WO1998058980A1

WO1998058980A1 - Use of oxime-protected isocyanate groups in the uv curing of resins at low temperature, and uv-curable resins that contain such oxime-protected isocyanate groups, and the use thereof in uv-curable coating compositions

Info

Publication number: WO1998058980A1
Application number: PCT/NL1998/000354
Authority: WO
Inventors: Gerhardus Antonius Roescher; Barteld De Ruiter
Original assignee: Nederlandse Organistatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
Priority date: 1997-06-20
Filing date: 1998-06-19
Publication date: 1998-12-30
Also published as: NL1006369C2; AU8132698A

Abstract

The invention relates to the use of an oxime-protected isocyanate group with the formula (I): -R3-NH-CO-O-N=CR1R2, where at least one of the groups R1, R2 or R3 includes or carries at least one UV-absorbing group which makes the group (NH-CO-O-N=C) susceptible to cleavage under the influence of UV radiation; in or as side chains of branched polymers or in cross-linkers, for giving UV curability to these polymers or to polymeric compositions which contain such polymers and/or cross-linkers, as well as such compounds and compositions. The invention also relates to a method for curing such compounds under UV irradiation, in particular at temperatures of less than 130 °C. The invention is especially suitable for use in powder coatings for temperature-sensitive substrates.

Description

Use of oxime-protected isocyanate groups in the UN curing of resins at low temperature, and UV-curable resins that contain such oxime-protected isocyanate groups, and the use thereof in UV-curable coating compositions.

The present application concerns the use of oxime-protected isocyanate groups in the curing of resins under the influence of UV radiation, in particular at low temperature, i.e. temperatures of 130°C or less.

The application also concerns UN-curable resins that contain such oxime- protected isocyanate groups, the use of these resins in coating compositions, in particular in powder coatings, and the coating compositions so obtained.

The market for so-called powder paint compositions has grown considerably in recent years because of the many advantages that powder paints offer. Powder paints are environment-friendly, because of the absence of solvents, and economically attractive (because of relatively low investment and running costs), give a good quality of coating, and can be made up to produce a wide variety of effects, colours, gloss gradations, etc.

One disadvantage, however, is the high temperature at which the chemical curing (hardening) reactions of commercial powder paint systems take place (>150°C). This makes it impossible to apply powder paints to wooden or plastic objects, for example, as the objects are not resistant to such temperatures. There is therefore a need for coating systems which can be rapidly hardened at lower temperature (<1 10°C), i.e. on the basis of chemical curing reactions which take place rapidly at lower temperature (<110°C). The invention is intended to meet this requirement. It has now been found that oxime-protected isocyanate groups can be used to give reactivity under the influence of UV radiation, in particular with regard to hardening, to compounds to be cross-linked, such as polymers, monomers which are incorporated in such polymers, and/or cross-linkers.

In a first aspect the invention therefore relates to the use of an oxime- protected isocyanate group with formula I - R₃ - NH - CO - 0 - N = CR,R₂ (I)

where at least one of the groups R_[, R₂ or R₃ includes or carries at least one UV- absorbing group which makes the group

( NH - CO - 0 - N = C )

susceptible to cleavage under the influence of UV radiation; in or as side chains of branched polymers or in cross-linkers, for giving UV curability to these polymers or to polymeric compositions which contain such polymers and/or cross-linkers.

In the above-mentioned formula T, preferably at least the group R, or the group R₂ carries or includes at least one UV-absorbing group, or both groups R, and R₂ carry and/or include at least one UV-absorbing group.

The invention also concerns specific compounds, in particular polymers, monomers and/or cross-linkers, which include such functional groups, and also the use of such compounds in the making up of UV-curable polymeric compositions and/or (in the case of monomers) UV-cross-linkable polymers, and also methods for cross-linking these polymers under the influence of UV radiation.

The invention concerns in particular UV-curable coating compositions obtained by this (these) use(s), and also methods for curing these coating compositions under the influence of UV radiation, particularly at temperatures below 130°C, more particularly below 110°C.

Oxime-protected isocyanate groups and polymers which contain such groups are known as such. They are used in the coating industry to give thermal hardenability to coating compositions, particularly as cross-linkers in amine- or hydroxyl-functional resins. When the protected isocyanates are heated to temperatures of 150°C or more, the original isocyanate groups, which subsequently ensure the cross-linking reaction, are reformed. The hardening times depend on the nature of (he uxime and isocyanate group. In addition, the curing times are highly temperature-dependent. Reference is made to the following literature: US-

A-4 375 539; US-A-4 596 744; US-A-4 997 990; US-A-4 722 969; US-A-4 824 925 (1989, corresponding to EP-A-0 319 929); EP-A- 0 182 996, and J.S. Witzeman, Progr. Org. Coat., (1996), 27, 269 and G.B. Guise, G.N. Freeland, G.C. Smith, J. Appl. Polym. Sci., (1979), 23, 353.

It is also known how to harden polymers or cross-linkers with functional groups such as carbamate groups, formylamine groups and acyloxime groups by means of UN radiation. This involves expensive "speciality compounds", however. The oxime-protected isocyanates used according to the invention are used on a large scale in the coating industry and can be produced simply and cheaply on a large scale by standard techniques or methods analogous thereto. US patent 4,215,175 describes oxime-protected isocyanates for use as an impregnating agent for non-wovens. According to this reference, column 13, lines 50-60, only free-radical induced curing is used; UN-curing is mentioned nor suggested.

International application WO 92/07823 describes oxime-protected TMI- isocyanates, inter alia for use in coatings and adhesives (page 1, lines 19/20).

Curing of these isocyanates by UV-radiation is not descried (vide page 6, lines 33- 35); also said oxime-protected TMI-isocyanates are solely used as monomers in polymerisation reactions in which the isocyanate grouping is converted, and not as (cross-linking) groups in polymers. US patent 4,203,889 describes a polyurethane polymer protected against ultraviolet light by the presence of one or more oxime groups (vide for instance column 2, lines 15-20). The use of oxime groups as cross-linking groups is not described.

According to the invention it has now been found that oxime-protected isocyanate groups can be used for cross-linking polymers and/or curing coating compositions under the influence of UN radiation, particularly when at least one UN-radiation-absorbing group is situated near the ( ΝH - CO - O - Ν = C ) structural unit. It will be clear that in the thermally hardened compounds (polymers) accordmg to the prior art such UV-absorbing groups (if present at all) are not present for the purpose of making the ( ΝH - CO - O - Ν = C ) group susceptible to cleavage under the influence of UV radiation, i.e. for providing UV hardenability.

The UV-absorbing group will generally be a group that can absorb UV radiation, i.e. electromagnetic radiation with a wavelength of 100-500 nm, in particular 200-400 nm. Such groups will be known to persons skilled in the art and as a rule contain at least one unsaturated bond that can absorb UV radiation.

As will be clear to persons skilled in the art, it is not a requirement per se here that R,, R₂ and R₃ are or carry groups which in themselves are highly UV- absorbent. It is also possible that these groups, together with the group

( NH - CO - O - N = C ), and in particular with the (- N = C) bond thereof, form a UV-absorbing structural unit, making the group ( NH - CO - O - N = C ) susceptible to cleavage.

The groups R,, R₂ and/or R₃ can thus be or carry auxochromic groups which by interactions such as resonance can shift or strengthen the UV absorption of the chromophore (i.e. the oxime group). An example is acetophenonoxime, where the phenyl and the methyl group are less strongly UV-active in themselves, but do provide a strongly UV-absorbing group in combination with the (- C = N) - bond. Such groups or combinations thereof with the oxime-protected isocyanate group also fall within the definitions of "UV-absorbing group" or the definitions of the groups R,, R₂ and or R₃ according to the invention. It is also possible according to the invention to use a separate UV sensitizer in combination with a compound/polymer that contains oxime-protected isocyanate group(s), with the UV sensitizer making the group ( NH - CO - O - N = C ) susceptible to cleavage under the influence of UV radiation, whether or not in combination with UV-absorbing groups present in the compound itself. This embodiment, where the use of a UV-sensitizing compound is in essence equivalent to the introduction of UV-absorbing groups into the compound/polymer itself (i.e. into one of the groups R„ R₂ and/or R₃ in Formula I), will be discussed in greater detail below.

UV-absorbing groups that are preferably used are: optionally substituted unsaturated hydrocarbon residues, in particular optionally substituted alkenyl groups with 2-6 carbon atoms and optionally substituted alkynyl groups with 2-6 carbon atoms, as well as optionally substituted cycloalkenyl and alkylcycloalkenyl groups with 4-10 carbon atoms in total and preferably 5 or 6 carbon atoms in the ring; optionally substituted aromatic groups, particularly with 4-8 ring atoms in total, chosen from carbon atoms, and/or optionally one or more hetero atoms O, S and N; more particularly with 4, 5 or 6 carbon atoms, optionally 1 or 2 hetero atoms, and 5 or 6 atoms in total in the ring, such as phenyl, furfuryl, pyranyl, pyridinyl and the like; optionally substituted carbonyl groups with 1-10 carbon atoms, carboxyl groups, cyanogen groups, nitro groups, hydroxyl groups, preferably cyanogen groups, nitro groups and/or carbonyl groups with 1-6 carbon atoms.

