WO2013081816A1

WO2013081816A1 - Clear coat coating composition

Info

Publication number: WO2013081816A1
Application number: PCT/US2012/064883
Authority: WO
Inventors: Carmen Flosbach; Thomas Grawe; Kristina HOHLER
Original assignee: U.S. Coatings Ip Co. Llc; Coatings Foreign Ip Co. Llc
Priority date: 2011-11-30
Filing date: 2012-11-13
Publication date: 2013-06-06

Abstract

A clear coat coating composition with a resin solids content comprising a hydroxyl-functional binder component and a crosslinker component, wherein the hydroxyl-functional binder component comprises at least one polyester polyol binder comprising at least one aliphatic polyether polyol having -OCH₂C_nF_2n+1 groups with n = 1 or 2 as a building block, and wherein said -OCH₂CnF_2n+1groups provide the clear coat coating composition with a fluorine content of 0.1 to 3 wt.%, calculated on the resin solids content of the clear coat coating composition.

Description

Title of Invention

CLEAR COAT COATING COMPOSITION

Field of the Invention

The invention relates to a clear coat coating composition which can be used in a process for the preparation of an outer clear coat layer of an automotive multi-layer coating.

Background of the Invention

Modern automotive multi-layer coatings typically comprise a two- layer topcoat consisting of a color- and/or special effect-imparting base coat layer and an outer clear coat layer on top of that base coat layer. The pigmented base coat layer provides the color of the automotive multi-layer coating and the clear coat has a protective as well as decorative function. It is desirable for the clear coat to be self-cleanable, i.e. to allow for easily washing off dirt from its surface just by the action of rain. Such clear coats are called easy-to-clean clear coats.

Easy-to-clean coating compositions have been developed which exhibit good initial self-cleanability due to a surface enrichment of hydrophobic substance in the easy-to-clean coating layer, see for example, WO 2007/1 04654 A1 , US 2004/01 27593 A1 , US 5,597,874 and US 5,705,276.

"Initial self-cleanability" means the maximum level of self- cleanability that an easy-to-clean clear coat layer has at the beginning of its service life. However, the self-cleanability of easy-to-clean clear coats often suffers over time during which the easy-to-clean clear coat layer is exposed to the weather, i.e. its self-cleanability reduces over time as compared to its initial self-cleanability.

The self-cleanability of a coating layer over time can be determined by the following method. First, the initial self-cleanability of a panel provided with the coating layer to be tested is determined by applying Leverkusen standard dirt 09 LD-40 (commercially available from wfk institute Krefeld, Germany) to all but a 4 centimeter portion of one end of the horizontally positioned panel. Dirt application is performed making use of a sieve. Three 25μΙ drops of deionized water are placed on the unsoiled area of the coated panel. The unsoiled end of the panel is slowly and continuously raised from the horizontal position to a 30° angle causing the water drops to move through the soiled area. After 5 minutes the position of the water drops is recorded and it is visually rated how much dirt the water drops on their move downwards have removed from the surface. The coated panel is then carefully cleaned to remove any remaining dirt and it is thereafter subjected to artificial weathering conditions (500 hours according to SAE J2527). Then the self-cleanability test is repeated followed by further cycles of artificial weathering and self-cleanability testing. Finally, self-cleanability data comprising the initial self-cleanability and self-cleanability after 500, 1000 and 2000 hours of artificial weathering are obtained and a trend can be estimated, if or to what extent the self- cleanability of the coating layer reduces over time when exposed to the weather.

SUMMARY OF THE INVENTION

The invention relates to a clear coat coating composition with a resin solids content comprising a hydroxyl-functional binder component and a crosslinker component, wherein the hydroxyl-functional binder component comprises at least one polyester polyol binder comprising at least one aliphatic polyether polyol having -OCH₂C_nF₂n+i groups with n = 1 or 2 as a building block, and wherein said -OCH₂CnF₂n+i groups provide the clear coat coating composition with a fluorine content of 0.1 to 3 wt.% (weight%), calculated on the resin solids content of the clear coat coating composition.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the description and the claims the term "aliphatic polyether polyol" is used. The phrase is intended to include moieties having linear, branched and/or cycloaliphatic groups in said polyether polyol. In the description and the claims the term "aliphatic polyether polyol having

groups with n = 1 or 2" is used. For brevity, it is also called "fluorine-containing polyether polyol" herein.

