Dispersant, coating liquid composition and thermal recording material

Abstract

To provide a dispersant capable of dispersing a thermosensitive coloring component such as a leuco dye, a developer, or a sensitizer to a desired particle size within a shorter time, a coating liquid composition for forming a thermosensitive recording layer containing a heat-sensitive color component and a dispersant, and a thermal recording medium having a thermal recording layer formed on a substrate with the coating liquid.SOLUTION: There is provided a dispersant for at least one thermosensitive coloring component selected from the group consisting of leuco dyes (A), color developers (B), and sensitizers (C), wherein the dispersant contains an alkali-neutrarized salt of a copolymer (D) satisfying the following conditions. (1) A copolymer (D-1) of monomers made of (meth)acrylic acid and (meth) acrylic acid ester (D-1), and / or, a copolymer (D-2) of monomers made of (meth)acrylic acid and (meth)acrylic acid esters and styrenes, (2) an acid value is 40 to 400 mgKOH / g, and (3) a weight-average molecular weight is 3,000 to 30,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dispersant for a thermosensitive color-forming component, a coating liquid composition for forming a thermosensitive recording layer containing the dispersant and the thermosensitive color-forming component, and a thermosensitive recording material having a thermosensitive recording layer formed from the coating liquid on a support. [Background technology]

[0002] Conventionally, thermosensitive recording media have been used as one type of information recording medium. A thermosensitive recording medium includes a sheet-like support such as paper or film, and has a thermosensitive recording layer on one side thereof. The thermosensitive recording layer is formed by dispersing thermosensitive color-forming components such as leuco dyes, color developers, and sensitizers, and then coating and drying the dispersion on a support.

[0003] To obtain a dispersion of thermosensitive color-forming components, water-soluble resins such as polyvinyl alcohol, which are also used as binders in protective layers and thermosensitive layers, are widely used as dispersants. However, water-soluble resins such as polyvinyl alcohol do not have sufficient dispersant capabilities, and there are issues with the dispersibility of thermosensitive color-forming components and the time required for dispersion.

[0004] For example, Patent Document 1 describes an invention that aims to provide a thermosensitive recording medium having good chemical resistance, oil resistance, recording sensitivity, background whiteness, etc., as well as excellent water resistance and water-resistant plasticizer resistance, and a method for producing the same, and in the examples it describes the use of an aqueous solution of styrene-acrylic acid-acrylamide copolymer ammonium salt that functions as a binder and a dispersant for leuco dyes and color developers.

[0005] Furthermore, Patent Document 2 describes an invention aimed at providing a thermal recording medium with excellent water resistance, alcohol resistance, and corrosion resistance, and describes a styrene-maleic acid copolymerized ammonium salt as a dispersant.

[0006] Furthermore, Patent Document 3 describes an invention in which a carboxylic acid-modified polyvinyl alcohol having a mass-average degree of polymerization of 100 to 400 and a modification degree of 0.2 to 1.0 mol % is used as a dispersant for a leuco dye, with the aim of providing a thermal recording material with high background whiteness by using a leuco dye dispersion that does not significantly increase the viscosity of the dispersion or decrease the stability over time even when the volume average particle diameter is reduced to 0.3 μm or less in the dispersion process.

[0007] However, the carboxylic acid-modified polyvinyl alcohol of Patent Document 3 is thought to have other problems, since there is no commercially available grade of it that can be used as a dispersant for leuco dyes.In addition, the dispersants described in Patent Documents 1 and 2 are each intended to solve the above-mentioned problems, but still have the problem that it takes a long time to finely disperse a dispersion containing a thermosensitive color-developing component such as a leuco dye to a desired particle size. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 5-301461 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-181781 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-254436 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a dispersant capable of finely dispersing thermosensitive color-forming components such as leuco dyes, color developers, and sensitizers to a desired particle size in a shorter time than conventional methods; a coating liquid composition for forming a thermosensitive recording layer containing the thermosensitive color-forming components and the dispersant; and a thermosensitive recording material having a thermosensitive recording layer formed on a support using the coating liquid. [Means for solving the problem]

[0010] The present inventors have discovered that by using a dispersant containing an alkali neutralized salt of a specific copolymer as a dispersant for heat-sensitive color-forming components such as leuco dyes, color developers, and sensitizers, a dispersion liquid with a desired particle size can be obtained in a shorter time than conventional methods.

