JP2000178544A - Cold storage material utilizing latent heat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold storage material utilizing latent heat, contg. water, a freezing point depressant and a water absorbing resin which does not show decrease of viscosity, and which is applicable to a long-time, repeated use between cool storage and cooling, without damaging the vessel accommodating the material. SOLUTION: This cold storage material utilizing latent heat contg. water, a freezing point depressant and a water absorbing resin is sealed with a multi- layered film comprising a layered structure of a plastic film (a)/ a metallic foil/ a plastic film (b), wherein the (a) layer is the inner layer, and the (b) layer, the outer layer. The (a) layer is pref. a polyethylene film or a laminate of a nylon film and a polyethylene film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a latent heat storage member in which a latent heat storage material is sealed with a multilayer film. More specifically, the present invention relates to a latent heat storage member that does not cause damage to a sealed container due to a reduction in viscosity of the latent heat storage material due to oxidation and a volume expansion of the latent heat storage material.

[0002]

2. Description of the Related Art Various efficient storage methods of electric power energy have been studied and developed for the purpose of utilizing surplus electric power. For example, development of a latent heat storage material utilizing absorption heat accompanying a phase change such as melting and solidification of a substance serving as a heat medium is one of them. A heat storage material is a material that accumulates heat or cold in a substance and effectively uses the flow of heat when necessary. In particular, a material utilizing heat generation / endothermic reaction mainly due to a phase change of a substance is referred to as a latent heat storage material, and more particularly, a case in which cold heat is stored in advance and then cooled when necessary is referred to as a latent heat storage material. There is no clear distinction. Examples of the latent heat storage material include those using an aqueous solution of an inorganic material such as an inorganic salt or an inorganic hydrate as a refrigerant, and those using an organic material such as paraffin, polyethylene, or polyhydric alcohol as a refrigerant. Inorganic materials have advantages such as higher thermal conductivity and latent heat, smaller volume change, and nonflammability than organic materials.

[0003] A latent heat storage material obtained by adding inorganic salts or the like to water is:
In order to prevent phase separation and to prevent leakage in the event that the container is damaged, a water-absorbing resin is added and used in a gelled state. However, when a latent heat storage material containing a water-absorbent resin is used repeatedly for a long period of time, the water-absorbent resin is decomposed by oxidation, resulting in a decrease in viscosity. In this case, when the container containing the latent heat storage material is broken, the peripheral equipment members may be corroded by the inorganic salts contained therein.

In order to prevent this, the strength of the latent heat storage member is improved by using a non-flexible container made of metal or plastic, or the oxidation of the water absorbent resin is suppressed by adding an antioxidant to the latent heat storage material. (Japanese Patent Laid-Open No. 6-2640)
No. 52) has been devised.

However, in the above-mentioned method using a metal or plastic container (but not a film), it is necessary to provide a space in the container in consideration of the volume expansion of the latent heat storage material. Also, in the method of adding an antioxidant, since the antioxidant does not contribute to latent heat, the amount of heat per unit weight of the latent heat storage material decreases, leading to an increase in cost,
Further, if the latent heat storage material is directly put into the metal container, the metal container is corroded. There is also a method of using a film of polyethylene alone as a flexible container, but there has been a problem that the cold storage material is deteriorated due to the permeation of oxygen gradually over a long period of use. From the above,
It has been desired to develop a latent heat storage member that can withstand repeated use for a long period of time.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide water,
Provided is a latent heat storage member that can withstand long-term use without causing the viscosity of a latent heat storage material containing a freezing point depressant and a water-absorbent resin to be reduced and the container to be damaged by volume expansion of the latent heat storage material. That is.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have found that a multilayer film capable of absorbing volume expansion due to a phase change of a latent heat storage material and sealing the latent heat storage material is provided. By using it as a container, it was found that a latent heat storage member capable of withstanding repeated use for a long period of time without causing a decrease in viscosity of the latent heat storage material due to oxidation of the water-absorbent resin and without damage to the container was obtained, The present invention has been completed.

