Note: Descriptions are shown in the official language in which they were submitted.
3~39
12428
BACKGRO~D OF THE INVENTIO~
Coatings play a useful role in the manufacture of a
great many articles which find wide use in nearly all facets of
contemporary life. Until recently, nearly all coatings were
applied with the employment of a hydrocarbon based vehicle
which evaporated leaving the dried coating on the article which
was to be coated. This system met with increasing disfavor as
the cost of energy needed to drive off the solvent at the -rate
required by industry increased, as the price of the organic
solvent itself increased and as the deleterious environmental
effects of the evaporated solvent became better understood.
Systems aimed at solvent recovery to reduce pollution and con-
serve solvent have generally proven to be energy intensive and
expensive.
In response, those s~illed in the art have devised
a class of coatings termed radiation curable coatings, These
curing systems have displayed high desirability because they
are relatively free of volatile solvent and cure quickly at
low temperatures,
~ nong the most successful of the radiation curable
coatings are those which are curable by ultraviolet light. This
success is attributable in part to the lower capital investment
required for equipment to cure these coatings, Thes,e ultra-
violet light curable coatings, termed photocurable coatings,
t~Jpically ernploy a solution of a photoinitiator in a reactive
coating liquid. The liquid approaches a pollution-free system
as almost all of the liquid is converted to cured coating with
little or no solvent emission upon the brief exposure to ultra-
-2- ~ ~
.~
3 ~
. 12428
violet light. Among ehe most successflll photocurable coating
systems have been the acrylate based systems because of the
toughness of the cured surface.
One of the disajdvantages of photocurable systems is
the need to employ expensive and possibly harmful photoini~iators.
Another disadvantage is the frequent requiremen~ that the
curing process be conducted in an inert atmosphere because of
the inhibiting effect of oxygen.
Responding to these problems, those skilled in the
art have devised photocurable coatings which cure through a
mechanismtermed cationic polymerization. In these systems the
starting materials are mixed with catalysts which form acids
when e~posed to ultraviolet light; the starting materials are
therefore polymeriæed via cationic catalysis which involves
the ~ormation and ~Lopagation of carboniu~.. ions ~o generate
the polymer molecules. This cationic pol~merization mechanism
is essentially limited to those monomers with electron-releasing
Rubstltuents.
Epoxy resins have been shown to be suitable starting
materials for photocure via cationic polymerization as disclosed
in U.S. 3,794,576, for example. However, the cured coatings
using these starting materials have not demonstrated strong
re~istance to wear~
A photocurable coating composition formulated with
a compound which can be cured via cationic polymerization and
when cured displays increased toughness over such compositions
as are currently known would be highly desirable.
12428
S~ARY OF THE INVENTI021
It has now been found that photocurable coatings can
be prepared by use of compounds containing a cyclic vinyl
ether moiety. These photocurable coatings can be cured thrcugh
cationic polymerization thereby avoiding the requirements of
conventional photocurable coatings of expensive photoinitiators
and an inert atmosphere. These novel photocurable coatings
cure to a surface which exhibits markedly increased toughness
over the cured surface of the heretofore known photocurable
coatings curable via cationic polymerization. A further
advantage of the novel photocurable coatings of this invention
is that they can be made from starting materia~s which are re-
latively inexpensive.
D ~
The compositions of this invention are radiation
curable coatings formulated with compounds of the formula:
kCH20X
wherein R is hydrogen or methyl and X is
- C ~O ~ , ~ H2fHO ~H or - C - R'
R R
--4--
1242~
wherein n has a value of from 1 to 10 and wherein R' is the
residue of a carboxylic acid and can be hydrogen, alkyl,
substituted with any substituent which does not unduly
interfere with the polymerization or unsubstituted,linear
or branched, containing up to 20 carbon atoms, such as
methyl, ethyl, isopropyl, decyl, eicosyl and the like, and
aryl, substituted with any substituent which does not un-
duly interfere with the polymerization or unsubsti~uted,
having 6 to 10 ring carbon atoms, such as phenyl, naphthyl,
benzyl, phenethyl, and the like.
Under acidic conditions these cyclic vinyl ethers undergo
facile cationic polymerization when exposed to ultraviolet
light to give hard, tack free, wear resistant films.
Among the many compounds which contain the cyclic
vinyl ether moiety and are therefore useful in the compositions
o~ this invention are the reaction products of the Diels-
Alder reaction of acrolein and the reaction products of
acrolein with alkene or with vinyl ethers and the subsequent
derivatives.
Another useful compound in the compositions of this
invention is the Tischenko reaction product of 3,4-dihydro-2H-
2-formylpyran as prepared, for example, in Example 2 of ~ S.
