Radiation curable cross linkable compositions containing an aliphatic polyfunctional alkenyl ether

This invention relates to a radiation curable crosslinkable composition containing (a) from about 0.1 to about 5 wt. % of an initiator containing at least 25% cationic initiator, (b) from about 0 to about 60 wt. % of a polymerizable vinyl ether, epoxide, vinyloxy alkyl urethane or acrylate and (c) from about 35 to about 99.9% wt. % of a polyfunctional alkenyl ether having the formula EQU A[(CH.sub.2 O).sub.m (Z).sub.r CH.dbd.CHR].sub.n wherein A is a carbon atom, --OCH.dbd.CHR or [C.sub.1 to C.sub.10 alkyl].sub.4-n ; R is C.sub.1 to C.sub.6 alkyl; Z is C.sub.2 to C.sub.8 alkyleneoxy; r has a value of from 0 to 6; m has a value of from 0 to 1 and at least one of r and m has a positive value; n has a value of from 1 to 4, with the proviso that m is 0 and n is one when A is --OCH.dbd.CHR, n has a value of 2 or 3 when A is [C.sub.1 to C.sub.10 alkyl].sub.4-n and n has a value of 4 when A is carbon. The invention also relates to the process of curing said composition and to a cured film on a substrate coated with the above composition.

BACKGROUND OF THE INVENTION 
Certain radiation curable coatings and films such as those formed from the 
acrylates, particularly trimethylol propane triacrylate, trimethacrylate, 
pentaerythritol triacrylate, and hexanediol diacylate or methacrylate, are 
in great demand because of their rapid curing properties. However, these 
compounds are normally highly viscous liquids or solids and thus are 
unsuitable as diluents for other polymeric components of a radiation 
curable formulation. Indeed, such compounds themselves require the 
incorporation of a diluent or solvent for uniform substrate coating, 
control of coating thickness and curing at low temperatures. Accordingly, 
low viscosity monofunctional diluents are usually included in their 
formulations. While these diluents are reactive, they materially reduce 
the cross-linked density of the finished product and consequently lower 
abrasion resistance and ability to withstand chemical attack. 
Although solvents have been used to reduce viscosity, they are detrimental 
in radiation curing due to their volatility which presents problems for 
uniform composition control unless their evaporation prior to radiant 
exposure is effected. Obviously, such procedure extends processing time 
and may pose environmental drawbacks. 
To some extent, the drawbacks of high viscosity monomers can be reduced by 
curing at elevated temperatures. However, this alternative significantly 
adds to the cost of the overall operation in the expenditure of energy, 
temperature control and loss of more volatile components in the 
composition or blistering of the coating resulting from entrained 
volatiles. 
Since acrylate monomers are not conducive to cationically induced radiation 
curing, they require free radical systems which are oxygen inhibited 
unless effected in an inert atmosphere, generally under a blanket of 
nitrogen. Although formulation with a photoinitiator which undergoes 
bimolecular reaction with a hydrogen donor minimizes the inhibitory effect 
of air, this benefit is realized at the expense of a greatly reduced cure 
rate. Also, it is found that polymerization or curing in free radical 
systems ceases almost immediately upon removal from the source of 
radiation; thus, the cured product often contains significant amounts of 
unpolymerized components. Accordingly, it is an aim of research to develop 
a monomer having the beneficial properties of acrylates but which is 
amenable to radiation curing at a rapid rate by cationically induced 
polymerization which is not oxygen inhibited and which permits continued 
polymerization after removal from the source of radiation exposure. 
The inherent deficiencies of the acrylate systems can be partially overcome 
by the use of epoxy resins. Epoxy resins can be polymerized by normal 
radiation techniques using cationic photoinitiators such as iodonium, 
sulfonium and ferrocene salts of hexafluorophosphate, hexafluoroantimonate 
or hexafluoroarsonate to produce a tack free film. Although in such 
formulations tack free products are almost immediately obtained, 
polymerization of the mixture is incomplete. It is well known that the 
polymerization of epoxy resins is extremely slow and requires as much as 
several days to achieve their ultimate physical properties. Thus, thermal 
post curing is often employed to increase the rate of or to complete the 
polymerization. 
Certain allyl compounds also have been used as coatings; however these 
monomers and their oligomers are not readily curable by cationic 
radiation. Thermal curing is generally required to increase the rate of 
polymerization. While allyl ethers such as polyethylene glycols are 
curable by UV light, they require a free radical initiated reaction which 
proceeds at a slow rate, generally over a period of from 2 to 10 hours in 
order to reach completion. 
