CA1072802A

CA1072802A - Ink containing radiation curable organic resin binder and electrically conductive filler of silver or copper

Info

Publication number: CA1072802A
Application number: CA234,723A
Authority: CA
Inventors: Donald A. Bolon; Gary M. Lucas; Ralph L. Bartholomew
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1974-09-27
Filing date: 1975-09-03
Publication date: 1980-03-04
Also published as: US3968056A; JPS5142606A; GB1519298A; DE2542737A1; DE2542737C3; DE2542737B2; JPS5619045B2; BE833857A

Abstract

ABSTRACT OF THE DISCLOSURE
A radiation curable ink is provided which is conver-tible to a conductive coating when cured on the surface of a substrate. A particulated electrically conductive metal-containing material is used in combination with an organic resin binder. Low temperature cure of the ink can be achieved with either actinic or ionizing radiation.

Description

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RD-7452 .
RADIATIO~ CT~LE INKS
Prior ~o l:he prsen~ inven~ion, various curable lnks w~re ~vailable consisting of conductive particles or flakes in a matr~x or binder in the form of an organic resin or a mixture o an organic res~n and volatlle solvent~ These :~
curable i~ks ar~ usad to make conduct~ve coatings for circuit boarlds and ground coatings on electrical equipment among other things. Unlike the etching method ~or making circu~t boards from copper clad la~ ates requiring a h~.gh :
degree of re~olut~on in which a nQgat~v~ photo resist ~s used in combination with a mask, the dir~ct ~mployment of ~he curabl~ conduckive ~nk is ofterl mors convenient ar~d :.
~co~om~c in partlcular applicationsO
OnQ ~orm o~ a curabl~ ~ used to ~akc conducti~7e c~a~ings consists of a metal powder or flal~ ~n c~m~ina~ion with an organic blnder aild an organ~c sol~ent~ Cure o the ir~c is achia~r~d upo;l ~vaporation of the organ~c sol~ent~ -Although curabl~ 8 bas~d on sol~en~ evapora~ion can be r~lld~d conduc~ wit:hout hea~ing, such inks are never- . .
~eld~s~ unsuitab~e on a var~e~y o plas~ic sub~trates. In addi~long a signiicasl~ amoun~ o air poïlu~ion is crea~ed, ' . ' ' 72~
~D~7452 A~other availabl~ curabl~ ink becom~s conduct~v~ upon firing at an elevated temperatureO It ls ba~ed on the use of a conductive powder in com~ina~ion with a glass as shown for example ~y J.E. Jolley, Solid St~a~, May 1974s pages 33-37~ In order to rendar the ink conduc-tive, ~ t is necessary to fire ~he ink at tempera~ur~s up to 900 C, As a resul~, the conductive ink can only be ~mployed on cera~ic substrates whicll are able to withstarld such extreme tempera~ur~ condition.s.
As shown by Ehrrcich et al, U.S. patent: 3~202,488 and Gillard pa~nt 3,412,043, additionlal conductive lnks ara available ba~ed on the employm~nt of an epoxy re~in which can be employed in ~he fonn of either a one~package or two-packaga sys~.em. A low temperature cure can b~ ~chieved with the two~package epoxy system requiring a mixing of the curing catalyst ~dia~ly prior to use. How~3~rer, ~wo package epoxy ink can be tacky for sevexal hours be ors the r~s~n cures. T~is drying cycle int~rferes wi~h ~he :
use o ~h~ ~e10~package ~poxgo sy~tem irl scraen prir~
` applications wher~3 ~a~ tack~fre~ cures are~ Iac~sa~y. ~-Xn addi~ion to remaln~rlg tacky ~oo long3, i~s xela~ively :

