Method of forming a tentative surface protective coating

A splendid tentative surface protective coating which is useful in treating a surface of a substance by soldering or plating and which is peeled off easily from the surface after the treating is formed by preparing a solventless or solvent free type screen ink based on essentially an ultraviolet ray-curable rubbery elastomer, applying a coating of the ink on the surface of the substrate by screen printing or thin film coating, and curing the coating of the ink by irradiation with an ultraviolet ray. The tentative surface protective coating can reproduce exactly a pattern of a mask or screen, have a high chemical resistance and heat resistance, even if it has a thin thickness of 30 .mu.m, and have no afraid of deformation caused by heat curing, whereby a precise and shortened surface treatment of the surface of the substance can be afforded. Also, working environment is improved, and air conditioning equipment can be dispensed with owing to an absence or diminishment of an organic solvent. In addition, according to the present invention, an excellent ink composition is provided which is much suited to screen printing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of forming a tentative surface 
protective coating cured by irradiation with an ultraviolet ray, an 
ultraviolet ray-curable rubbery elastomer, and a screen ink using the 
elastomer. More particularly, the present invention relates to a method of 
forming a tentative surface protective coating which is used for 
selectively surface treating a surface of a substance such as, a copper 
coated integrated plate usable to a printed circuit substrate, a steel 
plate, an aluminum plate, and a copper plate, a quartz plate, a glass 
plate, other inorganic substance, and organic substance by means of a 
surface treating method such as, electrolytic plating, electroless 
plating, soldering and the like, a rubbery elastomer which is used to the 
method, and a screen ink using the elastomer. 
2. Related Art Statement 
Heretofore, as surface treating methods such as, electrolytic plating, 
electroless plating, and soldering, there have been known the following 
methods: 
.circle.1 a method wherein a surface of a desired substance to be 
surface treated having an inorganic surface is placarded with an adhesive 
tape consisting of a crape paper or a polyester film and an adhesive layer 
laminated thereon, immersed in a plating liquid or a soldering liquid, 
subjected to a desired plating or soldering treatment, taken out from the 
liquid, cooled to ambient temperature, removed from the adhesive tape by 
peeling, rinsed by a rinsing solvent such as Freon (trade name of a 
commercial fluorohydrocarbon made by Du Pont Co.) etc., and dried to 
complete the method; 
.circle.2 a method wherein a surface of a desired substance to be 
surface treated having an inorganic surface is heated and placarded with a 
dry film type photoresist material which is used for plating (a commercial 
product sold by Asahi Chemical Industry Co., Ltd. etc), masked intimately 
by a nega or posi type photomask, cured by irradiation with an ultraviolet 
ray, removed from the photomask, developed at the uncured portions by 
means of a developer such as an alkaline aqueous solution, etc., or an 
organic solvent, dried by heating or irradiation with an infrared ray, 
etc., to form a tentative surface protective coating thereon, immersed in 
a plating or soldering liquid, subjected to a desired plating or soldering 
treatment, taken out from the liquid, cooled to ambient temperature, 
removed from the tentative surface protective coating by means of a 
peeling-off solution determined exclusively for the above dry film type 
photoresist material, such as an organic solvent, e.g., methylene 
chloride, trichloroethylene, etc., or a strong alkaline aqueous solution, 
e.g., a sodium hydroxide aqueous solution, rinsed by water, etc., and 
dried to complete the method; 
.circle.3 a method wherein a surface of a desired substance to be 
surface treated having an inorganic surface is coated with a solution of 
photoresist material in an organic solvent which is used for plating (a 
commercial product sold by Tokyo Ouka Kogyo K.K., etc.) by means of a 
coating machine such as spin coater, houeler, dried by a heating drying 
machine such as drier to remove the organic solvent, masked intimately by 
a nega or posi type photomask, cured by irradiation with an ultraviolet 
ray, removed from the photomask, developed at the uncured portions by 
means of a developer such as an alkaline aqueous solution, etc., or an 
organic solvent, dried by heating or irradiation with an infrared ray, 
etc. to form a tentative surface protective coating, immersed in a plating 
or soldering liquid, subjected to a desired plating or soldering 
treatment, taken out from the liquid, cooled to ambient temperature, 
removed from the tentative surface protective coating by means of a 
peeling-off solution determined exclusively for the above dry film type 
photoresist material, such as an organic solvent, e.g., methylene 
chloride, trichloroethylene, or a strong alkaline aqueous solution, e.g., 
a sodium hydroxide aqueous solution, rinsed by water, etc., and dried to 
complete the method; and 
.circle.4 a method wherein a surface of a desired substance to be 
surface treated having an inorganic surface is printed with a 
thermosetting screen printing ink by screen printing, heat treated to form 
a tentative surface protective coating, immersed in a plating or soldering 
liquid, subjected to a desired plating or soldering treatment, taken out 
from the liquid, cooled to ambient temperature, peeled off physically from 
the tentative surface protective coating to complete the method. 
