SE1851613A1 - Method for coating a substate comprising a secondary amine - Google Patents

Abstract

There is provided a method of coating a substrate comprising at least one secondary amine, by contacting the substrate surface with a compound comprising at least one carbon-carbon double bond, wherein an electron withdrawing group is on at least one side of the carbon-carbon double bond, so that a complex is formed between nitrogen in the secondary amine and the carbon-carbon double bond. Then a reaction is initiated to form a covalent bond by reaction of nitrogen in the secondary amine and the carbon-carbon double bond, by subjecting at least a part of the substrate surface to actinic radiation, wherein the wavelength of the actinic radiation is adapted to be absorbed by the complex. When a further top-coat is added resulting surface has a high hardness, and the scratch resistance is improved.

Description

lO COÅT ING AND PRIMER Technical field The present invention relates generally to a coating or aprimer. A further coating, a top coating may or may not beapplied on the coating. The thin coating is made by forming acomplex between a secondary amine at the substrate surfaceand a carbon-carbon double bond in a molecule contacted withthe surface, and then initiating a reaction forming a covalent bond by irradiating the complex.

Background GB 2 542 629 discloses a curable primer composition comprising copolymer where components of the copolymer may besubstituted with an anhydride. The composition may furthercomprise a curable acrylate compound. The anhydride is not free but instead reacted to form the copolymer.

US 2003/01502767 discloses a primer composition comprising a polymer reacted with for instance maleic anhydride.

CN lO4945983 and CN 104945985 disclose monofunctional methacrylates forming polymer chains with maleic acid anhydride. There is in a first step formed a poly-anhydridewhich in a subsequent step reacts with epoxy. Thus, theanhydride is reacted to a poly-anhydride. Since monofunctional methacrylates are used, no cross-linked network is formed. In the introduction there is disclosedthat there is first synthesized an acrylic resin havingpendant anhydride groups, which is then subjected to amodified epoxy resin, epoxy-modified acrylic resin preparedby the preparation of one-component epoxy modified acrylic coatings having excellent adhesion, good hardness and gloss. lO Even the coatings and primers according to the state of theart are used today there is still room for an improvementregarding for instance the adhesion, at least for some materials.

CN lO65l99l9 discloses a UV-curing composition, which may be added to a melamine substrate. The composition may comprisefor instance an acrylate. A photoinitiator is present and initiates the curing reaction.

CN lO2558928 discloses a UV-curing coating composition whichcan be used to coat melamine substrates. The coating maycomprise different acrylates. A photoinitiator is present, initiating the curing reaction.

US 2010/272920 discloses a radiation curable compositionwhich may comprise acrylates. They may be used on a melamine substrate. A photoinitiator is present.

US 2010/l7844O discloses a UV-curable binder which may beapplied on a base material of melamine. A photoinitiator orpossibly another initiating mechanism such as e-beam is present.

US 2015/218408 discloses a process for coating sheets comprising applying a coating formulation to a sheet of paperwhich has been impregnated with melamine formaldehyde resins,carrying out at least partial radiation curing, and applyingat least one further radiation-curable coating material, andfinally carrying out complete curing by radiation. It shouldbe noted that the melamine formaldehyde resins are not cured when contacted with the coating formulation. lO CN lO6634543 discloses a UV-curing primer comprising acrylates which may be applied on melamine. A photoinitiator is present.

Summary It is an object of the present invention to obviate at least some of the disadvantages in the prior art and to provide an improved coating and/or primer.

In a first aspect there is provided a method of coating a substrate, a) said method comprising the steps of providing a substrate, said substrate comprising at least one secondary amine, at least a fractionof the at least one secondary amines is at the surface of the substrate, contacting the substrate surface with a compoundcomprising at least one carbon-carbon doublebond, wherein an electron withdrawing group is onat least one side of the carbon-carbon doublebond, so that a complex is formed betweennitrogen in the secondary amine and the carbon- carbon double bond, initiating a reaction to form a covalent bond byreaction of nitrogen in the secondary amine and the carbon-carbon double bond, by subjecting at least a part of the substrate surface to actinicradiation, wherein the wavelength of the actinicradiation is adapted to be absorbed by the complex.

