Heat storage material and heat storage film

Abstract

[Problem] The present invention provides: a new heat storage material which can be easily formed into a film and can impart transparency; and a heat storage film. [Solution] The present invention pertains to a heat storage material which contains a comb polymer having an amorphous main chain and crystalline side chains, and in which the glass transition temperature of the comb polymer is higher than the melting point of the crystalline side chains. The present invention also pertains to a heat storage film containing such a heat storage material.

Description

Heat storage materials and films

[0001] The present invention relates to a heat storage material and a heat storage film.

[0002] In recent years, from the viewpoint of reducing carbon dioxide emissions, etc., active research and development efforts have been made to effectively utilize thermal energy in building materials such as wall materials, floor materials, ceiling materials, roof materials, etc. Latent heat storage materials are known as one of the materials for this purpose.

[0003] Latent heat storage materials are materials that can store thermal energy by utilizing the phase change of a material, such as from solid to liquid. Unlike thermal insulating materials, latent heat storage materials can efficiently utilize heat because the stored heat and cold can be used as thermal energy when needed. In particular, latent heat storage materials that utilize the phase change from solid to liquid are relatively easy to handle and can store a large amount of heat, so a variety of materials are known, including organic materials such as block copolymers and paraffins, and inorganic materials such as sodium sulfate salts.

[0004] For example, Non-Patent Document 1 discloses that the thermal efficiency of a building is improved when double glazing is used in which paraffin, a latent heat storage material, is filled between the panes of glass.

[0005] Non-Patent Document 2 reports that comb polymers of polyalkylacrylamide have crystallinity in the alkyl side chain portion, and that the temperature at which the crystals of the alkyl side chains melt (melting point) is lower than the glass transition temperature of the comb polymer.

[0006] Changyu Liu, et al., “Effect of PCM thickness and melting temperature on thermal performance of double glazing units”, Journal of Building Engineering, 11(2017), 87-95Kazuki Ebata, et al., “Nanophase Separation of Poly( N- alkyl acrylamides): The Dependence of the Formation of Lamellar Structures on Their Alkyl Side Chains”, Macromolecules, 2019, 52, 9773-9780

[0007] Conventional heat storage materials utilize phase changes during the heat storage and heat release processes, so they are assumed to become liquid either before or after the process. Furthermore, conventional heat storage materials are used in a powder solid state, so they are all cloudy. Furthermore, heat storage materials that use paraffin require encapsulation, making them difficult to form into films. Heat storage materials that use block copolymers utilize the latent heat associated with the melting of polymers, so even if they can be formed into films, they have the problem of significant changes in mechanical properties during the heat storage and heat release processes.

[0008] An object of the present invention is to provide a novel heat storage material and heat storage film that are capable of storing and releasing heat while maintaining a solid state.

[0009] The present inventors have found that the above-mentioned problems can be solved by the following aspects. Aspect 1: A heat storage material comprising a comb polymer having an amorphous main chain and crystalline side chains, wherein the glass transition temperature of the comb polymer is higher than the melting point of the crystalline side chains. Aspect 2: The heat storage material according to Aspect 1, wherein the comb polymer has the amorphous main chain, the crystalline side chains, and a linking group connecting the amorphous main chain and the crystalline side chains, the linking group containing a polar group. Aspect 3: The heat storage material according to Aspect 2, wherein the linking group contains one or more groups selected from the group consisting of an amide group, a urea group, a urethane group, a thioamide group, a thiourea group, and a thiourethane group. Aspect 4: The crystalline side chains are C4 to C ３０ The heat storage material according to Aspect 1, wherein the amorphous main chain is a hydrocarbon-based main chain having a degree of polymerization of 5 to 1000. Aspect 6 The heat storage material according to Aspect 1, wherein the comb polymer has a nanophase-separated structure having nanodomains due to crystals of the crystalline side chains. Aspect 7 The heat storage material according to Aspect 1, wherein the amorphous main chain is a hydrocarbon-based main chain having a degree of polymerization of 5 to 1000, and the crystalline side chains are linear or branched C １２ ~C １８and the linking group comprises one or more groups selected from the group consisting of an amide group, a urea group, and a urethane group. Aspect 8: The heat storage material according to Aspect 2, wherein the comb polymer has a second side chain different from the crystalline side chain, the second side chain comprises a polar group, and the molecular weight of the second side chain is 2000 or less. Aspect 9: The heat storage material according to Aspect 8, wherein the polar group of the second side chain comprises at least one of an ester group, a thioester, an ether group, a thioether, a carbonyl group, an amide group, an amine oxide group, an amino group, and a polyoxyalkylene group. Aspect 10: The heat storage material according to Aspect 8, wherein, in the comb polymer, first repeating units having the linking group and the crystalline side chain account for 60 mol % to 99 mol %, and second repeating units having the second side chain account for 1 mol % to 40 mol %. Aspect 11: The heat storage material according to Aspect 10, wherein the comb polymer contains 70 mol % or more and 95 mol % or less of first repeating units having the linking group and the crystalline side chain, and 5 mol % or more and 30 mol % or less of second repeating units having the second side chain. Aspect 12: A heat storage film comprising the heat storage material according to any one of Aspects 1 to 11. Aspect 13: The heat storage film according to Aspect 12, wherein when formed to a thickness of 100 μm on a glass substrate, the average absorbance in an absorption spectrum at a wavelength of 400 to 800 nm is 0.5 or less. Aspect 10: A laminated heat storage film comprising the heat storage film according to Aspect 8 and another polymer film.

