EP0888903A2 - Image-receptor sheet containing a foam layer for an image-recording process - Google Patents

Abstract

Image carrier with a base layer has a foam layer of radiation-cured surfactant foam.

Description

The invention relates to an image carrier (carrier material) for Image recording method, especially for thermal Dye transfer process, with a radiation cross-linked Foam layer.

Hardcopy" ermöglichen, gewinnen immer mehr an Bedeutung. Das Prinzip eines thermischen Farbstoffübertragungsverfahrens ist wie folgt:The reprographic processes developed in recent years (for example thermal dye transfer or the ink jet process), which reproduce an electronically generated image in the form of a

Hardcopy "are becoming increasingly important. The principle of a thermal dye transfer process is as follows:

A digital image is cyan in terms of the primary colors, Magenta, yellow and black processed and in corresponding electrical signals are converted into heat a thermal head in the printer. Through the The dye sublimes from the donor layer when exposed to heat one in contact with the receiving material Color material and diffuses into the receiving layer.

The aim of this technology is to adjust the image quality of color prints to the level of silver salt photography.

In order to achieve high quality images in terms of optical density, color tone and resolution, in addition to a smooth surface, heat and light stability, good dye solubility and anti-blocking "properties ensure good contact between the thermal head of the printer and the receiving material. If this is not guaranteed, unprinted areas on the image surface or density fluctuations can be observed.

It is known for example from JP 60-236794 Paper receiving materials with thermoplastic, to coat high molecular materials before the Image receiving layer is applied. These high molecular weight Thermoplastics can be polyolefins, polystyrene, Polyvinylidene chloride, polyethylene terephthalate or Be ionomer resin. This intermediate layer makes a good one Barrier effect between the receiving layer and the Paper pad reached. This can cause dyes Do not diffuse heat into the underlay (paper) and being dragged out of paper by what is expressed in a blurred image. Moreover should equalize the unevenness of the paper surface and thereby good contact between the receiving material and the thermal head can be guaranteed. The disadvantage of this is that this intermediate layer is the heat generated in the thermal head redirects, which does not release enough dye and is absorbed by the receiving layer. The resulting Image then has an insufficient color density.

In order to counter this problem, DE 39 34 014 describes a Intermediate layer proposed which is a heat insulating and also has a softening function. This Intermediate layer contains polymeric hollow microspheres and a Binder. A disadvantage of this layer is Flour effect.

Another way is taken as an intermediate layer a thermoplastic foamed layer on a support is applied (JP 02-274592). Here is supposed to be one Softness and good thermal insulation can be achieved. The disadvantage of this problem solution is that it is bad Surface quality of the foam layer is also poor Surface quality of the entire receiving material result Has. To improve this, one would have to on the foam layer surface-improving sealing layer are applied, the in turn adversely affects the thermal insulation.

In JP 04-110196 an intermediate layer is applied which consists of unsaturated compounds, is cured with the aid of UV or electron beams and which has a foam structure. The foam layer described consists of a so-called reactive foam, for the production of which chemical compounds which develop gas under the action of heat are used. Due to an uneven pore formation, such a foam layer has an uneven heat insulation and thus an uneven dye transfer, which is what is known as a mottle "of the picture.

JP 04-358889 uses a so-called additive foam produced image receiving sheet claimed. A disadvantage in the production of this foam, the acts as an intermediate layer and a radiation-curable Acrylic resin and hollow particles (hollow spheres) as a foam base contains, the difficulties are even Distribution of the hollow particles in the polymer matrix.

It is therefore an object of the invention to provide an image carrier for Provide imaging method that the Manufacture of receiving materials with excellent Surface quality enables images with high Color density as well as high color brilliance and image resolution can be generated and also such a receiving material to provide.

The task is solved by an image carrier, the one Contains base layer and a foam layer, the Foam layer made of a radiation-curable surfactant foam consists.

