US2595916A - Light sensitive positive printing diazotype paper having a calendered surface - Google Patents

Description

Patented May 6, 1952 OFFIQE LIGHT SENSITIVE POSITIVE PRINTING DIAZOTYPE PAPER HAVING A CALEN- DERED SURFACE Wilhelmus Hubertus Gerardus Bartels, Venlo, Netherlands, assignor to Chemische Fabriek L. Van Der Grinten, Venlo, Netherlands, a company of the Netherlands No Drawing. Application April 20, 1948, Serial No. 22,263. In the Netherlands April 21, 1947 9 Claims.

The invention relates to light sensitive positive printing diazotype paper and a process for its manufacture;

The conventional positive printing diazotype paper is manufactured as follows:

Suitable base paper is sensitized by coating it with an even layer of a liquid containing a diazo compound (for a so-called one component paper) and, if desired, in addition an azo coupling component (for a so-called two component paper), together with other substances, e. g. for improving its keeping quality, for decreasing the discoloration of the copies made, etc. This layer of liquid is then dried on the surface of the paper.

After exposure to light the image is developed. When a one component paper is used the developer contains an azo coupling component, for a two component paper an alkaline reaction of the liquid or of the vapour used for the development suffices.

It has also been proposed to apply to the surface of the diazotype paper a powder capable of bringing about the development after exposure, said powder being rubbed or calendered in for the sole purpose of causing it to adhere to the said surface.

The object of the invention is to provide a diazotype paper for the positive printing process showing improved qualities.

Another object is to provide a diazotype paper for the positive printing process which after exposure yields copies of improved qualities.

Other advantages will be clear from the following description.

For achieving these advantages no developing powder is applied to the sensitized surface of the paper, i. e., a sensitized layer free of developing powder must be employed.

Usually the base paper is calendered before it is sensitized for the purpose of flattening it and of giving its surface a satinage, this calendering being conventional for most papers.

But it has now been found, according to the present invention, that important advantages over the conventional positive printing diazotype papers are obtained by forming positive printing diazotype papers with a light-sensitive layer free of developing powder and thereafter calendering the surface of this layer. The paper so produced is flatter (this is even the case with the copies obtained therefrom by means of a double sided development with two thin films of liquid), while also its satinage and that of the eventual copy is better than that obtained by conventional calendering the base paper before its sensitization. The keeping-quality of the new sensitive paper is better, and its capacity for taking up the developing liquid is also improved. The advantages of the invention are particularly outstanding when the usual coating technique is applied, in which the paper is coated with an excess of the sensitizing solution and, after some time for enabling the solution to penetrate into the paper, the excess is scraped or doctored off.

It is surprising that these advantages, for example the better keeping-quality, are achieved by simply calendering the sensitized paper.

In the manufacture of the sensitized paper according to this invention one may start with a conventional calendered base paper suitable for the manufacture of light sensitive positive printing diazotype paper. It is preferred, however, to start with base paper which has not yet been calendered; in this case the eventual copy shows considerably softer, i. e. more even, tones, particularly half-tones, while also the details of the print are sharper.

The base paper is sensitized and thereafter calendered. The calendering can be done immediately after the sensitizing operation when the paper still contains large amounts of moisture, e. g. 10-16%. After or during the calendering operation this paper must be dried. It has been found, however, and surprisingly so, that it is also possible to calender the sensitized paper after drying, when it has only a moisture content of less than 6%; this amounts to a considerable simplification because in that practice it is no longer necessary to dry the paper after the calendering operation. The calender may be arranged so as to form a part of the coating machine or it may be provided in the immediate vicinity of said machine; this, however, is not necessary.

Ernample 1 Pinewood-cellulose base paper of a convgntional quality for making diazotype paper (for example of grammes per m is a non-calendered condition is coated with an excess of the following aqueous solution:

1.5% zinc chloride double sale of paradiazoethyl-benzylaniline 1% thiourea 1% tribasic ammonium citrate 0.5% citric acid 0.1% gelatine which solution is scraped off after some time to such extent that per m.'- of the paper 12 grammes of the solution remain on and in the surface of the paper.

