GB2054686A - Copying material, in particular writing sheet and method for producing a coating material - Google Patents

Abstract

Copy paper is coated with a chromogenic colouring agent which reacts with a developer to give a colour reaction on application of pressure. The colouring agent is provided on the paper as a fine dispersion in the form of micro- coagulated or micro-precipitated flock-like particles with a binding agent, whereby the copy paper may be solvent-free. The colouring agent may be converted into the requisite fine dispersion by dissolving or melting same in saponifiable chemicals followed by emulsification in water. Alternatively, the colouring agent may be converted to a water-soluble form by acidification, fine flock-like particles then being precipitated by addition of alkali.

Description

SPECIFICATION Copying material, in particular writing sheet and method for producing a coating material Copying materials, in particular writing sheets are known, which are coated with a chromogenic colouring agent, which with a second reagent, which contains a colour developer, produces a colouring reaction under pressure.

In known copying sheets of this type (German Auslegeschrift No. 22 28 430), a carrier sheet is coated with a chromogenic colouring agent having a basic reaction and/or with a phenolic material having an acid reaction. If this material comes into contact with the chromogenic colouring agent in a common solvent, it reacts by forming a colour, in which case the carrier sheet also comprises a metal salt which is soluble in a solvent. In the case of this known copying material, the colour is produced by the fact that a reaction takes place between an oil-soluble phenol formaldehyde resin and a colourless chromogenic colouring agent having a basic reaction, when both reagents are dissolved in a common solvent. The two reagents may thus be located either on the same carrier sheet or on separate sheets, which together form the copying material, for example a set of forms.The common solvent for the reagents is enclosed in micro-capsules in a polymeric material which can be broken open due to pressure at the time of writing or printing and when the two reagents are located on a single carrier sheet, the solvent is isolated from one or both of the reagents.

In a known set of forms, the encapsulated solvent is located on one of the two sheets of the set of forms and in particular on a single sheet or together with one of the two reagents, in which case the latter may already be dissolved in the solvent or may be separate from the latter.

In the case of these known copying sheets, it is a drawback that the quality of the copy, and the speed at which the copy develops as well as the intensity of the colour and resistance to ageing of the copy are not completely satisfactory. The solvent frequently causes the paper to have an unpleasant odour.

As a result of the encapsulation of the chromogenic colouring agent or of the other reacting agents, the known copying materials have further substantial drawbacks. For example, in practice it is impossible during production to give the walls of the capsules the same thickness and to distribute the capsules uniformly on the paper web. In practice, as a result of bunching of individual capsules, socalled clusters are produced which lead to problems as regards production and quality. Furthermore it is a drawback that the capsules may burst prematurely in an undesirable manner, due to which premature undesirable colourations occur.

Finally, the production of this known coating material is relatively expensive and requires special measures as regards quality control.

German Patent Specification 22 1 9 527 already discloses the use of solid dry chromogenic colouring agent, which is adsorbed on the surface of paper-coating pigments. In this known method, the chromogenic colouring agents must be dissolved in a suitable solvent and then mixed with the papercoating pigments. After this mixing operation, the solvent is driven off by the application of heat. This method has the drawback that for the fine, uniform distribution of the chromogenic colouring agent, large quantities of organic solvents are required, which represent a considerable burden on the environment. It is a further drawback that for possible recovery of the solvents, high investment and also continuous staff and operating costs are necessary. Finally, an additional, cost-intensive operation is unavoidable.It is a further drawback that for an optimum quality of the copies, increased quantities of chromogenic colouring agents are required, which is necessitated by the high adsorption of the chromogenic colouring agent on the paper-coating pigments.

Accordingly, the object of the invention is to provide copying material, in particular a copying or writing sheet, which whilst avoiding the above mentioned drawbacks, facilitates an extremely fine and uniform distribution of colouring agent with the lowest possible proportion of chromogenic colouring agents and ensures an optimum quality of the copy, high speed developmentof the copy with extremely good sharpness of the outlines as well as an adequate intensity of the colour of the copy.

