A thermal recording material and its preparation method

Abstract

A thermal recording material comprises a support, a thermal imaging layer disposed on the support, and a protective layer disposed on the thermal imaging layer. The protective layer is formed by drying a protective layer coating solution containing γ-methacryloxypropyltrimethoxysilane and silica sol. The protective layer coating solution comprises the following components by weight: 400-600 parts deionized water, 200-300 parts polyvinyl alcohol mixed solution (polyvinyl alcohol solid content 8%), 80-140 parts leveling agent aqueous solution (solid content 2%), 70-100 parts zinc stearate dispersion (volume average particle size 0.4 μm), 3-8 parts stearamide dispersion (volume average particle size 0.9 μm), and 0.8-1.8 parts fluorinated surfactant aqueous solution (solid content 8%). The thermal recording material prepared by the present invention has low fog density, excellent water resistance and heat resistance, and does not damage the thermal head during continuous use.

Description

Technical Field

[0001] The present invention relates to an information recording material, in particular to a heat-sensitive recording material suitable for outputting medical image diagnosis and a preparation method thereof. Background Art

[0002] Thermal information recording materials utilize heat energy to cause the developer and dye in the thermal layer to undergo a chemical reaction under high-temperature melting to develop color, thereby forming different text or images according to the selectivity of the heating. This type of thermal recording material does not require complicated processing such as development and fixing, and provides advantages such as shorter recording time with simple equipment, low noise generation, low price, and convenient daily maintenance. For these reasons, it is widely used in the fields of measuring recorders, fax machines, printers, computer terminals, label printing machines, ticket vending machines, etc. In addition, due to the development of thermal recording systems, the use environment of thermal recording materials has become more severe, especially when used in environments exposed to high temperature and high humidity, and there is a strong demand for thermal recording materials with a protective layer that is excellent in water resistance.

[0003] To improve the water resistance of thermal recording materials, known patents disclose methods for forming protective layers with various compositions on thermal recording materials. These methods typically require the use of modified polyvinyl alcohol or modified polyvinyl alcohol in combination with a crosslinking agent. For example, acetoacetyl-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol in combination with a vinyl sulfone compound, acetoacetyl-modified polyvinyl alcohol in combination with a hydrazide compound, acetoacetyl-modified polyvinyl alcohol in combination with an amino-containing silane coupling agent, acetoacetyl-modified polyvinyl alcohol in combination with a specific aldehyde compound, carboxyl-modified polyvinyl alcohol, and other modified polyvinyl alcohols are used in the thermal recording material's protective layer. These protective layers have the problem of easily discoloring the unrecorded portion of the thermal recording material under high temperature and high humidity conditions, increasing the viscosity of the protective layer coating liquid during preparation and coating, making stable production difficult, and making it difficult to obtain thermal recording materials with sufficient water resistance. These issues are insufficient to fully meet the requirements, and therefore, there is a need to improve the above-mentioned problems. Summary of the Invention

[0004] The present invention overcomes the drawbacks of the prior art and provides a thermal recording material and a preparation method thereof. γ-methacryloxypropyltrimethoxysilane and silica sol are added to the protective layer. The prepared thermal recording material has low fog density, excellent water resistance and heat resistance, and does not damage the thermal head during continuous use.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A heat-sensitive recording material comprising a support, a heat-sensitive imaging layer disposed on the support, and a protective layer disposed on the heat-sensitive imaging layer, wherein the protective layer is formed by drying a protective layer coating solution containing γ-methacryloxypropyltrimethoxysilane and silica sol, wherein the protective layer coating solution comprises the following components in parts by mass:

[0007] 400~600 parts of deionized water

[0008] Polyvinyl alcohol mixed solution (polyvinyl alcohol solid content 8%) 200~300 parts

[0009] Leveling agent aqueous solution (solid content 2%) 80~140 parts

[0010] Zinc stearate dispersion (volume average particle size 0.4 μm) 70-100 parts

[0011] 3-8 parts of stearamide dispersion (volume average particle size 0.9 μm)

[0012] 0.8~1.8 parts of aqueous solution of fluorinated surfactant (solid content 8%).

[0013] The above-mentioned thermosensitive recording material, the polyvinyl alcohol mixed solution comprises the following components in parts by mass:

[0014] 164.2~203.2 parts of deionized water

[0015] 20.8 parts of polyvinyl alcohol

[0016] 36~75 parts of Liquid A.

