EP2043876B1 - Heat-sensitive recording material - Google Patents

Abstract

A description is given of a heat-sensitive recording material comprising: a sheetlike carrier; a thermoreactive layer on at least one side of the sheetlike carrier; and an interlayer, formed between the sheetlike carrier and the respective thermoreactive layer, which comprises hollow-sphere pigments embedded in a binder; and also, if appropriate, comprising top layers and/or further layers. This recording material is characterized in that the hollow-sphere pigments take the form of a composite pigment, with nanoscale pigment particles attached to the surface of an organic hollow-sphere pigment. This material can be produced inexpensively at high operating speed. The interlayers that are proposed in accordance with the invention exhibit optimum insulation capacity. They also have the effect of reducing or preventing the unwanted phenomenon of the text showing through, particularly when the thermoreactive layers are formed on both sides of the sheetlike carrier. The recording material exhibits a high optical density, runs very well in the thermal printer, in particular without depositing on or sticking to the thermal printing head in application, and the thermal print exhibits a homogeneous appearance.

Description

The invention relates to a heat-sensitive recording material having a flat support, a thermal reaction layer on at least one side of the planar support and an intermediate layer formed between the planar support and the respective thermal reaction layer, which contains hollow-sphere pigments embedded in a binder, and optionally with further layers and / or or upper layers.

A thermosensitive recording material of the type described above is apparent from the US-A-6,759,366 , This has on the top and the bottom of the carrier substrate each have a thermal reaction layer. The carrier substrate is preferably based on cellulose. It is thermally insulating. This ensures that only a symbol appears on the printed page during thermal printing. Preferably, a primer layer is formed between the carrier substrate and the thermal reaction layers, which serves to improve the adhesion of the layers. It is also intended to protect the thermal reaction layer from the action of active ingredients of the substrate. The primer layers are made from an aqueous mixture containing mainly clays. The known thermosensitive recording material may have so-called topcoats, which cause further desirable properties of the material.

That from the US-A-6,759,366 known thermosensitive recording material has various disadvantages. Thus, the above-mentioned insulating properties are not satisfactory. When using a thin carrier substrate with normal insulating ability, it is necessary to form the primer layers with a high weight order, otherwise there would be an undesirable breakdown from one side to the other. If one were to choose a stronger carrier substrate, then this would be associated with higher costs, an undesirably high rigidity of the material and a poor nestling of the thermal head to the substrate surface. In addition, difficulties may arise in the simultaneous formation of the clay-containing intermediate layers when applying the respective coating slips, so that the rheological properties of the coating slips must be controlled in a targeted and costly manner. Further disadvantages show up in the selection of the application method with regard to the cost-effective simultaneous formation of the clay-containing intermediate layers is limited when it comes to achieve a printing properties particularly favorable high surface smoothness of the intermediate layers. Finally, the maximum application rate is limited due to the rheologically problematic behavior of the clay-containing coating.

The invention is therefore the object of developing the above-mentioned recording material so that the disadvantages mentioned are eliminated. In particular, a satisfactory insulating effect with the smallest possible surface weight of the intermediate layers and low basis weight of the sheet carrier and a sufficiently adsorptive fixability for the present in the molten state materials should be ensured. The intermediate layers are intended to favor the opacity of the entire recording material, so that a show through of the respective labels of the two sides of the recording material is largely excluded. It should be a desirable high optical density, good runnability in the thermal printer, in particular without deposition or sticking to the thermal printing in the application, as well as a homogeneous or uniform appearance of the thermal expression possible. The recording material should be inexpensive to produce. In particular, there should be the possibility of simultaneous formation of the mutual intermediate layers and / or the thermal reaction layers at a high coating speed.

According to the invention, this object is achieved by a heat-sensitive recording material of the type described above in that the hollow sphere pigments are present as a composite pigment, wherein nanoscale pigment particles adhere to the surface of an organic hollow sphere pigment.

The core idea of the invention is the special formation of the intermediate layer between the thermal reaction layer and the flat support, wherein at least one intermediate layer contains composite pigments of the type described in a suitable binder, i. it is a composite pigment whose core is an organic hollow sphere pigment, on the surface of which nanoscale pigment particles adhere.

