CA2300301A1

CA2300301A1 - Resin composition with improved radiation curability

Info

Publication number: CA2300301A1
Application number: CA002300301A
Authority: CA
Inventors: Aylvin Jorge Angelo Athanasius Dias; Johan Franz Gradus Antonius Jansen
Original assignee: Individual
Current assignee: Koninklijke DSM NV
Priority date: 1997-08-11
Filing date: 1998-07-30
Publication date: 1999-02-18
Also published as: KR20010022660A; NL1006761C2; WO1999007746A1; EP1003789A1; JP2001512751A; CN1274364A; BR9811894A; AU8651398A

Abstract

The invention relates to a radiation-curable resin composition containing at least a radiation-curable resin, a photo-excitable compound and an aliphatic amine, as amine a compound being chosen that has at least one tertiary amino group, at least one substituent of the tertiary amino group being an aliphatic chain that contains at least one electron-withdrawing group. Such a resin composition can be cured at a conversion that is superior to the conversion achieved according to the state of the art. In addition, the resin composition according to the invention can be cured at an accelerated curing rate, which exceeds or at least equals the curing rate of the resin composition according to the state of the art. Preferably the amine is a branched or star-shaped dendrimer that contains at least one tertiary amino group and in which an electron-withdrawing group is linked via an alkyl chain to the nitrogen atom of the tertiary amino group. Examples of suitable dendrimers are nitrile and ester-terminated polypropylene imine dendrimers.

Description

'.The invention relates to a radiation-curable resin composition comprising a radiation-curable resin, a photo-excitable compound and an l0 aliphatic amine.
Such a resin composition is known from Fouassier and Rabek, Radiation Curing in PolSrme_r Science and '.Pechno:Loctv, Vol. IIT (1993) , Chapter 5, pp.
153-176, which describes a radiation-curable resin composition containing a radiation-curable resin, a conjugated carbonyl compound, in particular benzophenone, as photo-excitable compound and an ethanol amine:.
7:'he combination of a photo-excitable 2o compound and an amine is also called a Norrish type II
radical initiator combination. Such a Norrish type II
combination is used to accelerate curing of a resin by means of, fox- instance, W radiation. In such a Norrish type II combination the photo-excitable compound reacts with the amine, also called amine synergist, to form an amine radical. which then initiates the polymerisation reaction. In said reference ethanol amines are mentioned as the mast excellent amine synergists, it also being stated that the reaction mechanism underlying the activity of the ethanol amines is unknown. Besides the ethanol amines that are mentioned, in practice use is often made of triethylamine, which however has a, significantly poorer activity than the ethanol aminea referred to.
The state of the art resin composition has the drawback that it can be cured only with a low conversion.

Conversion in the framework of the present invention is understood to mean the fraction of the _ monomer compounds that is converted into polymer compounds upon curing after a certain time period. The conversion can be determined by means of, for instance, Photo-DSC measurements or Real Time - Fourier Transform Infra Red mea.suremEnts .
The aim of the invention is to provide a radiation-curable resin composition that can be cured with a conversion that is higher than the state of the art conversion.
This aim is achieved according to the invention in that a,s aliphatic amine is chosen a compound containing at least one tertiary amino group, at least one substituent of the tertiary amino group being an aliphatic chain containing at least one electron-withdrawing group.
As a result, the resin composition can be cured with a conversion that is superior to or at least equal to the state of the art conversion.
Surprisingly, it was also found that the resin composition according to the invention could be cured at an increased curing rate, which exceeds or at least equals the curing rate for the resin composition according to the state of the art. A resin composition that can be cured with an increased conversion in combination with an increased curing rate is highly desirable.
From EP 045 494 A is known a resin composition, especially for dental applications, that can be easily cured and which shows no bad smell, comprising an aromatic or cyclic tertiary amine consisting of one tertiary amine group, of which one of the substituents is a cyanoethyl group.

