High-temperature-resistant thermosensitive coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of heat-sensitive materials, and provides a high-temperature-resistant heat-sensitive coating as well as a preparation method and application thereof. According to the high-temperature-resistant thermosensitive coating, the color developing agent, the leuco dye microcapsule emulsion, the cross-linking agent, the dispersing agent and the auxiliary are adopted as main components, leuco dye microcapsules in the leuco dye microcapsule emulsion are of a core-shell structure, the core is leuco dye, and the shell is organic silicon modified polyurethane; the organic silicon modified polyurethane is prepared from the following raw materials: flame-retardant modified polyol, polyisocyanate, an organic silicon modifier and a chain extender, and the dispersing agent comprises polyvinyl alcohol and nitrate. The heat-sensitive coating provided by the invention has excellent high temperature resistance and flame retardance, a heat-sensitive color development layer can be further obtained through coating, a high-temperature-resistant heat-sensitive material is prepared, printed patterns and bar codes have the characteristic of high definition, and the application field of the heat-sensitive material is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of thermosensitive materials, and more specifically, to a high-temperature resistant thermosensitive coating and a preparation method and application thereof. Background Art

[0002] Thermosensitive materials are materials that are extremely sensitive to temperature changes. Thermosensitive coatings are usually formed by a color reaction between a colorless dye and a developer by heating. The recorded image does not require the use of ink or printing ink. It is widely used and is commonly seen in printing materials such as supermarket receipts, movie tickets, and lottery tickets. With the continuous development of science and technology and industry, more and more fields have put forward higher requirements for the high temperature tolerance of thermosensitive materials. For example, in the field of industrial manufacturing, thermal paper is needed to print equipment labels, operation process instructions, and safety warning signs in heat treatment workshops, smelters, and ceramic manufacturing plants. They are used for production line identification, product tracking, equipment maintenance, etc. in these industries. Therefore, these labels are required to maintain stable performance at extremely high temperatures (≥100°C) and clearly display the required information; for example, in the food baking industry, the internal temperature of equipment such as ovens and microwave ovens often reaches above 100°C. Thermosensitive materials are attached to the inside or outside of these equipment to mark important information such as food name, baking time, temperature, etc. to ensure food safety and quality; for example, in the medical industry, during the high-temperature disinfection process of surgical instruments and experimental equipment, thermal labels are required to remain clear and identifiable to ensure the correct use and maintenance of the equipment. However, in the formula of thermal coatings used in traditional thermal materials (thermal paper, thermal materials, etc.), the colorless dye and the color developer are generally in direct contact. When stimulated by heat, a chemical reaction will occur and the color will develop rapidly, so it is difficult to control the reaction activity. At present, the only way is to adjust the type and ratio of the colorless dye and the color developer to reduce the reaction activity and increase the initial color development temperature. Due to the above limitations, the thermal coating of the thermal material basically starts to develop color when the environment is above 70°C, and the color is basically saturated at 100-130°C (the surface of the material is fully colored). It is easy to be damaged or faded in an extremely high temperature (≥100°C) environment, and it is impossible to keep the image or label clear and identifiable under higher temperature conditions. In addition, such thermal materials have no flame retardant and fireproof properties. There are great safety risks and limited use areas when used in high temperature environments, which limits their application in high temperature environments.

[0003] Therefore, there is an urgent need to develop a high-temperature resistant thermosensitive material with flame retardant and fireproof properties that can be used in extremely high temperature environments (≥100°C) to expand its application areas. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a high temperature resistant thermosensitive coating and a preparation method and application thereof. The thermosensitive material provided by the present invention not only has high temperature resistance (initial color development temperature ≥ 130°C, saturated color development temperature ≥ 180°C), can be used at high temperatures ≥ 100°C, but also has flame retardant and fireproof properties, reduces safety hazards, and can meet the use requirements of high temperature scenes.

[0005] A first aspect of the present invention provides a high temperature resistant thermosensitive coating.

[0006] Specifically, a high temperature resistant thermosensitive coating comprises the following components:

[0007] Color developer,

[0008] Leuco dye microcapsule emulsion,

[0009] Crosslinking agent,

[0010] Dispersants,

[0011] Additives;

[0012] The leuco dye microcapsules in the leuco dye microcapsule emulsion are of a core-shell structure, wherein the core is a leuco dye and the shell is an organosilicon-modified polyurethane, and the raw materials for preparing the organosilicon-modified polyurethane include flame-retardant modified polyols, polyisocyanates, organosilicon modifiers, and chain extenders;

[0013] The dispersant includes polyvinyl alcohol and nitrate.

[0014] The present invention utilizes colorless dye microcapsules with a core-shell structure to encapsulate the colorless dye. The microcapsules have good sealing properties, so that the colorless dye is highly isolated from the external environment, thereby separating the colorless dye and the developer, avoiding the problem of difficult control of reaction activity caused by direct contact between the colorless dye and the developer, and also protecting the colorless dye from the influence of the external environment, avoiding the occurrence of high background color and color development problems, and the regulation of thermal response performance is more precise and controllable. The color development is stable at high temperature and the color development pattern is still clear and recognizable, suitable for use in high temperature environments, and has the characteristics of fast development, high resolution, green environmental protection, etc. The flame retardant modified polyol in the colorless dye microcapsule forms the soft segment of the microcapsule shell, and the polyisocyanate forms the hard segment of the microcapsule shell. The flame retardant modified polyol not only does not destroy the strength of the material, but also has good flame retardant properties and high temperature resistance, so that the product can be used normally and safely under high temperature conditions, preventing the material from catching fire at high temperature and improving safety. Therefore, the present invention not only introduces flame retardant materials, thereby improving the flame retardant properties (soft segment) of the thermosensitive coating, but also improves the mechanical properties (hard segment), flame retardant properties and high temperature resistance of the polyurethane shell. The organosilicon modifier can increase the self-emulsification performance, reduce the amount of emulsifier, avoid the negative impact of excessive emulsifier on the water resistance of the product, etc., and can also increase the glass transition temperature Tg of the polyurethane shell, further enhancing the high temperature resistance of the polyurethane shell, which is mainly due to the unique chemical structure of the Si-O-Si chain in the organosilicon, which has excellent chemical stability, high temperature resistance, water resistance and moisture resistance, etc. Through copolymerization modification, organosilicon and polyurethane can be combined to complement each other. The chain segments formed by the chain extender, as part of the hard segment of the polyurethane shell, give the polyurethane shell good physical and mechanical properties, not only ensuring the normal coating of the colorless dye, but also further enhancing the high temperature resistance of the polyurethane shell. Polyvinyl alcohol can not only keep the dispersion liquid at a certain viscosity, but also prevent precipitation and agglomeration by forming hydrophilic clusters for its own long-chain molecules and non-polar particulate matter; while nitrate has good dispersibility, can form complexes or ion exchange with the developer and filler surface, enhance the dispersibility of particles, reduce the electrostatic attraction and surface tension between particles, prevent precipitation and agglomeration, and maintain storage stability, so the present invention uses polyvinyl alcohol and nitrate as dispersants, which prevents particle flocculation to a large extent, improves grinding efficiency, and meets the requirements of small particle size, so that the dispersion liquid has no crystallization, precipitation, and flocculation for more than six months, and the fine and stable particles further improve the compactness of the heat-sensitive color-forming coating, thereby further enhancing the high definition and high temperature resistance of the heat-sensitive material.

[0015] Preferably, the thermosensitive coating comprises the following components in parts by weight:

[0016] 10-80 parts of developer,

[0017] 10-50 parts of leuco dye microcapsule emulsion,

[0018] 1-10 parts of cross-linking agent,

[0019] Dispersant 10-80 parts,

[0020] 10-50 parts of additives.

[0021] Further preferably, the thermosensitive coating comprises the following components in parts by weight:

[0022] 10-50 parts of developer,

[0023] 10-40 parts of leuco dye microcapsule emulsion,

[0024] 1-8 parts of cross-linking agent,

[0025] Dispersant 10-60 parts,

[0026] 15-40 parts of additives.

