JPH0432756B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording material with good storage stability, and particularly to a heat-sensitive recording paper for adhesive labels without a protective layer. Thermosensitive recording paper has conventionally been used as a thermosensitive adhesive label. In the case of such heat-sensitive adhesive labels, when the plasticizer contained in the plastic film, such as dioctyl adipate (DOA) or dioctyl phthalate (DOP), penetrates into the heat-sensitive coloring layer, the printed area (colored area) disappears. Due to the problem of color, it could not be used as an adhesive label for plastic film packaging products containing plasticizers.
Furthermore, if water or oil penetrates into the heat-sensitive coloring layer, the printed image will smear or the image density will decrease over time. Furthermore, when printing is performed by bringing the thermal head into direct contact with the heat-sensitive coloring layer, if the amount of binder in the heat-sensitive coloring layer is too large, scum adhesion and stagnation will occur, so the amount of binder in the heat-sensitive coloring layer must be adjusted. It is necessary to reduce the amount of carbon, which has the disadvantage of weakening the surface strength. For this reason, when printing on the surface of the heat-sensitive coloring layer, the heat-sensitive coloring layer is taken away by the rubber roll, making it impossible to print. Therefore, conventionally, in order to apply such heat-sensitive recording materials to heat-sensitive adhesive labels, a protective layer was provided on the heat-sensitive coloring layer to prevent migration and penetration of plasticizers, water, and oil into the heat-sensitive coloring layer. It was intended to give surface strength. The main component of the protective layer is a water-soluble polymer such as polyvinyl alcohol and its modified type, starch and its modified type. However, in the case of conventional heat-sensitive adhesive labels having a protective layer mainly made of water-soluble polymers, the decolorization and surface strength of the printed area caused by the plasticizer described above cannot be improved. However, water and oil migrate from the edges and back side of the label to the heat-sensitive coloring layer.
At present, it has not been possible to improve the drawbacks that the printed area may be discolored by water or oil. In addition, by providing a protective layer on the heat-sensitive coloring layer, the thermal responsiveness and coloring sensitivity decrease when thermal coloring is performed using a thermal head, and furthermore, the manufacturing process of providing the protective layer increases, which increases costs. There was a drawback. The object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a heat-sensitive recording material which can prevent colored images from being erased by plasticizers, water and oil, and which can be manufactured at low cost. As a result of extensive studies in view of the above objectives, the present inventors have discovered a thermosensitive recording layer having a thermosensitive coloring layer containing as coloring components a colorless or light-colored leuco dye and an acidic substance that causes the leuco dye to develop color when heated. By combining a coloring agent made of a specific fluoran derivative, a color developer made of a specific sulfone compound, and a binder made of a specific polymer compound in the material, the objective can be achieved all at once. They discovered this and completed the present invention. That is, in the present invention, one surface of the support has the general formula () (However, R ₁ and R ₂ are lower alkyl groups and x is a halogen group.) A coloring agent consisting of a fluoran derivative represented by the general formula () (However, R ₃ and R ₄ represent hydrogen groups) A color developer consisting of bis-(P-hydroxyphenyl)sulfone or a derivative thereof, an ammonium salt of diisobutylene/maleic anhydride copolymer, and The present invention provides a heat-sensitive recording material characterized in that it is provided with a heat-sensitive coloring layer containing a binder made of a styrene/butadiene copolymer. The heat-sensitive recording material of the present invention can print or record images on one side of the support by a heating method, and by providing an adhesive layer on the other side, it can be used for various price tag labels, weighing labels, etc. Can be used as labels, name plates, stickers, etc. Examples of the fluoran derivatives of the general formula () include 3-dibutylamino-7-orthochloroanilinofluoran, 3-dibutylamino-7-orthofluoroanilinofluoran, and 3-diethylamino-7-orthochloroanilinofluoran. Examples include linofluoran, 3-diethylamino-7-orthofluoroanilinofluoran, and particularly preferred is 3-dibutylamino-7-orthofluoroanilinofluoran. Further, the color former represented by the general formula () used in the present invention can be used in combination with other color formers. A specific example of the compound represented by the general formula () is bis-(P-hydroxyphenyl)sulfone. Further, the color developer represented by the general formula () used in the present invention can be used in combination with other color developers. According to the above combination of color former and color developer,
