JPH07179056A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve whiteness, light fastness and water resistance by laminating a first thermal color forming layer containing a specific leuco dye and a coupler and a second thermal color forming layer containing a separate specific leuco dye and a coupler on a support. CONSTITUTION:A thermal recording material is formed by laminating a first thermal color forming layer based on a leuco dye represented by formula I (wherein R<1> and R<2> are an alkyl group) and a coupler represented by formula II and a second thermal color forming layer based on a leuco dye represented by formula III (wherein R<1> and R<2> are an alkyl group) and the coupler represented by the formula II on a support. If necessary, a filler, a dispersant or a developed color image stabilizer can be added along with the leuco dyes and the coupler. The obtained thermal recording material can be utilized as a reading recording material for an optical character reader or a bar code reader by utilizing its especially excellent near infrared absorbing characteristics.

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 material using a leuco dye as a color former, and more particularly to a heat-sensitive recording material having a characteristic of absorbing a wavelength in the near infrared region.

[0002]

2. Description of the Related Art Recording materials using leuco dyes have been known for a long time and are used as heat-sensitive recording papers, and the amount thereof is increasing year by year. The leuco heat-sensitive recording material is a leuco dye and a color developer supported on a support, and gives a colored image when an image signal is thermally applied by a minute heat-generating resistor element. Such a heat-sensitive recording material can be recorded in a relatively simple device in a short time without performing complicated processing such as development and fixing as compared with other recording materials such as electrophotography and electrostatic recording material. It has the advantages that it can be obtained, its maintenance is easy, and that it does not generate noise, and it is used only for so-called output recording, such as facsimiles, printers, industrial measuring recorders, computer terminals, etc. Instead, it is widely used for price labels used for food labels and the like, as well as industrial labels used for managing parts and products due to bar code compatibility.

Recently, as a bar code reader,
Those using semiconductor lasers that are inexpensive, have excellent durability, and are easy to maintain have been used. However, the wavelength of the semiconductor laser is a so-called near-infrared portion such as 780 nm or 900 nm, which is different from the wavelength of visible light used so far. Therefore, in order to deal with this, it is necessary for the heat-sensitive recording material to sufficiently absorb the near-infrared portion in the color-developed portion thereof to produce a clear contrast with the reflection by the background portion.

Conventionally, several proposals have been made for leuco dyes having a property of absorbing electromagnetic waves having wavelengths ranging from the long-wavelength portion of visible light to the near-infrared portion. For example, Japanese Patent Laid-Open No. 62-243653 discloses: Specific divinyl compound used in the present invention [compound represented by the general formula (I) described below]
Is disclosed. This compound has a light color and develops color and has a tentative absorption in the range of 700 nm to 1,000 nm. In particular, it exhibits strong absorption near 900 nm, and produces a clear contrast with the reflection by the background portion. Further, JP-A-2-139276 discloses a compound represented by the following general formula (IV). However, the compound represented by the general formula (I) described below generally has a low melting point,
Further, the compound represented by the following general formula (III) used for the purpose of further blackening the color tone is used in combination with a leuco dye that is generally used in heat-sensitive recording materials,
Large background color (low whiteness) under high temperature and high humidity
However, it has poor storage properties such as water resistance and light resistance.

[0005]

That is, a heat-sensitive recording material having absorption characteristics in the near-infrared region which is required for industrial label use generally has low background whiteness and storage stability such as water resistance and light resistance. Is not good. This is considered to be a potential problem of the combination of a leuco dye having near infrared absorption and a color developer.

Therefore, the present invention has been made in view of the above-mentioned conventional circumstances, has absorption in the visible to near-infrared region readable even by using a semiconductor laser, and has whiteness, light resistance, and water resistance. It is an object of the present invention to provide a thermosensitive recording material having excellent storage stability such as properties.

[0007]

According to the present invention, there is provided a thermosensitive recording material comprising a support and at least two thermosensitive coloring layers containing a leuco dye and a color developer as main components.
At least one compound represented by the following general formula (I) is used as a leuco dye in the heat-sensitive color forming layer, and a compound represented by the following formula (II) is contained as a developer, and a leuco dye represented by the following general formula (III) There is provided a heat-sensitive recording material comprising a second heat-sensitive color forming layer containing at least one compound represented by

[Chemical 1] (In the formula, R ¹ and R ² represent an alkyl group.)

[Chemical 2]

[Chemical 3] (In the formula, R ¹ and R ² represent an alkyl group.)

Further, according to the present invention, there is provided a thermosensitive recording material characterized in that a protective layer containing aluminum hydroxide is laminated on the second thermosensitive coloring layer.