Finally, it is noted that the unsubstituted acrylates are sensitizers and 
skin irritants as well as being carcinogenic, so that specialized safety 
precautions must be taken to protect operators from exposure. Although 
alkoxylation has lessened irritancy of the acrylates, their carcinogenic 
properties are not reduced. 
Accordingly it is an object of the present invention to overcome the above 
described deficiencies by an economical and commercially feasible 
composition and curing process. 
Another object of this invention is to utilize a multifunctional 
cross-linking agent which is a liquid and which is more economically 
employed in an efficient ether cross-linking process. 
Another object is to provide a non-toxic cross linkable homopolymeric 
compound suitable as a film or a substrate coating which possesses good 
adhesion, abrasion resistance and resistance to chemical attack. 
Still another object is to provide a more economical process for 
cross-linking monomeric or polymeric vinyl or epoxy ethers which can be 
effected in the presence of air. 
Another object is to provide a monomer which is curable at a rapid rate by 
cationically induced radiation. 
These and other objects will become apparent from the following description 
and disclosure. 
THE INVENTION 
In accordance with this invention there is provided a radiation curable, 
cross linkable composition containing (a) from about 0.1 to about 5 wt. % 
of an initiator containing at least 25% of a cationic initiator, (b) from 
about 0 to about 60 wt. % of one or more polymerizable components of the 
group of a vinyl ether, epoxide, acrylate or a vinyloxy alkyl urethane and 
(c) from about 35 to about 99.9% wt. % of an aliphatic polyfunctional 
alkenyl ether having the formula 
EQU A[(CH.sub.2 O).sub.m (Z).sub.r CH.dbd.CHR].sub.n 
wherein A is a carbon atom, --OCH.dbd.CHR or [C.sub.1 to C.sub.10 
alkyl].sub.4-n ; R is C.sub.1 to C.sub.6 alkyl; Z is C.sub.2 to C.sub.8 
alkyleneoxy; r has a value of from 0 to 6; m has a value of from 0 to 1 
and at least one of r and m has a positive value; n has a value of from 1 
to 4, with the proviso that m is 0 and n is one when A is --OCH.dbd.CHR, n 
has a value of 2 or 3 when A is [C.sub.1 to C.sub.10 alkyl].sub.4-n and n 
has a value of 4 when A is carbon. 
Of the above polyfunctional alkenyl ether compounds, those wherein R is 
methyl; A is --OCH.dbd.CH (lower alkyl), [lower alkyl].sub.4-n or carbon 
are preferred. Also, when alkenyl ether is asymmetrical, the compound most 
preferably contains at least 35% of the cis isomer with respect to the 
trans isomer. 
The most preferred compositions are those containing between about 20% and 
about 50% of component (b) and between about 50% and about 80% of 
component (c) where R is methyl. 
The present polyfunctional alkenyl, preferably propenyl, ether compounds 
are homopolymerizable resins independently useful as protective coatings 
and are also effective cross-linking agents for polymerizable vinyl ethers 
having at least 6 carbon atoms or epoxides such as the divinyl ethers of 
the bis(hydroxyethyl) ether of bisphenol A, the divinyl ether of 
triethylene glycol, the divinyl ether of dimethylolcyclohexane, 
vinyloxyalkyl urethanes, e.g. divinyloxybutyl urethane oligomers, the 
diglycidyl ether of bisphenol A and its oligomers, bisphenol A epoxy 
acrylate and its oligomers, 3,4-epoxycyclohexyl 
methyl-3',4'-epoxycyclohexane carboxylate, the ethers disclosed in U.S. 
Pat. Nos. 4,388,450; 4,749,807; 4,775,732 and 4,751,271 and corresponding 
alkoxylated compounds and similar comonomers in monomeric or oligomeric 
form having a number average molecular weight up to about 5,000 or 
mixtures of said comonomers and/or copolymers. Such monomeric or polymeric 
vinyl ethers, epoxides, acrylates or urethanes can be reacted with the 
polyfunctional alkenyl ethers of this invention to form a cross-linked 
copolymeric product having a high cross-linked density and extremely high 
resistance to abrasion and chemical attack. 