In the context of this invention curing rate is understood to be the ratio of the conversion (in %) over ithe curing time (in minutes or sec), calculated in the .first linear section of the curve representing the conversion versus the time for a resin composition i:hat is being cured.
'.the aliphatic amine according to the invention is preferably a compound according to Formula RzRaRaN (1) where Rl, RZ and R3 can each independently be chosen freely, it being understood that at least one of the substituents Rl, RZ and R3 is equal to Z.
~~uitable choices for Rl, RZ and R3 are aliphatic groups, for instance alkyl groups with for instance 1 to 100 atoms and alkenyl groups with for instance 2 to 100 atoms. Aliphatic groups are also understood to mean groups that contain one or more atoms that are not equal to carbon, for instance N, O, S and P. Two substituents to be chosen from R1, RZ and R3 can also form part of a ring structure. Examples of such a ring structure are pyrrolidine and piperidine.
It is also possible for a reactive unsaturation to be bound to the tertiary amine via R1, Rz and R3.
Z is an aliphatic chain that contains an electron-withdrawing group. The electron-withdrawing group can be chosen. freely from the group of electron-withdrawing groups, for instance as listed in March, gdvanced Organic Chemist,_rv, 3rd Ed. (1985) p. 238, Table 1. Examples of suitable electron-withdrawing groups are nitro groups, cyano groups, carboxy groups, oxycarboriyl groups, carbamoyl groups, formyl groups, WO 99/07746 PCTlNL98/00439 sulpho groups, nitroso groups, oxo groups, alkenyl groups and a:lkynyl groups. Preferably, the electron-withdrawing croup .is a cyano group, a carboxy group or an oxycarbonyl group.
'.the aliphatic chain can be chosen freely.
Examples of :3uitable aliphatic chains are alkyl, alkenyl and alkynyl chains, for instance methyl, ethyl, propyl or butyl chains. The length of the aliphatic chain, too, c:an be chosen freely ; however, the number of carbon atoms between the electron-withdrawing group and the N-atom on which the chain is substituted is preferably 1 to 20,. more preferably 1 to 10, most preferably 1 to 5. Optionally, the aliphatic chain is also substituted, for instance with (hetero)aliphatic and (hetero)aromatic groups. An example of such a substituted aliphatic chain is an isobutyl chain.
Examples of suitable amines or compounds according to Formula 1 are alkyl amines, in which an electron withdrawing group is linked via an alkyl chain to the nitrogen atam of the tertiary amino group, for instance cyanoalkyl. amines with an alkyl group of 1 to 5 carbon atoms, more preferably secondary or tertiary cyanoalkyl amines, for instance tris-(2-cyanoethyl)amine.
The amine is preferably a branched, highly branched or star-shaped dendrimer which contains at least one tertiary amino group and in which an electron-withdrawing group is linked to the nitrogen atom of the tertiary amino group via an alkyl chain.
Examples of suitable dendrimers are ester-terminated polyamidoamin.e dendrimers, for instance described in US-A-4507466, and nitrile-terminated polypropylene -imine dendrim.ers, for instance described in WO-A-93 14147 and WO-A-95 02008, or derivatives thereof, for instance esters, at least a portion of the terminal groups of the derivatives being an electron-withdrawing group.
Good results were achieved with a nitrile-terminated polypropylene imine dendrimer chosen from the grou;~ consisting of 4-cascade:l,4-diaminobutane[4]:propionitrile ( DAB ( ACN ) 4 ) , 8-cascade:l,4-diaminobutane[4]:(1-azabutylidene)'.
propionitrile (DAB (.ACN) e) , 16-cascade:l,~4-diaminobutane[4]:(1-azabutylidene)12.
propionitrile (DAB(ACN)16), 32-cascade:l,~4-diaminobutane[4] : (1-azabutylidene)ae.
propionitrile (DAB(ACN)32) and 64-cascade:l,~4-diaminobutane[4]:(1-azabutylidene)so, propionitrile (DAB(ACN)64) (for the nomenclature of dendrimers, see . Newkome, J. Polymer Science, Part A .
Polymer Chemistry, 31 (1993), pp. 641-651).
Good results were also achieved with ester-terminated polypropylene imine dendrimers chosen from the group consisting of the addition products of (meth)acrylat~es and polypropylene imine dendrimers;
these addition products contain terminal groups that are (partiall;y) modified with an oxycarbonyl group, for instance with a methyl acrylate or ethyl acrylate group. The ester-terminated polypropylene imine dendrimers are chosen, for instance, from the group of the addition :products of phenoxyethylacrylate and, respectively, the amino-terminated polypropylene amine dendrimers:
4-cascade:l,4-diaminobutane[4]:propylamine (DAB(PA)4), 8-cascade:l,4-diaminobutane[4]:(1-azabutylidene)4.
propylamine (:DAB ( PA) 8 ) , 16-cascade:l,4-diaminobutane[4]:(1-azabutylidene)12.
propylamine (DAB(PA)ls), 32-cascade:l,4-diaminobutane[4]:(1-azabutylidene)ae.
propylamine ( DAB ( PA) 3a ) and 64-cascade:l,4-diaminobutane[4]:(1-azabutylidene)s°.
propylamine (:DAB (PA) s4) .
The ester-terminated addition products can for instance be obtained by addition of a (meth)acrylate, for instance phen~oxyethylacrylate, to an amino-terminated polypropylene imine dendrimer. The use of the addition products of a polypropylene imine dendrimer and a (meth)acrylat~e has the added advantage that the compatibility, for instance with regard to the solubility of the amine and the radiation-curable resin to be cured c,an simply be selected by means of the choice of the type of acrylate function.
A further advantage of polypropylene imine dendrimers and derivatives thereof that are suitable as amine according to the invention is that they contain a large amount of tertiary amino groups per weight unit of compound.
An added advantage of polypropylene imine dendrimers and derivatives thereof that are suitable as amine according to the invention is that the volatility of said dendrimers is lower than that of the state of the art amine synergists. A low volatility is highly desirable as 'this facilitates handling and processing of the resin composition, for instance for safety and environmental considerations.
I:n the framework of this invention conjugated carbonyl compound is understood to mean a compound in which the carbonyl function is conjugated with one or more°double bonds. Examples of conjugated carbonyl compounds are benzophenone, xanthone, W0~99/07746 PCT/NL98/00439 -thioxanthone, a-keta-coumarine, aromatic 1,2-diketones, maleimides, acridone, pyruvates, phenylglyoxalates or - mixtures thereof. Other suitable examples are chemical derivatives of these compounds, for instance substituted benzophenones and substituted thioxanthones as well as compounds containing more than one conjugated carbonyl compound and compounds in which two.
or more carbonyl compounds are conjugated with one another.
It is obvious that Norrish type II
combinations may comprise a combination of more than one photo-excitable compound and/or a combination of more than one amine.
The radiation-curable resin preferably contains a reactive unsaturation on an electron-withdrawing group (a), optionally in combination with a reactive unsaturation on an electron-donating group (b) or an allyl group containing compound on an electron-donating group (c) or a mixture thereof (b+c).
The reactive unsaturation on an electron-withdrawing group (a) is characterised by the structural element according to Formula 2 O

