WO2022164313A1

WO2022164313A1 - Method for coating a polymer surface comprising ketone-treatment of the polymer surface

Info

Publication number: WO2022164313A1
Application number: PCT/NL2022/050036
Authority: WO
Inventors: Cornelis Johannes Gerardus Maria Van Peer
Original assignee: Nanogate Eurogard Systems B.V.
Priority date: 2021-01-26
Filing date: 2022-01-26
Publication date: 2022-08-04
Also published as: NL2027404B1

Abstract

The invention relates to a method for providing a polymer material with a surface coated with a UV-curable coating comprising priming the polymer material with a ketone or a ketone solution in an organic solvent. The invention also relates to a transparent polymer material comprising a surface coated with a UV-curable coating, obtained with or obtainable by this method and to the use of the polymer material in the manufacturing of a transparent pane or window or shield such as a transparent laminate or glass pane. In addition, the invention also relates to an article or formed article, preferably thermoformed article, or object comprising the polymer material.

Description

METHOD FOR COATING A POLYMER SURFACE COMPRISING KETONE-TREATMENT OF THE

POLYMER SURFACE

TECHNICAL FIELD

The invention relates to a method for providing a polymer material with a surface coated with a UV- curable coating. Typically, the coating is a solid coating and a hard-coat. The invention also relates to a transparent polymer material comprising a surface coated with a UV-curable coating, obtained with or obtainable by the method according to the invention. Furthermore, the invention relates to the use of the polymer material that is obtained with or obtainable by the method according to the invention, in the manufacturing of a transparent pane or window or shield such as a transparent laminate or glass pane. In addition, the invention relates to an article or formed article, preferably thermoformed article, or object comprising the polymer material obtained with or obtainable by the method according to the invention, or provided according to the use of the invention.

BACKGROUND

Manufacturers of articles and objects comprising (transparent) polymer film or polymer sheet, such as panes, shields, windows, or (parts of) mobile phones, (parts of) control panels, parts or objects for automotive applications, or using in-mould decoration processes and/or in-mould electronics, demand polymer film or sheet which meets high quality measures. An example are the stringent hardness criteria set by automotive industry. Another example are the stringent coating adhesion criteria set by high-tech industries wherein polymer materials are applied. In addition, such polymer film or sheet, for example polycarbonate film such as polycarbonate film based on bisphenol A, should meet high standards relating to polymer film formability, applicability of the film in moulding processes, and relating to chemical resistance of the film surface. In addition, these hi-tech industries, e.g. automotive industry, mobile phone manufacturing, domestic control panels applications, etc., demand constant quality, robust manufacturing processes when the application of the high quality polycarbonate film is concerned, and polymer film or sheet that does not demand much attention when maintenance of previous set quality standards are considered. Moreover, in order to meet the harsh and high technical standards, polymer films implied in the hi-tech manufacturing processes are mostly polymer films coated with a hard-coat, wherein the hard-coat should be firmly and tightly adhered to the surface of the polymer film or sheet, also when exposed to tough conditions which may induce wear.

Despite these demands for robust, hard, chemical resistant, wear resistant and easy-to-apply polymer sheets and films such as polycarbonate film or polyethylene terephthalate - glycol-modified (PET-g), for application in car-, phone-, control panel manufacturing, etc., still currently available polycarbonate films suitable for implication in such manufacturing processes, require laborious processing steps and require the purchase and maintenance of machinery specifically mandatory to provide and maintain polymer film at the required quality with regard to e.g. hardness, chemical resistance. That is to say, currently available polycarbonate film for polymer-film comprising article-, part-, object manufacturing is film provided with a hard-coat that is typically UV cured in a first necessary step of providing and keeping polymer film with the required specifications, said first UV curing performed typically directly after hard-coat polycarbonate film production at the site of manufacturing of film. Then, subsequently the hard-coat polycarbonate film is typically transferred to customers, e.g. car dashboard parts manufacturers, mobile phone casing manufacturers, control panel manufacturers, etc. Typically, the hard-coat polycarbonate film is subjected to a forming step. Hard-coat polycarbonate films now available do require a necessary second UV curing step after the forming of the film, in order to meet the stringent industry criteria such as those set in ASTM D1044-13 and ASTM D3363-5(201 1 )e2 industry standards. This induces the necessity to conduct crucial and additional steps as part of the manufacturing process and requires measures to handle formed film before and after the forming process with high care when avoidance of scratches, contacting film surfaces, applying pressure onto the film, etc. are concerned. Only applying a cumbersome second UV curing step, requiring UV curing equipment designed and suitable for the purpose, results in a formed film which can be treated and handled, stored, etc., with reduced caution when damaging the surface of the formed polycarbonate film is regarded. After all, such currently available film would not meet the high quality standards if the requirement of the second UV curing step would not be obeyed.

Another drawback of current polymer films and sheets applied in e.g. forming, back injectionmoulding, in-mould electronics, such as hard-coat polycarbonate films and sheets such as those based on bisphenol A, is the poor to moderate adherence of the hard-coat to the polycarbonate surface after the film has been subjected to standardized adhesion testing such as according to DIN 53151 ;1981 -05. ‘Poor to moderate adherence’ has here to be understood as the hard-coat coming loose from the (polycarbonate or PET-g) film, at least in part and/or locally. Therewith, such hard-coat (polycarbonate or PET-g) films do not meet the stringent requirements for use as a component or part in manufacturing of e.g. window panes, (transparent) (glass) shields, control panels, objects implemented in e.g. the dashboard of a car.

Therefore, a solution still needs to be found that allows for a less cumbersome and less critical process for applying polymer film in e.g. forming processes and moulding processes such as in-mould electronics for the purpose of manufacturing polymer-film comprising articles, parts and objects which should resist stringent hardness tests and stringent chemical resistance tests, and which should comprise a hard-coat which remains adhered firmly and tightly to the e.g. polycarbonate or PET-g film or sheet surface even under the harshest testing conditions resembling real-life user conditions accompanied by circumstances that would otherwise cause undesired and unacceptable wear and decay of the article or object or part comprising such hard-coat polymer film or sheet. SUMMARY OF THE INVENTION

An aspect of the invention relates to a method for providing a polymer material with a surface coated with a UV-curable coating, comprising the steps of or consisting of the steps of:

(a) providing the polymer material;

(b) providing a ketone or a ketone solution comprising 2% - 100% of a ketone and 0% - 98% of an organic solvent, based on the total weight of the ketone solution;

(c) contacting the surface of the polymer material of step (a) with the ketone or the ketone solution of step (b) for a defined period of time at a defined temperature;

(d) discarding the remainder of the ketone or the ketone solution at the end of step (c) from the surface of the polymer material, therewith providing a ketone-primed surface of the polymer material;

(e) providing a UV-curable coating composition;

(f) providing the UV-curable coating composition of step (e) onto the ketone-primed surface of the polymer material of step (d); and

(g) irradiating the ketone-primed surface of the polymer material overlayed with the UV-curable coating composition of step (f) with UV radiation to adhere the UV-curable coating composition at the ketone-primed surface of the polymer material, therewith providing the polymer material with a surface coated with the UV-curable coating.

Preferably, in the method of the invention, the UV-curable coating composition of step (e) is a solid UV-curable coating composition or a UV-curable hard-coating composition, preferably a solid UV- curable hard-coating composition.

Preferred is the method according to the invention, wherein the UV-curable coating composition comprises:

(i) a first aliphatic multi-functional urethane acrylate oligomer;

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(iv) optionally a second aliphatic multi-functional urethane acrylate oligomer, wherein the functionality of the first aliphatic multi-functional urethane acrylate oligomer and the second aliphatic multi-functional urethane acrylate oligomer is different; and optionally

(v) a flow modifier.

Also preferred is the method according to the invention, wherein the UV-curable coating composition comprises:

(i) a first aliphatic multi-functional urethane acrylate oligomer which is any one of an aliphatic three-functional - dodeca-functional urethane acrylate oligomer;

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(iv) optionally a second aliphatic multi-functional urethane acrylate oligomer which is any one of an aliphatic di-functional - dodeca-functional urethane acrylate oligomer, wherein the functionality of the first aliphatic multi-functional urethane acrylate oligomer and the second aliphatic multi-functional urethane acrylate oligomer is different; and optionally;

(v) a flow modifier.

Typically, in the method of the invention, the UV-curable coating composition comprises:

(i) a first aliphatic multi-functional urethane acrylate oligomer which is an aliphatic three- functional or tetra-functional urethane acrylate oligomer, preferably an aliphatic three-functional urethane acrylate oligomer;

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(iv) a second aliphatic multi-functional urethane acrylate oligomer which is any one of an aliphatic penta-functional - dodeca-functional urethane acrylate oligomer, preferably an aliphatic hexafunctional urethane acrylate oligomer; and optionally

(v) a flow modifier.

