JPH0197680A - Thermosensitive recording medium - Google Patents

Abstract

PURPOSE:To provide a clear, high-density image requiring very low energy without losing sticking, head-maching or other characteristics by using at least two foaming plastic fillers of different expansion ratios. CONSTITUTION:At least two foaming plastic fillers of different expansion ratios are heated to provide a foam layer between a carrier and a thermosensitive coloring layer. In such a structure, these foaming plastic fillers of different expansion ratios fill spaces among their particles. This provides a foam layer having a uniform smooth surface. Further, the foam layer serves as a heat insulator, and the energy from a thermal head is effectively absorbed in the thermosensitive coloring layer, thereby improving heat sensitivity. The foaming plastic fillers are preferably selected so that the ratio of the minimum to the maximum expansion ratios may fall within a range of 1:1.5-20. An undercoating composed mainly of a filler and a binder may be provided between the foam layer and the thermosensitive coloring layer if the foam layer is required to have a more uniform surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having improved various properties by providing a foam layer between a support and a heat-sensitive coloring layer.

[Prior art]

It has been known for a long time that color-forming leuco dyes, which are normally colorless or light-colored, and color developers such as organic acidic substances melt and react when heated, producing color. Examples of applications of this color-forming reaction to recording paper are published in Japanese Patent Publication No. 43-4160, Publication No. 45-
It is disclosed in Japanese Patent No. 14039 and the like and is well known. These thermal recording sheets are used in a wide range of fields, including measurement recorders, computer terminal printers, facsimile machines, automatic ticket vending machines, and barcode labels.
Recently, as these recording devices have become more diversified and more sophisticated, the required quality for thermal recording sheets has also become more advanced. There is a need for a heat-sensitive recording sheet that can record clear images and has good head matching properties such as sticking and head dregs.

The color development of a heat-sensitive recording sheet is achieved by the reaction of a color-forming leuco dye and/or a color developer by being dissolved by thermal energy supplied from a thermal head.
One way to improve color development sensitivity is to add a compound (generally called a thermofusible substance) that melts at a lower temperature than the leuco dye and color developer and has a high ability to dissolve both. It is widely known, and various compounds are disclosed in the following publications.For example, JP-A-49-3484
Publication No. 2 describes nitrogen-containing compounds such as acetamide, stearamide, ditroaniline, and dinitrile phthalate.
JP-A-52-106746 discloses acetoacetic anilide, and JP-A-53-39139 discloses alkylated biphenyl alkanes.

However, in recent years, especially in the thermal facsimile field, speeds have increased, and it has become common to open the thermal head at high speed. Therefore, it has become a challenge to increase the dynamic color development sensitivity without lowering the color development start temperature. However, although the above compounds improve the static coloring sensitivity, sufficient dynamic coloring sensitivity cannot be obtained unless they are added to the thermosensitive coloring layer. There is a lot of head scum),
If sticking occurs or the melting point is too low, the storage stability (background fog) of the heat-sensitive recording sheet may be deteriorated, making it impossible to obtain fully satisfactory results.

In addition, one way to improve dynamic coloring sensitivity is to improve the surface smoothness of the thermosensitive coloring layer, or to reduce the content of components that do not participate in the coloring reaction, such as fillers and binders, in the coloring layer. 1) There is also a method of increasing the density of the coloring component. Improving the surface smoothness can be easily achieved by calendering using a super calender or the like, but this can cause the background color to develop and the surface gloss to be high, which greatly impairs the appearance of the paper as a recording paper. .

In addition, fillers such as calcium carbonate, clay, urea-formalin resin, etc. are usually added to the heat-sensitive coloring layer to maintain the whiteness of the background, to prevent adhesion of residue to the head, and to prevent sticking. A water-soluble binder is added to fix the additives and their additives to the support, but reducing the content of these binders will inevitably lead to deterioration of the quality mentioned above and cause inconveniences. However, satisfactory results cannot be obtained.

Furthermore, for the purpose of effectively utilizing the energy from the thermal head, the following publication discloses that an intermediate layer containing microscopic cavities is provided between the support and the thermosensitive coloring layer. In JP-A No. 59-5093, a layer mainly composed of micro hollow spherical particles is provided between the support and the heat-sensitive coloring layer, and in JP-A No. 59-17168,
In Publication No. 5, a layer of a foaming agent and a thermoplastic polymer that generates gas when heated is provided on a support, and a heat insulating layer is provided by generating gas. Furthermore, JP-A-59-22
No. 5987 has a layer made of foamed plastic,
Laminated undercoat layers containing fillers and binders have been proposed.

