US3615550A

US3615550A - Water-resistant opaque papers for photographic purposes

Info

Publication number: US3615550A
Application number: US624736A
Authority: US
Inventors: Gregor J H Kemme
Original assignee: Schoeller Felix Jun
Current assignee: Felex Schoeller Jr and GmbH and Co KG
Priority date: 1966-03-31
Filing date: 1967-03-21
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26
Also published as: DE1696264C3; NL6704295A; DE1696264B2; DE1696264A1; BE696382A; FR1515669A; CH490695A; GB1183613A

Abstract

The invention relates to opaque water-resistant papers and methods of making such papers suitable for use as base material for light-sensitive coatings for photographic purposes. According to the invention a sealing coat is applied to the paper base to prevent damage to the paper by application of the other coatings particularly aqueous or waterbound coatings.

Description

United States Patent Inventor Gregor J. H. Kemme Ruckert-Strasse, Germany App]. No. 624,736 Filed Mar. 21, 1967 Patented Oct. 26, 1971 Assignee Felix Schoeller, Jr.

Lustringen am Osnabruck, Germany Priority Mar. 3 1, 1966 Germany Sch 38768 WATER-RESISTANT OPAQUE PAPERS FOR Primary Examiner-Ronald H. Smith Attorney-Hair, Freeman & Molinare ABSTRACT: The invention relates to opaque water-resistant papers and methods of making such papers suitable for use as base material for light-sensitive coatings for photographic purposes. According to the invention a sealing coat is applied to the paper base to prevent damage to the paper by application of the other coatings particularly aqueous or waterbound coatings.

WATER-RESISTAN T OPAQUE PAPERS FOR PHOTOGRAPHIC PURPOSES The invention relates to opaque water-resistant papers and a method of making opaque water-resistant papers, suitable for use as base material for light-sensitive coatings, that is to say as paper-based emulsion supports, which, with the aid of a combination of coatings,-of which, on one side at least, one is light absorbent-are made waterproof on both sides and opaque on one side and are thus suitable, in particular, for use in self-developing cameras.

It is already a practice to employ water-protected papers in self-developing cameras for silver salt and color diffusion processes, with an opaque coating for daylight development applied to the back before the light-sensitive emulsions are applied. Such opaque back coatings can be prepared by one or more applications of an aqueous plastics dispersion containing carbon black.

The coating of raw paper with aqueous dispersions of plastics has disadvantages, however, which come to the fore particularly in diffusion transfer processes and affect the quality of photographs made with such papers. The action of water on the unprotected paper has an adverse efi'ect on the high-grade sheet and surface structure achieved by the paper making machine, in the production of raw paper, by contactdrying on cylinders. Because of the partial swelling of the fibers associated with the irregularity of raw paper, because of the raising of the surface fibers caused by water and because of the nonuniformity of stress resulting from free drying in tunnel or hanging frames at necessarily rather high temperatures, which, as is well known, detract from flatness, not only is the surface spoilt, but the structure of the sheet as a whole. These undesirable effects become visible after the application of light-sensitive emulsions, when these are exposed and developed to a medium grey tone. They show up in photographs as a cloudy disturbance, termed mottle." It is too late for such mottling effects caused by mishandling" of the raw paper to be entirely corrected by smoothing the coated paper with the aid of calenders, for instance.