[0017] 3. The heat-sensitive recording material according to claim 2, wherein the liquid A is composed of the following components in parts by mass, where the parts by mass of the following components are calculated relative to 100 parts by mass of polyvinyl alcohol:

[0018] 30-100 parts of γ-methacryloxypropyltrimethoxysilane

[0019] 20~60 parts of silica sol.

[0020] In the above-mentioned heat-sensitive recording material, the silica sol is an acidic silica sol with a pH of 2-4 and a volume average particle size of 5-10 nm.

[0021] In the above-mentioned heat-sensitive recording material, the alcoholysis degree of the polyvinyl alcohol is greater than 80%, and the degree of polymerization is 1000-3000.

[0022] A method for preparing a heat-sensitive recording material comprises coating a heat-sensitive imaging layer coating liquid on a support, followed by drying to form a heat-sensitive imaging layer, and then coating a protective layer coating liquid containing γ-methacryloxypropyltrimethoxysilane and silica sol on the heat-sensitive imaging layer, followed by drying to form the protective layer.

[0023] The method for preparing the above-mentioned thermal recording material, wherein the protective layer coating liquid comprises the following preparation steps:

[0024] a. Preparation of Liquid A: γ-methacryloxypropyltrimethoxysilane and acidic silica sol are uniformly mixed to form Liquid A;

[0025] b. Mix the formulated amount of Solution A, polyvinyl alcohol, and deionized water, and heat to dissolve the mixture to prepare a polyvinyl alcohol mixed solution, wherein the content of polyvinyl alcohol is 8 wt.%;

[0026] c. Evenly mix the formulated amounts of deionized water, polyvinyl alcohol mixed solution, leveling agent aqueous solution, zinc stearate dispersion, stearamide dispersion and fluorine-containing surfactant aqueous solution to prepare a protective layer coating solution.

[0027] The beneficial effects of the present invention are:

[0028] 1. The heat-sensitive recording material of the present invention uses unmodified polyvinyl alcohol in combination with γ-methacryloxypropyltrimethoxysilane, which improves the water resistance and heat resistance of the protective layer of the heat-sensitive recording material and effectively reduces the production cost.

[0029] 2. The thermal recording material of the present invention uses silica sol, which effectively solves the problem that γ-methacryloxypropyltrimethoxysilane needs to be hydrolyzed separately before use, simplifies the production process, and improves production efficiency.

[0030] 3. The thermal recording material of the present invention has good heat resistance and can provide good protection for the thermal head.

[0031] 4. The present invention uses the unmodified polyvinyl alcohol, γ-methacryloxypropyltrimethoxy and silica sol as a whole after mixing, thereby avoiding the possibility of reaction between multiple components in the protective layer, simplifying the production process and improving production efficiency. DETAILED DESCRIPTION

[0032] The heat-sensitive recording material provided by the present invention comprises a support, a heat-sensitive imaging layer on the support, and a protective layer on the heat-sensitive imaging layer. The protective layer contains gamma-methacryloxypropyltrimethoxysilane and silica sol.

[0033] (1) Regarding the protective layer:

[0034] The protective layer of the present invention mainly comprises various additives and water-soluble polymers. The water-soluble polymer used in the protective layer is polyvinyl alcohol, which can be completely hydrolyzed, intermediately hydrolyzed, partially hydrolyzed, or modified. Although there are no particular requirements for the average degree of polymerization and degree of hydrolysis of the polyvinyl alcohol, from the perspectives of solubility, coating properties, and coating strength, unmodified polyvinyl alcohol with an average degree of polymerization of 1000 or more and less than 3000 and a degree of hydrolysis of 80% or more is preferred. This is because such polyvinyl alcohols are widely available and easily available. In the present invention, the amount of polyvinyl alcohol used in the coating liquid for the protective layer is not specifically specified; it is sufficient that the coating liquid for the protective layer does not cause coating defects due to excessive or insufficient viscosity during the coating process.

[0035] In the present invention, γ-methacryloxypropyltrimethoxysilane is selected as the crosslinker for polyvinyl alcohol. The amount of γ-methacryloxypropyltrimethoxysilane per 100 parts by mass of polyvinyl alcohol is preferably 30 to 100 parts by mass, and particularly preferably 45 to 80 parts by mass. If the γ-methacryloxypropyltrimethoxysilane content is too low, the protective layer of the thermal recording material will not provide adequate water resistance. If the γ-methacryloxypropyltrimethoxysilane content is too high, the protective layer coating solution will react violently with polyvinyl alcohol, resulting in excessive viscosity, which can lead to problems such as an unstable coating process and poor appearance. Furthermore, if the γ-methacryloxypropyltrimethoxysilane content is too high, the heat transfer effect of the protective layer will be significantly weakened, making it difficult for heat to transfer from the protective layer to the thermal imaging layer. This can cause the color density of the imaging layer to be too low, seriously affecting the performance.

