US 3582337 A
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June 1, 1971 w. H. GRIGGS El'AL 3,582,337
LIGHT-SENSITIVE PHOTOGRAPHIC PAPER Filed June 27, 1968 PHOTOGRAPH/G EMULSION LAYER GROSS-LINKED VINYL ACETATE POLYMER SIZING PHOTOGRAPH/G EMULSION LAYER POLYETHYLENE \mass-umxw VINYL my; mrs POLYMER s/znva l2 ,P-POL YETH YLENE F/ 3 /BLUE SENSITIVE EMULSION LAYER GREEN SENSITIVE EMULSION LAYER RED SENSITIVE EMULSION LAYER .4 "'A POL YETH YLENE mass L //VKED v//v YL PAPER ACETATE POLYMER SIZING POLYETHYLENE WILLIAM H. GRIGGS MERLE K. ELDRIDGE DAVID R. FULTON INVENTORS A GEN T United States Patent Office 3,582,337 Patented June 1, 1971 3,582,337 LIGHT-SENSITIVE PHOTOGRAPHIC PAPER William H. Griggs, Rochester, Merle K. Eldridge, Hilton, and David R. Fulton, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y.
Filed June 27, 1968, Ser. No. 740,581 Int. Cl. G03c 1/86 US. C]. 96-85 9 Claims ABSTRACT OF THE DISCLOSURE Photographic paper base is sized with a dispersion of cross-linked vinyl acetate polymer to avoid mottle, obtain improved stiffness and other properties.
This invention relates to the production of paper particularly suitable for use as a photographic paper base.
The use of paper as a base or support for light-sensitive photographic emulsions is well konwn in the art. A wide range of weight of papers is used for this purpose, for example, papers weighing from about to 60 pounds per 1,000 square feet. The lightweight papers are particularly useful Where it is desired to wind the maximum footage of sensitized paper on a spool. However, it is usually necessary to heavily tub size the lightweight papers to obtain the wet and dry stiffness desired or to obtain a stiffness actually required by apparatus in which the paper is to be handled. Often tub sizing is not adequate to obtain the desired stiffness and the weight of the paper must be increased. In the photographic art, in addition to imparting stiffness to the paper, the size should reduce penetration to aqueous solutions such as the conventional acid and alkaline photographic processing solutions. Also the sizing must produce a surface inert to the light-sensitive coating applied thereto. Moreover, the light-sensitive coating must coat uniformly onto the sized paper surface, for example, to avoid the production of light-sensitive coatings containing mottle. A silver halide emulsion layer which is subjected to an overall even exposure and developed to provide an image should have even density throughout. If it, instead, exhibits areas having distinctly higher or lower density than that of the remaining areas of the image, it may be said to have mottle. The areas having the higher or lower density exhibit densities of greater difference than would be expected or predicted from the photographic speed of the particular system.
We have discovered a method for tub sizing photographic paper base which imparts unexpected properties to the paper in addition to improved stiffness. Our process involves tub sizing this paper with an aqueous latex of an emulsion polymerized mixture of vinyl acetate and a cross-linking monomer such as N-methylol acrylamide or hydroxyethyl acrylate. The cross-linking monomer is, thus, a polymerizable vinyl compound'containing the vinyl group for copolymerizing with the vinyl acetate. In addition, the monomer contains a lower hydroxyalkyl group, such as a hydroxyethyl or methylol, capable of reaction with similar groups on other copolymer chains in the reaction mixture to produce a crosslinked polymer latex. As a result, papers of improved stiffness are obtained and sensitive coatings applied thereto are free of mottle even when lightweight paper stocks have been used. Resistance to solution penetration is also good. The sized paper surface has no adverse effect on the light-sensitive layers. It is probable that these advantageous properties obtained in the tub-sized paper result in part from reaction of residual methylol or other hydroxyalkyl groups of the cross-linked vinyl acetate polymer with similar groups present on the cellulose molecules of the paper base. A three-dimensional structure involving the polymer chains and cellulose chains is, thus, obtainable.
