WO2009074292A1

WO2009074292A1 - Heat sensitive recording material

Info

Publication number: WO2009074292A1
Application number: PCT/EP2008/010445
Authority: WO
Inventors: Hidetaka Tsukada
Original assignee: Mitsubishi Hitec Paper Bielefeld Gmbh
Priority date: 2007-12-11
Filing date: 2008-12-09
Publication date: 2009-06-18
Also published as: EP2070714B1; EP2070714A1; ES2369575T3; ATE516151T1

Abstract

The invention relates to a heat sensitive recording material having a substrate and a heat sensitive recording layer comprising color formers and color receptors, wherein an intermediate layer comprising hollow body pigments is configured between the substrate and the heat sensitive recording layer. Characterizing for the novel heat sensitive recording material is the combination of features, in that the intermediate layer further has at least one component, selected from the list consisting of boric acid and (di-)sodium tetraborate decahydrate, and that the heat sensitive recording layer is applied by means of curtain coater or SNd (curtain) coater.

Description

Heat-sensitive recording material

The invention relates to a heat-sensitive recording material comprising a substrate and a color-sensitive and heat-sensitive recording layer containing color acceptors, wherein an intermediate layer comprising hollow body pigments is formed between the substrate and the heat-sensitive recording layer.

A heat-sensitive recording material of the type mentioned is known for example from EP-A-O 570 186. Here, the intermediate layer of the known thermosensitive recording material is intended to contain crosslinked polymer particles having a particle diameter of 0.2 to 5.0 μm and additionally an inorganic pigment, the latter having an oil absorption of less than 170 ml / 100 g. The document discloses a mixing ratio of organic polymer particles to inorganic pigment in the range from 1: 1 to 1: 9. With regard to the question whether these are polymer particles with a cavity structure, this document contains no information. The effect of the intermediate layer is explained in the Scriptures in that the organic and inorganic pigment particles have a mutual effect and irregularities on the surface of the substrate used as a substrate are balanced or smoothed. Penetration of the recording layer-forming components into the substrate should be suppressed so as to obtain a heat-insulating layer having a high void ratio.

With the US 2006/0240981 A1, there is a document with which a heat-sensitive recording material with a novel Farbakzeptor is proposed in the recording layer. With regard to the structure of this heat-sensitive recording material and in particular with regard to the components of the recording layer as far as possible no limitation - but also no teaching - are disclosed: so the recording layer should have virtually all known color formers, all known binders and countless additives and applied by all known coating units could be. For the purposes of this disclosure, the known recording material can also have a recording layer applied by curtain coater, which comprises polyvinyl alcohol as binder and boric acid as additive. How a coating color is to be applied with these components by means of curtain coaters for the formation of the recording layer, the font reveals just as little details as whether such a recording material should then additionally have interlayer and protective layer.

The subject of EP 1 738 920 A1 is a heat-sensitive recording material whose recording layer can also contain polyvinyl alcohol in addition to leuco dyes and color acceptors. An optional intermediate layer formed below the recording layer may comprise organic hollow body pigments; the additional incorporation of boric acid into the intermediate layer can not be deduced from the document.

The two documents EP 1 348 569 A2 and EP 1 254 780 A2 propose heat-sensitive recording materials whose recording layers each have encapsulated color-forming components. While the first document for the recording material mentions an intermediate layer with boric acid as a possible variant, the second document prefers the inclusion of boric acid in a protective layer. The form in which the individual layers are applied does not belong to the disclosure content of the cited documents.

Finally, JP 02 121879 A proposes a recording material with boric acid-containing intermediate layer and heat-sensitive recording layer. The summary of this document is no indication of which other components has the intermediate layer and in what form the recording layer is formed.

From DE-A-39 01 234 a heat-sensitive recording material is known, in which in an intermediate layer, a foamed portion is provided with tiny gaps. For this purpose, it is proposed in one of the disclosed processes to produce tiny plastic hollow particles of thermoplastic material. in an expanded state in such an intermediate layer, wherein in the produced particles air or other gases are contained. According to a further variant of the method, an intermediate layer is provided which contains an expandable plastic filler which comprises hollow particles of a thermoplastic material and a low boiling point solvent contained in these particles. Upon heating, the intermediate layer expands and certain voids are created. Finally, an intermediate layer containing a blowing agent and a thermoplastic material has also been proposed. When heated, this creates an intermediate layer with a cellular structure.

