JP3727167B2 - Latex for heat-sensitive recording material, heat-sensitive recording material and method for producing the same - Google Patents

Description

【００６７】
【表２】

【００６８】
【表３】

【００６９】
【発明の効果】
以上説明したように、本発明の感熱記録材料用ラテックスは、特定の単量体を特定部数使用しているため、アルカリ可溶性および重合安定性に優れるとともに、感熱記録材料の保護層の結合材として用いた場合、感熱記録体の使用される諸環境下での耐久性や、捺印性、印刷適性を著しく向上させることができる。
【００７０】
また本発明の感熱記録材料は、上記感熱記録材料用ラテックスを保護層の結合材に用いているため、諸環境下における耐久性、捺印性、印刷適性に優れ、広範な分野への適用することができる。
【００７１】
また本発明の感熱記録材料の製造方法は、上記感熱記録材料用ラテックスをアルカリ溶解し、水溶性樹脂としたものを塗工液中に含有させ、これを所定箇所に塗布するという工程をとるため、上記のような利点を有する感熱記録材料を、煩雑な工程を経ることなく簡便に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat-sensitive recording material capable of recording an image by a heat-sensitive recording method, and a latex for a heat-sensitive recording material used as a protective layer binder for the heat-sensitive recording material.
[0002]
[Prior art]
The heat-sensitive recording material generally comprises a substrate and a heat-sensitive recording layer formed on the substrate, and the color former in the heat-sensitive recording layer reacts instantaneously when heated with a thermal head, a heat pen, laser light, or the like. A recorded image is formed (Japanese Patent Publication No. 43-4160).
[0003]
When such a heat-sensitive recording material is used, an image can be obtained simply by heating with a thermal head, a thermal pen or the like, and a complicated development process is not required. Further, since the recording function is provided on the support (paper, synthetic paper, synthetic resin film, etc.) of the heat-sensitive recording material, the recording device has a compact and relatively simple structure, and maintenance is easy. For this reason, it is used in a wide range of fields as output recording sheets for various printers including facsimiles, industrial measuring terminals, medical terminals, handy terminals, POS systems, ticketing systems, and the like.
[0004]
However, since the thermosensitive recording material is used in various fields, it has the following problems in daily handling.
(1) The recording layer sometimes fell off when water contacted the heat-sensitive recording material.
{Circle around (2)} When a PVC film or sheet is stacked, fading color may occur due to various plasticizers contained in the PVC.
(3) When the oil or fat or solvent is touched, fading color or color development may occur.
[0005]
In order to solve this problem, various improvements have been studied for the binder and color forming material in the heat-sensitive recording layer, but those that satisfy all of water resistance, plasticizer resistance, oil resistance, solvent resistance, etc. are obtained. Not. In particular, in recent years, the use of heat-sensitive recording materials has been increasingly expanded, and in situations where even higher durability is required, improvement of the above-mentioned problems can be achieved only by improving the binder and coloring material in the heat-sensitive recording layer. It is difficult.
[0006]
Therefore, as a countermeasure against such a problem, methods for forming a protective layer on the thermosensitive recording layer have been proposed (for example, JP-A-56126183, JP-A-56-13993, JP-A-57). -188394 publication).
[0007]
However, although the protective layer disclosed in the above publication can enhance the durability of the recording layer and the recorded image to some extent, it does not sufficiently satisfy the demand for high durability recently desired.
[0008]
On the other hand, Japanese Patent Application Laid-Open No. 60-059193 discloses a technique relating to the following surface protective layer forming agent. That is, (meth) acrylamide, (meth) acrylic acid lower alkyl ester and the like and a copolymer salt consisting of a specific proportion of a carboxyl group-containing vinyl monomer and an epoxy group-containing cross-linking agent, oil resistance and water storage resistance A technique relating to a surface protective layer-forming agent for processed paper that imparts the above is disclosed. Specifically, (A) (meth) acrylamide 45 to 85 (wt)%, (2) one or more of lower alkyl (preferably C1 to C4) ester or hydroxy lower alkyl ester of (meth) acrylic acid 10 (B) A crosslinking agent having an epoxy group (B) in an aqueous solution of an alkali metal salt, ammonium salt or amine salt of a copolymer of ˜50% and one or more of vinyl monomers having a carboxyl group and 5 to 20% Example: It is said that a surface protective layer-forming agent having excellent water resistance, oil resistance and the like can be obtained by blending water-soluble ones such as diglycidyl ether of polyethylene glycol.
[0009]
However, in this technology, (meth) acrylamide is an essential component and the composition ratio is high, so the surface protective layer forming agent obtained is an aqueous solution before the crosslinking agent is added, and the surface protective layer is formed. In order to achieve this, a crosslinking agent was essential.