[0036] The γ-methacryloxypropyltrimethoxysilane disclosed herein possesses unique structure and properties. It contains an organic functional group (γ-methacryloxy) and a silaneoxy group. Upon hydrolysis, γ-methacryloxypropyltrimethoxysilane forms a silanol, which plays a crucial role in the drying and curing of the protective layer coating solution. The silanol formed upon hydrolysis reacts with the hydroxyl groups in polyvinyl alcohol to form hydrogen bonds. During the curing process, the silanol undergoes further dehydration and polycondensation to form a polysiloxane. Furthermore, the organic functional group (γ-methacryloxy) in γ-methacryloxypropyltrimethoxysilane contains active double bonds and acyloxy groups, which can react with the hydroxyl groups in polyvinyl alcohol. While forming weak hydrogen bonds with the hydroxyl groups, the organic functional group (γ-methacryloxy) can also cross-link with the acetoxy groups in polyvinyl alcohol, further enhancing the water resistance of the coating. The use of γ-methacryloxypropyltrimethoxysilane in the reaction with polyvinyl alcohol effectively controls the molecular weight of the product. Therefore, while ensuring sufficient water resistance for the protective layer, the viscosity of the coating liquid does not change rapidly due to excessive molecular weight. Furthermore, due to the formation of polysiloxane, the protective layer can meet the requirements of good heat resistance. This is the most significant difference compared to other conventional crosslinking agents. For example, when using aldehyde crosslinking agents, the aldehyde groups and the hydroxyl groups in polyvinyl alcohol form strong crosslinks. If the aldehyde groups and polyvinyl alcohol are connected by chemical bonds, the viscosity of the coating liquid increases sharply after short storage due to the increase in the molecular weight of the polyvinyl alcohol, making it impossible to coat normally. Furthermore, thermal recording materials prepared using aldehyde crosslinking agents have poor aging resistance. Aldehyde crosslinking agents only improve the water resistance of the coating layer in one aspect.

[0037] The pigment in the protective layer is primarily silica sol. The addition of silica sol to the protective layer imparts excellent heat resistance and erasure resistance during use. A silica sol with a volume average particle size of 5 to 10 nanometers is preferred. A volume average particle size smaller than 5 nanometers significantly increases cost, while a volume average particle size greater than 10 nanometers reduces coating transparency. Considering the requirement that γ-methacryloxypropyltrimethoxysilane must be hydrolyzed before use, an acidic silica sol is preferred. γ-methacryloxypropyltrimethoxysilane is a bifunctional substance that first hydrolyzes to form silanols, which then interact with other active ingredients to achieve the desired performance. The optimal hydrolysis solution pH is 3 to 4. Furthermore, the silica sol used in this invention has a relatively small volume average particle size, which poses a risk of particle agglomeration during use. Using an acidic silica sol as the hydrolysis solution allows the hydrolysis of γ-methacryloxypropyltrimethoxysilane to allow the silanols to interact with the surface of the silica sol particles, improving their dispersion within the system. The combined use effect is particularly preferred for silica sol with a pH of 2 to 4. Relative to 100 parts by mass of polyvinyl alcohol, the silica sol is preferably 20 to 60 parts by mass, and particularly preferably 30 to 50%. If the amount of silica sol is too small, the hydrolysis of γ-methacryloxypropyltrimethoxysilane is insufficient, which in turn leads to insufficient water resistance and heat resistance of the protective layer. If the amount of silica sol is too large, the viscosity of the protective layer coating liquid is too high, which leads to problems such as unstable coating process and poor appearance. According to other requirements for the properties of the protective layer, the protective layer may also contain other types of additives, such as lubricants, UV absorbers, leveling agents, surfactants, antistatic agents, etc., which are not specifically explained here. They can be used alone or in combination as needed.

[0038] The protective layer coating liquid can be prepared by gradually adding the required materials in sequence. Alternatively, several materials, such as polyvinyl alcohol, γ-methacryloxypropyltrimethoxysilane, and silica sol, can be premixed before adding the other materials. For ease of production, ease of operation, and subsequent use, it is preferred to mix polyvinyl alcohol, γ-methacryloxypropyltrimethoxysilane, and silica sol before adding the other materials. The protective layer coating liquid is applied to the thermal imaging layer using methods such as slide extrusion coating, wire rod coating, slot coating, curtain coating, air knife coating, or doctor blade coating, and dried to form the protective layer. Alternatively, the thermal imaging layer and protective layer coating liquids can be applied simultaneously using slide extrusion coating, followed by drying to form a thermal recording material.