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~7Z~302 RD~7452 short po~-life limi~s its use ~o non-conti~uous ba~ch opera~lons, Although the one package system allows for fast~3r cures, higher ~empera~ur~s are requ~ red to xelease the curing catalyst. Such epoxy sys~ems ar~ therefore o~en undesirable on thermoplastic substrates bccause o possible subs~rate damage occuring at high ~empexatures.
In add~tion, where mass produc~ion procedures are conte~nplated~ the u8e of two-package systems are not ~as~hle,, Al~hough recent improYeman~s ha~e elimlnated thc need :~or ~ne consuming a~ch~ng procedures ~or making circui~ boards bas~d on the direc~ appl~cation of conduc- -irdcs wilich can be cured in various ways9 no curabl~
cond~c~i~Te prillting ink~ are a~ailablQ which can be r~ldly cur~d within two minut~s or less, and which can be used on a wids vari2~y o:l~ substrates9 including thenno-plast~c substrates ~
The present inv~nt~n is based on tha discov~ry ~hat ~ ::
certa~ra radiation curable organic r~æins, wh~ch include -- .
UV curable res~ns (i.e", ~hose that absorb ligh~ be~e~n .:
18~9 and 4000 A), and which ~iLll be de~in~d h~reina~ter~ .
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RDo7452 can be used in combination with certain particula~d elec~rically conductlv~ metal5 or electrlcally conduct~v~
me~al csntain~ng ma~erial~ such ~ m~t~l coated gla~8 spheres or f~ber~, to produce a radia~lon curable ink which is rendered conduct~v~ upon radiation cure~ A
surprising feature o th~ presan~ invention is that the shape of the particulated conduc~ive ma~erial largely de~Qrmlncs whether ~h¢ radiation curabl~ ink will cure sati~factor~ly to the conduct~v~ ~tateO For ex~mplQ, unsa~is~actory curas result, 1 t:he p~r~icula~ed alectri-cfllly conduc~ve ma~al containin~t m~arial i8 in the ~rm of flakesO Flakes ar~ d~in~d ~i.thin the mean~ng of the presen~ inv~ntion as being~n elec~rlcally conduc~ve m~tal con~aining matari~l which h~ve an ~spect ra~io D/T
o g~a~r ~han 20, whare '~ is eh~ diamQt~r of thc flake and "T'l is th~ thickn~ssO Exp~rience has shown tha~ the partlculated elec~rical~y conduc~iv~ me~al con~ai~ing ma~erial ~mploy~d in th~ praotic~ o ~he i~en~ion i8 pre~srably ~pherical~ ~ph~roidal or oblong sph~roidal in shap~ Althou~h le~s daslrable ~a~ ~pheras~ m~al ib~rs, or glass fibers coated with metal hav~ b`ee~ ~ound ~o ba

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mor~ ~ffec~ive than me~al flakes9 wi~h respect to allowing ~atisf~ctory cures of the photocurable ink w~en it is sub~ac~ed to radiatinn cureO It has been ~ound howev~r~
that up to about 15% by weigh~ of flakes based on the w~ight o par~icula~ed electrlcally conduc~ive metal co~ta~ning material can be tol~rated in the ink without -adverse results~
There ~s provided by the present ~nvent~on~ a radia~ion curable ink canvertible to a conduct~vQ coating exhibi~lng a speciflc r~istivity of less than lO o ~ -cm when curad on the surface of a 3ubstrate uslng actinic radia~ion a~ a temperature o~ up lto about 60 C~ hin 2 minutes or les~9 which radiation curable i~k compr~ses ~ by ~olumeO
; 15 (A? rom abou~ 1~% to 60% of an organic resln binder having a v~sco~ity o~ ~rom 50 to lQ~OOO CQntipoise5 at ~5 G~ and (B) ~r~m about 90% to 40% of a par~iculated Qlectri- : .
cally conduc~Ye metal containing material sub- : :
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~tantially ~re~ o metal contai~ing ma~arial having a~ aspec~ ratlo of di~m~ter to thickn~ of a ~5 :

