FR2496503A1 - PROCESS FOR CONFORMALLY COATING AN ARTICLE OF IRREGULAR SHAPE - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR COATING, ACCORDING TO ITS SHAPE, AN IRREGULAR SHAPED ARTICLE. ACCORDING TO THE INVENTION, THE ARTICLE IS COATED WITH A COMPOSITION COMPRISING: 1.A LIQUID, REACTIVE, HEAT AND UV-CURING RESIN, WITHOUT SOLVENT, CONTAINING AT LEAST TWO DOUBLE CARBON-CARBON OLEFINIC BONDS PER MOLECULE; 2.A RESIN PHOTO-INITIATOR; 3.A THERMAL INITIATOR OF THE RESIN; THE COATED ARTICLE IS EXPOSED TO UV RADIATION AND THEN THE ARTICLE IS EXPOSED TO A TEMPERATURE BETWEEN 50 AND 250C FOR SUFFICIENT TIME TO OBTAIN A COMPLETELY CURED SOLID COATING. THE INVENTION APPLIES IN PARTICULAR TO INTEGRATED CIRCUIT BOARDS USED IN THE AUTOMOTIVE INDUSTRY.

Description

The present invention relates to a method

  to coat, in its form, an article of irregular shape

  using a curable composition which is both activated by radiation and by heat. More particularly, the present invention relates to a method for coating, in its form, an article which comprises coating the article with a heat-curable composition and ultraviolet rays and then subjecting the article to coated with UV radiation and

the heat.

  Ultraviolet-terminated, ultraviolet-terminated polyene / polythiol compositions are well known from US Patents. No. 3,661,744; No. 3,697,402; Nos. 3,697,395 and 3,697,396. Ultraviolet-curable acrylic-terminated polyene / polythiol compositions and ultraviolet ray curing methods are also known from US Pat. Nos. 3,898,349 and 4,008. 341. The photocuring of aoelates, in itself, is also known from US Patent No. 2,760,863. The thermal curing of chemical free radicals of allyl terminated polyenes with polythids is also known from US Pat. Nos. 3,662,023; 3,697,621; 3,699,084; 3,714,290 and 3,653,959. British Patent No. 1,490,372 teaches thermic curing of radicals.

  chemical free of an acrylate / polythiol system.

  Also known from U.S. Patent No. 4,020,233,

  to form hardened polythioethers by mixing a

  comprising an ethylenically unsaturated compound containing at least two carbon / unsaturated carbons per molecule, a polythiol containing at least two thiol groups per molecule, a photoinitiator and a catalytic amount of a pinacol and then, subjecting the mixture to a UV radiation and heat. It is further known to partially polymerize acrylates in the presence of a pinacol, see U.S. Patent No. 3,378,533. In addition, in U.S. patent application N 177,658 filed

2 2496503

  on August 13, 1980, radiation and heat-activated compositions are disclosed which comprise di-and polyacrylic terminated liquid materials, in combination with a photoinitiator and a catalytic amount of a substituted or unsubstituted pinacol as well as hardening processes. U.S. Patent No. 4,171,252 discloses photopolymerization of a polymerizable mass in the presence of a phoW-4nitiator, a peroxygen-containing compound.

  organic and naphthalene or substituted naphthalene.

  US Patent No. 4,222,835 teaches that a composition containing a liquid vinyl monomer, a photoinitiator, a thermal initiator and an ultraviolet light exposure accelerator, initiates polymerization in the surface layer of the composition. thus producing enough heat to activate the thermal initiator and force the polymerization to

  produce in all the mass of the monomer.

  In current processes, coating materials are

  The following shapes are applied to circuit board assemblies to protect them from moisture during use. Traditional coatings of this type (which are based on silicones, epoxy resins, urethanes or acrylates) are either solvent-based or two-component or both. These present systems have, as typical examples of solvent flammability, the short shelf life, the long curing time and the unreliable recovery obtained.

by the coating.

  Moreover, in some systems where ultraviolet light may penetrate due to geometric constraints causing shadow areas or in systems rendered partially opaque to ultraviolet due to chargestels - that coatings on electronic circuit boards o are attached components, it is desirable to have a system that

  can be hardened to ultraviolet and heat.