Furthermore, the UV-absorbing group will as a rule be separated from the protected oxime group by at most three carbon, oxygen, nitrogen and/or sulphur atoms, and particularly carbon atoms; preferably by at most two such atoms, as in an ethyl(ene) group substituted in position 2 with a UV-absorbing group; more preferably by at most one further atom, as in a methyl(ene) group substituted with a UV-absorbing group. The UV-absorbing group can also be directly bound to the oxime-protected isocyanate group, as in a phenyl group. Furthermore, in alkenyl and alkynyl groups the unsaturated bond is preferably at position 2, and more preferably at position 1; and in carbonyl and ester groups the (C = O) bond is preferably at position 2, and more preferably at position 1.

Although not required, the UV-absorbing group or the unsaturated bond in the UV-absorbing group is preferably located at such a position relative to the protected isocyanate group that resonance can occur between the UV-absorbing group or bond and the bond(s) of the protected isocyanate group, as will be clear to persons skilled in the art. For this purpose it is also possible for the UV-absorbing group to be separated from the oxime-protected isocyanate group by a number of unsaturated bonds, hetero atoms and/or carbonyl groups, as in a 1,3-butadienyl group substituted in position 4 with a UV-absorbing group, where these unsaturated bonds can in themselves absorb UV radiation and/or can contribute to the UV-absorbing capacity of the UV-absorbing group and/or the group R,, R₂ and/or R₃ as a whole, optionally in combination with the oxime-protected isocyanate group as referred to above. When the UV-absorbing group is substituted, this can be by any of the substituents mentioned below, but preferably by a substituent which itself can also absorb UN radiation, such as nitro, cyano or phenyl groups. Examples of such UN-absorbing groups substituted with UV-absorbing groups are nitrophenyl, cyanophenyl, ethynylphenyl and the like. The groups R, and R₂ are preferably chosen independently from hydrogen; the above UV-absorbing groups, in particular cyano, nitro, 1 -alkynyl groups with 2-6 carbon atoms, 1 -carbonyl groups with 1-4 carbon atoms and the above-defined optionally substituted aromatic groups, notably optionally substituted phenyl groups; optionally substituted alkyl groups, with 1-10 carbon atoms, particularly

1-6 carbon atoms, more particularly optionally substituted methyl, ethyl, propyl or isopropyl; optionally substituted alkenyl groups with 2-10 carbon atoms; - optionally substituted alkynyl groups with 2-10 carbon atoms; optionally substituted cycloalkyl, alkylcycloalkyl, cycloalkenyl and alkyl cycloalkenyl groups with 3-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; halogen (fluorine, chlorine, bromine, iodine); - optionally substituted alkoxyl groups with 1-10 carbon atoms or alkoxyl- alkyl groups with 2-10 carbon atoms; hydroxyl; carboxyl; optionally substituted ester groups with 2-10 carbon atoms; amine groups with the formula -Ν T, T₂, where T, and T₂ can be hydrogen or an optionally substituted alkyl with 1-10 carbon atoms, or can together form a ring with at most 8 ring atoms; in particular with 3, 4 or 5 carbon atoms and optionally a further nitrogen atom in the ring; sulfhydryl and optionally substituted thioalkyl groups with 1-6 carbon atoms; where preferably at least one of the groups R, or R₂ includes or carries at least one

UV-absorbing group, as described above.

The groups R, or R₂, together with the carbon atom of the oxime-protected isocyanate group to which they are bound, can also form an optionally substituted ring, such as an optionally substituted cycloalkyl or cycloalkenyl ring, which can optionally be interrupted by, for example, one or more hetero atoms, carbonyl groups and/or ester groups (forming a lactone ring).

The groups R, and R₂ are more preferably chosen independently from hydrogen; the above UV-absorbing groups, in particular cyano, nitro, 1 -alkynyl groups with 2-6 carbon atoms, 1 -carbonyl groups with 1-4 carbon atoms and the above-defined optionally substituted aromatic groups, notably optionally substituted phenyl groups; optionally substituted alkyl groups, with 1-10 carbon atoms, particularly

1-4 carbon atoms, more particularly optionally substituted methyl, ethyl, propyl or isopropyl; optionally substituted alkenyl groups with 2-10 carbon atoms; optionally substituted alkynyl groups with 2-10 carbon atoms; optionally substituted cycloalkyl groups with 4-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; where preferably at least one of the R, or R₂ includes or carries at least one UV- absorbing group, as described above.

The groups R, and R₂ are most preferably chosen independently from the above UV-absorbing groups, in particular cyano, nitro, 1 -alkynyl groups with 2-6 carbon atoms, 1 -carbonyl groups with 1-4 carbon atoms and the above-defined optionally substituted aromatic groups, notably optionally substituted phenyl groups; optionally substituted alkyl groups, with 1-6 carbon atoms, more particularly optionally substituted methyl, ethyl, propyl or isopropyl; where preferably at least one of the groups R, or R₂ includes or carries at least one UV-absorbing group, as described above. The groups R, and R₂ can in particular be chosen from cyano, nitro, an optionally substituted 1 -ethynyl group, an optionally substituted phenyl group, optionally substituted methyl, ethyl or propyl groups, or methyl groups substituted with one or more UV-absorbing groups.

R, and R₂ can in particular be chosen from methyl, ethyl, phenyl, methylenephenyl (-CH2-C6H5), methylenediphenyl (-CH-(C6H5)2), nitromethyl, cyanomethyl, ethynyl, with more preferably at least one of R, and R₂ being phenyl.

In particular, R, and R₂ are both phenyl, or one of R, and R₂ is phenyl and the other methyl or ethyl. Further examples of suitable groups R, and/or R₂ are α-carbonyl groups with the general formula - (C=O) - R₄, where R₄ can be as defined above for R_t and R₂, and is preferably an optionally substituted alkyl group with 1-6 carbon atoms. These protected isocyanates can for example be produced by protecting suitable isocyanates with the mono-oximes of α,β-diketones with the formula R₄ - (C=O) - CR, = N - OH

forming protected isocyanates with the formula

R₄ - (OO) - CR, = N - O - (CO) - NH -

Oxime-protected isocyanates that are particularly suitable are ketoximes such as benzophenonoxime, acetophenonoxime and acetonaphtonoxime, for example.

When an alkyl, alkenyl or alkynyl group is referred to in the present description, this can be branched or unbranched and can optionally form a ring together with the atom to which it is bound and optionally also groups bound to this atom, such as an optionally substituted cycloalkyl or cycloalkenyl ring, which can optionally be substituted by one or more hetero atoms, carbonyl groups and/or ester groups (forming a lactone ring).

When an optionally substituted group or an optionally substituted carbon atom is referred to in the present description, this group or this atom can for example be substituted with the above-mentioned UV-absorbing groups and/or with one or more of the following substituents: halogen (fluorine, chlorine, bromine, iodine); alkyl with 1-6 carbon atoms, in particular methyl, ethyl, propyl or iso- propyl; alkenyl with 2-6 carbon atoms; alkynyl with 2-6 carbon atoms; cycloalkyl, alkyl cycloalkyl, cycloalkenyl, alkylcycloalkenyl, aryl, alkaryl, aralkyl with 3-10 carbon atoms in total, and in particular with 5 or 6 carbon atoms in the ring, such as phenyl, cyclohexyl, 1-cyclohexyl and methylcyclopentyl; hydroxy, cyano, nitro, -COOH; alkoxy with 1-6 carbon atoms; sulfhydryl and thioalkyl with 1-6 carbon atoms; - amine groups with the formula N T, T₂, where T, and T₂ can be hydrogen or an optionally substituted alkyl group with 1-6 carbon atoms, or can together form a ring with at most 8 ring atoms, in particular with 3, 4 or

5 carbon atoms and optionally a further nitrogen atom in the ring; and the like, where these substituents can optionally also in themselves be sub- stituted with such groups.

It should also be understood that where alkyl, alkenyl, alkynyl and similar groups are referred to in the description, these can optionally also contain or be interrupted by one or more S, N or O hetero atoms. All the cyclic saturated, unsaturated and aromatic carbon residues can also contain one or more N, O and S hetero atoms, or one or more carbon atoms can be replaced by such hetero atoms in such residues. Furthermore, all the carbonyl groups can contain or be interrupt- ed by a further hetero atom, such as an oxygen or a nitrogen atom, optionally with formation of an ester or amide group.

The alkyl, alkenyl and alkynyl groups, and also the cyclic saturated and unsaturated carbon residues, can also contain or be interrupted by at least one carbonyl group - (CO)-. The alkoxy, amine and thioalkyl groups can also contain a carboxyl group, optionally with formation of an ester, amide or thioester bond.