[0039] (2) Support

[0040] The support used as the thermal recording material of the present invention should have good thermal stability, no deformation or stretching when heated, low hygroscopicity, and high flatness. It can be a transparent support such as polyethylene film (PE), polypropylene film (PP), polyvinyl chloride film (PVC), polyester film (PET), polystyrene film (PS), polyvinylidene chloride film (PVDC), etc. Masterbatch can be added thereto to form different colors, or it can be used directly without adding masterbatch. The thickness of the support is not particularly limited, as long as it can meet the target requirements. The preferred thickness is 175 μm. The black and white density of PET tested using an X-Rite 310T densitometer is 0.20.

[0041] (3) Thermal imaging layer

[0042] The heat-sensitive imaging layer is formed by coating the support with the primer layer on its side containing at least a leuco dye, a developer, and, if necessary, other components.

[0043] (1) Leuco dye

[0044] The leuco dye is not particularly limited and can be appropriately selected from leuco dyes used for thermosensitive recording materials according to purpose. For example, the fluoran type includes 2-phenylamino-3-methyl-6-diethylaminofluoran, 2-phenylamino-3-methyl-6-dibutylaminofluoran, 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclopentylamino)-6-methyl-7-anilinofluoran, 3-dibutylamino-7-o-fluoroanilinofluoran, 3-diethylamino-7-(3,4-dichloroanilino)fluoran, etc., preferably 2-phenylamino-3-methyl-6-diethylaminofluoran; the triarylmethane type includes 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylaminoindol-3-yl)phthalide, 3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-2-yl)-6-dimethylaminophthalide, etc.; spiro compound type includes 3-methylspirodibenzopyran, 3-ethylspirodibenzopyran, 3,3,-dichlorospirodinaphthopyran, 3-benzylspirodibenzopyran, 3-propylspirodibenzopyran, 1,3,3-trimethyl-6-nitro-8,-methoxyspiro(dihydroindole-2,2,-benzopyran), etc.

[0045] These leuco dye compounds may be used alone or in combination.

[0046] (2) Color developer

[0047] The color developer that can be used in combination is not particularly limited, and any color developer commonly used for pressure-sensitive recording paper or heat-sensitive recording paper may be used, and may be α-naphthol, β-naphthol, p-octylphenol, 4-tert-octylphenol, p-tert-butylphenol, 3,3-diallyl-4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4-isopropoxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone dispersion and heat-sensitive recording material 4 -Hydroxy-4-methoxydiphenyl sulfone, 4-hydroxy-4-ethoxydiphenyl sulfone, 4-hydroxy-4-butoxydiphenyl sulfone, benzyl p-hydroxybenzoate, dibenzyl 4-hydroxyphthalate, dimethyl 4-hydroxyphthalate, 1-acetoxy-2-naphthoic acid zinc, 2-acetoxy-1-naphthoic acid zinc, 2-acetoxy-3-3 naphthoic acid zinc, 2,4-diphenylsulfonylphenol, 4-phenylsulfonylphenol, 2,4,6-triphenylsulfonylphenol, etc.

[0048] These colorants can be used alone or in combination.

[0049] (3) Other components

[0050] To further enhance the thermal sensitivity of the thermal recording material, a thermosensitizer may be added to the thermal imaging layer. This thermosensitizer can be ground and dispersed together with the developer or separately. The amount of thermosensitizer used is not particularly limited, as long as it meets the specific application requirements. Commonly used thermosensitizers include diethane, 2-benzylnaphthyl ether, 1,2-di-(3-phenoxy)ethane, 4-benzylbiphenyl, and benzyl p-hydroxybenzoate.

[0051] The binder in the thermal imaging layer of the present invention may be starch and its derivatives, carboxylated styrene-butadiene latex, methoxycellulose, carboxymethylcellulose, acrylamide-acrylate copolymer, styrene-butadiene copolymer, polyacrylate, polybutyl methacrylate, polyvinyl alcohol, etc. The polyvinyl alcohol may be completely alcoholyzed, intermediately alcoholyzed, partially alcoholyzed, or modified; the degree of polymerization of the polyvinyl alcohol used is generally 1000 to 3000. The binder may be used alone or in combination, and the polyvinyl alcohol used may be the same as or different from the polyvinyl alcohol used in the protective layer.