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RD~7452 value o~ greater ~han 200 Included by tha particula~ed elec~rically conductive metal containing ma~erlal which can be used in the practice o~ the inven~ion are pr~erably silver coa~ed glass spheres, or spherolds, somPt~mes re~err~d to as l~eads'~ ~hich have an ~erage diameter of abou~ 6 to 125 micro~s and preerably 10 to 50. These materials are commercially availabl~ and are made from glass spheres commonly employed as r~`1ectlve ~iller mat~rials~ Also included are particulatad metals such as lron, zinc, nich~l~ copper, etc~, which have average diameters as previously deined and are substan-tially ree o a nonconduc~ive oxide coatingr Procedures ~or mak~ng such cond~ct~ve par~icles by pla~ng wi~h s~lvar, or in~t~ally pr~mi~g wtth copper follow~d by plating with silver, or nobl~ ~etals, are shown by Ehrreich u.s. patent 3,202,483~ Glass ~ibers coat~d wi~h silv~r3 copper or nickel as shown ~or ~xample in French patent 1,531,272 also can bQ usedO

Particula~ed me~als such as ~ron, nic~el~ copper~ -zinc~ e~c~ in the orming o~ spheres9 ~pheroids, or oblon$
spheroids, metal or fibers also can b~ us~d wh~ch have been -6- .

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~. ~ . ~ . ,,.- -~7;~ 2 ~D~7452 subjec~ed to a hydrogen or other reducing a~mospher~ at elevated temperatures to e~ect the removal of an amount of nonconducting oxide coating suf~icien~ to rend~r ~he metal particles conductiveO The particulated metal in reduced ~orm can be shielded from oxygen prior to being treat~d with the organic resin binder. The resul~ing radia~cion curable ink can be s~ored under sealed cond~tions pr~or ~o use.
Some of the organic resin binders which can be used in making the W curable inks o the pres~nt invention in combination with ~he above~dasc:ribed conductive particulated material are in th~ f:orm of aither low molecular weigh~ alipha~ically unsatura~ed organic polymers~
or a mix~ur~ of an aliphatically unsaturat~d organic polym~r in further combination with a copolym~rlzable alip~atically unsa~urated organic nomer such as styrene.
~ne a~orementiorl~d solven~less alipha~is~lly unsaturated organic rQsin ma~erials carl hav~ a viscosity o~ from about 50 ~o 10,000 cen~ipoisa~ a~ ~5 CO
One varie~y o~ the solvelltless resins which ~an b~
employed in combination ~ith the particulat~d elec~rical~

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~7;Z~3~z RD~7452 conductiv~ m2tal containing material as described above, in ~he production of the W curable conduc~ive ink of the present invention3 are low molecular weigh~ polyimides con~aining acrylamide unsaturation, such as shown in U~ S, patent 3~535~1~8, Ra w eO These materials can be colorless liquids ha~ing relat~vely low viscos~tyv Another example is low molecular ~eight polyest~rs con~aining acryl~c unsaturat~orl show~ by U0 S0 patent 3,567,494, SetkoO AdditiQnal ex~nlples o~ solventless reslns ar2 acryla~e esters~ ox me~hacrylic esters o polyhydric alcohol~, such as shown by U0 Sc patents 3,551,246, and 3,551~235, BassemirO Eurther examples are shown by Nass U0 S0 patent 3,551,3110 In addi~ion, th~re also is included acrylate or methacrylat~ esters o~ ~-sil~co~ resins, acryla~e or methacrylate est~rsD m~lamin~
epoxy resins, allyl eth~rs o~ polyhydric alcohcls, allyl ~s~ers of polyfunct~llal a~iphatic s:~r aromat~c acids, low molecular w~ight male~mido substituted aromatic compounds~
cinnam~c es~exs of polyfunctional alcohols~, or mia~tures o~ :
such c~mpounds~ etsO