The clear coat coating composition of the invention is liquid, contains organic solvent(s) and may have a solids content of, for example, 45 to 65 wt.%.

The solids content of the clear coat coating composition consists of the solids contributions of the resinous constituents (the resin solids content) of the clear coat coating composition plus the solids contributions of optionally present non-volatile components like pigments, fillers

(extenders) and non-volatile additives.

It has been found that a clear coat layer exhibiting good optical appearance (smooth surface, high gloss) and having a sustainable easy- to-clean effect can be produced from a clear coat coating composition comprising a hydroxyl-functional binder component comprising at least one polyester polyol binder which comprises a special fluorine-containing building block. In this context "sustainable easy-to-clean effect" means that the initial self-cleanability hardly suffers or does not suffer over the clear coat layer's lifetime or service life during which it experiences long-term exposure to the weather including exposure to sunlight as well as rain water to name only two strain factors.

The resin solids content of the clear coat coating composition comprises a hydroxyl-functional binder component and a crosslinker component, or, to be more precise, it comprises the solids contributions of the hydroxyl-functional binder component and of the crosslinker component. In an embodiment, the resin solids content of the clear coat coating composition consists of the hydroxyl-functional binder component and of the crosslinker component. The resin solids content of the clear coat coating composition may be in the range of, for example, 40 to 65 wt.%, based on the total clear coat coating composition.

The hydroxyl-functional binder component comprises at least one polyester polyol binder which comprises at least one fluorine-containing polyether polyol as a building block. In other words, the at least one fluorine-containing polyether polyol is chemically incorporated in the at least one polyester polyol binder. In still other words, the at least one fluorine-containing polyether polyol is covalently built-in in the at least one polyester polyol binder via ester linkages which represent the result of an esterification reaction between some or all of the hydroxyl groups of the at least one fluorine-containing polyether polyol and carboxyl groups.

As already mentioned, the at least one fluorine-containing polyether polyol has -OCH₂C_nF2n+i groups with n = 1 or 2. The oxygen atom in the formula -OC H2CnF₂n+i represents an ether bridge. The fluorine-containing polyether polyol has two or more unetherified free hydroxyl groups.

The fluorine-containing polyether polyol has a fluorine content provided by its -OCH₂C_nF_2n+i groups in the range of, for example, 24 to 40 wt.%.

The fluorine-containing polyether polyol may have a calculated molar mass in the range of, for example, 470 to 5000. The molar mass can be calculated from the fluorine-containing polyether polyol's empirical or structural formula, which in the case of an oligomer or polymer may take the form of an average formula.

In a preferred embodiment, the fluorine-containing polyether polyol is a polyether diol with the formula

HO[CH₂C(CH3)(CH₂OCH₂CF3)CH₂0]_xCH₂C(CH3)₂CH₂- [OCH2C(CH3)(CH₂0CH₂CF3)CH2]yOH with x+y = 6 on average, which is commercially available under the trade name POLYFOX™ PF-636 from OMNOVA Solutions, Fairlawn, Ohio.

In another preferred embodiment, the fluorine-containing polyether polyol is a polyether diol with the formula

HO[CH2C(CH3)(CH₂OCH2C2F5)CH20]_xCH2C(CH3)2CH2- [OCH₂C(CH3)(CH₂OCH₂C₂F₅)CH₂]_yOH with x+y = 6 on average, which is commercially available under the trade name POLYFOX™ PF-656 also from OMNOVA Solutions. The -OCH₂C_nF_2n+i groups of the at least one fluorine-containing polyether polyol chemically incorporated in the at least one polyester polyol binder provide the clear coat coating composition with a fluorine content of 0.1 to 3 wt.%, preferably 0.2 to 1 .5 wt.%, calculated on the resin solids content of the clear coat coating composition. The composition of the at least one polyester polyol binder and its proportion in the hydroxyl- functional binder component is selected accordingly.

The total proportion of the at least one fluorine-containing polyether polyol chemically incorporated in the at least one polyester polyol binder in the clear coat coating composition may be in the range of, for example, 0.5 to 8 wt.%, preferably 0.5 to 4 wt.%, calculated on the resin solids of the clear coat coating composition.

The polyester polyol binder may have a number-average molar mass (Mn) in the range of, for example, 800 to 1 0000. Its hydroxyl number is in the range of 50 to 300 mg of KOH/g. Its acid number is in the range of, for example, 0 to 30 mg of KOH/g.