[0052] Depending on the performance and surface requirements of the thermal imaging layer, other functional additives, such as surfactants, leveling agents, and lubricants, may be added to the thermal imaging layer. Examples of surfactants include alkali metal salts of sulfosuccinic acid, fluorinated surfactants, and sulfonates. Examples of leveling agents include silicone oil, polydimethylsiloxane, polyether polyester-modified organosiloxane, alkyl-modified organosiloxane, end-group modified organosilicon, and fluorinated acrylic resin. Examples of lubricants include higher fatty acids or their metal salts, higher fatty acid amides, higher fatty acid esters, animal wax, vegetable wax, and polyethylene wax.

[0053] The thermal imaging layer can be formed by any known method. For example, a developer, binder resin, and other components are ground and dispersed together using a dispersing machine, such as a ball mill or sand mill, until the average diameter of the dispersed particles is ≤1 μm, thereby forming a developer dispersion. The dye is then encapsulated using a known microencapsulation method to form a microcapsule dispersion. The resulting developer dispersion, dye microcapsule dispersion, and other additives are mixed and then coated onto 175 μm thick, 0.20 density PET using a slide extrusion coating, wire rod coating, slot coating, curtain coating, air knife coating, or doctor blade coating method, followed by drying to form the thermal imaging layer.

[0054] In the present invention, both surfaces of the support contain a bottom layer, which is a water-soluble environmentally friendly resin layer. Its main function is to give the support surface hydrophilicity to ensure that other thermal imaging layers and back layers can be coated smoothly.

[0055] The heat-sensitive recording material of the present invention comprises a backing layer on the other side of the support without the protective layer, wherein the main components of the backing layer are one or both of an aqueous polyurethane emulsion and an aqueous acrylic resin. The main function of the backing layer is to give the support surface a certain degree of roughness.

[0056] The method for preparing a heat-sensitive recording material of the present invention comprises the following steps:

[0057] Coating a backing layer on any surface of the support;

[0058] A thermal imaging layer and a protective layer are coated on the other surface of the support.

[0059] The present invention will be further described below with reference to the embodiments.

[0060] The present invention is illustrated below by way of examples, but the present invention is not limited to these examples. In the following examples, "parts" and "%" represent "parts by mass" and "mass %" respectively, and the average particle size is determined using a Malvern laser particle size analyzer. Example 1

[0061] Preparation of thermal recording materials

[0062] (1) Preparation of thermosensitive dye microcapsule dispersion

[0063] 12 parts of ODB-2 (Shandong Ruikang Essence), 3 g of GN-2 (Tokyo Chemical Industry, Japan), 15 parts of dicyclohexyl phthalate, and 15 g of polyurethane with terminal isocyanate groups (Hangzhou Baochen Chemical) were heated and dissolved to obtain an oil phase.

[0064] The aqueous phase was obtained by mixing 200 parts of polyvinyl alcohol (PVA-224, Kuraray, Japan) with a concentration of 4% and 25 parts of 7# surfactant (Lucky, China).

[0065] The oil phase is added to the water phase under high-speed shear stirring to obtain a 7-oil-in-water dispersion. 150 parts of water and 5 parts of tetraethylenepentamine are then added, and microencapsulation reaction is carried out at a certain temperature to finally obtain a heat-sensitive dye microcapsule dispersion with an average particle size of less than 1 μm.

[0066] (2) Preparation of color developer dispersion

[0067] The following components were dispersed using a sand mill until the volume average particle size of the resulting mixture was less than 1.0 μm, thereby preparing a developer dispersion.

[0068] 25 parts of 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone

[0069] 25 parts of 10wt.% polyvinyl alcohol aqueous solution

[0070] 50 parts deionized water

[0071] (3) Preparation of coating solution for thermal imaging layer

[0072] The following components were added in sequence and mixed uniformly to obtain a coating solution for a thermal imaging layer.

[0073] 200 copies of thermosensitive dye microcapsule dispersion

[0074] 180 parts of developer dispersion

[0075] Polyvinyl alcohol (8wt.%, PVA-224) 50 parts

[0076] Carboxylated styrene-butadiene latex (32%) 20 parts

[0077] 1 part of dodecyldimethylamine betaine

[0078] (IV) Preparation of protective layer coating liquid

[0079] (1) Preparation of Liquid A

[0080] Mix the following components evenly to form liquid A.

