EP2634006A1 - Thermally writeable compound and thermally writeable recording material - Google Patents

Abstract

Thermally writable composition comprises white or light-colored mixture containing iron(III)- or molybdenum(VI) compounds (reactant A), phenols having at least two hydroxy groups (reactant B), a compound fusible at 70-150[deg] C, and a binding agent. Independent claims are also included for: (1) a thermally writable recording material comprising a carrier substrate and thermally writable composition, where the thermally writable composition is applied to the surface of the carrier substrate, and dried; and (2) producing the thermally writable recording material, comprising acidifying the carrier substrate, encapsulating at least one of the reactants, or applying an intermediate coating with barrier properties on a basic or neutral paper.

Description

The present invention relates to a heat-sensitive thermally recordable recording material. More particularly, the invention relates to a heat-sensitive recording material which has improved durability of a readable print image and is ecologically compatible.

Out EP 1 382 459 A is a heat-sensitive recording material for the labeling of food known, the label has direct contact with the food. The carrier material has a coating consisting of an iron salt and an ester of gallic acid and having no inhibitor.

Suitable iron salts are, for example, iron stearate, as gallic acid esters, for example, lauryl gallate, octyl gallate, propyl gallate, ethyl gallate or methyl gallate.

Out US 4,531,141 For example, a heat-sensitive composition is known which consists of two reactants which do not react with each other at room temperature but cause a color change upon temperature elevation. Further, the composition contains a non-complexing phenolic component.

Out US 3,983,279 A For example, a thermosensitive two-sided copying medium is known which comprises a thermosensitive coloring layer, a thermally conductive substrate and a thermosensitive transfer layer.

Out US 4,861,749 A For example, a thermosensitive recording material containing a colorless leuco dye, an iron salt of a saturated higher fatty acid and a polyvalent phenol derivative is known.

The object of the invention is to provide a thermally writable recording material with a heat-sensitive coating that is non-toxic and contains little to no allergy-causing components and that causes less pollution than the known leuco dye-based thermal papers.

In addition, the material should show high static and dynamic coloration sensitivity, can be applied without graying in the production and in particular have a significantly longer shelf life than leuco dye thermal papers.

The invention therefore provides a thermally writable composition according to claim 1 and a thermosensitive recording material using the recording composition according to the invention.

The heat-sensitive recording material has such a structure that a heat-sensitive recording layer capable of causing color development by heating is provided on a support substrate.

In this case, substantially carrier materials which may be composed of a plurality of layers, such as paper, synthetic paper or plastic films, which may optionally be coated, are suitable as carrier substrates.

The main layers of the novel recording material are at least raw paper, raw plastic or a corresponding material and the coating according to the invention.

In addition, the major layers may include a pre-coating and / or surface coating on one or both sides of the web. At a minimum, a color former, a developer and a binder are in the line. When heated to a suitable temperature melts at least a part of the components and leaves Thus, reactions from other components of the stroke, whereby as a result of the chemical reaction, a color is visible to the eye.

A heat-sensitive recording material is produced by applying a coating to a suitable carrier substrate, for example a base paper web, a plastic film, a resin-coated paper or a corresponding material using a coater, after which the carrier substrate is usually dried and optionally calendered. The bar used is normally prepared by separately pulverizing or micronizing at least one metal salt (Reactant A) and one Reactant B to prepare a dispersion.

The two reactants are ground to a suitable particle size to ensure low diffusion paths and thus rapid response of the material. The disperse mixture prepared in this way is mixed with the binder and other excipients and applied with the coater.

According to the invention reactants for an environmentally friendly thermal printing process are to be used, which are both biodegradable and on the other hand contain ubiquitous metals without toxic properties.

Both reactants are preferably introduced in a microencapsulated layer with a binder and protected against diffusion of the components. Thermal heating to less than 120 ° C, preferably less than 100 ° C, melts at least one of the two reactants, which then reacts in organic melt with the other reactant.

Reactant B used is essentially metal chelate or complex-forming di- or polyhydroxycarbon compounds which have at least two adjacent OH groups.

According to the invention, reactants B used are phenols having at least two hydroxyl groups, for example tannin, gallic acid, gallic acid esters or natural tanning agents or mixtures thereof.