Preferably, the binder of the intermediate layer is in the form of a synthetic and / or natural polymer. Here, the invention in the selection is essentially free, unless the desirable thermoreaction is impaired. A binder in the form of water-soluble starches, starch derivatives, hydroxyethylcelluloses, polyvinyl alcohols, modified polyvinyl alcohols, acrylamide (meth) acrylate copolymers and / or acrylamide-acrylate-methacrylate terpolymers is preferred. Such materials result in a coating that is water soluble. On the other hand, in addition to such materials, there are also those which, when the intermediate layers are formed, lead to a water-insoluble structure. These are, for example, latices, such as polyacrylate esters, styrene-acrylate ester copolymers, styrene-butadiene copolymers, polyurethanes, acrylate-butadiene copolymers, polyvinyl acetates and / or acrylonitrile-butadiene copolymers and the like. The binder is used in particular to combine the intermediate layers favorably with the flat support, but also to ensure optimum bonding to the subsequent layer. It is the expert's intention to use here in a particular case a particularly suitable binder or a binder mixture.

The organic hollow sphere pigments which constitute the core of the composite pigments used according to the invention are known in the prior art. So far, such organic hollow-sphere pigments are not known, on the surface of which nanoscale pigment particles adhere, as used in the context of the invention as "composite pigments". When forming the intermediate layers of the novel recording material, it is possible to use aqueous dispersions of the composite pigment after incorporation of suitable binders. In the course of the process for producing the recording material in which drying processes occur, the aqueous portion of the dispersion of the composite pigments is evaporated with the result that the aqueous phase contained within the hollow spheres of the composite pigments evaporates, so that air-filled hollow spheres in the Remain composite pigment. The composite pigment preferably has a spherical equivalent diameter of about 1 to 10 μm, more preferably about 1.5 to 2.5 μm. The hollow spheres contained therein preferably have a spherical equivalent diameter of about 0.7 to 5 .mu.m, in particular about 0.8 to 1.5 microns. It is particularly advantageous if the organic hollow-sphere pigments have a void volume of about 20 to 70%, in particular from about 20 to 55%. The wall material of the organic hollow sphere pigments is designed such that on the one hand it has the required strength, on the other hand the outlet of the aqueous originally contained therein Phase allows what is achieved by a sufficient porosity. The preparation of such organic hollow sphere pigments is well known in the art. Thereafter, their wall material generally consists of organic polymers, in particular based on styrene-acrylic resins. Other wall materials can also be used, as far as the desired thermal reaction is concerned. In the context of the invention are therefore not pure organic hollow-sphere pigments, which are known in the art, used, but organic hollow-sphere pigments, which are superficially modified.

The skilled person has no problems in producing the composite pigment used in the present invention from the organic hollow sphere pigments of the prior art in order to meet the requirements of the present invention. Thus, for example, it is possible to slightly heat the hollow sphere pigments used, so that their surface softens to a certain extent, in order then to adhere the nanoscale pigment particles to it in a mixing process. The organic hollow-sphere pigments can also be applied to the surface of the organic hollow-sphere pigments in aqueous media. This can be done by inclusion of a suitable adhesive. In the selection of adhesives, the expert is also subject to no significant restriction. It is in particular a copolymer based on the reaction of one or more dicarboxylic acids as monomer and one or more monomers in the form of diamine, triamine, dialkanolamine and / or trialkanolamine. Preferred among these amines is the diamine monomer in the form of diethanolamine and / or triethanolamine. In principle, a copolymer based on a polyamide is of particular advantage, this going back to saturated or unsaturated, branched or unbranched C ₂ -C ₁₀ dicarboxylic acids, in particular in the form of adipic acid and the designated amine. The entire production of the composite pigment is preferably carried out in an aqueous dispersion, incorporated in conventional homogenization measures. It is also possible to carry out a milling process in which it is advisable to use dispersants or grinding aids. In addition, the already mentioned binder is introduced into the finally applied aqueous dispersion. However, the aqueous coating dispersion for forming the intermediate layers may contain other additives in order to optimize them.

