COMPOSITIONS HARDENABLE BY UV RADIATIONS COMPRISING AN UNSATURATED EPOXY RESIN ESTER AND AN UNSATURED MONOMER

COMPOSITION A TENEUR D'ESTER DE RESINE EPOXYDIQUE ET DE MONOMERE INSATURES CURABLES A L'ULTRAVIOLET

English Abstract

ABSTRACT OF THE DISCLOSURE
A composition hardenable by means of ultra-violet
radiations, which comprises (a) an unsaturated epoxy resin
ester obtained by reacting an epoxy or epoxy novolak resin
with an unsaturated monocarboxylic fatty acid with 18 carbon
atoms per molecule and with acrylic and/or methacrylic acid,
the fatty acid being used in an amount of 20-80 moles for each
100 moles of the sum of the acids, (b) a mono- or poly-
functional unsaturated monomer and (c) a photosensitive
substance. She composition comprises 3-97 parts by weight
of component (a) and 1.2-3.5 parts by weight of component (c)
for each 100 parts by weight of the sum of components (a)
and (b).

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A composition hardenable by means of ultra-violet
radiations, which comprises:
(a) an unsaturated epoxy resin ester which is a reaction
product prepared by a process consisting essentially of reacting
an epoxy resin
(I) <IMG>
wherein R is the divalent radical of a diphenol HO-R-OH and n
has a value of from 0 to 14, or an epoxy novolak resin
(II) <IMG>
wherein n has a value of from 0 to 4, with one or more unsaturated
monocarboxylic fatty acids with 18 carbon atoms per molecule,
and then with one or more lower unsaturated acids chosen from
acrylic and methacrylic acids, said fatty and lower acids being
used in an overall amount equivalent, or about equivalent to the
number of oxirane bridges of the epoxy or epoxy novolak resin
and said fatty acids being used in an amount of from 20 to 80
moles for each 100 moles of the sum of the fatty and lower acids;
(b) one or more mono- or polyfunctional unsaturated monomers
copolymerizable with said unsaturated epoxy resin ester; and
(c) a photosensitive substance which decomposes under the action
of ultra-violet radiations and promotes cross-linking by ultra-
violet radiations; the component (a) being present in the com-
position in an amount of from 3 to 97 parts by weight for each
100 parts by weight of the sum of components (a) and (b) and
the component (c) in an amount of from 1.2 to 3.5 parts by weight
for each 100 parts by weight of the sum of the components (a)
13

and (b) and wherein said unsaturated epoxy resin ester (I)
contains unreacted internal hydroxy groups where n = 1 to 14.
2. The composition of claim 1, wherein said fatty acids
are obtained from dehydrated castor oil, linseed oil, soybean
oil and tall oil.
3. The composition of claim 1, wherein said monomers
are selected from the group consisting of styrene, vinyl toluene,
alpha methy] styrene, methyl methacrylate, vinyl cyclohexane,
pentaerythritol tetraacrylate, trimethylolpropane triacrylate,
butanediol diacrylate and glyceryl triacrylate.
4. The composition of claim 1, wherein said component (b)
is present in an amount of from 5 to 50 parts by weight for each
100 parts by weight of the sum of components (a) and (b).
5. The composition of claim 1, wherein said diphenol is
2,2-bis(4-hydroxyphenyl) propane.
6. The composition of claim 1, wherein said photosensitive
substance is selected from the group consisting of benzoin,
benzoin derivatives containing in the alpha position an alkyl
or alkyl ether radical with from 1 to 8 carbon atoms per molecule,
organic sulphur derivatives, nitrous compounds, organic sulfonyl
halides and carboxylated compounds containing a carbon atom linked
to a halogen in the alpha position with respect to the carboxyl
group.
7. The composition of claim 1, wherein the component (c)
is present in an amount of about 2.5 parts by weight for each 100
parts by weight of the sum of components (a) and (b).
14