Compounds form the basis for the surfactant foam unsaturated carbon double bonds such as acrylic, Methacrylic, allyl or vinyl compounds. You can additionally hydroxyl, carboxyl and other polar groups contain. Those are particularly preferred Substances that contain acrylate or methacrylate groups, such as Polyol acrylates, polyester acrylates, urethane acrylates, Polyether acrylates, epoxy acrylates, alkyd resin acrylates and the methacrylates corresponding to the acrylates mentioned. Water-compatible or are particularly suitable water-soluble monomers and / or oligomeric acrylates.

The water compatibility of a substance gives the amount of water which is absorbed by this substance without phase formation can be. If the solubility limit is water / substance exceeded, phase separation occurs.

It has been found that the foam quality, i.e. the Foam volume and foam stability with increasing Water tolerance of the acrylates increases. Both water-compatible acrylates, for example, dominate the Urethane acrylates, polyethylene glycol or Polypropylene glycol acrylates and the ethoxylated acrylates of polyfunctional alcohols of trimethylolpropane and Pentaerythritol.

For the surfactant foam, surfactants from the group of anionic, cationic, amphoteric and nonionic Products are selected. These include, for example Fatty acid salts (soaps), alkanesulfonates, Alkylbenzenesulfonates, olefin sulfonates, fatty alcohol sulfates, Fatty alcohol polyglycol sulfates, lignin sulfonates, Sulfosuccinates, fatty alcohol polyglycol phosphates, bile acids, Distearyldimethylammonium chloride, stearyl-N-acylamido-N-methylimidazolinium chloride, Dodecyldimethylbenzylammonium chloride, Alkyl betaine, N-carboxyethyl-N-alkylamidoethylglycinate, Amine oxides such as N-alkylamidopropyl-N-dimethylamine oxide, Dipalmitoyl lecithin, fatty alcohol polyglycol ether, Alkylphenol ether, fatty acid monoglyceride, ethoxylates, or Sultaine. But also mixtures of the compounds mentioned can be used. Particularly suitable as a surfactant is a fatty acid polyethylene glycol ester. The amount of Surfactant in the foam layer can be 0.3 to 5.5% by weight.

In a further embodiment of the invention, the coating composition according to the invention additionally a Foam stabilizer. Are as foam stabilizers Suitable compounds such as fatty acid alkanolamides and their ethoxylated derivatives, water-compatible polymers such as Polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives, Copolymers with acrylic acid and maleic acid and polyalkylene oxide modified polydimethylsiloxanes, but especially sugar compounds, for example that D-sorbitol. The amount of stabilizer in the foam layer can be 0.05 to 1.5% by weight.

In further attempts to produce stable surfactant foams have developed complete surfactant / stabilizer systems proven particularly suitable. Under a complete system it is understood that the surfactant and stabilizer, optionally with the addition of other auxiliaries such as Stearic acid, salts or silicates, processed and are then added to the polymer to be foamed.

38 - 51 Gew.%

Tensid

9 - 12 Gew.%

Stabilisator

0 - 8 Gew.%

andere Hilfsstoffe

ad 100 Gew.%

Wasser

Accordingly, the surfactant / stabilizer system can have the following composition:

38 - 51% by weight

Surfactant

9 - 12% by weight

stabilizer

0 - 8% by weight

other excipients

ad 100% by weight

water

Particularly good results have been achieved with a lot of the Surfactant / stabilizer system from 1 to 10 wt.%, In particular 2.5 to 7.5% by weight, based on the weight of the dry Coating mass.

With the coating composition according to the invention monomer (Oligomer) / water / surfactant or monomer (Oligomer) / water / surfactant / stabilizer has managed to Surfactant foam (whipped foam) with good foam properties regarding foam volume, bubble size and foam stability (Pressure stability and service life).

To increase the foam quality (foam volume, Foam stability) can additionally cosurfactants, in particular anionic cosurfactants. As particularly good Co-surfactants, which are compatible with the Surfactant / stabilizer system are compatible and Increase the elasticity of the foam slats, for example that Na coconut fatty acid N-methyl taurinate or the alkanesulfonate. The amount of cosurfactant can be 0.5 to 0.8% by weight, in particular 0.6 to 0.7% by weight, based on the weight of the dry coating compound.

To further increase the mechanical strength of the Foam base can make the coating composition a reactive one Crosslinking agents such as trimethylolpropane triacrylate are added become.