The intermediate layer may be applied to a basecoat covering the substrate containing inorganic pigment and binder. For the admixture of inorganic pigment to the intermediate layer, there is no disclosure in the document.

The known heat-sensitive recording materials could certainly convince in terms of their appearance in many areas of their potential applications, but the problem of such a resolution of the heat-induced print image, which also allows the representation of barcodes, which can be read without difficulty, the developer always big difficulties again. Barcodes must be pin-sharp: Missing dots in the presentation of the barcodes immediately lead to difficulties in recognizing the barcodes, which causes problems in the companies that use barcode labels on their products. Also, the barcodes must have a large print density, so even with fast printing by thermal print head must be sufficiently black, so that the barcode recognition works without any difficulty.

The heat-sensitive recording material solution which solves the above problems provides such a material with a heat-sensitive recording layer containing a color former and color acceptors, and an intermediate layer comprising a hollow body pigment is formed between the substrate and the heat-sensitive recording layer is. Characteristic of the novel heat-sensitive recording material is the combination of features,

_° that the intermediate layer further comprises at least one component selected from the list comprising boric acid and (di-) sodium tetraborate decahydrate, and

° that the heat-sensitive recording layer by means of Schlitzgießer, so-called curtain coater, or Gleitflächengießer, so-called SNd (Curtain) Coater, is applied.

It is of crucial importance that all the above features are combined with each other, since only by the combination of features, the task can be solved convincing.

The inclusion of hollow body pigments, better organic hollow body pigments, in the intermediate layer is essential for the present invention, since such organic hollow body pigments are beneficial to a particular extent, a high heat reflectivity of the intermediate layer. The organic hollow body pigments disposed in an intermediate layer of a thermosensitive recording material have air inside thereof, which is a good heat insulator. Thus, the intermediate layer optimized as a heat reflection layer enhances the response of the recording layer to heat: the heat emitted from the thermal head during the printing process consequently causes the color forming effect in the heat-sensitive recording layer and the reflection at the intermediate layer when it passes through the heat-sensitive recording layer again. This dual utilization of the heat emitted from the thermal head significantly increases the resolving power of the thermosensitive recording material. Furthermore, these relationships are able to set the printing speed in the thermal printer up.

Since the thermal head causes melting of the waxy components in the recording layer during the heat-induced printing process in the heat-sensitive recording layer, it is expedient that the Interlayer also contains inorganic pigments in addition to the organic hollow body pigments.

The inorganic pigments of this intermediate layer cause absorption of the melt. It is particularly advantageous if the pigments of the intermediate layer has an oil absorption of at least 80 ^cm3 / 100 g, and more preferably 100 ^cm3 / 100 g, determined according to the Japanese standard JIS K 5101, have. Calcined kaolin, calcium carbonate, silicon dioxide and kaolin have proven particularly useful due to their high absorbency. Also mixtures of several different types of inorganic pigments are conceivable.

The ratio between organic hollow body pigments and inorganic pigments is a compromise of the effects caused by the two types of pigments, which is particularly advantageously dissolved when the pigment mixture to 15 to 70 parts by weight or better to 20 to 60 parts by weight of organic hollow body pigment and 85 to 30 parts by weight or better to 80 to 40 parts by weight of inorganic pigment. It is very particularly preferred if the pigment mixture consists of 45 to 55 parts by weight of organic hollow-body pigment and 55 to 45 parts by weight of inorganic pigment. In this case, the data relating to the parts by weight relate here to the total pigment content in the intermediate layer, with which the parts by weight of organic hollow-body pigments and inorganic pigments each add up to 100 parts by weight.

In principle, the proportion of organic hollow body pigments can be determined specifically and preferably to a proportion of more than 60 parts by weight, up to 100 parts by weight, based on total pigment content in the intermediate layer, provided that the inventive recording material has a protective layer covering the heat-sensitive recording layer, the inorganic pigments an oil absorption as possible in a range of greater than 100 ^cm3 / 100 g, determined according to the Japanese standard JIS K 5101, contains.

The organic hollow body pigments have a wall of thermoplastic resin, preferably (meth) acrylonitrile copolymer, polyvinyl chloride, Polyvinylidene chloride, polystyrene, styrene acrylate, polyacrylonitrile or polyacrylic acid ester. Pigment mixtures of different organic hollow body pigments are conceivable. A glass transition temperature greater than or equal to

100 ⁰ C and preferably greater than or equal to 105 ⁰ C was recognized as positive, because below these temperatures, an increased degree of yellowing of the recording material according to the invention was found.

