JPH0214915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording sheet, and more specifically, it is designed to prevent abrasion of a heat-sensitive head (hereinafter simply referred to as a heat head) and prevent the adhesion of residue to the heat-sensitive head, and to prevent background fog. The present invention also relates to a new heat-sensitive recording sheet that has improved thermal head responsiveness and is capable of forming faithful and clear colored images.

A thermosensitive recording sheet is a recording material in which a thermosensitive coloring layer that can form a colored image by heating is provided on a support such as paper. It uses a thermal head such as a thermal pen.

The use of such thermal recording sheets has rapidly expanded with the development of the information industry, and today they are used in calculators, thermal printers for computer terminals, thermal pen recorders for medical measuring equipment, thermal facsimile machines, and self-winding devices. Widely used as recording material for vending machines, etc.

A thermal head is brought into contact with a heat-sensitive sheet comprising a color-forming substance on a support, a color developer such as an organic acidic substance that causes the color-forming substance to develop color when heated, a binder, and a heat-sensitive coloring layer consisting of various additives. When a conventional heat-sensitive recording sheet is used to form an image, the heat head is subject to significant abrasion, and the degree of abrasion becomes more severe as the recording time increases.Furthermore, during heat recording, thermal molten matter in the heat-sensitive coloring layer is generated. was deposited on the thermal head, and the recorded images thus obtained were very lacking in fidelity and sharpness.

The methods that have been taken to date to solve these problems include adding inorganic filler powders, such as carbon dioxide, into the heat-sensitive coloring layer, the support, or an intermediate layer between the heat-sensitive coloring layer and the support. This method attempts to improve the above drawbacks by incorporating calcium, kaolin, etc., or organic resin powders such as phenolic resin, polyurethane resin, urea-formalin resin, and polystyrene resin.

However, none of these methods gives satisfactory results; for example, in the method using inorganic filler powder, although some improvement was observed in terms of dust adhesion on the thermal head, In terms of wear, the degree of wear was so severe that it could not withstand long-term recording at all, and the method using organic resin powder was less likely to adhere to the thermal head than the above-mentioned method. In general, its effectiveness is inferior to that of urea-formalin resin, and although improvements were observed in terms of abrasion and residue adhesion when urea-formalin resin was used, even in this case, there was also an increase in background fog. In addition, they had drawbacks such as poor thermal head response.

The object of the present invention is to avoid such drawbacks, that is, to reduce the wear of the thermal head (hereinafter simply referred to as head wear) and to avoid the adhesion of debris to the thermal head (hereinafter simply referred to as scum adhesion). To provide a heat-sensitive recording sheet that is free from background fog, has excellent thermal head responsiveness (hereinafter simply referred to as head responsiveness), and can form faithful and clear colored images.

As a result of repeated research, the present inventors have found that the above object can be achieved by incorporating styrene/methacrylic acid copolymer fine particles into the heat-sensitive coloring layer instead of the above-mentioned inorganic filler powder or organic resin powder. I found it.

The present invention was completed based on this knowledge, and provides a heat-sensitive recording sheet provided with a heat-sensitive color-forming layer containing a color-forming substance and a color developer that causes the color-forming substance to develop color when heated. The present invention provides a heat-sensitive recording sheet characterized by containing fine particles of styrene/methacrylic acid copolymer.

The styrene/methacrylic acid copolymer contained in the heat-sensitive coloring layer of the heat-sensitive recording sheet of the present invention may be obtained by any conventional method.
Although there is no particular limitation on the blending ratio of styrene:methacrylic acid, it is preferable that the ratio of styrene:methacrylic acid is 1:0.1 to 1:1 and the molecular weight is 10,000 to 200,000.

In the present invention, the styrene/methacrylic acid copolymer is in the form of fine particles, e.g.
Particle sizes of 20μ, especially 0.1 to 3μ are preferred.

In the present invention, the above-mentioned styrene/methacrylic acid copolymer includes a color-forming main component of a usually colorless or light-colored color-forming substance (color-forming agent) and an organic acidic substance (color-developing agent) that causes this color-forming substance to develop color when heated. and other commonly used binders and various additives to form a heat-sensitive coloring layer forming liquid (hereinafter simply referred to as heat-sensitive coating liquid) according to conventional methods, and then coated on a support to form a heat-sensitive coloring layer. form.

