US3220842A - Electrically prepared subbing for photo-stencil film on polyethylene terephthalate support - Google Patents

Description

United States Patent p 3,220,842 ELECTRICALLY PREPARED SUBBING FOR PHOTO-STENCIL FILM 0N POLYETHYLENE TEREPHTHALATE SUPPORT John F. Carroll, Jr., and Robert D. Chapman, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Sept. 1, 1961, Ser. No. 135,431 4 Claims. (Cl. 9683) This invention concerns polyethylene terephthalate support which has been electron bombarded for use with stripping films.

For many purposes, it is desirable to have a photographic stripping material of the type in which the emulsion layer is carried by a temporary support and transferred from it subsequently. The types of stripping films which are particularly useful in this connection are those used for gravure resists and photo-stencil films. These films must have sufficient emulsion-to-base adhesion to resist the strains of emulsion drying after coating, and to withstand processing and drying. However, the emulsion must strip from the base as a unit without much difficulty for use as a resist or stencil.

Stripping films have been prepared on various temporary supports such as cellulose esters, paper, and the like. The photographic emulsion has often been coated onto some type of subcoating which was selectively soluble. For instance, a typical such soluble layer might be a cellulose acetate phthalate which would be soluble in the alkaline developer solution. Such a coating becomes strippable in the developer solution so that it cannot be retained on the support satisfactorily in every instance unless care is taken in handling the photographic element during processing.

It has been desirable in the graphic arts field to employ film base material which has a high degree of dimensional stability. Supports of this type include polystyrene, polyesters, and the like. Polyethylene terephthalate, in particular, has been suggested as a suitable dimensionally stable film support. However, this material is noted for being hydrophobic, and special treatments are necessary in order to obtain adhesion to the support.

Adhesion to polyethylene terephthalate can be obtained by flame treating as described in US. Patent 3,072,- 483, issued January 8, 1963, in the names of Trevoy and Phillips. Electron bombardment may be employed to obtain a hydrophilic surface. However, these treatments are used to obtain permanent adhesion of various materials to the surface of polyethylene terephthalate.

One object of this invention is to provide an electron bombarded polyethylene terephthalate film support having a photoresist film. An additional object is to provide a method of preparing a thin base photo-resist film employing polyethylene terephthalate as the film support.

The above objects may be obtained by electron bombarding a polyethylene terephthalate film base by passing it between two plates that are connected to the pulsating D.C. output of a high voltage induction coil. In our preferred embodiment, a sheet of glass is used over one electrode to prevent arcing, and the sheet of polyester passed over this glass plate between the two electrodes. This'leaves a gap of about 0.1" between the traveling film base and the exposed electrode. A corona discharge takes place in this space and treats the side of the polyethylene terephthalate support facing it. The support is then coated on the treated side with the photographic emulsion or with a subcoating over which is then coated a photographic emulsion.

The corona discharge must be produced from a source having an AC. component. However, it is not absolutely essential that a D.C. component be involved. Never- 3,220,842 Patented Nov. 30, 1965 theless, where a D.C. component is included, the direction of polarity may have an effect on the emulsion adhesion. The treatment is more effective if the electrode facing the surface to be treated is negative. It will be appreciated that the conditions can be varied substantially with respect to the frequency, voltage output, electrode shape and conformation, type and thickness of insulating sheet, electrode spacing, duration of treatment, and polarity of any existing D.C. component.

Polyethylene terephthalate must be treated to a degree of adhesion which provides good adhesion to a photographic emulsion so that it will be retained on the support during photographic processing but will permit stripping of the film after the film has been processed and dried. This treatment on polyethylene terephthalate is peculiar in that while it produces a tight bond which strongly resists accidental stripping, it is very susceptible to peeling off of the emulsion once a corner is started by means of a sharp edge.

The degree of wetability can be determined by the bubble method. A sample of the film is placed inside a water cell and a bubble holder comprising a glass rod having a concave depression in the end of the rod mounted in a suitable movable support a short distance from the sample so that a bubble of air can be placed between the bubble holder and the sample contacting both. The bubble holder should be mounted so that it can be moved smoothly in a vertical direction to provide for either compressing or stretching the bubble while it remains in contact with the sample. A suitable bubble is then placed under the bubble holder and the bubble holder moved in the direction of the sample to compress the bubble, permitting it to extend sidewise beyond the edges of the bubble holder. A line is taken tangent to the edge of the bubble where it contacts the sample and the angle between this line and the surface of the sample measured. This is known as the receding contact angle.

In untreated polyethylene terephthalate the receding contact angle is about 58, but in polyethylene terephthalate having a very high degree of wetability, the angle can be 5 or less. A contact angle of less than 45 indicates the correct amount of electron bombardment to provide an operative substrate for use with a strippable coating such as a photographic emulsion to provide a satisfactory stripping film.

Another method of determining the hydrophilic nature of the surface can be employed involving measuring the contact angle of a drop of water on the surface. A drop of distilled water is placed on a level sample. By projecting the image of the drop and sample on a suitable screen and measuring the angle obtained by drawing a line tangent to the drop image at the point the edge of the drop touches the sample, this contact angle can be measured quickly and accurately by using a Contour Projector as the means of projection. Untreated polyethylene terephthalate film base gives a contact angle of about The minimum electron bombardment needed for emulsion adhesion gives a contact angle of about 73f. Using the drop method, an angle of less than 73 would also be operative in adhering the coatings such as the photographic emulsions to the support for stripping.

The photographic emulsion layer coated over the treated polyethylene terephthalate support may be of any type, but for the copying of drawings, the emulsion is a high-contrast type. It is preferably unhardened, since such an emulsion adheres much more strongly to a support to which it may be transferred.