It is also possible to provide the surfaces of the organic hollow sphere pigments with functional groups. These may be, for example, carboxylate groups. By means of a chemical bond with the respectively specially selected nanoscale pigment particles, the functional groups cause them to adhere sufficiently firmly to the surface of the organic hollow-sphere pigments. The ultimately obtained composite pigment is not critically limited in its diameter. It has been found that the composite pigment preferably has a spherical equivalent diameter of about 1 to 10 μm, in particular of 1.5 to 2.5 μm.

The nanoscale pigment particles by means of which the known organic hollow-sphere pigments are surface-modified and optimized with regard to their surface properties are as follows: These are, in particular, alkaline earth carbonates, in particular calcium and / or magnesium carbonate, dolomite, crystalline and / or amorphous aluminum hydroxide, synthetic and / or natural field silicates, calcium and / or magnesium sulfate, titanium dioxide, calcined clays, clays, talc, mica, zinc oxide, transparent iron pigments, coloring pigments, synthetic polystyrene-based pigments and / or based on urea-formaldehyde Resin. It is particularly preferred that the calcium carbonate in the form of precipitated and / or natural calcium carbonate, in particular with calcitic, vateritic or aragonitic crystal structure, and / or in the form of ground natural calcium carbonate present. With respect to the spherical equivalent diameter of the nanoscale pigment particles, the invention is not subject to any critical limitation. It is preferred if their spherical equivalent diameter is about 20 to 500 nm, especially about 150 to 300 nm.

In addition, the following is said about the term " composite pigment " in the form of surface-modified organic hollow-sphere pigments: If this is referred to as "hollow spheres" , this should be understood as far as possible. On the one hand, this includes expressly spherical or spherical structures, on the other hand also hollow spherical particles, such as those which have a hollow hemispherical structure. It is crucial for the desired purposes that the "hollow spheres" or corresponding structures in the heat-sensitive recording material, in particular the to provide desirable insulating properties due to air entrapment and, in addition, to provide further modifying properties by the application of nanoscale particles to their surface. As a result, positively affecting surface properties are set herewith.

It has been found that the incorporation of the designated composite pigments leads to an optimal solution to the stated problem, as described above. It is surprising that they are not impaired in their effect during the entire manufacturing process when there is noticeable action of shear forces, as is the case with the film press application advantageously used here. Surprisingly, the smoothness of the intermediate layers achieved in this case is high even without the aid of additional smoothing measures, which has an advantageous effect on the quality of the printed image.

It is preferable that both intermediate layers of the heat-sensitive recording material of the present invention contain the designated composite pigments. The quantitative inclusion of these pigments is not subject to any critical limitation. However, at least one of the intermediate layers contains the composite pigments in an amount of 5 to 90 wt .-%, in particular from about 80 to 50 wt .-%, based on the dry mass of the intermediate layer material. Thus, it is particularly advantageous if the flat carrier of the recording material has on both sides a thermal reaction layer with intermediate layers containing composite pigments. In addition, further additives may be included in the recording material according to the invention within the scope of purely expert considerations for property favorability, in particular optical brighteners.

In individual cases, it has proved expedient that at least one of the intermediate layers contains further pigments for controlling the porosity and the adsorption capacity of the intermediate layer. The optimization of the porosity and the absorption behavior has an advantageous effect on the quality of the printed image and on the runnability in the thermal printer. Thus, the printed image is fixed by an optimized porosity in a particularly advantageous manner. The other pigments which may be contained in the intermediate layer are in the form of natural or precipitated calcium carbonate, clays or calcined clays, diatomaceous earths, alumina, aluminum hydroxide, Silicas, magnesium silicates and / or magnesium carbonates before. Organic pigments may also be considered, such as urea-formaldehyde condensates and the like. Advantageously, the further pigments are optimized with respect to the spherical equivalent diameter and adjusted to a spherical equivalent diameter of about 0.1 to 10 .mu.m, in particular from about 1 to 5 .mu.m.

The selection of the material of the flat carrier is not critical. For example, it can be a paper carrier based on cellulose fibers, a synthetic paper carrier whose fibers consist, in particular, wholly or partly of synthetic fibers, but also a plastic film.