TheL organic rasin b~nder w~ich can be used ~n o8 ' 7 2 ~ ~

combination with the above describ~d particula~ed electrically conducti~e metal con~aining ma~erials can b~
further defined as unsa~urated polymers, or exampla, a polyester ~rom a glycol and a,b-unsatura~ed dicarboxylic acids, such as maleic and fumaric acids, with ox without ~.
other dicar~xylic acids free of a,b unsa~uration, such as phthalic, isoph~halic, succinic, etc~, dissolved in a copolymerizable alipha~ically unsatura~d organic solvent, such as styrene, vinyl toluene, div~nyl benze~e, methyl me~hacrylate, etc., or mix~urQ~ oi. such materials~ :
Examples of such solv~ntles~ resin composltions are shown by U~ S~ pa~n~s 2,673~151 and 3,326a710, Brod~ a ~urther Q~ample ~s sho~n by South African patant 694~724.
Also included are unsa~urated organosiloxanes h~ving ~rom

5 to 18 ~ilicon a~oms~ which can be ~mploy~d in combination with a vin~lic organic monom~r~ :
In ~n~tances where .i~ is desir~d to ma~e UV
cura~le l~ks, W sensitizers can be employed when ~he organic resin binder is in ~he fonm of a polye~t~r or polyacrylate or oth~r polymarizabl0 UV curable mat~rial~ "
m8re can be ~mployed ~ro~ about 005 ~o 5% by weight o yg_ ~:

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the UV sensitizer based on the weight of resin. Included among the ultraviolet radiation photosensitizers which can be used are, or example, ketones such as benzophenone, acetophenone, benzil, benzyl methyl ketone; benzoins and substituted benzoins such as benzoin methyl ether, hydroxymethyl benzoin isopropyl ether; sulfur compounds such as thiourea, aromatic disulfides, and other photo-sensitizers such as azides, thioketones, or mixtures thereof. There also can be used in the ink, UV stabilizers and antioxidants such as hydroquinone, tert butyl hydroquinone, tert butyl catechol, p-benzoquinone, 2,5-diphenylbenzoquinone, 2,6-di-tert-butyl-p-cresol, benzotriazoles such as that available under the trade mark Tinuvin P (manufactured by Geigy Corp.), hydroxybenzophenones, such as 2,4-hydroxybenzophenone, 2-hydroxy-4-methoxy-benzophenone, 4-dodecyl-2-hydroxybenzophenone, substituted acrylonitriles such as ethyl-2-cyano-3,3-diphenyl acrylate, 2-ethylhexyl-2-cyano-3,3-diphenyl acrylate, etc.
In addition, as shown by Gebhartt et al, Farbe and Lack 64 30~ (1958), small amounts of a paraffin wax, up to 2% by weight, such as 135~ F. Mæ can be incorporated '""`''''.

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into resins which contain polymerizable groups subject to .
oxygen inhibition. Such wax substantially reduces such :-oxygen inhibition which manifests itself as surface tack.
Alternatively the wax may be omitted when radiation cures .
are to be conducted in an inert atmosphere. It also has been found that the conductivity of the cured ink can be impaired if chloride containing components are used which introduce more than 100 parts of chloride, per million .:
of organic resin binder.
Additional examples of an organic resin binder .
which can be used in the practice of the invention are one-package radiation curable epoxy resins con~aining aromatic onium salts of the Group VlA elements, such as sulfur, aromatic halonium salts, and Group VA
elements such as arsenic which break down under the influence of radiant energy to reIease a Friedel-Crafts catalyst such as borontrifluoride to effect the cure of the : . .
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epoxy resinD
The epoxy re~ins which also can be u~ilized as the organic resin binder ~o produce the photo curable inks of the presen~ invention includes any monomeric, dimeric or oligomeric or polymeric epoxy materi~l containing one or a plurality of epoxy functional groups. Diluents such as 4-vinylcyclohexene dioxide, limonene dioxide, 1,2-cyclo-hexen~ oxide, styrene oxide, e~c., may be added as viscosity modifying agents.
Xn the practice of the inllen~ion, ~he radiation curable ink can be made by s~mply blending the par~icu-la~ed electrically conductive me~al con~ain~ng material~
which may be r~ferred ~o hereinaf~er as ~he "conductiv~