The group R₃ is preferably a binding group or bridge via which the oxime-protected isocyanate group is bound to the compound to be cross-linked, i.e. the polymer to be cross-linked, preferably a side chain or terminal of the polymer to be cross-linked; a monomeric unit for the production of such a polymer; or (the remainder of) the cross-linker, provided that the oxime-protected isocyanate bond, i.e. the group

- NH - CO - O - N = CR,R₂

can also be bound directly to the (side chain or the terminal of the) polymer, the monomer or (the remainder of) the cross-linker. In these last cases the group R₃ will be: - a polymeric side chain, or optionally a polymeric base chain; a monomer, a structural unit which can be used as a monomer, or a structural unit which includes a polymerizable group; a cross-linker, a structural unit which because of the additional presence of the oxime-protected isocyanate group can be used as a cross-linker, or a structural unit which contains a further binding group; where it will be clear that in some cases the group R₃ can be a part of a polymer, monomer or cross-linker which at the same time serves as a binding group or bridge, notably when the group R₃ is the side chain of a polymer.

When the group R₃ is a binding group or bridge, this will be bound via a further bond to the remainder of the molecule, i.e. the polymer to be cross-linked, a monomeric unit for the production of such a polymer or (the remainder of) the cross-linker.

The group R₃ can optionally be substituted with one or more UV-absorbing groups or can be interrupted by a suitable similar UV-absorbing residue, such as an optionally substituted aromatic residue as defined above, a carbonyl residue or an optionally substituted unsaturated hydrocarbon residue or bond.

The UV-absorbing group will here as a rule be separated from the oxime- protected isocyanate group by not more than three (carbon or hetero) atoms: preferably by not more than two atoms; more preferably by only one further atom; or be directly bound to the oxime-protected isocyanate group. Furthermore, although not required, the UV-absorbing group will here preferably be located at such a position relative to the protected isocyanate group that resonance can occur between the UV-absorbing group or bond and the bond(s) of the protected isocyanate group, as will be clear to persons skilled in the art. The UV-absorbing group can here also be separated from the oxime-protected isocyanate group by a number of unsaturated bonds, hetero atoms and/or carbonyl groups, as will be clear to persons skilled in the art. These unsaturated bonds, hetero atoms and/or carbonyl groups will then also form part of the R₃ group and/or make a further contribution to the UV-absorbing capacity of the UV- absorbing group and/or the R₃ group as a whole, optionally in combination with the (bonds of the) protected isocyanate group, as will be clear to persons skilled in the art.

When the group R₃ is a binding group or a side chain of a polymer, this is for example: an optionally substituted alkyl group with 1-10 carbon atoms; - an optionally substituted alkenyl group with 2-10 carbon atoms; an optionally substituted alkynyl group with 2-10 carbon atoms; an optionally substituted alkoxyl group with 1-10 carbon atoms or alkoxy- alkyl group with 2-10 carbon atoms; an optionally substituted cycloalkyl, alkylcycloalkyl, cycloalkenyl or alkylcycloalkenyl group with 3-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; an optionally substituted aryl, alkylaryl, arylalkyl or alkylarylalkyl group with 4-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; where these groups can also contain or be interrupted by one or more S, N or O hetero atoms. In cyclic saturated, unsaturated and aromatic carbon residues one or more carbon atoms can also be replaced by O, N or S hetero atoms.

The alkyl, alkenyl and alkynyl groups, and also the cyclic saturated and unsaturated carbon residues, can also contain or be interrupted by at least one carbonyl group - (CO)-. The alkoxy, alkoxyalkyl, amine and thioalkyl groups can also contain a carboxyl group, optionally with formation of an ester, amide or thioester bond.

The group R₃ is preferably an optionally substituted alkyl group with 1-10 carbon atoms; an optionally substituted alkenyl group with 2-10 carbon atoms; - an optionally substituted alkynyl group with 2-10 carbon atoms; an optionally substituted alkoxyl group with 1-10 carbon atoms or alkoxyalkyl group with 2-10 carbon atoms; an optionally substituted cycloalkyl, alkylcycloalkyl, cycloalkenyl or alkylcycloalkenyl group with 5-10 carbon atoms in total, and with prefer- ably 5 or 6 carbon atoms in the ring; an optionally substituted aryl, alkylaryl, arylalkyl or alkylarylalkyl group with 5-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; where these groups can also contain or be interrupted by one or more S, N or O hetero atoms.

The group R₃ is more preferably a branched or unbranched, optionally substituted alkyl group with 1-10 carbon atoms, particularly with 1-6 carbon atoms, more particularly with 2-4 carbon atoms, which when it contains more than

2 carbon atoms can be interrupted by an optionally substituted phenyl group, a carbonyl group - (CO) - or an ester bond - O -(CO) -.

The group R₃ can also for example be an optionally substituted methyl- phenyl (-CH2-C6H4-) or phenyhnethyl (-C6H4-CH2-) group.

The above-mentioned oxime-protected isocyanate groups can be applied in almost all types of compounds or materials which have to be provided with UV hardenability, and suitable applications will be clear to persons skilled in the art. The invention can in particular be applied by providing these compounds with the oxime-protected isocyanate groups or by producing analogues of the known compounds/materials with the oxime-protected isocyanate groups, both in a manner known per se.

Here it is of course required that the oxime-protected isocyanate groups can be incoφorated in a suitable way in the compounds, i.e. that they must be compatible with other structural units and/or functional groups present in the compound.

The production of the oxime-protected isocyanates can be carried out in a manner known per se, for example by the reaction of a ketoxime with an iso- cyanate in accordance with the following reaction diagram:

Diagram 1 : Formation of oxime-protected isocyanates

H O ,R^'

R- N= C=0 ⁺ HO- N= C R- N-C-O-N ' S _R..

R"

where R,, R₂ and/or R₃ are as defined above.

Here the use of oximes ( HO - N = CR,R₂ ) with R, and/or R₂ groups which include or carry at least one UV-absorbing group offers the advantage that the compound to be cross-linked, together with the formation of the oxime-protected isocyanate group, can be provided in a simple and suitable manner with the UV-absorbing group(s) in the right position relative to the protected isocyanate group. By this approach compounds/polymers with oxime-protected isocyanate groups that are known per se, but without UV-absorbing groups in the groups R,, R₂ and R₃, can be provided in a simple manner with UV-absorbing groups, i.e. by replacing the protected oxime group present by an oxime ( HO - N = CR,R₂ ) with R, and/or R₂ groups which include or carry a UV-absorbing group, such as by exchanging the oxime group or by first removing the oxime group present (removal of protection) and then protecting it again with an oxime carrying UV groups. In a further aspect the invention therefore concerns the use of oximes with formula II

HO - N = CR,R₂ (II)

wherein at least one of the groups R, and/or R₂ includes or carries a UV-absorbing group as described above, for the protection of isocyanate groups in compounds, in particular in polymers, in order to provide these compounds/polymers with UV hardenability, as described herein.

Alternatively, UV-sensitizing compounds can also be used in combination with compounds/polymers (which may or may not be known per se) with oxime- protected isocyanate groups, but without UV-absorbing groups, as described in greater detail below.

The oxime-protected isocyanate groups can in particular be applied in all types of polymers to be cross-linked, with the groups as a rule being incoφorated in the side chains of the polymeric base chains. Polymers that can be mentioned in this connection are acryl polymers, vinyl polymers; polyalkenes such as poly- ethene, polypropene and polystyrene; polyethers; polyesters; polyamides; poly- imides; synthetic rubbers; polyurethanes and the like; which can all contain further functional groups known per se. The oxime-protected isocyanate groups are in particular suitable as a UV cross-linking system for use in epoxy-functional polymers, as explained in greater detail below.

The polymers with the oxime-protected isocyanate groups can be produced by applying monomers that already contain oxime-protected isocyanate groups during the polymerization, or by providing already formed polymers in a suitable manner with oxime-protected isocyanate groups, for example by convert- ing isocyanate groups bound to the side chains or terminals of the polymer into oxime-protected groups.

The number of oxime-protected isocyanate groups in the polymer will depend on the desired application and final degree of cross-linking, but will in general lie between 5 and 50%, relative to the total number of repeating units in the polymer.

The synthesis of particular polymers with oxime-protected isocyanate groups is described in the prior art, inter alia in G. Clouet and T. Sadoun, J.M.S.- Pure Appl. Chem., (1992), A29, 939. The invention can also be applied with advantage for the hardening of such polymers known per se under the influence of

UN radiation, optionally after (further) UV-absorbing groups have been incoφorated in the polymers in a suitable manner.

This makes the system of economic interest, especially because oxime- protected isocyanates are now already cross-linking groups in standard practice, for example in the coating industry. Activation of these known compounds/polymers by means of UV light can lead to entirely different products and a different crosslinking chemistry. In this manner, by means of UN activation, faster hardening can be achieved than with thermal activation.

As has already been stated, the oxime-protected isocyanate groups can also be incoφorated in monomers which are then incoφorated in a polymer by means of polymerization - as a rule with other suitable monomers. In addition to the oxime-protected isocyanate group, such monomers will as a rule also include a polymerizable group, i.e. a group which makes it possible for the monomer to be incoφorated into the polymeric base chain by/during the polymerization reaction, such as polymerizable acrylate groups, ester groups, vinyl groups, unsaturated groups (alkene and styrene groups) and the like. The monomer here is preferably such that the part of the monomer to which the oxime-protected isocyanate group is bound forms a side chain in the final polymer.