[0010] The heat storage material and heat storage film of the present invention are capable of storing and releasing heat while maintaining a solid state, making them extremely easy to handle. In one embodiment, these heat storage materials and heat storage films can easily provide heat storage and heat release performance at a practical level. In one embodiment, these heat storage materials and heat storage films can be easily formed into films and easily provided with transparency. While conventional heat storage materials are not transparent both before and after the phase transition, the heat storage material of one embodiment of the present invention can maintain transparency before and after the crystals of the crystalline side chains melt, making it extremely advantageous in applications requiring transparency, such as window glass and food packaging films.

[0011] Figure 1 shows the appearance of the heat storage laminate film produced in the example. Figure 2 shows the results of differential scanning calorimetry of polyoctadecylacrylamide. Figure 3 is a graph of the light absorption spectrum of the heat storage film, showing the transparency of the heat storage film. Figure 4 is a graph of the light absorption spectrum of the heat storage laminate film, showing the transparency of the heat storage film. Figure 5 shows the results of a temperature rise and temperature fall test of the heat storage film. Figure 6 shows the results of a temperature rise and temperature fall test of the heat storage laminate film. Figure 7 shows the results of DSC measurement of the first copolymer produced in Experiment 2 of the example.

[0012] In one embodiment, the thermal storage material of the present invention comprises a comb polymer having an amorphous backbone and crystalline side chains, the glass transition temperature of the comb polymer being greater than the melting point of the crystalline side chains.

[0013] In another embodiment, the present invention provides a method for using a comb polymer having an amorphous main chain and crystalline side chains in a heat storage material, wherein the glass transition temperature of the comb polymer is higher than the melting point of the crystalline side chains.

[0014] Here, the "glass transition temperature" and "melting point" are determined from the DSC curve measured when the comb polymer is measured with a differential scanning calorimeter (DSC). For example, at the "glass transition temperature", a shift in the baseline of the endotherm occurs, and at the "melting point", a peak appears in the endotherm. Here, a portion of the main chain of the comb polymer may be crystalline, and a portion of the side chain may also be amorphous, but the "glass transition temperature" is due to the amorphous main chain, and the "melting point" is due to the crystalline side chain. Furthermore, amorphousness and crystallineness refer to the state at the temperature at which this heat storage material is used. When used near room temperature, the amorphous main chain and the crystalline side chains may be amorphous and crystalline, respectively, at room temperature.

[0015] Typically, as the temperature of a polymer having an amorphous portion and a crystalline portion increases, the polymer first reaches the glass transition temperature, at which point the amorphous portion begins to move. At higher temperatures, crystallization occurs, followed by melting at the melting point, at which the crystalline portion of the crystalline portion melts. In contrast, the inventors have discovered that in some comb polymers having an amorphous main chain and crystalline side chains, the crystalline portion of the crystalline side chain first melts, causing the crystalline portion to begin to move, followed by the amorphous main chain. In this case, the glass transition temperature, which is usually lower than the melting point, is observed at a temperature higher than the melting point of the crystalline side chain.

[0016] The present inventors have found that such comb polymers are extremely useful as heat storage materials. That is, while latent heat storage materials typically store thermal energy by utilizing a phase change between liquid and solid, the comb polymers used in the present invention can undergo crystalline melting and crystallization of the crystalline side chains while remaining in a solid state below the glass transition temperature, thereby enabling heat absorption and heat release, resulting in extremely high handleability. Furthermore, the comb polymers used in the present invention can easily provide practically high levels of heat storage and heat release performance. Furthermore, such comb polymers can be easily formed into films and can easily be made transparent, making them extremely advantageous in applications requiring transparency, such as window glass and food packaging films, which are difficult to achieve with conventional heat storage materials.

[0017] The glass transition temperature of the comb polymer may be, for example, 30° C. or more, 40° C. or more, 50° C. or more, or 60° C. or more, and 120° C. or less, 100° C. or less, 90° C. or less, or 80° C. or less. For example, the glass transition temperature of the comb polymer may be 30° C. or more and 120° C. or less, or 50° C. or more and 100° C. or less.

[0018] The melting point of the crystalline side chains of the comb polymer may be, for example, −30° C. or higher, −20° C. or higher, −10° C. or higher, 0° C. or higher, 10° C. or higher, or 20° C. or higher, or may be 50° C. or lower, 40° C. or lower, 20° C. or lower, 10° C. or lower, or 0° C. or lower. For example, the melting point of the comb polymer may be −30° C. or higher and 50° C. or lower, or 0° C. or higher and 40° C. or lower.

