JP2010030060A - Heat-sensitive recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sensitive recording medium which shows excellent color developing sensitivity and image reproducibility by using a support having high smoothness and sizing properties. <P>SOLUTION: This heat-sensitive recording medium has a heat-sensitive recording layer containing at least, a colorless or pale-color electron donative leuco dye and an electron receptive developer formed on the support. The recording medium is characterized in that the support contains an internally added sizing agent having an ampholytic copolymer as an effective component, with a hydrophobic group and, at least a quaternary part of a cationic group. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material utilizing a color development reaction with an electron-donating leuco dye and an electron-accepting developer.

In general, a thermal recording material that obtains a recorded image by utilizing a color development reaction of a colorless or light basic leuco dye and a developer with heat is very clear in color, and there is no noise during recording, and the devices are also compared. It is widely used in POS cash registers, fax machines, various measuring instruments and the like because it is inexpensive, compact, and easy to maintain. Thermal printers have reduced the weight of the apparatus, increased printing speed, and reduced power consumption. For this reason, thermal recording media have been required to improve sensitivity and image quality. In particular, it is required to reproduce a high-definition image with high sensitivity at a low applied energy.
Conventionally, as a method for improving sensitivity, an undercoat layer and a heat-sensitive recording layer or a heat-sensitive recording layer are provided on a bulky (low density) support provided with heat insulation in order to effectively use heat from a thermal head. It is known to provide (Patent Document 1). In addition, as a method for improving the image quality, an undercoat is applied on a support that is flattened by a pressure nip composed of a metal roll and an elastic roll under specific conditions so that heat from the thermal head is uniformly applied. It is known to provide a heat-sensitive recording layer or a heat-sensitive recording layer (Patent Document 2). Furthermore, as a method to improve both sensitivity and image quality, a coating solution with a good dispersibility and fluidity consisting of a specific amount of oil-absorbing pigment, starch, thickener, and binder is used to insulate the support. It is also known to provide an undercoat layer having excellent surface smoothness (Patent Document 3).
As described above, the conventional technique improves the sensitivity and image quality of the thermal recording material by improving the heat insulating property and surface smoothness of the support or the undercoat layer provided on the support.

Japanese Patent No. 3608522 Japanese Patent No. 2535377 Japanese Patent No. 2528940

In the case of the prior art, in order to provide a uniform undercoat layer and a heat-sensitive recording layer or a heat-sensitive recording layer, the support for the heat-sensitive recording body has high smoothness and does not penetrate the coating material of the layer provided on the support. It is required to be sex. As a method for increasing the smoothness of the support, it is effective to add a filler in a high amount (increasing the ash content in the paper), and as a method for increasing the size, it is common to add a sizing agent.
However, when a high amount of filler is added to the support and acidic rosin, neutral rosin, AKD (alkyl ketene dimer), ASA (alkenyl succinic anhydride) is used as the internal sizing agent, the water repellent effect of the sizing agent The effect of water absorption of the filler becomes larger, and it becomes difficult to ensure the required size (water absorption resistance). In addition, when the addition amount of acidic rosin, neutral rosin, AKD (alkyl ketene dimer), ASA (alkenyl succinic anhydride) is excessive, a certain degree of size can be imparted, but the paper machine stains, Problems such as a decrease in the coefficient of friction, defects and paper breaks occur.
Accordingly, an object of the present invention is to provide a thermal recording excellent in color development sensitivity and image reproducibility by using a support having high smoothness and high size that can be produced without any operational problems (such as paper machine dirt). To provide a body.

  In the heat-sensitive recording medium having a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the support, the support mainly comprises pulp and filler. And a zwitterionic copolymer having a hydrophobic group as an internally added sizing agent and having at least a part of a cationic group quaternized therein, has found that this problem is solved. Invented.

  According to the present invention, a thermal recording material excellent in color development sensitivity and image reproducibility can be obtained by using a support having high smoothness and high size that can be produced without causing operational problems (such as paper machine contamination). can get.

1) Internally-added sizing agent of support for heat-sensitive recording material In the present invention, the support of the heat-sensitive recording material has a hydrophobic group and at least a part of the cationic group is quaternized. It is important to milk the internal sizing agent containing a copolymer as an active ingredient, and the reason for the excellent effect is presumed as follows.
When a zwitterionic copolymer (internal sizing agent) is included in the pulp and filler, the filler is highly blended in order to effectively fix on the surface of the pulp and various fillers with different surface charge strength. In this case, it is estimated that sufficient size can be obtained.
The internal sizing agent used in the present invention is an amphoteric copolymer from the viewpoint of fixability to pulp and filler, and includes a hydrophobic monomer (A), a cationic monomer (B), and an anionic monomer ( It is preferable that it is a thing obtained by superposing | polymerizing the monomer component which makes C) essential. This amphoteric copolymer comprises a hydrophobic group derived from the hydrophobic monomer (A), a cationic group derived from the cationic monomer (B), and an anionic group derived from the anionic monomer (C). It is what you have.

The hydrophobic monomer (A) is preferably at least one selected from the group consisting of styrenes and C1-C14 alkyl esters of (meth) acrylic acid (alkyl esters having 1 to 14 carbon atoms). It is not limited to these, For example, (meth) acrylonitrile etc. can also be used. Only one type of hydrophobic monomer (A) may be used, or two or more types may be used.
Examples of the styrenes include styrene, α-methylstyrene, vinyl toluene, ethyl vinyl toluene, chloromethyl styrene, vinyl pyridine, and the like. Among these, styrene is preferable.