The particle size of the organic hollow body pigments is ideally in a range of 0.4 .mu.m to less than 1, 5 .mu.m, more preferably a range of 0.9 microns to 1, 2 microns. Particle sizes below 0.4 microns can be associated in part with considerable disadvantages due to rheological processing difficulties. Particle sizes above 1, 5 microns show too coarse-grained behavior and prevent a preferred leveling effect of the intermediate layer. Particularly suitable for the inorganic pigments is a particle size of less than 2 μm, very particularly preferably in a range from 0.75 μm to 1.8 μm, the stated values for the particle size being used both for the organic hollow-body pigments and for the inorganic pigments D ₅₀ -WeIIe are to be understood. In experiments, it has been found to be advantageous if the ratio of the particle size of the organic hollow body pigment to the particle size of the inorganic pigment in a range of 1: 0.75 to 1: 2, and more preferably in a range of 1: 1, 5 to 1: 1 , 9 lies.

An inventive feature of the proposed recording material is the inclusion of a component selected from the list comprising boric acid and (di) sodium tetraborate decahydrate - that is borax, in the intermediate layer. The two components, which can be used alone or in combination with one another, bring about a particularly good ply adhesion between the interlayer comprising organic hollow body pigments and the heat-sensitive recording layer containing color formers and color acceptors, which is the result of numerous experiments with and without the two components in the intermediate layer was found out. The proportion of boric acid and / or borax in the intermediate layer is preferably between 0.5 and 5 parts by weight, based on 100 parts by weight of pigment. A good anchoring of the organic hollow body pigments having intermediate layer with the heat-sensitive recording layer using boric acid and / or borax in the intermediate layer is favored by the inclusion of polyvinyl alcohol in the recording layer. Incidentally, the polyvinyl alcohol may be incorporated as a binder in the recording layer from the beginning, and it is possible to diffuse the polyvinyl alcohol from a protective layer covering the recording layer or from a diffusion layer to be provided between such a protective layer and the recording layer. In all cases, the recording layer finally comprises polyvinyl alcohol, which then crosslinks with the boric acid or borax which diffuses from the intermediate layer into the recording layer.

In the sense of the previous embodiments, it is a first preferred embodiment, when the heat-sensitive recording layer comprises polyvinyl alcohol as a binder. In a second preferred embodiment, which is to be considered as an alternative or in addition to the first embodiment variant, the heat-sensitive recording layer is covered by a protective layer, the protective layer containing polyvinyl alcohol. A third preferred embodiment, which is to be considered as an alternative or in addition to the first and the second embodiment, provides for the formation of a diffusion layer between heat-sensitive recording layer and protective layer, wherein the diffusion layer consists primarily and mainly of polyvinyl alcohol.

The polyvinyl alcohol may be a commercially available unmodified polyvinyl alcohol, for example NM11, for all variants described. In tests, it has sometimes been found to be particularly advantageous if the polyvinyl alcohol is a

with carboxyl groups or with carbonyl groups,

- modified with silanol groups,

or diacetone-modified

Polyvinyl alcohol is why such polyvinyl alcohols are considered particularly preferred. The mixture of differently modified polyvinyl alcohols in The different layers are not only imaginable, but are considered to be preferred. For example, very good results could be achieved if a

Mixture of carbonyl group-modified polyvinyl alcohol and SiI nolgruppen modified polyvinyl alcohol is used.

A further feature of the invention for the recording material proposed here is that the heat-sensitive recording layer is applied by means of a slot coater, the so-called curtain coater, or by means of a sliding surface coater, the so-called curtain coater.

In the case of the so-called slot casters, the liquid coating material exits through an outlet gap which is directed downwards and is arranged transversely over the web-shaped carrier material to be coated, where it immediately forms the free-falling liquid curtain. In the so-called Gleitflächengießer the liquid coating material is first applied to a downwardly inclined sliding surface, where the liquid flows in a thin film under the influence of gravity, the sliding surface down and forms at the end of the free-falling liquid curtain. The color curtain strikes the carrier material along the wetting line, which in the present case comprises the substrate and the intermediate layer. In the context of the present invention, the wetting line is to be understood as the cross-over the path of the carrier material, ideally static and rectilinear cutting axis of the liquid curtain with the continuously moving carrier web.

