Heat storage material

Abstract

To provide a heat storage material which poses no risk of liquid leakage and which is superior in shape followability to a heat-retention target, capability for heat storage and release, and durability performance.SOLUTION: A heat storage material includes a gel containing a water-soluble heat storage polymer and a polymer of a monomer component including a (meth)acrylic water-soluble monomer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a heat storage material. [Background technology]

[0002] Heat storage materials that utilize the endothermic and exothermic phenomena that accompany the melting and solidification of substances are known and are used in a variety of applications, such as constant-temperature transportation of goods, air conditioning equipment, and keeping electric vehicle batteries warm.

[0003] With regard to such heat storage materials, Patent Document 1 discloses a gel body in which gel-forming components including a gel-forming polymer containing a carboxylic acid (salt) unit and a crosslinking agent having a metal cation are dispersed in an O / W emulsion formed from a dispersion containing a latent heat storage material and a surfactant, and a dispersion medium containing water and a polyhydric alcohol. Patent Document 2 discloses a heat storage material made of a thermosensitive gel that is composed of a thermosensitive polymer and a solvent and that reversibly changes between hydrophilic and hydrophobic properties at the lower critical solution temperature, with the solvent maintaining a liquid state during the change process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-292993 A [Patent Document 2] International Publication No. 2019 / 194022 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, heat storage materials have been known in which the heat absorbing and releasing agent oil is packaged in a bag, but if the bag is destroyed, it becomes unusable, and there is also the problem that the oil spills and contaminates the surrounding area. In addition, heat storage and releasing polymers have a cohesive force that keeps them solid even above their melting point, which makes the heat storage and releasing agent hard and poor at conforming to the shape of the object to be kept warm. In addition, heat storage beads in which the heat storage material is enclosed inside the beads are sometimes used, but the proportion of the shell (shell) in the heat storage beads is large to hold the heat storage agent, so the heat storage and releasing effect is low relative to the amount used, and furthermore, a binder is used to maintain the shape, such as in a sheet form, which further reduces the heat storage and releasing ability. In addition, heat storage materials are required to be highly durable so that they can be used for a long time.

[0006] An object of the present invention is to provide a heat storage material which is free from the risk of liquid leakage, has excellent conformability to the shape of an object to be kept warm, and has excellent heat storage and release capacity and durability. [Means for solving the problem]

[0007] The inventors have discovered that by making a heat storage material containing a water-soluble heat storage polymer and a gel containing a polymer of a monomer component including a (meth)acrylic water-soluble monomer, it is possible to obtain a heat storage material which is free from the risk of liquid leakage, has excellent conformability to the shape of the object to be kept warm, and has excellent heat storage and release capacity and durability, and have completed the present invention.

[0008] That is, the present invention relates to a heat storage material comprising a water-soluble heat storage polymer and a gel containing a polymer of a monomer component containing a water-soluble (meth)acrylic monomer.

[0009] The water-soluble heat storage polymer is preferably a polyalkylene glycol.

[0010] The water-soluble heat storage polymer preferably has a weight average molecular weight of 100-4,000.

[0011] The content of the water-soluble heat storage polymer is preferably 40 to 95 mass % of the entire heat storage material.

[0012] The monomer component containing a water-soluble (meth)acrylic monomer preferably contains a water-soluble (meth)acrylamide monomer.

[0013] The heat storage material of the present invention is preferably a laminate of nonwoven fabrics.

[0014] The heat storage material of the present invention preferably has a gel hardness of 70 or less as measured at 25° C. using a C-type hardness tester.

[0015] The heat storage material of the present invention preferably has a mass loss of 2% by mass or less after being left at 60° C. for 48 hours. Effect of the Invention

[0016] The heat storage material of the present invention is free from the risk of liquid leakage, has excellent conformability to the shape of the object to be kept warm, and has excellent heat storage and release capacity and durability, and therefore can be used in various applications where heat retention and heat storage materials are required. [Brief description of the drawings]

