In a preferred embodiment, the photo-initiator compound includes, consists of, or consists essentially of one or more α-hydroxy ketone photo-initiators. For instance, suitable α-hydroxy ketone photo-initiators are α-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropanone, 2-hydroxy-2-methyl-1-(4-isopropylphenyl)propanone, 2-hydroxy-2-methyl-1-(4-dodecylphenyl)propanone, 2-Hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one and 2-hydroxy-2-methyl-1-[(2-hydroxyethoxy)-phenyl]propanone.

In another embodiment, the photo-initiator compound includes, consists of, or consists essentially of: one or more α-aminoketones, such as 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-(4-methylbenzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone or 2-benzyl-2-(dimethylamino)-1-[3,4-dimethoxyphenyl]-1-butanone; one or more ketal compounds, for example 2,2-dimethoxy-1,2-diphenyl-ethanone; and one or more monomeric or dimeric phenylglyoxylic acid esters, such as methylphenylglyoxylic acid ester, 5,5′-oxo-di(ethyleneoxydicarbonylphenyl) or 1,2-(benzoylcarboxy)ethane.

Yet further suitable photo-initiators (D) include oxime esters, such as those disclosed in U.S. Pat. No. 6,596,445. Still another class of suitable photo-initiators (D) include, for example, phenyl glyoxalates, for example those disclosed in U.S. Pat. No. 6,048,660.

In another embodiment, the photo-initiator compound may comprise, consist of, or consist essentially of one or more alkyl-, aryl-, or acyl-substituted compounds not mentioned above herein.

According to another embodiment, the composition may contain a photo-initiator that is an alkyl-, aryl-, or acyl-substituted compound. In an embodiment the alkyl-, aryl-, or acyl-substituted photo-initiator possesses or is centered around an atom in the Carbon (Group 14) group. In such instance, upon excitation (via absorption of radiation) the Group 14 atom present in the photo-initiator compound forms a radical. Such compound may therefore produce a radical possessing or centered upon an atom selected from the group consisting of silicon, germanium, tin, and lead. In an embodiment, the alkyl-, aryl-, or acyl-substituted photo-initiator is an acylgermanium compound. Such photo-initiators are described in, U.S. Pat. No. 9,708,442. Known specific acylgermanium photo-initiators include benzoyl trimethyl germane (BTG), tetracylgermanium, or bis acyl germanoyl (commercially available as Ivocerin® from Ivoclar Vivadent AG, 9494 Schaan/Liechtenstein).

Photo-initiators according to the present invention may be employed singularly or in combination of one or more as a blend. Suitable photoinitiator blends are for example disclosed in U.S. Pat. No. 6,020,528 and U.S. Pat. app. No. 60/498,848. According to an embodiment, the photo-initiator compound includes a photo-initiator blend of, for example, bis(2,4,6-trimethylbenzoyl) phenyl phosphine oxide (CAS #162881-26-7) and 2,4,6,-trimethylbenzoylethoxyphenylphosphine oxide (CAS #84434-11-7) in ratios by weight of about 1:11, 1:10, 1:9, 1:8 or 1:7.

Another especially suitable photo-initiator blend is a mixture of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide, 2,4,6,-trimethylbenzoylethoxyphenylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone (CAS #7473-98-5) in weight ratios of for instance about 3:1:15 or 3:1:16 or 4:1:15 or 4:1:16. Another suitable photoinitiator blend is a mixture of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone in weight ratios of for instance about 1:3, 1:4 or 1:5.

Sensitizers for a sensitizer/H-donor system are compound like for example benzophenones, such as benzophenone, 2,4,6-trimethylbenzophenone, 4-methylbenzo-phenone, 2-methylbenzophenone, 2-methoxycarbonylbenzophenone, 4,4′-bis(chloromethyl)-benzophenone, 4-chlorobenzophenone, 4-phenylbenzophenone, 4,4′-bis(dimethylamino)-benzophenone, 4,4′-bis(diethylamino)benzophenone, methyl2-benzoylbenzoate, 3,3′-dimethyl-4-methoxybenzophenone, 4-(4-methylphenylthio)-benzophenone, 2,4,6-trimethyl-4′-phenyl-benzophenone or 3-methyl-4′-phenyl-benzophenone; Thioxantones such as for example thioxanthone and substituted thioxanthones like isopropylthioxantone and chlorothioxanthone.

In a sensithizer/H-donor system, the H-donors are preferably amines. Most preferably tertiary amines. The amines can be aromatic or aliphatic. A suitable example of an aromatic amine is ethyl 4-N,N-dimethylamino benzoate. Suitable examples of small aliphatic tertiary amines are compounds like N,N-dimethyl ethanol amine, N-methyl diethanol amine and triethanol amine. Also the Michael-addition products of amines with (meth)acrylates can be very suitable. For example the addition product of amonia with 3 equivalent of a diacrylate like diethylene glycol diacrylate, i.e. an acrylate functional tertiary aliphatic amine is can be very suitable. Other amines like for example ethanol amine, ethylene diamine, N-methyl ethanol amine can be used in the Michael addition as well, all being able to yield acrylate functional amines as H-donor, also called amine synergist.