  By using dual curing, the portion of the composition that is exposed to UV light can be radiation cured, thereby immobilizing any coating and the portion of the composition in the shadow areas can be subsequently heat cured. It is an object of the present invention to provide a process for the application of solvent-free coatings. It is another object of the present invention to produce cured products for use as the shape by exposing a composition to

  UV radiation with subsequent application of heat.

  Other objects will become more apparent when reading

of the following description.

  The present invention is directed to a process for coating or coating, in its form, an irregularly shaped article such as an electronic circuit board where components are attached, which comprises coating the article, for example by dipping it or spraying a composition comprising: (1) a reactive, UV-curable, solvent-free liquid resin containing at least two carbon-carbon olefinic doublings per molecule (2) a phbD-initiator of (1); and (3) a thermal initiator of (1); exposing the article thus coated to UV and e radiation by heating the article thus exposed to a temperature between 50 and 250 C for a time sufficient to obtain a hardened solid coating. If the UV radiation is replaced by an ionizing radiation ie strong energy,

  photoinitiator is necessary in the composition.

  The solvent-free, solvent-curable, liquid-reactive liquid resins usable herein include, without limitation, at least one ethylenically unsaturated element of the group consisting of: (a) an ethylenically unsaturated liquid monomer, oligomer or prepolymer having the formula

(CH2 = C-C-O-) IR1

  R 2 is H o CH 3, R 1 is an organic moiety and n is at least 2, (b) a polythiol in combination with (a) above (c) a polythiol in combination with a liquid monomer, oligomer or prepolymer at ethylenic unsaturation having the formula: (CH 2 C-CH 2) n -R 3 o R 2 is H or CH 3, R 3 is an organic moiety and n is

at least 2.

  Although the compositions above, in themselves

  can be used here to form useful products, they can also be used in combination with

  traditional copolyrrysable monomers or diluent reagents.

  The mixture of the composition according to the invention with other

  monomers is usually used to control the visco-

  sity and other application variables such as the rate of hardening and the final properties of

  pellicube, hardness like hardness and flexibility.

  These diluent reagents cure with the element of the unsaturated-ethylenic group on exposure to UV radiation and heat. Examples of conventional copolymerizable compounds useful as non-limiting diluent reagents include monofunctional acrylic esters, monofunctional methacrylic esters, styrene, vinyl-vinyl, acrylonitrile, methacrylonitrile, vinyl vinyl acetate, and the like. pynxolidone, chloride

  vinylidene choride, butadiene, iso-

  prene, chloroprene, divinyl benzene, di (vinyl-phenyl)

  nyl) carbonate, dialilyl phthalate, diallyl diallyl carbonate diallyl, triallyl isocyanurate diallyl fumarate, diallylp maleate diallylp chlorinate trially2t cyanurate and unsaturated polyesters and mixtures thereof . The term "unsaturated polyesters" means, in the present case, the usual polycondensation products which consist of residues linked in the manner of the esters of polyvalent and in particular divalent alcohols, as well as, optionally, residues of monovalent alcohols and / or monovalent carboxylic acids, the residues to contain at least partially unsaturated groups. Examples of acids are maleic acid, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, succinic acid, glutaric acid, adipic acid, lactic acid, phthalic acid, tetrachlorophthalic acid, hexachloroendomethylenetetrahydrophthalic acid, trimeLitic acid, benzoic acid, linseed oil fatty acid, and ricinoleic fatty acid and mixtures thereof. Examples of alcohols are ethylene glycol, diethylene glycol, propane, butane and hexane diols, trimethylolpropane, pentaerythritol, butanol and tetrahydrofurfuryl alcohol. The diluent reagents can be added to the system in reach 90% by weight of the 1elemet of the ethylenically unsaturated group, preferably

  from 20 to 50% by weight on the same basis.

  The thermal initiators used herein are selected from substituted or unsubstituted pinacols and gold peroxides. Azo initiators such as azobisisobutyronitrile can also be used as thermal initiators, but as nitrogen is evolved, the resulting coating or coating will contain

  bubbles or will have the shape of a foam.

