CA1212687A - Photocurable compositions - Google Patents

Abstract

TITLE: PHOTOCURABLE COMPOSITIONS

ABSTRACT OF THE DISCLOSURE

A composition useful in photopolymerizable coatings is provided which comprises 50% of a hemi-acrylate having the formula CH2=CHCOOCH2CH2O(CH2CH2CH2O)nCH2CH2OH
27% of a di-acrylate having the formula CH2=CHCOOCH2CH2O(CH2CH2CH2)nCH2CH2OOCCH=CH2 and 23% of a polyether diol having the formula HOCH2CH2O(CH2CH2CH2O)nCH2CH2OH;
wherein n is the number of repeating units in the polyether backbone.

Description

lZ~2687 ........
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TITLE: PHOTOCURABLE COMPOSITIONS '.. :
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BACKGROUND O~ THE INVENTION ...
Compositions which polymexize when exposed to light or :
other forms of radiation have become increasingly useful and popular in the field of coatings for various substrates.
Such photopolymerizable coating compositions have several advantages ~er c~atings:w~ich must either be appli~d in ....
molten form or as a solution in a suitable solvent followed ~
by removal of the s.olvent. Since the photopolymerizable .. ::
composftions do not reguire heating, either in their appli- ...
cation or in a drying process, they can provide substantial ~.
energy savings . Likewi.s.e, since they do not reguire solvent ._ removal, pollut~on problems ~an be minimized. ..
SUMMA~Y O~ THE INVENTION ~
Thi.s invention relates to processes for preparing .::.
compositions which are useful in photopolymerizable compo- ....
sï~i.ons: and the products of such processes. More particu- ....
larly, the processes of this invention comprise ...
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Process 1 ~:
reacting a polyether diol and an acrylic acia in about e~ual molar proporti.ons, and '.
Process 2 ~. reacting a polyether diol and an acrylic acid in r'~
about equal molar proportions; and B. reacting the product of step A, a hydroxyalkyl .:~
acrylate and an organic diisocyanate in about equal molar ;
proportions.
The compositions produced by the processes of this .
invention are particularly useful in photopolymerizable ....
compositi.ons which re~uire relatively low viscosity, such as in coating compositions which must have the ability to _ flow readily and uniformly over the surface of a substrate. .
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Gener~lly, the photopolymeriæable composi~ions prepared ! .'_'' from the compositions produced by the processes of this 1l~
invention will have viscosities below about 50 poise, !F
preferably in the range of about 20 to about 50 poise. ~
Such photopolymerizable compositions also possess excel~
lent stability at elevated temperatures, e.g. up to about 70C, and good flexibility when cured. ..
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lZ~26i87 DESCRIPTION O rHE PREFERRED EMBODIMENT' ,,", ,...
The pr~cesses of this invention comprise: , Process 1 ,.;
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reacting a polyether diol and an acrylic acid in about ,,;, equal molar proportionsJ and ; .
, Process 2 ,~", .....
A. reacting a polyether diol and an acryli,c acid in ~
about equal molar proportions; an~ ~"',',' B. reacting the product o step A, a hydroxyalk~1 ""
acrylate and an organic diisocyan~te in about e~ual molar ':
proportionC . ~,', The polyether diols useful in the processes of this ","
invention are polymers whose backbones contain the repeat- ,~
ing units tR-O~ where R is alkylene, and have free hydroxyl ,, groups attached to their terminal repeating unit, i.e. the ., polymers are tenminated at each end by a -R-OH group. The ,-hydroxyl group may be a primary or secondary hydroxyl, ~
although,the primary hydroxyl groups are preferred. ~he ,.
polyether dïols are preferably hydroxy~terminated polypropy- ' lene glycols having molecular weights in the 400-800 range ,~:
and having Hydxoxyl Nos. ~rom about 145 to about 265. _ Examples of the p~lyether diols include, but are not limited ., to, hydroxy-terminated adducts of propylene oxide to ._ di~ropylene glycol having an average molecular weight of about 425 and a Hydroxyl No. of a~out 263 (~IAX PPG 425, .. -.
sold by ~nion Carbide Corp.), hydroxy-terminated adducts '~'.' of propylene oxide to dipropylene glycol having an average ~.
molecular weight of about 725 and a Hydroxyl No. of about l~
147, (NIAX PPG 725, sold by Union Carbide Corp.), poly- ~
propylene glycol end-capped with ethylene oxide groups and having an average molecular weight of about 650 and an ~, Hydroxy No. of about 173 (POLYG 55-173, sold by Olin Corp.), ~,,' polypropylene glycol end-capped with ethylene oxide and ,,'"',', having an average molecular weight of about 775 and a .',' Hydroxy ~o. of about 150, polypropylene glycol end capped '~
with ethylene oxide and having an ~verage molecular weight :, of about 425 and a Hydroxyl No. of about 265, and the like. ~':' Other useful polyether diols include hydroxy-terminated ,,.
poly(l,4-butanediol)(dexived from tetrahydrofuran) and hydroxy-terminated copolymers of i,4-butanediol and ...
ethylene oxide. ..
* Trademark ~2~2687 ....
-4- , A particularly preferred polyether diol is PO~Y-G 55-173 ¦~.
which ha~ the formula: ¦~