The above described prior methods have many drawbacks as follows. 
The prior method .circle.1 of placarding the adhesive tape on the 
inorganic surface of the substance to be surface treated is economical in 
cost. However, the tape has an inferior chemical resistance to the plating 
liquid, so that it is frequently peeled off during the plating step, or 
the tape is melted on the inorganic surface due to the use of the 
soldering liquid at a high temperature of 250.degree.-260.degree. C., so 
that, when the adhesive tape is peeled from the inorganic surface, the 
adhesive agent of the tape is transferred to the inorganic surface to 
remain thereon, which adhesive agent is very difficult to remove. 
Moreover, if the areas of the inorganic surface of the substance to be 
placarded by the adhesive tape exist scatteredly on the inorganic surface, 
the tape has to be cut to the respective size of the areas and has to be 
placarded on the areas one by one, so that these procedures are very 
cumbersome and troublesome. 
The prior method .circle.2 of heating the inorganic surface and 
placarding the surface with the dry film type photoresist material has to 
arrange an exclusive laminating machine for the heating and placarding, 
and an exclusive developer machine and an exclusive draft chamber for 
dealing with the developer liquid containing a noxious organic solvent or 
alkaline aqueous solution. In addition, the developer liquid used for 
developing the uncured photoresist material has to be substituted after a 
long use period by a new developer liquid, and the old developer liquid 
has to be processed and discarded. Moreover, the method is laborsome in 
that it needs the drying treatment using the heating or infrared 
ray-irradiation after the developing treatment. Furthermore, the method is 
laborsome and cumbersome in that it requires the exclusive liquid for 
peeling off the tentative surface protective coating from the inorganic 
surface after the plating or soldering treatment. 
The prior method .circle.3 of coating the inorganic surface of the 
substance to be surface treated with the solution of photoresist material 
in an organic solvent has to arrange an exclusive developer liquid and a 
ventilation equipment such as a draft chamber, because apparatuses for 
applying and drying the solution of photoresist material, ventilation 
equipments such as a draft chamber, and the developer liquid for the 
developing treatment deal with a noxious organic solvent or an alkaline 
aqueous solution. In addition, the developer liquid used for developing 
the uncured photoresist material has to be substituted after a long use 
period by a new developer liquid, and the old developer liquid has to be 
processed and discarded. Moreover, the method is laborsome in that it 
needs the drying treatment using the heating or infrared radiation after 
the developing treatment. Furthermore, the method is laborsome and 
cumbersome in that it requires the exclusive liquid for peeling off the 
tentative surface protective coating from the inorganic surface after the 
plating or soldering treatment. 
The prior method .circle.4 of screen printing the inorganic surface of 
the substance to be surface treated with the thermosetting screen printing 
ink can obviate the above drawbacks of prior methods .circle.1 - 
.circle.3 , because the tentative surface protective coating is formed by 
screen printing and heat treatment so that both the cumbersome developing 
treatment and the expensive equipment necessary for the developing 
treatment can be dispensed with, and the tentative surface protective 
coating can be easily peeled off manually by hands. However, if a 
substrate of a laminar structure made of a thin copper layer and a paper 
layer impregnated with a phenolic resin or a glass layer impregnated with 
an epoxy resin tightly adhered to each other by an adhesive is used as a 
printed circuit substrate, the substrate is deformed due to differences of 
thermal expansion coefficients of the layers at the time of heat curing 
the screen printed ink, so that the plating or soldering treatment of the 
screen printed substrate is adversely influenced and difficult to be 
achieved with good precision. Moreover, the method has a drawback of 
necessitating a little long curing time of at least 5-10 min. in case of 
heat curing. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to obviate the 
aforementioned drawbacks of the prior arts. 
The inventors have made many studies and experiments leading to the present 
invention, wherein .circle.1 a solventless or solvent free type screen 
ink based on a rubbery elastomer of an ultraviolet ray-curable type is 
produced, .circle.2 a surface of a substance to be surface treated is 
coated with the ink by a screen printing machine or a thin film coater, 
and .circle.3 the ink is cured by irradiation with an ultraviolet ray 
thereby to form a tentative surface protective coating. 
Thus, the present invention is a method of forming a tentative surface 
protective coating which is used at the time of selectively surface 
treating a surface of a substance by means of a surface treating method of 
electrolytic plating, electroless plating or soldering, comprising, 
producing a solventless or solvent free type screen ink having a screen 
printing property based on essentially a rubbery elastomer having an 
ultraviolet ray-curable property, screen printing or coating an organic or 
inorganic surface of the substance to be surface treated with the ink, and 
curing the ink by irradiation with an ultraviolet ray thereby forming the 
tentative surface protective coating. 