[0010]
Further, in recent years, with the expansion of applications, the protective layer has been required to function as a new function-supporting layer of the thermal recording material as well as the protective function. In relation to this, a higher level of water resistance, oil resistance and the like has been required for the binder of the protective layer, and in the technique described in the above-mentioned JP-A-60-059193, It was not always possible to fully meet such needs. This point will be described below.
[0011]
As a new function required for the protective layer, for example, a printing property (receipt) on an output sheet and a printability on a label sheet can be cited. In order to express such a function, it is common to include an inorganic or organic filler in the protective layer. However, a large amount of these fillers is included to satisfy the sealability and printability. I have to let it. In this case, the protective function of the coating film is deteriorated, such that coating film defects are likely to occur, and particularly when a flexible support such as a sheet or film is handled, the protective layer is cracked. For this reason, it is difficult to achieve both a function as a function-supporting layer and a protective function, and the present situation is that a technique for achieving both of these functions has not yet been found.
[0012]
[Problems to be solved by the invention]
In view of the above circumstances, the present invention has a higher level of durability (water resistance, oil resistance, etc.) than before, and a protective layer excellent in printing performance, printability, color development sensitivity and running stability. It is an object of the present invention to provide a heat-sensitive recording material provided with the above and a latex for the heat-sensitive recording material used in the heat-sensitive recording material.
[0013]
[Means for Solving the Problems]
The present invention for solving the above problems is specified by the matters described in the following [1] to [8].
[0014]
  [1] A latex for a thermal recording material used as a binder for a protective layer of a thermal recording material after being alkali-dissolved with a neutralizer,In 100 parts by weight of latex solids,
(A) 10 to 40 parts by weight of (meth) acrylonitrile, (b) 15 to 40 parts by weight of hydroxyalkyl acrylate, and (c) 10 to 40 parts by weight of (meth) acrylic acid as polymer components, ), (B), and (c). The latex for heat-sensitive recording materials comprising a copolymer having a total content of 60 parts by weight or more and Tg of -10 to 50 ° C.
[0015]
[2] The latex for heat-sensitive recording material according to [1], wherein the neutralizing agent is ammonia.
[0016]
  [3] A heat-sensitive recording material in which a heat-sensitive recording layer that develops color by heat is provided on a support, and a protective layer mainly composed of a binder and a filler is provided on the support and / or on the back surface of the support. In
The binder for the protective layer is a water-soluble resin obtained by alkali-dissolving latex for heat-sensitive recording material with a neutralizing agent, and the latex for heat-sensitive recording material is:In 100 parts by weight of latex solids,(A) 10 to 40 parts by weight of (meth) acrylonitrile, (b) 15 to 40 parts by weight of hydroxyalkyl acrylate, and (c) 10 to 40 parts by weight of (meth) acrylic acid as polymer components, ), (B), and (c) is a thermosensitive recording material comprising a copolymer having a total content of 60 parts by weight or more and a Tg of −10 to 50 ° C.
[0017]
[4] The heat-sensitive recording material according to [3], wherein the neutralizing agent is ammonia.
[0018]
  [5] of the filleramount to useBut,Latex solidsThe heat-sensitive recording material according to [3] or [4], which is 40 to 200 parts by weight with respect to 100 parts by weight.
[0019]
  [6] (A) A step of forming a heat-sensitive recording layer that develops color by heat on a support;
(B) a step of adding a neutralizing agent to the latex for heat-sensitive recording material and dissolving it in an alkali to form a water-soluble resin;
(C) A method for producing a heat-sensitive recording material comprising a step of applying a coating liquid containing the water-soluble resin and a filler onto the heat-sensitive recording layer and / or the back surface of the support and drying. Because
The latex for heat-sensitive recording material is:In 100 parts by weight of latex solids,(A) 10 to 40 parts by weight of (meth) acrylonitrile, (b) 15 to 40 parts by weight of hydroxyalkyl acrylate, and (c) 10 to 40 parts by weight of (meth) acrylic acid as polymer components, ), (B), and (c), the total content of which is 60 parts by weight or more, and which is made of a copolymer having a Tg of −10 to 50 ° C.
[0020]
[7] The method for producing a heat-sensitive recording material according to [6], wherein the neutralizing agent is ammonia.