  The organic peroxides which can be used have the general formula: R-O-O- (R 1 -O-O) n R on = O or 1, R is independently selected from hydrogen, aryl, alkyl, aryl carbonyl, alkaryl carbonyl aralkyl carbonyl and alkyl carbonyl and R 1 is alkyl or aryl, alkyl groups containing from 1 to 20 carbon atoms. Examples of organic peroxides

  usable, without limitation, 2,5-dimethyl-2,5-di-

  (t-butylperoxy) -hexane, 1,3-bis (t-butylperoxyisopropyl)

  benzene, 1,3-bis (cumylperoxyisopropyl) benzene, the

  2,4-dichlorobenzoyl oxides, caprylyl peroxide, lauroyl peroxide, t-butyl peroxysobutyrate, benzoyl peroxide, p-chlorobenzoyl peroxide, hydroxyheptyl peroxide, di-t-butyl diperphthalate t-butyl peracetate, t-butyl perbenzoate,

  dicumyl peroxide and di-t-butyl peroxide.

  The organic peroxide is added to the composition in an amount of from 0.01 to 10%, preferably 0.1 to 5% by weight, based on the weight of

  the element of the ethylenically unsaturated group.

  The substituted or unsubstituted pinacols usable here as a thermal initiator have the general formula: tR1 R

R2- C R4

21 1 4

X Y

  R1 and R3 are identical or different substituted or unsubstituted aromatic radicals, R2 and R4 are substituted or unsubstituted aliphatic or aromatic radicals and X and Y which may be the same or

  different are hydroxyl, alkoxy or aryloxy.

  The preferred pinacols are those where R1, R2, R3 and R4 are aromatic radicals, in particular the radical

phenyl and X and Y are hydroxyl.

  Examples of this class of compo-

  without limitation, benzopinacol, 4,4'-dichloro-

  benzopinacol, 4,4'-dibromobenzopinacol, 4,4'-diodo-

  benzopinacol, 4,4r, 4 ", 4" - tetrachlorobenzopinacol,

24965 (

  2,4-2 ', 4'-tetrachlorobenzopinacol, 4,4'-dimethylbenzoate

  pinacol, 3,3'-dimethylbenzopinacol, 2,2'-dimethyl-

  benzopinacol, 3,4-3 ', 4'-tetramethylbenzopinacol,

  4,4'-Dimethoxybenzopinacol, 4,4 ', 4 ", 4" - tetramethoxy

  benzopinacol, 4,4'-diphenylbenzopinacol, 4,4'-dichlo-

  4'-4,4'-dimethylbenzopinacol, 4,4'-dimethyl-4 '', 4 '' - di

  phenylbenzopinacol, xanthonpinacol, fluorenonepinacol, acetophenonepinacol, 4,4'-dimethylacetophenone pinacol,

  4,4'-dichloroacetophenonepinacol, 1,1,2-triphenylpropane

  pane-1,2-diol, 1,2,3,4-tetraphenyl-butane-2,3-diol, 1,2-diphenylcyclobutane-1,2-diol, propiophenone-pinacol,

  4,4'-dimethylpropiophenone pinacol, 2,2'-ethyl-3,3'-

  dimethoxypropiophenone-pinacol, 1,1,1,4,4,4-hexafluoro-

  2,3-diphenyl-butane-2,3-diol. As other compounds according to the present invention,

  mention may be made of benzopinacol-mono-methylether, benzo

  pinacol-mono-phenyl ether, benzopinacol-mono-isopropyl ether, benzopinacolmonoisobutyl ether, benzopinacol mono

  (diethoxy methyl) ether and the like.

  The pinacol is added to the composition in quantities of between 0.01 and 10%, preferably between 0.1 and% by weight, based on the weight of the element of the

  ethylenically unsaturated group.

  The thermal initiator can be added to the system in a variety of ways. Indeed, the thermal initiator, in

  itself, can be mixed with the element of the unsatu-

  ethylenic ration. In addition, it can be mixed with a photo-

  initiator and add it to the unsaturated group element

  ethylene. Moreover, the thermal initiator can be dissolved or suspended in well-known commercial solvents such as dibutyl phthalate, ketones, such as acetone and methyl ethyl ketone or chlorinated hydrocarbons such as methylene chloride,

then be added to the system.

