WO1992018337A1

WO1992018337A1 - Heat-sensitive recording material

Info

Publication number: WO1992018337A1
Application number: PCT/EP1991/000763
Authority: WO
Inventors: Andrea Richter
Original assignee: Renker Gmbh & Co. Kg
Priority date: 1990-04-14
Filing date: 1991-04-20
Publication date: 1992-10-29
Also published as: DE4012186C1

Abstract

Heat-sensitive recording material with a heat-sensitive recording layer on a substrate containing 3-dibutylamino-6-methyl-7-anilinofluorane as a weakly basic colour precursor compound and an acid organic compound as the colour-developing reactant and having an electron-beam-cured protective layer of cross-linked polymers over the recording layer. The quantity of colour precursor compounds is 2 to 100 g per 100 g colour-developing organic compounds in the recording layer.

Description

Heat sensitive recording material

The invention relates to a heat-sensitive recording material whose heat-sensitive recording layer contains a special color precursor compound and which has a protective layer covering the recording layer, the film-forming agents of which are polymers produced from electron beams from oligomers.

Heat-sensitive recording materials with a protective layer protecting the recording layer and hardened by means of an electron beam are known from DE-A-3312716. The protective layer with a basis weight of

0.1 to 20 g per m ² , which can contain 5 to 300 parts by weight of pigment per 100 parts by weight of film-forming resin, is formed from oligomers liquid at room temperature with at least one ethylenically unsaturated bond per molecule and the oligomers are converted into polymers by curing with electron beams. The formation of the heat-sensitive layer is not critical, and as a color Ending reactants can be used both metal salts of higher fatty acids, such as iron III stearate and gallic acid or other polyhydric phenols, and weakly basic dye precursor compounds in combination with organic acidic substances. 3-Dibutylamino-6-methyl-7-anilinofluoran is not mentioned among the numerous dye precursor compounds based on fluoranes. EP-A-306916 discloses a particularly storage-stable, heat-sensitive recording material in which 3-dibutylamino-6-methyl-7-anilinofluorane and 3-dibutylamino-7-chloroanilinofluorane in combination with bis- (3-allyl-4 -hydroxyphenyl) sulfone and dibenzylo: xalate can be used as acidic reactants. The special combination of dye precursor compound with the special acidic color-developing compounds results in a storage-stable material whose heat-sensitive recording layer can optionally be covered with a protective layer made of a water-soluble polymer. This publication does not contain any references to the use of other acidic color-developing compounds.

The object of the invention is to provide a heat-sensitive recording material whose recording layer has a lower tendency to gray the background of the image than the known recording materials.

This object is achieved by a heat-sensitive recording material having a heat-sensitive recording layer which is arranged on a carrier material and which contains a weakly basic color precursor compound and acidic organic compounds (as a color-developing reactant) and that an agent is applied over the recording layer

Has electron beam cured protective layer of crosslinked polymers, which is characterized in that the Recording layer as the basic color precursor compound contains 3-dibutylamino-6-methyl-7-anilinofluoran in an amount of 2 to 100 g per 100 g of color-developing organic compounds.

The protective layer covering the heat-sensitive recording layer is produced from one or more oligomers which are liquid at room temperature and have at least one ethylenically unsaturated bond per molecule, the oligomers being polymerized and crosslinked by means of electron beams, so that a water-insoluble and solvent-insoluble protective layer is formed.

Completely surprisingly, it has been found that the combination of a special color precursor compound in the heat-sensitive recording layer with an electronically hardened and crosslinked polymeric protective layer results in heat-sensitive recording materials which show a higher contrast of the recording formed than can be achieved with other known color formers. If protective layers are formed from water-soluble polymers according to the teaching of EP-A-306916, this increase in the contrast and reduction in background fermentation is not achieved.

In a preferred embodiment of the recording material according to the invention, an intermediate layer of polymers hardened and crosslinked by means of electron beams is present between the carrier material and the heat-sensitive recording layer. The intermediate layer is formed with a basis weight of 1 g per m ² to 10 g per m ² . The formation of such an intermediate layer has the advantage that the influence of the carrier material on the color formation reaction and the contrast of the resulting recording is suppressed with respect to the image background. In particular when using paper as a carrier material, any coating base papers can be used. Backing papers with special surface smoothness are not required.

