JPH04344286A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a color-developed image with high resistance against plasti cizer and oil by adding a substatially colorless dye precursor and a chemical compound of specific structure as a color developer which chemically reacts with the dyeprecursor under heating, to a thermal color development layer. CONSTITUTION:A chemical compound containing two or more groups with a skeletal structure of 4,4'-dihydroxydiphenylsulfone(BPS) expressed by formula I is added as a color developer. This multi(BPS structure)chemical compound contains two(BPS structure)chemical compounds or three(BPS structure) chemical compounds having the second or third position of the BPS structure bonded to the second or third position of another BPS structure through a methylene group, and can contain a substituted group such as an alkyl group, a methylol group or halogen. In addition, the recommanded substantially colorless electron- donative dye precursors are 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N- isoamyl-N-ethylamino)-6-methyl-7-anilinofluoran.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heat-sensitive recording materials. More specifically, the present invention relates to a heat-sensitive recording material capable of forming colored images with excellent preservability, particularly plasticizer resistance and oil resistance.

0002

BACKGROUND OF THE INVENTION Heat-sensitive recording materials that form and record colored images by utilizing a heated color-developing reaction between at least one colorless or light-colored basic dye precursor and a color developer made of phenols, organic acids, etc. Various products have been published so far (for example, Japanese Patent Publication No. 45-14039) and have been widely put into practical use.

[0003] Such heat-sensitive recording materials have advantages such as the recording devices that use them are compact, inexpensive, and easy to maintain. machine, scientific measuring instrument, CD/
In addition to being used as a recording medium for ATMs, etc., it can also be used as a variety of printers for POS labels, CAD, CRT medical images, etc.
Widely used as a recording medium for plotters. However, color image recording formed on conventional thermosensitive recording materials has the problem that when it comes into contact with oil or plasticizer, the recording density decreases, or in severe cases, the recording disappears altogether.

For example, a pressure-sensitive adhesive (
A heat-sensitive label with an adhesive (adhesive) layer is used as a POS label.
When attached to polyvinyl chloride film, polypropylene film, etc., the plasticizer contained in the film may transfer from the back side of the label to the label, or the plasticizer may transfer from the film that is in direct contact with the label surface, causing the bars printed on the label to There was a problem that codes and characters became illegible. Additionally, even if oils such as edible oils and industrial oils come into contact with the heat-sensitive labels affixed to the film, the recorded images may disappear or become illegible, similar to the case with plasticizers. .

In order to solve these problems, attempts have been made to provide an overcoat layer on the surface of the heat-sensitive layer (for example,
-9909 Publication), but if there is a minute defect in the overcoat layer, oil or plasticizer will penetrate from that area and diffuse into the heat-sensitive coloring layer, and the entire printed area will disappear after a long period of time. This results in the problem of

[0006]

[Problems to be Solved by the Invention] The present invention provides that a colored image is
The object of the present invention is to provide a heat-sensitive recording material that exhibits extremely little decolorization even when it comes into contact with oil or plasticizer, and therefore has excellent image recording stability.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present inventors conducted research including a wide range of material searches, and as a result, we found that a thermosensitive coloring layer contains a dye precursor as well as a large number of
, 4'-dihydroxydiphenylsulfone) compound, it was discovered that the oil resistance and plasticizer resistance of colored images were significantly improved, and the present invention was completed.

The heat-sensitive recording material according to the present invention comprises a support,
A thermosensitive coloring layer formed on at least one surface of the support and containing a substantially colorless dye precursor and a color developer that reacts with the dye precursor to develop color under heating, The color developer has the following formula (I):

[Image Omitted] A poly(
It is characterized by containing a compound (4,4'-dihydroxydiphenylsulfone structure).

