PHOTOINITIATOR AND CURABLE COMPOSITION COMPRISING THE SAME

Abstract

The invention provides a photoinitiator which is prepared by ring-opening reaction of epoxidized vegetable oil with one or more Norrish II photoinitiators having a carboxylic acid group, hydroxyl group, mercaptan group and/or amine group, and one or more acrylic compounds. The invention also provides a photocurable composition comprising the photoinitiator. The photoinitiator of the present invention has the advantages of low migration, non-toxicity, low volatility, thermal stability and easy dissolution in organic solvents.

Claims

1. A photoinitiator, which is prepared by a ring-opening reaction of epoxidized vegetable oil with one or more Norrish Type II photoinitiators having carboxylic acid group, hydroxyl group, thiol group and/or amino group and one or more acrylic compounds.

2. The photoinitiator according to claim 1, wherein the epoxidized vegetable oil is epoxidized soybean oil.

3. The photoinitiator according to claim 1, wherein based on 1 molar equivalent of the epoxy groups in the epoxidized vegetable oil, a total of molar equivalents of the Norrish Type II photoinitiator and the acrylic compound is 1 molar equivalent.

4. The photoinitiator according to claim 1, wherein the ratio of the molar equivalents of the Norrish Type II photoinitiator relative to the molar equivalents of the acrylic compound is from 5:1 to 1:5.

5. The photoinitiator according to claim 1, wherein the photoinitiator has a structural unit of formula (I): ##STR00043## wherein R.sub.1 is selected from COO, O, S, NR.sub.4, COR.sub.5O or OR.sub.5COO; R.sub.2 and R.sub.3 are independently selected from C.sub.1-6 alkyl, C.sub.1-6 alkoxy, hydroxyl, halogen, COOC.sub.1-6 alkyl, C.sub.6-10 aryl or NR.sub.4R.sub.4; or R.sub.2 and R.sub.3 together form S, O, CO or CC; m is 0, 1, 2, 3 or 4; n is 0, 1, 2 or 3; R.sub.4 is independently selected from H or C.sub.1-6 alkyl; and R.sub.5 is selected from C.sub.1-20 alkylene or C.sub.2-20 alkenylene unsubstituted or substituted with one or more hydroxyl, halogen, C.sub.1-6 alkoxy, or acyloxy groups, with the proviso that in case m is higher than 1, the R.sub.3 groups can be part of a ring structure and/or in case n is higher than 1, the R.sub.2 groups can be part of a ring structure.

6. A photoinitiator, which is prepared by a ring-opening reaction of epoxidized vegetable oil with one or more acrylic compounds and one or more compounds of formula (II), ##STR00044## wherein R.sub.2 and R.sub.3 are independently selected from C.sub.1-6 alkyl, C.sub.1-6 alkoxy, hydroxyl, halogen, COOC.sub.1-6 alkyl, C.sub.6-10 aryl or NR.sub.4R.sub.4; or R.sub.2 and R.sub.3 together form S, O, CO or CC; m is 0, 1, 2, 3 or 4; n is 0, 1, 2 or 3; R.sub.6 is selected from OH, SH, NR.sub.4R.sub.4, COOH, COR.sub.5OH, or OR.sub.5COOH, wherein R.sub.4 is independently selected from H or C.sub.1-6 alkyl; and R.sub.5 is selected from C.sub.1-20 alkylene or C.sub.2-20 alkenylene unsubstituted or substituted with one or more hydroxyl, halogen, C.sub.1-6 alkoxy, or acyloxy groups, with the proviso that in case m is higher than 1, the R.sub.3 groups can be part of a ring structure and/or in case n is higher than 1, the R.sub.2 groups can be part of a ring structure.

7. The photoinitiator according to claim 5, wherein m and n are 0.

8. The photoinitiator according to claim 1, wherein a polymerization inhibitor is further added to the ring-opening reaction.

9. The photoinitiator according to claim 1, wherein the one or more acrylic compounds are selected from the group consisting of methacrylic acid, acrylic acid and 2-carboxyethyl acrylate.

