JPH05117642A - Cold reserving material - Google Patents

Abstract

PURPOSE:To prepare a water-base, liq. cold reserving material which exhibits a good fluidity even at low temp., stores latent heat, and is used for cooling various substances. CONSTITUTION:The title material is prepd. by using, as the main component, microcapsules comprising aminoplast resin shells and a water-immiscible, core compd. which undergoes a phase change and melts at 0-15 deg.C. Water-immiscib1e paraffins, fatty acids, and esters are examples of the compd.; a melamine resin and a urea resin, examples of the resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold storage material used for cooling a substance, and more specifically, an aqueous liquid cold storage material having good fluidity even at low temperature and capable of retaining latent heat of high density. Regarding materials The cold accumulating material according to the present invention can be used as a cooling material for air conditioning, or as a freshness maintaining material such as a portable cold insulating material or a fresh food product by holding it in various packaging materials or containers.

[0002]

2. Description of the Related Art Ice is the most commonly used regenerator material on a daily basis, and when water undergoes a phase change into ice, approximately 80 kcal /
It can store kg of cold latent heat, and is used in many ways in daily life, such as keeping fresh food products fresh and used for ice pillows.

Generally, a method of storing heat by utilizing latent heat associated with a phase change of a substance has a high density of a large amount of heat energy in a narrow temperature range including a melting point, as compared with a method utilizing only sensible heat without phase change. Since it can be stored at a low temperature, not only the heat storage material capacity can be reduced, but also a large temperature difference does not occur even if the heat storage amount is large, so that there is an advantage that heat loss can be suppressed to a small amount.

Conventionally, the following types of heat storage materials have been known as a latent heat type heat storage material that accompanies a phase change, particularly a phase change between a liquid and a solid. (1) Inorganic water containing a large amount of crystal water such as calcium chloride hexahydrate, sodium sulfate decahydrate, sodium hydrogen phosphate decahydrate, sodium thiosulfate pentahydrate, nickel nitrate hexahydrate, etc. Japanese products (2) Hydrocarbon compounds such as petroleum paraffin and waxes, fatty acids such as caprylic acid, lauric acid and stearic acid

In order to improve the heat exchange efficiency of these various heat storage materials, means for microencapsulating the heat storage material has been proposed (for example, Japanese Patent Laid-Open Nos. 62-1452 and 62-62).
-45680, 62-149334, 62-225241, 63-115718, 63-217196, and JP-A-2-2580.
No. 52).

Among the microencapsulation methods disclosed in the above publication, the microencapsulation method generally called an interfacial polymerization method can encapsulate either an aqueous substance or a substance immiscible with water. However, when water or an inorganic hydrate of (1) is used as the core substance (for example, JP-A-61-2192785), the dispersion medium of the capsule is an organic solvent immiscible with water (for example, Since various plasticizers such as cyclohexane, toluene, carbon tetrachloride, chloroform, and butyl phthalate are usually used, only water-in-oil type microcapsule dispersions can be obtained. Some desolvation step is required.

In addition, the method generally referred to as the in-liquid drying method has an advantage that microcapsules containing a water-soluble substance can be directly obtained in an aqueous dispersion system, but has a low boiling point as a solvent for a polymer compound as a film material. The organic solvent (for example, benzene, ether, chloroform, etc.) needs to be removed, and the stability of the microcapsule film also needs to be improved.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in the encapsulation method for heat storage and to obtain a cold storage material having the following effects.

[0009] First, to obtain a water-based cold accumulating material containing a strong microcapsule as a main component, which can be freely mixed with an aqueous antifreeze liquid and various inorganic salts and is not broken even in long-term use. .. This is difficult to manufacture by microcapsules of an aqueous substance by the interfacial polymerization method or a submerged drying method.

Secondly, even if the cold storage material is cooled to a temperature lower than the melting point of the phase change compound contained in the microcapsules, if the temperature is higher than the melting point of the microcapsule dispersion medium, the fluidity of the cold storage material itself. The purpose is to obtain a cold storage material that is always in a liquid state that does not change at all. This is a characteristic that cannot be obtained by the inorganic or organic heat storage material alone.

[0011]

Means for Solving the Problems As a result of studies to achieve the above object, the present inventor has found that a compound having a phase change immiscible with water and having a melting point of 0 to 15 ° C. is coated with an aminoplast resin film. By using the above-mentioned microcapsules as the main component of the cold storage material, it has become possible to obtain a cold storage material that can achieve the above-mentioned object. Next, the details will be described.