flllerl', with ~he organic r~sin binder, which hereinafter lS may be referred to as ~he.resinO
Depe~ding upon such ~actors as ~he v~scosi~y of the resin, and ~he particle size and ~ature of the conduc~ive ~iller~ ~he re8Ul ing W ~curable ink can vary wid~ly and can be a free flowing fluid or a pa~te~ In instances where i~ i8 desired to make a UOV. curable conduc~ve ink, a photoeensi~izer can b~ incorpora~ed into . -12 .. . .......... . . ~ .. . ,. . . , . , ~ ~ , . ...
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the resin prior to blending wi~h the conductive filler~
There can be amployed on a weight basis from about 0.5 part to 10 parts o~ flller per part of resin~ If desired, electron beam cure of the ink also can be e~ectedf Blending can be achieved by simply stirring the ingredien~s in a sui~able container. In instances where the condurt:ive filler is in ~he form of particula~ed metal whlch has been freshly subgec~ed to hydrogen reduction at temperatures o 300 to 800 CO to effect reduc~ion of oxide coatlngs, or a chemical ~relatment involvlng the use of ammonium persulate solution to dissolve the oxide coating a special blending technilque is pree~ably employed~ Th~ resln can be ~reated with a dry inert gas, such as passing the gas under the resin surace along with agitation to xemove any oxygen, or mo~sture therefrom4 Blend~ng with the fr~shly reduced filler i5 also achieved under sealad conditions such as a dry box. The reRulting UV-curable conductive ink can be usad in a standard manner ~o produce desirable conductive coat~ngs, if radiated with ultraviolet light within a reasonable t~me af~er being applled to a substra~a such as up to 10 minutes~.
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~ RD-7452 ~07Z8~:~

In order that those skilled in the art will be better able to practice the invention, the following -examples are given by way of illustration, and not by way of limitation. All parts are by weight unless otherwise indicated.
EXAMPLE I
A polyester prepolymer was prepared by effecting reaction between about 35.3 parts of fumaric acid, ll.9 ;~
parts of dicyclopentadiene and 25.3 parts of propylene glycol. The resulting prepolymer was blended with about 2~.4 parts of styrene containing 100 ppm of tert-butyl-hydroquinone and 1.~ parts of benzoin-sec-butylether along with 0.7 parts of 135 F. paraffin wax and warmed until a solution was obtained.
A photocurable ink was preparedl by blending the above organic resin binder with 67 parts of silver-coated -glass spheres having an average diameter of about 10--50 ~ -microns. On a volume basis, there were employed about 2 ~ ~ `
volumes of conductive ~iller per volume of resin. ~
The above photocurable ink was printed onto a 2 inch , ~ -by 6 inch polystyrene substrate in the pattern shown in the - 14 - ~
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~L~7Z~302 drawing to provide conductors (after curing) at 10 and 11, using the procedure described in our Canadian patent 1,040,318 issued October 10, 1978 and assigned to the same assignee as the present invention. The treated polystyrene substrate was then placed at a distance of about 8 inches from the arc tube of a lamp (available under the trade mark General Electric H3T7) which had been ballasted to permit operation at about 960 watts input. There were employed two quartz filters below the lamp, having dimensions of about 5" x 10". The ilters were supported on steel supports which formed a channel through which air was blown. The upper filter support was in contact with a 6' copper coil having an average diameter of about 3/8" through which water was passed at about 25 C~ The ull intensity of the lamps was measured at about 20,000 ~/cm , and the temperature of the substrate did not exceed about 50C.
After a 2 minute cure, the ink on the panel was tested for continuity. Cure of the ink on the panel was determined by a bake cycle of 60 minutes at 70 C after irradiation.
2Q If, after 2 minutes exposure, the ink strip was tack-free and it showed no more than a 2$ weight loss based on the weight of tack-free ink, the ink was considered cured. It .