Many naturally-occurring and synthetic polymeric materials have been proposed for tub sizing paper and have been more or less successful for the intended purpose. However, none of these polymers have possessed the combination of properties necessary to produce photographic paper base of the desired stiffness at low caliper and which paper base is inert to photographic emulsions and is uniformly coated by photographic emulsions. These polymers have often resulted in a paper sheet which tends to be sticky. Often the polymers would fog silver halide emulsions coated thereon. The present cross-linked vinyl acetate polymer latices are unique in imparting the mentioned desirable properties to the paper base.
Cross-linking vinyl monomers containing a lower hydroxyalkyl group especially useful for emulsion polymerization with vinyl acetate are: N-methylol acrylamide, N-methylol methacrylamide, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxpropyl acrylate or hydroxypropyl methacrylate. The cross-linking monomer is used particularly in an amount necessary to obtain the desired hardness in the vinyl acetate polymer and stiffness in the paper. About 0.5 to 10% by weight of the cross-linking monomer is useful with about 99.5 to by weight of vinyl acetate. N-methylol acrylamide and N-methylol methacrylamide are especially useful for emulsion polymeriza-- tion with vinyl acetate in these proportions. The emulsion polymerization is carried out in water in a well-known manner by heating in the presence of a surfactant and catalyst so as to produce a latex of about 40-50% solids by weight. The surfactant and catalyst are selected so as to be photographically acceptable, i.e., inert to lightsensitive photographic layers. Anionic surfactants such as sodium lauryl sulfonate are useful. Water-soluble catalyst, e.g. potassium persulfate, can be used with heating to about 70 C. or sodium meta-bisulfate with potassium persulfate and heating to about 40 C. The resulting latex should then be diluted to about 30-35% solids for use in tub sizing the paper.
The paper is tub sized with the cross-linked vinyl acetate polymer latex in the usual manner on the paper machine. The latex of about 30-35% solids concentration at about 90 F. is applied freely to both sides of the paper by passing the paper through a bath containing the latex or it can be sprayed onto the paper. Thereafter, excess size solution can be removed by passing the paper through press rolls and drying and calender-ing the paper as usual. The paper can be expected to contain from about 525% cross-linked polymer depending in part upon the solids concentration of the latex used, speed and temperature of applying the latex.
The paper stock to which the vinyl acetate polymerization latex is applied can vary widely as to fiber content but a sheet of good formation is desirable. The weight can vary, for example, from about 4 to 50 pounds per 1,000 square feet. An internal size such as rosin, aluminum stearate or a ketone dimer is useful to reduce solution penetration of the paper although for complete saturation by the latex the absence of an internal size is preferable. As mentioned, the invention is very useful with lightweight papers of about 610 pounds to avoid mottle.
The paper sized with the cross-linked vinyl acetate polymer is suitable for sensitizing directly with photographic emulsions. However, if desired, the usual baryta coating may first be applied. Also, the sized paper can be coated on each surface with hydrophobic polymer layers before coating photographic emulsion layers. For this purpose, polyolefins, especially polyethylene and polypropylene, are advantageously extruded onto the paper from a hot melt. The adhesion of the polymer layers applied to the sized paper at high speeds can be increased by activating the paper surface with corona discharge as disclosed in the Crawford et al., U.S. patent application Ser. No. 630,261, filed Apr. 12, 1967. For example, sparkgap type AC corona of about 50,000 volts can be applied to the sized paper surface and polyethylene extruded thereon in-line at about 200 to 1,000 f.p.m. from a melt at about 580 to 650 F. Similarly, chemical primers such as polyethylenimine can be used to increase adhesion of the polyolefin to the sized paper surface. Photographic emulsions, such as gelatin-silver halide emulsions are advantageously adhered to the surface of the polyolefin coated paper by activating the polyolefin surface with corona discharge as described in British Pat. 971,058. Spark-gap type or continuous wave corona of about 50,000 volts and high frequency is preferred and can be applied to the polyolefin surface at several hundred feet per minute.