[0027] More preferably, the thermosensitive coating comprises the following components in parts by weight:

[0028] 15-30 parts of developer,

[0029] 10-30 parts of leuco dye microcapsule emulsion,

[0030] 2-6 parts of cross-linking agent,

[0031] Dispersant 15-40 parts,

[0032] 15-30 parts of additives.

[0033] Preferably, the auxiliary agent is at least one of a filler, an adhesive, and a wetting and leveling agent.

[0034] Further preferably, in parts by weight, the additives in the thermosensitive coating include:

[0035] Filler 2-30 parts,

[0036] Adhesive 5-25 parts,

[0037] Wetting and leveling agent 0.1-5 parts.

[0038] More preferably, the additives in the thermosensitive coating include, by weight:

[0039] 3-15 parts of filler,

[0040] Adhesive 10-20 parts,

[0041] Wetting and leveling agent 0.1-2 parts.

[0042] Preferably, the average particle size of the leuco dye microcapsule emulsion is 0.5-2 μm.

[0043] Preferably, the flame retardant modified polyol is a polyol chemically modified with a flame retardant material, the flame retardant material is at least one of a nitrogen-containing flame retardant material, a nitrogen-phosphorus synergistic flame retardant material, a phosphorus-based flame retardant material, and a biomass flame retardant material, and / or the polyol is an aromatic polyester polyol.

[0044] Preferably, the flame retardant material is a nitrogen-containing flame retardant material.

[0045] Preferably, the nitrogen-containing flame retardant material is at least one of a cyanamide-based nitrogen-containing flame retardant material, a guanidine-based nitrogen-containing flame retardant material, a carbamate-based nitrogen-containing flame retardant material, a urea-based nitrogen-containing flame retardant material, and an imidazole-based nitrogen-containing flame retardant material.

[0046] Nitrogen-containing flame retardant materials (or nitrogen-containing flame retardants) mainly generate inert gas nitrogen when heated, and form a carbon layer on the surface of the material, which plays a role in isolating heat, isolating oxygen, and inhibiting smoke. By modifying polyols with nitrogen-containing flame retardant materials, nitrogen-containing flame retardant materials are introduced, thereby enhancing the flame retardant effect of heat-sensitive materials. Nitrogen-containing flame retardant materials are more economical, environmentally friendly and effective in flame retardancy.

[0047] Flame retardant modified polyols have the characteristics of good processing performance, good heat resistance, good flame retardancy, etc., while aromatic polyester polyols contain more ester groups and aromatic rings in their molecules, so they have higher cohesive strength and adhesion, and also show excellent heat resistance and flame retardancy. These characteristics are helpful to improve the high temperature resistance and flame retardancy of polyurethane shells.

[0048] Further preferably, the nitrogen-containing flame retardant material is a cyanamide-based nitrogen-containing flame retardant material.

[0049] Further preferably, the cyanamide nitrogen-containing flame retardant material is at least one of melamine, melamine cyanurate and dicyandiamide.

[0050] More preferably, the nitrogen-containing flame retardant material is a combination of melamine and dicyandiamide. The combination of melamine and dicyandiamide has the advantages of high flame retardancy, environmental protection and safety.

[0051] More preferably, the aromatic polyester polyol is phthalic anhydride polyester polyol and / or castor oil modified aromatic polyester polyol.

[0052] More preferably, the aromatic polyester polyol is castor oil-modified aromatic polyester polyol. Castor oil-modified aromatic polyester polyol has low viscosity and good fluidity.

[0053] Preferably, the polyisocyanate is an aliphatic polyisocyanate. Aliphatic polyisocyanate has stable chemical properties, excellent light resistance and weather resistance, and further improves the high temperature resistance of the polyurethane shell.

[0054] More preferably, the polyisocyanate is at least one of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexane diisocyanate (TMDI), and tetramethylxylene diisocyanate (TMXDI).

[0055] More preferably, the polyisocyanate is isophorone diisocyanate (IPDI). Isophorone diisocyanate has excellent high temperature resistance.

[0056] Preferably, the organosilicon modifier is a silane coupling agent.

[0057] Further preferably, the organosilicon modifier is at least one of vinyltriethoxysilane (A151), vinyltrimethoxysilane (A171), vinyltri(β-methoxyethoxy)silane (A172), γ-glycidyloxypropyltrimethoxysilane (H-560), bis-[γ-(triethoxysilyl)propyl]tetrasulfide (Si-69), γ-aminopropyltriethoxysilane (KH-550), γ-glycidyloxypropyltrimethoxysilane (KH-560), and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH-792).

[0058] More preferably, the organosilicon modifier is γ-aminopropyltriethoxysilane (KH-550). KH-550 is a silane coupling agent containing an amino group (-NH2) at one end, which forms a capping structure when reacting with -NCO, so that the molecular chain segments are restricted and the molecular weight is small, which can ensure the stability of the emulsion particle size during the emulsification process.

[0059] Preferably, the chain extender is a polyamine compound.

[0060] More preferably, the chain extender is at least one of ethanolamine, diethanolamine, triethanolamine, ethylenediamine, triethylenetetramine and tetraethylenepentamine.

[0061] More preferably, the chain extender is ethylenediamine. Ethylenediamine has a shorter molecular chain and relatively smaller molecular steric hindrance. During the cross-linking process with polyisocyanate, it can form a denser polyurethane shell with fewer gaps, and the colorless dye can be coated more completely.

[0062] Preferably, the crosslinking agent is at least one of an organic titanium crosslinking agent, an organic zirconium crosslinking agent, and an organic silicon crosslinking agent.

[0063] Further preferably, the crosslinking agent is an organic titanium crosslinking agent. The organic titanium crosslinking agent connects the titanium atoms with the active groups in the material (such as the hydroxyl groups in polyvinyl alcohol) through covalent bonds or coordination bonds to form a three-dimensional network structure, thereby enhancing the strength and thermal stability of the thermosensitive chromogenic layer, and the high temperature resistance is also significantly improved.

[0064] Preferably, the dispersant is polyvinyl alcohol and nitrate in a mass ratio of (10-30):1.

[0065] More preferably, the dispersant is polyvinyl alcohol and nitrate in a mass ratio of (20-30):1.

[0066] Preferably, the alcoholysis degree of the polyvinyl alcohol is 80-90 mol%. Too high or too low alcoholysis degree will affect the water solubility and will be disadvantageous for the particle size control of the developer and filler dispersion.

[0067] Preferably, the colorless dye is 3-pyrrolidinyl-6-methyl-7-anilinofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-(N-isopentyl-N-ethylamino)-7-(o-chloroanilino)fluoran, 3-(N-ethyl-p-toluylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-( At least one of 3-(N-isopentyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-(N-n-hexyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-di(n-butyl)amino-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(3-toluylamino)fluoran, 3-diethylamino-6-methyl-7-(2,6-dimethylanilino)fluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluoran and 2,4-dimethyl-6-(4-dimethylaminoanilino)fluoran.

[0068] More preferably, the colorless dye is 2-phenylamino-3-methyl-6-dibutylfluoran. 2-phenylamino-3-methyl-6-dibutylfluoran is a black color-developing colorless dye. The main color of the thermosensitive material is generally black, and the black dye is economical and practical.

[0069] Preferably, the melting point of the developer is ≥ 150° C. The developer with a higher melting point is selected in the present invention to help maintain color development in a high temperature environment.

[0070] Preferably, the color developer is at least one of a phenylsulfone color developer, an aromatic carboxylic acid zinc salt compound color developer, and a sulfonylurea color developer.

[0071] Preferably, the phenylsulfone color developer is at least one of phenylsulfone compounds such as 2,4'-dihydroxydiphenylsulfone, 4,4-dihydroxydiphenylsulfone, and bis(3-allyl-4-hydroxyphenyl)sulfone.

[0072] Preferably, the zinc salt compound of aromatic carboxylic acid developer is a zinc salicylate developer.

[0073] Preferably, the zinc salicylate type developer is at least one of 4-(n-octyloxy) zinc salicylate, 4-[2-(p-methylphenoxy)ethoxy] zinc salicylate, 4-[3-(p-toluenesulfonyl)propoxy] zinc salicylate, and 5-[p-(2-p-methoxyphenoxyethoxy)isopropylphenyl] zinc salicylate.

