EP1003789A1

EP1003789A1 - Resin composition with improved radiation curability

Info

Publication number: EP1003789A1
Application number: EP98937870A
Authority: EP
Inventors: Aylvin Jorge Angelo Athanasius Dias; Johan Franz Gradus Antonius Jansen
Original assignee: DSM NV
Current assignee: Koninklijke DSM NV
Priority date: 1997-08-11
Filing date: 1998-07-30
Publication date: 2000-05-31
Also published as: NL1006761C2; AU8651398A; BR9811894A; CN1274364A; KR20010022660A; CA2300301A1; JP2001512751A; WO1999007746A1

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

RESIN COMPOSITION WITH IMPROVED RADIATION CURABILITY

The invention relates to a radiation- curable resin composition comprising a radiation- curable resin, a photo-excitable compound and an aliphatic amine.

Such a resin composition is known from Fouassier and Rabek, Radiation Curing in Polymer Science and Technology. Vol. Ill (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 .

The combination of a photo-excitable 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, for instance, UV 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 most 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 amines 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 measurements .

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 as 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 the 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 that is being cured.

The aliphatic amine according to the invention is preferably a compound according to Formula 1

R^R^JN ( i :

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.

Suitable choices for R¹, R² 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, 0, S and P. Two substituents to be chosen from R¹, R² 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, R² 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, Advanced Organic Chemistry. 3rd Ed. (1985) p. 238, Table 1. Examples of suitable electron-withdrawing groups are nitro groups, cyano groups, carboxy groups, oxycarbo^'yl groups, carbamoyl groups, formyl groups, sulpho groups, nitroso groups, oxo groups, alkenyl groups and alkynyl groups. Preferably, the electron- withdrawing group is a cyano group, a carboxy group or an oxycarbonyl group. The aliphatic chain can be chosen freely.

Examples of suitable aliphatic chains are alkyl, alkenyl and alkynyl chains, for instance methyl, ethyl, propyl or butyl chains. The length of the aliphatic chain, too, can 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 atom 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 polyamidoamine dendrimers, for instance described in US-A-4507466, and nitrile-terminated polypropylene - imine dendrimers, 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 group consisting of:

4 -cascade: 1, 4-diaminobutane [4] :propionitrile

(DAB(ACN)₄) ,

8-cascade: 1, 4-diaminobutane [4] : (l-azabutylidene) : - propionitrile (DAB(ACN)₈),

16-cascade : 1,4-diaminobutane [4] : (l-azabutylidene) ¹² : - propionitrile (DAB (ACN) _1S) ,

32 -cascade : 1, -diaminobutane [4] : (l-azabutylidene) ²⁸ : - propionitrile (DAB (ACN) ₃₂) and 64-cascade : 1, 4-diaminobutane [4] : (l-azabutylidene) ⁶⁰ : - 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) acrylates and polypropylene imine dendrimers; these addition products contain terminal groups that are (partially) 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 : 1, 4-diaminobutane [4] :propylamine (DAB (PA) ), 8-cascade: 1, 4-diaminobutane [4] : (l-azabutylidene)⁴:- propylamine (DAB (PA) ₈) , 16-cascade: 1, 4-diaminobutane [4] : (l-azabutylidene) ¹² : - propylamine (DAB(PA)ι₆),

32-cascade: 1, 4-diaminobutane [4] : (l-azabutylidene) ²⁸ : - propylamine (DAB(PA)₃₂) and 64-cascade : 1, 4-diaminobutane [4] : (l-azabutylidene) ⁶⁰ : - propylamine (DAB(PA)_S4).