Generally, the temperature range in which the effect of the regenerator material is actually felt differs depending on the temperature of the outside air, the form and amount of the regenerator material, but it is judged that about 20 ° C. or less is necessary, and more notably A temperature of about 15 ° C. or lower is considered to be a preferable temperature to realize the effect. In addition, considering the freshness of fresh foods and the like, prevention of freezing, and appropriate skin feel, it is judged that it is most effective to set 0 to 15 ° C as the temperature to be kept cold.

As the compound having a melting point in this temperature range and having a phase change immiscible with water, tetradecane, p-chlorotoluene, 1-ethoxynaphthalene, o-anisidine, 1-
Iodonaphthalene, o-dibromobenzene, cyclohexane, benzene, o-bromophenol, d-phencon,
Dimethyl carbonate, dibutyl sebacate, diethyl cinnamate, oleic acid, 3,3-dimethylbiphenyl, dibromoethane, etc. can be used, but especially tetradecane has a heat of fusion of about 50 kcal / kg if it has a purity of 98% or more. The compound having a phase change is mentioned as the most preferable compound. These compounds accompanied by phase change may be used alone or in combination of two or more kinds, and if necessary, metal powder, various pigments may be added, and thermal conductivity and specific gravity adjusting material may be added. ..

The phase change compound used in the present invention is encapsulated using a suitable microencapsulation method. As a method for microencapsulating a water-immiscible liquid, a coacervation method using gelatin and an anionic polymer, an interfacial polymerization method, an in-situ method, a method using yeast (Japanese Patent Laid-Open No. 63- However, microcapsules with higher robustness are required for long-term use as a cold storage material, and for that purpose, aminoplast resin by in-situ method is used. It is most desirable to use microcapsules for coating.

The aminoplast resin used in the present invention refers to a resin obtained by a polymerization reaction of an amino compound and formaldehyde, and specifically, urea-formalin resin, melamine-formalin resin, benzoguanamine-formalin resin. , Melamine-
Formalin resin is mentioned as the most preferred aminoplast resin. Microencapsulation with these aminoplast resins is generally obtained by the following procedure. 1. A step of preparing an aminoplast resin precondensate. 2. A step of emulsifying and dispersing a compound with a phase change in an aqueous dispersant solution. After adding the initial condensate of 3.1 to the emulsified dispersion of 2.
A step of forming a film around compound particles accompanied by phase change by heating and stirring.

1. As a method for producing the aminoplast resin initial condensate, the melamine resin is mixed with melamine powder and formalin (37% aqueous formaldehyde solution) at a molar ratio of 1: 1 to 1: 4. A weakly alkaline water-soluble melamine-formalin initial condensate can be obtained by heating above about 60 ° C.

The amount of aminoplast resin added is in the range of about 1 to 30 (wt / wt)%, preferably 5 to 20%, based on the weight of the compound accompanied by the phase change. If the amount added is less than this range, the strength as a microcapsule is insufficient, and conversely, if it is more than this range, the ratio of the amount of film material in the cold storage material increases, and the cold storage efficiency decreases, which is not preferable.

2. Specific examples of the dispersant include acrylic acid copolymer, ethylene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, styrene-maleic anhydride copolymer, butadiene-maleic anhydride copolymer. Coalescence, vinyl acetate-maleic anhydride copolymers, and their sodium salts are used. These dispersants are added in the range of 1.0 to 20.0 (wt / wt)% with respect to the dispersant aqueous solution.

The pH of the aqueous dispersant solution is set to the pH at which the film-forming reaction of the aminoplast resin proceeds most efficiently, but it is generally on the acidic side of pH 2 to 7, preferably pH.
It is adjusted to the range of 3 to 6.

In the step of emulsifying the compound with phase change, the compound with phase change is added to the aqueous dispersant solution, and the mixture is stirred using a commercially available emulsifying and dispersing device until the emulsified particle size becomes about 1 to 50 μm. It is done by

Next, the aminoplast resin initial condensate prepared above is mixed with an emulsion of a compound accompanied by a phase change,
By heating and stirring to polymerize the initial condensate around the emulsified particles, a water-insoluble resin is formed to obtain microcapsules containing a compound accompanied by a phase change. The heating temperature at the time of encapsulation is 40 to 100 ° C., preferably 60 to 80
Stirring is performed at a temperature in the range of 30 ° C. for 30 minutes to 4 hours.