[0074] Preferably, the sulfonylurea developer is N-(p-toluenesulfonyl)-N'-(3-benzenesulfonyloxyphenyl)urea and / or 3-(3-methylureido)phenyl-4-methylbenzenesulfonate.

[0075] Further preferably, the developer is 4,4'-dihydroxydiphenyl sulfone, which has a high melting point, good stability, high clarity, and aging and high temperature resistance.

[0076] Preferably, the melting point of the filler is ≥ 1000° C. Fillers help reduce product costs, improve the physical and chemical properties of coatings, and increase the mechanical strength and wear resistance of coatings. The present invention uses high melting point fillers to further improve the high temperature resistance of the thermosensitive coating.

[0077] Preferably, the filler is at least one of heavy calcium carbonate, barite powder, quartz powder, talc, kaolin, mica powder, wollastonite, dolomite, attapulgite, light calcium carbonate, precipitated barium sulfate, synthetic calcium silicate, and sodium aluminosilicate. The filler of the present invention can be selected from natural mineral fillers and / or artificial synthetic fillers.

[0078] Further preferably, the filler is a combination of mica powder and talc. The present invention selects a combination of mica powder and talc as the filler, wherein mica powder is used as the main filler, which is heat-resistant, acid-resistant, and alkali-resistant, and can improve the weather resistance and high temperature resistance of the coating, but its appearance will be a little yellowish, so it needs to be matched with talc as a secondary filler to ensure that the coating has a normal appearance and reduce the use of additives such as fluorescent whitening agents, and talc has a high melting point, and its excellent suspension and dispersibility can improve the processing performance of heat-sensitive coatings.

[0079] Further preferably, the filler is a combination of mica powder and talc powder in a mass ratio of 0.5-1.5:0.5-1.5.

[0080] More preferably, the filler is a combination of mica powder and talc powder in a mass ratio of 1-1.2:1-1.2.

[0081] Preferably, the adhesive comprises a primary adhesive and a secondary adhesive, the primary adhesive has a minimum film-forming temperature ≥ 80°C, and / or the secondary adhesive has a minimum film-forming temperature ≤ 30°C.

[0082] Preferably, the mass ratio of the primary adhesive to the secondary adhesive is 1:(0.1-0.4).

[0083] Minimum film forming temperature (MFFT for short): the lowest temperature at which a substance coalesces from an aqueous dispersion into a continuous film, that is, the minimum film forming temperature.

[0084] The present invention uses a high MFFT (minimum film forming temperature) water-based latex (primary latex) and a low MFFT water-based latex (secondary latex) in combination as an adhesive, wherein the low MFFT water-based latex (secondary latex) adheres more firmly to the substrate, ensuring a firm bond between the coating and the substrate, and can ensure that the coating does not fall off or peel during cutting or printing, and maintains the firmness of the bond, while the high MFFT water-based latex (primary latex) has better high temperature resistance than the low MFFT water-based latex (secondary latex), and by using high and low MFFT (minimum film forming temperature) water-based latexes in combination, the adhesion performance and high temperature resistance of the heat-sensitive color-forming layer are improved at the same time.

[0085] Preferably, the main adhesive is water-based polyurethane latex and / or water-based acrylic emulsion.

[0086] Preferably, the secondary adhesive is at least one of water-based styrene-butadiene latex, water-based styrene-acrylic latex, and water-based chloroprene rubber latex.

[0087] Preferably, the wetting and leveling agent is at least one of a fluorocarbon leveling agent, an acrylate leveling agent, a nonionic associative polyurethane leveling agent, a polyether-siloxane leveling agent, and a polysiloxane leveling agent.

[0088] Further preferably, the wetting and leveling agent is a polysiloxane type leveling agent. The polysiloxane type leveling agent can strongly reduce the surface tension of the coating, improve the wettability of the coating to the substrate, and prevent the formation of shrinkage cavities.

[0089] Preferably, the nitrate is at least one of sodium nitrate, potassium nitrate and magnesium nitrate.

[0090] More preferably, the nitrate is sodium nitrate.

[0091] A second aspect of the present invention provides a method for preparing a high temperature resistant thermosensitive coating.

[0092] A method for preparing a heat-sensitive coating comprises the following steps:

[0093] The developer and the dispersant are mixed to obtain a developer dispersion; the filler and the dispersant are mixed to obtain a filler dispersion; the developer dispersion, the colorless dye microcapsule emulsion, the filler dispersion, the adhesive, the crosslinking agent and the wetting and leveling agent are mixed to obtain the thermal sensitive coating.

[0094] Preferably, after the developer and the dispersant are mixed, a first grinding is performed, and then heat-fixed at 50-70° C. for 0.5-2 h to obtain a developer dispersion.

[0095] Preferably, the first grinding is performed to an average particle size of ≥0.5 μm and ≤1 μm. The particle size of the developer dispersion should not be too small or too large. If it is too large, it will affect the activity of the developer in reacting with the colorless dye, resulting in unclear printed images, while if it is too small, it will increase production time and energy, resulting in high costs and uneconomical.

[0096] Preferably, after the filler and the dispersant are mixed, a second grinding is performed to obtain a filler dispersion.

[0097] Preferably, the filler dispersion includes a main filler dispersion and a secondary filler dispersion. The main filler and the dispersant are mixed and subjected to a second grinding to obtain the main filler dispersion; the secondary filler and the dispersant are mixed and subjected to a third grinding to obtain the secondary filler dispersion.

[0098] Preferably, the second grinding is performed to an average particle size of ≥0.5 μm and ≤1 μm, and / or the third grinding is performed to an average particle size of ≥0.5 μm and ≤1 μm. The particle size of the filler dispersion should not be too small or too large. Too large a particle size will affect the stability of the thermal-sensitive coating and the appearance performance of the product; too small a particle size will increase the production time and energy, resulting in high costs and uneconomical.

[0099] The present invention first mixes the developer, filler and dispersant respectively to prepare corresponding dispersions, wherein polyvinyl alcohol can keep the dispersion at a certain viscosity, and forms hydrophilic clusters with non-polar particulate matter through long-chain molecules to prevent precipitation and agglomeration; while nitrate has good dispersibility, and can form complexes or ion exchange with the developer or filler surface to enhance the dispersibility of particles, reduce the electrostatic attraction and surface tension between particles, prevent precipitation and agglomeration, and maintain the stability of the coating during storage. Therefore, the combination of polyvinyl alcohol and nitrate can prevent particle flocculation to a large extent, improve grinding efficiency, meet the requirements of small particle size, and make the dispersion liquid free of crystal precipitation, precipitation and flocculation for more than six months. Moreover, the fine and stable particles ensure the compactness of the heat-sensitive color-producing coating, and further enhance the high definition and thermal stability of the heat-sensitive material.

[0100] Preferably, the method for preparing the leuco dye microcapsule emulsion comprises the following steps:

[0101] Firstly, flame retardant modified polyol, polyisocyanate and silane coupling agent are mixed, and prepolymerization reaction is carried out under the action of catalyst to obtain silane modified polyurethane prepolymer; then colorless dye and solvent are added, and oil phase is formed after dissolution; protective colloid and emulsifier are mixed to form water phase; oil phase is added to water phase for emulsification to obtain emulsified dispersion; emulsified dispersion and chain extender are mixed, and polymerization reaction is carried out to obtain the colorless dye microcapsule emulsion; the solvent comprises low boiling point solvent and / or high boiling point solvent, the boiling point of the low boiling point solvent is ≤80°C, and the boiling point of the high boiling point solvent is ≥100°C.

[0102] The invention prepares a colorless dye microcapsule emulsion by an interfacial polymerization method, and uses microcapsules to encapsulate the colorless dye in a core, separates the colorless dye and a developer, and widens the temperature range of color change. In addition, a flame-retardant modified polyol is used as a raw material to realize the flame-retardant modification of a polyurethane shell, which not only improves the flame-retardant performance of the microcapsule, but also improves the mechanical properties and thermal stability of the microcapsule shell, thereby enhancing the high temperature resistance and flame retardancy of the thermal sensitive coating; Silane modification of the polyurethane shell can enhance the self-emulsification and dispersion performance of the microcapsule system, and can also reduce the use of emulsifiers. More importantly, the glass transition temperature Tg of the polyurethane shell can be increased by introducing Si-O-Si chains, and the high temperature resistance of the shell is further enhanced; high and low boiling point solvents are used in combination, which can not only further increase the high temperature resistance of the thermal sensitive coating, but also increase the solubility of organic substances.