In the method of the invention it is preferred that the polymer material is a polymer foil, a polymer film, a polymer plate or a polymer sheet, preferably with a thickness of 200 micrometer or more, preferably 200 micrometer - 100 millimeter, more preferably 200 micrometer - 80 millimeter, most preferably, 200 micrometer - 15 mm.

In the method of the invention, the polymer material is typically a polymer foil, a polymer film, a polymer plate or a polymer sheet made of an amorphous material or a semi-crystalline material, preferably a transparent amorphous material or a transparent semi-crystalline material.

Preferably, in the method of the invention, the polymer material is a polymer foil, a polymer film, a polymer plate or a polymer sheet made of polycarbonate or made of polyethylene terephthalate - glycol-mod ified (PET-g), preferably transparent polycarbonate ortransparent polyethylene terephthalate

- glycol-modified (PET-g), more preferably transparent polycarbonate.

Preferably, in the method of the invention, the polymer material is made of polycarbonate or made of polyethylene terephthalate - glycol-modified (PET-g).

Preferred is the method of the invention, wherein the ketone is selected from any one or more of a straight-chain ketone, a branched ketone, an unsubstituted cyclic ketone and a cyclic ketone substituted with at least one alkyl group, or a combination thereof, preferable selected from a straightchain ketone, a branched ketone and an unsubstituted cyclic ketone, more preferably, the ketone is selected from any one of propan-2-one, butan-2-one, 3-methylbutan-2-one, pentan-2-one, pentan-3- one, cyclopentanone, 2-methylpentan-3-one, 3-methylpentan-2-one, 4-methylpentan-2-one, 4- methylpent-3-en-2-one, pentane-2, 4-dione, hexan-2-one, 3,5,5-trimethyl-2-cyclohexene-1-one, 5- methylhexan-2-one, methyl-isobutyl ketone, 1-cyclohexylpropan-1-one, 1 -cyclohexylethanone, cyclohexanone, heptan-2-one, heptan-4-one, 2,6-dimethyl-4-heptanon, octan-3-one, octan-2-one, octan-4-one, or a mixture thereof, most preferably the ketone is cyclohexanone.

Also preferred is the method of the invention, wherein in step (b) a ketone solution is provided wherein the ketone, preferably cyclohexanone, is present in the ketone solution at a weight percentage of 2% - 50% based on the total weight of the ketone solution, preferably 3% - 40%, more preferably 4%

- 30%, most preferably 5% - 20%, such as 5% - 10%. Preferred is the method of the invention, wherein in step (b) a ketone solution is provided wherein the solvent in the ketone solution is any one of hexane, heptane, octane and diacetone alcohol, or a mixture thereof, preferably any one of hexane, heptane and octane.

It is part of the invention that in the method, in step (c) preferably at least the surface of the polymer material which is contacted with ketone or ketone solution is kept at a temperature or temperature range selected from 17°C - 40°C, preferably 18°C - 37°C, more preferably 19°C - 33°C, most preferably 20°C - 30°C.

Preferably, in the method according to the invention, in step (c) the ketone or the ketone solution is contacted with the surface of the polymer material while at room temperature or while at a temperature or temperature range selected from 17°C - 40°C, preferably 18°C - 37°C, more preferably 19°C - 33°C, most preferably 20°C - 30°C.

Preferred is the method of the invention, wherein in step (c) the ketone or the ketone solution is contacted with the surface of the polymer material for a time period selected from the range 5 minutes

- 90 minutes, preferably 6 minutes - 80 minutes, more preferably 7 minutes - 70 minutes, most preferably 8 minutes - 60 minutes, such as 9 minutes - 50 minutes, 10 minutes - 40 minutes or 10 minutes - 30 minutes, preferably 10 minutes - 20 minutes.

Also preferred is the method according to the invention, wherein in step (d) the remainder of the ketone orthe ketone solution is discarded at room temperature or at a temperature or temperature range selected from 17°C - 45°C, preferably 20°C - 40°C, more preferably 23°C - 37°C, most preferably 25°C

- 35°C, such as 17°C - 35°C.

Typically, in step (e) of the method of the invention, the provided UV curable coating composition comprises the diluent 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA), present at 10% - 40% by weight based on the total weight of the UV curable coating composition, preferably 15% - 30% by weight, more preferably 20% - 25% by weight, such as 20% - 35% by weight.

Preferred is the method according to the invention, wherein in step (e) of the method the provided UV curable coating composition comprises or consists of, based on the total weight of the UV curable coating composition:

(1) 20% - 60% by weight of the first aliphatic multi-functional urethane acrylate oligomer, preferably an aliphatic tri-functional urethane acrylate oligomer;

(2) 20% - 60% by weight of the second aliphatic multi-functional urethane acrylate oligomer, preferably an aliphatic hexa-fu notional urethane acrylate oligomer;

(3) 10% - 40% by weight 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA), preferably 15% - 35% by weight, more preferably 20% - 30% by weight;

(4) 0,3% - 3% by weight of the photo-initiator, preferably 0,5% - 1 ,5% by weight, preferably bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine oxide; and optionally

(5) 0,03% - 0,3% by weight of the flow modifier, preferably 0,05% - 0,2% by weight, preferably poly-ether-modified polydimethylsiloxane in a mixture of xylene and iso-butanol, preferably the flow modifier is present. Also preferred is the method of the invention, wherein in step (e) of the method the provided UV curable coating composition comprises or consists of, based on the total weight of the UV curable coating composition:

(1) 30% - 50% by weight of the first aliphatic multi-functional urethane acrylate oligomer, preferably an aliphatic tri-functional urethane acrylate oligomer, preferably 35% - 45% by weight;

(2) 25% - 45% by weight of the second aliphatic multi-functional urethane acrylate oligomer, preferably an aliphatic hexa-functional urethane acrylate oligomer, preferably 30% - 40% by weight;

(3) 15% - 35% by weight 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA), preferably 18% - 30% by weight, more preferably 20% - 27% by weight;

(4) 0,5% - 1 ,5% by weight of the photo-initiator, preferably 0,7% - 1 ,3% by weight, preferably bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine oxide; and

(5) 0,05% - 0,3% by weight poly-ether-modified polydimethylsiloxane in a mixture of xylene and iso-butanol, preferably 0,07 - 0,13% by weight.

Preferably, in step (f) of the method according to the invention, the UV curable coating composition has a temperature or temperature range selected from 45°C - 95°C, preferably 55°C - 85°C, more preferably 57°C - 83°C, most preferably 60°C - 80°C, and/or wherein in step (f) of the method at least the surface of the polymer material which is contacted with the UV curable coating composition is kept at a temperature or temperature range selected from 45°C - 95°C, preferably 55°C - 85°C, more preferably 57°C - 83°C, most preferably 60°C - 80°C, and preferably in step (f) of the method the UV curable coating composition and the surface of the polymer material which is contacted with the UV curable coating composition are kept at a temperature or temperature range selected from 45°C - 95°C, preferably 55°C - 85°C, more preferably 57°C - 83°C, most preferably 60°C - 80°C, preferably at the same temperature.

An aspect of the invention relates to a polymer material comprising a surface coated with a UV- curable coating, obtained with or obtainable by the method according to the invention, wherein the polymer material preferably is a transparent polycarbonate foil or sheet, or a transparent PET-g foil or sheet.

An aspect of the invention relates to use of the polymer material obtained with or obtainable by the method according to the invention, in the manufacturing of a transparent pane or window or shield such as a transparent laminate or glass pane, or of a formed article or formed object such as a thermoformed article or object and/or of a moulded article or object such as an injection-moulded article or object, preferably an article or object which comprises the polymer material comprising a surface coated with a UV-curable coating which is first formed and then back moulded such as back injection-moulded.

Preferred is the use according to the invention, wherein the article or object is an article or object such as a transparent glass pane or shield wherein the polymer material is transparent polycarbonate or PET-g, or a control panel and/or an article or object applied in automotive applications such as a radio panel, a control panel, a HVAC control system, or a part thereof, in telecom applications such as a housing, a keypad, an outer casing for a mobile phone. An aspect of the invention relates to an article or formed article, preferably thermoformed article, or object comprising the polymer material obtained with or obtainable by the method according to the invention, or provided according to the use according to the invention.

Preferred are an article or formed article, preferably thermoformed article according to the invention, which is a laminate comprising the polymer material obtained with or obtainable by the method according to the invention, such as a transparent window or shield, or which is an article or object applied in automotive applications such as a radio panel, a control panel, a HVAC control system, or a part thereof.

DEFINITIONS

The term “UV curable” has its regular scientific meaning throughout the text, and here refers to the curing of a coating composition which is applied onto a surface such as a polymer sheet or polymer film, with the aid of illuminating the polymer film surface provided with the coating composition with ultraviolet radiation.

The term “hard-coat” has its regular scientific meaning throughout the text, and here refers to a coating for a polymer film such as a polycarbonate film, which coating, after curing, meets the industry hardness standard set by one or more of car manufacturers such as Volkswagen, Ford, Mercedes, such as the automotive norms such as VWTL226 (VW/Porsche official test norm for automotive interior parts) and DBL9202 (Daimler Benz official test norm for automotive interior parts) and/or the taber abrasion test (ASTM D1044-13).