These are mainly di- or polyphenols (aromatic systems with two or more hydroxyl groups), which are usually derived from the gallic acid and are often condensed with other phenols and sugars.

According to the invention, these reactants B are hydrophobic or are hydrophobized by, in particular, esterification of the phenolic groups or acids.

Suitable compounds are, for example, lauryl gallate, octyl gallate, propyl gallate, ethyl gallate or methyl gallate.

Advantageously, these compounds are used as a solution in or as a suspension with a low-melting carrier material. The melting point of the support material is preferably below 100 ° C., more preferably below 80 ° C. Suitable carrier materials are free fatty acids, such as lauric acid, myristic acid, stearic acid, palmitic acid or behenic acid.

Reactant A are essentially compounds of elements of IV. VIII. Subgroup of the Periodic Table, which are redox-active and form complexes and have several redox-stable states.

Such elements are, for example, Ti, V, Mn, Fe, Zr, Nb, Mo, Ta, W. According to the invention, the other requirements (non-toxic, non-allergenic, high static and dynamic coloration sensitivity, low cost) as reactant A iron (III ) - or molybdenum (VI) compounds used.

The iron compound used is preferably an iron (III) compound having a molecular weight of more than 300. Suitable compounds are iron alkyl phosphates, preferably an iron bisalkylphosphate, more preferably iron bisethylhexyl.

The synthesis of the iron alkyl phosphates is usually carried out from iron salts of fatty acids, preferably from iron salts of palmitic acid, stearic acid palmitic acid, myristic acid or behenic acid with addition of alkyl phosphoric acids.

Alternatively, the synthesis of iron alkyl phosphates may be made from iron salts of fatty acids, thereby reacting the iron salt with the alkali metal salt of the fatty acid.

The iron alkyl phosphate is in a dispersion after synthesis. Preferably, this dispersion is aged for a few hours to a few days, for about 3 hours to 20 days, prior to further processing to the coating composition.

In another embodiment, the fatty acid liberated in the iron alkyl phosphate synthesis can not be separated and used as a fusible compound in the coating composition.

Alternatively, molybdenum (VI) compounds, in particular Alkalimetallmolybdate or ammonium or Alkylaminmolybdate be used. Preferably, sodium molybdate is used.

The reactants are processed to produce the recording material to particles of a size of not more than 25 .mu.m, preferably <10 .mu.m, more preferably <5 .mu.m. Suitable processing methods include, for example, milling, spray-drying, spray-drying, or processing with vibrating or rotating particle atomizers.

As fusible compound, for example, natural or artificial waxes or long-chain fatty acids having a chain length from 12 carbon atoms can be used. The fusible compound preferably has a melting point in the range of 70-150 ° C.

As binders, for example, cellulose derivatives, starch and starch derivatives, polyvinyl alcohol, polyvinylpyrrolidones and their derivatives, polyacrylates or polyacrylamides, styrenes, butadiene or Styrolacrylatlatex can be used.

Optionally, the coating composition may include stabilizers for graying or browning, especially when exposed to moisture and / or to prevent heat. Suitable stabilizers are pH stabilizers, reducing agents and polymerization inhibitors, preferably polymers such as polyacrylamides and strong or medium-strength nonvolatile acids. In particular, preference is given to phosphoric acid, citric acid, glycolic acid or lactic acid.

The reactants are processed to produce the thermally writable composition into particles of a size of not more than 25 microns, preferably 10 microns. Suitable processing methods include, for example, milling, spray-drying, spray-drying, or processing with vibrating or rotating particle atomizers.

In order to prevent premature contact of reactants A and B in the coating, at least one reactant may be provided with a protective coating or coating against diffusion. This coating or coating of the particles preferably consists of a suitable polymer, for example polyacrylamide, polyacrylic acid, dextrin, starch, resins, such as melamine resin, waxes, fats or else inorganic salts, ceramics, quartz, silicates or aluminum oxide.

The thermally writable composition is applied to a carrier substrate for producing a thermally recordable recording material, dried and is reactive at temperatures above 70 ° C with color change within 10 s.