[0081] γ-Methacryloxypropyltrimethoxysilane (stock solution) 7 parts

[0082] 40 parts of acidic silica sol (20 wt.%, volume average particle size 5 nm)

[0083] (2) Preparation of polyvinyl alcohol mixture

[0084] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0085] 192.2 parts deionized water

[0086] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0087] 47 parts of Liquid A

[0088] (3) The following components are mixed to prepare a coating solution for the preservation layer:

[0089] 549 parts of deionized water

[0090] Polyvinyl alcohol mixed solution (polyvinyl alcohol solid content 8%) 260 parts

[0091] Leveling agent aqueous solution (solid content 2%) 120 parts

[0092] Zinc stearate dispersion (Zhongjing Oil, volume average particle size 0.4μm) 100 parts

[0093] 5 parts of stearamide dispersion (Zhongjing Oil, volume average particle size 0.9μm)

[0094] 1 part of aqueous solution of fluorinated surfactant (solid content 8%)

[0095] Next, a PET base with a thickness of 175 μm and a density of 0.20 was used as a support, and the coating liquid for the thermal imaging layer and the coating liquid for the protective layer were coated together by slide extrusion coating (the coating liquid for the thermal imaging layer was 75 mL / m 2 , the protective layer coating amount is 30mL / m 2 ) onto a support and dried to prepare a heat-sensitive recording material of Example 1. Example 2

[0096] Preparation of thermal recording materials

[0097] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0098] γ-Methacryloxypropyltrimethoxysilane (stock solution) 15 parts

[0099] Acidic silica sol (20%, volume average particle size 8 nm) 40 parts

[0100] (2) Preparation of polyvinyl alcohol mixture

[0101] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0102] 4.2 parts deionized water

[0103] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0104] 55 parts of Liquid A

[0105] Other Steps A heat-sensitive recording material of Example 2 was prepared in the same manner as in Example 1. Example 3

[0106] Preparation of thermal recording materials

[0107] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0108] γ-Methacryloxypropyltrimethoxysilane (stock solution) 20 parts

[0109] Acidic silica sol (20%, volume average particle size 10 nm) 40 parts

[0110] (2) Preparation of polyvinyl alcohol mixture

[0111] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0112] 179.2 parts deionized water

[0113] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0114] 60 parts of Liquid A

[0115] Other Steps A heat-sensitive recording material of Example 3 was prepared in the same manner as in Example 1. Example 4

[0116] Preparation of thermal recording materials

[0117] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0118] γ-Methacryloxypropyltrimethoxysilane (stock solution) 15 parts

[0119] Acidic silica sol (20%, volume average particle size 6 nm) 21 parts

[0120] (2) Preparation of polyvinyl alcohol mixture

[0121] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0122] 203.2 parts deionized water

[0123] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0124] 36 parts of Liquid A

[0125] Otherwise, a heat-sensitive recording material of Example 4 was prepared in the same manner as in Example 1. Example 5

[0126] Preparation of thermal recording materials

[0127] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0128] γ-Methacryloxypropyltrimethoxysilane (stock solution) 15 parts

[0129] Acidic silica sol (20%, volume average particle size 7 nm) 60 parts

[0130] (2) Preparation of polyvinyl alcohol mixture

[0131] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0132] 164.2 parts deionized water

[0133] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0134] 75 parts of Liquid A

[0135] Otherwise, a heat-sensitive recording material of Example 5 was prepared in the same manner as in Example 1. Example 6

[0136] Preparation of thermal recording materials

[0137] A thermosensitive recording material of Example 6 was prepared in the same manner as in Example 1 except that the polyvinyl alcohol having a polymerization degree of 2400 in Example 1 was changed to polyvinyl alcohol having a polymerization degree of 1700. Example 7

[0138] Preparation of thermal recording materials

[0139] A thermal recording material of Example 7 was prepared in the same manner as in Example 1, except that the polyvinyl alcohol with a polymerization degree of 2400 and an alcoholysis degree of 88% in Example 1 was adjusted to polyvinyl alcohol with a polymerization degree of 1700 and an alcoholysis degree of 98%. Example 8

[0140] Preparation of thermal recording materials

[0141] A thermal recording material of Example 10 was prepared in the same manner as in Example 1, except that the polyvinyl alcohol with a polymerization degree of 2400 and an alcoholysis degree of 88% in Example 1 was adjusted to a silicon-modified polyvinyl alcohol with a polymerization degree of 1100 and an alcoholysis degree of 98%.

[0142] Comparative Example 1

[0143] Preparation of thermal recording materials

[0144] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0145] γ-Methacryloxypropyltrimethoxysilane (stock solution) 5 parts

[0146] Acidic silica sol (20%, volume average particle size 8 nm) 40 parts

[0147] (2) Preparation of polyvinyl alcohol mixture

[0148] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0149] 194.2 parts deionized water

[0150] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0151] 45 parts of Liquid A

[0152] Otherwise, a thermosensitive recording material of Comparative Example 1 was prepared in the same manner as in Example 1.