The surfactant foam is produced by dispersing air, CO ₂ or N ₂ in the coating composition. For this purpose, the colloid mills operating according to the rotor-stator principle, for example the Ultra-Turrax® agitator, can be used as dispersion machines.

The size of the bubbles produced is 0.5 to 20 µm. A whipped foam has particularly good properties a bubble size of 1 to 6 µm, but especially with a size distribution of 1 to 3 µm.

The target foam volume is 30 to 60%, in particular 45 or 50%, based on the volume of the Foam layer.

The thickness of the foam layer according to the invention is 5 to 30 µm, especially 8 to 25 µm.

80 - 90 Gew.%

wasserverträgliche Verbindungen mit ungesättigten Doppelbindungen

1 - 10 Gew.%

Tensidsystem (insbesondere 5 bis 10 Gew.%)

1 - 10 Gew.%

Wasser

In a particular embodiment, the coating composition according to the invention for producing a foam layer can contain the following components:

80 - 90% by weight

water-compatible compounds with unsaturated double bonds

1 - 10% by weight

Surfactant system (in particular 5 to 10% by weight)

1 - 10% by weight

water

The foam layer according to the invention is based on a base material (Base layer) applied and by high-energy radiation networked. This radiation can be electron radiation (ES) or UV radiation. The foam mass can with usual application units such as scraper or Gap metering systems or roller systems on the base material be applied.

A plastic film, for example, can be used as the base material or a coated or uncoated base paper be used. Among the uncoated papers is one a base paper with a smooth compacted surface particularly well suited. In a special embodiment of the Invention becomes at least one barrier layer having base paper used. A layer that the Function as a barrier layer under the foam layer, additionally prevents the penetration of the applied Foam mass in the paper interior and saved Coating material.

The base paper preferably consists of cellulose fibers or made of synthetic fibers and is common with other Glue agents and auxiliaries equipped. It can be surface-sized and / or resin-coated.

To ensure the adhesion of the foam layer to the paper backing can improve the paper surface with corona rays be treated.

According to the invention, the barrier layer can be different Be made from different fabrics. In In a special embodiment, the barrier layer made of a thermoplastic polymer, preferably one Polyolefin film applied by extrusion coating becomes. The thickness of the layer is 5 to 30 microns, preferably 7 to 20 µm. The polyolefin is, for example, polyethylene or polypropylene, an ionomer resin or another ethylene copolymer resin.

In a further embodiment, the barrier layer as an aqueous solution of a water-soluble film-forming Polymers are applied. Suitable water-soluble ones Polymers are, for example, polyvinyl alcohols, Acrylic acid / vinyl monomers, polyacrylamide, alginates or Starch derivatives. The thickness of such a barrier layer after drying is 3 to 30 µm depending on the type of polymer.

In a further embodiment of the invention, the Barrier layer radiation-curable (ES / UV) compounds contain. The materials used for this are varnishes Monomers, oligomers or prepolymers and their mixtures. They have carbon double bonds in the molecule. A radiation-curable is particularly suitable Acrylic layer. The layer thickness is 3 to 20 µm, especially 3 to 6 µm.

To produce particularly brilliant images, the foam layer is cross-linked by high-energy electron or UV rays in contact with high-gloss metal surfaces or high-gloss cylinders. As a result, the through on the layer surface "Blister damaged surface of the carrier material again repaired".

In another embodiment of the invention, the Another layer (top layer) applied become. This top layer can be radiation-curable Be a layer of paint for which a large number of highly crosslinking (i.e. multifunctional) acrylates is suitable, the Viscosities are in the range of 80 to 200 mPa · s (cP). Epoxy and polyester acrylates are preferred Acrylate thinners such as hexanediol diacrylate (HDDA), Trimethylolpropane triacrylate (TMPTA) or Tripropylene glycol diacrylate (TPGDA) used. The Quantity ratio of acrylate / acrylate thinner is preferably 1: 1 to 4: 1.

However, a layer on top of the foam layer can also be used laminated (laminated) thin plastic film, for example a polyester film can be used. To one special brilliance with the help of this carrier material To achieve generated images, the top layer White pigments are added.