Preferably, the rubbery elastomer is produced by polymerizing the following 
four components of 100 parts by weight of a liquidus dienic rubber having 
at least one or more hydroxyl group and a M.W. of 1,000-10,000, 5-190 
parts by weight of a diisocyanate compound, 1-90 parts by weight of 
dihydric alcohol having a M.W. of not over than 300, and 2-25 parts by 
weight of ethylenically unsaturated monomer having at least one or more 
hydroxyl group. 
Preferably, the main component of the rubbery elastomer is a rubbery 
urethaneacrylate having the following structural formula: 
##STR1## 
wherein R is an alkylene group having 2-8 carbon atoms, R.sub.1 is H or 
CH.sub.3, R.sub.2 is a residue of diisocyanate, R.sub.3 is a residue of 
dihydric alcohol from which one or two hydroxyl group is removed, X is a 
liquidus dienic rubber having at least one or more hydroxyl group from 
which at least one or more hydroxyl group is removed, l is an integer of 
1-4, n is an integer of 1-12, and m is a number of l&lt;m&lt;3. 
The present invention provides also an ink composition comprising, 100 
parts by weight of the ultraviolet ray-curable rubbery elastomer as an 
essential component, and at least one or more of 10-200 parts by weight of 
an ethylenically unsaturated monomer, 0.1-10 parts by weight of a 
photosensitizer, 0.01-10 parts by weight of a thermopolymerization 
inhibitor, 0.001-10 parts by weight of a coloring matter, 0.1-10 parts by 
weight of a defoamer, 0.5-200 parts by weight of thickening agent or 
thickener, 0.1-10 parts by weight of a peeling aid, 5-20 parts by weight 
of a general rubber, 5-20 parts by weight of a liquid rubber, and 5-20 
parts by weight of an organic solvent. 
The ultraviolet ray-curable rubbery elastomer used in the present invention 
is the rubbery urethaneacrylate having the formula (1), or it may be 
selected from polyether series urethaneacrylates and polyester series 
urethaneacrylates having a flexibility of the coating after the curing by 
irradiation with an ultraviolet ray and a pencil hardness of B-6B. 
The tentative surface protective coating according to the present invention 
is a far thinner film than conventional coatings. Despite of such thin 
thickness, the protective coating according to the present invention can 
exhibit a superior chemical resistance to the plating liquid, an excellent 
heat resistance to the soldering, and a splendid peeling-off property 
after the plating or soldering, so that the present invention can diminish 
extensively the drawbacks of the prior methods by using the protective 
coating according to the present invention. Moreover, according to the 
present invention, safety and workability of the prior methods are 
improved, vainness in the production processes can be dispensed with, and 
both the process steps and cost are largely decreased. Furthermore, the 
present invention can provide a surface treating method which can 
reproduce exactly a pattern of the mask or screen, etc. by the screen 
printing and which can produce a heat resistant and chemical resistant 
tentative surface protective coating even if the coating has a much small 
thickness of 30 .mu.m, which tentative coating can easily be handled in 
the plating or soldering treatment and peeled off after the plating or 
soldering treatment. Moreover, the present method can perform a precise 
surface treatment by the irradiation with an ultraviolet ray for a few 
seconds up to several tens seconds, namely, about a half of prior methods, 
without an afraid of deformation, deterioration, etc. of the surface 
treated substance caused by the heat curing. 
Illustrative examples of the liquidus dienic rubber having hydroxyl groups 
are isoprene, acrylonitrile-butadiene copolymer, styrene-butadiene 
copolymer, 1,2-polypentadiene, 1,4-polybutadiene, 1,2-polybutadiene, and 
the like having one or more hydroxyl group at an arbitrary position or 
positions in the molecule and an average molecular weight of about 
1,000-10,000 and the valence m of the hydroxyl group in the molecule is 
about l&lt;m&lt;3. 
Illustrative examples of the ethylenically unsaturated monomer having one 
or more hydroxyl group are 2-hydroxy ethylacrylate, 2-hydroxy 
ethylmethacrylate, 2-hydroxy propylacrylate, 2-hydroxy propylmethacrylate, 
polypropylene glycol monomethacrylate, and the like. 
Illustrative examples of the diisocyanate compound are 
tolylenediisocyanate, xylylenediisocyanate, naphthalenediisocyanate, 
hexamethylenediisocyanate, isophorondiisocyanate, 
4,4'-diphenylmethanediisocyanate, lysinediisocyanate, hydrated 
tolylenediisocyanate, and the like. 