  Examples of the C1-C14 alkyl ester of (meth) acrylic acid include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and iso-butyl (meth) acrylate. , T-butyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate and other aliphatic hydrocarbon esters, alicyclic and aromatic And (meth) acrylic acid ester containing a hydrocarbon group. Among these, methyl (meth) acrylate, butyl (meth) acrylate, iso-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and lauryl (meth) acrylate are preferable.

As the cationic monomer (B), at least one selected from the group consisting of tertiary amino group-containing (meth) acrylamide and tertiary amino group-containing (meth) acrylate is preferably used, but is not limited thereto. Rather than, for example, primary or secondary amino group-containing (meth) acrylamide, primary or secondary amino group-containing (meth) acrylate, quaternary ammonium base-containing (meth) acrylamide, quaternary ammonium base-containing (meth) acrylate, diallyl Cationic monomers such as dialkylammonium halides can also be used. Only one type of cationic monomer (B) may be used, or two or more types may be used.
Examples of the tertiary amino group-containing (meth) acrylamide include dialkylaminoalkyl (eg, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide) ( And (meth) acrylamide.

Examples of the tertiary amino group-containing (meth) acrylate include dialkylaminoalkyl (eg, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminoethyl (meth) acrylate, diethylaminopropyl (meth) acrylate) ( And (meth) acrylate.
Examples of the primary or secondary amino group-containing (meth) acrylamide include primary amino group-containing (meth) acrylamides such as aminoethyl (meth) acrylamide; methylaminoethyl (meth) acrylamide, ethylaminoethyl (meta) ) Secondary amino group-containing (meth) acrylamide such as acrylamide and t-butylaminoethyl (meth) acrylamide.

  Examples of the primary or secondary amino group-containing (meth) acrylate include primary amino group-containing (meth) acrylates such as aminoethyl (meth) acrylate; methylaminoethyl (meth) acrylate, ethylaminoethyl (meth) acrylate , Secondary amino group-containing (meth) acrylates such as t-butylaminoethyl (meth) acrylate, and the like.

  As the quaternary ammonium base-containing (meth) acrylamide and the quaternary ammonium base-containing (meth) acrylate, for example, the above-described tertiary amino group-containing (meth) acrylamide or tertiary amino group-containing (meth) acrylate will be described later. And mono-quaternary base-containing monomers quaternized with a quaternizing agent (for example, methyl chloride, benzyl chloride, methyl sulfate, epichlorohydrin, etc.). Specifically, acrylamidopropyltrimethylammonium chloride, acrylamidopropylbenzyldimethylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloylaminoethyltrimethylammonium chloride, (meth) acryloyl Aminoethyltriethylammonium chloride, (meth) acryloyloxyethyltrimethylammonium chloride, (meth) acryloyloxyethyltriethylammonium chloride, etc. are mentioned.

  As the anionic monomer (C), at least one selected from the group consisting of α, β-unsaturated carboxylic acids and α, β-unsaturated sulfonic acids is preferably used, but is not limited thereto. . One type of anionic monomer (C) may be sufficient, and 2 or more types may be sufficient as it.

Examples of the α, β-unsaturated carboxylic acids include (meth) acrylic acid, (anhydrous) maleic acid, fumaric acid, itaconic acid, (anhydrous) citraconic acid, and salts thereof (sodium salt, potassium salt, ammonium salt). Salt, etc.).
Examples of the α, β-unsaturated sulfonic acids include vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, sulfopropyl (meth) acrylate, 2- (meth) acrylamide-2-methylpropane sulfonic acid, And salts thereof (sodium salt, potassium salt, ammonium salt, etc.) and the like.

  In the monomer component, the anionic equivalent of the anionic monomer (C) is preferably 0.1 to 90% of the cation equivalent of the cationic monomer (B), more preferably 5 to 50%, More preferably, it is 5 to 20%. That is, the zwitterionic copolymer obtained by polymerizing the monomer component has a larger cation equivalent and a smaller anion equivalent tends to exhibit a size effect. When the cation equivalent is a value approximated or the same as the anion equivalent or the cation equivalent is smaller than the anion equivalent (specifically, when the ratio (percentage) of the anion equivalent to the cation equivalent exceeds 90%) The anion and cation sites of the polymer interact too strongly ionicly to reduce the number of active ionic groups, thereby reducing the cation fixing action on the pulp fiber, and the orientation balance between the hydrophobic and hydrophilic sites. Due to factors such as deterioration, there is a tendency that it is difficult to efficiently develop size characteristics.

  Therefore, the ratio of the anion equivalent to the cation equivalent in the zwitterionic copolymer obtained by polymerizing the monomer component is in the same range as above, as is the ratio of the anion equivalent to the cation equivalent in the monomer component. Is preferred. For example, when the monomer component is selected so that the monomer component is polymerized by a vinyl bond, when the cationic group and the anionic group are not involved in the polymerization, the cation equivalent in the zwitterionic copolymer The ratio of the anion equivalent to the cation is equal to the ratio of the anion equivalent to the cation equivalent in the monomer component.

