JP7746985B2 - heat-shielding film - Google Patents

Description

The present invention relates to a heat-shielding film.

Agricultural greenhouses have traditionally played an important role in cultivating horticultural crops such as vegetables, fruit trees, and flowers. Against the backdrop of global population growth, climate change, and a decline in the number of people working in agriculture, there is a need for a stable supply of horticultural crops and improved productivity, and the functionality required of agricultural greenhouses is becoming more sophisticated.

In order to improve the productivity of horticultural crops, temperature management of the cultivation environment is important from the perspective of growth. For example, in the summer, strong sunlight can cause the temperature inside a greenhouse to rise, hindering crop growth and potentially causing leaf burn. The main countermeasures to high temperatures are ventilation inside the greenhouse, the use of heat-shielding netting, and mist cooling using the evaporative heat of water. However, these have presented challenges in improving crop productivity, as ventilation inside the greenhouse can cause insect damage, heat-shielding netting reduces the penetration of sunlight necessary for growth, and mist cooling can have the adverse effects of drifting. Furthermore, in winter, sudden drops in temperature in the morning and evening can lead to frost, and drops in temperature inside the greenhouse due to a lack of sunlight can have a negative impact on crop growth.

To solve the above problems, the use of heat-shielding film has been proposed. For example, Patent Document 1 proposes a method of attaching heat-shielding film to the outer frame film of an agricultural greenhouse via an adhesive. Patent Document 2 proposes a method of using heat-shielding film installed in curtain or roll form on the inside of an agricultural greenhouse.

WO2015-025513 Patent Publication No. 2016-149977

However, the heat-shielding films in the above-mentioned prior art documents had insufficient heat-shielding properties and transparency, posing challenges to stable crop supply and improved productivity. They also had poor abrasion resistance and flexibility, which could result in durability issues. Furthermore, when using heat-shielding films in a method such as that described in Patent Document 2, the film's flexibility was insufficient, which could lead to problems such as poor handling and cracking of the heat-shielding layer.

Furthermore, improving the heat-shielding properties of a film tends to increase the film's haze, decrease light transmittance, or impair visibility. For this reason, there is a demand for heat-shielding films that not only have high heat-shielding properties, but also high light transmittance and high visibility.

The present invention has been made to solve the above-mentioned problems. Specifically, it provides a heat-shielding film that has excellent heat-shielding properties, transparency, abrasion resistance, and flexibility, and can contribute to the stable supply of horticultural crops and improved productivity. Furthermore, it provides a heat-shielding film that, due to its excellent heat-shielding properties, can also be used for building materials, such as window linings for automobiles and homes.

That is, the present invention comprises the following:
[1] A heat-shielding film having a heat-shielding layer laminated directly or via another layer on at least one surface of a base film,
the thermal barrier layer is formed from a thermal barrier layer-forming composition containing antimony-doped tin oxide and a binder resin,
the antimony-doped tin oxide contained in the thermal barrier layer has an average primary particle size of less than 50 nm, and the minimum diameter of the mandrel at which cracks occur in the thermal barrier layer by a cylindrical mandrel method is less than 4 mm,
A heat-shielding film having a spectral transmittance T _1400nm at a wavelength of 1400 nm of 20% or less and a haze value of 8% or less.
[2] In one embodiment, the heat-shielding film of the present invention has a base film that is a polyester film that is substantially free of particles, and has an easy-adhesion layer between the base film and the heat-shielding layer.
[3] In one embodiment, the heat-shielding film of the present invention has a pencil hardness of H or more in the heat-shielding layer.
[4] In one embodiment, when the relationship between the thickness n of the heat-shielding layer and the heat-shielding property is represented by the following (Equation 1),
The numerical value represented by (Equation 1) is 20 or more: (100-T _1400nm )/n (Equation 1).
[5] In one embodiment, the heat-shielding film of the present invention has a total light transmittance of 50% or more.
[6] In one embodiment, the heat-shielding film of the present invention has a weight ratio of antimony-doped tin oxide to binder resin in the heat-shielding layer-forming composition of antimony-doped tin oxide:binder resin=70:30 to 99:1.
[7] In one embodiment, the binder resin of the heat-shielding film of the present invention includes at least one resin selected from the group consisting of acrylate resins, acrylic resins, polyester resins, and polyurethane resins.
[8] In another aspect, there is provided an agricultural heat shielding film having the heat shielding film according to the present invention.
[9] In another aspect, a heat-shielding film for lining windows is provided, which comprises the heat-shielding film according to the present invention.

The heat-shielding film of the present invention has high heat-shielding properties. In addition to having high heat-shielding properties, the heat-shielding film of the present invention also has high transparency and light transmittance.
Furthermore, the heat-shielding film of the present invention has excellent abrasion resistance and coating strength, and therefore can be used for a long period of time without any deterioration in performance.
Furthermore, the heat-shielding film of the present invention has excellent flexibility and therefore excellent handleability, and can suppress film cracking in the heat-shielding layer even when used in a shape such as a curtain or roll. Moreover, even when used in such a shape, the film can have high heat-shielding properties, transparency, and light transmittance.

The present inventors have discovered a heat-shielding film having a heat-shielding layer laminated on at least one surface of a base film directly or via another layer,
the thermal barrier layer is formed from a thermal barrier layer-forming composition containing antimony-doped tin oxide and a binder resin,
the antimony-doped tin oxide contained in the thermal barrier layer has an average primary particle size of less than 50 nm, and the minimum diameter of a mandrel at which cracks occur in the thermal barrier layer by a cylindrical mandrel method is less than 4 mm,
It has been found that a heat-shielding film having a spectral transmittance T _{1400 nm at a wavelength of 1400 nm} of 20% or less and a haze value of 8% or less can provide a heat-shielding film that is excellent in heat-shielding properties, transparency, abrasion resistance, and flexibility.

The heat-shielding film of the present invention has high heat-shielding properties. In addition to having high heat-shielding properties, the heat-shielding film of the present invention also has high transparency and light transmittance.
Therefore, it can be suitably used for agricultural purposes and as a building material for automobile window coverings, residential window coverings, etc. Furthermore, it does not adversely affect the growth of horticultural crops, and when used for window coverings, it can let in outside light without blocking it.
Furthermore, the heat-shielding film of the present invention has excellent abrasion resistance and coating strength, and therefore can be used for a long period of time without any deterioration in performance.
Furthermore, the heat-shielding film of the present invention has excellent flexibility and therefore excellent handleability, and can suppress film cracking in the heat-shielding layer even when used in a shape such as a curtain or roll. Moreover, even when used in such a shape, the film can have high heat-shielding properties, transparency, and light transmittance.
Furthermore, since the heat-shielding film of the present invention has excellent adhesion between the base film and the heat-shielding layer, there is no risk of the heat-shielding layer peeling even when used for a long period of time, and the heat-shielding film can be used without deteriorating in various performance properties.
The present invention will be described in detail below.

(Film substrate)
The film substrate used in the present invention is not particularly limited, and various polymer films can be used. It is preferable to use a polyester film substrate formed from a polyester. The polyester constituting the polyester film substrate is not particularly limited. A crystalline linear saturated polyester composed of an aromatic dibasic acid component and a diol component is preferred. For example, polyethylene terephthalate, polyethylene 2,6-naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, or a copolymer primarily composed of these resin components is more preferred. Polyester film substrates formed from polyethylene terephthalate and polyethylene-2,6-naphthalate are particularly preferred, and polyester film substrates formed from polyethylene terephthalate are most preferred. The polyethylene terephthalate preferably contains 90 mol% or more, more preferably 95 mol% or more, of ethylene terephthalate repeating units, and may be copolymerized with small amounts of other dicarboxylic acid components or diol components. For example, from a cost perspective, those produced solely from terephthalic acid and ethylene glycol are preferred. In addition, known additives such as antioxidants, light stabilizers, ultraviolet absorbers, crystallizing agents, etc. may be added within a range that does not impair the effects of the film of the present invention. The polyester film substrate is preferably a biaxially oriented polyester film substrate because of its high bidirectional elastic modulus.

The method for producing the polyester film substrate in the present invention is not particularly limited, and conventional methods can be used. For example, the polyester can be melted in an extruder, extruded into a film, and cooled on a rotating cooling drum to obtain an unstretched film, which can then be biaxially stretched. A biaxially stretched film can be obtained by sequentially biaxially stretching a uniaxially stretched film in the longitudinal or transverse direction, or by simultaneously biaxially stretching an unstretched film in the longitudinal and transverse directions.

In the present invention, the stretching temperature during stretching of polyester film is preferably set to a temperature equal to or higher than the second-order transition point (Tg) of the polyester. Stretching of 1 to 8 times, and particularly 2 to 6 times, in both the longitudinal and transverse directions is preferred.

The polyester film substrate preferably has a thickness of 12-250 μm, more preferably 30-188 μm, and even more preferably 50-150 μm. A film substrate thickness of 12 μm or more is preferred because it is less likely to deform due to heat during film production, processing, molding, etc., and the film has a moderate stiffness, making it easy to handle. On the other hand, a film substrate thickness of 250 μm or less is preferred because it prevents excessive amounts of film from being discarded after use, thereby reducing the environmental impact.

There are no particular restrictions on the polycondensation catalyst used in producing polyester resins. For example, antimony trioxide is a suitable catalyst because it is inexpensive and has excellent catalytic activity. It is also preferable to use a germanium compound or a titanium compound. More preferred polycondensation catalysts include catalysts containing aluminum and/or its compounds and a phenolic compound, catalysts containing aluminum and/or its compounds and a phosphorus compound, and catalysts containing an aluminum salt of a phosphorus compound.