Further, according to the present invention, there is provided a thermosensitive recording material characterized in that the first thermosensitive coloring layer further contains a compound represented by the following general formula (IV) as a leuco dye.

[Chemical 4]

That is, the heat-sensitive recording material of the present invention is provided with at least two heat-sensitive color-forming layers containing a leuco dye and a color developer as main components, and the first heat-sensitive color-forming layer is a leuco dye represented by the general formula (I). A second heat-sensitive compound containing at least one compound represented by the formula (II) as a color developer and at least one compound represented by the general formula (III) as a leuco dye. Since the coloring layer is laminated, the image can be sufficiently read by an image reading device using a semiconductor laser as a light source, and storage stability, that is, whiteness of the background, light resistance and water resistance of the image area. Will be excellent. In addition, a protective layer containing aluminum hydroxide is further laminated on the second thermosensitive coloring layer, and the first thermosensitive coloring layer further contains a compound represented by the general formula (IV) as a leuco dye. Thereby, the storage stability, especially the light resistance of the image area, is further improved.

The present invention will be described in detail below. In general, a heat-sensitive recording material having an absorption characteristic in the near infrared region has a low whiteness and is not so good in the background fog prevention property, the water resistance and the light resistance. It is considered that this is because the near-infrared absorbing dye itself is a pale yellow color and that the melting point is lowered by the combination with the color developer. Further, it is considered that the water resistance and the light resistance are inferior due to the physical properties of the dye itself. In the present invention, the thermosensitive coloring layer mainly containing a leuco dye and a color developer is divided into two layers, and the first thermosensitive coloring layer (lower layer) is represented by the general formula (I) as a leuco dye. The compound [preferably the compound represented by the general formula (IV) is also used], the compound represented by the formula (II) having high water resistance and high light resistance is selected as a developer, and the second thermosensitive coloring layer is used. By using the compound represented by the general formula (III) as a leuco dye, the above-mentioned point is solved. Furthermore, in the present invention, a protective layer is provided on the second thermosensitive coloring layer to aim at the light shielding effect, and aluminum hydroxide is contained in the protective layer to enhance the shielding effect, whereby the storage stability is further improved. It will be improved.

Next, the substance used in the present invention will be specifically described, but the substance is not limited thereto. Compound represented by general formula (I) 3,3-bis [2- (4-dimethylaminophenyl)-
2- (4-methoxyphenyl) vinyl] -4,5,6
7-tetrachlorophthalide, 3,3-bis [2- (4-
Diethylaminophenyl) -2- (4-ethoxyphenyl) vinyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [2- (4-dimethylaminophenyl) -2- (4-ethoxy) (Phenyl) vinyl] -4,
5,6,7-Tetrachlorophthalide, 3,3-bis [2
-(4-Diethylaminophenyl) -2- (4-methoxyphenyl) vinyl] -4,5,6,7-tetrachlorophthalide and the like.

A compound represented by the general formula (III): 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-P-toluidino) -6-methyl-7-anilinofluorane, 3-diethylamino-6
-Methyl-7- (ortho, para-dimethylanilino) arolane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-ani Rinofluorane, 3-diethylamino-7- (ortho-chloroanilino) fluorane, 3-diethylamino-7- (meta-trifluoromethylanilino) fluorane, 3-diethylamino-6
-Methyl-chlorofluorane, 3-diethylamino-6
-Methyl-fluorane, 3- (N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluorine,
3-dibutylamino-6-methyl-7-anilinofluorane, 3-diamylamino-6-methyl-7-anilinofluorane and the like.

The compound of the general formula (IV) 1,5-bis- (4-dimethylaminophenyl) -3-
(4-Methylphenylsulfonyl) -1,4-pentadiene, 1,5-bis- (4-diethylaminophenyl)
-3- (4-ethylphenylsulfonyl) -1,4-pentadiene, 1,5-bis- (4-dimethylaminophenyl) -3- (4-ethylphenylsulfonyl) -1,
4-pentadiene, 1,5-bis- (4-diethylaminophenyl) -3- (4-methylphenylsulfonyl)
-1,4-pentadiene and the like.

As the color developer used in the second thermosensitive coloring layer, various electron-accepting compounds that cause the leuco dye to develop color upon contact are applied. Various failing substances, fatty acids, aromatic carboxylic acids, etc. Is mentioned. The following compounds are used as specific examples.