Preferably, the sheet carrier, the intermediate layers and the thermal reaction layers are optimized with respect to their basis weight. Thereafter, it is preferred that the sheet carrier has a basis weight of about 20 to 600 g / m ² , in particular from about 40 to 300 g / m ² , the intermediate layers have a basis weight of about 1 to 10 g / m ² , in particular of about 2 to 6 g / m ² , and / or the thermal reaction layers have a basis weight of 1 to 8 g / m ² , in particular about 2 to 6 g / m ² . The weight per unit area of the heat-sensitive recording material according to the invention is preferably between about 30 and 650 g / m ² , in particular between about 40 and 100 g / m ² , to meet the practical requirements.

Within the scope of the invention it is possible to provide further layers. For example, it may be an outer layer that has the function of a protective layer. Such one advantageously consists of film-forming polymers, such as polyvinyl alcohols, modified polyvinyl alcohols, polyacrylates and polyurethanes, into which pigments are still incorporated, it being expedient to crosslink the film-forming polymer. The function of the protective layer is particularly favorable if the film-forming polymer is substantially crosslinked. Crosslinking generally takes place by incorporation of crosslinking promoting agents during the drying of the coating used in the formation of the protective layer.

There is no relevant limitation in the selection of the color former and the color developer for the thermal reaction layers of the recording material of the present invention. In this case, preference is given to color formers in the form of 2-anilino-3-methyl-6-diethylamino-fluoran, 2-anilino-3-methyl-6-di-n-buthylamino-fluoran, 2-anilino-3-methyl-6 - (N-ethyl, Np-toluidino-amino) -fluoran, 2-anilino-3-methyl-6- (N-methyl-, N-propyl-amino) -fluoran, and / or 3.3-bis- (4 -dimethylaminophenyl) -6-dimethyl-amino-phthalide, and the color developers in the form of phenol derivatives such as 2,2-bis- (4-hydroxyphenyl) -propane, bis- (4-hydroxyphenyl) -sulfone, 4-hydroxy-4 '-iso-propoxy-diphenyl-sulfone, bis (3-allyl-4-hydroxyphenyl) -sulfone, 2,2-bis (4-hydroxyphenyl) -4-methyl-pentane, N- (benzenesulfonyl) - N '- (3-p-toluenesulfonyl-oxy-phenyl) -urea, zinc salts of derivatives of salicylic acid, the binders in the form of water-soluble starches, starch derivatives, hydroxyethylcelluloses, polyvinyl alcohols, acrylamide (meth) acrylate copolymers, acrylamide-acrylate lat-methacrylate terpolymers and / or latices, such as polyacrylates, poly (meth) acrylic acid esters, styrene-butadiene copolymers, polyurethanes, acrylates t-butadiene copolymers. In the thermal reaction layer, various other properties or auxiliaries may be present. These may be, for example, sensitizing melt aids, lubricants, rheological aids, fluorescent substances and the like.

The sensitizing melt aids are, for example, in the form of 2-benzyloxynaphthalene (BON), p-benzylbiphenyl (PBBP), oxalic acid dibenzyl ester, oxalic acid di (p-methylbenzyl) ester, 1,2-bis (phenoxy-methyl) benzene , 4- (4-Tolyloxy) biphenyl, ethylene glycol diphenyl ether, ethylene glycol m-tolyl ether and 1,2-bis (3,4-dime-phenyl-phenyl) -ethane and the lubricant in the form of fatty acid amides, such as. B. stearic acid amide, fatty acid alkanolamides, such as. As stearic acid methylolamide, ethylene bisalkanoylamides, such as. B. ethylene-bis-stearoylamide, synthetic waxes, such as. As paraffin waxes of different melting points, ester waxes of different molecular weights, ethylene waxes, propylene waxes of different hardness or natural waxes such. As carnauba wax and / or fatty acid metal soaps, such as. As zinc stearate, calcium stearate or behenate salts, the rheology aids in the form of water-soluble hydrocolloids, such as starches, starch derivatives, sodium alginates, polyvinyl alcohols, methylcelluloses, hydroxyethyl or hydroxypropylmethylcelluloses, carboxymethylcelluloses, poly (meth) acrylates, the optical brightener in Shape of whiteners z. B. from the substance groups diaminostilbene-disulfonic acid, distyryl-biphenyls, benzoxazole derivatives, the fluorescent substances in the form of daylight fluorescent pigments of different hues or fluorescent fibers, the aging inhibitors in the form of sterically hindered phenols, such as 1.1.3-tris- (2-methyl- 4-hydroxy-5-cyclohexyl-phenyl) -butane, 1.1.3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) -butane, 1,1'-bis (2-methyl-4-) hydroxy-5-tert-butyl-phenyl) -butane and 1,1'-bis (4-hydroxyphenyl) -cyclohexane.

