JPS61197277A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance resistance to water, plasticizers and oils, by providing a protective layer comprising a specified water-soluble high molecular weight compound and a cross-linking agent as main constituents on a thermal color forming layer provided on a base to produce a thermal recording material. CONSTITUTION:A colorless or light-colored color forming dye, a color developing substance such as acid clay, a binder such as starch and the like are mixed into an aqueous solution of an alcohol or the like to prepare a coating liquid. The coating liquid is applied to a base such as woodfree paper, a medium- quality paper, an art paper and a plastic film to provide the thermal color forming layer. A coating liquid for forming the protective layer is prepared which comprises a water-soluble high molecular weight compound containing an acetoacetic acid ester group, a cross-linking agent, a pigment and a lubricant or the like, and the coating liquid is applied to the color forming layer to provide the protective layer thereon. Ultra fine silicic acid having an oil absorption of not less than 100ml/100g, an apparent specific volume of not less than 3ml/g and an average particle diameter of not larger than 1.5mum is preferably incorporated in the protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color-developing method consisting of a normally colorless or slightly pale color-forming dye, and an organic acid or phenolic substance that causes the color-forming dye to develop color by heating. The present invention relates to a heat-sensitive recording material having a heat-sensitive coloring layer containing a binder and a binder.

More specifically, this heat-sensitive recording material has storage stability, especially the water resistance of the coating film, the water resistance of the colored part, the discoloration that occurs when it comes into close contact with a plastic film containing a large amount of plasticizer (hereinafter referred to as plasticizer resistance), and the resistance to meat. The present invention relates to a heat-sensitive recording material that has improved discoloration (hereinafter referred to as oil resistance) that occurs when oil is attached, such as on paper or edible materials.

(Prior Art) Conventionally, there are various known heat-sensitive recording sheets in which a paint obtained by dispersing a lactone compound such as crystal violet lactone and a phenol compound such as bisphenol A in a binder such as 4+7 vinyl alcohol solution is coated on a support. Tokukosho, Publication No. 15-14039).

(Problems to be Solved by the Invention) When this type of heat-sensitive recording sheet is heated, the color-forming lactone compound and the organic acid or phenol compound chemically react to develop color. In this case, the basic properties required of a heat-sensitive recording sheet are that it has good color development, is as white as possible in appearance and has the appearance of natural paper, and has long shelf life.In addition, particularly important properties include:
(b) High sensitivity, (b) No sticking, (no lees adhering to the thermal head, etc.) U7 and good compatibility with the thermal head are required. has been done.

In this way, heat-sensitive recording materials are desired to have the above-mentioned properties depending on their use, but this type of dye type 7P color-forming material is resistant to light, water, temperature, plasticizers, oil, etc. Due to its instability, changes over time during storage are always a problem. Therefore, when desired printing is performed using such a marking/green mark, the recorded color appears very clearly, but if the coloring area is covered with a plastic film containing a large amount of plasticizer (for example, a soft material made of vinyl chloride). If the film is placed in close contact with the product or if it is stored with oil or fat attached, there is a disadvantage that the adhesive part will fade.
Significant discoloration also often occurs when the colored part comes into contact with water for a long period of time.

These discolorations are particularly noticeable in color-forming type heat-sensitive recording materials that use dyes mainly composed of colorless or light-colored lactone compounds, and this discoloration depends on the chemical structure of the color-forming lactone compound used. It is presumed that the above-mentioned inconvenience occurs because plasticizers and oils, especially organic acids and phenolic compounds, dissolve in plasticizers and oils without contacting them. As such, it has traditionally been strongly recommended that the issue be resolved.

The present invention aims to solve these problems and provide a heat-sensitive recording material having improved water resistance, plasticizer resistance and oil resistance, and long-term storage stability.

(Means for Solving the Problems) The present inventors have developed a coloring layer obtained by copolymerizing a monomer having an acetoacetate group, acrylamide, and polyvinyl alcohol on a heat-sensitive coloring layer provided on a support. By providing a protective layer mainly composed of a water-soluble polymer compound and a crosslinking agent, it is possible to prevent plasticizers, oil, etc. from penetrating into the heat-sensitive coloring layer, and prevent oil from entering the thermosensitive coloring layer when it comes into close contact with a soft polyvinyl chloride film. The headline is that it shows an excellent effect on preventing discoloration when it is attached.