[0019] The glass transition temperature of the comb polymer may be, for example, 30° C. or more, 40° C. or more, 50° C. or more, or 60° C. or more, and may be 80° C. or less, 70° C. or less, 60° C. or less, or 50° C. or less, higher than the melting point of the crystallizable side chains. For example, the glass transition temperature of the comb polymer may be 30° C. or more and 80° C. or less, higher than the melting point of the crystallizable side chains.

[0020] The number average molecular weight (Mn) of the comb polymer may be, for example, 5,000 or more, 10,000 or more, 15,000 or more, 20,000 or more, or 30,000 or more, or 200,000 or less, 100,000 or less, 80,000 or less, 60,000 or less, or 50,000 or less. For example, the number average molecular weight (Mn) of the comb polymer may be 5,000 or more and 200,000 or less, 7,000 or more and 100,000 or less, or 10,000 or more and 50,000 or less. Here, the number average molecular weight (Mn) is determined in terms of standard polystyrene by gel permeation chromatography as described in the examples.

[0021] The molecular weight distribution (Mw / Mn) of the comb polymer may be, for example, 1.0 or more, 1.2 or more, 1.5 or more, 2.0 or more, or 2.5 or more, and may be 5.0 or less, 4.0 or less, or 3.0 or less. For example, the molecular weight distribution (Mw / Mn) of the comb polymer may be 1.0 or more and 5.0 or less, or 2.0 or more and 4.0 or less. The molecular weight distribution (Mw / Mn) is also determined in terms of standard polystyrene by gel permeation chromatography as described in the Examples.

[0022] The average degree of polymerization of the comb polymer may be 6 or more, 8 or more, 10 or more, 20 or more, or 50 or more, or 1000 or less, 500 or less, 300 or less, 100 or less, 50 or less, 30 or less, or 20 or less. This average degree of polymerization may be, for example, 6 or more and 1000 or less, or 8 or more and 300 or less. The average degree of polymerization can be determined by determining the molecular weight in terms of standard polystyrene by gel permeation chromatography as described in the examples. By adjusting the molecular weight, degree of polymerization, etc. of the comb polymer, the operating temperature range, transparency, etc. of the heat storage material can be changed.

[0023] In one embodiment, the heat storage material includes a comb polymer having an amorphous main chain, crystalline side chains, and a linking group connecting the amorphous main chain and the crystalline side chain, the linking group including a polar group. The comb polymer having such a linking group can reduce the degree of freedom of movement of the amorphous main chain by intermolecularly interacting with surrounding chemical groups, thereby melting the crystals of the crystalline side chains before the amorphous main chain begins to move. Therefore, such a heat storage material can store and release heat while maintaining a solid state.

[0024] The polar group is not limited as long as it can reduce the degree of freedom of movement of the amorphous main chain by intermolecular interaction with surrounding chemical groups, and may contain, for example, oxygen, nitrogen, sulfur, phosphorus, halogen, etc. For example, the linking group may be a group formed by at least one of an ester group, a thioester group, an ether group, a thioether, a carbonyl group, an amide group, an amine oxide group, an amino group, and a polyoxyalkylene group.

[0025] The linking group may include an amino group, particularly a secondary amino group, and may include an ether group, an ester group, a thioether group, and / or a thioester group in addition to the amino group. In this case, the linking group may exert a strong intermolecular interaction, such as a hydrogen bond, which tends to reduce the degree of freedom of movement of the amorphous main chain.

[0026] Specifically, the linking group may include one or more groups selected from the group consisting of an amide group (-CO-NH-), a urea group (-NH-CO-NH-), a urethane group (-NH-CO-O-), a thioamide group (-CS-NH-), a thiourea group (-NH-CS-NH-), and a thiourethane group (-NH-CS-O-, -NH-CO-S-, or -NH-CS-S-).

[0027] The main chain of the comb polymer is amorphous, but a portion of it may be crystalline as long as the advantageous effects of the present invention are achieved. The main chain of the comb polymer can form a structure called a nanophase-separated structure together with nanodomains formed by crystals formed by the crystalline side chains, and the entire comb polymer can be in an amorphous glass state.

[0028] The repeating units of the amorphous main chain of the comb polymer are not particularly limited as long as the advantageous effects of the present invention are obtained, and examples thereof include hydrocarbon groups. In this specification, the term "hydrocarbon group" refers to a hydrocarbon group that may contain a heteroatom (e.g., oxygen, nitrogen, sulfur, phosphorus, halogen, etc.), may be branched, or may contain a cyclic group. For example, the amorphous main chain of the comb polymer may be obtained by polymerizing an unsaturated hydrocarbon group.

[0029] The side chains of the comb polymer are crystalline, but a portion of them may be amorphous as long as the advantageous effects of the present invention are achieved. The side chains of the comb polymer can form nano-sized aggregates, which can become nanodomains of a nanophase-separated structure. The aggregates can have an average major axis of, for example, 100 nm or less, 50 nm or less, 30 nm or less, 20 nm or less, 10 nm or less, or 5 nm or less, thereby making the comb polymer transparent to visible light. The size of the aggregates can be determined by X-ray diffraction, as described in Non-Patent Document 2.

