JPH0781242A - Heat-sensitive recording sheet and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a negative-type OHP film in which the contrast between a transparent portion and an opaque portion is clear. [Structure] A heat-sensitive recording sheet comprising a support, on which a hydrophobic polymer emulsion as a main component, a heat-sensitive layer that becomes transparent by heating, and a protective layer made of an aqueous resin are sequentially provided, and at least melted in the heat-sensitive layer. In a heat-sensitive recording sheet containing a paraffin wax from which components having a starting temperature of 60 ° C. or less are removed, and a method for producing the heat-sensitive recording sheet, in drying the heat-sensitive layer and the protective layer,
This is a method for producing a heat-sensitive recording sheet in which the temperature of the surface of the heat-sensitive recording sheet does not exceed the minimum film-forming temperature of the hydrophobic polymer or the melting start temperature of the paraffin wax, whichever is higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording sheet suitable for thermal head recording, and in particular, an overhead projector which has a good contrast between a transparent portion and an opaque portion and has excellent visibility of a recorded image (hereinafter, referred to as The present invention relates to a heat-sensitive recording sheet which can be used as a negative type film sheet for image formation (referred to as OHP) 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. Further, there is also one in which a colorless or light-colored basic dye and a color developer are provided on a transparent support. However, for both methods,
There are advantages and disadvantages, and development of a film for forming a clear image with a simpler method is being advanced. 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, in the case of this recording medium, when recording with the thermal head recording device, the surface thereof is easily fused to the thermal head, and sticking or residue adhesion is likely to occur.

[0004]

From the actual situation as described above,
An object of the present invention is to provide a negative-type OHP film having a clear contrast between a transparent portion and an opaque portion.

[0005]

SUMMARY OF THE INVENTION The present invention comprises:
In a heat-sensitive recording sheet having a hydrophobic polymer emulsion as a main component, a heat-sensitive layer which becomes transparent when heated, and a protective layer made of an aqueous resin, which are sequentially provided, the melting start temperature is at least 60 ° C. or lower in the heat-sensitive layer. In a heat-sensitive recording sheet characterized by containing paraffin wax from which components have been removed, and a method for producing the heat-sensitive recording sheet, in drying the heat-sensitive layer and the protective layer, the temperature of the surface of the heat-sensitive recording sheet is hydrophobic. The method for producing a heat-sensitive recording sheet is characterized in that the heat-sensitive recording sheet is dried under a temperature condition which does not exceed the higher of the minimum film-forming temperature of the organic polymer and the melting start temperature of the paraffin wax.

[0006]

As described above, the present invention is a heat-sensitive recording sheet in which a hydrophobic polymer emulsion is a main component, and a heat-sensitive layer which is transparent by heating and a protective layer which is a main component of an aqueous resin are sequentially provided on a support. In the heat-sensitive recording sheet, wherein the heat-sensitive layer contains at least a melting start temperature of 60 ° C. paraffin wax, and in the production of the heat-sensitive recording sheet, in drying the heat-sensitive layer and the protective layer, The heat-sensitive recording sheet is characterized by being dried and finished under a temperature condition that does not exceed the minimum film-forming temperature of the hydrophobic polymer or the melting start temperature of the paraffin wax.

This heat-sensitive recording sheet is dried at a temperature below the minimum film-forming temperature (hereinafter referred to as MFT) of the hydrophobic polymer (emulsion), so that each particle of the hydrophobic polymer is separated. Since the particles are dried while maintaining the state of particles without being fused by heat to form a transparent film-like film, the coating layer after drying is in a turbid state (opaque). Then, when a temperature higher than the MFT of the hydrophobic polymer is applied to the opaque part, the particles in the heated part are melted and fused by heat to be transparent. The part is used as a print or an image. However, in this case, when the hydrophobic polymer emulsion is the only material that imparts opacity to the heat-sensitive layer, the heat fusion tends to be non-uniform, resulting in insufficient transparency and a projected image with poor contrast when projected with OHP. It is known that by incorporating a heat-fusible substance in the heat-sensitive layer, it is possible to obtain a heat-sensitive recording sheet in which the heat-melting is made uniform and the contrast between the opaque portion and the transparent portion is extremely good.

Specific examples of the heat-fusible substance that can be used together with the above specific paraffin wax include, 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-
Stearyl cyclohexyl amide, 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, shu 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- (2'-hydroxy-5 '
Examples thereof include compounds such as -methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone.