[0011] That is, the present invention provides: <1> A dispersant for at least one thermosensitive color-forming component selected from the group consisting of a leuco dye (A), a color developer (B), and a sensitizer (C), characterized in that the dispersant contains an alkali neutralized salt of a copolymer (D) that satisfies the following conditions: (1) Copolymer of (meth)acrylic acid and (meth)acrylic acid ester monomers (D-1) and / or Copolymers of (meth)acrylic acid, (meth)acrylic acid esters, and styrene monomers (D-2) is (2) Acid value is 40 to 400 mg KOH / g (3) Weight-average molecular weight is 3,000 to 30,000 <2> The alkali is at least one selected from the group consisting of ammonia, sodium hydroxide, and dimethylethanolamine. <1> The dispersant according to <3> At least one thermosensitive color-forming component selected from the group consisting of a leuco dye (A), a color developer (B), and a sensitizer (C), <1> or <2> a coating liquid composition for forming a thermosensitive recording layer, comprising the dispersant according to claim 1; <4> On a support, <3> a thermosensitive recording material having a thermosensitive recording layer formed from the coating liquid composition according to claim 1; is. [Effects of the Invention]

[0012] According to the present invention, a dispersion liquid having a desired particle size can be obtained in a shorter time than conventional methods. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail. Note that the following description is an example of an embodiment of the present invention, and the present invention is not limited to this description.

[0014] The dispersant of the present invention is a dispersant for a thermosensitive color-forming component, and contains an alkali neutralized salt of a copolymer (D) that satisfies the conditions described below.

[0015] <Thermal color-developing component> The thermosensitive color-forming components contained in the thermosensitive recording layer of the thermosensitive recording medium are mainly a leuco dye (A) and a color developer (B), and a sensitizer (C) may be used as needed to enhance the color-forming sensitivity of the thermosensitive recording layer. The dispersant of the present invention is used to obtain a dispersion liquid in which at least one of these thermosensitive color-forming components (A) to (C) is dispersed.

[0016] <Leuco dye> The leuco dye (A) is not particularly limited and can be used alone or in combination of two or more. Examples of the leuco dye (A) include triphenylmethanes such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide; fluorans such as 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, and 3-di(n-butyl)amino-6-methyl-7-anilinofluoran; and fluorenes such as 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide] and 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide].

[0017] <Developer> The developer (B) may be any electron-accepting compound capable of causing the leuco dye to develop color, and may be used alone or in combination of two or more. Examples of the developer (B) include organic acids such as benzoic acid, metal salts of organic acids such as zinc salicylate, phenols such as 4,4'-sulfonylbisphenol, thiophenols such as 4,4'-thiobis(6-tert-butyl-2-methylphenol), thiourea derivatives such as N,N'-diphenylthiourea, and diphenylsulfones such as 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone.

[0018] <Sensitizer> The sensitizer (C) may be any one that can increase the color-developing sensitivity of the thermosensitive recording layer, and may be used alone or in combination of two or more. Examples of the sensitizer (C) include 1,2-bis(3,4-dimethylphenyl)ethane, 1,2-diphenoxyethane, 1,2-bis(3-methylphenoxy)ethane, p-benzylbiphenyl, m-terphenyl, dimethyl phthalate, benzyl terephthalate, 2-naphthol benzyl ether, benzyl p-benzyloxybenzoate, 1-hydroxy-2-naphthonic acid phenyl ester, and di(p-methylbenzyl)oxalate.

[0019] <Dispersant> The dispersant of the present invention may contain an alkali neutralized salt of copolymer (D) that satisfies the following conditions. (1) Copolymer of (meth)acrylic acid and (meth)acrylic acid ester monomers (D-1) and / or Copolymers of (meth)acrylic acid, (meth)acrylic acid esters, and styrene monomers (D-2) is (2) Acid value is 40 to 400 mg KOH / g (3) Weight-average molecular weight is 3,000 to 30,000

[0020] The dispersant of the present invention contains an alkali neutralized salt of copolymer (D) that satisfies all of the above conditions (1) to (3), and thus can achieve dispersion to a predetermined particle size in a shorter time than with conventional dispersants.

[0021] The (meth)acrylic acid used in the copolymer (D) of the present invention refers to acrylic acid and / or methacrylic acid.