Illustrative examples of the dihydric alcohol having a M.W. of not over 
than 300 are ethyleneglycol, diethyleneglycol, triethyleneglycol, 
1,2-propyleneglycol, 1,3-propyleneglycol, 1,3-butanediol, 1,4-butanediol, 
1,5-pentanediol, 1,6-hexanediol, trimethylolpropanemonoacrylate, 
trimethylolpropane- monomethacrylate, glycerol-monoalkylether, and the 
like. 
Preferably, the isocyanate compound and the dihydric alcohol having a M.W. 
of not over 300 are respectively added at amounts of 5-190 parts by weight 
and 1-90 parts by weight relative to 100 parts by weight of the liquidus 
dienic rubber having one or more hydroxyl group and a M.W. of 
1,000-10,000. If the sum of the amounts of the two components exceeds 280 
parts by weight relative to 100 parts by weight of the liquidus dienic 
rubber, the characteristic properties of the ultraviolet ray-curable 
rubbery elastomer or copolymer, such as, chemical resistance, water 
resistance, flexibility, elasticity, elongation, restoring after bending, 
are damaged, resistances to plating or soldering (chemical resistance and 
water resistance to plating, heat resistance to soldering) are decreased, 
and the peeling-off property is deteriorated. While, if the sum of the 
amounts of the two components is lower than 6 parts by weight relative to 
100 parts by weight of the liquidus dienic rubber, microphases separation 
between hard segments and soft segments of the rubbery elastomer does not 
proceed well, so that the ultraviolet ray-cured copolymer of high strength 
and high elongation can hardly be obtained, resulting in poor peeling-off 
property of the cured copolymer. "Poor peeling-off property" herein means 
a problem of weak strength of the coating that causes severance of the 
coating in case of peeling off the coating from the surface-treated 
surface. The portion of the repeating unit n of the urethane bondage in 
the above formula (1) represents the hard segment, and the portion X of 
the formula (1) represents the soft segment corresponding to the main 
chain of the rubbery elastomer. The rubbery elastomer of the formula (1) 
is composed of such two segments, the soft segment exhibiting the soft 
properties such as flexibility, bend-withstanding, and the like property 
of the rubbery copolymer, and the hard segment exhibiting rigid properties 
such as strength, tenacity, tear strength, and the like property of the 
rubbery copolymer. Thus, the rubbery elastomer according to the present 
invention has an incorporated hard segment, so that it has an improved 
adhering property to the substance surface without an afraid of it being 
peeled off from the substance surface during the plating step. 
Preferably, the ethylenically unsaturated monomer having one or more 
hydroxyl group is added at an amount of 2-25 parts by weight relative to 
100 parts by weight of the liquidus dienic rubber having one or more 
hydroxyl group. If the amount of the ethylenically unsaturated monomer 
exceeds 25 parts by weight, unreacted components and polymers different 
from the polymer of the formula (1) are formed in the polymerization step, 
so that the yield and the shelve stability of the polymer of the formula 
(1) become worse and physically undesirable polymers are produced. In such 
case, only a limited amount of the ethylenically unsaturated monomer 
having one or more hydroxyl group contributes to the addition 
polymerization, and the remainder of the unsaturated monomer remains as an 
undesirable unreacted component. While, if the amount of the ethylenically 
unsaturated monomer is less than 2 parts by weight, unreacted components 
and polymers different from the polymer of the formula (1) are formed in 
the polymerization step, so that the yield and the shelve stability of the 
polymer of the formula (1) become worse and physically undesirable 
polymers of low photosensitivity in case of the addition polymerization 
are produced. As described above, the polymerization of the components is 
restricted by M.W. and number of reacting groups of each component, and 
the amounts of the main components are limited by the formula (1). These 
relations are listed in the following Table 1. 
TABLE 1 
______________________________________ 
Number of 
reacting 
group M. W. 
______________________________________ 
Dienic liquidus rubber 
1 &lt; m &lt; 3 1,000-10,000 
having at least one or 
more hydroxyl group 
Diisocyanate compound 
2 126-500 
(Commercially 
sold) 
Dihydric alcohol of 
2 62-300 
a M. W. of .ltoreq.300 Commercially 
sold) 
Ethylenically unsaturated 
1 102-214 
monomer having a hydroxyl 
group 
______________________________________ 
The ultraviolet ray-curable rubbery elastomer suitable to the use in the 
method of the present invention is selected from polyether series 
urethaneacrylates having flexibility and a pencil hardness of B-6B of the 
coating after cured by irradiation with an ultraviolet ray, polyester 
series urethaneacrylates having the similar property as that of the 
polyether series urethaneacrylates, and the mixture thereof. 