  The content of each essential monomer in the monomer component is preferably set so that the anion equivalent of the anionic monomer (C) with respect to the cation equivalent of the cationic monomer (B) is in the above-described range. Although there is no particular limitation, for example, the hydrophobic monomer (A) is about 60 to 90% by weight, the cationic monomer (B) is about 10 to 40% by weight, and the anionic monomer (B) C) is preferably about 1 to 10% by weight.

  In addition to the above-described hydrophobic monomer (A), cationic monomer (B), and anionic monomer (C), the monomer component may further include other components as long as the effects of the present invention are not impaired. These monomers can also be included. Examples of other monomers include hydroxyl-containing (meth) acrylates such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate, (meth) acrylamide, dimethyl (meth) acrylamide, diethyl (meth) acrylamide, and iso- Among the amide group-containing monomers such as propyl (meth) acrylamide, monomers not containing an amino group, vinyl acetate, vinyl propionate, methyl vinyl ether, and the like can be given. Only one type of other monomer may be used, or two or more types may be used.

  The polymerization of the monomer component is not particularly limited, and for example, a known polymerization method such as bulk polymerization, solution polymerization, emulsion polymerization, etc. can be employed, and charging of each monomer, initiator, etc. As a method, a known method such as batch, division, partial dripping, or whole amount dripping may be adopted as appropriate. The medium (solvent) for the polymerization may be appropriately selected from known ones according to the polymerization method.

  Examples of the azo polymerization initiator include azobismethylbutyronitrile, dimethylazobisisobutyrate, azobisdimethylvaleronitrile, azobisisobutyronitrile, azobis-2-amidinopropane hydrochloride, and the like. .

  Examples of the peroxide polymerization initiator include benzoyl persulfate, t-butyl peroxybenzoate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethylhexanoate, cumene hydroperoxide, and the like. Organic peroxides, inorganic peroxides such as hydrogen peroxide, ammonium persulfate, and potassium persulfate.

  As the redox initiator, for example, the above-described peroxide and a reducing agent such as sodium sulfite, iron (II) sulfate, iron (II) chloride, and tertiary amines may be used in combination.

  In addition, the polymerization can be carried out in the presence of a chain transfer agent, if necessary, in order to prevent the increase in viscosity and carry out the reaction smoothly. As the chain transfer agent, an oil-soluble and water-soluble chain transfer agent can be appropriately selected. However, in general, when polymerizing in a lipophilic organic solvent, the oil-soluble chain transfer agent is reversed. A water-soluble chain transfer agent is preferred when polymerizing in a hydrophilic organic solvent. Further, an oil-soluble chain transfer agent and a water-soluble chain transfer agent may be used in combination. Only 1 type may be used for a chain transfer agent and it may use 2 or more types together. Although the usage-amount of a chain transfer agent is not specifically limited, For example, about 1 to 5 weight% is preferable with respect to the monomer component whole quantity.

  Examples of the oil-soluble chain transfer agent include t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, mercaptans such as mercaptopropionate dodecyl, hydrophobic allyl compounds such as (meth) allyl methacrylate, cumene, Examples thereof include carbon tetrachloride, α-methylstyrene dimer, terpinolene and the like.

  Examples of the water-soluble chain transfer agent include mercaptans such as mercaptoethanol, thioglycerol, thiomalic acid, thioglycolic acid, and salts thereof, (meth) allyl alcohol, (meth) allylamine, (meth) allylsulfonic acid , And hydrophilic allyl compounds such as salts thereof, ethanolamine, isopropyl alcohol and the like.

  The amphoteric copolymer is obtained by quaternizing at least a part of the cationic group, and the quaternization rate of the cationic group of the amphoteric copolymer is 40 mol% or more. It is preferable that the content be 50 to 100 mol%. When the quaternization rate is less than 40 mol%, there is a possibility that an effective hydrophobicity imparting effect to pulp fibers and fillers may not be obtained when the papermaking pH is high.

  In quaternizing the cationic group of the zwitterionic copolymer, the copolymer obtained after polymerizing the monomer component may be quaternized with a quaternizing agent, You may make it superpose | polymerize using a quaternary ammonium group containing monomer as a cationic monomer (B) of a monomer component.

  Examples of the quaternizing agent that can be used for quaternization include dimethyl sulfate, dimethyl carbonate, methyl chloride, allyl chloride, benzyl chloride, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, epibromohydrin, and ethylene chloro. Examples thereof include one or more of hydrin, 3-chloro-1,2-propanediol, 3-chloro-2-hydroxypropyltrimethylammonium chloride, glycidol, butyl glycidyl ether, allyl glycidyl ether, glycidyl methacrylate, and the like. Among these, epichlorohydrin and benzyl chloride are preferable.

The weight-average molecular weight of the zwitterionic copolymer is preferably 10,000 to 1,000,000, and more preferably 30,000 to 600,000. When the weight average molecular weight is less than 10,000, the yield of the sizing agent tends to be remarkably lowered and it becomes difficult to obtain the size effect. On the other hand, when it exceeds 1,000,000, the sizing agent is used in the papermaking drying process. May not be efficiently diffused in the paper, and the sizing component may be non-uniformly present in the paper and the size effect may be reduced.
The internal sizing agent used in the present invention only needs to contain the zwitterionic copolymer as an active ingredient, and may be, for example, the zwitterionic copolymer itself or the copolymer. A solution or dispersion liquid (for example, a reaction liquid obtained by the polymerization and quaternization) may be used. In addition to the zwitterionic copolymer, conventionally known additives such as neutral rosin, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), etc., as long as the effects of the present invention are not impaired. May be included.