All number-average molar mass data stated herein are number- average molar masses determined or to be determined by gel permeation chromatography (GPC; divinylbenzene-cross-linked polystyrene as the immobile phase, tetrahydrofuran as the liquid phase, polystyrene standards).

The production of polyester polyols is known to the person skilled in the art; in particular, they may be produced by polycondensation of polyols and polycarboxylic acids.

The polyester polyol binder may be produced by reacting one or more carboxyl components comprising one or more polycarboxylic acids with one or more hydroxyl components comprising one or more polyols, wherein the one or more polyols comprise the at least one fluorine- containing polyether polyol. In an embodiment, the polyol(s) consist of one or more, in particular one, fluorine-containing polyether polyol. In addition to one or more polycarboxylic acids the carboxyl components may also comprise monocarboxylic acids and

hydroxycarboxylic acids.

Examples of polycarboxylic acids suitable for the production of the polyester polyol binder can include tetrahydrophthalic acid,

hexahydrophthalic acid, 1 ,3- and 1 ,4-cyclohexane dicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecane

dicarboxylic acid, maleic acid, fumaric acid, dimer fatty acids or a combination thereof.

Examples of monocarboxylic acids suitable for the production of the polyester polyol binder can include 2-ethylhexanoic acid, isononanoic acid, coconut fatty acid, decanoic acid, dodecanoic acid, tetradecanoic acid, stearic acid, palmitic acid or a combination thereof.

Examples of hydroxycarboxylic acids suitable for the production of the polyester polyol binder can include 12-hydroxystearic acid, 6- hydroxyhexanoic acid, citric acid, tartaric acid, dimethylolpropionic acid or a combination thereof.

In addition to one or more polyols the hydroxyl components may also comprise monoalcohols.

As already mentioned, the at least one fluorine-containing polyether polyol may be the only polyol building block of the polyester polyol binder. However, it is also possible to additionally employ other polyol building blocks. Examples of such other additional polyols suitable for the production of the polyester polyol binder can include, for example, polyols like ethylene glycol, the isomeric propane- and butanediols, 1 ,5- pentanediol, 1 ,6-hexanediol, 1 ,10-decanediol, 1 ,1 2-dodecanediol, 1 ,4- cyclohexanedimethanol, hydrogenated bisphenol A, dimer fatty alcohol, neopentyl glycol, butylethylpropanediol, the isomeric cyclohexanediols, the isomeric cyclohexanedimethanols, tricyclodecanedimethanol, but also polyols with more than two hydroxyl groups like glycerol,

trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol or a combination thereof. Examples of monoalcohols suitable for the production of the polyester polyol binder can include, for example, linear or branched saturated monoalcohols like hexanol, dodecanol, cyclohexanol or a combination thereof.

The person skilled in the art selects the nature and proportion of the one or more carboxyl components and the one or more hydroxyl components for the production of the polyester polyol binder in such a manner that a polyester polyol binder with the above characteristics regarding hydroxyl content and fluorine content provided by the - OCH₂C n ₂n+i groups of the at least one fluorine-containing polyether polyol is obtained.

The polyester polyol binder may be prepared by polycondensation of the one or more carboxyl components and the one or more hydroxyl components. Polycondensation may be carried out by the conventional methods known to the skilled person, for example, in the presence of conventional esterification catalysts and at elevated temperatures from, e.g. 1 20° C to 180° C, for example, in the melt. Optionally, entrainers, such as, e.g. xylene, may also be used. The one or more carboxyl components and the one or more hydroxyl components may be reacted together to form the polyester polyol binder in a multi-step or preferably one-step synthesis process. The one or more carboxyl components and the one or more hydroxyl components are preferably charged at the same time and heated together, optionally, melted and polycondensed with one another to form the polyester polyol binder.

In addition to the at least one polyester polyol binder, the hydroxyl- functional binder component may also comprise one or more other hydroxyl-functional binders as are conventionally used in the art of paint and coatings. In a typical embodiment, the hydroxyl-functional binder component consists of the polyester polyol binder or of the polyester polyol binder plus one or more other hydroxyl-functional binders.