In the present invention, styrene/methacrylic acid copolymer fine particles are preferably used in place of conventional inorganic filler powders and organic resin powders, but they may be used in combination with these powders depending on the characteristics of the intended final product. Needless to say, it is also possible.

In the present invention, the content of the styrene/methacrylic acid copolymer in the heat-sensitive coloring layer is based on the amount of inorganic filler powder and organic resin powder conventionally used, and is preferably based on the total weight of the heat-sensitive coloring layer. The amount is 5 to 60% by weight. However, when used in combination with these powders, the styrene/methacrylic acid copolymer should be used in an amount of at least 30% by weight of the total amount of the inorganic filler powder, organic resin powder, and styrene/methacrylic acid copolymer. preferable.

The components other than the styrene-methacrylic acid copolymer constituting the thermosensitive coloring layer of the thermosensitive recording sheet of the present invention, that is, the coloring agent and developer, which are the main coloring components, the binder, and various additives, have been conventionally used. All of the above can be used in the present invention.

Examples of the coloring agent include leuco forms of various dyes such as triphenylmethane, fluoran, phenothiazine, auramine, and spiropyran dyes, which are usually colorless or pale coloring substances.

Examples of color developers include naphthol, catechol, resolmine, 4,4'-isopropylidene diphenol, bisphenol A, 4,4'-cyclohexylidene diphenol, p-phenylphenol, benzoic acid and oxalic acid. Mention may be made of organic acidic substances.

As the binder, a water-soluble adhesive as detailed below is used, and as other various additives, for example, surfactants, antifoaming agents, waxes, and inorganic pigments are used as necessary. Can be mentioned.

As described above, the preparation of the heat-sensitive coating liquid can be carried out in accordance with conventional methods except for using the styrene-methacrylic acid copolymer as one of the components in the present invention. For example, first, the main components of the color former and the color developer are separately ground using a ball mill, colloid mill, attritor, sand grinder, or the like. Next, a water-soluble binder is added and further pulverized, the two are mixed, and the mixture is further pulverized and dispersed. If necessary, various additives such as a surfactant, antifoaming agent, wax, and inorganic pigment are further added to prepare a heat-sensitive coating liquid. As mentioned above, the pulverization process of the two main components is usually carried out in a water-soluble binder, and examples of the water-soluble binder include polyvinyl alcohol, casein, gelatin, styrene, and maleic acid copolymer. , hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, modified polyacrylamide, isobutylene/maleic anhydride copolymer, and the like are known. Surfactants known as dispersants can also be used in the present invention instead of the water-soluble binders mentioned above.

As the support in the present invention, all those commonly used as supports such as paper, synthetic paper, and plastic film can be used in the present invention.

In the heat-sensitive recording sheet of the present invention, a heat-sensitive coating liquid containing a styrene-methacrylic acid copolymer is applied onto the above-mentioned support by a conventional method, preferably at a rate of 3 to 15 g/m ^{2 .}
This is a heat-sensitive recording sheet formed by coating a heat-sensitive coloring layer in a coating amount of .

Such a heat-sensitive recording sheet of the present invention is a heat-sensitive recording sheet capable of forming faithful and clear colored images with little head abrasion, no residue adhesion, no background fog, and excellent head responsiveness.

The invention is explained in more detail by the following examples, print tests and image tests.

Examples Preparation of heat-sensitive coating liquid: Liquid A: Crystal violet lactone 60 parts by weight 5% Hydroxyethyl cellulose 60 parts by weight aqueous solution (BL-15 manufactured by Fuji Chemical Co., Ltd.) Water 180 parts by weight Liquid B: Bisphenol A 60 parts by weight 5% Hydroxyethyl cellulose 60 parts by weight aqueous solution (BL-15 manufactured by Fuji Chemical Co., Ltd.) Water 180 parts by weight Solutions A and B having the above component ratios were separately ground and dispersed in a ball mill for 24 hours to prepare each solution. did. Next, 1 part by weight of liquid A, 4 parts by weight of liquid B, 1 part by weight of 30% polyethylene wax aqueous dispersion (Polylon A, manufactured by Chukyo Yushi Co., Ltd.), and 1 part by weight of 40% styrene/methacrylic acid copolymer fine particle aqueous dispersion (Mitsui 2 parts by weight of Almatex PP (manufactured by Toatsu) and 2 parts by weight of a 20% polyvinyl alcohol aqueous solution (PVA-205, manufactured by Kuraray) were mixed and stirred to obtain a heat-sensitive coating liquid.

