JPH0446240B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a heat-sensitive recording material, and more specifically,
Related to improving the water resistance and chemical resistance of heat-sensitive recording materials containing as main components a color-forming substance that is normally colorless or light-colored at room temperature and a color-developing substance that reacts with the color-forming substance to form a color when heated. It is. [Prior Art] This type of heat-sensitive recording material, that is, a paint in which a normally colorless or light-colored color-forming substance and a color-developing substance that develops color from the color-forming substance when heated is dispersed in a binder, is used as a support. It is already known to make a heat-sensitive recording material by coating on top, as seen in Japanese Patent Publication No. 45-14039. Thermal paper, which originally started out as printer paper, has undergone explosive development as facsimile paper, and is now used not only for printers and facsimile paper, but also for train tickets, commuter passes, credit cards, horse racing tickets, etc.
Thermal printing methods are widely used on post paper and the like. Therefore, as the range of applications expands, the required properties become more stringent, and in particular, for banknotes, POS labels, and some facsimile papers, printing and non-printing areas must not be damaged by chemicals such as oil, water, and plasticizers. There is now a demand for performance that does not cause color fading in printed areas or color development in non-printed areas. In order to meet this demand, research is being carried out to meet the demand by selecting a coloring material and forming a protective layer. [Object of the invention] The present invention provides protection against oil and oil by forming a protective layer.
The present invention provides a heat-sensitive recording material that prevents deterioration of recorded images due to water, chemicals, etc., and can be used for tickets, POS labels, etc. [Structure of the Invention] As a result of various studies, the present inventors have found that a heat-sensitive coloring layer containing a normally colorless or light-colored leuco dye and a color-developing substance that develops color from the leuco dye when heated is formed on a support. In the heat-sensitive recording material formed in
~85% by weight, (B) acrylonitrile 10-50% by weight,
(C) A layer containing a crosslinkable aqueous emulsion type resin made by blending a crosslinking agent having an epoxy group into an aqueous emulsion of a copolymer containing 3 to 20% by weight of at least one type of vinyl monomer having a carboxyl group. The present inventors have discovered that the above-mentioned performance can be imparted by providing the above-mentioned structure. The present invention will be explained in more detail below. In a heat-sensitive recording material, the present invention provides a protective coating layer on the back of the support, between the support and the heat-sensitive coloring layer, and on the heat-sensitive coloring layer, thereby providing a heat-sensitive layer for oil and chemicals. The present invention relates to a method for improving water resistance by curing a protective coating and preventing blocking due to dissolution by water droplets, and more specifically relates to the material of the protective coating. In the protective film forming agent for the heat-sensitive recording material of the present invention, the base polymer is a copolymer component.
(A) Acrylamide or methacrylamide 45~
85% by weight, (B) acrylonitrile 10-50% by weight, (C)
3 to 20 vinyl compounds having carboxyl groups, such as acrylic acid, methacrylic acid, maleic acid, etc.
It is an aqueous emulsion resin of a copolymer containing % by weight. The present inventors have determined that the protective film forming agent should not impair the heat-sensitive properties of the heat-sensitive layer, have high adhesive strength with the heat-sensitive layer, be impermeable to oil and plastics, have a high softening temperature, and be a curing agent. The protective film-forming material was synthesized taking into account that it can be crosslinked by. (A) Using acrylamide or methacrylamide as the main ingredient eliminates staking, (B) Acrylonitrile improves water resistance, (C) Adding a carboxyl group-containing vinyl monomer makes the carboxyl group act as a crosslinking point, It allows for water resistance. The copolymerization ratio of (A), (B), and (C) is determined by the balance between staking resistance, hydrophobicity, and water resistance. Addition of (A) and (C) increases swelling and solubility after crosslinking. In addition, the addition of (B) causes severe statesking with the heat-sensitive head. Note that this copolymer is an emulsion type, which makes it easy to control the viscosity of the paint, generates less bubbles during coating, and is industrially easier to use and more effective than water-soluble resins. The copolymer of the present invention can be produced by the following method. That is, peroxide was added as a polymerization initiator to an aqueous solution containing components (A), (B), and (C) with a total monomer concentration of 50 to 65% by weight, and 2-4% of the mixture was added to boiling water. It takes about time to drop quantitatively and react.