[0021]
  [8] of the filleramount to useBut,Latex solidsThe method for producing a heat-sensitive recording material according to [6] or [7], which is 40 to 200 parts by weight with respect to 100 parts by weight.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The latex for heat-sensitive recording material of the present invention is used as a binder for the protective layer of the heat-sensitive recording material after alkali dissolution with a neutralizing agent. In the acidic region, it can be handled as a low-viscosity latex, and can be easily dissolved in water and water-solubilized by the addition of a neutralizing agent (alkali), making it easier to handle than using a water-soluble resin as a binder. There are advantages such as superiority. In the present invention, “alkali dissolution” means that at least a part of the latex is dissolved by addition of alkali such as ammonia (water) to form a water-soluble resin. The alkali solubility of the latex (ratio of the alkali-soluble portion with respect to the entire latex) is measured, for example, as follows. That is, ammonia water was added to latex prepared to a solid content of 10% to adjust the pH to about 8.0, and the light transmittance of the alkali-dissolved solution was measured with a visible spectrophotometer, and this value was used as an indicator of alkali solubility. can do. The light transmittance is preferably 30% or more, more preferably 50% or more, and most preferably 70% or more (with water as 100%). By setting the value of the light transmittance (alkali solubility) within the above range, the adhesive force to the filler and the like contained in the protective layer is sufficient, and various functions as a binder of the protective layer are exhibited well. In addition, the alkali solubility can be evaluated by, for example, a method for measuring viscosity other than the above-described measurement method.
[0023]
The heat-sensitive recording material in the present invention includes a heat-sensitive recording layer that develops color by heat on a support, and / or a protective layer mainly composed of a binder and a filler on and / or on the back surface of the support. Is a recording material. The heat-sensitive recording layer is usually composed mainly of an electron-donating basic dye and an organic or inorganic electron-accepting substance, and a binder, a filler, a sensitizer, a lubricant, and the like are appropriately disposed thereon. Become.
[0024]
  In the present invention, the latex for heat-sensitive recording material,In 100 parts by weight of latex solids,
(A) 10 to 40 parts by weight of (meth) acrylonitrile,
(B) 15 to 40 parts by weight of hydroxyalkyl acrylate,
(C) 10 to 40 parts by weight of (meth) acrylic acid,
Is contained as a polymer component. Further, as will be described later, monomers other than those described above may be included as necessary. Hereinafter, the action of each of these components on the characteristics of the heat-sensitive recording material will be described.
[0025]
  (Meth) acrylonitrile exhibits excellent effects in improving heat resistance (running stability), plasticizer resistance, oil resistance, and organic solvent resistance. The amount of (meth) acrylonitrile used is 10 to 40 weights in 100 parts by weight of the solid content of the latex for heat-sensitive recording materials.PartPreferably 15 to 35 weightsPartIt is. The amount of (meth) acrylonitrile used is 10%PartIf it is less than 1, the required heat resistance cannot be obtained, the running stability is hindered, and further sufficient plasticizer resistance may not be obtained. 40 weightPartIf it exceeds 1, water may not be water-soluble even if it is neutralized, and polymerization may not proceed stably.
[0026]
  Hydroxyalkyl acrylate has a role of imparting appropriate flexibility while maintaining plasticizer resistance. Latex for thermal recording materialIn 100 parts by weight of solid content15-40 weightPartAnd,Preferably 20-30 weightPartIt is. 15 weightPartLess than the required flexibility, less than 40 weightPartIf it exceeds 1, the hydrophilicity increases and the emulsion form cannot be maintained, and at the same time, the water resistance deteriorates.
[0027]
  (Meth) acrylic acid imparts alkali solubility by introducing a carboxy group into the resin skeleton of the latex for heat-sensitive recording materials, and has the role of making the latex a water-soluble resin by adding a neutralizing agent. By changing the latex to a water-soluble resin, the binding property to the filler is remarkably improved, and an excellent protective layer can be formed even when a large amount of filler is contained. Moreover, it acts usefully as a functional group of the low temperature crosslinking agent added as needed. The amount of (meth) acrylic acid used is latex for thermal recording materials100 parts by weight of solid content10 to 40 weightPartPreferably 15 to 30 wt.PartIt is. 10 weightPartIf it is less than 1, sufficient alkali solubility cannot be obtained, and the stability of the resulting water-soluble resin is also poor. 40 weightPartExceeding may cause color development (fogging) in the heat-sensitive layer.
[0028]
Moreover, the other monomer copolymerizable with the said monomer can also be included as needed. By selecting an appropriate monomer and including it in an appropriate amount in the polymer component, the production stability of the latex for heat-sensitive recording materials can be increased, and the water resistance can be increased.