It is also possible for the monomers to include a functional group which after polymerization can be converted into an oxime-protected isocyanate group, such as an isocyanate group. The oxime-protected isocyanate groups can also be incoφorated in cross- linkers. These cross-linkers will as a rule contain one or more further crosslinking groups, i.e. groups which ensure that the cross-linker can enter into a cross-linking reaction with the polymers to be cross-linked, in particular with functional groups on or in the side chains of these polymers. These can be crosslinking groups known per se, such as carboxylic acid, acid anhydride, hydroxy, phenol, isocyanate, amine, melamine or epoxy groups, or groups derived therefrom, but are preferably further oxime-protected isocyanate groups according to the invention. Some compounds, and particularly polymers, monomers and cross-linkers according to the invention are new, and form a further aspect of the invention, as discussed in greater detail below.

In addition to what has already been described herein, the invention offers the following advantages, separately and/or in combination: a. The hardening under the influence of UV radiation can be carried out at temperatures of less than 130°C, which makes the system suitable for application to temperature-sensitive substrates such as wood and plastic. b. The curing times in the case of UV irradiation at 100/110°C for example are very short in comparison with curing times in the case of purely thermal activation of protected isocyanates (up to 50 times faster than purely thermal curing at 110°C and up to 10 times faster than thermal curing at 150°C). This makes curing by UV irradiation economically attractive. c. In these systems there is a great deal of latitude with regard to the composition of the resin applied. In order to tune the mechanical properties of the final coating, in addition to the incoφoration of the functional groups which produce the chemical hardening, such as by copolymerization of APPIEM and optionally GMA in a system based on acrylate resins, for example, it is also possible to incoφorate many other monomers which can carry functional groups, such as other acrylate and other vinyl monomers. d. The functional groups can be incoφorated into the resin in such a way, for example by random copolymerization of similar monomers or suitable derivativization of the side chains, that a homogeneous distribution of these groups is ensured, as a result of which the hardening reaction is more efficient. e. Because the protected isocyanate groups are already linked to the resin, the hardening takes place in a more effective manner. This is explained by the fact that UV irradiation never converts all the protected isocyanate groups. In the case of bifunctional low-molecular-weight photo cross-linkers (as used in lithography) this means that a high percentage of the cross-linkers do not contribute to the curing reaction because cross-linker molecules both with no and also with only one converted photo group are unusable for cross-linking. f. The system, in particular the copolymer of APPIEM with methyl- methacrylate, can be applied together with epoxy-functional resins, for example, in powder coatings. There is a wide choice of commercially available epoxy-acrylate resins and epoxies based on polyester or bis- phenol resins, for example, as a result of which the applicability of poly(MMA-co-APPIEM), for example, is very large. g. The primary materials are relatively cheap and the synthesis and other reactions required for application of the invention are simple to carry out. h. Without UN irradiation the resin can be kept for some time, such as 15 minutes, at increased temperature, such as approximately 100°C, without cross-linking occurring. This means that the resin is suitable as a powder coating resin, where extrusion at about 100°C takes place during the production (time in extruder ± 2 min).

The oxime-protected isocyanate groups according to the invention, the polymers and cross-linkers with these groups, polymeric mixtures that contain such polymers and/or binders, and the hardening of such polymers or polymeric mixtures under the influence of UV radiation, can be used for any suitable pmpose. The invention can thus be applied in the manufacture of plastic objects such as films by means of UV hardening; application in photolithography, including the making of photolacquers, and the like.

This particularly concerns applications where hardening under the influence of UV radiation can be applied in a suitable manner. This means inter alia that the polymer and the polymer mixture must be resistant to the UV radiation to be used and that the UV radiation must be able to penetrate into the polymer mixture in such a way that all the oxime-protected isocyanate groups can be cross-linked to the desired extent. By means of the present description, the person skilled in the art will be able to determine the right conditions (wavelength, duration, intensity, etc.) for the UV hardening, if necessary after a number of simple preliminary tests.

The invention is for example suitable for the hardening of polymers or polymer mixtures which because of their properties cannot be hardened, or cannot be hardened well, at high(er) temperatures, for example because ageing, dis- coloration or other kinds of deterioration in the desired properties of the polymer or polymer mixture are obtained, or because it is not possible to obtain the desired properties in the final product at such temperatures. Here, according to the invention, analogues of these known polymers or polymer mixtures will be applied, which are provided with oxime-protected isocyanate groups according to the invention, and which are then hardened under the influence of UV radiation.

It is also possible simply to use cross-linkers with oxime-protected isocyanate groups according to the invention with these polymers or in these polymer mixtures.

The polymer mixtures according to the invention can also be made up in a manner known per se, i.e. by the application of known additives in amounts known per se. Here the polymers with the cross-linking groups and/or the cross- linkers according to the invention can also be applied in amounts known per se, for example 20-100% by wt. of the polymer or 5-50% by wt. of the cross-linker, relative to the total composition. It is of course required here that the oxime-protected isocyanate groups are compatible with the other components of the mixture, in particular any functional groups present therein, and that after UV irradiation they can enter into a cross-linking reaction with the desired components in the mixture.

The invention is in particular suitable for the manufacture of coating compositions and the hardening of these compositions on substrates by UV irradiation for the formation of a coating (layer) on the substrate. Here the invention can be applied for all known polymeric coating compositions, including water-borne systems, organic-solvent-borne systems, systems based on oil, alkyd resins, photoresists, lattices and the like, as well as the other systems mentioned below. The invention can here be applied with all types of base polymers for coating compositions, such as acryl polymers, vinyl polymers, epoxies, poly- urethanes and polyesters, for giving UN hardenability to these polymers, in particular where these polymers have until now been hardened by other methods, such as thermal methods, or as an alternative to UV-sensitive cross-linking groups already applied in such polymers, such as the carbamate, formylamine and acyloxime groups already mentioned.

These coating compositions can also be made up in a manner known per se, i.e. by the application of known additives for coating compositions in amounts known per se, for which the known reference books should be consulted. The polymers and/or cross-linkers according to the invention can here be applied in amounts known per se, for example 20-100% by wt. of the polymer or 5-50% by wt. of the cross-linker, relative to the total coating composition.

The hardening is carried out by applying the coating to the substrate to be coated and then exposing it to UV radiation with a suitable wavelength and suit- able intensity. The suitable wavelength will mainly depend on the UV-absorbing groups present, but is notably in the range of 200-400 nm. The final degree of cross-linking can here optionally be regulated by means of the duration and/or the intensity of the irradiation. As a rule the coating will be completely hardened within 1 hour of irradiation, preferably within less than 20 minutes of irradiation, preferably within 1 second to 10 minutes of irradiation.

In a polymer mixture (i.e. in different components of the mixture or even in the same compound or the same polymer) it may be possible here to apply oxime-protected isocyanate groups with different UV-absorbing groups (i.e. sensitive to UV radiation with different wavelengths) which can then be cross-linked, together or separately, by simultaneous or consecutive exposure to UN radiation with the suitable specific wavelengths.

The coating compositions according to the invention can be applied to any substrate to which the coating composition (after hardening) adheres adequately and which is compatible with the coating composition. As already stated, the cross-linking system of the invention offers the major advantage here that the UV hardening can be carried out at temperatures below 130°C, more particularly below

110°C, which makes the coating compositions according to the invention suitable in particular for application on temperature-sensitive substrates, such as wood or temperature-sensitive plastics such as thermoplastics. ln this way the invention makes it possible to apply known coating compositions with oxime-protected isocyanate groups on such substrates, where this has not been possible up to now because of the temperature required for thermal hardening.

The invention is particularly suitable for application in systems which contain little or no solvent, such as high-solid paints, and more particularly for application in powder coatings, as explained in greater detail below.

This generally means thermoplastic and/or thermosetting plastics which are applied in powder form to the substrate to be coated. Such powder coatings can be made up on the basis of different types of polymers, including acrylate resins, epoxy resins, epoxyacrylate resins, polyester resins, epoxy/polyester and polyurethane resins, and the like. The invention can be applied in all these known types of powder coatings, in particular in acrylate resins, epoxy resins and epoxyacrylate resins.

Although the system is self-curing, and can thus form hard coatings without further additions, it will be economically more advantageous to use the system as a hardener for epoxy-functional resins. Because these epoxy resins (based on acrylate, bisphenol A or polyester) make up one of the biggest market segments within the powder coatings market, the invention has broad applicability.

The powder coatings can also contain all known additives for powder coatings, in amounts known per se, such as fillers, pigments and colorants, flow improvers, catalysts, effects (for example for obtaining a metallic appearance) and the like.

The powder coatings according to the invention can be made up in a manner known per se, as a rule by mixing the above-mentioned components in the above-mentioned amounts.

The powder coatings so obtained can then be applied to the substrate in any manner known per se, for example by applying (sprinkling) by hand; by means of electrostatic techniques such as electrostatic spraying (corona or tribo spraying), by fluidized bed sintering (electrostatic or non-electrostatic), and can then be hardened by exposure to UV radiation with a suitable wavelength and intensity for a suitable time. The coating so applied can have any desired thickness, as a rule usual thicknesses for coating layers based on powder coatings such as 1-4000 μm, preferably 20-400 μm.