Illustrative examples of such polyether series urethaneacrylates are those 
produced by reacting (a) a prepolymer prepared by modifying the both 
terminals of polyethyleneglycol, polypropyleneglycol, 
polytetramethyleneglycol, etc. with a diisocyanate compound such as 
2,4-tolylenediisocyanate, i.e., a prepolymer having an isocyanate group 
--NCO at both terminals, and (b) an ethylenically unsaturated monomer 
having one or more hydroxyl group such as 2-hydroxyethylacrylate, 
2-hydroxyethylmethacrylate, 2-hydroxypropylacrylate, or the like, in a 
mole ratio of 1:2. 
Illustrative examples of polyester series urethaneacrylates are those 
produced by reacting (a) a prepolymer prepared by modifying the both 
terminals of a polyester made, for example, by polymerizing ethyleneglycol 
and adipic acid, or a polyester made by polymerizing adipic acid, 
ethyleneglycol and triethyleneglycol, namely, a prepolymer having an 
isocyanate group --NCO at both terminals, and (b) the above described 
ethylenically unsaturated monomer, in a mole ratio of 1:2. 
Such polyether series urethaneacrylates are commercially available in the 
market under the trade names of Aronix M-1100, Aronix M-1200, respectively 
produced by Toa Gosei Kagaku Kogyo K.K., and Gocerak UV2000B, Gocerak 
UV3000B, respectively produced by Nippon Gosei Kagaku Kogyo K.K., etc., 
for example. Such polyester series urethaneacrylates are commercially 
available in the market under the trade names of PU-122, PU-124, 
respectively produced by Arakawa Kagaku Kogyo K.K., etc., for example. 
"Flexibility and a pencil hardness of B-6B of the coating after cured by 
irradiation with an ultraviolet ray" hereby means that a cured coating of 
the above described polyether or polyester series urethaneacrylate added 
with a photosensitizer, such as benzoin, benzoinmethylether, benzophenone, 
michlersketone, azobisisobutyronitrile, benzyldimethylkethal, 
2-methylanthraquinone, 2,2-diethoxyacetophenone, etc., and irradiated with 
an ultraviolet ray to cause acryloyl groups or methacrylate groups react 
sufficiently, has a physical property of a pencil hardness B-6B and a 
rubber-like state. 
Preferably, the screen printable solventless or solvent free type screen 
ink suitable for the method of the present invention is an ink composition 
comprising, the above ultraviolet ray-curable rubbery elastomer, the 
ethylenically unsaturated monomer, and the photosensitizer as essential 
components, and further comprising at least one of a substance selected 
from the group consisting of a thermopolymerization inhibitor, a coloring 
matter, a defoamer, a thickening agent, a peeling aid, a general rubber, a 
liquid rubber, and some amount of an organic solvent. 
As the ethylenically unsaturated monomer for the ink composition, use is 
made of at least one of the above ethylenically unsaturated monomers 
having one or more hydroxyl group; methacrylates such as 
methylmethacrylate, ethylmethacrylate, butylmethacrylate, 
glycidylmethacrylate, 1,4-butylenedimethacrylate, 
ethyleneglycoldimethacrylate, and diethylaminoethylmethacrylate; acrylates 
such as methylacrylate, ethylacrylate, butylacrylate, laurylacrylate, 
trimethylolpropanediacrylate, trimethylolpropanetriacrylate, 
neopentylglycoldiacrylate, 1,6-hexanediacrylate, and 
diethylaminoethylacrylate; methacrylic acid; acrylic acid; acrylonitrile; 
acrylamide; N-methylolacrylamide, styrene; vinyltoluene; 
.alpha.-methylstyrene; vinylacetate; N-vinyl-2-pyrrolidone; and 
diallylphthalate, etc. The amount of the ethylenically unsaturated monomer 
to be added and blended is generally 10-200 parts by weight relative to 
100 parts by weight of the ultraviolet ray-curable rubbery elastomer. 
As the photosensitizer, use is made of at least one benzoin, 
benzoinmethylether, benzoinisopropylether, benzoinbutylether, 
benzophenone, michlersketone, 1-naphthalene-sulfonylchloride, 
2,5-naphthalenedisulfonylchloride, 2-naphthalenesulfonylchloride, 
azobisisobutylnitrile, 1-azobis-1-cyclohexanecarbonitrile, 
benzyldimethylkethal, 2-methylanthraquinone, biimidazole, thioxantone, 
2,4-diisopropylthioxantone, 2,2-diethoxyacetophenone, benzoinperoxide, and 
2,4-dichlorobenzoylperoxide, etc. The amount of the photosensitizer to be 
added and blended is generally 0.1-10 parts by weight relative to 100 
parts by weight of the ultraviolet ray-curable rubbery elastomer. 