Furthermore, the polyester film substrate in the present invention is not particularly limited in terms of its layer structure, and may be a single-layer polyester film substrate, a two-layer structure with different components, or a polyester film substrate consisting of at least three layers, including an outer layer and an inner layer.

In one embodiment, the substrate film is a polyester film that is substantially free of particles. Because the substrate film is substantially free of particles, the adhesion between the substrate and the heat-shielding layer can be increased, and peeling of the heat-shielding layer can be suppressed. In addition, the heat-shielding film can have excellent transparency.
In the present invention, "substantially free of particles" means that when the surface of the substrate is observed under a microscope, the number of particles having a diameter of 10 μm or more is 10/ ^mm2 or less, or no surface irregularities having a length of 10 μm or more are observed.
This is because even if inorganic particles are not actively added to the film, contaminants from foreign matter, raw material resins, and dirt adhering to the lines and equipment during the film manufacturing process may peel off and become mixed into the film.

Preferably, the substrate film may be a polyester film that is substantially free of inorganic particles. Since the substrate film is substantially free of inorganic particles, the adhesion between the substrate and the heat shield layer can be increased, and peeling of the heat shield layer can be suppressed. In addition, high transparency (light transmittance) can be exhibited.
In the present invention, "substantially free of inorganic particles" means that the content of inorganic elements is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit, when quantified by fluorescent X-ray analysis. This is because even if inorganic particles are not actively added to the film, contaminants derived from foreign matter, raw material resins, and dirt adhering to the lines and equipment in the film manufacturing process may peel off and be mixed into the film.

<Easy adhesive layer>
In the heat-shielding film of the present invention, the heat-shielding layer described below may be laminated directly on the film substrate.
In one embodiment, it is preferable to form an easy-adhesion layer on the film substrate and provide a heat-shielding layer on the surface of the easy-adhesion layer opposite to the film substrate. By providing the heat-shielding layer via the easy-adhesion layer, the adhesion of the heat-shielding layer to the substrate is further improved, and peeling and film cracking of the heat-shielding layer are less likely to occur even when used outdoors for a long period of time.

The adhesive layer may be provided on one or both sides of the film substrate. For example, it is preferred that a heat shield layer is formed on at least one side of the film substrate via the adhesive layer.
Furthermore, a resin coating layer may be provided on the surface of the film substrate opposite the heat-shielding layer. In this embodiment, for example, a second adhesive layer may be provided between the film substrate and the resin coating layer. For example, the resin coating layer may be an adhesive layer, a hydrophilic layer, an antifouling layer, or the like.

The easy-adhesion layer is preferably formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin. It is believed that the easy-adhesion layer is formed by curing a structure in which a urethane resin having a polycarbonate structure and a branched structure, and a polyester resin, are crosslinked by a crosslinking agent. Because it is difficult to describe the crosslinked chemical structure itself, the layer is expressed as being formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin.

The urethane resin having a polycarbonate structure in the present invention preferably has a urethane bond derived from at least a polycarbonate polyol component and a polyisocyanate component, and a branched structure, and further contains a chain extender as needed. The branched structure referred to here is one that is suitably introduced by forming a branched molecular chain structure after synthesis and polymerization due to the presence of three or more terminal functional groups in any of the raw material components that make up the molecular chain, as described above.

The urethane resin having a polycarbonate structure in the present invention is preferably one having 3 to 6 terminal functional groups in the molecular chain due to its branched structure, as this allows the resin to be stably dispersed in an aqueous solution and improves blocking resistance.

The lower limit of the mass ratio of the polycarbonate polyol component to the polyisocyanate component (mass of polycarbonate polyol component/mass of polyisocyanate component) when synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention is preferably 0.5, more preferably 0.6, even more preferably 0.7, particularly preferably 0.8, and most preferably 1.0. A ratio of 0.5 or higher is preferred because it improves adhesion to the heat-shielding layer. The upper limit of the mass ratio of the polycarbonate polyol component to the polyisocyanate component when synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention is preferably 3.0, more preferably 2.2, even more preferably 2.0, particularly preferably 1.7, and most preferably 1.5. A ratio of 3.0 or lower is preferred because it improves blocking resistance.

The polycarbonate polyol component used to synthesize and polymerize the urethane resin having a polycarbonate structure in the present invention preferably contains an aliphatic polycarbonate polyol, which has excellent heat resistance and hydrolysis resistance. Aliphatic polycarbonate polyols include aliphatic polycarbonate diols and aliphatic polycarbonate triols, with aliphatic polycarbonate diols being preferred. Examples of the aliphatic polycarbonate diol used for synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention include aliphatic polycarbonate diols obtained by reacting one or more diols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,8-nonanediol, neopentyl glycol, diethylene glycol, and dipropylene glycol with carbonates such as dimethyl carbonate, ethylene carbonate, and phosgene.

The number average molecular weight of the polycarbonate polyol in the present invention is preferably 1,000 to 3,000. More preferably, it is 1,200 to 2,900, and most preferably, it is 1,500 to 2,800. A molecular weight of 1,000 or more is preferable because it can improve the adhesion of the heat shield layer. A molecular weight of 3,000 or less is preferable because it can improve blocking resistance.

Examples of polyisocyanates used in the synthesis and polymerization of the urethane resin having a polycarbonate structure in the present invention include aromatic aliphatic diisocyanates such as xylylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane; aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; and polyisocyanates prepared by pre-addition of one or more of these compounds with trimethylolpropane or the like. The use of the aforementioned aromatic aliphatic diisocyanates, alicyclic diisocyanates, or aliphatic diisocyanates is preferred because they do not cause yellowing problems. Furthermore, they do not form an overly rigid coating, can alleviate stress caused by thermal shrinkage of the polyester film substrate, and provide good adhesion.

Chain extenders include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol; diamines such as ethylenediamine, hexamethylenediamine, and piperazine; amino alcohols such as monoethanolamine and diethanolamine; thiodiglycols such as thiodiethylene glycol; and water.

To form a branched structure in the urethane resin, a preferred method is, for example, to react the polycarbonate polyol component, polyisocyanate, and chain extender at an appropriate temperature and for an appropriate time, then add a compound having three or more functional hydroxyl or isocyanate groups and allow the reaction to proceed further.

Specific examples of compounds with three or more functional hydroxyl groups include caprolactone triol, glycerol, trimethylolpropane, butanetriol, hexanetriol, 1,2,3-hexanetriol, 1,2,3-pentanetriol, 1,3,4-hexanetriol, 1,3,4-pentanetriol, 1,3,5-hexanetriol, 1,3,5-pentanetriol, and polyethertriol. Examples of the polyethertriol include compounds obtained by addition polymerization of one or more monomers, such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, glycidyl ether, methyl glycidyl ether, t-butyl glycidyl ether, and phenyl glycidyl ether, using one or more compounds with three active hydrogens, such as alcohols (e.g., glycerin and trimethylolpropane) and diethylenetriamine, as initiators.

Specific examples of compounds having tri- or higher functional isocyanate groups include polyisocyanate compounds having at least three isocyanate (NCO) groups per molecule. In the present invention, tri- or higher functional isocyanate compounds include biuret compounds, nurate compounds, and adduct compounds obtained by modifying isocyanate monomers such as aromatic diisocyanates, aliphatic diisocyanates, araliphatic diisocyanates, and alicyclic diisocyanates, each of which has two isocyanate groups.
Examples of aromatic diisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, and 4,4'-diphenyl ether diisocyanate.
Examples of the aliphatic diisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.
Examples of the araliphatic diisocyanate include xylylene diisocyanate, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.
Examples of alicyclic diisocyanates include 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatomethyl)cyclohexane.
The biuret form is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer, and examples thereof include the biuret form of hexamethylene diisocyanate.
The nurate is a trimer of an isocyanate monomer, and examples thereof include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate.
The adduct refers to a tri- or higher functional isocyanate compound obtained by reacting the above-mentioned isocyanate monomer with a tri- or higher functional low-molecular-weight active hydrogen-containing compound, and examples thereof include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, and a compound obtained by reacting trimethylolpropane with isophorone diisocyanate.

Examples of chain extenders with three or more functional groups include trimethylolpropane, as described above in the chain extender description, and alcohols with three or more hydroxyl groups, such as pentaerythritol.

The easy-adhesion layer in the present invention is preferably formed using an aqueous coating liquid by the in-line coating method described below. Therefore, it is desirable that the urethane resin of the present invention be water-soluble or water-dispersible. Note that the term "water-soluble or water-dispersible" means that the resin disperses in water or an aqueous solution containing less than 50% by weight of a water-soluble organic solvent.

To impart water dispersibility to urethane resins, sulfonic acid (salt) groups or carboxylic acid (salt) groups can be introduced (copolymerized) into the urethane molecular backbone. To maintain moisture resistance, it is preferable to introduce weakly acidic carboxylic acid (salt) groups. Nonionic groups such as polyoxyalkylene groups can also be introduced.

To introduce carboxylic acid (salt) groups into a urethane resin, for example, a polyol compound containing a carboxylic acid group, such as dimethylolpropanoic acid or dimethylolbutanoic acid, is introduced as a copolymerization component and neutralized with a salt-forming agent. Specific examples of salt-forming agents include ammonia; trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine; N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine; and N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These can be used alone or in combination.

When a polyol compound having a carboxylic acid (salt) group is used as a copolymerization component to impart water dispersibility, the molar ratio of the polyol compound having a carboxylic acid (salt) group in the urethane resin is preferably 3 to 60 mol%, and more preferably 5 to 40 mol%, when the total polyisocyanate components of the urethane resin are taken as 100 mol%. A molar ratio of 3 mol% or more is preferred because water dispersibility is achieved. Furthermore, a molar ratio of 60 mol% or less is preferred because water resistance is maintained and moist heat resistance is achieved.

