US3155511A

US3155511A - Precoated diazo reproduction paper

Info

Publication number: US3155511A
Application number: US52083A
Authority: US
Inventors: Jahoda Edward; Muller Peter
Original assignee: Andrews Paper and Chemical Co Inc
Current assignee: Andrews Paper and Chemical Co Inc
Priority date: 1960-08-26
Filing date: 1960-08-26
Publication date: 1964-11-03
Anticipated expiration: 1981-11-03
Also published as: GB943113A; DE1240398B

Description

Nov. 3, 1964 E. JAHODA ETAL 3,155,511

PRECOATED DIAZO REPRODUCTION PAPER Filed Aug. 26. 1960 LIGHT SENSITIVE DIAZO LAYER INTERPENETRATION ZONE EASE SHEET PIGMENTED PRE-COAT LAYER United States Patent York Fiied Aug. 26, 1960, Ser. No. 52,683 2 Claims. (Cl. 96-75) This invention relates to the precoating of reproduction papers, such as those used for blueprints, diazo types, silver prints, brownline or Van Dyke negative prints and, more particularly, it relates to reproduction papers and base carrier sheets having an improved precoat thereon and to an improved method of making the same.

Among the objects of the present invention is the provision of an improved precoat and precoating method for reproduction sheets in which the precoat can be readily and successfully applied to the base sheet either at the prevailing, sensitizing speeds or at the much faster speeds used by paper mills in the coating of coated book and magazine paper; in which it is economically feasible to apply the precoat at the paper mill because it can be applied by existing high speed coating equipment available at the mill; and which may provide for a substantial upgrading of the base sheet stock and thereby permit of the use-of less costly paper stock.

A further object is the provision of an improved precoat and precoating method which yields a greater precoat effect than precoats and precoating methods heretofore used.

Other objects include the provision of a precoat that can be applied at greatly increased coating speeds and at the same time will yield prints of great smoothness at full coverage and in the intermediate tones and also the provision of a formulated precoat for prints of increased water fastness and with little or no color shift when wetted.

Precoating is the name applied to a processing step in the treatment of reproduction papers for the purpose of improving the print quality. Precoating was first introduced and was so named in United States Letters Patent No. 2,433,515, granted on December 30, 194-7, to Edward lahoda, assignor to H. P. Andrews Paper Company (now Reissue Patent No. 23,510, granted June 10, 1952).

Before the advent of precoating, the efforts to improve print quality in reproduction papers were restricted either to the paper base or to the composition and application of the sensitizing solution. Patent No. 2,433,- 515 provided an inert coating of colloidal silica which was applied to regular diazo type or blueprint base paer, then dried forming a precoat layer on to which the sensitizing layer is superimposed. The precoat layer has the effect of increasing the density and thereby the contrast of the final print as compared to the print density that could be obtained by the same sensitizing solution on the same base stock but without the intermediate precoat layer.

A precoat of the type disclosed in the above patent is not intended to change and, as a matter of fact, does not change the appearance or the feel of the paper stock and its only specific effect is to increase the density of the print resulting after superimposing a sensitized layer on the precoat and making a print therefrom.

Different types of coatings have been known and used for the purpose of changing certain characteristics of the paper stock and among these coatings are lacquer coatings to increase gloss and water-fastness of the base stock, baryta coatings to improve the smoothness of the coating surface and various other coatings of this type. While these coatings are useable and improve certain of the characteristics of the paper stock, they do not have the peculiar precoat effect mentioned above and they do not contribute to an increase of the print density. On the contrary, they frequently decrease the print density and make the base more difiicult to sensitize. As a result, to obtain acceptable prints on coated papers of this type, it is necessary to alter the sensitizing solutions by inclusion of special solvents or to lower the printing speed or to use specialized coating techniques.

Other types of coatings are known and used for the surfaces of film and other similar non-wettable surfaces. Such coatings are known as substrata or subbing and serve to make the non-wettable surfaces more receptive to the sensitizing layer. They generally contain large amounts of organic solvents or swelling agents for the base material and accordingly are not applicable to and do not improve print density if applied to the wettable surfaces of the ordinary reproduction base papers.

