JP2016049767A - Coating liquid for protective layer, protective layer, and thermosensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating liquid for a protective layer, capable of forming a protective layer of a thermosensitive recording medium excellent in adhesion to an organic solvent-based ink.SOLUTION: The coating liquid for a protective layer contains an acetoacetyl group-containing polyvinyl alcohol resin (A), a crosslinking agent (B), an inorganic filler (C), and a compound (D) represented by general formula (1). [In the formula, R, R, R, Rand Reach independently represent hydrogen or a 1-5C alkyl group; X represents a bonding chain having at least one of a carbon-carbon bond and an ether bond; and M represents a monovalent metal ion.]SELECTED DRAWING: None

Description

  The present invention relates to a protective layer coating solution for forming a protective layer of a heat-sensitive recording medium, and more particularly to a protective layer coating solution from which a protective layer excellent in adhesion to an organic solvent-based ink can be obtained. is there.

The heat-sensitive recording medium has a heat-sensitive color forming layer formed on a supporting substrate by coating and drying an aqueous dispersion containing, for example, a leuco dye, a developer and a dispersant. The developer melts and mixes and reacts to develop color. Further, a protective layer is provided on the thermosensitive coloring layer to protect the thermosensitive coloring layer from dirt such as water and oil.
Further, the inorganic filler is contained for the purpose of improving blocking resistance and improving the strength of the heat-sensitive recording medium, and kaolin, silica, calcium carbonate and the like are mainly used.

Thermal recording media are relatively inexpensive and can be easily maintained by recording equipment, and are therefore used as various recording media such as facsimiles, POS labels, and various ticket sheets. For heat-sensitive recording media that are used for labels, tickets, etc., common items such as store names and illustrations are printed in advance on the protective layer with organic solvent-based ink, and the date and price are printed by heat-sensitive at the time of ticketing. What you do is widely used.
Accordingly, the protective layer of such a thermal recording medium is required not only to protect the thermal coloring layer but also to have printing characteristics.

  Furthermore, in recent years, pre-printing may be performed before heating the thermal paper, and an ethylenically unsaturated carboxylic acid is added to a protective layer containing a pigment and a binder resin such as polyvinyl alcohol in order to improve offset printing characteristics. A protective layer containing a specific amount of a water-soluble graft copolymer of a polymer and a silicone and having a specific contact angle has been proposed (for example, see Patent Document 1).

  Generally, a polyvinyl alcohol resin is used as a protective layer of a heat-sensitive recording medium because it is excellent in oil resistance and organic solvent resistance. In particular, a crosslinking agent is reacted with an acetoacetyl group-containing polyvinyl alcohol resin to form a crosslinked structure. Therefore, it is used with water resistance. Moreover, as another method, in order to improve durability and workability, it is proposed to form a protective layer by applying and drying an acrylic emulsion using polyvinyl alcohol as an emulsifier (for example, Patent Document 2).

JP 2010-066441 A JP 2012-056218 A

  However, even if the techniques of Patent Documents 1 and 2 are used, the ink may be peeled off when the recording media are rubbed or contacted with an adhesive substance during use or storage. However, it was still unsatisfactory with respect to the recent increase in required performance.

  As a result of intensive studies in view of the above circumstances, the present inventors have applied a protective layer coating for a thermosensitive recording medium containing an acetoacetyl group-containing polyvinyl alcohol resin (A), a crosslinking agent (B), and an inorganic filler (C). The present inventors have found that the above-mentioned problems can be solved by using a protective layer coating liquid containing a compound (D) having a specific structure in the liquid, and completed the present invention.

[式中、Ｒ¹、Ｒ²、Ｒ³、Ｒ⁴，Ｒ⁵は各々独立して水素又は炭素数１〜５のアルキル基、Ｘは炭素−炭素結合及びエーテル結合の少なくとも一方を有する結合鎖、Ｍは一価の金属イオンを示す。]
また、本発明では、前記保護層用塗工液を塗工して得られた層を少なくとも１層有する感熱記録媒体をも提供するものである。 That is, the gist of the present invention includes an acetoacetyl group-containing polyvinyl alcohol resin (A), a crosslinking agent (B), an inorganic filler (C), and a compound (D) represented by the following general formula (1). The present invention relates to a coating solution for a protective layer of a heat-sensitive recording medium.

[Wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, X is a bond chain having at least one of a carbon-carbon bond and an ether bond. , M represents a monovalent metal ion. ]
The present invention also provides a thermosensitive recording medium having at least one layer obtained by applying the protective layer coating solution.

  In the compound (D), since the hydrophobic part derived from the aromatic ring and the hydrophilic part derived from the sulfonic acid group are bonded via a bonding chain, the hydrophobic part tends to be present on the surface of the protective layer. It is presumed that a protective layer having excellent ink adhesion is obtained.

  In the protective layer coating liquid of the present invention, it is a protective layer of a thermal recording medium excellent in the adhesion of organic solvent-based ink by coating it on a substrate and drying it. It is possible to provide a thermosensitive recording medium in which the surface ink does not peel off even when the recording medium is rubbed or in contact with an adhesive substance during use or storage.

The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

  The coating solution for the protective layer of the heat-sensitive recording medium of the present invention comprises an acetoacetyl group-containing polyvinyl alcohol resin (A) (hereinafter, acetoacetyl group-containing polyvinyl alcohol may be abbreviated as AA-PVA), and a crosslinking agent. (B), the inorganic filler (C), and the compound (D) represented by the above general formula (1).

[AA-modified PVA resin (A)]
First, the AA-PVA-based resin (A) used in the present invention will be described.
The AA-PVA-based resin (A) used in the present invention has an acetoacetyl group (AA group) bonded to the main chain of the PVA-based resin directly or through an oxygen atom or a linking group. And a polyvinyl alcohol-based resin including a structural unit having an AA group represented by 4). In addition, this AA-ized PVA-type resin (A) has a vinyl alcohol structural unit other than the structural unit which has AA group, and also has the vinyl ester structural unit of an unsaponified part.

The average degree of polymerization of the AA-PVA-based resin (A) of the present invention (based on JIS K6726) may be appropriately selected depending on the application, but is usually 200 to 4000, particularly 500 to 3000, and more particularly 800 to 2000. Are preferably used.
Moreover, the 4 mass% aqueous solution viscosity (based on JISK6726) in 20 degreeC is 3-100 mPa * s normally, Preferably it is 4-50 mPa * s, Most preferably, it is 5-20 mPa * s.
If the average degree of polymerization or the 4% by weight aqueous solution viscosity is too small, sufficient water resistance may not be obtained, or a sufficient crosslinking rate may not be obtained. Conversely, if too large, when used as an aqueous solution, There is a tendency that application to various processes becomes difficult, for example, the viscosity becomes too high and coating on a substrate becomes difficult.

  The saponification degree of the AA-PVA-based resin (A) used in the present invention is usually 80 to 100 mol%, more preferably 85 to 99.9 mol%, and particularly 90 to 99.8 mol%. In particular, 95 to 99.8 mol% is preferably used. When the degree of saponification is low, it tends to be difficult to make an aqueous solution, the stability of the aqueous solution is lowered, and the water resistance of the obtained crosslinked polymer tends to be insufficient.

  The AA group content in the AA-PVA-based resin (A) (hereinafter abbreviated as AA degree) is usually 0.1 to 20 mol%, more preferably 1 to 15 mol%, What is 3-10 mol% is generally used widely. If the content is too small, the water resistance tends to be insufficient, or a sufficient crosslinking rate cannot be obtained. Conversely, if the content is too large, the water solubility tends to decrease or the stability of the aqueous solution tends to decrease. There is.

In the present invention, it is preferable that all of the PVA resins used are AA-PVA resins (A), but PVA resins other than AA-PVA resins (A) may be used in combination. The content is usually 20% by weight or less, particularly 10% by weight or less, and more preferably 5% by weight or less based on the AA-PVA-based resin (A).
Examples of the PVA resin other than the AA-modified PVA resin (A) include unmodified PVA and various modified PVAs obtained by copolymerizing various monomers having copolymerizability with the above-described vinyl ester monomers. be able to.

  In addition, the AA-PVA-based resin (A) used in the present invention includes an alkali metal acetate such as sodium acetate used or produced as a by-product in the production process (mainly an alkali metal hydroxide used as a saponification catalyst). Organic acids such as acetic acid (derived from a reaction product with acetic acid produced by saponification of polyvinyl acetate) (organics occluded in PVA during reaction with diketene when introducing acetoacetate groups into PVA resin) Part of organic solvent (derived from reaction solvent of PVA resin, cleaning solvent at the time of production of AA-modified PVA resin, etc.) such as methanol and methyl acetate may remain.