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~D-7452 was ound ~hat the resulting conductive cured ink had a specific resistivity of ~015 ohm-cm.
The cured ink in the circuit board was then evaluated for adhesion by 1exing it at least ~ive t~mes S sufflcient to produce a distance of 1" between th~ center o~ the arc t~ an imaginary straight line drawn between the two ends of the board. No slgnificant change in conduc-tivity of the cured ink strip wa~: ound.
An abrasion test was also run on the connecting tabs by attaching the edge of the! circui~ board to a steel clamp a~ least 16 ~imes, whe~e the clamp spring had a compressive force of at least five times the weight of the board freely suspended~ Although the clamp contacted the cured strip connecting tabs, no adh2siv~ sQparation of the ; 15 strip was n~ed and the specific resis~ivity of ~he cured strip remained substan~ially the same~ -A further evaluation o ~he circuit board was made by ~xposing it to 96% rela~ive humidity at a temperature of 120 Fo or 14 days without allowing condensation of water on th~ surface of ~he boardO It is ound that ~he sp~ci~ic resistivity o~ the circuit board remains sub-~6~ :

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RD-7~52 stantially unchanged~
A printing ink is made consisting of 33 parts of the above organic resin binder and 67 parts of silver flake having an aspect ratlo greater than 20, A screen S printed pattern from this ink does no~ photocure ~ollowing the above described conditionsO An irradia~d strip has a specific resistivity of greater than 1000 ohm-cm~ In addition, the s~rlp is unsuitabl.e as a circui~ board materlal because it ails all of the above shown tests~
~e~ "
A photocurable ink wa~ prepared by blanding together about 2 parts o~ th~ silver coated gl~ss beads of Exa~ple I with one part o~ an organic rasin binder -.
consisting o~ 70 parts of the acrylated epo~idized soybean oil and 30 par~s o ethylhexyl acrylate wi~h 2 parts of the ; photosen~itizer o Example I. Prior ~o mixing, the s,t.'~ J~s~
volume of the~ u~ coated ~ beads was approximately 2 t~mes ~ha volume of the organic rasin binder.

Th~ photocurable ink was applied onto a polystyrene substrate in ac~-ordance with the procsdure of E~ample I

and th~reafter cured under ultraviolet lighto The ~7~

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~7Z8~z specific resistivity o~ the cured conductive coating was found to be .015 ohms-cm. After being ~ubjected to the tests described in Example I~ ~he specific resistivity on th~ circult board does not substantially change. The S conductive strip also exh~bits subs~ant~ally the same physical proper~ies as de~ined in E~ample Io - EXAMYLE III
. _ A pho~o~urabla ink was prepared by fonming a blend of 2 parts o~ the silver coated beads o~ Example I and one part o an epoxy resin binder. The epoxy resin binder ~:
consisted o abou~ 15 parts o~ ~inylcyclohexene dioxide and 85 parts o~ (3,4-epoxycyclohe!xyl~-m~thyl-3,4-epoxy- ;
cyclohexanecarboxylat~. In addition, there was also util~zed in the organic resin binder 2 par~s of triphenyl sul~oniumhe~afluoxo arsenate a~ a photosensitizer. Prior to mi~ng, it was ~ound that the vol~m. of the ~ilver ~:
beads was approx~mataly 2 times ~he volum~ of ~he bind~r ra~in~
Tha above descrilbed photocurabl~ ink was printed onto a polyethylen~erephthalat~ re~in subs~rata in accordance ~sith the procedures described in Eæ~mple I~