In a second aspect there is provided a substrate coated according to the method above.

The inventors have unexpectedly found that a reaction can beinitiated between a secondary amine and a C=C double bondwith adjoining electron withdrawing groups. It is requiredthat actinic radiation reaches the substrate surface througha layer of applied solution, since the complexes are at thesubstrate surface. In the prior art photoinitiators or otherUV-blocking compounds are utilized in similar systems whichmakes this method impossible to use or impossible to observein most systems since no or too little actinic radiationreaches the complexes. The inventors believe that this is the reason for not having observed this effect before.

The invention is highly suitable for applications where animproved adhesion to various substrates is desired.instance meiamine and other substrates comprising a secondaryamine can successfully be coated. The adhesion of a subsequent top coat is greatly improved.

Further, in particular when a top coating is added on the coating, the resulting surface has a high hardness, and the scratch resistance is improved.

No photoinitiator is required. This is because the reaction is initiated by irradiating the complex.

Detailed description Before the invention is disclosed and described in detail, itis to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of lO describing particular embodiments only and is not intended tobe limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

It must be noted that, as used in this specification and the ll appended claims, the singular forms ”a", an” and ”the”include plural referents unless the context clearly dictates otherwise.

If nothing else is defined, any terms and scientificterminology used herein are intended to have the meaningscommonly understood by those of skill in the art to which this invention pertains.

As used herein (meth)acrylate is a general term that encompasses both acrylate and methacrylate.

In a first aspect there is provided a method of coating a substrate, said method comprising the steps of a)providing a substrate, said substrate comprising at least one secondary amine, at least a fractionof the at least one secondary amines is at the surface of the substrate, b)contacting the substrate surface with a compoundcomprising at least one carbon-carbon doublebond, wherein an electron withdrawing group is onat least one side of the carbon-carbon doublebond, so that a complex is formed between nitrogen in the secondary amine and the carbon- carbon double bond, c)initiating a reaction to form a covalent bond byreaction of nitrogen in the secondary amine and the carbon-carbon double bond, by subjecting at lO least a part of the substrate surface to actinicradiation, wherein the wavelength of the actinicradiation is adapted to be absorbed by the complex.

The substrate comprises molecules being secondary amines,which are accessible at the surface of the substrate to formcomplexes. A compound comprising at least one C=C double bondis added to the substrate. This compound forms a complex with the secondary amine. The complex is referred to as a complex.

Without wishing to be bound by any particular scientifictheory, the inventors believe that this complex is a charge transfer (CT) complex. In such a complex, a fraction ofelectronic charge is transferred between the molecularentities. The resulting electrostatic attraction provides astabilizing force for the molecular complex. In the presentcase, the complex is able to undergo a transition into anexcited electronic state. The excitation energy of thistransition often occurs in the UV-region of theelectromagnetic spectrum, or sometimes towards the visible spectrum. Such a complex, which the inventors believe arecharge-transfer complexes are referred to as complexes.However, in view of the theory of the inventor they may also be referred to as charge-transfer complexes.

In particular a complex is formed between the unpairedelectrons of the nitrogen in the secondary amine and a C=Cdouble bond with electron withdrawing group(s) adjacent. Sucha C=C double bond is also referred to as an activated doublebond. The complex has a certain characteristics regardingabsorption of actinic radiation. When irradiating the complex with suitable wavelength(s) a reaction is initiated. The reaction can be viewed as a Aza-Michael addition. In general, lO no catalyst is required and in general no by products are formed.