The urethane resin of the present invention may have a blocked isocyanate structure at the end to improve hardness.

In the present invention, the crosslinking agent contained in the composition for forming an easy-adhesion layer is preferably a blocked isocyanate, more preferably a tri- or higher functional blocked isocyanate, and particularly preferably a tetra- or higher functional blocked isocyanate. This improves blocking resistance and adhesion to the heat-shielding layer.

The lower limit of the NCO equivalent of the blocked isocyanate is preferably 100, more preferably 120, even more preferably 130, particularly preferably 140, and most preferably 150. An NCO equivalent of 100 or more is preferred as this eliminates the risk of coating cracking. The upper limit of the NCO equivalent is preferably 500, more preferably 400, even more preferably 380, particularly preferably 350, and most preferably 300. An NCO equivalent of 500 or less is preferred as it maintains blocking resistance.

The lower limit of the boiling point of the blocking agent for the blocked isocyanate is preferably 150°C, more preferably 160°C, even more preferably 180°C, particularly preferably 200°C, and most preferably 210°C. The higher the boiling point of the blocking agent, the less volatilization of the blocking agent is suppressed by the drying process after application of the coating solution or by heat addition during the film formation process in the case of in-line coating. This suppresses the occurrence of minute irregularities on the coated surface and improves film transparency. While there are no particular limitations on the upper limit of the boiling point of the blocking agent, a limit of approximately 300°C is considered appropriate from the standpoint of productivity. Because boiling point is related to molecular weight, it is preferable to use a blocking agent with a high molecular weight to increase the boiling point of the blocking agent. The molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and even more preferably 80 or more.

The upper limit of the dissociation temperature of the blocking agent is preferably 200°C, more preferably 180°C, even more preferably 160°C, particularly preferably 150°C, and most preferably 120°C. The blocking agent dissociates from the functional group during the drying process after application of the coating solution, or during the film formation process in the case of in-line coating, by thermal addition, generating regenerated isocyanate groups. This allows crosslinking reactions with urethane resins and the like to proceed, improving adhesion. When the dissociation temperature of the blocked isocyanate is below the above temperature, the blocking agent dissociates sufficiently, resulting in good adhesion, particularly moist heat resistance.

Blocking agents used in the blocked isocyanate of the present invention that have a dissociation temperature of 120°C or lower and a boiling point of 150°C or higher include bisulfite compounds such as sodium bisulfite, pyrazole compounds such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 4-nitro-3,5-dimethylpyrazole, active methylene compounds such as malonic acid diesters (dimethyl malonate, diethyl malonate, di-n-butyl malonate, and di-2-ethylhexyl malonate), methyl ethyl ketone, and triazole compounds such as 1,2,4-triazole. Among these, pyrazole compounds are preferred in terms of resistance to moist heat and yellowing.

The tri- or higher functional polyisocyanate, which is the precursor of the blocked isocyanate of the present invention, can be suitably obtained by introducing an isocyanate monomer, such as a biuret, nurate, or adduct obtained by modifying an isocyanate monomer, such as an aromatic diisocyanate, aliphatic diisocyanate, araliphatic diisocyanate, or alicyclic diisocyanate, each having two isocyanate groups.
The biuret form is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer, and examples thereof include the biuret form of hexamethylene diisocyanate.
The nurate is a trimer of an isocyanate monomer, and examples thereof include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate.
The adduct refers to a tri- or higher functional isocyanate compound obtained by reacting an isocyanate monomer with a tri- or higher functional low-molecular-weight active hydrogen-containing compound, and examples thereof include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, and a compound obtained by reacting trimethylolpropane with isophorone diisocyanate.

The above-mentioned isocyanate monomers include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanate, phenylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3' Examples of suitable diisocyanates include aromatic diisocyanates such as 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, and 3,3'-dimethoxydiphenyl-4,4'-diisocyanate; aromatic aliphatic diisocyanates such as xylylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane; and aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate. From the viewpoints of transparency, adhesion, and moist heat resistance, aliphatic and alicyclic isocyanates and modified products thereof are preferred, and are preferred for optical applications where high transparency is required without yellowing.

The blocked isocyanate of the present invention can introduce hydrophilic groups into the precursor polyisocyanate to impart water solubility or water dispersibility. Examples of hydrophilic groups include (1) quaternary ammonium salts of dialkylamino alcohols and quaternary ammonium salts of dialkylaminoalkylamines, (2) sulfonates, carboxylates, and phosphates, and (3) polyethylene glycols and polypropylene glycols capped at one end with an alkyl group. When a hydrophilic moiety is introduced, the resulting polymer will be (1) cationic, (2) anionic, or (3) nonionic. Since many other water-soluble resins are anionic, anionic or nonionic polymers are preferred because they are easily compatible with other resins. Furthermore, anionic polymers have excellent compatibility with other resins, while nonionic polymers lack ionic hydrophilic groups, which improves resistance to moist heat.

Preferred anionic hydrophilic groups include those having hydroxyl groups for introduction into polyisocyanates and carboxylic acid groups for imparting hydrophilicity. Examples include glycolic acid, lactic acid, tartaric acid, citric acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypivalic acid, dimethylolacetic acid, dimethylolpropanoic acid, dimethylolbutanoic acid, and polycaprolactones with carboxylic acid groups. Organic amine compounds are preferred for neutralizing carboxylic acid groups. Examples thereof include ammonia, linear or branched primary, secondary or tertiary amines having 1 to 20 carbon atoms such as methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine and ethylenediamine, cyclic amines such as morpholine, N-alkylmorpholine and pyridine, and hydroxyl group-containing amines such as monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine and triethanolamine.

As the nonionic hydrophilic group, polyethylene glycol or polypropylene glycol capped at one end with an alkyl group preferably has 3 to 50 repeating units of ethylene oxide and/or propylene oxide, more preferably 5 to 30. Small repeating units result in poor compatibility with resins and increased haze, while large repeating units may result in reduced adhesion under high temperature and humidity conditions. To improve water dispersibility, the blocked isocyanate of the present invention can be supplemented with nonionic, anionic, cationic, or amphoteric surfactants. Examples include nonionic surfactants such as polyethylene glycol and polyhydric alcohol fatty acid esters; anionic surfactants such as fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, sulfosuccinates, and alkyl phosphates; cationic surfactants such as alkylamine salts and alkylbetaines; and surfactants such as amine carboxylates, amine sulfonates, and sulfate ester salts.

In addition to water, a water-soluble organic solvent can also be included. For example, the organic solvent used in the reaction can be removed and another organic solvent can be added.

In one embodiment of the present invention, the base film is a polyester film, and an easy-adhesion layer is provided between the base film and the heat-shielding layer, and the easy-adhesion layer contains a polyester resin.
This embodiment provides even better adhesion between the substrate and the heat shield layer, making it less likely that the heat shield layer will peel off or crack even when used outdoors for a long period of time.
In yet another embodiment, the substrate film is a polyester film that is substantially free of particles, and an easy-adhesion layer is provided between the substrate film and the heat-shielding layer, and the easy-adhesion layer contains a polyester resin. For example, the substrate film is substantially free of inorganic particles.
This embodiment further improves the adhesion between the substrate and the heat-shielding layer, making it less likely for the heat-shielding layer to peel or crack even when used outdoors for a long period of time. Furthermore, because the substrate exhibits high smoothness, the adhesion between the substrate and the easy-adhesion layer can be further improved, and the flexibility of the present invention can be more effectively exhibited. For example, even when the heat-shielding film is attached to a curved surface, delamination of the heat-shielding film can be suppressed.
Furthermore, since the base film is substantially particle-free, it exhibits excellent transparency, and is therefore preferable for agricultural use as it does not pose a risk of interfering with food growth, and for window coverings as it provides excellent visibility without blocking outside light.
Furthermore, since the base film does not substantially contain particles, it is easy to recycle after use and is therefore environmentally friendly, which is preferable.
Furthermore, since the base film does not substantially contain particles, it is possible to prevent particles contained in the film from falling off during long-term use.

The polyester resin used to form the easy-adhesion layer of the present invention may be linear, but is more preferably a polyester resin whose constituent components are a dicarboxylic acid and a diol having a branched structure. The dicarboxylic acid referred to here is one whose main component is terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. Furthermore, the branched glycol refers to a diol having a branched alkyl group, and examples thereof include 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2-methyl-2-butyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3-propanediol, 2-methyl-2-n-hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol.

The polyester resin preferably contains the branched glycol component, which is a more preferred embodiment of the invention, at a ratio of 10 mol% or more, and even more preferably 20 mol% or more, of the total glycol components. At 10 mol% or less, crystallinity increases, which may reduce the adhesion of the adhesive layer. The upper limit of the glycol component content of the total glycol components is preferably 80 mol% or less, and more preferably 70% by mass. At 80 mol% or more, the concentration of oligomers (by-products) increases, which may affect the transparency of the adhesive layer. Ethylene glycol is the most preferred glycol component other than the above compounds. Small amounts of diethylene glycol, propylene glycol, butanediol, hexanediol, or 1,4-cyclohexanedimethanol may also be used.