As mentioned above, the plasticizer resistance, water resistance, and oil resistance were significantly improved, but it was observed that the colored parts tended to fade when exposed to plastic films containing plasticizers, water, oil, etc. for a long period of time. . Furthermore, the surface strength of the heat-sensitive coloring layer is still weak, and even if a styrene/butadiene copolymer, which is used in coated paper, etc., is used as a binder to improve the surface strength, adhesion and states-king still occur. . In order to improve these points, the inventors of the present invention have conducted further intensive studies, and as a result, the following general formula () is used as a binder to be applied to the heat-sensitive coloring layer. (R ₅ represents a diisobutylene group) Ammonium salt of diisobutylene/maleic anhydride copolymer (preferably 1 mol per 1 mol of maleic anhydride group of diisobutylene/maleic anhydride copolymer (with diisobutylene group bonded) and general formula () It has been found that the object can be achieved by using in combination a styrene/butadiene copolymer represented by (preferably styrene mole percent is 58 to 62%). Diisobutylene used as a binder in the present invention/
The ammonium salt of maleic anhydride copolymer is preferably one with a molecular weight of 10,000 to 200,000, and one in which 1 mole of diisobutylene group is bonded to 1 mole of maleic anhydride group is effective for improving the storage stability. It was particularly effective. In addition, styrene/butadiene copolymers are effective in improving the surface strength of the heat-sensitive coloring layer, and those with a styrene mole% of 58 to 62% are particularly effective in improving the surface strength of the heat-sensitive coloring layer. When the mole percentage was too high, the thermosensitive coloring layer became hard and the surface strength was reduced, and when the mole percentage of butadiene was too high, scum adhesion and stagnation were likely to occur during printing with a thermal head. Regarding this binder, diisobutylene/
It is essential to use an ammonium salt of a maleic anhydride copolymer and a styrene/butadiene copolymer; using only an ammonium salt of a diisobutylene/maleic anhydride copolymer results in a low surface strength of the heat-sensitive coloring layer. However, when the styrene/butadiene copolymer alone was used, the plasticizer resistance was low, and scum adhesion and staking occurred. The mixing ratio of the binder components is preferably 0.5 to 1.0 parts by weight of the styrene/butadiene copolymer to 1 part by weight of the ammonium salt of the diisobutylene/maleic anhydride copolymer. Also polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose,
This does not preclude the use of other binders such as starch. The thermosensitive color forming layer of the present invention can be formed by a known method. That is, a sheet-like material such as paper, synthetic paper, or plastic film is used as a support, and the above-mentioned fluoran derivative and bis-(P-hydroxyphenyl) are coated on one side of the support.
A coating liquid containing sulfones and a binder may be applied to form a heat-sensitive coloring layer. In addition, the heat-sensitive coloring layer may contain conventional auxiliary additives as necessary, such as white pigment fine powder such as calcium carbonate, talc, clay, silica, titanium oxide, urea-formalin resin, various waxes, higher fatty acid metal salts, higher The clarity of the colored image can also be improved by adding fine powder of a thermal sensitivity enhancer such as fatty acid amide. One side of the support has a solid surface, e.g.
A heat-sensitive adhesive label can be obtained by providing an adhesive layer by a conventional method so that it can be attached to a plastic film, wrapping paper, etc., and then attaching a release liner to the surface of the adhesive layer. The heat-sensitive recording material of the present invention thus obtained had excellent recording properties and storage stability of the heat-sensitive coloring layer, and no scum adhesion or staking was observed during printing. Furthermore, the heat-sensitive recording type adhesive label obtained by using the heat-sensitive recording material of the present invention and applying an adhesive to the back side of the support was excellent and not found in conventional products. The present invention will be explained in more detail below using Examples. Example 1 Dispersion A and Dispersion B were prepared by mixing the following components for 24 hours using a ball mill. [Liquid A] (Parts by weight) 3-dibutylamino-7-orthofluoroanilinofluorane 1.0 20% polyvinyl alcohol 5.0 Water 44.0 [Liquid B] (Parts by weight) Bis-(P-hydroxyphenyl) sulfone 4.0 Calcium carbonate 3.0 Stearic acid amide 1.0 20% polyvinyl alcohol 10.0 Water 32.0 Next, Part A and Part B and 6 parts by weight of an aqueous solution of ammonium salt of 20% diisobutylene/maleic anhydride copolymer (molecular weight approximately 50,000) and 50% as a binder. 1.6 parts by weight of styrene/butadiene copolymer latex (styrene mole % 58-62%),