In considering precoating of the type with which we are concerned, it should be noted that such precoats do not contribute to keeping the sensitizing solution on the surface of the base as sometimes it has been wrongly assumed. Thus, the precoat eifect can be obtained on completely porous papers where the sensitizing solution penetrates through the base sheet. Such precoated absorbent papers are useful for chromatographic purposes. However, for reproduction papers, it is generally desired to keep the sensitizing layer as close to the surface as possible and as compatible with good anchorage and uniform and sutficient depth of the image-forming ingredients.

sensitizing layers kept close to the surface show greater brilliancy. However, a controlled penetration of a certain depth assures smoothness of the intermediate tones. If the coating speed is increased, the formerly known precoats do not make possible prints where the intermediate tones are of suflicient smoothness. The lack of smoothness is especially pronounced when fast coating speeds are combined with quick drying which is very desirable to create greatest brilliancy in the fully covered areas.

For the purpose of controlled penetration, the reproduction base papers are generally sized which allows only a small and controlled penetration. Sizing tends to reduce the final print density. Precoating does not effect the penetration resistance of the sizing in any way. In other words, it does not improve it nor does it detract from it. Generally speaking, the combination of a sized base paper with a precoat is especially useful.

The precoat effect is a physical effect depending on the discontinuity of the precoat layer. The discontinuous precoat layer is an artificial surface much more receptive for the sensitizing solutions than any natural coating surface. Silica was and still is the most effective precoat chemical. its chemical nature.

- most fibrous surfaces essentially without binder and adheres thereto due to its own nature. But the precoat effect can be obtained by materials of larger than colloidal size if their adherence to the base is assured by suitable binders.

Many attempts have been made to achieve the precoat effect by the inclusion of pigments or resins in the sensitizing solution. Such solutions came to be known as pseudo precoats or one-pot solutions alluding to the inclusion of precoat chemicals such as silica or small angular grain starch in any one pot with the sensitizing solution. While the pseudo precoat led to lasting improvements over prior clean sensitizing solutions, they can themselves be applied to precoated paper and show the precoat effect all over again, on a higher level. Thus, precoating stimulated improvements of the sensitizing solution, but it cannot be replaced by the same.

The precoat process is now a generally accepted and established part of the art. While precoats containing colloidal silica, such as is disclosed in the above-referred to Patent No. 2,433,515, have generally been the most satisfactory, it has also been proposed to form the precoats from various other materials, such as non-colloidal silica and a suitable binder or from finely-divided alumina or non-colloidal alumina with a suitable binder. In addition, various synthetic resins, combinations of silica and synthetic resins, metal silicates, titanium dioxide and calcium fluoride have been suggested as precoats.

At the present time, precoating of reproduction papers is mostly performed by the sensitizers in a continuous operation with the sensitizing and the prevailing coating speeds are between 40 and 120 feet per minute. While attempts have been made to precoat the paper at paper mills using paper coating machines which operate at much greater speeds, this did not prove to be economically feasible or practical. In addition, the precoats heretofore available did not contribute to or enhance the qualities of the base paper. By intensifying the print which was made from the papers, the precoats generally brought out the bad characteristics as well as the good characteristics of the base sheet. The heretofore available precoats do not serve to upgrade the base paper and they do not permit use of less costly stocks.

Accordingly, it is a prime object of the present invention to overcome the difficulties heretofore encountered in the precoating of reproduction papers especially at high coating speeds and to provide a new precoat and precoating method which not only increases the precoat effect but which also improves and upgrades the base paper stock and which can be applied by high speed coating machines with the result that the precoating can now be accomplished economically at the paper mill.

The precoats used at the present time consist generally of silica or polystyrene or of a combination of the two and include sometimes certain binders. We have found that the precoat effect can be greatly refined and increased and that the objects of the present invention can be accomplished by compounding or formulating more sophisticated precoats consisting of particles of silica preferably of colloidal size with particles of barium sulfate which may be larger or smaller than colloidal size in predetermined proportion with or without fine particles of starch and preferably adding thereto a'suitable binder for the barium sulfate and for the starch if any.

In the accompanying drawing we have indicated a crosssectional view of reproduction paper embodying our invention. It will be seen that the reproduction material consists of a base sheet or layer which may be paper, cloth or a suitable wettable plastic. Our improved precoat is applied to the surface of the base sheet and the light sensitive layer is, in turn, applied thereto. The precoat layer as shown is discontinuous and is in finely divided particle form although as indicated the particles may agglomerate to some extent. When the light sensitive layer is applied to the precoat layer it not only fills the interstices between the particles but also there is a certain amount of interpenetration between the precoat layer and the light sensitive layer as indicated by the cross sectional lines in the drawing and by the dotted line which shows the depth of the interpenetration.

As indicated above, our improved precoat consists of a uniform mixture of particles of silica preferably of colloidal size with particles of barium sulfate which may be larger than colloidal size and with or without fine particles of starch having a suitable binder for the barium sulfate and the starch, if any.

