US3580720A - Photographic sensitized papers excellent in fluorescent brightening effect and process for preparing the same - Google Patents

Abstract

A PHOTOGRAPHIC SENSITIZED PAPER CAN BE GREATLY ENHANCED IN FLUORESCENT BRINGTNEING EFFECT BY INCORPORATING INTO A BINDER IN THE PHOTOGRAPHIC LAYER A STARCH DERIVATIVE HAVING IN COMBINATION A AMINOGULANIDINE GROUP AND AN ALKEHYDE GROUP. THIS STARCH DERIVATIVE IS A MORDANT WHICH MAKES THE BINDER COMPLETELY NON-DIFFUSIBLE TO A FLUORESCENT DYE.

Description

United States Patent PHOTOGRAPHIC SENSITIZED PAPERS EXCEL- US. Cl. 96--82 4 Claims ABSTRACT OF THE DISCLOSURE A photographic sensitized paper can be greatly enhanced in fluorescent brightening effect by incorporating into a binder in the photographic layer a starch derivative having in combination an aminoguanidine group and an aldehyde group. This starch derivative is a mordant which makes the binder completely non-diifusible to a fluorescent dye.

This invention relates to photographic sensitized papers which are excellent in fluorescent brightennig effect and to a process for preparing the same. More particularly, the invention pertains to a photographic sensitized paper which contains in the photographic layer, an aminoguanidized dialdehyde starch in a form bonded to an anionic fluorescent brightening agent, and to a process for preparing a photographic sensitized paper which is excellent in fluorescent brightening effect by incorporating into a binder forming the photographic layer, an aminoguanidized dialdehyde starch either in a form previously bonded to an anionic fluorescent brightening agent or in the form as it is so as to be bonded thereto within the photographic layer.

H-eretofore, a process for enhancing the whiteness of textiles or papers by the use of a group of organic compounds called fluorescent brightening agents or optical bleaching agents has been developed and has come to be widely applied to photographic sensitized papers, and the use of said process is common at present. However, in said process, there are several problems which have not sufficiently been solved yet.

The above-mentioned fluorescent brightening agents are organic compounds which absorb ultraviolet rays and emit blue to purple fluorescence, and were developed to overcome such drawbacks that fibers employed for the production of papers and cloths, regardless of whether the fibers are natural or synthetic, have a very slight yellowish color and are not sufiiciently white, in general. As such fluorescent brightening agents, there have chiefly been developed those of the anionic type which possess direct dyeability for many fibers such as cotton, silk, nylon, etc. Depending on the use, however, there are those which are different in structure. Generally, the said agents adsorb on fibers and are not removed by water-washing. Further, they are ordinarily direct dyes as mentioned above, and therefore they adsorb well on wood fibers for papers and are markedly excellent in brightening effect on the papers themselves. However, when they are applied to photographic sensitized papers which have been prepared by placing a baryta layer or photographic layer on a paper base such as mentioned above, there are many cases where the photographic sensitized papers are not always whitened sufficiently. The reason therefore is that gelatine, which is the main component of a binder used in the photographic layer or baryta layer, absorbs ultraviolet rays to a considerable extent and, moreover, does not have sufficient dyeability for any optical bleaching agents which are commercially available at present. In the case of a baryta layer, no problem occurs if a fluorescent brightening agent, which is well adsorbed on barium sulfate particles, is used, since the amount of binder contained in said layer is very slight, and thus a brightening effect can be sufficiently achieved, in general, by the use of a fluorescent brightening agent for paper. However, when an ordinary photographic emulsion layer or an over layer is coated thereon, the intensity of the ultraviolet rays reaching the base is weakened and the brightening effect of the fluorescent brightening agent is greatly disturbed, because the binder contained in said layer is composed mainly of gelatine, which absorbs ultraviolet rays. This fact, coupled with the color of gelatine (yellowish brown), lowers the brightness and clarity of the white background of the printing paper. If several emulsion layers and intermediary layers are laminated, as in the case of a color paper, the clarity of the background is further deteriorated, coupled with coloration due to incorporated couplers and light-sensitive dyes. Such detrimental effects can be reduced to a certain extent by replacing part or all of the gelatine with a synthetic resin having less coloration, such as polyvinyl alcohol. This, however, cannot be a complete solution to the problem. It has therefore been absolutely necessary to add suflicient amounts of fluorescent brightening agents to photographic emulsion layers, intermediary layers and over layers.