Description

1111~5~7
The present invention relates to a composition hardenable
by means of UV (ultra-violet) radiations, which comprises an
unsaturated epoxy resin ester and an ethylenically unsaturated
monomer copolymerizable with the latter.
It is known in the art how to react an epoxy resin with
an unsaturated monocarboxylic acid, such as acrylic or
methacrylic acid. The reaction between the oxirane bridge of
the epoxy resin and the carboxyl group of the unsaturated
monocarboxylic acid, leads to the formation of unsatura~ed
epoxy resin esters soluble in styrene and the resulting
solutions can be hardened by peroxide catalysts in the same
way as conventional unsaturated polyester resins. Hardening
occurs by cross-linking b.etween the double bond of styrene
and that of the unsaturated acid interacted with the epoxy
resin.
. It is also known in the art how to react an epoxy novalak
resin with acrylic or methacrylic acid to produce unsaturated
epoxy resin esters, who~e solutions in styrene-can be hardened
by means of peroxides. In this case, one generally obta.ins
a higher degree of cross-linking by hardening, because the
epoxy function is higher than that of the epoxy resin ester
obtained from the epoxy resin.
Hardening of the compositions under discussion by means
of UV radiations has also been described in the art, since
this method affords a quicker hardening cycle-and a lower
energy consumption, in addition to a reduction of the pollution
phenomena.
In prac~ice, the compositions described have a poor
wetting power for pigments and fillers in general. Moreover,
ehe articles obtained by cross-linking by means of peroxides
or by means of UV radiations have some undesired properties,
especially somewhat poor bending strength values.
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Finally, when using UV radiations, the velocity and degree
of completion of the hardening reaction may be unsatisfactory.
The drawbacks described above are overcome, or at
least greatly reduced by means of the compositions of the
present invention, which harden quickly and completely
under the action of UV radiations to give articles endowed
with high properties, especially those relating to the
bending strength and toughness. Moreover, said compositions
easily wet pigments and fillers in general, so that their
practical uses are facilitated.
Thus, the invention provides a composition
hardenable by means of ultra-violet radiations, which
comprises:
(a) an unsaturated epoxy resin ester which is the reaction
product of an epoxy resin
_ ~H
(I~ H2C/CH-CH2~ O-R-O-CH2 - CH-CH2 - O-R-O-CH2 -CH\-~H2
t n O
wherein R is the divalent radical of a diphenol HO-R-OH
and n has a value of from O to 14, or an epoxy novolak resin
~ f ~ ~\ /\
CH-CH2 CH-CH2 fH-CHz
CIH2 CH2 ~ CH2
O I _ O ._ .
(II) ~ -CH2 ~ _ - C~2-
n
wherein n has a value of from O to 4, with one or more
unsaturated monocarboxylic fatty acids with 18 carbon atoms
per molecule, and with one or more lower unsaturated acids
chosen from acrylic and methacrylic acids, said fatty and
lower acids being used in an overall amount equivalent, or
about equivalent to the number of oxirane bridges of the
epoxy or epoxy novolak resin and said fatty acids being used