[0103] Preferably, the mass ratio of the flame retardant modified polyol, the silane coupling agent and the polyisocyanate is 1:(0.3-0.5:):(1-2).

[0104] Preferably, the solvent includes a low boiling point solvent and a high boiling point solvent.

[0105] Preferably, the mass ratio of the colorless dye, silane-modified polyurethane prepolymer, low boiling point solvent, high boiling point solvent, protective colloid (mass concentration is 10%), emulsifier and chain extender is 10:(2-4):(2-4):(0-1):(1-4):(1-4):(1-2).

[0106] Preferably, the catalyst is at least one of triethylenediamine, dimethylethanolamine, bis(dimethylaminoethyl) ether, stannous octoate, dibutyltin dilaurate, and triethylamine.

[0107] More preferably, the catalyst is dibutyltin dilaurate.

[0108] Preferably, the low boiling point solvent is at least one of methyl formate, ethyl acetate, methyl ether, ethyl ether, dichloromethane, acetone and benzene.

[0109] More preferably, the low boiling point solvent is ethyl acetate. Ethyl acetate has excellent volatility and solubility and can dissolve a variety of organic substances.

[0110] Preferably, the high boiling point solvent is at least one of 1-methoxynaphthalene, 2-methylnaphthalene, 1-methylnaphthalene and 1-aminotetralin.

[0111] Further preferably, the high boiling point solvent is 1-methoxynaphthalene. The boiling point of 1-methoxynaphthalene is 136° C. The high boiling point can not only more effectively improve the high temperature resistance of the colorless dye microcapsules, but also increase the solubility of organic substances.

[0112] Preferably, the protective colloid is at least one of polyvinyl alcohol, gelatin, carboxymethyl cellulose, hydroxypropyl methyl cellulose, and styrene-maleic anhydride copolymer.

[0113] More preferably, the protective colloid is polyvinyl alcohol, which has good mechanical strength and emulsifying properties.

[0114] Preferably, the emulsifier is at least one of polysorbate 80, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and polyoxyethylene dodecylphenol ether.

[0115] Further preferably, the polysorbate 80 is more environmentally friendly and has good emulsifying properties.

[0116] Preferably, the method for preparing the flame retardant modified polyol comprises the following steps:

[0117] The flame retardant material, polyol and organic solvent are mixed and subjected to polycondensation reaction to obtain the flame retardant modified polyol.

[0118] Preferably, the organic solvent is at least one of formaldehyde, ethanol and acetone.

[0119] Further preferably, the organic solvent is formaldehyde, which is economical and safe.

[0120] A third aspect of the present invention provides an application of a high temperature resistant thermosensitive coating.

[0121] The invention discloses an application of a high temperature resistant thermosensitive coating in the preparation of thermosensitive materials.

[0122] A fourth aspect of the present invention provides a high temperature resistant thermosensitive material.

[0123] A high temperature resistant thermosensitive material comprises a substrate, a thermosensitive chromogenic layer and a protective layer which are stacked in sequence, wherein the thermosensitive chromogenic layer is made of the thermosensitive coating.

[0124] The thermosensitive material provided by the present invention contains two coating layers, wherein the thermosensitive color-forming layer can display color and has high temperature resistance; and the protective layer is arranged on the outermost layer, and absorbs part of the light that can cause the thermosensitive color-forming coating to produce a chemical reaction, thereby slowing down the deterioration of the thermosensitive material and protecting the thermal sensitive element of the printer from damage, thereby ensuring the quality of the thermosensitive material and extending the storage time after printing, which further ensures the high temperature resistance of the thermosensitive color-forming layer.

[0125] Preferably, the protective layer is made of a protective layer coating liquid, and the raw material components of the protective layer coating liquid include polyvinyl alcohol, silicon dioxide, a lubricant, a polysiloxane wetting and leveling agent, and an ultraviolet absorber.

[0126] Further preferably, the raw material components of the protective layer include, by weight, 50-60 parts of polyvinyl alcohol, 10-20 parts of silicon dioxide, 5-10 parts of lubricant, 5-10 parts of polysiloxane wetting and leveling agent, and 5-10 parts of ultraviolet absorber.

[0127] Preferably, the lubricant is at least one of paraffin emulsion, carnauba wax, polyethylene wax, zinc stearate emulsion, and zinc stearamide emulsion.

[0128] Preferably, the substrate is a paper base and / or a polymer film.

[0129] Preferably, the paper base is coated paper and / or coated base paper.

[0130] Preferably, the polymer film is a film made of at least one of polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polyester (PET), and polypropylene (PP).

[0131] A fifth aspect of the present invention provides a method for preparing a high temperature resistant thermosensitive material.

[0132] A method for preparing a high temperature resistant thermosensitive material comprises the following steps:

[0133] The heat-sensitive coating and the protective layer coating liquid are coated on the surface of the substrate in sequence to obtain a heat-sensitive color-forming layer and a protective layer respectively, thereby obtaining the heat-sensitive material.

[0134] Preferably, the coating amount of the thermosensitive color-forming layer is 2-10 g / m 2 , and / or, the coating amount of the protective layer is 2-10g / m 2 At this coating amount, the color optical density value of the thermal color-forming layer can reach ≥1.0, which is saturated color.

[0135] The solvent of each coating liquid is water, which is more environmentally friendly and safe.

[0136] Preferably, the coating method is at least one of gravure coating, reverse roller coating, knife roller coating, metering rod coating, slot die coating, dipping, curtain coating, and air knife coating.

[0137] Preferably, drying is performed after coating.

[0138] Preferably, the drying temperature is 90-120°C.

[0139] A sixth aspect of the present invention provides an application of a high temperature resistant thermosensitive material.

[0140] A high temperature resistant thermosensitive material is used in the preparation of thermosensitive printing materials, thermosensitive recording materials, temperature monitoring materials and food baking materials.

[0141] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0142] The high-temperature resistant thermosensitive coating provided by the present invention adopts a color developer, a colorless dye microcapsule emulsion, a crosslinking agent, a dispersant, and an auxiliary agent as main components, wherein the colorless dye microcapsules in the colorless dye microcapsule emulsion are of a core-shell structure, the core is a colorless dye, and the shell is an organosilicon-modified polyurethane. The raw materials for preparing the organosilicon-modified polyurethane include flame-retardant modified polyols, polyisocyanates, organosilicon modifiers, and chain extenders, and the dispersant includes polyvinyl alcohol and nitrates. The thermosensitive coating provided by the present invention has an initial color development temperature of ≥130°C, a saturated color development temperature of ≥180°C, an oxygen index of 24-26%, and has excellent high temperature resistance and flame retardancy. It can be further coated to obtain a thermosensitive color development layer to prepare a high temperature resistant thermosensitive material. Since the thermosensitive color development layer is resistant to high temperatures, the coating temperature can be higher than that of traditional thermal paper coating, thereby increasing vehicle speed and greatly reducing production costs. Moreover, the thermosensitive coating is suitable for different types of thermal printers on the market, and the printed patterns and barcodes have the characteristics of high definition. Even the patterns at high temperatures can still be clearly identifiable, so it can be used normally under extremely high temperatures (≥100°C), and has clear and readable printed images and flame retardant properties, which broadens the use field of thermosensitive materials and ensures the fire safety of use, such as being applied to high temperature environments such as industrial manufacturing, food baking industry, and medical industry. DETAILED DESCRIPTION

[0143] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0144] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or can be obtained by existing known methods. In the description of the present invention, unless otherwise specified, all "parts" are parts by weight.

[0145] Example 1

[0146] A high temperature resistant thermosensitive coating comprises the following components:

[0147] Color developer, colorless dye microcapsule emulsion, filler, adhesive, cross-linking agent, wetting and leveling agent, dispersant.