It is a very important feature that the reaction is initiatedby irradiation of the complex directly. The complex absorbsenergy directly from the actinic radiation. No photoinitiatoris required. Actually, addition of a photoinitiator is mostoften not suitable since it is likely to absorb actinicradiation, which then cannot be utilized for initiating thereaction. Only very small insignificant amount of UV-absorbing compounds such as photoinitiators should generallybe tolerated. Amounts of photoinitiators which are normallyused to initiate various reactions are generally too high. Inone embodiment, no photoinitiators are added. Aphotoinitiator or another compound that absorbs actinicradiation is in one embodiment not be present at all. Undersome conditions, certain amounts of certain photoinitiators can be tolerated. Such conditions include: a)The wavelengths at which the complex absorbs energy issufficiently far from the wavelengths at which thephotoinitiator absorbs light. This is particularly true for complexes comprising two electron withdrawing groups such as those involving for instance maleic acid their absorbance is often anhydride. For such complexes, shifted towards longer wavelengths (i.e. lower energy) so that a photoinitiator absorbing mainly at shorterwavelengths (i.e. higher energy) can be tolerated. Thephotoinitiator does not absorb a significant amount ofthe actinic radiation in the relevant wavelengthinterval, allowing a reaction to be initiated in the complex. lO b)The applied layer comprising a photoinitiator is verythin so that a sufficient amount of radiation reaches the complex anyway, and/or the applied layer comprising a photoinitiator is dilute so that a sufficient amount of radiation reaches the complex anyway.

The above conditions can also be combined with an increase in the intensity and/or dose of the actinic radiation.

The absorbed energy is determined by the extent of formationof complexes. With maleic anhydride the wavelength is shiftedtowards lower energy so that adhesion occurs even if afraction of photoinitiator is in the solution. For acrylatesthere is required a higher energy which is blocked byphotoinitiators or other chemical groups present in thearomatics etc. at normal mixture such as carbonyl, esters, use. This is most probably the reason that this effect has not been observed before.

In general, the levels of any photoinitiators or otherabsorbing compounds must not be so high that the reaction inthe complex is not initiated. Thus in one embodiment aphotoinitiator is present in an amount, which does notprevent initiating a reaction to form a covalent bond byreaction of nitrogen in the secondary amine and the carbon-carbon double bond. This limit has to be determined for eachsystem depending on the absorbance of the complex and a photoinitiator.

For instance e-beam is not intended to be used to initiate the complex. Thus, e-beam is not used to initiate the reaction.

A covalent bond is formed as a result of the reaction. lO The actinic radiation (typically UV-radiation) should reachthe surface of the substrate where the complexes are located.This can be achieved by irradiation on the surface. In oneembodiment, this can be achieved by irradiation through thesubstrate provided that it is transparent at the relevantwavelength and/or very thin. A solution comprising thecompound comprising at least one C=C double bond should notabsorb too much of the actinic radiation. The product of thethickness of such an applied solution and the absorption atthe relevant wavelength should not be too high so thatsufficient actinic radiation can reach the surface of thesubstrate where the complexes are. A higher absorption ofradiation in such a solution can to some extent be compensated with a thinner applied solution.

The substrate is a cured substrate. It is conceived that forinstance a melamine formaldehyde substrate is cured before the present method starts.

There is the possibility to form patterns on the substrate byonly irradiating parts of the surface, where the complex is.In addition or alternatively it is possible to form patternsby applying the compound comprising at least one C=C double bond in a desired pattern.

In general, there is no reaction in the bulk of an applied solution, the reaction takes place only where the complexes have formed. Hence, the surplus can be removed after the reaction.

In one embodiment, the at least one secondary amine is melamine formaldehyde. This corresponds to a substrate of melamine formaldehyde resin, or "melamine". In one embodiment, the secondary amine is urea formaldehyde. This lO lO corresponds to a substrate of urea-formaldehyde resin. In oneembodiment the substrate comprises at least one selected fromthe group consisting of melamine formaldehyde resin, urea formaldehyde resin, poly paraphenylene terephthalamide (Kevlar®), and polyamide (Nylon®>.

The electron withdrawing group is in one embodiment adjacent to the carbon-carbon double bond.

In one embodiment, there is an electron withdrawing group on both sides of the carbon-carbon double bond. Such compounds generally form stronger complexes.