However, these materials may have insufficient foaming properties, resulting in inflexible wall materials, insufficient heat insulation, or insufficient adhesion between the thermal head and the heat-sensitive recording material. Satisfactory results have not yet been obtained.

〔the purpose〕

The object of the present invention is to provide a thermal recording medium with high dynamic color density and high sensitivity, which can record clear images with high density even with minute thermal energy without impairing other properties such as sticking or head matching properties. The purpose is to provide materials.

[Oval]

According to the present invention, in a heat-sensitive recording material in which a foam layer formed by heating and foaming a foamable plastic filler is provided between a support and a heat-sensitive coloring layer, two foaming layers having different expansion ratios as the foamable plastic filler are provided. A heat-sensitive recording material characterized by using at least one expandable plastic filler is provided.

That is, in the heat-sensitive recording material of the present invention, a foam layer formed by heating and foaming two or more types of foamable plastic fillers having different expansion ratios is provided between the support and the heat-sensitive coloring layer. With the above structure, two or more types of foamable plastic fillers with different expansion ratios fill the gaps between particles, so a foam layer with excellent surface uniformity and smoothness is formed, and the insulation of the foam layer The function as a layer is improved, and thermal energy from the thermal head is effectively absorbed by the thermosensitive coloring layer, resulting in improved thermal sensitivity.

In the present invention, a foam layer is formed by providing a layer containing two or more types of foamable plastic fillers with different expansion ratios on a support, and then heating and expanding the layer. The extent to which the expansion ratios of plastic fillers differ is usually such that the expansion ratio of the filler with the minimum expansion ratio and the filler with the maximum expansion ratio is 1:1.
5-20. Preferably, l:2 to 10 is suitable (expansion ratio is based on volume). For example, a filler with a low expansion ratio of 5 to 40 times is used, and a filler with a high expansion ratio of 40 to 10 times is used.
It is preferable to use one with a magnification of 0 times. This magnification ratio is 1=2
If it becomes too large, such as exceeding 0, the gaps between the particles of the foam filler become wider, which is not preferable.

The expandable plastic filler used in the present invention is conventionally known in this type of heat-sensitive recording material. Specifically, the expandable plastic filler used in the foam layer of the present invention is unfoamed microscopic hollow plastic particles having a thermoplastic material as a shell and containing a low boiling point solvent inside.
It foams and expands when heated. The particle diameter is 2-50 μm, preferably 2-20 μm in the unfoamed state, and 3.4-230 μm, preferably 3.4-9 μm in the foamed state.
It is 2 μm. Examples of the thermoplastic resin that forms the shell of the plastic filler include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic ester, polyacrylonitrile, polybutadiene, and copolymers thereof. Also, as a low boiling point solvent contained within the shell.

Examples include hydrocarbons such as methane, ethane, propane, and isobutane.

To form a foam layer on a support, a foam layer coating solution is prepared by dispersing the above-described foamable plastic filler in an unfoamed state together with a binder in water, and then the coating solution is applied to paper, plastic film, or synthetic paper. It may be applied to a support such as the like, and heated and foamed.

In the present invention, the binder used in forming the unfoamed foam layer is appropriately selected from conventionally known aqueous polymers and/or aqueous polymer emulsions.

Specific examples include water-soluble polymers such as polyvinyl alcohol, starch and its derivatives, cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide/acrylic Acid ester copolymer, acrylamide/acrylic ester/methacrylic acid terpolymer, styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate,
Examples include gelatin and casein. Also, as an aqueous polymer emulsion, styrene/butadiene copolymer is used.

Examples include latex such as styrene/butadiene acrylic copolymer, emulsions such as vinyl acetate resin, vinyl acetate/acrylic acid copolymer, styrene/acrylic acid ester copolymer, acrylic acid ester resin, and polyurethane resin. .

The amount of foamable plastic filler applied to the support is at least 1 as unfoamed filler for 1-1 of the support.
g, preferably about 2 to 5 g.