One or more of the aforementioned photo-initiators can be employed for use in the photoinitiator compound in compositions according to the present invention in any suitable amount and may be chosen singly or in combination of one or more of the types enumerated herein. In a preferred embodiment, the photo-initiator compound comprises, consists of, or consists essentially of free radical photo-initiators. In an embodiment, the photo-initiator compound is present in an amount, relative to the entire weight of the composition, of from about 0.1 wt. % to about 10 wt. %, or from about 0.1 wt. % to about 5 wt. %, or from about 1 wt. % to about 5 wt. %.

Preferably, the one or more photo-initiators present in the composition according to the invention are α-cleavage photo-initiators. Even more preferably the one or more photo-initiators present in the composition according to the invention are an α-hydroxy ketone and/or an acyl phosphine oxide.

The composition according to the invention comprises one or more thermal initiators (E). A thermal initiator is a compound that chemically changes due to the action of increasing temperature to produce at least one of a radical, an acid, and a base. In the present invention, the one or more thermal initiators (E) are free radical thermal initiators. Suitable examples of free radical thermal initiators are for instance azo-compounds and peroxides. The free radical thermal initiator can be a single initiator or mixtures of initiators. The activity of thermal initiators can be characterized in many ways. As a minimum stability is required, i.e. the thermal initiator should not initiate the polymerization before the UV-initiation has taken place, a suitable way to select preferred thermal initiators is via the 0.1 hr half-life temperature, i.e. the temperature at which 50% of the thermal initiator has generated radicals in 0.1 hr.

The one or more thermal initiators (E) are preferably selected from the group consisting of free radical thermal initiators having a 0.1 hour half-life temperature equal to or greater than 70° C., more preferably equal to or greater than 75° C., more preferably equal to or greater than 80° C., and even more preferably equal to or greater than 85° C. and preferably lower than 280° C., more preferably lower than 250° C., even more preferably lower than 220° C. and even more preferably lower than 200° C. For ensuring a good reactivity during the thermal curing step, the free radical thermal initiator preferably has a 0.1 hr half-life temperature equal to or lower than 280° C., more preferably equal to or lower than 250° C., more preferably equal to or lower than 220° C., and most preferably equal to or lower than 200° C.

The thermal curing step can take place immediately after having carried out the UV-cure but also much later. During this storage of the UV-cured coating composition comprising the thermal initiator, it is preferred that the temperature at which the UV-cured formulation is stored is such that it is below the preferred maximum storage temperature of the thermal initiator. Therefore the thermal initiator preferably has a maximum storage temperature equal to or greater than 5° C., preferably equal to or greater than 10° C. more preferably equal to or greater than 15° C., even more preferred equal to or greater than 20° C. or equal to or greater than 25° C.

Without wishing to be bound by theory, it is hypothesized that in the UV cured coating composition, especially when the UV cure has resulted in a tack free formulation, that the solid nature of the UV cured formulation increases the ability to safely store the substrates containing the partially cured coating. As example, as demonstrated in the experimental part, a formulation comprising tert-amyl peroxy-2-ethylhexanoate (Trigonox 121) having a maximum storage temperature of 5° C., could after UV cure be stored for at least 24 hr at room temperature before applying the thermal process step.

A person skilled in the art can, using for example the brochure “Initiators for thermoplastics” by Nouryon February 2021, determine which peroxides and/or azo compounds are best suited for the thermal process at hand, especially since both time and temperature, during the thermal process step might vary.

Suitable thermal initiators are for example carbonates like mono- and di-percarbonates, peresters, peranhydrides, perketals, hydroperoxides and azo compounds.

Examples of suitable di-percarbonates are for instance: di(4-tert-butylcyclohexyl) peroxydicarbonate, Perkadox 16 (Maximum storage temperature 20° C., 0.1 hr half life temperature 82° C.); diacetyl peroxydicarbonate, Perkadox 24 (Maximum storage temperature 20° C., 0.1 hr half life temperature 84° C.); dimyristyl peroxydicarbonate, Perkadox 26 (Maximum storage temperature 15° C., 0.1 hr half life temperature 84° C.).

Examples of suitable monopercarbonates are for instance: tert-butylperoxy isopropyl carbonate, Trigonox BPIC-C75 (Maximum storage temperature 25° C., 0.1 hr half life temperature 137° C.); tert-butylperoxy 2-ethylhexyl carbonate, Trigonox 117 (Maximum storage temperature 20° C., 0.1 hr half life temperature 137° C.).

Examples of suitable peranhydrides are for instance: dilauroyl peroxide, Laurox (Maximum storage temperature 30° C., 0.1 hr half life temperature 99° C.); didecanoyl peroxide, Perkadox SE-10 (Maximum storage temperature 10° C., 0.1 hr half life temperature 100° C.); dibenzoyl peroxide, Perkadox L-W75 (Maximum storage temperature 40° C., 0.1 hr half life temperature 113° C.).