  In the practice of the present invention, it is sometimes desirable to add a polythiol to the composition prior to curing. This is particularly

  true when the ethylenic unsaturation is an allyl group.

  In this case, during the curing step, the polythiol is added through the double bond of the allyl group resulting in solid materials cured in a commercially acceptable time. In the case where unsaturation

  polyethylene is an acrylic or methacrylic group

  crylic, the addition of a polythiol in the system prevents the presence of a viscous surface due to inhibition

hardening by air.

  In this case, the term polythiols indicates

  simple or complex organic compounds having a mul -

  tiplicity of functional groups -SH pendani or placed

  at the end, per average molecule.

  On average, the polythiols must contain two or more -SH gropes per molecule and they usually have a viscosity between slightly more than zero and 20 million centipoise (cps) at 70 C, measured by a Brookfield Viscometer. In the term "polythiold"

  as used here are included materials which, in addition to

  it is an inert solvent, an aqueous dispersion or a

  plasticizer, fall into the range of viscosity

  The polythiols which can be used in the present invention usually have molecular p> ids.

  between 94-20,000 and preferably between 100 and 10,000.

  The polythiols which can be used in the present invention

  may be represented by the general formula:

  R8 - (SH) n is at least 2 and R8 is an organic fragment

  pclyva.ent without carbon-reactive unsaturation

  carbon. Thus, R8 may contain cyclic groupings and minor amounts of heteroatoms such as N, S, Pou 0, but it mainly contains chain bonds

  containing carbon-hydrogen, carbon-oxygen or silicon-

  oxygen devoid of any carbon-reactive unsaturation

carbon.

  A class of polythiols usable with the polyenes in the present invention to obtain substantially odorless polythio-etheb products is composed of thiol-containing acid esters of

  HS-R9-COOH, where R9 is an organic moiety

  that does not contain carbon-carbon unsaturation ", with polyhydrohy compounds of general structure R10- (OH) n, o R10 is an organic moiety containing no" reactive "carbon-carbon unsaturation and is not 2 or

  more. These components will react under appropriate conditions

  taken to give a polythiol having the general structure R10- (08-R9 SH) No. R and R10 are organic moieties not containing "reactive" carbon-to-carbon unsaturation and n is 2 or more. Some polythiols such as polythiols monomers

  aliphatics (ethane dithiol, hexamethylene dithiol, deca-

  methylene dithiol, tolylene-2,4-dithiol and others) and

  certain polymeric polythiols such as the ethyl

  Thiol-terminated cyclohexyl dimercaptan and the like, and similar polythiols which are advantageously and usually commercially synthesized, although having unpleasant odors, are useful in the present invention but many of the end products are not widely accepted. a practical and commercial point of view. Examples of polythiol compounds which are preferred in the context of the invention because of their relatively low level of odor, without limitation, thioglycolic acid esters (HSCH2COOH), alpha-mercaptoprogaic acid ( HS-CH (CH 3) -COOH) and beta-mercaptopropyl β (HS-CH 2 CH 2 COCH) with polyhydroxy compounds such as glycols, triols, tetraols, pentaols, hexaols and the like. Specific examples of the preferred polythiols may be mentioned, without limitation,

  ethylene glycol bis (thioglycolate), ethylene

  (beta-mercatopropionate), trimethylcyclic letris (thioglycolate)

  propane, trisbeta-mercaptopropionate), trimethylol

  propane, tetrakis (thioglycolate) pentaeryt-itol., tetrakis (beta-mercaptopropionate) pentaerythritol, all being marketed. A specific example of a preferred polymeric polythiol is polypropylene ether glycol bis (beta)

  mercaptopropionate) which is prepared from poly-

  propylene ether glycol (such as Pluracol P2010, Wyandotte Chemical Corp.) and beta-mercaptopropionic acid by esterification.