The intermediate layer prevents the coating composition for the recording layer from penetrating too deeply into the carrier material and reduces the outflow of heat into the carrier material during use.

However, plastic films can also be used as the carrier material.

Coating base papers suitable as a carrier material preferably have a surface sizing which contains polymers which, under the influence of electron radiation, adhere

are capable of graft copolymerization with the oligomers of the intermediate layer. Such a graft copolymerization can also occur with plastic films as the carrier material and improve the adhesion of the intermediate layer.

When an intermediate layer is formed from oligomers, these are first polymerized out only to such an extent that the heat-sensitive recording layer can be applied. The final hardening then takes place when the protective layer is treated with electron beams.

In a preferred embodiment of the invention, the heat-sensitive recording layer contains as film-forming binder at least one synthetic polymer which is capable of a graft copolymerization, so that under the action of the electron beams when the liquid oligomers harden, a graft copolymerization of the oligomers with the or Polymers of the binder system of the heat sensitive

Recording layer at the interface between the

Protective layer and / or the intermediate layer takes place. This leads to a stronger bond between the layers.

While according to the teaching of EP - A - 306916 as a color-developing compound bis (3'-allyl-4'-hydroxyphenyl) sulfone and or dibenzyl oxalate or derivatives thereof are required to achieve advantageous results, other organic acidic developers can also be used according to the invention. Materials are used that can form a color image with the special dye precursor. These include organic acidic materials such as phenolic compounds, e.g. B. 4-tert-butylphenol, 4-tert.-octylphenol, 4-phenylphenol, 4-acetylphenol, α-naphthol, β-naphthol, hydroquinone, 2,2'-dihydroxydiphenyl, 2,2'-methylene-bis (4th -methyl-6-tert-butylphenol), 2,2'-methylene-bis- (4-chlorophenol), 4,4'-dihydroxy-diphenyl-methane, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene - bis (2-tert-butylphenol),

4,4'-sec-butylidene diphenol, 4,4'-cyclohexylidene diphenol, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-methylphenol) 4,4'-dihydroxydiphenyl sulfone, Benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolak phenolic resins and phenolic polymers; aromatic carboxylic acids such as B. benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert- Butyl salicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3-chloro-5 (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-phenyl-5- ( α, α-dimethylbenzyl) salicylic acid, 3,5-di (α-methylbenzyl) salicylic acid and terephthalic acid; furthermore the salts of such phenolic compounds or aromatic carboxylic acids with polyvalent metals such as e.g. B. zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel. Bisphenol-A is very particularly preferred according to the invention as an acidic color developer. In the production of the heat-sensitive recording materials according to the invention, the recording layer is formed by applying a coating composition which, in addition to the special fluorane derivative, also contains the acidic developer compound in addition to the customary auxiliaries for this layer. The heat-sensitive recording layer contains starch as a binder. Hydroxyethyl cellulose, methyl cellulose, CMC, casein, polyvinyl alcohol, copolymers of styrene and maleic anhydride or copolymers of styrene and acrylic acid or methacrylic acid and polymer dispersions which are used as binders for paper coatings. The binder content is 2 to 40, preferably 5-25 percent by weight, based on the total solids of the heat-sensitive recording layer.

The heat-sensitive recording layer particularly preferably contains at least one synthetic polymer which is capable of graft copolymerization. Particularly suitable synthetic polymers are polyacrylates, polymethacrylates, polyacrylamides, polymethacrylamides, polystyrene copolymers, polyacrylonitrile, polymethacrylonitrile, polyvinylidene chloride, polyvinyl alcohols, polyvinolpyrrolido.n, polyvinyl acetals, cellulose derivatives. The chemical valence bonds in these film-forming polymers are activated by high-energy electron beams to the extent that they are capable of reactions, in the presence of monomers and oligomers, in particular of graft copolymerization and crosslinking. According to the invention, the binder system of the recording layer preferably contains a proportion of such

Polymers. Suitable meltable compounds such as amide waxes, fatty acid amides, carnauba wax, paraffin wax, calcium stearate, ester waxes, dimethyltherephthalate and p-benzylbiphenyl are used to adjust the heat sensitivity of the recording layer.

The recording layer can also contain inorganic pigments such as kaolin, clay, calcium carbonate, titanium dioxide, silicon dioxide.