[0022] The (meth)acrylic acid esters used in the copolymer (D) of the present invention may be any (meth)acrylic acid ester, specifically, linear, branched, or cyclic alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate; aryl esters such as benzyl (meth)acrylate; functional group-containing esters such as 2-hydroxyethyl (meth)acrylate and glycidyl (meth)acrylate; and esters having a glycol structure such as 2-methoxyethyl (meth)acrylate. These may be used alone or in combination of two or more. Esters of linear, branched, or cyclic alkyls are preferred, more preferably esters of linear, branched, or cyclic alkyls having 2 to 18 carbon atoms, even more preferably esters of linear, branched, or cyclic alkyls having 2 to 8 carbon atoms, and particularly preferably esters of linear, branched, or cyclic alkyls having 2 to 8 carbon atoms. Of these, methyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred.

[0023] The styrenes optionally used in the copolymer (D) of the present invention refer to aromatic compounds capable of addition polymerization, and specific examples thereof include styrene; styrene derivatives such as 4-methylstyrene, p-hydroxymethylstyrene, and divinylbenzene; and α-methylstyrene. These may be used alone or in combination of two or more kinds, with styrene being preferred.

[0024] The copolymer (D) can be obtained by any known production method without any particular limitation. It is usually obtained by solution polymerization in a solvent such as alcohol that can dissolve the monomers and their polymers, or by emulsion polymerization of the monomers in a state where the monomers are emulsified in water with an emulsifier or the like. In the case of solution polymerization, the solvent used during solution polymerization may be distilled off, if necessary, before or after the step of converting the copolymer (D) into an alkali neutral salt.

[0025] The copolymer (D) must be a copolymer (D-1) of monomers consisting of at least (meth)acrylic acid and (meth)acrylic acid esters, or a copolymer (D-2) of monomers consisting of (meth)acrylic acid, (meth)acrylic acid esters, and styrenes, but may also be a mixture of the copolymer (D-1) and the copolymer (D-2).

[0026] The acid value of copolymer (D) must be 40 to 400 mgKOH / g from the viewpoint of dispersibility of the thermosensitive color-forming component. If the acid value is less than 40 mgKOH / g or more than 400 mgKOH / g, the ability to disperse the thermosensitive color-forming component will be insufficient. It is preferably 50 to 350 mgKOH / g, and more preferably 60 to 320 mgKOH / g. In the present invention, the acid value refers to a value measured based on the neutralization titration method of JIS K0070-19K0070-1992.

[0027] The weight-average molecular weight of copolymer (D) must be 3,000 to 30,000. If the weight-average molecular weight is less than 3,000, the dispersion ability may be insufficient and the stability of the coating liquid composition after dispersion may be poor. If the weight-average molecular weight exceeds 30,000, handling may be inconvenient in the process of neutralizing with alkali to prepare an aqueous solution, in handling during preparation of the coating liquid composition, or in adjusting the coating suitability and coating amount when forming a thermosensitive recording layer. A weight-average molecular weight of 4,000 to 28,000 is preferred, and a weight-average molecular weight of 6,000 to 25,000 is more preferred. In the present invention, the weight-average molecular weight is measured in terms of polystyrene by the GPC method under the following conditions. Device: HLC-8320GPC (Tosoh Corporation) Column: Tosoh Corporation TSK-gel SUPER MULTIPORE HZ-H and SUPER MULTIPORE HZ-M connected together Eluent: tetrahydrofuran, 0.35 mL / min Standard: TSKgel standard polystyrene (manufactured by Tosoh Corporation)

[0028] <Preparation of Alkali Neutralized Salt of Copolymer (D)> The alkali neutralized salt of copolymer (D) of the present invention can be obtained by preparing an aqueous solution using an alkali in an amount equivalent to 50 to 110% of the acid value of copolymer (D). Here, the aqueous solution is a solution that can be uniformly diluted with water. While it is usually an aqueous solution, it may contain a solvent other than water, such as a water-compatible alcohol, as long as it forms a uniform aqueous solution. The concentration of the alkali neutralized salt of copolymer (D) contained in the dispersant can be adjusted appropriately taking into account the optimal concentration and viscosity of the coating liquid composition for forming a thermosensitive recording layer, but is preferably 20 to 40% by mass.

[0029] Examples of alkalis used to obtain the alkali neutralized salt of copolymer (D) include ammonia, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and organic amines such as dimethylethanolamine, triethanolamine, and morpholine, among which at least one selected from the group consisting of ammonia, sodium hydroxide, and dimethylethanolamine is preferred. Among these, dimethylethanolamine is more preferred from the viewpoint of dispersibility of the thermosensitive color-developing component.