[0029]
  The amount of monomer used is the latex for thermal recording materials.100 parts by weight of solid contentMedium, 40 weightPartLess, preferably 25 weightPartLess than. 40 weightPartIf the above is satisfied, it becomes difficult to balance the water resistance and the plasticizer resistance, for example, the plasticizer resistance deteriorates and the water resistance deteriorates depending on the case. Examples of this monomer include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate, 2-hydroxyethyl methacrylate, 2-hydroxy methacrylate Propyl, 2-hydroxybutyl methacrylate, 2-aminoethyl (meth) acrylate, 2- (N-methylamino) ethyl (meth) acrylate, 2- (N, N-dimethylamino) (meth) acrylate (Meth) acrylic acid esters such as ethyl and glycidyl (meth) acrylate, unsaturated carboxylic acids such as maleic anhydride, fumaric acid, itaconic acid and crotonic acid, and aromatics such as styrene, α-methylstyrene and divinylbenzene N-substituted unsaturated hydrocarbons such as vinyl monomers, (meth) acrylamide, N-methylol (meth) acrylamide Bon acid amide. Among them, relatively oleophilic ones such as (meth) acrylic acid esters having a long styrene and / or alkyl chain length are preferably used.
[0030]
The glass transition point of the latex for heat-sensitive recording material in the present invention is −10 to 50 ° C., preferably 0 to 30 ° C. If the glass transition point is less than −10 ° C., the heat resistance is not sufficient, so that the so-called sticking phenomenon in which the protective layer sticks to the thermal head tends to occur. On the other hand, when the temperature exceeds 50 ° C., the protective layer becomes brittle. In particular, when a soft sheet is used as a support, the protective layer may be cracked during handling to impair the intended function.
[0031]
The average particle size of the latex for heat-sensitive recording material of the present invention is not particularly limited, but is preferably 50 to 500 nm, more preferably 100 to 300 nm. If it is less than 50 nm, the viscosity of the system may be remarkably increased. In this case, the resin concentration during production must be lowered, which is economically disadvantageous. Moreover, when an alkali is added, since the surface area is large, solubilization partially proceeds to become mama powder, and uniform solubilization may be difficult. On the other hand, if it exceeds 500 nm, the surface area is large, so that the solubilization time becomes long, which may cause a problem in work.
[0032]
The method for obtaining the latex for heat-sensitive recording material of the present invention may be in accordance with a known emulsion polymerization technique, and an emulsifier may be used as necessary to impart polymerization stability. For example, anionic surfactants such as sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, alkyl diphenyl ether sulfonates, non-polyethylene glycol alkyl ester types, alkyl phenyl ether types, alkyl ether types, etc. An ionic surfactant can also be used individually or in combination of 2 or more types. Although there is no restriction | limiting in particular about the usage-amount of these emulsifiers, Taking into consideration the water resistance of resin, it is preferable to set it as a required minimum amount.
[0033]
Furthermore, examples of the polymerization initiator used when polymerizing the latex for heat-sensitive recording materials include those used in usual emulsion polymerization. These include water-soluble initiators such as persulfates and hydrogen peroxide, oil-soluble initiators such as azobisisobutyronitrile and benzoyl peroxide, or redox initiators. There is no restriction | limiting in particular about the quantity of a polymerization initiator, Although what is necessary is just to follow a well-known technique, It is used in 0.1-10 weight part with respect to 100 weight part of monomers, Preferably it is 0.1-5 weight part It is.
[0034]
Moreover, as molecular weight regulators (chain transfer agents), mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, octyl mercaptan, α-methylstyrene dimer, low molecular halogen compounds and the like are used as necessary. The molecular weight can be adjusted depending on the amount used, but if the molecular weight is too high, when the latex for heat-sensitive recording material is alkali-dissolved with a neutralizing agent, the viscosity becomes extremely high and the workability is hindered. The molecular weight is preferably in the range of 100 to 3000 millipascals.
[0035]
By using a resin obtained by water-solubilizing the latex for heat-sensitive recording materials obtained as described above with a neutralizing agent as a binder for the protective layer, it has excellent durability, imprintability, printability, and color development sensitivity and running. A heat-sensitive recording material having excellent stability can be obtained.
[0036]
Ammonia (ammonia water) is preferably used as a neutralizing agent added to make the latex for heat-sensitive recording material of the present invention water-soluble. Other examples include sodium hydroxide, potassium hydroxide, and various amines, but it is preferable to avoid use. If sodium hydroxide or potassium hydroxide is used, the water resistance may be lowered and the thermal head may be damaged, and if various amines are used, the desensitizing action during thermal coloring is increased. When ammonia water is used, such a problem does not occur, and it can be easily detached at a relatively low temperature, so that good water resistance can be obtained after forming the protective layer.