The ester-terminated addition products can for instance be obtained by addition of a (meth) acrylate, for instance phenoxyethylacrylate, to an amino-terminated polypropylene imine dendrimer. The use of the addition products of a polypropylene imine dendrimer and a (meth) acrylate 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 can 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. In 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 , thioxanthone, α-keto-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

.0

^

/

-X (2)

R / \

Here X is one of the following groups OR⁷, NR⁷R⁸ or SR⁷. R⁴, R⁵ and R⁶ can be chosen freely, independently of one another; suitable choices are: H, alkyl groups with 1 to 20 carbon atoms, aryl groups, COOR⁹, C0NR⁹R¹⁰, CH₂COOR⁹, CH₂OR⁹, OR⁹, NR⁹R¹⁰, SR⁹, Cl and CN. R⁷, R⁸, R⁹ and R¹⁰ 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, CH₂C0Y, CH₂0Y, CH₂NYZ, CH₂SY, CH₂CH₂OY, CH₂CH₂NYZ, CH₂CH₂SY, CH₂CH(CH₃)OY, CH₂CH (CH₃) NYZ , CH₂CH (CH₃) SY, CH(CH₃)CH₂OY, CH(CH₃)CH₂NYZ, CH (CH₃) CH₂SY, (CH₂0)_nY, (CH₂NZ)_nY, (CH₂S)_nY, (CH₂CH₂0)_nY, (CH₂CH₂NZ) _nY, (CH₂CH₂S)_nY, (CH₂CH(CH₃)0)_nY, (CH₂CH(CH₃)NZ)_nY, (CH₂CH (CH₃) S) _nY,

(CH(CH₃)CH₂0)_nY, (CH(CH₃)CH₂NZ)_nY and (CH (CH₃) CH₂S) _nY, where n is an integer, for instance between 1 and 100. Y and Z 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 and aromatic or aliphatic heterocyclic groups containing 0, S, N of P atoms.

Other suitable choices are derivatives of compounds containing the structural element according to Formula (2) , for instance esters, anhydrides, urea, urethanes, thiourea and thiourethanes . Preferably, the compound with the structural element according to Formula (2) can be chosen from the group formed by acrylates (X=OR⁷, R⁴=H, R⁵=H, R⁶=H) , methacrylates (X=0R⁷, R⁴=CH₃, R⁵=H, R⁶=H) , acrylamides (X=NR⁷R⁸, R⁴=H, R⁵=H, R⁶=H) , fumarates (X=0R⁷, R⁴=H, R⁵=COOR⁹, R⁶=H) , maleates (X=OR⁷, R⁴=H, R⁵=H, R⁶= COOR⁹) , itaconates (X=OR⁷, R⁴=CH₂COOR⁹, R⁵=H, R^S=H) , citraconates (X=0R⁷, R⁴=CH₃, R⁵=H, R^e=COOR⁹) and mesaconates (X=OR⁷, R⁴=CH₃, R⁵=COOR⁹, R⁶=H) and derivatives thereof, for instance fumaramide esters, maleamide esters and fumaramides. Other suitable examples are cyclic structures, in which X is linked to R⁴, R⁵ or R⁶. Examples of such cyclic structures are maleimides, for instance N- cyclohexylmaleimide .

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, allyl amines or allyl 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 unsaturation 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 mol% 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%.

The reactive unsaturation on an electron- withdrawing group (a) can be linked to polymers or oligomers via R⁷. Examples of such polymers or oligomers are polyurethanes, 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^7, another functionality in the form of R⁴ , R⁵ or R⁶, for instance COOR⁹, CONR⁹R¹⁰, CH₂COOR⁹ or CH₂OR⁹, 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.

Besides 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, for 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.

The resin composition can also contain additives, for instance pigments, fillers and matting agents .

The 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 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 UV 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 according 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 ^(TM) (2 -hydroxy-2 -methyl- 1-phenylpropane- 1- one as active component), Irgacure 184^<TM1 (hydroxy- cyclohexyl phenylketone as active component) , Irgacure 369^(TM) (2-benzyl-2-dimethylamino-l- (morpholinophenyl) - butanone-1 as active component) , acylphosphines such as for instance Lucerine TPO^(TM) (2 , 4, 6-trimethylbenzoyl- diphenyl-phosphine-oxide) .

The 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.

The invention will be elucidated on the basis of the following examples, without being limited thereto.

Examples

Photo-DSC measurements

The polymerisation reactions were monitored by means of the Photo-DSC (Differential Scanning

Calorimetry) technique, 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.