[0030] <Coating liquid composition for forming a thermosensitive recording layer and its preparation> The coating liquid composition for forming a thermosensitive recording layer of the present invention (hereinafter sometimes simply referred to as the coating composition) contains at least one thermosensitive color-forming component selected from the group consisting of a leuco dye (A), a color developer (B), and a sensitizer (C), and a dispersant. As other components, various conventional binder components may also be appropriately mixed and used to form a thermosensitive recording layer. Specific examples include water-soluble polymers such as polyvinyl alcohol, starch or its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymers, acrylamide / acrylic acid ester / methacrylic acid terpolymers, alkali salts of styrene / maleic anhydride copolymers, alkali salts of isobutylene / maleic anhydride copolymers, polyacrylamide, sodium alginate, gelatin, and casein, as well as emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride / vinyl acetate copolymers, polybutyl methacrylate, and ethylene / vinyl acetate copolymers, and latexes such as styrene / butadiene copolymers and styrene / butadiene / acrylic copolymers. Other components may include inorganic or organic fillers such as silica, talc, calcium carbonate, and polystyrene; lubricants such as fatty acid metal salts and waxes; ultraviolet absorbers, storage stabilizers, colorants, and antifoaming agents, as needed. The coating composition can be obtained by mixing and dispersing a thermosensitive color-forming component and a dispersant. When a coating liquid composition containing multiple thermosensitive color-forming components is used, the dispersion method is not particularly limited; each component may be dispersed individually and then mixed, or all thermosensitive color-forming components may be dispersed together. Examples of dispersing devices that can be used include a bead mill, a ball mill, an attritor, a sand mill, and a high-pressure jet mill. A dispersion method using beads (also called media) is preferred, and microparticulation can be achieved by using zirconia beads with a diameter of 0.5 mm or less, or by coarsely pulverizing the material using zirconia beads with a diameter of 0.5 to 1.0 mm, followed by dispersing the material using zirconia beads with a diameter of 0.5 mm or less.

[0031] The particle size of the coating liquid composition refers to the 90% cumulative particle size (hereinafter simply referred to as particle size D90) measured using a particle size distribution analyzer (Microtrac UPAEX150, manufactured by Nikkiso Co., Ltd.) by dynamic light scattering / laser Doppler method. The particle size D90 is preferably 2.0 μm or less. From the viewpoints of coatability and handling, the viscosity of the coating liquid composition is preferably 10 to 800 mPa·s as measured with a Brookfield viscometer at 25°C. In the examples of the present invention, in order to simply evaluate the reduction in dispersion time, 25 parts of 0.3 mm zirconia beads, a dispersant (6 parts as copolymer (D)), 30 parts of a thermosensitive color-developing component, 50 parts of ion-exchanged water, and 0.1 parts of Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd.) were weighed into a 250 cc plastic bottle, and the bottle was shaken with a paint shaker (manufactured by Toyo Seiki Seisakusho, Ltd.) to obtain a particle diameter D90 of the coating liquid composition after a certain period of dispersion. The particle diameter D90 was used as an index for evaluating the dispersion state.

[0032] <Thermal Recording Material and Its Preparation> The thermosensitive recording medium of the present invention has a thermosensitive recording layer formed from the coating liquid composition on a support. The support is not particularly limited as long as it is one that is commonly used as a support for thermosensitive recording mediums, and examples thereof include paper, synthetic paper, and laminated paper.

[0033] The thermosensitive recording layer can be formed on a support by applying a coating liquid composition onto the support and drying it. The coating method is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include blade coating, air knife coating, gravure coating, roll coating, spray coating, dip coating, bar coating, and extrusion coating.

[0034] <Layers other than the thermosensitive coloring layer> The thermosensitive recording medium of the present invention may have at least the thermosensitive recording layer on a support, but may also have a protective layer for protecting the thermosensitive recording layer or an intermediate layer between the support and the thermosensitive recording layer. The protective layer or intermediate layer contains a binder and an inorganic or organic filler, and may further contain other components as necessary.

[0035] The binder used in the protective layer or intermediate layer is not particularly limited, and any known binder can be appropriately selected depending on the purpose, such as polyvinyl alcohol, cellulose derivatives, starch or its derivatives, carboxyl-modified polyvinyl alcohol, and polyacrylic acid or its derivatives.