[0037]
Examples of the filler in the present invention include inorganic fillers such as kaolin, calcined kaolin, talc, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, and aluminum hydroxide, urea-formalin resin, polystyrene fine powder, and the like. These organic fine particles can be used, and one kind or a combination of two or more kinds can be used. However, since the printing density may be lowered if the hiding power of the filler is too large, it is necessary to appropriately select the type and the addition amount so as not to hinder the printing density.
[0038]
The amount of the filler used is preferably 40 to 200 parts by weight, more preferably 60 to 150 parts by weight, with respect to 100 parts by weight of the latex for heat-sensitive recording material. If it is less than 40 parts by weight, running stability and sealability may not be sufficiently obtained. On the other hand, if it exceeds 200 parts by weight, the filler may not be sufficiently bonded, and the plasticizer resistance, solvent resistance, and printability may not be sufficiently obtained.
[0039]
In addition to the filler, components used as necessary include water resistance agents (crosslinking agents), higher fatty acid metal salts for improving sticking resistance, higher fatty acid amides, lubricants such as highly crystalline polyolefin fine particles, Examples include ultraviolet absorbers, antioxidants, antifoaming agents, wetting agents, pH adjusting agents, viscosity adjusting agents, other auxiliaries, and additives.
[0040]
Among them, the water-resistant agent (cross-linking agent) makes the protective layer more robust, further improves the durability of the heat-sensitive layer and the recorded image, and at the same time, improves the thermal head suitability (sticking property, running stability). Preferably used. Examples of such crosslinking agents include glyoxal, dimethylol urea, glycidyl ether of polyhydric alcohol, ketene dimer, dialdehyde starch, epichlorohydrin modified product of polyamidoamine, ammonium zirconium carbonate, aluminum sulfate, calcium chloride, boric acid and the like. It is done.
[0041]
As the binder of the heat-sensitive recording material of the present invention, a resin in which the latex for the heat-sensitive recording material is water-solubilized is used, but it may be used in combination with other known binders as necessary. As such a binder, generally known natural resins (for example, sodium alginate, starch, casein, celluloses) and synthetic resins can be used in accordance with the purpose. Among them, a modified product of polyvinyl alcohol is preferable, for example, Examples of the modified product include carboxyl group modification, acetoacetyl group modification, epoxy group modification, silanol group modification, amino group modification, olefin modification, amide modification, nirolyl modification and the like.
[0042]
The part to which the binder using the latex for heat-sensitive recording material of the present invention is applied is not limited to the back surface of the support on the heat-sensitive recording layer, and can be appropriately applied to a part that can improve the function of the protective layer.
[0043]
Further, the coloring system of the heat-sensitive recording layer portion to which the present invention is applied is not particularly limited. Incidentally, as these coloring systems, there are those using an acidic substance typified by a leuco dye and a phenolic substance, those using an imino compound and an isocyanate compound, and those using a diazo compound and a coupler.
[0044]
  The protective layer of the present invention is usually an air knife on a known thermosensitive recording layer provided on paper, synthetic paper, film, etc. as a support and / or between the back surface of the support, between the support and the thermosensitive recording layer. 1-10 g / m in weight after drying with a coater, gravure coater, roll coater, rod coater, etc. ² It is preferably applied.
[0045]
Hereinafter, the present invention will be specifically described with reference to production examples, comparative production examples, examples, and comparative examples, but the present invention is not limited to these examples. In addition, the number of parts and% in the following examples all represent parts by weight and% by weight unless otherwise specified.
[0046]
【Example】
  (Manufacture of latex for thermal recording materials)
  Production Example A1
  In a separable flask equipped with a stirrer and a reflux condenser, 146 parts of water, 0.1 part of sodium dodecylbenzenesulfonate andExcessiveAfter charging 1.0 part of potassium sulfate and replacing with nitrogen gas, the temperature was raised to 70 ° C. Subsequently, an emulsion having the following composition was continuously added over 4 hours, and then the temperature was raised to 80 ° C. and maintained for 3 hours to complete the polymerization. The resulting aqueous copolymer resin is an emulsion having a milky white appearance, a non-volatile content of 35%, a viscosity of 10 millipascals,pH was 4.5.
[0047]
Monomer emulsion composition
30 parts acrylonitrile
20 parts of hydroxyethyl acrylate
5 parts hydroxypropyl acrylate
20 parts methacrylic acid
20 parts of butyl acrylate
5 parts of styrene
n-dodecyl mercaptan 1 part
40 parts of water
Sodium dodecylbenzenesulfonate 0.1 parts
Production Examples A2 to A7 and Comparative Production Examples B1 to B7
Latex A2 to A7 for thermosensitive recording materials and comparative production examples B1 to B7 were produced in the same manner as in Production Example A1 except that the monomer composition was changed. The composition and results are summarized in Table 1.