[0017] [Figure 1] 1 is a photograph showing the result of breaking down the heat storage material 3 obtained in Example 3 to check for leakage of liquid. [Diagram 2] 1 is a photograph of the heat storage material 1 obtained in Example 1 (bottom) and the heat storage material obtained in Comparative Example 1 (top) after heating at 60° C. for 48 hours. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 1.Heat storage material The heat storage material of the present invention is characterized by comprising a gel containing a polymer of a monomer component containing a water-soluble heat storage polymer and a water-soluble (meth)acrylic monomer. The heat-absorbing and heat-generating agent oil packaged in a bag cannot be used if the bag is destroyed, but the heat storage material of the present invention is a material in which a water-soluble heat storage polymer is enclosed between the molecules of a polymer of a (meth)acrylic water-soluble monomer component, and since a bag is not used, leakage due to the destruction of the bag does not occur, and even if the gel is destroyed, leakage hardly occurs. In addition, the heat storage material of the present invention is soft at temperatures above the melting point of the water-soluble heat storage polymer, so it has excellent shape conformability to the target object. Furthermore, the heat storage material of the present invention contains a gel-like (meth)acrylic water-soluble polymer, and can sufficiently retain its shape even if the mass ratio of the gel is 30% or less of the entire heat storage material.

[0019] The water-soluble heat storage polymer is not particularly limited as long as it is a water-soluble polymer that melts and solidifies in the temperature range expected for use, but examples thereof include polyalkylene glycols consisting of polyoxyalkylene having 100 to 4000 carbon atoms, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and block and random copolymers mainly consisting of these; paraffin; olefin; naphthene; aromatics, etc. Among these, polyalkylene glycols consisting of polyoxyalkylene having 200 to 1000 carbon atoms, such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and block and random copolymers mainly consisting of these, are preferred because they dissolve acrylic water-soluble monomers, have high compatibility with water, and are easy to gel.

[0020] The water-soluble heat storage polymer preferably has a weight average molecular weight of 100 to 4000. More preferably, it is 200 to 1000. When the water-soluble heat storage polymer has such a weight average molecular weight, it is liquid at room temperature, so that a gel having excellent flexibility can be produced, and when it hardens at the solidification point, it generates heat, so that the heat retention effect can be more fully exhibited. The weight average molecular weight of the water-soluble heat storage polymer can be measured by gel permeation chromatography under conditions that are usually used for measuring the weight average molecular weight of the polymer to be measured.

[0021] Examples of the (meth)acrylic water-soluble monomer contained in the monomer component containing a (meth)acrylic water-soluble monomer include (meth)acrylamide monomers such as acrylamide, dimethylacrylamide, and isopropylacrylamide; and (meth)acrylic acid monomers such as acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, methylhexyl acrylate, magnesium acrylate, zinc acrylate, calcium acrylate, potassium acrylate, and sodium acrylate, and these may be used alone or in combination.

[0022] The monomer component may contain other monomers in addition to the water-soluble (meth)acrylic monomer. Examples of other monomers include vinyl ester monomers such as vinyl acetate; vinyl amide monomers such as vinyl acetamide; and the like.

[0023] The proportion of the (meth)acrylic water-soluble monomer in the monomer component containing the (meth)acrylic water-soluble monomer is preferably 10% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more, based on 100% by mass of the monomer component.

[0024] The proportion of other monomers than the (meth)acrylic water-soluble monomer in the monomer component containing the (meth)acrylic water-soluble monomer is preferably 90% by mass or less, more preferably 60% by mass or less, even more preferably 40% by mass or less, particularly preferably 20% by mass or less, and most preferably 10% by mass or less, based on 100% by mass of the monomer component.

[0025] By using a crosslinking agent when polymerizing a monomer component containing a water-soluble (meth)acrylic monomer, a network chain polymer gel having a crosslinked structure within the polymer structure can be obtained. Examples of the crosslinking agent include bisacrylamide compounds such as methylenebisacrylamide, diacrylate compounds, dimethacrylate compounds, divinylbenzene compounds, and divinylbiphenyl compounds.

[0026] The amount of the crosslinking agent used is preferably 0.5 to 20.0% by mass, and more preferably 1.0 to 10.0% by mass, based on 100% by mass of the monomer components including the (meth)acrylic water-soluble monomer.

[0027] The heat storage material of the present invention contains a water-soluble heat storage polymer and a polymer of a monomer component containing a (meth)acrylic water-soluble monomer having a network chain structure, and the content of the water-soluble heat storage polymer in the heat storage material of the present invention is preferably 40 to 95 mass% of the entire heat storage material. More preferably, it is 50 to 90 mass%. When the content of the water-soluble heat storage polymer is 50 mass% or more of the entire heat storage material, the heat storage material has a better heat storage and release ability.