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It was subjected to ultraviole~ radia~ion and cured wl~hin 2 minutesQ I~ was found ~o ha~Te a volume resistivity of about .05 ohms~cm~ This panel pas~ed substan~ially all the ~ests describ~d in Example I.
EXA~PLE IV
The procedur~ of Exampl~ I is repeatsd excep~ that in plac~ o the silver coate~ glass beads, there is ~mployed copper coated glass beads where the copper has its oxide coa~ing reduced by hydrogen. Hydrog2n reductio il9 achieved by sub~ecting the copper coated glass beads ~o a hydrogen a~mospher~ fos about 30 mi~utes at a temperature of about 400 C.
In accordarlce w1th the prwedure of Ex~mple I, a photocurable ink i~ ~btained which is found to have lS approximately the same conductivity upon cur~ on a poly-sty~3nQ substrate as described ~n Example I, Physical testing of ~h~ cured s~r~p alQo produc~s substa~tially the 9~mt3 re~ult$ a~ shown in Exam~?le Ir A photocurablQ resln i~ pr~pared by blending togeJcher about 5 par~ o silver coa~ed ccpper b~ads : ..... . , . - ......... , . ....... . - ... .. . . . ..
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RD-7~52 having an average particle siæe of about 200 microns with : one part of the polyester resin of Example I con~aining ~he same photosen~ltizerO It is ound ~ha~ the volume of ~he silver coa~ed copper beads is about the same as ~he volume of the organic rcsin binder prior to blending.
The above described photocurable ink is applied onto a polystyrene subst~ate a~ described in Example I patterned in accordance with th~ attached drawing~ It is found ~hat af~er the applied ink i8 cured in accordance with the proc~dure o Example I, i~8 sp~ci~Eic resist~vity ls le~s than about ol ohm~cm~ The circul~ board i8 ~hen sub~ected to the tests as described in Ex$mple I. The res~lts are substan~ally the sama as show~ in Ex~mple Io EX~MPLE VI
A photoc~rable in~ is pr~pared by blending together abou~ S par~s o~ chemically treat~d copper powder having ; an av~ra~e part~cle s~ze of about 10 ~o 50 mlcron~ wi~h ~n~ part o ~he polya~t~r o~ Example I contain~ng the ~am~
photos~nsi~iæers Th~ copper powd~r has been treated with 2Q a ~olution consistin~ o~ 240 part~ ~f ammonium persulfa~e in 1000 par~s o~ water, whi.ch has been purged with ni~rogen, to 0 -~
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efect removal of oxide coating on the copper~ After ~he chemically reduced copper powder has been thoroughly dried by agi~ating it in a dry n~trogen a~mosphere, the copper powder ls th~n blended under nitrogen with the organic resin binder~ It was ound that about 5 parts of the copper powder is equ~valen~ in volume to a~out one part o~
the polyester resin.
Th~ pho~ocurable ink is ~hen applied on~o a poly-s~yrane subQtrate in accordance wi~h the printillg procedure o~ Example I. Upon cure o the ink within the 7. minute~
us~ng ~he sam~ curing appara~us as de3cribed ln Exampla I, ~h~ volume resis~ivity o~ the ink is found to be less than about .1 ohm-cm~ The resul~lng circul~ bvard sa~isfac-torily pa~seq ~e~s dascrib~d in Exampl~ I.
EX~NPLE VII
A pho~ocurabl~ ~nk is made ~n accordance ~ith the procedNre of Ex~mple I, e~cept that a curable llquid polyene~polyth~ol ¢~mpositlon, as shown ~ Ex~mple II of Lard patent 3,728,240, is used. Thare is employed 2 par~s ;~
o~ silver coa~ed glass _pheres per part of the liqu~.d polyene-poly~h~ol r~sin.