The dicarboxylic acid as a constituent component of the polyester resin is most preferably terephthalic acid or isophthalic acid. In addition to the above dicarboxylic acids, in order to impart water dispersibility to the copolymerized polyester resin, it is preferable to copolymerize 5-sulfoisophthalic acid or the like in a range of 1 to 10 mol %, and examples of such acids include sulfoterephthalic acid, 5-sulfoisophthalic acid, and 5-sodium sulfoisophthalic acid. A polyester resin containing a dicarboxylic acid having a naphthalene skeleton may be used, but in order to prevent a decrease in the adhesion of the heat shield layer, the quantitative proportion of such an acid is preferably 5 mol % or less of the total carboxylic acid components, and it may not be used at all.
The polyester resin contained in the easy-adhesion layer and the polyester film used for the base film may be the same polyester resin, or polyester resins having different physical properties may be appropriately selected.

When the total solids content of the polyester resin, urethane resin having a polycarbonate structure, and crosslinking agent in the coating solution is taken as 100% by mass, the lower limit of the crosslinking agent content is preferably 5% by mass, more preferably 7% by mass, even more preferably 10% by mass, and most preferably 12% by mass. A content of 5% by mass or more is preferred as it can improve blocking resistance. The upper limit of the crosslinking agent content is preferably 50% by mass, more preferably 40% by mass, even more preferably 35% by mass, and most preferably 30% by mass. A content of 50% by mass or less is preferred as it increases transparency.

When the total solids content of the polyester resin, urethane resin having a polycarbonate structure, and crosslinker in the coating solution is 100% by mass, the lower limit of the content of the urethane resin having a polycarbonate structure is preferably 5% by mass. A content of 5% by mass or more is preferable because it improves adhesion to the heat shield layer. The upper limit of the content of the urethane resin having a polycarbonate structure is preferably 50% by mass, more preferably 40% by mass, even more preferably 30% by mass, and most preferably 20% by mass. A urethane resin content of 50% by mass or less is preferable because it improves blocking resistance.

When the total solid content of the polyester resin, urethane resin, and crosslinking agent in the coating solution is 100% by mass, the content of the polyester resin is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 35% by mass or more, and most preferably 40% by mass or more. When the content of the polyester resin is 10% by mass or more, the adhesion between the easy-adhesion layer and the polyester film substrate becomes good, which is preferable.
The content of the polyester resin is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.
A polyester resin content of 80% by mass or less is preferred because the heat shield layer has good resistance to moist heat, and a polyester resin content of 10% by mass or more is preferred because the heat shield layer has good adhesion to the substrate.

The easy-adhesion layer of the present invention may contain known additives, such as surfactants, antioxidants, heat stabilizers, weather stabilizers, UV absorbers, organic lubricants, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc., within the range that does not impair the effects of the present invention.

In the present invention, it is also a preferred embodiment to add particles to the adhesion layer to further improve the blocking resistance of the adhesion layer. Examples of particles to be contained in the adhesion layer in the present invention include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, etc., or mixtures thereof. Further examples include other common inorganic particles, such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc., used in combination with other inorganic particles, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles.

The average particle size of the particles in the easy-adhesion layer (average particle size on a number basis as measured with a scanning electron microscope (SEM); the same applies below) is preferably 0.04 to 2.0 μm, and more preferably 0.1 to 1.0 μm. If the average particle size of the inactive particles is 0.04 μm or more, it becomes easier to form irregularities on the film surface, improving the film's handleability, such as its slipperiness and winding ability, and providing good processability during lamination, which is preferable. On the other hand, if the average particle size of the inactive particles is 2.0 μm or less, particle detachment is less likely to occur, which is preferable. The particle concentration in the easy-adhesion layer is preferably 1 to 20% by mass of the solid components.

The average particle size of the particles was measured by observing the particles on the cross section of the laminated polyester film using a scanning electron microscope, observing 30 particles, and taking the average value as the average particle size.

There are no particular limitations on the shape of the particles as long as they meet the objectives of the present invention; spherical particles and irregular, non-spherical particles can be used. The particle size of irregular particles can be calculated as the equivalent circle diameter. The equivalent circle diameter is calculated by dividing the observed particle area by π, taking the square root, and then multiplying it by two.

The adhesive layer can be formed after the film substrate is manufactured or during the manufacturing process. From the standpoint of productivity, it is particularly preferable to form the adhesive layer by applying a coating liquid to at least one side of an unstretched or uniaxially stretched PET film at any stage in the film manufacturing process.

Any known method can be used to apply this coating solution to PET film. Examples include reverse roll coating, gravure coating, kiss coating, die coating, roll brushing, spray coating, air knife coating, wire bar coating, pipe doctor coating, impregnation coating, and curtain coating. These methods can be used alone or in combination.

In the present invention, the thickness of the easy-adhesion layer can be set appropriately in the range of 0.001 to 2.00 μm, but to achieve both processability and adhesion, a range of 0.01 to 1.00 μm is preferred, more preferably 0.02 to 0.80 μm, and even more preferably 0.05 to 0.50 μm. A thickness of 0.001 μm or more provides good adhesion, which is preferable. A thickness of 2.00 μm or less is preferred, as blocking is less likely to occur.

<Heat barrier layer>
The heat-shielding film of the present invention has a heat-shielding layer laminated directly or via another layer on at least one surface of a substrate film. The heat-shielding layer is a layer formed from a cured product of a heat-shielding layer-forming composition containing antimony-doped tin oxide and a binder resin.

The primary average particle size of the antimony-doped tin oxide is less than 50 nm, preferably 1 nm or more but less than 50 nm, more preferably 1 nm or more but less than 40 nm, for example, 1 nm or more but less than 30 nm, even more preferably 1 nm or more but less than 20 nm, and may be 1 nm or more but less than 10 nm, for example, 1 nm or more but less than 10 nm is particularly preferred. A primary average particle size of 1 nm or more is preferred because it prevents aggregation of the antimony-doped tin oxide and the risk of impairing the transparency of the heat-shielding layer. A primary particle size of less than 50 nm is preferred because it distributes the antimony-doped tin oxide uniformly throughout the heat-shielding layer, resulting in excellent heat-shielding properties. The primary average particle size was measured by cutting the resin-embedded heat-shielding film with a microtome and observing the cross-section of the heat-shielding layer with a TEM.

It is preferable that antimony-doped tin oxide be uniformly distributed throughout the heat-shielding layer from the standpoints of heat-shielding properties and transparency. Uniform distribution throughout the heat-shielding layer is also preferable because it allows the cross-linking reaction of the binder components contained in the heat-shielding layer to proceed efficiently, resulting in a heat-shielding layer with high coating strength. The distribution of antimony-doped tin oxide within the heat-shielding layer can be confirmed from the degree of brightness when a cross-section of the heat-shielding film is observed with a TEM, as described above.

In the present invention, "antimony-doped tin oxide is uniformly distributed in the thermal barrier layer" can take various forms.
In one embodiment, the antimony-doped tin oxide may be uniformly distributed over the entire surface of the thermal barrier layer. For example, when the thermal barrier layer has a single-layer structure, the antimony-doped tin oxide may be uniformly distributed over at least one surface region. Alternatively, the antimony-doped tin oxide may be uniformly distributed over both surface regions of the thermal barrier layer.
For example, when the thermal barrier layer has a multi-layer structure, the antimony-doped tin oxide may be uniformly distributed in the outermost layer or in an intermediate region in the thickness direction of the thermal barrier layer.
In one embodiment, the antimony-doped tin oxide may be uniformly distributed throughout the thickness of the thermal barrier layer, that is, throughout the entire thermal barrier layer.
In one embodiment, the antimony-doped tin oxide may be uniformly distributed at a higher density in the surface region of the thermal barrier layer. For example, the density of the antimony-doped tin oxide on the substrate film side of the thermal barrier layer may be set to a different value from the density of the antimony-doped tin oxide on the surface of the thermal barrier layer opposite the substrate (the surface in contact with the atmosphere).

The binder resin contained in the heat-shielding layer preferably contains at least one resin selected from the group consisting of acrylate resin, acrylic resin, polyester resin, and polyurethane resin, more preferably selected from the group consisting of acrylate resin and acrylic resin, and even more preferably selected from acrylate resin. While not intended to be limited to a specific theory, using an acrylate resin as the binder resin crosslinks the binder resins while incorporating antimony-doped tin oxide particles, improving coating strength and resulting in a heat-shielding layer with excellent abrasion resistance, substrate adhesion, and flexibility.

Acrylate resins in the present invention include acrylate compounds, methacrylate compounds, and urethane acrylate compounds. When an acrylate resin is used as a binder resin, each can be used suitably. It is most preferable to use a urethane acrylate compound. By using a urethane acrylate compound, cure shrinkage can be suppressed and a heat-shielding layer with excellent flexibility and adhesion to the substrate can be obtained.

The binder resin may be a monomer, oligomer, or polymer. From the standpoint of solubility in organic solvents and ease of handling, it is preferable to use a monomer or oligomer. These may be used alone or in combination of two or more types.

When a monomer is used as the (meth)acrylate compound, examples include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate. The term "(meth)acrylate compound" encompasses both methacrylate and acrylate.

When an oligomer is used as the (meth)acrylate compound, examples include multifunctional (meth)acrylate oligomers, polyester acrylate oligomers, epoxy acrylate oligomers, polyether acrylate oligomers, polybutadiene acrylate oligomers, and silicone acrylate oligomers.

The urethane acrylate compound used in the present invention is one that contains a urethane bond and one or more radically curable functional groups selected from acryloyl and methacryloyl groups in the molecular chain. There are no particular restrictions on the synthesis method, but it can be obtained, for example, by reacting a polyhydric alcohol and an organic polyisocyanate with a hydroxyacrylate.