As a result of earnest studies, the inventors have found that a heat-sensitive recording sheet having an extremely good contrast between an opaque portion and a transparent portion can be obtained by using paraffin wax as a heat-fusible substance. However,
General paraffin wax also contains a component having a melting start temperature of 60 ° C. or lower, and is coated with a coating liquid for a heat-sensitive recording layer.
There are drawbacks that it is very difficult to control the drying temperature during drying, and the opaque part of the obtained sheet becomes transparent at a temperature of 60 ° C. or lower (hereinafter, referred to as “poor storage stability”). It was

The paraffin wax used in the present invention is a paraffin wax from which components having a melting start temperature of 60 ° C. or lower are removed, and has excellent contrast between the opaque portion and the transparent portion and a coating liquid for the heat-sensitive recording layer. The advantage is that the drying temperature during coating and drying can be easily controlled and the storability of the obtained sheet is improved. The paraffin wax from which components having a melting start temperature of 60 ° C. or less have been removed is preferably used in the range of 5 to 50% by weight based on the solid content of the heat-sensitive layer. By the way, 5% by weight
If it is less than the above, the desired effect is hardly obtained.

The heat-sensitive layer has a melting start temperature of 60.
In addition to the paraffin wax from which the component having a temperature of not higher than 0 ° C has been removed, two or more commonly known heat-fusible substances having a melting start temperature of not lower than 60 ° C may be used in combination. These heat fusible substances are preferably used in the range of 5 to 50% by weight based on the solid content of the heat sensitive layer. Incidentally, if it is less than 5% by weight, the desired effect is hardly obtained. On the other hand, when it exceeds 50% by weight, the transparent portion is likely to become cloudy over time.

The present invention is to obtain a negative type heat-sensitive recording sheet by utilizing the above characteristics. However, in consideration of practical drying conditions and temperature range of the heat-sensitive head, the hydrophobic polymer emulsion to be used is used. Is also limited to some extent. That is, the hydrophobic polymer used in the present invention has an MFT of 20 to 180 ° C., more preferably 35 to 1 ° C.
It is preferably in the range of 50 ° C. Specific examples of the hydrophobic polymer emulsion include styrene-butadiene type, vinyl acetate-ethylene-vinyl chloride type, ethylene-vinyl chloride type, vinyl chloride type, acrylic type and the like.

Further, within the range that does not impair the effects of the present invention, various auxiliary agents such as dioctyl sodium sulphosuccinate are contained in the aqueous coating liquid for heat-sensitive recording layer (hereinafter, simply referred to as coating liquid). Dispersants such as sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate / sodium salt, and fatty acid metal salts, ultraviolet absorbers such as triazoles, other defoamers, fluorescent dyes, coloring dyes, antioxidants, etc. are appropriately added. . In addition, if necessary, starches such as grain starch, pregelatinized starch, oxidized starch, etherified starch and esterified starch, proteins such as gelatin, albumin and casein, carboxymethyl cellulose, celluloses such as hydroxyethyl cellulose, agar, It is also possible to add water-soluble natural polymer compounds such as polysaccharides such as sodium alginate and gum arabic, and water-soluble synthetic polymer compounds such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, and maleic acid copolymers. it can. 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 40% by weight based on the total solids content of the recording layer, preferably 3
It is preferably adjusted to 0% by weight or less.

A transparent film is desirable for the support, and a plastic film is mainly used. Specific examples include films of polyethylene, polyester, polypropylene, polyvinyl chloride, polystyrene, nylon and the like. The coating device for coating the coating liquid on the support is not particularly limited,
For example, generally known and publicly used devices such as a bar coater, an air knife coater, a rod blade coater, a pure blade coater, and a short dwell coater are appropriately used. Of course, in the drying, as described above, the temperature at which the surface of the recording layer at the time of drying does not exceed either the melting temperature of MFT of the hydrophobic polymer compounded in the coating liquid for the recording layer or the melting temperature of paraffin wax. It is important to dry under the conditions. By the way, if the coating is dried at a temperature exceeding the above conditions, the coating film becomes transparent and the desired effect cannot be obtained. When a plastic film is used as the support, the coating efficiency can be increased by appropriately performing a pretreatment such as corona discharge or electron beam irradiation on the surface thereof.