  In addition, the polythiols usable here for

  polythioether derivatives of iset salibs with lepcilyene in the presence of a free radical generator include

  mercaptoester derivatives of styrene copolymers

  Allyl allylic allylic in U.S. Patent No. 3,904,499 and isocyanurate-containing polythiols disclosed in U.S. Patent No. 3,676,440 as well as thiol-terminated liquid polymers according to U.S. Patent 3,258,495, all incorporated herein by reference. As an example of this latter type of thiol-terminated liquid polymer, CAPCURE 3-800, marketed by Diamond Shamrock, is exemplified.

Chemical Company.

  The preferred polythiol compounds are

  low level, initially, of odor resembling

  mercaptan and after reaction, it doroedes substantially odorless polythioether end products which are commercially attractive and useful elastomeric rzizs

  in practice both for applications in the field of

  outside and outside. In the case of a polythiol in the

  pairing with allylic polyenes, the molar ratio of thiol groups for the preparation of the composition

  curable range is from 0.2: 1 to about 2: 1 and

  tagously between about 0.75 / 1 and about 1.5 / 1

group report.

  In the case of a polythiol in combination with acrylic components, the molar ratio of the thiol groups in the preparation of the curable composition is between 0j01 / 1 and about 1/1 and advantageously

  from about 0.02: 1 to about 0.5: 1 group ratio.

  Prior to curing, the poly-polythiol polyene components are suitably mixed to form a curable homogeneous liquid mixture. Thus, the reactive polyenes and polythiols can be mixed without the use of a solvent at room temperature or slightly elevated temperatures to about 44 if one of the components is a solid or, if desired, the reagents can be dissolved in a suitable solvent

  and then the solvent can be removed by a means

propriety as an evaporation.

  It will be understood that in order to obtain the maximum mechanical strength, the maximum solvent resistance, the maximum creep resistance, the maximum heat resistance and no adhesivity, the reaction components consisting of the reactive liquid resin containing at least one

  two doubles' iBlisans! niqoes cerbone-carbon per ml (that is,

  polyene) and the polythiol according to the invention are

  formulated to give polymeric systems of poly-

  Thioether in three-dimensional network, solid and

crosslinked, hardening.

  In order to obtain such a durability Imfn, the

  individual polyenes and polythiols must have a function

  at least 2 and the sum of the functionalities of: polyene and polythiol components must always be greater than 4. Mixtures of polyenes and polythioli containing this functionality are also usable:

right here.

  The compositions according to the invention may, if desired, contain additives such as

  oxidants, inhibitors, fillers, anti-oxidants,

  static, combustion retardants, agents

  thickeners, thixotropic surfactants

  active ingredients, viscosity modifiers, plasticizers, tackifiers and the like in

  the scope of the invention. Such additives are usually

  premixed with the ethylenically unsaturated compound before or during the mixing step. Usable fillers include spirits and fibers, glass fibers, wood flour, clay, silica, alumina, carbonates, oxides, hydroxides,

  silicates, glass pallets, borates, phos-

  phates, talcum diatomite, kaolin, barium sulfate, calcium sulfate, calcium carbonate and the like. The above additives may be present in amounts up to 500 or more per 100 parts of the ethylenically unsaturated compound by weight and preferably in the range of 0.005 to about 300 parts by weight on the mone

based.

  In addition, UV stabilizers traditionally

  and oxidizing agents such as hydroquinone, tert-

  butyl hydroquinone, tert-butyl catechol, p-benzoquinone, 2,5-diphenylbenzoquinone, 2,6-di-tert-butyl-p-cresol, benzotriazols such as Tinuvin-P (manufactured by Geigy Corp.) hydroxybenzophenones, like 2,4-hydroxybenzophenone,

  2-hydroxy-4-methoxy-benzophenone, 4-dodecyl-2-hydroxy-

  ben ophenone, substituted acrylonitriles such as acrylate

  of ethyl-2-cyano-2,3-diphenyl; 2-ethylhexyl acrylate;

  2-cyano-3,3-diphenyl and others are added to the system.