Gallic acid, salicylic acid, 1-hydroxy-
2-naphthoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, 2-hydroxy-p-toluic acid, 3,
5-xylenol, thymol, p-tert-butylphenol, 4-hydroxyphenoxide, methyl-4-
Hydroxybenzoate, 4-hydroxyacetophenone, α-naphthol, β-naphthol, catechol, resorcin, hydroquinone, 4-tert-octylcatechol, 4,4′-sec-butylidenephenol,
2,2'-dihydroxydiphenyl, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-bis (4'-hydroxyphenyl) propane (alias; bisphenol A), 4,4 '-Isopropylidene-bis (2-tert-butylphenol), pyrogallol, phloroglucin, phloroglucincarboxylic acid, p-methylphenol, p-tert-butylphenol, p-phenylphenol, 4,4'
-Cyclohexylidene diphenol, 4,4 '-(1-
Methyl-n-hexylidene) diphenol, 4,4'-
Isopropylidene dicatechol, 4,4'-benzylidene diphenol, 4,4-isopropylidene bis (2-
Chlorophenol), 3-phenylsalicylic acid, 3,5
-Di-tert-butyl salicylic acid, 1-oxy-2
-Naphthoic acid, gallic acid ester, salicylic acid ester, p-hydroxybenzoic acid ester, 4-hydroxyphthalic acid ester.

In order to obtain the heat-sensitive recording material of the present invention, a leuco dye, a color developer and an auxiliary component described below may be bound and supported on a support. As the binder in this case, various conventional binders can be appropriately used. Specific examples of such a binder include the followings.

Polyvinyl alcohol, starch and its derivatives, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose,
Cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / Maleic anhydride copolymer alkali salt, polyacrylamide,
In addition to water-soluble polymers such as sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, polyacrylic acid ester, polymethacrylic acid ester, vinyl chloride /
Emulsion of vinyl acetate copolymer, ethylene / vinyl acetate copolymer, etc., latex such as styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, etc.

Further, in the present invention, together with the above leuco dye and developer, if necessary, auxiliary additives commonly used in this type of heat-sensitive recording material, such as a filler and a dispersant,
Colored image stabilizer, antioxidant, antifoaming agent, light stabilizer,
A fluorescent whitening agent, a surfactant, a heat-fusible substance (or a lubricant), etc. may be contained. In this case, as the filler, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powder such as surface-treated calcium or silica, etc. , Urea-formalin resin, styrene / methacrylic acid copolymer, polystyrene resin, and other organic fine powders.

Examples of the heat-fusible substance include fatty acids such as stearic acid and behenic acid; fatty acid amides such as stearic acid amide and palmitic acid amide; zinc stearate, aluminum stearate, calcium stearate and palmitin. Fatty acid metals such as zinc acidate and zinc behenate; p-benzylbiphenyl, terphenyl; triphenylmethane, benzyl p-benzyloxybenzoate, β-benzyloxynaphthalene, β-naphthoic acid phenyl ester, 1-hydroxy-2 -Naphthoic acid phenyl ester, 1-hydroxy-2-naphthoic acid methyl ester, diphenyl carbonate, terephthalic acid dibenzyl ester, terephthalic acid dimethyl ester, 1,
4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dibenzyloxynaphthalene, 1,2-
Bis (phenoxy) ethane, 1,2-bis (3-methylphenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane, 1,4-bis (phenoxy) butane,
1,4-bis (phenoxy) -2-butene, dibenzoylmethane, 1,4-bis (phenylthio) butane, 1,
4-bis (phenylthio) butene, 1,3-bis (2-
Vinyloxyethoxy) benzene, 1,4-bis (2-
Vinyloxyethoxy) benzene, p- (2-vinyloxyethoxy) biphenyl, p-aryloxybiphenyl, p-propargyloxybiphenyl, dibenzoyloxymethane, 1,3-dibenzoyloxypropane,
Dibenzyl disulfide, 1,1-diphenyl ethanol, 1,1-diphenyl propanol, p- (benzyloxy) benzyl alcohol, 1,3-diphenoxy-
2-propanol, N-octadecylcarbamoyl-p
-Methoxycarbonylbenzene, N-octadecylcarbamoylbenzene and the like can be mentioned.

Further, in the heat-sensitive recording material of the present invention, a protective layer may be provided on the heat-sensitive recording layer for the purpose of improving matching property of a thermal head or the like and further improving storability of recorded image. preferable. In this case, as the resin constituting the protective layer, the same resins as those exemplified as the binder in relation to the thermosensitive color developing layer can be mentioned. In addition to the above resins, auxiliary additives that have been conventionally used, such as fillers (fillers), surfactants, heat-fusible substances (or lubricants), etc., can be used in combination in the protective layer. In this case, specific examples of the filler include the same as those exemplified in connection with the thermosensitive coloring layer, but from the viewpoint of the effect of enhancing the light shielding effect as described above, aluminum hydroxide is used. Is particularly preferred.