2,537,921. This compound being 3,4-hydropyran-2-methyl(3,4-
di.hydropyran-2-carboxylate).
Another group of compounds which are useful in the
compositions of thi.s invention are the alkylene oxide adducts
of 3,4-hydropyran-2-methanol of the general formula
12567
/\
~ , ~ C~O ~ ~-CHO ~ H
where R and n are as hereinbefore defined. This
class of compounds is prepared by the ethoxylation or propoxy-
lation of 3,4-dihydropyran~2-methanol with a base catalyst
such as potassium or sodium metals, The catalyst concentration
can be rom 0.1 weight percent toO.4 weight percent, preferably
from 0.2 weight percent to 0.3 weight percent based on the
weight of the final product. The reaction can be carried out at
a temperature of from 75C to 150C, preferably from 100C to
120C. If, desired, the ethoxyl~ted or propoxylated 3,4-dihydro-
pyran-2-methanol can be lin~;ed by multifunctional diisocyanates,
such as, for example, the toluene diisocyanates.
Still another group of compounds which can be used
in the compositions of this invention are the esters of at least
one organic carboxylic acid and 3,4-dihydropyran-2-methanol
corresponding to the formula
~ O
C ~ CH20C R
--6--
3 ~ ~ ~
12~28
wherein R and R' are as hereinbefore defined.
These compounds are prepared by conventional esterification or
transesterification procedures with a suitable catalyst and
can contain substituents in the molecule provided they do not
unduly interfere with the reaction. These procedures and catalysts
are well known to those skilled in the art and require no further
elaboration. In the transesterification, the lower alkyl esters
of organic acids are preferred sources of the acid moiety.
The photocurable coatings of this invention also
contain a catalytically effective amount of a catalyst sufficient
to catalyæe the reaction. This amount can vary from 0.1
weight percent to 10 weight percent, preferably from 0.5
weight percent to 5 weight percent, based on the weight of
the cyclic vinyl ether moiety containing compound ! The catalysts
are those which form an acid when exposed to ultraviolet radiation
such as the aryldiazonium salts, the aryliodionium salts and
the arylsulfonium salts. Illustrative of such catalysts one
can name p-methoxybenzenediazonium he afluorophosphate, benzene-
diazonium tetrafluoroborate, toluenediaæonium tetrafluoro
arsenate, diphenyliodionium hexafluoroarsenate, benzenesulfo~ium
hexafluorophosphate, toluenesulfonium hexachloroantimonate,
and the like.
The catalyst can be introduced directly but preferably
it i9 introduced in solution with a suitable solvent such as
sulEolane or the aromatic hydrocarbons such as xylene.
3 ~ ~ ~
12428
The cyclic vinyl ether moiety containing compound and
the catalyst can be combined under any practicable conditions
of temperature, preferably from 10C to 40C.
The photocurable compounds of this invention can be
used per se as coatings or in admixture with conventional
solvents, pigments, fillers and other additives. They can be
applied by conventional means including, spray, curtain, dip, pad,
rollcoating and brushing procedures. They can be applied to any
acceptable substrate such as wood, metal, glass, fabric, paper,
fiber or plastic that is in any shape.
The photocurable coating compositions of this
invention are cured by exposure to particulate or nonparticulate
radiation. The exposure time will vary and will depend upon a
number of factoxs such as the coatings components and the film
thlckness, as well as the type and intensity of radiation used,
but is generally quite short, generally less than 30 seconds and
~sually less than lO seconds.
The radiation curable coatings of this invention find
~ide use in many coating applications. The novel coatings of
this invention, because of their cationic polymerization curing
mechanism are advantageous over conventional photocurab-le coatings
in that neither expensive photoinitiators nor an inert curing
atmosphere need to employed. Furthermore the novel coatings of
this invention cure to a surface having better wear characteristics
than cured films of many of the heretofore known cationically
--8--
3~
12428
polymerizable photocurable coatings. It was completely unexpected
and unobvious that this would be so. Neither the fact that
coatings containing compounds having at least one cyclic vinyl
ether moiety could be cured when exposed to ultraviolet light
via cationic polymerization nor the fact that the cured films of
such coatings would display distinct advantages over heretofore
available cationically polymerized photocured films could have
been predicted.
The following examples serve to further illustrate
the invention. In these examples the following definitions apply
to the testsemployed and to the values reported.
Acetone resistance is a measure of the resistance
of the cured film to attack by acetone and is reported in the
number of double rubs or cycles of acetone soaked material
required to remove one half of a film from the test area. The
test is perfor~ed by stroking the film with an acetone soaked
cheesecloth until that amo~nt of film coating is removed. The
number o cycles required to remove this amount of coating is a
measure of the coating solvent resistance.
