JPS60245590A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material enhanced in resistance to folding, water, plasticizers, solvents and oils, by a method wherein a surface protective layer comprising casein, a cross-linking agent and a styrene-butadiene latex as main constituents in provided on a thermal color forming layer. CONSTITUTION:The surface protective layer comprising casein, a cross-linking agent and a styrene-butadiene latex as main constituents is provided on the thermal color forming layer. Accordingly, a protective layer can be obtained which has favorable plasticizer resistance and oil resistance, shows excellent flexibility even after a coated film is hardened by drying, and has such a favorable adaptability that it is hardly cracked.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-sensitive recording medium. More specifically, the protective layer provided on the heat-sensitive coloring layer to prevent the heat-sensitive recording image from being discolored by organic solvents, oils, plasticizers, etc., is resistant to physical deformation during the manufacturing process and heat-sensitive recording process, such as folding and ironing. This invention relates to a heat-sensitive recording material whose performance is improved so as not to deteriorate.

(Prior Art) Paper 1 A thermosensitive recording sheet is known as a recording material in which synthetic paper, film, or the like is used as a support, and a thermosensitive coloring layer that develops color when heated is formed on the support.

A heat-sensitive recording sheet is a sheet that records images by utilizing physical and chemical changes in substances caused by heat treatment and energy, and many processes are being studied.

A heat-sensitive recording sheet that utilizes the physical change of a substance due to heat is a heat-sensitive recording sheet in which a coating layer made of metal stearate, gallic acid, etc. is provided on a support.

In addition, various coloring mechanisms have been proposed that utilize chemical changes caused by heat, and among these, a so-called two-component coloring type thermosensitive recording sheet is representative.

Two-component color-forming heat-sensitive recording sheets are made by dispersing an acid color-forming colorless leuco dye and a solid acid component such as bisphenol A (BPA) in the form of fine particles, and adding a pigment to the fine particles.

A paint mixed with an adhesive, etc. is applied onto a support, and records are obtained by utilizing the coloring reaction that occurs when one or both of the color-forming substances and color-developing substances melt and come into contact with each other when heated. It is.

Such heat-sensitive recording sheets are already used in calculators, medical measuring equipment,
It is widely used for recording purposes in facsimiles, automatic ticket vending machines, etc.

However, conventional heat-sensitive recording sheets of this type have the disadvantage of lacking storage stability in both colored and non-colored areas.

That is, when plastics such as polyvinyl chloride and polyvinylidene chloride come into contact with the surface of the heat-sensitive layer, the plasticizers and stabilizers contained in the plastics are removed.

Colored parts may fade or disappear due to additives, etc.

For example, if a polyvinyl chloride wrap film, bag, or the like is stored in direct contact with a heat-sensitive recording sheet on which recording or printing has been performed for a long period of time, the colored portion will disappear.

Uncolored areas are easily colored by organic solvents such as alcohol, toluene, and ethyl acetate, so if organic solvents are accidentally dropped during storage or exposed to organic solvent vapor, uncolored areas may become colored. The image becomes indistinguishable from the recorded image. The use of adhesives containing organic solvents also has the disadvantage that uncolored areas develop color, so their use must be avoided.

In order to improve these drawbacks, it has been patently proposed that the heat-sensitive coloring layer provided on the support be preserved with a surface layer mainly composed of a water-soluble polymer with barrier properties against organic solvents and a crosslinking agent. Publication No. 57-188392, Japanese Unexamined Patent Publication No. 57-29
This method is known from Japanese Patent No. 491 and the like.

However, this method takes advantage of the phenomenon in which a water-soluble polymer is hardened with a crosslinking agent and develops barrier properties, but on the other hand, the protective layer is hard and brittle, making it difficult for thermal recording media to pass through the recording device. 9, which was squeezed in the process of passing through the mechanism,
If the recorded matter is used after being folded for arranging purposes, fine racks are generated in the protective layer, and its function as a protective layer against organic solvents and plasticizers is significantly reduced.

(Problems to be Solved by the Invention) The present invention aims to eliminate the above-mentioned drawbacks and provide a thermosensitive recording material with improved bending resistance, water resistance, plasticizer resistance, solvent resistance, and oil resistance. .

(Means for Solving the Problems) The present invention provides a thermosensitive recording material in which a thermosensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound as main components is provided on a support. This heat-sensitive recording material is characterized in that a surface protective layer containing casein, a crosslinking agent, and styrene-butadiene latex as main components is provided on the surface of the heat-sensitive recording material.