[0030] The crystalline side chain of the comb polymer is not particularly limited as long as the advantageous effects of the present invention are obtained, but examples thereof include hydrocarbon-based groups, such as linear or branched alkyl groups.

[0031] The number of carbon atoms in the crystalline side chain may be, for example, 4 or more, 6 or more, 8 or more, 10 or more, 12 or more, or 15 or more, or may be 50 or less, 40 or less, 30 or less, 25 or less, 20 or less, or 18 or less. The number of carbon atoms may be, for example, 4 to 50 or 10 to 30. By adjusting the number of carbon atoms in the crystalline side chain, the operating temperature range of the heat storage material, etc., can be changed.

[0032] The method for producing the comb polymer is not particularly limited, but for example, the comb polymer can be obtained by reacting a first precursor compound containing a main chain and a portion that will become a part of the linking group with a second precursor compound containing a portion that will become a part of the linking group and a portion that will become a side chain, and then polymerizing the portion that will become the main chain. Alternatively, the first precursor compound can be polymerized and then the second precursor compound can be grafted.

[0033] For example, when producing poly(meth)acrylamide having alkyl side chains, a comb polymer can be produced by reacting a (meth)acryloyl halide such as acryloyl chloride with an alkylamine to obtain an N-alkyl(meth)acrylamide, which can then be radically polymerized in an organic solvent. For example, the side chains of the comb polymer can be changed by adjusting the type and number of alkyl groups in the alkylamine.

[0034] The comb polymers produced in this manner have a single repeat unit with a pendant side chain provided by a single monomer, but may also be copolymers having multiple repeat units in a block or random configuration by copolymerizing such a monomer with other monomers. Preferably, the comb polymer contains at least 50 mol%, at least 70 mol%, at least 80 mol%, at least 90 mol%, at least 95 mol%, or even 100 mol% of repeat units with side chains.

[0035] When the comb polymer is a copolymer, the copolymer can have a first side chain provided by a first monomer, the first side chain being composed of a linking group and a crystallizable side chain, and a second side chain provided by a second monomer, the second side chain preferably including a polar group and having a molecular weight of 2000 or less.

[0036] Because comb polymers absorb and release heat through the melting and crystallization of the crystals in the crystalline side chains, a larger amount of crystalline side chains is advantageous for increasing the latent heat. However, the present inventors have discovered that copolymerizing comb polymers using the second monomer described above can sometimes increase the resulting latent heat, even though the amount of crystalline side chains is reduced. This is thought to be because the introduction of the second side chains having polar groups facilitates the formation of nanodomains formed by the first side chains. Furthermore, copolymerization is advantageous in that it allows for various physical properties to be modified while still maintaining a practical latent heat.

[0037] Examples of the polar group of the second side chain include polar groups similar to those of the linking group of the first side chain. For example, the second side chain may contain oxygen, nitrogen, sulfur, phosphorus, halogen, etc. The second side chain may contain, for example, at the position directly bonded to the main chain, at least one of an ester group, a thioester group, an ether group, a thioether group, a carbonyl group, an amide group, an amine oxide group, an amino group, and a polyoxyalkylene group, and these may further contain other polar groups such as a hydroxyl group, a carboxyl group, an amino group, a heterocyclic group, etc., and these may further contain a hydrocarbon group with a molecular weight of 2000 or less.

[0038] The second side chain can have a polar group as a linking group at the position directly bonded to the main chain, and a side chain terminal group linked to the linking group. The side chain terminal group may be a relatively small moiety, for example, the molecular weight of the side chain terminal group may be 100 or less, 80 or less, 60 or less, or 50 or less, or 10 or more, 20 or more, 30 or more, or 40 or more. Alternatively, there may be no side chain terminal group, and the polar group may directly serve as the side chain terminal group.

[0039] The molecular weight of the second side chain refers to the molecular weight up to the terminal portion of the second side chain, excluding the main chain, and may be 2000 or less, 1500 or less, 1000 or less, 500 or less, 300 or less, 250 or less, 200 or less, 180 or less, 160 or less, 150 or less, 120 or less, 100 or less, 90 or less, 85 or less, 80 or less, or 70 or less, or may be 40 or more, 50 or more, 70 or more, 80 or more, 100 or more, 130 or more, 140 or more, 150 or more, or 200 or more.

[0040] When the comb polymer is such a copolymer, the first repeat unit having a linking group and a crystallizable side chain may account for 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, or 95 mol% or more, or 99 mol% or less, 98 mol% or less, 95 mol% or less, 90 mol% or less, 85 mol% or less, or 80 mol% or less. In this copolymer, the first repeat unit is preferably 60 mol% or more and 99 mol% or less, or 70 mol% or more and 95 mol% or less.