At this time, when ultrafine silicic acid powder with an oil absorption of 100mV1019 or more, an apparent specific volume of 3rnl/9 or more, and an average particle size of 15μ or less is included as a filler, the compatibility with the head such as sticking and head dregs will be even better, and the above-mentioned resistance will be improved. There is no deterioration in plasticizer properties, oil resistance, water resistance, etc., and high density, clear images can be recorded even with minute thermal energy.

For example, when the surface of the heat-sensitive recording material is simply coated with cottonseed oil, a conventional heat-sensitive recording material without a protective layer, or simply a water-soluble polymer compound with barrier properties such as ordinary saponified PTA, casein, etc., and a crosslinking agent. When left at 40C for heat-sensitive recording materials provided with a protective layer containing
The colored part disappears in 05 to 5 hours. On the other hand, in the heat-sensitive recording material containing the water-soluble polymer compound containing the acetoacetate group of the present invention, the colored portion does not disappear even after 24 hours or more.

The protective layer of the heat-sensitive recording material of the present invention contains a crosslinking agent, a lubricant, and/or a pigment in addition to the above-mentioned water-soluble polymer compound containing an acetoacetate group, thereby imparting water resistance to the coating film. It is possible to further prevent discoloration when immersed in water, and when recording on the coating surface,
It is possible to prevent sticking of the thermal head to the film surface and adhesion of dregs to the thermal head.

Therefore, the present invention can be used, for example, as a heat-sensitive recording type ticket for automatic ticket vending machines, as well as for use in coupon tickets and commuter rolls that require shelf life, and for PO8 barcode pricing for fresh food using the system. It is not only suitable for use as label paper to be attached to the packaging surface of food items and meat with a lot of oil wrapped in vinyl chloride film, but also as facsimile paper and printer paper for long-term storage.

The materials used in the heat-sensitive recording material of the present invention will be explained in detail below.

(1) 3-diethylamino-6-methyl- as a color-forming dye that is usually colorless and pale in color and is used in the thermosensitive color-forming layer.
7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-bi-relenol-6-methyl-anilinofluorane, 3-(N-methyl-N-
cyclohexylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-chloroanilinofluorane, 3-[:N-ethyl-N-(p-methylphenyl)aminecy6-methyl-fluorane Fluorane series such as niritsufluorane, 3-diethylamino-7-(metatrifluoromethyl)anilinofluorane, 3.3-bis-(p->methylaminophenyl)-6-dimethylaminophtaribi (crystal violet) lactone), 3
．． Triphenylmethane-based compounds such as 3-bis-(p-dibutylaminophenyl) phthalide, 3,3-bis-(p-dimethylaminophenyl) phthalide, 4-hibiloxy 1'-dimethylaminotrinoenylmethane lactone, 3
-Methyl-di-β-naphthospirolane, 1,3.3-
)! /Methyl-6'-chloro-87-medoxyindolinobenzoshydrolane, and leuco dyes such as auramine, rhodamine lactam, and phenothianone are also used.

However, the present invention is not limited to these representative examples.

(2) Color-developing substances that cause color-developing dyes to develop characteristic heat are inorganic solid acidic substances such as acid clay, zeolite, and silicon oxide; organic acids such as oxalic acid, maleic acid, gallic acid, and benzoic acid; Although conductors and metal salts can also be used, it is preferable to use heptanolic compounds with low water solubility, and among them, phenolic compounds having two or more hydroxyl groups in the molecule are preferred. For example, 4,4'-improhy.

Ritin diphenol, 4.4'-isopropylidene bis(2-chlorophenol), 4.4'-iso7'rohi0
lydene (2-methylphenol), 4.4'-impropylidene bis(2,1-tert-)f-fluorphenol), 4. , 4'-5ec-butylidenediphenol, 4.4'-cyclohexylidenediphenol, 4-
tert-butylphenol, 4,4'-cyclohexylitine diphenol, 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, naphthol, β-naphthol, methyl-4-hibiloxybenzoate, 4-hydroxyphthal Examples include dimethyl acid, 4-hydroxyacetophenone, p-oxybenzoic acid esters, novolac type phenolic resin, halogenated novolac type phenolic resin, and one or more of them can be used arbitrarily. However, it is not limited to these.