Many variations of method are known, whereby papers are extrusion coated by means of wide-slit nozzles, and likewise the use of papers coated by this method with thermoplastic substances for photographic purposes. This process offers a possibility of coating papers without adversely affecting their structure. Although it would thus be possible to apply opaque coatings to paper by extrusion, using mixtures of polyalkylenes and carbon black, with a high content of the latter, in a standard extrusion-coating installation, I have found, that it is not possible to produce even faultless coatings with mixtures of polyalkylenes and carbon black in which the content of the latter exceeds percent. However, if one employs the usual mixtures of polyalkylenes and carbon black, containing 2 percent to 5 percent of the latter, a coating approximately 0.05 mm. to 0.06 mm. thick is needed to give the opacity required for daylight use, whereas a coating 0.02 mm. to 0.04 mm. thick suffices if one uses carbon black lacquers or water bound colors. Even a difference in thickness of 0.02 mm. means, that the raw paper base must be worked correspondingly thinner, the natural irregularities in the paper consequently being brought out more strongly. Experience shows that this very factor results in enchanced mottling. Moreover, the mechanical strength of polyalkylene films thicker than 0.03 mm. is so unfavorable as to make it questionable whether papers coated in this way should be used, for example, in self-developing cameras. It is indeed the mechanical properties of coated papers which are so important in cameras of the type in which negative and positive papers are inserted in roll form, because each individual photograph has to be torn off against a straight edge.

It is an object of the invention to provide a water-resistant opaque paper for photographic purposes which has improved mottling characteristics. l have now discovered that all the above adverse effects on paper and picture quality can be avoided by the adoption of a process, for manufacturing the coated paper, in which a very thin sealing coat is applied by conventional means to the paper base, the opaque lacquers or suitable water bound colors being applied over the sealing coat.

The sealing coat may be applied by extrusion coating. All resins that can be extruded from the melt are suitable for this process. For preference, polyalkylenes with carbon-black fillers should be used. The thickness of the coating, which will be determined by the structure of the paper as a whole and by the particular purposes for which it is required, should preferably be in the range 0.008 mm. to 0.02 mm.

However, the sealing coat may also be applied within the papermaking machine by the use of water-soluble binders and/or aqueous dispersions of plastics. A material feature in this case is that the addition of waterbound colors is carried out only when the drained paper has dried sufficiently to be entirely free from stresses. After a brief predrying of the coating, the coated paper is then dried throughout with the aid of heated cylinders. The sealing coat in this case should preferably be in the range 0.005 mm. to 0.015 mm.

Papers that have first been given a sealing coat on one side or both sides by one or other of these methods, without adversely affecting the structure of the sheet, can then be coated on one side for opacity and on the other for light reflection. This will result in an improvement in photographic mottling, as compared to papers given a waterbound coating in the usual way.

The photographic properties of papers coated in accordance with the invention have been compared with those of papers manufactured in the conventional manner, a lightsensitive emulsion being applied to the coated paper and exposed to light. After development or after transference of the image, comparison of the observable mottling is made. Some typical results of this mottling test are summarized in table I.

Specimen Nature of Coating Relative No. Moltling l Aqueous dispersion of plastics 4-5 2 Cellulose lacquer in bulyl 23 acetate 3 Back: polyethylene lacquer 2 Front: lacquer 4 Back: polyethylene lacquer 2-3 Front: polyethylene 5 Back: latex sealing coat 2-3 lacquer Front: polyethylene When a polyalkylene is used for the sealing coat, the adhesion of the outer coating can be achieved by conventional chemical, mechanical or electrical treatment of the polyalkylene surface. in particular, electrical treatment of the surface by means of corona discharge is a simple and reliable method, but it does not always produce adequate adhesion of the coatings in the case of nonpigmented polyalkylene. It is therefore proposed, in accordance with the invention, that the sealing coat be pigmented with titanium dioxide or carbon black, for example. Carbon black in particular is advantageous, in any technically usable portion, as regards the opacity required in the end product. With pigmented sealing coats, the effect of electrical surface treatment is that there is practically no limit to the choice of binders for the outer coating. One binding medium that is to be preferred for lacquers is nitrocellulose, whereas preference should be given to mixed polyacrylate polymers and/or gelatine as the binding medium for coatings made from an aqueous phase.