The paper is now dried within 30 seconds at a temperature of approximately 120 C. to a moisture-content of 4%. It is then calendered on a paper-calender with a pressure of 50 kilogrammes per centimetre and with a speed of 60 metres per minute. After this operation it is cut to sheets of foolscap size. The sheets obtained are flatter and have a more beautiful satinage and show a greater keeping-quality than sheets obtained without calendering after sensitization, or even than sheets the base paper of which had been calendered in the conventional way before sensitization, that is to say between the papermaking and the sensitization operation. After printing by exposure to light in contact with an original containing half-tones the sheets are developed on both sides, on the front side with 8-9 grammes per m3 and on the back with 5-6 grammes per m. of an aqueous developer of the following formula:

8% sodium thiosulfate 2% thiourea 2.5% sodiumcarbonate 0.1% isopropylnaphtalenesulfonate of sodium 0.7% phloroglucinol 0.7% resorcinol and immediately thereafter dried freely.

The paper shows a better capacity of taking up the developing solution; the copies have a more beautiful satinage and are flatter than those obtained from sheets which have not been calendered after sensitization, even if the-base paper of these sheets had been subjected to the conventional calendering operation before sensitization. The omission of the conventional calendering step before sensitization causes the half tones of the copies to be better, i. e. softer'and" more even.

Example 2 The printed copies are developed in an atmosphere of moist ammonia vapours. tages of the new sensitized sheets are the same as those'indicated in Example 1, while the advantages with respect to the copies are essentially the same. However, in so far as the flatness and the satinage of the copies are concerned, the advantages are relatively greater, while in so far as the ease of development is concerned the advantage is relatively smaller than in Example 1.

As follows from the foregoing, calenderin'g'after sensitization of the base paper yields certain advantages both when the base paper had alpara-diazodimethyl- The advanready been calendered and when it had not been; other advantages are only achieved when the calendering step according to the invention is carried out with a sensitized paper the base paper of which had not been calendered before sensitization. Naturally the extent to which the advantages are achieved depends on the nature of the base paper used.

What I claim is: a

1. The process of manufacturing light-sensitive positive printing diazotype paper, which comprises applying a sensitizing solution containing a diazo compound to base paper to form diazotype paper having a sensitized layer free of developing powder, and thereafter, without having applied developing powder to said layer, calendering and drying said diazotype paper.

2. The process of manufacturing light-sensitive positive printing diazotype paper, which comprises applying a sensitizing solution containing a diazo compound to base paper to form diazotype paper having a sensitized layer free of developing powder, then calendering said diazotype paper without having applied development powder to said layer, and then drying it.

3. The process described in claim 2 wherein the base paper used is uncalendered paper.

4. The process of manufacturing light-sensitive positive printing diazotype paper, which comprises applying a sensitizing solution containing a diazo compound to base paper to form diazotype paper having a sensitized layer free of developing powder, then drying said diazotype paper to a moisture content of less than 6%, and then calendering it without having applied developing powder to said layer.

5. The process described in claim 4 wherein the base paper used is uncalendered paper.

6. Light-sensitive positive printing diazotype paper produced by the process described in claim 1.

7. Light-sensitive positive printing diazotype paper produced by the process described in claim 3.

8. Light-sensitive positive printing diazotype paper produced by the process described in claim 4.

9. Light-sensitive positive printing diazotype paper produced by the process described in claim 5.

WILHELMUS HUBERTUS GERARDUS BARTELS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name I Date 2,216,137 SChmidt el) al. 00b. 1, 19 0 2,501,874 Peterson Mar. 28, 1950 FOREIGN PATENTS Number v Country Date 454,665 7 Great Britain Oct. 6, 1936 467,313 Great Britain June 15, I937

Claims (1)

1. THE PROCESS OF MANUFACTURING LIGHT-SENSITIVE POSITIVE PRINTING DIAZOTYPE PAPER, WHICH COMPRISED APPLYING A SENSITIZING SOLUTION CONTAINING A DIAZO COMPOUND TO BASE PAPER TO FORM DIAZOTYPE PAPER HAVING A SENSITIZED LAYER FREE OF DEVELOPING POWDER, AND THEREAFTER, WITHOUT HAVING APPLIED DEVELOPING POWDER TO SAID LAYER, CALENDERING AND DRYING SAID DIAZOTYPE PAPER.