HocH2cH2o(cH2c~2cH2o)c3~cH~g~

tavg. molecular wei~ht approximately 650) s The acrylic acids useful in the proces~es of this invention include acrylic acid and alkyl acrylic acids :
such as methacrylic acid and the like. As used herein .. ~w-the phrase "an acrylic acid" is intended to represent both acrylic acid and ~he alkyl acrylic acids~ w.w The hydroxyalkyl acrylates which may be used in the ..
processes of this invention are c~mpounds having the -.
formula: O .
H2C = CH-C-O-Rl-OH :"
w.here Rl is C2 to C3 ~lene. Examples of the hydroxyalkyl -.
acrylates include, but are not limited to, 2-hydroxyethyl _ acxylate, 2-hydroxypropyl acrylate and ~he like, 2-hydroxy- .
ethyl acrylate is particularly preferred. ..
The organi.c dfi.socy~nates used in the processes of thi.s ïnventï~n have the f ormula: ~.
OCN-R2-NCO ~'_ where.R2 is a divalent organic .. ~adical such as alkylene, ..
arylene, alkary.l2ne or aralkyleneO Examples of organic :
diisocyanates useful in this invention include, but are not .
limited to, i.s:ophorone diisocyanate; 2,4-tolylene diisocya- i..... :
nate; 2,6-tolylene di.isocyanate; hexamethylene diisocyanate; w trimethyl hexamethylene diisocyanate;dicyclohexylmethane ....
diisocyanate and the like. The preferred diisocyanates :::
are the aliphatic diisocyanates which impart improved properties such as light sta~ility, stain resistance and ....
flexibility to the cured photopolymerizable compositions :.
made from them. :::
The following reaction schemes illustrate the processes ....
~f this invention: ..

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Process 1 1.0 HocH2cH2o~cH2cH2cH2otcH2cH2oH ~ 1.0 CH2=CHCOOH , ;,.:"
Polyether diol acrylic acid ~I ", "
O . 50CH2=cHcoocH2cH2o~cH2cH2cH~o~l2cH2oH + ~'",' .,:
Hemi-acrylate 0.2~ CH~cHcoocH2cH2o~cH2cH2cH2otncH2cH2ooccH-cH2 ~ _ Di-acrylate _ oc 2CX2o~c~2cH2cH2otncH2cH2o~
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Polyether diol . .. -The above reaction scheme illustrates a typical compo- _ s:ition produced whe~ a polyether diol and acrylic acid are ..
reacted in about ~qual molar proportions. The reaction .
depicted ~s based on a statistical approximation, assuming . .. -the hydroxyl groups are e~ually reactive. It is estimated .
that the product contains about 50% Hemi-acrylate, about ~
27% Di-acrylate and about 23~ Polyether diol, ~.
In Process 2, the product of the above reaction is ~=
further reacted with a hydroxyalkyl acrylate acid and an organic dii.socyanate as illustrated below. ~.
Process 2 ...
_..
CH2=CHCOOCH2CH2-X-CH2CH20H + CH2=CHCOOCH2CH2-X-CH2CH200CCH=~H + ,-Hemi-acrylate Di-acrylate .-HCH2CH2-X-CH2CH2H + CH2=CHCR OH ~-OCN-R -NCO
Polyether diol hydroxyalkyl organic i.-acrylate diisocyanate ~