. The photographic emulsions which are coated upon the sized paper surface are the conventional black-and-white emulsions or a plurality of known differently sensitized emulsions for color photography. When color development is carried out with color development solutions containing couplers, especially useful couplers are Couplers 1-64 listed in columns 3-5 of Spath U.S. Pat. 2,956,876, issued Oct. 18, 1960 and also the couplers as described in the same patent in column 5 as Couplers 6577 in which the couplers are included in the photographic silver halide emulsion layers are equally useful. Other couplers suitable for use in the emulsions include those described in Spence and Carroll, U.S. Pat. 2,640,776, issued June 2, 1953, Weissberger et a1. U.S. Pat. 2,407,210, issued Sept. 3, 1946 and Weissberger et al. U.S. Pat. 2,474,293, issued June 28, 1949. Other couplers which can be used in the emulsions include the acylamino-substituted couplers, as disclosed in Salminen and Weissberger U.S. Pat. 2,423,730, issued July 8, 1947. The couplers usually produce dye images in the emulsion layers of color complementary to the sensitivity of the respective emulsion layers. U.S. Pat. 3,168,400 can be referred to for a procedure for color processing the sized papers provided with the color emulsion layers.
The accompanying drawings show in greatly enlarged cross-sectional view the appearance of representative photographic elements of the invention.
FIG. 1 shows a paper support sized with the crosslinked vinyl acetate polymers and carrying a single emulsion layer 11 such as a black-and-white gelatin-silver halide emulsion layer.
FIG. 2 shows an element wherein the sized paper 10 is provided on each surface with layers 12 of polyethylene, e.g. using corona discharge to adhere the polyethylene to the paper. Gelatin-silver halide emulsion layer 11 is adhered to one of the polyethylene layers 12, e.g. by means of corona discharge.
FIG. 3 represents a multilayer element for color photography wherein the support of FIG. 2 is provided with red, green and blue light-sensitive emulsion layers which may contain the mentioned coupler compounds. The polyethylene surface is preferably activated with corona to effect adhesion of the emulsion layers. The vinyl acetate polymer sized paper support of the invention is especially useful for preparing the color products illustrated in FIG. 3 because the polyolefin layers 12 tend to produce a limp paper objectionable to the customer. Adequate stiffness can be imparted to the product by increasing the amount of paper fiber in layer 10 by about 50% which is obviously costly. However, by use of the sized paper stock of the invention adequate stiffness is imparted to the product without increase in fiber content of the paper. Thus, as shown in the examples below, a paper sheet of about pounds per 1,000 square feet sized with the cross-linked polymers can be expected to have a stiffness comparable to the same type of paper of about 40 pounds per 1,000 square feet not sized with the polymers.
The following examples will serve to illustrate our invention.
EXAMPLE 1 A 37-pound softwood bleached sulfite aluminum stearate internally sized paper stock is tub sized at about 90 F. with a solids latex of a cross-linked vinyl acetate polymer resulting from emulsion polymerizing about 5 parts of N-methylol acrylamide and 95 parts of vinyl acetate in the presence of catalyst and surfactant in water. The same paper stock is tub sized with 4% starch solution and with water alone for comparison. The stiffness and acid penetration values of the resulting papers are shown in the following table:
Taber Valley acid Thickness stiffness penetration Size (mils) (length) (seconds) The improvement in stiffness and penetration is apparent. The polymer sized paper coats uniformly with gelatinsilver halide photographic emulsion, handles well in processing and no mottle is observed in the emulsion layer whereas the water and starch sized papers exhibit significant mottle in the emulsion layer.