The term “Hansen Solubility Parameters” has its regular scientific meeting throughout the application, and here refers to the three parameters 8D (dispersion force interactions; dispersive aspect), 8P (polar force interactions; polar aspect), and 8H (hydrogen bond force interactions; hydrogen-bonding aspect) for a molecule such as a solvent molecule, as for example outlined in the paper by Steven Abbott, 29 March 2018, “Science-based formulation: the xl power of HSP for coatings compatibility issues” (reference for example accessible at the online information source: coatings.specialchem.com).

The term “solid coating” or “solid coat” has its regular scientific meeting throughout the application, and here refers to a coating composition that essentially does not comprise solvents (is solvent-free) and that is in a solid state at room temperature (18°C - 22°C).

The term “outer surface tension” has its regular scientific meeting throughout the application, and here refers to the calculated outer fiber strain (OFS) subjected on a coating that is adhered on the outer surface of a bend layer of polymer material such as a bend film, sheet, pane, plate or foil of coated polymer material such as bend coated polycarbonate foil, expressed as 8f = 10Or / R, wherein r is half the thickness of the layer of coated polymer material (foil, sheet, film, pane, plate, etc.) and R is the nominal bending radius to the mid of the thickness of the layer of coated polymer material.

The term “transparent” has its regular scientific meeting throughout the application, and here refers to luminous transparency of polymer material according to the ASTM standard D1003 as in force in January 2021 . The term “elongation test” has its regular scientific meeting throughout the application, and here refers to the visual inspection by eye and/or by the use of a microscope (typically at 5x - 3.000x magnification such as 10x-250x magnification), of a coated polymer surface that is bend and/or elongated and/or formed such as thermoformed, such that the coating on the coated polymer surface is elongated upon the forming or bending or elongation, for the assessment of the presence of hair crack(s) in the elongated coating.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein.

The embodiments of the invention described herein can operate in combination and cooperation, unless specified otherwise.

The various embodiments, although referred to as “preferred” or “e.g.” or “for example”, “particularly” or “in particular” are to be construed as exemplary manners in which the invention may be implemented rather than as limiting the scope of the invention.

The term “comprising”, used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a coating comprising components A and B” should not be limited to a coating consisting only of components A and B, rather with respect to the present invention, the only enumerated components of the coating are component A and component B, and further the claim should be interpreted as including equivalents of those components.

In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element are present, unless the context clearly requires that there is one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one".

DETAILED DESCRIPTION

It is a first goal of the present invention to provide an improved polymer material with a surface coated with a UV curable hard-coat.

It is an objective of the current invention to provide a polymer material with a UV curable hard- coat which improvingly tightly adheres to the surface of aromatic ester comprising polymer films and sheets such as PET-g film and sheet and polycarbonate film and sheet such as polycarbonate based on bisphenol A, when compared to extent of adherence of current hard-coats after e.g. the hard-coated polymer film surface has been subjected to a VWTL226 test and coat adhesion is determined according to DIN 53151 ; 1981 -05. Furthermore, it is an objective of the current invention to provide polymer material that is provided with a hard coat, wherein the polymer material is a sheet with a thickness of 1 mm or more, wherein the coating is established according to a method conveniently executable in common coating practice, without the demand for excessive energy and heat in the process. That is to say, an objective of the current invention is the provision of a method that is suitably applicable for providing a polymer sheet with a coating, wherein the coating composition is a 100% (no solvent) hard-coat UV curable coating composition.

At least one of the above objectives is achieved by providing a polymer sheet or film provided with a UV curable hard-coat of the invention. At least a further objective is achieved by providing a method for manufacturing the polymer film or sheet onto which the UV curable hard-coat is applied, therewith providing a polymer sheet or film provided with the UV curable hard-coat of the invention.

The present invention will be described with respect to particular embodiments but the invention is not limited thereto but only by the claims.

A first aspect of the invention relates to a method for providing a polymer material with a surface coated with a UV-curable coating, comprising the steps of or consisting of the steps of:

(a) providing the polymer material;

(e) providing a UV-curable coating composition;

(g) irradiating the ketone-primed surface of the polymer material overlayed with the UV- curable coating composition of step (f) with UV radiation to adhere the UV-curable coating composition at the ketone-primed surface of the polymer material, therewith providing the polymer material with a surface coated with the UV-curable coating.

Applying a solid hard-coat composition onto the surface of a sheet of polymer material, before UV curing, can be cumbersome. The absence of solvent in the solid coat composition influences the ease, or difficulty, to get the coating distributed fast and evenly over the surface area of the polymer sheet. One way of overcoming such difficulties is providing the coating composition at elevated temperature, e.g. at a temperature above room temperature or ambient temperature, such as at 50°C - 90°C. At such temperatures, the solid coat composition has lowered viscosity, which adds in distributing the coating over the surface and contacting the coating with the polymer material. Another apporach or additive approach is heating the polymer material during the contacting of the polymer sheet with the coating formulation, such that the coating warms up and is more readily spread over the sheet surface. Of course, both approaches are conveniently combined: heated coating composition is applied onto the surface area of a heated sheet of polymer material, followed by a UV curing step. Such an approach is suitably applied when hard-coat formulations are coated onto polymer foil or film with relatively limited film or foil thickness of for example 1 mm or less. However, at higher thickness, heating of such a thick sheet of polymer material can be a challenge. At first, it requires a relatively high amount of energy to heat up a sheet of polymer material to a temperature of for example 55°C - 85°C. Second, heating a sheet of polymer material with a thickness of 1 mm or more evenly when the surface area that is to be contacted with the coating composition is considered, is difficult, therewith introducing the risk for non- uniform coating layer thickness and/or non-uniform strength of adherence of the coating onto the sheet, after curing. Third, heating a sheet of polymer material takes a relatively reasonable amount of time, when compared to heating a foil or film with a thickness of less than 1 mm such as 250 micormeter. That is to say, for example heating a sheet of PC that has a thickness of 2 mm or more such as 10 mm, for the purpose of efficiently and fastly overlaying the sheet surface with a solid coat composition, is hampered by the prolonged time it takes before such a sheet has the desired temperature, when compred to heating a thinner foil which is in most occassions heated almost instantly when for example provided on a heated roll. Fourth, heating a sheet of polymer material demands a heating device having a surface area suitable for heating a desired surface area of the sheet which is relatively large. For example, fastly and evenly heating one square meter sheet of e.g. PC would require a heating device suitable for receiving such a sheet at such a large size.

All these shortcomings of heating polymer sheet with a thickness larger than what is commonly referred to as a film or foil, e.g. sheets which are self-supporting material unlike foil or film of the same size, are overcome by application of the method of the invention. The inventors surprisingly found that the step of heating a sheet of polymer material for the purpose of distributing a solid coat composition evenly over the surface of the sheet is not any more mandatory when the surface of the sheet that is to be coated, is first primed with a ketone or with a solution comprising a ketone. The ketone typically is cyclohexanone. The ketone is typically mixed with or dissolved in a short-chain alkane such as hexane, heptane, octane, or mixtures thereof, or DAA. Priming the sheet surface of for example transparent PC or transparent PET-g with ketone, before the UV curable hard-coat composition is applied onto the surface, makes the heating of the coating composition and/or of the sheet of polymer material superfluous. Coating at room temperature or ambient temperature provides a sufficiently firm adhered coating after UV curing, which passes hardness tests like the taber abresion test and the adhesion cross-hatch test, according to applicable standards and norms (see also the Examples section). According to the invention, the provision of a sheet of polymer material with a hard-coat that is properly adhered and bound to the sheet surface, is aided by priming the surface of the sheet with a ketone while omitting the step of heating the solid coating composition during contacting the sheet surface, or while omitting the provision of heated polymer material during overlaying the sheet surface with coating composition, or while omitting both the heating of the coating composition and the heating of the sheet. Of course, if desired, the method of the invention is also suitable for including the step of heating the coating composition and/or the sheet during the contacting of the sheet with the coating. The inventors established that with the method of the invention it is sufficient and enough to prime a sheet of e.g. PC or PET-g with a ketone (100% or diluted) and to subequently overlay the primed surface area with solid coating composition at room temperature. Coating at elevated temperature is not a prerequisite due to the priming with the ketone such as cyclohexanone. The inventors also found that the priming step is relatively fast since a priming step of as short as 10 seconds already suffices in order to arrive at the maximum adherence-stimualting effect of the priming with ketone, e.g. cyclohexanone, e.g. at 2,5%, 5%, 10%, 15%, 20% or higher based on the total weight of the primer solution, e.g. in hexane, heptane octane and/or DAA. Thus, the method of the invention provides for a fast and easy protocol for manufacturing hard-coated sheets of polymer material such as PC and PET-g, wherein the sheets have a thickness offer example 1 mm - 2 cm. Fast priming in a time period of 5 seconds - 30 seconds makes the method of the invention suitable for high-volume production of coated sheets. No relatively large oven or plate heater is necessary and required; spraying or applying a sufficient amount of ketone (solution) that wets the surface area of a sheet intended for coating, suffices according to the method of the invention.