[0028] The mass ratio of the polymer of the monomer component containing the water-soluble (meth)acrylic monomer having a network chain structure in the heat storage material of the present invention is preferably 5 to 60 mass% relative to the mass of the entire heat storage material. More preferably, it is 10 to 40 mass%. When the content of the polymer having a network chain structure is 10 mass% or more relative to the mass of the entire heat storage material, the water-soluble heat storage polymer can be more sufficiently confined inside the polymer having a network chain structure, and leakage of the water-soluble heat storage polymer can be more sufficiently prevented.

[0029] The heat storage material of the present invention may contain other components in addition to the water-soluble heat storage polymer and the polymerized product of the monomer components including the (meth)acrylic water-soluble monomer having a network chain structure. Examples of the other components include a crosslinking agent, a polymerization initiator, a polymerization accelerator, a nucleating agent, a dye, and a pigment.

[0030] The content of components other than the network chains of the polymer of the monomer components including the water-soluble heat storage polymer and the (meth)acrylic water-soluble monomer is preferably 5 mass % or less, more preferably 1 mass % or less, based on the total mass of the solid content of the heat storage material.

[0031] The heat storage material of the present invention preferably contains as little hydrophobic components as possible, and the content of hydrophobic components is preferably less than 10% by mass relative to the mass of the entire heat storage material, more preferably 8% by mass or less, and even more preferably contains no hydrophobic components other than the polymer of the monomer component containing the (meth)acrylic water-soluble monomer. The hydrophobic component referred to here means a component having a solubility of 1 g or less in 100 g of water.

[0032] In the heat storage material of the present invention, the gel of the polymerized monomer component containing the (meth)acrylic water-soluble monomer with the water-soluble heat storage polymer incorporated therein preferably has a gel hardness of 70 or less as measured at 25°C using a C-type hardness tester. With such a hardness, the heat storage material of the present invention has better shape conformability to the target object. The gel hardness is more preferably 50 or less.

[0033] One of the preferred embodiments of the heat storage material of the present invention is a laminate of a gel containing a water-soluble heat storage polymer and a polymer of a (meth)acrylic water-soluble monomer component and a porous body such as a nonwoven fabric or a foam. In this way, by placing a porous material such as a highly porous nonwoven fabric or foam in contact with a gel containing a water-soluble heat storage polymer and a polymer of a (meth)acrylic water-soluble monomer component, the gel can be insulated from the outside air and temperature changes of the gel can be suppressed, thereby further improving the heat retention and cold insulation effect of the heat storage material.

[0034] When the heat storage material of the present invention is a laminate of a gel containing a water-soluble heat storage polymer and a polymer of a (meth)acrylic water-soluble monomer component and a porous body, it is sufficient that a laminate structure with the porous body is formed in at least a part of the gel, but in order to more fully exert the effect of arranging the porous body, it is preferable that the area ratio of the part covered with the porous body to the entire gel surface is 30% or more, and more preferably 50% or more.

[0035] The porous body is not particularly limited, and examples thereof include polyester nonwoven fabric containing polylactic acid, etc., polyolefin nonwoven fabric, polyamide nonwoven fabric, polyaramid nonwoven fabric, polyurethane nonwoven fabric, polyether nonwoven fabric, polythioether nonwoven fabric, etc., organic fiber nonwoven fabric such as polyimide nonwoven fabric, polyetherimide nonwoven fabric, recycled fiber nonwoven fabric, semi-synthetic fiber nonwoven fabric, and natural fiber nonwoven fabric, and inorganic fiber nonwoven fabric such as glass nonwoven fabric, carbon nonwoven fabric, and ceramic nonwoven fabric, and the like. These materials have a shape in which air is separated by cells of 100 μm or less when viewed from one side in the direction in which heat insulation is desired, regardless of whether they have air permeability in the direction in which heat insulation is desired.