The particles are coated to produce a thermally recordable recording material on a suitable carrier substrate, for example on paper, corrugated cardboard, cardboard or plastic, which may optionally be coated, or paper-plastic laminates.

Such paper coating processes are known from the prior art and are familiar to the person skilled in the art.

The composition according to the invention can also be produced by other printing, lacquer or paper technology processes, such as doctoring, spraying, dip coating or conventional printing processes, such as gravure, screen, offset, digital printing, curtain coating or roller application methods with rollless or countercurrent be applied to the carrier substrate.

Regardless of the carrier material, it is advantageous to bind the particles to the surface of the coated material with an adhesive, for example with a starch-based adhesive or based on biocompatible and / or degradable polymers. Such adhesives are known to those skilled in the art.

In a particular embodiment, the carrier substrate to prevent graying acid (pH <7) may be set, for example, by a precursor containing mineral or polymeric fractions, such as kaolin or polyethylene.

Furthermore, one of the reactants or both reactants may be in encapsulated form to avoid premature reaction of the reactants with each other.

The reactants can be applied in one or in separate strokes, with the application of the strokes then being sequential.

In another embodiment, to prevent premature reaction of the two reactants, an intermediate coat having blocking properties may be applied to base or neutral paper. Such an intermediate line preferably contains mineral or polymeric components, for example kaolin or polyethylene.

The thermal melt, ie the coating with the reactants, in one or both lines has, depending on the thickness of the chromophore, usually a thickness of 0.5 to 30 microns.

By adding further stabilizers, the premature discoloration of the material can be delayed as well by the addition of Eisenchelatbildnern, acids forming stable iron salts or by adding diffusion-blocking polymers and minerals such as PVA, cellulose and starch derivatives, polyacrylates and methacrylates and their derivatives but also talc and other preferred platelet-shaped minerals.

Optionally, a top coat may be applied over the coating (the thermostrich) to protect the product, in particular against contamination. Preferably, this topcoat comprises a lubricant from the group of layered silicates, for example talc.

The energy sources required for the thermal inscription preferably have low thermal divergence (narrow temperature range), a high energy density (due to the strong bundling and the self-amplification of the energy) and high temporal and spatial coherence. Thus, in addition to thermal heads, lasers are also primarily suitable as light sources. Other thermal light sources are also to be used after suitable optical processing (LEDS, high-energy lamps with Hg, or metal vapor or the like), however, often have low energy density. Thermal release of the effect by a hot surface is also possible and can be done by thermal stamping or rolling.

The thermal intensity can be controlled purely black / white (or bicolor) or is controlled by assigning each color used in the graphic drawing a percentage of the intensity from 0 - 100%. Since the thermal head is proportionately pulsed or otherwise controlled in intensity, this percentage represents how long the heat pulses last or how high the intensity of the heat action is. Basically, the intensity setting is directly related to how deep the color effect is.

High-temperature effects produce toxic emissions and material changes are undesirable or unsustainable in office operations. The thermal printer should therefore achieve thin, chromophoric layers about 0.5 to 30 μm thick, without significant emission of ablation products, at material surface temperatures of typically less than 100 ° C., depending on the intensity of the chromophore.

The total energy consumption of the system results primarily only from the thermal power plus waste heat, the energy consumption of the feed is negligible, an additional fixing process of the toner with heat is not primarily provided, but can be combined secondarily with the process. Therefore, the device only consumes energy primarily in direct printing mode. Typical printers currently have "standby" power of between about 5 and 30 watts and draw up to 1000 watts of power during printing. The thermal printer can also be distinguished from existing printing methods by lower energy consumption and the lack of any heating time to the first sheet.

