PROCESS FOR PREPARING ELECTROMAGNETIC RADIATION IMAGED MATERIAL

Abstract: A manufacturing process for producing a controllable membrane (28) within a layer of a light-sensitive material (20) laminated on a support (22) comprising steps: exposing the light-sensitive material layer (20) with light irradiation in presence of an image transfer means to produce unrevealed image (26) in said light-sensitive layer, and re-exposing the unrevealed image (26) to light radiation (24) on the side opposite to light sensitive material layer with respect to the support (22) in the absence of an image transfer means for a time sufficient to produce the integral membrane (28) within the unrevealed image (26).

Description: PROCESS FOR PREPARING ELECTROMAGNETIC RADIATION IMAGED MATERIAL This invention relates to a process for preparing electromagnetic radiation imaged material and to an article of manufacture comprising an adherent sheet-like photoresist laminate which can be transferred to a surface to introduce a pattern into the surface using a particulate etchant such as a sandblast. More particularly, the invention relates to a photoresist laminate which can be adherently applied to the surface of an object or material, for the purpose of revealing or exposing in the surface of the object or material, a pattern. The resist laminate contains a layer of photoresist composition which when exposed to light a specific desired pattern can be developed when the resist is applied to the surface of the object or material, the pattern can be selectively revealed by the action of an etchant. Over the years a great deal of interest has been focused on the art of etching patterns into surfaces of objects. Such patterns can be decorative, informative, can be for the purpose of providing nonskid surface properties, can be useful in forming copper printed wiring board pat¬ terns, and can be useful in many other application where a specific pattern is desired. Grit blasting has been effected in the past by employing a pattern mask prepared manually from rubber, paper, or various plastics and attaching the pattern mask to the article to be etched employing an adhesive. This method is time consuming and cannot be used to etch fine image details on a repetitive basis. In the past, expensive metal templates have been held or attached to the surfaces and grit blasted at the templates to produce the etch. This method, since the templates must have small metal parts holding the template together, cannot produce fine detail. Ad- ditionally the metal template loses its shape with repeated use, and distorts the design. The surface of the article can also be etched by silk screen printing an image in relief onto a very fine sticky backing paper. This method requires a very strong ink image. The sticky backing paper is dampened and adhered to the surface. The ink image is then grit blasted. The grit material must, however, penetrate through the paper and its adhesive before affecting the surface. During this time, the ink image must withstand the grit blasting. The resultant image is more of a frost than an etch, and is best suited for producing large numbers of etched items since the method is too costly for etching small numbers of items. Die cut vinyl stencils are also produced as an etchant mask, and the time, effort and cost factors make the use of such stencils undesirable. Several companies produce photoresist masks commercially in the United States. Each such mask has a commonalty in that an emulsion containing a photosensitizer and a reactive monomeric and/or polymeric substance is applied to a substrate which is then exposed, either dry or wet, to sufficient quantities of electromagnetic radiation of an appropriate wave length to activate polymerization or crosslinking catalysts, agents, initiators or mixtures thereof. The unexposed areas remain soluble to the action of solvents such as water, alcohols, hexane, benzene and when exposed to such solvents by the use of a washout device reveal the desired pattern or design. The exposed areas are rendered insoluble and form the mask. While the commercial productions can produce reasonable detail, some detail is destroyed during the washout. The method by which these marks are, by simple adhesive, transferred to the object to be etched, requires the masks to be burnished while applying. The failure rate for loss of pieces and fine detail which does not make the transfer, or is blown off the glass in the blasting is substantial. One American company produces a laminated resist, produced much the same as the previous commercial mask, which has as an additional production step a thin film laminated to the polymerized resist. The transfer of this mask is better, but the production costs of this additional step make the mask very expensive. The loss of fine detail during washout is a problem. Liquid photoresists are also commercially available which are painted or sprayed onto the surface of the object to be etched, and then exposed when dry to achieve a desired image. While the process does work, there are serious problems when working with any but a planer surface, and presents problems on water sensitive surfaces. The process is time consuming, expensive, and must be cleaned using special expensive removers. Accordingly, a substantial need exists for a photoresist that is extremely easy to use, can readily develop an image or pattern, can be used on both water sensitive surfaces and