Outstanding advantage of Gleitflächengießer is in particular that more than one coating material can be deposited simultaneously on the support material. In the present case, this means that in addition to the heat-sensitive recording layer, the optionally provided protective layer and optionally also the diffuser layer provided between the recording layer and the protective layer can be applied to the substrate provided with the intermediate layer in a single operation with a single slip surface caster. When using several slot casters arranged one behind the other, in particular the energetically advantageous wet-in-wet Coating method advantageous and is considered to be particularly preferred. In such a case, no drying aggregates are necessary between the individual Schlitzgießern and the recording material is dried only after the

Recording layer and the optionally provided protective and diffusion layers are applied.

In addition to the advantage explained above, the recording layer applied according to the invention by means of slot caster or sliding surface caster optionally together with the protective layer and / or diffusion layer also has the positive properties that a layer applied in this way or layers applied in this way represent their surface properties are optimized by bar code labels, without the need for this after their application to the support material of a post-treatment for further conditioning, for example by means of metering rod or doctor blade, such a treatment is not excluded in the context of the present invention. This means that in the preferred case with the application of the recording layer - optionally together with the protective layer and / or diffusion layer - on the carrier material, the recording material according to the invention is completed. A subsequent smoothing and densification of the recording material by means of on-line calender or on-line calender and / or by means of offline calender or offline calender is possible and is considered to be particularly preferred because of an optimized appearance of the novel recording material.

A major problem with applied by liquid curtain layers is the non-optimal anchoring of the respective layer on the carrier material carrying them. The inventive incorporation of boric acid and / or borax in the organic hollow body pigments having intermediate layer of this problem is permanently solved, which - as already stated - the good anchoring of the intermediate layer is promoted with the heat-sensitive recording layer by the inclusion of polyvinyl alcohol in the recording layer. The intermediate layer of the heat-sensitive recording material according to the invention comprises, in addition to the organic hollow body pigments and the at least one component selected from the list comprising boric acid and (di-) sodium tetraborate decahydrate, further a binder

selected from the group comprising styrene-butadiene latex, starch, carboxymethyl cellulose and cellulose derivatives, with styrene-butadiene latex being preferred, alone or in combination, in particular, with starch. In binder mixtures, the binder content in the intermediate layer is preferably 10 to 40 parts by weight, more preferably 15 to 25 parts by weight, of styrene-butadiene latex and 5 to 20 parts by weight, more preferably 7 to 15 parts by weight of starch, each based on 100 parts by weight of pigment.

The intermediate layer positioned between the substrate and the heat-sensitive recording layer can make a positive contribution to equalization of the substrate surface, thus reducing the mass of the coating film to be applied to the heat-sensitive recording layer. Inter alia, a film press may be used to apply the interlayer; however, preference is given to leveling applicators such as, for example, a doctor blade and a doctor or blade.

Particularly advantageous is the formation of the intermediate layer with a basis weight in a range of 3 g / m ² to 20 g / m ² and even better between 5 g / m ² and 8 g / m ² .

The heat-sensitive recording layer may in principle include all known color formers as well as in particular suitable color acceptors, in particular organic Farbakzeptoren. Particularly preferred are color formers

- 6 '- (dipentylamino) -3'-methyl-2' - (phenylamino) -spiro [isobenzofuran-1 (3H), 9 '- [9H] xanthene] -3-one and

Spiro [isobenzofuran-1 (3H), 9 '- [9H] xanthene] -3-one-6' - (diethylamino) -3'-methyl-2'- (3-tolylamino) and those selected from the group of fluoran compounds, such as

3- (N-methyl-N-propyl) amino-6-methyl-7-anilinofluoran,

3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran,

3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran,

3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran and

- 3- (N-ethyl-N-tetrahydrofuryl) -amino-6-methyl-7-anilinofluoran. and especially

3- (ethylisoamylamino) -6-methyl-7-anilinofluoran and

- 3-dibutylamino-6-methyl-7-anilinofluoran (= ODB 2).