10. The photoinitiator according to claim 1, wherein an amine synergist is incorporated into the photoinitiator.

11. The photoinitiator according to claim 1, wherein the photoinitiator is according to formula (III): ##STR00045## wherein R.sub.A1, R.sub.B1, R.sub.A2, R.sub.B2, R.sub.A3, R.sub.B3, R.sub.A4, R.sub.B4, R.sub.A5, R.sub.B5, R.sub.A6 and R.sub.B6 are independently selected from ##STR00046## wherein R.sub.1 is selected from COO, O, S, NR.sub.4, COR.sub.5O or OR.sub.5COO; R.sub.2 and R.sub.3 are independently selected from C.sub.1-6 alkyl, C.sub.1-6 alkoxy, hydroxyl, halogen, COOC.sub.1-6 alkyl, C.sub.6-10 awl or NR.sub.4R.sub.4; or R.sub.2 and R.sub.3 together form S, O, CO or CC; m is 0, 1, 2, 3 or 4: n is 0, 1, 2 or 3; R.sub.4 is independently selected from H or C.sub.1-6 alkyl; and R.sub.5 is selected from C.sub.1-20 alkylene or C.sub.2-20 alkenylene unsubstituted or substituted with one or more hydroxyl, halogen, C.sub.1-6 alkoxy, or acyloxy groups, with the proviso that in case m is higher than 1, the R.sub.3 groups can be part of a ring structure and/or in case n is higher than 1, the R.sub.2 groups can be part of a ring structure, and with the proviso that (1) the total amount of ##STR00047## is from 4 to 6; (2) the total amount of ##STR00048## is from 1 to 5; (3) the total amount of ##STR00049## is from 1 to 5; (4) for each i, wherein i is from 1 to 6: if R.sub.Ai is ##STR00050## then the corresponding R.sub.Bi is ##STR00051## and (5) for each i, wherein i is from 1 to 6: if R.sub.Bi is ##STR00052## then the corresponding R.sub.Ai is ##STR00053##

12. A photocurable composition, comprising an ethylenically unsaturated curable compound and the photoinitiator of claim 1.

13. The photocurable composition of claim 11, wherein the photocurable composition comprises a (meth)acrylate functionalized oligomer and a (meth)acrylate functionalized monomer.

14. The photoinitiator according to claim 11, wherein: (1) the total amount of ##STR00054## is 5 or 6; (2) the total amount of ##STR00055## is 2 or 3; and (3) the total amount of ##STR00056## is 3 or 4.

15. The photoinitiator according to claim 11, wherein m and n are 0.

16. The photoinitiator according to claim 11, wherein a polymerization inhibitor is further added to the ring-opening reaction.

17. The photoinitiator according to claim 11, wherein an amine synergist is incorporated into the photoinitiator.

18. The photoinitiator according to claim 11, wherein (1) the total amount of ##STR00057## is 5 or 6; (2) the total amount of ##STR00058## is 2 or 3; (3) the total amount of ##STR00059## is 3 or 4, and wherein m and n are 0.

Description

DETAILED DESCRIPTION

[0029] The present disclosure is described with reference to the following embodiments. Aside from the following embodiments, the present disclosure may be performed according to another method without departing from the spirit of the present disclosure.

[0030] For ease of understanding of the disclosure of this specification, a plurality of terms are defined as follows. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms include, have or comprise when used in this specification, specify the presence of stated features, numbers, steps, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0031] All numerical values expressing the contents, proportions, and physical characteristics, etc. used in the specification and claims are to be construed as being modified by the term about. Herein, the term about refers to an acceptable error of a specific value determined by those skilled in the art, depending in part on how the value is measured or determined.

[0032] The present invention provides a photoinitiator, which is prepared by a ring-opening reaction of epoxidized vegetable oil with one or more Norrish Type II photoinitiators having carboxylic acid group, hydroxyl group, thiol group and/or amino group and one or more acrylic compounds.

[0033] As used herein, the epoxidized vegetable oil may be any product obtained by epoxidizing unsaturated vegetable oil, which may include, but not limited to, epoxidized soybean oil, cottonseed oil, rapeseed oil, corn oil, peanut oil, sunflower seed oil and/or safflower seed oil. In an embodiment of the present invention, the epoxidized vegetable oil is epoxidized soybean oil.

[0034] As used herein, the Norrish Type II photoinitiators are those known in the art, preferably aromatic ketones. Examples of suitable aromatic ketones include, but not limited to, benzophenone and its derivatives.

[0035] The term alkyl as used herein refers to straight chain and branched saturated hydrocarbon groups having from 1 to 20 carbon atoms or, 1 to 12, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Alkyl groups further include cycloalkyl groups. Examples of straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups include, but are not limited to, isopropyl, iso-butyl, sec-butyl, tert-butyl, neopentyl, isopentyl, and 2,2-dimethylpropyl groups. Additionally, the alkyl group may be optionally substituted.