\ / \
~C = C X (2) Here X is one of the following groups OR', NR'Re or SR'. R'', RS and R6 can be chosen freely, independently of one another; suitable choices are: H, alkyl groups with 1 to 20 carbon atoms, aryl groups, COORS, CONR9Rlo, CHZCOOR9 , CHZOR9 , ORS , NR9R1° , SRS , C1 and CN . R' , Re , R9 _ g _ and Rl° can be chosen freely, independently of one another; suitable choices are: H, alkyl groups with 1 - to 20 carbon .atoms (including linear and cyclic structures), ,aryl groups, aromatic or aliphatic heterocyclic groups containing 0, S, N or P atoms, COY, CHaCOY, CHZOY, CHZNYZ, CHZSY, CHZCHZOY, CHZCH2NYZ, CHzCHZSY, CHaCH ( CH3 ) OY, CH2CH { CH3 ) NYZ , CHZCH ( CH3 ) SY, .
CH ( CH3 ) CH20Y, CH ( CH3 ) CH2NYZ , CH ( CH3 ) CH2SY, ( CH20 ) aY, (CHZNZ)aY, (CHZS)aY, (CHaCHzO)aY, (CHZCHzNZ)nY, {CHZCHZS)aY, (CH2CH (CH3) 0) a:Y, (CHaCH (CH3) NZ) aY, (CHZCH (CH3) S) aY, ( CH ( CH3 ) CH20 ) a:i' , ( CH ( CH3 ) CH2NZ ) aY arid ( CH ( CH3 ) CH2 S ) aY , where n is an integer, for instance between 1 and 100.
Y and Z can be chosen freely, independently of one another; suit<~ble choices are: H, alkyl groups with 1 to 20 carbon atoms (including linear and cyclic structures), aryl groups and aromatic or aliphatic heterocyclic groups containing O, S, N of P atoms.
Ol:her suitable choices are derivatives of compounds coni~aining the structural element according to Formula (2;1, for instance esters, anhydrides, urea, urethanes, th:iourea and thiourethanes. Preferably, the compound with the structural element according to Formula (2) c<~n be chosen from the group formed by acrylates (X=c7R', R°=H, RS=H, Rs=H) , methacrylates (X=OR', R4=CH3, RS=H, R6=H) , acrylamides (X=NR'RB, R'=H, RS=H, R6=H) , fumarates (X=OR', R4=H, RS=COORS, R6=H) , maleates (X=01~', R4=H, RS=H, R6= COORS) , itaconates (X=OR', R4=CHZCOOR9, RS=H, R6=H) , citraconates (X=OR', R4=CH3, RS=H, R6=COORS) and mesaconates (X=OR', R4=CH3, RS=COORS, R6=H) and derivatives thereof, for instance fumaramide esiters, maleamide esters and fumaramides.
Other suitable examples are cyclic structures, in which X is linked to R4, RS or R6. Examples of such cyclic _ g _ structures are maleimides, for instance N-cyclohexylmal.eimide.
The reactive unsaturation on an electron-donating group (b) is preferably chosen from the group comprising vinyl ethers, vinyl esters, vinyl amides, vinyl amines, vinyl thioethers and vinyl thioesters.
The compound comprising an allyl group on an electron-donating group (c) is preferably chosen from the group comprising allyl ethers, allyl ester, ZO allyl amines or all.yl amides.
The amount of reactive unsaturation on the electron-withdrawing group (a) of the radiation-curable resin is preferably between 25 and 100 mol%. The amount of reactive u,nsaturation on an electron-donating group (b) or a compound comprising an allyl group on an electron-donating group (c) or a mixture thereof (b+c) of the radiation-curable resin before curing takes place, is preferably between 0 and 75 mol%, depending on the amount of reactive unsaturation on an electron-withdrawing group (a) of the radiation-curable resin.
More preferably, the amount of reactive unsaturation on an electron-withdrawing group (a) of the radiation-curable resin is 100 mol%. More preferably, the amount of reactive unsaturation on an electron-withdrawing group (a) of the radiation-curable resin is 50 m.ol% and the amount of reactive unsaturation on an electron-donating group (b) or a compound comprising an allyl group on an electron-donating group (c) or a mixture hereof (b+c) of the radiation-curable resin 50 mol%.
T'he reactive unsaturation on an electron-withdrawing group (a) can be linked to polymers or oligomers via R'. Examples of such polymers or oligomers are polyureth.anes, polyesters, polyacrylates, polyethers, polyolefines, for instance polyethylene, polypropylene, polybutadiene, polystyrene, polysilicates, polycarbonates, polyvinylesters, rubbers, for instance polyisoprene, natural rubbers and polyepoxides and mixed polymers, for instance polyether urethanes, polyester urethanes, polyether carbonates and polyepoxide esters. Combinations of polymers or oligomers are other suitable examples.
If the reactive unsaturation on the electron-withdrawing group (a) has, besides R'' another functionality in the form of R4 , RS or R6, for instance COORS, CONR9Rl°, CHZCOOR9 or CHZOR9, then the reactive unsaturation can be incorporated in the polymer or oligomer chain. Examples of such polymers or oligomers are unsaturated polyesters in which fumarate, maleate, itaconate, citraconate or mesaconate functionalities have been incorporated.
Preferably the number of reactive unsaturations on an electron-withdrawing group on a polymer or oligomer is larger than 1.
The reactive unsaturation on an electron-donating group (b) or the compound comprising an allyl group on an electron-donating group (c) can be bound to the polymers or oligomers described above via ether, ester, amine or amide bonds, or, in the case of bifunctional reactive unsaturation on an electron-donating group or a bifunctional allyl compound, it can also be incorporated in a polymer or oligomer chain.
Resides the reactive unsaturations on or in a polymer or oligomer as described above, the radiation-curable resin can also contain low-molecular compounds with a reactive unsaturation. These low-molecular compounds contain a reactive unsaturation in the molecule with substituents that may be of an aromatic, aliphatic or cycloaliphatic nature.
Furthermore, these molecules can contain various . functionalities, i.e. be mono- and multifunctional.
Examples of radiation-curable resins that can be applied are based on, for instance, ethyl acrylate, ethyl methacrylate, methyl methacrylate, hexane diol diacrylate, hexane diol dimethacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate, acrylamides, for instance acrylamide, N-methyl acrylamide, N-lauryl acrylamide, maleate esters, for instance ethyl maleate, diethyl maleate, methyl maleate, maleamides, for instance N,N'-bismaleamide, N,N'-dimethyl maleamide, maleimides, for instance maleimide, N-hexyl maleimide, fumarate esters, for instance ethyl fumarate, diethyl fumarate, fumaramides, itaconic acid esters, for instance methyl itaconate, dimethyl itaconate, ethyl itaconate, itaconamides, itaconimides, citraconic acid esters, for instance methyl citraconate, diethyl citraconate, mesaconic acid ester, for instance methyl mesaconate, diethyl mesaconate, vinyl ethers, for instance butylvinyl ether, cyclohexyl ether, triethylene glycol divinyl ether and hydroxybutyl vinyl ether, allyl compounds, fo:r instance allyl alcohol, allyl ether, diallyl ether, allyl amine, diallyl amine, triallyl amine, allyl .esters, for instance acetic acid allyl ester, adipic acid diallyl ester and phthalic acid diallyl ester.
T:he resin composition can also contain additives, fo:r instance pigments, fillers and matting agents.
T:he amount of amine according to the invention that is applied in the resin composition can be chosen freely. In practice an amount between 0.1 and WO 99/0'1746 PCT/NL98/00439 15 wt.% is applied and the amount depends, inter alia, on the solubility of the amine in the resin composition. Preferably the amount of amine according to the invention is 1-10 wt.%, calculated relative to the total resin composition.
The amount of photo-excitable compound used can also be chosen freely. In practice an amount of between 0.1 and 15 wt.%, calculated relative to the total resin composition, is used. The amount of photo-excitable compound used influences the conversion and the curing rate to a lower degree than the amount of amine according to the invention.
The radiation used for curing of the resin composition can be chosen from W radiation, i.e.
radiation at a wavelength of 0.6-380 nm, and electron beam (EB) radiation. The amount of radiation used depends, inter alia, on the curing conditions, the resin composition and the specific application, and can be chosen freely by one skilled in the art.
Amines are generally used not only to serve as synergist, i.e. to initiate the reaction, but also as oxygen scavenger. Oxygen has an inhibiting effect, which can be decreased by the use of amines. Besides the amines ac~~ording to the invention that serve as synergist and,/or oxygen scavenger, other amines may also be added which serve as synergist and/or as oxygen scavenger.
Besides the Norrish type II initiator combinations as already described, the resin composition may optionally also contain Norrish type I
initiators. With these initiators radicals are generated by means of splitting-up of a molecule by the action of radiation. Examples of these initiators, which are mostly based on aromatic ketones, include:

Darocure 1173 «~ (2~-hydroxy-2-methyl-1-phenylpropane-1-one as active component), Irgacure 184 «''~ (hydroxy-cyclohexyl phenylketone as active component), Irgacure 369~~''~ (2-benzyl-2-dimethylamino-1-(morpholinophenyl)-butanone-1 as active component), acylphosphines such as for instance :Lucerine TPO «''~ (2,4,6-trimethylbenzoyl-diphenyl-phosphine-oxide).
T:he invention also relates to the cured resin composition, obtained with the resin composition according to 'the invention , as well as to objects manufactured .from the cured resin composition.
Tihe invention will be elucidated on the basis of the :following examples, without being limited thereto.
Photo-DSC measurements The polymerisation reactions were monitored by means of tlae Photo-DSC (Differential Scanning Calorimetry) i~echnique, in which the heat development during a photo polymerisation is monitored. From the exotherms thus obtained, the degrees of conversion and curing rates are calculated. Use was made of a Perkin Elmer DSC-7, equipped with a Hg-lamp.
R~;FTI~measurement ~
TIZe polymerisation reactions were monitored by means of tlae Real Time - Fourier Transform Infra Red (RT-FTIR) teclanique. One of the main differences of this technique and 'the Photo-DSC technique is that the light dose ha;s a much higher intensity (about 500 mW/cm2). Thex:efore, the time scale of curing is one of seconds instead of minutes, as is the case with Photo-DSC. Use was made of a Bruker IFSS 55 RT-FTIR equipped with an Oriel. system fitted with a 200 W Hg-lamp. All experiments were performed under nitrogen, unless otherwise stated.
Comy~arative Exam~lQ~
20 mg il wt.%) of dimethylethanol amine (MeaNEtOH) and 20 mg (1 wt. %) of benzophenone were dissolved in 1.96 g of phenoxyethyl acrylate. 11.9 mg of this solution was transferred to a DSC pan and cured in the Photo-DSC, use being made of UV light. The results are presented in Tables 1 and 2.
Comparative E~am~le H
20 mg (1 wt. %) of triethyl amine (Et3N) and mg (1 wt.%) of benzophenone were dissolved in 1.96 g of phenoxyethyl acrylate. 11.9 mg of this solution was transferred to a DSC pan and cured in the Photo-DSC, use being made of UV light. The results are presented 20 in Tables 1 and 2.
E,~,amp 1 a I
nitrile-terminated ~o,~,yp~o~vlene imine dendrimer DAB(ACN?4 20 mg (1 wt.%) of nitrile-terminated polypropylene imine dendrimer DAB(ACN)4 (DSM Astramol~, generation 0.5) and 20 mg (1 wt.%) of benzophenone were dissolved in 1.96 g of phenoxyethyl acrylate. 12.3 mg of this solution was transferred to a DSC pan and cured in the Photo-DSC, use being made of UV light. The results are presented in Table 1. The polypropylene imine dendrim,ers (DSM Astramol~) were obtained from DSM
N.V. (Heerlen, the Netherlands).