The polymeric substance used for the surface protective layer must have excellent film-forming performance and the film must not be dissolved by organic solvents, plasticizers, etc. Furthermore, since thermosensitive recording sheets cannot be exposed to high temperatures during coating and drying of the protective layer due to their basic property of developing color due to heat, they must have sufficient film-forming performance even when drying at low temperatures.

In addition, in order to minimize the decrease in print density due to the influence of the protective layer, the amount of coating must be small, and even if the thickness of the protective layer is thin, the required performance such as water resistance, plasticizer resistance, and solvent resistance can be met. It must be satisfactory.

As a protective layer, casein, starch, modified starch.

Water-soluble polymer compounds such as polyvinyl alcohol, modified polyvinyl alcohol, acrylamide/acrylonitrile copolymers, etc., and commonly used glyoxal, polyaldehyde, and epoxy compounds to harden these and impart water resistance. It is often used in combination with other crosslinking agents.

However, when the protective layer film obtained by these combinations dries and hardens, it becomes brittle, prone to minute cracks, and easy to seep through of oils and plasticizers.

As a result of extensive research, the present inventors developed a crosslinking agent consisting of a compound containing casein and a methylol group.

By providing a surface-retaining layer on the heat-sensitive coloring layer with a combination of styrene-butadiene latex and styrene-butadiene latex, it has good plasticizer resistance and oil resistance, and the film exhibits excellent flexibility even after drying and hardening. It has been found that a protective layer with good suitability that is resistant to cracking as described above can be obtained.

You can also use paint with this composition on Meyer bars, air knives,
The coating properties were also good when applied using a coating machine such as a blade.

The styrene-butadiene latex used in the present invention can have any composition within the range of 20 to 40 butashev 1 styrene 10 to 60 weight (a) and methyl methacrylate 5 to 30 weight (4). The diameter is 2,
It is desirable that the glass transition temperature be 0OOA or less and the glass transition temperature be 20°C or less.

Examples of compounds containing a methylol group suitable for the present invention include dimethylol urea, dimethylol methylene, dimethylol melamine, dimethylol ethylene, dimethylol acetamide, dimethylol triazone, and polymethylol urea.

In the present invention, the mixing ratio of casein and the compound containing a methylol group is preferably 30 to 70 parts of the compound containing a methylol group per 100 parts of casein. Styrene
Favorable results can be obtained when butadiene latex is applied in an amount of 10 to 100 parts based on 100 parts of the total mixture.

If the amount of styrene-butadiene latex added is less than the above range, sufficient flexibility cannot be imparted to the protective layer coating, while if it is more than the above range, the oil resistance and plasticizer resistance of the protective layer will decrease. . Furthermore, the amount of styrene-butadiene latex added can be smaller if one with a low glass transition temperature is used than if one with a high glass transition temperature is used.

In the present invention, a protective layer mainly composed of casein, a compound containing a methylol group, and styrene-butadiene latex gold is provided on the heat-sensitive layer, but pigments and waxes are also added to improve compatibility with the thermal head. In addition, other polishing agents may be used in combination to improve marking properties and adhesion to printing ink. Pigments used for this purpose include calcium carbonate, clay, talc,
These include inorganic pigments such as titanium oxide, magnesium carbonate, and aluminum silicate, and organic pigments such as polystyrene particles. Mayu waxes include fatty acids such as oleic acid, fatty acid salts such as zinc stearate, and polyolefins such as halaffin wax.

Other oils such as silicone oil and whale oil can also be used.

Starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol, polyurethane, etc. may be used in combination, and in addition to these, monosaccharides such as sorbitol may also be used. Antifoaming agent if necessary.

Dispersants, leveling agents, etc. may also be used. however,
The invention is not limited to these components.

The coating amount of the protective layer is 0.21β to 92β, preferably 21β to 52β. If the amount is less than this range, coating properties will be poor and there will be problems in developing solvent resistance, and if it is more than this range, heat transfer in the thermal head will be insufficient and print density will decrease.

Coating the protective layer in two layers is effective in developing solvent resistance, and using this method is also effective.

Typical examples of the colorless or light-colored color-forming substance (electron-donating colorless dye) used in the heat-sensitive layer of the present invention are as follows, but the present invention is not limited to these typical examples.