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CH2=CHCOOCH2CH2-X-CH2CH20CNH-R -NHcocH2cH2-x-cH2cH2ooccH-cH2 t "''"' ,,;,;;, CH2=CHCOOCH2CH2-X-CH CH OOCCH-CH

2 :~
HOCH2CH2-X-CH2CH20~NH-R -NHcocH2cH2-x-cH2cH2oH ,, ,~, CH2=CHCOOR OCN~-R -NHCOR OOCCH_CH2 ~:
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where X represents the polyether backbone of the Polyet~er ~
diol. ~::
It will be apparent to one skilled in the art that other side reactions may occur which are not illustrated above. Thus, it should be emphasized that the above reac-tion scheme is presented for illustrative purposes only and ~-is not intended to limit this invention in any manner.
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The reaction of the polyether diol and an acrylic r',',~
acid (Process 1) may be carried out by mixing the poly-ether diol and acrylic acid in any suitable v~ssel together with an effective amount of catalyst, e.g. methane sulfonic acid, sulfuric acid, toluene sulfonic acid and the like, and a polymerization inhibitor such as, for example,- pheno-thiazine, MEH~ and the like. The resulting reaction ::
mixture is then heated, preferably at reflux temperature to remove water formed during the reaction, until the acrylation is complete. The resulting reaction product may then be shaken with a 20% Na2CO3 solution until the : . ~
acid number of the product is below about 1Ø
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In Process 2, the product of Process 1, a hydroxy-alkyl acrylate and an organic diisocyanate are blended together in a suitable vessel. More preferrably the product of Process 1 and the hydroxyalkyl acrylate are blended together and the organic diisocyanate is added ~;
slowly over the course of the reaction. (This slow addition of the organic diisocyanate prevents premature or possibly violent reaction of the reaction mixture ) t":,"
Also blended into the reaction mixture are an e~fective amount of catalyst, e.g. dibutyl tin dilaurate, and, :
if desired, additional polymerization inhibitor (the total amount of polymerization inhibitor in Process 2, whethex :
carried over from Process 1 or added during Process 2 should be about 75-300 ppm). The reaction may be con- -ducted under an inert atmosphere, e.g. nitrogen, if desired. The reaction is begun by heating the reaction mixture to ~out 60C to about ~0C, preferably about 60~C
to about 70C, and such hearing is maintained until the isocyanate content of the reaction mixture drops to about 1.0% or less. :
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The compositions produced by the processess of this invention generally have viscosities in the range of about 20 to about 30 poise, preferrably about 25 poise, and average molecular weights of less than about 1500.
The compositions produced by the processes of this invention may be employed in photopolymerizable compositions, :
i.e. compositions which are capable of polymerizing or curing upon exposure to actinic radiation, e.g. ultra-violet radiation or election beam. Generally, they may be blended in any convenient manner with the other ingredients commonly employed in suoh photopolymerizable compositions.
Thus, for example, the photopolymerizable composition may contain the composition of this invention, a photo- ,~
initiator, a polymerization inhibitor and other additives as may be desirable.
The preparation of the compositions of this invention is illustrated by the following examples in which all parts are by weight unless otherwise indicated.

~21Z68~

EXAMPLE 1 ~
To a suitable v~ssel fitted with a drop ~unnel, ther- ,.
mometer and condenser is added 1287.6g of a polyether diol ,~
which is a hydroxy-terminated addu~t of propylene oxide t~
to dipropylene glycol having an average molecular weight o about 725 and a Hydroxy No- of about 147 (NIAX PPG r,~
725, s.old ~y Union Car~i.de Corp.l, .

