Description

PHOTOPOLYMERISABLE SYSTEMS CONTAINING RADIATION CURABLE, LOW-EXTRACTABLE AND LOW-VOLATILE COINITIATORS

[0001] This invention concerns photopolymerisable systems containing radiation curable coinitiators having low-extractability and low-volatility.

[0002] Photopolymerisable systems contain photoinitiators characterised by the presence within their molecule of a functional group that, by electromagnetic excitation, generally UV radiation, generates radicals that are able to start a polymerisation process.

[0003] Some processes involving the photochemical generation of radicals depend on the presence of coinitiators.

[0004] In the present text, with the term coinitiator we mean a molecule that, by absorption of UV radiation, does not generate itself active radicals, but cooperates with the photoinitiator in originating active radical species or acts itself as oxygen-inhibitor.

[0005] As it is known, photoinitiators, coinitiators and radicals must follow some restrictive precondition like low toxicity, low extractability, low volatility and low odour and must be highly compatible with the photopolymerisable system.

[0006] These properties are very important in coatings and printing inks for food- packaging, that are subject to particular restrictions concerning the quantity of substances that can be extracted from the packaging itself.

[0007] Contamination by this substances is not allowed by the present legislative regulations and can also modify the organoleptic characteristics of food.

[0008] Moreover, and not only in food-packaging, it is always important to minimise the migration of compounds that might give rise to other undesired effects, such as adhesion loss between coating and substrate.

[0009] The most commonly used coinitiators are alkyl-amine systems like, for example, methyldiethanolamine, or aromatic-ami ne systems like, for example, ethyl-4-dimethyl-aminobenzoate and other similar systems.

[0010] These compounds give some problems before and after polymerisation because of their bad odour, their high volatility and their high tendency to migrate, that persists after polymerisation.

[0011] We have now found that coinitiators of formula I

[0014] wherein

[0015] Ri is a linear or branched C1-C4 alkyl;

[0016] R2, R3 and R4 are, independently of one another, hydrogen or linear or branched Ci-C4alkyl;

[0017] A is linear or branched C1-C10 alkylene or cycloalkylene,

[0018] n is O or i

[0019] exhibit low-extractability and low-volatility.

[0020] Photopolymerisable systems containing reactive ethylenically unsatured oligomers and/or monomers, one coinitiator of formula I and at least one photoinitiator are therefore a fundamental object of this invention.

[0021] Photoinitiators which are suitable for the realisation of this invention are photoinitiators reacting by homolytic cleavage or hydrogen transfer mechanism and are benzophenones, ketosulphones, thioxanthones, 1 ,2- diketones, anthraquinones, fluorenones and xanthones, acetophenone derivatives (like α-hydroxyacetophenones, α-aminoacetophenones, α- hydroxycycloalkyl-phenyl-ketones, dialkoxyacetophenones, benzoin ethers, benzyl ketals, phenylglyoxylates, mono- and bis- acylphosphine oxides.

[0022] In particular, among the photoinitiators useful for this invention we cite:

[0023] within benzophenones: 2-methylbenzophenone, 3- methylbenzophenone, 4- methylbenzophenone, 2,4,6-trimethylbenzophenone, mixtures of methylbenzophenone and 2,4,6-trimethylbenzophenone, linearyl benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone,4-(4- methylphenylthio)-benzophenone, 4,4'-dimethylamino-benzophenone, 4,4'-diethylamino-benzophenone;

[0024] within thioxanthones: 2-isopropyl-thioxanthone, mixture of 2- and 4- isopropylthioxanthone, 2,4-diethyl-thioxanthone, 2-chloro-thioxanthone, 1- chloro-4-n-propyloxythioxanthone, thioxanthone;

[0025] within ketosulphones: 1-[4-(4-benzoyl-phenylsulphanyl)-phenyl]-2-methyl- 2-(toluene-4-sulphanyl)-propane-1-one;

[0026] within 1 ,2-diketones: benzyl, 1 ,2-camphoroquinone

[0027] within anthraquinones: 2-ethyl-anthraquinone;

[0028] within xanthones: xanthone;