As the thermopolymerization inhibitor, use is made of at least one of 
hydroquinone, t-butylcathecol, o-dinitrobenzene, o-nitrophenol, 
m-nitrophenol, p-nitrophenol, 2,4-dinitrirophenol, 2,4,6-trinitrophenol, 
phenothiazine and ferric chloride, etc. The amount of the 
thermopolymerization inhibitor to be added and blended is generally 
0.01-1.0 parts by weight relative to 100 parts by weight of the 
ultraviolet ray-curable rubbery elastomer. 
As the coloring matter, use is made of at least one of dyes and pigments, 
generally in an amount of 0.01-1.0 parts by weight relative to 100 parts 
by weight of the ultraviolet ray-curable rubbery elastomer. 
As the defoamer, use is made of at least one of silicone series-, acryl 
series-, polyglycol series-, and polyether series-surfactants, generally 
in an amount of 0.1-10 parts by weight relative to 100 parts by weight of 
the ultraviolet ray-curable rubbery elastomer. 
As the thickening agent or viscosity increasing agent, use is made of at 
least one of inorganic fillers, such as silica, talc, magnesium carbonate, 
calcium carbonate, titanium oxide, etc. generally in an amount of 0.5-200 
parts by weight relative to 100 parts by weight of the ultraviolet 
ray-curable rubbery elastomer. 
As the peeling aid or stripping agent, use is made of at least one of 
silicone series-, glycol series-, acryl series-, and wax series-peeling 
aids, etc. generally in an amount of 0.1-10 parts by weight relative to 
100 parts by weight of the ultraviolet ray-curable elastomer. 
As the general rubber, use is made of at least one of polybutadiene rubber, 
isoprene rubber, chlorosulfonated polyethylene rubber, natural rubber, and 
polybutylene rubber, etc. generally in an amount of 5-20 parts by weight 
relative to 100 parts by weight of the ultraviolet ray-curable elastomer. 
The general rubber is occasionally added and blended in the ink 
composition expected to be used in especially severe conditions for 
improving the chemical resistance and the heat resistance of the cured ink 
composition. The amount of blending the general rubber is dependent on the 
screen ink property, and the influence to the ultraviolet ray-curability 
of the screen ink. If the blending amount of the general rubber exceeds 
the upper limit of the above blending range, the ultraviolet raycurability 
of the ink is decreased because the general rubber is a non-photosensing 
substance. The addition of such excessive amount of general rubber is also 
not preferable from the viewpoints of public pollution and workability, 
because the general rubber is added to the ink in a form of a solution in 
an organic solvent. 
As the liquid rubber, use is made of at least one of the above general 
rubber of liquid type, generally in an amount of 5-50 parts by weight 
relative to 100 parts by weight of the ultraviolet ray-curable elastomer. 
Similarly to the general rubber, the liquid rubber is occasionally added 
and blended in the ink composition expected to be used in especially 
severe conditions for improving the chemical resistance and the elastic 
property of the cured ink. The amount of blending the liquid rubber 
depends on the screen ink property, and the influence to the ultraviolet 
raycurability of the screen ink, similarly to the case of the general 
rubber. The influence of the addition of an excessive amount of the liquid 
rubber is similar to that of the general rubber. However, the liquid 
rubber is added and blended into the ink without using an organic solvent, 
so that the problems of public pollution and workability do not occur at 
all. 
If necessary, in case when, for example, adding the general rubber in a 
form of a solution in an organic solvent to the ink, an organic solvent of 
an arbitrary type is optionally added to the general rubber for imparting 
a screen printing property to the ink, generally in an amount of 5-20 
parts by weight relative to 100 parts by weight of the ultraviolet 
ray-curable rubbery elastomer. The amount of the organic solvent is such 
that the screen printing property and the working environment are not 
adversely influenced and the screen is not caused to clog by evaporation 
of the organic solvent, that the curing speed and the curing of the 
ultraviolet ray-curable rubbery elastomer are not adversely influenced, 
and that it is usually used depending on its solvent power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, the present invention will be explained in more detail with 
reference to examples, which however, should not be construed by any means 
as limitations of the present invention. 
EXAMPLE 1 
(Preparation of the polymerized ultraviolet ray-curable rubbery copolymer) 
29.2 g of 2,4-tolylenediisocyanate is dissolved in 87.6 g of dioxane. The 
solution is charged in a 500 ml capacity reactor, and added with dropwise 
of 7.5 g of 1,4-butanediol in 22.5 g of dioxane, while agitating in 
nitrogen atmosphere. During the addition, the reaction temperature is held 
at 45.degree.-50.degree. C., and the reaction is effected for 3 hrs. at 
45.degree.-50.degree. C. after finishing the addition. Thereafter, the 
solution is added with dropwise of a solution of 10 g of 
2-hydroxyethylmethacrylate, 0.15 g of hyroquinone and 0.075 g of 
triethylenediamine in 33 g of dioxane. During the addition, the reaction 
solution is held to 75.degree.-80.degree. C., and the reaction is effected 
for 2 hrs. at 75.degree.-80.degree. C. after finishing the addition. The 
reaction solution is added dropwise to a solution of 100 g of hydroxyl 
groups terminated liquidus polybutadiene rubber (average M.W.=2,800, 
content of hydroxyl groups is 0.83 meg/g, sold in the market under the 
trade name of "Poly bd R-450" from Idemitsu Petrochemistry K.K.) in 300 g 
of dioxane in a separate 1,000 ml capacity reactor, while agitating in 
nitrogen atmosphere. During the addition, the reaction solution is held at 
75.degree.-80.degree. C., and reacted at 75.degree.-80.degree. C. for 8 
hrs. after finishing the addition. The completion of the reaction is 
confirmed by disappearance of absorption of isocyanate group in infrared 
absorption spectrum. 