As stated, a number of polymers, monomers and cross-linkers according to the invention are new compounds. This concerns polymers in particular which contain repeating structural units with the general formula III

^• R₅ →-

R, - NH - CO - 0 - N = CR. ιR^lv ₂. (III)

where R,, R₂ and/or R₃ are as described above, and Rj is a repeating unit of the polymeric base chain which is derived from the monomer used in the polymerization, for example an optionally substituted alkene, vinyl, ester or urethane unit.

In particular R₅ is an optionally substituted acrylate or methacrylate unit and R₃ an optionally substituted alkyl bridge with 1-10 carbon atoms, in particular 2-6 carbon atoms. Such structural units have the general formula IV:

- CH.-CR,-)- I

C=0 (IV)

I

0 - (CH₂)_n - NH - CO - 0 - N = CR,R₂

where n is 1 to 10, preferably 2-6; and R^ is hydrogen or methyl.

The polymer can include other suitable repeating structural units in the base chain, in suitable/desired amounts relative to the total number of monomeric units. These other structural units may optionally include functional groups known per se, especially in the side chains thereof, for giving desired properties to the polymer, and are preferably derived from the same type of monomer as the structural unit with formula III or IV. As a rule these other structural units will be derived from monomers known per se.

The polymers according to the invention can here be both randomly chosen copolymers and copolymers with a specific, predetermined sequence of the monomeric units, depending on the monomeric units used and the method of production/polymerization.

A special class of polymers according to the invention are copolymers based on acrylate or methacrylate units which contain the oxime-protected isocyanate groups according to the invention in the side chain, in particular the acryl copolymers which also contain side chains with epoxy-functional groups with which the oxime-protected isocyanate groups can enter into a cross-linking reaction. These polymers are as a rule built up from inter alia the following structural units:

The invention also concerns monomers for the production of the above- mentioned polymers. These are in general monomers with the general formula V

R₇

I (N) R₃ - NH - CO - 0 - N = CR,R₂

wherein R,, R₂ and R₃ have the above meanings and R₇ is a polymerizable group as described above, such as an alkenyl group, vinyl group or ester group, or a monomeric structural unit which carries such a polymerizable group.

In particular, R₇ is an optionally substituted acrylate or methacrylate unit and R₃ an optionally substituted alkyl bridge with 1-10 carbon atoms, in particular 2-6 carbon atoms. Such structural units have the general formula VI: CH₂ — CR^

I c=o I

0 (VI)

I

(CH₂)„ - NH - CO - O - N = CR,R₂

wherein R,, R₂ and R₃ have the above meanings, n is 1 to 10, preferably 2-6; and

R^ is hydrogen or methyl.

The invention also concerns a method for the manufacture of polymers and copolymers, in particular by polymerization in a manner known per se, using the above-mentioned monomers, as well as the polymers so obtainable. The amount of oxime-protected isocyanate groups can here be simply regulated by means of the amount of the corresponding monomer (i.e. with the oxime-protected isocyanate group or a preliminary product therefrom) which is incoφorated in the initial mixture for the polymerization.

Finally, the invention concerns cross-linkers which contain at least one oxime-protected isocyanate group according to the invention, as well as at least one further cross-linking group as described above.

The cross-linkers according to the invention have the general formula VII

R, - R, - NH - CO - O - N CR,R₃ (VII)

where R,, R₂ and R₃ are as described above and R₈ is the other cross-linking group, or a structural unit which carries another cross-linking group. This other cross-linking group R₈ is preferably a second oxime-protected isocyanate group.

The group R₃ is preferably an optionally substituted binding alkyl group. Such cross-linking compounds with two oxime-protected isocyanate groups have the general formula VIII NH - CO - O - N = CR,R₂

where R,/ R,', R₂/R₂' and R₃ are as described above, with n being 1 to 10, prefer- ably 4 to 6.

Here R,, R,', and R₂ and R₂' are preferably all phenyl, or R„ R,' are both methyl and R₂ and R₂' both methyl. Examples of such cross-linking agents are:

These cross-linkers can be incoφorated in suitable amounts in compositions of polymers with cross-linkable functional groups, including coating compositions such as commercially available epoxy resins, after which these compositions can then be hardened by exposure to UV radiation.

The invention also concerns hardened polymeric products, in particular hardened coatings, which have been obtained by UV hardening of polymeric compositions that include compounds with the oxime-protected isocyanates according to the invention. The invention also concerns substrates which have been provided with such a coating.

These products and coatings will as a rule differ from products and coatings which have been obtained by thermal hardening from the same primary materials (polymers), notably because the UV hardening will usually take place by other reaction mechanisms, which results in other reaction products and/or another structure of the hardened product. Although the invention is not limited in any special way, it is assumed that the cross-linking reaction under the influence of UV irradiation according to the invention takes place via at least one of the following mechanisms, or a combination thereof:

- formation of amine radicals;

- formation of free primary amines;

- formation of hydrazines;

- expulsion/elimination of CO₂, where free amines, hydrazines or radicals can be formed which can enter into a cross-linking reaction with other functional groups present, such as epoxy- functional groups. In this way a system can be completely hardened within a few minutes at about 100°C.

The chemistry behind the UV reactions of oxime-protected isocyanates is complicated by the many possible reactions that can occur. The UV reaction is probably analogous to UV reactions of carbamates and acyloximes:

Diagram 2: Postulated mechanism of the UN reaction of oxime-protected isocyanates

The re-formation of the original isocyanates by thermal treatment is applied in commercial systems. Hydrazines or amines are formed by UV irradiation, however. The hydrolysis step which results in a hydrazine already takes place via small traces of water in the system. The addition of extra water to the system is therefore generally not necessary. The self-hardening of resins which contain protected isocyanate groups can be explained in various ways. During UV irradiation at 100°C the greatest part of the groups will disintegrate to amines or hydrazines. A smaller part, however, will be converted by the reverse reaction to isocyanate because of the increased temperature and can link with amine or hydrazine groups (Diagram 3). During thermal hardening only isocyanate groups will be formed which can react with a protected isocyanate group (Diagram 4). Less probable, but in principle possible, is the cross-linking of resin chains by recombination of radicals generated under UV irradiation (Diagram 5).

Diagram 3: Self-hardening, reaction of a hydrazine with an isocyanate, analogous to amine-isocyanate reaction

N 1 *^■ I NH - N-C - N f

Diagram 4: Self-hardening, reaction of an isocyanate with an oxime-protected isocyanate

Diagram 5: Self-hardening, recombination of radicals

The reaction of formed amines or hydrazines with epoxy groups is generally known (Diagram 6).

Diagram 6: Reaction of an amine group with epoxy groups

O / \ vw^{y w} CH CH₂ * H₂N v«\

OH V^ΛWV^Λ CH CH2 NH - *4

OH

V-w«v*» c » CH, N ^■**. CH₂

HO CH

Hydrazines are more reactive to esters than amines. For this reason it is quite conceivable that ester groups in the resin are attacked by hydrazines, which can lead to cross-linking: Diagram 7: Reaction between a hydrazine group and a methacrylate group

^•NH-NH-, ^♦ H3C.O-C-J . j NH-_NH-I-I

The radical intermediaries during the UV reaction also offer in principle the possibility of cross-linking of resins which contain double bonds. This can explain the hardening of poly(MMA-co-APPIEM)/Viaktin VAN 1743 mixtures. A radical generated by UV light can attack a double bond and produce linking of double bonds (Diagram 8).

Diagram 8: Cross-linking of unsaturated resins by radical mechanisms

CROSS-LINKING

In addition, amines or hydrazines can also add on to double bonds:

Diagram 9: Reaction of a hydrazine with a double bond

The reaction with amines is similar.

Other variations are also possible, however, for example: UV hardening of a mixture of 2 resins which consists of a resin with epoxy side groups and a resin with protected isocyanate side groups, or UV hardening of an exoxy- functional resin with a low-molecular-weight cross-linker which contains several protected isocyanate groups:

Compounds which contain ketoxime-protected isocyanate groups can cross-link epoxy-functional resins under the influence of UV irradiation with correct choice of the ketoxime. The oxime-protected isocyanate group must absorb UV light in the right range (200-300 nm). This is achieved with ketoximes such as benzophenonoxime, acetophenonoxime and acetonaphtonoxime, for example.

The oxime-protected isocyanate groups can be incoφorated into a resin as side chains, optionally together with epoxy side groups. The use of low- molecular-weight cross-linkers with protected isocyanate groups is also possible, however. The system is economically attractive, especially because oxime-protected isocyanates are already now cross-linking groups in standard use in the coating industry. They are exclusively thermally activated, however. Activation by means of UV light leads to completely different products and different cross-linking chemistry. In this way, by means of UV activation, faster hardening can be achieved than with thermal activation. The choice of the oxime is absolutely critical for an efficient UV reaction. The oxime-protected isocyanate group must show good absoφtion of UV light between about 200 and 300 nm, because lamps with light in this range are generally used. UV-active protected isocyanates can be produced with acetophenon-, benzophenon- or acetonaphtonoxime, for example. It is probable, however, that isocyanates which are protected with UV-inactive oximes (e.g. MEK or acetonoxime) are capable of a UV reaction in the presence of a suitable sensitizer (e.g. benzophenone).