[0029] within acetophenones: oligo-[2-hydroxy-2-methyl-1-[4-(1- methylvinyl)phenyl]-propanone], 2-hydroxy-2-methyl-1-phenyl-propanone, 2-hydroxy-1 -[4-(2-hydroxy-ethoxy)-phenyl]-2-methyl-propan-1 -one, 2- dimethylamino-2-(4-methylbenzyl)-1-(4-morpholine-4-yl-phenyl )-butan-1- one,2-benzyl-2-dimethylamino-1 -(3,4-dimethoxy-phenyl)-butan-1 -one, 2- benzyl-2-dimethylamino-1-(4-morpholine-4-yl-phenyl)-butan-1- one, 2- methyl-1 -(4-methylsulphanyl-phenyl)-2-morpholine-4-yl-propan-1 -one, 1 - [2,3-dihydro-1 -[4-(2-hydroxy-2-methyl-1 -oxopropyl)phenyl]-1 ,3,3-trimethyl- 1 H-inden-5-yl]-2-hydroxy-2-methyl-1 -propanone, 1 -[2,3-dihydro-3-[4-(2- hydroxy-2-methyl-1-oxopropyl)phenyl]-1 ,1 ,3-tri methyl- 1 H-inden-5-yl]-2- hydroxy-2-methyl-1 -propanone, 4,3'-bis(α-hydroxy-isobutiryl)-

diphenylmethane, 4,4'-bis(α-hydroxy-isobutiryl)-diphenylmethane, 4,4'- bis(α-hydroxy-isobutiryl)-diphenylether, benzyl dimethyl ketal;

[0030] within phenylglyoxylates: methylphenylglyoxylate , ethyl ester of the 2-(2- oxo-2-phenyl-acetoxy-ethoxyethyl) oxyphenylacetic acid, methyl ester of [4-(4-methoxyoxallyl-phenoxy)-phenyl]-oxo-acetic acid;

[0031] within monoacylphosphine oxides and bisacylphosphine oxides: (2,4,6- trimethylbenzoyl)-diphenyl-phosphine oxide, ethyl ester of phenyl-(2,4,6- trimethylbenzoyl)-phosphinic acid, bis (2,6-dimethoxybenzoyl)-(2,4,4- trimethyl-pent-1 -yl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenyl- phosphine oxide, bis(2,4,6-trimethylbenzoyl)-(2,4- dipentoxyphenyl)phosphine oxide.

[0032] The photopolymerisable systems of the present invention are in particular suitable for the preparation of coatings for food-packaging.

[0033] Due to their high reactivity, the preferred coinitiators of the invention are coinitiators of formula I wherein Ri is methyl or ethyl, A is a linear Ci-Cs, more preferably CH2 or CH2CH2, and n is 0.

[0034] According to advantageous embodiments of the invention the photopolymerisable systems comprise at least a coinitiator of formula I in which: A is CH2CH2, Ri is methyl and R2, R3 and R4 are hydrogen; or A is CH2CH2, Ri is methyl, R2 and R3 are hydrogen and R4 is methyl; or

[0035] A is CH2, Ri is methyl, and R2, R3 and R4 are hydrogen; or A is CH2, Ri is methyl, R2 and R3 are methyl and R4 is hydrogen.

[0036] The coinitiators of formula I can be prepared by methods which are well known by the man skilled in the art.

[0037] In particular coinitiators of formula I can be prepared by reaction of 4- dimethylamino benzoyl chloride with the corresponding linear or branched, unsaturated alcohols, such as vinyl alcohol, 3-methyl-3-buten-1-ol, 3- buten-1-ol, 9-decen-1-ol, ethyleneglycol monovinyl ether, 1 ,4-butanediol monovinylether.

[0038] The esterification reaction can be carried out also from sodium 4- dimethylamino benzoic acid and the corresponding alkyl chloride.