Preferably, in the method of the invention, the UV-curable coating composition of step (e) is a solid UV-curable coating composition or a UV-curable hard-coating composition, preferably a solid UV- curable hard-coating composition. A solid coating composition is essentially free of solvent.

(i) a first aliphatic multi-functional urethane acrylate oligomer;

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(v) a flow modifier.

Such coating compositions are typical solid coating compositions applied in automotive industry and for manufacturing of e.g. glass panes, shields, etc. That is to say, for applications wherein a high hardness is desired and firm adhesion of the coating onto the bearing polymer sheet. Indeed, the inventors established that the method of the invention is particularly suitable for firmly adhering UV curable solid hard-coats of the similar type, i.e. based on aliphatic multi-functional urethane acrylate oligomer.

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA); (iv) optionally a second aliphatic multi-functional urethane acrylate oligomer which is any one of an aliphatic di-functional - dodeca-functional urethane acrylate oligomer, wherein the functionality of the first aliphatic multi-functional urethane acrylate oligomer and the second aliphatic multi-functional urethane acrylate oligomer is different; and optionally;

(v) a flow modifier.

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(iv) a second aliphatic multi-functional urethane acrylate oligomer which is any one of an aliphatic penta-functional - dodeca-functional urethane acrylate oligomer, preferably an aliphatic hexa-fu notional urethane acrylate oligomer; and optionally

(v) a flow modifier.

The skilled person will appreciate that the method of the invention provides for a highly flexible way to manufacture hard-coated polymer sheet surfaces based on solid coating compositions comprising one or more aliphatic multi-functional urethane acrylate oligomers. That is to say, the method of the invention is suitable for application with aliphatic multi-functional urethane acrylate oligomers- based solid coatings known in the art, being it coatings comprising tri-, tetra, penta-, hexa-, hepta-, octa, nona-, deca-, etc, functional urethane acrylate oligomer or oligomers of the aliphatic type. Mixtures of aliphatic multi-functional urethane acrylate oligomers are commonly applied in such solid UV curable hard-coat compositions. The inventors established that such hard-coat compositions can be firmly adhered to sheets of polymer material at room temperature, if the surface of such as sheet is primed with a ketone or a solution comprising a ketone, such as cyclohexanone, or cyclohexanone in any of hexane, heptane, octane, DAA. In the method of the invention, the commonly applied step of heating a foil or film of polymer material during coating is now conveniently replaced by priming the sheet of polymer material with the ketone and subsequently contacting the primed surface area with the coating composition at ambient temperature, or at higher temperature if desired and if suitably applicable. Thus, coating while heating the coating composition and/or the polymer sheet is also possible according to the method of the invention, but it is not a requirement for arriving at a sheet of polymer material such as PC or PET-g provided with a strongly adhered hard-coat.

Since the method of the invention does not a mandatory step of contacting the sheet of polymer material with solid hard-coat composition, while heated at elevated temperature (e.g. 40°C - 90°C), there is in fact no limit as to the thickness of the sheet of polymer material that is coated with the hard-coat. A thin foil with a thickness of 200 micrometer or less is equally suitable for application in the method of the invention as a plate of fer example PC or PET-g with a thickness of about 1 cm - 12 cm, or more. Since an essential step in the method of the invention relates to covering the surface area of the sheet intended for coating, with the ketone such as cyclohexanone, the thickness of the sheet is not a limiting dimension in the method. The same for the coating step and subsequent UV curing step: these steps are alos independent from the sheet thickness. Since the sheet can be at room temperature or ambient temperature during priming and coating and UV curing, no heating of the sheet is involved in the method of the invention, therewith posing no limitation as to the thickness of the sheet that is selected for provision of a hard-coat. This way, the inventors provide a highly flexible and broadly applicable method for hard-coating a wide array of polymer material, i.e. sheets with a wide range of thicknesses from the thinnest foils available (PC, PET-g) up to the thickest sheets and plates commonly coated in e.g. automotive industry, glazing, window pane manufacturing, production of shields, and also including any laminates comprising e.g. a PC outer surface layer, being it a foil or plate with a thickness of 100 micrometer or larger.

Preferably, in the method of the invention, the polymer material is a polymer foil, a polymer film, a polymer plate or a polymer sheet made of polycarbonate or made of polyethylene terephthalate - glycol-mod ified (PET-g), preferably transparent polycarbonate ortransparent polyethylene terephthalate - glycol-modified (PET-g), more preferably transparent polycarbonate.

Also suitable are plates which are laminates comprising an outer surface layer of e.g. PC or PET-g of any thickness, which is to be provided with a hard-coat, for application in the method of the invention. Thus, the method of the invention is not limited to coating (at room temperature, or at elevated temperature if desired) of sheets made of a single polymer material, but instead the method is also suitably applied for coating of laminates that have an outer surface layer of PC or PET-g. Since the method does not require a step of heating the single-material sheet or laminate comprising an outer layer of a PC or PET-g foil, film, plate or sheet, laminates can be used in the method of the invention. There is no risk for damaging the laminate structure, composition, etc. by heating, because heating during coating is optional and not a requirement in order to arrive at a hard-coated laminate.

Preferred is the method of the invention, wherein the ketone is selected from any one or more of a straight-chain ketone, a branched ketone, an unsubstituted cyclic ketone and a cyclic ketone substituted with at least one alkyl group, or a combination thereof, preferable selected from a straightchain ketone, a branched ketone and an unsubstituted cyclic ketone, more preferably, the ketone is selected from any one of propan-2-one, butan-2-one, 3-methylbutan-2-one, pentan-2-one, pentan-3- one, cyclopentanone, 2-methylpentan-3-one, 3-methylpentan-2-one, 4-methylpentan-2-one, 4- methylpent-3-en-2-one, pentane-2, 4-dione, hexan-2-one, 3,5,5-trimethyl-2-cyclohexene-1-one, 5- methylhexan-2-one, methyl-isobutyl ketone, 1-cyclohexylpropan-1-one, 1 -cyclohexylethanone, cyclohexanone, heptan-2-one, heptan-4-one, 2,6-dimethyl-4-heptanon, octan-3-one, octan-2-one, octan-4-one, or a mixture thereof, most preferably the ketone is cyclohexanone. Also preferred is the method of the invention, wherein in step (b) a ketone solution is provided wherein the ketone, preferably cyclohexanone, is present in the ketone solution at a weight percentage of 2% - 50% based on the total weight of the ketone solution, preferably 3% - 40%, more preferably 4%

- 30%, most preferably 5% - 20%, such as 5% - 10%.

In the method of the invention, the amount of cyclohexanone (weight percentage based on the total weight of the primer solution) can be selected from a broad range of suitable amounts of ketone. Also priming with the sole ketone is possible in the method of the invention, when the resulting hard- coated polymer surface is considered. Since the primer solution may comprise less than 100% of the ketone, preferably cyclohexanone, the method is highly flexible. For any application, e.g. coating a broad range of solid hard coats comprising one or more aliphatic multi-functional urethane acrylate oligomers onto sheets of PC or PET-g, a suitable primer solution is selected based on the suitable ketones such as cyclohexanone and based on the suitable solvents and their relative amounts in the primer composition: 0-97.5% of e.g. hexane, heptane, octane, DAA. Based on the surface to be provided with a hard coat, such as PC or PET-g, and based on the composition of the solid hard-coat formulation, a ketone is selected, preferably cyclohexanone, the relative content of the ketone in the primer solution is selected, typically from 2,5% - 100% based on the total weight of the primer solution, and the solvent is selected if the ketone is not applied in pure form. This way, the method of the invention provides for a high degree of flexibility and applicability, when the type of polymer material is considered, when the characteristics and composition of the solid hard-coat is considered, and when the combination of the hard-coat and the polymer material is considered.

Preferred is the method of the invention, wherein in step (b) a ketone solution is provided wherein the solvent in the ketone solution is any one of hexane, heptane, octane and diacetone alcohol, or a mixture thereof, preferably any one of hexane, heptane and octane.

In the method of the invention, a sheet of polymer material such as PC and PET-g can be provided with a tightly bound hard-coat under room temperature conditions. However, coating at elevated temperature is equally possible when applying the method of the invention. Once the surface of the sheet is primed with ketone, adherence of the solid hard-coat is already facilitated at ambient temperature but coating at elevated temperatures is possible.