Examples of suitable peresters are for instance: 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, Trigonox 421 (Maximum storage temperature 5° C., 0.1 hr half life temperature 109° C.); tert-amyl peroxy-2-ethylhexanoate, Trigoxox 121 (Maximum storage temperature 5° C., 0.1 hr half life temperature 111° C.); tert-butyl peroxy-2-ethylhexanoate, Trigonox 21S (Maximum storage temperature 10° C., 0.1 hr half life temperature 113° C.); tert-butyl peroxy-3,5,5-trimethylhexanoate, Trigonox 42S (Maximum storage temperature 25° C., 0.1 hr half life temperature 135° C.); tert-amyl peroxybenzoate, Trigonox 127 (Maximum storage temperature 20° C., 0.1 hr half life temperature 139° C.); tert-butyl peroxybenzoate, Trigonox C (Maximum storage temperature 25° C., 0.1 hr half life temperature 142° C.).

Examples of suitable perketals are for instance: 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, Trigonox 29 (Maximum storage temperature 25° C., 0.1 hr half life temperature 128° C.); 1,1-di(tert-butylperoxy)cyclohexane Trigonox 22B50 (Maximum storage temperature 25° C., 0.1 hr half life temperature 134° C.); 2,2-di(tert-butylperoxy)butane, Trigonox D-C50 (Maximum storage temperature 30° C., 0.1 hr half life temperature 136° C.); butyl 4,4-di(tert-butylperoxy)valerate, Trigonox 17 (Maximum storage temperature 30° C., 0.1 hr half life temperature 143° C.); dicumyl peroxide, Perkadox BC-FF (Maximum storage temperature 30° C., 0.1 hr half life temperature 154° C.); tert-butyl cumyl peroxide, Trigonox T (Maximum storage temperature 40° C., 0.1 hr half life temperature 159° C.).

Examples of suitable azo compounds are for instance: 2,2′-azodi(isobutyronitrile), Perkadox AIBN (Maximum storage temperature 25° C., 0.1 hr half life temperature 101° C.); 2,2′-azodi(2-methylbutyronitrile), Perkadox AMBN-GR (Maximum storage temperature 25° C., 0.1 hr half life temperature 104° C.); 1,1′-azodi(hexahydrobenzonitrile), Perkadox ACCN (Maximum storage temperature 35° C., 0.1 hr half life temperature 123° C.).

The one or more thermal initiators (E) preferably comprises an initiator selected from the group of monopercarbonates, peresters and/or peranhydrides. More preferably, the one or more thermal initiators (E) present in the inventive coating composition are selected from the group consisting peresters, monopercarbonates, peranhydrides or any mixture thereof.

Next to the thermal initiator also an accelerator or accelerator mixture for facilitating decomposition of the thermal initiator might be present. As accelerator various compounds can be used. Especially transition metals, for example selected from the group of V, Cr, Mn, Fe, Co, Ni, Cu salts and complexes and any mixture thereof can be selected as accelerator.

The thermal initiator may be present in a thermal initiator composition. In a preferred embodiment, the thermal initiator composition consists of, or consists essentially of free radical thermal initiators. In an embodiment, the thermal initiator is present in an amount, relative to the entire weight of the coating composition, of from about 0.1 wt. % to about 10 wt. %, or from about 0.1 wt. % to about 5 wt. %, or from about 1 wt. % to about 5 wt. %.

The inventive coating composition preferably further comprises one or more thermal cure retarders. Examples of suitable thermal cure retarders are for example compounds like phenotiazines like for example phenothiazine and substituted derivatives; phenols like for example p-methoxy phenol (Mequinol), 2,6-di-t-butyl phenol, 2,6-di-t-butyl-4-methyl phenol (BHT), tocopherol; Hydroquinone like for example hydroquinone, 2-methyl hydroquinone (MeHQ), 2-t-butyl hydroquinone, 2,3-dimethyl hydroquinone, 2,5-dimethyl hydroquinone, 2,6-dimethyl hydroquinone, trimethyl hydroquinone; catechols like for example catechol, 4-t-butyl catechol, benzoquinones like for example benzoquinone, 2-methyl benzoquinone; orthoquinones like for example orthoquinone, 3-methyl orthoquinone, pyrogallols like for example pyrogallol, gallic acid, propyl gallate; stable radicals like for example N-oxyl radicals, for example compounds like Tempo, Tempol, Proxyl, Doxyl and derivatives. Instead of a single thermal cure retarder, mixtures of thermal cure retarders can be used as well.

Preferably at least one of the thermal cure retarders present in the coating composition according to the invention is selected from the group of (substituted) phenols, hydroquinones, pheonols, catchols, benzoquinones and orthoquinones, more preferably selected from the group of (substituted) hydroquinones, catchols and benzoquinones and even more preferably the one or more inhibitors are selected from the group consisting of alkyl substituted hydroquinones, alkyl substituted phenols, alkoxy substituted phenols, alkyl substituted catechols, alkyl substituted benzoquinones, alkyl substituted orthoquinones and mixtures thereof.

The present invention further relates to a method for obtaining a coated substrate, wherein the method comprises

- (1) providing a substrate having a major surface,
- (2) applying the radical-curable coating composition as defined herein above on at least a portion of the major surface of the substrate in a layer thickness preferably in the range of from 0.1 micron to 1 mm, and
- (3) photo-curing of the coating composition to obtain a substrate with a partially cured coating, and
- (4) thermally curing the partially cured coating to obtain the coated substrate.