Most of these water-soluble fluorescent brightening agents are anionic and are not injurious to the photographic emulsions themselves. However, sensitizing dyes, anti-fogging agents and similar additives for silver halide emulsions are cationic, in general, and therefore the brightening agents agglomerate by interaction with said additives and adversely effect the adsorption of said additives onto the silver halide particles to bring about detrimental effects in general.

Accordingly, the fluorescent brightening agents, which are usable at present by addition to photographic emulsions, are not only greatly restricted in kind but also limited in the amount which is to be added, and hence they display sufficient brightening effects only with difficulty. Moreover, in the acidic state, gelatine adsorbs anionic dye quite well, but in an alkaline state, it readily desorbs and liberates the dye, as is well known, so that a considerable portion of the dye is lost during such photographic treatments as development, fixing and water-washing. That is, the dye elutes in an alkaline developing solution and, even though the adsorption amount again increases due to the acidity of the fixing solution and the elution ceases, the escape of fluorescent dye is inevitable if long term waterwashing is effected by the use of water with a high pH. Moreover, in the water-washing of a printing paper, another peculiar disadvantage occurs, which is not seen in the water-washing of a film. This disadvantage is that most of the fluorescent dyes are acidic direct dyes and hence adsorb well on the fibers of the paper rather than on the gelatine. Accordingly, the dye tends to gradually transfer from the emulsion layer to the base. Furthermore, in the case where printed paper pieces may have overlapped one another in water during the water-washing treatment and the water has not sufficiently been stirred, the fluorescent dye in the emulsion layer of one sheet of paper is transferred and adsorbed, according to the principle of imbibition, onto the paper bases of a different sheet of paper which was kept over-layed on it in the washing water. Consequently, the effect of water-Washing cannot be realized at all on the surfaces of the printed paper facing the back of another sheet but rather the fluorescent dye is partly lost and causes a rapid decrease in brightening effect. Thus, it is not the completeness or incompleteness of the water-washing but rather the skillfulness or lack of skill in performing the water-washing treatment and the 3 superiority or inferiority of the equipment result in marked unevenness in the whiteness of finished prints and thus great difficulties in the treatment of large quantitles of small sheets of printed papers are usually brought about.

Further, the disadvantages and difliculties due to lnteraction of the aforesaid fluorescent brightening agents added to emulsions with such emulsion additives as sensitizing dyes, anti-fogging agents, etc. are particularly marked in the case where a plurality of layers of delicate light-sensitive emulsions containing various kinds of sensitizing dyes and couplers are laminated, as in the case of color printing papers. As a means to overcome the difficulties encountered in the above cases, there has been devised and practiced a process in which the fluorescent brightening agents are added, not to the light-sensitive emulsion layers, but to intermediary layers or over layers. However, the said dyes not only easily diffuse and penetrate into the emulsion layers but also readily diffuse and escape, during the photographic treatments, into the paper bases and treating liquids. Accordingly, in treating the printing papers in the form of rolls, no substantial problem arises but in treating them in the form of sheets, there are brought about such disadvantages that unless much care is taken, the finished prints become markedly uneven in whiteness and definite finishing can only be difficultly attained; as in the case of the aforesaid black-white prints. In the case of black-white printing papers, therefore, fluorescent dyes are added in sufficient amounts to the paper bases and in small amounts to emulsion layers and over layers, in general. In the case of color printing papers, however, fluorescent dyes are not added, in general, to the emulsion layers, intermediary layers and over layers, but the fluorescent brightening effects are displayed, in general, in such a manner that prints which have been washed at the final step in the course of developing and finishing treatment are immersed in a liquid containing a hardening agent such as formalin and a fluorescent bleaching agent, which is called a stabilizing bath, to a thoroughly saturated state with a fluorescent dye, followed by immediate drying. In this case, the fluorescent dye in the liquid absorbed in the binder layer remains as it is in the photographic layers even though the dye has not been completely adsorbed on the binder, and therefore the above process is tentatively effective. However, the adsorption of a fluorescent dye varies depending on such conditions as concentration and pH of the said liquid. Since the concentration gradually decreases in the case Where large quantities of printed papers are treated, it is quite difficult to control the concentration to a definite value because the concentration cannot be visually observed. Accordingly, a technique of a high degree of skill becomes necessary in order to manage the concentration so as not to bring about unevenness in whiteness of finished prints.

