example 1.

• Workability (experimental ambient temperature 20 to 22 ° C)

A: Low viscosity and easy mixing and stirring. The composition for cold storage materials has self-pelling properties, making it extremely easy to load flat.

〇: High viscosity, but relatively low thixotropy, allowing mixing and stirring. The composition does not have self-pelling properties, but is easy to load flat.

Δ: High viscosity and large thixotropy. Also difficult to load flat

(Therefore, some voids are observed in the gel body after thawing).

X: High viscosity and extremely high thixotropic properties, making it extremely difficult to load flatly (for this reason, voids are observed in the gel body after thawing).

XX: Can be stirred, but a lot of air is mixed in by mixing, and the composition becomes creamy.

• Resin disintegration (frozen and thawed once)

〇: The gel body is elastic when pressed with a finger, and elastically recovers to its original shape when released.

X: When the gel body is pressed with a finger, the swelling particles of the water-absorbent resin near the pressed part are separated (separated) from the gel body and collapse.

• Strength of the waist (after freezing and thawing twice)

When the gel body is extruded 40 mm from the top edge of the desk (longitudinal direction of the gel body: a in Fig. 1), how much the gel body hangs down from the desk top surface, and how long it hangs down (b in Fig. 1) ) Was measured. The length of the sag was defined as the “strength of the waist” of the gel body, and the subtle differences in shape stability were quantified. The smaller the value, the stronger the stiffness. The better the shape stability. The value of the waist strength is reduced by repeated freezing and thawing (the waist becomes stronger). Table 3 shows frozen → thawed Freeze-thaw and freeze-thaw are shown twice.

Table 2

*: Mass ratio of PVA aqueous solution to 100 parts by mass of resin after water absorption

Table 3

*: Hanging length in 40mm extrusion test From Tables 2 and 3, it can be seen that the workability is poor in Experiments Nos. 8 and 9 having a low water absorption capacity. Experiments No. 10 to 14 all within the scope of the present invention exhibited excellent characteristics.

Example 4

The gel body after thawing was evaluated in the same manner as in Example 3 except that the composition for a cold storage material having the composition shown in Table 4 was used. Table 5 shows the results. Table 4

*: Mass ratio of PVA aqueous solution to 100 parts by mass of resin after absorption

8 Table 5

*: Hanging length experiment in 40 mm extrusion test No. 15 to 18 are experimental examples in which the ratio of resin to water in the entire system was the same, and the water absorption ratio and the concentration of the PVA aqueous solution were changed. There is a clear difference in waist strength, indicating that a PVA concentration of 10% or more is required to reduce this value to 20 mm or less. Experiment Nos. 19 to 22 are the results of examining the amount of the PVA aqueous solution. When the amount of the aqueous solution was smaller than the specified amount of the present invention (25 parts by mass or more), the continuous phase of the PVA aqueous solution could not be formed in the step of preparing the composition for the cold storage material. In addition, the shape stability after thawing was inferior, and it fell apart without sagging, so the waist strength could not be measured. Even at No. 20, the workability was poor, and the obtained gel body exhibited some degree of shape stability, but was inferior in resin retention, resin disintegration, and stiffness.

Example 5

A cold storage material composed of a composition for a cold storage material containing pulp fibers was examined. table The amount of pulp fiber (pulp board) shown in Table 6 and the amount of water in excess of the amount shown in Table 6 were placed in a mixer and stirred for 2 minutes to defibrate the board pulp. A portion of the water is discarded to obtain the amount of water shown in Table 6, and the unabsorbed superabsorbent resin powder is added thereto, and the mixture is stirred for about 15 seconds. Water. Transfer the mixture of resin and pulp fiber after water absorption to a beaker, add a separately prepared PVA aqueous solution (amount and concentration shown in Table 6), stir as much as possible to avoid bubbles, and use it for cold storage materials. A composition was prepared.