The inventors established that the surface of a sheet of polymer material has to be contacted with the ketone for as short as 10 seconds, in order to improve the adherence of the solid hard coat after UV curing. In practice, it is suitable when applying the method of the invention at room temperature, to flow a solution comprising ketone or the ketone over the sheet surface and to subsequently allow the remainder of the ketone to evaporate at room temperature or at elevated temperature (e.g. < 40°C). The inventors established that at a temperature of typically 17°C - 40°C such as room temperature or 35°C it takes about 5 - 40 minutes before a PC sheet or PET-g sheet is dry again after the ketone solution has been flown over the surface. Thus, the contact time can be shortened to 5 minutes or less than 5 minutes, e.g. 10 seconds - 5 minutes, when the temperature during drying of the ketone-contacted surface is elevated and/or when the remainder of the ketone solution is actively discarded, e.g. by wiping, blowing a gas over the ketone-primed surface, etc. That is to say, contacting the polymer sheet surface for 10 seconds with the ketone or the ketone-comprising primer solution is sufficient for establishing firm adherence ofthe solid hard coat in the subsequent steps of the method ofthe invention: coating and UV curing. Again, this way the method provides for flexibility when the time required from start to hard-coated end-product is considered. The coating time is controllable by selecting the drying time after priming the sheet with ketone.

Also preferred is the method according to the invention, wherein in step (d) the remainder of the ketone or the ketone solution is discarded at room temperature or at a temperature or temperature range selected from 17°C - 45°C, preferably 20°C - 40°C, more preferably 23°C - 37°C, most preferably 25°C - 35°C, such as 17°C - 35°C.

It is described in US2016/0193826A1 that it is believed that the use of cyclohexanone as a solvent in an ink and the use of a polycarbonate as (thermoformable) polymeric sheet has the advantage to greatly improve the penetration into the polymeric sheet of the ink material containing the ink composition and the solvent in which the ink composition is soluble. In the method of the invention, the priming, i.e. the treatment, of the polycarbonate sheet surface or surface of the PET-g sheet in step (c) ofthe method, with the ketone-containing primer or with the sole ketone, results in swollen or plasticized areas where the surface ofthe PET-g or the polycarbonate sheet is primed with the ketone. This swelling is caused by the one or more (cyclic) ketones being liquid at a temperature between 15 and 35°C in the primer solution penetrating the polycarbonate sheet or the PET-g sheet. As a result, the one or more (cyclic) ketones are distributed across at least part of the thickness of the sheet of PET-g or polycarbonate. As will be appreciated by those skilled in the art, if the thickness of the polycarbonate sheet or the PET-g sheet is limited, and/or if both sides of the polycarbonate sheet or PET-g sheet are treated with the ketone such as cyclohexanone and/or if the period of treatment (priming) is extended, the one or more (cyclic) ketones can be distributed across the whole thickness of the polycarbonate sheet or PET-g sheet.

The inventors have found that the use of a diluent chosen from the group consisting of diacetone alcohol (DAA), n-hexane, n-heptane and n-octane in the primer composition comprising the ketone can diminish the visual patterns, whitening, haze and/or orange peel of the primed areas of the polycarbonate sheet surface or the PET-g sheet surface and further the adhesion of the UV curable hard-coat during UV curing. Without wishing to be bound by any theory, it is believed that diluting the one or more (cyclic) ketones such as cyclohexanone, being liquid at a temperature between 15°C and 35°C, with a diluent chosen from the group consisting of diacetone alcohol, n-hexane, n-heptane and n- octane reduces the rate of evaporation of the one or more (cyclic) ketones from the surface of the polycarbonate sheet or PET-g sheet such that the one or more (cyclic) ketones can swell the polycarbonate sheet or PET-g sheet whereas they can also be (partially) removed at room temperature or at an elevated temperature such as < 40°C, without forming haze, whitening and visual patterns on the polycarbonate sheet or the PET-g sheet.

After priming of the surface of the sheet of polymer material with the ketone, the solid hard-coat composition is applied onto the primed surface, followed by UV curing. During curing, typically, the sheet surface is irradiated with UVA and UVB. During UVA-UVB irradiation of the coated polymer sheet surface, the surface becomes activated with regard to, without wishing to be bound by any theory, the presence of opened aromatic bonds and presence of newly created C-O bonds upon exposure to UV radiation, such that the ketone, e.g. the cyclohexanone, that is imbibed in the sheet surface, can form stable covalent bonds with said activated polymer surface, therewith enhancing the adherence and bonding interactions between the hard-coat and the polymer surface. Thus, the UV irradiated polymer surface is activated which triggers the ability for formation of stable bonds with ketone imbibed in the polymer sheet. Thus, since the surface of the PC sheet or PET-g sheet is imbibed with the ketone, e.g. cyclohexanone, UV irradiation results in improved cross-linking between the polymer and the hard-coat constituents, therewith forming an improved hard-coat, even at room temperature. The priming of the sheet with cyclohexanone is sufficient and enough to compensate for the coating at ambient temperature instead of coating at elevated temperature. UV radiation during curing not only serves the role of initiating the coat polymerization and adherence to the sheet, but in addition induces the bonding of cyclohexanone to the PC or PET-g, which further improves the binding of the hard-coat to the PC or PET-g surface.

Presence of HDDA in the coat composition lowers the viscosity of the coat composition, during the application of the coat composition onto the sheet surface and during subsequent evenly spreading of the coat composition over the intended surface area of the sheet of PET-g or PC. In particular, at elevated temperature during coating, the HDDA may aid in lowering the viscosity of the coat composition. In addition, the HDDA comprises two double bonds, available for cross-linking of e.g. the one or more aliphatic multi-functional urethane acrylate oligomers in the coat composition, therewith contributing to the hardness of the provided hard coat. For example, hardness of the provided hard coat on PC or PET-g can be improved when HDDA is added to a solid hard-coat composition comprising two aliphatic multi-functional urethane acrylate oligomers such as a combination of a tri-functional and a hexa-fu notional aliphatic urethane acrylate oligomer. Preferred is the method according to the invention, wherein in step (e) of the method the provided UV curable coating composition comprises or consists of, based on the total weight of the UV curable coating composition:

(5) 0,03% - 0,3% by weight of the flow modifier, preferably 0,05% - 0,2% by weight, preferably poly-ether-modified polydimethylsiloxane in a mixture of xylene and isobutanol, preferably the flow modifier is present.

Incorporating HDDA in the solid hard-coat compositions for application in the method of the invention further contributes to the widening of possible ketones, ketone concentrations, diluents of the ketones, selection of hard-coat constituents, e.g. combinations of various aliphatic multi-functional urethane acrylate oligomers at various ratio, coating temperature, etc. since the presence of HDDA can have a positive effect on the hardness of the final hard-coat achieved with the method, and can have a positive effect on the firmness of the adhesion of the hard-coat onto the surface of the sheet of polymer material.

Also preferred is the method of the invention, wherein in step (e) of the method the provided UV curable coating composition comprises or consists of, based on the total weight of the UV curable coating composition:

Without wishing to be bound by any theory, it is assumed that HDDA is penetrating the polymer surface layer, e.g. the PC film or sheet or PET-g film or sheet, when the coating formulation and/or the PC surface or PET-g surface are heated. Adding HDDA to the coating formulation improves the binding and adherence of the hard-coat to the PC or PET-g upon curing, as has been established in a comparative water-soak test for assessing binding of a hard-coat to a polymer surface. It is assumed that at elevated temperature, the HDDA penetrates or diffuses into the surface of the PC film or sheet or the PET-g film or sheet: an effect referred to as ‘inter penetration layer’. The inter penetration layer is thought to contribute to binding and adherence of the coating to the PC film or sheet or the PET-g film or sheet by the migration (or: penetration, diffusion) of the coating into the surface layer of the film or sheet, by enhanced mobility of the molecules (constituents) in the coating formulation during heating of the coating.

A second aspect of the invention relates to a polymer material comprising a surface coated with a UV-curable coating, obtained with or obtainable by the method according to the invention, wherein the polymer material preferably is a transparent polycarbonate foil or sheet, or a transparent PET-g foil or sheet.

A third aspect of the invention relates to use of the polymer material obtained with or obtainable by the method according to the invention, in the manufacturing of a transparent pane or window or shield such as a transparent laminate or glass pane, or of a formed article or formed object such as a thermoformed article or object and/or of a moulded article or object such as an injection-moulded article or object, preferably an article or object which comprises the polymer material comprising a surface coated with a UV-curable coating which is first formed and then back moulded such as back injection-moulded.

Preferred is the use according to the invention, wherein the article or object is an article or object such as a transparent glass pane or shield wherein the polymer material is transparent polycarbonate or PET-g, or a control panel and/or an article or object applied in automotive applications such as a radio panel, a control panel, a HVAC control system, or a part thereof, in telecom applications such as a housing, a keypad, an outer casing for a mobile phone.

A fourth aspect of the invention relates to an article or formed article, preferably thermoformed article, or object comprising the polymer material obtained with or obtainable by the method according to the invention, or provided according to the use according to the invention.