  As a method for producing the AA-PVA-based resin (A), it can be produced by the method described in paragraphs [0059] to [0065] of JP-A-2010-077385.

[Crosslinking agent (B)]
The AA-PVA-based resin (A) needs to contain a crosslinking agent (B) in order to improve water resistance. Aldehyde compounds such as glyoxal, which are generally used for PVA-based resins, and organic hydrazine Examples thereof include salts, hydrazine compounds such as adipic acid dihydrazide, metal salts of glyoxylic acid, methylol compounds such as methylolated melamine, and metal compounds such as basic zirconium chloride, preferably metal salts of glyoxylic acid, particularly preferably glyoxyl. Acid alkali metal or alkaline earth metal.
Although content of this crosslinking agent is based also on the kind of crosslinking agent (B), it is 0.5-30 weight part normally with respect to 100 weight part of AA-ized PVA-type resin (A), Preferably 1-20 weight part More preferably, it is 2 to 15 parts by weight. The content of glyoxylic acid metal salt is usually 0.5 to 30 parts by weight, preferably 1 to 20 parts by weight, more preferably 2 to 100 parts by weight of the AA-PVA-based resin (A). ~ 15 parts by weight. If the content of the crosslinking agent (B) is too much or too little, the water resistance tends to decrease.

[Inorganic filler (C)]
Examples of the inorganic filler (C) used in the present invention include calcined kaolin, talc, light calcium carbonate, aluminum hydroxide, and amorphous silica, and kaolin is preferably used from the viewpoint of oil resistance.
As content of an inorganic filler (C), it is 50-300 weight part normally with respect to 100 weight part of AA-ized PVA-type resin (A), Preferably it is 50-200 weight part. When there is too much content of an inorganic filler (C), there exists a tendency for binder strength to fall, and when there is too little, there exists a tendency for blocking resistance to fall.

[Compound (D)]
The compound (D) used in the present invention is represented by the following general formula (1).

[式中、Ｒ¹、Ｒ²、Ｒ³、Ｒ⁴，Ｒ⁵は各々独立して水素又は炭素数１〜５のアルキル基、Ｘは炭素−炭素結合又はエーテル結合の少なくとも一方を有する結合鎖、Ｍは一価の金属イオンを示す。]

[Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, X is a bond chain having at least one of a carbon-carbon bond or an ether bond. , M represents a monovalent metal ion. ]

R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen or 1 to 5 alkyl groups, and among R ¹ , R ² , R ³ , R ⁴ and R ⁵ , 2 to It preferably has 4 alkyl groups, more preferably 3 alkyl groups. Moreover, the same alkyl group is preferable.
The position of the substituent is preferably the position of R ^{3 in} the case of mono-substitution, the position of R ² and R ⁴ in the case of di-substitution, the position of R ¹ , R ³ and R ^{5 in} the case of tri-substitution, In the case of 4-substitution, R ³ is preferably a hydrogen atom.
Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group. Not only a straight chain structure but also a branched structure such as iso and tertiary are cyclic structures. May be. A butyl group is preferable, and an isobutyl group is particularly preferable.

X in the general formula (1) represents a bond chain having at least one of a carbon-carbon bond and an ether bond. Examples of such a linking chain include an alkylene chain and an oxyalkylene chain. The alkylene chain usually has 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms. Moreover, the oxyalkylene chains usually - [C _m H _2m O] _n - is represented as being, m is generally 1 to 10, preferably 2 to 4, particularly preferably 2. n is usually 1 to 20, preferably 3 to 10.
Moreover, as long as it has at least one of a carbon-carbon bond and an ether bond, it may have a bond chain other than that, for example, bond chains, such as -COO- and -O-. A compound having a bond chain represented by the following general formula (2) is preferable.

[式中、Ｒ¹、Ｒ²、Ｒ³、Ｒ⁴，Ｒ⁵は各々独立して水素又は炭素数１〜５のアルキル基、ｎは１〜２０の正の整数、Ｍは一価の金属イオンを示す。]
また、Ｍは一価の金属イオンであり、かかる金属としては、Ｌｉ、Ｎａ、Ｋ、Ｒｂ、Ｃｓなどが挙げられ、好ましくはＬｉ、Ｎａ、Ｋであり、特に好ましくは、他の物性に与える影響が小さい点で、Ｎａである。

[Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, n is a positive integer of 1 to 20, and M is a monovalent metal. Indicates ions. ]
M is a monovalent metal ion. Examples of the metal include Li, Na, K, Rb, Cs, etc., preferably Li, Na, K, and particularly preferably given to other physical properties. It is Na in that the influence is small.