The amount of binder to be used may be such as to strongly bond the foam layer to the support. Usually, the amount is 5 to 50% by weight based on the total amount of the plastic filler and binder. Note that the heating and foaming temperature is a temperature at which the thermoplastic resin constituting the shell of the plastic filler is softened.

In addition, in the present invention, an undercoat layer containing a filler and a binder as main components may be provided between the foam layer and the thermosensitive coloring layer, if necessary, for the purpose of making the surface of one foam layer more uniform. Can be done.

As the filler in this case, one or more fillers commonly used in this type of heat-sensitive recording material can be appropriately selected. Specific examples include calcium carbonate, silica, zinc oxide, and titanium oxide.

Inorganic fillers such as aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, and surface-treated calcium and silica, as well as organic fillers such as urea-formalin resin, styrene/methacrylic acid copolymer, and polystyrene resin. can be mentioned.

The binder in this case is appropriately selected from the same aqueous polymers and aqueous polymer emulsions as shown in connection with the foam layer formation.

This undercoat layer has a filler coating amount of 0.2g/M
As mentioned above, the binder content is preferably about 0.5 to 1 Og/i, and the binder content in the undercoat layer is usually about 5 to 50 parts by weight.

In the present invention, on the foam layer obtained in one or more ways or optionally on the undercoat layer.

A heat-sensitive coloring layer containing a commonly used known leuco dye and a color developer as main components is provided.

The leuco dyes used in the present invention can be applied singly or in combination of two or more types, but such leuco dyes include:
Those applied to this type of heat-sensitive material can be arbitrarily applied. For example, leuco compounds of dyes such as triphenylmethane, fluoran, phenothiazine, auramine, spiropyran, and indolinophthalide are preferably used. It will be done. Specific examples of such leuco dyes include:
For example, the following can be mentioned.

3.3-bis(p-dimethylaminophenyl)-phthalide, 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone), 3.3-bis(P- dimethylaminophenyl)-6-dibutylaminophenyl.

3.3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3.3-bis(p-dibutylaminophenyl)phthalide.

3-Cyclohexylamino-6-chlorofluorane.

3-dimethylamino-5,7-dimethylfluorane, 3
-N-methyl-N-isobutyl-6-methyl-7-anilinofluorane, 3-toethyl-N-isoamyl-6-methyl-7-anilinofluorane, 3-diethylamino-7-chlorofluorane, 3- Diethylamino-7-methylfluorane, 3-diethylamino-7,8-benzfluorane, 3-diethylamino-
6-Methyl-7-chlorofluorane, 3-(N-p-tolyl-N-ditylamino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane , 2-(N-(3'-trifluoromethylphenyl)
amino)-6-dinithylaminofluorane.

2-(3,6-bis(diethylamino)-9-(o-
chloranilino)xantylbenzoic acid lactam), 3-
Diethylamino-6-methyl-7-(o-trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran.

3-dibutylamino-7-(o-chloroanilino)fluoran, 3-N-methyl-N-amylamino-6-methyl-7-
Anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane.

3-diethylamino-6-methyl-7-(2',4'-
dimethylanilino)fluoran, 3-(N,N-diethylamino)-5-methyl-7-(
N,N-dibenzylamino)fluorane, benzoylleucomethylene blue, 6'-chloro-8'-methoxy-benzoindolino-pyrylospirane, 6'-bromo-3'-methoxy-benzoindolino-pyrylosvirane.

3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3- (2'-Methoxy-51-nitrophenyl)phthalide, 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalide.

3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'
-methylphenyl)phthalide, 3-morpholino-7-(N-propyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7-( N-benzyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluorane.

3-Diethylamino-5-chlorofu-(α-phenylethylamino)fluoran.

3-(N-ethyl-p-toluidino)-7-(α-phenylethylamino)fluoran, 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7-( α-phenylethylamino)fluorane.

3-diethylamino-7-piperidinofluorane.

2-chloro-3-(N-methyltoluidino)-7-(p
-n-butylanilino)fluorane, 3-(N-methyl-N-isopropylamino)-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3.6 -bis(dimethylamino)fluorene spiro(9
゜3')-6'-dimethylaminophthalide.