As stated above, the present polyfunctional alkenyl ethers, particularly 
the prop-1-enyl ethers, are homopolymerizable forming an exceedingly 
branched structure. As such, these agents can be used as rigid coatings on 
substrates which require an exceptionally high strength, resistance to 
abrasion and solvent attack. Substrates on which the copolymerized or 
homopolymerized agent is suitably coated include metal, wood, ceramic, 
plastic, leather, paper, glass and the like. The present composition is 
coated on the substrate by any convenient and conventional technique in 
the desired thickness, usually in a thickness of between about 0.1 to 
about 5 mils. 
Instant alkenyl ethers having the structure C[CH.sub.2 O(Z).sub.r 
CH.dbd.CHR].sub.4 produce homopolymers and copolymers which are totally 
etheric in composition and which have greatly increased surface 
substantivity and other advantages derived from their poly etheric nature, 
such as high UV resistance and the ability to form hydrogels on exposure 
to water. 
As cross-linking agents, the alkenyl ethers of this invention can be 
admixed with the above acrylate, urethane, epoxide or vinyl ether monomers 
or their oligomeric counterparts to effect cross-linking in the presence 
of a cationic initiator, such as a triphenyl sulfonium salt of phosphorous 
hexafluoride, diphenyl iodonium salt, a mixture of aromatic complex salts 
of butyrolactone (FX-512, supplied by Minnesota Mining & Mfg. Co.), a 
phenyl onium salt or an aryl alkyl onium salt, etc. The initiators 
suitable to effect polymerization reactions of the present invention 
include the above named cationic initiators which can be employed alone or 
in admixture with a free radical initiator to provide a hybrid system. 
Suitable free radical initiators include 1-hydrocyclohexyl phenyl ketone 
(e.g. IRGACURE 184), 2-hydroxy-2-methyl-1-phenyl-1-propan-1-one (DAROCUR 
1173), 2,2-dichloro-1-(4-phenoxy- phenyl) ethanone (SANDORAY 1000) and the 
like. Other free radical and cationic initiators which are suitably 
employed in this invention are those described by M.J.M. Abadie, 
Advantages and Development of Photochemical Initiators, in the European 
Coatings Journal 5/1988, pages 350-358. When initiator mixtures are 
employed, the free radical component can comprise up to 75%, preferably 
between about 30 and about 70%, of the cationic initiator component. A 
particularly preferred initiator mixture includes between about 30 wt. % 
and about 40 wt. % of FX-512 and between about 60 and about 70% of 
IRGACURE 184. The present initiator mixtures are recommended for blends of 
(b) and (c) where component (b) contains an acrylate. The total amount of 
initiator employed is generally between about 0.1 and about 5 wt. % with 
respect to reactant or reactants. 
In accordance with this invention, one or more of the present aliphatic 
alkenyl ethers can be employed or blended with one or more of the 
polymerizable epoxides, vinyl ethers, acrylates or vinyloxy alkyl 
urethanes, thus benefiting from the properties of each monomer in the 
blend. Further, it is found that blends of the present propenyl ether and 
the divinyl ether of dimethylol cyclohexane enhance solubilization of the 
cationic initiator. Such blends may contain up to about 60%, preferably 
from about 20 to about 50% of component (b). 
The propenyl ether of component (c) in the present composition, serves not 
only as a reactant, but also as an essential diluent for the vinyl ether 
and/or epoxide which compounds are highly viscous and difficult to apply 
as coatings. Thus, the propenyl ether provides a coatable composition 
without the need for extraneous diluents which in many cases can cause 
blisters and non-uniformity in the coating product. 
The compositions of the present invention are cured within a period of up 
to one second by exposure to a source of radiation, e.g. UV light, 
electron beam, laser emissions, gamma rays etc. Radiation curing in the 
present cationic system takes place at a fast rate, e.g. from about 200 to 
about 1,000 feet per minute of coated surface or free formed film, 
depending upon the intensity and type of radiation employed. UV light 
radiation dosages at room temperature of from about 100 to about 1500 
milli J/cm.sup.2 are effective and dosages of from about 200 to about 600 
milli J/cm.sup.2 are preferred. Equivalent dosages for curing are employed 
when using alternative sources of radiation. For example, curing with 
electron beam radiation can be carried out at between about 0.5 and about 
20 Mrads, preferably between about 1 and about 10 Mrads. Specific 
techniques for radiation curing are well known, thus further amplification 
is not required. 