In one embodiment, the electron withdrawing group is at leastone selected from the group consisting of a triflyl group, atrihalide group, a nitro a cyano group, a sulfonate group, group, an ammonium group, an aldehyde group, a keto group, a carboxylic group, an acyl chloride group, an ester group, an amide group, and ether group, and a halide.

In one embodiment, the compound comprising at least onecarbon-carbon double bond is at least one selected from the group consisting of maleic anhydride and maleimide.

In one embodiment, the compound comprising at least onecarbon-carbon double bond is at least one selected from thegroup consisting of a maleate and a fumarate. Ihis refers toions and it is conceived that any suitable counter ions canbe utilized. The compound is suitable dissolved in a solution when applied to the substrate.

In one embodiment, the compound comprising at least onecarbon-carbon double bond is at least one selected from the group consisting of an acrylate and a methacrylate. lO ll In one embodiment, the compound comprising at least one carbon-carbon double bond is provided in a solution. Thesolution is then added to the substrate surface in a desired thickness.

In one embodiment, the reaction of the complex initiates an anionic polymerization reaction. In such an embodiment, apolymerizable substance is added in a layer on the substratesurface. When the complexes are irradiated and react theyinitiate a polymerization chain reaction in the bulk abovethe surface so that the polymerizable substance polymerizes.Such a chain reaction is partially or fully extending intothe bulk of the layer. Such a polymerizable substance istypically a monomer or could also be a polymerizableoligomer. The polymerizable substance should be able topolymerize in a chain reaction once the reaction is initiated.

In one embodiment, any surplus of the compound comprising at least one carbon-carbon double bond is removed after step c).

In one embodiment, the thickness of an applied coatingcomprising the compound comprising at least one carbon-carbondouble bond and the absorbance of the coating at thewavelength of the actinic radiation are adapted so that the reaction is still initiated in step c).

In one embodiment the compound comprising at least one carbon-carbon double bond is: a) at least l6wt% of at least one compound selected from thegroup consisting of an unreacted organic acid anhydride, anester of maleic acid anhydride, an ester of fumaric acid anhydride, and maleimide, and lO b) at least lO wt% of i) at least(meth)acrylate group, (meth)acrylate groups ii) l2 at least one from: one compound comprising awherein the average number of per molecule is larger than l, and at least one compound selected from polyfunctional allyl compounds and vinylether, In one embodiment there is provided a method of coating a substrate, a) b) said method comprising the steps of providing a substrate, applying a coating composition to at least a partof the substrate, said coating compositioncomprising at least lOwt% of at least one compound comprising a (meth)acrylate group,wherein the composition fulfils at least one ofthe conditions selected from; i) the averagenumber of (meth)acrylate groups per molecule is larger than l, and ii) the coating compositioncomprises polyfunctional allyl compounds orvinylether, said coating composition comprisingat least one photoinitiator, and said coatingcomposition comprising at least l6wt% of at leastone compound selected from the group consistingof an unreacted organic acid anhydride, an esterof maleic acid anhydride, an ester of fumaric acid anhydride, and maleimide, and initiating a polymerisation reaction in at leasta part of the applied coating composition bysubjecting at least a part of the applied coating to actinic radiation and heat. l3 In the above method, it is conceived that the photoinitiatorshould not absorb actinic radiation in such a spectrum and tosuch an extent that the initiation of the complex is blocked.This is solved by selecting a suitable photoinitiator.Further, the above method comprises for instance organic acid anhydride, an ester of maleic acid anhydride, an ester of fumaric acid anhydride, and maleimide. These compounds give acomplex with an absorbance shifted towards a longer wavelength making it possible to use a UV-photoinitiator withan absorbance at a higher wavelength. This this embodiment is an exception where it is possible to use a photoinitiator.

In a second aspect there is provided a substrate coated according to the method described above.

In one embodiment, a second coating is applied after step c).This second coating can be referred to as a top-coat if nofurther coatings are to be applied. The properties of theresulting finished coated substrate including the top-coat isdrastically improved when using the present method. In oneembodiment, at least one further coating is applied afterstep c). Thus the coating is used as a primer in oneembodiment. The coating can also be used as a single coating or as a top coat on another coating.