[0036] The inorganic or organic fillers used in the protective layer or intermediate layer may be the same as those used in the thermal recording layer, but aluminum hydroxide and silica are particularly useful. The amount of inorganic or organic filler is preferably 30% to 80% by mass, more preferably 40% to 70% by mass, of the entire protective layer. The coating weight of the protective layer is 3.0 g / m 2 If the amount is more than this, the transfer of heat to the thermosensitive recording layer below the protective layer may be hindered.

[0037] The protective layer and intermediate layer are formed on the support in the same manner as in the formation of the heat-sensitive recording layer.

[0038] The thermosensitive recording medium of the present invention is not particularly limited in shape and can be appropriately selected depending on the purpose, and suitable shapes include label, sheet, roll, etc. Applications include cash register receipts, etc. In addition, it can be used as a pressure-sensitive thermosensitive recording label by laminating an adhesive layer and a release liner on the back surface, or as a heat-activated thermosensitive recording label that does not require a release liner by providing a heat-activated adhesive layer on the back surface that has no adhesiveness at room temperature (10°C to 30°C) but develops adhesive strength when heated. [Example]

[0039] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" and "%" without a unit are all "parts by mass" and "% by mass".

[0040] (Production Example 1) <Production of Copolymer (D)> A four-neck separable flask equipped with a stirrer, condenser, thermometer, nitrogen inlet tube, and dropping funnel was charged with 1,000 parts of propylene glycol monomethyl ether acetate as a solvent, and the internal temperature was raised to 143 ° C. under a nitrogen atmosphere while stirring. A monomer mixture was charged into the dropping funnel, which consisted of 50 parts of acrylic acid, 40 parts of methacrylic acid, 710 parts of methyl methacrylate, 200 parts of butyl acrylate, and 25 parts of di-tert-butyl peroxide as a polymerization initiator. The mixture was added dropwise to the flask at an internal temperature of 143 ° C. over 3 hours. After the addition was complete, the internal temperature was maintained at 140 ° C. for 2 hours, then the temperature was raised to 190 ° C., and the solvent and unreacted materials in the flask were distilled off. After distillation, the mixture was removed from the flask and cooled to obtain a solid copolymer (D-1-1). The copolymer (D-1-1) had a weight average molecular weight (Mw) of 10,000 and an acid value of 60 mgKOH / g. <Preparation of Dispersant 1> A four-neck flask equipped with a stirrer, a condenser, and a thermometer was charged with 671 parts of ion-exchanged water, and 300 parts of powdered copolymer (D-1-1) was added while stirring. 29 parts of dimethylethanolamine (acid value equivalent of copolymer (D-1-1)) was then added as an alkali, and the internal temperature was raised to 80°C. The internal temperature was then maintained at 80°C for 2 hours to dissolve the copolymer (D-1-1), and a dispersant 1 containing 30% by mass of copolymer (D-1-1) was prepared.

[0041] (Examples 2 to 14, 16) <Production of Copolymer (D)> Solid copolymers (D-1-2), (D-2-1) to (D-2-12), and (RD-2) were obtained in the same manner as in Production Example 1, except that the type and amount of solvent, the type and amount of monomer, and the amount of polymerization initiator were changed as shown in Table 1. The weight average molecular weight (Mw) and acid value of each copolymer are shown in Table 2. <Preparation of Dispersants 2 to 14 and 16> Dispersants 2 to 14 and 16 containing 30 mass% of copolymers (D-1-2), (D-2-2) to (D-2-12) and (RD-2) were prepared in the same manner as in Production Example 1, except that the amount of water charged and the type and amount of alkali charged (all acid value equivalents of each copolymer (D)) were changed as shown in Table 3. 28% aqueous ammonia was used.

[0042] (Manufacturing Example 15) <Production of Acrylamide-Containing Monomer Copolymer (RD-1) and Preparation of Dispersant 15> A four-neck flask equipped with a stirrer, condenser, thermometer, and nitrogen inlet tube was charged with 429 parts of isopropyl alcohol, 300 parts of acrylic acid, 30 parts of methacrylic acid, 470 parts of styrene, 100 parts of butyl acrylate, 100 parts of acrylamide, 15 parts of normal dodecyl mercaptan, and 20 parts of azoisobutyronitrile. The mixture was heated to an internal temperature of 85 ° C. over 30 minutes under nitrogen atmosphere with stirring. After maintaining the temperature at 85 ° C. for 1 hour, 1 part of azoisobutyronitrile was added. After maintaining the temperature for another 1 hour, 274 parts of 28% aqueous ammonia and 2160 parts of ion-exchanged water were added and stirred for 10 minutes. The internal temperature was then raised to 95 ° C. and distilled under atmospheric pressure to remove the isopropyl alcohol, yielding a dispersant 15 containing 30% by weight of styrene-acrylic acid acrylamide copolymer (RD-1). The copolymer (RD-1) had a weight average molecular weight (Mw) of 15,000 and an acid value of 250 mgKOH / g.

