CA1247442A - Sequential automatic registration and imagewise exposure of a sheet substrate - Google Patents

Abstract

TITLE
SEQUENTIAL AUTOMATIC REGISTRATION AND
IMAGEWISE EXPOSURE OF A SHEET SUBSTRATE
ABSTRACT OF THE DISCLOSURE
Method for repetitive registering and imagewise exposing to actinic radiation a sheet substrate containing a photosensitive layer with use of a sequence of related photomasks.

Description

l `
~4~ 2 '1 TITLE
SE~UENTIAL AUTOMATIC REGISTRATION AND
IMAGEWIS~ EXPOSURE Of A SHEET SUBSTRATE
8ACKGROUNO or T lE INVClTlO~
5There is a continuing need in the printed circuit, graphlc arts, and other related industries, to transfer images photographically From a sequence of original ~positiYe or negatlve) photomasks to one or both sides of a light sensitive sheet support.
Th~re is a particular need to prepare ~our-colQr surprint proo~s ~rom original artwork uslng suitablc photomasks. In making tho surprint proof, ~or example, it is very important to align each photomask with the p~eceding image so that the final image is p~ecisely in re9ister with the preceding image.
There is also a need to make multilayer circuit boards on one or both sides o~ a support also using a multitude of photomasks~ In the case where multilayered printed clrcuit boards are being made with multiple images on one or both sides of the board, lt is also important to precisely register these images with each other. In all instances, the phntograQhLc process must be carried out in a manner which maintains the de~inition, locat~on and image ~eatures of the original and minimizes the image dislocation. Finally, it is important to automate as much ~ this process as possible in order to reduce operator handling and improve reproduclbility.
Four-color surprint proofs can be prepared 3~as taught for exampla in U.~. Patent No. 3,649,268 and U.S. Patent No. 3,854,950 (positive working process) and U.S. Patent No~ 4,174,216 (negative working process). In these processes, a pnotopolymer ~ilm element is first laminated to a suitable support PD-1984 35 such as paper card stock. This film is th~n given an lmagewise oxposure to actinic llght through one of four photomasks (e.g. color separation films reprosenting each o~ the four colors ~rom the ori9inal artwork) which bears one of the primary colors. Normally, a vacuum ~rame device i5 used during the exposure process to insure good photomask/photosensltive layer contact. In the posltive working process, the photopolymer ~ilm is lnherently tacky and ~hose areas struck by li~ht during exposure r harden and bec~me less tacky. In the negati~e worklng process, the photopolymer Pilm is ass~ciated wlth a tacky, adherent layer and exposure oauses the photopolymer layer to ~racture imagewlse. When the cover layer assoclated with this structure ls then peeled off, the exposed areas relative to this process are removed uncovering imagewise areas of the tacky adherent layer. The remaining, une~posed areas are not tacky. In both of thes~ processes, the final image is developed by app}ying a colored, powdered t~ner to the tacky areas. The color o~ the toner should correspond to the color recordsd in the photomask image. The toner adhare~ to the tacky portion of the image revealing the copy. For each additional color record, an additional !ayer of photopolymer is laminated over the preceding image and exposed to its photomask.
Each exposure must be made in precise registry with the preceding exposure ln order to malntain the correct image location. Typically, a set of four photomask image records usins colored, powdered toners of yellow, magenta, cyan and black are used to prepare a final image in this sequential operation.
This process, then, will produce an exact surprint proof of the original artwork and is an excellent method for proofing originals for the printing 7~

industry. Each colored toner carl be matched closely to the desired printing ink and t:hu~ the process is very use~ul. It is desirable to automate the surprint making process since the need to expose each photomask in a vacuum fra~me apparatus is tlme consuming. Addltionally, registration of eaoh record is di~ficult to do by hand and even more dlf~icult to automate.
MuLtilayer printed circuit boards can also be prepared by a sequentlal lmage trans~er proce~s using a dry photopalymer ~llm and an addltLv~ platlng proc~ss such as that desoribed in U.S~ Patent Nos.
4,054,4a3; 4,û54,479; and 4,157,407. In the general proces3es dsscribed in these patents, a photopolymer ~ilm ~lement is laminat~d to a sheet ~ubstrate matcrial te,g., a thin insulated board) and the photnpolymer layer is exposed lmagewlse to actinic radiation through a photomask bearing a printed circuit image. When the sheet substrate contains circuit components such as through~holes or a circuit conductor pattern~ the photomask must first be registered to the component before the exposure - step. Eithsr the imaging exposure itself, or subsequent process steps will produce adherent image areas on the laminated substrate into which powdered catalyst can be suitably imbedded. The powdered catalyst (e.g., copper powder) is then appLied to the imaged sur~ace to produce a catalytic circuit pattarn which is then plated (e.g., with an electroless plating bath). These process steps will produce a highly conductive circuit pattern from the original artwork. For each additional layer of circuitry needed to complete the multilayered circuit, a fresh photopolymer film is laminated to the sur~ace of the previously imaged and plated laminate, exposed again '7~
l, imagewi~e to Its photomask which is held in precise registry with khe previous image, and the entire process outlined above repeated. Using this process, multiple circult layers can be applied to ane or ~oth sides o~ a substrate and circuit layer interconnections and through-holes can be ~ormed~
Typlcally, manual trans~er and positioning o~ the substrate element has occurred between eaoh stcp o~ the process described above. The steps ~F
application of the catalyst are also carried out by hand~ Attempts have been made to automat~ these processes but this has been adupted only tQ a limit~d extent such as the application o~ the catalyst.
Automation will result in a substanttal C09t savings to the user and is a highly desirable ~eature.
Nevertheless, many o~ the above-described steps o~
th~s process remaln labor intensive and prone to human ~rror. This is particularly true o~ the registrat~on and exposure steps.