[0036] The term alkenyl as used herein refers to straight chain and branched groups having from 1 to 20 carbon atoms or, 1 to 12, 1 to 8, 1 to 6, or 1 to 4 carbon atoms, and at least one CC bonding. Additionally, the alkenyl group may be optionally substituted.

[0037] The terms alkylene and alkenylene, as used herein refer to divalent radicals which are derived from the respective monovalent radicals by further abstraction of a hydrogen. For example, alkylene is derived from alkyl.

[0038] The term alkoxy refers to the group O-alkyl. Examples include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, cyclohexyloxy and the like.

[0039] The term acyloxy as used herein refers to a R(CO)O radical wherein R can be alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, aryl, cyclohexyl, heteroaryl or heterocycloalkyl. The acyloxy group is attached to the parent molecular structure through the oxygen functionality.

[0040] The term alkynyl refers to a straight or branched hydrocarbon chain radical group consisting solely of carbon and hydrogen atoms, containing at least one triple bond, having from two to ten carbon atoms (i.e., C.sub.2-C.sub.10 alkynyl). The alkynyl is attached to the parent molecular structure by a single bond, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, and the like.

[0041] As used herein, heteroalkyl, heteroalkenyl and heteroalkynyl include alkyl, alkenyl and alkynyl radicals, respectively, which have one or more skeletal chain atoms selected from an atom other than carbon, e.g., oxygen, nitrogen, sulfur, phosphorus or combinations thereof.

[0042] As used herein, aryl or aromatic groups are cyclic aromatic hydrocarbons that do not contain heteroatoms. Aryl groups include monocyclic, bicyclic and polycyclic ring systems. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenylenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodiments, aryl groups contain 6-14 carbons, and in others from 6 to 12 or even 6-10 carbon atoms in the ring portions of the groups. The phrase aryl groups includes groups containing fused rings, such as fused aromatic-aliphatic ring systems (e.g., indanyl, tetrahydronaphthyl, and the like). Aryl groups may be substituted or unsubstituted.

[0043] As used herein, heteroaryl or, alternatively, heteroaromatic refers to a radical of a 5-18 membered monocyclic or polycyclic (e.g., bicyclic or tricyclic) aromatic ring system (e.g., having 6, 10 or 14 (pi) electrons shared in a cyclic array) having ring carbon atoms and 1-6 ring heteroatoms provided in the aromatic ring system, wherein each heteroatom is independently selected from nitrogen, oxygen, phosphorous and sulfur (5-18 membered heteroaryl).

[0044] As used herein, heterocyclic, heterocycloalkyl or heterocarbocyclic each refer to any 3- to 18-membered non-aromatic radical monocyclic or polycyclic moiety comprising at least one heteroatom selected from nitrogen, oxygen, phosphorous and sulfur. A heterocyclic group can be a monocyclic, bicyclic, tricyclic or tetracyclic ring system, wherein the polycyclic ring systems can be a fused, bridged or spiro ring system. Heterocyclic polycyclic ring systems can include one or more heteroatoms in one or both rings. A heterocyclic group can be saturated or partially unsaturated. Partially unsaturated heterocycloalkyl groups can be termed heterocycloalkenyl if the heterocyclic contains at least one double bond, or heterocycloalkynyl if the heterocyclic contains at least one triple bond.

[0045] As used herein, the phrase substituted refers to a group in which one or more bonds to a hydrogen atom contained therein is replaced by a bond to a non-hydrogen or non-carbon atom. Examples of substituent groups include: halogens, hydroxyls, alkoxy, CN, alkenyl, carboxyls, C.sub.6-C.sub.4 aryl, heterocyclic and so on.

[0046] As used herein, the term acrylic compound refers to acrylic acid or derivatives thereof with carboxylic acid group, including but not limited to acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, itaconic acid, maleic acid and fumaric acid which may be used alone or in combination of two or more. The acrylic compound may undergo a ring-opening reaction with epoxide groups of the epoxidized vegetable oil so as to be grafted onto the epoxidized vegetable oil. Preferably, (meth)acrylic acid and/or 2-carboxyethyl acrylate are used. More preferably, acrylic acid and/or 2-carboxyethyl acrylate are used. Even more preferably, acrylic acid is used.

[0047] The symbol represents a point of attachment.

[0048] According to an embodiment of the present invention, based on 1 molar equivalent of the epoxy groups in the epoxidized vegetable oil, a total of molar equivalents of the Norrish Type II photoinitiator and the acrylic compound is 1 molar equivalent. The ratio of the molar equivalents of the Norrish Type II photoinitiator relative to the molar equivalents of the acrylic compound is preferably from 5:1 to 1:5, more preferably from 3:1 to 1:3.