Claims (24)

Thermally writable composition, characterized in that the composition consists of a white or light mixture of iron (III) or molybdenum (VI) compounds (reactant A) with phenols having two or more hydroxyl groups (reactant B), one at 70. 150 ° C meltable compound and a binder. Thermally writable composition according to claim 1, characterized in that as iron (III) compound an iron alkyl phosphate, preferably having a branched structure is used. A thermally writable composition according to claim 2, characterized in that the molecular weight of the iron (III) compound is more than 300 and is preferably an iron bisalkyl phosphate, more preferably an iron bisethylhexyl. Thermally writable composition according to claim 1, characterized in that as molybdenum (VI) compound, a Alkalimetallmolybdat or an ammonium or Alkylaminmolybdat, preferably sodium molybdate, is used. Thermally writable surface according to one of claims 1 to 4, characterized in that are used as phenols having at least two hydroxyl groups tannin, gallic acid, gallic acid esters or natural tanning agents or mixtures thereof. Thermally writable composition according to any one of claims 1 to 5, characterized in that as a fusible link natural or artificial waxes or long-chain fatty acids with a chain length from 12 carbon atoms are used. Thermally writable composition according to one of claims 1 to 6, characterized in that are used as binders cellulose derivatives, starch and starch derivatives, polyvinyl alcohol, polyvinylpyrrolidones and their derivatives, polyacrylates or polyacrylamides, styrene, butadiene or Styrolacrylatlatex. Thermally writable composition according to any one of claims 1 to 7, characterized in that the mixture is treated with an acid, preferably phosphoric acid, citric acid, glycolic acid or lactic acid. Thermally writable composition according to any one of claims 1 to 8, characterized in that the reactants A and B each have a particle size less than 25 microns, preferably less than 5 microns. A thermally writable composition according to any one of claims 1 to 9, characterized in that at least one of the reactants A or B for preventing premature reaction with a coating of a polymer such as polyacrylamide, polyacrylic acid, dextrin, starch, resins, such as Melamine resin, waxes, fats or inorganic salts, ceramics quartz, silicates or alumina is provided. Thermally writable composition according to any one of claims 1 to 3 and 5 to 10, characterized in that the synthesis of the iron alkyl phosphates is carried out from iron salts of fatty acids, preferably the palmitic acid, stearic acid, lauric acid, myristic acid or behenic acid. A thermally writable composition according to any one of claims 1 to 3 and 5 to 12, characterized in that the synthesis of iron alkyl phosphates from iron salts of fatty acids is carried out with the addition of alkyl phosphoric acids. Thermally writable composition according to any one of claims 1 to 3 and 5 to 12, characterized in that the synthesis of the iron alkyl phosphates is carried out from iron salts of fatty acids, while the iron salt is reacted with the alkali metal salt of the fatty acid. Thermally writable composition according to any one of claims 1 to 3 and 5 to 13, characterized in that the dispersion of the iron alkyl phosphate is aged for a few hours to days. Thermally writable composition according to any one of claims 1 to 3 and 5 to 14, characterized in that the fatty acids liberated in the Eisenalkylphosphatsynthese not separated are used as fusible compounds. A thermally recordable recording material comprising a carrier substrate and a thermally writable composition according to any one of claims 1 to 15, characterized in that the thermally writable composition is applied to the surface of the carrier substrate, and dried. A thermally recordable recording material according to claim 16, characterized in that the thermally writable composition at a temperature of more than 70 ° C with color change within less than 10 seconds is reactive. Thermally writable recording material according to one of claims 16 or 17, characterized in that the thermally recordable recording material as a carrier substrate paper, corrugated cardboard, cardboard or plastic, which may be coated, or paper-plastic laminates. Thermally writable recording material according to one of claims 16 to 18, characterized in that it is writable by thermal heads or laser. A method for producing a thermally recordable recording material, characterized in that the carrier substrate is acidified or an encapsulation of at least one of the reactants is made or an intermediate line with blocking properties is applied to a basic or neutral paper. Process for the preparation of a thermally recordable recording material according to claim 20, characterized in that a topcoat for protecting the product is applied above the thermal head, which preferably contains a lubricant, such as talcum. Process for producing a thermally recordable recording material according to one of Claims 20 to 21, characterized in that the coating is between 0.5 and 30 μm thick. Process for the preparation of a thermally recordable recording material according to one of Claims 20 to 22, characterized in that the iron (III) or molybdenum (VI) compounds and the phenols are applied sequentially in separate lines. A process for producing a thermally recordable recording material according to any one of claims 20 to 23, characterized in that further stabilizers retard the premature discoloration of the material, preferably encapsulation of one of the components, addition of iron chelating agents or addition of diffusion-blocking polymers and minerals.