The reaction is completed by further aging for 2 to 4 hours. The ratio of the monomer aqueous solution to the water containing the polymerization initiator is preferably adjusted so that the polymer concentration is 25 to 40% by weight. The peroxide used as a polymerization initiator is not necessarily limited, but water-soluble ones such as hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, and potassium persulfate are usually suitable. There are no particular restrictions on the amount of polymerization initiator used, but usually the amount of peroxide is
It is desirable to use about 0.1 to 2.0% by weight. Although there is no particular restriction on the polymerization temperature, a higher temperature is desirable in terms of increasing the reaction rate and making the monomer composition distribution of the polymer uniform, and in particular, the boiling point of the reaction solution is most effective. An appropriate value for the degree of polymerization is determined based on the characteristics of the protective film and workability; for example, 10% for 10%.
A viscosity of about 1000 cp is appropriate. Note that this copolymer is in the form of an emulsion. The crosslinking agent having an epoxy group that crosslinks with the protective coating material is preferably a water-soluble epoxy crosslinking agent, and must have the property of being able to crosslink at room temperature after coating and drying. The water-soluble epoxy crosslinking agent used in the present invention is not particularly limited, but includes nonionic water-soluble epoxy compounds such as diglycidyl ether of polyethylene glycol, glycerin diglycidyl ether, and trimethylolpropane diglycidyl ether; Water-soluble copolymers of glycidyl esters of acrylic acid or methacrylic acid and acrylamide, polyamide epoxy resins, etc. are selected. As the protective coating material, a copolymer emulsion and a water-soluble epoxy crosslinking agent are mixed to make a protective coating paint, but as time passes after mixing, the reaction progresses and the viscosity increases, so check the pot life before use. I have to. The mixing ratio of the protective coating material and the epoxy crosslinking agent is determined based on the balance between water resistance and pot life. This ratio is preferably 10/1 to 10/7. In forming the protective film, other polymer compounds, pigments, and fillers such as wax may be added as necessary. In order to form the thermosensitive color forming layer of the present invention, a leuco dye as a color forming substance and its color developing substance are
It can be produced by dispersing fine powder in a binder together with other fillers, ie, sensitizers and pigments, and coating it on a support. However, when a protective film is provided on the heat-sensitive layer, it is necessary to maintain the heat resistance of the heat-sensitive layer to some extent. An example of heat-sensitive materials is as follows. The normally colorless or light-colored leuco bodies used in the heat-sensitive coloring layer include triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, and spiropyran-based leuco bodies, including, for example, 3,3-bis(p -dimethylaminophenyl)
-6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)
Phthalide, 3,3-bis(p-dimethylaminophenyl)
-6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)
-6-chlorophthalide, 3-(N-p-tolyl-N-ethylamino)-6
-Methyl-7-(N-phenylamino)fluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7-(3-fluoromethyl)fluoran enylaminofluorane, benzoylleucomethylene blue, 6'-chloro-8'-methoxy-benzoindolino-pyrylospirane, 6'-bromo-8'-methoxy-benzoindolino-bilythrospiran, 2-[3.6-bis(diethylamino) -9-(o-
chloroanilino)xanthyl], benzoic acid lactam, etc. In addition, examples of acidic substances that cause a coloring reaction with the leuco body under heat and cause the leuco body to develop color include, for example, α.
-Naphthol, β-naphthol, 4-t-buterphenol, 4-t-octylphenol, 4-
Phenylphenol, 2,2-bis(p-hydroxyphenyl)propane (also known as bisphenol A), 2,2-bis(p-hydroxyphenyl)
Butane, 4,4'-cyclohexylidenephenol, 2,2-bis(2,5-dibromo-4-hydroxyphenyl)propane, 4,4'-isopropylidenebis(2-t-butylphenol), 2 ，
Examples include 2'-methylenebis(4-chlorophenol), benzoic acid, parahydroxybenzoic acid ester, salicylic acid, tartaric acid, and gallic acid. Examples of the binder include the following. polyvinyl alcohol, methoxycellulose,
Water-soluble ones such as hydroxyethyl cellulose, carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or water-based emulsions such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. In addition, fillers, thermofusible substances, etc. can be added to the heat-sensitive layer of the present invention as required. Examples of fillers include calcium carbonate, magnesium carbonate, alumina, silica, talc, barium sulfate, and water. magnesium oxide, aluminum hydroxide,
Examples include urea-formalin resin. Examples of thermofusible substances include beeswax, shellac, carnauba wax, montan wax, paraffin wax, microcrystalline wax, higher fatty acid esters, higher amides, chlorinated paraffins, higher fatty acid salts, and the like. [Explanation of Examples] Hereinafter, the present invention will be specifically explained with reference to Examples. Hereinafter, parts represent parts by weight. Example 1 (a) Preparation of heat-sensitive recording paper Mixtures having the following compositions were pulverized and dispersed in a ball mill for 24 hours to prepare liquids A and B. Solution A 3-N-methyl N-cyclohexylamino-6methyl-7-anilinofluorane 10 parts Acrylic acid amide 10 parts 10% polyvinyl alcohol aqueous solution 20 parts Water 20 parts Solution B Bisphenol A 10 parts Calcium carbonate 10 parts Stearic acid Amide 2 parts 10% polyvinyl alcohol aqueous solution 22 parts Water 10 A heat-sensitive recording material coating prepared by mixing 12 parts of liquid A and 54 parts of liquid B was coated on high-quality paper (45 g/m ² ) with a dry weight of 6 g/m ² on one side. A heat-sensitive recording paper was prepared by coating and drying the mixture to give the following properties. (b) Preparation of protective film-forming coating solution 0.84 parts of peroxide was added to 129 parts of water, and the mixture was raised to a boiling point in a reactor and refluxed. Add 68% of acrylamide/acrylonitrile/acrylic acid to this.