Examples of such other hydroxyl-functional binders include conventional hydroxyl-functional binders known to the person skilled in the art, and they are readily available commercially or may be prepared by conventional synthesis procedures. Examples are polyester polyols other than the at least one polyester polyol binder comprising the fluorine-containing polyether polyol, polyurethane polyols and (meth)acrylic copolymer resin polyols, but also hydroxyl-functional polymer hybrid resins derived from these classes of resin binders, for example, wherein two or more of said resin types bound by covalent bonds or in the form of interpenetrating resin molecules are present. (Meth)acryl or (meth)acrylic is to be understood, both here and in the following, as acryl and/or methacryl or as acrylic and/or methacrylic. The other hydroxyl-functional binders are oligomeric or polymeric compounds with a number-average molar mass (Mn) in the range of, for example, 500 to 1 0000, preferably 1 000 to 5000. Their hydroxyl numbers are in the range of, for example, 60 to 300 mg of KOH/g.

The crosslinker component comprises one or more cross-linking agents conventionally used in clear coating systems based on hydroxyl- functional binders. Examples can be selected from transesterification cross-linking agents; amino resin cross-linking agents, such as, melamine- formaldehyde resins; free or reversibly blocked polyisocyanate cross- linking agents; and/or trisalkoxycarbonylaminotriazine cross-linking agents. In case of free or reversibly blocked polyisocyanate cross-linking agents it is preferred not to employ polyisocyanates with aromatically bonded NCO groups.

As already mentioned, the clear coat coating composition of the invention contains organic solvent(s). The organic solvent content may be, for example, 35 to 55 wt.%; the sum of the wt.% of the solids content and the organic solvent content is, for example, 90 to 100 wt.% (any possible difference in the corresponding range of above 0 to 10 wt.% to make up to the total of 1 00 wt.% is in general formed by volatile additives). The organic solvents are in particular conventional coating solvents, for example, glycol ethers, such as, butyl glycol, butyl diglycol,

ethoxypropanol, dipropylene glycol dimethyl ether, dipropylene glycol monomethyl ether, ethylene glycol dimethylether; glycol ether esters, such as, ethyl glycol acetate, butyl glycol acetate, butyl diglycol acetate, methoxypropyl acetate; glycols, for example, propylene glycol and oligomers thereof; esters, such as, butyl acetate, isobutyl acetate, amyl acetate; ketones, such as, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone; alcohols, such as, methanol, ethanol, (iso)propanol, butanol, hexanol; N-alkyl pyrrolidones, such as, N-ethyl pyrrolidone; aromatic hydrocarbons, such as, xylene, SOLVESSO® 100 (mixture of aromatic hydrocarbons with a boiling range from 1 55°C to 185°C), SOLVESSO® 150 (mixture of aromatic

hydrocarbons with a boiling range from 1 82°C to 202°C) and aliphatic hydrocarbons. A combination of any of the solvents can also be used.

The clear coat coating composition of the invention may also contain volatile or non-volatile additives. Examples include catalysts, levelling agents, wetting agents, anticratering agents, dyes, rheology control agents, antioxidants and/or light stabilizers. The additives are used in conventional amounts of, for example, up to 10 wt.% in total, calculated on the resin solids of the clear coat coating composition.

The clear coat coating composition is a transparent coating composition which can be applied and cured to form a transparent clear coat layer. However, this does not necessarily exclude the presence of a small amount of pigments in the clear coat coating composition. For example, if a colored clear coat coating composition is desired, pigments may be comprised.

The clear coat coating composition may also comprise transparent fillers like, for example, silica.

The clear coat coating composition can be spray-applied to form a clear coat layer on an automotive substrate. Therefore, the invention relates also to a process for producing an outer clear coat layer of an automotive multi-layer coating, or, respectively, to a process for the production of an automotive base coat/clear top coat two-layer coating. The process comprises the steps: (1 ) providing an automotive substrate provided with an uncured pigmented base coat layer,

(2) applying the clear coat coating composition of the invention on the uncured base coat layer to form a clear coat layer thereon, and

(3) jointly curing the base coat and the clear coat layers.

The automotive substrate provided with the uncured pigmented base coat layer may be an automotive substrate to be OEM (original equipment manufacture) clear coated or an automotive substrate to be repair clear coated. The term "automotive substrate to be OEM clear coated" refers to the case where the clear coat is to be applied as an original coating. The term "automotive substrate to be repair clear coated" refers to the case where the clear coat is to be applied as a refinish clear coat.