[0148] The preparation method of the above-mentioned high temperature resistant thermosensitive coating comprises the following steps:

[0149] (1) Preparation of flame retardant modified polyether polyols:

[0150] Use ammonia water (mass concentration 10%) to adjust the formaldehyde aqueous solution with a mass concentration of 37% to pH = 9-10, and put it into a four-necked flask connected to a reflux condenser. Then put 25 parts of melamine and 5 parts of dicyandiamide into the above four-necked flask containing 20 parts of formaldehyde solution. Heat to 60°C, wait until the solution becomes clear and transparent, and then react for 40 minutes. Add 50 parts of castor oil-modified aromatic polyester polyol, heat to 75°C, and react at a constant temperature for 3 hours. After the reaction is completed, adjust the pH to 8 with 10% ammonia water. Put the product into a vacuum drying oven with a vacuum degree of ≤-0.1MPa, and dry it at 105°C for 1 hour to remove water and part of the free formaldehyde, and obtain a flame-retardant modified polyether polyol without impurities.

[0151] (2) Preparation of silane-modified polyurethane prepolymer:

[0152] Under a nitrogen atmosphere, in a four-necked flask equipped with a thermometer, a stirring rod, and a reflux condenser, 40 parts of the flame retardant modified aromatic polyether polyol prepared above, 12 parts of a silane coupling agent KH-550, and 48 parts of isophorone diisocyanate were gradually added, the temperature was raised to 90°C, and under the action of 0.2 parts of a catalyst dibutyltin dilaurate, the reaction was stirred at a uniform speed for 4 hours to obtain a nitrogen-containing silane-modified polyurethane prepolymer.

[0153] (3) Preparation of leuco dye microcapsule emulsion:

[0154] 50 parts of colorless dye 2-phenylamino-3-methyl-6-dibutylfluoran (ODB-2) were heated and dissolved at 80°C, and then mixed with the above-mentioned 10 parts of nitrogen-containing silane-modified polyurethane prepolymer, 12 parts of ethyl acetate (low boiling point solvent) and 3 parts of 1-methoxynaphthalene (high boiling point solvent), and the resulting solution was slowly added to an aqueous solution containing 10 parts of polyvinyl alcohol (Japan Kuraray PVA-220, alcoholysis degree is 89.0mol%) with a mass concentration of 10% as a protective colloid and 10 parts of polysorbate 80 (Merck Chemical Reagent) with a mass concentration of 100% as an emulsifier, and emulsified and dispersed by stirring at a rotation speed of 8000rpm using a homogenizer. 20 parts of water and 5 parts of ethylenediamine (Shanghai Aladdin Biochemical Technology) as a chain extender were added to the obtained emulsified dispersion for homogenization and emulsification. The emulsified dispersion was heated to 65°C and polymerized for 4 hours to prepare a colorless dye microcapsule emulsion with a volume average particle size of 0.8 μm. Finally, after dilution with water, a colorless dye microcapsule emulsion with a solid content of 30% was prepared.

[0155] (4) Preparation of developer dispersion:

[0156] Preparation of developer dispersion: 50 parts of 12% polyvinyl alcohol aqueous solution (Kuraray PVA-205, alcoholysis degree 88 mol%) were added to the dispersion tank for stirring, and then 40 parts of 4,4'-dihydroxydiphenyl sulfone (BPS, Shanghai McLean) were added. After stirring for 30 minutes, 2 parts of 12% sodium nitrate and 8 parts of defoamer BYK-024 (Bick, Germany) were added. After stirring for 30 minutes, the dispersion was ground in a vertical rod-cut ball mill for 8 hours until the average particle size = 0.5-1μm; the dispersion was transferred to an insulation tank, heated to 60°C, maintained at 60°C for thermal stabilization for 1 hour, and diluted to 30% concentration with ionized water after natural cooling. Experiments show that the developer dispersion can be stored at room temperature for more than 6 months without crystallization, precipitation, or flocculation.

[0157] (5) Preparation of main filler dispersion:

[0158] 50 parts of 12% polyvinyl alcohol aqueous solution (Kuraray PVA-205, alcoholysis degree 88mol%) were added to the dispersion tank for stirring, and then 40 parts of 10μm ultrafine mica powder (Anhui Ge Ruixin) were added. After stirring for 15 minutes, 2 parts of 12% sodium nitrate and 8 parts of defoamer BYK-024 (Germany Bick) were added. After stirring for 30 minutes, the dispersion was ground in a vertical rod-cut ball mill for 5 hours until the average particle size = 0.5-1μm, and then deionized water was added to dilute it to a mass concentration of 30%. Experiments show that the main filler dispersion can be stored at room temperature for more than 6 months without crystallization, precipitation, or flocculation, and has excellent stability.

[0159] (6) Preparation of secondary filler dispersion:

[0160] 50 parts of 12% polyvinyl alcohol aqueous solution (Kuraray PVA-205, alcoholysis degree 88 mol%) were added to the dispersion tank for stirring, and then 40 parts of ultrafine talcum powder with a particle size of 10 μm (Quanzhou Xufeng) were added. After stirring for 15 minutes, 2 parts of 12% sodium nitrate and 8 parts of defoamer BYK-024 (Germany Bick) were added. After stirring for 30 minutes, the dispersion was put into a vertical rod-cut ball mill and ground for 5 hours to an average particle size of 0.5-1 μm, and then deionized water was added to dilute it to a mass concentration of 30%. Experiments show that the secondary filler dispersion can be stored at room temperature for more than 6 months without crystallization, precipitation, or flocculation, and has excellent stability.

[0161] (7) Preparation of thermosensitive coating:

[0162] 25 parts of colorless dye microcapsule emulsion, 40 parts of developer dispersion, 7.5 parts of mica powder dispersion (primary filler), 7.5 parts of talc dispersion (secondary filler), 10 parts of water-based acrylic latex (primary adhesive, Shandong Shoucheng Chemical PT-2003, MFFT is 90°C), 4 parts of water-based styrene acrylic latex (secondary adhesive, Dow Chemical TX-600, MFFT is 21°C), 5 parts of organic titanium crosslinking agent (Tianchen Chemical, TA-9-2), 1 part of polysiloxane wetting and leveling agent (BASF Hydropalat WE 3229) and 80 parts of deionized water are mixed and stirred to obtain a thermosensitive coating.

[0163] Example 2

[0164] A heat-sensitive coating, which differs from Example 1 in that, in step (1), the amounts of 25 parts of melamine and 5 parts of dicyandiamide are adjusted to 30 parts of melamine and 10 parts of dicyandiamide, respectively.

[0165] Example 3

[0166] A heat-sensitive coating, which differs from Example 1 in that in step (2), the amount of KH-550 silane coupling agent is increased from 12 parts to 15 parts.

[0167] Example 4

[0168] A heat-sensitive coating, which differs from Example 1 in that in step (3), the amount of ethylenediamine used as a chain extender is increased from 5 parts to 10 parts.

[0169] Example 5

[0170] A heat-sensitive coating, which differs from Example 1 in that, in step (7), the amounts of 7.5 parts of mica powder dispersion (main filler) and 7.5 parts of talcum powder dispersion (secondary filler) are adjusted to 10 parts of mica powder dispersion and 10 parts of talcum powder dispersion, respectively.

[0171] Example 6

[0172] A heat-sensitive coating, which is different from Example 1 in that in step (7), the amount of 10 parts of water-based acrylic latex is increased to 15 parts.

[0173] Example 7

[0174] A heat-sensitive coating, which differs from Example 1 in that in step (7), the amount of 5 parts of organic titanium cross-linking agent is increased to 10 parts.

[0175] Example 8

[0176] A heat-sensitive coating, which is different from Example 1 in that in step (3), 1-methoxynaphthalene (high boiling point solvent) is 0 parts.

[0177] Example 9

[0178] A thermosensitive coating, which differs from Example 1 in that, in step (7), 7.5 parts of mica powder dispersion (main filler) and 7.5 parts of talcum powder dispersion (secondary filler) are replaced by 5 parts of mica powder dispersion (main filler) and 10 parts of talcum powder dispersion (secondary filler), respectively.