The thickness of the cover layer can be 1 to 10 μm, in particular 2 to 9 μm. Particularly good results are achieved with a cover layer with a thickness of 4 to 6 μm (corresponds to 4 to 6 g / m ^{2 of} dry coating composition).

An improvement in the adhesion of the top layer on the Foam base can be caused by corona radiation on the foam surface can be achieved.

The according to the embodiments described above manufactured image carrier according to the invention is made to order of color receiving layers as image receiving material for thermal transmission process (e.g. D2T2 process) or Ink jet process used. For the image receiving layers all suitable materials can be used as they are known from the literature.

The following examples are intended to illustrate the invention:

example 1

Starting from the recipes listed in Table 1 below, a whipped foam was first produced using an Ultra-Turrax S 50® agitator (Janke and Kunkel GmbH, Staufen) at 3000 rpm with a stirring time of 1 to 5 min. In the next step, this was then applied to a lab coater using a multi-roller application system on a neutral sized calendered paper with a basis weight of 135 g / m ² at a machine speed of 100 m / min. Corona pretreatment of the paper surface was carried out before coating. The coated paper was pressed with the layer side against a water-cooled high-gloss cylinder and irradiated from the back of the paper by means of accelerated electrons. The foam layer was cured at an energy dose of 30 kGy under an inert N ₂ atmosphere. Components 1a 1b 1c 1d ethoxylated TMPTA ^*) degree of ethoxylation = 3 - - 28.6 - ethoxylated TMPTA degree of ethoxylation = 20 80.0 - 28.6 42.85 water-dilutable aliphatic. Urethane acrylate functionality = 2-3 - 85.8 28.6 42.85 Surfactant / stabilizer system (with 50% water) 10.0 7.1 7.1 7.1 water 10.0 7.1 7.1 7.1 Application weight, g / m ² 20th 19th 10th 20th TMPTA = trimethylolpropane triacrylate

The amounts in the table are expressed in% by weight and refer to the coating mass.

On the subsequent coating of the paper with a Image receiving layer will be discussed later.

Example 2

A paper with 135 g / m ² basis weight glued with stearic acid, alkyl ketene dimer and epoxidized fatty acid amide was coated on the front with polyethylene (application weight: 15 g / m ² ) in the melt extrusion process and after a corona pretreatment with a whipped foam produced according to Example 1 as follows Recipes coated: Components 2a 2 B 2c 2d 2e 2f ethoxylated TMPTA degree of ethoxylation = 3 28.6 28.9 14.3 14.3 13.2 - ethoxylated TMPTA degree of ethoxylation = 20 28.6 28.9 35.7 35.7 33.1 35.5 aliphatic urethane di / triacrylate functionality = 2.5 28.6 28.9 35.7 35.7 6.6 35.5 aliphatic urethane diacrylate functionality = 2 33.1 14.2 Surfactant / stabilizer system (with 50% water) 7.1 5.8 7.1 5.7 5.3 5.6 Na coconut fatty acid N-methyl taurinate - 0.6 - 0.6 0.7 0.7 water 7.1 6.9 7.1 8.0 8.0 8.5 Application weight, g / m ² 19th 19th 19th 21.5 19th 19th

The coated paper was pressed with the layer side against a water-cooled high-gloss cylinder and irradiated from the back of the paper by means of accelerated electrons. The foam layer was cured with an energy dose of 25 kGy under an inert N ₂ atmosphere.

Example 3

A barrier layer of radiation-curable acrylates was applied to a base paper as in Example 2 in an amount of 5 g / m ² . The coating was then carried out using a foam coating composition prepared according to Example 2a. The layers were hardened using electron beams with an energy dose of 30 kGy with N ₂ inertization.

Example 4

A polyethylene-coated base paper with a basis weight of 135 g / m ² (see Example 2) was coated in accordance with the recipe from Example 2a and provided with a smoothing layer in a further step. The smoothing layer was made from a mixture of epoxy diacrylate based on bisphenol A and trimethylolpropane triacrylate in a ratio of 1: 1 and with the addition of 2% by weight of the photoinitiator 2-hydroxy-2-methyl-1-phenylpropan-1-one in an amount of 6 g / m ² applied.

