US2642362A - Light-sensitive baryta-coated photographic paper - Google Patents

Description

FIG. 2.

g, FORMALDEHYDE R40- 8 Q A GA YOXAL o 5 1 0 1. 5 F1 HAKDENER ,6? 1.5% FORMALDEHYDE I40 '8 Q /20 7.5% h GLYOXAL/ 80 g 60 4 GEORGE R. CLARK LLOYD F. MILLER Z0 INVENTORS 0.3 1 FORMALDEHYDE Jamil) 9.)! u l l I 0 4 8 I2 I6 20 24 (41% 9.9M

June 16,- 1953 G. R. CLARK ET AL 2,642,362

LIGHT-SENSITIVE BARYTA-COATED PHOTOGRAPHIC PAPER Filed March 18, 1949 5/1. VER HAL/DE EMULSION G L YOXAL HA RDENED GELA 77N0'7 BIRYTA LA YER \PA PER SUPPORT HOLD/N6 TIME (HRS) ATTORNEY w AGENT Patented June 16, 1953 LIGHT- SENSITIVE BARYTAe COATED PHOTO GRAPHICPAPER George R. Clark and Lloyd F; Miller, Rochester, N. Y., assignors to. Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 18, 1949; Serial No; 82,118

1 Claim.

1 This invention relates to the preparation. of light-sensitive photographic elements and: more particularly to photographic elements; having.

baryta-coated paper supports.

It is a well-known procedure in the art of making photographic papers toprovide a gelatinobaryta-coated paper support, upon which is coated .a light-sensitive silver halide emulsion layer- The over-all physical and. chemical characteristics of the sensitive paper are reflections of the quality of the sensitive emulsion layer; the gelatino-baryta coating: and the paper stock carrying: these layers; For example, physical irregularities: present on the. surface. of a baryta' coated'paper. are. reflected andpftimesmagnified in subsequentv sensitizing and, processing operations partly because these. defects prevent the application of a uniform emulsion layer during mosphere of the coating alleyswhich is a definite hazard.

One' object of our invention therefore is to provide baryta-coated photographic papers havmg improved. photographic qualities. Another obgectris to provide a method of stabilizing the coating characteristics of baryta coating comthe sensitizing operation. It is therefore essential, during the baryta coating operation, to apply the. baryta composition in a uniform and consistent manner so that. maximum. quality of product can be assured.

Physical non-uniformities in baryta coatings.

in part can be attributed to variations inthe physical and handling properties of the: liquid coating compositions and more basically" appear to be markedly influenced by the manner in which the gelatin of the baryta coating is hardened. That is, a given gelatino-baryta composition containing formaldehyde or chromium chloride hardening agents when freshly made from a predetermined formula can be expected to coat without difiiculty; however, if, because of circumstances beyond control of the operator, the composition must be held for coating at a later time, it is not uncommon to find the composition useless because the viscosity and flow characteristics have changed to the extent that the machine will not coat a uniform layer on the paper stock. This difliculty has been attributed to the chemical action of formaldehyde or chromium chloride on the gelatin in the composition.

Similarly, baryta coatings hardened by means of formaldehyde and chromium chloride or similar gelatin hardening agents do not possess the optimum degree of hardness. As a result, during processing of exposed photographic papers,

the processing solutions may unduly soften the baryta coating and cause reticulation of the emulsion layer. Other disadvantages of the usua1 hardeners for baryta layers, particularly formaldehyde, lie in the fact that during the drying of such coatings large quantities of the irritating formaldehyde fumes are released to the atpositions. Other objects of our invention will become apparent from consideration of the'following'description of our invention. I

The objects of our invention are accomplished principally by utilizing glyoxal as a gelatin hardeningagent in gelatino barytacoating compositions.

We have discovered that when glyoxal is used as a gelatin hardening agent in baryta coat,- ings most of. the; objections to other hardening agents are overcome. In addition, the novel hardening agent ismore eflicient since appreciably less of the new hardening. agentneed be used to obtain. as good. or better hardeningthan is obtainable with other hardening agents.

In the accompanyingdrawingst in Fig. l.v is shown in greatly enlarged. cross+sectional view,

the. appearance of a photographic; element of.

our invention. and in. Figs. 2 and 3, by meansof. graphical representation are. compared theaviscosity stabilizing qualities of glyoxal and formaldehyde.