  The amount of the compound (D) used in the present invention dissolved in 100 g of water is usually 0.1 g or more, preferably 1 g or more, particularly preferably 5 g or more. If the amount is too small, it tends to be difficult to produce a coating solution. If the amount is too large, there is no particular problem, but in practice, the upper limit is about 200 g.

The number of groups (Davis) of the compound (D) is usually 1 to 150, preferably 10 to 100, particularly preferably 20 to 50. If this value is too small or too large, the effects of the present invention tend to be difficult to obtain.
The value of the radix (Davis) is, -SO ₃ Na is 38.7, -COO- is 2.4, -O- is 1.3, -CH ₂ CH ₂ O- is 0.33, -CH ₂ - is -0.475, = CH- is _{-0.475, -CH 2 CH 2 CH 2} O- are those with -0.15, calculated.

  Moreover, the molecular weight of a compound (D) is 50-1000 normally, Preferably it is 200-800, Most preferably, it is 400-700.

［式中、ｎは１〜２０の正の整数、Ｍは一価の金属イオンを示す。]
上記式のｎは通常１〜２０で、好ましくは３〜１０、特に好ましくは５〜９である。かかるｎが大きすぎると親水性が強くなりすぎ、インキ密着性が低下する傾向がある。 The following general formula (3) is a particularly preferred structure of the compound (D).

[Wherein, n represents a positive integer of 1 to 20, and M represents a monovalent metal ion. ]
N of said formula is 1-20 normally, Preferably it is 3-10, Most preferably, it is 5-9. When n is too large, the hydrophilicity becomes too strong and the ink adhesion tends to be lowered.

  The production method of the compound (D) used in the present invention is not particularly limited and can be obtained by a known method. For example, the compound (D) represented by the general formula (3) is CLARIANT. It can be obtained from the company as Hostal BV conc (sodium tributylphenoxypolyethoxysulfate, n = 7).

  The content of the compound (D) is usually 1 to 70 parts by weight, preferably 20 to 60 parts per 100 parts by weight of the AA-PVA-based resin (A) when the compound (D) is blended without making an emulsion. Part by weight, particularly preferably 30 to 50 parts by weight. If the content is too small, the effects of the present invention tend to be difficult to obtain. If the content is too large, other physical properties of the coating liquid tend to be affected.

The compound (D) can be used as it is, but an emulsion can be prepared by using the compound (D) as a dispersant and contained as an emulsion.
The emulsion (d) using the compound (D) as a dispersant will be described.

[Emulsion (d)]
The emulsion used in the present invention contains the compound (D) represented by the above general formula (1) as a dispersant and a polymer as a dispersoid. As a method for producing such an emulsion (d), a) a method in which a monomer is emulsion-polymerized using the compound (D) as an emulsifier, and a) a method in which a polymer solution is post-emulsified in the presence of the compound (D). And c) A method of adding the compound (D) to an emulsion obtained by an arbitrary method to obtain a more stable emulsion.

  The dispersoid of the emulsion (d) used in the present invention is usually a polymer obtained by polymerizing at least one unsaturated monomer selected from an ethylenically unsaturated monomer and a diene monomer, Examples of such ethylenically unsaturated monomers and diene monomers include monomers frequently used in emulsion polymerization, such as vinyl ester monomers, acrylic acid or its ester monomers, diene monomers, and others. Examples of the monomer include olefin monomers, acrylamide monomers, acrylonitrile monomers, styrene monomers, vinyl ether monomers, allyl monomers, and the like.

Such vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate and the like, and acrylic acid or ester monomers thereof include methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylic acid n. Examples of the diene monomer include -propyl, i-propyl (meth) acrylate, n-butyl (meth) acrylate, and the like, and butadiene-1,3,2-methylbutadiene, and the like.
Furthermore, ethylene, propylene, 1-butene, isobutene and the like can be exemplified as the olefin monomer, and (meth) acrylamide, N-methylolacrylamide, N, N-dimethylacrylamide and the like can be exemplified as the acrylamide monomer.
Of these, acrylic acid or its ester monomers and acrylic monomers are preferred from the viewpoint of ink adhesion.