  In the practice of the present invention, the composition is preferably subjected to UI radiation with subsequent heat activation. The inversion of

  hardening steps is also helpful but general-

  less desirable. There is no need for photoinitiators to initiate the UV reaction. A class of photoinitiators is composed of aldehydes and carbonyl ketone compounds having at least one aromatic ring directly attached to the group. Various photoinitiators include, without limitation, benzophenone, acetophenone, omethoxybenzophenone,

  acenaphthene-quinone, methyl ethyl ketone, valence

  phenone, hexanophenone, alpha-phenylbutyrophenone, pmorpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone, 4'-morpholinodeoxybenzolne,

  p-diacetylbenzene, 4-aminobenzophenone, 4'-metho-

  xyacetophenone, benzaldehyde, alpha-tetralone,

  9- acetylphenanthrene, 2-acetylphenanthrene, 10-

  thioxanthenone, 3-acetylphenanthrene, 3-acetylindone,

  9-fluorenone, 1-indanone, 1,3,5-triacetyl -

  benzene, thioxanthen-9-one, xanthrene-9-one, 7-H-benz [de] anthracen-7-one, 1-naphthaldehyde, 4,4'-bis (dimethylamino) benzophenone, fluorene -9-one,

  1-acetonaphthon, 2'-acetonaphthon, 2,3-butane-

  dione, triphenylphosphine, tri-o-tolyl phosphine, acetonaphthon, 2,3-butanedione, benz [a] anthracene

7.12 dione and others.

  Another class of photoinitiators is composed of benzene ethers, such as benzolene methyl ether, benzoic ethyl ether, benzoin isopropyl ether,

  benzol isobutyl ether and 2,2-dimethoxy-2-phenyl-

  acetophenone. A third class of photo-initiators

  is represented by benzil dimethyl ketal. The photo-

  initiator or mixtures thereof are usually added in an amount of from 0.0005 to 30% by weight of

  ethylenically unsaturated compound.

  One type of radiation used for curing is ultraviolet light and other forms of actinic radiation normally found in sunlight or artificial sources such as sun lamps of the RS type, arc lamps carbon, xenon arc lamps, mercury vapor lamps, tungsten halide lamps and the like. Ultraviolet radiation can be used very effectively if the photocurable composition

  contains a suitable photoinitiator.

  Hardening times can be adjusted to be very short and therefore commercially economical

  by a good choice of the source of UV rays, the photo-initia-

  and its concentration, temperature and weight

  as well as the function of reactive groups

  of the element of the ethylenically unsaturated group.

  Hardening times of the order of 1 to 80 seconds are possible, particularly in film applications as desired, for example in

conformal coatings.

  When using UV radiation, an intensity of 0.0004 to 60.OwattsY cm2 is usually employed

  in the region of 200 to 400 nanometers.

  The heating step for curing requires heating the reactants to at least 500 ° C and preferably 80 ° to 2500 ° C to form the cured product. In the practice of the present invention, the UV and heat curable composition is mixed in any order and is applied to the

  substrate by various traditional means such as a pulveri-

  sation or a dive. Following application, the composition is exposed to UV radiation for a short period of time, for example about 1 second to 1 minute, and thereafter is exposed to heat, for example, by residence of a single step in a single step.

  traditional for a time sufficient to harden total--

  the composition into a solid product. In addition to traditional sources of heat, it is also possible to use a radiation such as infra-red, a microwave or a high frequency capable of producing the temperature

required in the coating.

  The following examples will help explain, but

  not particularly limited, the present invention.

  Unless otherwise noted, all parts and percentages are by weight.

  In the automotive industry, circuits intended for use under the hood must survive extreme conditions and withstand the attack of antifreeze mixtures. To predict such a performance, the thermal cycling test and a resistance test at

ethylene glycol are used.

  In the thermal cycling test, 51x51x 0.25 mm Mylar circuit boards with a copper circuit but without attached components are dipped in the same dual UV and heat curable compositions according to the invention. The coatings are cured by UV radiation for 20 seconds with heating at 1200C for 60 minutes. The boards are subjected to a thermal cycle by placing them in a freezer at -25oC for one hour and then immediately transfer to an oven at 1200C for one hour. After twenty such cyc:

  the deterioration, if any, is visibly noted.