Preferred are an article or formed article, preferably thermoformed article according to the invention, which is a laminate comprising the polymer material obtained with or obtainable by the method according to the invention, such as a transparent window or shield, or which is an article or object applied in automotive applications such as a radio panel, a control panel, a HVAC control system, or a part thereof. The invention is further illustrated by the following examples, which should not be interpreted as limiting the present invention in any way. Modifications and alternative implementations of some parts or elements or compounds are possible, and are included in the scope of protection as defined in the appended claims.

EXAMPLES

With sheets of polycarbonate (PC), polyethylene terephthalate - glycol-modified (PET-g), poly(methyl methacrylate) (PMMA) and polyethylene terephthalate (PET), the effect of priming the polymer surface with a ketone, before a solid UV-curable hard-coat was applied onto the surface and UV cured, was tested. The thickness of the sheets was 2 mm or more. For firm adherence of the hard-coats that are tested, on for example polymer foil such as PC foil, heating the foil and the coating formulation is required, in order to establish proper contact between the surface and the coating formulation. Heating sheets of polymer material which has a certain thickness, for example 1 mm or larger, may be cumbersome. Heating such sheets sufficiently fast may cause difficulties. Equally heating such thick sheets may cause difficulties. It may be impossible to provide sufficient energy and heat to the thick polymer sheet that should be coated, such that the sheet cannot be heated at all to the desired temperature for coating. In this example, the inventors provide the insight that the heating can be omitted if the polymer surface is primed with a ketone, such as cyclohexanone at a concentration of 100% v/v or less, when dissolved or mixed with an alkane such as hexane, heptane, octane.

The transparent optical-grade polycarbonate was bisphenol A-based PC sheet with a thickness of 3 mm (Lexan ULG1003 (Sabie)).

The PET-g was Vivak clear 099 solid copolyester sheet (exoIon group (BE)), which is a clear transparent sheet with high light transmission. The thickness of the applied sheets was 3 mm. The sheets are thermoformable.

The polymer surfaces were optionally first irradiated with UV light using an F300s H-bulb Noblelight (Heaeus; power 120 W/cm, 1 pass provides 500 mJ/cm² UVA, 435 mJ/cm² UVB, 105 mJ/cm² UVC). The surfaces were irradiated with 0, 1 , 2 or 3 passes.

Primers that were applied onto the polymer surfaces are outlined in Table 1-4, here below, for the PET-g sheets and the PC sheets. PET sheets were only primed with 100% cyclohexanone (control: no priming). PMMA sheets were primed with 100% cyclohexanone or with 2,5% cyclohexanone mixed with 97,5% heptane (control: no priming). All solvents in the primer compositions are given as a weight percentage based on the total weight of the primer composition. For priming the polymer sheets, the primer compositions were provided onto the surface area of the sheets, and the primers were allowed to flow from the sheets in about 10 seconds (sheets were kepted at an angle of about 45° relative to the horizontal, allowing the primer to flow over the polymer sheet surface). Subsequently, a flash-off time was applied at the temperature indicated in Table 1-4 and for the indicated time period. For the PMMA the flash-off time was 15 minutes at 35°C (until complete dryness) for the 100% cyclohexanone and 10 minutes at room temperature for the 2,5% cyclohexanone in heptane. For PET, the flash-off time was 15 minutes at 35°C (until complete dryness). In general, for each primed polymer surface, the flash-off time and the drying temperature during the flas-off time period was selected such that within the time period the surface became dry.

After priming (controls: no priming or 100% alkane solvent, i.e. no ketone), either of two UV- curable 100% solid (no solvents present) hard-coat compositions was applied onto the primed surface area of the polymer sheets, or onto control surface area that was not primed. Coating compositions were as follows:

See Table 1 and 2: The UVFHCLED coating is a UV curable 100% solid (no solvent) hard-coat, for which the composition consists of:

Ebecryl 8465 41 ,7 % (w/w)

Ebecryl 5129 34,1 % (w/w)

HDDA 23,1 % (w/w)

IRG 819 1 % (w/w)

BYK300 0,1 % (w/w)

Ebecryl 8465 is an aliphatic urethane tri-acrylate oligomer (Ebecryl 8465 UV/electron beam (EB) energy curable resin; Allnex Group), an aliphatic tri-functional urethane acrylate oligomer.

Ebecryl 5129 is hexa-functional aliphatic urethane acrylate oligomer (Ebecryl 5129 UV/EB energy curable resin; Allnex Group), an aliphatic tri-functional urethane acrylate oligomer.

IRG 819 is a photo-initiator for radical polymerization of unsaturated resins upon UV light exposure, bis(2,4,6-trimethylbenzoyl)-phenyl-phosphine oxide, molecular weight 418,5 g/mol (Ciba IRGACURE 819 Photo-initiator; Ciba Specialty Chemicals, Inc.); BYK300 is a solution of a poly-ether-modified polydimethylsiloxane, a silicone surface additive for solvent-borne coating systems (BYK-300, BYK- Chemie GmbH, Wesel, DE) (density (20°C) is 0.94 g/ml, non-volatile matter (10 min., 150°C) is 52%, solvents are xylene and iso-butanol in a 4(:)1 volume/volume ratio, flash point is 23°C).

See Table 3 and 4: The EB8603 was the UV curable hard-coating Ebecryl 8603 binder (Allnex) which comprises acrylic resin oligomers (20-50%), photoinitiator 2-benzoil-2-propanol (5-10%) and functional monomers (acrylic acid, pentaerythritol, and hexamethylene diacrylate) (40-70%).

A line of coating composition was transferred onto a side area of the surface of the polymer sheet (base material). A layer of UV transparent sheet (stamp) was applied onto the coating composition and with the use of a laminator, the rollers of the laminator devided and pressed the coating composition over the surface of the polymer sheet. The roller temperature was room temperature. The coating thickness obtained was 7 - 10 micrometer. Subsequently, the coatings were cured onto the surfaces of the polymer sheets upon irradiation for 15 seconds with blue UV-LED of 395 nm (Ex 4Pico, 1 kW). Coated surface area was 27 cm times 18 cm. The curing was at 2,76 W/cm² and 41 JCm^-2. As a control, a sheet of the PC was also coated with the UV-curable hard-coat composition EB8603, without pre-treatment of the PC surface with a primer, i.e. neither of a solvent, cyclohexanone diluted in a solvent or with cyclohexanone. During the step of overlaying the surface area of the PC sheet with the solid coat composition, the temperature of the solid coat and of the sheet of PC was 80°C.

Adhesion of the hard-coat to the polymer surface was assessed according to the adhesion cross-hatch test commonly used in the art (norm ASTM 3359 Method A, as in force in Q4-2020; crosshatch set applied was from Gitter Schnitt, BYK Gardner and tape was Tesa Masking Tape 4651). The adhesion was assessed directly after the curing step. In addition, the water soak test was performed, and adherence of the coating after 1 , 2 and 3 days of soaking in water at 65°C was assessed. Furthermore, the quality of the coating was assessed by visual inspection after the curing step.

RESULTS

For the sheets of PMMA and PET, it was determined that no firm adhesion of the hard-coat onto the polymer sheet was established with any of the primer / coating protocols. That is to say, directly after UV curing, the coatings scored GT5 in the adhesion cross-hatch test.

For PC sheets, the results are depicted in Table 1 and Table 3, here below. The inventors established that for the UVFHCLED coating (Table 1) a hard coat was achieved when the surface of the PC sheet was first primed with a primer comprising cyclohexanone. The alkane solvent could be selected from hexane, heptane and octane. Hardness of the coating was high (GTO) and unaltered upon soaking in warm water for up to three days. Priming with the alkane only had no effect: hardness score of GT5 directly after curing. Thus, heating the coating composition was no prerequisite for arriving at a hard-coated PC sheet which has a hardness that makes application of the coated sheet in e.g. automotive applications suitable. Typically, a high hardness is achieved when the PC sheet is first primed with 5% cyclohexanone in hexane, and subsequently overlaid with the primer composition at room temperature, before UV curing.

For PET-g sheets, the results are depicted in Table 2 and Table 4, here below. The inventors established that for the UVFHCLED coating (Table 2) a hard coat was achieved when the surface of the PET-g sheet was first primed with a primer comprising cyclohexanone at an amount of larger than 2,5% by weight, in heptane. That is to say, a hard coat that scored GTO in the hardness test was obtained when the PET-g sheet was first primed with 5% or 10% cyclohexanone in heptane before the hard-coat composition was applied onto the surface and subsequently UV cured. At 2,5% cyclohexanone, no adherence of the coating composition, applied at room temperature, was established. Pre-treatment of the polymer surface with 1 , 2 or 3 passes of UV light had no positive influence on the firmness of the adhesion.