According to a further embodiment of the invention it is also possible not to incoφorate the UV-absorbing groups in the same compound as the oxime- protected isocyanate group (i.e. in one of the groups R„ R₂ or R₃) but combine a compound with an oxime-protected isocyanate group with at least one other compound which makes the group ( NH - CO - O - N = C ) susceptible to cleavage under the influence of UV radiation. This can be achieved, for example, by incoφorating such UV-activating compounds (UN sensitizers) in suitable amounts in a composition of polymers with oxime-protected isocyanate groups in the side chains, and then hardening the compositions so obtained under the influence of UV radiation in a manner known per se.

This embodiment can be applied in all compounds with oxime-protected isocyanate groups, such as those in which R„ R₂ and/or R₃ have the meanings given above, but without the (additional) presence of an additional UV-absorbing group in one of the groups R,, R₂ and/or R₃ being required.

This embodiment is especially suitable for application in polymers known per se with oxime-protected isocyanate groups, which in addition contain no or only weak UV-absorbing groups in the vicinity of the ( NH - CO - O - N = C ) structural unit. It will be clear to the person skilled in the art that the use of a UV-sensitizing compound in combination with such a polymer is in essence equivalent to the introduction of UV-absorbing groups into this polymer itself, i.e. into one of the groups R,, R₂ and or R₃ as described above. All UV-sensitizers known per se can in principle be applied for this puφose, such as the sensitizers which are now already applied in known UV systems based on carbamate groups, formylamine groups and acyloxime groups, such as benzophenone. By means of simple tests the person skilled in the art will be able to determine which UV sensitizer is suitable for application with a specific oxime-protected isocyanate compound, and also what are suitable conditions for this specific combination (such as concentration/amount of the sensitizer, the wavelength to be used, the intensity and the duration of irradiation). Benzophenone can thus be used as a sensitizer with, for example, aliphatic oxime protected isocyanates, such as acetonoximes or MEK-oximes. The invention will now be explained by means of the following non- limiting examples, and also by means of the figures, which show the results of hardening tests on oxime-protected isocyanates under the influence of UFV radiation according to the invention.

Example 1 : Synthesis of low-molecular-weight oxime-protected isocyanate cross- linkers Acetophenonoxime was obtained by overnight refluxing of a solution of 23.3 mL of acetophenone, 16 mL of pyridine, 13.9 g of hydroxylamine hydro- chloride in 200 mL of ethanol. The solution was then concentrated by evaporation to about 50 mL and poured into demineralized water. The solid product was recrystallized twice from water/methanol.

9.4 g of acetophenoxime and a catalytic amount of triethylamine were dissolved in 65 mL of dry toluene. 5 mL of hexamethylenediisocyanate was slowly added while the solution was vigorously stirred under N₂. The solution became cloudy white. After 1 hour of stirring at room temperature the solution was stirred for a further 5 hours at 80°C. The solution was concentrated by evaporation and the crude product was recrystallized from dichloromethane/- toluene. Example 2: Synthesis of resins with oxime-protected isocyanate groups

Acrylate resin with oxime-protected isocyanate groups, poly(MMA-co-

APPIEM), 2.8 g of acetophenonoxime (see 2.1) and a catalytic amount of dibutyl- tin dilaurate were dissolved in 15 mL of dry toluene. 3 mL of 2-isocyanato-ethyl- methacrylate was slowly added drop by drop and the solution was stirred for 3 hours under nitrogen at 60°C. After 3 hours 0.5 mL of glycidylisopropylether was added and the solution was stirred for a further 30 minutes to get rid of any aminomethacrylates.

9 mL of the solution was added to a solution of 13.5 mL of methacrylate in 50 mL of toluene. 0.16 g of AIBN was added and the solution was degassed by blowing dry nitrogen through. The polymerization was carried out by stirring overnight at 70°C. The polymer solution was concentrated and the product was precipitated in n-hexane. After drying in vacuum at 30°C a quantitative yield was obtained.

Example 3: Synthesis of acrylate resin with both epoxy- and oxime-protected isocyanate groups, poly(MMA-co-GMA-co-APPIEM). The synthesis was carried out in a similar way to Example 2, but glycidylmethacrylate was also added for the polymerization.

Example 4: Characterization of synthesized polymers

The composition of the polymers according to the invention was analysed by 'H-NMR. Table 1 shows the percentages of functional monomer units in the polymers.

TABLE 1

Theoretical polymer compositions (based on added monomer ratios) compared with the compositions determined by 'H-NMR

The molecular weights of the copolymers were determined by gel permeation chromatography in chloroform, using polystyrene calibration curves. Table 2 shows the results.

TABLE 2

Molecular weights of the copolymers, measured by G.P.C. in chloroform.

Calculation of molecular weights by means of polystyrene calibration curves

Example 5: UV hardening of epoxyfunctional resins with the aid of low- molecular-weight oxime-protected isocyanate compounds

Acrylate resins with different percentages of glycidylmethacrylate, poly(MMA-co-GMA), were cross-linked with acetophenonoxime-protected hexamethylenediisocyanate (AOPDIC). The results are given in Fig. 1, which shows the insoluble fraction as a function of epoxy content in acrylate resin for poly(MMA-co-GMA) with 0.3 mol AOPDIC/mol epoxy groups, with 10 minutes of UV irradiation at 100°C and 90 minutes of post-hardening at 120°C. The best results were obtained with acrylate resins with higher epoxy contents (>50 mol%), where a reasonable degree of cross-linking could be determined.

Example 6: Cross-linking with acrylate resins with oxime-protected isocyanate side groups, poly(MMA-co-APPIEM10)/Self-cross-linking of Poly(MMA-co- APPIEM 10)

Poly(MMA-co- APPIEM 10) can be hardened without further additions. See Fig. 2, which shows the results of self-cross-linking, for poly(MMA-co- APPIEM10), by UV irradiation at 100°C and (for comparison pvuposes) thermally at 120°C.

It can be seen from Fig. 2 that poly(MMA-co- APPIEM 10) can be completely hardened within a few minutes at 100°C. Thermal hardening is also possible but is slower, even at higher temperature (120°C).

Example 7: Hardening of poly(MMA-co- APPIEM 10) with triglycidylisocyanurate (TGIC)

Films of poly(MMA-co- APPIEM 10) with 7.5% by wt. of TGIC were hardened both with UV irradiation and purely thermally. See Fig. 3, which shows the results for hardening of poly(MMA-co- APPIEM 10) with 7.5% by wt. of TGIC, by UV irradiation at 100°C or (for comparison puφoses) thermally at 120°C.

It can be seen from Fig. 3 that UV hardening in the presence of TGIC is faster than UV hardening of poly(MMA-co- APPIEM 10) alone, as shown in Fig. 2.

Moreover, in the presence of TGIC an induction period is observed when the system is thermally hardened.

Example 8: Hardening of poly(MMA-co- APPIEM 10) with poly(MMA-co- GMA65)

Mixtures of poly(MMA-co- APPIEM 10)/poly(MMA-co-GMA65) (1/1) were hardened both thermally and with UV irradiation. See Fig. 4, which shows the results for hardening of poly(MMA-co-APPIEM10)/poly(MMA-co-GMA65) by UV irradiation at 100°C or thermally at 120°C.

In the case of both UV and thermal hardening, the hardening of mixtures of poly(MMA-co- APPIEM 10) and poly(MMA-co-GMA65) is slower than when poly(MMA-co- APPIEM 10) is hardened with TGIC or without further additions. This can probably be attributed to the lower degree of homogeneity of these films. Nevertheless, relatively fast hardening is observed, especially with UN irradiation. The thermal hardening curve again shows an induction period, as can also be seen in the TGIC-containing system.

Example 9: Hardening of poly(MMA-co- APPIEM 10) with an unsaturated polyester resin

Because it is likely that the oxime-protected isocyanate reaction under the influence of UV light also occurs via radical intermediaries, attempts were made to harden mixtures of poly(MMA-co- APPIEM 10) with an unsaturated polyester resin. The radicals generated can in principle start polymerization of the unsaturated system. Viaktin VAN 1743 (Vianova Resins, Hoechst) was chosen as the polyester resin. The results are shown in Fig. 5 for the hardening of poly(MMA-co- APPIEM10)/Niaktin VAN 1743 mixtures as a function of the composition, with 4 minutes of UV irradiation at 100°C and 1 hour of post-hardening at 100°C.

From Fig. 5 it can be seen that Viaktin VAN 1743 does not harden well without further additions under the conditions set up. Improved curing is obtained in the presence of poly(MMA-co- APPIEM 10), however. The highest degree of hardening is found in films which contain 70% by weight of poly(MMA-co- APPIEM10). The optimum in the graph shows that the unsaturated polyester resin really does take part in the hardening reaction and is not inert.