That is, the present invention provides (1) a latent heat storage material containing water, a freezing point depressant, and a water-absorbing resin, having a layer structure of a plastic film (a) / metal foil / plastic film (b); And (a) a latent heat storage member sealed with a multilayer film in which the (a) layer is an inner layer and (b) an outer layer, (2) the latent heat storage member of (1), which is capable of repeatedly performing cold storage and cooling, (3) (1) the latent heat storage member according to (1) above, wherein the (a) layer is a polyethylene film or a laminate of a nylon film and a polyethylene film;
(4) The latent heat storage member of (1) above, wherein the layer (b) is a nylon film or a polyethylene terephthalate film; (5) the latent heat storage member of (1) above, wherein the metal foil is an aluminum foil; 50-200 μm
(7) the latent heat storage member according to (1) above, which has a total thickness of (7), (7) the latent heat storage member according to (1) above, wherein the multilayer film is composed of structural units of polyethylene film / nylon film / aluminum foil / nylon film; The latent heat storage member according to (1), wherein the latent heat storage member has a surface area of 2000 to 20000 mm ² with respect to a total thickness of the latent heat storage member of 1 mm.

The present inventors have studied the cause of the decrease in the viscosity of the latent heat storage material when the latent heat storage material comprising water, freezing point depressant, and water absorbent resin is repeatedly used for a long period of time. As a result, it has been found that the water absorbing resin, which is one of the constituent units of the latent heat storage material, is oxidized and the crosslinked portion or the main chain is cut, thereby reducing the water absorption. From this, the present inventors have found that a container made of a film capable of absorbing the volume expansion of the latent heat storage material due to the phase change is optimal as the container for the latent heat storage material.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The "container" in the present invention is not particularly limited as long as it can attain the object of the present invention, and is preferably in the form of a bag, box, sphere, ellipsoid, or the like. Is mentioned.

The water used in the present invention includes pure water, ion-exchanged water, tap water and the like.

The freezing point depressants used in the present invention include:
There is no particular limitation as long as it is a water-soluble inorganic or organic material that causes a freezing point drop. Examples of the inorganic material include salts that generate monovalent ions by dissociation. Sodium, sodium carbonate, sodium fluoride, sodium dihydrogen phosphate,
Sodium salts such as sodium formate, sodium acetate, sodium nitrate, sodium chloride, sodium hydroxide, sodium bromide, sodium iodide, potassium nitrate, potassium hydrogen carbonate, potassium hydrogen fluoride, potassium chloride, potassium fluoride, potassium nitrite, iodine Potassium salts such as potassium chloride, tripotassium phosphate, potassium carbonate and potassium hydroxide; ammonium salts such as ammonium bicarbonate, ammonium dihydrogen phosphate, ammonium chloride, ammonium sulfate and ammonium fluoride. Includes glycine, urea, methanol, ethanol and the like. In the present invention, a freezing point depressant suitable for a desired temperature is selected and used, and one or more kinds thereof may be used.

The amount of the freezing point depressant used in the present invention depends on the type of the freezing point depressant, and is not particularly limited as long as it is soluble in water. For example, in the case of sodium chloride, the temperature difference between coagulation and melting is small,
From the viewpoint that the temperature of the cold storage and the temperature of the cooling become close to constant, preferably 5 to 26% by weight, more preferably 18 to 25% by weight.
An aqueous solution having a concentration range of

The water-absorbing resin used in the present invention is resin 1
The water-insoluble resin preferably has a water absorption of 20 g or more per g, has a water absorption function by an osmotic pressure based on a high ion concentration inside the resin, and partially has a three-dimensional crosslinked structure. As the water-absorbing resin used in the present invention, a commercially available water-absorbing resin may be used.For example, starch-based resins such as graft-polymerized starch-based resins, carboxymethylated-type starch-based resins, and graft-polymerized Cellulosic resins such as cellulosic resins, carboxymethylated cellulose resins, synthetic resins such as polyacrylate resins, polyvinyl alcohol resins, polyacrylamide resins, polyoxyethylene resins, isoprene maleic resin, etc. And the like. Specifically, a crosslinked polyacrylate, a self-crosslinked sodium polyacrylate, a starch-acrylonitrile graft copolymer, a starch-acrylic acid graft copolymer, a starch-acrylamide graft copolymer, a vinyl acetate-acrylic acid Saponified ester copolymer, maleic acid-α-
An olefin copolymer, polyN-vinylacetamide (hereinafter, also referred to as PNVA, which may be either a linear or three-dimensional crosslinked product), and a polymer compound obtained by copolymerizing a strongly dissociable sulfonate group; From the viewpoint of water absorption and stability, a crosslinked polyacrylate and a starch-acrylic acid graft copolymer are preferred.