surfaces having curves and contours. Such a photoresist, which can be produced quickly and inexpen¬ sively while providing extremely fine detail which transfers intact and adheres so fine detail is not blown off during the blasting is in demand. We have found that by exposing a previously imaged photoresist sheet to a proper amount of electromagnetic radiation for a specific time period, prior to exposure to solvents by the use of a washout device, we can produce a controllable integral membrane layer in the imaged photoresist sheet. Surprisingly, we have found SUBSTITUTE that when exposed to solvent by use of a washout device, the integral membrane remains intact, and greatly enhances the amount of detail that is available for transfer. By being integral, this membrane actually increases the amount of fine detail that can be easily transferred to the object to be etched. Using this invention line widths of .0039 inches can be imaged, washed out, transferred and successfully etched. Additionally we have found that any or all of the following advantages may be achievable: (a) The method is very simple. (b) No appreciable additional costs are incurred. (c) Compound and inward curves can be masked without distortion. (d) Water sensitive materials can be masked and etched without damage. (e) Substrate, material can be quickly and easily stripped off. (f) Application time of the mask on the object to be etched is greatly reduced. (g) Clean up or mask removal is fast; no special agents needed. (h) Etching time is reduced per object since all detail stays in place, resulting in increasec production. (i) Better resolution, finer detail, and higher quality are produced which increases product sales. Brief Description of the Drawings Fig. 1 is a view of a generally rectangle portion diagram of a preferred resist laminate which is made of a substrate which has been coated with a photosensitive resist. Fig. 2 is an enlarged side view diagram of a method of forming an unrevealed pattern in the surface of the photosensitive resist by exposure to a film image and a electromagnetic radiation source. Fig. 3 is an enlarged side view diagram of a method of forming an integral membrane in the previously imaged photo resist sheet, Fig. 2. Fig. 4 is an enlarged side view diagram of the wash out device, and water or chemical solvent spray, reveal¬ ing the imaged pattern, leaving the integral membrane intact on the substrate. Fig. 5 is an enlarged side view diagram of the imaged photoresist, applied to the object to be etched, by means of an adhesive coating. The integral membrane holds all pattern pieces in place while the substrate is stripped away. Fig. 6 is an enlarged side view diagram of the applied photoresist, on the object to be etched, being blasted with abrasive, propelled from an abrasion etching device, producing an etched pattern in the object. Fig. 7 is an enlarged side diagram of a method of forming an integral membrane in photosensitive laminates for later use. Reference Numerals In Drawings 20 photo sensitive resist 33 revealed image 22 substrate 34 adhesive layer 24 electromagnetic source 36 surface to be etched 25 timing device 38 etched area 26 unrevealed image 40 abrasion etching device 27 image transfer means 42 abrasive 28 integral membrane 44 repelled abrasive 30 wash out device 46 etched image 32 water or chemical solvent spray SUBSTITUTESHEET Detailed Discussion of the Invention Resist Layer The resist laminate of the invention generally is made of a resist layer, a substrate layer, and an adhesive layer. The resist layer of the laminate generally comprises compositions that are photosensitive. The photosensitive compositions typically interact with light to transform the composition from a soluble state into an insoluble film. Typically, resist compositions contain reactive mono/or polymeric substances along with photo activated initiators. Such polymer suspensions are well known in the art and are available from a number of suppliers. One of the preferred resists is sold by The Chromaline Corporation under the name SBX. Substrate The support layer of this invention commonly comprises a web, film, or other such substrate which can be coated with the resist composition of the invention. The substrate may be mechanically strong to permit rapid manufacture of the resist laminate and may be flexible to allow for the easy removal after transfer of the resist mask to the object to be etched. Such substrate materials are readily available from a number of suppliers. The preferred substrate of this invention is a transpar¬ ent or translucent sheet-like material which is less than 4 mil mylar polyester, produced by DuPont. Adhesive layer The photoresist laminate of the invention comprises an adhesive layer that is used to adherently apply the laminate to the object for etching. The adhesive layer can be water activated, pressure sensitive, heat ac¬ tivated, or other adhesive form. The adhesive layer is preferably a pressure sensitive adhesive which is typically an adhesive composition having a high degree of tack and cohesive strength. Such adhesives may be applied by a large variety of means; spray, brush, roll coating, or in the photoresist polymer suspension. Pressure sensitive adhesives tend to bond almost instan¬ taneously to a surface with slight contact pressure at the interface between the adhesive and the contacted surface. In practice pressure sensitive adhesives commonly are used in conjunction