[0153] Comparative Example 2

[0154] Preparation of thermal recording materials

[0155] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0156] γ-Methacryloxypropyltrimethoxysilane (stock solution) 25 parts

[0157] Acidic silica sol (20%, volume average particle size 8 nm) 40 parts

[0158] (2) Preparation of polyvinyl alcohol mixture

[0159] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0160] 174.2 parts deionized water

[0161] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0162] 65 parts of Liquid A

[0163] Otherwise, a thermosensitive recording material of Comparative Example 2 was prepared in the same manner as in Example 1.

[0164] Comparative Example 3

[0165] Preparation of thermal recording materials

[0166] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0167] γ-Methacryloxypropyltrimethoxysilane (stock solution) 15 parts

[0168] Acidic silica sol (20%, volume average particle size 8 nm) 10 parts

[0169] (2) Preparation of polyvinyl alcohol mixture

[0170] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0171] 214.2 parts deionized water

[0172] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0173] 25 parts of Liquid A

[0174] Otherwise, a thermosensitive recording material of Comparative Example 3 was prepared in the same manner as in Example 1.

[0175] Comparative Example 4

[0176] Preparation of thermal recording materials

[0177] (1) Mix the solution A described in Example 1 according to the following ingredients.

[0178] γ-Methacryloxypropyltrimethoxysilane (stock solution) 15 parts

[0179] Acidic silica sol (20%, volume average particle size 8 nm) 70 parts

[0180] (2) Preparation of polyvinyl alcohol mixture

[0181] Mix solution A with the following components and heat to dissolve to prepare a polyvinyl alcohol mixed solution containing 8% polyvinyl alcohol.

[0182] 154.2 parts deionized water

[0183] PVA-224 (alcoholysis degree 88%, polymerization degree 2400) 20.8 parts

[0184] 85 parts of Liquid A

[0185] Otherwise, a thermosensitive recording material of Comparative Example 4 was prepared in the same manner as in Example 1.

[0186] Comparative Example 5

[0187] Preparation of thermal recording materials

[0188] The heat-sensitive recording material of Comparative Example 5 was prepared by the same method as in Example 1 except that the γ-methacryloxypropyltrimethoxysilane in Example 1 was replaced with glyoxal.

[0189] Next, the obtained thermosensitive recording materials were rated.

[0190] (1) Print 21 grayscale density films using a Lucky DryMate 320 dry imager to establish density values ​​at different grayscales; record the minimum density corresponding to the grayscale (i.e., the coating density after deducting the film base density).

[0191] (II) Image stability is defined as the density difference before and after printing 21 grayscales using a Lucky DryMate 320 dry imager at different temperatures and humidities, then summing the differences, averaging the differences, and then taking the square root of the differences. The selected temperature conditions are (1) 25°C, 50% relative humidity, and then testing the grayscale density after 1 hour; (2) 35°C, 60% relative humidity, and then testing the grayscale density after 1 hour; (3) 35°C, 70% relative humidity, and then testing the grayscale density after 1 hour. The calculation formula is as follows:

[0192] Image stabilization index =

[0193] (3) Water resistance is defined as the following: cut the obtained thermal recording material into samples with a size of 10×10 cm, soak them in water for 3 minutes, remove them, and dry them naturally before calculating the water resistance using the following formula.

[0194] Water resistance =

[0195] (IV) Haze data were measured using a WGT-S transmittance / haze tester for the thermal recording material prepared above.

[0196] (V) Apparent smoothness of thermal imaging layer: The coating is defined as the apparent quality of the thermal imaging layer when visually inspected during the coating process and after drying of the thermal imaging layer coating solution.

[0197] (VI) Heat resistance is defined as cutting the obtained thermal recording material into samples with a specification of 14×17 (ins), using a Lucky DryMate 320 dry imager to print 100 sheets continuously, and rating the samples based on the apparent scratch degree, as shown in Tables 1 and 2 below.

[0198] Table 1 Apparent scratch degree rating table

[0199] grade A-level Class B C-level D-Class Continuous printing 100 pages No scratches on the surface Surface scratch area ≤5% 20%≥Surface scratch area>5% Surface scratch area>20%

[0200] Table 2 Test data of examples and comparative examples

[0201]

[0202] As can be seen from the table above, compared with the examples, the amount of γ-methacryloxypropyltrimethoxysilane (stock solution) added to the protective layer of Comparative Example 1 is 5 parts by mass. After conversion, this amount is lower than the minimum amount specified in the present invention. This prevents the cross-linking reaction of the polyvinyl alcohol from being complete, resulting in poor image stability of the thermal recording material (a larger value indicates that the thermal recording material is more affected by temperature and humidity) and poor water resistance (a larger value indicates that the thermal recording material has stronger water absorption).