In principle, with the formation of the thermosensitive recording material of the present invention shown above, a functional material is present. It is expedient in individual cases to form further layers on-line or off-line on the thermal reaction layer as a protective layer and / or as a printability-promoting layer.

A variety of methods are available to those skilled in the art to prepare the thermosensitive recording material of the invention. Thus, for example, both sides of the carrier substrate can be provided on-line in the paper machine simultaneously with the coating compound for forming the intermediate layers. It is also possible first to provide the one and then the other side of the carrier substrate with intermediate layers. The respective order procedure is therefore subject to no restrictions and can be carried out in the usual way. The same applies to the formation of the thermal reaction layer, in which an aqueous dispersion containing the necessary and promoting constituents is applied and dried in a conventional manner. The skilled person therefore requires no further technical instructions.

The advantages associated with the present invention can be summarized essentially as follows: The two thermal reaction layers are excellently isolated in the thermal printing process. This leads to high quality prints. This is achieved with a small basis weight of the intermediate layers. The interlayers further favor the opacity of the recording material so that bleed through of the respective labels of the two sides of the recording material is reduced or largely eliminated. The recording material is economical and technically easy to produce. This can be done with high coating speeds, which applies to all layers. In addition, the chemical modification of the surface of the organic hollow sphere pigments with nanoscale particles leads to a porous structure of the intermediate layer and thereby favors the adsorption of the melt forming in the thermal layer in the application case, whereby an optimal runnability in the thermal printer, in particular without deposition or sticking to the thermal print head , And a homogeneous appearance of the thermal printing is achieved. The edge sharpness of the printout and the machine readability of a bar code are improved. Furthermore, due to the high thermal insulating effect of the composite pigments used in the present invention from the intermediate layer, the dissipation of heat energy from the thermal layer is suppressed, thereby obtaining a recording material having a high dynamic sensitivity.

Finally, one must point out a significant advantage that results over a pure mixture of organic hollow sphere pigments and nanoscale particles. The nanoscale particles tend to form agglomerates. This reduces the reactive surface. On the other hand, such a mixture, when applied in the form of an aqueous dispersion, leads to a considerable extent to segregation when the dispersion is applied to the flat support. The heavier inorganic particles settle down, while the organic hollow sphere pigments float more or less. It has been shown by comparative experiments, which will be discussed below, that the composite pigments according to the invention in terms of the desired physical effects show a clear superiority over such pure mixtures.

The invention will now be explained in detail by way of non-limiting examples. All weights are based on otro (oven dry) percentages by weight.

Examples 1. Production of the coating compounds for the formation of the intermediate layers