The inventors established that for the EB8603 coating (Table 3) a hard coat was achieved when the surface of the PC sheet was first primed with a primer comprising cyclohexanone. The alkane solvent was heptane or octane or diacetone alcohol, and good results were obtained with heptane and 5% cyclohexanone or higher and with 20% cyclohexanone in octane and with 20% cyclohexanone in diacetone alcohol. Hardness of the coating was high (GTO) and unaltered upon soaking in warm water for up to three days (primer comprises 10% cyclohexanone in the test). Priming with the alkane only had no effect: hardness score of GT5 directly after curing. Priming with 2,5% cyclohexanone in alkane provided a coating with modest adherence to the PC sheet, GT4. Thus, heating the coating composition was no prerequisite for arriving at a hard-coated PC sheet which has a hardness that makes application of the coated sheet in e.g. automotive applications suitable. Typically, a high hardness is achieved when the PC sheet is first primed with 5% or more cyclohexanone in heptane, and subsequently overlaid with the primer composition at room temperature, before UV curing. Typically, a high hardness is achieved when the PC sheet is first primed with 20% or more cyclohexanone in octane, and subsequently overlaid with the primer composition at room temperature, before UV curing. Priming the PC sheet with heptane or octane only, had no effect on coat adherence: GT5. Furthermore, priming with 100% cyclohexanone provided a coated PC sheet that scored GTO after UV curing.

The inventors established that for the EB8603 coating (Table 4) a hard coat was achieved when the surface of the PET-g sheet was first primed with a primer comprising cyclohexanone at an amount of 5% or higher by weight, such as 10% or more, in heptane. That is to say, a hard coat that scored GTO in the hardness test was obtained when the PET-g sheet was first primed with 10% cyclohexanone in heptane before the hard-coat composition was applied onto the surface and subsequently UV cured. At 5% cyclohexanone, adherence of the coating composition was also established (GT3), when the coating composition was applied at room temperature. Pre-treatment of the polymer surface with 1 , 2 or 3 passes of UV light had no positive influence on the firmness of the adhesion.

For the PMMA sheets and the PET sheets, priming with cyclohexanone at 100% concentration or less, had no influence on coating quality, when the coating compositions were applied onto the sheets at room temperature and subsequently UV cured: adhesion test score GT5.

TABLE 1 . Test results with PC sheet coated with UVFHCLED.

CHX: cyclohexanone; hept: heptane; DAA: diacetone alcohol; oct: octane; hex: hexane; visual insp.: visual inspection; 2d: at day 2; RT: room temperature (ambient temperature)

TABLE 2. Test results with PET-g sheet coated with UVFHCLED.

CHX: cyclohexanone; hept: heptane; visual insp.: visual inspection; min: minutes; RT: room temperature (ambient temperature)

TABLE 3. Test results with PC sheet coated with EB8603.

CHX: cyclohexanone; hept: heptane; DAA: diacetone alcohol; oct: octane; visual insp.: visual inspection; d3: at day 3; RT: room temperature (ambient temperature)

TABLE 4. Test results with PET-g sheet coated with EB8603.

CHX: cyclohexanone; hept: heptane; visual insp.: visual inspection Hardness test of coats/coating - taber abrasion

The hardness of the coatings on PC or on PET-g as tabulated in Table 1-4, provided with the method of the invention, is assessed in a taber abrasion test according to the ASTM D1044 standard as in force in Q4-2020 (version ASTM D1044 - 13). The hardness is compared for example to XtraForm hard- coated PC film (MacDerwind Enthone). The taber abrasion is a test to determine resistance of a polymer material to abrasion. Resistance to abrasion is defined as the ability of a material to withstand mechanical action such as rubbing, scraping, or erosion. Before subjecting coated film specimens to the taber abrasion test, the haze is measured. After subjecting the specimens to the taber abrasion test, the haze is again measured. Results of the test with a coated film or sheet are expressed by changes in % haze after the indicated number of test cycles (‘Delta haze’).

The UV curable hard-coated PC sheets and PET-g sheets, provided with low Delta haze after 100 cycles of taber abrasion in the taber abrasion test as executed according to ASTM D1044-13. In a comparative test with the XtraForm hard-coated polycarbonate film (MacDermid Enthone, Oxfordshire, UK), the test is revealing that the taber abrasion for this standard hard-coated PC film known in the art was 9,2%.

Hardness test of coats/coating - pencil test

The hardness of the coatings on the coated polymer materials provided with the method of the invention is assessed in a pencil test according to the ASTM D3363 standard as in force in Q4-2020 (version ASTM D3363 - 5(2011)e2). Determination of the coated PC sheet hardness or coated PET-g sheet hardness, i.e. the hardness of a coating on a substrate, involves the use of pencil leads of known hardness.

The UV curable hard-coated PC sheets and PET-g sheets provided with the method of the invention are presenting with a pencil hardness similar if not equivalent or the same to the pencil hardness of the XtraForm hard-coated PC film of MacDermid Enthone.

Chemical resistance test with coats/coatings

The chemical resistance of the coated PC sheet and the coated PET-g sheet provided with the method of the invention, and comparative example coatings (see Table 1-4) is assessed by determining the effect of exposure of a coat to liquid acetone. To this end, a coat applied onto a polymer film as a carrier of the coat, is provided with a cavity in the exposed top surface of the coat. Acetone is applied into the formed cavity and left for ten minutes at room temperature. After ten minutes, the acetone is removed and the effect of contacting the coat surface with acetone is assessed as a measure of chemical resistance of the coat.

The UV curable hard-coated PC sheets and PET-g sheets provided with the method of the invention are expressing high chemical resistance. After exposure of the coated PC sheets according to the method of the invention to the acetone, no detectable change is apparent, there is not any slight change in color or gloss apparent, not even a slight surface etching or severe staining is apparent, and not any of pitting, cratering, swelling or erosion of coating is apparent, and in addition none of obvious and significant deterioration is observed. In contrast, for XtraForm coated PC film it was obvious that the coated surface was less stable. An opaque surface with opalescent spots was observed for the XtraForm exposed to the acetone in the chemical resistance test.

Formability test with coatings

Polycarbonate sheets or PET-g sheets provided with the coatings according to Table 1-4 of the method of the invention are tested for their applicability in thermoforming applications. To this end, PC sheets or PET-g sheets are provided with a coat according to the method of the invention, and after UV curing of the coat as here above described, the coated sheets are subjected to thermofolding procedures known in the art. The applied process for forming the coated PC sheets is the so-called “Niebling process”. Note: the XtraForm PC sheet requires a second UV curing step, which is not required for the coatings outlined in Table 1-4.

The Niebling process for the forming of plastic sheets

The Niebling process is for the isostatic High Pressure Forming (HPF) of polymer materials. This “Niebling process” is applied for processing plastic films and other thin-layer materials. In brief, the Niebling process is described as follows (source: website of niebling Formtechnologie, Penzberg, DE). The heart of the Niebling process is a non-contact heating system. It comprises heating modules with individual heating elements; the temperatures of the elements are specifically adjusted. In this way a distinct temperature profile can be produced depending on the material and forming task. During this process, unlike during thermoforming, the substrate is only heated to the “glass transition temperature” (e.g. polycarbonate: approx. 148°C), as result the material can be formed, but it is not melted. Once placed in the form, the heated material is then formed using compressed air (forming pressures up to 300 bar). The result: low material stretching and minimal position tolerances for graphic motifs (depending on material and geometry 0.3 mm). At the same time, cycle times of 10 sec. to 15 sec. are achievable. The heating system interacts with a continuously pressure profile controller.

For the PC sheet or PET-g sheet coated with UVFHCLED or EB8603 according to the method of the invention, the formability is tested on a positive mould moulding set-up at an angle of 95° in a Niebling HPF forming process (forming temperature is 180°C).

Characteristics of applying the Niebling process of “isostatic” high pressure forming:

Low material stretching

Highest precision during the positioning of graphic motifs combined with reliable repeatability of the forming result ■ Retention of gloss levels, surface structures and surface feel (e.g. on matt or textured films)

■ Suitable for relatively large formats (up to 1 ,000 mm x 500 mm; forming height: up to 300 mm) and larger material thicknesses (up to 12 mm for polycarbonate)

■ Suitable for amongst other materials, PC

■ Excellently suited to the forming of films with chemically-resistant and scratch-resistant surfaces.