with a pressure sen- sitive release liner comprising a backing material such as paper, textile, plastic film, or metal foil which has a generally silicone release coating to ensure that a release liner can be removed from the pressure sensitive adhesive without reducing the adhesive properties of the adhesive mass and without any removal of the pressure sensitive adhesive. The removable release liner makes it practical to store imaged sheets with the adhesive applied for later use, or for shipment. The preferred pressure sensitive adhesives are well known to the art, and are commonly available through a variety of sources including 3-M. Methods of use The photoresist laminate articles of manufacture of the invention are typically used by adhering the exposed, re- exposed, washed out laminate to the object to be etched. The substrate is stripped off and the resist is exposed to the action of a particulate etchant. Many variations of this basic etching process can be formed without departing from the spirit and scope of the invention since the steps can be rearranged to suit a particular SUBSTITUTESHEET resist laminate construction, and the desired end use of the resultant sheets. Fig. 1 is a diagram of a generally rectangle portion of a preferred resist laminate which is made of a substrate 22 which has been coated with a photosensitive resist 20. The coating may be produced by various well known coating methods, and can be applied in a variety of thicknesses directly related to the intended use of the resist. The preferred thickness of the photosensitive resist 20 is between 3 mil and 5 mil. Fig. 2 is an enlarged side view diagram of a method of forming an unrevealed image 26 in the surface of the photosensitive resist 20, by exposure to a image transfer means 27 and a electromagnetic radiation source 24. This known art generally requires sufficient electromagnetic radiation 24 to be applied to photosensitive resist 20 to cause the crosslinking or polymerization of the resist into an insoluble state. The image transfer means 27 repels the electromagnetic radiation 24 and the un- revealed image 26 remains soluble. Fig. 3 is an enlarged side view diagram of a method of forming an integral membrane 28 in the previously imaged photosensitive resist sheet Fig. 2. The previously imaged photosensitive resist sheet is re-introduced, or exposed a second time to the electromagnetic radiation 24. The image transfer means 27 is not present. The preferred method exposes the laminate with the photosen¬ sitive resist 20 in the reverse of Fig. 2, with the substrate 22 in the direct path of the electromagnetic radiation 24. The areas of unrevealed image 26 are now briefly exposed for a specific time period, using a timing device 25, through the substrate 22, forming a integral membrane 28. The specific time to produce the membrane varies in direct relation to the time of electromagnetic radiation from a specific source, a.s is well known. The steps can be rearranged to suit a t=ET * particular manufacturing or use method with substantially the same results. Fig. 4 is an enlarged side view diagram of the wash out device 30, and water or chemical solvent spray 32, revealing the revealed image 33 and the integral membrane 28 left intact on the substrate 22. The integral membrane 28 spans all the revealed image areas 33 and has held them in place during the wash out process. The stabilizing effect of the integral membrane greatly improves the resolution capability of the photosensitive resist since all fine detail is held in place, and is not eroded at the roots. Fig. 5 is an enlarged side view diagram of the imaged photoresist 20, applied to the object to be etched 36, by the means of an adhesive coating 34. The integral membrane 28 now holds all pattern pieces in place without loss or distortion while substrate 22 is stripped away manually. The transfer method allows previously dif¬ ficult surfaces including compound and inward curves to be successfully masked, as well as application to other surfaces which are sensitive to the presence of water. Fig. 6 is an enlarged side view diagram of the applied photoresist 20, applied to the object to be etched 36, by means of an adhesive coating 34. The integral membrane 28 holds the various small parts in place while exposed to the abrasive 42. The membrane rapidly erodes when exposed to the action of the abrasive, and after suf¬ ficient exposure to the etchant, the etched image 46 is developed in the object surface. The holding in place of the small pieces by the membrane allows deeper etching of the image since the small pieces do not blow off. Fig. 7 is an enlarged side view diagram of the photores¬ ist 20 on substrate 22 exposed to electromagnetic radiation 24. The preferred method for producing photoresist laminates for storage or shipment for use at SUBSTITUTESHEET a later time is to expose the laminate briefly for a specific time to produce a membrane 28' by means of a timing device 25 and deposit the exposed laminate in exposure proof means for later re-exposure, Fig. 2, washout Fig. 4, application with adhesive coating Fig. 5, stripping of substrate Fig. 5, and etching Fig. 6. Although the description above contains many specificati¬ ons these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, the invention can be utilised on sheets which are produced and exposed while liquid or semi-liquid as well as dry. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.

