Permanent Yellow Imaged Light Modulating Film

In one aspect the invention relates to a permanent yellow imaged modulating or printing plate master film for improved negative image transfer by energy generated from a blue light source to a image receiving photoresist having a coating which is sensitive to blue light. In another aspect the invention relates to the preparation of said modulating film by a non-chemical process.

Of the various light sources suitable for photoimaging including red, green and blue, blue light is the most economical and efficient In general, the process of preparing a master printing plate having a photoresist layer involves passing energy from a light source through non-imaged portions of a modulator, e.g. a film imaged in a color which absorbs the transmitted light and transmits light radiation passing through non-imaged areas to the printing plate coated with a material which is imageable in discrete exposed areas upon exposure to radiant energy. Because of the ready availability and economy of blue light energy sources and the numerous films which are sensitive to blue light, extensive research has been directed to finding compounds which are imageable to a permanent yellow hue since such imaged compounds most efficiently absorb blue light and provide the highest duplicating properties. A yellow imaged modulating film would be capable of transferring energy from its non-imaged areas in a negative configuration of its pattern to a printing plate having a photoresist layer whereupon the photoresist layer develops color or is polymerized in the negative pattern dictated by the modulating film in the highest degree of acuity. Accordingly, a negative or positive of the desired image can be developed on the printing plate depending upon the yellow pattern or design inscribed on the modulating or master film.

Polyacetylenic compounds have enjoyed great popularity in imaging processes. However, it is well recognized that thermochromic behavior of polyacetylenic compounds is unpredictable and has been found only in certain narrow classes of this species. Further, within these classes, development to a permanent yellow hue is extremely rare.

While a few polyacetylenic monomers are capable of providing a yellow image at excessively high temperatures, this thermochromic effect is ephemeral, so that upon cooling, the image reverts to an initial transition color of darker shades e.g. red, blue, bronze, etc. (U.S. Pat. No. 3,501,303). Such color reversible compounds are useful as temperature or time-temperature indicators dependent on thermal changes but are not practical for use as modulating films in the preparation of printing plates, circuit boards and the like.

Accordingly, it is an object of this invention to provide a permanent yellow imaged film for use as a reverse image transmitting agent or master film in the production of printing plates and circuit boards.

Another object is to provide a commercially acceptable and economical chemically processless method for preparation of a permanent yellow imaged film.

Another object is to provide a commercially acceptable and economical process for using a permanent yellow imaged recording film as a master film in the production of printed circuit boards or master printing plates.

These and other objects of the invention will become apparent from the following description and disclosure.

In accordance with this invention there is provided a process which comprises exposing a supported layer of colorless, crystalline 10,12-docosadiyndioic acid monomer having the formula

to short wavelength radiation in order to polymerize the monomer to a blue colored homopolymer and subjecting the resulting homopolymer layer to radiation at a longer wavelength from laser emissions, preferably focused to impinge discrete areas of the homopolymer in a predetermined pattern or design so as to form a permanent yellow image thereon. The laser operating at the longer wavelength is one having sufficient beam power to directly or indirectly generate heat of at least 140.degree. C., preferably between about 140.degree. and about 200.degree. C., in the exposed portions of the homopolymer. Laser emissions in a wavelength of 575 nm or less are directly absorbed by the homopolymer. However, the emissions of lasers generating energy in wavelengths above 575 nm, e.g. between about 600 and about 1,500 nm or longer, are not absorbed; accordingly, in these cases an energy absorbing, heat transmitting agent is employed in conjunction with the diyndioic acid monomer in the preparation of the initial film before coating on a substrate.

The method of preparing the colorless, thermochromic, crystalline diyndioic acid monomer of this invention is known and is described in the Journal of Polymer Science, Polym. Chem. Ed 17, 1631, 1979 by G. Wegner et al.

In accordance with this invention, the monomer is applied to the substrate in a coating thickness of from about 0.002 to 100 um, preferably from about 0.01 to about 5 um. Suitable substrates include polyethylene terephthalate, nylon, polystyrene, cellulose acetate, cellulose nitrate, cellophane, polyvinyl chloride, polyvinylidene chloride, teflon, polychlorotrifluoroethylene, polypropylene, paper, ceramic, glass, metal, wood and the like, however, for use as a modulating film, a transparent substrate is recommended.