[0009]

[Action] Poly(4,4'-dihydroxydiphenylsulfone structure) compound used in the present invention (hereinafter referred to as poly(B)
PS structure) compound. ) is a 2 (BPS structure) compound in which the 2- or 3-position of a 4,4'-dihydroxydiphenylsulfone (BPS) structure is bonded to the 2- or 3-position of another BPS structure via a methylene group; , and 3 (BPS structure) compounds in which another BPS structure is further bonded. Also, such a multi (BPS structure)
The compound may contain a substituent such as an alkyl group, a methylol group, or a halogen atom.

According to the research results of the present inventors, 4,4'
-Thermal recording paper using dihydroxydiphenylsulfone (BPS) as a color developer compound is 2,2'-bis(P
-Compared to ordinary thermal recording paper containing hydroxyphenylpropane (BPA) as a color developer, the oil and plasticizer resistance of thermally recorded images after color development has improved somewhat, but it is still not sufficient. Alternatively, in a thermally recorded image that is colored by contact with a plasticizer, 70% or more of the color density is erased. However, the poly(BPS structure) compound used in the present invention is
This has an excellent effect in that there is almost no decoloring of the thermally recorded image. This seems to be because, although BPS also has low solubility in oil and plasticizers, the solubility of the poly (BPS structure) compound used in the present invention is even lower, and it hardly dissolves.

The poly (BPS structure) compound used in the present invention is present in the heat-sensitive coloring layer in the form of fine particles, and its content is 0.1 to 3 parts by weight per 1 part by weight of the dye precursor. The amount is preferably 1 to 2 parts by weight, and more preferably 1 to 2 parts by weight. It is also possible to use it in combination with other color developing compounds.

The substantially colorless electron-donating dye precursor used in the present invention includes, for example, 3,3-bis(P-dimethylaminophenyl)-6-dimethylaminophthalyl as a triarylmethane compound. diphenylmethane compounds such as 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5
- trichlorophenyl leuco auramine, and N-2
, 4,5-trichlorophenylleucoauramine, etc.
As xanthene compounds, rhodamine B-anilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-butylaminofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-7-dibenzylaminofluoran, Piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-anilinofluorane, 3-cyclohexyl-
methylamino-6-methyl-7-anilinofluorane,
3-diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluorane, 3-diethylamino-6-
Chloro-7-(γ-chloropropyl)aminofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, and 3-(N-isoamyl-N-ethylamino)-6-methyl-7- One type of anilinofluorane or a mixture of two or more types can be used.

Among the above dye precursors, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-(N
-isoamyl-N-ethylamino)-6-methyl-7-
Anilinofluorane has excellent whiteness and color development, and is suitable for the heat-sensitive recording material of the present invention.

These dye precursors can be used alone or in combination of two or more, and are appropriately selected and used depending on the purpose and desired properties of the heat-sensitive recording material. Generally, the dye precursor is added to the heat-sensitive coloring layer by 5 to 2% of the total weight of the dye precursor.
Contained at a content of 0%.

Examples of electron-accepting color-developing compounds that can be used in combination with the poly (BPS structure) compound in the color developer of the present invention include various phenol derivatives and aromatic carboxylic acid derivatives. To specifically illustrate this, examples of phenols include p-octylphenol, p-te
rt-butylphenol, p-phenylphenol, 2
, 2'-bis(p-hydroxyphenyl)propane, 2
, 2'-bis(p-hydroxyphenyl)pentane, 1
, 1'-bis(p-hydroxyphenyl)hexane, 2
, 2'-bis(p-hydroxyphenyl)hexane, 1
, 1'-bis(p-hydroxyphenyl)-2-ethylhexane, 2,2'-bis(4-hydroxy-3,5-
Examples include dichlorophenyl)propane, dihydroxydiphenyl ether, 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropyloxydiphenylsulfone, and bis(3-allyl-4-hydroxyphenyl)sulfone. Further, as aromatic carboxylic acid derivatives, p-hydroxybenzoic acid, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-
Di-α-methylbenzyl salicylic acid, polyvalent metal salts of the above carboxylic acids, and the like can be used. The amount of these color developing compounds used in combination is preferably 500% or less of the weight of the poly(BPS structure) compound in the heat-sensitive coloring layer.