It is therefore the primary object of the present invention to provide photographic printing papers which are excellent in fluorescent brightening effect by the use of high molecular weight compounds, which can be completely mixed with gelatine and like binders, can be chemically combined therewith and can form firm bonds with the anionic fluorescent dyes employed.

The present invention intends to accomplish the abovementioned object by overcoming at one time the series of disadvantages derived from such a fundamental cause that fluorescent dyes do not completely adsorb on binders. According to the prior art, it is a theoretically deducible conclusion that in order to remove the above-mentioned fundamental cause and to completely adsorb or bond fluorescent dyes onto binders, there may be adopted such procedures that the dyes are enhanced in direct dyeability to make them completely non-diffusible in gelatine layers; the molecules of the dyes are incorporated with reactive groups to bond them through direct chemical bonds to the molecules of gelatine and like binders; or gelatine and like binders are modified so as to be completely deposited on the dyes. In practice, however, the above procedures en- 4 counter extraordinary difficulties in synthetic technique and have not yet been successful.

As the result of various studies, the present inventors have been successful in overcoming the abovementioned difficulties using existing, commercially available, fluorescent brightening agents. That is, the essence of the present invention resides in that high molecular weight compounds, which can be completely mixed and chemically bonded to gelatine and like binders and which can form firm bonds (chiefly complex bonds) with said anionic fluorescent dyes, are incorporated in suitable amounts into binders thereby making the binders non-diffusible to the dyes. Such an idea has never been attempted heretofore. In the above case, the high molecular Weight compounds may previously have been bonded to the fluorescent dyes or may later be bonded and incorporated therewith by treatment with solutions of the fluorescent dyes. This is a kind of mordanting, which is quite often effected in the case of dyes other than the fluorescent dyes. For example, in the case of transfer papers of the color print process called irnbibition or dye transfer, substances serving as mordants for acid dyes are generally mixed with binders, and polyvinyl pyridines or various polymers containing vinylpyridines as copolymerization components have been known as such mordants. These polymers surely form firm bonds with acid dyes and are effective as mordants for ordinary dyes, but they are not applicable to fluorescent dyes. For example, polyvinyl pyridines are not homogeneously miscible with gelatine and hence are ordinarily mixed therewith after forming them into quaternary salts. When formed into quaternary salts, polyvinyl pyridines bond firmly to fluorescent dyes to cause a so-called quenching phenomenon and the fluorescent dyes are completely deprived of their fluorescence. Consequently, no brightening effect at all can be attained, and only a yellow color due to inherent absorption is developed. In the case of polyvinyl pyridines which have not been formed into quaternary salts, no complete quenching is brought about. However, said polymers greatly weaken the fluorescence of fluorescent dyes and hence are not suitable for this purpose.

Further, diphenyl biguanide, 1,1,3-triphenyl-guanidine, anhydro-biguanide, benzyl alcohol, and the condensate of dicyandiamidine and formalin are sometimes used for the purpose of firmly bonding direct azo dyes to gelatine. Most of them, however, are low in molecular weight and have an insufficient aflinity for gelatine and like binders, and precipitates formed by bonding the binders to the dyes not only have a certain extent of diffusibility but also lower the bonding strength of gelatine and like binders themselves. Accordingly, they are effective as dyeing assistants for fibers but are not suitable as mordants for colorants of photographic layers, particularly for fluorescent dyes.

In contrast thereto, in the present invention, the mordants themselves are not only high in molecular weight and low in ditfusibility but also crosslink with the binders to firmly bond thereto through the aldehyde groups contained in the mordants, as will be described below. Accordingly, the mordants do not absolutely come out of the photographic layers but act as a kind of hardening agent for the binders.

The object of the present invention can be accomplished by using, as a kind of high molecular weight mordant capable of making binders of photographic layers completely non-diffusible in fluorescent dyes, starch derivatives containing aminoguanidine groups in combination with aldehyde groups which not only have no such detrimental actions such as lowering the bonding strength of binders or weakening the fluorescence but also serve as a kind of hardening agent for enhancing the bonding strength of the binders.

The above-mentioned aminoguanidine group-containing starch derivatives are obtained by reacting aminoguanidine with conventional dialdehyde starches formed by the oxidation of starch with periodic acid. These reactions may be diagrammatically shown in the following drawing:

CHzOH J L Eta) Ethel...

ctr-on I OH OH Aminoguanidation l (Aminoguanidlzed dialdehyde starch) All the reactions go to completion with difliculty but they can be freely controlled. It is therefore possible to synthesize various aminoguanidized starches different in free aldehyde group content and in aminoguanidation degree.