[0041] Furthermore, the content of the second repeating unit having a second side chain having a polar group in the copolymer may be 1 mol% or more, 2 mol% or more, 5 mol% or more, 10 mol% or more, or 15 mol% or more, and may be 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, 15 mol% or less, 10 mol% or less, or 5 mol% or less. The content of the second repeating unit in the copolymer is preferably 1 mol% or more and 40 mol% or less, or 5 mol% or more and 30 mol% or less.

[0042] The comb polymer can have high heat storage and heat release performance, and the resulting latent heat amount can be, for example, 5 J / g or more, 10 J / g or more, 20 J / g or more, or 30 J / g or more, and can be 200 J / g or less, 100 J / g or less, 80 J / g or less, 50 J / g or less, or 30 J / g or less. The latent heat amount obtained by the comb polymer can be, for example, 5 J / g or more and 200 J / g or less, or 30 J / g or more and 100 J / g or less.

[0043] As long as the advantageous effects of the present invention are not lost, the heat storage material can contain other substances in addition to the comb polymer depending on its application. For example, the heat storage material can be used by blending the comb polymer with other polymers. Examples of such polymers include polystyrene-based resins, polyester-based resins, acrylic-based resins, polyamide-based resins, polyvinyl alcohol-based resins, polyurethane-based resins, polyolefin-based resins, polycarbonate resins, polysulfone resins, and derivatives thereof, as well as mixtures thereof. The heat storage material can further contain optional additives such as fillers, lubricants, antistatic agents, release agents, plasticizers, antioxidants, antibacterial agents, antifungal agents, and UV absorbers, as needed, depending on its application.

[0044] The thermal storage material may contain 10% or more, 10% or more, 30% or more, 50% or more, 70% or more, 90% or more, or 95% or more by weight of the comb polymer, or 100% or less, 95% or less, 90% or less, 80% or less, 60% or less, or 40% or less by weight of the comb polymer. For example, the thermal storage material may contain 10% or more and 100% or less by weight of the comb polymer.

[0045] In one embodiment, the present invention relates to a heat storage film containing the heat storage material described above. When the heat storage material is used as a film, it is preferable because it can be used for various purposes, such as by being attached to a window glass or being used as part of a packaging film.

[0046] In another embodiment, the method of use of the present invention is to use the comb polymer as described above in a heat storage film.

[0047] In one embodiment, the heat storage film can be transparent to visible light. Conventional heat storage materials formed into films have not been able to be transparent throughout the entire process of heat storage and heat release, whereas the heat storage film of the present invention can be transparent throughout the entire process of heat storage and heat release. Here, "transparent" means that when a film having a thickness of 100 μm is formed on a glass substrate, the average absorbance of the absorption spectrum in the wavelength range of 400 to 800 nm is 0.5 or less, particularly 0.3 or less, 0.1 or less, 0.05 or less, or 0.01 or less.

[0048] Such a heat storage film can be very suitably used in windows of buildings, front and rear windows of cars, food films for covering fresh food, greenhouses for plant production, and the like.

[0049] The thickness of the heat storage film is not particularly limited, and may be, for example, 10 μm or more, 50 μm or more, 100 μm or more, 500 μm or more, 1 mm or more, or 5 mm or more, or 100 mm or less, 10 mm or less, 1 mm or less, 500 μm or less, 100 μm or less, or 50 μm or less.

[0050] As a method for forming the heat storage film, known methods such as solution casting (solution casting), melt extrusion, calendaring, and compression molding can be used. Among these, solution casting and melt extrusion can be mentioned. Examples of devices for performing solution casting include drum-type casting machines, band-type casting machines, and spin coaters. Examples of melt extrusion methods include T-die and inflation methods. When a film is formed by melt extrusion, it may be stretched to form a stretched film.

[0051] The heat storage film can be laminated with other polymer films to form a laminated heat storage film. By using other polymer films as the base film, the heat storage film can be used for a variety of purposes.

[0052] Examples of other polymer films include polyolefin films such as polyethylene and polypropylene, polyester films such as polyethylene terephthalate and polybutylene terephthalate, polyamide films such as 6-nylon and 6,6-nylon, polystyrene films, vinyl chloride films, and synthetic paper.

[0053] When a laminated heat storage film is obtained, the heat storage film and another polymer film can be laminated by a known method such as coextrusion, thermocompression bonding, extrusion lamination, or dry lamination.

[0054] The present invention will be explained in more detail in the following examples, but the present invention is not limited thereto.

[0055] Experiment 1: Homopolymer Comb Polymer Preparation Example Comb Polymer N-octadecylamine (3.60 g) was dissolved in chloroform (60 mL) and stirred at 0°C. To this solution was added triethylamine (2.00 mL), followed by dropwise addition of acryloyl chloride (1.17 mL). After the addition of acryloyl chloride, the reaction mixture was stirred at 20°C for 4 hours before adding methanol (5 mL). The majority of the solvent was then evaporated under reduced pressure, and THF (120 mL) was added. The resulting precipitate was filtered, and the filtrate was evaporated under reduced pressure to precipitate a white solid of N-octadecylacrylamide (ODA).