Examsles II-Ice:
Nitrile-termin~t~d nol ro~YlenP~ ;mime dendrimer~
Example I was repeated with 20 mg(1 wt.%) of the nitrile-terminated polypropylene imine dendrimers DAB(ACN)e and DAB(ACN)16 (generations 1.5 and 2.5) . The results are presented in Table 1. The dendrimers DAB(ACN)4, DAB(ACN)a and DAB(ACN)16 yield a conversion that is superior to that according to Comparative Examples A and B while the curing rate is superior or comparable to that according to Comparative Examples A and B.
Table 1 .
Conversions a:nd curing rates for different amines, determined using Photo-DSC.
Example Amine Conversion Curing rate after 20 (%/min) minutes (%) A MeaNEtOH S3 16.8 B :Et3N 18 5 . 4 I DAB(ACN)4 80 22.2 II DAB(ACN)8 70 14.2 III DAB(ACN)16 56 11.4 W(J 99/0774b PCT/NL98/00439 20 mg (1 wt.%) of amino-terminated polypropylene imine dendrimer DAB(PA)4 (DSM Astramol~, generation 1) and 20 mg (1 wt.%) of benzophenone were dissolved in 1.96 g of phenoxyethylacrylate. The clear solution was stirred for a week. Of the solution of the formed phenoxyethylacrylate-modified dendrimer DAH(acrylate)4 11.9 mg was transferred to a DSC pan and cured in the Photo-DSC, use being made of W light. The results are presented in Table 2.
E'~Sles V-VIA:
x~henoxyeth~la~~ryl ate-terminated ply ~,~ro~y~ Pip imine dendrimers Example IV was repeated with 20 mg (1 wt.%) of the amino-iterminated polypropylene imine dendrimers DAB (PA) e, DAB I; PA) 16, DAB (PA) g2 and DAB (PA) 64 (DSM
Astramol~, generations 2, 3, 4 and 5) . The results are presented in ',table 2. All modified dendrimers that were tested give a conversion that is higher than the conversion achieved according to Comparative Examples A
and B. All dendrimers also give a curing rate that is superior or comparable to that according to Comparative Examples A and B.