The amount of inorganic pigments in the recording layer can be 10 to 60 percent by weight based on the total weight of the coating composition.

Furthermore, various conventional auxiliaries can be added to the heat-sensitive coating composition, such as dispersants, anti-foaming agents, UV absorbers, stabilizers.

The amount of meltable compounds such as waxes, amides or organic compounds with melting ranges from 60 ° to 180 ° C. is generally 10 to 1000 parts by weight per 100 parts by weight of color-forming compounds.

The components of the coating composition are dispersed using water as the dispersing medium with the aid of suitable dispersing devices. The reactants can be dispersed both separately and together, with separate dispersing being preferred. So-called agitator ball mills are particularly preferred as the dispersing device. The composition for the heat-sensitive recording layer can be applied using customary methods of paper coating technology. The amount of coating is generally 2 to 12 g per m ² , preferably 3 to 10 g per m ² , the values relating to the dry weight.

The polymer layer crosslinked by the electron radiation is then formed on the dried, heat-sensitive recording layer as a protective layer.

The protective layer is made from a coating composition containing one or more oligomers with at least one ethylenically unsaturated bond in the molecule. The oligomers which are liquid at room temperature can be used as oligomers or a mixture and generally have a molecular weight of up to 50,000. It is essential that the oligomers may be combined so that the viscosity of the coating composition allows the application of a uniform liquid film.

Examples of such oligomers are:

1. Unsaturated polyesters, such as condensation products from

Maleic acid, fumaric acid and other unsaturated

dibasic acids, phthalic acid and ethylene glycol or other dihydric alcohols.

2. Polyester acrylates or polyester methacrylates, such as condensation products of phthalic acid, maleic acid, fumaric acid or other dibasic acids, ethylene glycol, glycerin, pentaerythritol or other polyhydric alcohols with acrylic acid or methacrylic acid. 3. Urethane acrylates or urethane methacrylates, ie condensation products of ethylene glycol or other polyhydric alcohols, adipic acid and other dibasic acids, polyisocyanates, especially di-isocyanates and acrylic acid or methacrylic acid.

4. epoxy acrylates or epoxymethacrylates, these are reaction products of an epoxy resin with acrylic acid or

Methacrylic acid.

5. Silicone acrylates or silicone methacrylates, that is

Reaction products of an acryloyl- or methacryloylalkoxysilane and an organopolysiloxane.

6. Polybutadiene acrylates or polybutadiene methacrylates, that are reaction products of a polybutadiene oligomer of a polyisocyanate and hydroxyalkyl acrylate or hydroxyalkyl methacrylate.

7. Polyether acrylates or polyether methacrylates, that are

Condensation products of acrylic acid or methacrylic acid and addition products of trimethylol, propane, pentaerythritol and other polyhydric alcohols and alkylene oxide.

8. Melamine acrylates or melamine methacrylate, these are condensation products of methylolmelamine and hydroxyalkyl acrylate or hydroxyalkyl methacrylate.

The same oligomers can also be used to form an intermediate layer between the support material and the heat-sensitive recording layer. The protective layer and the intermediate layer can also contain pigments in addition to the film-forming polymer. Suitable pigments are inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, caolin, clay, calcined clay. However, organic pigments such as polystyrene, microspheres, nylon powder, polyethylene powder, zinc stearate, magnesium stearate, calcium stearate and barium stearate can also be used. Suitable pigments have one

Particle size of 0.3 - 5 microns and can be used in amounts of 0.2 to 300 parts by weight per 100 parts by weight of polymer component. Amounts of 0.2 to 4.5 parts by weight per 100 parts by weight of the polymer component of the resin layer are particularly preferred.

The protective layer is applied in amounts of 1 g per m ² to 10 g per m ² (as a crosslinked polymer coating). Amounts of 2 to 5 g per m ² , based in each case on the weight of the crosslinked protective layer, are particularly preferred.

Electron beam accelerators suitable for hardening the protective layer or the intermediate layer are commercially available.

