LU86103A1 - PROCESS FOR MANUFACTURING PAPER FOR USE IN REPROGRAPHY - Google Patents

Description

The present invention relates to a process for manufacturing paper which can be used in reprography. In one application, the paper comprises a thin paper support, coated on its front surface with a light-sensitive compound diazo, and this thin support is stiffened by applying a coating according to the invention to the back of the support. In another application for a plain-paper reprography process, the compound diazo layer is omitted from the front surface.

In the known technique, medium and strong paper supports are used to avoid curling or curling of the diazo paper.

The method according to the invention therefore makes it possible to use thinner papers as a support and to make substantial savings by reducing the price per kilo of paper produced, making it possible to save cellulose and this while obtaining results at least identical.

The present invention is characterized in that an emulsion comprising 0.5% to 1.5% (by dry weight) of polyvinylpyrro-lidone or one of its emulsions is applied to the dorsal face of a thin paper support derivatives 25 0% to 1% (by dry weight) of optical brightener 90% to 98% of a solvent chosen from the following solvents: water, alcohols or mixture of water and alcohol in order to stiffen the support of paper.

According to a preferred embodiment, the emulsion 30 comprises 1.5% (by dry weight) of polyvinylpyrrolidone, 0.5% of optical brightener and the remainder is solvent. When the solvent is a water-alcohol mixture, the preferred alcohol is ethanol, but other alcohols may also be suitable. The amount of alcohol in the water-alcohol mixture can vary from 0 to 30%.

As optical brighteners, it is possible to use the usual products known in the art such as by

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- 2 - example, methylene blue, methylene violet, SUPRACEL violet or alizarin IRXSOL RL. The invention is not limited to these brighteners mentioned solely for the purpose of illustration.

Polyvinylpyrrolidone seuh can be used, either one of its derivatives or mixed in all proportions with one of its derivatives. In addition, these compounds can be mixed in any proportion with sodium carboxymethylcellulose or one of its derivatives or another salt of carboxymethylcellulose.

The method according to the invention is implemented in the following way: a roll of raw paper of quality suitable for reprographic use is unrolled and its dorsal face is coated with the emulsion described above. This coated paper then passes through a dryer, at an adequate temperature, and by a set of rollers, the other face of the paper is coated in a diazo emulsion tank, with a compound diazo, then the paper crosses the dryer again and is wound up. on the final roll of emulsified paper.

The emulsion according to the invention applied to the dorsal side of the paper counterbalances the effect of the diazo emulsion applied to the other side and the phenomenon of curling or bulging on the finished paper is avoided, which remains flat at the time of its use. The finished paper behaves in the same way as the other papers during its development in an automatic machine and during its passage through an automatic folder.

In the known technique for manufacturing diazo paper 2 the support is a paper of 60 to 90 g / m for example while with the present invention a paper can be used

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on the order of 30 to 50 g / m. The method according to the invention therefore makes it possible to achieve a substantial saving in cellulose and reduces the price of manufacture. In order that the invention may be better understood, reference is made to the drawing describing the basic scheme of the technique.

The emulsifying paper 1 is unrolled and turns around the roller 2 in the direction of the arrow while passing through the emulsion 4 according to the invention comprising the solvent 40, the polyvinylpyrrolidone and the brightener - 3 -

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optical. This will coat the back of the paper.

The coated paper, after turning around the roller 5 passes through a dryer 11 at a suitable temperature 5 to dry the emulsion. By the play of the rollers 6 and 7 the paper passes through the compound diazo emulsion, presenting it with its front face. The coated paper after turning around the roller 10 returns to the dryer and the emulsified paper obtained is collected on the roller 13.

The process according to the invention can also be implemented for the production of paper used in the so-called "Plain-Paper" reprography process. The paper used to make the copies a raw paper for reprographic use consisting essentially of pure cellulose, and not containing heavy metals such as iron or heavy metal salts. The paper usually used weighs 70 to 90 g / m ^.

The process according to the invention makes it possible to use a paper weighing only 50 to 60 g / m 2, which allows a saving in cellulose of 15 to 35%.

This paper will only be coated with the emulsion according to the invention on its dorsal side using the installation shown in the drawing where the compound diazo emulsion tank will be empty. The paper having passed through the tray comprising the polyvinylpyrrolidone emulsion, is dried in the dryer, passes through the empty tray and then through the extinct dryer. The dryer is a device known in the art comprising separate gas ramps making it possible to use different parts of the dryer at the same time at different temperatures.

The following table gives examples, having a purely illustrative purpose, of application of the polyvinylpyrrolidone emulsion according to the preferred embodiment.

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7 '- 4 - c 1 2 3 4 width of the paper to be treated 5 (meters) 1.20 1.20 2.50 2.50 average coating speed (m / sec) 3 6 6 10 average drying temperature (° C) 50 75 50 65 10 average time spent in the dryer (seconds) 60 30 60 30

The average coating speed depends on the width of the paper to be treated. The wider the paper, the higher the drying speed.

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Claims (6)

1. A method of manufacturing paper that can be used in reprography, characterized in that an emulsion comprising 0/5% to 1/5% (by dry weight) of polyvinylpyrrolidone is applied to the dorsal face of a thin paper support. of its derivatives or a mixture of these in all proportions, 0% to 1% (by dry weight) of optical brightener, and 90% to 98% of a solvent chosen from the following solvents: water, 10 alcohols, or water-alcohol mixtures in order to stiffen this paper backing, and dry. 2. Method according to claim 1 characterized in that the emulsion comprises 1.5% (by dry weight) of polyvinylpyrrolidone, 0.5% by weight of optical brightener and the remainder is solvent. 3. Method according to claim 1 characterized in that the solvent is a mixture of water and ethanol which can comprise up to 30% ethanol. 4. Method according to claim 1, for the manufacture of diazo paper characterized in that after having applied the polyvinylpyrrolidone emulsion and after having dried, a diazocompound emulsion is applied to the front face and dried. 5. Method according to any one of claims 1 or 4 characterized in that the polyvinylpyrrolidone is mixed in all proportions with the sodium carboxymethylcellulose or one of the derivatives thereof. 6. Method according to claimCharacterized in that the carboxymethylcellulose is replaced, in whole or in part, by another salt of carboxymethylcellulose.