The thickness of the light-absorbent rear coating is approximately 0.015 mm. to 0.03 mm. Carbon black should preferably be used by way of light-absorbent pigment. Other light-absorbent substances may also be used, so long as they serve to provide or improve opacity. To test opacity, the following method may be employed. A highly sensitive photographic paper (speed about 30/ DIN) is brought into contact with the test piece in a printing frame. An exposure of 1 minute is then given, with an intensity of illumination of approximately 25,000 lux. When the photographic material thus exposed is developed, the nonopaque portions show as black or grey dots on a white ground. Papers rendered opaque by the invention method show fewer then 10 pinhead-sized dots to the square meter.

According to special requirements imposed on the base material for light-sensitive emulsions, the opaque rear coating may have properties specially called for in particular cases. Thus, for example, it may be antistatic, hot-sealing, matt and/or capable of being written upon. Moreover, it may have special sliding properties, as is particularly necessary with certain self-developing cameras. These sliding properties are obtained either by the addition of the usual lubricating agents to the opaque coating or, preferably, by the application of a separate lubricating coating characterized by the fact of its containing, in addition to a suitable binder, finely dispersed graphite and/or finely dispersed tetrafluorethylene (co- )polymer.

Papers coated for opacity in accordance with the invention are used in the self-developing camera as a base both for negative emulsions and also for positive emulsions. On the other side, accordingly, they cannot only be coated with ordinary white-pigmented lacquers or white-pigmented polyalkylene, but can also carry a coating of ordinary gelatine-sized barium sulfate.

As regards the process of image transfer by diffusion in selfdeveloping cameras, it is observed that papers rendered opaque and water-resistant in accordance with the invention, by extrusion-coating followed by lacquering or other coating, can be still further improved by calendering after the coating processes. The calendering is carried out either after the coating of the rear side or after completion of the base and should preferably be done with the aid of highly polished steel rolls.

The following examples are given to provide a clearer understanding of the invention.

EXAMPLE I l. A very smooth white, untreated photographic paper (approx. 80 g./sq.m.) is extrusion coated on one side with a mixture of polyethylene and carbon black (for example, 95:5 The thickness of the coating is approx. 0.012 mm. The surface of the polyethylene is electrically treated by corona discharge. 2. A standard lacquer made of nitrocellulose, softener, carbon black and solvent is applied to the coating of polyethylene and carbon black. The thickness of the dried coat of lacquer is approximately 0.025 mm. The content of carbon black is about percent in relation to the total solid.

3. A lubricating coating consisting, for example, of colloidal graphite and ethyl cellulose in alcohol solution, is applied over the coating of lacquer.

4. The paper coated on one side as in (1H3) above is extrusion-coated on the other side, in the conventional way, with a mixture of polyethylene and titanium dioxide (85:15,) to a thickness of approximately 0.025 mm. The surface is rendered matt and is electrically treated. This polyethylene coating is coated with a normal adhesive for light-sensitive emulsions.

EXAMPLE ll 1. An untreated photographic paper is painted on one side or both sides, in the usual way, within the paper making machine with a normal waterbound color containing, for example, clay and/or titanium dioxide (and perhaps also some carbon black) as the pigment, and reduced starch and a commercial latex (Dow Latex 5l2-R, for example) as the binder medium. The body content of the color and the addition of further secondary substances depend on the coating composition used and the condition of the color. It is of advantage to adjust the body content to 45-50 percent with the aid of a sizing press. The rate of application should preferably be 8 to 10 g./sq.m. If necessary, to improve the adhesion of further coatings, a second coating device within the papermaking machine may be used to apply a 0.5-3 percent solution of a colloidal preparation of silicic acid (such as Ludox).

2. Over the sealing coat appliedwithin the papermaking machine as in (l), a lacquer containing carbon black may be applied by conventional means, to give the paper whatever properties are desired in each particular case (such as sealability, low friction, acceptance of writing and so forth). The carbon black content of the lacquer is about 25 percent of the total solids. The coating is approximately 0.3 mm. thick.

3. The other side of the paper, already coated on one side for opacity in accordance with (l) and (2), is lacquered with an ordinary nitrocellulose lacquer containing titanium dioxide, on which an adhesive substratum for light-sensitive emulsions is added. Then the fully coated base material is calendered.

