Photo curable polyester with benzoyl oxime carbonate, photo reducible dye (eosin), and a benzyl amine

A photo-initiator system of a polyester resin is disclosed which consists of an oxime carbonate of a vicinal diketone (I), a photo-reducible dye (II) and an amine (III). This system is capable of polymerizing and curing unsaturated polyester resins by irradiation with visible light to provide coatings, adhesives, castings and fibre reinforced composites. The formulae of the ingredients of the system are ##STR1## where R' and R" are independently alkyl, aryl or aralkyl (R' preferably being CH.sub.3 and R" C.sub.2 H.sub.5) ##STR2## wherein X=Br or I on at least 2 positions PA1 Y=H, Br, I PA1 Z=H, COOM, COOR wherein R=C.sub.1 -C.sub.5 alyl. PA1 M=H, K, Na, Li, NH.sub.4 (there preferably being 4X substituents which are Br, and Z preferably being --COOM or --COOR), and wherein also 4Y substituents may be present and preferably be I) and (III) ##STR3## wherein R.sub.1 is H, alkyl, hydroxy-substituted alkyl, aryl or aralkyl. R.sub.2 is independently alkyl, hydroxyl substituted alkyl, aryl or aralkyl. The alkyl groups are preferably C.sub.1 -C.sub.5, the aryl group phenyl and the aralkyl benzyl (preferred such compounds being tribenylamine and dibenzylethanolamine).

FIELD OF THE INVENTION 
This invention relates to the polymerisation and curing of unsaturated 
resinous compositions by irradiating the composition with visible light. 
BACKGROUND OF THE INVENTION 
It is known that unsaturated resins capable of free-radical polymerisation 
can be cured by the addition of photoinitiators and exposure to 
ultra-violet (UV) or visible radiation. The use of UV radiation in 
particular is very well established in the curing of thin films of resin 
used as surface coatings and inks. However UV curing is not suitable for 
thick coatings, or for glass-reinforced resins due to the poor penetration 
of the UV radiation which is strongly absorbed by the resin and the glass 
reinforcement if used. This means that cure is incomplete or takes an 
unacceptably long time to complete. Furthermore UV radiation is very 
dangerous to the eyes and skin and it is therefore necessary to use 
elaborate shielding and safety devices in order to safeguard the health of 
operatives. Such devices add considerably to the cost and inconvenience of 
the use of UV radiation. 
In contrast visible light has none of these disadvantages. Furthermore it 
is readily available as natural sunlight, from tungsten filament bulbs, 
fluorescent tubes and so on, and is not harmful to the eyes or skin under 
normal conditions. 
Systems for curing of resins with visible light have been described but 
have a number of disadvantages. For example, the components of some 
systems are extremely toxic or expensive, or show insufficient sensitivity 
to normal visible light and therefore require special and expensive light 
sources to perform satisfactorily. 
It is already known that eosin plus a suitable reducing agent, such as 
ascorbic acid, can act as photoinitiator for the polymerisation of 
monomers in aqueous solutions in which water is part of the reaction 
chain. For example this system can be used to polymerise acrylamide (see 
G. Delzenne, S. Toppet, G. Smets J.Polymer Sci., 68; 347 (1960) and Ibid. 
Part A Vol. 2 1539 (1964)), in aqueous solution. 
It has been previously suggested that a ketonic photosensitizer, especially 
.alpha.-diketones, plus a reducing agent capable of acting on the 
photosensitizer when the latter is in an excited state could be used for 
the curing of unsaturated polyester resins, (see GB PS No. 1,408,265). The 
reducing agent could in general be a tertiary amine. In a comparative 
example this patent discloses the use of rose bengal 
(tetrachlorotetraiodofluorescein, a polyhalogenated fluorescein) as 
photosensitizer, with unfavourable results. It is stated that if a pigment 
is present it must be absorbent of light wavelenghts different from those 
which excite the photosensitizer. 
Benzoyl substituted-oxime carbonate esters (BOCE) have been claimed as 
potent U.V. photo initiators requiring low irradiation doses for curing 
resins (B.P. No. 1,537,921). However they are poor initiators when 
incorporated into unsaturated polyester resins and irradiated with visible 
light. 
SUMMARY OF THE INVENTION 
We have now discovered that compounds of this type, when used with certain 
photo-reducible dyes and a reducing agent capable of reducing the dye when 
it is in a photo-excited stated, can be used to cure unsaturated polyester 
resins by irradiation with visible light. 
The visible light curing systems of this invention must include 
A. An unsaturated polyester 
B. A BOCE of the general formula I as photo initiator 
##STR4## 
where R',R" are alkyl, aryl or aralkyl 
One commercially available such BOCE is Quantacure.RTM. PDO wherein R' is 
--CH.sub.3 and R" is --C.sub.2 H.sub.5, made by Ward Blenkinsop & Co. 
Ltd., Empire Way, Wembley, Middlesex. 
C. A photo-reducible dye which is capable of absorbing electromagnetic 
radiation in the visible region i.e. about 400 nm to 800 nm wavelength, 
which raises it to an excited state in which it is capable of reacting 
with a suitable reducing agent. Especially suitable dyes are eosins of the 
general formula II. 
##STR5## 
wherein X=Br or I on at least 2 positions 
Y=H, Br, I 
Z=H, COOM, COOR wherein R=C.sub.1 -C.sub.5 alkyl. 
M=H, K, Na, Li, NH.sub.4 
or a mixture of such dyes. 
D. A reducing agent which is an amine of the general formula III. 
##STR6## 
wherein R.sub.1 is H, alkyl, hydroxy-substituted alkyl, aryl or aralkyl. 
R.sub.2 is independently alkyl, hydroxyl substituted alkyl, aryl or 
aralkyl. The alkyl groups are preferably C.sub.1 -C.sub.5, the aryl group 
phenyl and the aralkyl benzyl. 
Preferably the concentration of the photo-initiator (B) is in the range 
0.01-1.0% weight, more preferably 0.02-0.5% by weight and most preferably 
0.05-0.2% by weight. This contrasts with the concentrations necessary when 
U.V. curing is envisaged which are 0.5-15% by weight. 
Preferred compounds of the formula II are those in which each X is Br or I 
and Z is COOM or COOR. 
An overlapping preferred group of compounds of the formula II is that in 
which each X is Br or I and each Y is I. 
The dye (C) is normally used at a concentration of 100-5000 ppm or more 
advantageously 150-2000 ppm or preferably 200-1000 ppm. Commercially 
available dyes of this type are frequently mixtures of closely related 
compounds and are used within the invention. 
The amine (D) can be present in the range 0.1-10% by weight but it is 
preferable to use less than 5% by weight of the total composition. 
The unsaturated polyesters in this invention are those formed by the 
reaction of an .alpha..beta. unsaturated dibasic acid or anhydride (with 
or without the presence of a saturated dibasic acid or anhydride) and one 
or more glycols. The resulting condensation product is dissolved in a 
vinyl type monomer. 
Typical examples of the basic starting materials for such polyesters are: 
(i) Unsaturated dibasic acids/anhydrides-maleic anhydride, fumaric acid. 
(ii) Saturated dibasic acids/anhydride-phthalic anhydride, isophthalic 
acid, terephthalic acid, endomethylene tetrahydrophthalic anhydride, 
tetrahydrophthalic anhydride, adipic acid, sebacic acid, 
tetrachlorophthalic anhydride, tetrabromophthalic anhydride, chlorendic 
acid or anhydride 
(iii) Glycols-ethylene glycol, 1.2 propanediol, 1.3 propanediol, diethylene 
glycol, dipropylene glycol, neopentyl glycol, dibromonepentyl glycol, 
glycols made from the reaction of alkylene oxides and bisphenol A. 
(iv) Monomers 1 styrene, vinyl toluene, methyl methacrylate, bromostyrene, 
ethylene glycol dimethacrylate, .beta. hydroxyethyl acrylate. 
The ingredients BC and D are added in any desired order to form the resin 
composition which is sent out as a complete system. 
These resins can be admixed either in the factory or on site with 
conventional materials such as fillers, thixotropes, fire retardants and 
pigments to form gelcoats and/or with glass or other fibres such as carbon 
or Kevlar.RTM. to yield high-strength composite material by the usual 
laminating techniques. 
The light source used for curing the resin system of this invention may be 
any source of visible light, of which the most economical are natural 
sunlight, tungsten filament lamps and fluorescent tubes. 
When exposed to such a source polymerization and cure is induced in the 
resin which will simultaneously fade in colour so that the final colour of 
the resin is unobjectionably pale. This can serve also as an indication of 
the progress of the reaction.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Example 1 
To 100 grams of Crystic.RTM.196, (an unsaturated polyester resin sold by 
Scott Bader Company Limited, of acid value 22.0 mgKOH/g and containing 35% 
styrene monomer), were added 30 milligrams of eosin Y (Eastman Kodak), 2.5 
grams of tribenzylamine and 0.10 grams of Quantacure PDO (ex Ward 
Blenkinsop and Company Limited). Slight warming was necessary to dissolve 
the tribenzylamine but finally a clear pink-orange coloured resin was 
obtained. Part of the resin was poured into a mould fabricated from two 
sheets of plate glass each 92 mm.times.154 mm separated by a U-shaped 
stainless steel divider 6 mm thick. The filled mould was then placed six 
feet from a bank of sixteen 150 watt tungsten-filament spot/food lamps 
which produced an even light intensity at the mould surface. Gelation of 
the resin was observed after 35 minutes irradiation, and after 50 minutes 
a strong exotherm was detected. After one hour the lights were 
extinguished and when the cured resin had cooled it was separated from the 
mould. The colour of the resin had faded to a straw colour. Samples were 
cut from the moulded sheet and their heat deflection temperature measured 
according to British Standard No. 2782:102G. The average heat deflection 
temperature was 81.degree. C. The standard heat deflection temperature for 
Crystic 196 cured with methyl ethyl ketone peroxide and cobalt octoate is 
72.degree. C. after post curing at 80.degree. C. for 3 hours. 
Example 2 
The conditions of Example 1 were repeated except only four 150 watt 
tungsten filament spot/flood lamps were used. Gelation of the resin 
started in 80 minutes and an exotherm was noted after 100 minutes. After 
two hours the lights were extinguished and the sample was left in the dark 
for 16 hours. The sample was then irradiated under the same conditions for 
a further 2 hours. The cast sheet obtained recorded a heat deflection 
temperature of 79.degree. C. 
Example 3 
A sample of Crystic.RTM.272 an isophthalic acid based polyester made by 
Scott Bader Company Limited was made up to the formulation given in 
Example 1 and used to fabricate a glass fibre reinforced laminate 
containing four layers of 450 g/m.sup.2 powder bound chopped strand glass 
mat at a resin:glass ratio of 2.3:1. The laminate was cured by visible 
light irradiation provided by sixteen 150 watt spot/flood lamps. 
Irradiation was continued for 2 hours after which the laminate was placed 
in an oven at 40.degree. C. for 16 hours. Samples were cut from the 
laminate and tested in tension according to ISO 3268. The results are 
shown below in comparison with a laminate made using Crystic 272 cured by 
MEK peroxide and cobalt and also post cured at 40.degree. C. 
______________________________________ 
Peroxide-cured 
Photo-cured 
Laminates 
Laminates (comparative) 
______________________________________ 
Barcol Hardness 
Air surface 35 ND 
Mould surface 50 ND 
Tensile Break Load/mm width 
(MN/mm) 444 .+-. 17.6 
415 .+-. 13.7 
Tensile Strength 
(MPa) 125 .+-. 7.6 
104 .+-. 5.7 
Tensile Stiffness 
(MN/mm) 28150 .+-. 906 
29370 .+-. 1853 
Tensile Modulus (GPa) 
7.9 .+-. 0.4 
7.4 .+-. 0.6 
Elongation to Break (%) 
1.99 1.80 .+-. 0.11 
______________________________________ 
ND = not determined 
Example 4 
2.5 Parts by weight (p.b.w.) of tribenzylamine were dissolved in 97.36 
p.b.w. of Crystic.RTM.272 (an isophthalic based polyester resin ex Scott 
Bader Company Limited). Also added were 0.10 p.b.w. of Quantacure.RTM. PDO 
(Ward-Blenkinsop and Company Limited), 0.02 p.b.w. of eosin Y (the 
disodium salt of tetrabromofluorescein i.e. each X is Br, Z is COOH and M 
is Na) and 0.02 p.b.w. of spiritlsoluble eosin (the sodium or potassium 
salt of the ethyl ester of tetrabromofluorescein) (both products of 
Eastman Kodak Company) to obtain a clear orange-red resin. 10 grams of the 
resin were poured into a shallow aluminium-foil mould, the top surface 
being left open to the air. The mould was irradiated with visible light 
from a household tungsten filament bulb. The resin gelled in five minutes. 
After one hour the cured resin had a hardness of Barcol 30 on the top 
(air) surface and of Barcol 40 on the lower (mould) surface. The colour of 
the resin had bleached to a pale straw colour. 
Example 5 
(a) Comparative 
Eosin (spirit soluble, ex BDH 0.06 parts by weight) and tribenzylamine (2.5 
parts by weight) were admixed with 97.5 parts by weight of Crystic.RTM.196 
(a general purpose orthophthalic-based polyester resin ex Scott Bader 
Company Limited) and the resin poured into a mould and irradiated as in 
Example 4 but at a light intensity 3/5 of that used in Example 4. Although 
the resin gelled in less than 10 minutes and the colour of the dye faded 
cure was incomplete as indicated by a zero Barcol hardness and poor 
mechanical properties of the product. 
(b) When this experiment was repeated with the addition of 0.5 parts by 
weight of Quantacure.RTM.PDO the resin gelled within less than 3 minutes 
and reached a Barcol hardness of 40 in 2 hours of irradiation. 
Example 6 
A sample of Crystic.RTM.196 was supplemented to the formulation given in 
Example 1 and used to fabricate a glass fibre reinforced laminate 
containing twelve layers of 450 g/m.sup.2 powder bound chopped strand mat 
at a resin to glass ratio of 2.3:1. The laminate was cured by visible 
light irradiation provided by sixteen 150 watt spot/flood lamps giving a 
light intensity at the laminate surface half that used in Example 4. 
Irradiation was continued for two hours after which the laminate was 
placed in an oven at 40.degree. C. for 16 hours. 
Samples cut from the laminate had the following mechanical properties. 
______________________________________ 
Sample thickness 11.37 .+-. 0.60mm 
Tensile strength (MPa) 103 .+-. 6 
Tensile modulus (GPa) 9.1 .+-. 0.5 
Tensile elongation (%) 1.63 .+-. 0.20 
Single lap shear strength (MPa) 
9.7 .+-. 0.8 
Bend strength (MPa) 177 .+-. 14 
Bend modulus (GPa) 8.0 .+-. 0.3 
______________________________________ 
Example 7 
Cast sheets were prepared for determination of heat deflection temperatures 
and mechanical properties by preparing resins of the following 
formulations. 
______________________________________ 
Crystic 196 or Crystic 272 
97.2 p.b.w. 
Tribenzylamine 2.5 p.b.w. 
Quantacure PDO 0.25 p.b.w. 
Eosin Y 0.04 p.b.w. 
______________________________________ 
Moulds, as described in example 1 were used to prepare samples for the 
determination of heat deflection temperatures, but 3 mm thick rubber 
separators were used between the glass plates of the moulds to prepare 
samples for the determination of mechanical properties. The mouldings were 
cured by irradiation with visible light from a bank of sixteen 150 watt 
spot/flood tungsten filament lamps two feet from the moulds. The resins 
gelled in less than four minutes but during subsequent cure the high 
temperatures developed by the exothermic polymerisation reactions caused 
many of the moulds and mouldings to crack. The light intensity was 
therefore reduced by reducing the voltages applied to the lamps from 240 
volts to 210 volts. Uncracked samples were then obtained. The following 
results were obtained from specimens cut from the cast sheets. 
______________________________________ 
Crystic 196 
Crystic 272 
______________________________________ 
Hardness (Barcol tester) 
39 (42) 42 (45) 
Heat deflection 
86.5 (78) 90 (75-80) 
temperature (.degree.C.) 
Tensile strength (MPa) 
85.4 .+-. 
(73) 57 .+-. 5.8 
(65-75) 
4.7 
Elongation (%) 
3.1 .+-. 0.5 
(4.1) 1.5 .+-. 0.1 
(2.0-2.5) 
Initial tensile 
4.03 (2.95) 4.47 (3.5-4.5) 
modulus (GPa) 
Water absorption 
(mg %) 
(24 hours at room 
16.5 (&lt;20) 17.1 (&lt;20) 
temperature) 
______________________________________ 
Figures in parentheses indicates typical values obtained for the same 
resins cured with methyl ethyl ketone peroxide and cobalt octoate and post 
cured at 80.degree. C. (Heat deflection temperature samples received 
further post cure at 120.degree. C.). 
Example 8 
A photocuring formulation based on Crystic 196 was prepared containing 0.1% 
Quantacure PDO, 0.04% Eosin Y and 2.5% tribenzylamine and used to 
impregnate two layers of Kevlar.RTM.49 polyaramide fibre woven roving 
(Kevlar is a registered trademark of DuPont Limited) to give a laminate 
with a nominal resin content of 80% by weight. 
When exposed to visible light from tungsten-filament lamps with an 
intensity equal to that used in Example 4 the resin gelled in twelve 
minutes, bleached in twenty minutes, exothermed noticeably after 30 
minutes and was fully cured in an hour. 
Example 9 
An unsaturated polyester resin equivalent to Crystic 196 but in which the 
styrene was replaced by an equal weight of .beta. hydroxyethyl acrylate 
was formulated with 0.1% Quantacure PDO, 0.01% Eosin Y, 0.03% eosin-spirit 
soluble, and 2.5% tribenzylamine. 10 Grams of the formulated resin were 
poured into a circular shallow aluminium foil mould and irradiated with 
visible light with an intensity equal to that used in Example 4. The 
sample gelled in less than 3.5 minutes and bleached in 13 minutes to 
produce a hard, water-white casting with a perfectly dry air-surface. 
Example 10 
A photocurable resin was formulated as follows: 
______________________________________ 
Crystic.RTM. 272 
97.2 p.b.w. (parts by weight) 
Tribenzylamine 2.500 p.b.w. 
Quantacure PDO 0.25 
Wax 0.020 
Spirit soluble eosin 
or potassium 
(sodium/salt of ethyl 
0.015 
ester of eosin) 
Eosin Y 
(disodium salt of eosin) 
0.015 
100.000 
______________________________________ 
This resin was used to prepare a filament-wound glass-fibre reinforced pipe 
by means of a laboratory filament-winding machine in which twenty 
glass-fibre rovings were led through a shallow tray containing the resin, 
so as to coat the glass with resin, and then between two rollers which 
removed excess resin before the resin-coated glass fibre rovings were 
wound round a rotating stainless steel mandrel. The mandrel was irradiated 
with the light from two fifteen hundred watt tungsten-halogen floodlamps 
each about one meter from the mandrel. After twenty five minutes the 
winding of additional glass fibre rovings was stopped but irradiation and 
rotation of the mandrel was maintained. After forty five minutes rapid 
bleaching of the resin was observed and after a total time of seventy 
minutes the mandrel was stopped and the filament-wound glass fibre 
reinforced polyester pipe produced was released. 
This pipe was approximately one meter long, 30 mm in internal diameter and 
6.5 mm thick. It had a Barcol hardness of fifty and its colour was reduced 
to a pale straw. 
Example 11 
A series of photocuring resins was prepared in duplicate using the 
following formulation: 
______________________________________ 
Crystic.RTM. 600 97.35 p.b.w. 
(an unsaturated polyester 
based on propoxylated 
bisphenol A and maleic 
anhydride) 
Tribenzylamine 2.50 
Quantacure PDO 0.10 
Dye 0.05 
______________________________________ 
The dyes used and the average results obtained from the duplicate samples 
are shown in Table 1. 10 grams of each sample was poured into a shallow 
aluminium foild mould and exposed to light intensity from tungsten 
filament lamps equal to that used in Example 4. The final colour in each 
case was pale straw. 
TABLE 1 
______________________________________ 
Barcol 
Initial Bleach Hardness 
Colour Gel Time Time 60 120 
Dye of Resin (minutes) 
(minutes) 
mins mins 
______________________________________ 
Eosin-spirit 
Orange 10-12 15-20 35 
soluble (1) 
Erytheosin B (2) 
Orange/red 
8-10 10-15 35 
Rose Bengal (3) 
Crimson 12-14 14-20 35 
Dibromo- Yellow 40-45 ca 60 0 35 
fluorescein (4) 
Rhodamine B (5) 
Crimson 40-45 240 0 0 
______________________________________ 
Notes: According to formula II; 
(1) each X = Br, each Y = H, M = Na and Z = CO.OEt 
(2) each X = I, each Y = H, M = Na and Z = CO.ONa 
(3) each X = I, each Y = Cl, M = Na and Z = CO.ONa 
(4) two X's = Br, two X's = H, each Y = H, M = Na, Z = CO.ONa 
(5) Rhodamine B has the formula: 
##STR7## 
This shows that Rhodamine B, a dye of similar chemical structures to those 
of formula II but containing no halogen atoms is not effective in the 
claimed system. 
Example 12 
A series of photocuring resins was prepared in duplicate according to the 
following formulation: 
______________________________________ 
Crystic .RTM. 198 97.26 p.b.w. 
(an unsaturated polyester resin 
ex Scott Bader Co. Ltd) 
Amine 
(see Table 2) 2.50 
Quantacure PDO 0.20 
Eosin-spirit soluble 0.03 
Eosin Y 0.01 
______________________________________ 
10 Grams of each sample was poured into a shallow aluminium foil mould and 
exposed for 60 minutes to visible light with an intensity equal to that 
used in Example 4 provided by tungsten filament lamps. The results of this 
experiment are given in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Gel Time 
Bleach Time 
Amine (Minutes) 
(Minutes) 
Comments 
__________________________________________________________________________ 
N,N--Dibenzylethanolamine 
4 6 Well cured, no air surface tack 
N--Benzyldiethanolamine 
81/2 18 Well cured, slight air surface tack 
N--benzyl-N--methylethanol 
amine 81/2 161/2 Well cured, no air surface tack 
N,N,--dimethylbenzylamine 
21 28 Well cured, slight air surface tack 
Tribenzylamine 3 7 Well cured, slight air surface tack 
Dibenzylamine 23 321/2 Well cured, slight air surface tack 
N--Ethylmorpholine 
19 28+ Incomplete bleaching, air surface 
tacky 
__________________________________________________________________________ 
These results show that N ethylmorpholine, often used as a reducing agent 
in photocure systems, is much less effective than the claimed system. 
Example 13 
A photocuring white gelcoat was prepared by adding 71/2% by weight white 
pigment paste to a sample of gelcoat 65 (Scott Bader Co. Ltd) containing 
0.1% Quantacure PDO, 2.5% Tribenzylamine and 0.05% eosin-spirit soluble. 
A female mould of a model boat hull approximately 4 ft.times.1 ft.times.9 
ins was treated with a suitable mould release agent before the white 
gelcoat was brushed onto it to provide a coating approximately twenty 
thousandths of an inch thick. The mould was irradiated by light from two 
1500 watt tungsten-halogen floodlamps at a distance of one meter. The pink 
colour of the gelcoat bleached white in less than three minutes and it was 
possible to lay-up a glass fibre laminate on the gelcoat within ten 
minutes without the glass fibres penetrating the gelcoat. After curing the 
laminate it was possible to release the moulding from the mould without 
difficulty. The gelcoat was fully cured and showed no residual colour due 
to the dye. 
Example 14 
Ten grams of a fire retardant unsaturated polyester resin based on 
dibromoneopentyl glycol and containing tris (chloroethyl) phosphate (fire 
retardant additive), Quantacure PDO (0.2%), eosin-spirit soluble (0.03%), 
Eosin Y (0.01%) and tribenzylamine (2.5%) was poured into a shallow 
aluminium foil mould and irradiated with visible light from a tungsten 
filament bulb. The resin gelled in three minutes, fully bleached in 11 
minutes and after 60 minutes had a Barcol hardness of 30. 
Crystic.RTM.386 a clear fire retardant resin (i.e. passing B.S.476 part 
VII, Glass I) based on maleic and chlorendic acid anhydrides and 
containing proprietory fire retardant additives was formulated with 
Quantacure PDO (0.1%) eosin-spirit soluble (0.04%) and tribenzylamine 
(2.5%). 10 grams of this formulated resin was poured into a shallow 
aluminium foil mould and irradiated with visible light with an intensity 
1.5 times that used in Example 4. The resin gelled in less than one 
minute, bleached in two minutes and had an average Barcol hardness of 30 
after one hour.