The silica preferably should be of an average particle size less than approximately one micron. The silica may be in dry powdered fluffy form or may be in aqueous dispersion. If our precoat is used in connection with diazo type reproduction paper, the silica must meet the rigid purity requirements of this process and must be free from iron contamination.

We may employ either natural or synthetic barium sulfate. However, we prefer to employ the synthetic type known as blanc fixe. The particles of barium sulfate may be larger or smaller than colloidal size. We prefer, however, that the particles be no larger than five microns and that the average particle size be approximately one micron or less. If the precoat is used in connection with diazo type reproduction paper, the barium sulfate must meet the rigid purity requirements of this process and must be free from iron contamination.

Vegetable flour or starch in uncooked form may be used as an addition to the precoat. We prefer to use starches which have a small angular grain such as rice starch, buckwheat starch and pepper starch. Particles of starch of this type having a particle size of 3 to 5 microns serve very satisfactorily.

No binder is required to cause the colloidal silica to adhere to the base sheet. However, a binder should be included in the precoat material mixture to cause the barium sulfate and the starch, if any, to adhere and this is particularly true where the particles of barium sulfate are larger than colloidal size. Any of the known binders used for thi purpose can be employed, such as casein and its salts, gelatin, non-ionic or cationic aqueous emulsions of polyvinyl acetate, polyvinyl alcohol, gum arabic, or the like. Where casein is used as the binder, a small quantity of alkali, such as ammonia or borax, is added to the slurry so that the casein will be readily soluble in water.

The proportions of the silica and barium sulfate particles, or of the silica plus barium sulfate, plus the starch particles to each other may be varied depending upon the particular effects desired. The silica particles serve primarily to enhance the sparkle, brilliance and the color of the dye in the finished print. The barium sulfate serves primarily to upgrade the paper or base stock and to improve the smoothness in full and half tones and to increase the apparent whiteness of the sheet.

The starch in combination with the silica and the barium sulfate forms a tripartite mixture and improves further and greatly half tone smoothness as well as ink and water fastness of the finished prints. The starch further increases the resistance of the paper or base stock to handling marks such as finger prints.

By varying the proportions of the ingredients, variations in these effects can be achieved. In this connection, we have found that in our improved precoat, a synergistic effect is achieved by mixing the different types of particles together and the results obtained exceed those if particles of one type alone were employed. Generally speaking, We have found that satisfactory results are achieved if the proportions of the different size particles are maintained between a lower limit of equal parts of silica and barium sulfate particles or of silica on the one hand and barium sulfate plus starch on the other hand and an upper limit of one part of silica particles to twenty parts of barium sulfate particles or of one part of silica particles to twenty parts of barium sulfate and starch aggregates combined by weight. The proportion of barium sulfate and starch particles may vary from ten parts to tWo parts and ten parts to twenty parts by weight. Sufficient binder should be added to cause the barium sulfate and starch particles, if any, to adhere to the base sheet. We have found that we achieve satisfactory results if the binder added is between approximately eight percent and thirty percent by weight of the barium sulfate and starch, if any, in the precoat.

In preferred embodiments of our invention, We mix together approximately one part by weight of silica with about ten parts by weight of the barium sulfate or one part by weight of silica with about five parts by weight of barium sulfate and five parts of starch, and add suflicient binder within the indicated limits to cause the barium sulfate and starch particles if any to adhere to the base sheet while maintaining a discontinuous coating with separate and discrete particles.

While we prefer to use all ingredients in the precoat it is possible to add either the silica or the starch if any in the sensitizing solution. However, the barium sulfate should not be added to the sensitizing solution.

By using the precoat process of this invention, it is possible to improve the line density still further by adding additional silica to the sensitizing solution. Silica may be contained in the precoat as well as in the sensitizing solution.

In making our improved precoat, a slurry is first prepared by mixing the silica and barium sulfate and starch particles if any in the indicated propontions with water. In this connection, the different types of particles may be added together to the Water or each may be mixed separately with the water and then added together. A separate aqueous dispersion is preferably prepared from the resin binder and this dispersion isthen added to the water. The proportion of water to solid material added to the slurry may be varied but we have found that satisfactory results are obtained if the solid materials make up from etween and 40% of the mix. When the various materials have thus been thoroughly mixed together so as to obtain a uniform distribution of materials, the precoat is then ready to be used. It may be applied to the base sheet either at the paper mill using conventional high-speed coaters, such as the Ross off-machine airknife coater, or it may be applied at the sensitizing plant using conventional blueprintor-reproduction paper coating machines.