Originally, dialdehyde starches have been developed in order to use them in admixture with pulps for papermaking so that the resulting papers can be made high in water resistance. The aldehyde groups contained in said starches are partly converted into hydrazones by means of hydrazide compounds or aminoguanidine compounds. The reason therefor is that by said treatment, the dialdehyde starches are made cationic so that they can be readily adsorbed, in water, on wood fibers of pulps which is charged anionic in water and can be used with high efficiency.

Aminoguanidized dialdehyde starches, which are commercially available at present, are high in content of aldehyde groups and are excellent as hardening agents for photographic layers, but are low in content of guanidine groups, which serve as seats for the adsorption and bonding of fluorescent dyes. Accordingly, said starches are not always said to be excellent, though they are not unusable for the object of the present invention. It is rather preferable to use those which have been decreased in degree of initial oxidation with periodic acid and increased in amount of reacted aminoguanidine. Generally, however, starch derivatives high in content of guanidine groups have a tendency to lower the Water resistance of gelatine and like binders. Accordingly, it is desirable to use starch derivatives which are considerably high in free aldehyde group content and which can overcome the above-mentioned tendency to be enhanced in hardening power. However, the extent of these factors varies depending on the kind and properties of binders and on the kind and amounts of fluorescent bleaching agents to be introduced, and therefore no decisive conclusion can be made with respect thereto. Accordingly, it is necessary to use suitable starch derivatives in optimum amounts from an economic viewpoint.

In the process of the present invention, the amount of the aminoguanized dialdehyde starch to be incorporated into the binder is desirably up to 50% of the amount of the binder.

Further, the starch derivatives in the present invention can be incorporated not only into the photographic layers but also into the baryta layers thereby saving formalin.

aldehyde starch) (162)1+( )m The following examples illustrate the invention.

EXAMPLE 1 To a dispersion of 250 g. of a commercially available dialdehyde starch (Sumstar-l75 produced by Miles Co., U.S.A.; oxidation degree about 75%) in 750 ml. of water there is added, under stirring, a solution of 25 g. of a commercially available aminoguanidine bicarbonate in 250 ml. of water which has been adjusted to pH 3 by addition of a small amount of hydrochloric acid, and the mixture is reacted at below 40 C. for 2 hours. After filtration and water-washing, the reaction mixture is washed with methanol and is dried at a low temperature to obtain a white powder containing about 3% of nitrogen and 13% of water. In view of the amount of nitrogen, the amount of the resulting aminoguanidized dialdehyde starch is only about 6% of the total aldehyde group. However, said starch is favorably bonded to a fluorescent dye and has no detrimental effect on the fluorescence of the dye. Further, the starch is high in free aldehyde group content and hence is very effective as a hardening agent to make it possible to use no such photographically injurious hardening agent as formalin. As a result, the aminoguanidized dialdehyde starch is excellent not only for warm tone printing paper but also for color printing paper.

EXAMPLE 2 A dispersion of g. of a commercially available starch (Sumstar-lSO produced by Miles Co.; oxidation degree about 50%) in 300 ml. of water is slightly heated to a semi-solid. To this semi-solid is added a solution of 45 g. of aminoguanidine hydrochloride in 450 ml. of Water which has been adjusted to pH 2, and the mixture is reacted at room tempertaure for 20 hours. After filtration and water-washing, the reaction mixture is Washed with methanol and is dried at below 40 C. to obtain, as a white powder, a starch oxide in which about one half of the total aldehyde group content has been aminoguanidized. The thus obtained starch oxide is considerably weaker in hardening power than the starch obtained in Example 1. However, it is markedly effective in bonding power to a fluorescent dye and hence is particularly excellent for effecting the object of the invention.

7 EXAMPLE 3 T o a dispersion of 30 g. of a specially made dialdehyde starch (oxidation degree 10%) in 100 ml. of water is added, under stirring, a solution of 5 g. of a commercially available aminoguanidine bicarbonate in 50 ml. of Water which has been adjusted to pH 2.5 by addition of a small amount of hydrochloric acid, and the mixture is reacted at about 50 C. for 3 hours. The reaction liquid is adjusted to pH 7-7.5 by addition of a small amount of caustic soda, and is then heated to 90 C. to form a 20% solution. This solution is low in both oxidation degree and aminoguanidation degree but can be incorporated in a large amount into a binder. Accordingly, it is economically advantageous to use this solution as a part of such an expensive binder as gelatine. Further, the solution has less coloration and hence is favorable in brightening effect.