The microcapsule dispersion liquid containing the compound accompanied by the phase change thus obtained can achieve the object of the present invention as it is, but if necessary, ethylene glycol, propylene glycol, various inorganic salts, antiseptic Agents, various anti-deterioration agents, thickeners, colorants, dispersion aids,
A specific cold storage material is obtained by adding a specific gravity adjusting material, a wetting material and the like.

The higher the proportion of the microcapsules in the regenerator material, the higher the latent heat amount, which is preferable, but 20 to 70 (wt / wt)%, preferably 40 to 6 to maintain good fluidity.
It is preferable to set in the range of 0 (wt / wt)%. If the content is above this range, the viscosity of the cold storage material will increase and the fluidity will be poor, and if it is below this range, the cold storage effect will be poor, which is not preferable.

[0024]

EXAMPLES The present invention will be described in detail below with reference to examples. The present invention is not limited to the embodiments.

Example 1 [Preparation of initial condensate] To 5 g of melamine powder, 6.5 g of 37% aqueous formaldehyde solution and 10 g of water were added to adjust the pH to 8.
Then, the mixture was heated to about 70 ° C. to obtain an aqueous melamine-formaldehyde initial condensate solution.

[Emulsification step] 5% adjusted to pH 4.5
N-tetradecane (melting point: about 5 ° C., heat of fusion: 50.8 kcal / kg) as a compound accompanied by a phase change in 100 g of a sodium salt aqueous solution of styrene-maleic anhydride copolymer.
80 g was added with vigorous stirring, and the particle size was 10 μm.
Was emulsified until.

[Encapsulation Step] The whole amount of the above melamine-formaldehyde initial condensate aqueous solution was added to the above emulsion and stirred at 70 ° C. for 2 hours, and then the pH was adjusted to 9 to complete the encapsulation.

[Preparation of Regenerator Material] A hard polyethylene bag was filled with a mixed solution of 100 parts of the obtained microcapsule dispersion liquid and 30 parts of ethylene glycol to obtain a portable regenerator material. When this cold storage material was left in a domestic freezer for about 1 hour, the cold storage material did not solidify, and the cold storage effect continued for a long time.

[Measurement of heat of fusion] The heat of fusion of this regenerator material was measured by a differential scanning calorimeter (DSC7 manufactured by Perkin Elmer, USA).
Type), a heat of fusion of 18 kcal / kg was observed in the range sandwiching the melting point of n-tetradecane.
In addition, the heat of fusion of this cold storage material was measured at -20 to 30 ° C.
Within the range, good fluidity was always maintained.

Example 2 [Preparation of initial condensate] To 10 g of melamine powder was added 12.9 g of 37% aqueous formaldehyde solution and 10 g of water, and the pH was adjusted.
Was adjusted to 8 and then heated to about 70 ° C. to obtain a melamine-formaldehyde initial condensate aqueous solution.

[Emulsification step] 5% adjusted to pH 3.5
N-pentadecane (melting point: about 10 ° C, heat of fusion: 40 kcal / kg) as a compound accompanied by a phase change in 100 g of an aqueous sodium salt solution of ethylene-maleic anhydride copolymer
0 g was added with vigorous stirring, and the mixture was emulsified until the particle size became 5 μm.

Thereafter, the initial condensate and the emulsion were mixed and encapsulated in the same manner as in Example 1, and 30 parts of ethylene glycol was added to 100 parts of the obtained microcapsule dispersion to obtain a cold storage material. It was

[Measurement of heat of fusion] The heat of fusion of this regenerator material was measured by using a differential scanning calorimeter of the same type as in Example 1, and found to be 14 kcal / in the range sandwiching the melting point of n-pentadecane.
A heat of fusion of kg was observed. Further, in the range of −20 to 30 ° C. at which the heat of fusion measurement of the present cold storage material was performed, good fluidity was always maintained.

[0034]

As is apparent from the examples, the regenerator material according to the present invention is capable of accumulating a large amount of cold heat in the range sandwiching the freezing point of the compound accompanied by the phase change, and the compound It becomes possible to obtain an aqueous liquid regenerator material having a high fluidity even at a temperature below the melting point, and it is useful as a regenerator material.

Claims (2)

[Claims] 1. A regenerator material comprising, as a main component, microcapsules encapsulating a compound with a phase change, the compound with a phase change is a compound which is immiscible with water and has a melting point in the range of 0 to 15 ° C. A cold storage material characterized in that the film of the microcapsule is made of aminoplast resin. 2. The regenerator material according to claim 1, wherein the compound accompanied by a phase change is tetradecane.