The thickness or weight of the precoat layer may be varied. By using a relatively heavy precoat layer, we can upgrade and increase the weight of the base stock. For this purpose we have obtained very satisfactory results by applying approximately three gnams of precoat material (at dry precoat Weight) per square meter of base stock. However, very satisfactory precoat effects can be obtained by using :a substantially lighter precoat layer and we have obtained very satisfactory results by using as little as one gram (precoat dry Weight) per square meter of base stock.

The precoats embodying our invention exhibit a slight curing effect and they improve on standing for several days. The reproduction sheets precoated in this fashion may immediately thereafter have the sensitizing coating applied thereto or they may be stored or shippedto another point to have the sensitizing coating applied thereto at a later date. Any suitable light-sensitive layer may be applied to the precoated sheets, such as a blueprint coating layer, a diazo solution, silver emulsion, or a Van Dyke solution. The precoated reproduction paper thus formed is of general type shown in the accompanying drawing. Where the precoat is applied to the base sheet at the paper mill by a high-speed coater, it is usually desirable to increase the viscosity of the precoat mixture and this can be accomplished by using a relatively higher proportion of binder.

We have found that a precoat layer embodying our invention is not in the form of a soft rubbery mass or coherent film. The particles agglomerate to some extent but nevertheless remain in discontinuous, finely-divided particle form as shown in the drawing and the layer, if not supported, is brittle. A layer of this type provides the desirable physical conditions for receiving the lightsensitive layer and for enhancing the sparkle, brilliance and color of the dye in the finished print and for improving the smoothness in full and half tones and increasing the apparent whiteness of the;sheet. Where starch is also employed it provides increased resistance to handling marks such as finger prints.

In the following examples illustrating specific embodiments of our invention, the substance weight means the Weight in pounds of five hundred sheets, 17" x 22" in size.

Example I A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc 1000 Colloidal silica such as'Cab-O-Sil g 30 Blame fixe g 300 Casein g 35 Ammonia cc 4.5 Borax g 2.5

At a paper mill, the precoat composition thus prepared was applied by an off-machine airknife coaterto a sulfite diazo base paper of 20 /2 lb. substance weight at a coating speed of 600 f.p.m. and dried by hot air at a temperature of 250 F.

The substance weight of the precoated dried paper Was 22 lbs. The precoated paper thus formed was ready to be immediately coated with a light-sensitive layer or, if preferred, it was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated paper with a conventional ammonia .blueline solution, such as Water cc 1000 Citric acid g 3.0 Thiourea g 30 Zinc chloride g 30 2,3dioxy-6-sulfonaphthalene g 60 p-Diazo-diethylaniline zinc chloride double salt g 2 Diethylene glycol cc 20 Saponine g 1 After sensitizing, the paper was dried with .hot air of 250 F.

The prints of this paper showed considerably more sparkle, more line density and excellent smoothness in the intermediate tones in comparison with prints made from paper precoated with a dispersion of Cab-O-Sil or blanc fixe alone. The visual whiteness of the background increased considerably over the sensitized non-precoated base paper.

Due to the substance weight increase, the material costs of the precoated paper are the same as for regular 22 lb.-diazo paper.

Example II A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc 1000 Colloidal size silica particles such as Aerosil g 20 Blane fixe, pulp grade g 200 Gelatin -g 1O Casein g 12.5 Ammonia cc 1.7 Borax g 1.3

On a reproduction paper coating machine designed with two front and one back coating station, each consisting of an applicator roller and an airknife and a convection hot air drier after each coating station, the precoat thus prepared was applied to a 19 lb. sulfite base paper, at a coating speed of 120 f.p.m. and dried with hot air of a temperature of 220 F.

The substance weight of the paper increased to 21 lbs. The precoated paper thus formed was ready to be immediately coated with a light-sensitive layer or, if preferred, it Was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated paper with the following conventional semi-moist process diazo solution, such Water cc 1000 Ammonia oxalate g 20 Oxalic acid g 12 Aluminum sulfate g Thiourea g 10 p-Diazo-benzyl-ethyl aniline zinc chldride double salt g Saponine g 1 Example [I] A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc 1000 Colloidal silica such as Cab-O-Sil g Blane fixe g 200 Casein g Ammonia cc 3.3 Borax g 1.7