  In addition, the above ethylenically unsaturated monomers and diene monomers can be used alone for polymerization, but it is of course possible to mix two or more types for polymerization (copolymerization). is there.

Next, the manufacturing method of the emulsion (d) of this invention is demonstrated.
In obtaining the emulsion (d), there are methods such as emulsion polymerization and post-emulsification. In carrying out the former emulsion polymerization, i) ethylene in the presence of water, a dispersant (surfactant) and a polymerization catalyst. A conventional emulsion polymerization method in which a water-soluble unsaturated monomer and / or diene monomer is added temporarily or continuously, followed by heating and stirring, ii) water, a dispersant (surfactant) and a polymerization catalyst. In the presence, a dispersion (pre-emulsion) in which an ethylenically unsaturated monomer and / or diene monomer is mixed and dispersed in an aqueous solution of a dispersant (surfactant) is added temporarily or continuously and heated. An emulsion polymerization method such as stirring can be carried out.

  The amount of the compound (D) used in the present invention is slightly different depending on the type and the resin content of the emulsion, but is usually 0.1 to 30% by weight, more preferably 1 to 30% by weight based on the whole emulsion polymerization reaction system. 25% by weight, particularly 2 to 20% by weight is preferable. If the amount used is too small, it tends to be difficult to maintain the polymer particles in a stable emulsified state. However, the workability tends to decrease and the water resistance tends to be too low.

As the polymerization initiator, usually potassium persulfate, ammonium persulfate, potassium bromate, etc. are used alone or in combination with sodium sulfite, and further hydrogen peroxide-tartaric acid, hydrogen peroxide-iron salt, hydrogen peroxide Water-soluble redox polymerization initiators such as ascorbic acid-iron salt, hydrogen peroxide-longalite, hydrogen peroxide-longalit-iron salt are used.
The addition method of the polymerization initiator is not particularly limited, and a method of adding all at once in the initial stage, a method of adding continuously as the polymerization progresses, or the like can be employed.

Moreover, a polymerization inhibitor, another dispersing agent (surfactant), a dispersion stabilizer, a pH adjuster, etc. can also be mix | blended as needed.
The solid content concentration of the emulsion (d) thus obtained is usually 10 to 80% by weight, preferably 20 to 70% by weight, particularly preferably 30 to 60% by weight. If the concentration is too low, drying takes time and the efficiency tends to decrease. If the concentration is too high, coating tends to be difficult.
Moreover, the average particle diameter of the resin particles in the emulsion (d) is usually 200 to 1000 nm, preferably 300 to 800 nm. In addition, the average particle diameter in this case refers to the number average particle diameter (Dn) calculated by the histogram method, and is measured using, for example, a dynamic light scattering photometer “DLS-700” manufactured by Otsuka Electronics Co., Ltd. can do.

The content of the emulsion (d) of the present invention is usually 1 to 70 parts by weight, preferably 20 to 60 parts by weight, particularly preferably 30 to 50 parts by weight based on 100 parts by weight of the AA-PVA-based resin (A). is there. The content of the compound (D) in the emulsion (d) is slightly different depending on the kind of the monomer, but is usually 0.1 to 30% by weight, more preferably 1 to 25% by weight based on the whole emulsion polymerization reaction system. %, In particular 2 to 20% by weight.
If the content is too small, the effects of the present invention tend to be difficult to obtain. If the content is too large, other physical properties of the coating liquid tend to be affected.

[Coating liquid for protective layer]
The protective layer coating liquid of the present invention contains an AA-PVA-based resin (A), a crosslinking agent (B), an inorganic filler (C), and a compound (D), and preferably an AA-PVA-based The resin (A) is used as an aqueous solution and various components are blended. The concentration of the AA-PVA-based resin (A) aqueous solution is usually 1 to 50% by weight, preferably 5 to 30% by weight.
Further, the content ratio of the AA-PVA-based resin (A) in the coating liquid is usually 0.5 to 30% by weight, preferably 1 to 15% by weight, based on the whole coating liquid. preferable. If the content is too small, the effect as the protective layer tends not to be sufficiently exhibited. Conversely, if the content is too large, the viscosity of the coating liquid tends to be high, so that coating tends to be difficult.