2~ Contact printing is virtually the universal method o~ exposure used today in the surprint proof and printed circult photo~abrication industrles despite certain known shortcomings. Although low in equipment costs, simple to use, and capable of excellent line and hal~tone de~inition, contact printing is labor intenslve and slow because of the praviously mentioned vacuum drawdown times. It is also subject to losses due to damaged and dirty photomasks resultin~ ~rom repeated use. This, in turn, requires ~requent and expensive touch up and replacement o~ expensive photomasks to avoid yield losses. Much time is also lost in the constant and tedious process o~ inspecting the photomasks ~or defects between exposures. In addition, variations in ,rame temperature and ambient humidity a~ect ~2~ q~
s carner~to-corner registration, especially when uslng larger formats.
Alternative exposure methods such as gap printing, pro~ection print:ing and laser scanning each o~fer some signlficant advantages over contact printing. However, in the current state of development, all have serious limitations for high productivity applications and are intrinsically hlgher ln equipment costs~, 5UMMA~ OF THE INVENTION
The present invention is dlrected to a process ~or registering and ima~ewlse exposing a sheet substrate containing a photosensltive layer, wlth the use o~ a sequence oP related photomasks comprising the steps o~:
(l) advancing the supstra-te containing a photosensitive layer to a po~ition in a device to undertake either in order or concurrentl~ the steps o~:
ta) allgning the substrate and a photomask o~
. . the sequence in a predetermined relationship to one another, ~b) applying a liquid between the photosensitive layer and the photomask;
(2) contacting through the liquid th~ substrate containinq the photosensitive layer and the photomask whereby during said contacting substantially no movement of the photosensitive layer relative to the photomask occurs other than a more intimate contact due to displacement of the liquid in a llquid layer whereby at least one of inter~acial or viscous force due to the liquld layer aids in holding the photosensitive layer and photomask in a fixed position relative to one another;

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(3) ~xposing khe photosensitive layer to actinic radiation through said photomask causLng an image to be ~ormed thereon;

(4) removlng the photomask ~rom the exposed photosensitive layer;

(5) modifyin~ the sur~ace o~ the exposed photos~nsitive layer;
~6) repeatlng steps l to 5 for each o~ the remaining photomasks ot said sequence.
lû In particular embodim6nts o~ this invention th~ cur~ace n~ th~ expos~d photosensitive layer may be modi~ied by an image lntensi~ication st~p, e.g., such as ombedding ima~e areas wlth a powdered toner or cataly~t and/or by applying a second photosensltive layer thereto. In yet another ~mbodiment a~ thls invention, both sides oF the substrate contain photosensitive layers and the pro~ess steps outlined above occur simultaneously to both photnsensitive layers.
~
FIG. 1 shows a side view o~ apparatus-use~ul ln the process o~ this invention applying a photomask in registry with a substrate having a photosensitive layer applied to only one side.
FIG. 2 shows a side view of the process of this invention applying photomasks in registry with a substrate having photosensitive layers applied to both sides thereof.
D~TAILEO OESCRIPTION OF THE INVENTION
In the process o~ this invention a substrate containing a photosensitive layer with or without a top support sheet is introduced into a registration and exposure device.
The photosensitive layer composition 35 pre~erably comprises a photopolymerizable composition ~2~