[0056] This white solid was dissolved in methanol (300 mL) and stored in a refrigerator for 1 day to promote recrystallization of ODA. The resulting crystals were identified by proton NMR measurement. Subsequently, ODA was dissolved in toluene, and 1 mol% of 2,2'-azobisisobutyronitrile (AIBN) was added as an initiator. Free radical polymerization was then carried out by reaction at 60°C for 12 hours. The polymerization solvent was concentrated, and the comb polymer polyoctadecylacrylamide (p(ODA)) was produced by reprecipitation using acetonitrile as a poor solvent.

[0057] The above reaction formula is shown below.

[0058]

[0059] <Heat storage film> A film was formed on a glass substrate by a casting method using pODA as the comb polymer. The film thickness measured with a stylus step gauge was 100 μm.

[0060] <Heat storage laminated film> A pODA film was produced by casting onto commercially available plastic wrap (NEW Polywrap, Ube Films Co., Ltd.). For ease of handling, the commercially available plastic wrap was placed on a glass substrate, and the pODA film was produced on top of that. When pODA was cast onto the plastic wrap, the wrap wrinkled as shown in Figure 1, but its transparency was maintained. This is thought to be due to the shrinkage of the pODA as the solvent dries.

[0061] Evaluation and Results Glass Transition Temperature and Melting Point The glass transition temperature and melting point of the comb polymer were measured using a differential scanning calorimeter (DSC; DSC 8231, Rigaku Corporation) at a nitrogen flow rate of 50 mL / min and a heating rate of 10° C. / min.

[0062] The results of DSC measurement of pODA are shown in FIG.

[0063] The DSC spectrum of pODA in Figure 2 shows a large endothermic peak at 31.9°C and a baseline shift around 82.3°C. The former is a first-order phase transition, which is thought to be due to the melting of alkyl chains aggregated by nanophase separation of the polar main chain and hydrophobic alkyl chains. On the other hand, the latter is a second-order phase transition, which corresponds to the glass transition temperature. Since the difference between these temperatures is more than 50°C, it was found that polyoctadecylacrylamide heat storage materials exhibit latent heat storage function without significant changes in their mechanical properties.

[0064] The number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of pODA were measured by gel permeation chromatography (GPC; Shodex GPC-101, Resonac Co., Ltd.) using standard polystyrene. The column used was a combination of TSKgel Super HZ2000, TSKgel Super HZ3000, TSKgel Super HZ4000, and TSKgel Super HZM-M, Tosoh Corporation, connected in this order.

[0065] As a result, the number average molecular weight of pODA was 40,000, and the molecular weight distribution (Mw / Mn) was 3.4.

[0066] <Light Absorption Spectrum> The absorbance of a sample of only the glass substrate and a sample of the glass substrate on which the heat storage film was formed was measured for light having a wavelength of 300 nm to 800 nm by ultraviolet-visible-near-infrared spectroscopy (UV3600i Plus, Shimadzu Corporation).

[0067] Similar measurements were also carried out on both a sample in which only a commercially available wrap was laminated on a glass substrate and a sample in which a commercially available wrap was laminated on a glass substrate and coated with pODA.

[0068] The results are shown in FIGS.

[0069] As shown in Figure 3, the sample with only a glass substrate and the sample with a glass substrate on which a heat storage film is formed have substantially the same absorbance in the visible light range, which shows that the heat storage film is transparent.

[0070] Furthermore, as shown in Figure 4, when a sample in which only plastic wrap was laminated on a glass substrate was compared with a sample in which plastic wrap was laminated on a glass substrate and coated with pODA, the sample coated with the pODA film did not show any specific absorption peak, and only an increase in background due to scattering caused by wrinkles in the plastic wrap was observed.

[0071] <Temperature Increase and Decrease Test> For the above-mentioned heat storage film formed on a glass substrate, a fiber thermometer was attached to the glass substrate, and the film was left at 23°C for 20 seconds. Then, the film was placed with the glass substrate side facing down on a hot plate at 48°C to measure the temperature change. The film was then removed from the hot plate and left at room temperature. The same measurement was also carried out on the glass alone.

[0072] Similar measurements were also carried out on both a sample in which only plastic wrap was laminated on a glass substrate and a sample in which plastic wrap was laminated on a glass substrate and coated with a pODA film.

[0073] The temperature transitions are shown in FIGS.

[0074] As shown in Figure 5, when measuring the glass substrate alone, a temperature rise was observed immediately after placing it on the hot plate (at 20 seconds), whereas when measuring the pODA-coated glass substrate, a temperature rise was observed 2 seconds later and at a more gradual rate. Furthermore, the maximum temperature was 43.2°C for the glass substrate alone, whereas it was 42.2°C for the pODA-coated glass substrate, a 1°C decrease.

[0075] Furthermore, when the glass substrate was removed from the hot plate (at 80 seconds) and left at room temperature, the temperature of the glass substrate alone dropped rapidly, while the temperature of the glass substrate coated with pODA dropped slowly. This is likely because, when placed on the hot plate, the alkyl side chains melted and absorbed heat, preventing the temperature from rising too high. However, when removed from the hot plate, the molten alkyl chains caused nanocrystallization, generating heat. The transparency of the pODA did not change during this temperature change. This demonstrates that the pODA film exhibits latent heat storage functionality while maintaining its transparency.