EXAMPLE 4 T 100 g. of the aminoguanidized dialdehyde starch there is added a solution of got a commercially available fluorescent dye (Leucophol B produced by Ciba Co., Switzerland) in 1 l. of water. After stirring, the mixture is allowed to stand for more than hours at a relatively low temperature (about 10 C.), and is then suctioned, filtered, water-washed and dried to obtain a fluorescent granular substance which is pale yellow in color. A suitable application amount of the thus obtained substance is 10-20 times as great as the ordinarily employed amount of a fluorescent dye.

EXAMPLE 5 To 100 g. of the aminoguanidized dialdehyde starch obtained in Example 2 there is added a solution of g. of a commercially available photographic fluorescent dye (Tinopal B, PHOTO, produced by Geigy Co., Switzerland) in 5 l. of water, and the mixture is treated in the same manner as in Example 4 to obtain a pale yellow powder. This powder can sufficiently display a fluorescent brightening effect when used in 3-5 times the amount of a fluorescent dye itself.

EXAMPLE 6 (A) A 5% gelatine solution incorporated with 0.01% of Leucophol B, and (B) a 5% gelatine solution incorporated with 0.1% of the Leucophol B-dyed aminoguanidized dialdehyde starch obtained as in Example 4 are separately applied each in an amount of about 100' g./m. onto baryta papers and are then dried. The thus treated papers are cut into small pieces and are washed with water, whereby both paper pieces emit strong fluorescence and no marked difference is seen between the two. 'However, when the paper pieces are immersed in alkaline water and are then washed with water, it is observed that the paper piece (A) is reduced in fluorescence. Further, when the two are removed from the water, individually placed, while wet, on filter papers with the emulsion surfaces facing the filter papers, are squeezed and are peeled off from the filter papers after 15 minutes, it is understood that the filter paper surface which is contact with (A) emits strong fluorescence whereas the filter paper surface which is contact with (B) emits no fluorescence. From this, it is substantiated that a part of the fluorescent dye in the paper piece (A) has diffused and transferred into the filter paper whereas the fluorescent dye in the paper piece (B) has been made substantially completely nonditfusible.

EXAMPLE 7 (A) A mixture comprising gelatine and 10% based on the gelatine of the aminoguanidized dialdehyde starch obtained in Example 1, and (B) a mixture comprising gelatine and 3% of formalin are separately applied onto baryta papers, so that the solid content of each mixture applied becomes about 5 g./rn. and are then dried. The thus treated baryta papers are cut into small pieces, and

8 the paper pieces are immersed for 10 minutes in a 0.25% solution of Tinopal BOP and are then dried. Both of the two paper pieces are substantially the same in appearance, strongly emit fluorescence and seem to be pure white. The two kinds of paper pieces are washed with water in separate vessels with much care so that the paper pieces do not overlap each other. In a period of about 1 hour, it is not considered that any marked difference has occurred between the two. However, when the film surfaces of the paper pieces are closely contacted, while wet, with filter papers, like in the case of Example 6, are put between polyethylene films or acetate bases so as not to dry, allowed to stand for a while and then taken up, it is found that the portions of filter papers which have contacted with the two paper pieces (A) and (B), emit considerable fluorescence. This is not because the mordant employed in (A) is inferior but because in the film of (A), gelatine is present in substantially the same amount as in (B), in addition to the fluorescent dye firmly adsorbed and bonded loosely onto the mordant, and said gelatine has loosely adsorbed the fluorescent dye, as in the film of (B). When the films are repeatedly contacted, in the same manner as above, with the surfaces of fresh filter papers wetted with water so as not todry the films and are repeatedly allowed to stand, considerable transfer of fluorescence is seen at the initial stage in both paper pieces (A) and (B). After a while, however, it is observed that (B) is substantially completely deprived of fluorescence, whereas (A) still retains strong fluorescence. According to the above process also, it is possible to clearly substantiate the fact that mordant-dyed fluorescent brightening agents are excellent in non-diffusibility.