[0048]
  In the table, glass transition point (Tg),EmulsionPolymerization stability and alkalisolubleThe evaluation criteria for sex are as follows.
[0049]
(Glass transition point)
The glass transition temperature (Tg) was measured by differential scanning calorimetry (DSC).
[0050]
  (EmulsionPolymerization stability)
○: Stable emulsion particles showing a milky white appearance, and there is no generation of aggregates, adhesion to the stirring blade, and generation of residues during production.
Δ: Stable emulsion particles showing a milky white appearance can be obtained, but some agglomerates are attached to the stirring blade during production. Alternatively, during production, a large amount of water-soluble polymer is generated, and the viscosity in the system is remarkably increased.
X: Production is difficult due to a large amount of aggregate formation.
[0051]
  (alkalisolublesex)
  To the latex prepared so that the solid content is 10%, 28% aqueous ammonia is added with stirring to a pH of 8.0 to perform alkali dissolution. The degree of dissolution was measured using a UV-visible spectrophotometer (manufactured by Shimadzu Corporation, UV-600) in a glass cell having an optical path length of 10 mm and a light transmittance of 550 nm. When the light transmittance of deionized water was 100%, the determination was made according to the following criteria.
○: Light transmittance of 70% or more
Δ: Light transmittance 30% or more and less than 70%
X: Light transmittance less than 30%
  Next, Production Examples A1 to A7 and Comparative Production Examples B1 to B7Latex for thermal recording material obtained inIs used as a heat-sensitive recording materialExampleI will explain. AnywayExampleAlso, the composition is parts by weight. In the comparative production example, a problem occurred in the polymerization stability.Comparative production exampleB2LatexIsExampleDid not apply to.
[0052]
Example 1
After adding 250 parts of water to 100 parts of the latex for heat-sensitive recording material obtained in Production Example A1 and diluting, 28% ammonia water was gradually added to PH8 as a target to dissolve the latex for heat-sensitive recording material in water. Further, 35 parts of fine powder silica (manufactured by Mizusawa Chemical Co., Ltd .: Mizukasil P-527) and an appropriate amount of water for viscosity adjustment were added thereto, and then mixed and dispersed in a sand mill for 3 hours to obtain a coating solution. Next, 8 parts of a 30% zinc stearate dispersion is added to this coating solution, mixed again to be uniform, and then dried on a commercially available facsimile paper at 3 g / m 2 by dry weight.²Then, it was applied and dried by a bar coater (forced drying at 60 ° C. for 30 seconds, followed by curing in a 20 ° C./65% RH atmosphere for 7 days) to obtain a heat-sensitive recording material.
[0053]
  Example 2
  The latex for heat-sensitive recording material obtained in Production Example A5 was used, and light calcium carbonate (Maruo calcium instead of 35 parts of fine powder silica)Made) A heat-sensitive recording material of Example 2 of the present invention was obtained in the same manner as Example 1 except that 14 parts were used. In this embodiment, ammonia water is used.ofThe alkali solubility of the latex at the time of addition was slightly insufficient.
[0054]
Example 3
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the latex for heat-sensitive recording material obtained in Production Example A4 was used and that 52.5 parts of light calcium carbonate was used instead of 35 parts of fine powdered silica. It was.
[0055]
Example 4
The latex for heat-sensitive recording material obtained in Production Example A2 was used, and instead of 35 parts of fine powdered silica, a dispersion containing 28 parts of light calcium carbonate was added to a water-based epoxy resin (Mitsui Chemicals, Inc.) as a crosslinking agent. (Product: Eulamin P-5600) Except for adding 12 parts, a thermosensitive recording material was obtained in the same manner as in Example 1. In this example, the alkali solubility of the latex was slightly insufficient when ammonia water was added.
[0056]
Example 5
The latex for heat-sensitive recording material obtained in Production Example A3 was used, and in place of 35 parts of finely divided silica, 24.5 parts of aluminum hydroxide (Showa Denko: H-42) was used as a crosslinking agent. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 14 parts of a 13% aqueous solution of zirconium ammonium (manufactured by Daiichi Rare Element Co., Ltd .: Zircosol AC-7) was added.
[0057]
Example 6
The same procedure as in Example 1 except that the latex for heat-sensitive recording material obtained in Production Example A6 was used and that 42 parts of barium sulfate (Sakai Chemical Industry: Varifine BF-1) was used instead of 35 parts of finely divided silica. Thus, a heat-sensitive recording material was obtained.