(3) The binder for the heat-sensitive coloring layer is not particularly limited and any known binder can be used. It is preferable that the liquid does not develop color, aggregate, or become highly viscous when mixed with the liquid. In addition, characteristics such as not inhibiting color development and strong film formation are required, but compatibility with the thermal head, such as sticking, adhesion of residue, and abrasion, is particularly required in order to provide a storage layer. For example, polyvinyl alcohol, lees II, hydroxyethyl cellulose, 7/7 beer gum, polyvinylpyrrolibin, alkali salts of acrylic acid (or methacrylic acid) ester copolymers, alkali salts of styrene/maleic anhydride copolymers. salts, alkali salts of inbutylene/maleic anhydride copolymers, water-soluble polymer compounds such as acrylamide copolymers, and polymer latexes such as styrene/butadiene copolymers, polyvinyl acetate, and acrylic ester copolymers; Or emulsion etc. can be mentioned.

Furthermore, the thermosensitive coloring layer in the present invention includes the coloring dye,
In addition to a color developing substance, a binder, etc., various substances shown below can be added as necessary. For example, inorganic pigments,
Other fillers are used to improve color development sensitivity, such as various waxes such as higher fatty acid amides, higher fatty acid metal salts, dibenzyl terephthalate, and other thermofusible substances, and melting point depressing substances, as well as dispersibility and coating suitability. Compatible defoamers, dispersants, wetting agents, etc. can be used to improve the

In the present invention, as the material for the protective layer formed on the surface of the thermosensitive coloring layer, a water-soluble polymer compound copolymerized with acetoacetate is used as a protective layer forming agent, and a crosslinking agent, a pigment, a lubricant, etc. are used in combination as necessary.

The monomer having an acetoacetate group used in the copolymerization of the water-soluble polymer compound having an acetoacetate group of the present invention includes alcohols having a double bond, tatoeha allyl alcohol, croton alcohol, futhynyl alcohol, improvised It is a reaction product of diketene and diketene, and allyl acetoacetate is obtained when allyl alcohol and diketene are reacted. The chemical reaction formula in this case is -)cH2=CH-CH2-oc-CH2=C-CH
3.

Polyvinyl alcohol (PVA), which is also used for copolymerization,
) has an average degree of polymerization usually selected from the range of 300 to 2,000, and preferably has an average saponification degree of 70-100 molar ratio. If the average degree of polymerization is less than 300, the adhesive strength will be insufficient,
If it exceeds 2,000, the viscosity of the chisel inder itself becomes too high, making it inconvenient to use. The average degree of saponification is 70
If it is less than the molar coefficient, it becomes difficult to dissolve in water, which is not preferable.

As mentioned above, the water-soluble polymer compound containing an acetoacetate group used in the present invention is a copolymer of a monomer having an acetoacetate group, acryamide, and polyvinyl alcohol.

For example, a copolymer using allyl acetoacetate as a monomer having an acetoacetate group can have the following structure.

CHCONH2 CH2 CH-CH2-〇-C-CH 2-(, -CH3 These copolymerizations are carried out by adding a mixture of acrylamide and the above monomer having an acetoacetate group in the above PVA aqueous solution, In the polymerization method, peroxide (ammonium persulfate, hydrogen peroxide, etc.) is used as a polymerization initiator, and the temperature is 80° to 100°C for grafting to PVA.
The usual method is to polymerize with PVA, but another method is to graft-polymerize a copolymer of acrylamide and the above-mentioned monomer having an acetoacetate group onto PVA.

The content of the acetoacetate group is 0.05 mole or more with respect to the water-soluble polymer compound, and can be up to the maximum within the range of water solubility, but it is usually 0.1 to 20 mole,
Above all, it is often selected from the range of 0.5 to 10 mol. If the content of acetoacetate groups is too small, it is difficult to obtain the effects of the present invention, and conversely, if the content is more than necessary, the expected effects cannot be obtained considering the amount used.