Coatings of the present 10,12-docosadiyndioic acid monomer in the presence or absence of an energy absorbing, heat transmitting agent, are applied to a substrate by any of the known techniques, including application of crystalline dispersions or of one or more monomolecular layers; however, an aqueous dispersion of diyndioic acid crystals fixed in any of the known binders is preferred. One or more monomolecular layers of the 10,12-docosadiyndioic acid compound applied to the substrate by the Langmuir-Blodgett technique, spin or spray coating method is also suitable. Any energy absorbing, heat transmitting agent, which in certain situations may be required, can be applied as a separate, contiguous layer. The preparation of useful binder dispersions and coating techniques are more particularly described in my copending U.S. patent application Ser. No. 07/601,499*, now U.S. Pat. No. 5,095,134. By way of illustration, a dispersion, emulsion or suspension of the crystalline diyndioic acid/binder, preferably an aqueous dispersion with a binder, is prepared under atmospheric conditions by mixing the crystalline diyndioic acid crystals in a binder solution optionally containing an energy absorbing, heat transmitting agent, until a uniformly dispersed, suspended or emulsified liquid mixture is obtained. The mixture is then processed by known procedures e.g. chilled or frozen by the process described in U.S. Pat. No. 4,784,934 to provide a dispersion of microcrystals in a binder. The 10,12-docosadiyndioic acid crystals have a diameter of from about 0.02 um to about 5 um, preferably from 0.1 um to 1.0 um, and are fixed in the binder to provide a uniform dispersion containing from about 1 to about 50 wt. %, preferably from about 4 to about 15 wt. % of solid microcrystals. This dispersion is then coated on a substrate and dried to form a layer of between about 0.3 to about 10, preferably 0.5 to 5 um thickness. Monomolecular layers of 10,12-docosadiyndioic acid are, of course, much thinner; however a plurality of monomolecular layers as well as one or more layers of the energy absorbing component, when needed, can be sequentially applied to any thickness desired.

The resulting dried diyndioic acid film is then imaged by the process of this invention which comprises, in a first stage of a preferred two stage process, exposing the film, at ambient temperature and pressure to short wavelength radiation; i.e. at a wavelength of between about 200 and about 350 nm, to polymerize the diyndioic acid to a blue colored homopolymer. Short wavelength exposure is effected by conventional techniques using a xenon flash lamp, mercury arc lamp, mercury xenon arc lamp, tungsten quartz halogen lamp, electron beam, UV light, actinic light, gamma-rays, X-rays, beta-rays, neutrons, alpha-particles, or UV laser, e.g. an argon ion laser transmitting energy at about 275 nm wavelength, a krypton ion laser, a GaAlP laser and the like. The short wavelength exposure can be employed to homopolymerize all or a portion of the diyndioic acid film, that is a broad beam of UV light can be used to homopolymerize the entire colorless 10,12-docosadiyndioic acid layer (case a) or the layer can be scribed, in one or several steps, to define a predetermined pattern or image with a short wavelength transmitting device e.g. a UV laser or electron beam operated in the writing mode, e.g. an electron beam, UV laser or the like (case b). In case (a), the entire film acquires a blue color of the homopolymer; whereas in case (b) a homopolymerized blue image is inscribed on the colorless background of the unexposed diyndioic acid. In the writing mode, exposure with an electron beam is carried out under vacuum of from about 10.sup.-3 to about 10.sup.-9 torr, preferably from about 10.sup.-5 to about 10.sup.-8 torr, using a beam diameter of from about 0.1 to about 25 nm, an energy of from about 10 to about 30 KeV, and a current flow of from about 10.sup.-9 to about 10.sup.-6 amps. The beam is adapted to scan the target area at a fast rate, e.g. a dwell time of between about 10.sup.-3 and about 10.sup.-8 second. UV laser exposure at a wavelength up to about 375 nm, e.g. 200-350 nm, an intensity of from about 5,000 to about 15,000 mW for a dwell time of from about 0.1 second to about 10 minutes is also effective for polymerizing the diyndioic acid monomer to produce the blue colored homopolymer. Equivalent dosages are employed for alternate sources of short wavelength exposures.