Table I Recipe 1 wet ground
100% kg OTRO
kg water 0.21 --- Dow latex (48.5%) * ¹ 15,12 7.34 Ropaque HP-1055 (26.5%) * ² 75.22 19.93 PVA low viscosity, highly saponified (20%) 8.95 1.79 Leukophor UO (31.3%) * ³ 0.27 0.08 Rheology tools (25%) * ⁴ 0.23 0.06 order bulk 100 29.2 Notes :
* ¹ styrene-butadiene latex type binder
* ² hollow sphere pigment Fa. Rohm & Haas (styrene-acrylate polymer) Average diameter: about 1 μm, wall diameter: about 0.1 μm
* ³ optical brightener (anionic stilbene derivative) (Clariant)
* ⁴ Sterocoll type (BASF) (copolymer of acrylic acid esters and carboxylic acids)
pH: 7.7; Brookfield viscosity (100 rpm, spindle 3, 20 ° C): 550 mPas;
Order: about 3 g / m ² Table II Recipe 2 wet ground
100% kg OTRO
kg water 1.88 --- Dow latex (48.5%) * ¹ 5.03 2.44 VP Composite * ² 83,99 29.4 PVA low viscosity, highly saponified (20%) 8.62 1.72 Leukophor UO (31.3%) * ³ 0.31 0.1 Rheology tools (25%) * ⁴ 0.17 0.04 order bulk 100 33.7 Notes :
* ¹ styrene-butadiene latex type binder
* ² Composite pigment from Ropaque HP-1055 and nanoscale calcium carbonate (75%: 25% otro) from Omya AG
* ³ optical brightener (anionic stilbene derivative) (Clariant)
* ⁴ Sterocoll type (BASF) (copolymer of acrylic acid esters and carboxylic acids)
pH: 8.2; Brookfield viscosity (100 rpm, spindle 3, 20 ° C): 400 mPas; Order: about 3 g / m ² Table III Recipe 3 wet ground
100% kg OTRO
kg water 1.88 --- Dow latex (48.5%) * ¹ 5.03 2.44 Mixture Ropaque HP-1055 and calcium carbonate * ² 83,99 29.4 PVA low viscosity, highly saponified (20%) 8.62 1.72 Leukophor UO (31.3%) * ³ 0.31 0.1 Rheology tools (25%) * ⁴ 0.17 0.04 order bulk 100 33.7 Notes :
* ¹ styrene-butadiene latex type binder
* ² physical mixture of Ropaque HP-1055 and nanoscale calcium carbonate (75%: 25% otro) Fa. Omya AG
* ³ optical brightener (anionic stilbene derivative) (Clariant)
* ⁴ Sterocoll type (BASF) (copolymer of acrylic acid esters and carboxylic acids)
pH: 8.4; Brookfield viscosity (100 rpm, spindle 3, 20 ° C): 400 mPas;
Order: about 6 g / m ²

Recipe 4 :

analogous formulation 2, but with about 5 g / m ² order

Recipe 5 :

analogous formulation 2, but with about 7 g / m ² order

Second Training of the intermediate layer

The order of an application suspension for forming the intermediate layer of a thermal paper was carried out on one side on-line in the paper machine by means of a Film press at an operating speed of 1000 m / min on a paper web of a basis weight of 65 g / m ² . After application of the aqueous application suspension, the drying process of the coated paper support was carried out in a customary manner.

Third Preparation of the coating composition for forming the heat-sensitive layer

A coating dispersion A is prepared by milling 25 parts by weight of 2-anilino-3-methyl-6- (N-ethyl-, N-isopentyl-amino) -fluoran with 45 parts by weight of a 15% aqueous polyvinyl alcohol solution in a ball Mill produced to an average particle size of 1.5 microns.

A coating dispersion B is prepared by milling 50 parts by weight of 2,2-bis (4-hydroxyphenyl) propane together with 35 parts by weight of benzyl naphthyl ether 90 parts by weight of a 15% polyvinyl alcohol aqueous solution and 24 Parts by weight of water in a mill to an average particle size of 1.5 microns.

A heat-sensitive coating dispersion was prepared using dispersions A and B according to the following recipe. Table IV wet ground
100% kg OTRO
kg PVA highly viscous, highly saponified (10%) 32.3 3.23 Leukophor UO (31.3%) * ¹ 0.77 0.24 PCC slurry (55%) * ² 18.25 10.04 Dispersion B 21.64 10.71 Stearic acid amide dispersion * ³ 12,92 5,65 3.23 1.13 Dispersion A 7.66 3.45 Rheology tools (25%) * ⁴ 0.65 0.16 water 0.16 --- Notes :
* ¹ optical brightener (anionic stilbene derivative) (Clariant)
* ² d ₅₀ : 1.0 μ, calcite type,
* ³ Fa. Chukyo
* ⁴ Sterocoll type (BASF) (copolymer of acrylic acid esters and carboxylic acids)

Dry content about 32.2% by weight; pH: 8.6; Brookfield viscosity (100 rpm, spindle 3, 20 ° C): 420 mPas; Surface tension (static ring method according to Du Noüy) 47 mN / m.

4th Formation of a heat-sensitive layer

The heat-sensitive coating suspension thus obtained was used to prepare a thermosensitive recording material in the form of a thermal paper. The order was carried out at about 5.0 g / m ² (otro) with the aid of an in-line curtain coating coating unit. The application speed was 1200 m / min. After the application of the aqueous coating dispersion, the drying process of the coated paper carrier took place in a customary manner.