Suitable organic color acceptors in particular for the color formers mentioned are in particular those selected from the group comprising

2,2 bis (4-hydroxyphenyl) propane (= BPA),

4-[(4- (1-methylethoxy) phenyl) sulfonyl] phenol,

- ^{4,4'-dihydroxy-diphenyl} sulfone,

- 4-hydroxy-4 ^{'-isopropoxy-diphenyl} sulfone,

N- (p-toluenesulphonyl) -N ^' - (3-p-toluenesulphonyl-oxy-phenyl) -urea,

- ^{2,4'-dihydroxy-diphenylsulfone,}

- N- (2-hydroxyphenyl) -2 - [(4-hydroxyphenyl) thio] acetamide, of course, without being limited to the color acceptors mentioned. For the color formers, an average particle size in a range from greater than 0.3 μm to a maximum of 1 μm, in particular from 0.45 μm to 0.9 μm, is recommended. The limits are given upwards by a too low sensitivity and down by an otherwise too strong inclination of the heat-sensitive recording material for graying.

As already mentioned, the heat-sensitive recording layer comprises polyvinyl alcohol for promoting a good anchorage of the organic hollow body pigment-containing intermediate layer to the heat-sensitive recording layer. Additional suitable binders for incorporation into the heat-sensitive recording layer are, for example, starch, hydrous xyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, sodium polyacrylates, acrylamide-acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, alkali salts of styrene-maleic anhydride copolymers or ethylene-maleic anhydride copolymers exemplified as water-soluble binders alone or can be used in combination with each other; also water-insoluble latex binders such as styrene-butadiene

Copolymers, acrylonitrile-butadiene copolymers and methyl acrylate-butadiene copolymers are useful as additional binders for incorporation into the heat-sensitive recording layer. For the purposes of the present invention, in addition to polyvinyl alcohol, in particular starch in combination with styrene-butadiene copolymers are particularly preferred binders. The binders, individually or in combination with each other, incorporated in the heat-sensitive recording layer should preferably be in the range of 12 to 21% by weight in the heat-sensitive recording layer based on the total weight of the recording layer.

To avoid excessive wear of the thermal head during the times in which the heat-sensitive recording material is guided along the thermal head during the printing process, and to avoid excessive deposition of the recording material during these times on the thermal head, the Beschichtungsmatehal to form the heat-sensitive Recording layer Lubricating and separating agents include metal salts of higher fatty acids, for example, zinc stearate, calcium stearate and waxes, such as paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearamides and castor wax. To ensure a stable liquid curtain of the coating material for forming the heat-sensitive recording layer, the coating material contains wetting agents such as Nopcowet 50 from Nopco Paper Technology GmbH, Germany, without being limited to this particular product in any way.

Further constituents of the recording layer are, for example, pigments, preferably inorganic pigments such as, for example, aluminum (hydr) oxide, silica and calcined kaolin and calcium carbonate, where calcined kaolin and calcium carbonate, which are preferably incorporated in the recording layer, are preferably present in each case in an amount of 15 to 28% by weight and more preferably between 20 and 26.5% by weight, based on the total weight of the recording layer should.

[0035] The recording layer of the thermosensitive recording material of the invention can be used to increase the thermal response sensitivity also preferred sensitizers having a melting point ideally between 60 ⁰ C and 180 ⁰ C, particularly preferably having a melting point between 80 ° C and 140 ⁰ C, included. Such sensitizers are, for example: benzyl p-benzyloxybenzoate, stearamide, N-methylol stearamide, p-benzylbiphenyl, 1, 2-di (phenoxy) ethane, 1, 2-di (m-methylphenoxy) ethane, m-terphenyl, Dibenzyl xalate, benzylnaphthyl ether (= BNE), diphenylsulfone and 2- (2H-benzotriazol-2-yl) -p-cresol, with benzylnaphthyl ether, diphenylsulfone, 1,2-di (m-methylphenoxy) ethane and 1, 2 Di (phenoxy) ethane are preferred.

Furthermore, it is considered preferable if a permanent color or typeface can be formed in the recording layer under the action of heat.

The basis weight of the heat-sensitive recording layer should preferably be between 1, 5 and 10 g / m ² and more preferably between 2 and 5.5 g / m ² .

It is preferred if the coating used to form the recording layer is aqueous. The subsequent drying of the coating color can be done by means of microwave irradiation. Usually and proven it is just as much to supply heat, as happens by hot-air floatation dryer or contact dryer. Also conceivable is a combination of the listed dry processes.