[0049] According to an embodiment of the present invention, a polymerization inhibitor is further used in the ring-opening reaction. Suitable polymerization inhibitors may be selected from phenols such as hydroquinone, mono methyl ether of hydroquinone, mono-tert-butylhydroquinone, catechol, para-tert-butylcatechol, 2,6-di-tert-butyl-m-cresol, 2,6-di-tert-butyl-4-methylphenol, pyrogallol and -naphthol; quinones such as benzoquinone, 2,5-diphenyl-p-benzoquinone, methyl-p-benzoquinone and p-xyloquinone; nitro compounds or nitroso compounds such as nitrobenzene, m-dinitrobenzene, 2-methyl-2-nitrosopropane, -phenyl-tert-butyl nitrone and 5,5-dimethyl-1-pyrroline-1-oxide; amines such as tetrachlorobenzoquinone-amine, diphenylamine, diphenyl-picrylhydrazine, phenyl a-naphthylamine, pyridine and phenothiazine; and sulfides such as dithiobenzoyl sulfide and dibenzyl tetrasulfide. These polymerization inhibitors may be used alone or in a mixture of two or more.

[0050] According to an embodiment of the present invention, the photoinitiator of the present invention has a structural unit of formula (I):

##STR00011## [0051] wherein [0052] R.sub.1 is selected from COO, O, S, NR.sub.4, COR.sub.5O or OR.sub.5COO; [0053] R.sub.2 and R.sub.3 are independently selected from C.sub.1-6 alkyl, C.sub.1-6 alkoxy, hydroxyl, halogen, COOC.sub.1-6 alkyl, C.sub.6-10 aryl or NR.sub.4R.sub.4; or R.sub.2 and R.sub.3 together form S, O, CO or CC; [0054] m is 0, 1, 2, 3 or 4; [0055] n is 0, 1, 2 or 3; [0056] R.sub.4 is independently selected from H or C.sub.1-6 alkyl; and [0057] R.sub.5 is selected from C.sub.1-20 alkylene or C.sub.2-20 alkenylene unsubstituted or substituted with one or more hydroxyl, halogen, C.sub.1-6 alkoxy, or acyloxy groups. In case m is higher than 1, the R.sub.3 groups can be part of a ring structure. In case n is higher than 1, the R.sub.2 groups can be part of a ring structure. Preferably n and m are 0.

[0058] The present invention further provides a photoinitiator, which is prepared by a ring-opening reaction of epoxidized vegetable oil with one or more acrylic compounds and one or more compounds of formula (II),

##STR00012##

wherein R.sub.2, R.sub.3, R.sub.6, m and n are as defined above.

[0059] According to an embodiment of the present invention, a polymerization inhibitor, such as mono methyl ether of hydroquinone, may be added to the ring-opening reaction.

[0060] The photoinitiator described above may be prepared by the reaction of the step shown in the following reaction scheme. The epoxidized vegetable oil is exemplified by the epoxidized soybean oil with the representative chemical formula shown on the left side of the reactants. The Norrish Type II photoinitiator is exemplified by the representative chemical formula shown on the upper right side of the reactants, and acrylic acid is further is used as the reactant:

##STR00013## [0061] wherein R is the residue of the Norrish Type II photoinitiator or the acrylic acid after carrying out the ring-opening reaction with the epoxide group. In an embodiment of the present invention, the product epoxidized soybean oil photoinitiator of the above reaction scheme is prepared by the following steps: To a reaction vessel, 1 molar equivalent of epoxidized soybean oil, and a total of 6 molar equivalents of photoinitiator (such as benzophenone acid, BPA) and acrylic acid (in a ratio that may be arbitrarily adjusted, as long as the total is 6 molar equivalents) are added, and heated to 100 C. under exclusion of light and under atmospheric pressure to react for 12 h, thereby obtaining the epoxidized soybean oil photoinitiator (ESBO-ABPA).

[0062] According to an embodiment of the present invention, in the method for preparing the photoinitiator, based on the total molar equivalents of the epoxidized vegetable oil, the total of molar equivalents of the Norrish type II photoinitiator and the acrylic acid is about the total molar equivalents of epoxide of the epoxidized vegetable oil. In an embodiment of the present invention, epoxidized soybean oil is used as the epoxidized vegetable oil raw material, and based on 1 molar equivalent of the epoxidized soybean oil, the total of molar equivalents of the Norrish type II photoinitiator and the acrylic acid is about 6 molar equivalents. The molar amount of the Norrish Type II photoinitiator relative to total molar amount of the Norrish Type II photoinitiator and of the acrylic compound preferably varies from 5 to 95%, more preferably from 30 to 70%, even more preferably from 40 to 60%.