A sensitizer can be used to improve the sensitivity of a heat-sensitive recording material, and as such a sensitizer,
For example, parabenzylbiphenyl, dibenzyl terephthalate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, di-o-chlorobenzyl adipate,
1,2-di(3-methylphenoxy)ethane, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, 1,2-bis(3,4-dimethylphenyl)ethane, etc. are appropriately selected. and can be used. These sensitizers are preferably used in an amount of 0.5 to 4 parts by weight, more preferably 1 to 2 parts by weight, per 1 part by weight of the electron-donating dye precursor.

[0017] In order to further improve the storage stability of the colored image, it is also possible to add a storage stability improver. Phenolic compounds are effective as such storage improvers, such as 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,
1,1,3-tris(2-methyl-4-hydroxy-5
-cyclohexylphenyl)butane, 1,1-bis(2
-methyl-4-hydroxy-5-t-butylphenyl)
Butane, 4,4'-(1-phenylethylidene)bisphenol, 4,4'-[1,4-phenylenebis(1-
methylethylidene)] bisphenol, and 4,4'
-[1,3-phenylenebis(1-methylethylidene)
] Bisphenol, etc. can be mentioned. In general, the preservability improver is 5 to 80% of the weight of the dye precursor.
It is added in an amount of %.

The above-mentioned components for forming a heat-sensitive coloring layer are processed into polyacrylamide, polyvinylpyrrolidone, polypinyl, etc. by various wet grinding machines such as a sand grinder, attritor, ball mill, or Kobo mill using water as a dispersion medium. A binder made of alcohol, carboxymethyl cellulose, and a water-soluble synthetic polymer compound such as styrene-maleic anhydride copolymer salt, and optionally a surfactant, etc. are pulverized and dispersed.
The obtained dispersion liquid is used as a paint for forming a heat-sensitive coloring layer.

In the present invention, other materials added to the heat-sensitive coloring layer include binders, inorganic or organic pigments, waxes, metal soaps, and, if necessary, ultraviolet absorbers.

The binder is generally water-soluble, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyacrylic. acid, starch, casein,
and gelatin are used. Furthermore, in order to impart water resistance to these binders, a water-resistant agent such as glyoxal may be added, or an aqueous emulsion of a hydrophobic resin, specifically styrene-butadiene rubber latex, acrylic resin emulsion, etc. may be added. can.

As the inorganic pigment, kaolin, calcined kaolin, talc, waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, titanium oxide, silica, aluminum silicate, barium sulfate, barium carbonate, etc. can be used. can. Further, as the organic pigment, urea, phenol, epoxy, melamine, guanamine resin, etc. can be used.

[0022] As the wax, paraffin wax,
carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides,
For example, stearamide, ethylene bisstearamide, higher fatty acid ester, etc. can be used.

As the metal soap, higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, zinc oleate, etc. can be used.

The heat-sensitive coloring layer coating is coated on one surface of the support and dried to a dry weight of 3 to 8 g/m 2 , thereby forming a heat-sensitive coloring layer.

In the heat-sensitive recording material of the present invention, a water-soluble polymeric substance such as polyvinyl alcohol, an aqueous solution of starch, etc. A protective layer formed using a latex of an insoluble polymeric substance, for example, SBR latex, or a polyethylene or polypropylene film may also be provided.

The support material used in the present invention is not particularly limited, and for example, paper, pigment-coated paper, synthetic fiber paper, synthetic resin film, etc. can be used as appropriate. Generally, a sheet-like body having a basis weight of 40 to 200 g/m2 is used.

Methods for forming the thermosensitive coloring layer on the support include known coating methods such as the air knife method, blade method, gravure method, roll coater method, spray method, dip method, bar method, and extrusion method. You may use any of the following.

In the heat-sensitive recording material of the present invention, a back layer made of starch, oxidized starch, polyvinyl alcohol, or the like may be provided for curl control. Furthermore, if necessary, various modifications may be made, such as providing an undercoat layer containing a highly oil-absorbing pigment such as calcined clay or a plastic pigment between the heat-sensitive coloring layer and the support.