2) Production of thermal recording medium support The thermal recording medium support of the present invention is produced by adding the internal sizing agent to a pulp slurry and wet-making it. At this time, it is preferable that the amount of the internally added sizing agent is usually 0.05 to 1% by weight of the active ingredient (a zwitterionic copolymer) per the dry weight of the pulp. More preferably, it is 0.1 to 0.8% by weight based on the dry weight of pulp. If it is less than 0.05% by weight, the effect of the sizing agent may be insufficient, and if it is added more than 1% by weight, another problem such as a concern about contamination in the paper machine may occur.

  The pulp fiber constituting the pulp slurry is not particularly limited, and wood pulp such as NBKP and LBKP, mechanical pulp such as TMP and GP, deinked pulp (DIP), and linter pulp that are usually used for papermaking. Non-wood pulp such as hemp, bagasse, kenaf, esparto grass and straw, semi-synthetic fibers such as rayon and acetate, synthetic fibers such as polyolefin, polyamide and polyester can be used.

  You may mix | blend a filler with the said pulp slurry. The filler is not particularly limited as long as it is a filler generally used in acidic papermaking or neutral papermaking. For example, in neutral papermaking, clay, silica, kaolin, calcined kaolin, deramikaolin, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, hydroxylated Inorganic fillers such as aluminum, calcium hydroxide, magnesium hydroxide, and zinc hydroxide, and organic fillers such as urea-formalin resin, polystyrene resin, phenol resin, and fine hollow particles are used alone or in appropriate combination of two or more. . In addition, recycled fillers made from papermaking sludge, deinking floss, etc. can also be used. In the present invention, it is preferable to use calcium carbonate because the amphoteric copolymer in the present invention is excellent in action on calcium carbonate, and calcium carbonate is inexpensive and excellent in optical properties. As the calcium carbonate, spindle-shaped or rosetta-type plasma calcium carbonate, in which the strikethrough is remarkably improved by the interaction with the internally added sizing agent, is preferable. Further, a calcium carbonate-silica composite (light calcium carbonate-silica composite described in JP2003-212539A or JP2005-219945A) can also be used. In acidic papermaking, a filler obtained by removing acid-soluble ones from the filler used in the neutral papermaking is used, and these are used alone or in appropriate combination of two or more. As a compounding quantity of a filler, 2-30 weight% is preferable with respect to pulp weight from points, such as opacity.

In the present invention, the ash content in the paper is desirably 10% or more in order to impart high smoothness to the support of the heat-sensitive recording material. When the ash content in the paper is 10% or more, a relatively low molecular weight sizing agent such as neutral rosin is adsorbed by a filler having a large specific surface area, and it becomes difficult to ensure the size. Necessary and the harmful effects associated therewith increase.
A known internal sizing agent such as acidic rosin, neutral rosin, AKD and ASA can be used in combination with the pulp slurry as long as the effects of the present invention are not impaired.

In addition, various nonionic and cationic retention agents, freeness improvers, bulking agents and the like, which are conventionally used, are appropriately selected and used as required.
In addition, an internal additive for papermaking may be added. For example, it may be easily added to basic aluminum compounds such as sulfate band, aluminum chloride, sodium aluminate, basic aluminum chloride, basic polyaluminum hydroxide, and water. Examples thereof include water-soluble aluminum compounds such as decomposable alumina sol, polyvalent metal compounds such as ferrous sulfate and ferric sulfate, and silica sol.

  In addition, various starches as paper making aids, polyacrylamide, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide, polyamine resin, polyamine, polyethyleneimine, plant gum, polyvinyl alcohol, latex, polyethylene oxide, hydrophilic cross-linking Various compounds such as polymer particle dispersion and derivatives or modified products thereof can be used. Furthermore, internal additives for papermaking such as dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be appropriately added depending on the intended use. What is necessary is just to set the addition amount of these additives suitably according to desired performance.

The support of the heat-sensitive recording material of the present invention is not particularly limited in the type of paper machine, and can be appropriately made with a long net paper machine, twin wire machine, Yankee paper machine, etc., and the press linear pressure is used within the normal operating range. It is done. Moreover, there is no restriction | limiting also regarding acidic papermaking, neutral papermaking, etc.
The support for the heat-sensitive recording material of the present invention may or may not be coated with a surface treatment agent. When the surface treatment agent is applied, there are no particular limitations on the components of the surface treatment agent, and there is no limitation on the size press type, and liquids such as a two-roll size press, a gate roll size press, and a rod metering size press. A film transfer size press or the like can be used as appropriate. Moreover, in order to obtain the target surface smoothness, the linear pressure within the operating range of the calendar and the soft calendar can be appropriately adjusted.