EXAMPLE 2 27-pound paper not internally sized and not calendered is tub sized at about 300 f.p.m. with a 30% solids latex of the vinyl acetate polymer of Example 1 at -90 F. and for comparison tub sized with water and 4% starch solution. The papers have the following properties:
Taber stiffness Valley acid Thickness penetration Size L O (mils) (seconds) Water 6. 6 4. O 5. 8 91 Starch 7. 4 5. 8 197 Polymer l2. 0 6. 0 5. 8 607 A paper is prepared as in Example 2 except the initial paper stock is internally sized with aluminum stearate. The stiffness of the paper before polyethylene coating L/ C is 12.1/6.4 to l3.5/6.5 compared to stiffness 8.0/5.0 for the same paper not polymer sized. When this polyethylene coated paper is sensitized and processed, it shows improved resistance to edge penetration by the processing chemicals.
This internally sized paper, tub sized with the crosslinked polymer latex and polyethylene coated, is especially useful for coating with differently sensitized emulsions for color photography to produce an element such as shown in FIG. 3. The emulsions containing color couplers can, for example, be processed by reversal methods as shown in U.S. Pat. 3,168,400 to obtain substractively colored pictures free of mottle. The emulsions and polymer layers of the element adhere well to the sized paper and the paper has good feel and handling properties.
EXAMPLE 4 This example illustrates an important embodiment of the invention wherein lightweight photographic paper stocks of about 6-10 pounds are sized with the vinyl acetate polymer latex to provide photographic paper bases Unsized 3. 4 2. 1 Sized 4. 9 3. 1
The paper sensitizes uniformly with the gelatin-silver halide emulsion and handles satisfactorily in the apparatus when recording the oscillograph tracing. Mottle is not evident in the processed emulsion layer.
In the above examples the acid penetration values are obtained by a well-known method wherein the instrument is calibrated to 40 milliamps and the test is run to a 20 milliamp end-point. The penetrating solution is an aqueous solution of acetic acid, water and sodium chloride.
In the above examples the cross-linked vinyl acetate polymer sized paper can be coated with gelatin baryta layers prior to sensitizing with photographic emulsions. In this case it is advantageous to include a small amount of the vnyl acetate polymer latex into the aqueous gelatin baryta dispersion. About 10-15% of the polymer based on the weight of gelatin present (dry weight basis) is useful with the result that adhesion of a gelatin-silver halide emulsion layer to the baryta coating is improved.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be eflected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.
1. A light-sensitive photographic paper comprising a paper support tub sized with an emulsion polymerized mixture of from about 90 to 99.5% by weight of vinyl acetate and about 10 to 0.5% by weight of a ethylenically N-methylol acrylamide or N-methylol methacrylamide or a mixture thereof.
4. The paper of claim 1 wherein an extruded polyolefin layer separates one surface of the sized paper support from the emulsion layer and the other surface of the sized paper carries an extruded polyolefin layer.
5. The paper of claim 4 wherein the polyoleln is polyethylene or polypropylene.
I 6. The paper of claim 2 wherein the paper support before tub sizing has a weight of about 5 to pounds per 1,000 square feet.
7. The-"paper of claim 2 wherein the paper support before tub sizing has a weight of about 6 to 10 pounds per 1,000 square feet.
8. The paper of claim 2 wherein a baryta coating separates one surface of the sized paper from the emulsion layer.
9. The paper of claim 5 wherein one surface of the polyoleln coated paper carries differently sensitized superposed silver halide emulsion layers useful for color photography.
I References Cited UNITED STATES PATENTS 2,748,029 5/1956 Spear et al. 968S 2,721,801 10/1955 Clark et a1 96--85 3,062,679 11/ 1962 Heardle et al 9685 3,161,519 12/1964 Alsup 96-85 2,928,736 3/ 1960 Laakso et a1. 96-85 3,369,901 2/1968 Fogge et a1 96-85 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner U.S. Cl. X.R. 96--87; 162-168