A monomer aqueous solution prepared by mixing 58 parts/14 parts of water and 140 parts of water was added dropwise over 4 hours, and
The reaction was completed after aging. Further concentration 10
% diluted with water. In addition, this particle size distribution was observed to be centered at 0.2 μm by centrifugal particle size distribution measurement, and it was recognized that it was in the form of an emulsion. 50 parts and 20% of an aqueous emulsion of the above copolymer
A protective film coating solution was prepared by mixing 6 parts of a polyamide epoxy resin aqueous solution. This protective coating coating liquid was applied to the heat-sensitive layer of the heat-sensitive recording paper and/or the back surface of the support by a dry weight of 4.
The heat-sensitive recording paper of the present invention was prepared by coating each of them so as to give a coating weight of g/m ² . Example 2 The polymerization method for the protective film forming material was the same as in Example 1, except that the composition of the copolymer was changed. To 10 parts of a 10% aqueous solution of acrylamide/acrylonitrile/methacrylic acid 50 parts/40 parts/10 parts, add glycerin diglycidyl ether.
A protective film coating solution was obtained by adding 0.2 part of the solution, and heat-sensitive recording paper was prepared in the same manner as in Example 1. Comparative Example 1 20% to 50 parts of 10% polyvinyl alcohol aqueous solution
A thermosensitive recording paper was prepared in exactly the same manner as in Example 1, except that 6 parts of an aqueous polyamide epoxy resin solution was used as the protective coating coating solution. Comparative Example 2 40% in 50 parts of 10% polyvinyl alcohol aqueous solution
A thermosensitive recording paper was prepared in exactly the same manner as in Example 1, except that 5 parts of glyoxal aqueous solution was used as the protective coating coating solution. Example 3 The protective film coating solution of Example 1 was applied onto a support,
A heat-sensitive recording paper was produced under the same conditions as in Example 1, except that the heat-sensitive recording paint of Example 1 was applied thereon and the layer structure was changed. Comparative Example 3 A common thermal recording paper was used as a sample. The quality of the heat-sensitive recording material produced as described above was evaluated using a sample. The results are shown in the table. For recording, color was developed in a heat block at 120° C. at 200 g/cm ² for 5 seconds. Plasticizer resistance is determined by applying a plasticizer-containing wrap film of PVC to the front or back side of the colored area for 25 minutes in a constant temperature bath at 60°C.
The plasticizer resistance was observed by color selection after contacting with a pressure of g/cm ² for 24 hours. Water resistance was determined by rubbing the surface after immersion in water at 20°C for 24 hours and comparing the surface strength.

〔Effect of the invention〕

As shown in the above example, a layer containing the crosslinkable aqueous emulsion type resin of the present invention is provided at one or more locations on the back of the support, between the support and the thermosensitive coloring layer, and on the thermosensitive coloring layer. The recording material has significantly improved plasticizer resistance and water resistance, and since it is an emulsion type, the viscosity can be easily controlled and foaming is less likely to occur, making it more practical than water-soluble resins.

Claims (1)

[Claims] 1. In a heat-sensitive recording material in which a heat-sensitive coloring layer containing a colorless or light-colored leuco dye and a color-developing substance that develops color from the leuco dye as a main component on a support is provided on a support, the back of the support, the support (A) 45 to 85% by weight of acrylamide or methacrylamide, (B) 10 to 50% by weight of acrylonitrile, and (C) a carboxyl group between the body and the thermosensitive coloring layer and at one or more places on the thermosensitive coloring layer. 1. A heat-sensitive recording material comprising an aqueous emulsion of a copolymer of 3 to 20% by weight of at least one vinyl monomer having a layer containing a crosslinkable aqueous emulsion type resin having an epoxy group.