The copying material of the aforementioned type according to the invention is characterised according to the invention in that the colouring agent is in a fine dispersion on the copying sheet in the form of micro-coagulated or micro-precipitated flock-like particles using a binding agent. In this case, the colouring agent formed according to the invention may be provided in the donor or receiver layer of the copying material.

The invention thus relates to a solvent-free copying sheet, in which the chromogenic colouring agent is provided in a fine, micro-coagulated or micro-precipitated flock-like form.

With a copying material of this type, any migration of the chromogenic colouring agents, which may lead to premature colouring on the boundary layers between the individual reaction agents, is prevented. Since the copying material is free from solvents, there is no harm to the environment nor any odour due to solvents. The material is further characterised by high resistance to light and ageing. In addition, on account of the low raw material costs, the copying sheets and the actual coating material are inexpensive to produce.

The invention also relates to a method for producing a coating material containing a chromogenic colouring agent for application to a copying material, in particular writing sheet of the aforementioned type, in which the coating material enters into a reaction with a layer containing the colour developer, upon the application of pressure and thus forms a colour and which is characterised according to the invention by the fact that the chromogenic colouring agent is converted into a dispersion-like form by being dissolved or melted in saponifiable chemicals and by subsequent emulsification in water, in which case a micro-coagulated or micro-precipitated structure of the chromogenic colouring agent is preferably produced by the addition of alkalies.

The method according to the invention for producing the coating material may also be carried out in such a way that the chromogenic colouring agent is converted into a flock-like micro-coagulated or micro-precipitated form by being dissolved in an organic or inorganic acid and by neutralisation of the latter by leaching.

Thus, in a further embodiment of the invention, the micro-coagulated colouring agent may be hardened on the surface of the paper with binding agents, for example a synthetic material dispersion, aqueous resin solutions, a micro-wax dispersion or natural binding agents.

The micro-coagulated or micro-precipitated colouring agent according to the invention may be embedded in a wax type donor layer or receiving layer. Furthermore, it can be applied to the surface of the copying material, for example to the surface of the paper in combination with organic and inorganic pigments. Thus, in a further embodiment of the method, fatty acids, preferably stearic acids may be used for dissolving or melting the colouring agents. Acid amides or fatty acid amides are also suitable for dissolving or melting the colouring agents.

Due to the fact that the chromogenic colouring agent is decomposed according to the invention into very fine flock-like particles by micro-coagulation or micro-precipitation, it is possible that a very high colouring power can be obtained with very small quantities of chromogenic colouring agents.

In contrast to the known method, in which the chromogenic colouring agent is applied by means of solvents to the paper-coating pigments, it appears that due to the use according to the invention of micro-coagulated or micro-precipitated chromogenic colouring agents, with the same intensity of colour, the use of chromogenic material can be reduced by a substantial amount, namely by up to 40%.

This is attributed to the fact that the chromogenic colouring agent is applied to the surface of the paper exclusively in its active form and is not, as in known solutions, partially adsorbed by the coating pigments. In the method according to the invention for producing the coating material, the colouring agent is dissolved or melted according to the invention in a cold, warm or even hot saponifiable chemical, for example an organic or inorganic acid, for example a stearic or maleic acid. A temperature of 30 to 1 400C is provided according to the dissolving properties of the colouring agent. In this process, attention should be paid to the fact that complete dissolution or melting takes place. It was found that stearic acid is particularly suitable for carrying out the method.When using colouring agents which dissolve with difficulty or are insoluble or if the dissolving intermediary has a poor solvent power for the colouring agent, it is appropriate to increase the heating up to the range of the melting temperature of the colouring agent.

The colouring agents dissolved or melted in the saponifiable chemicals, i.e. the dissolving intermediary are added with vigorous stirring to water, which may be warmed or heated. Depending on the type of saponifiable chemical, an emulsion is produced, in which the dissolved colouring agent forms a component of a mixture already having a fine distribution.

If colouring agents and dissolving intermediaries are soluble in cold water, for example certain acid amides, stirring may take place at normal temperatures. A dispersion is thus formed in which the colouring agent is already in a fine distribution.