[0043] (Manufacturing Example 17) <Preparation of anionic polyvinyl alcohol (RD-3) dispersant> A four-neck flask equipped with a stirrer, a condenser, and a thermometer was charged with 800 parts of ion-exchanged water, and while stirring, 200 parts of anionic polyvinyl alcohol having sulfonic acid groups (Gohsenex L3266, manufactured by Mitsubishi Chemical Holdings Corporation), a common polyvinyl alcohol for dispersing dyes and color developers, was added. The internal temperature was then raised to 80°C and maintained at that temperature for 2 hours to obtain Dispersant 17, which contains 20% by mass of anionic polyvinyl alcohol (RD-3).

[0044] [Table 1]

[0045] [Table 2]

[0046] Explanation of abbreviations in Tables 1 and 2 PGM-Ac: Propylene glycol monomethyl ether acetate (reflux temperature: 143-146°C) Xy: Xylene (reflux temperature: 138-141°C) AA: acrylic acid MAA: methacrylic acid St: styrene MMA: methyl methacrylate BA: butyl acrylate AAm: acrylamide MAn: Maleic anhydride MA-nBu: Maleic acid mono-n-butyl ester (half ester of maleic anhydride and n-butanol) DTBP: Di-tert-butyl peroxide

[0047] [Table 3]

[0048] Explanation of abbreviations in Table 3 DMEA: Dimethylethanolamine NaOH: Sodium hydroxide KOH: Potassium hydroxide TEA: Triethanolamine

[0049] <Evaluation of leuco dye dispersibility in dispersants> Example 1 In a 250cc plastic bottle, 25 parts of 0.3mm zirconia beads, 16 parts of Dispersant 1 described in Production Example 1 as a dispersant (4.8 parts as copolymer (D-1-1)), 30 parts of leuco dye (3-di-butylamino-6-methyl-7-anilinofluoran (ODB-2)), 54 parts of ion-exchanged water, and 0.1 parts of Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd.) were weighed and shaken for 120 minutes using a paint shaker, and then 70 parts of ion-exchanged water was added and mixed until uniform. Thereafter, the zirconia beads were removed, and coating liquid composition L1 was obtained. 25 parts of the coating composition were sampled 60 minutes and 90 minutes after the start of shaking, and the particle size (D90) of the coating composition, along with that of the coating composition after 120 minutes of shaking, was measured using a particle size distribution analyzer (Microtrac UPAEX150, manufactured by Nikkiso Co., Ltd.) using dynamic light scattering / laser Doppler methods. The measurement results are shown in Table 4. The faster the D90 value reaches 2.0 μm or less, the better the dispersibility.

[0050] (Examples 2 to 14, Comparative Examples 1 and 2) Coating liquid compositions L2 to L16 were obtained in the same manner as in Example 1, except that the type of dispersant was changed as shown in Table 4. The particle diameters of coating liquid compositions L2 to L16 at each time were measured in the same manner as in Example 1. The measurement results are shown in Table 4.

[0051] (Comparative Example 3) 25 parts of 0.3 mm zirconia beads, 24 parts of Dispersant 17 described in Production Example 17 as a dispersant (4.8 parts as copolymer (RD-3)), 30 parts of leuco dye (3-dibutylamino-6-methyl-7-anilinofluoran (ODB-2)), 46 parts of ion-exchanged water, and 0.1 parts of Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd.) were weighed into a 250 cc plastic bottle and shaken for 120 minutes using a paint shaker. 70 parts of ion-exchanged water was then added and mixed until uniform. The zirconia beads were then removed to obtain Coating Liquid Composition L17. The particle diameter of Coating Liquid Composition L17 at each time point was measured in the same manner as in Example 1. The measurement results are shown in Table 4.