Claims: CLAIMS 1. A process for preparing an electromagnetic radiation imaged material for use in applying a pattern to a surface, the process comprising exposing a layer of a radiation-sensitive material to said radiation in the presence of an image transfer means to produce an unrevealed image in said material, and exposing the material to said radiation in the absence of said image transfer means for sufficient time to produce an integral membrane of radiation-exposed material within the unrevealed image. 2. A process according to claim 1, wherein the exposure in the absence of the image transfer means is performed after the exposure in the presence of the image transfer means. 3. A process according to claim 1 or claim 2, wherein the layer of radiation-sensitive material forms part of a laminate optionally including a substrate transparent to said radiation. 4. A process according to any one of the preceding claims, wherein one exposure to radiation is carried out from the opposite side of the layer to the side of the other exposure. 5. A process according to any one of the preceding claims, wherein the electromagnetic radiation is light. 6. A process according to any one of the preceding claims, wherein the radiation-sensitive material is capable of changing from a soluble form prior to exposure to an insoluble form after exposure. 7. A process according to any one of the preceding claims, wherein the material is adapted to be adhered to the surface for said pattern application. ET 8. A process according to claim 7 when dependent upon claim 3, wherein the substrate is adapted to be manually removed from the imaged material prior to said pattern application. 9. A process according to any one of the preceding claims, wherein the radiation-sensitive starting material is pre-exposed to said radiation for sufficient time to form a protective integral surface membrane of radiation- exposed material to facilitate storage of the material prior to use in preparing the imaged material. 10. A process according to any one of the preceding claims for preparing an imaged material for use in etching a pattern to a surface by means of a particulate etchant. 11. An electromagnetic-radiation imaged material when prepared by a process according to any one of the preceding claims. 12. An electromagnetic-radiation imaged laminate when prepared by a process according to claims 3. 13. A process for applying a pattern to a surface, comprising removing unexposed material from the imaged material or laminate of claim 11 or claim 12 to create a revealed image in the material, subsequently locating the imaged material to the surface, and treating the imaged material with means adapted to break the integral membrane within the image and to eat into the surface to apply the image to the surface as the desired pattern. 14. A process for preparing an imaged material for use in applying a pattern to a surface, substantially as hereinbefore described with reference to the accompanying drawings. 15. A process for applying a pattern to a surface, UTESHEET substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings. 16. An electromagnetic-radiation imaged material substantially as hereinbefore described with reference to the accompanying drawings. 17. An electromagnetic-radiation imaged laminate substantially as hereinbefore described with reference to the accompanying drawings. 18. A manufacturing process of producing a controllable integral membrane in photosensitive laminates for transfer, comprising the steps of: exposing the photosensitive laminate to an imaging exposure means with an image transfer means to produce an unrevealed image; re-introducing the photosensitive laminate to said imaging exposure means without the said image transfer means for a specific period of time to produce the integral membrane; revealing the unrevealed image by means of a washout device; and revealing the integral membrane. 19. A manufacturing process of producing a controllable integral membrane in photosensitive laminates for transfer, comprising the steps of: exposing the photosensitive laminate to an imaging exposure means for a specific period of time without use of any image transfer means to produce the integral membrane; depositing the exposed photosensitive laminate in exposure proof means; removing the stored, exposed photosensitive laminate from storage and exposing same to said imaging exposure means with an image transfer means to produce an un¬ revealed image; revealing the unrevealed image by means of a washout TITUTE SHEET device; and revealing the integral membrane. SUBSTITUTESHEET

Inventors: BIRKHOLM JAMES G, BIRKHOLM, JAMES, G.
Applicants: BIRKHOLM JAMES G, BIRKHOLM, JAMES, G.
Application year: 1992
Main classification: G03F7
IPC codes: B24C1, G03F7