Suitable substrates for the process according to the invention are for example mineral substrates such as fiber cement board, wood, wood containing materials, paper including cardboard, textile, leather, metal, thermoplastic polymer, thermosets, ceramic, glass. Suitable thermoplastic polymers are for example polyvinylchloride PVC, polymethylmethacrylate PMMA, acrylonitrile-butadiene-styrene ABS, polycarbonate, polypropylene PP, polyethylene PE, polyamide PA and polystyrene. Suitable thermosets are for example linoleum, epoxy, melamine, novolac, polyesters and urea-formaldehyde.

Preferred substrates are flat (i.e. not containing sharp edges or angles <150° in the surface to be coated) and non-porous substrate (i.e. not so porous that the coating composition when it is applied would essentially only penetrate into the substrate). The substrate is optionally pre-treated and/or optionally pre-coated. For example, thermoplastic plastic films can be treated with corona discharges before application or pre-coated with a primer. Mineral building materials are also usually provided with a primer before the coating composition is applied.

The photo-curing step (3) is preferably carried out applying an UV dose ranging from 0.02 J/cm²to 10 J/cm². The UV dose is preferably at least 0.05 J/cm², more preferably at least 0.1 J/cm², even more preferably at least 0.2 J/cm², even more preferably at least 0.6 J/cm². The UV dose is preferably lower than 9 J/cm², more preferably lower than 8 J/cm². According to an embodiment of the invention, the UV dose is in the range of from 1 J/cm²to 5 J/cm².

The photo-curing can be performed in air or under inert conditions like under a nitrogen blanket. Performing the photo-curing under a nitrogen blanket is preferred when the photo-cured coated substrate is stored for a period of time prior to carrying out the thermal process step (4).

The thermal cure step (4) is preferably carried out at a temperature in the range from 100° C. to 300° C. The temperature during the thermal cure step is preferably higher than 125° C., more preferably higher than 150° C. and preferably lower than 275° C., more preferably lower than 250° C.

Preferably the thermal cure step (4) is carried out while hot pressing the partially cured coating, more preferably the hot pressing is carried out on a stack that comprises the substrate with the partially cured coating obtained in step (3). The hot pressing may carried out with the help of a structured pressing element wherein a relief is formed in the coating. The thermal cure step (4) can suitable be carried out in a laminating step in which the coated substrate is laminated onto another material. An example of such a process is laminating a coated paper onto a thin wooden substrate or a vinyl tile. The thermal cure step (4) can also be suitable performed in an embossing step. This is especially useful for the production of materials with a structured surface. Lamination and embossing can also be performed in the thermal cure step (4).

The inventive coating composition can in particular advantageously be used on a floor or on furniture, on window frames or on façade panels.

The coated substrate obtained with the method of the invention is preferably a coated panel, more preferably a furniture panel or a floor panel.

The invention further relates to objects comprising or coated with a coated substrate obtained with the method of the invention.

The present invention is now illustrated by reference to the following examples. Unless otherwise specified, all parts, percentages and ratios are on a weight basis.

Table 1 describes the various components used for preparing the compositions used in the present examples.

TABLE 1

Molar

mass
Functionality
Amount and type

Resins
Supplier
Type
(g/mol)
(theor.)
of inhibitor

NeoRad ™ U-25
DSM
Urethane
1300
2
100-1000 ppm

(neat)
Coating
acrylate

2,6-di-t-butyl-4-

Resins

methyl phenol

B.V.

(BHT)

AgiSyn ™ 230A2
DSM
Urethane
1000
6
100-1000 ppm

Coating
acrylate

BHT

Resins

B.V.

NeoRad ™ U-65
DSM
Urethane
1700
6
100-1000 ppm

(neat)
Coating
acrylate

BHT

Resins

B.V.

AgiSyn ™ 670T 1
DSM
Urethane
1600
2
<3000 ppm BHT

Coating
acrylate

Resins

B.V.

AgiSyn ™ 730
DSM
Polyester
1500
4
<1000 ppm 2-

Coating
acrylate

methyl

Resins

hydroquinone

B.V.

(MeHQ)

AgiSyn ™ 705
DSM
Polyester
1300
4
<3000 ppm

Coating
acrylate

Mequinol

Resins

B.V.

AgiSyn ™ 9760
DSM
Novolac
1500
3
100-1000 ppm

(supplied in 50%
Coating
glycidyl epoxy

MeHQ

TMPTA)
Resins
acrylate

B.V.

AgiSyn ™ 2020
DSM
Epoxidized
1100
2
100-1000 ppm

Coating
soy bean oil

MeHQ

Resins
acrylate

B.V.

Resinous reactive

diluents

NeoRad ™ P-11
DSM
Polyester
750
3
<3000 ppm

Coating
acrylate

p-methoxy phenol

Resins

(Mequinol)

B.V.

AgiSyn ™ 1010
DSM
Bisphenol A
500
2
100-1000 ppm

Coating
glycidyl epoxy

MeHQ

Resins
acrylate

B.V.

Reactive diluents

BMA (butyl
Aldrich
Methacrylate
142
1
1000 ppm

methacrylate)

diluent

methoxyphenol

TEGDMA
Aldrich
Methacrylate
286
2
100 ppm MeHQ

(triethyleneglycol

diluent

dimethacrylate)

TMP(EO)₉TMA
KPX
Methacrylate
724
3
100-300 ppm

(Ethoxylated (9)
Green
diluent

MeHQ

Trimethylolpropane
Chemical

trimethacrylate,
Co., Ltd.