On a reproduction paper coating machine designed with two front and one back coating station, each consisting of an applicator roller and an airknife and a convection hot air drier after each coating station, the precoat thus prepared was applied to a 20 lb. sulfite base paper, at a coating speed of 140 f.p.m. and dried at a temperature of the hot air of 250 F. l

The substance weight of the paper increased to 22 lbs. The precoated paper thus formed was ready to be immediately coated with a light-sensitive layer or, if preferred, it was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated sheet with the following redline ammonia process diazo solution:

Water cc 1000 Citric acid g 1,3,6-naphthalene trisulfonic acid g 25 F-salt g 50 Thiourea g p-Diazo-N-oxyethyl-N-ethyl aniline zinc chloride double salt g 20 Diethylene glycol cc 30 After drying, prints were made from this paper. They excelled by their sparkle, line density, and smoothness in the intermediate tones from prints made with paper precoated with either Cab-O-Sil or blame fixe in any practicable concentration alone.

8 Example IV A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc 1000 Colloidal silica such as Santocel FR-C g 20 Blanc fixe g 200 Gelatin g 20 On a blueprint paper coating machine of conventional design, equipped with a precoating station, consisting of an applicator roller, and an airknife, a sensitizing solution, consisting of two applicator rollers and an airknife and a hot air convection drier pass after each coating operation, the precoat thus prepared was applied to a 20 lb. substance weight paper of rag content, on the precoat station at a coating speed of f.p.m.

After drying the precoated paper, the substance weight was 21 lbs. The precoated paper thus formed was ready to be immediately coated with a light-sensitive layer or, if preferred, it was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated sheet with the following blueprint coating solution:

Water cc 1000 Urea g 50 Ammonium oxalate g 50 Ferric ammonium oxalate g Potassium ferricyanide g 40 Ferric oxalate g 40 Saponine g 2 Prints made from this paper after drying showed more sparkle, deeper blue color, better contrast, more smoothness in full and intermediate tones than paper precoated with either the indicated concentration of colloidal silica or blanc fixe alone. The prints excelled by their good washout properties.

Example V A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc 1000 Colloidal silica such as Cab-O-Sil g 30 Blane fixe g 150 Rice starch, uncooked g 150 Polyvinyl alcohol, such as Elvanol -g 30 At a paper mill, the precoat composition thus prepared was applied by an off-machine airknife coater to a sulfite diazo base paper of 20 lb. substance weight at a coating of 600 f.p.m. and dried by hot air at a temperature of 250 F.

The substance weight of the precoated dried paper was 21 /2 lbs. The precoat thus formed was ready to be immediately coated with a light-sensitive layer or,'if preferred, it was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated paper with a conventional semi-moist process diazo solution, such as:

Water cc 1000 Ammonium oxalate g 20 Oxalic acid g 12 Aluminum sulfate g 10 Thiourea g 10 pDiazo-benzyl-ethyl aniline zinc cloride double salt g 20 Saponine g 1 Prints made from this paper and developed with a conventional alkaline phloroglucinol developer showed more sparkle, line color of higher density, more contrast, better coverage, more smoothness in half tones than prints made from paper which was precoated either with a dispersion of Cab-O-Sil, or with a dispersion of blanc fixe or a dispersion of starch alone. The visual whiteness of the background increased considerably over that obtained from a sensitized non-such-precoated sheet.

Example VI A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc 1000 Colloidal size silica particles such as Aerosil g 20 Blane fixe g 100 Rice starch, uncooked g 100 Casein g On a reproduction paper coating machine designed with two front and one back coating station, each consisting of an applicator roller and an air knife and a convection hot air drier after each coating station, the precoat thus prepared was applied to a 20 lb. sulfite base paper, at a coating speed of 250 f.p.m. and dried with hot air of a temperature of 280 F.

The substance weight of the paper increased to 21 lbs. The precoated paper thus formed was ready to be immediately coated with a light-sensitive layer or, if preferred, it was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated paper with the following conventional ammonia blueline solution, such Water cc 1000 Citric acid g 30 Thiourea g 30 Zinc chloride g 30 2,3-dioxy-6-sulfonaphthalene g 60 p Diazo diethylaniline zinc chloride double salt g Diethylene glycol cc 20 Saponine g 1 A precoat composition embodying our invention is prepared by mixing together the following materials in the following indicated proportions:

Water cc Colloidal size sillica particles such as Aerosil g Blanc fixe g Rice starch, uncooked g Casein g 25 Borax g 2 Ammonia cc 7 On a reproduction paper coating machine designed with two front and one back coating station, each consisting of an applicator roller and an air knife and a convection hot air drier after each coating station, the precoat thus prepared was applied to a 20 lb. sulfite base paper, at a coating speed of 250 f.p.m. and dried with hot air of a temperature of 280 F.