In one embodiment the coating is a thin layer since there is no reaction in the bulk. Only the complexes can be transformed to covalent bonds. p \ å surface treatment because the applied layer is verythin. The order of magnitude of the thickness corresponds toone molecule in such an embodiment. Because of the covalentbonding with the substrate, there is no or essentially no formation of covalent bonds above the substrate surface, and thus no cross linked film is formed in such an embodiment.

The coating can thus be viewed l4 The coating should in this embodiment be viewed as a verythin coating of covalently attached molecules. The thicknessin this embodiment roughly corresponds to the size of the covalently attached molecules.

In an alternative embodiment an optional component is addedto the substrate surface. Such an optional component is ableto bind to the covalently attached molecules with non- covalent bonds, such as dipole-dipole bonds. Thereby a film is formed on the substrate surface. In one embodiment thethickness of such a film is in the interval 50-200 nm. In oneembodiment the optional component comprises cellulose.In one embodiment, an acrylate based coating is applied as the at least one further coating, i.e. the second coating.

In one embodiment, a solution comprising the at least one C=Cdouble bond is applied with a thickness in the range l-l00um,the thickness being measured directly after application ofthe coating composition. The average thickness is considered.If the coating is not applied with a uniform thickness theaverage thickness is calculated as if the coating would havebeen applied with an even thickness over the surface. Afterstep c) the remaining unattached molecules can be removed.Thus the resulting attached layer is generally much thinner than the applied solution in step b) In one embodiment, step c) is performed so that only a partial reaction occurs, wherein at least one further coatingis applied after step c), and wherein a further initiation ofa reaction is performed after application of the at least onefurther coating. It is intended that the further initiation completes the reaction. lO Other features and uses of the invention and their associatedadvantages will be evident to a person skilled in the art upon reading the description and the examples.

It is to be understood that this invention is not limited tothe particular embodiments shown here. The embodiments areprovided for illustrative purposes and are not intended tolimit the scope of the invention since the scope of thepresent invention is limited only by the appended claims and equivalents thereof.

Examples All percentages are calculated by weight throughout the description and the claims.

Example l Pure hexanediol diacrylate (HDDA) was applied in anapproximately 6 um thick layer on a melamine flooringsurface using an applicator rod. The melamine with theHDDA layer was put in a curing device comprising aconveyor belt and a fixed medium pressure mercury lampThe UV dose that gives light in UVA, UVB, UVC and UVV. was measured to be l.5 J/cm? (UVA) Hg spectrum. Since HDDA does not contain photoinitiator, it was still liquid andnon-reactive on the melamine surface and needed to beremoved to avoid blending with the next layer (top coat).Unreacted acrylate was rinsed with acetone and dried withpaper. This was repeated once.

A UV-curing acrylate-based topcoat from Bona AB was thenapplied and cured at l.5 J/cm2. The adhesion to the substrate was tested with a device specifically intended l0 16 for adhesion tests of thin films, a Hamberger Hobel.Values above 2ON are considered commercially acceptableand values above 3ON are better than all parquet floorsin the market.

Result: 4ON Hamberger.

A standard tape test was also performed. There were madecuts through the coating to the substrate in a squarepattern with 25 areas each being approximately lmm2. Astandard packing tape was pressed onto the coating andpulled off quickly. The resulting damage was estimated bycounting the number of lmmê pieces that are removed. Therating O was given for no noticeable change and the score5 corresponds to that all areas have been removed.Result: 0 Crosshatch.Several experiments with exactly the same method havebeen done with maleic anhydride dissolved in DMSO,diethyl maleate dissolved in DMSO and HDDA dissolved inDMSO and all provide the same good adhesion as above.

A common UV curing coating (containing acrylates, fillers, photoinitiators and additives) from Bona AB was diluted with DMSO to lO% 90% (dimethylsulfoxide) acrylate in DMSO. Same method as above.

Adhesion and crosshatch: same good results.

At 24 um application thickness (2.4 um after the solventhad disappeared), adhesion deteriorated drastically.