  In the present invention, the surface treatment agent for the support of the heat-sensitive recording material is not particularly limited. For example, raw starch, oxidized starch, esterified starch, cationized starch, enzyme-modified starch, aldehyde-modified starch, hydroxyethylated starch Modified starch such as carboxymethyl cellulose, hydroxyethyl cellulose, cellulose derivatives such as methyl cellulose, modified alcohols such as polyvinyl alcohol, carboxyl modified polyvinyl alcohol, styrene butadiene copolymer, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polychlorinated Vinyl, polyvinylidene chloride, polyacrylic acid ester, polyacrylamide and the like can be used alone or in combination. Among them, the application of hydroxyethylated starch, which is excellent in the effect of improving the surface strength, is most preferable. In addition to the above-mentioned agents, surface sizing agents such as styrene acrylic acid, styrene maleic acid, olefinic compounds, and cationic sizing agents can be applied to the surface treatment agent.

3) Production of heat-sensitive recording material The heat-sensitive recording material of the present invention is a support containing a zwitterionic copolymer having a hydrophobic group as an internal sizing agent and at least a part of a cationic group being quaternized. A thermosensitive recording layer containing at least a colorless to light-colored electron-donating leuco dye and an electron-accepting developer on the body, and if necessary, an undercoat layer between the support and the thermosensitive recording layer A protective layer can be provided on the thermosensitive recording layer.

  In the present invention, the undercoat layer is mainly composed of a pigment and a binder, and various known materials can be used as the pigment and binder contained in the undercoat layer. Examples of the pigment include inorganic pigments such as kaolin, clay, zinc oxide, calcined clay, calcined kaolin, aluminum hydroxide, magnesium hydroxide, titanium oxide, diatomaceous earth, calcium carbonate, finely shaped silica, polystyrene resin, styrene-methacrylic acid. Examples include copolymer resins, styrene-acrylic copolymer resins, nylon powder, polyethylene powder, benzoguanamine resins, urea / formalin resins, and organic pigments such as raw starch particles. As the binder, a generally used water-soluble polymer or hydrophobic polymer emulsion or the like can be appropriately used. For example, cellulose derivatives such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch, modified starch, polyacrylic acid soda, acrylamide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer , Styrene / maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, casein and other water-soluble polymers, polyvinyl acetate, polyurethane, styrene / butadiene latex, polyacrylic acid, sodium polyacrylate, polyacrylic Such as acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer emulsion, styrene / butadiene / acrylic copolymer latex, etc. It can be used an emulsion of sexual polymer.

  Furthermore, various auxiliary agents can be added as necessary. For example, in order to further improve the water resistance, curing agents such as glyoxal, boric acid, dialdehyde starch, epoxy-based compound melamine formaldehyde resin, and ammonium zirconium carbonate are added. Add as appropriate.

  Although the compounding quantity of each component is not specifically limited, Usually, a binder is about 10-40 weight part by solid content with respect to 100 weight part of pigments.

The undercoat layer needs to be applied in an amount of about 3 to 30 g / m ² , and preferably 5 to 15 g / m ² . When the coating amount of the under layer is less than 3 g / m ² , it is difficult to completely hide the unevenness of the base paper and make the support flat, and it is difficult to sufficiently improve the target image quality. On the other hand, when it is more than 30 g / m ² , the coating layer strength of the under layer tends to decrease, and the drying load increases, so the productivity decreases.

  The coating method is not particularly limited and can be applied according to well-known conventional techniques. For example, an off-machine coating machine or an on-machine equipped with various coaters such as an air knife coater, a rod blade coater, a blade coater, a roll coater, and a curtain coater. A coating machine is appropriately selected and used.

  In the present invention, as the electron-accepting developer contained in the heat-sensitive recording layer, all known ones in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used and are not particularly limited. For example, inorganic acidic substances such as activated clay, attapulgite, colloidal silica, aluminum silicate, 4,4′-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxy) Phenyl) -4-methylpentane, 4,4′-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4-hydroxy -4′-isopropoxydiphenyl sulfone, 4-hydro Cis-4′-n-propoxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4′-methyldiphenylsulfone, 4-hydroxyphenyl-4′-benzyloxyphenylsulfone, 3, 4-dihydroxyphenyl-4′-methylphenylsulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α -Methyl- [alpha]-(4'-hydroxyphenyl) ethyl] benzene, , 3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2 , 2′-thiobis (4-tert-octylphenol), diphenylsulfone bridged compound described in International Publication WO97 / 016420, phenolic compound described in International Publication WO02 / 081229 or JP2002-301873, international publication A phenyl novolak type condensation composition described in WO02 / 098774 or WO03 / 029017, a urea urethane compound described in International Publication WO00 / 14058 or JP 2000-143611, N, N′-di-m-chlorophenylthiourea Thiourea compounds such as p- 2-benzoic acid, stearyl gallate, bis [4- (n-octyloxycarbonylamino) salicylic acid zinc] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- ( p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid aromatic carboxylic acids, and zinc, magnesium, aluminum, calcium, titanium of these aromatic carboxylic acids And salts with polyvalent metal salts such as manganese, tin and nickel, zinc thiocyanate antipyrine complexes, and complex zinc salts of terephthalaldehyde acid with other aromatic carboxylic acids. These developers can be used alone or in combination of two or more. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  In the present invention, as the electron-donating leuco dye contained in the heat-sensitive recording layer, all known ones in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and are not particularly limited. Methane compounds, fluorane compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.