[0203] Compared with the embodiments, the amount of γ-methacryloxypropyltrimethoxysilane (stock solution) added to the protective layer of Comparative Example 2 is 25 parts by mass. After conversion, it is higher than the maximum value of the addition amount specified in the present invention, resulting in high coating density (the larger the value, the lower the local density of the coating and the worse the permeability), high haze (the larger the value, the lower the transparency, especially the imaging quality, of the thermal recording material), poor appearance of the protective layer, and poor heat resistance of the coating.

[0204] Compared with the embodiment, the amount of silica sol added in Comparative Example 3 is lower than the minimum amount of silica sol specified in the present invention, resulting in poor heat resistance of the coating and failure to meet the requirements of continuous use.

[0205] Compared with the examples, in Comparative Example 4, the amount of silica sol added is higher than the maximum amount of silica sol defined in the present invention, resulting in high haze and poor appearance during the coating process, with streaking.

[0206] Compared with the examples, Comparative Example 5 uses an aldehyde cross-linking agent outside the scope of the present invention, resulting in high haze, apparent streaks during the coating process, and poor heat resistance of the coating.

Claims

1. A heat-sensitive recording material comprising a support, a heat-sensitive imaging layer disposed on the support, and a protective layer disposed on the heat-sensitive imaging layer, characterized in that: The protective layer is formed by drying a protective layer coating solution containing γ-methacryloxypropyltrimethoxysilane and silica sol, wherein the protective layer coating solution includes the following components in parts by mass: 400~600 parts of deionized water 200-300 parts of polyvinyl alcohol mixed solution with a solid content of 8% 80~140 parts of 2% solid content leveling agent aqueous solution 70-100 parts of zinc stearate dispersion with a volume average particle size of 0.4 μm 3-8 parts of stearic acid amide dispersion with a volume average particle size of 0.9 μm 0.8-1.8 parts of an aqueous solution of a fluorinated surfactant with a solid content of 8%; The polyvinyl alcohol mixed solution comprises the following components in parts by mass: 164.2~203.2 parts of deionized water 20.8 parts of polyvinyl alcohol 36 to 75 parts of Liquid A; The liquid A is composed of the following components in parts by mass, where the following components are calculated relative to 100 parts by mass of polyvinyl alcohol: 7 parts of γ-methacryloxypropyltrimethoxysilane and 40 parts of silica sol, 15 parts of γ-methacryloxypropyltrimethoxysilane and 40 parts of silica sol, 20 parts of γ-methacryloxypropyltrimethoxysilane and 40 parts of silica sol, 15 parts of γ-methacryloxypropyltrimethoxysilane and 21 parts of silica sol, or 15 parts of γ-methacryloxypropyltrimethoxysilane and 60 parts of silica sol; The silica sol is acidic silica sol with a pH of 2-4 and a volume average particle size of 5-10 nm; The polyvinyl alcohol is unmodified polyvinyl alcohol.

2. The thermal recording material according to claim 1, wherein: The alcoholysis degree of the polyvinyl alcohol is greater than 80%, and the polymerization degree is 1000-3000.

3. A method for preparing a thermal recording material according to any one of claims 1 to 2, characterized in that: A thermal imaging layer coating liquid is coated on the support and then dried to form a thermal imaging layer, and a protective layer coating liquid containing γ-methacryloxypropyltrimethoxysilane and silica sol is coated on the thermal imaging layer and then dried to form the protective layer.

4. The method for preparing a thermal recording material according to claim 3, wherein: The protective layer coating solution comprises the following preparation steps: a. Preparation of Liquid A: γ-methacryloxypropyltrimethoxysilane and acidic silica sol are uniformly mixed to form Liquid A; b. Mix the formulated amount of Solution A, polyvinyl alcohol, and deionized water, and heat to dissolve the mixture to prepare a polyvinyl alcohol mixed solution, wherein the content of polyvinyl alcohol is 8 wt.%; c. Evenly mix the formulated amounts of deionized water, polyvinyl alcohol mixed solution, leveling agent aqueous solution, zinc stearate dispersion, stearamide dispersion and fluorine-containing surfactant aqueous solution to prepare a protective layer coating solution.

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