WO~ 99/07746 PCT/NL98/00439 Table 2 .
Conversions and curing rates for different amines, determined using Photo-DSC. DAB(acrylate)X = reaction product of DAB(PA)X and phenoxyethyl acrylate.
Example Amine ConversionCuring after 20 rate minutes (%/min) (%) A Me2NEtOfi 53 16.8 B Et3N 18 5.4 IV DAB (acrylate) 83 21.1 V DAH (acrylate) 71 19.4 VI DAB (a.crylate)62 15 . 3 is VII DAH (a.crylate)62 12 . 3 VIII DAB (a.crylat:e)62 12 .2 s4 Examples IX - XV:
Effect of the amount of amine Example I was repeated with varying amounts of amine (0.1 to 10%). The results are presented in Table 3. They show i~hat at an approximately constant and high conversion a curing rate can be achieved that increases with the amount of amine.

Table 3 .
Effect of the: concentration of the amine DAB(ACN)4 in the resin composition, determined using Photo-DSC.
Example ConcentrationConversion Curing (wt.%) after 20 rate minutes (%/min) (%) IX 0.1 79 18.1 X 0.2 79 18.3 XI 0.4 $5 22.3 XII 1 86 27.6 XIII 2 84 34.0 XIV 4 84 46.5 XV 10(*) 82 44.6 * At this concentration a fraction of the amine no longer dissolves in the reaction mixture.
RT-F'~IR-experiments From the data in Tables 1 and 2, the wrong conclusion could be drawn that the higher generations of amine terminated polypropylene imine dendrimers initiate less efficient, compared to the lower generations. However, as the end groups have identical structures, all generations should initiate with the same efficiency.
A possible explanation for this 'generation effect' is that due to t:he amount of radicals formed in close proximity of each other at higher generations, the termination reaction, which is mainly a radical-radical recombinatior.~, is the main cause for the observed differences i.n reactivity, determined using Photo-DSC
and employing a monofunctional acrylate. Therefor, a series of RT-FTIR experiments was conducted to verify this hypothesis with a multifunctional acrylate.
During curing' using RT-FTIR, network formation will occur very rapidly. This will lead to a fast onset of composition vitrification and consequently, the termination reaction will be greatly absent.
Comparat i ve Examy~~C
mg (1 wt.%) of dimethylethanol amine (MeZNEtOH) and 20 mg (1 wt. %) of benzophenone were 15 dissolved in 1.96 g of ethoxylated trimethylpropane trisacrylate (TMPTA,)(Mw = 607). A 10 micrometer thick film was prepared of this composition on a gold-coated Alumide plate, transferred to the RT-FTIR and subsequently cured. The results are presented in Table 20 4.
Examples XVI -- XX:
nitri l e-terminated p~,'~,y~r~p y ~ p"A imine dendrim r~
DAB ( ACN ) gyp, ( ACN ) g , DAB ( ACN ) ~ DAB ( ACN ) ~~
DAB(ACN)~, cured with RT-FTIR.
20 mg (1 wt.%) of a nitrile-terminated polypropylene imine dendrimer (DSM Astramol~, generation 0.5) and 20 mg (1 wt.%) of benzophenone were dissolved in 1.96 g of ~ethoxylated TMPTA (MW = 607). A 10 micrometer thick film was prepared of this composition on a gold-coated Alumide plate, transferred to an RT-FTIR and subsequently cured. The results are presented in Table 4. 'The nitrile-terminated polypropylene imine dendrimers were obtained from DSM N.V. (Heerlen, the Netherlands).
Table 4:
Conversions and curing rates for different amines, determined ue;ing RT-FTIR.
Example Amine Conversion Curing rate after 20 (%/sec) seconds (%) C MeZNEtOH 8 0 2 8 XVI DAE(ACN)4 89 38 XVII DAE(ACN)8 90 36 XVIII DAB(ACN)16 89 35 XIX DAIS (ACN) 89 38 g2 XX DAF3 ( ACN 8 9 3~
) 64 From Table 4, it ca.n be concluded that in the compositions all dendrimers initiate the photopolymerisation with the same efficiency, a finding that corroborates the proposed hypothesis on the 'generation effect', observed with Photo-DSC.
Moreover, after 20 seconds of irradiation, the compositions also all reach the same levels of conversion. The curing rate as well as the levels of conversion are higher for all compositions comprising the dendrimers as compared to compositions according to the state of the art (dimethylethanol amine).