The substance weight of the paper increased to 21 lbs. The precoated paper thus formed was ready to be immediately coated with a light-sensitive layer or, if preferred, it was suitable for storing or shipping to be coated at a later date. A satisfactory reproduction paper was produced by sensitizing the precoated paper with the following conventional ammonia blueline solution, such as:

After sensitizing, the paper was dried with hot air of 280 F.

The prints of this paper showed considerably more sparkle, more line density and excellent smoothness in full tones and intermediate tones in comparison with prints made from paper precoated with a dispersion of Aerosil or blanc fixe or rice starch alone. The visual whiteness of the background increased considerably over the sensitized non-precoated base paper.

Due to the substance weight increase, the material costs of this precoated paper are the same as for regular 21 lb. diazo paper.

In each of the foregoing examples, it should be understood that the proportions of the ingredients may be varied within the indicated limits and different binders may be substituted for those specifically indicated in the examples. Also under certain circumstances where it is not desired or where it is not necessary to upgrade the base paper stock a lighter precoat layer may be applied to the stock.

From the foregoing description and examples of our precoated reproduction paper and method of making the same, it will be seen that we obtain a greater precoat effect than precoats or precoating methods heretofore employed; that the precoat can be readily applied to the base sheet either at the prevailing speeds or at the much faster speeds used by paper mills and that substantial upgrading of the base sheet stock is obtained.

Modifications may be made in the illustrated and described embodiments of our invention without departing from the invention as set forth in the accompanying claims.

We claim:

1. An improved reproduction sheet comprising a nonmetallic base sheet, a precoat layer applied thereto and including a mixture of silica particles, particles of barium sulfate and particles of uncooked starch and a lightsensitive diazo layer applied to said precoat l-ayer, said precoat layer being formed of discontinuous particles substantially uniformly mixed and distributed over said base sheet and with said two layers being in at least partially interpenetrating relationship with respect to each other, with the proportions of the materials being approximately one part by weight of silica and between 1 and 20 parts by weight of barium sulfate and uncooked starch.

2. An improved reproduction sheet as set forth in claim 1 in which the precoat layer includes a binder.

References Cited in the file of this patent UNITED STATES PATENTS 1,989,879 Murck Feb. 5, 1935 2,207,695 Cummings July 9, 1940 2,287,161 Ball June 23, 1942 2,433,515 lahoda Dec. 30, 1947 (fither references on following page) 1 1 12 UNITED STATES PATENTS 2,807,545 Frederick Sept. 24, 1957 66,709 t D 51 2,993,793 Beersn 1ans et a1. July 25, 1961 3,291,309 2g? 13 3,015,575 McKmght et a1. Ian. 2, 1962 2,662,013 Sulich et a1 Dec. 8, 1953 2,726,956 Jahoda Dec. 13, 1955 v OTHER REFERENCES 2,772,974 Kosalek et a] Dec 4 1955 Kroger: Some Aspects of the Lumlnescense of Sohds, 2,7 0,547 F l e 1, 5, 1957 Elsevier Publishing Co., Inc., N.Y., Amsterdam, London 2,781,265 Von Meister Feb. 12, 1957 and Brussels, pages 291 and 2,784,089 Frederick Mar. 5, 1957

Claims

1. AN IMPROVED REPRODUCTION SHEET COMPRISING A NONMETALLIC BASE SHEET, A PRECOAT LAYER APPLIED THERETO AND INCLUDING A MIXTURE OF SILICA PARTICLES, PARTICLES OF BARIUM SULFATE AND PARTICLES OF UNCOOKED STARCH AND A LIGHTSENSITIVE DIAZO LAYER APPLIED TO SAID PRECOAT LAYER, SAID PRECOAT LAYER BEING FROMED OF DISCONTINUOUS PARTICLES SUBSTANTIALLY UNIFORMLY MIXED AND DISTRIBUTED OVER SAID BASE SHEET AND WITH SAID TWO LAYERS BEING IN AT LEAST PARTIALLY INTERPENETRATING RELATIONSHIP WITH RESPECT TO EACH OTHER, WITH THE PROPORTIONS OF THE MATERIALS BEING APPROXIMATELY ONE PART BY WEIGHT OF SILICA AND BETWEEN 1 AND 20 PARTS BY WEIGHT OF BARIUM SULFATE AND UNCOOKED STARCH.