By coating base paper with the interlayer coating dispersions it. Formulation 1-5 and subsequent application of the heat-sensitive layer, the thermal papers Example 1-5 are obtained from Table 1. Prior to printing, all papers were brought to comparable smoothness (350 ± 30 Bekks).

Scanning electron micrographs of the paper surface before coating with the heat-sensitive layer illustrate the different surface properties of the intermediate layers of formulation 1 (FIG. Fig. 1 ), Recipe 2 ( Fig. 2 ) and recipe 3 ( Fig. 3 ).

5. The performance of the precursors was evaluated on the basis of application technology tests on heat-sensitive recording material (Table V):

1. 1. Dynamic Sensitivity
2. 2. Bar code readability
3. 3. Place on the thermal bar

The thermal prints were generated on an Atlantek Thermo Test Printer Model 200 (Atlantek USA). A Kyocera thermal head of 200 dpi was used.

Dynamic Sensitivity : Dynamic image density (optical density) was measured on a Gretag Macbeth densitometer type D19C on a checkerboard pattern produced with the Atlantek test printer at 0.25 mJ / dot and 0.50 mJ / dot.

Bar Code Readability : A bar code sample printout (code UPC-A and code 39) was generated at 0.60 mJ / dot energy on the Atlantek test printer.

The evaluation was carried out with the REA PC-Scan bar code tester (REA Elektronik Deutschland) according to ISO 15416. The laser scanner operates at a wavelength of 670 nm. The evaluation was carried out on the basis of the scan reflection profile class (descending quality of the barcode): A (4), B (3), C (2), D (1), E (0).

Depositing on the thermal bar : 5 m thermal paper was continuously printed with a checkerboard pattern using the manufacturer's settings with two commercially available thermal printers: Epson TM-T88 II (Printer A) and Mettler LP (Printer B). The thermal bar was visually scored for deposits and soils and rated as follows: 0 = none, 1 = detectable / light, 2 = medium, 3 = strong / unacceptable. Table V template optical density Drop thermal bar Reflection profile class * 0.25
mJ / dot 0.50
mJ / dot A B example 1 1.23 1.36 1-2 2 D (1), E (0), D (1) Example 2 1.26 1.40 0 0-1 C (2), D (1), C (2) Example 3 1.25 1.36 1-2 2 D (1), E (0), D (1) Example 4 1.30 1.41 0 0-1 C (2), D (1), B (3) Example 5 1.29 1.43 0 0-1 C (2), D (1), B (3) Note :
* Evaluation of three different barcodes: longitudinal - transverse - longitudinal

Claims (25)