The water-absorbent resin used in the present invention is preferably 0.1 to 0.1% of the total weight of water and freezing point depressant used.
10 to 10% by weight, more preferably 0.5 to 5% by weight.

The latent heat storage material used in the present invention contains water, a freezing point depressant, and a water absorbent resin, and may further contain additives such as a supercooling inhibitor and a pH adjuster.

As the supercooling inhibitor and the pH adjuster,
There is no particular limitation. For example, when sodium chloride is used as a freezing point depressant, examples of the supercooling inhibitor include sodium sulfate, sodium carbonate, and sodium borate. Examples of the pH adjuster include sodium carbonate and sodium borate.

The supercooling inhibitor and pH used in the present invention
The adjusting agent is preferably used in an amount of 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the total weight of the water and the freezing point depressant.

The main role of the layer (a) used in the present invention is to provide a gap between the latent heat storage material and the layer (a) or a layer in contact with the latent heat storage material when the layer (a) is a laminate. Sealing in the absence of oxygen may be mentioned, and another role may be to provide impact resistance.

Examples of the plastic film (a) used in the present invention include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate (hereinafter referred to as PET), polystyrene, nylon, polycarbonate, and ethylene-vinyl alcohol copolymer. (For example, EVAL, Kuraray Co., Ltd.), and films such as ethylene-vinyl acetate copolymer, aluminum vacuum-deposited films, aluminum oxide-deposited laminated films, and ceramics-deposited laminated films. One or more kinds may be used, and a single layer or a laminate may be used.

The layer (a) used in the present invention is a layer in contact with the latent heat storage material, and the presence of oxygen between the film and the latent heat storage material leads to oxidation of the water absorbing resin. For this reason,
When the layer (a) or the layer (a) is a laminate, it is necessary to arrange a sealant layer as a layer in contact with the latent heat storage material. The sealant layer is a layer that seals inside the bag made of a multilayer film, that is, the bag is sealed by this layer, and the invasion of external gas and water vapor from the seam of the bag can be prevented. As the sealant layer, a polyethylene film is preferable among the plastic films (a). The layer (a) may be a single layer or a laminate, and preferably includes a single layer of a polyethylene film and a laminate of a nylon film and a polyethylene film. It also has cold resistance and impact resistance.

When the layer (a) is a polyethylene film, the thickness of the film is 20 to 100 μm, and preferably 50 to 60 μm from the viewpoint of the function as a sealant layer.
It is.

When the layer (a) is a laminate of a nylon film and a polyethylene film, the film thickness of the nylon film is 12 to 37 μm, preferably 15 to 37 μm in terms of strength, and 20 to 1 μm for the polyethylene film.
It is preferably from 50 to 60 μm from the viewpoint of the function as a sealant layer.

The main role of the layer (b) used in the present invention is to provide impact resistance and cold resistance, and the other role is to provide pinhole resistance and abrasion resistance. No.

Examples of the plastic film (b) used in the present invention include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, PET, polystyrene, nylon, polycarbonate, and ethylene-vinyl alcohol copolymer (for example, EVAL, Inc. Films such as Kuraray (registered trademark) and ethylene-vinyl acetate copolymer, aluminum vacuum-deposited films, aluminum oxide-deposited laminated films, ceramics-deposited laminated films, and the like, preferably, nylon films, PET
Films. One or more of these may be used as the plastic film (b), or a single layer or a laminate may be used.

The total thickness of the layer (b) used in the present invention is 10
To 50 μm, preferably 12 μm or more from the viewpoint of strength, and more preferably 30 μm or less from the viewpoint of thermal conductivity. (B)
When the total thickness of the layer is less than 10 μm, pinhole resistance and abrasion resistance decrease, and when it exceeds 50 μm, thermal conductivity decreases.

The main role of the metal foil used in the present invention is to provide a barrier property against water vapor and gas, in particular, to provide a barrier property against oxygen and prevent oxidation. For preventing the decomposition of UV light by ultraviolet rays.

The metal foil used in the present invention is preferably an aluminum foil because it does not transmit water vapor and gas. The thickness of the metal foil is 7 to 25 μm, preferably 9 μm or more in order to ensure sufficient barrier properties against oxygen, and more preferably 15 μm or less from the viewpoint of moldability. Metal foil thickness is 7
If it is less than μm, the barrier properties will decrease, and if it exceeds 25 μm, the moldability will decrease.