3-(N-benzyl-N-cyclohexylamino)-5
, 6-penzo7-α-naphthylamino-4'-bromofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-N-ethyl-N-(2-ethoxypropyl)amino-6 -Methyl-7-anilinofluorane, 3-N-ethyl-N-tetrahydrofurfurylamino-
6-Methyl-7-anilinofluorane.

3-diethylamino-6-methyl-7-mesitidino 4
',5'-benzofluorane etc.

In addition, as the color developer used in the present invention, various electron-accepting compounds that cause the leuco dye to undergo catalytic color development are preferably used, such as phenolic compounds, thiophenolic compounds, thiourea derivatives, organic acids, and metal salts thereof. applied,
Specific examples include those shown below.

4.4'-Isopropylidene bisphenol.

4.4'-isopropylidene bis(0-methylphenol).

4.4'-Secondary-butylidenebisphenol 4.4'-Isopropylidenebis(2-tert-butylphenol), 4.4'-Cyclohexylidenediphenol.

4.4'-isopropylidene bis(2-chlorophenol), 2.2'-methylenebis(4-methyl-6-tert-butylphenol).

2.2'-methylenebis(4-ethyl-6-tert-butylphenol)-4,4'-butylidenebis(6-tert-butyl-2-methylphenol).

1.1.3-tris(2-methyl-4-hydroxy-5
-tert-butylphenyl)butane, 1.1.3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 4.4'-thiobis(6-tert-butyl-2-methylphenol), 4.4'-Diphenolsulfone, 4-isopropoxy-41-hydroxydiphenylsulfone.

4-Benzyloxy-41-hydroxydiphenylsul.

4.4'-diphenol sulfoxide, isopropyl P-hydroxybenzoate, benzyl P-hydroxybenzoate, benzyl protocatechuate, stearyl gallate.

Lauryl gallate.

Octyl gallate, 1,7-bis(4-hydroxyphenylthio)-3,5
-dioxahebutane, 1,5-bis(4-hydroxyphenylthio)-3-oxapentane.

1.3-bis(4-hydroxyphenylthio)-propane, 1.3-bis(4-hydroxyphenylthio)-2-hydroxypropane, N,N'-diphenylthiourea, N,N'-di(m -chlorophenyl)thiourea, salicylanilide, 5-chloro-salicylanilide.

2-Hydroxy-3-naphthoic acid.

2-hydroxy-1-naphthoic acid, l-Hydroxy-2-naphthoic acid.

Metal salts of hydroxynaphthoic acid such as zinc, aluminum and calcium, bis-(4-hydroxyphenyl)acetic acid methyl ester, bis-(4-hydroxyphenyl)acetic acid benzyl ester, 1,3-his(4-hydroxycumyl) Benzene, 1.
4-bis(4-hydroxycumyl)benzene, 2.4'
-diphenolsulfone, 3,3'-diallyl-4,4'-diphenolsulfone, α,α-bis(4-hydroxyphenyl)-α-methyltoluene, antipyrine complex of zinc thiocyanate, tetrabromobisphenol A.

Tetrabromobisphenol S, etc.

In the thermosensitive color forming layer of the present invention, various conventional binders can be used as appropriate in order to apply the leuco dye and color developer onto the foamed layer or optionally onto the undercoat layer. Specific examples thereof include those similar to those exemplified in the foam layer coating described above.

'Furthermore, in the present invention, in addition to the leuco dye and color developer, if necessary, auxiliary additive components commonly used in this type of heat-sensitive recording material, such as fillers, surfactants,
A thermofusible substance (or lubricant), etc. can be used in combination.

In this case 1. As the filler, the same inorganic and/or organic fillers as those exemplified as the filler used in the undercoat layer can be mentioned, and as the thermofusible substance, For example, higher fatty acids or their esters.

In addition to amides or metal salts, various waxes, condensates of aromatic carboxylic acids and amines, phenyl benzoate, higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalates, higher ketones, etc. Examples include thermofusible organic compounds having a melting point of about 50-200°C.

Furthermore, in the heat-sensitive recording material of the present invention, a protective layer can be provided on the heat-sensitive coloring layer for the purpose of improving matching properties with a thermal head etc. and further enhancing recorded image storage stability. case.

Components constituting the protective layer include the above-mentioned fillers, binders,
Surfactants and thermofusible substances can also be used.