The resulting film is then subjected to laser emissions at a longer wavelength above 375 nm in the second stage of the reaction. The laser employed is capable of generating heat sufficient to raise the temperature of the homopolymer in the exposed areas to at least 140.degree. C., preferably to between about 140.degree. and about 200.degree. C., and most preferably between about 140.degree. and about 180.degree. C., thus causing a permanent color change from blue to yellow in the areas impinged by the laser emission generated at the longer wavelength in the second stage. In case (a) above, the laser is employed in the writing mode to inscribe a predetermined permanent yellow image on the blue colored homopolymer layer. In case (b) above, the laser generating at the longer wavelength can be synchronized with the scribing device operating at the short wavelength and used in the writing mode to retrace the previously inscribed image or it can be used to expose the entire polymerized and non-polymerized portions of the 10,12-docosadiyndioic acid layer so as to induce a change to a permanent yellow color to the preinscribed blue image. The second stage of the reaction is carried out under ambient pressure for a period sufficient to complete the transition to the permanent yellow color usually from about 0.1 to about 10 seconds, depending upon the laser beam power and type of laser imaging device selected. The second stage heat generation can be supplied by substantially any laser generating energy in the 450 nm or longer wavelength regions of the spectrum. Such lasers include a compact semi-conductor diode, solid state, gas, metal vapor, or dye laser. However, semi-conductor diode lasers, having an output power of from about 1 microwatt to about 10 watts, are preferred. Specific examples of suitable lasers include GaAlAs, NaYtAl garnet, Ar, He-Ne, He-Cd, GaAs NeYAl garnet, ruby, NaYAg, krypton ion, copper vapor lasers, etc. Thus, crystalline, gas or amorphous solid, pulsed or continuous wave lasers may be used. The laser selected should be capable of transmitting the desired heat needed to induce the thermochromic color change in the laser exposure areas of the homopolymerized 10,12-docosadiyndioic acid layer at between about 450 and about 575 nm wavelength, which is within the direct absorption capability of the homopolymer. Alternatively, a laser transmitting energy at a longer wavelength, for example above about 575 up to about 1,500 nm or higher can be employed, provided that a suitable energy absorbing, heat transmitting component, (e.g. an energy absorbing polycarbocyanine, pyrylium, squarilium dye, or dye mixtures or dye intermixtures, etc. as described in more detail in copending U.S. patent application Ser. No. 07/601,537*), is used in conjunction with the 10,12-docosadiyndioic acid to absorb energy from the laser and to transmit sufficient heat to the homopolymer so that a permanent yellow image or pattern is inscribed thereon. The energy absorbing, heat transmitting agent is one having absorption capability in a wavelength similar to the transmitting laser and is capable of raising the temperature of the homopolymer to at least 140.degree. C. When an energy absorbing dye is employed, the weight ratio of 10,12-docosadiyndioic acid homopolymer to dye can vary between about 1000:1 and about 1:10, depending upon the amount of homopolymer present and the amount of radiation energy needed to be converted to heat energy. Most often the dye comprises between about 0.005 and about 1 wt. % of the imaging compound. For scribing, a laser beam diameter of 0.5 to about 2 nm with an exposure time of from about 180 to 250 ns/dot and an output of 2.5-3.5 mW is generally employed to create an image of high resolution.

In the writing mode, exposure with an electron beam is carried out under vacuum of from about 10.sup.-3 to about 10.sup.-9 torr, preferably from about 10.sup.-5 to about 10.sup.-8 torr, using a beam diameter of from about 0.1 to abut 25 nm, an energy of from about 10 to about 30 KeV, and a current flow of from about 10.sup.-9 to about 10.sup.-6 amps The beam is adapted to scan the target area at a fast rate, e.g. a dwell time of between about 10.sup.-3 and about 10.sup.-8 second. UV light exposure with a wavelength up to about 385 nm, e.g. 200-350 nm, an intensity of from about 5,000 to about 15,000 mW for a dwell time of from about 0.1 second to about 10 minutes is also effective for polymerizing the diyndioic acid monomer to produce the blue colored homopolymer. Equivalent dosages are employed for alternate sources of short wavelength exposures.

The resulting permanent yellow imaged film product supported on a transparent substrate can then be employed as a master film in the preparation of a printing plate or etch resist coated with a layer which is photosensitive to blue light transmission.

The image receptive device, e.g. an etch resist for a printed circuit board, a master printing plate, etc. can be composed of any durable support material such as metal, glass, ceramic, polyester, and the like which is coated with a photosensitive layer, comprised of any known photosensitive material which undergoes photopolymerization or a photochromic change in response to radiation from a blue light source. Of these materials, colorless, thermochromic conjugated polyacetylenic monomers, their monomeric derivatives, diazo resins, cinnamic ester resins, polymethacrylates or silver halide based films are suitable; however, crystalline, imageable diacetylene derivatives are preferred. Examples of preferred diacetylenic compounds comprising the photosensitive surface layer of the image receiving device include any of the art recognized hydrocarbon diacetylenes, and their derivatives such as the carboxyl, amino, amido, ester, ether, urea or carbamate substituted diacetylenes as well as tri- and tetra- acetylene derivatives of these species.

The homopolymerized diyndioic acid of the present invention has other uses in addition to photoimaging. For example this homopolymer is useful as time-temperature or temperature indicator coatings as warming means for equipment which is subject to overheating. However, the photoimaging application of the homopolymer is emphasized since this product possesses unusual properties such as a permanent yellow thermochromic imaging and development to images of superior resolution and intensity, which are so important in the photographic arts.

Having generally described the invention, reference is now had to the accompanying examples which are presented to illustrate preferred embodiments but which are not to be considered as limiting to the scope of this invention as is more broadly described above and in the appended claims.