The multilayer film of the present invention has a layer structure of plastic film (a) / metal foil / plastic film (b), and may further include other layers. The other layers are not particularly limited as long as they do not affect the effects of the present invention. For example, an adhesive layer is provided between the plastic film (a) and the metal foil and between the metal foil and the plastic film (b). It may be.

The latent heat storage member of the present invention can be obtained by sealing the latent heat storage material using the (a) layer as an inner layer and the (b) layer as an outer layer. In order to achieve the object of the present invention, the multilayer film has a function of preventing oxygen from permeating. When the latent heat storage material is sealed with a multilayer film, the material is deoxygenated so that no oxygen is present, and then sealed with a sealant layer. At this time, a gap may be provided between the latent heat storage material and the sealant layer, and oxygen may be replaced with an inert gas. As the multilayer film of the present invention, preferably, in order from the inner layer ((a) layer) side, a polyethylene film / nylon film / aluminum foil / nylon film;
And polyethylene film / nylon film / aluminum foil / PET film, with polyethylene film / nylon film / aluminum foil / nylon film being particularly preferred. In the use stage,
As the multilayer film in the case where the latent heat storage member is not moved after being installed once, polyethylene film / aluminum foil / nylon film and polyethylene film / aluminum foil / PET film are preferred in order from the inner layer ((a) layer) side. Can be

The total thickness of the multilayer film of the present invention is from 50 to
200 μm, preferably 80 μm or more in terms of strength, moldability of bag (relative to continuous molding by machine)
In view of this, it is preferably 120 μm or less. Total thickness 5
If it is less than 0 μm, the strength is reduced and the material is easily broken,
If it exceeds 200 μm, it will be difficult to continuously form a bag with a machine.

When the multilayer film is a polyethylene film / nylon film / aluminum foil / nylon film, the thickness of each film is 60 μm, 15 μm
m, 9 μm and 15 μm are particularly preferred. In order to form the multilayer film into a bag, it is preferable to reduce the thickness of the multilayer film from the viewpoint of cost. When the thickness of each film is smaller than the above-mentioned value, it becomes difficult to exhibit the film characteristics required for the present invention.

The method of producing the latent heat storage material is not particularly limited. For example, a freezing point depressant, a supercooling inhibitor, and a pH adjuster are added to water in a mixing vessel to a predetermined amount while gradually stirring. After sufficient mixing, there is a method of adding a predetermined amount of a water-absorbing resin while gradually stirring and stirring and mixing, and a method of pouring an aqueous solution in which a freezing point depressant or the like is previously mixed on the resin. The order of adding the cold storage material (eg, freezing point depressant, additive) other than water is arbitrary, and heating to about 50 ° C. is possible to promote dissolution. After the freezing point depressant and the additives are mixed, the mixture may be poured into water.

The multilayer film of the present invention can be produced by a commonly used laminating method such as a wet lamination method, a dry lamination method, a solventless dry lamination method, a hot melt lamination method, an extrusion lamination method, and a co-extrusion lamination method. Can be.

For the latent heat storage member of the present invention, for example, two multilayer films of the same size obtained by the above method are prepared,
(A) A bag is prepared by heat-sealing the three sides so that the layers are on the inner side, and then filling a required amount of a gel-like regenerator material mixed in advance, and suctioning and degassing the inside of the bag to remove the remaining side of the bag. Is heat-sealed. When the latent heat storage member is flat, the relationship between the overall thickness and the surface area is such that the surface area is 2,000 to 20,000 for a thickness of 1 mm.
mm ² is preferred. When the surface area with respect to the thickness of 1 mm is less than 2000 mm ² , the thickness becomes uneven, and a portion containing no latent heat regenerating agent is formed.
If it exceeds ² , it takes time for the entire regenerator to solidify and melt. Alternatively, the bag may be filled with a required amount of cold storage material before adding the water-absorbent resin, and then the necessary amount of the water-absorbent resin may be further added, followed by mixing and stirring in the bag to gel. The amount of cold storage material in the bag at this time is not particularly limited,
It suffices to leave enough capacity to seal the bag after filling. For example, when the size of the bag is A4 size, the filling amount of the cold storage material is 400 to 1600 g (thickness: 5 to 5 g).
20 mm).