3.32g of methane ~ulfonic acid catalyst, 0.25g phenothia- ' :.::
zine and 351.45 g toluene. The resulting mixture is heated : .. ~
to a~out 68C and 144.12 g of acrylic acid is added to the ..
vessel via ~he drop f~mnel over a period of about 1 hour -.
during which time the temperature of the mixtur~ rises to ! _ abou~ 124C. About lOOcc of toluene is added to the mixture ...
and a slow reflux is ~egun. The reflux is maintained for _.
a period of time sufficient to remove water which is formed ....
during the reaction. When the reaction is completed the _.
resul~ing product i~ shaken with a 20~ solution o~ Na2CO3 ...
until the acid number of the mixture is below about lo D. I ~
The product is recovered ~y fi.ltering and removing the toluene l ....
by di.stillation. I _ ~Z~687 ...........

EXAMP~E 2 :.
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To a 2 liter, 4 neck round bottom flask equipped with ., a stirrer, condenser, thermometer, N2 inlet ~d condensex ,~
are added 500g of the product of Example 1, 88g ~-hydroxy-ethyl acrylate, and 0.12g dibutyl tin dilaurate. The mix- .
ture is stirred, blanketed with N2 and slowly heated to about 60~C for àbout 1 h~ur during which time 201g of dicyclohexyl methane diisocyanate is added to the reaction ;
mixture. ~Ieating is maintained for an additional 1.5 hours. .
The reaction mixture is analyzed periodically for isocyanate .
content (~y titration with amine) and the reaction is .~
continued until the isocyanate content drops to about 1-1.1%. ._.
The re~ulting product has a density of 1.11 and a viscosity ::
of 26.1 poises.

~Z615'7 --10-- , A photopolymerizable composition is prepared by blending together 70 parts of the product of Example 1, 15 pa*rts o N~vinyl-2-pyrrolidone, and 4 parts of a photoinitiator (CG 184 sold by Ciba Geigy). The resulting composition is coated onto polycarbonate, paper and primed aluminum substrakes and exposed under a nitrogen atmosphere by a mercury lamp in a Radiation Polymer Company processor at a rate of about 20 feet per minute. 1'he coating cures completely and has excellent physical properties. F:
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Trademark , ,. , ~. ..
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EXAMPI,E 4 -A photopolymerizable composition is prepared by blending together 70 parts of the product of Example 2, 15 parts o~ ,.
N-vinyl-2-pyrrolidone, ~ 2 parts of a photoinitiator (~ 184 sold by Ciba Geigy). The composition is coated onto paper and polycarbonate substrates and exposed under air atmosphere by a mercury lamp in a Radiation Polymer ,:
Company processor. The composition is also coated onto a primed aluminum substrate and exposed in the ,-same manner except that a nitrogen atmosphere is employed. All coatings cure completely and has , :.,,.:
excellent physical properties. '-~r-, _, t . '`, ~
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-Other ~eatures, advantages and specific embodiments of this invention will become readily apparent t9 those exercising ordinary skill in the art after reading the ~oregoing dfsclosures. These specific embodiments re within the scope of the claimed subj~ct matter unless o~her-wise expressly indicated t~ the contrary. Moreover, while ;:
a few specific embodimen~s of thi;s invention ha~e bee~
descri~ed in considera~le detail, variation8 and modi~ica- :
tlons ~f these em~odlments can be effected wit~out departing from the spirit and scope of the invention as disclosed and _ clai~ed.

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Claims (2)

WHAT IS CLAIMED IS:

1. In a photopolymerizable composition comprising a photocurable composition and an unsaturated monomer, the improvement comprising a photocurable composition comprising 50% of a hemi-acrylate having the formula CH2=CHCOOCH2CH2O(CH2CH2CH2O)nCH2CH2OH

27% of a di-acrylate having the formula CH2=CHCOOCH2CH2O(CH2CH2CH2)nCH2CHCH2OOCCH=CH2 and 23% of a polyether diol having the formula HOCH2CH2O(CH2CH2CH2O)nCH2CH2OH
wherein n in each formula is the number of repeating units in the polyether backbone of each compound.

2. The photopolymerizable composition of claim 1 wherein n averages 9.38.