  Moreover, as pH of a coating liquid, 10 or less is preferable, Furthermore, it is 3-10. If the pH is too high, the hot water resistance and plasticizer resistance may decrease, which is not preferable. In addition, since AA-PVA-based resin (A) is weakly acidic when made into an aqueous solution, such pH adjustment is usually unnecessary, but if necessary, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, The pH may be adjusted with an organic acid such as tartaric acid, succinic acid, or acetic acid, or a basic compound such as sodium hydroxide, potassium hydroxide, sodium bicarbonate, or ammonia.

Furthermore, a thermoplastic resin, a pigment, other additives, etc. can also be mix | blended with a coating liquid as needed.
Examples of the thermoplastic resin include acrylic resins, polyester resins, polyvinyl chloride resins, saponified ethylene-vinyl acetate copolymers, and acrylic resins are preferred from the viewpoint of ink adhesion.
The blending amount of the thermoplastic resin is usually 10 to 70% by weight, preferably 20 to 60% by weight, based on the total solid content of the coating liquid.
Examples of the pigment include organic pigments such as nylon resin fillers, urea / formalin resin fillers, and starch particles. Other additives include lubricants such as zinc stearate, calcium stearate, and paraffin wax, and surfactants. Agents, ultraviolet absorbers, fluorescent dyes, release agents, antioxidants, and the like.

The protective layer coating liquid of the present invention contains AA-PVA-based resin (A), a crosslinking agent (B), an inorganic filler (C), and a compound (D). The order is not particularly limited, and examples thereof include the following methods.
Examples of the blending method include a method of making each component an aqueous solution or an aqueous dispersion, a method of dissolving or dispersing in water after mixing in a solid state, and a method of blending in an aqueous solution or aqueous dispersion of a certain component in a solid state. . A method in which each component is an aqueous solution or an aqueous dispersion is preferable.
The concentration of each component as an aqueous solution or aqueous dispersion is usually 1 to 50% by weight, preferably 2 to 30% by weight. If the concentration is too low, drying tends to take time and efficiency tends to decrease. If it is too high, coating tends to be difficult.

Moreover, as a mixing | blending order, the following orders are mentioned, for example.
(A) Method of blending one component at a time (a) Method of blending any two to three components and then blending the remaining components sequentially or collectively (c) Method of blending all components simultaneously (D) ) Method of blending the cross-linking agent (B) last in accordance with the speed of the cross-linking reaction

  Examples of the coating method for the protective layer coating liquid include a roll coater method, an airy coater method, a blade coater method, a bar coater method, a size press method, a gate roll method, and a curtain coater method. It is coated on a heat-sensitive recording layer described later. Moreover, as drying conditions after apply | coating the coating liquid for protective layers, it is 5-150 degreeC normally, Furthermore, 30-120 degreeC, Especially 40-100 degreeC temperature conditions, 0.1 to 60 minutes Further, a drying time of 0.1 to 30 minutes, particularly 0.2 to 20 minutes is preferably used.

The protective layer obtained by applying the protective layer coating solution of the present invention is formed by applying the protective layer coating solution on the heat-sensitive color developing layer and drying it.
The thickness of the protective layer is usually 0.01 to 100 μm, preferably 0.05 to 20 μm, particularly preferably 0.1 to 10 μm.

[Thermosensitive coloring layer]
In a thermosensitive recording medium, a thermosensitive coloring layer is provided on a substrate, and the thermosensitive coloring layer is further provided with a coloring material in a binder (for example, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, starches, latexes, etc.). Can be formed by applying the aqueous solution to a substrate.

  Such a heat-sensitive color developing layer may be obtained by obtaining an aqueous solution in which a binder, a color developing material and a developer are blended, and then applying the aqueous solution to a substrate. At this time, the color-developing substance and the developer are blocked in an aqueous solution and are pulverized to about 0.1 to 5 μm by a bead mill, ball mill, viscomill or the like.

  Examples of the color-developing substance include 3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide [crystal violet lactone], 3,3-bis (p-dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3-dimethylamino-6-methoxyfluorane, 7-acetamino -3-diethylaminofluorane, 3-diethylamino-5,7-dimethylfluorane, 3-diethylamino-5,7-dimethylfluorane, 3,6-bis-β-methoxyethoxyfluorane, 3,6-bis- Examples include leuco bodies of triphenylmethane dyes such as β-cyanoethoxyfluorane.