The heat-sensitive recording material of the present invention is produced, for example, by applying a coating liquid for forming a heat-sensitive coloring layer containing the above-mentioned components onto the foam layer or, if necessary, onto the undercoat layer and drying.

〔effect〕

The heat-sensitive recording material of the present invention has the above structure, so that
Thermal energy from the thermal head can be utilized with increased efficiency for the melting reaction of the thermosensitive color layer, resulting in improved thermal sensitivity and dynamic color density of the product.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples. Note that all parts and percentages shown below are based on weight.

Example 1 A foam layer coating solution was prepared by stirring and dispersing a mixture having the following formulation using a disper.

10% polyvinyl alcohol aqueous solution 30 parts water 1
20 parts of the above foam layer coating solution is applied in an unfoamed state to the surface of commercially available high-quality paper so that the dry adhesion amount is 2.0 to 3.0 g/- and dried, and then the coated surface is heated with a heater. Closely attached to the surface of the rotary drum dryer.

It was heated and foamed for about 2 minutes at a surface temperature of 120-140°C.

A mixture having the following formulation was stirred with an agitator to prepare an undercoat layer coating solution.

40% polystyrene resin dispersion 52.5 parts 20% starch aqueous solution 17.5 parts Water 2
2.7 parts of the above undercoat layer coating solution was coated and dried on the foamed layer so that the dry adhesion amount was 4.0-5.0 g/yrr.

In addition, each mixture consisting of the following formulations was ball milled,
Liquids (A) and (B) were prepared by pulverizing and dispersing the particles in an attritor until the volume average particle diameter became 1.5 μm.

(A) Liquid composition 1 part polyvinyl alcohol aqueous solution 16 parts water

54 parts (B) Liquid composition Benzyl p-oxybenzoate 20 parts Calcium carbonate 10 parts 10% polyvinyl alcohol aqueous solution 30 parts Water
40 parts Next, the liquid (A):liquid [L] was mixed and stirred at a weight ratio of 1:4 to prepare a heat-sensitive coloring layer coating liquid.

This heat-sensitive coloring layer coating solution is coated on the support provided with the foam layer and undercoat layer so that the dry adhesion amount is 3.0 to 4.0.
After coating and drying, it is calendered to a gloss level (measured according to JIS-P-8142) of 10 to 13% using a super calender.
A heat-sensitive recording material of the present invention was prepared.

Example 2 A heat-sensitive recording material of the present invention was produced in the same manner as in Example 1 except that the undercoat layer was not provided.

Comparative Example 1 Matsumoto microspheres with a foaming ratio of 40 to 100 times were used as the expandable plastic filler in Example 1.
A comparative heat-sensitive recording material was prepared in the same manner as in Example 1, except that only F-30 was used to form the foam layer.

Comparative Example 2 A comparative heat-sensitive recording material was produced in the same manner as in Example 1, except that the foam layer was not provided.

The heat-sensitive recording material obtained as described above was printed using a thermal printing experimental device manufactured by Matsushita Electronic Components@ with a thin film head at a head power of 0.4511/dot and a recording time of 20 m5e per line.
c/Q, the scanning line density was 8 x 3.85 dots/mva, and the pulse width was 0.2, 0.4 and 0.6 sec. -106). The results are shown in Table-1.

Table 1 As can be seen from Table 1, the heat-sensitive recording material of the present invention can obtain high color density and sensitivity even with extremely small thermal energy. Further, there was no sticking in the image, and it was confirmed that the image had extremely good sticking properties.

Claims (3)

[Claims] (1) In a heat-sensitive recording material in which a foam layer formed by heating and foaming a foamable plastic filler is provided between a support and a heat-sensitive coloring layer, two or more types of foamable plastic fillers having different expansion ratios are used as the foamable plastic filler. A heat-sensitive recording material characterized by using an expandable plastic filler. (2) The heat-sensitive recording material according to claim 1, wherein an undercoat layer containing a filler and a binder is provided between the foam layer and the heat-sensitive coloring layer. (3) Claim 1 or 2, wherein two or more types of foamable plastic fillers are used as the expandable plastic filler, with a minimum and maximum expansion ratio of 1:1.5 to 20.
Heat-sensitive recording material described in Section 1.