[0036] When the heat storage material of the present invention is a laminate of a gel containing a water-soluble heat storage polymer and a polymer of a (meth)acrylic water-soluble monomer component and a porous body, the thickness of the porous body is preferably 0.5 to 100 mm, and more preferably 1 to 50 mm. In this case, the thickness of the gel made of the polymer of the water-soluble heat storage polymer and the (meth)acrylic water-soluble monomer component is preferably 1 to 100 mm, and more preferably 1 to 50 mm. With such a thickness, the heat storage material is not bulky, and the heat insulating effect against the outside air can be more fully exhibited, thereby further improving the heat retention and cold retention effect of the heat storage material.

[0037] The heat storage material of the present invention preferably has a mass loss of 2% by mass or less after being left at 60° C. for 48 hours. More preferably, it is 0.5% by mass or less. A heat storage material with such a small mass loss is preferable because it has excellent durability and can stably exert a heat retention or cold retention effect for a long period of time. The mass loss of the heat storage material after being left at 60°C for 48 hours refers to the mass loss of a heat storage material that has not absorbed moisture due to the moisture in the environment and that has been left at 60°C for 48 hours immediately after being produced by the heat storage material production method described below.

[0038] 2. Manufacturing method of heat storage material The method for producing the heat storage material of the present invention is not particularly limited, but it can be produced by adding a crosslinking agent and a water-soluble heat storage polymer to a monomer component containing a (meth)acrylic water-soluble monomer during the polymerization reaction of the monomer component. In this case, the timing of adding the crosslinking agent and the water-soluble heat storage polymer to the monomer component is not particularly limited, but in order to form a sufficient crosslinked structure in the polymer, it is preferable to add the crosslinking agent to the monomer component before the start of the polymerization reaction.

[0039] When polymerizing a monomer component containing a (meth)acrylic water-soluble monomer, it is preferable to use a catalyst (initiator) for a polymerization reaction or a crosslinking reaction. Examples of the catalyst include peroxides such as ammonium persulfate and benzoyl peroxide, azo compounds such as azoisobutyronitrile and dimethylvaleronitrile, and photopolymerization initiators such as 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone. These catalysts are preferably added to the monomer component as an aqueous solution or aqueous dispersion.

[0040] When using a polyalkylene glycol having a molecular weight of about 200 to 600 as the water-soluble heat storage polymer, in order to prevent supercooling of the monomer component due to the addition of the water-soluble heat storage polymer, a polyalkylene glycol having a molecular weight of about 1000 to 20,000 may be added in advance to the monomer component in an amount of about 0.05 to 5.0% of the polyalkylene glycol having a molecular weight of about 200 to 600.

[0041] (Meth)acrylic water-soluble monomers are used as the monomer components, and the polymerization reaction temperature is not particularly limited as long as the polymerization reaction proceeds, but it is preferably 10 to 100 °C, more preferably 50 to 80 °C. The polymerization reaction time may be appropriately set according to the amount of the monomer component, etc., but it is preferably 5 to 60 minutes, more preferably 10 to 30 minutes. When adding the catalyst as an aqueous solution or aqueous dispersion to the monomer component, it is preferable to continue heating until the water added together with the catalyst evaporates.

Examples

[0042] Examples will be described below, but the present invention is not limited to these examples only.

[0043] The measurement methods for various physical properties are as follows. <Type C hardness> The Type C hardness was measured with an Asker Type C hardness meter or a durometer E. <Heat release point (freezing point)> The heat storage material was placed in an environmental tester, and the freezing temperature was measured with a thermometer. <Heat release amount (heat storage amount)> Measured by DSC.

[0044] Example 1 Solution A was prepared by dissolving 0.033 g of ammonium persulfate, which is a catalyst (polymerization initiator), in 10 g of water, and solution B was prepared by dissolving 0.5 g of methylenebisacrylamide, which is a crosslinking agent, in 6.3 g of dimethylacrylamide, which is a monomer component. Solution A and solution B were mixed, and 25 g of PEG400 (polyethylene glycol with an average molecular weight of 400, freezing point 4 to 8 °C, non-volatile below 50 °C) was added thereto and stirred. The obtained mixed solution was heated to 60 °C and left for 30 minutes to prepare a gel. Then, heating was continued at 60 °C to evaporate water, and about 32 g of heat storage material 1 was obtained. The total heating time at 60 °C was 48 hours.

