JPH0717135A - Thermal recording sheet and production thereof - Google Patents

Abstract

PURPOSE:To obtain a negative thermal recording sheet not causing sticking or the adhesion of refuse, excellent in thermal head recording aptitude and especially clear in the contrast of a transparentized part and a non- transparentized part. CONSTITUTION:In a thermal recording material wherein a thermal layer based on hydrophobic polymer particles and transparentized by heating and a protective layer are successively provided on a support, boric acid or borate is added to the thermal layer and polyvinyl alcohol is added to the protective layer and the thermal layer is formed by drying a layer of a hydrophobic polymer emulsion at the lowest film forming temp. thereof or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative-type heat-sensitive recording sheet having particularly good contrast and excellent thermal head suitability, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as an OHP sheet, a colored powder is fixed on a film by xerography,
There are those in which unevenness is generated on the surface of the heated portion due to the shrinkage of the film, those in which bubbles are generated inside the film by heating, or those by the heat-sensitive transfer method. However, each method has advantages and disadvantages, and a simpler method and a film for forming a clear image are being developed. On the other hand, most of the conventional type is a positive type, but recently, a negative type image forming film is desired from the viewpoint of reducing eye fatigue as much as possible.

As a negative type image forming method, for example, a heat-sensitive recording medium utilizing heat fusion of polymer particles of a hydrophobic polymer emulsion (JP-A-60-44388) has been proposed. However, with this recording medium, when recording with a thermal head recording device, the surface thereof is fused to the thermal head, sticking and residue adhesion are likely to occur, and the contrast is insufficient and it is difficult to read. It was Further, when a protective layer is formed on such a heat-sensitive recording medium for the purpose of improving the thermal head recording aptitude, there is a problem that the contrast of a recorded image is lowered.

[0004]

From the actual situation as described above,
An object of the present invention is to provide a negative-type heat-sensitive recording sheet which is free from sticking and residue adhesion, has excellent thermal head recording suitability, and in particular has a clear contrast between a transparent portion and a non-transparent portion, and a method for producing the same. .

[0005]

DISCLOSURE OF THE INVENTION The present inventors have proposed a thermosensitive recording sheet comprising a support, a thermosensitive layer containing hydrophobic polymer particles as a main component, which is transparent by heating, and a protective layer, which are successively provided on a support. The heat-sensitive layer contains boric acid or borate, and the protective layer contains polyvinyl alcohol, and the heat-sensitive layer is formed by drying the hydrophobic polymer emulsion at a temperature not higher than the minimum film-forming temperature in the production method thereof. As a result, they have found that the above objects can be achieved, and have completed the present invention.

[0006]

As described above, in the heat-sensitive recording sheet in which the heat-sensitive layer containing hydrophobic polymer particles as a main component, which becomes transparent by heating, and the protective layer having polyvinyl alcohol are sequentially provided on the support, the heat-sensitive layer is formed in the heat-sensitive layer. In the method for producing the same, boric acid or borate is contained, and in the method for producing the same, the heat-sensitive layer has a minimum film-forming temperature of the hydrophobic polymer emulsion (hereinafter referred to as MFT).
It is characterized in that it is formed by drying under a temperature condition not exceeding the above.

When boric acid or borate is contained in the heat-sensitive layer, when forming the protective layer, the polyvinyl alcohol in the protective layer undergoes gelation reaction with boric acid or borate so that the opacity of the heat-sensitive layer and the protective layer is reduced. As a result, a thermosensitive recording sheet having a clearer contrast between the recording portion and the non-recording portion can be obtained. Specific examples of the borate added to the heat-sensitive layer include potassium borate, sodium borate, ammonium borate and the like. The amount of boric acid or borate added is preferably in the range of 0.1 to 30% by weight, preferably 3 to 10% by weight, based on the total solid content of the heat-sensitive layer.