Since the present propenyl ethers are normally liquid, they can be directly 
mixed with the polymerizable vinyl ether, epoxide or vinyloxy alkyl 
urethane monomer or oligomer without further conditioning; however, in 
certain cases where dilution is desired, as in cases where higher 
molecular weight alkenyl ethers of this invention are employed as 
component (c) or where the blend provides a highly viscous mixture, the 
alkenyl ether can be dissolved in an inert organic solvent such as methyl 
ethyl ketone, toluene, a hydrocarbon, acetone, an ether or a halogenated 
compound such as methylene chloride. However, dilution with the above 
solvents should not exceed 50% when highly resistant coatings are 
required. 
Alternatively, the alkenyl ether monomer or oligomer, in the absence of a 
comonomer can be applied directly to any of the above substrates and 
subjected to radiation for curing under the above conditions to form a 
more highly cross-linked homopolymeric protective coating. 
It should also be understood that the present compositions can optionally 
contain minor amounts of conventional adjuvants such as a surfactant e.g. 
a fluorocarbon surfactant such as a mixture of fluoroaliphatic polymeric 
esters (FC-430 supplied by Minnesota Mining & Mfg. Co.) or a silicane 
copolymer surfactant (DC-193 supplied by Dow Corning Corp.) or others. It 
is also to be understood that the present compositions can be cured 
thermally or by radiation induced free radical polymerization; however, an 
advantage of this invention is the ability to cure the compositions by 
cationically induced radiation which avoids the disadvantages discussed in 
the foregoing disclosure. It is to be understood however that concurrent 
free radical and cationic induced polymerization using a mixture of such 
photoinitiators achieves benefits of this invention and is recommended 
where component (b) of the composition is an acrylate, e.g. bisphenol A 
epoxyacrylate.

Having generally described the invention, reference is now had to the 
accompanying examples which illustrate preferred embodiments but which are 
not to be construed as limiting to the scope of the invention as more 
broadly set forth above and in the appended claims. 
EXAMPLE 1 
Into an amber bottle, 50 wt. % of diprop-1-enyl ether of diethylene glycol 
(70% cis, cis) and 50 wt. % of a diglycidyl ether of bisphenol A were 
charged and mixed at 50.degree. C. for 1 hour. To this mixture, 2 
parts/hundred parts of the triphenyl sulfonium salt of hexafluorophosphate 
were added with agitation. The resulting low viscosity liquid was directly 
coated on an aluminum panel in a thickness of 0.15 mil. The coated 
substrate was then exposed for less than one second at room temperature to 
400 milli J/cm.sup.2 radiation from a medium pressure mercury vapor lamp; 
after which the substrate having a highly crosslinked strongly adhesive 
coating* was removed. The coating is resistant to attack by methyl ethyl 
ketone and is abrasion resistant. 
EXAMPLE 2 
A two mil thick layer of a mixture of 98 wt. % of the tetraprop-1-enyl 
ether of pentaerythritol and 2.0 wt. % of the triphenyl sulfonium salt of 
hexafluorophosphate is applied to a polyester substrate. The coated layer 
is then crosslinked by exposure for about one second at room temperature 
to electron beam radiation at a dosage of 3 Mrad. The resulting highly 
crosslinked polymer exhibits strong adhesion, is highly resistant to 
chemical attack and has superior abrasion resistant properties. 
EXAMPLE 3 
A. Into an amber bottle, 50 grams of substantially pure (&gt;95%) cis, cis 
dipropenyl ether of triethylene glycol, 50 grams of a diglycidyl ether of 
bisphenol A, 2 grams of the triphenyl sulfonium salt of 
hexafluorophosphate and 1 gram fluorocarbon surfactant were charged and 
thoroughly mixed. The resulting liquid mixture was coated on an aluminum 
panel with a #3 coating rod. 
B. The above procedure was repeated except that a mixture of 48% cis, cis, 
42% cis, trans mixture and 10% trans, trans was substituted for the cis, 
cis reactant in A. 
C. The procedure in part A was repeated except that 
3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate was 
substituted for the dipropenyl ether. 
Each of the samples A, B, and C were coated in a thickness of 0.11-0.15 mil 
on an aluminum panel and then cured by exposure to UV light as described 
in Example 1. The cured coatings were evaluated and the results are 
reported in the following Table. 