which c~n be negative or positive working. Convention-ally the substrate is rectangular. The registration portion of the apparatus consists of one or two film elements, preferably rectan~ular and flexible, at least one of which is a photomask. The leading edges of the elements can be joined in parallel, hinged, relationship on each side of a thin rectanyular carrier whose thickness approximakes the thlckness o the photosensitive sheet. The hlnged relat~onship maintains the registration between the photomasks and the carrier. When both film elements are photomasks, they are mai~tained in precise register with each other by virtue of their hinged relationship to a common carrier. The apparatus disclosed in concurrently filed application Serial No. 387,534 ~P~-1923) now Ratent Nos~ 4,518,667 and 4,527,890 can be employed in the present invention except it is ordinarily necessary to employ a different photomask when each photosensitive layer of a sequence is to be registered and exposed.
With the photomasks hinged outward from the carrier, the sensitized substrate is positioned or aligned between the film elements so that one substrate edg~ is in registration contact and approximately parallel to the length of the carrier.
In some instances registration cor.tact can be simple edge-to-edge contact of the substrate with the carrier wherein the only added criterion is that the image pattern portion of the photomask is completely contained within the area of the sheet to be imaged.
However, registration contact more generally requires the precise alignment of details contained on the photosensitive sheet of the substrate with details of the photomask image or images. In this instance at 3~ least two contact points on or in the sheet are brought into a fixed relationship with two -~r 7~
a corrospondlng contact paints Pixe~d to the carrler.
Such palnts may be notches and tabs suitably spaced cn the sheet and carrier edges. Alternatively khe points may consist o~ reg1stration pin and hole S combinations wherein the sheet contain~ precision drilled registration hole!s which are positLoned in the d~sired orientation to the bar by registration pins. For each substrate! the registration ls substantially identical f'rom photomask to photomask to obtain a~ter suitable processlng a serles oP
dif~erently 0xposed photosensitive layers precl5elY
reglstered on the substralte to produce a composite imaged element.
Once the substrate containing the photosensitive la~er is in registration relatlonship to the car~ler, the ~lexible film photomasks can be .~ppli~d to at least one side o~ the substrate cohtalning the phatosensitive layer in the presence o~ a llquid inter~ace by applying normal pressure in a line roughly parallel to the carrier on the outer sur~aces o~ the photomasks at or near the hinged edges and advancing (relatively) the pressure line in the direction perpendic~lar to the hinge line and parallel to the sensitized substrate surface and, concurrent with the advance, applying the liquid, e.g., by spraying, to the nip between the substrate and the inner sur~ace o~ the photomask ~ormed by the advancing pressure line. In Pf~ect a photomask is temporarily wet laminated to a side o~ the substrate to give a registered sandwich structure in which the substratz is separated ~rom each photomask surface by a liquid inter~ace. This lamination process step is pre~erably carried out by passing the hinged photomask-registered sheet assembly through a pair o~
35 pressure rollers. In this mode o~ operaticn, ~'7~
g prossure is applled a-t or near the hlnged leading edgo o~ the substrate and the fle~xible photomasks and the tralling portions o~ each photomask wrap p~rtially around the curved sur~ace o~ each pressure roll. Liquid, preferably w.ater, is th0n sprayed into the two nips on each slde! of the substrate.
Pre~erably, the registrat.ion apparatus is oriented so - that the general direction of th~ wet lamination is upward, i.e., the substxate travels in an upward l~ directinn relative to the pressure rolls and llquid applicators. When so ori~nted, a cleaning action of the liquid can be achiev~d on both the photomask and the photosensitive }ayor ar support sheet which i~
~nhanced by the use o~ excess liquid directed at both sur~aces and which will simply drain lnto a catchlng basin carry1ng any extraneous matter with lt. In addltion, the area above the pressure roll~ where actlnic exposure pre~erably occurs can more easily be kept ~re0 of unwanted liquid. This process o~
o~taining alignment o~ a substrate and photomask is obtained without the use o~ vacuum. HoweYer, a vacuum can be used to remove excess liquid, It is understood that in the present spec$fication l'substantially no movement" means that sur~aces o~ the photosensitive layer and the photomask do not move relative to one anather in dlrections parallel to their sur~aces, i.e., the - surfaces do not slide relative to one another to change the alignment o~ the photomask to the substrate. Howevsr, lt is understood that "substantially no movement" allows relative movement .o~ the photomask and the photosensitive layer in tne direction perpendicular to their sur~aces to ~orm a more int$mate contact, e.g., as liquid is squeezed ~rom the interface bet~een the photosensitive layer ~ t~ 4 ~
1~
and th~ photomask. Howe~ex, the photosensitiv0 layer and photomask, already contacted by the advancing pressure line, will remain ln a ~ixed relationship in clirectlons parallel to their sur~aces.
Also it is understoad that in the present speci~icatlon "contactingl' through ths liquid layer a substrate containiny a photosensitive layer and a photomask does not exclude intermediate layers. For example the photosensitiva layer may have a support sheet which allows actinic radiatlon to pass nr the photomask may contain a release coating. Such support sheet or relzase coating could contact the liquid layer.
In the present speci~ication a photosensitive lay~r is employed to msan a pre~ormed layer and excludes a photosensitlve layer present as a liquid.
ûnce a photomask has been ~ixed in register over the photo ensitive layer, thé substrate with its photosensitive material may be expos~d to any source of radiation actinic to the photosensitive material ~or a prescribed period o~ time. In a preferred mode of operation, the laminated element emerges from the pressure rollers, is stopped and sus,oended in a fixed upright position and uniformly exposed to actinic radiation in the 3aoo to 4000 A or above region.
Whsn both sides o~ the substrate are photosensitive, both sides preferably are exposed simultaneously. In an alternative mode of operation, the sensitized substrate is irradiated with actinic radiation as it emerges from the pressure rolls and is carried past the irradiation region. In this mode, the irradiation may be focused to a band or a transversely scanned spot o~ intense actinic radiation may be used whose intensity is adjusted to '7~

match th~ cxposure characte~lstics o~ the photosensltive sur~ac~ and the rate of transport. It is also possible to completely r~move the sensitized substrate ~om the registratlon device and expose it on any suitable exposure unlt. In this instance the photo~asks and carrler remain ~ixed in registration with the photosensitive layer by the action of surface or viscous forces induced by the inter~ace liquid. It is understood that both surface and lû viscous ~orces may be present.
In th0 above process steps the rectangular, flexible film ~lements hclve been identified a5 photomasks. When both sid0s of an element to be lmaged are photosensltiv~, as with two si~ed circuit boards, both ~ilm el2ments contain opaque and transparent image areas. However, when only one sida of a phatosensltlve element is to be imaged, e.g., a one~slded circuit board, only one film ele~nt (af a pair, if present) ls required to be a photomask.
When imaging exposure is complete, the photomask is p~eled ~rom the sur~ace of the exposed photosensitive element thus releasing the imaged elemsnt from registration. The imaged element is then transferred from the registration-exposure apparatus and the hinged photomask-carrier assembly is returned to its initial position. After the photomask is removed from the exposed photosensitive layer the surface of the exposed photosensitive layer is modified by an image intensification or fixing step and/or by applying an additional photosensitive layer thereto. Typical image in~ensification steps include toning by embedding ~inely divided particulate material directly into tacky image areas produced on the photosensitive layer, e.g., such as ~ith colorants as describe~ in Chu and Cohen U.S.P.