EXAMPLE Ill 1, A white photographic paper is given a sealing coat on one side, as in example I or II.

2. Over this sealing coat, a waterbound color containing carbon black is applied evenly with the aid of an airbrush, for example. By way of hinder, the color contains a styrene/butadiene latex, which is film forming at room temperature, and by way of pigment a 3:2 mixture of titanium dioxide and carbon black. The ratio of pigment to binder is 3:2.

3. Over this opaque combination coating, a pigment-free lubricating coating is applied, consisting of ethylcellulose in alcohol/toluol, for instance.

4. The front side may be coated as in examples I or ll.

lclaim:

1. An improved photographic base paper consisting essentially of:

a. paper sheet having a front side and back side,

b. said front side having adhered thereto a nonaqueous polyalkylene sealing coat of thickness ranging from about 0,005 to 0.02 mm. and containing from 0 to about 15 percent titanium dioxide pigment,

c. said back side having adhered thereto a nonaqueous polyalkylene sealing coat of thickness ranging from about 0.005 to 0.02 mm. and containing from 0 to about 5 percent carbon black pigment,

d. said front side sealing coat having adhered thereto a water proof plastic overlayer selected from polyalkylene plastic and lacquer containing titanium dioxide pigment, e. said backside sealing coat having adhered thereto a water proof plastic overlayer selected from polyalkylene plastic lacquer and styrene/butadiene latex containing a pigment selected from carbon black and mixtures of carbon black and titanium dioxide,

f. said overlayers having thickness of less than about 0.06

g. said base paper having a relative mottling of less than about 3, an opacity of less than about 10 inhead-sized dots per square meter, and exhibiting improved tear characteristics for use in self-developing camera film.

2. A base paper as in claim 1 wherein said sealing coat polyalkylene is polyethylene.

3. A base paper as in claim 2 which includes a photosensitive layer adhered to said front side overlayer.

4. A base paper as in claim 2 which includes a lubricating coating applied to said back side overlayer.

5. An improved photographic base paper consisting essentially of:

a. paper sheet having a front side and a back side,

b. said front side having adhered thereto a nonaqueous polyalkylene sealing coat of thickness ranging from about 0.005 to 0.02 mm. and containing from 0 to about percent titanium dioxide pigment,

d. said back side sealing coat having adhered thereto a water proof overlayer selected from lacquer and styrene/butadiene latex containing a pigment selected from carbon black, titanium dioxide, and mixtures thereof, said overlayer having a thickness of about 0.6 mm., and

e. said base paper having a relative mottling of less than about 3, an opacity of less than about I0 pinhead-sized dots per square meter, and exhibiting improved tear characteristics for use in self-developing camera film.

a: s t r w

Claims

2. A base paper as in claim 1 wherein said sealing coat polyalkylene is polyethylene.
3. A base paper as in claim 2 which includes a photosensitive layer adhered to said front side overlayer.
4. A base paper as in claim 2 which includes a lubricating coating applied to said back side overlayer.
5. An improved photographic base paper consisting essentially of: a. paper sheet having a front side and a back side, b. said front side having adhered thereto a nonaqueous polyalkylene sealing coat of thickness ranging from about 0.005 to 0.02 mm. and containing from 0 to about 15 percent titanium dioxide pigment, c. said back side having adhered thereto a nonaqueous polyalkylene sealing coat of thickness ranging from about 0.005 to 0.02 mm. and containing from 0 to about 5 percent carbon black pigment, d. said back side sealing coat having adhered thereto a water proof overlayer selected from lacquer and styrene/butadiene latex containing a pigment selected from carbon black, titanium dioxide, and mixtures thereof, said overlayer having a thickness of about 0.6 mm., and e. said base paper having a relative mottling of less than about 3, an opacity of less than about 10 pinhead-sized dots per square meter, and exhibiting improved tear characteristics for use in self-developing camera film.