As the protective layer forming agent, in addition to the water-soluble polymer compound containing an acetoacetate group, other water-soluble polymers can also be used in combination. As the water-soluble polymer, polyvinyl alcohol, casein, in. Hydroxyethyl cellulose, gum arabic, polyvinylpyrrolidone, alkali salts of acrylic acid (or methacrylic acid) ester copolymers, alkali salts of styrene/maleic anhydride copolymers, alkali salts of inbutylene/maleic anhydride copolymers , alkali salts of diisobutylene/maleic anhydride copolymers, acrylamide (or methacrylamide 9)/acrylic acid (or methacrylic acid) ester copolymers, water-soluble polymer compounds and emulsions such as vinyl acetate, and still SBR. An example is latex.

The requirements for a protective layer forming agent are to have excellent film forming performance,
It is necessary that the obtained film is not dissolved by plasticizers, oils, organic solvents, etc., and at the same time, in order to prevent color development of the heat-sensitive coloring layer during coating, it is necessary to dry under relatively low temperature drying conditions of 1,000 C or less. The water-soluble polymer compound must also have sufficient film-forming performance.

Examples of crosslinking agents include dialdehydes such as glyoxal and polyaldehyde, polyamines such as polyethyleneimine, epoxy holamide resins, diglycidyls such as chrycerin diglycidyl ether, dimethylol urea, ammonium persulfate, and dichloride. Known compounds such as iron, metal salts such as magnesium chloride, and ammonium chloride are used.

Water-resistant polymer compounds that do not contain acetoacetate groups require treatment at considerably high temperatures, whereas the water-resistant polymer compounds that contain acetoacetate groups of the present invention require water-resistant treatment using these mounting agents. Polymeric compounds have remarkable reactivity, so they have the unique advantage of being able to exhibit practical water resistance at temperatures as low as drying.

Fillers include kaolin, clay, Merck, calcium carbonate, calcined clay, titanium oxide, silica, synthetic aluminum silicate, synthetic magnesium silicate,
Examples include aluminum oxide, polystyrene fine particles, urea-formalin resin fine particles, and the like.

In the present invention, ultrafine silicic acid powder having an oil absorption of 1.00 mV1009 or more, an apparent specific volume of 3 mVg or more, and an average particle size of 15 μ or less has good compatibility with the protective layer forming agent of the present invention, satisfies the above requirements, and is compatible with the head. It has also been found that it is an optimal filler that can also provide printing properties.

Further, as the lubricant, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, paraffin wax, microcrystalline wax, etc. can be used.

Therefore, the amount of the protective layer forming agent and the crosslinking agent must be equal to or equal to 50 weight plates of all the components of the protective layer, and if it is less than this, the properties of plasticizer resistance and oil resistance will deteriorate, making it unsuitable. It is. The amount of the crosslinking agent per 100 parts by weight of the water-soluble polymer compound is 5 to 100 parts by weight, preferably 10 to 80 parts by weight. In this case, if the amount of crosslinking agent is less than 5% by weight, crosslinking will not be able to proceed sufficiently, and therefore not only will sufficient water resistance and compatibility with the thermal head not be obtained.
Since the molecular structure cannot be made dense by crosslinking, the plasticizer resistance and oil resistance deteriorate, and the desired effect cannot be obtained.

The coating amount of the protective layer is adjusted as appropriate to the extent that heat conduction from the thermal head to the coloring layer is not inhibited.
Usually 1 to 1] 09/m2, preferably 2 to 7 so/m2. In this way, desired effects can be obtained without reducing thermal sensitivity.

Supports used in the present invention include wood-free paper, medium-quality paper,
Papers such as art paper, coated paper, cast coated paper, paperboard, tissue paper, etc. are generally used, but plastic films, synthetic papers, laminated papers, aluminum foils, etc. can also be used.

(Examples) The present invention will be explained in more detail below using Examples. Parts in each example indicate parts by weight.

Example I (1) Liquid preparation 3-(N-methyl-N-cyclohexolamine)-6-
Methyl-7-anirite fluorane
6 parts 5% hydroxyethyl cellulose aqueous solution 24 parts + 2) B* Preparation! +, 4'-Isopropylidenediphenol 25 parts Stearic acid amyl 1 16 parts 5 Hydroxy-engineered tylcellulose water fgo, 140 parts The above A and B solutions were separately ground and dispersed in a Sanvi mill to an average particle size of 3μ or less. .