However, if the dissolving intermediary, for example stearic acid, does not dissolve or only with difficulty at normal temperature, then it is recommended to heat the water to the melting point of the dissolving intermediary, in order to be able to emulsify the latter in the liquid phase. Higher acid amides, such as fatty acid amides, palmitic acids etc., which are not soluble in water or only with difficulty, must be emulsified, before they form a suitable dispersion.

Subsequently, due to the addition of alkalies, the saponifiable chemicals are converted into the corresponding soap, in which case they are converted into a colloid-soluble form. As a result of the chemical saponification reaction, with increasing saponification, the colouring agent which is insoluble in water is slowly liberated by flocculation. In this case, the size of the particles and the shape of the particles can be controlled, in that the lye for example is added slowly, e.g. drop-wise, in order to produce large flocks. Smaller flocks of the colouring agent can be produced by faster addition. With slow saponification, a fine colour distribution is achieved, with a rapid saponification, a coarser colouring agent distribution will occur. The resulting soap also has a high capillary action or boundary surface action, which promotes a further improvement of the dispersion of the colouring agent.

After the completion of the saponification reaction, the appropriate pigments, such as calcium carbonate, titanium dioxide as well as calcium stearate or similar pigments can be added. The mixture is cooled for example to 300C. After this, the binding agents such as starch, polyvinyl alcohol, synthetic material dispersions or micro-wax dispersions may be added. One then obtains a finished liquid coating material, which can be applied to a copying sheet without further treatment.

In the case of a copying sheet, for example a set of forms, the coating mass produced according to the invention may be applied either as a donor layer or as a receiving layer. In this case, a donor layer is present if as a result of the application of pressure when writing or printing, the colouring agent is transferred to another layer, in which the colour developer is located. The colouring agent may be incorporated for example in a wax-like material, which is transferred to the layer of the adjacent sheet upon the application of pressure, in which case the colouring reaction is initiated as a result of the combination of the colouring agent and colour developer.If, upon the application of pressure, only the wax of the wax layer with the colour developer is pressed into the adjacent layer containing the colouring agent, so that there is no transfer or transmission of colouring agent particles to the other layer, then this constitutes a receiving layer.

If the material according to the invention is applied as a receiving layer, then the donor layer contains the counter-reaction material, i.e. the developer material, so that due to pressure, the donor layer is transferred to the receiving layer, whereby the colouring reaction takes place in the boundary surfaces.

In contrast to known copying materials, in which the colouring agent is stored in capsules in the layered material, whereby due to pressure, i.e. when writing or printing, a chemical reaction takes place, in that the capsules bursts, the colouring liquid escapes and a colour-forming chemical reaction takes place with the substance of the counter-reaction liquid, or in which the chromogenic colouring agent is finely distributed on paper-coating pigments due to solvents, whereby coiouration occurs due to intimate contact with the counter-reaction layer, in the invention, the colouring agent is no longer stored in a capsule or adsorbed on the surface of paper-coating pigments, but is present in a fine microcoagulated or micro-precipitated flock-like form directly on the surface of the paper, hardening on the surface of the paper being able to be achieved with small quantities of binding- agents.

Due to the fact that according to the invention the colouring agent is provided on the surface of the paper in a micro-coagulated or micro-precipitated form, in comparison with the known method, in which the colouring agent is stored in capsules, the sensitivity to pressure of the coated paper is considerably reduced.

Also, it is no longer necessary that a special spacer member must be embedded, as in the known papers comprising micro capsules, in order to prevent premature accidental bursting of the colouring capsules, for example when the paper is rolled up.

A further possibility of providing a fine dispersion of chromogenic colouring agents in an aqueous coating material in a manner according to the invention consists in that the chromogenic colouring agent is converted by a chemical reaction into the water-soluble form, for example by the addition of organic acids, due to which certain chromogenic colouring agents can be dissolved in water. Also, in this case, due to the addition of alkalies, the acid may be neutralised once more, in which case the colouring agent precipitates in a fine and flock-like form. This produces an aqueous pulp, in which the chromogenic colouring agent is present in the finest dispersion and which after the addition of binding agents, such as starch or a synthetic material dispersion, solely needs to be spread on the paper.