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A circui~ board made in accordance with th~
proc~dur~ of Exa~ple I exh~bits substantially ~he same specific res~s~ y and passe~ the phys~cal ~ests and humid~y test ~n a ~atisfac~ory mannerO
~lthough the above examples are limited to only a few of the very many radiation curable printing inks within the scope of the present inven~ion, it should be under~tood that the present invention is directed to a much broader class of printing inks based on the use of a wide variety of organic resin binders and pa~ticulated electrically conductive metal containing mater~als set forth in the description preceding these ex les.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A screen printable radiation curable ink convertible to an abrasion resistant conductive coating exhibiting a specific resistivity of less than 10 ohm-cm when cured on the surface of a substrate, consisting essentially of by volume (A) from about 10 to 60 percent of a radiation curable organic resin binder having a viscosity of from about 50 to 10,000 centipoises at 25°C, and (B) from about 90 to 40 percent of an electrically conductive filler consisting essentially of silver or copper containing particles with about 0 percent to about 15 percent by weight of silver or copper containing particles having an aspect ratio of diameter to thickness of a value greater than 20 based on the total weight of conductive filler.

2. A radiation curable ink in accordance with claim 1, where the electrically conductive filler is in the form of silver coated glass spheres.

3. A radiation curable ink in accordance with claim 1, where the electrically conductive filler is in the form of chemically reduced copper coated glass spheres.

4. A radiation curable ink in accordance with claim 1, where the electrically conductive filler is in the form of chemically reduced copper powder.

5. A radiation curable ink in accordance with claim 1, where the organic resin binder is in the form of a mixture of polyester prepolymer and styrene.

6. A radiation curable ink in accordance with claim 1, where the organic resin binder is in the form of a polyacrylate.

7. A radiation curable ink in accordance with claim 1, where the electrically conductive filler consists essentially of silver or copper containing spheres or spheroids having from about 0 percent to about 15 percent by weight of silver flake, based on the weight of conductive filler.

8. A radiation curable ink in accordance with claim 1, where the radiation curable resin is a polyester resin and the electrically conductive filler is in the form of silver coated copper beads.

9. A screen printable radiation curable ink convertible to an abrasion resistant conductive coating exhibiting a specific resistivity of less than 10 ohm-cm when cured on the surface of a substrate, consisting essentially of by volume (A) from about 10 to 60 percent of an epoxy resin containing an effective amount of an aromatic onium salt selected from the class consisting of an onium salt of a Group VIA
element, an onium salt of a Group VA element, and an aromatic halonium salt, and (B) from about 90 to 40 percent of an electrically conductive filler consisting essentially of silver or copper containing particles having from about 0 percent to about 15 percent by weight of silver or copper containing particles having an aspect ratio of diameter to thickness of a value greater than 20 based on the total weight of conductive filler.

10. A radiation curable ink in accordance with claim 9, where the organic resin binder is in the form of a mixture of vinylcyclohexene dioxide, (3,4-epoxy cyclohexyl)-methyl-3,4-epoxy cyclohexane carboxylate and an effective amount of tri-phenylsulfonium hexafluoro arsenate.

11. A radiation curable ink in accordance with claim 9, where the electrically conductive filler consists essentially of silver or copper containing spheres or spheroids having from about 0 to 15 percent by weight of silver flake, based on the weight of conductive filler.

12. A screen printable UV curable ink convertible to an abrasion resistant conductive coating exhibiting a specific resistivity of less than 10 ohm-cm when cured on the surface of a substrate,consisting essentially of by volume (A) from about 10 percent to 60 percent of a radiation curable organic resin binder having a viscosity of from about 50 to 10,000 centipoises at 25°C, (B) from about 90 percent to 40 percent of an electrically conductive filler consisting essentially of silver or copper containing particles with about 0 percent to about 15 percent by weight of silver or copper containing particles having an aspect ratio of diameter to thickness of a value greater than 20 based on the total weight of conductive filler, and (C) from 0.5 to 5 percent by weight of a UV sensitizer based on the weight of (A).

13. A UV curable ink in accordance with claim 12,comprising (A) a polyester reaction product of propylene glycol, fumaric acid and dicyclo pentadiene, (B) silver coated glass spheres having an average diameter of from about 10-50 microns.

14. A UV curable ink in accordance with claim 12, where the conductive filler consists essentially of silver or copper containing spheres or speroids having from about 0 percent to about 15 percent by weight of silver flake based on the weight of conductive filler.