Our invention will be understood by consideration of the following example which is merely illustrative of our invention:

Example A suitable quantity of gelatin is swelled in tepid water and dispersed by melting in approximately five times the weight of water. Blane fixe paste comprising approximately 55 per g cent barium sulfate is then added to the gelatin solution in the quantity required to obtain from 20 to 5 0 per cent baryta in the final coating composit1on. The composition is then diluted with water to give the required concentration of solids, following which an aqueous solution of glyoxal is added. Following addition of the customary defoaming or wetting agent, the pigment composition is then passed through dispersion equipment such as a colloid mill to increase the degree of dispersion of the baryta particles in the gelatin solution, and the dispersion is ready for coating on a paper support. Coatings on paper are made in the conventional manner and at this point the superior coating properties of the composition become most evident. It is observed that the compositions uniformly wet the paper stock with the result that a baryta layer of uniform thickness and freedom from irregularities results when the coating is subsequently dried down in the coating alley. Preferably, following calendaring of the baryta-coated sheet, a light-sensitive silver halide emulsion layer is applied in a manner well known in the art. The product would appear substantially as shown in Fig. 1 of the accompanying drawings wherein the paper support I0 is shown as carrying the glyoxal-hardened gelatino-baryta layer and the silver halide emulsion layer 12 over the baryta layer.

In the above example, the concentration of gelatin in the coating composition may be varied from about 1 to 15 per cent by weight and the glyoxal (added as an aqueous solution of strength of from about 1 to 40 per cent) is added to obtain a concentration of from about 1 to 6 per cent based on the weight of gelatin present. In general, 2 per cent glyoxal produces satisfactory hardening.

We have mentioned that glyoxal is more efficient as a hardening agent in baryta compositions than other hardening agents and particularly in comparison with formaldehyde we find that glyoxal is at least six times as eiiicient and this is rather unexpected considering that the compound contains in its molecule only twice as many reactive aldehyde groups as does formaldehyde.

This increase in efficiency becomes quite evident when baryta coatings are cured down under conditions of high temperature and humidity which tend to volatilize formaldehyde rapidly. Under such conditions glyoxal tends to be retained by the product during the hardening period.

Fig. 2 of the accompanying drawings illustrates the advantage from a viscosity standpoint of using glyoxal as a hardener. The graph shows that as the concentration of glyoxal (based on the weight of gelatin present) in a formula compounded as in the above example, is varied from 1 to 15 per cent, the viscosity remains reasonably constant; Whereas over the range of from 5 to 15 per cent, the compositions containing formaldehyde steadily increase in viscosity. Therefore, since machine operating conditions must be varied with changes in viscosity of the coating compositions, when using formaldehyde the manufacturer must coat under a Wide variety of machine operating conditions to obtain quality comparable to glyoxal-hardened coatings.

Fig. 3 of the drawings illustrates the viscosity eiiect of holding typical baryta formulas containing formaldehyde and glyoxal as hardening agents. According to the graph, at concentrations of 0.3 per cent hardener, the increase in viscosity over the 24-hour holding period increses more using formaldehyde; whereas at concentrations of 1.5 per cent, which is the more common hardener concentration, the viscosity of the formaldehyde compositions reaches excessive values in considerably less than 4 hours of holding time; while the viscosity of the glyoxal compositions has not increased to the extent that the solutions are not usable. This advantageous behavior of glyoxal as a hardener agent appears quite unexpected when considering the fact that the compound has two reactive aldehyde groups in its molecule compared to formaldehyde and on this basis might be expected to produce greater viscosity increases than does formaldehyde.

It is to be understood that the disclosure herein is by way of example and that We consider as included in our invention all modifications and equivalents falling within the scope of the appended claim.

What we claim is:

A light-sensitive photographic element comprising a paper support having on one surface thereof a gelatino-baryta layer containing glyoxal uniformly dispersed therein as a gelatin hardening agent, and over said layer a silver halide emulsion layer.

GEORGE R. CLARK. LLOYD F. MILLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,870,354 Brunken Aug. 9, 1932 2,309,492 Albers et al Jan. 26, 1943 2,414,858 Davidson Jan. 28, 1947

Images