[0045] Examples 2 to 4 Heat storage materials 2 to 4 were obtained in the same manner as in Example 1, except that the blending amounts of each component were changed as shown in Table 1. Ammonium persulfate was used as the initiator in all of Examples 1 to 4. Similarly, experiments were carried out in Examples 1 to 4 using AIBN (azobisisobutyronitrile) as the initiator, but air bubbles were generated in the completed gel due to the nitrogen gas generated during the initiation reaction.

[0046] Example 5 A heat storage material 5 was obtained in the same manner as in Example 1, except that PEG400 and PEG300, which is a polyethylene glycol having an average molecular weight of 300, were used in combination and the blending amounts of each component were changed as shown in Table 1. In Example 5, ammonium persulfate was used as the initiator.

[0047] Comparative Example 1 A heat storage material of Comparative Example 1 was obtained in the same manner as in Example 1, except that 15 g of water was added to the mixture of liquids A and B instead of 25 g of PEG400 in Example 1. In Comparative Example 1, ammonium persulfate was used as the initiator.

[0048] For the heat storage materials obtained in Examples 1 to 5 and Comparative Example 1, the C-type hardness, the weight of the heat storage material after heating at 60°C for 48 hours, the heat release point (solidification point), and the amount of heat release (amount of heat storage) were measured. The heat storage material was also destroyed to check for leakage. Furthermore, a comprehensive evaluation as a heat storage material was performed based on these characteristics and was indicated with ◯ or ×. The results are shown in Table 1. The C-type hardness needle of the heat storage material of Example 3 did not move at all, so the C-type hardness was rated 0.

[0049] [Table 1]

[0050] From the results in Table 1, it can be seen that the heat storage materials of Examples 1 to 5 have sufficient heat retention performance and durability from the measurement results of the heat release point (freezing point), heat release amount (heat storage amount), and the weight of the heat storage material after heating at 60°C for 48 hours. In addition, from the measurement results of C-type hardness, it can be seen that they have excellent shape conformity to the object to be kept warm. Since the heat storage materials of Examples 1 to 5 are gels in which the water-soluble heat storage polymer is trapped between the molecules of the polymer of the (meth)acrylic water-soluble monomer component, there is no need to worry about liquid leakage. To confirm this, a photograph of the heat storage material of Example 3 that has been destroyed is shown in Figure 1. As can be seen from Figure 1, even in the heat storage material of Example 3, which has the lowest weight ratio of the monomer component in the heat storage material material among Examples 1 to 5, the water-soluble heat storage polymer is completely trapped between the molecules of the polymer of the (meth)acrylic water-soluble monomer component, and there is no liquid leakage at all. On the other hand, the heat storage material of Comparative Example 1, which used water instead of PEG, had a high heat storage and release capacity, but dried up after heating at 60°C for 48 hours, and was inferior in terms of durability. The state in which the heat storage material of Comparative Example 1 was dried after heating at 60°C for 48 hours can be seen from a photograph (Figure 2) comparing the heat storage material 1 of Example 1 (bottom) and the heat storage material of Comparative Example 1 (top) after heating. From these results, it is evident that the heat storage material of the present invention is free from the risk of liquid leakage, has excellent conformability to the shape of the object to be kept warm, and has excellent heat storage and release capacity.

Claims

1. A heat storage material comprising a gel containing a polymer of a water-soluble heat storage polymer and a monomer component containing a water-soluble (meth)acrylic monomer.

2. 2. The heat storage material according to claim 1, wherein the water-soluble heat storage polymer is a polyalkylene glycol.

3. 3. The heat storage material according to claim 1, wherein the water-soluble heat storage polymer has a weight average molecular weight of 100 to 4,000.

4. 3. The heat storage material according to claim 1, wherein the content of the water-soluble heat storage polymer is 40 to 95 mass % of the entire heat storage material.

5. 3. The heat storage material according to claim 1, wherein the monomer component containing a water-soluble (meth)acrylic monomer contains a water-soluble (meth)acrylamide monomer.

6. 3. The heat storage material according to claim 1, further comprising a nonwoven fabric laminated thereon.

7. 3. The heat storage material according to claim 1, wherein the hardness of the gel measured at 25° C. with a C-type hardness tester is 70 or less.

8. 3. The heat storage material according to claim 1, which has a mass loss of 2 mass% or less after being left at 60°C for 48 hours.

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