[0029]

[Examples] The present invention will be explained in more detail below with reference to Examples.

Examples 1-2 and Comparative Examples 1-2 Formation of thermosensitive coloring layer ■ Preparation of dye precursor dispersion A Components
Amount (parts by weight)
3-dibutylamino-6-methyl-7-
40 Anilinofluorane 10% polyvinyl alcohol aqueous solution
40 (polymerization degree 500, saponification degree 90%) water

20

■ Preparation of color developer dispersion B Components
Amount (parts by weight)
2 (BPS structure) compound (*) 1
40 Polyvinyl alcohol 10% aqueous solution 4
0 (polymerization degree 500, saponification degree 90%)
water
20 notes (*
)1: 2 (BPS structure) compound of chemical formula (II)

[Chemical formula 3]

■ Preparation of sensitizer dispersion C Components
Amount (parts by weight)
Di-P-methylbenzyl oxalate
40 Polyvinyl alcohol 1
0% aqueous solution 40
(Polymerization degree 500, saponification degree 90%)
water
20

[0033]
Each of the above-mentioned dispersions A, B, and C was separately dispersed using a vertical sand mill (manufactured by Imex Corporation, sand grinder).

■ Preparation of pigment dispersion D Components
Amount (parts by weight)
light calcium carbonate
40 (Brilliant 15, Shiraishi Kogyo Co., Ltd.) Sodium hexametaphosphate 0.7% solution 60
This composition was dispersed using a Cowles disperser.

Furthermore, a 20% zinc stearate dispersion E and a 20% stearamide dispersion F were prepared. Further, a 10% polyvinyl alcohol aqueous solution was used as a binder.

In Example 1, using the above dispersions A to F and a binder, the weight ratio after drying was A:B:C.
:D:E:F:Polyvinyl alcohol=10:20:2
A coating liquid was prepared by blending the components in a ratio of 0:25:5:5:10.

This coating solution was applied onto one side of a 50 g/m2 high-quality paper so that the coating amount after drying was 7.5 g/m2, and dried to form a heat-sensitive coloring layer, thereby producing heat-sensitive recording paper A. Created.

In Example 2, instead of the compound of formula (II), the compound of formula (III):

Thermosensitive recording paper B was prepared using compound 3 (BPS structure) of formula 4.

In Comparative Example 1, thermal recording paper C was prepared using 4,4'-dihydroxydiphenylsulfone instead of the compound of formula (II).

In Comparative Example 2, thermal recording paper D was prepared using 2,2'-bis(p-hydroxyphenyl)propane instead of the compound of formula (II).

The four types of heat-sensitive recording papers thus obtained were smoothed using a supercalender and then subjected to the following plasticizer resistance test.

In the plasticizer resistance test, high-speed thermal facsimile: UF60 manufactured by Matsushita Electric Transmission Co., Ltd.
The image is printed using the Mitsui Toatsu Co., Ltd.
Polyvinyl chloride wrap film (trademark: KMA)
, apply a load of 500g/cm2 to it, and
After one week in an environment of 0° C. and 65% RH, the degree of decolorization of the image was visually determined. Table 1 shows the results. ◎ indicates that no decolorization was observed, and ○ indicates that some decolorization was observed, but the level was sufficiently legible.
△ indicates that the color was severely erased and it became difficult to read, and × indicates that the color was completely erased.

[Table 1]

[0043]

[Effects of the Invention] According to the present invention, a heat-sensitive recording material with excellent plasticizer resistance and oil resistance and high practicality was obtained.

Claims (1)

[Claims] Claim 1: A support; and at least one of the supports.
a thermosensitive coloring layer formed on the surface and containing a substantially colorless dye precursor and a color developer that reacts with the dye precursor under heating to develop color, the color developer comprising: The following formula (I): [Chemical formula 1]
-dihydroxydiphenylsulfone structure) A heat-sensitive recording material.