[0063] As the exact composition of vegetable oils is variable (depends on factors such as soil conditions, climate and plant variety), the exact composition of an epoxidized vegetable oil is also variable. As a consequence, it is difficult to give an exact structure of the photoinitiators according to the invention. An idealized structure is depicted in formula (III).

[0064] Preferably, the photoinitiator is according to formula (III):

##STR00014## [0065] wherein R.sub.A1, R.sub.B1, R.sub.A2, R.sub.B2, R.sub.A3, R.sub.B3, R.sub.A4, R.sub.B4, R.sub.A5, R.sub.B5, R.sub.A6 and R.sub.B6 are independently selected from

##STR00015## [0066] with the proviso that [0067] (1) The total amount of

##STR00016##

is from 4 to 6, preferably 5 or 6, more preferably 6; [0068] (2) The total amount of

##STR00017##

is from 1 to 5, preferably 2 or 3; [0069] (3) The total amount of

##STR00018##

is from 1 to 5, preferably 2, 3 or 4, more preferably, 3 or 4; [0070] (4) For each i, wherein i is from 1 to 6: if R.sub.Ai is

##STR00019##

then the corresponding R.sub.Bi is

##STR00020##

and [0071] (5) For each i, wherein i is from 1 to 6: if R.sub.Bi is

##STR00021##

then the corresponding R.sub.Ai is

##STR00022##

Accordingly, in this preferred embodiment of the invention, in case R.sub.A1, R.sub.A2, R.sub.A3, R.sub.A4, R.sub.A5, or R.sub.A6, respectively, is

##STR00023##

then R.sub.B1, R.sub.B2, R.sub.B3, R.sub.B4, R.sub.B5, or R.sub.B6, respectively is

##STR00024##

and in case R.sub.B1, R.sub.B2, R.sub.B3, R.sub.B4, R.sub.B5, or R.sub.B6, respectively, is

##STR00025##

then R.sub.A1, R.sub.A2, R.sub.A3, R.sub.A4, R.sub.A5, or R.sub.A6, respectively is

##STR00026##

[0072] Undergo photopolymerization under short-wavelength light (200 nm to 400 nm), the photoinitiator of the present invention based on the epoxidized vegetable oil (e.g., ESBO-BPA) may cause UV curable resins (e.g. ethylenically unsaturated curable compounds) commonly used in industry to form cured coatings. These coatings may be subsequently applied in industry: for example, as optical fiber coatings, inks, varnishes or floor coatings, etc. In low-migration testing using 500 MHz Nuclear Magnetic Resonance (NMR), the inventors of the present invention surprisingly found that when the polymer photoinitiator (e.g., ESBO-BPA) of the present invention is used to cause photopolymerization of resin monomers, the polymer photoinitiator of the present invention has excellent low migration and high conversion efficiency. Due to the excellent low migration, the present invention can effectively reduce the possibility of harm to human health caused by the photoinitiator in the coating in industrial applications especially in indirect food contact applications.

[0073] The present invention further provides a photoinitiator according to formula (III):

##STR00027##

wherein R.sub.A1, R.sub.B1, R.sub.A2, R.sub.B2, R.sub.A3, R.sub.B3, R.sub.A4, R.sub.B4, R.sub.A5, R.sub.B5, R.sub.A6 and R.sub.B6 are independently selected from

##STR00028## [0074] with the proviso that [0075] (1) The total amount of

##STR00029##

is from 4 to 6, preferably 5 or 6, more preferably 6; [0076] (2) The total amount of

##STR00030##

is from 1 to 5, preferably 2 or 3; [0077] (3) The total amount of

##STR00031##

is from 1 to 5, preferably 2, 3 or 4, more preferably 3 or 4; [0078] (4) For each i, wherein i is from 1 to 6: if R.sub.Ai is

##STR00032##

then the corresponding R.sub.Bi is

##STR00033##

and [0079] (5) For each i, wherein i is from 1 to 6: if R.sub.Bi is

##STR00034##

then the corresponding R.sub.Ai is

##STR00035##

[0080] Accordingly, in case R.sub.A1, R.sub.A2, R.sub.A3, R.sub.A4, R.sub.A5, or R.sub.A6, respectively, is

##STR00036##

then R.sub.B1, R.sub.B2, R.sub.B3, R.sub.B4, R.sub.B5, or R.sub.B6, respectively is

##STR00037##

and in case R.sub.B1, R.sub.B2, R.sub.B3, R.sub.B4, R.sub.B5, or R.sub.B6, respectively, is

##STR00038##

then R.sub.A1, R.sub.A2, R.sub.A3, R.sub.A4, R.sub.A5, or R.sub.A6, respectively is

##STR00039##

[0081] The present invention further provides a photocurable composition, including an ethylenically unsaturated curable compound and a photoinitiator as described above.