W~ 99/07746 PCT/NL98/00439 ~ombarative examtiles D E and F and ExamnlP~ xxT XXI r Effect of the shoto-excirarlP com~oy 20 mg (1 wt.%) of respectively dimethyl ethanol amine and the nitrite-terminated polypropylene imine dendrimer DAB(ACN)4(DSM Astramol~, generation 0.5) and 20 mg (1 wt.%) of respectively benzophenone, isopropylthioxanthone and trismaleimide, were dissolved in 1.96 g of ethoxylated TMPTA (Mw = 607). A 10 micrometer thick film was prepared of this composition on a gold-coated Alumide plate, transferred to an RT-FTIR and subsequently cured. The results are presented in Table 5.
Table 5:
Effect of different photo-excitable compounds, determined using RT-FTIR.
Example Photo-excitable Amine Curing Conversion compound rate after 10 (%/sec)seconds (%) D benzophenone MeZNEtOH 28 74 XXI benzophenone DAB(ACN)4 38 83 E isopropylthioxan- Me2NEtOH 62 89 thone XXII isopropylt.hioxan-DAB(ACN)4 201 96 thone F trismaleimide Me2NEtOH 31 86 XXIII trismaleimide DAB(ACN)4 135 91 For all photo-excitable compounds, it is demonstrated in Table 5 that the compositions according to the - invention show the highest curing rate and the highest conversion after l0 seconds of irradiation in comparison to the compositions according to the state of the art(di.methylethanol amine).
Comna__rative Examples G and ~ and Examgles XXIV-XXX rr Curing of Eber~l ~
Comparative Example C and Examples XVI-XX were repeated for Ebercryl 80, a commercially available tetra-functional polyester acrylate resin, obtainable from UCB, Belgium, with the following changes . the RF-FTIR
equipment was equipped with a Mecam-system, equiped with a Hg-halide lamp (400 W) and the formulation used was 96 weight% Ebercryl 80, 2 weigth% benzophenone and 2 weight% amino-terminated polypropylene imine dendrimer. z'he light intensity was about 250 mW/cm2.
The results a.re presented in Table 5.

Table 5 . Conversion and cure rate of Ebercryl 80, initiated by 2 weight% benzophenone and 2 weight% of amino-terminated polypropylene imine dendrimer under both nitrogen. and air at 30 °C.
Example Amine Atmosphere Curing Conversion rate after to (%/sec) seconds (%) G Me2NEtOH N2 127 84 H MeZNEtOH air 90 80 XXI V DAF3 ( ACN NZ 16 6 9 0 ) 9, XXV DAH(ACN)~, air 111 87 XXVI DA~3 (ACN) N2 170 90 ~

XXVI I DAF3 (ACN) air 12 0 8 8 ~, XXV I DAH ( ACN NZ 171 8 9 I I ) 16 XXIX DAH.(ACN)16air 114 86 XXX DAH ( ACN N2 15 7 8 8 ) 3 Z

XXXI. DAH (ACN) air 111 86 XXX I DAH~ ( ACN NZ 15 5 8 9 I ) 6 4 XXXIIT DAH~ (ACN) air 109 87 The results in Table 5 show that the compositions according to the invention, comprising aliphatic amines, have the higher curing rates and conversions.
Performing th.e curing in air leads to reduced curing rates and conversion levels. However, in both air and WCt 99/07746 PCT/NL98/00439 N2, the curing rates and conversions of the compositions according to the invention are significantly higher in comparison with the compositions comprising the conventional amine synergists.
10 A set of films were made, consisting of 96 weight%
Ebercryl 80, 2 weigth% benzophenone and 2 weight%
amino-terminated polypropylene imine dendrimer.
The films were cured with a Fusion F600 D-lamp (Fusion Systems Inc. ) with a 1 J/cm2 total dose (W-A, W-B and W-C). After curing, the 200 micrometer thick films were left at ambient conditions for 24 hours, after which a constant weight is obtained. Next, a 3 by 4 cm piece was taken out, weighted and immersed into 100 m1 acetone for 24 hours. Next, the film was removed and left to dry for another 24 hours, after which it was weighted (total amount of extractables = weight before and weight after extraction). The acetone was evaporated and the residue was analysed using NMR, giving the composition of the extractables (in weight%). The results are given in Table 6.