~ 7~

3,649,26~ and Abele et al. U.S.~ 4~2~3,7~1t or with catalytic or metal powders as disclosed in Pei~fer U.S.P. 4,05~"4a3. Alternative or additional intensification steps can be used such as dissolution development such as described in U.S. Patents Pei~fer, 4,054,483; Pe~f'er, 4,157,407; and fan 4,053,313 or as so-callecl peel-apart development as described in U~S. Patents Cohen and Fan, ~,174,21G
and 4,191,572. ~hen dissolution or peel apart development are used, th~ photosensitlve element may itself contain a colorant or have a photo~ormed color~d image. Image intensi~ying or fixing processes ean include uni~orm exposure o~ the imaged layer to the -qame or dif~erent actinic radiation or heat. In instances where a metalllzed or catalyzed image is ~ormed the add~d steps of plating or soldering may be included. Image lntensi~lcation by toning may include dry or liquid toners. In - lnstanc-es wher~ surprints are formed the sur~ace is typically modi~ied by the application of additional photosensitive layers a~ter some ~orm o~ image intensl~ication as described above has ~een carried out. Therea~ter the exposed photosensitive layer is processed, e.g., as taught in U.S.P. 37649J268~
U.S.P. 3,854~950 and U.S~P. 4,174,216 in making a ~our color surprint proof or as taught in U.S.P. 4,054,48~, U.S.P~ 4,054,479 and U.S.P. 4,157,407 in making a multilayer circuit board.
In one mode, after the modification step a ne~N photosensitive layer may be applied to the processed imaged layer and registration and exposure step may be repeated. In a pre~erred mode o~
operation, after exposure, the pre-exposure process steps, ~or the most part, are reversed. Thus the exposed laminated element passes back through the pressurc means such as roll~rs and the photomask 1~
pulled back over lts r~spectlve pressure raller into a storage area until the hlnged area on the carrier is reached. Other means than rollers may be used ko apply pressure, e.g., a sque2gee.
The sheet substrate during the registra'cion and imagewise exposure process may be in any orientat~on lncludLn~ a horizontal plane or v~rtical plane. Pre~erably the substrate will be in a substantially vertical plane. In the process o~ this invention any means can ~e used -to convey the substrate to and ~rom th~ registration position ln the appa~atus.
The liquid which is applied to the photosensitive layer or support sheet and photomask serves several vital ~unctions in the process o~ this invention. The liquid serves to uniformly fix the photomask in lntimate registered contast to the photos~nsikive surtace or support sheet during actlnic exposure and a~ter exposure allows the photomask to be easlly removed ~rom the expnsed sensitized substrate wlthout damage or transfer o~
either. The excess liquid serves to clean the sur~ace o~ the photomasks an~ individually clean each photosensitive sur~ace or support layer thus preventing deterioration of the photomask image and/or the resulting exposed image particularly by element born dirt. aesides these vital functions the liquid also serves to condition and cool the photomask during the exposures. 8y spraying liquid on the photomask, the environment and temperature o~
the photomask is maintained constant and less susceptible to changes ln ambient temperature or humidity. In this respect, it is also desirable to spray liquid on the exterior surface of the photom~sk, provldnd the llquid forms a uni~orm film on the exterior sur~ace or is removed there~rom be~ore actinic exposure. The liquid intex~ace should be substantially transparent to actinic radiation and should not damage the photomask (or the photosensitive sheet surf~aces or cover sheet unless sur~ace modi~ication is desired). Also it should not interfere with the exposure of the photos~nsitlYc layer. The liquid should pre~erably wet both 5ur~ces o~ the photomask and photos~nsltive layer ur support sheet, have low volatility at ambient temperatures, and have su~lcient viscosity to ~ul~ill the vital ~unctions of the lLquid. The pre~srred liquid is water or aqueous solutions contalning ~d~uvan~s which improve liquid characteristics~ e~g., surface active agents, viscosity ad~usting agents, etc. Other liquids, of course, can be used d~panding on the conditions - - required, e.g. 9 al¢ohols, glycols, glycol ethers7 2û halogenated hydrocarbons? para~ins, etc., provided they ~ullfil the above criteria. Since the llquid remains a llquid a~ter the exposure step, a photossnsitive liquid is not used ~or this component of the process.
The process o~ this invention is useful ~or imaging any substrate ccntaining a photosensitive layer which is compatible with the liquid treatment.
I~ the photosensitive composition is not compatible with the liquid, preferably a support or cover sheet is used to protect this composition. In such case the support sheet will contact the Iiquid. The process is particularly useful ~or exposing elements having a photopolymerizable surface or surfaces which are typicaLly used ~or producins multilayer printed 3S circuit boards, or ~our-color surprint proofs.