[0039] It is a further object of the present invention a process for preparing coatings for metal, wood, paper and plastic surfaces characterised by:

[0040] a) applying a photopolymerisable system containing reactive ethylenically unsatured monomers or/and oligomers, at least one coinitiator of formula I and at least one photoinitiator of the benzophenone, ketosulphone, thioxantone, 1 ,2-diketone, anthraquinone, fluorenone, xanthone, acetophenone, phenylglyoxylate, monoacylphosphine oxide or bisacylphosphine oxide type, in such a quantity to obtain, after polymerisation, a coating having a thickness between 0.5 and 100 microns; b) photopolymerising with UV-visible light.

[0041] The term "photopolymerisation" is used in its broad sense and includes the polymerisation or cross-linking of polymeric material, for example of

prepolymers, the homopolymerisation and copolymerisation of monomers and the combination of these reactions.

[0042] The monomers that can be used in the above described system include, for example: acrylonitrile, acrylamide and its derivatives, vinyl ethers, N- vinylpirrolidone, mono and polyfunctional allyl ethers like for example trimethylolpropandiallyl ether, styrenes and a-methyl styrene, esters of acrylic and methacrylic acid with aliphatic alcohols, with glycols, with polyhydroxylated compounds like, for example, penthaeritritol, trimethylolpropane, esters of vinyl alcohol with aliphatic or acrylic acids, derivatives of fumaric and maleic acid.

[0043] Oligomers which are useful for this invention include, for example, polyacrylates, polyurethanes, epoxidic resins, polyethers with acrylic, maleic or fumaric functionalities.

[0044] The photopolymerisable systems of the present invention may contain other photoinitiators like, e.g., trisacylphosphine oxide, halogenomethyltriazine, ferrocene or titanocene compounds, photoinitiators containing borate or O-acyloximic group.

[0045] The photoinitiators represent from 0.01 to 20% w/w, preferably from 0.5 to 10% w/w, more preferably from 1 to 5% w/w of the photopolymerisable system of the present invention.

[0046] The photopolymerisable system may contain other ingredients, e.g. thermal stabilisers, sensitisers, photo-oxidation stabilisers like sterically hindered amines, antioxidants, oxygen-inhibitors, thermal generators of radicals, like organic and inorganic peroxides, peresters, hydroperoxides, benzopinacoles, azoderivatives such as azoisobutironytrile, metal compounds like cobalt(ll) and manganese salts, antifoaming agents, fillers, dispersants, pigments, dyes and/or matting agents, other additive of general use, dispersed solids, glass and carbon fibres, thixotropic agents.

[0047] Other ingredients that can be contained in the photopolymerisable system are non-photopolymerisable polymers, present as chemically inert substances, like e.g. nitrocellulose, polyacrylic esters, polyolefin, etc., or polymers which are crosslinkable by other systems, like peroxide or atmospheric oxygen or by acid catalysis or by thermal activation, like e.g. polyisocyanates, urea, melamine or epoxidic resins.

[0048] The coinitiators of formula I are normally used in the photopolymerisable system in a quantity between 0.01 and 20% w/w, preferably between 0.5 and 10% w/w, more preferably between 1 and 5% w/w, referring to the total weight of the system.

[0049] The coinitiators of formula I are suited both for clear and pigmented photopolymerisable systems, and are useful, for example, even for the preparation of photocurable inks.

[0050] Because of the low extractability and volatility of the coinitiators, the photopolymerisable systems of this invention are particularly useful for photopolymerisable inks used in food-packaging. [0051] Some examples of light sources that are useful for photopolymerisation of photopolymerisable systems of the invention are mercury or superactinic or excimer lamps, emitting in the UV-visible region. [0052] Within the light sources that can be used for the present invention, sun light and other artificial sources emitting electromagnetic radiation having a wavelength between 180 nm and the IR zone are included. [0053] Some examples of the preparation of coinitiators of formula I and of photopolymerisable systems of the invention are here reported to illustrate, and not to limit, the invention. [0054] Example 1

[0055] Preparation of but-3-enyl 4-(dimethylamino) benzoate (Coinitiator Ia).

To a well stirred suspension of 1.5 g (0.0082 mole) of 4- (dimethylamino)benzoyl chloride in 20 ml of dichloromethane, at room temperature, 0.64 g (0.0088 mole) of 3-buten-1-ol and 0.95 g (0.0094 mole) of triethylamine were added. After 60 min stirring at room temperature the mixture was poured into water (50 ml) and the organic phase was washed with water (2x50 ml). After drying (Na2SO-i), the solvent was removed under vacuum and the oily product was purified with a flash cromatography (Siθ2). Gradient elution CH2CI2 was performed to give 1.5 g (84%) of a light yellow oil.