In the first thermosensitive coloring layer, the amount of the compound represented by the general formula (II) added to the compound represented by the general formula (I) is 100 to 2,000% by weight. The amount of the color developer added to the compound represented by the general formula (III) in the second thermosensitive coloring layer is preferably 100 to 1,000% by weight. When a protective layer is further provided and aluminum hydroxide is added to the protective layer, 10 to 1 is added to the resin component in the protective layer.
00 wt% is preferred.

Although paper is mainly used as a support for the heat-sensitive recording material of the present invention, various non-woven fabrics, plastic films, synthetic papers, metal foils, or composite sheets obtained by combining these are arbitrarily used. be able to.

The heat-sensitive recording material of the present invention is used in various fields like the conventional ones, and in particular, by utilizing its excellent near-infrared light absorption property, it can be used for optical character readers, It can be used as a recording material for reading the record of a barcode reader.

[0025]

EXAMPLES The constitution and effects of the present invention will now be described in more detail with reference to examples. However, the present invention is not limited to these. In addition, the parts and% shown below
Are based on weight.

Example 1 [Solution A], [Solution B], [Solution C], [Solution D] and [Solution E] having the following compositions were dispersed using a sand grinder, and the average exhaust diameter was 1.0 μm or less. A dispersion was obtained. [Liquid A] 3,3-bis [2- (4-dimethylaminophenyl) -2- (4-methoxyphenyl) vinyl] -4,5,6,7-tetrachlorophthalide 20 parts 10% aqueous polyvinyl alcohol solution 20 parts Water 60 parts [B liquid] 4,4-thiobis- (3-methyl-6-t-butylphenol) 20 parts 10% polyvinyl alcohol aqueous solution 20 parts Water 60 parts [C liquid] 3-dibutylamino-6-methyl -7-anilinofluoran 20 parts 10% aqueous polyvinyl alcohol solution 20 parts water 60 parts [Solution D] 4,4'-thiobis- (3-methyl-6-t-butylphenol) 20 parts 10% aqueous polyvinyl alcohol solution 20 parts Water 60 parts [Liquid E] Silica 20 parts 10% polyvinyl alcohol aqueous solution 20 parts Water 60 parts

Next, a heat-sensitive coating liquid and a protective layer coating liquid having the following compositions were prepared. [Heat-sensitive coating liquid 1] [A liquid] 10 parts [B liquid] 50 parts [Heat-sensitive coating liquid 2] [C liquid] 10 parts [D liquid] 50 parts Water 6 parts [Overcoat liquid] [E liquid] 10 parts 10% aqueous solution of polyvinyl alcohol 10 parts 20% aqueous solution of polyamide epichloroylhydrin 5 parts water 20 parts Adjusted heat-sensitive coating solution 1 is applied to a woodfree paper having a basis weight of 47 g / m ^{2 so} that the dry coating amount is 4 g / m ^2.・ Dry, then apply the heat-sensitive coating liquid 2 on it so that the dry coating amount becomes 2 g / m ² , and finally dry the overcoat liquid on it so that the dry coating amount becomes 3 g / m ² . After coating and drying as described above, a thermosensitive recording paper of the present invention was obtained.

Example 2 A thermosensitive recording paper of the present invention was obtained in the same manner as in Example 1 except that aluminum hydroxide was used instead of silica in [E-liquid].

Example 3 3-dibutylamino-6 in [C liquid] in Example 1
-Methyl-7-anilinofluorane was added to 3-N-methyl-
N-n-propylamino-6-methyl-7-anilinofluorane was substituted, and 4,4′-thiobis- (3-methyl-6-t-butylphenol) in [D liquid] was replaced with 4,
A thermosensitive recording paper of the present invention was obtained in the same manner as in Example 1 except that 4'-methylenebis (oxyethylenethio) diphenol was used instead.

Example 4 3,3-bis (2- (4
-Dimethylaminophenyl) vinyl-4,5,6,7-
Reduce the amount of tetrachlorophthalide by 7 parts to 13 parts,
Instead, 1,5-bis- (4-dimethylaminophenyl) -3- (4-methylphenylsulfonyl-1,4-
7 parts of pentadiene were added. Further, the silica in [solution E] was replaced with aluminum hydroxide. A thermal recording paper of the present invention was obtained in the same manner as in Example 1 except for the above.