(3) 10% manufactured by C Liquid Groove (allyl acetoacetate-acrylamide-PVA copolymer composition ratio: 2/315) 60 parts (PVA: degree of nylation 88%, M dust content 1100) 60% kaolin dispersion liquid
4 parts 30% zinc stearate 2 parts 30
% polyaldehyde solution 3 parts (4) Formation of coloring layer 40 parts of kaolin 60 aqueous dispersion, 30 parts of liquid A, 20 parts of liquid B
0 parts and 100 parts of a 10-functional polyvinyl alcohol aqueous solution as a binder were mixed to prepare a coating liquid. 50g/of this coating liquid
After coating on the base paper of rrL2 so that the dry weight is 7g/rrL2, it is calendered and the Bekk smoothness is 2.
A heat-sensitive coloring layer was provided for 50 seconds.

(5) Formation of protective layer A protective layer was formed by coating liquid C on the above coloring layer to a dry weight of 397 m 2 to obtain a heat-sensitive recording material having a two-layer structure.

Comparative Example 1 Saponified PV with a saponification degree of 98 molti and a polymerization degree of 1100 was used instead of the acetoacetate group-containing copolymer, which is a water-soluble polymer compound of liquid C (protective layer paint) used in Example 1.
A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1 except that A was used.

Example 2 Instead of the filler kaolin in liquid C (protective layer paint) used in Example 1, oil absorption was 200 mV1009 and apparent specific volume was 3 ml.
/jj, except for using ultrafine silicic acid powder with an average particle size of 13μ (d
A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1.

Comparative Example 2 Saponified Pv with a saponification degree of 88 mol and a polymerization degree of 1100 was used instead of the acetoacetate group-containing copolymer, which is a water bathable polymer compound of CM (protective layer paint) used in Example 2.
A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 2 except that A was used.

Comparative Example 3 Same as Example 1 except that an ammonium solution of casein (10 aqueous solution) was used instead of the acetoacetate group-containing PVA0, which is a water-soluble polymer compound of liquid C (protective layer paint) used in Example I. In the same manner, a heat-sensitive recording material having a two-layer structure was obtained.

Each of the heat-sensitive recording materials of the above Examples and Comparative Examples was
After leaving it for a day, I colored it with a solid black record using Copix 7100 (trade name, manufactured by Toshiba Electric Corporation), and a clear black colored image with a high density of 1.2 or more was obtained using a Macbeth reflection densitometer (RD-514). . Next, a predetermined test piece was prepared from this in a conventional manner, and the water resistance, vinyl chloride film resistance, and oil resistance of the colored portion were measured by the following tests. The results are shown in the table. As is clear from this table, in each of the Examples, satisfactory results were obtained, but in the Comparative Examples, appropriate results were not obtained in some respects.

(1) Water resistance test: A test piece is immersed in water for 24 hours (at room temperature) and then taken out, and evaluated based on the elution state of the protective layer and the residual concentration after drying.

(2) PVC film resistance test: A soft polyvinyl chloride film is superimposed on the specimen, and the density is measured when both are brought into contact for 24 hours under a load of 20C13001/m2.

(3) Oil resistance test: Cottonseed oil is applied to a test piece according to a conventional method, and the residual concentration after being left at temperatures of 201Z' and 40C for 24 hours is evaluated.

(Table) The symbols in the table are the results of evaluating various physical properties in the order of ◎○@△X. ◎ means extremely good, and X means extremely poor.

As is clear from the above table, it is known that Examples 1 to 3 have the same PVC film resistance and oil resistance as Comparative Examples 1 to 3.

(Effects of the Invention) According to the present invention, heat-sensitive recording materials with excellent water resistance, plasticizer resistance, and oil resistance can be used for paper for commuter passes, coupon tickets, and labels that require long-term shelf life. It is also extremely useful as printer paper.

Claims (2)

[Claims] (1) A monomer having an acetoacetate group and acrylamide on a thermosensitive coloring layer provided on a support,
A heat-sensitive recording material characterized by having a protective layer mainly composed of a water-soluble polymer compound obtained by copolymerizing with polyvinyl alcohol and a crosslinking agent. (2) The protective layer further has an oil absorption capacity of 100ml/100g
The heat-sensitive recording material according to claim 1, which contains ultrafine silicic acid powder having an apparent specific volume of 3 ml/g or more and an average particle size of 1.5 μ or less.