[0057] ¹ H NMR (CDCI ₃ ): δ (ppm): 7.9 (d, 2H); 6.65 (d, 2H); 5.9 (m, 1 H); 5.1 (m, 2H); 4.3 (dd, 2H); 3.05 (s, 6H); 2.5 (m, 2H).

[0058] Example 2.

[0059] Preparation of 3-methylbut-3-enyl 4-(dimethylamino) benzoate (Coinitiator Ib).

[0060]

To a well stirred suspension of 1.5 g (0.0082 mole) of 4- (dimethylamino)benzoyl chloride in 20 ml of dichloromethane, at room temperature, 0.76 g (0.0088 mole) of 3-methyl-3-buten-1-ol and 0.95 g (0.0094 mole) of triethylamine were added.

[0061] After 60 min stirring at room temperature the mixture was poured into water (50 ml) and the organic phase was washed with water (2x50 ml).

[0062] After drying (Na2SO-i) the solvent was removed in vacuum and the oily product was purified with a flash cromatography (Siθ2). Gradient elution CH2CI2 was performed to give 1.51 g (79%) of a white solid.

[0063] ¹ H NMR (CDCI ₃ ): δ (ppm): 7.9 (d, 2H); 6.65 (d, 2H); 4.8 (m, 2H); 4.4 (dd, 2H); 3.05 (s, 6H); 2.45 (m, 2H); 1.7 (s, 3H).

[0064] Example 3.

[0065] Preparation of 4-dimethylamino benzoic acid allyl ester (Coinitiator Ic).

[0067] A suspension of 1.5 g (0.0082 mole) of 4-(dimethylamino)benzoyl chloride in 20 ml of dichloromethane at room temperature was reacted under stirring with 0.50 g (0.0086 mole) of allyl alcohol and 0.95 g (0.0094 mole) of triethylamine. The mixture was stirred for 60 min at room temperature, poured into water (50 ml) and the organic phase was washed with water (2x50 ml). After drying (Na2SO-i) the solvent was removed to give 1.41 g (84%) of light yellow oil.

[0068] ¹ H NMR (CDCI ₃ ): δ (ppm): 7.9 (d, 2H); 6.65 (d, 2H); 6.05 (m, 1 H); 5.37 (m, 1 H); 5.22 (m, 1 H); 4.8 (m, 2H); 3.05 (s, 6H).

[0069] Example 4.

[0070] Preparation of dec-9-enyl 4-(dimethylamino) benzoate (Coinitiator Id).

[0071]

[0072] To a well stirred suspension of 3.0 g (0.016 mole) of 4-

(dimethylamino)benzoyl chloride in 50 ml of dichloromethane at room temperature 3 ml (0.017 mole) of 9-decen-1-ol and dropwise 3.79 ml (0.027 mole) of triethylamine were added under stirring. The mixture was stirred for 30 min at room temperature, poured into water (50 ml) and the organic phase was washed with water (2x50 ml). After drying (Na2SO-i) the solvent was removed and the organic phase was treated with ethyl ether; after filtration the solvent was removed by rotary evaporator to give an oil that spontaneously crystallises.

[0073] The solid was treated with 10 ml of 80%methanol, collected by suction filtration and dried in vacuum to give 3.52 g of a light yellow solid (73%).

[0074] ¹ H NMR (CDCI ₃ ): 1 (ppm): 7.9 (d, 2H); 6.65 (d, 2H); 5.8 (m, 1 H); 5.0 (m, 2H); 4.25 (dd, 2H); 3.05 (s, 6H); 2.05 (m, 2H); 1.7 (m, 2H); 1.3 (mb, 10H).