Hamberger 17 Example 2 A mixture of 1% tripropylene glycol diacrylate (TPGDA), 1.5% cellulose thickener, 0.1% SDBS (surface active agentfor better effluence) and 97% tap water was applied in the same manner as in the first example. The melamine wasnot washed with acetone since a dry surface was obtainedafter evaporation of the water, which occurs during the illumination. A dose of 1.5 J/cm? was used. Immediately after the UV curing, 6 um Bona topcoat was applied andcured 1.5 J/cm2.

Hamberger 4ON, Crosshatch O Example 3 In the same manner as in Example 1, TATATO (1,3,5-Triallyl-1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione), DVE3(triethylene glycol divinyl ether), TAOE (tetraallyloxy ethane) were tested.Result: TATATO 3ON Hamberger, DVE3 and TAOE 15NHamberger.

Example 4To test the wavelength dependence of different doublebonds, a 365nm LED lamp was used with 17mJ/cm2 intensity.

A mixture of 1% tripropylene glycol diacrylate (TPGDA), 1.5% cellulose thickener, O.1% SDBS (surface active agentfor better effluence) and 97% tap water was applied in the same manner as in the first example. The melamine wasnot washed with acetone since a dry surface was obtained after evaporation of the water, which occurs during the 18 illumination of 120s 365nm LED (approx. 2J/cm2).

Immediately after the UV light, 6 um Bona topcoat wasapplied and cured 1.5 J/cm2.

Hamberger 10N Crosshatch 4Example 5A mixture 1.5% 0.l% of 1% vinylacetate, cellulose thickener, SDBS (surface active agent for better effluence), 5%PEG 8000 and 92% tap water was applied in the same manneras in the first example. The melamine was not washed withacetone since a dry surface was obtained afterevaporation of the water, which occurs during the illumination of 120s 365nm LED (approx. 2J/cm2).

Immediately after the UV light, 6 um Bona topcoat was applied and cured 1.5 J/cm2.

Hamberger 5N Crosshatch 5 Example 6 A mixture of 1% diethyl maleate, 1.5% cellulose thickener, 0.1% SDBS (surface active agent for better effluence), 5% PEG 8000 and 92% tap water was applied in the same manner as in the first example. The melamine wasnot washed with acetone since a dry surface was obtainedafter evaporation of the water, which occurs during the illumination of 120s 365nm LED (approx. 2 J/cm2).

Immediately after the UV light, 6 um Bona topcoat was applied and cured 1.5 J/cm2.

Hamberger 45N Crosshatch 0 Example 7 19 A mixture of 1% diethyl maleate, 1.5% cellulose thickener, 0.l% SDBS (surface active agent for better effluence), 5% PEG 8000 and 92% tap water was applied in the same manner as in the first example. The melamine was not washed with acetone since a dry surface was obtainedafter evaporation of the water, which occurs during the illumination of l20s 395nm LED (approx. 8 J/cm%.

Immediately after the UV light, 6 um Bona topcoat was applied and cured 1.5 J/cm2.

Hamberger 0N Crosshatch 5 Example 8 The following mixes were prepared; 100% SR344, 75% SR344 and 25% tap water, 50% SR344 and 50% tap water, 25% SR344and 75% tap water, 0% SR344 and 100% tap waterrespectively. The respective mixture was applied in 6, 12 and 24 um thick layers on different melamine flooringsurfaces respectively. A dose of 630 mJ/cm? was used.

Excess primer was washed twice with paper and acetone.Immediately after UV curing and wash, 6 um Bona topcoatwas applied and cured 1.5 J/cm2. The results can be seen in Table 1.