[0058]
Example 7
The latex for heat-sensitive recording material obtained in Production Example A7 was used, and a polyhydric alcohol as a crosslinking agent was added to a dispersion containing 17.5 parts of kaolin (Engelhard: UW-90) instead of 35 parts of finely divided silica. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 3.5 parts of glycidyl ether (Nagase Sangyo: Denacol 512) was added.
[0059]
Comparative Example 1
A heat-sensitive recording material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the latex for heat-sensitive recording material obtained in Comparative Production Example B1 was used. In this comparative example, the alkali solubility of the latex when ammonia water was added was somewhat insufficient.
[0060]
Comparative Example 2
A heat-sensitive recording material was obtained in the same manner as in Example 4 except that the latex for heat-sensitive recording material obtained in Comparative Production Example B3 was used. In addition, in this comparative example, when ammonia water was added, the alkali solubility of latex was inadequate and it did not become water-soluble.
[0061]
Comparative Example 3
A heat-sensitive recording material was obtained in the same manner as in Example 3 except that the latex for heat-sensitive recording material obtained in Comparative Production Example B4 was used. In this comparative example, the alkali solubility of the latex when ammonia water was added was somewhat insufficient.
[0062]
Comparative Example 4
A heat-sensitive recording material was obtained in the same manner as in Example 2 except that the latex for heat-sensitive recording material obtained in Comparative Production Example B5 was used.
[0063]
Comparative Example 5
A thermosensitive recording material was obtained in the same manner as in Example 4 except that the latex for thermosensitive recording material obtained in Comparative Production Example B6 was used. In addition, in this comparative example, before adding ammonia water to latex, it was already a semi-water soluble state.
[0064]
Comparative Example 6
A thermosensitive recording material was obtained in the same manner as in Example 4 except that the latex for thermosensitive recording material obtained in Comparative Production Example B7 was used.
[0065]
  As described above, the heat-sensitive recording materials obtained in Examples 1 to 7 and Comparative Examples 1 to 6 were evaluated by the following methods. Evaluation resultsTable 3Shown in
(1) Water resistance
  Using a Gakushin friction fastness tester (used without load), the heat-sensitive recording surface developed by applying an uncolored part and a 140 ° C heat block for 1 second was used 20 times with gauze soaked in water. The state of the rubbing and thermal recording surface was visually evaluated.
A: No change.
○: A trace of rubbing remains.
Δ: Some missing.
X: Missing.
(2) Oil resistance
  A drop of tempura oil was dropped onto the heat-sensitive recording surface, which was colored in the same manner as described above, and further spread by lightly wiping with gauze. The degree of fading after standing at room temperature for 6 hours was visually evaluated.
○: No fading.
Δ: Slightly faded.
X: It has faded considerably.
(3) Plasticizer resistance
  A transparent type polyvinyl chloride adhesive tape for electrical insulation (manufactured by Nitto Denko) is applied to the heat-sensitive recording surface that has developed color in the same manner as described above, left at 40 ° C. for 24 hours, and then peeled off.PastedPaste and tapePastedThe density of the soldered part was measured with a Macbeth densitometer, and the density retention rate (%) was calculated by the following formula (the higher the value, the better).
Concentration retention rate (%) = (tapePastedMacbeth density of the glued part) ÷ (Macbeth density of the non-tape stuck part) × 100
(4) Solvent resistance
  The non-colored surface was traced with gauze impregnated with ethanol, and the degree of color development was visually evaluated.
○: No color development.
Δ: Color is slightly developed.
X: Color is developed.
(5) Running stability (sticking resistance)
  Using a thermal printing device (TH-PND manufactured by Okura Electric Co., Ltd.), printing was performed under the following conditions, and the degree of sound (cracking sound) at that time and the degree of dirt on the head were comprehensively evaluated.
Applied voltage: 24V
Pulse width: 1.74 ms
Applied energy: 0.34mJ/Dot
○: No sound, no head contamination, and smooth paper feed.
Δ: Although there is a slight noise, the head is not soiled and paper feeding is not hindered.
×: Cracking and loud sound. Head dirt is seen and paper feeding is hindered.
(6) Color sensitivity
  Printing was performed under the same conditions as described above, and the density of the printed surface was measured with a Macbeth densitometer.
(7) Fracture resistance
  With the uncolored thermal recording surface side facing up, lightly fold it in half with your finger pad. Next, after the surface was repaired, the crease portion on the recording surface side was traced with an oily light color marker (manufactured by Zebra: Himackey (yellow)), and the degree of cracking of the protective layer was observed. When cracking occurs, the organic solvent in the marker is impregnated into the heat-sensitive recording layer and develops color, and the degree thereof is visually evaluated.
○: No cracking occurred.
