GB2203258A - Heat-sensitive recording sheet - Google Patents

Abstract

A heat-sensitive recording sheet comprises an effectively opaque support (1) having on one side thereof a heat- sensitive recording layer (2), and, laminated thereon, a protective layer (3), and optionally on the back a tacky layer (5) and a release paper (6). The heat-sensitive recording layer is covered with a thin polymer film (3) using a low temperature lamination technique, and the sheet is then particularly useful as a label for bar-code printing. The effectively opaque support may comprise a transparent sheet covered with an opacifying layer. <IMAGE>

Description

HEAT-SENSITIVE RECORDING SHEET The present invention relates to a heatsensitive recording sheet which is very suitable for use as labels for bar-code printing, etc.

In recent years, bar-codes have come into strikingly wide use, and they are not only affixed to a great deal of merchandise, e.g., foodstuffs, sweet stuffs and miscellaneous goods, but also incorporated in ID cards and the like.

A bar-code is fixed in various forms. In one form, it is printed on a package, and in another form, it is printed on a label and then affixed to goods. In still another form, a bar-code is made into a card. When a barcode is attached to a commodity, a commodity name, quantity, selling price, and date, if necessary, are generally recorded together with the bar-code so as to effect the checkup with the commodity.

As described above, a bar-code is particularly effective in attaching it individually to each commodity or object different from every other one in, e.g., quantity, and in its turn price, rather than uniformly to a great deal of the same commodity. In the former case, it is convenient to adopt the method that items necessary in merchandise management, such as commodity classification, commodity name, quantity, maker, commodity number, selling price, date, etc., are supplied to a management system as input data with respect to every individual commodity, and taken out as output from a printer connected to the management system. As the recording method for this system, heatsensitive recording processes have been frequently adopted in recent years.

Depending on circumstances under which goods are handled, however, it not infrequently happens that labels with printed bar-codes are stained with dust, oil or the like, or spoiled by exposure to water, solvents or so on through processings like refrigeration, so it becomes difficult to. read them with an optical character reader (abbreviated as OCR, hereinaffer).

In addition, bar-codes on labels attached to commodity cases are frequently subjected to repeated reading operations with OCR for the purpose of merchandise management including checkup at the stage of distribution, and so on. Therefore, it sometimes happens that printed bar-codes are damaged to make it impossible to read them with OCR.

As one of methods for solving the foregoing problems, "a heatsensitive recording label" which has a special protective layer on a heatsensitive recording layer has been proposed in Japanese Patent Application No.

206390/86.

The heatsensitive recording label of this kind, although, has many advantages in that it has excellent water resistance and solvent resistance, and enables ready removal of stains which are responsible for disturbance of readout with OCR, leaves room for improvement in respect of damage resistance upon repeated reading operations with OCR.

Moreover, an increase in number of coating processes in manufacturing labels causes problem of complicating the manufacturing process and requiring a large-scale apparatus, for each coating process needs to include a coating step, a drying (desolvation) step, and optionally a solvent recovering step.

For the purposes of coping with the repetition of readout operation with OCR and preventing bar-codes from being damaged under inferior circumstances, another measure in which a plastic film is superposed on the surface of a label with a printed bar-code and united in a laminate has so far been taken. However, this measure is limited in applicable range because the lamination must be carried out before attachment of the printed label.

As the results of concentrating our energies on solution of the above-described problems, it has now been found that when a thin transparent polymer film is superposed on a heatsensitive layer and united in a laminate at a low temperature, remarkably favorable results described below can be obtained, thus achieving the present invention.That is, a protective layer excellent in damage resistance can be provided on the heatsensitive layer without causing thermal coloration, whereby removal of stains from the surface becomes easy, water resistance and solvent resistance can be acquired, protection is given to the heatsensitive recording layer so that abrasion due to the repetition of readout operations with OCR may not damage the recorded images like bar-codes, and what is more, heatsensitive recording can be effected after the formation of the protective layer having the above described functions, and further the foregoing manufacturing problems resulting from the coating of a protective layer can be swept off.

i Therefore, a first object of the present invention is to provide a heatsensitive recording sheet free from surface stains and excellent in damage resistance.

A second object of the present invention is to provide a heatsensitive recording sheet which can smoothly effect heatsensitive recording, notwithstanding the possession of a sturdy surface-protecting layer.

A third object of the present invention is to provide a heatsensitive recording sheet which has high resistance to damage, and can be manufactured by a simple process.

The above-described objects of the present invention are attained with a heatsensitive recording sheet which comprises an opaque support having thereon a heatsensitive recording layer, on which a polymer film which functions as a protective layer is laminated.

Embodiments of the present invention will now be described, by way of example, with reference to the following accompanying drawings.