7~2 ]5 The registration and lmacJewise exposure proceqs of the present invention i~ applicable to a wide variety of sheet substrates provided at least one surface contains a photosensitive layer which may have an optional support or cover sheet. In one mode, opposite surfaces of the sheet sub~trates carry photosensitive layers with ~he registration and imagewise exposure performed simultaneously or substantially simultaneously on both surfaces.
In one of the modes o~ the invention, the sheet sub~trate will contain a ~mooth surface, e.y., paper card stock, onto which the photosen~it:ive layer is laminated.
~lternatively, the substrate sur~ace onto which the photosensitive layer is laminated may con~
tain circuitry in rellef and need not be smooth. In such case, the registration and imagewise exposure process can take place in sumilar fashion to a smooth surface, including simultaneous or substantially simultaneously registration and imagewise expo~ure of opposite surfaces which have photosensitive polymer layers.
The composition~ of substrates and the compositions of the photosensikive layers are well known in the art, e.g., in the patents referred to previously and also in concurrently filed Canadian Patent Application ~erial ~o. ~30,017 of Heiart et al.
Figure 1 is a pictorial representation of an apparatus useful in carrying out the process of the invention. This process will now be described with raference to this apparatus. In this process, a substrate with a photosensitive layer and its corresponding set of photomasks are aligned and punched (or drilled) along one edge using a commercially available punch (or drill). The 2' prnpunched sensitized substra~e deslgnated as ~ s taken, and the holes in its lead.ing edge are ~itted over the corresponding pins in p:ln registration set t2). The punched photnmask (6) :Ls then af~i~ed in a parallel~ hinged relationship to photomask carrier (S) the prepunched holes in the photomask (6) corresponding to the regiLstration pin receiving hol~
(9) ~n carrier (5). The photomask carrier (5) is then lowered and registered to substrate (1) using pin rcgi5tration set (2)" (Alternatively a photomask with holes can ~it on th~ same plns as the substrate.) Stop pins (4) are retraoted and nip rolls (3) and ~31) are then actlvated bringing upper roll ~31) in contact with lower roll ~3) thus ~ormin9 a nip bet~een the substrate (1) and photomask ~6). Slnce Figure 1 ls only a slde view, only one pin in the registration pin set and one hole is shown. In reality, two or more holes are present ~n the photomask carrier and a like nu~ber o~ pins in 2û the reglstration pln set are provided. Liquid spray (7~ is turned on so liquid is sprayed at the nip ~ormed b~tween the photomask (6) and the substrate (1). The substrate (l~ in register ~ith photomask

(6) is then moved to the exposur0 position (5~), and exposed using exposure unit (8). Intimate contact is achieved prior to exposure by squeezing out the excess liquid between substrate (1) and photomask (6) with the aid o~ nlp rolls (3) and (31) A~ter exposure the mechanism is reversed. Substrate (1) in register with photomask (6) is moved back, nip rolls (3) and (31) are moved apart, photomask carrier (~) is li~ted so it is out of contact with the pins in registration pin set (2) and the exposed substrate (1) and photomask (6) are released. The process is then repeated, 9.9., a~ter applying a ne~

photosensltive layor to the substrate, uslng a remalnlng photomask of the set.
In Fig. 2, is shown a registration and imagewise.exposur~ process in a Yertlcal mode. The 5 substrate contains photosensit~ve Layers on both sides and at least 2 pin register holes along lts leading edge. Before a substrate is Inkroduced, the .~ollowing conditions are established:
Nip rolls ~12 and 12') are open;
Clamp ~13) is open;
Photomask assembly ~15) which contains a palr of matching photomasks (16 and 16'3 and its carri0r ~s registere~ to clamp ~13) by carrier regi.~ter p~ns ~19) with the photomasks kept taut around nip rolls (12 and 12');
Pin register bar (14) is not engaged;
Liquid spray (17 and 17') is on; and Exposure Sources (18 ~nd 18') is on standby.
Substrate (Ll) is then li~ted up to register posltion lnside clamps ~13) through nip rolls (12 and 12').
Pin register bar ~14) closes; ~irst engaging carrier register pins (19) on clamp (13) and then picklng up predrilled register holes (not shown) on substrate (11) with its own pins. Registration o~ substrate (11) to photamasks assembly (15) is achieved when the pins are engaged. Next clamp (13) is closed to maintain ragistratlon and pin reg~ster bar (14) is subs~quently retracted. Clamp (13) is moved down, carrying photomask assembly (15) and substrate (11) to nip rolls (12 and 12'). Then nip rolls are closed and clamp (13) is moved up to exposure positicn (18). Intimate contact o~ photomasks (16 and 16') and substrate (11) is achieved by squeezing out excess liquid with nip rolls (12 and 12'). '-xposure on both sldes is macle. A~ter ths bxpasure, the mechanlsm is reversed, clamp (13) moves down to lts inltlal registered positlon and then both it and nlp rolls (12 and 12') are opened. The exposed substrate (11) is released to allow processLng, e.g., with toner and appllcation of new photosensitive layers and the process is then repeated using remaining photomasks in a set. Although imaging exposures of both sides are depicted in figure 2, it is apparent 1~ that imaging exposure o~ only one side may also be carried out using the apparatus disclosed.
This invention will n~w be illustrated by the Pollowing spec~ic examples o~ which Example 1 is consldored to be the best mode. All parts are by w~lyht unless otherwise included.

This e~ample demanstrates the making oF a positive four-color surprint proof using multiple layers and exposures in registry and is iLlustrated schematicalLy by FIG. 1.
A photosensitive composition simllar to that described by Held, U.S. Patent Na. 3,g54,950, Example II, is prepaxed and coated by means o~. a 0O003 inch doctor knife on a 0~001 inch thick polyethyl2ne terephthalate ~ilm support at room temperature. This material is allowed to dry at room temperature and a sample of the dried ~ilm is laminated at 100C to the smooth side of a Kromkote~
cast-coated one side cover paper support (the Champion Paper and Fiber Company) using heated, pressure rallers. A sample of 0.001 inch thick tacky polyethylene terephthalate film is laminated to the other side of the paper support to protect the support during the processing steps to image the ~5 photopolymer layers on the opposite side thereof.