Specific examples of the hydrophobic polymer particles contained in the heat-sensitive layer which becomes transparent by heating include MFT of 30 to 18
The temperature is preferably 0 ° C., more preferably in the range of 45 to 150 ° C., and examples thereof include styrene-butadiene type, vinyl acetate-ethylene-vinyl chloride type, ethylene-vinyl chloride type, vinyl chloride type, and acrylic type. The heat-sensitive layer is formed by applying a coating solution containing a hydrophobic polymer emulsion as a main component on a support and drying the coating solution.
By drying at a temperature below the minimum film-forming temperature of the hydrophobic polymer emulsion, each particle of the hydrophobic polymer is dried without fusing and forming a transparent film-like film. The heat-sensitive layer of is in a cloudy state (opaque).

Further, a heat-fusible substance may be used in the heat-sensitive layer in order to increase the transparency of the recorded image. As the heat-fusible substance, a substance having a melting point of 50 to 150 ° C. that is solid at room temperature and melts by heating with a thermal head is preferable, and specifically, for example, caproic acid amide, capric acid amide,
Palmitic acid amide, stearic acid amide, oleic acid amide, erucic acid amide, linoleic acid amide, linolenic acid amide, N-methylstearic acid amide, stearic acid anilide, N-methyloleic acid amide, benzanilide, linoleic acid anilide, N- Ethylcapric acid amide, N-butyllauric acid amide, N-octadecylacetamide, N-oleinacetamide, N-oleylbenzamide, N-stearylcyclohexylamide, polyethylene glycol, 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 1- Hydroxynaphthoic acid phenyl ester, 1,2-diphenoxyethane, 1,4-diphenoxybutane, 1,2-bis (3-methylphenoxy) ethane, 1,2-bis (4-
Methoxyphenoxy) ethane, 1-phenoxy-2-
(4-chlorophenoxy) ethane, 1-phenoxy-2
-(4-Methoxyphenoxy) ethane, terephthalic acid dibenzyl ester, oxalic acid dibenzyl ester, oxalic acid di (4-methylbenzyl) ester, p-benzyloxybenzoic acid benzyl ester, p-benzylbiphenyl, 1,5- Bis (p-methoxyphenoxy) -3-
Oxapentane, 1,4-bis (2-vinyloxyethoxy) benzene, p-biphenyl-p-tolyl ether, benzyl-p-methylthiophenyl ether, 2-
Compounds such as (2′-hydroxy-5′-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, paraffin wax, polyethylene wax, carnauba wax, microcrystalline wax, candelia wax, montan wax, etc. Can be mentioned. Of course, it is possible to use two or more kinds of these heat-fusible substances together if necessary. In addition, these heat-fusible substances are 5 to the solid content of the heat-sensitive layer.
It is preferably used in the range of 50% by weight. By the way, 5
If it is less than wt%, the desired effect is hardly obtained. On the other hand, if it exceeds 50% by weight, the heat-transparent part tends to become cloudy over time.

Further, within the range that does not impair the effects of the present invention, various auxiliary agents such as dioctyl sodium sulfosuccinate and dodecyl are contained in the aqueous coating solution for heat-sensitive layer (hereinafter, simply referred to as coating solution). Dispersants such as sodium benzene sulfonate, sodium lauryl alcohol sulfate / sodium salt, and fatty acid metal salts, ultraviolet absorbers such as triazoles, other defoaming agents, fluorescent dyes, coloring dyes, antioxidants and the like are appropriately added.

If necessary, grain starch, pregelatinized starch,
Oxidized starch, etherified starch, esterified starch and other starches, gelatin, albumin, casein and other proteins, carboxymethyl cellulose, hydroxyethyl cellulose and other celluloses, agar, sodium alginate,
It is also possible to add water-soluble natural polymer compounds such as polysaccharides such as gum arabic, and water-soluble synthetic polymer compounds such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide and maleic acid copolymers. The addition of the above materials to the coating liquid is appropriately adjusted within a range that does not impair the desired effects of the present invention. Generally, it is preferably adjusted to 40% by weight, preferably 30% by weight or less, based on the total solid content of the recording layer.