1. A heat-sensitive recording material comprising a sheet-like carrier, a thermoreactive layer on at least one side of the sheet-like carrier and an interlayer which is formed between the sheet-like carrier and the respective thermoreactive layer and contains hollow-sphere pigments embedded in a binder, as well as, if appropriate, comprising further layers and/or top layers, characterised in that the hollow-sphere pigments are present as composite pigment, with nanoscale pigment particles adhering to the surface of an organic hollow-sphere pigment.
2. A recording material according to claim 1, characterised in that the nanoscale pigment particles are alkaline earth carbonates, especially calcium and/or magnesium carbonate, dolomite, crystalline and/or amorphous aluminium hydroxide, synthetic and/or natural field silicates, calcium and/or magnesium sulphate, titanium dioxide, calcined clays, clays, talc, mica, zinc oxide, synthetic pigments based on polystyrene and/or based on urea-formaldehyde resins or mixtures of said pigment particles.
3. A heat recording material according to claim 2, characterised in that the calcium carbonate is present in the form of precipitated and/or natural calcium carbonate, especially with a calcitic, vateritic or aragonitic crystal structure, and/or in the form of ground natural calcium carbonate.
4. A recording material according to any one of claims 1 to 3, characterised in that the wall material of the organic hollow-sphere pigments is based on organic polymers, in particular on styrene/acrylic polymers and/or polystyrene.
5. A recording material according to any one of claims 1 to 4, characterised in that the organic hollovv-sphere pigments of the composite pigment have a spherical equivalent diameter of about 0.6 to 5 µm, especially from about 0.8 to 1.5 µm and the nanoscale pigment particles have a spherical equivalent diameter of about 20 to 500 nm, especially from about 150 to 300 nm.
6. A recording material according to claim 5, characterised in that the composite pigment has a spherical equivalent diameter of about 1 to 10 µm especially from about 1.5 to 2.5 µm.
7. A recording material according to at least any one of claims 1 to 6, characterised in that the organic hollow-sphere pigments have a cavity volume of about 20 to 70% especially from about 20 to 55%.
8. A recording material according to at least any one of claims 1 to 7, characterised in that at least one of the interlayers contains the composite pigment in a quantity of 5 to 90 % by weight, especially from 50 to 80 % by weight, based on dry mass.
9. A recording material according to at least any one of claims 1 to 8, characterised in that the adhesion of the nanoscale pigment particles to the surface of the organic hollow-sphere pigments is brought about by an adhesive.
10. A recording material according to claim 9, characterised in that the adhesive is a copolymer which originates from the reaction of one or more dicarboxylic acids as a monomer and of one or more monomers in the form of diamines, triamines, dialkanolamines and/or trialkanolamines.
11. A recording material according to claim 10, characterised in that the copolymer is a polyamide, which originate from saturated or unsaturated, branched or unbranched C₂-C₁₀ dicarboxylic acids, especially in the form of adipic acid, and the designated amines.
12. A recording material according to claim 10 or claim 11, characterised in that the diamine monomer is diethanolamine and/or triethanolamine.
13. A recording material according to at least any one of the preceding claims, characterised in that the sheet-like carrier of the recording material has, on both sides, a thermoreactive layer with interlayers containing composite pigments.
14. A recording material according to at least any one of the preceding claims, characterised in that at least one of the interlayers contains further pigments in order to control the porosity and absorption capacity thereof.
15. A recording material according to claim 14, characterised in that the further pigments are present in the form of natural and/or precipitated calcium carbonate, clays or calcined clays, diatomaceous earths, aluminium oxide, aluminium hydroxide, silicic acid, magnesium silicates and/or magnesium carbonates.
16. A recording material according to claim 14 or claim 15, characterised in that the further pigments have a spherical equivalent diameter of about 0.1 to 10 µm, especially from about 1 to 5 µm.
17. A recording material according to at least any one of the preceding claims, characterised in that further additives, especially optical brighteners, are incorporated to promote properties.
18. A recording material according to at least any one of the preceding claims, characterised in that the sheet-like carrier is a paper carrier based on cellulose fibre, a synthetic paper carrier, the fibres of which comprise completely or partially of plastics material fibres, or a plastics material film.
19. A recording material according to at least any one of the preceding claims, characterised in that the sheet-like carrier has a weight per unit area of about 20 to 600 g/m², especially from about 40 to 300 g/m², the respective interfayer(s) have a weight per unit area of about 1 to 12 g/m², especially from about 2 to 7 g/m² and/or the thermoreactive layer(s) have a weight per unit area of 1 to 8 g/m², especially about 2 to 6 g/m².
20. A recording material according to at least any one of the preceding claims, characterised in that it has, as the top layer, a protective layer of film-forming polymers, which contains pigments, especially.
21. A recording material according to claim 20, characterised in that the film-forming polymer is cross-linked.
22. A recording material according to at least any one of the preceding claims, characterised in that the weight per unit area of the recording material is between about 30 and 650 g/m², especially between about 40 and 100 g/m².
23. A recording material according to at least any one of claims 9 to 22, characterised in that about 0.25 to 9 % by weight, especially about 0.5 to 6.5 % by weight of adhesive, are allotted to 1 part by weight dry weight of the composite pigment.
24. A recording material according to at least any one of the preceding claims, characterised in that the binder of the respective interlayer is a synthetic and/or natural polymer.
25. A recording material according to claim 24, characterised in that the binder is present in the form of vvater-soluble starches, starch derivatives, hydroxyethyl celluloses, polyvinyl alcohols, modified polyvinyl alcohols, acrylamide-(meth-)acrylate copolymers and/or latices, such as especially polyacrylates,' styrene-butadiene copolymers, polyurethanes, acrylate-butadiene copolymers, polyvinyl acetates and/or acrylonitrile-butadiene copolymers.

Images