[0075] Example 5

[0076] Preparation of 3-methylbut-2-enyl 4-(dimethylamino) benzoate (Coinitiator

Ie)

[0078] To a stirred mixture of 2.76 g (0.015 mole) of 4-(dimethylamino)benzoyl chloride in 20 g of dichloromethane at room temperature 1.30 g (0.015 mole) of 3-methyl-2-buten-1-ol were added and stirred for 60 min. 0.30 g (0.0029 mole) of triethylamine dissolved in 1 g of dichloromethane were added during 10 min dropwise and stirred for 60 min. The reaction mass was then poured into water and the organic phase was washed with 10 ml of HCI 1 N, then with 20 ml of water, dried over anhydrous Na2SU4and the solvent removed in vacuum. The organic product was purified with a flash cromatography (Siθ2, gradient elution = petroleum ether : ethyl acetate 6:4) to give 2.30 g (65.8%) of a white solid.

[0079] ¹ H NMR (CDCI ₃ ): δ (ppm): 7.9 (d, 2H); 6.65 (d, 2H); 5.45 (t, 1 H); 4.76 (d, 2H); 3.05 (s, 6H);1.77(d,6H).

[0080] Example 6 [0081] Preparation of 2-methylbut-3-en-2-yl 4-(dimethylamino) benzoate (Coinitiator If)

To a mixture of 2.76 g (0.015 mole) of 4-(dimethylamino)benzoyl chloride in 20 g of dichloromethane at room temperature 1.32 g (0.015 mole) of 2- methyl-3-buten-2-ol were added under stirring. 0.30 g (0.0029 mole) of ) of triethylamine dissolved in 1 g of dichloromethane were added during 60 min dropwise and stirred for 60 min. The reaction mass was poured into water and the organic phase was washed with water. After drying (Na2SO-i) the solvent was removed and the organic product was purified with a flash cromatography (Siθ2, gradient elution = petroleum ether : ethyl acetate 6:4) to give 1.85 g (52.8%) of a pale yellow oil.

[0083] ¹ H NMR (CDCI ₃ ): δ (ppm): 7.9 (d, 2H); 6.65 (d, 2H); 6.24-6.15 (dd, 1 H); 5.27-5.08 (dd,2H); 3.05 (s, 6H);1.65 (s,6H).

[0084] [0085] [0086] Example 7

[0087] Preparation of 2-(vinyloxy)ethyl 4-(dimethylamino) benzoate (Coinitiator

Ig)-

A suspension of 372 mg (2.025 mmole) of 4-(dimethylamino)benzoyl chloride in 10 ml of dichloromethane at room temperature was reacted under stirring with 200 mg (2.27 mmole) of 2-(vinyloxy) ethanol and 180 mg (2.27 mmole) of pyridine. The mixture was stirred for 60 min at room temperature then was pourred into water (50 ml) and the organic phase was washed with water (2x50 ml). After drying (Na2SO-i) the solvent was removed and the organic product was purified with a flash cromatography (Siθ2) [gradient elution= dichloromethane ] to give 50 mg (10.5%) of white solid.

[0089] ¹ H NMR (CDCI ₃ ): δ (ppm): 7,9 (d, 2H); 6,65 (d, 2H); 6,52 (dd, 1 H); 4.50 (t, 2H); 4.23 (dd, 1 H); 4,05 (dd, 1 H);4.00 (t,2H); 3,05 (s, 6H).

[0090] m/z=236.1

[0091]

[0092] Application tests.

[0093] The substances used for the preparation of photopolymerisable systems evaluated in the following application tests are:

[0094] Ebecryl ® 600 (epoxy acrylate by UCB, Belgium);

[0095] Ebecryl ® 220 ( aromatic polyurethane by UCB, Belgium);

[0096] Ebecryl ® 350 (slip agent by UCB, Belgium);

[0097] TMPTA (trimethylol propane triacrylate);

[0098] TPGDA (tripropyleneglycol diacrylate);

[0099] OTA 480 g (trifunctional acrylated oligomer derived from glicerol, from UCB, Belgium).

[0100] The product Ia-If synthesised as described in the Examples 1-6 were used as coinitiators and Esacure ® 1001 (ketosulphone from Lamberti SpA) was used as photoinitiator.