Fig. 1 depicts a basic type of the heatsensitive recording sheet of the present invention in which an opaque layer 1 is employed as the support. Therein, the numeral 2 designates a heatsensitive layer, and the numeral 3 a protective layer (a polymer film) provided by using a low temperature lamination technique.

Fig. 2 depicts a label-form heatsensitive material which is obtained by adding a tacky layer 5 and release paper 6 to the back of the heatsensitive recording sheet shown in Fig. 1.

Fig. 3 depicts a heatsensitive recording sheet in which a transparent support sheet lc covered with an opa;cifying layer 4 constituted with a pigment and a binder, is used as the opaque support of Fig. 1.

Fig. 4 depicts a heatsensitive recording sheet wherein the foregoing opacifying layer 4 is provided on both sides of the transparent support sheet 1c.

Fig. 5 shows the heatsensitive recording sheet prepared in accordance with the present invention, wherein tacky layer 5 and release paper 6 are added to the back of the heatsensitive recording sheet depicted in Fig.3.

As the recording sheet of the present invention has a transparent film of high molecular weight on the upside of a heatsensitive recording layer, the stains even though they adhere to the surface, can be easily wiped off, and the recording sheet is not damaged in its recorded data by chemical factors, e.g., water, solvents, etc., or mechanical factors, e.g., scratching, etc., after recording is over. Further, by the sufficient reduction of a thickness of the surface transparent film, heat recording can be readily achieved via the protective layer(transparent film) using a conventional method as the protective layer maintains its effects resulting from sturdiness.

A color-producing agent to be used in the heatsensitive recording sheets of the present invention can be arbitrarily chosen from known combinations of aromatic diazo compounds with couplers, and other known combinations of electron donating dye precursors with color developing agents.

Suitable examples of the foregoing aromatic diazo compounds include aromatic diazonium slats, diazosulfonate compounds, diazoamino compounds, and so on. When combinations of these diazo compounds with couplers are employed, basic substances, as is well known, may be used together therewith in order to accelerate the color production, if needed.

An electron donating dye precursor to be used in the heatsensitive recording sheets of the present invention can be arbitrarily chosen from substances having a property of producing a color by donating an electron, or accepting a proton from an acid or the like. In general, such substances are almost colorless, and have a partial skeleton,such as a lactone, lactam, sultone, spiro-pyran, ester, amide or so on, which undergoes a ring-opening or cleavage reaction upon contact with a color developing agent. Specific examples of electron donating dye precursors include Crystal Violet lactone, benzoyl leuco methylene blue, Malachite Green lactone, Rhodamine B lactam, 1,3, 3-trimethyl-6'-ethyl- 8'-butoxyindolinobenzospiropyran, and so on.These compounds are described, e.g., in Kami Pulp Gijutsu Times (which means "technical times of pulp and paper") for September, page. 99(1982), and Japanese Patent Application (OPI) No. 42876/87 ( the term (OPI) as used herein means "an unexamined published application").

Color developing agents to be suitably combined with color formers of the above-cited type, are phenolic compounds, organic acids or the salts thereof, oxybenzoates, and so on. Of these compounds, waterinsoluble phenols and organic acids which have a melting point of 50 t to 250 cm, particularly 60 OC to 200 t, are favored over others.

The heatsensitive layer concerned in the present invention can be obtained with ease by coating a composition containing other necessary additives in addition to a color-producing agent and a binder according to a known method.

An opaque support to be used in the present invention can be chosen from among papers, and polymer films to which substantial opacity is imparted. From the standpoint of surface smoothness and strength, films rendered opaque in a substantial sense are preferable to paper. These films can be chosen arbitrarily from known materials having a thickness and/or rigidity of such a degree as not to cause curling by coating the heatsensitive layer, and dimensional stability of such an extent as not to cause deformation by providing a protective layer on the heatsensitive layer using a low temperature lamination technique. In particular, polyethylene terephthalate films are favored over others in respect of low price in addition to excellence in physical properties required.

As for the method of imparting substantial opacity to a support film, a method of adding dyes or pigments at the time of film formation, and method of providing an opacifying layer constituted with at least a pigment and a binder on one side or both sides of a transparent film can be adopted. Specific examples of pigments usable therein include kaolin, burned gypsum, burned kaolin, talc, agalmatolite, diatomaceous earth, calcium carbonate, aluminium hydroxide, magnesium hydroxide, magnesium carbonate, titanium oxide, barium carbonate, ureaformaldehyde filler, cellulose fillers, and so on.

Binders to be used for dispersing pigments therein may be the same as or different from binders to be used for forming the heatsensitive layer. Specific examples of binders which can be preferably used for both purposes include polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, polyacrylic acid, polyacrylic acid amides, denatured polyacrylamides, starch derivatives, casein, gelatin, and other water-soluble high molecular compounds. For the purpose of imparting a water resisting property to these binders, water resistanceimparting agents (including a gelling agent and a crosslinking agent ) and emulsions of hydrophobic polymers, such as styrene-butadiene rubber latex, acryl resin emulsions, etc., can be added, too.