The obtained composition for a cold storage material was frozen and thawed in the same manner as in Example 3, and evaluated. In this experimental example, the waist strength was measured by setting the extrusion distance (a in Fig. 1) to 80 mm for the gel after freezing and thawing once. Since the system containing pulp fiber had more excellent shape stability, resilience and self-sustainability were evaluated according to the following criteria. The surface tactile sensation was also evaluated. The tactile sensation on the surface is a sensual indication of the feeling of sliminess and stickiness, and is related to the adhesion to the aluminum foil when the outermost layer is provided as a cold storage material. The results are shown in Table 7. • Rebound (frozen and thawed twice)

：: When the gel body is placed horizontally on the palm, both ends of the gel body are slightly radiused. 〇: Both ends of the gel body are slightly lowered.

Δ: Both ends of the gel body were considerably lowered.

X: Both ends of the gel body hang down.

• Independence (after freezing and thawing twice)

：: The gel body stands upright and the center part is self-supporting by lightly supporting both sides of the center with one finger.

〇: Barely independent.

X: Not independent.

* Surface feel (after freezing and thawing once)

〇: There is a slimy feeling and a sticky feeling. Δ: No slimy feeling and no sticky feeling.

X: Great stickiness (water separation).

Table 6

*: Mass ratio of PVA aqueous solution to total 100 parts by mass of resin and pulp fiber after water absorption

Test No Surface shape Resin Resin

Workability Development Independence Waist strength * Tactile stability Stability Retention

23 O Δ ◎ 〇〇〇 o 34. 0

24 〇 Δ ◎ 〇〇〇〇 36. 5

25 room ◎ 〇〇〇〇 35.5

26 〇 ◎ ◎ 〇〇 △ X 44.3

27

CO 〇〇〇〇 Δ X 39.8

28 〇〇 ◎ 〇〇〇〇 33. 8

29 〇 ◎ ◎ 〇〇 Δ X 46.5

30 〇 X ◎ 〇〇 X X 51.0

31 〇 △ ◎ 〇〇 △ X 46.0

32 〇 Δ ◎ 〇〇 △ X 39.5

33 〇〇 ◎ ο 〇 Δ X 46.3

*: Hanging length in 80mm extrusion test;

In this experiment, the amount of pulp fiber was unified to 4 parts by mass with respect to 100 parts by mass of water absorbed by the superabsorbent resin. Of the experiments No. 23 to 33, No. 30 is a comparative example. The water absorption capacity exceeds the specified range of the present invention. Although pulp fiber is included, shape stability is exhibited, but the stiffness is significantly inferior to other experimental examples (Examples of the present invention). The touch on the surface was too sticky.

Example 6

The regenerator material of the present invention was set in a small refrigerating refrigerator (forced convection type) with a built-in freezing device, and its regenerative effect was studied. The composition of the regenerator material is basically the same as that of Example 2, and it is 275 g of water, 27.5 g of superabsorbent resin, and 100 g of 11% PVA aqueous solution. After placing the aluminum foil and then the non-woven fabric in the wooden frame, loading the composition for cold storage material, placing the non-woven fabric and the aluminum foil, freezing them, and fixing the aluminum foil on all sides with adhesive tape, 500 mm width 10 pieces of sheet-shaped regenerative material having a length of 100 mm and a thickness of about 8 mm were prepared.

FIG. 2 is a sectional side view of the refrigerator, and FIG. 3 is a sectional view taken along line AA of FIG. The right side of Fig. 2 is the front of the refrigerator 1, 2 is a freezing device, 3 is a cooling fan (4 units), 4 is a cold storage material layer, 5 is a space, and 6 is a cold storage room (luggage room). As can be seen from FIG. 3, the sheet-like cold storage material 41 is arranged in five rows, two on the left and right sides of the cold storage material layer 4. The cool air is sent through the fan 3 to the cool room 6 (arrow in Fig. 2). Cold chamber 6 is the height H is 1 4 5 0 mm, the width W is 1 1 5 0 mm, the depth-out D is about 1 3 0 0 mm, its volume, 2. a 2 m ^3.

In conducting the cold storage effect study experiment, the refrigerators were placed in a constant temperature room at 32 ° C so that they would be close to the actual use conditions. After freezing, the sheet-like cold storage material 41 that has been thawed is set in the cold storage material layer 4, then the freezing device 2 is operated for 8 hours, and the cold storage material 41 is stored at 110 ° C. Frozen. Subsequently, the operation of the freezing device 2 is stopped, and when the temperature of the cool room 6 exceeds + 5 ° C, cool air is sent to the cool room 6 by the cooling fan 3. Then, the temperature change of the cool room 6 in a sealed state was measured.