The recording material according to the invention may have a protective layer which is applied to the heat-sensitive recording layer and covers it in whole or in part. The protective layer takes on the one hand the task of protecting the recording layer arranged below it against environmental influences such as oils, fats, water and plasticizers and, on the other hand, to improve the printability of the proposed recording material, in particular in offset and flexographic printing.

A possible embodiment for a protective layer completely or partially covering the thermosensitive recording layer comprises zinc stearate,

as a binder polyvinyl alcohol, as a pigment aluminum hydroxide and / or alternatively also silica and one or more crosslinkers before, with particularly preferred amounts for such a protective layer in the following Table 1 are shown:

Table 1 :

Product% by weight [otro]

Aluminum hydroxide 10 - 25

Polyvinyl alcohol 55 - 70

Zinc stearate 7 - 9

Crosslinker 6 - 7

The protective layer itself may be applied by means of conventional brushing, for which, inter alia, a coating color is used, as described above and for a surface-related mass in a range of 1, 0 to 4.5 g / m ^{2 is} preferred. Most preferably, the protective layer is applied by Schlitzgießer or by Gleitflächengießer. If it is applied by means of Gleitflächengießer, the simultaneous application of the recording layer and protective layer or of the recording layer, diffusion layer and protective layer is considered to be very particularly preferred.

As an alternative to the coating technology application of the protective layer, the protective layer may also be printed.

Processing technology and in terms of their technological properties are particularly suitable such protective layers by means of actinic radiation hardening are curable. The term "actinic radiation" UV or ionizing radiation, such as electron beams to understand.

As the substrate, paper and more particularly a non-surface treated base paper is preferred, without the invention being limited to such substrates. A non-surface treated base paper is to be understood as meaning a base paper not treated in a size press or by means of a coater. For the invention, films of, for example, polyolefin and polyolefin-coated papers as a substrate are possible to the same extent, without such an embodiment having an exclusive character.

In a particular embodiment, the recording material of the present invention may also have a backcoat layer coated on the substrate side opposite to the side provided with the thermosensitive recording layer. Such a backside coating is proposed, for example, in DE-A-197 48 258 and then serves for improved backside printability of the recording sheet in the offset and flexographic printing processes and an improved blocking effect of the backside against plasticizers, oils and fats. For the basis weight of the backcoat application amounts in a range of 1 to 3 g / m ² and especially between 1, 5 and 2.5 g / m ^{2 have} proven to be advantageous.

The details given in the description and in the claims relating to the basis weight,% by weight (% by weight) and parts by weight are in each case based on the "otro" weight, ie on absolutely dry parts by weight.

The invention will be explained in more detail with reference to the following inventive examples 1 and 2 and the comparative examples 3 and 4:

On a fourdrinier paper machine, a paper web made of a mixture of bleached and ground softwood sulphate pulp and eucalyptus pulp is first used as a substrate for all examples and comparative examples a basis weight of 66 g / m ² with the addition of conventional blending substances in conventional quantities.

The following formulations from Table 2 are used to form the respective intermediate layer for the two examples 1 and 2 according to the invention and for the two comparative examples 3 and 4:

Table 2:

Where to Buy

Dispex N40 CIBA Speziahtatenchemie Lampertheim GmbH, 68623 Lampertheim, Germany

- Ansilex 93 Engelhard, 101 Wood Avenue, New Youk, USA

Ropaque AF 1055 Rohm & Haas, In der Kroen 4, 60489 Frankfurt, Germany

Litex P5100 Polymer Latex GmbH & Co. KG, 45764 Mari, Germany

Using a separate coating machine, the coating slips It. Table 2 are applied to the substrate on the front and by means of a blade applicator respectively to form an intermediate layer of 6 g / m ² , wherein the intermediate layer in each of the examples and comparative examples Completely covering the substrate.