<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)
<Fluoran leuco dye>
3-diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-diethylamino- 6-methyl-7-chlorofluorane, 3-diethylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane, 3- Diethylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl-7-n-octylanilinofluorane, 3-di Tilamino-6-methyl-7-n-octylaminofluorane, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-diethylamino- 6-chloro-7-methylfluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-chloro-7-p-methylanilinofluorane 3-diethylamino-6-ethoxyethyl -7-anilinofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-7 -(O-chloroanilino) fluorane 3-diethylamino-7- (p-alkyl Loloanilino) fluorane, 3-diethylamino-7- (o-fluoroanilino) fluorane, 3-diethylamino-benzo [a] fluorane, 3-diethylamino-benzo [c] fluorane, 3-dibutylamino-6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino-6-methyl-7- ( o-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-dibutylamino-6 -Methyl-7- (m-trifluoromethylanilino) fluorane, 3-dibutylamino-6 Methyl-chlorofluorane, 3-dibutylamino-6-ethoxyethyl-7-anilinofluorane, 3-dibutylamino-6-chloro-7-anilinofluorane, 3-dibutylamino-6-methyl-7- p-methylanilinofluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane 3-di-n-pentylamino-6-methyl- 7-anilinofluorane, 3-di-n-pentylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-di-n-pentylamino-7- (m-trifluoromethylanilino) fluorane 3-di-n-pentylamino-6-chloro-7-anilinofluorane, 3-di-n-pentylamino-7- (p-chloroanilino Fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl-7 -Anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-cyclohexylamino) -6-methyl-7-ani Linofluorane, 3- (N-ethyl-N-xylamino) -6-methyl-7- (p-chloroanilino) fluorane, 3- (N-ethyl-p-toludino) -6-methyl-7-anilinofluor Oran, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-chloro-7-anilinov Oran, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilino, fluorane, 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinofluorane , 3- (N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 2- (4-oxahexyl) -3-dimethylamino -6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-dipropylamino -6-methyl-7-anilinofluorane, 2-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 2-methoxy-6-p- (p -Dimethylaminophenyl) aminoanilinofluorane, 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-chloro-6-p- (p-dimethylaminophenyl) ) Aminoanilinofluorane, 2-nitro-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-amino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-diethylamino -6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-phenyl-6-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-benzyl-6-p- (P-phenylaminophenyl) aminoanilinofluorane, 2-hydroxy-6-p- (p-phenylaminophenyl) Nyl) aminoanilinofluorane, 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 3-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 3 -Diethylamino-6-p- (p-dibutylaminophenyl) aminoanilinofluorane, 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluorane

<Fluorene leuco dye>
3,6,6′-tris (dimethylamino) spiro [fluorene-9,3′-phthalide] 3,6,6′-tris (diethylamino) spiro [fluorene-9,3′-phthalide]

<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl -4,5,6,7-tetrachlorophthalide

<Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-diethylamino-2-ethoxyphenyl) -3- (1 -Octyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4 -Azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,6-bis (diethylamino) fluorane-γ- (3'-nitro) anilinolactam, 3,6- Bis (diethylamino) fluorane-γ- (4′-nitro) anilinolactam, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) Enyl) -ethenyl] -2,2-dinitrileethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2, 2-diacetylethane, bis- [2, 2,2 ′, 2′-tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

  The heat-sensitive recording layer can contain various additives such as a sensitizer, a stabilizer, a pigment, and a binder as long as the desired effects on the above-described problems are not impaired. As sensitizers, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, 1, 2-diphenoxyethylene, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate ), Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolylca Examples include Bonate, Phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, 4- (m-methylphenoxymethyl) biphenyl, orthotoluenesulfonamide, paratoluenesulfonamide. However, the present invention is not particularly limited thereto. These sensitizers may be used alone or in combination of two or more.

  As stabilizers, 4,4′-butylidene (6-tert-butyl-3-methylphenol), 2,2′-di-tert-butyl-5,5′-dimethyl-4,4′-sulfonyldiphenol 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenylbutane, 4- Benzyloxy-4 ′-(2,3-epoxy-2-methylpropoxy) diphenyl sulfone, epoxy resin, and the like can also be added.

  Examples of the pigment include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide. In addition, lubricants such as waxes, benzophenone and triazole ultraviolet absorbers, water resistance agents such as glyoxal, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

  The binder includes fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy modified polyvinyl alcohol, amide modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose. , Styrene-maleic anhydride copolymers, and cellulose derivatives such as ethyl cellulose, acetyl cellulose, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyllar polystyrene, and copolymers thereof , Polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumaro resin. That. These polymer substances are used by dissolving in water, alcohol, ketones, esters, hydrocarbons and other solvents, and are used in a state of being emulsified or pasted in water or other media, depending on the required quality. Can also be used together.

  In the present invention, the types and amounts of the electron donating leuco dye, electron accepting developer, and other various components used in the heat-sensitive recording layer are determined according to the required performance and recording suitability, and are not particularly limited. However, usually about 0.5 to 10 parts of the developer and 0.5 to 10 parts of the pigment are used with respect to 1 part of the basic leuco dye. The binder is suitably about 5 to 25% by weight based on the solid content of the heat-sensitive recording layer.

  The electron-donating leuco dye, the developer, and the material to be added as necessary are finely divided to a particle size of several microns or less by a pulverizer such as a ball mill, an attritor, a sand glider, or an appropriate emulsifying device. Depending on the purpose, various additive materials are added to form a coating solution. The thermal recording material of the present invention can be obtained by applying this coating liquid on the undercoat layer.