The reaction solution is gradually dropped in 5,400 ml of n-hexane in a 
beaker, while agitating, to obtain a white precipitate. The precipitate is 
purified from n-hexane, dried in a vacuum drier for 2 days to obtain a 
rubbery urethaneacrylate of a solid state. The urethaneacrylate is 
dissolved in tetrahydrofuran, added with 5% of a photosensitizer 
commercially available in the market under the trade name of Irgacure 631 
produced by Ciba Geigi Co., and the photosensitizer is dissolved to 
prepare a photosensing solution. The photosensing solution is applied on a 
glass plate to evaporate tetrahydrofuran to dryness to obtain a dry film 
of a thickness of 100 .mu.m. 
Then, the dry film is exposed to a 3 kW input super high pressure mercury 
light device produced by K.K. Oak Seisakusho positioned at a distance of 
50 cm for 30 seconds, to obtain a cured film. The cured film is tested on 
a tensile test machine. It has physical properties of a tensile strength 
of 120 kg/cm.sup.2, an elongation of 250%, and a Shore A hardness of 70. 
EXAMPLE 2 
(Preparation of a solvent free type screen ink having screen printing 
property based on essentially the ultraviolet ray-curable rubbery 
elastomer) 
Based on the rubbery urethaneacrylate produced by the procedure of Example 
1, an ethylenically unsaturated monomer, a photosensitizer and other 
additives as listed in the following Table 2 are blended in a recipe as 
shown in Table 2 to prepare an ink A. While, based on a commercial 
polyether series urethane-acrylate of a trade name of Aronix M-1100, an 
ethylenically unsaturated monomer, a photosensitizer and other additives 
as listed in Table 2 are blended in a recipe as shown in Table 2 to 
prepare and ink B. 
TABLE 2 
______________________________________ 
(g) 
Component Ink A Ink B 
______________________________________ 
Ultraviolet ray- 
(Rubbery 100 
curable rubbery 
urethaneacrylate of 
elastomer Example 1) 
Ultraviolet ray- 
(.sup.(1) Polyether series 
100 
curable rubbery 
urethaneacrylate) 
elastomer 
Ethylenically 
(N-vinyl-2-pyrrolidone) 
50 80 
unsaturated 
monomer 
Ethylenically 
1,6-hexanediacrylate) 
100 20 
unsaturated 
monomer 
Thickener (.sup.(2) Aerosil #130) 
10 4 
Thickener (.sup.(3) Mistron vapor talc) 
100 -- 
Defoamer (.sup.(4) Foamaster AP) 
5 5 
Sensitizer 
(Irgacure 651) 5 5 
Peeling aid 
(.sup.(5) Separ 404) 
5 5 
Dye (Phthalocyanine blue) 
1 1 
Sum 376 220 
______________________________________ 
Notes: 
.sup.(1) Aronix M1100 produced by Toa Gosei Kagaku Kogyo K.K. 
.sup.(2) Trade name, produced by Nippon Aerosil K.K. 
.sup.(3) Trade name, produced by Nippon Mistron K.K. 
.sup.(4) Trade name, produced by Sunnopco K.K. 
.sup.(5) Trade name, produced by Chukyo Yushi K.K. 
Preparation method of ink A is first to dissolve the rubbery 
urethaneacrylate of Example 1 in N-vinyl-2-pyrrolidone and 
ethylcarbitolacrylate while agitating, then to add the whole of the above 
additives to the solution and agitate, and further to pass through an ink 
roll three times. 
Preparation method of ink B is the same as that of ink A, except that 
Aronix M-1100 is used instead of the rubbery urethaneacrylate of Example 
1. 
Inks A and B are tested on viscosity and thixotropic index by a BH type 
viscosimeter produced by K.K. Tokyo Keiki at 25.degree. C. The results are 
shown in the following Table 3. 