The foam base was corona-treated to improve adhesion. The foam layer was hardened with electron beams at an energy dose of 20 kGy under an N ₂ atmosphere and the smooth layer was hardened by means of UV radiation (Hg fusion lamp 120W / cm).

The underlay produced in this way was treated with a Receiving layer coated.

Comparative example

For comparison, one was available on the market Image receipt sheet used. The said Image receiving sheet has a support which on both a pigmented front and back has stretched polyolefin film on a base paper is glued on. The results are shown in Table 3.

Application of the image receiving layer

The image-receiving material from Examples 1 to 4 provided with the foam layer was coated with the following coating composition from aqueous solution using a roller application unit to form the receiving layer: plasticized vinyl chloride / vinyl acetate copolymer 50% aqueous dispersion 49.5% by weight Vinyl chloride / acrylic acid ester copolymer 50% aqueous dispersion 49.5% by weight Polytetrafluoroethylene 30% aqueous dispersion 1.0% by weight

The machine speed was 130 m / min, the drying temperature was 110 ° C. The application weight after drying was 5 to 7 g / m ² .

Test results

All image receiving materials were made using a D2T2 printer from Mitsubishi using a Mitsubishi original ribbons printed.

The color density of the individual colors of the images obtained was determined using a density meter Gretag "® measured.

The compressibility is determined by the uniformity of the Contact pressure of the image receiving material on the thermal head and the resulting print image appearance assessed. For this grades 1 to 5 were awarded.

The grade 1 stands for an evenly printed image (without unprinted places).

The grade 5 is for a print image with many unprinted Vacancies.

Gloss values were used to assess the surface quality. The gloss of the image-receiving material was measured using a three-angle gloss meter according to Dr. Measured for a long time at a measuring angle of 20 °. Test results example Color density Compressibility grade Surface quality gloss Cyan magenta yellow black 1a 1.60 1.49 1.50 1.60 2.5 84 1b 1.76 1.75 1.52 1.60 1 68 1c 1.60 1.68 1.48 1.62 1.5 81 1d 1.75 1.72 1.53 1.58 1 71 2a 1.60 1.68 1.47 1.63 1.5 80 2 B 1.76 1.75 1.52 1.60 1.5 85 2c 1.62 1.66 1.43 1.52 1 78 2d 1.72 1.74 1.52 1.57 1 79 2e 1.74 1.74 1.52 1.60 1 72 2f 1.75 1.74 1.52 1.57 1 70 3rd 1.60 1.68 1.50 1.63 1.5 80 4th 1.72 1.70 1.50 1.63 1.5 90 See. 1.71 1.64 1.48 1.59 1 -

Claims (13)

Image carrier with a base layer and a foam layer, characterized in that the foam layer consists of a radiation-hardened surfactant foam. Image carrier according to claim 1, characterized in that the foam layer contains a water-compatible acrylate. Image carrier according to claims 1 and 2, characterized in that the foam layer additionally contains foam stabilizers. Image carrier according to Claims 1 to 3, characterized in that the foam layer contains a complete surfactant / stabilizer system. Image carrier according to Claim 1, 2 and 4, characterized in that the amount of the surfactant / stabilizer system is 2.5 to 7.5% by weight, based on the foam layer. Image carrier according to Claims 1 to 5, characterized in that the bubble diameter of the pores of the foam layer is 1 to 6 µm, in particular 1 to 3 µm. Image carrier according to Claims 1 to 6, characterized in that a barrier layer is contained between the base layer and the foam layer. Image carrier according to claim 7, characterized in that the barrier layer is a polyolefin layer. Image carrier according to claim 7, characterized in that the barrier layer contains radiation-curable compounds. Image carrier according to Claims 1 to 9, characterized in that a cover layer is additionally arranged on the foam layer. Image carrier according to claim 10, characterized in that the cover layer is a laminated polyester film. Image carrier according to claim 10, characterized in that the cover layer is a radiation-curable layer. Receiving material containing an image carrier after a of claims 1 to 12.