1111:5~7
in an amount of from 20 to 80 moles for each 100 moles of
the sum of the fatty and lower acids;
(b) one or more mono- or polyfunctional unsaturated monomers
copolymerizable with said unsaturated epoxy resin ester;
and
(c) a photosensitive substance which decomposes under the
action of ultra-violet radiations; the component (a) being
1~ present in the composition in an amount of from 3 to 97
parts by weight for each 100 parts by weight of the sum
of components (a~ and (b~ and the component (c) in an
amount of from 1~2 to 3.5 parts by weight for each 100
parts by weight of the sum of components (a) and (b).
The epoxy resin (12 may be prepared by conventional
methods, by contacting epichlorohydrin and a diphenol,
especially 2,2~bis ~4-hydroxyphenyl) propane ;(bisphenol-A),
in a molar ratio generally higher than-about 8:1, operating
in the presence of an inorganic base added in an amount equal
2~ to, or about equal to 2 moles for each mole of diphenol.
Thus, for example, a concentrated aqueous solution of
the inorganic base ~sodium hydroxide~ may be added to a
solution of bisphenol-A in epichlorohydrin, using a feed
rate and a temperatur~e such that the water introduced with
the base be distilled off in the form of an azeotrope
with epichlorohydrin.
The reaction between bisphenol-A and epichtorohydrin
may also be carried out at a temperature such as to sub-
stantially avoid boiling of the reagents, even if generally
the temperature is-not kept below 80C.
In each case, upon completion of the reaction, the
unreacted epichlorollydrin is removed, generally by distillation,
and the alkali metal chloride obtained as a by-product of the
reaction is removed from the distillation residue.
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11~1597
To this end the epoxy resin may be dissolved in a solvent,
such as toluene, and the latter is finally removed.
The properties of the epoxy resin thus obtained are
typically within the following ranges of values:
- epoxy equivalent : 180-2~0
- Visoos~ty (cps~ : 3000-50,000.
The said epoxy resin, with a low epoxy equivalent value,
is suitable for the reaction with the unsaturated acids.
According to another embodiment the epoxy equivalent
value of the resin prepared as described above is increased
by~reaction with a further amount of bisphenol-A, prior to the
reaction with the unsaturated acids.
To this end it is possible to use those conventional
methods, which permit the production of epoxy resins with
epoxy equivalent vàlues higher than 270 up to about 4,500,
~;` having a semi-solid or solid appearance. These epoxy resins
with a high epoxy equivalent value are also suitable for the
reaction with the unsaturated acids.
The epoxy novolak resins (II) are generally prepared
by forming a solution of the novolak phenolic resin in
epichlorohydrin, maintaining the ratio between the moles of
epichIorohydrin and the number of phenolic hydroxyls of said
novo}ak at a value higher than about 2.5:1.
The a~ueous alkali metal hydroxide is then added to the
solution thus prepared, until the num~er of moles of said
alkali metal hydroxide is eyuivalent, or about e~uivalent, to
the number of phenolic hydroxyls of said novola~ resin.
The reaction is preferably carried out at a temperature
of from 60 to 80C and at a pressure lower than atmospheric
during the addition of the alkali metal hydroxide, the water
being distilled off from the reaction medium in tlle form
of an azeotropic mixture with epichlorohydrin and the unreacted
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epichlorohydrin being recycled, and a water content of from
0.5 to 2.5% by weight and a pH value of from 7 to 8 being
continuously maintained in the reaction medium.
Upon completion of the addition of the alkali metal
hydroxide, the water is completely removed from the reaction
medium by distillation and the epoxy novolak resin is recovered.
By operating according to the procedure described, a
practically complete epoxidation of the phenolic hydroxyl
groups of the novolak phenolic resin is obtained, while avoiding,
or at least substantially reducing the side reactions and obtaining
an epoxy novolak resin particularly suitable for the reaction
with the unsaturated acids.
The unsaturated epoxy resin ester may be prepared by
contacting and reacting, in a first step, the epoxy resin (I)
or the epoxy novolak resin (II~ with an unsaturated mono-
carboxylic fatty acid with 18 carbon atoms per molecule.
The fatty acids deriving from dehydrated castor oil,
linseed oil, soybean oil and tall oil are particularly
suitable for the purpose.
The said first step is preferably carried out by maintaining
a ratio of from 0.2:1 to 0.8:1 between the number of carboxyl
groups of the unsaturated fatty acid and the number of oxirane
groups of the epoxy or epoxy novolak resin and maintaining
the temperature at a value of from 200 to 240C, until the
acid value of the ~eaC~on mixture i6 reduced to very low
values and in general to values equal to, or lower than 2.
The reaction duration is generally of the order of 6-12
hours, The reaction is generally carried out in the presence
of a catalyst such as sodium acetate, ammonium, sod~um, potassium-
or lithium carbonate, or a carbonate or acetate of an alkaline
earth metal such as calcium and magnesium.
In a preferred embodiment the ratio between the number
of carboxyl groups of the unsaturated fatty acid and the number
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~1~15~7
of oxirane groups of the epoxy o} epoxy novolak resin is maintained
at a value of the order of 0.5:1 and the reaction is carried out at
a temperature of about 220-230C, using from 1 to 6 moles of
catalyst for each 100 moles of unsaturated acid.
The reaction product thus obtained is contacted and
reacted with one or more unsaturated acids with a low carbon atom
number, chosen from acrylic and methacrylic acids, the quantity
of said acids being equivalent, or about equivalent to the number
of residual oxirane groups. This second step is carried out under
conditions similar to those of the first one, excepting the
temperature which is maintained at a value from 100 to 140~C and
preferably at a value of the order of 115-120C. The reaction is
completed when the acid value of the reaction mixture is equal to,
or lower than about 20.
The unsaturated epoxy resin esters thus obtained have
properties which depend on the selected epoxy or epoxy novolak resin,
on the unsaturated acids with a high and a low carbon atom number
which have reacted with the resin~ and on the ratio between said
acids.
The properties are generally within the following ranges
of values:
Viscosity in a 70 wt.% solution in n-butyl Carbitol at 25C(cps):150-8000
Acid Value : 2 - 20
Hardening time (minutes) 3 - 20
Peak exotherm temperature (C) : 60 - 100
The epoxy resin esters thus o~tained are admixed with one or
more mono- or poly-functional liquid unsaturated monomers copolymer-
izable with the epoxy resin esters. Examples of monofunctional
unsaturated monomers are styrene, vinyltoluene, alpha methyl styrene,
methyl methacrylate and vinyl cyclohexene. Examples of polyfunctional

unsaturated monomers arc pentaerytllritot tetraa~rylate~trimethylolpropane
triacrylate, bu~aned~ol diacrylate and glyceryl triacrylate.
The unsaturated monomers are pre~erebly used in amounts
of the order of 5-50 parts by weight for each 100 parts by
weight of the corresponding solution of epoxy resin ester
ln the monomers.
The composition comprises a photosensitive substance,
which may be chosen from among those known in the art, in
order to obtain crosslinking by means of UV radiations.
Examples of said substances are benzoin, derivatives of
benæoin containing in the alpha position an alkyl or alkyl
ether group with from l to 8 carbon atoms, carbonylated
compounds containing a carbon atom bonded to a halogen in the
alpha position with respect to the carbonyl group, organiC
~ulphur derivatives, nitrous compounds and organic sulfonyl
halides. Preferably, the photosensitive substance is pres~nt
in an amount of the order to 2.5 parts by weight for each 100
parts by weight of the sum of the epoxy resin ester and
unsaturated monomer.
The composition of the present invention may contain
conventional additives such as pigments, for example titanium
dioxlde.
In the following experimental examples the parts and
percentages are by w~ight unless otherwise indicated.
Example_l
In a glass f~ask provided with a stirrer, a thermometer,
a pipe for introducing nitrogen near the surface of the reaction
medium, and a bubble cooler there are loaded: lS00 parts of
epoxy resin (I3 (epoxy equivalent 185, Gardner viscosity
%5-Z6, chlorine content 0.02%), 1130 parts of unsaturated
fatty acids obtained from de~ydrated castor oil and 3.7
parts of a ~0% aqueous solutioss ol sodium carbonate.
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597
The mixture is heated to a temperature of 220-230C in
30 minutes and maintained under such condi~ions until the
reaction product has the following characteristics: epoxy
equivalent 650-700; Gardner viscosity (at 25C in a 80%
solution in butyl carbitol~ O-P; acid value - 2.
2600 parts of the reaction product thus obtained are
brought to a temperature of 115-120C and a mixture of 276
parts of acrylic acid and 8.3 parts of sodium carbonate is
added over a pèriod of about 2 hours.
The whole is maintained at the temperature shown until
an unsaturated epoxy ester is produced with the following
characteristics:
-Holde-Hubbelhode viscosity in a 70%
solution in butyl carbitol : 180-220 cps
-Gardner colour number in a 70% solution
in butyl carbitol : 3 as a ma.;imum
-acid value (dry matter~ : 6 as a maximum
- gel time at 25C : 6 minutes
-peak exotherm tempe~ature : 75C
-peak exotherm time : 20 minutes.
The gel time is determined by using a composition
containing 100 parts of unsaturated epoxy resin ester, one part
of benzoyl peroxide, 0.2 parts of cobalt octoate with 6% of
metal and 0.3 parts of dimethylani~ine.
Example 2
Operating as in ~xample 1, the reactor is charged with
1900 parts of an epoxy resin (I) (epoxy equivalent 473, melting
point 50-55C), 550 parts of unsaturated fatty acids obtained
3G from dehydrated castor oil and 3.7 parts of a 10% aqueous
solution of sodium carbonate.
The whole is heated to 215C in 30 minutes and maintained
under such conditions until the reaction product has the
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following characteristics: epoxy equivalent 1000-1150;
Gardner viscosity at 25C in a 80% solution in butyl carbitol:
%5-Z6; acid value (dry matter)- 2.