The ~sulting composlte support/photopolymer element is deslgnated as the support ~1) ln fIG. 1 and is then placed in the position showll in the drawing.
Nip rolls ~3) and (3') are then activated~ Roll (3) is lowered onto the support causing registration pln (2) to enter through a prepunched hole in the support and into a like hole matched in registratlon in the photomask carrier (5). Since FIG~ 1 is only a slde view of this embodiment, only one pin set and one hole is shown. In realil:y, two or more holes are present ln the carrler and are prepunched in the support and a llke number of pin sets are provided to ~it same. A photomask ~6) cantaining th0 blue recard image of a ~our~color separatlon Lmage (the yellow Prlnter Pasitive) is attached to carrier ~S~ and extends around the upper nip roll (3) as shown. The upper nip roll is shown ln the raised position (dashed lines) and in the lowered, contacting posltion (-solid line).~ Water ls applied between the photopolymer layer on the substrate and the photo~ask. In thls particular example, the sheet o~
polyethylene terephthalate on which the photopolymer is coated still remains on the composite elament as a cover sheet. Thus, the water is applied between this cover sheet and the photomask. After water is applied and the upper nip roll lowered, the stop pin (4) is removed and the carrier transported (means not shown in this drawing) into an area directly under the light source (8). The light source is a aerkey~Ascor Vertical exposure source using a 2 KW
photopolymer lamp and a Kokomo~ No. 400 glass filter (Kakomo Opalescent Glass Co., Kokomo, IN) and a 30 second exposure is given with the light source at a distance of 38 inches from the photomask/photopolymeL
surface; Thz application of water between the

7~2, phatomask and photopolymor allows superb image contact with the photosensitive element and thus excellent resolution ls achlevable. After exposure, the procedure is reversed and the substrate contalning the now exposed photopolymer layer is removed from the automatic registration and e~poslng device. The cover sheet 1s removed ~rom ~he photopolym~r layer and a toner of ca. 30~ Dalamar Yellow (C.I. Pigment Yel:Low 74) in ca. 70% cellulose acetatc is applied using a catton pad. The excess ton~r i5 removcd by wiping w1th a cloth and a positlve yellow image is lefk on the photosensitive layer. ~his image is a duplicate ln yellow or a positive of the photomask. A second layer o~ the sam~ photopolymer is then laminated over the yellow image and the photomask in the automatlc registration and exposure device is replaced with one containing the green record lmase of the four-color separation (the Magenta Printer Positive)~ The subskrate is again inserted into the automatic registration and exposing device and transported in liquid contact with this second photomask as previously descrlbed.
The exposure is repeated and th0 substrate removed from the device and the cover sheet is removed. The resulting image is developed by applying a magenta toner comprising ca. 3C% quinacridone magenta tC.I.
Pigment Red 122) in ca. 70~ cellulose acetate to reveal a magnetic image over the previous yellow image. Another layer of the same photopolymer is laminated over the two-color material and the photomask is replaced with the red record image of the ~our~color separation (the Cyan Printer Positive) and the processes described above repeated. After removal o~ the cover sheet the image is developed by toning with ca. 25~ phthalocyanine blue (C.I. Pigment 7~ ~3 Blue L5) ln ca. 75% cellulose aceta~e toner. A
fourth photopolymer layer is then laminated over this three-oolor image and the photomask is replaced with the alack Printer Positive o~ the four-color separation and the entire process repeated ~or yet a ~ourth time. A~ter removal o~ the cover sheet the final i~age is developed by t,onlng w~th ca. 25~
carbon black (C.I. Pigment 01ack 7) also dispersed ln ca~ 75% cellulose acetate taner. The ~inal image achieved by this example ls to result in an excellent ~our-color surprint hal~ton~ positive of the original imag~.
~e~
Re~erring now sp~cifically to FIG. 2) this example demQnstrates the utility of the process of this invention wherein photomasks are used in ~egistry with a support coated on both sides wlth photosensltive layers.
In ~his example, a photopolymerizable element is prepa~e~ comprising the following major ingredlents:
40~ o~ an unsaturated polyurethane having O.S% unsaturation and a molecular weight of 1900;
20% of an acrylonitrile/butadiene/styrene copolymer having a speci~ic gravity of ca.
1.07;
30% trimethylolpropane triacrylate;
5% benzophenone; and 5~ 4,4'-bis(dimethylamino) benzophonone.
This composition is dissolved in methylene chloride and is caated on a suitable 0.001 inch thick polyethylene terephthalate film support which is strippable from the photopolymerizable layer. A
~5 0.001 inch thick polyethylene cover sheet having less ~47~
~ 2 adhor~nco to the layer than the ~;upport is laminated on the oth~r side of the photopolymerzable layer ko form a sandwich tacky element.
The polyethylene cover sheet is removed from the layer and the surfac~ ~ust uncovered is laminated by means of heated, pressure rollers to a typlcal glas~s~epxoy G-lO circuit board (see Printed Circuits Handbook. edit. by C. f. Coombs, Jr., McGraw-Hill ~ook Co., 1967, pages 2-1.8). In the same manner, another portion o~ the same pho~opolymerizable element is laminated to the opposlte surface a~ thls board. This results in ~ ~ouble-side coated board.
Through-holes are then introduced ln the appropriate places in this composite element using a hl~h speed (ca~ 15,000 rpm) drill and an approprlate drill bit.
The b~ard sur~aces are cleaned a~ter this drilling operation to remove any bits o~ photopolymer that adhere to the surface. This cleaning is accomplished by wiping wikh a rag dampened wlth methylene ohlsride. The resulting composite ele~ent is shown as (ll) in FIG. 2 and called the substrate.
Complimentary contact p~sitive transparenc1es (photomasks) of oircuit patterns are th2n mounted in the automatic registering and exposing device and are shown as (16) and (16'). Thesa photomasks are mount~d on photomask assembly (15) above a pair of movable, opposable nip rolls (12) and (12'). Each photomask is aligned and prepunched to receive pin (ll) attached to pin bar assembly (14).
Concurrently, the pin bar assembly is set to receive pin (l9) attached to the clamp (13). rhe substrate ls also prepunched in the appropriate places to receive pins. It should be here noted that FIG. 2 is a side view of thls embodiment and that other pins ~5 and holes are prasent along the length to permit ~ 3 perfect regis~tration. When the device i actuated, liquid twater) from (17) and (17') i9 sprayed between the photo~ensitive layers on the composite element (11) and the photomasks ~16) ancl (16') and ~he nip rolls (12) and (12') are closed. Concurrently, pins ~20) and (19) engage into their respective holes prepunched through the composite substrate and the photomask and the holes provided in the clamps and pin sets respectively. A means (not shown) a~tachecl to -the clamp~ moves the entixe as~embly into an exposing posikion between a pair of light bankn exposure ~ources (18) and (18'). These light banks have 14 fluorescen~ light bulb~ located in each bank.
The~e bulbs (high intensity 48 inch, Du Pont P/N
276208-001, base RDC, bulb T12*, E. I. du Pont de Nemours ana Company, Wilmington, DE) are used to expose the photopolymer layer on both sides of ths circuit board substrate through the appropriate photomask. Exposure is carried out for abowt 10 ~econds. After exposure, the movement of the nip rolls is reversed and the exposed, composite element is removed from the device. The strippable support is removed from each imaged layer and copper powder having an averaye particle size of 11 microns is dusted onto the exposed surfaces and into the through-holes. Excess powder is removed by spraying with water to give a clean, clearly defined, cata-lyzed copper circuit pattern. The board is then immersed in an electroless copper plating solution ~see Example rl of Zeblisky et al., U.S. Patent No.
3,095,309) and copper is deposited in the holes and on the circuit patterns for about 1 hour to form a complete, copper circuit.
Another layer of the same photopolymerizabl~
material is laminated again over the copper circuit * denotes trade mark pattern ~ust formed. A second photomask complim~ntary set o~ another desired circuit pattern is inserted at (1~) and (16') in the automa~ic reglstration and e~posing device and the just 5 laminated element is again inserted as (11). The elements are wetted with water, contacted with the photomasks, exposed, the cover sheets remoYed, and copper powder applied as desc~ibed above.
A thlrd photomask set complimentary to the second set is inserted at (16) and ~16') in the automatic reglstration and exposing devic~ and the ~ust imaged element with the copper powder patt~rns thereon ls again inserted as ~ The elem0nts are wetted with water, contacted with photomasks, exposed 15 and the cover sheets removed as described aboYe. The ima~ed sample is then d~veloped in methyl chloraform as descrlbed in Example 1 o~ Pei~fer U.S.P. 4,157,407 to remove the c~pper powder and photopolymerizable composition only in the areas which are not exposed 2n to actinic radiatlon in either the second or third imaging exposure. This element is baked at 160-16SC
for 2bout 65 minutes and placed in the electroless copper plating solution ~or about 8 hours. The result is a multilayered printed circult board with 25 two printed clrcuit layers interconnected by plated through-holes sandwiched between and, except ~or electrical intsrconnects produced by design, electrically insula~ed ~rom kwo additianal printed circuit layers~ All desired elements ars in registry.
. ~ e~
The following ~ormulation is prepared:
5 9 styrene/maleic acid anhydride copolymer 2 9 triethylene glycol diacetate 100 ml acetone '7~2 These lng~edlents are stlrred to dissolve the solids and the following dihydropyridine compound is added:
(1 9) 2,4,6-trimethyl-3,5-bis(carb-terbutoxy~-1,4-dihydropyridine along with 2 9 of the following hexarylbiimidazole compound: 2,2'-bis(2-ch10rophenyl)-4,4',5,5'-tetraphenylbiimidazole. Thls solution ls then coated on a polypropylene support and dried. The coated and dried sample is exposed under the same conditions as those described in Example 1 in a similar d~vlce using a screened negative yellow scparation o~ a colo~d master copy ~or a photomask~ ~ontact between th~ photomask and the photopolymer element 15 accomplished wlth water as described in Example 1.
After exposure, the element is removed from the automatlc registratlon and exposure device and the image developed using the same yellow toner described thereon. Another photosensitive layer is then - laminated over ~hls yellow image and exposéd in reg~st~y to yet another co10r separation as the photomask. The exposure is carried out in the same manner and the image developed using a cyan toner similar to that described in Example 1. The resulting image is a two-color cnpy of the original in registry.