Examples of the polyhydric alcohols include neopentyl glycol, 3-methyl-1,5-pentanediol, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, tricyclodecanedimethylol, bis-[hydroxymethyl]cyclohexane, etc.; polyester polyols obtained by reacting the above polyhydric alcohols with polybasic acids (e.g., succinic acid, phthalic acid, hexahydrophthalic anhydride, terephthalic acid, adipic acid, azelaic acid, tetrahydrophthalic anhydride, etc.); polycaprolactone polyols obtained by reacting the above polyhydric alcohols with ε-caprolactone; polycarbonate polyols (e.g., polycarbonate diol obtained by reacting 1,6-hexanediol with diphenyl carbonate, etc.); and polyether polyols. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene oxide-modified bisphenol A.

Examples of the organic polyisocyanates include isocyanate compounds such as isophorone diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, xylene diisocyanate, diphenylmethane-4,4'-diisocyanate, and dicyclopentanyl isocyanate, as well as adducts of these isocyanate compounds and polymers of these isocyanates.

Examples of the hydroxy(meth)acrylate compound include pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, dimethylolcyclohexyl mono(meth)acrylate, and hydroxycaprolactone (meth)acrylate. Among these, pentaerythritol tri(meth)acrylate and dipentaerythritol penta(meth)acrylate are preferred in terms of hardness.

The acrylate compounds used in the present invention, such as urethane acrylate compounds, can also be commercially available. Examples of commercially available products include Mitsubishi Chemical's UV1700B (10 functional), UV7620EA (9 functional), UV7610B (9 functional), UV7600B (6 functional), and UV7650B (5 functional), Nippon Kayaku's DPHA40H (10 functional) and UX5003 (6 functional), Arakawa Chemical's Beamset 577 (6 functional), Taisei Fine Chemical's 8UX-015A (15 functional), and Shin-Nakamura Chemical's A-701A (2 functional), A-TMM-3 (3 functional), A-TMMT (4 functional), A-DPH (6 functional), and U15HA (15 functional).

The number of functional groups in the binder resin is preferably two or more, more preferably three or more, and even more preferably four or more. Two or more functional groups are preferred because they crosslink with each other, resulting in a heat-shielding layer with excellent curing properties and coating strength. The higher the number of functional groups, the better the curing properties. It is most preferred to use a polyfunctional urethane acrylate compound, preferably one with 20 or fewer functional groups and 16 or fewer functional groups, as this can prevent excessive curling and adverse effects on substrate adhesion and flexibility.

The thickness of the heat-shielding layer is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. A release layer thickness of 5 μm or less is preferred because it provides excellent flexibility and adhesion to the substrate. The smaller the thickness, the better from the perspective of flexibility and adhesion to the substrate. For example, a thickness of 0.5 μm or more is preferred to achieve excellent heat-shielding properties and coating strength.

The content of antimony-doped tin oxide contained in the thermal barrier layer is important for obtaining a thermal barrier layer with excellent thermal barrier properties. Increasing the content can improve the thermal barrier properties. On the other hand, when the thermal barrier properties are improved, the thickness of the thermal barrier layer tends to increase as the content of antimony-doped tin oxide increases, which may impair the mechanical properties of the thermal barrier layer.
In contrast, in the present invention, the content of antimony-doped tin oxide contained in the heat-shielding layer is increased, thereby providing high heat-shielding properties and also exhibiting high flexibility, substrate adhesion, and transparency. For example, the heat-shielding layer according to the present invention has a thickness of 5 μm or less, which satisfies all of high heat-shielding properties, high flexibility, substrate adhesion, and transparency, and can also be made thinner. This reduces adverse effects on food growth and improves durability when used repeatedly outdoors. Furthermore, the weight of the heat-shielding film itself can be reduced, which can contribute to fuel savings and reduce environmental impact, for example, in applications such as automotive window coverings.
As described above, in the present invention, the use of fine antimony-doped tin oxide having a primary particle size of less than 50 nm makes it possible to provide a heat shielding layer having excellent heat shielding properties while keeping the film thickness thin. Furthermore, the use of antimony-doped tin oxide having a primary particle size of less than 50 nm facilitates the crosslinking reaction of the binder resin, making it possible to provide a heat shielding layer having excellent coating strength.

The relationship between film thickness and heat-shielding properties can be expressed by the following formula 1. In the formula, the film thickness of the heat-shielding layer is n (μm), and T _1400nm means the spectral transmittance (%) at a wavelength of 1400 nm. The larger the value expressed by formula 1, the thinner the heat-shielding layer is and the higher its heat-shielding performance. The value of formula 1 is preferably 20 or more, more preferably 25 or more, and even more preferably 30 or more, with the larger the value being more preferable. A value of formula 1 of 20 or more is preferred because the film has excellent heat-shielding properties, flexibility, and adhesion to substrates, and is also excellent in durability when used outdoors for long periods of time.
(100-T _1400nm )/n... (Formula 1)

In one aspect, the relationship between the thickness n of the heat-shielding layer and the heat-shielding property, expressed by the following (Equation 1), may be 90 or less, for example 80 or less.

The surface roughness (Sa) of the surface of the heat-shielding layer opposite the film substrate is preferably 10 nm or less, more preferably 8 nm or less, and even more preferably 5 nm or less. If it is 10 nm or less, when the heat-shielding film is used in curtain or roll form, there is no risk of scratches caused by rubbing between the heat-shielding layer of the heat-shielding film and the surface of the substrate film opposite the heat-shielding layer, which could impair transparency. The smaller the surface roughness, the better. For example, a surface roughness of 0.1 nm or more is preferred, taking into account the slipperiness with the transport rolls in the heat-shielding film manufacturing process.

The content of antimony-doped tin oxide and binder resin in the heat-shield layer-forming composition is preferably antimony-doped tin oxide:binder resin = 70:30 to 99:1 by weight, more preferably 80:20 to 99:1, and particularly preferably 85:15 to 98:2. Keeping the content within the above range is preferable because it results in a heat-shield layer with excellent heat-shielding properties, flexibility, and coating strength.

The heat shield layer-forming composition may contain more than 50 mass% of antimony-doped tin oxide, for example, 60 mass% or more, or 70 mass% or more, relative to 100 parts by mass of the total of the antimony-doped tin oxide and the solid content of the binder resin, and may also contain 80 mass% or more of antimony-doped tin oxide.
By ensuring that the thickness is within this range, the heat-shielding film can have high heat-shielding properties, and can also exhibit high flexibility, substrate adhesion, and transparency.
In one embodiment, the thermal barrier layer-forming composition may contain 99% by mass or less, for example, less than 97% by mass, for example, 95% by mass or less, of antimony-doped tin oxide relative to 100 parts by mass of the total of the antimony-doped tin oxide and the solid content of the binder resin.
By keeping the thickness within this range, the heat-shielding film can have high heat-shielding properties, and can also exhibit high flexibility, substrate adhesion, and transparency. Furthermore, with the present invention, the thickness of the heat-shielding layer according to the present invention can be made 5 μm or less, which satisfies all of high heat-shielding properties, high flexibility, substrate adhesion, and transparency, and further thinning is also possible.

When using an acrylate resin as the binder resin, it is preferable to include a polymerization initiator. The polymerization initiator is preferably one that generates radicals upon exposure to heat or active energy rays. One or more types of initiators may be used, and a photoradical initiator and a thermal radical initiator may be used simultaneously.

There are no particular restrictions on the photoinitiator, and commonly used ones can be used. Specific examples include benzophenone, acetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoic acid, benzoin methyl benzoate, benzoin dimethyl ketal, 2,4-diethylthioxanthone, 1-hydroxycyclohexyl phenyl ketone, benzyl diphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, β-chloroanthraquinone, (2,4,6-trimethylbenzyldiphenyl)phosphine oxide, and 2-benzothiazole-N,N-diethyldithiocarbamate.

As photoinitiators, α-hydroxyalkylphenones and α-aminoalkylphenones, which are known to have particularly excellent surface curing properties, are suitable for use as they can suppress oxygen inhibition and increase coating film strength. Examples of α-hydroxyalkylphenones include 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one. Examples of α-aminoalkylphenones include 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholyl)phenyl]-1-butanone, and the like.

When using a photoinitiator, adding a sensitizer can promote absorption of active energy rays and further improve curing properties. There are no particular restrictions on the sensitizer, and any common one can be used, but anthracene derivatives and naphthalene derivatives are preferred. One or more types of sensitizers may be used.

The amount of polymerization initiator added is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, and most preferably 1% by mass or more and 7% by mass or less, relative to 100% by mass of the binder components in the heat shield layer. Amounts of 0.1% by mass or more are preferred because they do not generate an insufficient amount of radicals, which could result in insufficient curing. Amounts of 10% by mass or less are preferred because they reduce the amount of polymerization initiator residue contained in the heat shield layer, reducing contamination of the heat shield layer surface and preventing adverse effects on crop growth.

The amount of sensitizer added is preferably 0.1 to 5 times the mass of the photoinitiator. 0.1 to 2 times is more preferable. Amounts greater than 0.1 times are preferred because a sufficient sensitizing effect can be obtained. Amounts less than 5 times are preferred because they inhibit the photoinitiator's absorption of active energy rays, preventing the risk of an insufficient amount of radicals being generated.

The heat shield layer-forming composition preferably contains a leveling agent to improve its coatability. There are no particular restrictions on the leveling agent, and any common agent can be used, but polyorganosiloxane is preferably used, polydimethylsiloxane is more preferably used, and polydimethylsiloxane having a functional group is most preferably used. The use of polydimethylsiloxane having a functional group is preferred because it improves the leveling properties of the heat shield layer-forming composition when it is applied and dried, resulting in a uniform film.