Example 10: Cross-linking with acrylate resins with oxime-protected isocyanate groups and epoxy side groups, poly(MMA-co-GMA30-co-APPIEM30)

When both oxime-protected isocyanate groups and epoxy groups are incoφorated into an acrylate resin, a very efficient hardening reaction can be expected under the influence of UN irradiation because the functional groups are distributed very homogeneously through the resin. See Fig. 6, which shows the results of UV hardening of poly(MMA-co-GMA30-co-APPIEM30) as a function of the UN irradiation time at 100°C.

As can be seen in Fig. 6, the UV hardening reaction is in fact faster than is generally observed with poly(MMA-co- APPIEM 10). There is almost complete hardening within 1 minute. Too long UV irradiation apparently leads to poorer film properties (overcure).

The thermal hardening behaviour was also investigated for poly(MMA-co- GMA30-co-APPIEM30). See Fig. 7, which shows the insoluble fraction of poly(MMA-co-GMA30-co-APPIEM30) as a function of temperature, with 15 minutes of hardening.

From Fig. 7 it can be seen that below 100°C there is no significant reaction within 15 minutes. Around 120°C the curve begins to rise rapidly and the system begins to harden thermally.

Example 11: Application of a coating under the influence of UV cross-linking

a. Film formation:

A solution of the relevant resin with any co-reagents was made in chloro- form or methylene chloride (40 mg of solid per mL). Glass plates (25 x 25 mm or 26 x 76 mm) were cleaned with an alcoholic solution and washed with demineralized water. After drying, the polymer solution was dripped onto the plates and the solvent evaporated. The resultant thin films (±60 μm) were dried in a forced-air oven at 40°C overnight and then in vacuum at 40°C for 6 hours.

b. UN hardening:

Films were irradiated with a Philips Mercury HOK 20/100 (100 W/cm²). The distance between films and the lamp was 30-35 cm, so that the temperature of the films was 100°C.

c. Determination of insoluble fraction: The weight of the empty clean glass plates and the weight of the glass plates with the film before and after the hardening were weighed [sic]. After UV or thermal hardening the films were placed for 48 hours in DMSO. The films were then dried in vacuum at 100°C for 5 hours and the weight was again determined. The insoluble fraction was calculated from the different weight determinations.

It was found that the results of the solubility test were in good agreement with the standard rub test. For the acrylate systems here described, an insoluble fraction greater than 75% usually meant 100 or more chloroform double rubs. The solubility test was used because this test made more accurate comparison possible within series of measurements.

d. Chloroform rub test:

Films were formed on glass plates of 26 x 76 mm as described above. A rod wrapped with cotton was used. The pressure of the cotton surface on the coating was constant during all the experiments (100 N/m²). The surface tested was 0.5 x 4 cm. The number of double rubs needed to reach the substratum was counted. After 100 rubs the test was stopped and the film regarded as completely hardened.

1. Use of an oxime-protected isocyanate group with formula I

- R₃ - NH - CO - O - N = CR,R₂ (I)

where at least one of the groups R„ R₂ or R₃ includes or carries at least one UV- absorbing group which makes the group ( NH - CO - O - N = C ) susceptible to cleavage under the influence of UV radiation: in or as side chains of branched polymers or in cross-linkers, for giving UV curability to these polymers or to polymeric compositions which contain such polymers and/or cross-linkers.

2. Use according to Claim 1, where at least the group R, or the group R₂ carries or includes at least one UV-absorbing group, or where both groups R, and R₂ include or carry one UN-absorbing group.

3. Use according to one of the preceding claims, where the UV-absorbing group is chosen from optionally substituted unsaturated hydrocarbon residues, in particular optionally substituted alkenyl groups with 2-6 carbon atoms and optionally substituted alkynyl groups with 2-6 carbon atoms, as well as optionally substituted cycloalkenyl and alkylcycloalkenyl groups with 4-10 carbon atoms in total and with preferably 5 or 6 carbon atoms in the ring; optionally substituted aromatic groups, particularly with 4-8 ring atoms in total, chosen from carbon atoms, and/or optionally one or more hetero atoms O, S and Ν; more particularly with 4, 5 or 6 carbon atoms, optionally 1 or 2 hetero atoms, and 5 or 6 atoms in total in the ring, such as phenyl, furfuryl, pyranyl, pyridinyl and the like; optionally substituted carbonyl groups with 1-10 carbon atoms, carboxyl groups, cyanogen groups, nitro groups, hydroxyl groups, preferably cyanogen groups, nitro groups and/or carbonyl groups with 1-6 carbon atoms; where the UN-absorbing group is separated from the oxime-protected isocyanate group by at most three atoms; preferably by at most two atoms; more preferably by at most one further atom; or is directly bound to the oxime-protect- ing isocyanate group; and/or where the UV-absorbing group is located at such a position relative to the protected isocyanate group that resonance can occur between the UV- absorbing group and the protected isocyanate group.

4. Use according to one of the preceding claims, where the groups R, and R₂ are chosen independently from hydrogen; the UV-absorbing groups according to Claim 3, in particular cyano, nitro,

1 -alkynyl groups with 2-6 carbon atoms, 1 -carbonyl groups with 1-4 carbon atoms and the above-defined optionally substituted aromatic groups, notably optionally substituted phenyl groups; optionally substituted alkyl groups with 1-10 carbon atoms, particularly 1-

6 carbon atoms, more particularly optionally substituted methyl, ethyl, propyl or isopropyl; - optionally substituted alkenyl groups with 2-10 carbon atoms; optionally substituted alkynyl groups with 2-10 carbon atoms; optionally substituted cycloalkyl, alkylcycloalkyl, cycloalkenyl and alkyl- cycloalkenyl groups with 3-10 carbon atoms in total, and with preferably

5 or 6 carbon atoms in the ring; - halogen; optionally substituted alkoxyl groups with 1-10 carbon atoms or alkoxyl- alkyl groups with 2-10 carbon atoms; hydroxyl; carboxyl; - optionally substituted ester groups with 2-10 carbon atoms; amine groups with the formula -Ν T, T₂, where T, and T₂ can be hydro- gen or an optionally substituted alkyl with 1-10 carbon atoms, or can together form a ring with at most 8 ring atoms; in particular with 3, 4 or 5 carbon atoms and optionally a further nitrogen atom in the ring; sulfhydryl and optionally substituted thioalkyl groups with 1-6 carbon 5 atoms; where the groups R, or R₂, together with the carbon atom of the oxime- protected isocyanate group to which they are bound, can also form an optionally substituted ring, which can optionally be interrupted by one or more hetero atoms, carbonyl groups and/or ester groups (forming a lactone ring); 10 where the above groups can optionally also contain or be interrupted by one or more S, N or O hetero atoms; or can optionally also contain or be interrupted by at least one carbonyl group - (CO)-, optionally with formation of an ester, amide or thioester group; and where preferably at least one of the groups R, and R₂ includes or carries at 15 least one UV-absorbing group.

5. Use according to one of the preceding claims, where the groups R, and R₂ are chosen independently from hydrogen; - 20 the UV-absorbing groups according to Claim 3, in particular cyano, nitro,

1 -alkynyl groups with 2-6 carbon atoms, 1 -carbonyl groups with 1-4 carbon atoms and the above-defined optionally substituted aromatic groups, notably optionally substituted phenyl groups; optionally substituted alkyl groups with 1-10 carbon atoms, particularly 1- 25 4 carbon atoms, more particularly optionally substituted methyl, ethyl, propyl or isopropyl; optionally substituted alkenyl groups with 2-10 carbon atoms; optionally substituted alkynyl groups with 2-10 carbon atoms; optionally substituted cycloalkyl groups with 4-10 carbon atoms in total, 30 and with preferably 5 or 6 carbon atoms in the ring; where the above groups can optionally also contain or be interrupted by one or more S, N or O hetero atoms; or can optionally also contain or be interrupted by at least one carbonyl group - (CO)-, optionally with formation of an ester, amide or thioester group; and where preferably at least one of the groups R, and R₂ includes or carries at least one UV-absorbing group.

6. Use according to one of the preceding claims, where the groups R, and R₂ are chosen independently from the UV-absorbing groups according to Claim 3, in particular cyano, nitro, 1 -alkynyl groups with 2-6 carbon atoms, 1 -carbonyl groups with 1-4 carbon atoms and the above-defined optionally substituted aromatic groups, notably optionally substituted phenyl groups; optionally substituted alkyl groups with 1-6 carbon atoms, more particularly optionally substituted methyl, ethyl, propyl or isopropyl; and where preferably at least one of the groups R, and R₂ includes or carries at least one UV-absorbing group.

7. Use according to one of the preceding claims, where the groups R, and R₂ are chosen independently from methyl, ethyl, phenyl, methylenephenyl (- CH2-C6H5), methylenediphenyl (-CH-(C6H5)2), nitromethyl, cyanomethyl, ethynyl, and α-carbonyl groups with the general formula - (CO) - R₄, where R₄ is an optionally substituted alkyl group with 1-6 carbon atoms.

8. Use according to one of the preceding claims, where R, and R₂ are both phenyl, or one of R, and R₂ is phenyl and the other methyl or ethyl.