Pencil hardness is a measure of film hardness. The
,
adhesion and cohesive strength of the film also influences pencil
hardness, Pencils of known lead hardness are shaped to a
cylindrical point with a flat tip. The pencils are manually
pushed into the coating surface at a 45 angle. Pencil hardness
is recorded as the hardest pencil which does not cut the coa~ing.
Revers_ impact measures the ability of a given film
to resist rupture from a falling weight. A Gardner Impact Tester
using a eight pount dart is used to test the films cast and cured
_g_
12428
on a steel panel. The dart is raised to a given height in
inches and dropped on to the reverse side of a coated metal
panel. The inches ti.mes po~nds,designated inch-po-~nd, absorbed
by the film without rupturing is a ~easure of the reverse-
impact resistance of the film.
Exam~le 1
A coating composition was produced by uniformly
blending 20 ~rams of 3,4-dihydropyran-2-methyl (3,4-dihydro-
pyran-2-carboxylate) and 0.8 grams of a 25 p~rcent solution of
p-methoxybenzenediazonium hexafluorophospha~e in sulfolane.
The ~ixture was coated on steel panels with a No.40 wire wound
rod. The coatings were cured by passing through an ultraviolet
photocuring unit which delivered an ultraviolet flux density of
about 2500 watts per square foot; ~he path length was 2 feet and
the conveyor belt speed was 40 feet per minute, giving an
exposure time to the ultra~iolet radiation of about 3 seconds.
clear tack ree film about 1.5 mils in thickness was thus
obtained. The cured film was evalua~ed and the r~sults were
as follows:
Acetone Resistance ~ 100
Pencil Hardness 3H
Reverse Impact ~ 5 in-lbs.
For comparative purposes a cationically polyrnerizable
photocurable coating based on a blend o 20 grams of (3,4-epoxy-
cyclohexoyl)me~hyl 3,4-epoxycyclohexanecarboxylate and 0.8 grarl~s
of a 25 percent solution o$ p methoxybenzenediazoniurn hexzfluoro-
-10 -
9 9
12428
phosphate in sulfolane was produced and coated on a steel pan~l
and cured using a procedure similar to that described above.
A clear, tac~ free film of abou~ 2.6 mils in thickness was
obtained. The cured film was evaluated and the results were
as follows:
Acetone Resistance 8
Pencil Hardness B
Reverse Impact < 5 in-lbs
The results establish the superior toughness of ~he
films of photocurable coatings of this invention o~er films of
the heretofore available cationically polymerizable epoxide
based photocurable coatings.
Exam~le 2
There were charged to a 1 liter 4 neck flask 49.8
grams of 3t4-dihydropyran-2-methanol and 0.4 gram of potassiu~.
metal. The reactor was purged with dry nitrogen during the
addition of the potassium metal. Thereafter, 111.8 grams of
ethylene oxide was fed in~o the reactor over a 4-1/2 ho~lr period
while the reaction temperature was maintained at from 110C to
120C. The unreacted ethylene oxide was then removed under
reduced pressure at from 70C to 80C using a Rotova ~evaporator.
The ethylene oxide adduct of 3,4-dihydropyran-2-methanol produced
weighed 168.4 grams and had an average of 6 e~hyleneoxy units
in the molecule,
There were charged to a dry 500 ~1 ,4 neck, round
bottom 1ask 40 grams of the above adduct, 0.42 gram of stannous
octoate as catalyst and 50 grams of 3,4-dihydropyran-2-methyl
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(3,4 dihydropyran 2-carboxylate). Thereafter ~here was added
18.8 grams of toluene diisocyanate over a 35 minute period
while the temperature was kept below 40C, while the mixture
was stirred and purged with nitrogen. Then, while stirring at
room temperature for an additional 2-1/2 hours, 50 gra~s more
of 3,4-dihydropyran-2-methyl (3,4-dihydropyran-2-carboxylPte)
were added to the reaction mixture to give a final product having
a total solids content of 37 percent.
Twenty grams of this 37 percent solids composition
was combined with 17 grams of 3,4-dihydropyran-2-methyl (3,4-
dihydropyran-2-carboxylate) and 1.1 grams of a catalyst of a
25 percent solution of p-methoxybenzenediazonium hexafloro-
phosphate in sulfolane to produce a photocurable coating. Films
o about 1 mil in thickness of this coating were applied on
steel panels and cured, by passing through an ultraviolet photo-
curing unit which delivered a flux density of about 2500 watts
per square foot; the path length was 6 feet and the conveyor belt
~peed was 50 feet per minute, giving a exposure time to the
ultraviolet radiation of about 7.2 seconds. The hard, tack
~ free cured film was evaluated and the results were as follows:
Acetone Resistance > 100
Pencil Hardness 4H
- Reverse Impact 10 in-lbs.