Elongation test - forming at elevated temperature

For testing the resistance to formation of hair-like cracks in the coating on PC sheet or PET-g sheet, the coated PC sheet and PET-g sheet coated with the formulations of Table 1-4, were subjected to an outer elongation test. That is to say, the sheets were first heated for 5-10 minutes at 161-170°C in an oven and subsequently forced over a mold, i.e. a pipe made of polyvinylchloride (PVC) with an outer diameter of 79 mm, therewith thermoforming the heated sheets, followed by cooling to room temperature. The appearance and presence of cracks, e.g. hair-like cracks, in the coating at the formed and bend outer surface of the coated PC sheets ad PET-g sheets pointing away from the PVC pipe, was assessed by irradiating the outer surface with a fluorescence lamp. The tested PC and PET-g sheets had a thickness of 2 mm or 3 mm, respectively. The data are achieved with a bisphenol A-based PC film with a thickness of 2 mm. The tested hard-coated PC sheets were bisphenol A-based PC sheets that were provided with the UV curable solid hard-coat composition UVFHCLED or EB8603 according to the method of the invention. In the elongation test, the assessment of the appearance of hair-like cracks was assessed at constant outer fiber strain (OFS) which was the same for all coated sheets. The OFS is calculated as follows: it is assumed that after forming the PC sheet does not experience any strain in the middle of the sheet of foil, when the thickness of the foil is considered (for a sheet of PC foil with a thickness of 2 mm, the middle of the sheet of foil is defined as the location in the sheet, at half the thickness of the foil, i.e. 1 mm below the surface). After thermofolding, the radius of the outer surface of the sheet bend around the pipe minus the radius of the middle of the bend sheet, divided by the radius of the middle of the bend sheet, multiplied by 100, provides the OSF as a percentage elongation of the coating at the outer foil surface.

Claims

1 . Method for providing a polymer material with a surface coated with a UV-curable coating, comprising the steps of or consisting of the steps of:

(a) providing the polymer material;

(e) providing a UV-curable coating composition;

2. Method according to claim 1 , wherein the polymer material is made of polycarbonate or made of polyethylene terephthalate - glycol-modified (PET-g).

3. Method according to claim 1 or 2, wherein the UV-curable coating composition of step (e) is a solid UV-curable coating composition or a UV-curable hard-coating composition, preferably a solid UV- curable hard-coating composition.

4. Method according to any one of the claims 1-3, wherein the UV-curable coating composition comprises:

(i) a first aliphatic multi-functional urethane acrylate oligomer;

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(v) a flow modifier.

5. Method according to any one of the claims 1-4, wherein the UV-curable coating composition comprises: (i) a first aliphatic multi-functional urethane acrylate oligomer which is any one of an aliphatic three-functional - dodeca-functional urethane acrylate oligomer;

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(v) a flow modifier.

6. Method according to any one of the claims 1-5, wherein the UV-curable coating composition comprises:

(ii) a photo-initiator;

(iii) a diluent, preferably 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA);

(v) a flow modifier.

7. Method according to any one of the claims 1-6, wherein the polymer material is a polymer foil, a polymer film, a polymer plate or a polymer sheet, preferably with a thickness of 200 micrometer or more, preferably 200 micrometer - 100 millimeter, more preferably 200 micrometer - 80 millimeter, most preferably, 200 micrometer - 15 mm.

8. Method according to any one of the claims 1-7, wherein the polymer material is a polymer foil, a polymer film, a polymer plate or a polymer sheet made of an amorphous material or a semi-crystalline material, preferably a transparent amorphous material or a transparent semi-crystalline material.

9. Method according to any one of the claims 1-8, wherein the polymer material is a polymer foil, a polymer film, a polymer plate or a polymer sheet made of polycarbonate or made of polyethylene terephthalate - glycol-modified (PET-g), preferably transparent polycarbonate or transparent polyethylene terephthalate - glycol-modified (PET-g), more preferably transparent polycarbonate.

10. Method according to any one of the claims 1-9, wherein the ketone is selected from any one or more of a straight-chain ketone, a branched ketone, an unsubstituted cyclic ketone and a cyclic ketone substituted with at least one alkyl group, or a combination thereof, preferable selected from a straightchain ketone, a branched ketone and an unsubstituted cyclic ketone, more preferably, the ketone is selected from any one of propan-2-one, butan-2-one, 3-methylbutan-2-one, pentan-2-one, pentan-3- one, cyclopentanone, 2-methylpentan-3-one, 3-methylpentan-2-one, 4-methylpentan-2-one, 4- methylpent-3-en-2-one, pentane-2, 4-dione, hexan-2-one, 3,5,5-trimethyl-2-cyclohexene-1-one, 5- methylhexan-2-one, methyl-isobutyl ketone, 1-cyclohexylpropan-1-one, 1 -cyclohexylethanone, cyclohexanone, heptan-2-one, heptan-4-one, 2,6-dimethyl-4-heptanon, octan-3-one, octan-2-one, octan-4-one, or a mixture thereof, most preferably the ketone is cyclohexanone.

11. Method according to any one of the claims 1-10, wherein in step (b) a ketone solution is provided wherein the ketone is present in the ketone solution at a weight percentage of 2% - 50% based on the total weight of the ketone solution, preferably 3% - 40%, more preferably 4% - 30%, most preferably 5%

- 20%, such as 5% - 10%.

12. Method according to any one of the claims 1-11 , wherein in step (b) a ketone solution is provided wherein the solvent in the ketone solution is any one of hexane, heptane, octane and diacetone alcohol, or a mixture thereof, preferably any one of hexane, heptane and octane.

13. Method according to any one of the claims 1-12, wherein in step (c) at least the surface of the polymer material which is contacted with ketone or ketone solution is kept at a temperature or temperature range selected from 17°C - 40°C, preferably 18°C - 37°C, more preferably 19°C - 33°C, most preferably 20°C - 30°C.

14. Method according to any one of the claims 1-13, wherein in step (c) the ketone or the ketone solution is contacted with the surface of the polymer material while at room temperature or while at a temperature or temperature range selected from 17°C - 40°C, preferably 18°C - 37°C, more preferably 19°C - 33°C, most preferably 20°C - 30°C.

15. Method according to any one of the claims 1-14, wherein in step (c) the ketone or the ketone solution is contacted with the surface of the polymer material for a time period selected from the range 5 minutes

16. Method according to any one of the claims 1-15, wherein in step (d) the remainder of the ketone or the ketone solution is discarded at room temperature or at a temperature or temperature range selected from 17°C - 45°C, preferably 20°C - 40°C, more preferably 23°C - 37°C, most preferably 25°C - 35°C, such as 17°C - 35°C.

17. Method according to any one of the claims 1-16, wherein in step (e) the provided UV curable coating composition comprises the diluent 6-prop-2-enoyloxyhexyl prop-2-enoate (HDDA), present at 10% - 40% by weight based on the total weight of the UV curable coating composition, preferably 15% - 30% by weight, more preferably 20% - 25% by weight, such as 20% - 35% by weight.

18. Method according to any one of the claims 1-17, wherein in step (e) of the method the provided UV curable coating composition comprises or consists of, based on the total weight of the UV curable coating composition:

(5) 0,03% - 0,3% by weight of the flow modifier, preferably 0,05% - 0,2% by weight, preferably poly-ether-modified polydimethylsiloxane in a mixture of xylene and iso-butanol, preferably the flow modifier is present.

19. Method according to any one of the claims 4-18, wherein in step (e) of the method the provided UV curable coating composition comprises or consists of, based on the total weight of the UV curable coating composition:

20. Method according to any one of the claims 1-19, wherein in step (f) of the method the UV curable coating composition has a temperature or temperature range selected from 45°C - 95°C, preferably 55°C - 85°C, more preferably 57°C - 83°C, most preferably 60°C - 80°C, and/or wherein in step (f) of the method at least the surface of the polymer material which is contacted with the UV curable coating composition is kept at a temperature or temperature range selected from 45°C - 95°C, preferably 55°C - 85°C, more preferably 57°C - 83°C, most preferably 60°C - 80°C, and preferably in step (f) of the method the UV curable coating composition and the surface of the polymer material which is contacted with the UV curable coating composition are kept at a temperature or temperature range selected from 45°C - 95°C, preferably 55°C - 85°C, more preferably 57°C - 83°C, most preferably 60°C - 80°C, preferably at the same temperature.

21 . Polymer material comprising a surface coated with a UV-curable coating, obtained with or obtainable by the method according to any one of the previous claims.

22. Polymer material according to claim 21 , wherein the polymer material preferably is a transparent polycarbonate foil or sheet, or a transparent PET-g foil or sheet.

23. Use of the polymer material of claim 21 or claim 22 in the manufacturing of a transparent pane or window or shield such as a transparent laminate or glass pane, or of a formed article or formed object such as a thermo-formed article or object and/or of a moulded article or object such as an injection- moulded article or object, preferably an article or object which comprises the polymer material comprising a surface coated with a UV-curable coating which is first formed and then back moulded such as back injection-moulded.

24. Use of claim 23, wherein the article or object is an article or object such as a transparent glass pane or shield wherein the polymer material is transparent polycarbonate or PET-g, or a control panel and/or an article or object applied in automotive applications such as a radio panel, a control panel, a HVAC control system, or a part thereof, in telecom applications such as a housing, a keypad, an outer casing for a mobile phone.

25. Article or formed article, preferably thermoformed article, or object comprising the polymer material of claim 21 or 22, or provided according to claim 23 or 24.

26. Article or formed article according to claim 25, being a thermoformed article.

27. Article or formed article, preferably thermoformed article of claim 26, which is a laminate comprising the polymer material, such as a transparent window or shield, or which is an article or object applied in automotive applications such as a radio panel, a control panel, a HVAC control system, or a part thereof.