RT-FTIR measurements

The polymerisation reactions were monitored by means of the Real Time - Fourier Transform Infra Red (RT-FTIR) technique. One of the main differences of this technique and the Photo-DSC technique is that the light dose has a much higher intensity (about 500 mW/cm²) . Therefore, 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.

Comparative Example A

20 mg (1 wt.%) of dimethylethanol amine (Me₂NEtOH) 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 Example B 20 mg (1 wt.%) of triethyl amine (Et₃N) 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.

Example I : nitrile-terminated polypropylene imine dendrimer

DAB (ACN) Λ 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 dendrimers (DSM Astramol⁰) were obtained from DSM N.V. (Heerlen, the Netherlands) . - 15 -

Examples II-III:

Nitrile-terminated polypropylene imine dendrimers

Example I was repeated with 20 mg(l wt.%) of the nitrile-terminated polypropylene imine dendrimers DAB (ACN) ₈ and DAB (ACN) ₁₆ (generations 1.5 and 2.5) . The results are presented in Table 1. The dendrimers DAB (ACN) ₄, DAB (ACN) ₈ 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 and curing rates for different amines, determined using Photo-DSC.

Example IV : phenoxyethylacrylate-terminated polypropylene imine dendrimer

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 DAB (acrylate) ₄ 11.9 mg was transferred to a DSC pan and cured in the Photo-DSC, use being made of UV light. The results are presented in Table 2.

Examples V-VIII: phenoxyethylacrylate-terminated polypropylene imine dendrimers

Example IV was repeated with 20 mg (1 wt.%) of the amino-terminated polypropylene imine dendrimers DAB(PA)₈, DAB(PA)₁₆, DAB(PA)₃₂ 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. 17

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.

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 that at an approximately constant and high conversion a curing rate can be achieved that increases with the amount of amine. - 18 -

Table 3 :

Effect of the concentration of the amine DAB (ACN) ₄ in the resin composition, determined using Photo-DSC.

* At this concentration a fraction of the amine no longer dissolves in the reaction mixture.

RT-FTIR-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 the amount of radicals formed in close proximity of each other at higher generations, the termination reaction, which is mainly a radical-radical recombination, is the main cause for the observed differences in 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.

Comparative Example C

20 mg (1 wt.%) of dimethylethanol amine (Me₂NEtOH) and 20 mg (1 wt . %) of benzophenone were dissolved in 1.96 g of ethoxylated trimethylpropane- trisacrylate (TMPTA) (M_w = 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 4.

Examples XVI - XX: nitrile-terminated polypropylene imine dendrimers

DAB (ACN) _ DAB (ACN) « , DAB (ACN) _1£_ DAB (ACN) ^and 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 (M„ = 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 /077

20 -

dendrimers were obtained from DSM N.V. (Heerlen, the Netherlands) .

Table 4 : Conversions and curing rates for different amines, determined using RT-FTIR.

From Table 4, it can 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) . /077

- 21 -

Comparative examples D. E and F and Examples XXI-XXIII: Effect of the photo-excitable compound.

20 mg (1 wt.%) of respectively dimethyl ethanol amine and the nitrile-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 (M_w = 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.

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 10 seconds of irradiation in comparison to the compositions according to the state of the art (dimethylethanol amine).

Comparative Examples G and H and Examples XXIV-XXXIII Curing of Ebercryl 80

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. The light intensity was about 250 mW/cm². The results are presented in Table 5.

23

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.

The results in Table 5 show that the compositions according to the invention, comprising aliphatic amines, have the higher curing rates and conversions. Performing the curing in air leads to reduced curing rates and conversion levels. However, in both air and 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.

Comparative Examples I and J and Examples XXXIII- XXXXIII : Extraction of extractable compounds from a cured Ebercryl 80 composition.

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 (UV-A, UV-B and UV-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 ml 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.

Table 6 : Extraction results for a cured Ebercryl 80 composition (< 0.1 = lower than detectio limit) .

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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

C L A I M S

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 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

R^XR²R³N (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 .

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 l 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) 6 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.

14. Resin composition as described an elucidated on the basis of the examples .