TABLE 
__________________________________________________________________________ 
NO BAKE* 
BAKE** 
NO BAKE 
BAKE NO BAKE 
BAKE 
A B C 
__________________________________________________________________________ 
Pencil Hardness (ASTM D3363) 
F 2H F 2H H 2H 
% Adhesion (ASTM D3359) 
-- 100 -- 100 -- 100 
% Adhesion -- 100 -- 100 -- 100 
30 Min. Boiling H.sub.2 O 
Double MEK Rubs 1 2 1 2 1 2 
Reverse Impact (M-lbs) 
-- 65 -- 60 40 40 
Mandrel Bonds (inch - 
1/8 1/8 1/8 1/8 1/4 1/4 
ASTM D3111) 
Coating Thickness 
-- 0.11 -- 0.20 -- 0.15 
Min Exposure for Tack-free 
80 -- 80 -- 400 -- 
coatings (m J/cm.sup.2) 
__________________________________________________________________________ 
*Immediately after exposure to 400 m J/cm.sup.2 UV. 
**Baked for 10 minutes at 170.degree. C. after UV exposure. 
It will be appreciated from the above results that changing the 
distribution from cis isomer to a cis/trans isomeric mixture did not 
materially affect the properties of the final coating. Example 3 also 
demonstrates the high cure speed of the di-propenyl ethers as compared to 
the di-epoxy compound. 
EXAMPLE 4 
A. Into an amber bottle, 50 grams of substantially pure (&gt;95%) cis,cis- 
dipropenyl ether of triethylene glycol, 50 grams of a bisphenol A epoxy 
acrylate oligomer, 1 gram silicone surfactant (DC-193), 1 gram cationic 
photoinitiator (FX 512) and 1.5 gm free radical initiator (IRGACURE 184) 
were charged and mixed at 50.degree. C. until homogeneous. The resulting 
liquid was coated on polyester using a #6 coating rod (approx. 0.5 mil) 
and cured by an exposure for less than 1 second at room temperature to 400 
millijoules/cm.sup.2 from a UV lamp. 
B. The above procedure A was repeated except that the free radical 
initiator was omitted from the formulation. 
C. The procedure in part A was repeated except that the cationic initiator 
was omitted from the formulation. 
The cured coatings were evaluated immediately after UV exposure and the 
results are reported in the following Table. 
TABLE 
______________________________________ 
Formula A B C 
______________________________________ 
Result tack free tack free 
wet 
Adhesion 100% 100% none 
Double MEK Rubs 
&gt;100 89 none 
Pencil Hardness 
F F none 
______________________________________ 
This example illustrates the necessity of the cationic photoinitiator and 
the superior solvent resistance obtained using a cationic and free radical 
initiator. 
EXAMPLE 5 
A. Example 4A is repeated except that the 50 grams of cis,cis- dipropenyl 
ether of triethylene glycol is replaced with 50 grams of a 1 to 1 wt. % 
blend of cis,cis-dipropenyl ether of triethylene glycol and the divinyl 
ether of 1,4-cyclohexane dimethanol. 
B. Example 4A is repeated except that the 50 grams of cis,cis-dipropenyl 
ether of triethylene glycol is replaced with 50 grams of the divinyl ether 
of 1,4-cyclohexane dimethanol. The cationic initiator failed to dissolve 
in the absence of the propenyl ether and an in compatible mixture was 
formed. 
The above cured coatings were compared with that of 4A and were evaluated 
immediately after UV exposure. The results are as reported in the 
following table. 
TABLE 
______________________________________ 
Formula 4 A 5 A 5 B 
______________________________________ 
Adhesion 100% 100% incompatible 
Double MEK Rubs 
&gt;100 &gt;100 none 
Pencil Hardness 
F 2H none 
______________________________________ 
This example illustrates that coating hardness can be significantly 
improved by adding the divinyl ether of 1,4-cyclohexane dimethanol; and 
that, the dipropenyl ether of triethylene glycol is needed to insure 
compatibility. 
EXAMPLE 6 
Into an amber bottle, 50 grams of &gt;95% cis, cis-dipropenyl ether of 
triethylene glycol, 50 grams of a divinyl ether of urethane oligomer 
(prepared as described in the Degree Thesis of Lennart Carlson, Dept. of 
Polymer Technology, the Royal Institute of Technology, Stockholm, Sweden, 
1987), 4 phr* cationic photoinitiator (FX 512), and 1 phr fluorochemical 
surfactant (DC-193) were charged and mixed at 50.degree. C. until 
homogeneous. The resulting liquid was coated on an aluminum panel to a 
0.25 mil thickness using a #3 coating bar and then cured as described in 
Example 4. 
A tack free coating with the following properties was produced 
______________________________________ 
Pencil Hardness 3B 
Mandrel Bend 3/16 inch 
Double MEK rubs 5 
______________________________________