Crystal violet lactone, malachite green lactone, 3,3-bis()dimethylaminophenyl)4,5,6,7tetra-rolfthalide, benzo β
Naphthospiropyran, 3-methyl-di-βnaphthospiropyran, 1,3,3-trimethyl-6'-chloro-8-
Methoxyindolinovage spiropyran, N-phenylrotamy 2cutam, 3-ethylamino-6-chlorofluorane, 3-morpholino-5,6-benzofluorane, 3-diethylamine-6-methyl-7-chlorofluoran , 3-diethylamino-6,7-dimethylfluorane, 3-diethylamino 7,8-benzofluorane, 3
-diethylamino-6-methoxyfluorane, 3-diethylamino-7-sibenzylaminofluorane, 3-diethylamine-7-anilinofluorane, 3-diethylamino-5,6-pendi-tupendylaminofluorane, 3-Piperidino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methy/I/-7-anilinofluorane, 3-N ether tolylamino-6-methyl-7-anilinofluorane , 3-diethylamine-7
-(N-3-)lifluoromethylphenyl)aminofluorane.

The color-developing substance (electron-accepting compound) used in the present invention is the following substance, which liquefies or vaporizes at room temperature or above, preferably 70°C or above, and reacts with the above-mentioned color-forming substance to develop color. 4,4'-isopropylidene diphenol 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'-isopropylidene bis(2-tert-butylphenol)
'-Secantarybutyldendiphenol, 4,4'-
Cyclohexylitene diphenol, 4-7dynylphenol, 4-hydroxydiphenoxide, methyl-4-
h) "roxybenzoate), 7z2/l/-4-hydroxybenzoate, 4-human tetraxyacetophenone,
Salicylic acid anilide, novolak phenolic resin, halogenated novolak phenolic resin, α-naphthol, β-naphthol, 2,2-bis-(4-hydroxyphenyl)-n-hebutane 4,4'-thiobis-(6 -t-butyl-3-methylphenol), 4,4'-butyrythenebis-(6-t-butyl-3-methylphenol), 4,4'-X) Among them, phenolic substances that generally have two or more hydroxyl groups in one molecule exhibit particularly excellent effects.Also, phenolic substances such as butyl hydroxybenzoate, benzyl hydroxybenzoate, etc. Use of benzoic acid esters,
Can also be used together.

In the present invention, a color forming substance and a color developing substance are dispersed in a binder, but in this case, the dispersed particles are specifically made into as small particles as possible using a dispersing machine such as a sand grinder. It is desirable to disperse the particles into particles of 5 μm or less. As a dispersion aid, a dispersant, a surfactant such as an antifoaming agent can be used as necessary, and in order to further prevent the coating material from adhering to a whitening agent or a thermal head,
Talc, clay, calcium carbonate, titanium oxide.

Fillers such as starch can also be added. It is also possible to add antifoaming agents to suppress foaming during coating, and surfactants to make the coating easier. Further, in order to improve color development, waxes can be pulverized or used in the form of an emulsion.

As the binder, natural polymers such as starch, synthetic polymers such as polyvinyl alcohol, etc. are used.

The coating method for both the heat-sensitive layer and the protective layer is air knife,
, <-, after coating with a roll or Frednato coater, drying is performed at a relatively low temperature.

If a smoothing treatment is performed using a supercalender or the like after forming the heat-sensitive layer and/or after applying the protective layer, good results can be obtained in the uniformity of the color image with a color density of 9.

By providing a solvent-resistant layer on the back side of the support or as an undercoat layer for the heat-sensitive layer, it is possible to suppress the penetration of organic solvents from the back side, and it is also possible to obtain products with improved storage stability. can.

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

Example 1 (1) A-wave preparation 3-(N-methyl-N-cyclohexylamino)-6-
Methyl-7-anilinofluorane 4 parts 3-diethylamino-7-orthochloroanilinofluorane 1 part hydroxyethyl cellulose 5% aqueous solution 240 A composition of this ratio was ground to an average particle size of 2 with a sand grinder.
Grind down to microns.

(21B Solution Preparation 4.4'-Isopropylidene diphenol (bisphenol A) 25 parts Stearic acid amide 15 parts hydroxyethyl cellulose 5% aqueous solution 140 parts The composition of this ratio was sand-grinded to an average particle size of 2.
Grind down to microns.

(3) Formation of coloring layer 50 parts of talc, 70 parts of aqueous dispersion, 25 parts of liquid A, 180 parts of liquid B
and 240 parts of a 5% aqueous solution of hydroxyethyl cellulose as a binder are mixed to prepare a coating liquid.

The weight of this coating after drying is 7 f/rr? The mixture was coated on 60 t/d high-quality paper using a Mayer bar to obtain a thermal recording sheet (1) before the protective layer was coated.