Komerate T093M)

PPTTMA (penta
KPX
Methacrylate
610
4
100-300 ppm

ethoxylated
Green
diluent

MeHQ

pentaerythritol tetra
Chemical

methacrylate,
Co., Ltd.

Komerate M044M)

LA (Lauryl acrylate,
DSM
Acrylate
240
1
60-100 ppm

AgiSyn ™ 2896)
Coating
diluent

Methoxy phenol

Resins

B.V.

DPGDA (Dipropylene
DSM
Acrylate
242
2
400-800 ppm

glycol diacrylate,
Coating
diluent

MeHQ

AgiSyn ™ 2833)
Resins

B.V.

TMPTA
DSM
Acrylate
296
3
100-300 ppm

(Trimethylolpropane
Coating
diluent

MeHQ

triacrylate, AgiSyn ™
Resins

2811)
B.V.

GPTA (glycerol
DSM
Acrylate
428
3
200-500 ppm

propoxylate
Coating
diluent

MeHQ

triacrylate, AgiSyn ™
Resins

2837)
B.V.

PPTTA
DSM
Acrylate
55
4
200-600 ppm

(pentaethoxylated
Coating
diluent

MeHQ

pentaerythritol
Resins

tetraacrylate,
B.V.

AgiSyn ™ 2844)

Photoinitiators

Omnirad 1173
IGM
α-hydroxy

Resins
ketone

Omnirad TPO-L
IGM
Monoacyl

Resins
phosphine oxide

Omnirad BP
IGM
Benzophenone

Resins

AgiSyn ™ 002
DSM
Amine synergist

Coating

Resins

B.V.

Thermal initiators

MBPO (4-methyl
Nouryon
Peranhydride

benzoyl peroxide,

powder with 25%

water, Perkadox

PM-W75)

LPO (Lauroyl
Nouryon
Peranhydride

peroxide, Laurox S)

TBPEH (t-butyl
Nouryon
Perester

peroxy 2-

ethylhexanoate,

Trigonox 21S)

TAPEH (t-amyl
Nouryon
Perester

peroxy 2-

ethylhexanoate,

Trigonox 121)

TBH (t-butyl
Nouryon
Hydroperoxide

hydroperoxide,

Trigonox A-80)

Preparation of Urethane (Meth)Acrylate Oligomers 1 to 3

Urethane (meth)acrylate oligomers 1 to 3 used herein were prepared using the molar amounts specified below. After charging the diisocyanate, the catalyst (100 ppm, Dibutyltin dilaurate DBTDL, obtained from Evonik), and the stabilizer (250 ppm BHT, Aldrich) into the reactor, the hydroxy-functional compounds were added sequentially after completion of the previous urethane reaction.

Urethane acrylate resin 1 (Resin 1): 2 mols isophorone diisocyanate IPDI (obtained from Covestro AG), 1 mol PPG₂₀₀₀(bifunctional polypropylene glycol with a theoretical molar mass of 2000, obtained from Covestro AG) and 2 mols 2-hydroxyethyl acrylate HEA (obtained from Aldrich) resulting in HEA-IPDI-PPG₂₀₀₀-IPDI-HEA as idealized structure and with a calculated theoretical molar mass of 2676 g/mol and an acrylate functionality of 2.

Urethane methacrylate resin 2 (Resin 2): 2 mols IPDI, 1 mol PPG₂₀₀₀and 2 mols 2-hydroxymethyl acrylate HEMA (obtained from Aldrich) resulting in HEMA-IPDI-PPG 2000-IPDI-HEMA as idealized structure and with a calculated theoretical molar mass of 2704 g/mol and a methacrylate functionality of 2.

Urethane acrylate resin 3 (Resin 3): 3 mols toluene diisocyanate TDI (obtained from Covestro AG), 2 mols PPG₂₀₀₀and 2 mols ethoxylated (5) trimethylolpropane diacrylateTMP(EO)₅DA (with a theoretical molar mass of 462 obtained from DSM Resins) resulting in TMP(EO)₅DA-TDI-PPG₂₀₀₀-TDI-PPG₂₀₀₀-TDI-TMP(EO)₅DA as idealized structure and with a calculated theoretical molar mass of 5446 g/mol and an acrylate functionality of 4.

Preparation of the Formulations

The ingredients listed in Table 2 to 11 were added into a HDPP jar and mixed thoroughly using a speedmixer (DAC 150.1 FV, Hauschield GmbH) for 2 min @ 3500 rpm.

Application and Curing of the Formulations

The formulations were applied as a 100 micron wet layer on a melamine impregnated paper (ex Schattdecor GmbH).

- UV Cure: Within 20 seconds after application, the formulations were UV cured under nitrogen (<100 ppm O₂) on a UVio curing rig with a conveyor belt speed of 60 m/min (unless otherwise stated) using a 240W Hg lamp at 50% power (LightHammer Mark III ex Heraeus Holding, Hg doped UV lamp generating UV light with wave lengths ≥300 nm, 86 mJ/cm²total dose as determined with am Power Puck II (EIT Inc)).
- Thermal Cure: The coated and UV cured papers were thermally laminated on high-density fibreboard HDF board and cured using a lamination press (LAP20, ex Joos GmbH) during 60 seconds, at 210° C. (upper surface only) with a force of 45 kg/cm².