The coating amount of the coating liquid is not particularly limited, but generally it is 1 to 30 g / dry weight.
m ² , more preferably adjusted in the range of about 1 to ²⁰ g / m ² . Further, by providing a protective layer on the heat-sensitive recording layer, it is possible to obtain a heat-sensitive recording sheet in which sticking and dust adhesion hardly occur. The adhesive component used for forming the protective layer of the present invention is a polyvinyl alcohol, a carboxyl group-modified polyvinyl alcohol, an acetoacetyl group-modified polyvinyl alcohol, a silicon-modified polyvinyl alcohol, or another modified polyvinyl alcohol. Examples of other water-soluble or water-dispersible polymer adhesive components that can be used in combination include hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and its derivatives, casein, sodium alginate, polyvinylpyrrolidone, polyacrylamide, and styrene. -Maleic acid copolymer salt, polyurethane resin, urea resin, melamine resin, polyamide resin, epichlorohydridone polyamide resin, styrene-butadiene emulsion, styrene-acrylate emulsion, acrylic It includes such synthetic polymer emulsions such as an ester-based emulsion may be used in combination these same two types or more.

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 and 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 10 to 200 parts by weight with respect to 100 parts by weight of the adhesive component. Further, in the coating liquid for forming the protective layer, if necessary, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, a surfactant such as sodium dioctylsulfosuccinate, an antifoaming agent. It is also possible to appropriately add various auxiliaries such as.

Further, a curing agent such as glyoxal, boric acid, dialdehyde starch, or an epoxy compound may be added to further improve the water resistance. The coating amount of the protective layer is adjusted to a dry weight of 0.5 to 12 g / m ² , preferably 1 to 10 g / m ² . As the coating method, the same method as the coating method of the heat-sensitive coating liquid is appropriately used. Needless to say, even when the protective layer coating liquid is dried, the surface temperature of the protective layer should be dried at a temperature which does not exceed either the MFT of the hydrophobic polymer contained in the recording layer or the melting start temperature of the paraffin wax. is important. If necessary, 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 for the purpose of improving the adhesion between the support and the recording layer, Proteins such as gelatin, albumin and casein, celluloses such as carboxymethyl cellulose and hydroxyethyl cellulose, water-soluble natural polymers such as agar, soda 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.

The coating liquid for the undercoat layer thus prepared is
Usually as a water dispersion on a support, for example a bar coater,
Air knife coater, blade coater, curtain coater
It is applied as an undercoat layer by coating with a suitable well-known conventional coating device such as a coater and drying. The coating amount is adjusted to a dry weight of 2 to 30 g / m ² , more preferably 3 to 25 g / m ² .

In addition, water-soluble to add high gloss,
An overcoat layer made of a water dispersible, electron beam curable, or ultraviolet 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 thermosensitive recording medium production can be provided. Can be used as appropriate. Of course, in this case as well, it is necessary to consider that the hydrophobic polymer and paraffin wax contained in the recording layer do not melt and become transparent due to heat. Further, the heat-sensitive recording sheet of the present invention is not limited to an OHP film. For example, when a high-quality paper of a color material is used as a support, heating is performed when a heat-sensitive recording layer (white) is provided. The part you made transparent
The color of the background appears as an image such as a pattern or a figure, and can be used as a recorded image. Therefore,
As the support according to the present invention, in addition to the transparent film and the high-quality colored paper, a printing paper, an aluminum plate, a metal vapor-deposited paper or the like can be appropriately used for the support and applied.

[0020]

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 [Formation of thermosensitive recording layer] Emulsion type paraffin wax (trade name: KW-622 / manufactured by Kyouso Chemical Co., Ltd./solid content 30%) excluding components having a melting start temperature of 64 ° C. or lower 1
0 part, vinyl chloride emulsion (trade name: Vinyl Blanc 200C / manufactured by Nissin Chemical Industry / solid content of 45% / resin MFT = 60 ° C.) 35 parts, stirred to prepare a coating liquid for the heat-sensitive recording layer . The coating liquid thus obtained has a thickness of 75 μm.
It is coated on the transparent polyethylene terephthalate film of to a dry weight of 12 g / m ² with a wire bar,
It was dried for 90 seconds with a dryer at 55 ° C. to provide a white and opaque thermosensitive recording layer.