TABLE 3 
______________________________________ 
Ink type 
Test Ink A Ink B 
______________________________________ 
Viscosity (cps) 300,000 300,000 
Thixotropy index 6.5 7.2 
______________________________________ 
EXAMPLE 3 
(Screen printing) 
Screen printings are effected using the inks A and B prepared by Example 2. 
Conditions of the screen printings are a screen of 150 mesh, a screen 
emulsion thickness of 50 .mu.m, a screen plate of fine lines resolving 
pattern, an urethane squeeze of a Shore A hardness of 60, a print 
circuited substrate (as thin plate of glass epoxy-copper having on both 
sides printed circuits after punching out of throughholes and formation of 
the circuits by etching), and a manual screen printing. The results of the 
screen printings are shown in the following Table 4. 
TABLE 4 
______________________________________ 
Ink type 
Property Ink A Ink B 
______________________________________ 
Thickness of printed 
46 50 
coating (.mu.m) (Note) 
Defoaming property 
Good Good 
Levelling property 
Good Good 
Reproducibility of 
Fairly Fairly 
fine lines reproduced 
reproduced 
a fine line 
a fine line 
of 500 .mu.m 
of 500 .mu.m 
______________________________________ 
Note: 
Measured on the ink screen printed on a glass plate and cured by an 
ultraviolet ray under the irradiation condition of Example 4. The 
measurements are effected by means of a micro gauge. 
EXAMPLE 4 
(Curing by an ultraviolet ray) 
The inks A and B screen printed on glass plates by the procedure of Example 
3 are cured under the following curing conditions. 
Curing condition: 
A 3 kW input super high pressure mercury light device "polymer printer" 
produced by K.K. Oak Seisakusho is used at a distance of 50 cm from the 
glass plate for an irradiation of 30 seconds. 
After curing, both the inks A and B assume a tack-free state, and no defect 
is seen of a wrinkle caused by uncure of the inks. The pencil hardnesses 
of the inks A and B are B and 6B, respectively. 
EXAMPLE 5 
(Plating treatment) 
The print circuited substrates (A' and B') having screen printed and 
ultraviolet ray-cured inks A and B prepared by Example 4 are respectively 
immersed in an electrolytic plating aqueous solution of AgCN of a hydrogen 
ion concentration of 14 at 30.degree. C. for 2 hrs. to perform a plating 
treatment. After the plating, the print circuited substrates are taken out 
from the plating solution, and rinsed with water. Thus obtained tentative 
surface protective coatings according to the present invention show no 
peeling and adhered well to the glass plates. An end of the coating is 
peeled away from the glass plate by nail, and then pulled away from the 
glass plate by fingers. The peeled-off coating has a rubber-like 
elasticity, and was not severed during the peeling-off or pulling-away 
step. 
EXAMPLE 6 
(Plating treatment) 
The print circuited substrates A' and B' having screen printed and 
ultraviolet ray-cured inks A and B prepared by Example 4 are respectively 
immersed in a soldering liquid at 250.degree. C. for 5 seconds. After the 
immersion, the substrates are taken out from the soldering liquid, and 
cooled to ambient temperature. Thus obtained tentative surface protective 
coatings according to the present invention show no peeling and adhered 
well to the glass plates. An end of the coating is peeled away from the 
glass plate by nail, and then pulled away from the glass plate by fingers. 
The peeled-off coating has a rubber-like elasticity, and was not severed 
during the peeling-off or pulling away step. 
As explained in detail in the foregoings, the tentative surface protective 
coating according to the present invention is formed by preparing a 
solventless or solvent free type ink of a screen printable characteristic 
property based on essentially the ultraviolet ray-curable rubbery 
elastomer, applying a coating of the ink on a surface of an organic or 
inorganic substance to be coated by screen-printing or a thin film 
coating, and then irradiating the coating of the ink with an ultraviolet 
ray to cure the coating of the ink. Therefore, despite of the thin 
thickness of, e.g., 30 .mu.m, of the surface protective coating, the 
surface protective coating has superior chemical resistance and heat 
resistance in case of soldering as well as excellent peeling-off property 
after a soldering or plating treatment. In forming the tentative surface 
protective coating the solventless or solvent free type screen ink is 
used, so that working environment is improved and air conditioning 
equipment can be dispensed with owing to the absence of an organic 
solvent. In addition, the tentative surface protective coating is formed 
by screen printing of the ink and curing of the ink with irradiation of an 
ultraviolet ray, so that an exact pattern of screen or mask can be 
reproduced, a precise surface treatment can be afforded, deformation of 
the surface treated substance and other drawbacks of prior art due to heat 
curing can be obviated, and curing time can be shortened extensively. 
Although the present invention has been explained with specific examples 
and numeric values, it is of course apparent to those skilled in the art 
that various changes and modifications thereof are possible without 
departing the broad spirit and aspect of the present invention as defined 
in the appended claims.