~
m ll1~ M M W W -i G1 l~ I~ O
~
,~C
', ~ r ~ O~ tl1l~ u7 d~ d~ d~ Lf1 .1 r1 Qj ~

3 ;

O
~ a t~ m n cw n w '~
.
CI

'e-I ~ f~ r-IM lD lD M M O O O
dl ri r-I r-Ir-I O O O O

V V V
3~

v O

c~ o o w n ~ 0 0 0 0 0~ ".a ~' I' ri ri M r-Il0 01 l0 01 O 00 00 rl ~
~

Jy ~~

O f-i Lf1al d~ ~0 M tIl M M M M di ~

U
~
3.

O

U

O

ri O

O

U

0 0 ~ r ao o m o~ o ri o~

w o c~ r co ao t~ o, ao 00 ' i a 1 ~ 0 0 0 0 0 0 o r- r r- 0 ~

r d v ' U

v a~

~ ~ ~ v ~

z ' z z z z - z o ~ ~ b ~ b ~D \O N N
x x ~ ~ m ~ ,, ~ ~ ~ ~ V U U U
~

-I - . W W FC ~ ~C
i r-I

z W ~ ~ ~ ~ A ~ A

' A A A A A

W ri 'J H H H ',X',. H
, U ~ H f ' ~ ' '~ ~ ' ~ . ''~' ' ' ''%''' 7 ~ ~ ~ , ~

~ ~

x ~

rtf W DC

H

w v ~r ~o rd a ~o U
La H
H
H
x The results show that for all compositions the total amount of extractables is higher for coatings cured in air than under nitrogen, which is consistent with the RT-FTIR experiments. However, surprisingly, the higher generations of dendrimers (> 2) give rise. to an amount of extractables in air that is comparable to the amount of extractables under nitrogen, while both amounts are very low. Because of this findings, the higher generations of the nitrile terminated polypropylene dendrimers would be extremely suitable for resin compositions in food applications.

Claims

1. Radiation-curable resin composition containing at least a radiation-curable resin, a photo-excitable compound and an aliphatic amine, characterised in that as amine is chosen a compound containing at least one tertiary amino group, at least one substituent of the tertiary amino group being an aliphatic chain containing at least one electron-withdrawing group, excluding the case where the aliphatic amine is either dimethylaminoethylmethacrylate consists of one tertiary amine group with the aliphatic chain being a cyanoethyl-group and the other two substituents of the tertiary amino group forming part of an alkyl ring with 4 or 5 carbon atoms.

2. Radiation-curable resin composition according to claim 1, characterised in that the aliphatic compound contains two tertiary amino groups.

3. Radiation-curable resin composition according to any one of claims 1-2, characterised in that the aliphatic chain contains two electron-withdrawing groups.

4. Radiation-curable resin composition according to any one of claims 1-3, characterised in that as amine a compound is chosen with Formula 1 R1R2R3N (1) where:
R1, R2 and R3 can each independently be chosen freely, it being understood that at least one of the substituents R1, R2 and R3 is equal to Z ;
Z is an aliphatic chain that contains an electron-withdrawing group, excluding the case where the compound is dimethylaminoethylmethacrylate.

5. Radiation-curable resin composition according to any one of claims 1-4, characterised in that the electron-withdrawing group is a cyano group, a carboxy group or an oxycarbonyl group.

6. Radiation-curable resin composition according to any one of claims 1-5, characterised in that the number of carbon atoms between the electron-withdrawing group and the N
atom on which the chain is substituted is preferably 1 to 20, more preferably 1 to 10, and most preferably 1 to 5.

7. Radiation-curable resin composition according to any one of claims 1-6, characterised in that the amine is an alkyl amine in which an electron-withdrawing group is linked via an alkyl chain to the nitrogen atom of a tertiary amino group.

8. Radiation-curable resin composition according to any one of claims 1-6, characterised in that the amine is a branched, strongly branched or star-shaped dendrimer that contains at least one tertiary amino group and in which an electron-withdrawing group is linked via an alkyl chain to the nitrogen atom of the tertiary amino group.

9. Radiation-curable resin composition according to claim 8, characterised in that the dendrimer is a polypropylene imine dendrimer.

10. Radiation-curable resin composition according to claim 9, characterised in that the polypropylene imine dendrimer is chosen from the group formed by DAB(ACN)4, DAB(ACN)8, DAB (ACN)16, DAB (ACN)32, DAB (ACN)64 and the addition products of amino-terminated polypropylene imine dendrimers and (meth)acrylates.

11. Radiation-curable resin composition according to any one of claims 1-10, characterised in that the amount of amine used is 1-10 wt.%, calculated relative to the total resin composition.

12. Cured resin composition, obtained with the resin composition according to any one of claims 1-11.

13. Object manufactured from the cured resin composition according to claim 12.