A negative working color proof o~ the surprint type is made ~ollowing the teaching of Cohen et al~, U.S. Patent No. 4,174,216, Example 2 and laminated to a Kromkote~ paper support as described thereLn. rhis eIement (designated as the substrate) is then exposed to a suita~le halftone negative minus-blue color separation film r0cord (designated as the photomask) in the same manner as described previously in this application (Example 1) :lZ4~
~ 6 uslng watsr as the liquid. The au~omatic ~egistratLon and exposure devlc~ ls used in this example also. The element is given about lO seconds e~posure and held for abaut 5 minutes after removal ~rom the device. The energy treated clear cover sheet is removed and image photoadhered to the electrostat~c discharge treated film thus exposing ~quLvalent areas of negative, tacky elastom~r contlguous layer. These bared areas are toned with lû the yellow toner o~ Example 1. Using a second photosensitiYe element, the release film ls strlpped of~ and cantlguous layer i~3 laminated ta the sur~ace of the yellow image ~ust produced and thls element ls exposed in the automatic registration and exposing d~vlce using a negative minus~green color separatlon ~ilm record held in perfect registration by this device. This composite is exposed as described above and the surface treated cover sheet is strlpped there~ram leavinq bared a positive image which is toned with the magenta toner o~ Example 1. rhe proc~ss is repeated for the minus-red and black negative records to give a high quality surprint color proof useful in the lithographic printing arts. The images to be obtained are clear, sharp and in registry.
The automatic registration and exposure - devices described in this ~nventlon are use~ul i.n the processes described in the examples, among others. A
single devics can be used to automatically register a multitude o~ photorecords one on top of the other.
Alternatively, one might use a number of automatic devices in sequence to improve operability and product throughput. The unique ~eatures of this process utilize an ideal means to accomplish the registration and exposure and in addition utilize a ~ '7~
~ 7 unlque manner o~ contact between the photosensitive el0ment and the photomask - namely a relativ2 unmoving liquid lnterface. It ls thus possible to achieve multiple lmages on one or both sides o~ a sultable support all of which are in perfect alignment and registry. All uf the elements described are use~ul within the lithographic lndustry to proo~ or check images prior to the actual prlnting. It is extremely .important here that the final image be a true renditlon or copy of the original so that satis~actory prlnting can result.