[0082] As used herein, the term ethylenically unsaturated curable compound means a compound containing polymerizable carbon-carbon double bonds. The polymerizable carbon-carbon double bond is a carbon-carbon double bond that can react with another carbon-carbon double bond in the polymerization. The polymerizable carbon-carbon double bond is usually selected from the group consisting of acrylate (including cyanoacrylate), methacrylate, acrylamide, methacrylamide, styrene, maleate, fumarate, itaconate, allyl, propenyl, vinyl and combinations thereof.

[0083] According to an embodiment of the present invention, the ethylenically unsaturated curable compound may be selected from (meth)acrylate functionalized monomers, (meth)acrylate functionalized oligomers, amine modified acrylates and mixtures thereof. As used herein, the term (meth)acrylate functionalized monomers means monomers containing a (meth)acrylate group, specifically an acrylate group. The term (meth)acrylate functionalized oligomers means oligomers containing a (meth)acrylate group, specifically an acrylate group. The term (meth)acrylate group includes an acrylate group (OCOCHCH.sub.2) and a methacrylate group (OCOC(CH.sub.3)CH.sub.2).

[0084] Preferably, the photocurable composition comprises an oligomer and a reactive diluent. The oligomer is preferably an UV curable oligomer preferably selected from urethane (meth)acrylates, polyether urethane (meth)acrylates, polyester urethane (meth)acrylates, epoxy (meth)acrylates polyether acrylates and polyester (meth)acrylates.

[0085] For viscosity reasons it is in general beneficial that reactive diluents are used in the photocurable composition. With reactive diluent is meant a compound being able to reduce the viscosity of the formulation while being able to free radically copolymerize. As reactive diluent various acrylic, methacrylic or vinyl functional monomers can be used. Suitable examples are for instance diacrylates or dimethacrylates of diols or of polyetherdiols, such as propoxylated neopentyl glycol diacrylate, 1,6- hexanediol diacrylate, dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), diethylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, neopentylglycol diacrylate, 1,4-butanediol diacrylate (e.g, SR213), alkoxylated aliphatic diacrylate (e.g. SR9209A), alkoxylated hexanediol diacrylate (e.g, SR561, SR562, SR563, SR564 from Sartomer Co., Inc), polyethylene glycol (200) diacrylate (SR259), polyether glycol-200-diacrylate, PEG300-diacrylate, polypropylene glycol diacrylate, ethoxylated (3) bisphenol-A-diacrylate, BDDA butanediol diacrylate, BDDMA butane diol dimethacrylate or higher functional acrylates such as trimethylolpropane triacrylate (TMPTA), ethoxylated trimethylolpropane triacrylate, TMP3EOTA ethoxylated (3) trimethylolpropane triacrylate, TMP6EOTA ethoxylated (6) trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol(4)-propoxylated triacrylate, pentaerythritol tetraacrylate, ethoxylated or propoxylated neopentylglycol, propoxylate (4) glycerol triacrylate, tri-functional monomers, such as Laromer types from BASF or Ebecryl 2047 or Ebecryl 12 from Allnex, di-trimethylolpropane tetraacrylate, dipentaerythritol-pentaacrylate (Di-PEPA), dipentaerythritol hexaacrylate (DPHA). Examples of vinyl compounds are compounds like butanediol divinyl ether or as mono functional compound N-vinyl caprolactam. Although mono functional (meth)acrylates like for example lauryl (meth)acrylate, phenoxyethyl (meth)acrylate can be used as well, it is preferred for low migratability to employ reactive diluents with at least two free radical curable ethylenically unsaturated groups. Obviously mixtures can be used as well. The reactive diluent is preferably selected from the group consisting of mono-, di-, tri-, tetra-, penta- and hexa-(meth)acrylates with a molecular weight lower than 800 g/mol and any combination of at least two thereof. The photocurable composition of the invention may comprise from 10 to 80 wt. %, in particular from 15 to 75 wt. %, more particularly from 20 to 70 wt. % (meth)acrylate-functionalized oligomer, relative to the entire weight of the photocurable composition. The one or more reactive diluents having one or more, preferably two or more, free radical curable ethylenically unsaturated groups may be present in the photocurable composition in an amount of at least 1 wt. %, or at least 5 wt. %, or at least 10 wt. %, and in an amount of at most 85 wt. %, or at most 80 wt. %, or at most 75 wt. %, or at most 70 wt. %, relative to the entire weight of the photocurable composition.