[0179] Example 10

[0180] A thermosensitive coating, which differs from Example 1 in that, in step (7), the amounts of 7.5 parts of mica powder dispersion (main filler) and 7.5 parts of talcum powder dispersion (secondary filler) are replaced by 10 parts of mica powder dispersion (main filler) and 5 parts of talcum powder dispersion (secondary filler), respectively.

[0181] Embodiment 11

[0182] A heat-sensitive coating, which differs from Example 1 in that, in step (7), the amounts of 10 parts of water-based acrylic latex (primary adhesive) and 4 parts of water-based styrene-acrylic latex (secondary adhesive) are replaced by 0 parts of water-based acrylic latex (primary adhesive) and 14 parts of water-based styrene-acrylic latex (secondary adhesive), respectively.

[0183] Example 12

[0184] A heat-sensitive coating, which differs from Example 1 in that, in step (7), the amounts of 10 parts of water-based acrylic latex (primary adhesive) and 4 parts of water-based styrene-acrylic latex (secondary adhesive) are replaced by 14 parts of water-based acrylic latex (primary adhesive) and 0 parts of water-based styrene-acrylic latex (secondary adhesive), respectively.

[0185] Example 13

[0186] A heat-sensitive coating, which differs from Example 1 in that, in step (7), the amounts of 10 parts of water-based acrylic latex (primary adhesive) and 4 parts of water-based styrene-acrylic latex (secondary adhesive) are replaced by 9 parts of water-based acrylic latex (primary adhesive) and 4.5 parts of water-based styrene-acrylic latex (secondary adhesive), respectively.

[0187] Embodiment 14

[0188] A heat-sensitive coating, which differs from Example 1 in that, in step (4), the 12% aqueous solution of polyvinyl alcohol is replaced by a 12% aqueous solution of hydroxypropyl methylcellulose (degree of polymerization 10,000).

[0189] Comparative Example 1

[0190] A heat-sensitive coating, which is different from Example 1 in that in step (1), melamine and dicyandiamide (flame retardant material) are both 0 parts.

[0191] Comparative Example 2

[0192] A heat-sensitive coating, which is different from Example 1 in that in step (2), the amount of KH-550 (silane coupling agent) is 0 parts.

[0193] Comparative Example 3

[0194] A heat-sensitive coating, which differs from Example 1 in that, in step (3), the amount of ethylenediamine (chain extender) is 0 parts.

[0195] Comparative Example 4

[0196] A heat-sensitive coating, which differs from Example 1 in that, in steps (4)-(6), the polyvinyl alcohol aqueous solution in the developer dispersion, the main filler dispersion, and the secondary filler dispersion is replaced by an equal amount of sodium nitrate aqueous solution of the same concentration.

[0197] Comparative Example 5

[0198] A heat-sensitive coating, which differs from Example 1 in that, in steps (4)-(6), the sodium nitrate aqueous solution in the developer dispersion, the main filler dispersion, and the secondary filler dispersion is replaced by an equal amount of polyvinyl alcohol aqueous solution of the same concentration.

[0199] Comparative Example 6

[0200] A heat-sensitive coating, which differs from Example 1 in that in step (7), the organic titanium cross-linking agent is replaced with 0 parts.

[0201] Comparative Example 7

[0202] A heat-sensitive coating, which differs from Example 1 in that step (1) is omitted, and in step (2), 7.5 parts of a 37% formaldehyde aqueous solution (adjusted to pH 9-10 with 10% ammonia water in advance), 12.5 parts of melamine, 2.5 parts of dicyandiamide, 25 parts of castor oil-modified aromatic polyester polyol, 12 parts of KH-550 silane coupling agent and 48 parts of isophorone diisocyanate are gradually added to a four-necked flask equipped with a thermometer, a stirring rod and a reflux condenser under a nitrogen atmosphere, and the mixture is heated to 90° C. and stirred at a uniform speed for 4 hours under the action of 0.2 parts of a catalyst, dibutyltin dilaurate, to obtain a nitrogen-containing silane-modified polyurethane prepolymer having a large amount of opaque impurities (insoluble polyurea). The other steps are the same as those in Example 1.

[0203] In Comparative Example 7, the weight ratio of melamine, dicyandiamide, and castor oil modified aromatic polyester polyol is 25:5:50, totaling 40 parts, which is consistent with the amount of 40 parts of flame retardant modified aromatic polyether polyol used in step (2) of Example 1. Since formaldehyde (which dissolves melamine and dicyandiamide in step (1) of Example 1) has been removed during the vacuum drying process of step (1) of Example 1, step (2) is free of formaldehyde, so the formaldehyde ratio is set to 50% of the total weight of melamine and dicyandiamide.

[0204] Application Example 1

[0205] A thermosensitive material comprises a PE film substrate, a thermosensitive chromogenic layer and a protective layer which are stacked in sequence. The thermosensitive chromogenic layer is obtained by coating a thermosensitive coating, and the protective layer is obtained by coating a protective layer coating liquid.

[0206] A method for preparing a thermosensitive material comprises the following steps:

[0207] (1) Preparation of protective layer coating liquid:

[0208] 60 parts of polyvinyl alcohol (Kuraray PVA-220, degree of alcoholysis of 88 mol%), 10 parts of silicon dioxide, 10 parts of polyethylene wax emulsion, 10 parts of stearic acid amide emulsion, 5 parts of 100% polysiloxane wetting and leveling agent (BASF Hydropalat WE 3229), 5 parts of ultraviolet absorber and 80 parts of deionized water were mixed and stirred to obtain a protective layer coating solution.

[0209] (2) Preparation of thermosensitive materials:

[0210] The heat-sensitive coating prepared in Example 1 was evenly coated on the PE film by a scraper (the coating amount was controlled at 5 g / m 2), and then dried (drying temperature is 120℃, drying time is 3min) to obtain a thermosensitive color-forming layer. Then, the protective layer coating liquid is evenly coated on the thermosensitive color-forming layer by an air knife (the coating amount is controlled at 2g / m 2 ), and then dried (drying temperature is 90°C, drying time is 2min) to obtain a protective layer and obtain a heat-sensitive material.

[0211] Application Example 2-14

[0212] Application Examples 2-14 provide thermosensitive materials, which differ from Application Example 1 in that the thermosensitive coating of Example 1 is replaced with an equal amount of the thermosensitive coating of Examples 2-14, respectively.

[0213] Comparative Application Examples 1-7

[0214] Comparative Application Examples 1-7 provide thermosensitive materials, which differ from Application Example 1 in that the thermosensitive coating of Example 1 is replaced with an equal amount of the thermosensitive coating of Comparative Examples 1-7, respectively.

[0215] Product effect testing

[0216] 1. Test Method

[0217] The particle size of each dispersion in the above-mentioned examples and comparative examples was tested, and the static color development and image printing performance of the thermosensitive materials prepared in each application example and comparative application example were evaluated.

[0218] 1. Average particle size of each dispersion: The average particle size of the developer dispersion, main filler dispersion, secondary filler dispersion, and colorless dye microcapsule emulsion was measured using a Malvern Mastersizer 3000 laser diffraction particle size analyzer.

[0219] 2. Shelf life of each dispersion: The average particle size of the developer dispersion, main filler dispersion, secondary filler dispersion, and colorless dye microcapsule emulsion prepared in each embodiment and comparative example is tested every month. If the tested particle size is unchanged from the initial particle size, it is considered normal.

[0220] 3. Test method for color development performance of thermosensitive materials: Test static color development and whiteness performance with reference to GB / T 28210-2011 "Thermal Paper", the national standard of the People's Republic of China. For static color development performance, test the color development optical density of thermosensitive materials at 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ and 195℃ respectively, where the color development optical density of 0.15 is the color development optical density of the blank, and the color development optical density of 1.3 is the saturated color development optical density. The lower the color development optical density at the same temperature, the better the high temperature resistance.