These are devices with which the electron beam can be accelerated with an energy of up to 1000 KeV, preferably with an energy of 100 to 500 KeV. The oligomer layer is irradiated with the electron beam of a suitable dosage, the dosage being based on the

Requirements of the special oligomer or the oligomer mixture are adapted such that the oligomers are polymerized and crosslinked to form a water-insoluble and solvent-insoluble layer. The radiation dose required is 0.1 Mrad to 20 Mrad, preferably 3 to 10 Mrad. If, according to a preferred embodiment of the invention, a graft copolymerization between monomers and oligomers and a synthetic polymer is desired in the recording layer at the interfaces between the recording layer and the protective layer and / or the intermediate layer, a somewhat higher radiation dose is used than for crosslinking and curing the oligomers to activate the synthetic polymers in the recording layer to the extent that the desired graft copolymerization occurs.

The yield of free radicals and graft copolymers formed by radiation can be expressed by a so-called G value, where

The G value is an expression of the yield of the

Radiation caused chemical reactions between the oligomers with one another and the polymers in the adjacent recording layer.

The G values for the different reactions are described in the literature.

The combination of a polymer protective layer which has been polymerized by radiation and crosslinked with a heat-sensitive recording layer gives heat-sensitive recording materials which are compared to the known ones Materials have a lower graying of the background and a better contrast than conventional heat-sensitive recording materials with protective layers of different compositions.

The invention will now be explained in more detail with reference to the examples.

Dispersion A:

80 g of 3-dibutylamino-6-methyl-7-anilinofluoran

200 g of an aqueous PVA solution (7.5% by weight) of a low molecular weight, partially saponified type are finely dispersed by grinding

Dispersion B:

15 g bisphenol A

30 g CaCO ₃

210 g of an aqueous PVA solution (2.9% by weight)

low molecular weight, highly saponified types are also dispersed by grinding.

To produce the color-forming layer 1, 1 part of dispersion A and 10 parts of dispersion B are mixed. Dispersion C

80 g of 3-N-ethyl-N-i-pentylamino-6-methyl-7-anilinofluorane 200 g of an aqueous PVA solution (7.5% by weight) of a low molecular weight, partially saponified type

To prepare the color-forming layer 2, 1 part of dispersion C and 10 parts of dispersion B are mixed.

Dispersion D

80 g 3 N, N-methylamino-6-methyl-7-anilinofluorane

200 g of an aqueous PVA solution (7.5% by weight) of a low molecular weight, partially saponified type

To produce the color formation layer 3, 1 part of dispersion D and 10 parts of dispersion B are mixed.

The heat sensitive coating compositions are applied to uncoated paper with a weight of 70 g / m ² in an amount of 5 g / m ² and then dried.

example 1

A commercially available polyester tetra-acrylate oligomer MW = 1000, visc. = 500 mPas according to Höppler is applied in an amount of 5 g / m ² to the heat-sensitive recording layer 1 and cured with the aid of an electron beam at a dose of 3 Mrad in order to produce a resin-coated, heat-sensitive recording material. Comparative Example 1

The resin mentioned in Example 1 is applied to the heat-sensitive recording material 2 and treated as above.

Comparative Example 2

The resin mentioned in Example 1 is applied to the heat-sensitive recording material 3 and treated as above.

Example 2

Another commercially available epoxy acrylate oligomer MW = 500, visc. = 7,500 mPas according to Höppler is applied to material 1 and treated as above.

Comparative Example 3

The resin mentioned in Example 2 is applied to the heat-sensitive recording material 2 and treated as above.

Comparative Example 4

The resin mentioned in Example 2 is applied to the heat-sensitive recording material 3 and treated as above. Of the 6 resin-coated, heat-sensitive recording materials thus produced, the background whiteness and the color intensity, produced by an energy supply of 12.6 to 37.8 mJ / mm ² , were measured with a Macbeth densitometer model RD 920 without color filter. Tab. 1 shows the results.

Table 1 opt. density

mJ / mm ² Example Example Comp. Cf. Cf. Cf.