[0076] As shown in Figure 6, similar to Figure 5, the sample in which the pODA film was coated on the wrap on the glass substrate had a longer delay in the temperature rise and the rise was also slower. Furthermore, the temperature reached was 0.5°C lower than that in the case of only the wrap.

[0077] Furthermore, the transparency of the pODA film coated on plastic wrap was maintained. Thus, it was found that pODA can be easily applied not only to hard glass substrates but also to soft plastic wrap, while maintaining its transparency and latent heat storage function. This is because the melting and crystallization of the crystalline side chains, which are the origin of latent heat storage, occur below the glass transition temperature, maintaining the glassy state of the film.

[0078] In addition, when similar experiments were performed by changing the number of carbon atoms in the octadecyl group (alkyl group) of octadecylamine from 12 to 17 to obtain comb polymers with various side chain lengths, roughly similar results were obtained, although the appropriate temperature range, etc. changed depending on the melting point.

[0079] Experiment 2: Copolymer Comb Polymers First Copolymer: p(ODA / HEAm) Polymerization was carried out using N-octadecylacrylamide (ODA) as the first monomer and N-(2-hydroxyethyl)acrylamide (HEAm) as the second monomer in the amounts shown in Table 1 below.

[0080] 2,2'-azobis(isobutyronitrile) (AIBN) was added to a pressure-resistant glass tube at a concentration of 1 mol% relative to the total monomer amount. Toluene and N,N-dimethylformamide (DMF) (toluene:DMF = 4:1) were also added to achieve a concentration of 0.20 M (Table 1). Polymerization was carried out at 60°C for 12 hours. After completion of the reaction, the reaction solution was exposed to air and then cooled on ice. The solvent was evaporated under reduced pressure, and the copolymer was dissolved in chloroform and reprecipitated three times using acetonitrile as a poor solvent. The polymer was then recovered by suction filtration and dried at room temperature under reduced pressure to obtain a white powder of copolymer (p(ODA / HEAm)).

[0081]

[0082] The above reaction formula is shown below.

[0083]

[0084] <Evaluation and Results> <Glass Transition Temperature, Melting Point, Latent Heat, Molecular Weight> The glass transition temperature, melting point, and molecular weight of each copolymer were measured in the same manner as in Experiment 1. The latent heat of each copolymer was also measured by the T M The calculated area was the area on the endothermic peak side.

[0085] The results of DSC measurement of each copolymer are shown in FIG.

[0086] The results are shown in the table below:

[0087]

[0088] As shown in Table 2, the copolymer using 12 mol% of the second monomer had the highest latent heat. This is thought to be because the introduction of the polar second side chain promoted the formation of nanodomains by the hydrophobic alkyl chains of the first side chain.

[0089] On the other hand, in the case of copolymers using 36 mol% or more of the second monomer, the amount of latent heat was lower than that of homopolymers containing only the first monomer, which is thought to be due to the reduced amount of crystalline side chains of the first monomer that generate latent heat.

[0090] It should be noted that as the proportion of the second monomer increases, the molecular weight tends to decrease. This is thought to be because the molecular weight of the second monomer is lower than that of the first monomer, so that the molecular weight of the resulting copolymer is lower even if the degree of polymerization is the same, and because the polarity of the second monomer is high, the molecular weight tends to be lower in GPC measurement.

[0091] Second copolymer: p(ODA / NAS). N-octadecylacrylamide (ODA), N-succinimidyl acrylate (NAS), and 2,2'-azobis(isobutyronitrile) (AIBN) were added to a pressure-resistant glass tube. Toluene was added to a concentration of 0.20 M (Table 2). Polymerization was carried out at 60°C for 12 hours. After completion of the reaction, the reaction solution was exposed to air and cooled on ice. Most of the solvent was evaporated under reduced pressure. The copolymer was then dissolved in chloroform and reprecipitated three times using acetonitrile as a poor solvent. The polymer was then recovered by suction filtration and dried at room temperature under reduced pressure to obtain a white powder of the copolymer (p(ODA / NAS)).

[0092]

[0093] The structural formula of the second copolymer (p(ODA / NAS)) is shown below:

[0094]

[0095] Third Copolymer: p(ODA50 / Alanine50) p(ODA50 / Alanine50) was synthesized by a polymer reaction using p(ODA50 / NAS50) as a precursor.

[0096] p(ODA50 / NAS50) (0.30 g, 1.2 mmol) was added to a recovery flask, and tetrahydrofuran (20 ml) was added to prepare a 0.060 M dilute solution. In addition, β-alanine (0.32 g, 3.6 mmol) (6 equivalents per NAS unit) was added to a screw cap tube, and distilled water (5 ml) was added to prepare a 0.7 M saturated solution. Next, the β-alanine aqueous solution was added dropwise to the stirred p(ODA50 / NAS50) solution, followed by the dropwise addition of 12 equivalents per NAS unit of triethylamine (1.0 ml). The polymerization reaction was carried out at room temperature for 24 hours, after which the solution was concentrated under reduced pressure and chloroform (approximately 60 ml) was added. Using a separatory funnel, the organic phase was washed three times with 1.0 M hydrochloric acid. The organic phase was concentrated under reduced pressure and dried to obtain a brown powder of the copolymer (p(ODA50 / Alanine50)).