[0221] 4. Flame retardant properties of thermosensitive materials: Refer to the National Standard of the People's Republic of China GB / T 2406.2-2009 "Determination of Combustion Behavior of Plastics by Oxygen Index Method", and use the oxygen index LOI value (detected by oxygen index tester) to intuitively reflect the flame retardant properties of thermosensitive materials. A high oxygen index indicates that the material is not easy to burn, and a low oxygen index indicates that the material is easy to burn. Among them, oxygen index less than 21% is non-flame retardant material; oxygen index between 21% and 27% is difficult to burn material; oxygen index greater than 27% indicates that this type of material has good flame retardant properties.

[0222] 5. Adhesion between the heat-sensitive coloring layer and the substrate: Refer to the National Standard of the People's Republic of China GB / T 9286-1998 "Cross-cut Test for Paint and Varnish Films", and use the cross-cut adhesion test to evaluate the adhesion of single-coat or multi-coat coatings. The results are as follows: Grade 5B means that the edge of the cut is completely smooth, and there is no peeling at the edge of the grid; Grade 4B means that there is small peeling at the intersection of the cut, and the actual damage in the cross-cut area does not exceed 5%; Grade 3B means that the edge and / or intersection of the cut are peeled, and the area is greater than 5%, but less than 15%; Grade 2B means that the edge of the cut is partially peeled or peeled in large pieces, and / or some grids are peeled in whole pieces. The peeled area exceeds 15%, but less than 35%; Grade 1B means that the edge of the cut is peeled in large pieces and / or some squares are partially or completely peeled, and the area is greater than 35% of the cross-cut area, but not more than 65%.

[0223] The results of the above tests are shown in Table 1.

[0224] 2. Test Results

[0225] Table 1 Performance test results of the dispersion, thermosensitive coating and thermosensitive material of the above embodiments and comparative examples

[0226]

[0227]

[0228]

[0229] Note: In the above table, flocculation means agglomeration, abnormality, and larger particle size; grinding failure means that the particle size of the material has no obvious change or is even larger than the initial size.

[0230] As can be seen from the above table, the storage period of the colorless dye microcapsule emulsion, developer dispersion, main filler dispersion, and auxiliary filler dispersion of Examples 1-13 of the present invention is more than 6 months, indicating good stability. The thermosensitive material prepared by the thermosensitive coating of Examples 1-14 has a high initial color development temperature (≥130°C) and a high saturated color development temperature (≥180°C). It shows that the present invention utilizes the colorless dye microcapsule emulsion, introduces the flame retardant material through the flame retardant polyol, and combines the organosilicon modification, so that the thermosensitive coating has good flame retardant performance, high temperature resistance and stability, so that the thermosensitive material prepared by the thermosensitive coating can be used normally and safely in an extremely high temperature (≥100°C) environment. In addition, the present invention further enhances the high temperature resistance of the thermosensitive material by using high and low boiling point solvents in combination, using two main and auxiliary fillers (mica powder and talc), high and low MFFT water-based latexes in combination, and an organic titanium crosslinking agent, and adopts two different types of emulsifying dispersants to ensure that the developer dispersion and the filler particle size meet the requirements, do not flocculate, can be stably stored for a long time, help to improve the compactness of the thermosensitive color-forming coating, and further improve the high-definition performance and thermal stability of the thermosensitive material.

[0231] In addition, the following conclusions can be drawn from the above table:

[0232] 1. Combining the static color development performance test results of Example 1 and Example 8 in Table 1, it can be seen that the color development optical density of Example 1 is lower than that of Example 8 at the same temperature, and the particle size of the colorless dye microcapsule emulsion is 0.2 μm smaller. This is because the colorless dye microcapsule emulsion of Example 1 contains a high boiling point solvent (1-methoxynaphthalene). Therefore, it is shown that the high boiling point solvent (1-methoxynaphthalene) improves the emulsification performance of the microcapsule emulsion (increases the solubility of the colorless dye in the organic solvent), and also enhances the high temperature resistance of the microcapsule emulsion.

[0233] 2. Combining the static color development and whiteness performance test results of Example 1, Example 5, Example 9, and Example 10 in Table 1, it can be seen that: (1) Comparing Example 1 and Example 5, it can be seen that the higher the proportion of fillers (mica powder and talcum powder) in the thermosensitive coating, the lower the color development optical density at the same temperature, and the better the high temperature resistance. (2) Example 9 has an initial color development temperature of 10°C higher than that of Example 1, but the whiteness is reduced by 11%. In addition, Example 10 has an initial color development temperature of 10°C lower than that of Example 1, but the whiteness is increased by 4%. Therefore, in view of the static color development and whiteness performance, it is most appropriate to control the mass ratio of the main filler (mica powder) and the secondary filler (talcum powder) to be 1:1.

[0234] 3. Combining the static color development performance test results of Example 1, Example 6 and Example 11 in Table 1, it can be seen that since Example 11 does not add high MFFT latex (water-based acrylic latex), the initial color development temperatures of Example 1 and Example 6 are 10°C and 15°C higher than those of Example 11, respectively, indicating that adding high MFFT latex (water-based acrylic latex) to the thermosensitive coating helps to improve the high temperature resistance, and the higher its proportion, the lower its color development optical density at the same temperature.

[0235] 4. Combining the coating and substrate adhesion test results of Example 1 and Example 12 in Table 1, it can be seen that the low MFFT latex (water-based styrene acrylic latex) is not added to the thermosensitive coating of Example 12, and its adhesion performance grade is poor, which is 2B, while Example 1 has the best adhesion performance, which is 5B.

[0236] 5. Combining the coating and substrate adhesion performance test grade results and static color development performance test results of Example 1 and Example 13 in Table 1, it can be seen that increasing the proportion of low MFTT water-based styrene acrylic latex has no obvious effect on the adhesion performance, but reducing the proportion of high MFTT water-based acrylic latex, its color development optical density increases at the same temperature, and its high temperature resistance decreases.

[0237] From the above, it can be seen that high MFFT water-based latex (acrylic latex) needs to be used together with low MFFT water-based latex (styrene acrylic latex) as an adhesive for the preparation of thermosensitive coatings. High MFFT water-based latex helps to improve the high temperature resistance of thermosensitive coatings, and low MFFT water-based latex helps to improve the adhesion between the coating and the substrate. It is more appropriate to control the mass ratio of high MFFT water-based latex and low MFFT water-based latex at 1: (0.1-0.4).

[0238] 6. Combining the test results of Example 1 and Example 14 in Table 1, it can be seen that when the commonly used hydroxypropyl methylcellulose dispersant is used instead of the polyvinyl alcohol dispersant in the developer dispersion and filler, the grinding efficiency is low and the storage period is short (it can only be stably stored for one month), which leads to large particle sizes of the developer and filler, further affecting the static color development performance of the thermosensitive material (the static color development of Example 14 is low, with basically no color development, which is mainly because the large particle sizes of the developer and filler affect the sufficient contact reaction between the developer and the colorless dye microcapsules).

[0239] 7. Combining the static color performance and oxygen index LOI test results of the thermosensitive materials prepared by the thermosensitive coatings of Examples 1-2 and Comparative Example 1 in Table 1, it can be seen that the LOI value and initial color temperature of the thermosensitive materials of Examples 1-2 are 9-11% and 10°C higher than those of Comparative Example 1, respectively. As the proportion of flame retardant materials (melamine and dicyandiamide) increases, the LOI value of the thermosensitive material increases, and the color optical density thereof decreases at the same temperature. This indicates that in Examples 1-2, flame retardant modified polyols are prepared by using flame retardant materials, which are then further used to prepare polyurethanes. The flame retardant materials have been successfully introduced into the polyurethane shell structure, and play an important role in the flame retardancy and high temperature resistance of the thermosensitive materials. However, the particle size of the colorless dye microcapsule emulsion in Example 2 is 0.4 μm larger than that in Example 1, indicating that the flame retardant material has a negative impact on emulsification and dispersion, so the amount of colorless dye microcapsule emulsion added should not be too much.