Support: Commercially available high-quality paper (basis weight 52 g/m ² ) Manufacturing method of thermosensitive recording sheet: Coating amount 7 g/m ² (dry matter) of the heat-sensitive coating liquid obtained as described above on the above support A heat-sensitive coloring layer was formed by applying the coloring layer according to the standard).

The heat-sensitive recording sheet thus obtained was surface-treated by supercalendering to give a Beck smoothness of 500 seconds to obtain a heat-sensitive recording sheet of the present invention.

Comparative Example A comparative heat-sensitive recording sheet (Comparative 1) was prepared in the same manner as in the above Example except that a 40% calcium carbonate aqueous dispersion was used instead of the 40% styrene/methacrylic acid copolymer fine particle aqueous dispersion. Obtained.

Similarly, instead of the above 40% styrene/methacrylic acid copolymer fine particle aqueous dispersion, 40% polystyrene resin fine particle aqueous dispersion (Lytron, manufactured by Monsanto) and 40% urea formalin resin fine particle aqueous dispersion (Ciba Geigy) were used. Comparative heat-sensitive recording sheets (Comparison 2 and Comparison 3) were obtained using Pergopack M) manufactured by Co., Ltd.

Printing Test Each heat-sensitive recording sheet obtained as described above was subjected to a 100,000-line printing test using a PU-1800 printer manufactured by Oripetsutei.

As a result, the heat-sensitive recording sheet of the present invention showed clear recording until the end, and when the amount of head wear after 100,000 lines of printing was measured using a 1/1000 mm micrometer, no wear was observed. Furthermore, no dirt was observed around the head.

The results for the heat-sensitive recording sheet of Comparison 1, which were conducted in the same manner, show that the print at 100,000 lines is slightly lighter than the initial print, and the stains around the head are different from those of the heat-sensitive recording sheet of the present invention. The results were equally good, but the head wear was worse at 8 μm.

Furthermore, in the heat-sensitive recording sheet of Comparison 2, which was made in the same manner, the printing became faint in the middle of printing 100,000 lines and the stain around the head was severe.

The results of Comparison 3 thermal recording sheet show head wear.
At 3 μm, there was little head staining and the print quality was good until the end, but the background was blue (Macbeth densitometer showed
0.10; the heat-sensitive recording sheet of the present invention was 0.07),
Furthermore, the printed characters themselves were slightly distorted and the recording was somewhat ugly.

Image test Next, an electrocardiograph manufactured by Fukuda Denshi was placed on each heat-sensitive recording sheet.
Using DU-3S, pen current 0.7A, pen pressure 2g and
Electrocardiographic waveforms were recorded at 7 g.

As a result, in the case of the heat-sensitive recording sheet of the present invention, extremely clear and faithful recorded images were obtained even when the pen pressure was changed, and no residue was observed.

On the other hand, the comparative thermal recording sheets, especially those of Comparisons 1 and 2, had poor pen responsiveness and distorted waveforms when the pen pressure was 7 g, and the image of Comparison 3 was cut off in the middle of recording. As a result, there was a lot of debris attached.

From the results of the above printing test and image test, the heat-sensitive recording sheet of the present invention has less head abrasion and residue adhesion even during long-term recording, has no background fog, has excellent head responsiveness, and produces faithful and clear colored images. It is clear that this is a heat-sensitive recording sheet capable of forming.

Claims (1)

[Claims] 1. In a heat-sensitive recording sheet provided with a heat-sensitive color-forming layer containing a color-forming substance and a color developer that causes the color-forming substance to develop color when heated, fine particles of styrene-methacrylic acid copolymer are contained in the heat-sensitive color-forming layer. A heat-sensitive recording sheet featuring: