CA1078095A - Radiation curable coating - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A radiation curable coating composition for various substrates contains an adduct of acrylic acid and an epoxy resin (which may be modified with an anhydride, such as maleic anhydride), and a reactive acrylate monomer vehicle.
The coating composition can be pigmented and can also contain additives commonly used in coatings, such as wetting agents and flow control agents. The coating composition does not require the usual hydrocarbon vehicles that give rise to air pollution problems. Surface gloss of a UV cured film obtained from a pigmented coating composition can be increased by using a photosensitizer combination of 2-chlorothioxanthone and a phenylketone, such as benzophenone. Adhesion of a cured coating is improved by replacing the tertiary amine co-sensitizer, at least in part, with dimethylaminoethyl acrylate.

Description

~07809S
BACKGROUND OF THE INVENTION
Field of the Invention This invention is directed to epoxy acrylate ester coatings for substrates, that are curable with radiation.
Description of the Prior Art British Patent No. 1,241,851 describes a process for coating an article that comprises applying a film of an ethylenically unsaturated ester having hydroxyl groups and exposing it to ionizing radiation. No liquid vehicle is used.
The coating composition of this invention comprises a similar resin in a vehicle that is a reactive monomer. This vehicle, when the coating composition is exposed to radiation and set, reacts with the resin and becomes an integral part of the resultant coating.
S MARY OF THE INVENTION
This invention provides a coating composition that comprises an adduct of acrylic acid and an epoxy resin, or an anhydride modified adduct, an~a reactive acrylate monomer. A
photosensitizer and a tertiary amine co-sensitizer are used in the case of ultraviolet (UV) light cured coatings.
It also provides a UV curable pigmented coating composition that contains a photosensitizer combination of

2-chlorothioxanthone and a phenyl ketone.

It further provides a W curable coating composition that affords improved film adhesion, in which at least part of the tertiary amine co-sensitizer is replaced with dimethylamino-ethyl acrylate.
It still further provides substrates coated with the aforedefine~ coating compositions.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Prior practice has been to coat substrates, such as metals useful for container manufacture, with a variety of coating compositions comprising heat curable resinous components and non-reactive, volatile organic solvents that are removed from the coating during the curing process. Recent restrictions on allowable atmospheric pollutants, the shortage of organic solvents, and the shortage of fuels useful for firing curing ovens has created a need for coating compositions which can be cured wih lower energy requirements and which eliminate the need for non-reactive organic solvents.
The present invention, in one aspect, resides in a UV
light curable coating composition that comprises an adduct of acrylic acid and an epoxy resin, a monofunctional ester of acrylic acid, 2-chlorothioxanthone, a tertiary amine co-sensitizer, wherein at least part of said tertiary amine is replaced with dimethylaminoethyl acrylate.
According to another aspect of this invention, there is provided a W light curable coating composition that comprises 10-30 weight percent of an adduct of acrylic acid and an epoxy resin, 40-60 weight percent of a monofunctional ester of acrylic acid, 0.1-2.0 weight percent of 2-chloro-thioxanthone, 0.1-2.0 weight percent of a phenyl-ketone, 0.5-6 weight percent of a tertiary amine, and a pigment.
~' This aspect of the invention is described herein, and is also described and claimed in Canadian Patent Application No.
222,006, of which the present application is a divisional.
The epoxy resin can be any polyglycidyl ether of polyhydric organic compounds, especially polyhydric phenols.
Particularly preferred are the glycidyl ethers of bisphenols, a class of compounds which are constituted by a pair of phenolic groups interlinked through an intervening aliphatic bridge.

-3a-While any of the bisphenols may be used, the compound 2,2-bis (p-hydroxyphenyl) propane, commonly known as bisphenol A, is more widely available in commerce and is preferred.
While polyglycidyl ethers can be used, diglycidyl ethers are preferred.
Depending upon whether the epoxy resin is sub-stantially monomeric or polymerized to some degree, the pre-ferred epoxy resins will have an epoxy equivalent weight of between about 170 and about 2,000 and an epoxy value between about 0.60 and about 0.05. The preferred epoxy resins, i.e., those made from bisphenol A, will have two epoxy groups per molecule. Accordingly, the stoichiometric amount of acrylic acid to form a diacrylate adduct would be two moles of acid for each two epoxy groups. In practice, however, it is pre-ferred to use slightly less acid than the amount necessary to cover both epoxy groups to be certain that there is no free acrylic acid remaining in the reaction product. Free acid would contribute to excessive volatility of deposited films, while minor amounts of free epoxy are not objectionable.
Therefore, the amount of acrylic acid reacted can be between ; about 1.85 moles to 2.0 moles of acid per two epoxy groups.
The esterification reaction between the acrylic acid and epoxy resin is carried out at an esterification temperature, e.g.
between about 90C. and about 110C. Esterification is con-tinued until an acid number of 5-15 is obtained. This reaction ordinarily takes place in 8-15 hours.
; In another embodiment of this invention, the epoxy diacrylate is further reacted with an anhydride. Maleic ~078095 anhydride is preferred but other anhydrides are contemplated for this purpose, such as citraconic anhydride, succinic an-hydride, ethylsuccinic anhydride, amylenesuccinic anhydride, itaconic anhydride, glutaric anhydride, 4-tetrahydro-phthalic anhydride, phthalic anhydride, hemimellitic anhydride,trimellitic anhydride, and pyromellitic anhydride. The amount of anhydride used will be between about 0.1 and about 1.0 mole anhydride per mole diacrylate resin. This reaction is general-ly carried out at temperatures between about 80C. and about 90C. The reaction is considered complete when the alcoholic KOH and aqueous KOH acid numbers agree, i.e., about 10-40.
This evidences a complete absence of anhydride functionality.
The esterification reaction and the further reaction with anhydride can occur without the aid of a catalyst. How-ever, catalysts are preferred such as tertiary amines; quater-nary ammonium hydroxides, such as benzyltrimethylammonium hydroxide; N,N-dimethylaniline; N,N-benzylmethylamine; tri-ethylamine; and KOH. It is also advantageous to use small . amounts of hydroquinone as a polymerization inhibitor.
The epoxy diacrylate or the anhydride modified epoxy diacrylate, prepared as aforedescribed, is then dissolved in a reactive monomer vehicle to prepare the coating composition.
The reactive monomer vehicle contemplated nerein is a mono-functional ester of acrylic acid having from 4 to about 20 carbon atoms. The acrylate ester can be an alkyl or hydroxy-alkyl acrylate, such as methyl acrylate, ethylacrylate, hydroxy-- ethyl acrylate, propyl acrylate, isopropyl acrylate, hydroxy-propyl acrylate, butyl acrylate, isobutyl acrylate, amyl 10~8095 acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, tetradecyl acrylate, and hexadecyl acrylate. Also contemplated are the acrylic esters of the well known class of ether alcohols having the formula: ROCH2CH20H, wherein R is Cl-C6 alkyl or phenyl, i.e. the "Cellosolve"*. Examples of such esters are methoxyethyl acrylate (Methyl "Cellosolve" acrylate), ethoxy-ethyl acrylate ("Cellosolve" acrylate), butoxyethyl acrylate (Butyl "Cellosolve" acrylate), isobutoxyethyl acrylate (Iso-butyl "Cellosolve" acrylate), hexoxyethyl acrylate (Hexyl "Cel-losolve" acrylate), and phenoxyethyl acrylate (Phenyl "Cello-solve" acrylate). The contemplated reactive monomer vehicle can be designated by the formula: CH2=CH2COOR', wherein R' is hydrogen, Cl-Cl5 alkyl, or -C2H40R" wherein R" is Cl-C6 ; 15 alkyl or phenyl. The reactive monomer vehicle can contain a minor amount (up to about 20 weight per cent) of a poly-functional acrylate, e.g., neopentyl glycol diacrylate, but it is pre~ominantly monofunctional.
The coating composition is cured by exposure to radiation. When the radiation used is electron beam radiation a photosensitizer is not needed, but when ultraviolet light is used, a photosensitizer is needed. Suitable sensitizers include acetophenone, benzophenone, xanthone, benzoin iso-butyl ether, and 2-chlorothioxanthone. 2-Chlorothioxanthone is preferred, particularly when the formulation is pigmented.
A tertiary amine co-sensitizer is also used in the U.V. curable coating fbrmulation and serves to speed up the cure rate. In order to realize this function, it is necessary to have free amine present. Accordingly, the amine concentration range is *Trademark for mono- and dialkyl ethers of ethylene glycol and their derivatives.

. 1078095 - .

from about 1.25 to about 3 times the amour.t required to neutralize free acidity. The amount required for neutrali- -zation can be readily calculated from the determined acid m~mber of the resin. The tertiary amines are normally liquid trialkylamines, trialkanolamines, or tertiary mixed alkyl-alkanolamines. Non-limiting examples of such amines are tri-ethyl~mine, triisopropylamine, tributylamine, trihexylamine, tri-2-ethyl-hexylamine, tridodecylamine, methyldiethanolamine, dimethylethanolamine, 2-hydroxyeth~ldiisopropylamine, ar.d tr~ethanolamine.
- m e coating compositions described so far produce clear coatings and are useful as such.
Although a pigment is not necessary, it is pre~erred to incorporate a pigment into the coating composition of this ~5 lnvention. The preferred pigment is titanium dioxide for white base coats, but any well known filler pigment can be used, such as zinc oxide, bent~nite, silica, ochers, and ~hrome yellows or greens. ~`
Depending upon whether the coating composition is ;pigmented or not, the broad and preferred ranges of concentra-tion of the components are as set forth in the following Table 1.

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The coating composition is applied to a usual ~ubstrate metal, paper, leather, clotn, etc. using any of the usual methods of application, including wiping, spraying and rollcoat application. Su~table metallic substrates in-clude aluminum, steel, and tin-plated steel. The rate of application will be sufficient to apply the coating at about -1-20 mg/sq. ln. After app;ication, the coating is set by exposure to radiation for between about 0.01 æecond and about 30 seconds. In some cases, the coating will be set by short exposure to radiation, e.g. less than one sec~nd, which s sufficient to set the film so that it will accept ink and/or a wet-ink varnish. Following the printing or varnishing operation, these coats may be further set by bak~ng at about 250F. to 450F. for between about 3 seconds and about 5 minutes.
Suitable sources of radiation are ultraviolet light or electron beam radiation. Preferably, an ultravLolet light 3f a wave length below 4000 Angstrom Units is used.
The electron beam radiation is obtained from high energy elec-? - trons produced by high voltage electron accelerators. m ese are well known and include the VandeGraaff accele-ator, re-` sonant transformers, transformer rectifiers, micro-wave waveguide linear accelerator, and synchrotrons.
The following examples demor.strate ~he preparation ~5 of adducts and coatings containing them, in accordance with this invention.

. ~ . .

i078095 .

Using a vessel equipped with an agitator, a reflux condenser, an inert gas inlet and a charging port, there was charged 660 grams "~nl'* 828. '~n"
828 iæ a diglycidyl ether of bisphenol A having an epoxy equivalent wei~ht Or about 185-192 ~d an epo~de ~alue of 0.50-0.54. Through the gas inlet was ~ntro-duc'ed a nitrogen flow which was maintained throughout the resin preparation cycle. Nhile under agitation, 238 grams glacial acrylic acia was added and stirred v until epoxy resin dissolved. Upon dissolution o~ the acrylic acid, 1.3 grams triethyl amine and 0.1 gram hydroquinone were added. Under continued agitation, heat was raised to 205-212F. and held at this 'tempera-ture until an acid number of 5-lO'was obtained (ap-proximately 10 hours). Temperature was reduced to 150-160~F. and 600 grams hydroxypropyl acrylate was added and the m~xture was stirred until uniform. me ... . .
- ~inal product was a clear solution of prepolymer in ) monomer at a 60/40 weight ratio~ -- EXAMPLE 2 _ -. . .
Using a vessel equipped as in the previous example, there were charged 7200 g."~n-- 828, 2590 g.
glacial acrylic acid, 1~ g. triethyl amine and 1.2 g.
j hydroq~inone. Agitation was started along with nitrogen ; flow and the mixture was heated to ~00C. Temperature *"EFon" ~esins is the trademaIk for a series of oondensation prodNcts of epichlorohydrin and bisphenol-A.

- . 1078~95 .
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sS - ; was mainta~ned at 95-100C. unt~l an acid number of 5-10 was obtained; at this point, was added 432 g.
: male~c anhydride and the temperature was held at 90C.
unt~l the acid number, as determined by alcoholic KOH
and aqueous KOH, agreed, thereby indicating the co~plete absence of anhydride functionality. The normal time for this phase of the resin preparation was 1.5 hours. At this point, was added 6835 g. hydroxypropyl acrylate.
; nle final product was a 60/40 ratio of prepolymer/mono-~ LO mer having a viscosity of 850-goo cp at ~0F. a weight/
,~ gallon of 9.5 pounds/gallon, and an acid value of 28-35.
e Jolar ratio of maleic anhydride to epoxy resin was 0.2 Ihe f~low~g Examples 3 and 4 demonstrate coa~n~ ~ ~le by elect~
be~-. r~a~on.

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'5 In a su$table sized high speed disperser, were .... .
thoroughly mixed 27.1 pounds of the product from ; ExaDple 1 and 42.8 pounds titanium dioxide pigment and the mi~.ture was stirred until a fineness of grind - of 7 or better was obtained. Then were added 31.4 ~ ~ pounds hydroxypropyl acrylate, and 20.2 pounds of the - ; product from ~xample 1 and the mixture was stirred unt~l uniform. The resultant finish had a pigmen~/
binder ratio of O.52/1 and a prepolymer/total binder .. .
. . ratio of 0.4/1.

-5 : EXA~PLE 4 , Us~ng the equipment o~ Example 3, were thoroughly m~ed 27.3 pounds of the resin solution of Example 2, .

- . ~078095 .
and 42.~o po-~nds of titanium dioxide pigment. Continued hlgh speed agitation until a fineness of grind of 7 minimum was obtained. Agitation was continued but at elower speed, while adding 10.0 pounds o resin solution of Example 2 and 1~.5 pounds of hydroxypropyl acrylate.
This was stirred until uniform. The resultant finish had a pigment/binder ratio of 0.78/1 and a prepoly~er/
to~al binder ratio of 0.4/1.

, To a suitable sized pebble mill, were charged ; one pound 2-chlorothioxanthone and 2 pounds hydroxy-prop~Jl acrylate. mis was ground for 24 hours, until thoroughly dispersed. m e product is suited for use a~ a photoinitiator for pigmented finishes.

In ~ suitably sized high speed disperser, were thoroughly mixed 27.1 pounds of the product from Example 1, 42~8 pounds titanium dioxide pigmen~, and 1.5 pounds of the product of Example 5. This was - stirred until a fineness of grind of 7 or better was obtained. Then, were added 31.4 pounds h-~droxypropy acrylate, 2.0 pounds methyldiethanolamine and 20.2 pounds of the product of Example 1. The mixture was - stirred until un form. The resultant finish had a pigment/binder ratio of 0.52¢i and a prepolymer/total binder ratio of 0.4/1.

' `

.'- - -`' - . . ' .' .. . . .

~ .
Usin~ the equipment of Example 6~ were thoroughly mixed 27.3 pounds of the resin solution of Example 2, 42.9 pounds of titanium dioxide pigment, i and o.8 pounds of 2-chlorothioxanthone. High speed -- ~gitation was continued un~il a fineness of grind o~
7 minimum was obtained. ~itation was continued but at slower speed while adding 10.0 pounds of resin - -solutlon of Example 2, 17.~ pounds of hydroxypropyl i- acrylate, and.1.5 pounds of methyldiethanolamine.
This was stirre~ until uniform. m e resultant finish had a pigment/binder ratio of 0.78/1 and a prepolymer/
. . .
- total binder ratio of 0.4/1.

EXAMPLES 8 through 27 ~5 - In Table II are set forth data on various coat-lngs prepared using the techniques and methods set forth in Examples 1 through 7. Each coating was applied to various substrates, cured by ultraviolet light ( W) or electron bea~ (EB), and tested ~or film properties.
~0 The ~dhesion test is carried out by cross-hatching a . coated area with indiYidual score lines approximately 1/16 inch apart. m en "Scotch"* t~pe is firlrly applied to the cross-hatched are~ and removed with 8 auick snap.
m e amount of coating remain~ng on the panel is observed visually and rated on a percentage basis. Pasteuriz~tion is carried out b~ immersing the coated panels in wat2 ~t 1~5F. for 30 minutes. Then, the psnels are wiped *Traæemark of the 3-M Cbmpany, for a line of pressure-sensitive adhesi~e tapes.

-. ............ dry with an absorbent towel and the adhesion test .
- ~s carried ~ut as aforedescribed.

-. . In Table II, the following abbreviations are . used:
~ 1004 = Epon 1004 Reaction product epichlorohydrin ~. and bisphenol A. M.W. a.bout 1400, Epoxide value 0.10 - 0.12.
~- . 828 = 'Epon 828 Diglycid lether of bisphenol A.
M.W. about 350 - ~00. Epoxide value : . . -5 - 0.54.
. .A = 2 moles a.crylic ac~d per mole epoxy - ~ = .25 moles ma.leic anhydride per mole ep~xy HPA = Hydroxypropyl Acrylate HEA = Xydroxyethyl Acrylate . 2-~HA = 2-Ethylhexyl Acrylate ... MDEOA = Methyldiethanolamine . TEOA = Trietha.nolamine c~s = Centipoise .
Al z: Aluminum - CCO = Chrome-chrome oxide treated steel . . CDC5 = #5 grade of t~nplate steel .
TiO2 = Titanium Dioxide THP = ~ 4-Tetrahydro~hthalic anhydride CTX = 2-Chlorothicxanthone Monome~ = ~eactive mGnomer vehicle W -25 = Ultraviolet light at line speed 25 ft./min per lamp.
E~-2 = Electron beam radiation at 2 megarad dosa~e ., .

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-; 10780~5 The results given in Table I indicate that:
a) Increasing epoxy resin molecular weight improves adhesion to metals.
b) Maleic anhydride adducts have better adhesion to metals and demonstrate better leveling than compositions containing resins containing no maleic anhydride.
c) Coatings containing TiO2 have better adhesion to metals than do coatings of identical composition but without liO2.
The coating compositions that have been described and illustrated hereinbefore can be considered the "basic"
coating compositions. It has been found that certain pro-perties of the cured film can be markedly improved by incor-porating additional chemicals into the basic coating compo-sitions.
With the basic UV curable coating compositions, the gloss of the cured film is usually lower than desired, particularly at higher cure rates. This gloss can be markedly increa.sed by u~ing in the coating composition a sensitizer combination of 2-chlorothioxanthone and a phenyl ketone.
Benzophenone is the preferred phenyl ketone, but other phenyl ketones are contemplated, such as acetophenone, propionphenone, and butyrophenone.
The following examples demonstrate this gloss im-provement. In each example, using the techniques and methods of Examples 1-7, a pigmented coating composition (A) without benzophenone (Bzph) and (B) with benzophenone were coatéd on aluminum and exposed to UV at various cure speeds. The re-sulting films were tested for 60 gloss.

', ' ' ~ 10780g5 ~

... . . ..
An epoxy diacrylate of "Ep~" 828w~ mx~fied - wlth 0.25 mole maleic anhydride per mole epoxy.
This resin (Resin A) was admixed wlth hydroxy-.
propyl acrylate, TiO2 p~gment, and sensitizers and co-sensitizers. The f~llowing tsbulation sets ; ; forth amounts of comp~nents, pigment/~inder ratio (P/B), resin/binder ratio (R/B), and pertinent test data.

" O Example TiO2 CTX MDEOA ~esin A
~ 28A 36.6 9 3.6 24.5 ~8B 36.6 9 3;6 24.5 .' ' . ' - ', ' . . ' ' ', ' .
Example H M Bzph P~B R/B

28~ 34.4 O -.58 .39 28B- 32.4 2.0 .58 ~39 . _ _ _ .
No BzPh 2% Bzph W Cure Speed 25 FPM- Yield 90 90 Glo~s 79 88 . .
.

'O An epoxy diacry~ate of"~n" ~28 (~s~ B) was ~dmixed with hydroxypropyl acrylate, TiO2 pigment, and sensitizers and co-sensitizers.- m e follow~ng - tabulation sets forth amounts Or components ar.d per-tinent tes~ data.
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1(~78095 ... ~ ".. ' . .

.
: ....... . Ex~mple TiO2 Resin B HPA CTX
..
29A 42.828.6 . 25.6 1.0 29B 41.527. 7 24.8 1.0 .. . . . . . . .
.
: . . Example MDEOA Bzph- P/B- R/B
29A 2.0 0 - .7~ .$o 29B 3. ~- .71 .a7s ; : ' W Cure Speed, ~PM
. .
No Bzph Bzph ~5 Yield 94 ' 91 Gloss 95 95 Yield 91 87 Gloss 7? 93 100 Yield 87 84 Gloss . 39 go , ; . . . EXAMPLE 30 .~ , . An epoxy diacrylate f~xn~ 1ooa w~ mLdified wlth 0.25 mole maleic anhydride per mole epoxy. m is . . resin (Resin C) was admixed wLth hydroxypropylacry-. late, TiO~ pigment, and sensitizers and co-sensitizers.
) m e following tabulation sets forth amounts o~ com-ponents and pertinent test data.
. . .

.
. ~ . .

- .

- .

~ 1078095 Example TiO2 Resin C CTX

30A 33.320.0 1.0 30B 33.019.8 1.0 _ ample MDEOA HPA Bzph 30A 4.041.7 0 30B 4.041.2 1.0 UV Cure Speed, FPM
No Bzph 2% ~zph Yield 88 88 Gloss 89 89 Yield 86 85 Gloss 75 8 100 Yield 73 77 Gloss 45 62 'rhe preceding examples illustrate that benzophenone (a phenyl ketone) combined with 2-chlorothioxanthone has es-sentially no effect on film yield, but increases the gloss of pigmented UV curable coatings. Each sensitizer is used, as described hereinbefore, in amounts of between about 0.1% and about 2% by weight.
It has been found that adhesion of the cured coating to some substrates, particularly pasteurized adhesion (Past.
Adh.), is improved by using dimethylaminoethyl acrylate (DMAEA) in the coating composition. In the case of E~ curable coatings, the DMAEA is added to the coating composition in amounts of between about 0.5% and about 6% by weight. In the case of UV
curable coatings the DMAEA is used in amounts of between about 0.5% and about 6% by weight to replace all or a part of the tertiary amine co-sensitizer.

;

'1~78095 ': ' ' . , .

~ EXAMPLE 31 .
Resin B (Example 2~) was admixed with hydroxy-propyl acrylate, 2-chlorothloxanthone, and MDEOA or DMhEA. Each csating was coated on ~luminum panels 5 ` and W cured. The c~ated panels were subjected to &dhesion tests. Amounts of c~mponents and test re-sults are set forth in the fo~lowing tabulation.

Example Resin B CTX HPA MDEOA DMAEA

31A 49.5 1.0 44.5 O 5 31B 50.~ i.o 47.0 2 O

50 FPM W Cure Film Example Yield Adhesion Past. Adh.
; 31A ~2 100 50 31~ 89 20 o E~AMPLE 32 Res~n C (Example 30) was adm~xed with hydroxy-propyl acrylate, 2-chloroth~oxanthone, and MDEOA or . DMAEA. Each coating was coated on aluminum panels . and W cured. The coated panels were subjected to ~dhesion tests. Amounts of components and test re-sults are set forth in the follo~ ng tabulation.

.
-' Resin Ex~mple C HPA CTX MDEOA DMAEA

32A 29.2 68.2 0.5 2 0 , 32B 29.2 68.2 0.5 0 2 .
W Cure - ' 5peed, Film ' Past.
Example FP~ Yield Adh. Adh .
32A 25 ~2 lOO 85 I 5 87 lOO 70 '4, ' 32~ 25 8~ lOO lOO
' 50 87 lOO lOO
.
. .
EXAMPL~ 33 ... .
Resin B (Example 29) was admixed with hydroxy-propyl acrylate, T102 pigment, 1.0% 2-~lo~ ~io~one, and MDEOA or DMAEA. The P/B of ea,ch coating was 0.75 and the ~/B was 0.40. Each coating was coated on metal panels 'and W cured. m e coated panels were sub~ected t~ ad, hesion tests. Results are set forth in the following tabulation. '--.
, Viscosity, cp ; ExamPle Amine 222 sec~l 0228 sec 33A 4~ MDEOA 395 29,100 ; 33B 5~ DMAEA 283 564 50 EPM Adhesion t~
Example ,Yield Al CCO

33A 89 lOO O
' . ' 33B 89 lOO lOO

' '' ' ~ ' , ' . 1078095 ~ ~
. .
, ~ esin B (Example 29) was admixed with hydroxy-propyl acrylate, TiO2 pigment, 1.0% 2-~lor~
oxanthone, and MDEOA or DMAEA. m e P/B of each coating was 0.75 and the R/B was o.6. Each coat-lng was coated on metal panels and W cured. The coated panels were sub~ected to sdhesion tests.
Result~ are set forth in the ~ollowing tabu~ation.

, ~ . . , - E~ample Amine222 sec 1 0228 sec 1 34A 4% MDEOA800 86,100 34B 5% DMAEA598 14,800 . . ' ' , ' ' ..
50 FPM Adhesion to Example Yield Al CCO

''.' '''' ' " '' "
It will be noted from the preceding examples that the use of d~methylaminoethyl acrylate gives at ~8 st equl-~alent UV cure. It also provides improved adhesion, both dry ., . - _, 'and wet.
e following examples.are illustrative of preferred O coating compositions of this invention.
. , EXAMPLE 35 Using a reaction vessel equipped with an agitator, a reflux condenser, an inert gas inlet and ~ charging port, there were charged 525 g. "~ 1004 end 70 g. toluene. Heat, agitation, and sl w inert , -23- ~

' ' ' , . ' gas flow were started. Temperature was raised to reflux to remove water ( a pot temperature of 150 -160~C.). The mixture was cooled to 80-85DC. and there were added 4~ g. glacial acrylic ac1d, l e. triethyl amine and 0.1 g. hydroqu~none. Temperature was raised to 95-100C. for esteriflcati?n and the reaction continued until an acid number of 8-~3 was obtained. This was cooled t~ 80-85C. and there was added 7 g. maleic anhydride. Temperature was held a,t 8G-85C. for 1-1/2 to 2 hours unt~l alcoholic KOH and aqueous KOH acid numbers agreed (10-15). Heat source .. . .
was removed and 175 g. hydroxypropyl acrylate was added.

~e mixture was,reheated to 80-8~C. and vacuum appl~ed ,, ' for toluene removal. Removed heat and added an additional ; ~ , 182 g. hydroxypropyl acrylate. The final product had a co~ity Or 45-50,000 cp., a wt./gal. of 9.6 lb., an acld number of 10.5 a,nd a total solids of approx~mately , 97%. m is res1n was used in the formulations of Exa~ples ' 36-38 (amounts are wt. % of for~ulati~n):

. EXAMPLES 36-38 (Clear Finishes) In~redient ~ 37 3~

' Example 35 Composition 40.3 56.4 33.2 ~ydroxypropyl acrylate 56-3 40.2 37-6 Phenyl "~llosolve" ac~la~ - - 21.8 Methyldiethanolamine 1.9 1.9 2.9 Dimethylamin~ethyl acrylate - - 3.5 ~-C~lor~thioxanthone o.5 o.5 , o.5 Fluorocarbon wetting agent - ~ _ o.

_ -24_ t, .. - 1C~78095 ... .
Ingredien~ (Cont.) 36 37 38 Silicone lubricant 1.0 1.0 - Ylscosity (sec~nds ~4 - Ford Cup) 50-60 175-225 30-35 Wt./gal. (lb.) 9 o4 9 40 8.95 Examples 36 and 37 were fo~muiated as an abrasion resistant c~ating for can bottoms, which is applied by a wiping action and given a W trestment ~f 1-2 seconds with no post bake requlred.
- Examp~e 38 was formulated as a coating for flat sheet and is suitable for rollcoat application and given 1 .- second exposure to W radiation, followed by a 10 minute oven bake at 3~o-400F. m e Phenyl~lcell~olve~ ac~la~ ~ Ex~
38 impar~s impro~ed corrosion reslstance and flexibility.

There were charged 312 g. of an ep~xy diacrylate made from "~x~" 828 ~d ac~lic a~d, 430 g. ~ium dioxide, 198 g "~llosolve" ac~la~, 10 g. 2-~lor~
thioxanthone, 40 g. dimethylaminoethyl acrylate and ) 10 g. benzophenone to a suitably sized pebble mill and ground to a fineness of 7 when measured on a ~egman fineness of grind gauge. Grind time is 24-48 hours.
Ihe f~nal product was a white finish suitable for rollcoat application on flat sheet. The finish had a Ylsc~sity of 90-100 sec. ~4 Ford ~up and a height per gallon of 13.1-13.3 pounds. lt is normally applied ~ 1078095 at 10 mg./sq. in. and cured using a 1 sec. UV
exposure followed by a 6 minute bake at 325~.
After the W exposure, the film was sufficiently set to accept inks and a wet ink varnish. 1he 6 min. at 325E. bake indicated above followed inking and varnishing operations.

It will be noted that in Examples 38 and 39, Dimethylaminoethyl acry]ate was used. This compound has a tertiary amine functionality. Thus, as aforedescribed, it can replace the tertiary amine (used to speed up the cure rate) partially (Example 38) or entirely (Example 39). This compound also has reactive ethylenically unsaturated func-tionality (acrylate) and therefore acts as a reactive monomer.
Its use affords a coating composition having improved rheology, as evidenced by better flow characteristics, and the cured coating has improved adhesion to metal substrates. The ad-dition of benzophenone to the coating composition (Example 39) im~r~ve~ th~ ~loss of the pigmented finish.
Other well known adjuvants may be added to the coat-ing composi-tion such as flow control agents and waxes. Waxes, if used, are added as slurries or emulsions of petroleum (paraffin) wax, natural waxes such as montan wax, beeswax, and carnauba wax, or synthetic waxes such as polyethylene wax.
Although the present invention has been described with preferred embodiments, it is to be understood that modi-fications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A UV light curable coating composition that comprises an adduct of acrylic acid and an epoxy resin, a monofunctional ester of acrylic acid, 2-chlorothioxanthone, a tertiary amine co-sensitizer, wherein at least part of said tertiary amine is replaced with dimethylaminoethyl acrylate.

2. The coating composition of claim 1 wherein said adduct is modified with an anhydride.

3. The coating composition of claim 1 wherein said coating composition contains a pigment.

4. The coating composition of claim 1 wherein said adduct is the diacrylate of diglycidyl ether of bis-phenol A, said ester is hydroxypropyl acrylate and said tertiary amine is methyldiethanolamine.

5. The coating composition of claim 4 wherein said adduct is modified with maleic anhydride.

6. The coating composition of claim 4 wherein said coating composition contains titanium dioxide pigment.

7. The coating composition of claim 5, wherein said coating composition contains titanium dioxide pigment.