[0086] According to an example of the present invention, the photocurable composition of the present invention may further include an amine synergist. The amine synergist is introduced into the photocurable composition of the present invention in order to synergize with the photoinitiator and/or reduce oxygen inhibition. The amine synergist is typically a tertiary amine. When used in combination with the photoinitiator, the tertiary amine provides an active hydrogen donor site for exciting the triplet of the photoinitiator, thus generating reactive alkyl-amino radicals, which can subsequently initiate polymerization. The tertiary amine can also convert non-reactive peroxo species formed by the reaction between oxygen and radicals into reactive alkyl-amino radicals, thus reducing the influence of oxygen on curing.

[0087] The reaction mechanism of benzophenone and the amine synergist to generate radicals at 200 nm to 400 nm can be shown in the following reaction scheme:

##STR00040##

[0088] Examples of suitable amine synergists include low-molecular-weight tertiary amines (i.e., having a molecular weight of less than 200 g/mol), such as triethanolamine and N-methyldiethanolamine (MDEA). Other types of amine synergists are aminobenzoates. Examples of aminobenzoates include ethyl 4-(dimethylamino)benzoate (EDB), amyl 4-(dimethylamino)benzoate, 2-ethylhexyl 4-(dimethylamino)benzoate and 2-butoxyethyl 4-(dimethylamino)benzoate (BEDB). Next to these amine synergists, also acrylated amine synergists like AgiSyn 002, AgiSyn 003 and/or AgiSyn 008 can be suitably used. Next to these amine synergists, oligomeric amine synergists like AgiSyn 701 and/or AgiSyn 703 can be employed. An example of an oligomeric dimethylaminobenzoate is Omnipol ASA. The amine synergist can also be incorporated into the photoinitiator according to the invention. Especially when using acid functional amine synergists like dimethylamino benzoic acid, they can be readily incorporated during the synthesis of the photoinitiator. So according to an embodiment of the invention the photoinitiator comprises Norrish type II group(s), acrylic compound(s) and amine synergist group(s).

[0089] According to an embodiment of the present invention, in the photocurable composition, based on 1 molar equivalent of the total amount of the ethylenically unsaturated curable compound, the photoinitiator may be in the range of about 0.01 to about 0.1 molar equivalents (for example, about 0.05 molar equivalents); and the amine synergist may be in the range of about 0.03 to about 0.3 molar equivalents (for example, about 0.15 molar equivalents).

[0090] The examples disclosed herein are intended to illustrate the embodiments of the present invention and to explain the technical features of the present invention, and are not intended to limit the scope of the present invention. Any changes or equivalents that can be easily made by those skilled in the art are intended to be within the scope of the present invention. The scope of the present invention shall be subject to the scope of the appended claims.

Comparative Experiment 1 Preparation of ESBO-BPA

[0091] 1 g (1.025 mmol) of epoxidized soybean oil and 1.392 g (6.154 mmol) of 2-benzoylbenzoic acid were added to a 100 ml single-neck round-bottom flask, and heated to 100 C. to react in the dark under atmospheric pressure for 12 h, thereby obtaining the epoxidized soybean oil photoinitiator (ESBO-BPA, which may include an exemplified component having a structure of the following chemical formula)

##STR00041##

Comparative Experiment 2 Preparation of BP Acrylate (BPHEA)

[0092] To a stirred mixture of 0.512 g hydroxyethyl acrylate, 1.0 g 2-benzoylbenzoic acid, and 0.054 g 4-dimethylaminopyridine in CH.sub.2Cl.sub.2, a solution of 0.912 g dicyclohexylcarbodiimide in CH.sub.2Cl was slowly added at 0 C., under a nitrogen atmosphere. After the addition was complete, the temperature was raised to room temperature and the reaction mixture was stirred overnight. Next the reaction mixture was filtered and washed with 1 mol/L NaHCO.sub.3 aqueous solution, saturated NaCl solution, and distilled water. After evaporation of the solvent the product was purified by silica gel column chromatography (ethyl acetate/hexane=1:15) to obtain BPHEA.