  In the ethylene glycol resistance test, boards of the same size as those used in the thermal cycle are coated and cured as in the thermal cycle test. The boards are placed in an oven at 1000C for one hour, removed and immediately immersed in a 70/30 solution of ethylene glycol / water at ambient temperatures for one hour. The boards are removed, rinsed, dried and inspected. if there is one, is noted visibly

after twelve of these cycles.

Exemple.1I

  To 231 g of triallyl cyanurate, 30 g of Irgacure-651, a photoinitiator marketed by Ciba Geigy, 5 g of powdered benzopinacol, 0.5 g of pyrogallol, 0.2 g of phosphorous acid, 2 g of triphenylphosphine and g of triphenylphosphite were added. and the additives were dissolved by mixing at 35C for two hours. To the mixture was added 769 g of CAPCURE-3-800, polythiol marketed by Diamond Shamrock, and 2.5 g of Schoenmann odor mask NO 2180. The formula had a viscosity of about 2,700 centipoise. In the above formula, a 10x10cm electronic circuit board was dipped, where resistors, diodes and other components were attached. The total surface area of the board and components was estimated to be in the order of 310 cm2. After diving, the board was immediately turned by hand under a medium pressure mercury lamp of 23.6watt / icm in a parabolic reflector at a distance of

  the order of 30 cm from the lamp for 40 seconds in total.

  The coating was cured in situ on the board, but areas under UV protected components were still uncured. The board was then heated to 110 C for 60 minutes to complete the hardening of these protected areas. The total weight of the coating was 41g. Another board received an initial coating of 18 g allowing it to drain for a few seconds before curing with TJUV, then applying a second coating of 10 g followed by UV curing and heating at 110 C for 60 minutes. For the thermal cycling test, the same formula was coated and cured on three 51x51x0.25 mm Mylar circuit boards.

  with a copper circuit but without fastener components.

  Each board had a coating weight of 4 to 6g.

  After 20 cycles, no deterioration of the coating was observed. For the ethylene glycol resistance test, 3 boards were coated and cured as for the thermal cycle test. After 12 cycles, we did not

  observed no deterioration of the coatings.

Example 2

  Preparation of an urethane triacrylate oligomer

Neascui diacrylate thinner.

  To a mixture of 341.25 g (1.27 moles) of methylene

  bis (cyclohexylisocyanate) containing 0.315 g of stannous octoate and 5.625 g of triphenyl phosphite, 40 g (1.31 moles) of hydroxypropyl acrylate were added. After 2 hours at 50 ° C., 0.225 g was added. of hydroquinone monomethyl ether, 0.315 g of stannous octoate and 280.05 g of hexanediol diacrylate, followed by 324.75 g (0.44 moles of PLURACOL TP740 (730 molecular weight triol

  by reaction of trimethylpropane with

  pylene). After one hour at 80 ° C., the isocyanate content

  It had reached zero, and 0.300 g of hydroquinone monomethyl ether, 0.375 g of pyrogallol, 0.195 g of phosphorous acid and 376.20 g of hexanediol diacrylate were added. The resulting product contained about 56% of an oligomer

  of urethane triacrylate and 44% of hexanediol diacrylate.

Example 3

  160 g of the urd-e triacrylate / hexanediol dacaylate product of Example 2 were mixed with 40 g of

  CAPCURE 3-800, 4.0 g benzopinacol, 2.0 g 2,2-dimethoxy-

  2-phenylacetophenone, marketed by CIBA-GEIGY under the trade name IRGACURE-651 and 2.0 g of triphosphon phosphite. The resulting formula had a viscosity of 2: 300 cp. Parts of this formula could be cured by UV radiation (100mW / cm) in less than 10 seconds or by heating for 30 minutes at 120 C. Circuit boards were dipped, UV-coated (100mW / cm2 for 20 seconds), then heated for one hour at C and subjected to the thermal cycling test between -25 and + 120 C. After 20 cycles, there were no cracks in the coating. Plates coated and cured in a similar manner were subjected to 70% ethylene glycol and

  after 12 cycles they showed no deterioration

tion.