The latent heat storage member of the present invention has a eutectic temperature of ± 20.
When repeatedly used for storage and cooling at ℃, it can be used for about 10 years or more.

The latent heat storage member of the present invention comprises a regenerative freezer,
It can be used for refrigerators, showcases, insulated vehicles, cooler box coolers, courier materials for home delivery, and take-away materials for frozen foods and ice cream.

[0038]

The present invention will be described below in more detail with reference to examples. However, the present invention is not limited to the following examples. Production Example 1 The percentages by weight in parentheses indicate the weight ratio of each sample contained in the latent heat storage material. Water (76.7 g, 71.7 wt%), sodium chloride (23.3 g, 21.8 wt%), sodium sulfate (2 g, 1.9 wt%), and sodium borate (1 g, 0.9 wt%) ) Was placed in a beaker and stirred to dissolve. This aqueous solution was mixed with Sunfresh ST-550 (manufactured by Sanyo Chemical Industries, cross-linked polyacrylic acid partially neutralized product) (4
g, 3.7% by weight) while stirring, and slowly stirred so that the inside of the container became uniform. The obtained gel-like latent heat storage material was used in Examples 1 to 3 and Comparative Examples 1 to 3.

Example 1 A multilayer film of nylon (15 μm) / aluminum foil (9 μm) / nylon (15 μm) / polyethylene (60 μm) was prepared by a laminating method, and 150 mm × 2
Two pieces were cut to a size of 10 mm. The two cut multilayer films were overlapped so that the polyethylene layer was on the inner layer side, and heat sealed on three sides to form a bag, and the bag was filled with the above-described latent heat storage material (100 g). The remaining piece of the bag was heat-sealed while being suctioned and deaerated so that no air remained in the bag, thereby obtaining a latent heat storage member. Put the cool storage member in the low temperature thermostat, and set the thermostat to -10 ° C.
And then gradually lower to -50 ° C, then gradually raise the temperature to -10 ° C again as one cycle of 500
After the cycle, the latent heat storage material in the bag was observed. After leaving the latent heat storage member in a thermostat at 50 ° C. for 60 days, the latent heat storage material was similarly observed (acceleration test). Table 2 shows the results.

Examples 2 and 3 and Comparative Examples 1 to 3 Using a multilayer film having the structure shown in Table 1,
A latent heat storage member was manufactured in the same manner as in Example 1. Table 1
The numbers in parentheses in the middle indicate the thickness of each layer (μm). Further, the same test as in Example 1 was performed, and the latent heat storage material was observed. Table 2 shows the results.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

According to the present invention, it is possible to obtain a latent heat regenerator member sealed with a multilayer film which does not cause damage due to volume reduction of the latent heat regenerator material due to oxidation and a volume expansion of the latent heat regenerator material. Thus, a latent heat storage member that can withstand repeated use of cooling can be provided. Thereby, the latent heat storage member of the present invention does not cause damage to peripheral devices due to damage of the container, and a regenerative freezer, refrigerator, showcase, insulated car, cooler for a cooler box, a courier material for courier service, and frozen food. Can be used for applications such as ice cream and other take-away cold insulators.

Claims (8)

[Claims] 1. A latent heat regenerating material containing water, a freezing point depressant, and a water-absorbing resin is mixed with a plastic film (a) /
Including a metal foil / plastic film (b) layer structure,
And a latent heat storage member sealed with a multilayer film in which (a) is an inner layer and (b) is an outer layer. 2. The latent heat storage member according to claim 1, wherein the storage and the cooling can be repeatedly performed. 3. The latent heat storage member according to claim 1, wherein the layer (a) is a polyethylene film or a laminate of a nylon film and a polyethylene film. 4. The latent heat storage member according to claim 1, wherein the layer (b) is a nylon film or a polyethylene terephthalate film. 5. The method according to claim 1, wherein the metal foil is an aluminum foil.
The latent heat storage member according to any one of the preceding claims. 6. The latent heat storage member according to claim 1, wherein the multilayer film has a total thickness of 50 to 200 μm. 7. The multi-layer film is a polyethylene film /
2. The latent heat storage member according to claim 1, comprising a constituent unit of nylon film / aluminum foil / nylon film. 8. A flat latent heat storage member, wherein the thickness of the latent heat storage member is 2000 to 20,000 with respect to the entire thickness of 1 mm.
The latent heat storage member according to claim 1, which has a surface area of the latent heat storage member of ² mm2.