For use as a stencil, the emulsion also may contain a matting material such as starch grains, diatomaceous earth, ground glass, barium sulfate or the like, which adds a tooth to the emulsion layer so that after exposure and development, it can take pencil lines; thus permitting additions to be made through the drawings.

In order to permit strong electron bombardment and yet achieve good stripping when desired, the product is washed after processing by contacting with 1-15 solution of stannous chloride, sodium stannite or other similar reducing agents for a long enough period for the solution to penetrate the emulsion sufiiciently. This would normally be about one to five minutes, but might be longer. This helps to loosen the prepared bond.

The following examples are intended to illustrate our invention but not to limit it in any way:

Example 1 A length of oriented polyethylene terephthalate film base to which no surface layers had been applied was treated by passing it through two electrodes that were connected to the pulsating DC. output of a high voltage induction coil. A sheet of glass was placed over one electrode, and a length of film rested on this glass plate as it passed between the plates. This left a gap of about 0.1" between the traveling support and the other electrode. The corona discharge took place in this space and treated the side of the support facing it. The receding contact angle was less than 45, measured using the bubble method. The support was then coated with a gravure resist emulsion. No subbing layer was used. This film was not susceptible to accidential damage either when dry or when wet. However, after it had been processed and dried, its dry stripping case was quite satisfactory.

Example 2 A length of organic polyethylene terephthalate film was treated as in Example 1, but the support was coated in the same operation with a thin cellulose nitrate film having a thickness of .3 mil from a solvent solution of cellulose nitrate in acetone. It was then subbed using a gelatino aqueous solution and coated with a high-contrast unhardened photographic silver halide emulsion. After processing, the dry stripping ease was quite satisfactory.

Example 3 Organic polyethylene terephthalate as described in Example 1 was washed following processing with water, in which sodium stannite was added to form a solution. The ease of stripping was improved over that obtained in Example 1.

Example 4 A 5% solution of stannous chloride was used instead of sodium stannite as in Example 3, with almost the same improvement in stripping over that obtained in Example 1.

It was found that when a photo-stencil image was formed that there were usually areas where the dots were very small and formed isolated islands of gelatin rather than a continuous skin. These areas have been recognized as very diflicult to strip. This is in direct contrast with the normal kind of adhesion wherein the ease of stripping is increased by dividing up the gelatin continuum into separate and discreet islands. However, the use of these added agents in the wash water resulted in stripping these areas when the photo-stencil type emulsions were employed.

Various subs which may be used for coating the polyethylene terephthalate film subsequent to the electron bombardment are those well known in the art. These include cellulose esters, such as cellulose nitrate, cellulose acetate, and the like; as well as other cellulose derivatives, such as cellulose ethers. Since some of the subs which are known in the art become soluble in developers or in aqueous solutions, these subs will affect the adhesion of the emulsion coating which is placed over the sub.

The degree and nature of stripping is the same beforeprocessing of the raw film as it is subsequent to processing, except when a special agent, such as a stannous derivative, is used as described above in the wash water. Although the examples show the use of the glass plate as a support for the polyethylene terephthalate when it is passed between the electrodes, it will be clear that other insulating materials may be used, such as several layers of polyethylene terephthalate, polytetrafiuoroethylene, and the like.

Our method of treating the polyethylene terephthalate support may be employed for use for other stripping films. For instance, this specially treated support may be coated with separable sensitive layers which can be transferred to suitable supports and capable of use in the imbibition process of motion picture color photography.

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 effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. The method of facilitating the stripping of a gelatin silver halide emulsion from the electron bombarded surface of a polyethylene terephthalate support which comprises contacting the support with the silver halide emulsion thereon with a dilute aqueous solution containing a tin salt.

2. The method of facilitating the stripping of a gelatin silver halide emulsion layer from the electron bombarded surface of a polyethylene terephthalate support which comprises contacting the support with the emulsion coating thereon with an aqueous solution containing 1-15 of a compound selected from a group consisting of the alkali metal stannite salts and the stannous halide salts.

3. The method of facilitating the stripping of a gelatin silver halide emulsion from the electron bombarded surface of a polyethylene terephthalate support which comprises washing the support with the emulsion thereon in about a 5% aqueous solution of sodium stannite.

4..The method of facilitating the stripping of a gelatin silver halide emulsion from the electron bombarded surface of a polyethylene terephthalate support which comprises washing the support with the emulsion thereon in about a 5% aqueous solution of stannous chloride.

References Cited by the Examiner UNITED STATES PATENTS 3,035,915 5/1962 Cohen etal 96-83 3,037,862 6/1962 Neth 9687 X 3,043,695 7/1962 AlleS 96-83 3,072,483 1/1963 Trevoy of al 96-87 FOREIGN PATENTS 788,365 1/1958 Great Britain.

1,159,702 2/1958 France.

OTHER REFERENCES Bopp et al.: Radiation Stability of Plastics and Elastomers, US. Atomic Energy Commission, ORNL-1373, July 23, 1953, Oak Ridge National Laboratory, Oak Ridge, Tenn, pp. 1, 32, 33 and 64.

NORMAN G. TORCHIN, Primary Examiner.

Claims (1)

1. THE METHOD OF FACILITATING THE STRIPPING OF A GELATIN SILVER HALIDE EMULSION FROM THE ELECTRON BOMBARDED SURFACE OF A POLYETHYLENE TEREPHTHALATE SUPPORT WHICH COMPRISES CONTACTING THE SUPPORT WITH THE SILVER HALIDE EMULSION THEREON WITH A DILUTE AQUEOUS SOLUTION CONTAINING A TIN SALT.