The polyvinyl alcohol used for forming the protective layer of the present invention includes completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. Examples include modified polyvinyl alcohol. Other water-soluble or water-dispersible polymers that can be used in combination are, for example, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and its derivatives, casein, sodium alginate, polyvinylpyrrolidone, and polyacrylamide as long as the effects of the present invention are not impaired. ,
Styrene / maleic acid copolymer salt, polyurethane resin,
Examples include synthetic polymer emulsions such as urea resin, melamine resin, polyamide resin, epichlorohydridone-modified polyamide resin, styrene / butadiene emulsion, styrene / acrylic ester emulsion, and acrylic ester emulsion.

A pigment may be added to the protective layer, and specific examples thereof include calcium carbonate, zinc oxide,
Inorganic pigments such as aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined kaolin, calcined clay, colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea Examples include formalin resin fillers and organic pigments such as raw starch particles. It is generally desirable to adjust the amount used in the range of about 20 to 500 parts by weight with respect to 100 parts by weight of the polymer compound.

Furthermore, in the coating liquid for forming the protective layer, zinc stearate, calcium stearate,
Lubricants such as polyethylene wax, carnauba wax, paraffin wax and ester wax, surfactants such as sodium dioctyl sulfosuccinate, and various auxiliaries such as defoaming agents can be appropriately added. Further, a curing agent such as glyoxal, boric acid, dialdehyde starch, or an epoxy compound can be added to further improve the water resistance.

In the present invention, the shapes of the heat-sensitive layer and the protective layer are
The method of composition is not particularly limited, but
Bar coater, air knife coater, rod breaker
Do coater, pure blade coater, short dwell
Coating and protection for heat sensitive layer by coating equipment such as le coater
It is formed by coating and drying a layer coating liquid on a support. Heat sensitivity
The coating amount of the layer coating liquid is 1 to 20 g / m on a dry weight basis.², Preferred
3-10 g / m ²Adjusted in the range of. Also,
The coating amount of the protective layer coating liquid is 1 to 10 g / m on a dry weight basis.², Good
More preferably 1 to 6 g / m²Adjusted in the range of. Of course, dry
As mentioned above, the surface of the recording layer during drying
The temperature is M of the hydrophobic polymer compounded in the coating liquid for the recording layer.
Temperature below FT and below the melting temperature of the heat-fusible substance
It is important to dry under moderate conditions. Heat sensitive layer and protection
The coating amount of the layer may be MFT and / or melting temperature.
Drying at a temperature above the temperature will make the coating transparent and achieve the desired effect.
Can't get

Examples of the support include paper, synthetic paper, non-woven fabric, transparent paper, transparent plastic film and the like, and transparent films such as polyethylene, polypropylene, polyvinyl chloride, polyester and nylon are preferable. In addition,
When a plastic film is used as the support, the coating efficiency can be increased by appropriately subjecting the surface thereof to pretreatment such as corona discharge and electron beam irradiation.

If desired, an undercoat layer containing a synthetic resin as a main component may be provided on the support. Examples of the synthetic resin as the main component of the undercoat layer include homopolymers of polyvinyl acetate, polypropion vinyl acetate, etc., styrene-butadiene, vinyl acetate-ethylene, vinyl acetate-ethylene-vinyl chloride, vinyl acetate-ethylene-acryl. , Styrene-acrylic, styrene-acrylic, vinyl chloride-based or acrylic-based copolymers. Among these, it is particularly preferable to use a resin having a glass transition point of 0 to 50 ° C. The undercoat layer contains a pigment such as calcium carbonate or kaolin for preventing blocking, and starches such as oxidized starch, etherified starch, esterified starch, gelatin for the purpose of improving the adhesion between the support and the recording layer, gelatin, Proteins such as albumin and casein, celluloses such as carboxymethyl cellulose and hydroxyethyl cellulose, and water-soluble natural polymers such as agar, sodium alginate, and gum arabic can also be blended. The addition of these materials is preferably 60% by weight or less, and more preferably 50% by weight or less, based on the solid content of the undercoat layer.

In addition, water-soluble in order to add high gloss,
An overcoat layer made of a water dispersible, electron beam curable or UV curable resin or the like can be provided, and a protective layer can be provided on the back surface of the support, and various known techniques in the field of heat-sensitive recording sheet production can be provided. Can be used as appropriate. In addition, when a high-quality colored paper is used as a support, when a heat-sensitive layer (white) is provided, the heated part becomes transparent, and the background color appears as an image such as a pattern or figure. And can be used as a recorded image.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
Unless otherwise specified, parts and% in the examples mean parts by weight and% by weight, respectively.