(4) Formation of a protective layer As a protective layer, ammonium 15% aqueous solution of casein 33
Part 3, dimethylol urea (J-001 manufactured by Showa Denko)
25 parts, styrene-butadiene latex (S-01
7,G Made by Japan Synthetic Rubber Glass transition temperature -4℃2 Particle size 14
A coating solution consisting of 20 parts of calcium stearate and 5 parts of calcium stearate was applied at a coating weight of 3 f/rd to obtain a heat-sensitive recording sheet according to the present invention.

Example 2 200 parts of a 15% aqueous ammonium solution of casein and 10 parts of dimethylol urea (J-001) were placed on the heat-sensitive recording sheet used in Example 1 before the protective layer was applied.

Styrene-fatadiene latex (T-032 made by Japan Synthetic Rubber, glass transition temperature 17℃, 9 particle size 1300 mm)
A coating liquid consisting of 50 parts of zinc stearate and 10 parts of zinc stearate was applied so that the coating cover was 42 parts thick to obtain a heat-sensitive recording sheet according to the present invention.

Example 3 30 parts of an acrylamide/acrylonitrile copolymer (Pavirol C-1013G manufactured by Showa Denko) and 200 parts of an ammonium 15% aqueous solution of casein were placed on the heat-sensitive recording sheet used in Example 1 before the protective layer was applied.

20 parts of dimethylolurea (J-001), styrene
Butadiene latex (0632 manufactured by Nippon Synthetic Rubber, glass transition temperature -12°C, particle size 1650 k) 15 parts,
A coating solution consisting of 5 parts of zinc stearate was applied in a 4-fold area to obtain a heat-sensitive recording sheet according to the present invention.

Comparative Example 1 A coating solution consisting of 400 parts of a 15% ammonium casein aqueous solution, 35 parts of dimethylol urea (J-001), and 5 parts of calcium stearate was applied on the heat-sensitive recording sheet used in Example 1 before the protective layer was applied. was applied so that the coating amount was 3tβ.

Comparative Example 2 35 parts of acrylamide/acrylonitrile copolymer (Papilol C-1013G), 233 parts of a 15% ammonium casein aqueous solution, and dimethylol urea were placed on the heat-sensitive recording sheet used in Example 1 before the protective layer was applied. 25
A coating amount of 4 parts of a coating solution consisting of 5 parts of zinc stearate and 5 parts of zinc stearate was applied.
The coating was applied in such a manner that t/rl was obtained, thereby obtaining a heat-sensitive recording sheet 1 according to the present invention.

The heat-sensitive recording materials of the above examples and comparative examples were subjected to color recording using a commercially available heat-sensitive recording device, and various tests were conducted.

Table IK summarizes the results of each example.

(Test method) Print density: After printing with a label printer JP-N manufactured by Ishida Juki, it was measured with a Bretag densitometer.

Water resistance: Commercially available barcode printer (Tokyo Electric HP -
After printing a sample with 9303), it was immersed in water at 20° C. for 24 hours, left indoors to dry, and then the degree of decolorization of the print was sensory evaluated in comparison with the initial print.

Plasticizer Resistance 2 Place PVC rubber (Mitsui Toatsu Hi-Lap) on the sample printed with the above commercially available barcode printer.
00f/r? The degree of decolorization of the print was sensory-evaluated after being left at 40° C. for 24 hours under a load of .

Oil Resistance 2 Cottonseed oil was applied to a sample printed using the above-mentioned commercially available barcode printer, and the degree of decolorization of the print was sensory evaluated after being left at 40° C. for 24 hours.

5cn1x20c at the corner of steel desk for hardening test
A test piece cut to rn (width/length) was stretched 9 times with a load of 100 t 10 times, and the water resistance, oil resistance, and plasticizer resistance of that part were measured and compared with a blank.

Note that the coating amount is the coating amount when completely dry.

(Effects of the Invention) As is clear from the above description, the heat-sensitive recording material according to the present invention has a flexible protective layer that has significantly superior oil resistance and plasticizer resistance when the recording sheet is squeezed. It is.

Patent applicant: Oji Paper Co., Ltd. Agent Masaaki Kobayashi

Claims (4)

[Claims] (1) A thermosensitive recording material comprising a support and a thermosensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound as main components on the support, in which casein, a crosslinking agent and A heat-sensitive recording material characterized by having a surface protective layer containing styrene-butadiene latex as a main component. (2) The heat-sensitive recording material according to claim (1), wherein the crosslinking agent contains a compound having a methylol group as a main component. (3) The surface protective layer further contains inorganic and/or organic pigment fine particles and waxesff:
A heat-sensitive recording material according to claim (1) or (2). (4) The heat-sensitive material according to claim (1), wherein the styrene-butadiene latex has a glass transition temperature of 20° C. or less and a weight of 50% or less of the surface protective layer component. record body.