[0101] A matrix for photopolymerisable systems was prepared mixing (w/w):

[0102] Ebecryl ® 600 40%

TMPTA 30%

OTA 480 ® 30%

[0103] The photopolymerisable systems to be evaluated are then prepared; their composition is reported in the following table (Table 1)

[0104]

[0105]

[0106]

[0107] Comparative

[0108] The evaluation of photocurable systems is made by determining the reactivity parameters, yellow index and white index. [0109] Reactivity [0110] The photopolymerisable system is laid with a thickness of 50 microns on a varnished cardboard using a bar-coater mounted on an electric stretch-film and thereafter irradiated at a distance of 26 cm from the light source. A

Fusion ® photopolymerisator was used, equipped with a medium pressure mercury lamp with a power of 120 W/cm. [0111] The photopolymerisation speed, measured in m/min, is the maximum possible speed that results in perfect superficial crosslinking of the system

("tack free"). [0112] The maximum speed (expressed in m/min) that results in a surface resisting to any visible damage after rubbing with abrasive paper was also measured (superficial abrasion). The greater is the maximum speed, the greater the efficiency of the system. [0113] The obtained results are reported in Table 2. [0114]

[0115] Comparative

[0116] The comparison of the photopolymerisable system X with the systems A-D shows the high activity of the products of the invention as coinitiators.

[0117] White and Yellow index

[0118] The photopolymerisable system is laid with a thickness of 50 microns on a varnished cardboard using a bar-coater mounted on an electric stretch-film and thereafter is passed to a distance of 26 cm from the light source at a speed corresponding to 70% of the tack-free speed. A Fusion® photopolymerisator was used, equipped with a medium pressure mercury lamp with a power of 120 W/cm.

[0119] White and yellow indexes were measured according to ASTM D1925-70 standard test method. A low value of yellow and a high value of white index correspond to a good stability of the colour of the formulation.

[0120] The results are reported in Table 3. [0121] Table 3. Yellow and white index [0122]

Table 3

[0123] Extractability [0124] As a non limiting example, the evaluation of the extractability of the Coinitiators Ia and Ic, in comparison with the reference coinitiator EDB (ethyl 4-dimethylaminobenzoate) is reported.

[0125] A matrix (M2) for photopolymerisable systems was prepared, mixing (w/w): [0126] Ebecryl ® 600 38.46% [0127] Ebecryl ® 350 1.10% [0128] Ebecryl ® 220 9.89% [0129] TPGDA 50.55% [0130] Two photopolymerisable systems are made of 94% w/w of matrix M2, 3% w/w of benzophenone and 3% w/w of coinitiator.

[0131] The EDB system of Table 4 contains Esacure ® EDB (EDB from Lamberti SpA) as coinitiator; the A ¹ and C systems respectively contains the Coinitiators Ia and Ic as coinitiators.

[0132] The photopolymerisable system is laid with a thickness of 6 microns on an aluminium sheet (3x3 inches) using a bar-coater mounted on an electric stretch-film and thereafter photopolymerised with a speed of 5 m/min. A Fusion® photopolymerisator was used, equipped with a medium pressure mercury lamp with a power of 160 W/cm. Photopolymerised samples are placed in glass jars containing as test liquids, 200 ml of 10% ethanol in water, or 200 ml of 3% acetic acid in water. The glass jars are closed and kept for 10 days at 4O ⁰ C. After 10 days, the liquids are decanted and put in a glass dark bottle. The liquids are then analysed by HPLC (column: C18, 15Ox 3.9 mm, 4 micron; eluent CH3CN/H3PO4 0.08M, 60/40, flux 1 ml/min; detector at 310 nm) and the quantity of the coinitiators is determined. The results are reported in Table 4.

Table 4. Extractabilty

EDB* A C

EtOH 10% 85 ppb n d _** n.d _***

AcOH 3% 45 ppb n d _** n.d _***

[0133] Comparative [0134] ** not detectable (less than 10 ppb) [0135] *** not detectable (less than 5 ppb)

[0136] It can be noted that the coinitiators of the invention were much less extracted by 10% ethanol and by 3% acetic acid than the reference coinitiator, and its extractability falls within the commonly accepted range for food packaging.

[0137]