2~

.

Claims (25)

28

1. A process of registering and imagewise exposing a sheet substrate containing a photosensitive layer with the use of a sequence of related photomasks comprising the steps of:
(1) advancing the substrate containing a photosensitive layer to a position in a device to undertake either in order or concurrently the steps of:
(a) aligning the substrate and a photomask of the sequence in a predetermined relationship to one another;
(b) applying a liquid between the photosensitive layer and the photomask;
(2) contacting through the liquid the substrate containing the photosensitive layer and the photomask whereby during said contacting substantially no movement of the photosensitive layer relative to the photomask occurs other than a more intimate contact due to displacement of the liquid in a liquid layer whereby at least one of interfacial or viscous force due to the liquid layer aids in holding the photosensitive layer and photomask in a fixed position relative to one another;
(3) exposing the photosensitive layer to actinic radiation through said photomask, causing an image to be formed thereon;
(4) removing the photomask from the exposed photosensitive layer;

(5) modifying the surface of the exposed photosensitive layer;
(6) repeating steps 1 to 5 for each of the remaining photomasks of said sequence.

2. The process of Claim 1 wherein modifying the surface of the exposed photosensitive layer comprises an image intensification step.

3. The process of Claim 2 wherein the image intensification step includes application of powdered toner or catalyst.

4. The process of Claim 3 wherein powdered toner is applied.

5. The process of Claim 1 wherein modifying the surface of the exposed photosensitive layer includes application of an additional photosensitive layer.

6. The process of Claim 1 wherein modifying the surface of the exposed photosensitive layer includes both an image intensification step and application of an additional photosensitive layer;
provided however a photosensitive layer need not be applied after use of the last photomask of said sequence.

7. The process of Claim 1 wherein steps 1 to 5 are repeated four separate times to obtain a four-color surprint proof.

8. The process of Claim 1 wherein a printed circuit board is obtained.

9. The process of Claim 1 wherein both sides of the sheet substrate contain photosensitive layers and are exposed to actinic radiation.

10. The process of Claim 1 wherein liquid between the photosensitive layer and a photomask is displaced when the substrate and photomask are brought into more intimate contact by an advancing pressure line.

11. The process of Claim 10 wherein said advancing pressure line employs a nip.

12. The process of Claim 1 wherein the application of liquid is to a substrate surface held in a substantially vertical plane.

13. The process of Claim 1 wherein steps 1 to 4 are with the substrate surface held in a substantially vertical plane.

14. The process of Claim 10 with the substrate held in a substantially vertical plane.

15. The process of Claim 1 wherein the photosensitive layer is positive working.

16. The process of Claim 1 wherein the photosensitive layer is negative working.

17. The process of Claim 1 wherein the photosensitive layer contains a photohardenable component.

18. The process of Claim 1 wherein the photosensitive layer contains a photohardenable addition polymerizable component.

19. The process of Claim 18 wherein the photohardenable component is photocrosslinkable or photodimerizable.

20. The process of Claim 1 wherein the photomask is flexible.

21. The process of Claim 1 without a support or cover sheet present to separate the substrate from the photomask.

22. The process of Claim 1 wherein the photosensitive layer is separated from the liquid layer by a support or cover sheet which allows actinic radiation to pass.

23. The process of Claim 1 wherein the liuqid comprises water.

24. A process of registering and imagewise exposing a sheet substrate containing a photosensitive layer with a sequence of related photomasks in making a four-color surprint comprising the steps of:
(1) advancing the substrate containing a first photosensitive layer to a position in a device to undertake either in order or concurrently the steps of:
(a) aligning the substrate and a first photomask of the sequence in a predetermined relationship to one another;
(b) applying a liquid between the photosensitive layer and the photomask;
(2) contacting through the liquid the substrate containing the photosensitive layer and the photomask whereby during said contacting substantially no movement of the photosensitive layer relative to the photomask occurs other than a more intimate contact due to displacement of the liquid in a liquid layer whereby at least one of interfacial or viscous force due to the liquid layer aids in holding the photosensitive layer and photomask in a fixed position relative to one another;
(3) exposing the photosensitive layer to actinic radiation through said photomask, causing an adherent image to be formed on the substrate;

(4) removing the photomask from the exposed photosensitive layer;
(5) developing the adherent image on the substrate by application of a particulate colorant.
(6) applying a further photosensitive layer to the exposed substrate whereby steps 1 to 5 can be repeated with a further photomask of said sequence; and (7) repeating steps 1 to 6 for each of the remaining photamasks of said sequence, whereby a four-color surprint is obtained; provided, however, step (6) need not be employed with use of the last photomask.

25. The process of Claim 24 wherein a support or cover sheet is present between the photosensitive layer and the photomask and is removed after step 4 and before step 5.