Table 1 Crosshatch and Hamberger results of melamine flooring surfaces with different thick layers (6, 12 and24 um) of 0% SR344, 25% SR344, 50% SR344, 75% SR344 and100% SR344.0wt% 25wt% 50wt% 75wt% SR 100%SR344 SR344 SR344 344 SR344 lO 6um Crosshatc Crosshatc Crosshatc Crosshatc Crosshatch 5 h O h O h O h 2Hamberger Hamberger Hamberger Hamberger Hamberger<6N 2lN llN l4N 7N l2u Crosshatc Crosshatc Crosshatc Crosshatc Crosshatc m h 5 h O h O h l h 5Hamberger Hamberger Hamberger Hamberger Hamberger<6N l6N lON 6N <6N 24u Crosshatc Crosshatc Crosshatc Crosshatc Crosshatc m h 5 h 5 h 2 h 2 h 5Hamberger Hamberger Hamberger Hamberger Hamberger<6N <6N <6N <7N <6N Example 9 A mixture of 2% SR344, l.5% cellulose thickener, O.l% SDBS (surface active agent for better effluence) and 96% tap water was applied in a 6 um thick layer on the melamine flooring surface.

The melamine surfaces were not washed with acetone since a dry surface was obtained after a minute.

No irradiation was applied.

Immediately after 6 um Bona topcoat was applied and cured l.5 J/cm2.

Hamberger 6N Crosshatch 2 Example lO A mixture of 2% SR344, l.5% cellulose thickener, O.l%SDBS (surface active agent for better effluence) and 96% tap water was applied in a 6 um thick layer on the melamine flooring surface. This time, the melamine surfaces were not washed with acetone since a dry surface 21 was obtained after the evaporation ofoccurs during the illumination. used.

Immediately after the UV illumination, the water, which A dose of 53 mJ/cm? was 6 um Bona topcoat was applied and cured 1.5 J/cm2.

Hamberger 45N Crosshatch O Example ll A mixture of 2% SR344, l.5% cellulose SDBS (surface active agent for bettertap water was applied in a 6 um thickmelamine flooring surface. This time,surfaces were not washed with acetonewas obtained after the evaporation ofoccurs during the illumination. used.

O.1%and 96% thickener,effluence)layer on thethe melaminesince a dry surface the water, which A dose of 53 mJ/cm2 was The melamine flooring surface was allowed to be in room temperature for 8 days before 6 um Bona topcoat was applied and cured 1.5 J/cm2.

Hamberger 28 N Crosshatch O Example 12 A mixture of 2% SR344, l.5% cellulose SDBS (surface active agent for bettertap water was applied in a 6 um thickmelamine flooring surface. This time,surfaces were not washed with acetonewas obtained after the evaporation ofoccurs during the illumination.used. Immediately after the UV light, was applied and cured 1.5 J/cm2.

Hamberger 45N Crosshatch O thickener, O.1% effluence) and 96%layer on thethe melaminesince a dry surface the water, which A dose of 29 mJ/cm? was 6 um Bona topcoat lO 22 Example l3 A mixture of 2% SR344, l.5% cellulose thickener, 0.l%SDBS (surface active agent for better effluence) and 96% tap water was applied with 6 um thick layers of 4different melamine flooring surfaces. The surfaces wereallowed to heat-cured in the oven at 50 °C for l5 min, 30 min, 45 min and 60 min, respectively. Immediately after heat setting, 6 um Bona topcoat was applied and cured l.5J/cm2 on all samples except for the floor surfacepreviously thermosetting for 60 minutes. This sample wasallowed to room temperature for 8 days before 6 um Bonatopcoat was applied and cured 1.5 J/cm?. The result can be seen in Table 2.

Table 2 Crosshatch and Hamberger results from melamineflooring surfaces exposed to different times of heat curing.

Heat hardening of Crosshatch Hamberger Primer l5 min 0 l2 N 30 min 0 l0 N 45 min 0 l6 N 60 min + 8 days at 3 9 N room temperature A mixture of 5% SR344, l.5% cellulose thickener, 0.l%SDBS (surface active agent for better effluence) and 93% tap water was applied in a 6 um thick layer on themelamine flooring surface. The melamine surfaces were not washed with acetone since a dry surface was obtained 23 after the evaporation of the water, which occurs during the illumination. A dose of 800 mJ/cm? was used.Immediately after the UV light, 6 um Bona topcoat was applied and cured 1.5 J/cm2.