In any cases it is to be desired that opacity required for the support should be 30 % or less, expressed in terms of transmittance.

The low temperature lamination concerned in the present invention is a known technique, and heat resistance of such a degree as to enable thermal recording after lamination is, required of the laminate film. As examples of usable laminate films, mention may be made of films of polyolefins such as polyethylene, polypropylene, etc., films of polyesters such as polyethylene terephthalate, etc., films of cellulose derivatives such as cellulose triacetate, etc., and so on. Of these films, polyethylene terephthalate films are particularly favored over others in respects of transparency, heat resistance, cost and so on. In order to carry out the recording without attended by any trouble after lamination, it is to be desired that a thickness of the laminate film should be controlled to below 20 microns.

In accordance with preferred embodiments of the present invention, a sturdy film with high molecular weight is laminated on the surface of a heatsensitive recording sheet, whereby even though not only water but also oils, solvents and others adhere to the sheet surface,they can be easily wiped up, and even though the recording sheet is allowed to stand in contact with a solvent or the like for a long time, the image formed therein is not spoiled. In addition, as a thin laminate film is used, thermal recording can be performed by applying heat from the upside of the laminate film.

Therefore, the troublesome task of carrying out lamination after thermal recording, as has so far been done, becomes unnecessary. Thanks to the elimination of such troublesome tasks, a great convenience is obtained, and on the occasion of using the recording sheet in the form of a label, which has a tacky layer on the back of the recording sheet, the value as a label can be remarkably enhanced.

Further, even though reading operations with OCR are performed many more times than usual, the recorded image is not damaged, so it can be used for an ample time as long as change in content of the record is not required, resulting in saving not only the trouble of renewing but also the cost..

The present invention will now be illustrated in greater detail by reference to the following examples.

However, the invention should not be construed as being limited to these examples. In the examples, all parts and percentages are by weight, unless otherwise indicated.

EXAMPLE 1 Thirty parts of titanium oxide and 1 part of sodium hexametaphosphate were added to 70 parts of water, and dispersed with a homogenizer. To the resulting dispersion, 20 parts of a 10 % water solution of polyvinyl alcohol (PVA-105) was added, and coated on a 50 microns thick PET(polyethylene terephthalate) base at a coverage of 20 g/m2 on a solids basis, followed by drying. Thus, an opacified base was prepared.

After a heatsensitive color-producing composition was coated on the opacified base, polyethylene terephthalate film (16 microns thick ) was superposed on the surface of the heatsensitive color-producing layer, 'and united therewith in a laminate at a low temperature. The heatsensitive recording layer was provided using a known method (described, e.g., in Japanese Patent Application (OPI) No. 42876/87 ) in which the combination of the, mixture constituted with equal quantities of 2-anilino-3chloro-6-diethylaminofluoran and the following electron donating dye precursor

with 4-p-Phenoxyethoxysalicylic acid was employed as a heatsensitive color-producing agent.

To the thus prepared heatsensitive recording paper, thermal energy of 30 mJ/cm2 was applied to produce a color, resulting in the formation of a bar-code. When oils were dropped onto the .bar-cod'e, any change was not observed in the bar-code. After. the dropped oils were wiped up with cloth, the bar-code performed its function perfectly.

EXAMPLE 2 Another heatsensitive recording sheet was prepared in the same manner as. in Example 1, except the combination of the following electron-donating dye precursor with bisphenol A was used as the heatsensitive color-producing agent, and therein was recorded a bar-code.

Even after a repeated readout operation of bar-code with OCR for 500 times, . the resulting bar-code sufficiently fulfilled its function.

Claims (7)

CLAIMS:

1. A heat-sensitive recording sheet which has at least one heat-sensitive recording layer on an opaque support, characterised in that a polymer film is laminated on said heat-sensitive recording layer.

2. The heat-sensitive recording sheet as claimed in Claim 1, wherein said polymer film is laminated by means of allow temperature lamination technique.

3. The heat-sensitive recording sheet as claimed in Claim 1 or Claim 2, wherein said opaque support comprises a transparent film and an opacifying layer on at least one side of the transparent film.

4. The heat-sensitive recording sheet as claimed in Claim 3, wherein said opacifying layer is made up of a binder in which a pigment is dispersed.

5. The heat-sensitive recording sheet as claimed in any preceding Claim, wherein a tacky layer is provided on a surface of said support opposite to said heat-sensitive recording layer, and release paper is further provided on said tacky layer.

6. A heat-sensitive recording sheet, substantially as hereinbefore described with reference to any of Figures 1 to 5 of the accompanying drawings.

7. The features herein described, or their equivalents, in any patentably novel selection.