The micro-coagulated or micro-precipitated chromogenic colouring agent which is in an aqueous suspension can be emulsified to form a wax-like hot material by vigorous stirring. The chromogenic colouring agent is then in the donor layer and is transmitted by the application of pressure to the receiving layer, in which the colour-developed reaction agent is located.

EXAMPLE 1 Colouring mixture 720 g Water 60 g Starch 8 g Polyacrylic salt 1 6 g Polyvinyl alcohol 30 9 Titanium dioxide The individual components are dissolved or made into a suspension by stirring. By heating the mixture to 95"C, the starch is made into paste.

Colouring agent mixture 80 g Stearic acid (saponification factor 200) 15 9 Crystal violet lactone (KVL) 5 9 Sprio-dibenzopyrane 5 9 diaza-rhodamine lactone The colouring agents are dissolved with stirring at a temperature of 1 200C.

The colouring agent mixture is added slowly to the colouring mixture with very vigorous stirring.

The shearing forces must be so high that an emulsion-like distribution of the colouring agent mixture occurs.

Then, 5g caustic potash solution are dissolved in 20g water and added drop-wise to the total mixture.

The mixture is mixed vigorously for 20 minutes at a temperature of 950C.

After completed partial saponification, the mixture is cooled to 300C and the other chemicals are added in the following order: +600 g calcium carbonate + 120 g calcium stearate dispersion +250 g acrylic styrene copolymerizate dispersion papers are coated on one side with the coating material at a rate of 2-4 g/m2.

EXAMPLE 2 Dry Parts Wet Parts Calcium carbonate 250 250 Maleic acid 24 24 Triarylmethane colouring agent 12 12 Titanium dioxide 60 60 Polyvinyl vinyl chloride copolymerizate 200 400 Water 254 24 parts maleic acid are dissolved in 254 parts water. The chromogenic colouring agent is stirred slowly into this solution, which dissolves immediately. After complete dissolution, the calcium carbonate is stirred in slowly and thus.initiates the neutralisation. Termination of the neutralisation is indicated by the decolouration of the chromogenic colouring agent. After this, the titanium dioxide is added with stirring as a pigment and the polyvinyl acetate vinyl chloride dispersion is added.

Claims (11)

1. Copying material, in particular writing sheet, which is coated with a chromogenic colouring agent, which with a second reagent, which contains a colour developer, produces a colouring reaction under pressure, characterised by the fact that the colouring agent is provided in a fine dispersion on the copying sheet in the form of micro-coagulated or micro-precipitated flock-like particles using a binding agent.

2. Copying material according to claim 1, characterised by the fact that the colouring agent is provided in the donor or receiving layer.

3. Method for producing a coating material containing a chromogenic colouring agent for application to a copying material according to claim 1, characterised by the fact that the chromogenic colouring agent is converted into the form of a dispersion by being dissolved or melted in saponifiable chemicals and by subsequent emulsification in water.

4. Method according to claim 3, characterised by the fact that a further saponification of the saponifiable chemicals takes place due to the addition of alkalies.

5. Method according to any one of claims 3 to 4, characterised by the fact that the microcoagulated or micro-precipitated colouring agent is embedded in a wax-like donor layer.

6. Method according to any one of claims 3 to 5, characterised by the fact that the microcoagulated or micro-precipitated colouring agent is applied to the surface of the paper in conjunction with organic and/or inorganic pigments.

7. Method according to any one of claims 3 to 6, characterised by the fact that fatty acids, preferably stearic acids are used for dissolving or melting the colouring agent.

8. Method according to any one of claims 3 to 7, characterised by the fact that acid amides or fatty acid amides are used for dissolving or melting the colouring agent.

9. Method for producing a coating material containing a chromogenic colouring agent for application to copying material according to claim 1, characterised by the fact that for dissolving the chromogenic colouring agent in water, the latter is converted by a chemical reaction, for example by the addition of organic acids, into a water-soluble form and that due to the addition of alkalies, the acid is subsequently once more neutralised so that the colouring agent precipitates in a fine and flock-like manner and that subsequently binding agents such as starch or a synthetic material dispersion are added.

1 0. Copying material, substantially as hereinbefore described in Example 1 or Example 2.

11. Method for producing a coating material substantially as hereinbefore described in Example 1 or Example 2.