Δ: Slightly cracked.
X: Fracture occurs along the crease.
(8) Sealability
  Imprinting was performed on the heat-sensitive recording surface side using “Sachihata X Stamper Ink” (manufactured by Sachihata Kogyo Co., Ltd.).
○: No change is observed in the stamped part.
Δ: Slight bleeding occurs in the stamped part.
X: The stamped part blurs and cannot be read.
(9) Printability
  Using an RI printing aptitude tester (Meiji Seisakusho), printing was performed with ink (manufactured by Toyo Ink: SMX Tack 25), and the degree of peeling (picking) of the protective layer was visually evaluated.
○: No picking occurs.
Δ: Some picking occurred
X: Picking occurred.
[0066]
[Table 1]

[0067]
[Table 2]

[0068]
[Table 3]

[0069]
【The invention's effect】
As described above, the latex for heat-sensitive recording material of the present invention uses a specific amount of a specific monomer, so that it is excellent in alkali solubility and polymerization stability, and as a binder for the protective layer of the heat-sensitive recording material. When used, it is possible to remarkably improve the durability in various environments where the thermal recording material is used, the sealability, and the printability.
[0070]
In addition, since the heat-sensitive recording material of the present invention uses the latex for heat-sensitive recording materials as a binder for the protective layer, it is excellent in durability, sealability, and printability under various environments, and can be applied to a wide range of fields. Can do.
[0071]
In addition, the method for producing the heat-sensitive recording material of the present invention takes a step of dissolving the above-mentioned latex for heat-sensitive recording material with an alkali, containing a water-soluble resin in a coating solution, and applying this to a predetermined location. Thus, a heat-sensitive recording material having the above-described advantages can be easily produced without going through complicated steps.

Claims (8)

A latex for a thermal recording material used as a binder for a protective layer of a thermal recording material after being alkali-dissolved by a neutralizing agent, in a solid content of 100 parts by weight of the latex,
(A) 10 to 40 parts by weight of (meth) acrylonitrile, (b) 15 to 40 parts by weight of hydroxyalkyl acrylate, and (c) 10 to 40 parts by weight of (meth) acrylic acid are contained as polymer components. ), (B), and (c). The latex for heat-sensitive recording materials comprising a copolymer having a total content of 60 parts by weight or more and Tg of -10 to 50 ° C.   The latex for heat-sensitive recording material according to claim 1, wherein the neutralizing agent is ammonia. In a thermosensitive recording material provided with a heat-sensitive recording layer that develops color by heat on a support, and further provided thereon and / or a back surface of the support, a protective layer mainly composed of a binder and a filler,
The binder for the protective layer is a water-soluble resin obtained by alkali-dissolving the latex for heat-sensitive recording material with a neutralizer, and the latex for heat-sensitive recording material is contained in 100 parts by weight of the solid content of the latex. (a) 10 to 40 parts by weight of (meth) acrylonitrile, (b) 15 to 40 parts by weight of hydroxyalkyl acrylate, and (c) 10 to 40 parts by weight of (meth) acrylic acid as polymer components, A heat-sensitive recording material comprising a copolymer having a total content of (b) and (c) of 60 parts by weight or more and a Tg of -10 to 50 ° C.   The heat-sensitive recording material according to claim 3, wherein the neutralizing agent is ammonia. The heat-sensitive recording material according to claim 3 or 4, wherein the amount of the filler used is 40 to 200 parts by weight with respect to 100 parts by weight of the solid content of the latex . (A) forming a heat-sensitive recording layer that develops color by heat on a support;
(B) a step of adding a neutralizing agent to the latex for heat-sensitive recording material and dissolving in alkali to form a water-soluble resin;
(C) A method for producing a heat-sensitive recording material comprising a step of applying a coating liquid containing the water-soluble resin and a filler onto the heat-sensitive recording layer and / or the back surface of the support and drying. Because
The latex for heat-sensitive recording material comprises : (a) 10 to 40 parts by weight of (meth) acrylonitrile, (b) 15 to 40 parts by weight of hydroxyalkyl acrylate, and (c) (meth) acrylic in 100 parts by weight of the solid content of the latex. 10 to 40 parts by weight of acid as a polymer component, and the total content of (a), (b), and (c) is 60 parts by weight or more, and Tg is −10 to 50 ° C. A method for producing a heat-sensitive recording material comprising a polymer.   The method for producing a heat-sensitive recording material according to claim 6, wherein the neutralizing agent is ammonia. The method for producing a thermosensitive recording material according to claim 6 or 7, wherein the amount of the filler used is 40 to 200 parts by weight with respect to 100 parts by weight of the solid content of the latex .