Example 1 Preparation of ESBO-ABPA

[0093] 1 g (1.025 mmol) of epoxidized soybean oil, 0.696 g (3.078 mmol) of 2-benzoylbenzoic acid, 0.222 g (3.078 mmol) of acrylic acid, and 0.002 g of mono methyl ether of hydroquinone (MEHQ) as a polymerization inhibitor were added to a 100 ml single-neck round-bottom flask, and heated to 100 C. to react in the dark under atmospheric pressure for 12 h, thereby obtaining the epoxidized soybean oil-acrylate photoinitiator (ESBO-ABPA, which may include an exemplified component having a structure of the following chemical formula)

##STR00042##

[0094] Structural identification by 500 MHz Nuclear Magnetic Resonance (NMR) showed that the epoxidized soybean oil photoinitiator (ESBO-BPA) and the epoxidized soybean oil-acrylate photoinitiator (ESBO-ABPA) had been successfully prepared.

[0095] The glass transition temperatures (Tg) of the polymer photoinitiators were measured by differential scanning calorimetry (DSC). Upon measurement, the glass transition temperatures of the epoxidized soybean oil photoinitiator (ESBO-BPA) and the epoxidized soybean oil-acrylate photoinitiator (ESBO-ABPA) were 1.84 C. and 21.46 C., respectively.

Example 2 Synthesis of Thin Film Polymer

[0096] 1 molar equivalent of each of monomers tripropylene glycol diacrylate (TPGDA), 2-hydroxyethyl acrylate (HEA) and lauryl acrylate (LA) underwent a photopolymerization reaction, under short-wavelength light (365 nm) within 5 seconds, with 0.05 molar equivalents of photoinitiator (i.e., ESBO-BPA or ESBO-ABPA described above) and 0.15 molar equivalents of N-methyldiethanolamine as the amine synergist. Then, thin film polymers of these monomers can be obtained.

Example 3 Conversion Rate Test

[0097] The monomer conversion rate was measured by using Fourier-transform infrared spectroscopy (FTIR). The conversion rate was determined as follows: tripropylene glycol diacrylate was taken as the monomer for testing, and its Fourier-transform infrared spectra before and after curing were obtained. The conversion rate could be calculated based on the ratio of carbonyl to propenyl. Upon measurement, the conversion rates of the epoxidized soybean oil photoinitiator (ESBO-BPA) and the epoxidized soybean oil-acrylate photoinitiator (ESBO-ABPA) were both 99.9%. The data shows that these photoinitiators can achieve high reactivity.

Example 4 Migration Test

[0098] The obtained resin of tripropylene glycol diacrylate was used as the resin to be tested. The cured resin film was immersed in acetonitrile (ACN) and stirred at room temperature for 4 h. After the sample was filtered, its filtrate was taken, and mesitylene was added to the liquid to serve as an internal standard. The migration can be calculated from the integral ratio of mesitylene to photoinitiator according to the data of the nuclear magnetic resonance instrument. Upon measurement, the migration rates of the epoxidized soybean oil photoinitiator (ESBO-BPA) and the epoxidized soybean oil-acrylate photoinitiator (ESBO-ABPA) were respectively 8.7% and 0.8%, and the migration rate of the traditional benzophenone (BP) and BPHEA were 87% and 19%, respectively. The results are presented in Table 1.

TABLE-US-00001 TABLE 1 Reduction factor in Migration migration upon Photoinitiator rate (%) acrylation Example 1 ESBO-ABPA 0.8 10.9 times Comp 1 ESBO-BPA 8.7 Comp 2 BPHEA 19 4.6 times Comp 3 BP 87

[0099] The experimental results demonstrate a remarkably low migration level, as low as 0.8%, that can be achieved with the epoxidized soybean oil-acrylate photoinitiator of the present invention. This finding is particularly noteworthy when considering the comparative effects of acrylation of benzophenone: Acrylation of the epoxidized soybean oil (ESBO) photoinitiator results in a migration reduction factor of nearly 11-fold, despite the already low initial migration value of the ESBO photoinitiator. In contrast, acrylation of benzophenone photoinitiator yields a migration reduction factor of 4.6-fold (or nearly 5-fold). This substantial difference in migration reduction factors (11-fold vs. 5-fold) indicates an unexpected synergistic effect arising from the combination of ESBO and acrylation for obtaining low-migration photoinitiator.