1 2 1 3 2 4 0 0.09 0.08 0.13 0.11 0.12 0.12

12.6 0.09 0.08 0.13 0.11 0.12 0.12

15.1 0.09 0.09 0.13 0.11 0.12 0.12

17.7 0.11 0.11 0.14 0.12 0.13 0.13

20, 2 0.18 0.17 0.17 0.12 0.18 0.15

20.7 0.24 0.25 0.22 0.16 0.25 0.22

25.2 0.38 0.40 0.34 0.25 0.40 0.32

27.7 0.51 0.52 0.49 0.34 0.53 0.47

30.3 0.71 0.70 0.70 0.54 0.65 0.60 32.8 0.92 0.94 0.90 0.65 0.80 0.77 35.3 1.11 1, 05 1.05 0.88 0.97 0.96 37.8 1.22 1.20 1.20 1.05 1.12 1.15

Furthermore, one unreacted and one at 120 ° C for 1 min. Ausreagierres samples stored in heat and moisture and the optical density measured before and after the tests as already mentioned.

Heat test: 24 h - storage at 60 ° C in a drying cabinet

Climate test: 24 h - storage at 40 ° C and 90% RH in one

Climate box.

The results are shown in Table 2. Table 2

Example Example Comp. Cf. Cf. Cf.

1 2 1 3 2 4 ww 0.09 0.08 0.13 0.11 0.13 0.12

SW 1.51 1.48 1.50 1.40 1.39 1.35

60 ° C WW 0.15 0.14 0.23 0.21 0.29 0.30 SW 1.01 1.00 1.10 1.09 1.00 0.95

Climate WW 0.16 0.15 0.27 0.28 0.35 0.34

SW 1.12 1.15 1.20 1.21 1.18 1.15

WW = white value = background white

SW = black level

Example 3

The polyester acrylate oligomer from Example 2 is applied in an amount of 5 g / m ² to the support (an uncoated paper with a weight of 70 g / m ² ) and cured with the aid of an electron beam. The heat-sensitive recording formulation from d. Example 1 applied in an amount of 5 g / m ² and dried. The resin from Example 2 is again applied to this recording material in an amount of 5 g / m ² and cured with an electron beam.

The heat-sensitive recording material according to Example 3 is without color development and after color formation at 120 ° C for 1 min. measured the optical density. The material is then placed in water at 20 ° C for 24 h (Tab. 3). Furthermore, from d. heat-sensitive recording material according to Example 4 the dyn. Sensitivity in an energy range of 12.6 to 37.8 mJ / mm ² determined and compared with the pattern without an intermediate resin layer.

The results are shown in Table 4.

Table 3

Example 3 without test 24 h - water test

WW 0.09 0.10

SW 1.57 1.02

Example 1 without test 24 h - water test

WW 0.09 0.10

SW 1.51 0.40

Table 4 mJ / mm ² / opt. Density Example 1 Example 3

0 0.09 0.08

12.61 0.09 0.08

15.13 0.09 0.09

17.65 0.11 0.12

20.18 0.18 0.15

22.70 0.24 0.29

25.22 0.38 0.37

27.74 0.51 0.62

30.26 0.71 0.81

32.79 0.92 1.05

35.31 1.11 1.44

37.83 1.22 1.50

Claims

1. Heat sensitive recording material with one on

a heat-sensitive recording layer arranged on a carrier material, which contains a weakly basic color precursor compound and acidic organic compounds as color-developing reactants and which has a protective layer of crosslinked polymers hardened by means of electron beams over the recording layer, characterized in that the recording layer as the basic color precursor compound 3-dibutylamino-6-methyl Contains 7-anilinofluoran in an amount of 2 to 100 g per 100 g of color-developing organic compounds.

2. Heat-sensitive recording material according to claim 1, characterized in that the protective layer has been formed from one or more oligomers which are liquid at room temperature and have at least one ethylenically unsaturated bond per molecule.

3. Heat-sensitive recording material according to claim 1 or 2, characterized in that an intermediate layer of polymers hardened and cross-linked by means of electron beams is present between the carrier material and the heat-sensitive recording layer.

4. Heat-sensitive recording material according to claim 2 or 3, characterized in that the heat-sensitive recording layer contains at least one synthetic polymer as a binder and a graft copolymerization of the oligomers with the polymers of the recording layer has taken place at the boundary layer between the protective layer and / or intermediate layer by the action of the electron beams.

5. Heat-sensitive recording material according to any one of claims 1-4, characterized in that the protective layer and / or the intermediate layer contain one or more pigments.

6. Heat-sensitive recording material according to claim 5, characterized in that the protective layer and / or the intermediate layer contain 0.02 - 4.5 parts by weight of pigment per 100 parts by weight of polymer.