Evaluations of the Coatings

24 hrs after UV cure, the coating was evaluated regarding visual appearance, surface quality and tack. 24 hrs after the subsequent thermal cure, the final appearance was visually evaluated. 0 being very bad and 5 very good. Only rating of 4 and 5 are considered acceptable.

Calculation of Average Functionality of (Meth)Acrylate Reactive Diluents

The average (meth)acrylate functionality of the (meth)acrylate reactive diluents with a molar mass as defined for (B) and (C) (less than 800 g/mol) (further referred to as calculated average functionality of (meth)acrylate diluents) is calculated according to

f
¯

=

∑

k

⁢

w
k

M
k

⁢

f
k

∑

k

⁢

w
k

M
k

,

in which w_kis the amount of (meth)acrylate reactive diluents in g present in the radiation curable coating composition with a specific molar mass M_kas defined for (B) (or (C)) and with a specific (meth)acrylate functionality f_kwhich can be 2 or lower or higher 2. We illustrate this calculation with a theoretical example for an acrylate reactive diluent mixture: For a formulation consisting of 60 grams of urethane acrylate oligomer having molar mass >800 g/mol, 30 grams of DPGDA (having molar mass 242 g/mol and acrylate functionality of 2), 10 grams of ditrimethylolpropane tetraacrylate Di-TMPTA (having molar mass 466 g/mol and acrylate functionality of 4), and 2.5 grams of photoinitiator: the summation over components k includes only DPGDA and Di-TMPTA and the calculated average functionality of acrylate diluents of this theoretical formulation is

f
¯

=

30
⁢

g

242
⁢

g
mol

×
2

+

10
⁢

g

466
⁢

g
mol

×
4

30
⁢

g

242
⁢

g
mol

+

10
⁢

g

466
⁢

g
mol

=

2
.
3
.

Calculation of Molar Acrylate/Methacrylate Ratio in the Reactive Diluent(s) (Molar A/M Ratio in RD)

The molar amount of acrylate functionalities in the acrylate reactive diluents is divided by the molar amount of methacrylate functionalities in the methacrylate reactive diluents.

We illustrate this calculation with the following theoretical example:

- For a formulation consisting of 70 grams of AgiSyn™ 670T1 (urethane acrylate oligomer having molar mass >800 g/mol), 12.5 grams of GPTA (having a molar mass of 428 g/mol and an acrylate functionality of 3), 2.5 grams of DPGDA (having a molar mass of 242 g/mol and acrylate functionality of 2), 12.5 grams of TMP(EO)9TMA (having a molar mass of 724 g/mol and a methacrylate functionality of 3), 2.5 grams of TEGDMA (having a molar mass of 286 g/mol and a methacrylate functionality of 2), 0.15 grams Omnirad 1173 and 0.5 grams
- MBPO: The acrylate reactive diluents are GPTA and DPGDA, the methacrylate reactive diluents are TMP(EO)9TMA and TEGDMA. The calculation of the molar acylate/methacrylate ratio is as follows

=

(

3
*
12.5

g

428
⁢

g
/
mol

+

2
*
2.5

g

242
⁢

g
/
mol

)

(

3
*
12.5

g

724
⁢

g
/
mol

+

2
*
2.5

286
⁢

g
/
mol

)

=

1.56
.

Tables 2 to 11 give the relative amounts of the components used to prepare the formulations of the Examples and the Comparative Experiments and report the evaluation of the coatings obtained with these formulations.

Example 1 and Comparative Experiments C1-C6; Variation in Reactive Diluent

TABLE 2

Ex 1
C1
C2
C3
C4
C5
C6

NeoRad ™ U-25
70
70
70
70
70
70
70

(neat)

TEGDMA

30

TMP(EO)₉TMA
15

30

PPTTMA

30

DPGDA

30

GPTA
15

30

PPTTA

30

Molar A/M
1.7
NA
NA
NA
0
0
0

ratio in RD

Omnirad 1173
0.15
0.15
0.15
0.15
0.15
0.15
0.15

MBPO
0.50
0.50
0.50
0.50
0.50
0.50
0.50

After UV
Wrinkles
Wet
Fine
Wrinkles
Smooth
Smooth
Smooth

wrinkles

Surface
Tack
Wet
Tack
Tack
Tack
Tack
Tack

free

free
free
free
free
free

Score
4
0
4
4
5
5
5

Final
Good
Coating
Flaking
Flaking
Cracking,
Cracking,
Cracking,

Appearance

sunk in

blistering,
blistering,
blistering,

paper

flaking
flaking
flaking

and
and
and

delamination
delamination
delamination

Final score
5
0
2
2
1
1
1

These results clearly indicate that good final results can only be obtained in the presence of both a methacrylate functional reactive diluent and an acrylate functional reactive diluent. In C4-C6 it is further shown that a smooth tack free surface after UV cure does not guarantee a good final coating