Additives such as adhesion improvers and antistatic agents may be added to the heat-shielding layer of the present invention, as long as they do not impair the effects of the present invention.

The method for forming the heat-shielding layer is not particularly limited, and a method is used in which a heat-shielding layer-forming composition, in which antimony-doped tin oxide and a binder resin are dissolved or dispersed in an organic solvent, is spread on one side of the film substrate by coating, etc., the solvent is removed by drying, the film is dried by heating, and then the film is cured by irradiation with active energy rays or heat.

When curing using a photoinitiator, the drying temperature for solvent drying is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The heating time is preferably 30 seconds or less, and more preferably 20 seconds or less. A temperature of 110°C or lower reduces the thermal load on the film, making it less likely to cause poor appearance due to thermal shrinkage of the film and reducing the risk of flatness problems due to sagging when used in agricultural greenhouses or for window coverings. A temperature higher than 50°C is preferable because the dilution solvent used during application will not dry sufficiently, eliminating the risk of process contamination.

As the active energy rays for curing the coating film using a photoinitiator, ultraviolet rays, electron beams, X-rays, etc. can be used, but ultraviolet rays are preferred because they are easy to use. The amount of ultraviolet light to be irradiated is preferably 30 to 500 mJ/ ^cm2 in terms of cumulative light dose, and more preferably 30 to 300 mJ/ ^cm2 . A dose of 30 mJ/cm2 or ^more is preferred because the resin cures sufficiently. A dose of 500 mJ/ ^cm2 or less is preferred because the processing speed can be improved, allowing the heat-shielding film to be produced economically.

In the present invention, it is preferable to add a solvent with a boiling point of 90°C or higher as the organic solvent in the heat shield layer-forming composition. Adding a solvent with a boiling point of 90°C or higher prevents bumping during drying, levels the coating film, and improves the smoothness of the coating film surface after drying. The amount added is preferably about 10 to 80% by mass of the total coating liquid.

Any known coating method can be used to apply the coating liquid, including roll coating methods such as gravure coating and reverse coating, bar coating methods such as wire bars, die coating, spray coating, and air knife coating.

<Physical properties of heat-shielding film>
The heat-shielding property can be evaluated by the transmittance in the infrared region measured using spectral transmittance.

The spectral transmittance at a wavelength of 1200 nm (T _1200nm ) is preferably 20%, more preferably 15% or less, and even more preferably 10% or less, with the smaller the better. A T _1200nm of 20% or less means that infrared rays are less likely to transmit when the heat-shielding film is used, which is preferred as it provides excellent heat-shielding properties.
For example, T _{1200 nm} is 0.1% or more.

The spectral transmittance at a wavelength of 1400 nm (T _{1400 nm} ) is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less, with the smaller the better. For the reasons mentioned above, a T _{1400 nm} of 20% or less is preferred because it provides excellent heat insulation. For example, T _{1400 nm} is 0.1% or more.

The spectral transmittance at a wavelength of 1800 nm (T _{1800 nm} ) is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less, with the smaller the better. For the reasons mentioned above, a T _{1800 nm} of 5% or less is preferred because it provides excellent heat insulation. For example, T _{1400 nm} may be 0 or 0.01% or more.

In the present invention, when T _{1200 nm,} T _{1400 nm, and} T _{1800 nm} have such a relationship, heat rays from sunlight can be more effectively blocked, and the effect of excellent heat-shielding properties can be achieved.

In the present invention, the spectral transmittance such as T _{1400 nm} can be measured using an ultraviolet-visible-near infrared spectrophotometer, and can be evaluated using a commercially available product such as UV-3150 manufactured by Shimadzu Corporation.

Transparency can be evaluated using the haze value. A haze value of 8% or less is preferred, 5% or less is more preferred, 3% or less is even more preferred, and 1% or less is most preferred. A haze value of 8% or less is preferred because it allows light necessary for food growth to pass through, contributing to a stable supply of crops and improved productivity. It is also preferred when used for window coverings because it provides excellent visibility both indoors and outdoors. For example, the haze value is 0.01% or more, and may be 0.05% or more.

Transparency can also be evaluated by total light transmittance. A total light transmittance of 50% or more is preferable, 60% or more is more preferable, and 65% or more is even more preferable. A total light transmittance of 50% or more is preferable because it allows light of wavelengths necessary for food growth to be efficiently introduced from the outside into the indoor environment. For example, the total light transmittance may be 95% or less.

Flexibility can be evaluated using the cylindrical mandrel method. The minimum mandrel diameter at which cracks occur in the heat-shielding layer is preferably less than 4 mm, more preferably less than 3 mm, and the smaller the better. If it is less than 4 mm, there is no risk of cracks occurring in the heat-shielding layer when the heat-shielding film is used in curtain or roll form, and handling is also excellent, making it preferable. Evaluation using the mandrel method can be performed in accordance with JIS K 5600-5-1.

Curability can be evaluated using pencil hardness. The pencil hardness of the heat-shielding layer is preferably H or higher, and more preferably 2H or higher. A pencil hardness of H or higher is preferred because it means that the coating film is sufficiently hardened, preventing the heat-shielding layer from being scraped off even when used outdoors for long periods of time, and providing excellent durability.

Scratch resistance can be evaluated by steel wool evaluation. For example, #0000 steel wool can be moved back and forth over the heat shield layer under a constant load, and the number of scratches created on the heat shield layer can be evaluated. Preferably, the number of scratches is 5 or less, more preferably 3 or less, and most preferably no scratches at all. The fewer scratches there are, the less likely the heat shield layer is to be scratched when used outdoors, and there is no risk of a decrease in heat shielding properties or transparency, making it more durable, which is preferable. Detailed evaluation methods will be described later.

The adhesion of the heat shield layer to the substrate can be evaluated by cross-cut evaluation. For example, a grid-shaped cut is made on the heat shield layer, adhesive tape is applied to the cut surface, and the number of squares that come off when peeled off can be evaluated. When quantified as substrate adhesion (%) = 100 - (number of peeled squares), a substrate adhesion rate of 95% or more is preferred, 98% or more is more preferred, and 100% is most preferred. A rate of 95% or more is preferred because there is no risk of the heat shield layer peeling off when used outdoors for long periods of time, and it has excellent durability. Detailed evaluation methods are described below.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. The property values used in the present invention were evaluated using the following methods.

(Primary particle size of antimony-doped tin oxide)
The heat-shielding film was embedded in epoxy resin, and ultrathin sections were prepared using an ultramicrotome. Carbon deposition was then applied to prepare samples for TEM observation. The cross sections of these samples were observed using a transmission electron microscope (JEOL, JEM2100). Measurements were performed at an accelerating voltage of 200 kV and a direct magnification of 50,000. The diameters of 10 randomly selected particles were measured from the obtained image, and the average value was used as the primary particle size.

(Base film thickness)
Using a Millitron (electronic microindicator), four 5 cm square samples were cut out from four arbitrary points on the film to be measured, and measurements were taken at five points on each sample (total of 20 points), and the average value was taken as the thickness.

(Thermal barrier layer thickness)
The cut-out heat-shielding film was embedded in resin and cut into ultrathin sections using an ultramicrotome, which were then directly observed at a magnification of 20,000 times using a JEOL JEM2100 transmission electron microscope, and the film thickness of the release layer was measured from the observed TEM image.

(spectral transmittance)
The transmittance at each wavelength was measured using an ultraviolet-visible-near infrared spectrophotometer (Shimadzu Corporation, UV-3150).

(Haze value)
The haze was measured in accordance with JIS K 7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH7000II).

(Total light transmittance)
The haze was measured in accordance with JIS K 7361-1 using a haze meter (manufactured by Nippon Denshoku Industries, Ltd., NDH7000II).

(Pencil hardness)
Measurement was carried out in accordance with JIS K 5600-5-4.

(Steel wool hardness)
A steel wool evaluation jig was prepared by attaching steel wool (Bonstar (registered trademark) No. 0000, manufactured by Japan Steel Wool Co., Ltd.) weighing 200 g to a metal base measuring 700 ^mm2 . Using this jig, the release surface side of the heat shielding film was rubbed back and forth 10 times while applying a load of 200 g so that the steel wool was in contact with the heat shielding layer side of the heat shielding film. A 2 x 2 cm area in the center of the rubbed surface was observed under reflected fluorescent light, and the number of scratches visible to the naked eye was evaluated. The number of scratches was determined according to the following criteria and evaluated as follows:
◎: Number of scratches = 0 ○: 1 ≦ Number of scratches < 3 △: 3 ≦ Number of scratches ≦ 5 ×: 5 < Number of scratches

(Mandrel Evaluation)
Measurement was carried out in accordance with JIS K 5600-5-1.

(cross cut)
Using a cutter guide with a gap spacing of 2 mm, 100 grid-shaped cuts are made on the surface of the heat-shielding layer, penetrating the heat-shielding layer and reaching the film substrate. Next, cellophane adhesive tape (manufactured by Nichiban, No. 405; 24 mm wide) is attached to the grid-shaped cut surface and rubbed with an eraser to ensure complete adhesion. Thereafter, the cellophane adhesive tape is peeled vertically from the heat-shielding layer surface of the heat-shielding film, and the number of grids that have peeled off from the heat-shielding layer surface of the heat-shielding film is counted visually, and the adhesion between the heat-shielding layer and the film substrate is calculated using the following formula. Note that even grids that are partially peeled off are counted as peeled grids.
Adhesion to substrate (%) = 100 - (number of peeled squares)
The adhesion to the substrate (%) was evaluated according to the following criteria.
◎: 100%
〇: 98% or more, less than 100% △: 95% or more, less than 98% ×: Less than 95%

(Method for measuring number average molecular weight of polycarbonate polyol)
When a urethane resin having a polycarbonate structure is measured by proton nuclear magnetic resonance spectroscopy (H-NMR), a peak derived from a methylene group adjacent to the OCOO bond is observed at around 4.1 ppm. Furthermore, a peak derived from a methylene group adjacent to the urethane bond formed by the reaction of polyisocyanate with polycarbonate polyol is observed about 0.2 ppm higher in the magnetic field than the peak. The number average molecular weight of the polycarbonate polyol was calculated from the integral values of these two peaks and the molecular weights of the monomers constituting the polycarbonate polyol.