The means for applying the heat-sensitive recording layer is not particularly limited, and a coating machine similar to the undercoat layer is appropriately selected and used. The coating amount of the heat-sensitive recording layer is not particularly limited and is usually in the range of ² to 12 g / m ^{2 by} dry weight.

  The heat-sensitive recording material of the present invention is further provided with a protective layer (overcoat layer) such as a polymer material on the heat-sensitive recording layer for the purpose of improving the storage stability, or on the opposite surface of the support to the heat-sensitive recording layer. It is possible to correct the curl by providing a layer. Also, various known techniques in the heat-sensitive recording material field, such as supercalendering after the application of each layer other than the undercoat layer, can be appropriately added.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, naturally this invention is not limited to these. In the examples, “parts” and “%” respectively represent “parts by weight” and “% by weight” unless otherwise specified. In addition, the chemical addition rate indicates the solid content addition rate unless otherwise specified.

<Manufacture of internal sizing agent>
(Synthesis Example 1)
As a chain transfer agent, a monomer component comprising 30 parts by weight of styrene, 50 parts by weight of butyl acrylate, 15 parts by weight of dimethylaminoethyl methacrylate, 3 parts by weight of dimethylaminopropylacrylamide, 1 part by weight of methacrylic acid, and 1 part by weight of itaconic acid 2 parts by weight of t-dodecyl mercaptan and 50 parts by weight of methyl isobutyl ketone as a solvent were placed in a four-necked flask and heated to 85 ° C., then 2.5 parts by weight of benzoyl peroxide was added as an initiator, and then 90 ° C. For 3 hours. Next, 300 parts by weight of water and 7.7 parts by weight of 90% aqueous acetic acid were added to make it water-soluble, and then heated to distill off methyl isobutyl ketone. Thereafter, 8.5 parts by weight of epichlorohydrin was added as a quaternizing agent at 85 ° C. and reacted at the same temperature for 3 hours. At this time, the reaction solution after the reaction was completely water-soluble. Next, the mixture was cooled and diluted with water, and the ratio of the anion equivalent to the cation equivalent (anion equivalent / cation equivalent × 100) was 24%, the weight average molecular weight was 26 × 10 ⁴ , the quaternization rate was 80 mol%, and the solid content was 20%. The amphoteric copolymer (internal sizing agent for papermaking (1)) having a hydrophobic group was obtained.

(Synthesis Example 2)
A monomer comprising 50 parts by weight of styrene, 26 parts by weight of butyl methacrylate, 15 parts by weight of dimethylaminoethyl methacrylate, 6 parts by weight of dimethylaminopropyl acrylamide, 1 part by weight of methacrylic acid, 1 part by weight of acrylic acid, and 1 part by weight of maleic anhydride. The components, 1.5 parts by weight of thioglycolic acid as a chain transfer agent, and 50 parts by weight of isopropanol as a solvent were placed in a four-necked flask and heated to 85 ° C., and then 2,2-azobisisobutyrate as an initiator. 2.5 parts by weight of nitrile was added, followed by polymerization at 90 ° C. for 3 hours. Next, 300 parts by weight of water and 9 parts by weight of 90% aqueous acetic acid were added to make the solution water-soluble, and then distilled by heating to distill off isopropanol. Thereafter, 13.5 parts by weight of dimethylsulfuric acid as a quaternizing agent was added at 85 ° C. and reacted at the same temperature for 3 hours. At this time, the reaction solution after the reaction was completely water-soluble. Subsequently, the mixture was cooled and diluted with water, the ratio of anion equivalent to cation equivalent (anion equivalent / cation equivalent × 100) 34%, weight average molecular weight 35 × 10 ⁴ , quaternization rate 80 mol%, solid content 20% An amphoteric copolymer having a hydrophobic group (internal sizing agent for papermaking (2)) was obtained.

<Manufacture of support>
[Example 1]
For raw pulp (LBKP 100%) with freeness adjusted to 360 mL, 0.5% liquid sulfuric acid band with respect to pulp solids, cation-modified starch with 0.5% pulp solids, 0 with pulp solids .2% of the internal additive sizing agent for papermaking (1) obtained in Synthesis Example 1, light calcium carbonate ("TP-121" manufactured by Okutama Kogyo Co., Ltd.), and a yield improver with a solid content of 100 ppm to pulp are sequentially added. A stock was prepared. This stock is made using an on-top type twin wire paper machine (press roll: 4 units) at a paper making speed of 900 m / min, and then oxidized starch (made by Nippon Cornstarch “ SK20 ") was coated and dried at 0.7 g / m ² on both sides to obtain a support having an ash content of 10% and a basis weight of 50 g / m ² . Thereafter, the degree of sizing of the support and the degree of soiling of the paper machine were evaluated. The results are shown in Table 1.
<Under layer paint>
A composition comprising the following composition was stirred and dispersed to prepare an under layer coating solution.
Baked kaolin (trade name: Ensilex 90, manufactured by Engelhard) 100 parts styrene / butadiene copolymer latex (solid content 48%) 40 parts polyvinyl alcohol (10% aqueous solution) 15 parts water 150 parts After coating on one side of a support (50 g / m ² base paper) with a blade coater, drying was performed to obtain an under paper with a coating amount of 8 g / m ² .
<Thermal layer coating>
The developer dispersion liquid (liquid A) and the basic colorless dye dispersion liquid (liquid B) having the following composition were separately wet milled with a sand grinder until the average particle diameter became 1 micron.
Liquid A (developer dispersion)
4-hydroxy-4'-isopropoxydiphenylsulfone 6.0 parts polyvinyl alcohol (10% aqueous solution) 18.8 parts water 11.2 parts B liquid (basic colorless dye dispersion)
3-dibutylamino-6-methyl-7-anilinofluorane (ODB-2) 2.0 parts polyvinyl alcohol (10% aqueous solution) 4.6 parts water 2.6 parts Thus, a recording layer coating solution was obtained.
Liquid A (developer dispersion) 36.0 parts Liquid B (basic colorless dye dispersion) 9.2 parts kaolin clay (50% dispersion) 12.0 parts Next, the recording layer coating liquid is the undercoat paper. On the under layer, a bar blade coater was applied so that the coating amount would be 3.0 g / m ² , followed by drying, and the sheet was dried with a super calendar so that the smoothness was 500 to 600 seconds. Got.