Example 4

!

  25 g of the urethane triacrylate / dia-

  hexanediol crylate of Example 2 was added 0.125 g.

  of benzoyl peroxide, 0.025 g of monomethyl ether of hydro-

  quinone and 0.25g of IRGACURE-651. The resulting formula had a viscosity of 2900 cp. Parts of this formula could be UV cured (100mW / cm2) less

  10 seconds or in 5 minutes at 110 C.

Example 5 To 50 g of the urethane triacrylate / hexanediol diacrylate product of Example 2 was added 0.25 g of 90% t-butyl hydroperoxide, 0.05 g of hydroquinone monomethyl ether and 0.5 g of IRGACURE-651. The resulting formula had a viscosity of 2,800 cp. Parts of this formula could be UV cured (100mW / cm2) in less than 10 seconds or heated for 30 minutes

at 1800C.

Claims (8)

R E V E N D I C A T I 0 N S   1. A method of coating, in its form, an article of irregular shape, characterized in that it comprises coating said article with a composition comprising: (1) a liquid resin, reactive, heat-curable and radiation UV and solvent-free, containing at least two carbon-carbon olefinic double bonds per molecule; (2) a 3-initiator of (1); and (3) a thermal initiator of (1);   exposing said coated article to UV and UV radiation.   to heat the article thus exposed to a   between 50 and 250 ° C for a time sufficient to obtain a fully hardened solid coating. A process for coating, in its form, an irregularly shaped article characterized by coating said article with a liquid, reactive, heat-curable, solvent-free UV composition comprising: (1) at least one ethylenically unsaturated organ of the group consisting of: (a) an ethylenically unsaturated monomer, oligomer or liquid prepolymer of formula: (CH = CC) R   R is H or CH3, R1 is an organic moiety and n is at least 2, (b) a polythiol in combination with (a) above, and (c) a polythiol in combination with a monomer, oligomer or prepolymer. ethylenically unsaturated liquid having the formula: (CH2 = C-CH2) -R3   R2 is H or CH3, R3 is an organic moiety and n is at least 2; (2) a photoinitiator of (1); and (3) a thermal initiator of (1); exposing said coated article to UV radiation and then heating said article so exposed to a temperature of 50 to 250 C for a time sufficient to   obtain a hardened hard coating.   3. Process according to any one of the claims   1 or 2, characterized in that the aforementioned thermal initiator is an organic peroxide of general formula: ROO- (R 1 -O-O) n R on = O or 1, R is independently selected from hydrogen, aryl) an alkyl, an aryl carbonyl, an alkaryl carbonyl, an aralkyl carbonyl and an alkyl carbonyl and R 1 is an alkyl or aryl, said alkyl groups containing 1 to 20 carbon atoms.   4. Process according to any one of the claims   1 or 2, characterized in that the aforementioned thermal initiator is a substituted or unsubstituted pinacol having the general formula: R 1 3 R4   R1 and R3 are substituted or unsubstituted aromatic radicals, which are identical or different, R2 and R4 are substituted or unsubstituted aliphatic or aromatic radicals and X and Y which may be identical or   different are hydroxyl, alkoxy or aryloxy.   5. Process according to claim 2, characterized in that the element of the aforementioned ethylenically unsaturated group is a monomer, oligomer or ethylenically unsaturated liquid prepolymer of formula: ## STR2 ## CH3, R1 is an organic moiety and n is at least 2.   6. Process according to claim 2, characterized in that the organ of the aforementioned ethylenically unsaturated group is an ethylenically unsaturated monomer, oligomer or prepolymer of formula: ## STR2 ## (CH2 = -C-O-) -R1   o R is H or CH5, R1 is an organic moiety and n is at least 2, and a polythiol.   7. Process according to claim 2, characterized in that the element of the ethylenically unsaturated Irreq group is a polythiol in combination with an ethylenically unsaturated liquid monomer, oligomer or prepolymer of the formula: (CH2 = C-CH2) nR3 R2 o R2 is H or CH R3 is an organic fragment and n is at least 2.   8. Process according to claim 2, characterized in that the aforementioned composition contains a diluent reagent.