  Further, the developer develops color by reacting with the color-developing substance when heated, and is preferably liquefied or vaporized at room temperature or higher, preferably 70 ° C. or higher. For example, phenol, p-methylphenol, p-tertiary butylphenol. P-phenylphenol, α-naphthol, β-naphthol, 4,4′-isopropylidene diphenol [bisphenol A], 4,4′-secondary butylidene diphenol, 4,4′-cyclohexylidene diphenol, 4, 4′-isopropylidenebis (2-tertiarybutylphenol), 4,4 ′-(1-methyl-n-hexylidene) diphenol, 4,4′-isopropylidene dicatechol, 4,4′-pentylidene diphenol 4,4-isopropylidenebis (2-chlorophenol), phenyl- 4-hydroxybenzoate, salicylic acid, 3-phenylsalicylic acid, 5-methylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 1-oxy-2-naphthoic acid, m-oxybenzoic acid, 4-oxyphthalic acid, gallic acid Etc.

In providing the thermosensitive coloring layer, an aqueous solution containing the above-mentioned binder, color-developing substance, and developer is applied by any coating method such as roll coater method, air yarder method, blade coater method, bar coater method, size press method, and gate roll method. What is necessary is just to apply | coat to a base material by a construction means, solid content of a coating liquid should just be about 10 to 60 weight%, and the coating amount of this aqueous solution is about 0.1-20 g / m < ² > by dry weight. It is.

If necessary, an undercoat layer may be provided under the heat-sensitive color developing layer. The undercoat layer may be a known PVA, hollow particle, starch, methylcellulose, ethylcellulose, hydroxymethylcellulose, casein, or acrylate ester. A water-soluble and water-dispersible resin such as a polymer and a styrene-butadiene copolymer-based latex and the above-described pigments may be used alone or in combination of two or more. In the application of the undercoat layer, the same coating method, coating solution concentration and coating amount as the protective layer are employed.
The resulting thermal recording medium has a layer structure of base material / (undercoat layer) / thermosensitive color developing layer / protective layer.

[Thermal recording medium]
The heat-sensitive recording medium of the present invention has an arbitrary heat-sensitive color-developing layer on a substrate and is coated with the protective layer coating solution of the present invention and dried.

  The base material is usually paper (manila balls, white balls, liner paper, etc., general high quality paper, medium quality paper, gravure paper, printing paper, upper / middle / lower grade paper, newsprint paper, release paper, carbon paper, etc. , Non-carbon paper, glassine paper, etc.) and plastic films (polyester film, nylon film, polyolefin film, polyvinyl chloride film, laminates thereof and the like).

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis.

Example 1
[Production of AA-PVA Resin (A)]
A reactor equipped with a stirrer capable of heating was charged with 100 parts of raw material PVA (degree of saponification 99.2 mol%, average degree of polymerization 1200), and then 20 parts of acetic acid was added to swell and rotated at 20 rpm. While stirring, the temperature was raised to 50 ° C., 14 parts of diketene was added dropwise over 5 hours, and the mixture was further reacted for 1 hour. After completion of the reaction, the mixture was washed with 500 parts of methanol three times and dried at 60 ° C. for 10 hours to obtain an AA-PVA-based resin (A) having an acetoacetyl group content of 5 mol%. The saponification degree and average polymerization degree are in accordance with the raw material PVA.

[Preparation of inorganic filler (C) dispersion]
50 parts of kaolin as inorganic filler (C) (“Kao gloss 90” manufactured by Shiraishi Calcium Co., Ltd.) is added to 50 parts of water and stirred for 30 minutes at 2000 rpm with a homogenizer (manufactured by TK Robotics Primics Co., Ltd.). Dispersed. Using a laser diffractometer ("Partica LA-950V2" manufactured by HORIBA, Ltd.), it was confirmed that kaolin was dispersed to about 0.2 μm, and then diluted with water to obtain a 10% aqueous dispersion of kaolin. .

[Preparation of protective layer coating solution]
100 parts of a 10% aqueous solution of AA-PVA-based resin (A) obtained above, 50 parts of a 10% aqueous dispersion of kaolin obtained above and 10% aqueous solution of sodium glyoxylate as a crosslinking agent (B) 6 Part and 40 parts of a 10% aqueous solution of the compound (D) represented by the following formula (5) were mixed to prepare a coating solution.