[Example 2]
A heat-sensitive recording material of Example 2 was obtained in the same manner as in Example 1 except that the amount of calcium carbonate added was adjusted so that the ash content in the paper was 18%.
[Example 3]
A heat-sensitive recording material of Example 5 was obtained in the same manner as in Example 1 except that 0.6% of the solid additive for papermaking (1) was added to the solid content of pulp.
[Example 4]
A heat-sensitive recording material of Example 6 was obtained in the same manner as Example 2 except that 0.6% of the solid additive for papermaking (1) was added to the pulp solid content.
[Example 5]
The heat-sensitive recording material of Example 7 was the same as Example 1 except that 0.2% of the solid additive for pulp was added in place of the internal additive sizing agent (1) for papermaking. Got.
[Example 6]
The heat-sensitive recording material of Example 8 was the same as Example 2 except that 0.2% of the solid additive for pulp was added in place of the internal additive sizing agent (1) for papermaking. Got.

[Comparative Example 1]
A heat-sensitive recording material of Comparative Example 1 was obtained in the same manner as in Example 1 except that a neutral rosin-based sizing agent was added in place of the internal additive sizing agent for papermaking (1) and 0.6% solid content of pulp was added. .
[Comparative Example 2]
A heat-sensitive recording material of Comparative Example 2 was obtained in the same manner as in Example 2 except that a neutral rosin-based sizing agent was added instead of the internal sizing agent for papermaking (1) and 0.6% solids content to pulp. .
[Comparative Example 3]
A heat-sensitive recording material of Comparative Example 4 was obtained in the same manner as in Example 2 except that 0.15% of the solid content of the alkyl ketene dimer was added instead of the internal sizing agent for papermaking (1). .
[Comparative Example 4]
A heat-sensitive recording material of Comparative Example 5 was obtained in the same manner as in Example 1 except that alkenyl succinic anhydride-based sizing agent was added in an amount of 0.2% to the pulp solid content instead of the paper making internal sizing agent (1). It was.
[Comparative Example 5]
A heat-sensitive recording material of Comparative Example 6 was obtained in the same manner as in Example 2 except that alkenyl succinic anhydride-based sizing agent was added in an amount of 0.2% to pulp solid content instead of the internal additive sizing agent for papermaking (1). It was.

<Evaluation of support>
-Ash content in paper: measured in accordance with JIS P 8251 and ISO 1762.
-Steffith sizing degree: Measured according to JIS P 8122.
-Evaluation of dirt on paper machine: After papermaking for 8 hours under the above conditions, dirt on the press roll and felt was evaluated according to the following criteria.
○: Dirt is not seen on the press roll and felt Δ: Dirt is slightly seen on the press roll and felt x: Quite dirt is seen on the press roll and felt

<Evaluation of thermal recording material>
The thermal recording materials obtained in Examples and Comparative Examples were evaluated according to the following evaluation items.
(Print density evaluation)
Printing was performed using TH-PMD manufactured by Okura Electric Co., Ltd. with an applied energy of 0.34 mj / dot. The image density after printing was measured with a Gretag Macbeth densitometer RD-19I.
(Image quality evaluation)
The thermal papers obtained in the examples and comparative examples were allowed to stand in an oven at 105 ° C. for 10 minutes for color development, and color unevenness was visually evaluated.
○: Coloring unevenness is hardly seen. Δ: Coloring unevenness is slightly seen.
X: Coloring unevenness is observed.
The results are shown in Table 1.

Claims (2)

  A thermosensitive recording medium having a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the support, wherein the support is mainly composed of pulp and filler, and has an internal size. A thermosensitive recording material comprising a zwitterionic copolymer having a hydrophobic group as an agent and at least a part of a cationic group being quaternized.   The amphoteric copolymer includes a hydrophobic monomer (A), a cationic monomer (B), and an anionic monomer (C), and the anionic equivalent of the anionic monomer (C) is the cationic monomer ( The heat-sensitive recording material according to claim 1, wherein the quaternization rate obtained by polymerizing the monomer component of 0.1 to 90% of the cation equivalent of B) is 40 mol% or more.