Automotive substrates include in particular automotive bodies and automotive body metal or plastic parts. Examples of automotive bodies include truck and vehicle bodies, for example, passenger car bodies and van bodies. Examples of automotive body metal or plastic parts include doors, bonnets, boot lids, hatchbacks, wings, spoilers, bumpers, collision protection strips, side trim, sills, mirror housings, door handles and hubcaps.

The uncured pigmented base coat layer on the automotive substrate represents the color and/or special effect-imparting coating layer of the automotive multi-layer coating produced by the process of the invention. The uncured pigmented base coat layer may have been applied from an automotive OEM base coat or from an automotive repair base coat.

The clear coat coating composition may be applied by spraying in a dry film thickness in the range of, for example, 20 to 60 μηη. The clear coat application is performed by the so-called wet-on-wet method on the uncured pigmented base coat layer. Preferably after a brief flash-off phase the clear coat layer is jointly cured together with the so far uncured pigmented base coat layer. The curing conditions depend on the binder/crosslinker system of the clear coat coating composition and the circumstances under which the coating and curing process is carried out. The curing temperature may range from 20 to 160°C, for example. If the clear coat coating composition is used for refinish coating purposes, more gentle curing conditions may be required than in automotive OEM clear coating. Curing conditions as prevail in automotive OEM coating mean, for example, 20 to 30 minutes at an object temperature of, for example, 80 to 160°C, whereas curing conditions in refinishing may mean an object temperature of, for example, 20 to 80°C, in particular, 20 to 40 minutes at an object temperature of, for example, 40 to 80°C.

The cured automotive multi-layer coating produced by the process of the invention has an outer easy-to-clean clear top coat layer. Its self- cleanability is sustainable; even when exposed to the weather it hardly reduces or it does even not reduce over the clear coat layer's service life.

Claims

CLAIMS What is claimed is:

1 . A clear coat coating composition with a resin solids content comprising a hydroxyl-functional binder component and a crosslinker component, wherein the hydroxyl-functional binder component comprises at least one polyester polyol binder comprising at least one aliphatic polyether polyol having -OCH2C_nF2n+i groups with n = 1 or 2 as a building block, and wherein said

groups provide the clear coat coating composition with a fluorine content of 0.1 to 3 wt.%, calculated on the resin solids content of the clear coat coating composition.

2. The clear coat coating composition of claim 1 , wherein the crosslinker component comprises one or more cross-linking agents selected from transesterification cross-linking agents; amino resin cross- linking agents, free polyisocyanate cross-linking agents, reversibly blocked polyisocyanate cross-linking agents, and trisalkoxycarbonylaminotriazine cross-linking agents.

3. The clear coat coating composition of claim 1 or 2 containing organic solvent(s).

4. The clear coat coating composition of claim 1 , 2 or 3, wherein the at least one fluorine-containing polyether polyol has a fluorine content provided by its

groups in the range of 24 to 40 wt.%.

5. The clear coat coating composition of any one of the preceding claims, wherein the at least one fluorine-containing polyether polyol is a polyether diol of the formula HO[CH2C(CH3)(CH₂OCH2CF3)CH20]_xCH2C(CH3)2CH2-

[OCH₂C(CH₃)(CH₂0CH₂CF₃)CH₂]yOH with x+y = 6 on average.

6. The clear coat coating composition of any one of claims 1 to 4, wherein the at least one fluorine-containing polyether polyol is a polyether diol of the formula

HO[CH2C(CH3)(CH₂OCH2C2F5)CH20]_xCH2C(CH3)2CH2- [OCH2C(CH3)(CH₂0CH₂C₂F5)CH2]yOH with x+y = 6 on average.

7. The clear coat coating composition of any one of the preceding claims, wherein the proportion of the at least one fluorine-containing polyether polyol chemically incorporated in the at least one polyester polyol binder in the clear coat coating composition is in the range of 0.5 to 8 wt.%, calculated on the resin solids of the clear coat coating

composition.

8. A process for the production of an automotive base coat/clear top coat two-layer coating comprising the steps:

(1 ) providing an automotive substrate provided with an uncured pigmented base coat layer,

(2) applying the clear coat coating composition of any one of the preceding claims on the uncured base coat layer to form a clear coat layer thereon, and

(3) jointly curing the base coat and the clear coat layers.