[0240] 8. Combining the static color development performance test results of Example 1, Example 3 and Comparative Example 2 in Table 1, it can be seen that the initial color development temperature of Example 1 and Example 3 is 20°C higher than that of Comparative Example 2. In addition, the particle size of the colorless dye microcapsule emulsion in Example 3 is 0.2 μm smaller than that in Example 1. This shows that since the polyurethane shells of Examples 1 and 3 contain silane coupling agent KH-550 as an organosilicon modifier, and the higher the proportion, the lower the color development optical density at the same temperature, the organosilicon modifier not only helps to improve the high temperature resistance, but also helps to enhance the emulsification and dispersion performance of the system.

[0241] 9. The static color performance test results of Example 1, Example 4 and Comparative Example 3 in Table 1 show that: (1) The higher the proportion of chain extender (ethylenediamine) in Example 1 and Example 4, the lower the color optical density at the same temperature. (2) In Comparative Example 3, since no chain extender (ethylenediamine) was added, the particle size of the colorless dye microcapsule emulsion was abnormal and the emulsion flocculated, indicating that the polyurethane shell was not formed and could not normally encapsulate the colorless dye. Therefore, the chain extender (ethylenediamine) as a hard segment not only gives the polyurethane shell good physical and mechanical properties, but also plays an important role in forming the colorless dye microcapsule emulsion and achieving the encapsulation of the colorless dye.

[0242] 10. Combining the test results of Example 1 and Comparative Examples 4-5 in Table 1, it can be seen that there is no polyvinyl alcohol dispersant in the developer dispersion and filler dispersion in Comparative Example 4, resulting in grinding dispersion flocculation, and it is impossible to further prepare the thermosensitive coating, indicating that polyvinyl alcohol plays a decisive role in the grinding effect and can prevent particle flocculation. There is no sodium nitrate dispersant in the developer dispersion, main filler dispersion, and auxiliary filler dispersion in Comparative Example 5, resulting in a slightly larger particle size (a certain degree of flocculation occurs), and the storage period is short (1 month), which further affects the static color development performance of the obtained thermosensitive material (the static color development of Comparative Example 5 is low, and there is basically no color development, which is mainly because the developer and filler particle sizes are large, resulting in the developer and the colorless dye microcapsules cannot fully contact and react). This indicates that polyvinyl alcohol and sodium nitrate work together to improve grinding efficiency and prevent particle flocculation, thereby extending storage time, so that the particle size of the thermosensitive coating can meet the requirements within the specified grinding and dispersion time (the total grinding and dispersion time of the developer dispersion and filler dispersion in each embodiment and comparative example is 8h and 5h, respectively).

[0243] 11. Combining the static color development performance test results of Example 1, Example 7 and Comparative Example 6 in Table 1, it can be seen that the initial color development temperature of Example 1 and Example 7 is 10°C higher than that of Comparative Example 6, indicating that due to the addition of organic titanium crosslinking agent in Example 1 and Example 7, the high temperature resistance of the thermosensitive coating is improved under its action, and the higher the proportion, the lower the color development optical density at the same temperature.

[0244] 12. It can be seen from the performance test results of Examples 1-14 and Comparative Example 7 in Table 1 that the flame retardant modification of aromatic polyester polyols is not performed alone, but the flame retardant materials (melamine and dicyandiamide), aromatic polyester polyols, silane coupling agents and polyisocyanates are directly prepared together to obtain polyurethane prepolymers (i.e., the flame retardant materials are directly introduced into the coating), which is accompanied by more side reactions and generates more insoluble impurities (polyurea), which affects the formation and encapsulation of the polyurethane shell, which is the main reason for the failure (flocculation) of the preparation of colorless dye microcapsules in the next step. Therefore, it is shown that the present invention first uses flame retardant materials to modify polyols, and then uses the obtained flame retardant modified polyols for the preparation of heat-sensitive coatings, which is conducive to the control of the particle size of colorless dye microcapsules.

[0245] From the above, it can be seen that the flame retardant modified polyol, silicone modifier, high boiling point solvent, chain extender, filler, crosslinker and high MFFT water-based latex used in the present invention all improve the high temperature resistance of the polyurethane shell, reduce the thermal response of the system, and achieve the purpose of high temperature resistance.

Claims

1. A heat-sensitive coating, characterized in that: The components include: Color developer, Leuco dye microcapsule emulsion, Crosslinking agent, Dispersants, Additives; The leuco dye microcapsules in the leuco dye microcapsule emulsion are of a core-shell structure, wherein the core is a leuco dye and the shell is an organosilicon-modified polyurethane, and the raw materials for preparing the organosilicon-modified polyurethane include flame-retardant modified polyols, polyisocyanates, organosilicon modifiers, and chain extenders; The dispersant includes polyvinyl alcohol and nitrate.

2. The heat-sensitive coating according to claim 1, characterized in that: According to parts by weight, it includes the following components: 10-80 parts of developer, 10-50 parts of leuco dye microcapsule emulsion, 1-10 parts of cross-linking agent, Dispersant 10-80 parts, 10-50 parts of additives.

3. The heat-sensitive coating according to claim 1, characterized in that: The auxiliary agent is at least one of a filler, an adhesive, and a wetting and leveling agent.

4. The heat-sensitive coating according to claim 1, characterized in that: The flame retardant modified polyol is a polyol chemically modified with a flame retardant material, the flame retardant material is at least one of a nitrogen-containing flame retardant material, a nitrogen-phosphorus synergistic flame retardant material, a phosphorus-based flame retardant material, and a biomass flame retardant material, and / or the polyol is an aromatic polyester polyol.

5. The heat-sensitive coating according to claim 1, characterized in that: The organosilicon modifier is a silane coupling agent, and / or the chain extender is a polyamine compound.

6. The heat-sensitive coating according to claim 1, characterized in that: The dispersant is polyvinyl alcohol and nitrate in a mass ratio of (10-30):

1.

7. The heat-sensitive coating according to claim 3, characterized in that: The adhesive comprises a main adhesive and a secondary adhesive, the minimum film-forming temperature of the main adhesive is ≥80°C, and / or the minimum film-forming temperature of the secondary adhesive is ≤30°C.

8. The heat-sensitive coating according to claim 1, characterized in that: The average particle size of the leuco dye microcapsule emulsion is 0.5-2 μm.

9. A method for preparing a heat-sensitive coating, characterized in that: The steps include: The developer and the dispersant are mixed to obtain a developer dispersion; the filler and the dispersant are mixed to obtain a filler dispersion; the developer dispersion, the colorless dye microcapsule emulsion, the filler dispersion, the adhesive, the crosslinking agent and the wetting and leveling agent are mixed to obtain the thermal sensitive coating.

10. The preparation method according to claim 9, characterized in that: The preparation method of the leuco dye microcapsule emulsion comprises the following steps: Firstly, flame retardant modified polyol, polyisocyanate and silane coupling agent are mixed, and prepolymerization reaction is carried out under the action of catalyst to obtain silane modified polyurethane prepolymer; then colorless dye and solvent are added, and oil phase is formed after dissolution; protective colloid and emulsifier are mixed to form water phase; oil phase is added to water phase for emulsification to obtain emulsified dispersion; emulsified dispersion and chain extender are mixed, and polymerization reaction is carried out to obtain the colorless dye microcapsule emulsion; the solvent comprises low boiling point solvent and / or high boiling point solvent, the boiling point of the low boiling point solvent is ≤80°C, and the boiling point of the high boiling point solvent is ≥100°C.

11. Use of the thermosensitive coating according to any one of claims 1 to 8 or the thermosensitive coating prepared by the preparation method according to claim 9 or 10 in preparing thermosensitive materials.

12. A heat-sensitive material, characterized in that: The invention comprises a substrate, a thermosensitive color-forming layer and a protective layer which are stacked in sequence, wherein the thermosensitive color-forming layer is made of the thermosensitive coating according to any one of claims 1 to 8 or the thermosensitive coating prepared by the preparation method according to claim 9 or 10.

13. The method for preparing a thermosensitive material according to claim 12, characterized in that: The steps include: The heat-sensitive coating and the protective layer coating liquid are coated on the surface of the substrate in sequence to obtain a heat-sensitive color-forming layer and a protective layer respectively, thereby obtaining the heat-sensitive material.

14. Use of the thermosensitive material according to claim 12 in preparing thermosensitive printing materials, thermosensitive recording materials, temperature monitoring materials, and food baking materials.

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