TABLE 3

Molar

Resin
mass
F
E2
E3
E4
E5
E6
E7
C7
C8
C9
C10
C11

NeoRad ™
1300
2
70

U-25

AgiSyn ™
1000
6

70

230A2

NeoRad ™
1700
6

70

U-65

Resin 1
2676
2

70

Resin 2
2704
2

70

AgiSyn ™
1100
2

70

2020

epoxy Soy

oil - AA

Resin 3
5446
4

70

AgiSyn ™
1500
4

70

730

Polyester

acrylate

AgiSyn ™
1300
4

70

705

Polyester

acrylate

AgiSyn ™
500
2

70

1010

BADGE-AA

AgiSyn ™
1500
3

42.5

9760 (50%

in TMPTA)

novolac

epoxy

acrylate

TMP(EO)₉TMA
724
3
15
15
15
15
15
15
15
15
15
15
15

TMPTA (via
296
3

42.5

AgiSyn ™

9760)

GPTA
428
3
15
15
15
15
15
15
15
15
15
15

Molar A/M

1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
6.9

ratio in

RD

Omnirad

0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15

1173

MBPO

0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50

After UV

Wrinkles
Some
Some
Many
Many
Many
Wet
Smooth
Some
Many
Many

wrinkles
wrinkles
wrinkles
wrinkles
wrinkles

wrinkles
wrinkles
wrinkles

Surface

Tack
Tack
Tack
Tacky
Tacky
Oily
Wet
Tack
Tack
Tacky
Tacky

free
free
free

free
free

Score

4
4
4
3
3
3
0
5
4
3
3

Final

Good
Few
Good
Good
Good
Few
Coating
Cracking,
Gloss
Cracking,
Gloss

Appearance

cracks

spots
sunk in
blistering,
defects
blistering,
defects

paper
flaking

flaking

and

and

delamination

delamination

Final score

5
4
5
5
5
4
0
1
3
1
3

These results clearly indicate that good final results can only be obtained with resins selected from the group of urethane (meth)acrylates or acrylated epoxidized triglycerides with a molar mass >800 and <4500.

Examples 8-13 and Comparative Experiments C12-C14: Variation in Amount of Reactive Diluents

TABLE 4

C12
E8
E9
E10
E11
E12
E13
C13
C14

AgiSyn ™ 670T1
90
80
70
60
50
40
30
20
10

TMP(EO)₉TMA
5
10
15
20
25
30
35
40
45

GPTA
5
10
15
20
25
30
35
40
45

Molar A/M
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7

ratio in RD

Omnirad 1173
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15

MBPO
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50

After UV
Smooth
Smooth
Smooth/
Smooth/
Slight
Slight
Slight
Slight
Slight

slight
slight
wrinkling
wrinkling
wrinkling
wrinkling
wrinkling

wrinkling
wrinkling

Surface
Tack
Tack
Tack
Tack
Tack
Tack
Tack
Slight
Slight

free
free
free
free
free
free
free
oily
tacky

Score
5
5
4-5
4-5
4
4
4
3
2

Final
Some
Good
Good
Good
Good
Some
Some
Some
Many

Appearance
delamination

blisters
blisters
blisters &
big and

cracks
small cracks

Final score
2
5
5
5
5
4
4
3
1

These results clearly indicate that good final results can only be obtained with an amount of reactive diluent of more than 10 wt. % and less than 80 wt. %.

Examples 14-17 and Comparative Experiments C15-C18: Variation in Reactive Diluent Functionality

TABLE 5

Molar

mass
f
C15
C16
E14
E15
C17
C18
E16
E17

AgiSyn ™ 670T1
1600
2
70
70
70
70
70
70
70
70

BMA
142
1

15

TEGDMA
286
2

15

TMP(EO)₉TMA
724
3
15
15
15
15

15

PTTMA
610
4

15

LA
240
1
15

DPGDA
242
2

15

GPTA
428
3

15

15
15
15
15

PPTTA
550
4

15

Molar A/M

1.0
2.3
1.7
1.8
1.0
1.0
1.7
1.1

ratio in RD

Omnirad 1173

0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15

MBPO

0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50

After UV

Wet
Slight
Slight
Smooth
Wet
Wet
Slight
Smooth

wrinkling
wrinkling

wrinkling

Surface

Wet
Slight
Tack
Tack
Wet
Wet
Tack
Tack

tacky
free
free

free
free

Score

0
3
4
5
0
0
4
5

Final

Coating
Big
Good
Good
Coating
Coating
Good
Good

Appearance

sunk in
blisters

sunk in
sunk in

paper

paper
paper

Final score

0
2
5
5
0
0
5
5

These results clearly indicate that good final results can only be obtained with reactive diluents having an average functionality higher than 2 both for the methacrylate as well as the acrylate.

Examples 18-21 and Comparative Experiments C19-C20: Variation in Molar A/M Ratio in Reactive Diluent

TABLE 6

Molar

mass
f
C19
E18
E19
E20
E21
C20

AgiSyn ™ 670T1
1600
2
70
70
70
70
70
70

TMP(EO)₉TMA
724
3
30
25
20
15
10
0

GPTA
428
3
0
5
10
15
20
30

Molar A/M

0
0.3
0.8
1.7
3.4
NA

ratio in RD

Omnirad 1173

0.15
0.15
0.15
0.15
0.15
0.15

MBPO

0.50
0.50
0.50
0.50
0.50
0.50

After UV

Slight
Slight
Slight
Slight
Slight
Smooth

wrinkling
wrinkling
wrinkling
wrinkling
wrinkling

Surface

Tack
Tack
Tack
Tack
Tack
Tack

free
free
free
free
free
free

Score

4
4
4
4
4
5

Final

Slight
Good
Good
Good
Good
Cracking,

Appearance

delamination

blistering,

flaking and

delamination

Final score

3
5
5
5
5
1

These results clearly indicate that good final results can only be obtained when the molar ratio of acrylate functionalities and methacrylate functionalities in the reactive diluent is higher than 0.2.