[Formation of protective layer] A composition comprising 80 parts of a silicon-modified polyvinyl alcohol 10% aqueous solution, 5 parts of kaolin, 5 parts of a 30% aqueous dispersion of zinc stearate, and 10 parts of water is mixed and stirred to obtain. The coating liquid thus obtained was coated on the above-mentioned thermosensitive recording layer with a wire bar so that the weight after drying was 4 g / m ^2, and dried with a dryer at 55 ° C. for 120 seconds to give a white opaque thermosensitive recording sheet. Got

Example 2 In Example 1, instead of the emulsion type paraffin wax (trade name: KW-622 / manufactured by Kyowa Chemical Industry Co., Ltd.), an emulsion type paraffin wax (trade name: excluding components having a melting start temperature of 75 ° C. or lower) was used. Hydrin E-
A white and opaque thermosensitive recording sheet was obtained in the same manner as in Example 1 except that 139 / Chukyo Yushi Co., Ltd./solid content 30%) was used.

Example 3 In Example 1, a vinyl chloride emulsion (trade name:
Vinyl chloride type emulsion (product name: Vinyl Blanc 60) instead of 35 parts of Vinyl Blanc 200C / manufactured by Nissin Chemical Industry Co., Ltd.
2 / manufactured by Nisshin Chemical Co., Ltd./45% solid content / resin MFT = 130 ° C.)
A heat-sensitive recording sheet was obtained in the same manner as.

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 provide a white and opaque thermosensitive recording layer.

[Formation of Thermosensitive Recording Layer and Protective Layer] Next, a thermosensitive recording layer was formed on the above thermosensitive recording layer in the same manner as in Example 1.
A protective layer was sequentially provided to obtain a white and opaque thermosensitive recording sheet.

Comparative Example 1 Emulsion type paraffin wax (trade name: in Example 1 except components having a melting start temperature of 64 ° C. or lower) was removed.
A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that 10 parts of KW-622 / manufactured by Kyodo Chemical Co., Ltd. was excluded.

Comparative Example 2 Emulsion type paraffin wax (trade name: excluding the components having a melting start temperature of 64 ° C. or lower in Example 1)
Emulsion type paraffin wax with a melting point of 54 ° C. (trade name: Hydrin P-7 / Chukyo Yushi / 30% solid content) with a melting point of 54 ° C. instead of 10 parts
A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that 10 parts were used.

Comparative Example 3 Emulsion type paraffin wax (trade name: excluding the components having a melting start temperature of 64 ° C. or lower in Example 1)
Instead of 10 parts of KW-622 / Kyoso Chemical Co., Ltd., an aqueous dispersion of parabenzyl biphenyl (trade name: Hydrin G
-148 / Made by Chukyo Yushi, with a solid content of 30%) 1
A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that 0 part was used.

With respect to the thermal recording sheets in the seven types of Examples and Comparative Examples thus obtained, applied energies of 1.00 mj / dot and 1.50 mj were measured by a thermal recording evaluation machine (trade name TH-PMD: manufactured by Okura Electric Co., Ltd.). / Do
It was recorded at t, 2.00 mj / dot and evaluated. The haze value of the obtained transparent recorded image was measured with a haze number meter (trade name TC-H3: manufactured by Tokyo Electric Co., Ltd.). The obtained results are shown in Table 1.

[0031]

[Table 1] Each recording sheet was left under conditions of 50 ° C. DRY and 60 ° C. DRY for 15 hours, and the storability of the opaque part was evaluated. The haze value of the obtained opaque part was measured with a haze number meter (TC-H3: manufactured by Tokyo Electric Co., Ltd.). The obtained results are shown in Table 2.

[Table 2]

As is clear from the results shown in Tables 1 and 2, the heat-sensitive recording sheet of the present invention is a negative type heat-sensitive film sheet for image formation, particularly for OHP, which is excellent in the contrast between the opaque portion and the transparent portion. It was a thermal recording sheet with high utility value.

Claims (3)

[Claims] 1. A heat-sensitive recording sheet comprising a support, a heat-sensitive layer containing a hydrophobic polymer emulsion as a main component, which is transparent when heated, and a protective layer, and a melting start temperature of 60 in the heat-sensitive layer. A heat-sensitive recording sheet containing paraffin wax at a temperature of ℃ or above. 2. The heat-sensitive recording sheet according to claim 1, wherein the support is a transparent plastic film. 3. The method for producing a heat-sensitive recording sheet according to claim 1, wherein the temperature of the surface of the heat-sensitive recording sheet when the heat-sensitive layer and the protective layer are dried is the minimum film-forming temperature of the hydrophobic polymer or paraffin wax. A method for producing a heat-sensitive recording sheet, which comprises drying under a temperature condition that does not exceed the higher one of the melting start temperatures.