Comparative Example 1 In Example 1, 4,4'-thiobis-in Solution B was used.
Replacing (3-methyl-6-t-butylphenol) with 4-hydroxy-4'-isopropoxydiphenylsulfone, 4,4'-thiobis- (3-methyl-6-t-butylphenol) in [D liquid] 4-hydroxy-
Replaced with 4'-isopropoxydiphenyl sulfone,
Further, a heat-sensitive recording paper for comparison was obtained in the same manner as in Example 1 except that the silica in [Solution E] was replaced with aluminum hydroxide.

Comparative Example 2 In Example 1, 4,4'-thiobis-in Solution B was added.
Same as Example 1 except that (3-methyl-6-t-butylphenol) was replaced with 4-hydroxy-4′-isopropoxydiphenyl sulfone, and the silica in the [solution E] was replaced with aluminum hydroxide. A heat sensitive recording paper for comparison was obtained.

Comparative Example 3 In [Heat-sensitive coating liquid 1] of Example 1, 5 parts of [solution C] was further added, and silica in [solution E] was replaced with aluminum hydroxide. Then, the [heat-sensitive coating liquid 1] is grammage 47
Applying and drying so that the dry coating amount becomes 5 g / m ² on high quality paper of g / m ² , and then [overcoat liquid] is dried and coating amount becomes 3 g / m ² After coating and drying, a thermosensitive recording paper for comparison was obtained.

The following quality evaluations were carried out using the thermal recording paper of the present invention and the comparative thermal recording paper obtained as described above. The results are shown in Table 1. (1) Dynamic color development In a thermal printing experimental device having a thin film head manufactured by Matsushita Electronic Components Co., Ltd., head power 0.45 W / dot, 1 line recording time 4 msec / line, scanning line density 8 ×
Under the condition of 3.85 dots / mm, pulse width 0.2, 0.
Printed at 6, 1.0 msec and the print density is Macbeth density
Measured with RD-914. (2) IR coloring property The sample printed in the above (1) was measured for 900 by using an auto scan 6000 manufactured by Cygnode.
The reflectance in nm was measured. (3) Whiteness 40 ° C, 90% RH environment, 24Hr
The background density after storage was measured with a Hunter whiteness meter. (4) Light resistance For samples printed with the pulse width of 1.0 msec in (1) above, fluorescent lamp 5000Lux, 100H
r The image density after storage was measured by Macbeth RD-914 and Autoscan 6000. (5) Water resistance With respect to the sample printed with the pulse width of 1.0 msec in (1) above, the density of the image area after storing for 24 hours in water was measured by Macbeth RD-914 and Autoscan 6000.
It was measured at.

[0035]

[Table 1]

From the above results, the heat-sensitive recording material of the present invention has higher sensitivity than that of the comparative material, and has a whiteness, light resistance, and
It can be seen that it has excellent water resistance and is extremely practical.

[0037]

The heat-sensitive recording material of claim 1 is provided with at least two heat-sensitive coloring layers containing a leuco dye and a color developer as main components, and the first heat-sensitive coloring layer has the above-mentioned general formula (I) as a leuco dye. A second compound containing at least one compound represented by the formula (II) as a color developer and at least one compound represented by the general formula (III) as a leuco dye. Since the thermosensitive coloring layer is laminated, it is visible to the near infrared region (600 to 9
It has a strong absorption power over a range of 00 nm), and its image can be sufficiently read by an image reading device using a common conductor laser as a light source, and further, storage stability, especially whiteness of the background part, light resistance of the image part, and image part It has excellent water resistance.

In the heat-sensitive recording material of claim 2, a protective layer containing aluminum hydroxide is further laminated on the second heat-sensitive color forming layer, and the heat-sensitive recording material of claim 3 is the first
Since the thermosensitive coloring layer further contains the compound represented by the general formula (IV) as a leuco dye, both have the effect of further improving storage stability, particularly light resistance.

Front Page Continuation (72) Inventor Tomohisa Kakuda 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A thermosensitive recording material comprising at least two thermosensitive coloring layers containing a leuco dye and a color developer as main components on a support, wherein the first thermosensitive coloring layer has the following general formula (I) as a leuco dye. A second compound containing at least one compound represented by the following formula (II) as a developer and further containing at least one compound represented by the following general formula (III) as a leuco dye. A heat-sensitive recording material comprising a heat-sensitive coloring layer laminated. [Chemical 1] (In the formula, R ¹ and R ² represent an alkyl group.) [Chemical 3] (In the formula, R ¹ and R ² represent an alkyl group.) 2. The thermosensitive recording material according to claim 1, wherein a protective layer containing aluminum hydroxide is laminated on the second thermosensitive coloring layer. 3. The thermosensitive recording material according to claim 1, wherein the first thermosensitive coloring layer further contains a compound represented by the following general formula (IV) as a leuco dye. [Chemical 4]