Examples 22-24 and Comparative Experiments C21-C22: Variation in Photo-Initiator

TABLE 7

Molar mass
f
E22
E23
E24
C21
C22

AgiSyn ™ 670T1
1600
2
70
70
70
70
70

TMP(EO)₉TMA
724
3
15
15
15
15
15

GPTA
428
3
15
15
15
15
15

Molar A/M

1.7
1.7
1.7
1.7
1.7

ratio in RD

Omnirad 1173

0.15

0.15
—

Omnirad TPO-L

0.15

—

Omnirad BP

0.15

AgiSyn ™ 002

0.50

MBPO

0.50
0.50
0.50
—
0.50

After UV

Slight
Slight
Slight
Slight
Wet

wrinkling
wrinkling
wrinkling
wrinkling

Surface

Tack
Tack
Tack
Tack
Wet

free
free
free
free

Score

4
4
4
4
0

Final

Good
Good
Good
Cracking,
Coating

Appearance

blistering,
sunk in

flaking and
paper

complete

delamination

Final score

5
5
5
0
0

These results clearly indicate that good final results can only be obtained when both a photo and a thermal initiator are present. Furthermore these results show that various photoinitiators can be used.

Examples 25-29: Variation in Thermal Initiator

TABLE 8

Molar mass
f
E25
E26
E27
E28
E29

NeoRad ™ U-25 (neat)
UA
1300
2
40
40
40
40
40

NeoRad ™ P-11
PE
750
3
20
20
20
20
20

TMP(EO)₉TMA

724
3
15
15
15
15
15

DPGDA

214
2
10
10
10
10
10

GPTA

428
3
15
15
15
15

PPTTA

550
4

15

Molar A/M

4.5
4.5
4.5
4.5
4.5

ratio in RD

Omnirad 1173

0.15
0.15
0.15
0.15
0.15

MBPO

0.50

0.50

LPO

0.50

TBPEH

0.50

TAPEH

0.50

TBH

After UV

Some
Some
Some
Some
Slight

wrinkles
wrinkles
wrinkles
wrinkles
wrinkles

Surface

Tack
Tack
Tack
Tack
Tack

free
free
free
free
free

Score

4
4
4
4
4

Final

Good
Good
Good
Good
Good

Appearance

Final score

5
5
5
5
5

Neorad ™ P-11 with an molar mass according to the brochure of 750 is here considered an acrylate functional reactive diluent. These results show that various peroxides can be used.

Examples 30-33 and Comparative Experiments C23-C27: Variation in Reactive Diluent

TABLE 9

C23
C24
E30
E31
C25
C26
C27
E32
E33

AgiSyn ™ 705
20
20
20
20
20
20
20
20
20

Resin
16.8
16.8
16.8
16.8
16.8
16.8
16.8
16.8
16.8

Tris (2-
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2

hydroxy ethyl)

isocyanurate

triacrylate

AgiSyn ™
50
50
50
50
50
50
50
50
50

670T1

BMA

15

TEGDMA

15

TMPTMA9EO
30
15
15
15

15

PPTTMA

15

LA

15

DPGDA

15

GPTA

15
30
15
15
15
15

average
3
3
3
3

1
2
3
4

methacrylate

functionality

RD

average
3
1.2
2.1
3
3
3
3
3
3

acrylate

functionality

RD

Molar A/M
0.18
1.4
2.6
2.1

1.2
1.2
2.1
1.3

ratio in RD

Omnirad 1173
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15

MBPO
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5

After UV
Slight
Slight
Some
Some
Some
Wet
Slight
Some
Some

wrinkling
wrinkling
wrinkles
wrinkles
wrinkles

wrinkling
wrinkles
wrinkles

Surface
Slight
Slight
Tack
Tack
Tack
Wet
Slight
Tack
Tack

tacky
tacky
free
free
free

tacky
free
free

Score
3
3
4
4
4
1
3
4
4

Final
Cracking
Coating
Some
Very
Cracking
Coating
Coating
Very
Very

Appearance

sunk in
irregular
few

sunk in
sunk in
few
few

paper
gloss
blisters

paper
paper
blisters
blisters

Final score
2-3
0
4
4
2-3
0
0
4
4

According to the MSDS AgiSyn ™ 705 contains on average 16 wt. % of tris (2-hydroxy ethyl) isocyanurate triacrylate which is an acrylate reactive diluent with a molar mass of 261 g/mol. These examples show that an average acrylate functionality of the reactive diluents RD of 2.1 is already sufficient for obtaining a good performance.

Examples 34-38 and Comparative Experiments C30-C31: Variation in Average (Meth)Acrylate Functionalities

TABLE 10

C30
E34
E35
E36
C31
E37
E38