2400 parts of the reactions product are heated to 120C
and a mixture of 212 parts of acrylic acid and 6.4 parts of
sodium carbonate is added over two hours.
The whole is maintained at 120C until an unsaturated
epoxy resin ester is obtained having the following characteristics,
determined in the same manner as in Example 1:
viscosity 5000-5500 cps
- ~ardner colour number : 4 as a maximum
- acid value Cdry matter~ : 20 as a maximum
- gel time : 7.5 minutes
- peak exotherm temperature : 70C
- peak exotherm time : 25 minutes
Example 3
Operating as in Example 1, the reactor is charged with 860
parts of an epoxy novolak resin (II) (epoxy equivalent 169,
Gardner viscosity Z7~! chlorine percent P.07, Gardner colour
number 3), 775 parts of unsaturated fatty acids obtained
from dehydra~ed castor oil and 2.5 parts of a 10% aqueous
solution of sodium carbonate. The whole is heated to 215C
in 30 minutes and maintained under such conditions until the
reactiOn product has the following characteristics- epoxy
e~uivalent 700-750; Gardner viscosity at 25C in a 80%
solution in butyl carbitol: U; acid value (dry matter)~ 2.
1500 parts of the reaction product thus obtained are
brought to 120~C and a mixture consisting OI 174 parts of
acrylic acid and 4.2 parts of sodium carbonate is added over
2 hours.
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ilii,~9~
Tl~c whole i~ mnintnined at thc temperàture shown until
an unsa~urated cpoxy resin ester ls ob~aincd, havlng the following
characteristic6, dctermined in the same manner 88 in example 1:
- viscosity : 350-400cps
- Gardner colour : 3 as a maximum
- acid value (dry matter) : 15 as a maximum
- gel time : 12 minutes
- peak exotherm temperature : 82C
- peak exotherm time : 32 minutes
The epoxy resin esters obtained in Examples 1 to 3 are
usod for the preparation of the compositions which are submitted
to irradiation by means of UV radiations.
More particularly, these compositions are formed of:
- unsaturated epoxy resin ester 84 parts
- photosensitive substance 2.4 parts
- pentaerythritol tetraacrylate 6.3 parts
- cobalt octoate (12% of Co) 0.68 parts
The photosensitive substance is benzoin tertiary butyl
ether.
Films having a thickness of 25, 50 and 100 microns are
applied on glass slides by means of a film spreader. Each film
is maintained at room temperature fcr 3 minutes prior to the
irradiation; the latter is carried out with a time of ~sure
to radiations of 15,30 and 45 seconds.
More particularly, the films are exposed to radiations
~n a tunnel hav~ng a length of 0.5 metres, containing 'our
2000 Watts ~hilips HT~-7 lamps, irradiating on the 2400-5900
A U~ band with a maximum intensity from 3,200 to 3,600 A. The
tunnel i5 equipped with a belt con~eyor having a variable
speed, so as to select the desired exposure times.
After exposure to the rad~ations the surface hardness cf
the test pieces ~s determined by using the Albert-Ko~n~g
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pendulum according to the DIN 53-171 standards.
The results obtained with the compositions containing
the epoxy resin esters of Examp-es 1 to 3 and with the different
film thicknesses, are shown in the Table.

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Table
Exposure time ~seconds) Film Thickness (microns)
100 50 25
Time (seconds)
Comp. Ex.l
4 7 12
24 36
28 30 50
&omp. Ex.2
6 8 9
14 . 17 32
42 44 56
Comp. Ex.3
12 25
32 35
32 40 53
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