The temperature in the cool room 6 was maintained at + 5 ° C or lower for 16 hours, and then the temperature was gradually increased (about 1.6 ° C for Z hours). It was confirmed that the cool storage effect of the cool storage material was exhibited for more than 16 hours. Industrial applicability

The regenerative material of the present invention utilizes a gel, but has excellent shape stability after thawing, so that it can be used alone by hanging. Therefore, it can be used in a plate shape that is thinner and has a larger surface area than a conventional cold storage material using a gel that is sealed in a non-breathable case with high thermal insulation and becomes amorphous after thawing. Therefore, the air contact area per unit mass of the cold storage material can be increased, and the center of the cold storage material can be frozen in a short time, and the cooling efficiency as the cold storage material is also high.

Normally, even if the amorphous gel itself is coated with a sheet-like material such as nonwoven fabric or aluminum foil which cannot hold the gel in a rectangular shape, the regenerator material of the present invention has a rectangular shape even after thawing. Since it can be maintained, it can be arranged vertically in a narrow cold storage material zone, or hung on a wall using hook members ゃ mechanical surface fasteners. Therefore, it is useful, for example, as a cold storage material for cold storage vehicles and cold storage. Further, according to the method for producing a cold storage material of the present invention, a cold storage material having excellent gel strength can be efficiently produced.

Claims

The scope of the claims

1. With respect to 100 parts by mass of the water-absorbent resin having absorbed 40 to 150 mass times its own weight of the water-absorbent resin at the time of drying, an aqueous solution of polyvinyl alcohol having a concentration of 10% by mass or more is added to 250 parts by mass. A cold storage material having excellent shape stability, characterized in that the composition for a cold storage material contained in a proportion of at least part by mass is frozen.

2. The cold storage material according to claim 1, wherein the concentration of the aqueous polyvinyl alcohol solution in the composition for a cold storage material is 11 to 20% by mass.

3. The method according to claim 1 or 2, wherein the ratio of the aqueous polyvinyl alcohol solution in the composition for cold storage material is 100 parts by mass or less based on 100 parts by mass of the superabsorbent resin that has absorbed water. Cold storage material as described.

4. The cold storage material according to any one of claims 1 to 3, wherein the water absorption of the superabsorbent resin in the composition for cold storage material is 70 to 120 times by mass of its own weight.

5. The composition for a cold storage material according to any one of claims 1 to 4, wherein the composition contains 2 to 8 parts by mass of pulp fiber based on 100 parts by mass of the superabsorbent resin that has absorbed water. The cold storage material as described in or.

6. The cold storage material according to any one of claims 1 to 5, wherein the frozen body of the composition for a cold storage material is covered with at least one sheet.

7. The cold storage material according to claim 6, wherein the sheet is a metal foil.

8. The cold storage material according to claim 6, wherein the sheet is a breathable material.

9. A method for producing a cold storage material as set forth in any one of claims 1 to 4, wherein the water is 40 to 150 times the weight of the weight of the superabsorbent resin when dried. In addition to absorbing the water-absorbing resin, a polyvinyl alcohol aqueous solution having a concentration of 10% by mass or more is separately prepared. Then, the water-absorbing superabsorbent resin and the polyvinyl alcohol aqueous solution are mixed to obtain a composition for a cold storage material. Then, the method for producing a cold storage material is characterized by freezing the composition for a cold storage material.

10. The method for producing a cold storage material according to claim 5, wherein a pulp fiber dispersion water in which a predetermined amount of pulp fiber is dispersed in a predetermined amount of water is prepared. By adding a water-absorbent resin that has not yet absorbed water to the water, the water-absorbent resin absorbs 40 to 150 times the weight of the weight of the water-absorbent resin at the time of drying. A mixture of pulp fiber in a ratio of 2 to 8 parts by mass with respect to 100 parts by mass of the water-absorbent resin is prepared, and this mixture is mixed with a separately prepared aqueous solution of polyvinyl alcohol having a concentration of 10% by mass or more. A method for producing a cold storage material, comprising: forming a composition for a cold storage material; and subsequently freezing the composition for a cold storage material.