[Production of coated paper]
Instead of evaluating as a protective layer of a heat-sensitive recording medium, evaluation was made with a coated paper having a coating layer formed on the surface of a commercially available copy paper.
The coating solution obtained above was applied to a commercially available copy paper with an applicator having a clearance of 50 μm, dried at 105 ° C. for 5 minutes, and then dried at 23 ° C. and 50% RH for 3 days to obtain a coated paper. .
In the above evaluation method, a coated paper having no heat-sensitive recording layer is used, but what is important in the present invention is the adhesion between the protective layer and the ink. The effect of the present invention can be sufficiently confirmed by the above evaluation method.

[Ink adhesion evaluation]
On the coated paper obtained above, UV offset ink ("Dicure Avillo Process EP" manufactured by DIC Graphics), which is an organic solvent-based ink, is printed in a range of 20 mm x 100 mm and is irradiated with an ultraviolet irradiation device. The ink was cured by irradiating with ultraviolet rays under the following conditions.
Equipment: UV irradiation equipment (I-Graphics)
Lamp: Metal halide Irradiation amount: 1140 mW / cm ²
Irradiation time: 1 second Cellophane tape on the printed part {Cellotape (registered trademark) No. 405 width 24 mm} was applied and the ratio of the area where the ink was peeled when peeled was visually observed and evaluated as follows. The results are shown in Table 1.
○: No ink peeling or substrate (paper) peeled ×: Ink peeled off the coated surface

Example 2
[Preparation of emulsion (d)]
In a container, 20 parts of water, 1.0 part of the compound (D) used in Example 1, 0.2 part of a nonionic surfactant (New Coal 568 manufactured by Nippon Emulsifier Co., Ltd.), 26 parts of styrene, 2-methyl 19 parts of hexyl acrylate, 0.9 part of methacrylic acid and 0.6 part of 80% acrylamide were weighed to prepare a monomer emulsified mixture.
Next, it was put into a glass reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet tube and a dropping funnel, 25 parts of water, 0.1 part of disodium hydrogen phosphate, and the compound used in Example 1 (D) 0.8 part and 0.3 part of nonionic surfactant (Nippon Emulsifier Co., Ltd. New Coal 568) were melt | dissolved.

  10% of the previously prepared monomer emulsified mixture is added to the glass reaction vessel, heated to 80 ° C., heated to 80 ° C., and 5% potassium persulfate (polymerization initiator) 1.2. Was added to the glass reaction vessel and allowed to react. Thereafter, the remaining monomer emulsified mixture and 3 parts of 5% potassium persulfate were dropped into a glass reaction vessel over 3 hours, and polymerization was carried out at 80 ° C. After completion of the dropwise addition, aging was performed at 80 ° C. for 60 minutes to complete the polymerization. After cooling to 40 ° C., 0.8 part of a pH adjuster (10% aqueous ammonia) was added to obtain an emulsion (d).

  In Example 1, a coating solution and a coated paper were prepared in the same manner as in Example 1, except that 4 parts of the emulsion (d) obtained above was added in terms of solid content instead of the compound (D). And evaluated in the same manner. The results are shown in Table 1.

Comparative Example 1
In Example 1, it carried out similarly except not mix | blending compound (D), the coating liquid and the coated paper were produced, and it evaluated similarly to Example 1. FIG.
The results are shown in Table 1.

  In Examples 1 and 2 using the protective layer coating liquid of the present invention, the ink did not peel off even after being peeled off after being applied with a cellophane tape, and the ink adhesion was excellent. On the other hand, in Comparative Example 1 containing no specific compound, the ink peeled off and the ink adhesion was poor.

  The heat-sensitive recording medium of the present invention is useful as a heat-sensitive recording medium on which various types of printing can be performed in advance because the ink adhesion of the protective layer is excellent.

Claims (4)

A protective layer coating comprising an acetoacetyl group-containing polyvinyl alcohol resin (A), a crosslinking agent (B), an inorganic filler (C), and a compound (D) represented by the following general formula (1) Engineering liquid.

[Wherein R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, X is a bond chain having at least one of a carbon-carbon bond and an ether bond. , M represents a monovalent metal ion. ] The protective layer coating solution according to claim 1, wherein the compound (D) is a compound represented by the following general formula (2).

[Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, n is a positive integer of 1 to 20, and M is a monovalent metal. Indicates ions. ] A protective layer obtained by applying and drying the protective layer coating solution according to claim 1 on a substrate. A heat-sensitive recording medium comprising at least one protective layer according to claim 3.