To form a heat-sensitive recording layer of identical construction for all examples and comparative examples, the following recipe from Table 3 is used. Table 3:

Ingredient Weight (otro) Wt% (otro) ^{* 1}

Various dispersants 0,93 2,86

Color former ODB 2 3 9,22

Color acceptor BPA 7 21, 51

Sensitizer ESD 7 21, 51

Pigment calcium carbonate 8 24,59

Continuation, Table 3:

Component parts by weight (otro)% by weight (otro) ^{* 1}

Wetting agent ^{* 2} Nopcowet 50 0.1 0.31

Lubricant - 1 3.07

Polyvinyl alcohol Gohsenol NM 11 5.5 16.91

^{* 1} )% values valid for examples 1 and 2 * ² ) Entry only in examples 1 and 2

Where to Buy

Gohsenol NM 11 Nippon Gohsei, Osaka, Japan

In the case of the two inventive examples 1 and 2 using a Schlitzgießer-applicator (Curtain Coater) and in the case of the two Comparative Examples 3 and 4 using a Lüftbürsten-applicator is on the intermediate layer, a heat-sensitive recording layer It. Formulation of Table 3 applied with a basis weight of 2.5 g / m ² . In the case of the two examples 1 and 2 according to the invention, the same coating machine is used, with which the intermediate layer was previously applied and dried. In this case, thus, the two layers, intermediate layer and recording layer, can be formed in a single coating machine passage.

In the same operation and after drying of the intermediate layer and recording layer within the inventive Example 2 by means of a second curtain coater a recording layer completely covering protective layer of 1, 5 g / m ² applied. For the formation of the protective layer For example, a formulation as shown in Table 4 below is used.

Table 4.

Component weight (otro)

Dispersant Dispex N40 0,05

Pigment Al (OH) ₃ 5

Lubricant - 2

Polyvinyl alcohol NM 11 15

The two examples 1 and 2 according to the invention and the two comparative examples 3 and 4 are to be evaluated with regard to the reproduction of barcodes and the presence of missing dots. For this purpose, thermal prints are made with a device of the type Atlantek 400 from. Atlantek (USA) on samples according to the two examples of the invention and the two comparative examples. In this case, a thermal head with 300 dpi at 11, 74 mJ / mm ^{2 is} used. The black-and-white transitions of the thermal prints as well as the areas in full-color black are assessed visually with the aid of magnifying glasses with the following results, see Table 5:

Table 5:

^* ) Scale school grades from 1 to 6

Table 5 demonstrates the superiority of the heat-sensitive recording material of the invention over the prior art.

Claims

claims

Anspruch [en] A heat-sensitive recording material comprising a thermosensitive recording layer containing a substrate and a color acceptor and color acceptors, wherein an intermediate layer comprising a hollow body pigment is formed between the substrate and the thermosensitive recording layer, characterized in that

■ the intermediate layer further comprises at least one component selected from the list comprising boric acid and (di-) sodium tetraborate decahydrate, and,

^■ that the heat-sensitive recording layer by means of slot coater, so-called curtain coater, or Gleitflächengießer, so-called slid (curtain) coater, is applied.

2. Heat-sensitive recording material according to claim 1, characterized in that the intermediate layer comprises organic hollow body pigments.

3. Heat-sensitive recording material according to claim 2, characterized in that the intermediate layer also contains inorganic pigments in addition to the organic hollow body pigments.

4. Heat-sensitive recording material according to one of claims 1 to 3, characterized in that the intermediate layer contains a binder selected from the group comprising styrene-butadiene latex, starch, carboxy-methyl cellulose and cellulose derivatives.

5. Heat-sensitive recording material according to claim 4, characterized in that the intermediate layer has a binder combination of styrene-butadiene latex together with starch.

6. A heat-sensitive recording material according to any one of claims 1 to 5, characterized in that the heat-sensitive recording layer comprises polyvinyl alcohol as a binder.

7. A heat-sensitive recording material according to any one of claims 1 to 5, characterized in that the heat-sensitive recording material comprises a recording layer covering, polyvinyl alcohol-containing protective layer.

The heat-sensitive recording material according to any one of claims 1 to 5, characterized in that the heat-sensitive recording material has a protective layer covering the recording layer and a polyvinyl alcohol-containing diffusion layer located between the heat-sensitive recording layer and the protective layer.

9. Heat-sensitive recording material according to any one of claims 7 and δ, characterized in that the protective layer comprises zinc stearate, as a binder, a polyvinyl alcohol, as a pigment aluminum hydroxide or / and silica and one or more crosslinkers.

10. A heat-sensitive recording material according to any one of claims 7 and 8, characterized in that the recording layer, the protective layer and, if provided, the diffusion layer are applied simultaneously by Gleitflächengießer.

11. A heat-sensitive recording material according to any one of claims 1 to 10, characterized in that the heat-sensitive recording material has a backside coating.