[0097] The structural formula of the third copolymer (p(ODA50 / Alanine50)) is shown below:

[0098]

[0099] The melting point (Tm) and glass transition temperature (Tg) of p(ODA50 / Alanine50) were 35.6° C. and 77.9° C., respectively. The latent heat of this copolymer was also found to be within a practical range.

[0100] Fourth Copolymer: p(ODA / Histamine) p(ODA / Histamine) was synthesized by a polymer reaction using p(ODA / NAS) as a precursor.

[0101] To a three-neck round-bottom flask, 3-3.2 equivalents of histamine dihydrochloride per NAS unit were added. Acetone was added to the mixture to a concentration of 0.05-0.1 M, and nitrogen was bubbled through the mixture. To this mixture, 6-12 equivalents of triethylamine per NAS unit were added. Furthermore, p(ODA / NAS) was added to a recovery flask, and dehydrated chloroform was added to a concentration of 0.1 M, followed by stirring under a nitrogen atmosphere (Table 3). Next, the p(ODA50 / NAS50) solution was added dropwise to the stirred histamine solution. The reaction was allowed to proceed at room temperature for 17-30 hours and in a 40°C oil bath for 5-24 hours. The reaction was terminated when the disappearance of the succinimide group was confirmed by FT-IR measurement. After completion of the reaction, the solution was ice-cooled and the solvent was concentrated under reduced pressure. After concentration, tetrahydrofuran (approximately 100 ml) was added to precipitate the by-product. The by-product was filtered off, and the filtrate was concentrated under reduced pressure. After concentration, acetone was added to the solid to precipitate the product, which was collected and dried at room temperature.

[0102]

[0103] The structural formula of the fourth copolymer (p(ODA / Histamine)) is shown below:

[0104]

[0105] The melting point (Tm) and glass transition temperature (Tg) of p(ODA50 / Histamine50) were 28.6°C and 102°C, respectively. The melting point (Tm) and glass transition temperature (Tg) of p(ODA70 / Histamine30) were 19.6°C and 104°C, respectively. The latent heat values ​​of these copolymers were also found to be within a practical range.

Claims

1. A thermal storage material comprising a comb polymer having an amorphous backbone and crystalline side chains, the glass transition temperature of the comb polymer being greater than the melting point of the crystalline side chains.

2. The heat storage material according to claim 1, wherein the comb polymer has the amorphous main chain, the crystalline side chain, and a linking group that links the amorphous main chain and the crystalline side chain, and the linking group includes a polar group.

3. The heat storage material according to claim 2, wherein the linking group comprises one or more groups selected from the group consisting of an amide group, a urea group, a urethane group, a thioamide group, a thiourea group, and a thiourethane group.

4. The crystallizable side chain is C ４ ~C ３０ The heat storage material according to claim 1 , comprising a hydrocarbon group of the formula:

5. The heat storage material according to claim 1, wherein the amorphous main chain is a hydrocarbon-based main chain having a degree of polymerization of 5 to 1,000.

6. The heat storage material according to claim 1, wherein the comb polymer has a nano-phase-separated structure having nano-domains due to crystals of the crystalline side chains.

7. The amorphous main chain is a hydrocarbon main chain having a degree of polymerization of 5 to 1000, and the crystalline side chain is a straight or branched C １２ ~C １８ and the linking group comprises one or more groups selected from the group consisting of an amide group, a urea group, and a urethane group.

8. The heat storage material according to claim 2, wherein the comb polymer has a second side chain different from the crystallizable side chain, the second side chain includes a polar group, and the molecular weight of the second side chain is 2000 or less.

9. The heat storage material according to claim 8, wherein the polar group of the second side chain comprises at least one of an ester group, a thioester, an ether group, a thioether, a carbonyl group, an amide group, an amine oxide group, an amino group, and a polyoxyalkylene group.

10. The heat storage material according to claim 8, wherein in the comb polymer, the first repeating unit having the linking group and the crystalline side chain is from 60 mol % to 99 mol %, and the second repeating unit having the second side chain is from 1 mol % to 40 mol %.

11. The heat storage material according to claim 10, wherein in the comb polymer, the first repeating unit having the linking group and the crystalline side chain is from 70 mol % to 95 mol %, and the second repeating unit having the second side chain is from 5 mol % to 30 mol %.

12. A heat storage film comprising the heat storage material according to any one of claims 1 to 7.

13. The heat storage film according to claim 12, which has an average absorbance of 0.5 or less in an absorption spectrum of wavelengths from 400 to 800 nm when formed on a glass substrate to a thickness of 100 μm.

14. A laminated heat storage film comprising the heat storage film according to claim 12 and another polymer film.

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