The heat-sensitive recording material of the present invention was obtained by coating and drying on one side of high-quality paper (basis weight 50 g/m ² ) to form a heat-sensitive coloring layer with a coating weight of 7 g/m ² . Comparative example 1 3-dibutylamino-7 of liquid A formulation of Example 1
- other than using 3-diethylamino-7-parachloro-anilinofluorane or 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluorane in place of orthofluoroanilinofluorane. Comparative heat-sensitive recording materials 1-A and 1-B were obtained in the same manner as in Example 1. Comparative Example 2 Comparative heat-sensitive recording was made in the same manner as in Example 1 except that 4,4'-isopropylidene diphenol was used instead of bis-(P-hydroxyphenyl)sulfone in the B liquid formulation of Example 1. I got the material. Comparative Example 3 A comparative heat-sensitive recording material was obtained in the same manner as in Example 1, except that 10 parts by weight of ammonium salt of 20% diisobutylene/maleic anhydride copolymer was used as the binder. . Comparative Example 4 A comparative heat-sensitive recording material was obtained in the same manner as in Example 1, except that 4 parts by weight of 50% styrene/butadiene copolymer latex was used as the binder. Comparative Example 5 In Example 1, 3 parts by weight of a latex of 50% styrene/butadiene copolymer was mixed with 2.5 parts by weight of an aqueous ammonium salt solution of 20% diisobutylene/maleic anhydride copolymer as a binder. A heat-sensitive recording material for comparison was obtained in the same manner as in Example 1, except for the use. On the back side of such heat-sensitive recording material, an acrylic adhesive layer is provided on the silicone resin side of release paper coated with silicone resin so that the coating amount is 20 g/m ² . A heat-sensitive adhesive label was obtained by pasting the labels together through a wafer and then cutting them out to an appropriate size. Next, the seven types of heat-sensitive adhesive labels obtained as described above were applied to a label printer [manufactured by Tokyo Electric Co., Ltd., product name: HP].
-9303], and a color development test, a dust adhesion/state king test, various preservability tests, and a surface strength test were conducted. The results are shown in the table.

[Table] Good ○ Bad ×
The method for each test is as follows. Color density: print color with a label printer,
The colored area was measured using Macbeth density system RD-514. (Hereinafter, all concentrations were measured using Macbeth Densitometer RD-514.) Skin density: The density at the skin area was measured. Plasticizer resistance: The colored portion printed using a label printer was covered with a soft polyvinyl chloride sheet, and the density was measured after 24 hours at room temperature. Water resistance: The colored portion printed using a label printer was immersed in water at room temperature, and the density was measured 24 hours later. Oil resistance: Sesame oil was applied to the colored area printed using a label printer, and the concentration was measured after 24 hours at room temperature. Surface strength: UV curing ink (manufactured by Toka Shiki)
Printing was performed using an RI tester (manufactured by Mei Seisakusho), and the amount of transfer of the thermosensitive coloring layer to the rubber roll side was observed. As shown in the table, the heat-sensitive recording material of the present invention has excellent color development, high whiteness in the background area, has good storage stability without being erased by plasticizers, water, or oil, and is printable. It can be seen that it is a high quality product with no king. However, comparative example 1-
A. In Comparative Example 2, the printed portion was discolored by the plasticizer, oil, and water and became illegible. In Comparative Example 1-B, the density in the background area was as high as 0.25, and the image of the label was significantly deteriorated. Further, in Comparative Example 3, the printed area density after the preservability test with plasticizer, oil, and water was 1.10 or more, and although a clear image was maintained, there was no surface strength at all. Furthermore, in Comparative Examples 4 and 5, the printed area was decolored by the plasticizer, and scum adhesion and staking occurred, making them impractical.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material in which a heat-sensitive color-forming layer is provided on a support, the heat-sensitive color-forming layer containing as a main component a color-forming component consisting of a colorless or light-colored leuco dye and an acidic substance that causes the leuco dye to develop color when heated. , the thermosensitive coloring layer has the general formula (However, R ₁ and R ₂ are lower alkyl groups and X is a halogen); (However, R ₃ and R ₄ represent hydrogen groups) A color developer consisting of bis-(P-hydroxyphenyl) sulfone and its derivatives, an ammonium salt of diisobutylene/maleic anhydride copolymer, and 1. A heat-sensitive recording material comprising a binder comprising a styrene/butadiene copolymer. 2. The heat-sensitive recording material according to claim 1, wherein the amount of the styrene/butadiene copolymer as the binder is 0.5 to 1.0 parts by weight per 1 part by weight of the ammonium salt of the diisobutylene/maleic anhydride copolymer.