Hamberger 45N Crosshatch O Thus: An activated double bond (electron-deficient) incontact with melamine laminate provides very goodadhesion if a sufficient UV dose with the right energy isreaching down to the complex. Even less favourable doublebonds provide some improved adhesion at high UV doseswith energy-rich light (UVC, UVB).

The energy is determined by how good complexes areformed. With maleic anhydride, the wavelength was shiftedto lower energy so that adhesion occurs even when a lotof photoinitiator was present in the mixture. Thephotoinitiator then had a different absorption wavelengthallowing at least some actinic radiation with the rightwavelength to reach the complex.

With acrylates, higher energy was required, which was blocked by photoinitiatorat normal application rates. This is probably one reason why this has not been observed before.

Claims (14)

1. l. A method of coating a substrate, 24 said method comprising the steps of ä)

2. The method according to claim l, providing a substrate, said substrate comprising at least one secondary amine, at least a fractionof the at least one secondary amines is at the surface of the substrate, contacting the substrate surface with a compoundcomprising at least one carbon-carbon doublebond, wherein an electron withdrawing group is onat least one side of the carbon-carbon doublebond, so that a complex is formed betweennitrogen in the secondary amine and the carbon- carbon double bond, initiating a reaction to form a covalent bond byreaction of nitrogen in the secondary amine and the carbon-carbon double bond, by subjecting at least a part of the substrate surface to actinicradiation, wherein the wavelength of the actinicradiation is adapted to be absorbed by the complex. wherein the substrate comprises at least one selected from the group consisting of melamine formaldehyde resin, resin, poly urea formaldehyde paraphenylene terephthalamide, and polyamide.

3. The method according to any one of claims l-2, wherein there is an electron withdrawing group both sides of the carbon-carbon double bond. lO

4. The method according to any one of claims l-3,wherein the electron withdrawing group is at least oneselected from the group consisting of a triflyl group, atrihalide group, a nitro a cyano group, a sulfonate group, an ammonium group, an aldehyde group, a keto group, a glfOUp, carboxylic group, an acyl chloride group, an ester group, an amide group, and ether group, and a halide.

5. The method according to any one of claims l-4,wherein the compound comprising at least one carbon-carbondouble bond is at least one selected from the group consisting of maleic anhydride and maleimide.

6. The method according to any one of claims l-5,wherein the compound comprising at least one carbon-carbondouble bond is at least one selected from the group consisting of a maleate and a fumarate.

7. The method according to any one of claims l-6,wherein the compound comprising at least one carbon-carbondouble bond is at least one selected from the group consisting of an acrylate and a methacrylate.

8. The method according to any one of claims l-7,wherein the compound comprising at least one carbon-carbon double bond is provided in a solution.

9. The method according to any one of claims l-8,wherein any surplus of the compound comprising at least one carbon-carbon double bond is removed after step c).

10. lO. The method according to any one of claims l-9,wherein the thickness of an applied coating comprising thecompound comprising at least one carbon-carbon double bond and the absorbance of the coating at the wavelength of the lO 26 actinic radiation are adapted so that the reaction is still initiated in step c).

11. ll. The method according to any one of claims l-10, wherein a second coating is applied after step c).

12. The method according to any one of claims l-ll,wherein the compound comprising at least one carbon-carbon double bond is: a) at least l6wt% of at least one compound selected from thegroup consisting of an unreacted organic acid anhydride, anester of maleic acid anhydride, an ester of fumaric acid anhydride, and maleimide, and b) at least lO wt% of at least one from: i) at least one compound comprising a (meth)acrylate group, wherein the average number of (meth)acrylate groups per molecule is larger than l, andii) at least one compound selected from polyfunctional allyl compounds and vinylether.

13. The method according to any one of claims l-12, wherein a polymerizable substance is added in at least asurrounding on the substrate, wherein the initiation of thecomplexes in step c) further initiates a polymerization reaction of the polymerizable substance.

14. A substrate coated according to any one of claims l-l3.