Example 1 [Preparation of solution A] 1,2-bis (3-methylphenoxy) ethane (melting temperature = 98 ° C.) 10 parts 5% aqueous solution of methylcellulose 10 parts water 15 parts Sandwiching the above composition Average particle size is 2μ with a grinder
The solution was pulverized to m.

[Formation of heat-sensitive layer] 10 parts of liquid A, 45% aqueous dispersion of vinyl chloride emulsion (trade name: VINYBRAN 200C / manufactured by Nissin Chemical Industry Co., Ltd.) (resin MFT = 60 ° C.)
35 parts and 2 parts of boric acid were mixed and stirred to obtain a heat-sensitive layer coating liquid. The coating solution thus obtained was coated on a 75 μm thick corona discharge-treated transparent polyethylene terephthalate film with a wire bar so that the dry weight was 12 g / m ^2, and dried for 90 seconds with a dryer at 45 ° C. to give a white color. An opaque heat sensitive layer was provided.

[Formation of protective layer] Silicon-modified polyvinyl alcohol 10% aqueous solution 80 parts Kaolin 5 parts Zinc stearate 30% emulsion liquid 5 parts Water 10 parts The coating solution obtained by mixing and stirring the above composition It was coated on the heat-sensitive layer with a wire bar so that the weight after drying was 4 g / m ^2, and dried with a dryer at 45 ° C. for 120 seconds to obtain a white opaque heat-sensitive recording sheet.

Example 2 A white opaque thermosensitive recording sheet was prepared in the same manner as in Example 1 except that emulsion type paraffin wax (trade name: Hydrin P-7 / produced by Chukyo Yushi Co., Ltd.) was used in place of the liquid A. Got

Example 3 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the solution A was not used.

Example 4 [Formation of Undercoat Layer] 50% aqueous dispersion of vinyl acetate-ethylene copolymer (glass transition point: 15 g / m ² on dry weight) on a transparent polyethylene terephthalate film having a thickness of 75 μm. 15 ℃) is applied with a wire bar, and 7
It was dried with a dryer at 0 ° C. for 90 seconds to form an undercoat layer.

[Formation of Heat-Sensitive Layer and Protective Layer] Next, a heat-sensitive layer and a protective layer were sequentially provided on the undercoat layer in the same manner as in Example 1 to obtain a white opaque heat-sensitive recording sheet.

Comparative Examples 1 to 3 Thermal recording sheets were obtained in the same manner as in Examples 1 to 3 except that boric acid was not used (Comparative Examples 1 and 2, respectively). Comparative Example 3).

With respect to the heat-sensitive recording sheets in the seven kinds of Examples and Comparative Examples thus obtained, applied energy of 1.0 mj / dot, 1.5 mj was measured by a heat-sensitive recording evaluation machine (trade name TH-PMD: manufactured by Okura Electric Co., Ltd.). / Dot,
It was recorded at 2.0 mj / dot and evaluated. The haze value of the obtained transparent recorded image was measured by a measuring device (trade name TC-H3: manufactured by Tokyo Electric Co., Ltd.), and the obtained results are shown in Table 1.

[0029]

[Table 1]

[0030]

As is clear from the results of Table 1, the heat-sensitive recording sheet of the present invention was a negative type heat-sensitive recording sheet excellent in the contrast between the background portion and the recording portion.

Claims (3)

[Claims] 1. A heat-sensitive recording sheet comprising a support, a heat-sensitive layer comprising hydrophobic polymer particles as a main component, which is transparent when heated, and a protective layer, which are sequentially provided with boric acid or borate. And a polyvinyl alcohol is contained in the protective layer. 2. The heat-sensitive recording sheet according to claim 1, wherein the support is a transparent plastic film. 3. A method for producing a heat-sensitive recording sheet, wherein the heat-sensitive layer of the heat-sensitive recording sheet according to claim 1 is formed by drying at a temperature not higher than the minimum film-forming temperature of the hydrophobic polymer emulsion.