9. Use according to one of the preceding claims, where the group R₃ is a binding group or bridge, and preferably an optionally substituted alkyl group with 1-10 carbon atoms; - an optionally substituted alkenyl group with 2-10 carbon atoms; an optionally substituted alkynyl group with 2-10 carbon atoms; an optionally substituted alkoxyl group with 1-10 carbon atoms or alkoxy- alkyl group with 2-10 carbon atoms; an optionally substituted cycloalkyl, alkylcycloalkyl, cycloalkenyl or alkylcycloalkenyl group with 3-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; an optionally substituted aryl, alkylaryl, arylalkyl or alkylarylalkyl group with 4-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; where the above groups can optionally also contain or be interrupted by one or more S, N or O hetero atoms; or can optionally also contain or be interrupted by at least one carbonyl group - (CO)-, optionally with formation of an ester, amide or thioester group; where the group R₃ can optionally be substituted with one or more UV- absorbing groups according to Claim 3 or can be interrupted by one or more UV- absorbing groups according to Claim 3; where the UV-absorbing group is usually separated from the oxime- protected isocyanate group by not more than three atoms; preferably not more than two atoms; more preferably by at most one further atom; or is directly bound to the oxime-protected isocyanate group; and/or where the UV-absorbing group is located at such a position relative to the protected isocyanate group that resonance can occur between the UV- absorbing group and the protected isocyanate group.

10. Use according to one of the preceding claims, where the group R₃ is a binding group or bridge, being an optionally substituted alkyl group with 1-10 carbon atoms; an optionally substituted alkenyl group with 2-10 carbon atoms; an optionally substituted alkynyl group with 2-10 carbon atoms; an optionally substituted alkoxyl group with 1-10 carbon atoms or alkoxy- alkyl group with 2-10 carbon atoms; an optionally substituted cycloalkyl, alkylcycloalkyl, cycloalkenyl or alkylcycloalkenyl group with 5-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; an optionally substituted aryl, alkylaryl, arylalkyl or alkylarylalkyl group with 5-10 carbon atoms in total, and with preferably 5 or 6 carbon atoms in the ring; where these groups can optionally also contain or be interrupted by one or more S, N or O hetero atoms; or can optionally also contain or be interrupted by at least one carbonyl group - (CO)-, optionally with formation of an ester, amide or thioester group;

11. Use according to one of the preceding claims, where the group R₃ is a branched or unbranched, optionally substituted alkyl group with 1-10 carbon atoms, particularly with 1-6 carbon atoms, more particularly with 2-4 carbon atoms, which when it contains more than 2 carbon atoms can be interrupted by an optionally substituted phenyl group, a carbonyl group - (CO) - or an ester bond

-O-(CO)-; or an optionally substituted methylphenyl (-CH2-C6H4-) or phenyl- methyl (-C6H4-CH2-) group.

12. Use according to one of Claims 1-8, where the group R₃ is - a polymeric side chain; a monomer, a structural unit which can be used as a monomer, or a structural unit which includes a polymerizable group; a cross-linker, a structural unit which because of the additional presence of the oxime-protected isocyanate group can be used as a cross-linker, or a structural unit which contains an additional cross-linking group.

13. Use of a compound which contains at least one oxime-protected isocyanate group with formula I

- R₃ - NH - CO - O - N = CR,R₂ (I) where R,, R₂ and R₃ are as described in Claims 1-12, in the giving of UV curabilty to polymeric compositions and/or in the production of UV-curable polymeric compositions.

14. Use according to Claim 13, where the compound is a polymer which includes at least one oxime-protected isocyanate group with formula I

- R₃ - NH - CO - O - N = CR,R₂ (I)

where R,, R₂ and R₃ are as described in Claims 1-11, in the side chain.

15. Use according to one of Claims 13-14, where the polymer is a polymer based on acrylate or mefhacrylate.

16. Use according to one of Claims 13-15, where the polymer contains further side chains with functional epoxide groups.

17. Use according to Claim 13, where the compound is a cross-linker which contains at least one oxime-protected isocyanate group with the formula

- R₃ - NH - CO - O - N = CR,R₂ (I)

where R,, R₂ and R₃ are as described in Claims 1-11, and at least one further cross-linking group.

18. Use according to Claim 17, where the further cross-linking group is a further oxime-protected isocyanate group with the formula

- NH - CO - O - N = CR,R

where R, and R, are as described in Claims 1-8. 19. Use of a polymerizable monomer which contains at least one oxime- protected isocyanate group with formula I

- R₃ - NH - CO - O - N = CR,R₂ (I)

where R„ R₂ and R₃ are as described in Claims 1-11, and a further polymerizable group, in the production of polymers cross-linkable under the influence of UV and/or of polymers for giving UN curability to polymeric compositions.

20. Use according to Claim 19, where the monomer is such that the polymerizable group is incoφorated in the base chain of the polymer, while at least the part of the monomer that contains the oxime-protected isocyanate group forms a side chain of the polymer.

21. Polymer that is curable/cross-linkable under the influence of UV radiation, comprising a polymeric base chain and at least one side chain, where the side chain contains at least one oxime-protected isocyanate group with the formula

- R₃ - ΝH - CO - O - Ν = CR,R₂ (I)

where R,, R₂ and R₃ are as described in Claims 1-11, and/or R,, R₂ and R₃ are as described in Claims 1-8 and R₃ is a side chain of the polymer.

22. Polymer according to Claim 21, being an acrylate polymer.

23. Polymer according to Claim 21 or 22, which also contains a side chain with functional epoxide groups. 24. Monomer, for the production of polymers cross-linkable under the influence of UV and/or of polymers for giving UV curability to polymeric compositions, which contains at least one oxime-protected isocyanate group with formula I

- R₃ - NH - CO - O - N = CR,R₂ (I)

where R,, R₂ and R₃ are as described in Claims 1-11, and a further polymerizable group,

and/or where R, and R₂ are as described in Claims 1-8 and R₃ is a monomer, a structural unit which can be used as a monomer, or a structural unit which includes a polymerizable group.

25. Monomer according to Claim 24, where the monomer is such that the polymerizable group is incoφorated in the base chain of the polymer, while at least the part of the monomer that contains the oxime-protected isocyanate group forms the side chain of the polymer.

26. Cross-linker, including at least one oxime-protected isocyanate group with the formula

- R₃ - NH - CO - O - N = CR,R₂ (I)

where R,, R₂ and R₃ are as described in Claims 1-11, and at least one further cross-linking group, or where R, and R₂ are as described in Claims 1-8 and R₃ is a cross- linker, a structural unit which because of the additional presence of the oxime- protecting [sic] isocyanate group can be used as a cross-linker, or a structural unit which contains a further cross-linking group. 27. Use, according to one of Claims 1-12 or 13-20, of a polymer according to one of Claims 21-23 or of a cross-linker according to Claim 26, for giving UV curability to polymeric coating compositions and/or for producing UV- curable polymeric coating compositions.

28. Use according to Claim 27, for giving UV curability to polymeric powder coatings and/or for producing UV-curable polymeric powder coatings.

29. UV-curable polymeric composition, obtained or obtainable by the use according to one of Claims 1-12, 13-20 or 27-28, or including a polymer according to Claims 21-23 or of a cross-linker according to Claim 26.

30. UV-curable polymeric composition according to Claim 29, being a coating composition.

31. UV-curable polymeric composition according to Claim 29 or 30, being a powder coating.

32. Method for the curing/cross-linking of a polymeric composition according to one of Claims 29-31 , or for the curing/cross-linking of a polymer according to one of Claims 21-23, including the exposure of the polymeric composition or the polymer to suitable UV radiation.

33. Method according to Claim 31, where the curing/cross-linking is carried out at a temperature of less than 130°C, more particularly less than 110°C.

34. Cured polymeric product, obtained or obtainable by the method of Claims 32-33.

35. Product according to Claim 34, being a coating and/or a coated product/substrate. 36. Use of oximes with formula II

HO - N = CR,R₂ (II)

wherein at least one of the groups R, and/or R₂ includes or carries a UN-absorbing group as described above, for the protection of isocyanate groups in compounds, in particular in polymers, in order to provide these compounds/polymers with UV curability.

37. Use of a UV-activating agent in a composition which contains at least one further compound with an oxime-protected isocyanate group with formula I,

- R₃ - ΝH - CO - O - Ν = CR,R₂ (I)

where R,, R₂ and R₃ can be as defined in Claims 1-11, where the UV-activating agent makes the group ( ΝH - CO - O - Ν = C ) susceptible to cleavage under the influence of UV radiation.

38. Use according to Claim 37, where the further compound with the oxime-protected isocyanate group according to formula I is a polymer with the oxime-protected isocyanate group in the side chain.

39. Polymeric composition, containing at least a polymer with oxime-protected isocyanate groups with formula I,

- R₃ - ΝH - CO - O - Ν = CR,R₂ (I)

where R,, R₂ and R₃ can be as defined in Claims 1-11, in the side chain, as well as a UV-activating agent which makes the group ( ΝH - CO - O - Ν = C ) susceptible to cleavage under the influence of UV radiation.