EXAMPLE 8 To a high speed silver chlorobromide emulsion prepared from 1 kg. of silver nitrate is added, together with other ingredients and additives, 1.6 l. of a 5% solution of the bonded product of Leucophol B and aminoguanidized dialdehyde starch which has been obtained as in Example 4 and the total amount of the mixture is made about 50 kg. This mixture is applied onto an ordinary, whitened baryta paper to form a layer. Onto this layer is applied, as an over layer, a mixture comprising 10 kg. of a 1% gelatine solution and 200 l. of a 5% solution of the bonded product obtained as in Example 4, whereby a pure white sensitized paper favorable for enlargement is prepared. The merits of the dye employed in this example are that it has no detrimental effect on the emulsion and is not deteriorated in whiteness even when the printed paper is subjected to a prolonged washing treatment.

EXAMPLE 9 In the case of a color paper of the multi-layered emulsion type which is prepared according to a known manner, if each of the emulsion layers, intermediary layers and over layer is incorporated with about 12 g. per liter of the coating liquid therefor of the product of Example 5, there is obtained a color paper which does not suffer from variation in fluorescent brightening effect during the treatment thereof and which is not particularly required to be treated with a brightening dye solution in a stabilizing bath. It is, of course, possible to further increase the whiteness of the paper by subjecting same, immediately before the final ferrodrying treatment of the paper, as in the case of an ordinary color paper. In this case, said treatment is not useless but the brightening efiect attained by said treatment is not great and the consumption of fluorescent dye in the bath is not much. Accordingly, there are such advantages that the bath may be low in dye concentration and is easily operated and managed for a long period of time, and less unevenness is seen in finishing. Thus, the color paper prepared according to the above process is far more easily subject to handling than a common color paper.

9 EXAMPLE 10- In a color paper of the multi-layered emulsion type which is prepared according to a known process, a fluorescent brightening agent, which tends to give detrimental effects to the photographic properties thereof, is not used at all and, in place thereof, only an amino-guanidized dialdehyde starch, which becomes a mordant therefor, is added to each of the emulsion layers, intermediary layers and over layer in an amount of about 1-5 g. per liter of the coating liquid therefor. The amount of said starch to be added is increased or decreased depending on the concentration of binder in each layer, or on the presence or absence and kind of coupler, and the degree of hardening and swelling properties of each layer is so controlled as to become definite without adding other hardening agent, e.g. formalin or a compound yielding formalin by decomposition which later gives deterrnental effects to color dyes or couplers. In this case, the aminoguanidized dialdehyde starch acts, in the raw printing paper, only as a hardening agent, and the function thereof as a mordant is latent until the treatment has been complete. Accordingly, the color paper of this example may be treated, after the developing treatment and immediately before the drying treatment, by immersing the paper in a socalled stabilizing bath containing a suflicient amount of a fluorescent brightening dye, as in the case of a common color paper. The operation and control required therefor should be slightly more accurate than the case of Example 9. Unlike in the case of a conventional paper, however, the fluorescent dye in an amount exactly proportional to the amount of the aminoguanidized dialdehyde starch added is firmly adsorbed on the paper, so that the consumption of the fluorescent dye is exactly proportional only to the surface area of the paper under treatment, substantially regardless of the concentration of the bath. Accordingly, the replenishment of the dye is simple, and an 10 excellent brightening effect less varied and free from unevenness can be easily attained. Moreover, the raw printing paper contains neither an injurious fluorescent dye nor formalin and hence is favorable in storability. Thus, there are attained added advantages.

What is claimed is:

1. In a photographic sensitized paper containing a fluorescent brightening agent, an improvement wherein the fluorescent brightening agent is bonded to an aminoguanidized dialdehyde starch.

2. In a process for preparing photographic sensitized papers with a fluorescent brightening effect, an improvement wherein an anionic fluorescent brightening agent is bonded to an aminoguanidized dialdehyde starch either before being incorporated into a binder forming the photographic layer, or after said agent and aminoguanidized starch is incorporated in said binding layer.

3. A photographic sensitized paper according to claim 1, wherein the aminoguanidized dialdehyde starch is also contained in the baryta layer, in addition to the photographic layer.

4. A process according to claim 3, wherein the aminoguanidized dialdehyde starch is incorporated into the binder in an amount of up to based on the amount of the binder.

References Cited UNITED STATES PATENTS 2,882,156 /1959 Minsk 9684 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl. X.R.