[0052] [Table 4]

[0053] Table 4 shows that the particle sizes of Coating Liquid Compositions L1 to L14 of Examples 1 to 14 were all less than 2.0 μm in D90 value after 90 minutes of shaking, indicating that the dispersants used were excellent in dispersing leuco dyes. On the other hand, the particle sizes of Coating Liquid Compositions L15 to L17 of Comparative Examples 1 to 3 were all 2.0 μm or more in D90 value after 90 minutes of shaking, indicating that the dispersibility was inferior to that of the Examples.

[0054] <Evaluation of developer dispersibility in dispersants> Example 15 Coating liquid composition M1 was obtained by replacing the leuco dye of Example 1 with a developer (4,4'-sulfonylbisphenol). The particle diameters of coating liquid composition M1 at each time were measured in the same manner as in Example 1. The measurement results are shown in Table 5.

[0055] (Examples 16 to 28, Comparative Examples 4 to 5) Coating liquid compositions M2 to M16 were obtained in the same manner as in Example 15, except that the type of dispersant was changed as shown in Table 5. The particle diameters of coating liquid compositions M2 to M16 at each time were measured in the same manner as in Example 1. The measurement results are shown in Table 5.

[0056] (Comparative Example 6) Coating liquid composition M17 was obtained by replacing the leuco dye of Comparative Example 3 with a developer (4,4'-sulfonylbisphenol). The particle diameters of coating liquid composition M17 at each time were measured in the same manner as in Example 1. The measurement results are shown in Table 5.

[0057] [Table 5]

[0058] Table 5 shows that the particle sizes of Coating Liquid Compositions M1 to M14 of Examples 15 to 28 all had D90 values ​​of less than 2.0 μm after 90 minutes of shaking, indicating that the dispersants used were excellent in dispersing leuco dyes. On the other hand, the particle sizes of Coating Liquid Compositions M15 to M17 of Comparative Examples 4 to 6 all had D90 values ​​of 2.0 μm or more even after 90 minutes of shaking, indicating that all of them had inferior dispersibility compared to the Examples.

[0059] <Evaluation of dispersing ability of dispersing agent to color former> Example 29 Coating liquid composition N1 was obtained by replacing the leuco dye of Example 1 with a color former (1,2-diphenoxyethane). The particle diameter of coating liquid composition N1 at each time point was measured in the same manner as in Example 1. The measurement results are shown in Table 6.

[0060] (Examples 30 to 42, Comparative Examples 7 to 8) Coating liquid compositions N2 to N16 were obtained in the same manner as in Example 29, except that the type of dispersant was changed as shown in Table 6. The particle diameters of coating liquid compositions N2 to N16 at each time were measured in the same manner as in Example 1. The measurement results are shown in Table 6.

[0061] (Comparative Example 9) Coating liquid composition N17 was obtained by replacing the leuco dye of Comparative Example 3 with a color former (1,2-diphenoxyethane). The particle diameters of coating liquid composition N17 at each time were measured in the same manner as in Example 1. The measurement results are shown in Table 6.

[0062] [Table 6]

[0063] Table 6 shows that the particle sizes of coating liquid compositions N1 to N14 of Examples 29 to 42 all had D90 values ​​of less than 2.0 μm after 90 minutes of shaking, indicating that the dispersants used were excellent in dispersing leuco dyes. On the other hand, the particle sizes of coating liquid compositions N15 to N17 of Comparative Examples 7 to 9 all had D90 values ​​of 2.0 μm or more even after 90 minutes of shaking, indicating that all of them had inferior dispersibility compared to the Examples.

Claims

1. A dispersant for at least one thermosensitive color-forming component selected from the group consisting of a leuco dye (A) and a sensitizer (C), characterized in that the dispersant contains an alkali neutralized salt of a copolymer (D) that satisfies all of the following conditions, and the alkali is dimethylethanolamine: (1) Copolymer of a monomer consisting of (meth)acrylic acid and a (meth)acrylic acid ester (D-1) and / or Copolymer (D-2) of a monomer consisting of (meth)acrylic acid, a (meth)acrylic acid ester, and a styrene is (2) The acid value is 40 to 400 mg KOH / g. (3) The weight average molecular weight is 3,000 to 30,000.

2. A coating liquid composition for forming a thermosensitive recording layer, comprising at least one thermosensitive color-developing component selected from the group consisting of a leuco dye (A) and a sensitizer (C), and the dispersant according to claim 1.

3. A thermosensitive recording medium having a thermosensitive recording layer formed from the coating liquid composition according to claim 2 on a support.

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