(Polymerization of urethane resin A-1 having a polycarbonate structure)
27.5 parts by mass of hydrogenated m-xylylene diisocyanate, 6.5 parts by mass of dimethylolpropanoic acid, 60 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 1800, 6 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added to a four-neck flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer. The mixture was stirred for 3 hours at 75°C under a nitrogen atmosphere, and it was confirmed that the reaction solution had reached the predetermined amine equivalent. Next, 5 parts by mass of trimethylolpropane was added, and the mixture was stirred for 1 hour at 75°C under a nitrogen atmosphere. It was confirmed that the reaction solution had reached the predetermined amine equivalent. After the reaction solution was cooled to 40°C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the temperature was adjusted to 25°C. The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 2000 min ^-1 . Thereafter, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-1) with a solids content of 34 mass%.

(Polymerization of urethane resin A-2 having a polycarbonate structure)
A four-neck flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer was charged with 25 parts by weight of 4,4-dicyclohexylmethane diisocyanate, 5 parts by weight of dimethylolpropanoic acid, 52 parts by weight of polyhexamethylene carbonate diol having a number average molecular weight of 2600, 6 parts by weight of neopentyl glycol, and 84.00 parts by weight of acetone as a solvent. The mixture was stirred for 3 hours at 75 ° C. under a nitrogen atmosphere, and it was confirmed that the reaction solution reached the predetermined amine equivalent. Next, 18 parts by weight of a polyisocyanate compound having an isocyanurate structure made from hexamethylene diisocyanate (manufactured by Asahi Kasei Chemicals, Duranate TPA, trifunctional) was added, and the mixture was stirred for 1 hour under a nitrogen atmosphere at 75 ° C. It was confirmed that the reaction solution reached the predetermined amine equivalent. Then, the reaction solution temperature was lowered to 50 ° C., and 8 parts by weight of methyl ethyl ketoxime was added dropwise. After cooling this reaction solution to 40°C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the temperature was adjusted to 25°C. While stirring and mixing at 2000 min-1, the polyurethane prepolymer solution was added and dispersed in water. Thereafter, acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-2) with a solids content of 35% by mass.

(Polymerization of Blocked Isocyanate Crosslinking Agent B-1)
In a flask equipped with a stirrer, thermometer, and reflux condenser, 66.04 parts by mass of a polyisocyanate compound having an isocyanurate structure derived from hexamethylene diisocyanate (Duranate TPA, manufactured by Asahi Kasei Chemicals Corporation) and 95 parts by mass of 3,5-dimethylpyrazole (dissociation temperature: 120°C, boiling point: 218°C) were added dropwise to 17.50 parts by mass of N-methylpyrrolidone, and the mixture was maintained at 70°C for 1 hour under a nitrogen atmosphere. Subsequently, 30 parts by mass of dimethylolpropanoic acid were added dropwise. The infrared spectrum of the reaction solution was measured, and after confirming that the absorption of the isocyanate group had disappeared, 5.59 parts by mass of N,N-dimethylethanolamine and 132.5 parts by mass of water were added to obtain a blocked polyisocyanate aqueous dispersion (B-1) with a solids content of 40% by mass. The blocked isocyanate crosslinking agent had 4 functional groups and an NCO equivalent of 280.

(Polymerization of Blocked Isocyanate Crosslinking Agent B-2)
A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 100 parts by weight of a polyisocyanate compound having an isocyanurate structure derived from hexamethylene diisocyanate (Duranate TPA, manufactured by Asahi Kasei Chemicals), 55 parts by weight of propylene glycol monomethyl ether acetate, and 30 parts by weight of polyethylene glycol monomethyl ether (average molecular weight 750), and the mixture was maintained at 70°C for 4 hours under a nitrogen atmosphere. The reaction mixture was then cooled to 50°C, and 47 parts by weight of methyl ethyl ketoxime was added dropwise. The infrared spectrum of the reaction mixture was measured, and it was confirmed that the absorption of the isocyanate group had disappeared. 210 parts by weight of water was added to obtain an oxime-blocked isocyanate crosslinking agent (B-2) with a solids content of 40% by weight. The blocked isocyanate crosslinking agent had 3 functional groups and an NCO equivalent of 170.

(Polyester Resin Polymerization C-1)
A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate, 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate, and a transesterification reaction was carried out at a temperature of 160 to 220°C over 4 hours. The temperature was then raised to 255°C, and the reaction system was gradually reduced in pressure, followed by reaction for 1 hour and 30 minutes under a reduced pressure of 30 Pa to obtain a copolymer polyester resin (C-1). The obtained copolymer polyester resin (C-1) was pale yellow and transparent. The reduced viscosity of the copolymer polyester resin (C-1) was measured and found to be 0.70 dl/g. The glass transition temperature measured by DSC was 40°C.

(Preparation of Polyester Water Dispersion Cw-1)
A reactor equipped with a stirrer, a thermometer, and a reflux device was charged with 15 parts by mass of polyester resin (C-1) and 15 parts by mass of ethylene glycol n-butyl ether, and the mixture was heated to 110°C and stirred to dissolve the resin. After the resin was completely dissolved, 70 parts by mass of water was gradually added to the polyester solution with stirring. After the addition, the liquid was cooled to room temperature with stirring to produce a milky white polyester water dispersion (Cw-1) with a solids content of 15% by mass.

(Production of Polyester Film X1)
As a raw polymer for the film, PET resin pellets having an intrinsic viscosity of 0.62 dl/g (solvent: phenol/tetrachloroethane = 60/40) and containing substantially no particles were dried at 135°C for 6 hours under a reduced pressure of 133 Pa. Thereafter, the pellets were fed into an extruder, melt-extruded into a sheet at about 280°C, and rapidly cooled and solidified on a rotating cooled metal roll maintained at a surface temperature of 20°C, to obtain an unstretched PET sheet.

This unstretched PET sheet was heated to 100°C using a group of heated rolls and an infrared heater, and then stretched 3.5 times in the longitudinal direction using a group of rolls with different peripheral speeds to obtain a uniaxially stretched PET film.

Next, the following easy-adhesion layer-forming coating solution, which had been left to stand at room temperature for 5 hours or more, was applied to one side of the PET film by roll coating, and then dried at 80°C for 20 seconds. The final coating amount after drying (after biaxial stretching) was adjusted to 0.15 g/ ^m2 (coating layer thickness after drying: 150 nm). Subsequently, the film was stretched 4.0 times in the width direction at 120°C using a tenter, and with the width direction length of the film fixed, it was heated at 230°C for 5 seconds, and further subjected to a 3% width direction relaxation treatment at 100°C for 10 seconds to obtain a 100 μm polyester film X1.
(Preparation of coating solution for forming adhesive layer)
The following coating agent was mixed with a mixed solvent of water and isopropanol to prepare a coating solution with a solids mass ratio of urethane resin solution (A-2)/crosslinking agent (B-1)/polyester water dispersion (Cw-1) of 22/10/68.
Urethane resin solution (A-2) 2.71 parts by weight Crosslinking agent (B-1) 1.00 parts by weight Polyester water dispersion (Cw-1) 19.05 parts by weight Particles 0.47 parts by weight (dry-process silica with an average particle size of 200 nm, solid content 3.5% by weight)
Particles: 1.85 parts by mass (silica sol with an average particle size of 40 to 50 nm, solid content concentration: 30% by mass)
Surfactant: 0.30 parts by mass (silicone-based, solid content: 10% by mass)

(Production of Polyester Film X2)
Polyester film X2 was obtained in the same manner as polyester film X1, except that the urethane resin was changed to (A-1).

(Production of Polyester Film X3)
Polyester film X3 was obtained in the same manner as polyester film X1, except that the crosslinking agent was changed to (B-2).