In a glass container, 1.2 g. of 10,12-docosadiyndioic acid were dissolved at about 50.degree. C. in 4 g. of cyclohexanone and the resulting solution was filtered and designated Solution A. A second solution, designated Solution B, was prepared by dissolving 1.2 g. of photographic gelatin and 0.05 g. of ALKANOL XC (an alcohol-containing wetting agent, supplied by E.I. duPont) in 30 g. of water. Solution B was heated to 60.degree. C. and introduced into a 250 ml Waring Blender. While blending at high speed, Solution A was added to Solution B after which the blending was continued for 2 minutes. The resulting mixture was then poured into a crystallizing dish to chill set at about 12.degree. C. The resulting gelled dispersion was then cut into approximately 1 cm cubes and allowed to warm in an air stream at approximately 32.degree. C. to remove ethanol by evaporation. After the ethanol had been removed, the gelled dispersion was reconstituted by melting at 40.degree. C. and adding sufficient water to replace the weight loss that occurred during drying.

The reconstituted dispersion was coated at about 8 micrometers thickness on a poly(ethylene terephthalate) film base which had been overcoated with a 1 micrometer thick layer of an adhesion promoting material composed of about 50 wt. % gelatin and 50 wt. % of a latex polymer. The coated film was then allowed to dry in air at ambient temperature.

A 3.5.times.6 inch sample of the above film was placed in a holding device over which is mounted a low pressure mercury arc lamp having a 100 watt output and emitting UV radiation at a wavelength of about 253.7 nm. The colorless film is exposed for 1.5 minutes to emissions from the lamp so as to absorb energy and polymerize colorless 10,12-docosadiyndioic acid to a blue colored homopolymer.

The resulting homopolymer is then scribed with a copper vapor laser having an output of 3 watts which transmits energy at about 560 nm wavelength and impinges discrete areas of the surface of the film defined by a series of diamond shaped figures and lines. The energy generated by this transmission is absorbed by the homopolymer and heats the exposed areas of the film to a temperature of about 140.degree. C. in a fraction of a second whereby an image of said diamond shaped figures and lines is transmitted in high acuity in a permanent golden yellow color on the blue background which is not exposed to the laser emissions.

The above sample is employed as a modulating film in the following test. A blue light source, i.e. a high pressure mercury arc lamp operating at an output power of 1 kilowatt and transmitting energy in a wavelength of 350-450 nm is focused to scan the entire area of the film sample which is positioned about 3.6 feet from the light outlet. Contiguous with the surface of the film and on the surface directly opposite the surface being radiated, is positioned the imageable surface layer, i.e. 4-diazodiphenylamine/formaldehyde condensate, supported on cellulose triacetate sheet of the photoresist master printing plate.

The blue light from the lamp is absorbed in the imaged areas of the film sample and is transmitted from the non-imaged areas, in an exact negative imaged pattern to the imageable surface layer of the photoresist where it attacks the polymer condensate and renders the decomposed areas insoluble in water.

Example 1 is repeated except that in Part A, 0.1 wt. % of IR-125 dye (a polycarbocyanine dye supplied by Eastman Kodak) is added to solution B and a GaAlAs semiconductor diode laser with a wavelength of about 830 nm is substituted for the copper vapor laser in Part D. The image produced is one of high resolution defined in a golden yellow color on a blue colored background.

Example 1 is repeated except that in Part C, an electron beam writing device is used in place of the high pressure mercury arc lamp. The electron beam is used to instantly homopolymerize diyndioic acid and to write an image consisting of a series of lines by homopolymerizing the monomer in the corresponding discrete areas of exposure. The image is instantly visible as blue lines on a colorless non-exposed monomer background. After about 1 hour, in the same manner, dots between the blue lines are inscribed on the film with the electron beam scriber to provide a blue image of lines and dots on the unexposed colorless background. Also in Part C, a broad exposure of the entire film is made with the copper vapor laser instead of impinging discrete areas. Within a fraction of a second the well defined image of the blue lines and dots is transformed to a permanent golden yellow image.

It is to be understood that many modifications and substitutions can be made in the above examples without departing from the scope of this invention. For example, any of the other radiation devices which transmit energy in a short wavelength of 200-350 nm and/or any of the lasers which transmit energy in the longer wavelength above 350 nm can be substituted in the above examples in accordance with the teachings of this invention. Also any of the energy absorbing, heat transmitting dyes including other polycarbocyamine dyes, squarilium or pyrilium dyes and dye complexes mentioned or described in copending U.S. patent application Ser. No. 07/601,532, filed concurrently herewith, and in U.S. Pat. No. 4,513,071 which absorb energy in a wavelength similar to that of the energy generated from the laser can be substituted in the above examples or examples indicated by the above substitutions. Additionally, substitutions of other base films in Parts B and Parts C of the above examples or substituted examples, as well as other photoresist coatings for the image receiving device in Parts D can be made without departing from the scope of this invention.