(Production of Polyester Film X4)
Polyester film X4 was obtained in the same manner as polyester film X1, except that the following coating agent was mixed into a mixed solvent of water and isopropanol, and the solid mass ratio of urethane resin solution (A-1)/crosslinking agent (B-1)/polyester water dispersion (Cw-1) was changed to 25/26/49.
Urethane resin solution (A-1) 3.55 parts by weight Crosslinking agent (B-1) 3.16 parts by weight Polyester water dispersion (Cw-1) 16.05 parts by weight Particles 0.47 parts by weight (dry-process silica with an average particle size of 200 nm, solid content 3.5% by weight)
Particles: 1.85 parts by mass (silica sol with an average particle size of 40 to 50 nm, solid content concentration: 30% by mass)
Surfactant: 0.30 parts by mass (silicone-based, solid content: 10% by mass)

Example 1
The following composition for forming a heat shield layer was applied to the adhesive layer side of polyester film X1 using reverse gravure coating so that the thickness of the heat shield layer after drying would be 2.7 μm, and the coating was dried at 90° C. for 15 seconds. The dried coating was irradiated with ultraviolet light (LightHammer MARK II, H bulb, manufactured by Heraeus) at an integrated light intensity of 200 mJ/ ^cm2 to obtain a heat shield film. The obtained heat shield film was evaluated for flexibility, heat shielding properties, curing properties, abrasion resistance, transparency, and substrate adhesion, and good evaluation results were obtained.
Methyl ethyl ketone 59.70 parts by mass Propylene glycol monomethyl ether 14.93 parts by mass
Antimony-doped tin oxide (primary particle size 8 nm) 22.50 parts by mass Binder resin: dipentaerythritol hexaacrylate 2.50 parts by mass (product name: A-DPH, Shin-Nakamura Chemical, hexafunctional acrylate compound)
Polymerization initiator: 0.13 parts by mass of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (product name: Omnirad 907, manufactured by IGM Resins)
Leveling agent: 0.24 parts by mass (product name: BYK-3510, manufactured by BYK Japan)

Example 2
A heat shielding film was obtained in the same manner as in Example 1, except that the composition for forming the heat shielding layer was changed to the following.
Methyl ethyl ketone 59.75 parts by mass Propylene glycol monomethyl ether 14.94 parts by mass
Antimony-doped tin oxide (primary particle size 8 nm) 23.75 parts by mass Binder resin: dipentaerythritol hexaacrylate 1.25 parts by mass (product name: A-DPH, Shin-Nakamura Chemical, hexafunctional acrylate compound)
Polymerization initiator: 0.06 parts by mass of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (product name: Omnirad 907, manufactured by IGM Resins)
Leveling agent: 0.25 parts by mass (product name: BYK-3510, manufactured by BYK Japan)

Example 3
A heat shielding film was obtained in the same manner as in Example 1, except that the composition for forming the heat shielding layer was changed to the following.
Methyl ethyl ketone 59.77 parts by mass Propylene glycol monomethyl ether 14.94 parts by mass
Antimony-doped tin oxide (primary particle size 8 nm) 24.25 parts by mass Binder resin: dipentaerythritol hexaacrylate 0.75 parts by mass (product name: A-DPH, Shin-Nakamura Chemical, hexafunctional acrylate compound)
Polymerization initiator: 0.04 parts by mass of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (product name: Omnirad 907, manufactured by IGM Resins)
Leveling agent: 0.25 parts by mass (product name: BYK-3510, manufactured by BYK Japan)

Example 4
A heat shielding film was obtained in the same manner as in Example 1, except that the composition for forming the heat shielding layer was changed to the following.
Methyl ethyl ketone 59.60 parts by mass Propylene glycol monomethyl ether 14.90 parts by mass
Antimony-doped tin oxide (primary particle size 8 nm) 20.00 parts by mass Binder resin: 10-functional urethane acrylate compound 5.00 parts by mass (product name: UV-1700B, manufactured by Mitsubishi Chemical Corporation)
Polymerization initiator: 0.25 parts by mass of 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (product name: Omnirad 907, manufactured by IGM Resins)
Leveling agent: 0.25 parts by mass (product name: BYK-3510, manufactured by BYK Japan)

Example 5
A heat-shielding film was obtained in the same manner as in Example 1, except that the binder resin was changed to a 10-functional urethane acrylate compound (product name: UV-1700B, manufactured by Mitsubishi Chemical Corporation).

Example 6
A heat-shielding film was obtained in the same manner as in Example 1, except that the binder resin was changed to a 15-functional urethane acrylate compound (product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd.).

Example 7
A heat-shielding film was obtained in the same manner as in Example 1, except that the binder resin was changed to a tetrafunctional acrylate compound (product name: A-TMMT, manufactured by Shin-Nakamura Chemical Co., Ltd.).

(Example 8)
A heat-shielding film was obtained in the same manner as in Example 1, except that the binder resin was changed to a trifunctional acrylate compound (product name: A-TMM-3, manufactured by Shin-Nakamura Chemical Co., Ltd.).

Example 9
A heat-shielding film was obtained in the same manner as in Example 1, except that the binder resin was changed to a bifunctional acrylate compound (product name: A-701A, manufactured by Shin-Nakamura Chemical Co., Ltd.).

Example 10
A heat shielding film was obtained in the same manner as in Example 1, except that the coating was carried out so that the thickness of the heat shielding layer was 3.8 μm.

Example 11
A heat-shielding film was obtained in the same manner as in Example 1, except that the coating was carried out so that the heat-shielding layer had a thickness of 4.9 μm.

Example 12
A heat-shielding film was obtained in the same manner as in Example 1, except that the coating was carried out so that the thickness of the heat-shielding layer was 1.3 μm.

Example 13
A heat shielding film was obtained in the same manner as in Example 1, except that the primary particle size of the antimony-doped tin oxide was changed to 10 nm.

Example 14
A heat shielding film was obtained in the same manner as in Example 1, except that the primary particle size of the antimony-doped tin oxide was changed to 20 nm.

Example 15
A heat-shielding film was obtained in the same manner as in Example 1, except that the polyester film was changed to Polyester Film X2.

Example 16
A heat-shielding film was obtained in the same manner as in Example 1, except that the polyester film was changed to Polyester film X3.

(Example 17)
A heat-shielding film was obtained in the same manner as in Example 1, except that the polyester film was changed to Polyester film X4.

(Comparative Example 1)
A heat shielding film was obtained in the same manner as in Example 1, except that the composition for forming the heat shielding layer was changed to the following.
Methyl ethyl ketone 59.80 parts by mass Propylene glycol monomethyl ether 14.95 parts by mass
Antimony-doped tin oxide (primary particle size 8 nm) 25.00 parts by mass Leveling agent 0.25 parts by mass (product name: BYK-3510, manufactured by BYK Japan)
Since the heat-shielding film did not contain a binder resin in the composition for forming a heat-shielding layer, a uniform coating film was not formed, resulting in a high haze value. Furthermore, the coating film strength was insufficient, resulting in poor pencil hardness and steel wool hardness. Furthermore, the adhesion to the polyester film X1 was poor, and the durability was insufficient for long-term outdoor use.

(Comparative Example 2)
A heat-shielding film was obtained in the same manner as in Example 1, except that the primary particle size of the antimony-doped tin oxide was changed to 50 nm. Because the primary particle size of the antimony-doped tin oxide in this heat-shielding film was 50 nm or more, the heat-shielding property was insufficient and the haze value was also high. Furthermore, because the crosslinking reaction of the binder resin did not proceed easily, the curability and abrasion resistance were insufficient, and the durability was insufficient for long-term outdoor use.

As is clear from the results of the examples, the heat-shielding film of the present invention has high heat-shielding properties. Furthermore, the heat-shielding film of the present invention has high transparency (light transmittance) while also having high heat-shielding properties.
Therefore, it can be suitably used for agricultural purposes and as a building material for automobile window coverings, residential window coverings, etc. Furthermore, it does not adversely affect the growth of horticultural crops, and when used for window coverings, it can let in outside light without blocking it.
Furthermore, the heat-shielding film of the present invention has excellent abrasion resistance and coating strength, and therefore can be used for a long period of time without any deterioration in performance.
Furthermore, the heat-shielding film of the present invention has excellent flexibility and therefore excellent handleability, and can suppress film cracking in the heat-shielding layer even when used in a shape such as a curtain or roll. Moreover, even when used in such a shape, the film can have high heat-shielding properties and transparency (light transmittance).
Furthermore, the heat-shielding film of the present invention also has excellent abrasion resistance.

The heat-shielding film of the present invention has high heat-shielding properties and high transparency, so it does not adversely affect the growth of horticultural crops and can let in outside light without blocking it when used for window coverings. Furthermore, it has excellent abrasion resistance and coating strength, so it can be used suitably for long periods of time without its performance decreasing. In addition, it has excellent flexibility, so it is easy to handle, and can be used suitably in the form of a curtain or roll without causing problems such as film cracking in the heat-shielding layer.

Claims (9)

A heat-shielding film having a base film and a heat-shielding layer,
an easy-adhesion layer between the base film and the heat-shielding layer,
the thermal barrier layer is formed from a thermal barrier layer-forming composition containing antimony-doped tin oxide and a binder resin,
the antimony-doped tin oxide contained in the thermal barrier layer has an average primary particle size of less than 50 nm, and the minimum diameter of a mandrel at which cracks occur in the thermal barrier layer by a cylindrical mandrel method is less than 4 mm,
The heat-shielding film has a spectral transmittance T1400nm at a wavelength of 1400 nm of 20% or less and a haze value of 8% or less. the base film is a polyester film that does not substantially contain particles , and the easy-adhesion layer is formed by curing a composition that contains a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin;
The heat-shielding film according to claim 1 . The heat-shielding film according to claim 1 or 2, wherein the pencil hardness of the heat-shielding layer is H or higher. When the relationship between the thickness n of the thermal barrier layer and the thermal barrier property is expressed by the following (Equation 1),
The heat-shielding film according to any one of claims 1 to 3, wherein the value represented by (Formula 1) is 20 or more:
(100-T1400nm)/n (Formula 1)
In formula 1, the film thickness n is 0.5 μm or more and 5 μm or less. The heat-shielding film according to any one of claims 1 to 4, having a total light transmittance of 50% or more. The heat-shielding film according to any one of claims 1 to 5, wherein the content of antimony-doped tin oxide and binder resin in the heat-shielding layer-forming composition is antimony-doped tin oxide:binder resin = 70:30 to 99:1 by weight. The heat-shielding film according to any one of claims 1 to 6, wherein the binder resin comprises at least one resin selected from the group consisting of acrylate resin, acrylic resin, polyester resin, and polyurethane resin. An agricultural heat-shielding film comprising the heat-shielding film described in any one of claims 1 to 7. A heat-shielding film for window covering, comprising the heat-shielding film according to any one of claims 1 to 7.