TWI808232B - Coating composition comprising polysiloxane-modified polyurethane for soft-feel, stain resistant coatings - Google Patents

Abstract

The invention relates to a 2K coating composition comprising a polysiloxane-modified polyurethane and a hardener, wherein the polysiloxane-modified polyurethane obtainable by a method comprising the following steps: a) subjecting a polyol to a reaction with an isocyanate-functional silane coupling agent to obtain a silane-grafted polyol, and b) subjecting the silane-grafted polyol to a condensation reaction with a hydroxyl-functional polysiloxane, to obtain the polysiloxane-modified polyurethane. The polysiloxane-modified polyurethane can be used in a coating composition to form a coating which has smooth feel, stain resistance and easy clean properties, particularly desired in the field of e.g. consumer electronics and automotive industry.

Description

Coating composition comprising polysiloxane-modified polyurethane for soft-feel antifouling coating

The present invention relates to coating compositions containing polysiloxane-modified polyurethanes for the production of coatings with soft feel and anti-fouling properties, which coatings are intended for use in consumer electronics or in the automotive industry.

In consumer electronic devices (eg, mobile phones, laptops, laptops) and in the automotive industry, various substrates such as plastic, metal and glass are used. It is often desirable to cover such substrates with a coating having tactile properties such as soft feel. Soft-feel coatings transform hard surfaces into textures that feel like velvet, silk or rubber.

The soft feel effect is known to be produced by using resins with low glass transition temperature (Tg) and low crosslink density. However, these resins and resulting coatings are generally not durable, they scratch easily and have sticky surfaces. Also, these coatings generally have poor stain repellency against stains such as fingerprints, coffee, and the like. For good antifouling properties, resins with high Tg and high crosslink density are required. Therefore, improvement in antifouling is usually accompanied by deterioration in soft feel properties. As a result, most soft-feel coatings are generally limited to application to black or other dark-colored substrates where staining is less noticeable, and not to white or other light-colored substrates. However, it is desirable to provide coatings that exhibit a combination of good antifouling and soft feel properties.

Silicone-based resins are known to provide soft touch and stain resistance due to their physical elasticity and hydrophobic properties. However, most Si-resins are electrostatically charged and attract small particles to surfaces (eg dust particles). Therefore, the surface looks dirty. It is desirable to have a clean looking surface. Other disadvantages of conventional silicone-based resins include poor mechanical properties and poor adhesion to some substrates such as plastics.

It is therefore desirable to provide coatings that exhibit a combination of good antifouling and soft feel properties. It is further desired that the coating has good mechanical properties, such as scratch resistance. It is further desired that the coatings adhere well to substrates, particularly plastic substrates, used in the consumer electronics or automotive industries.

To meet the above needs, in a first aspect, the present invention provides a 2K coating composition comprising polysiloxane-modified polyurethane and a hardener, wherein the polysiloxane-modified polyurethane can be obtained by a method comprising the following steps: a) reacting polyols with isocyanate-functional silane coupling agents to obtain silane-grafted polyols, b) subjecting the silane-grafted polyol to a condensation reaction with a hydroxyl-functional polysiloxane to obtain a polysiloxane-modified polyurethane, wherein the polysiloxane-modified polyurethane has a hydroxyl value of at least 30 mg KOH/g, and Wherein the hardener comprises at least one isocyanate.

In another aspect, the present invention also provides a method of coating a substrate comprising applying a coating composition of the present invention to a substrate, and curing the coating composition to obtain a coated substrate.

In yet another aspect, the invention provides a coated substrate.

The polysiloxane-modified polyurethane used in the present invention can be prepared by a process comprising at least two steps.

In the first synthesis step (a), polyols are reacted with isocyanate-functional silane coupling agents to obtain silane-grafted polyols.

As used herein, "polyol" refers to a compound comprising two or more hydroxyl groups, preferably three or more hydroxyl groups. In some embodiments of the present invention, the polyol may be a polyol selected from the list consisting of: polyester polyol, polyurethane polyol, polyether polyol.

Preferably, the polyol used in the synthesis step (a) is polyester polyol. Polyester polyols are obtainable from alcohol and acid components. In a typical example, polyester polyols can be prepared from a mixture comprising at least one diol, at least one polyol comprising 3 or more hydroxyl groups, and at least one acid component.

"Diol" is defined as an alcohol having only two hydroxyl groups. It can be linear, branched and/or cyclic aliphatic diols. The reaction mixture may comprise one or more aliphatic diols, for example at least two, at least three or at least four aliphatic diols. Suitable aliphatic diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, propylene glycol, Tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, heptaethylene glycol, octaethylene glycol, nonaethylene glycol, decaethylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, and combinations thereof.

The polyol containing 3 or more hydroxyl groups may include various types of polyols, such as aliphatic, aromatic, linear, branched and/or cyclic polyols containing 3 or more hydroxyl groups. Suitable polyols containing 3 or more hydroxyl groups include trimethylolpropane, trimethylolethane, 1,2,5-hexanetriol, polyethertriol, di-trimethylolpropane, neopentylthritol, di-neopentylthritol, trimethylolbutane, glycerol, ginseng(2-hydroxyethyl)isocyanurate, and combinations thereof.

The acid component may include linear, branched and/or aromatic acids, anhydrides and esters thereof. Suitable acids include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, decahydronaphthalene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,1-cyclopropanedicarboxylic acid, hexahydrophthalic acid, hexahydrophthalic anhydride, terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, trimellitic acid, trimellitic anhydride, succinic acid, adipic acid, hydrogenated C36 diacid Polymeric fatty acids, azelaic acid, sebacic acid, glutaric acid, and combinations thereof.

The weight average molecular weight Mw of the polyol used in the synthesis step (a) of the invention is preferably less than 10,000 g/mol, or less than 8,000 g/mol, or less than 5,000 g/mol or even less than 3,000 g/mol, as determined by gel permeation chromatography (GPC) against polystyrene standards using tetrahydrofuran as mobile phase.

The hydroxyl value of the polyol used in the synthesis step (a) of the present invention is preferably higher than 100 mg KOH/g, or at least 105 mg KOH/g, or at least 125 mg KOH/g, or at least 150 mg KOH/g, or at least 175 mg KOH/g, or at least 200 mg KOH/g, or at least 225 mg KOH/g, or at least 250 mg KOH/g, or at least 275 mg KOH/g OH/g, or at least 300 mg KOH/g, or at least 325 mg KOH/g. Furthermore, the polyol preferably has a hydroxyl value of up to and including 550 mg KOH/g. The polyol may have a hydroxyl number in the range of 100 to 550 mg KOH/g, 150 to 425 mg KOH/g, or 200 to 325 mg KOH/g. The hydroxyl value of polyester polyols was determined by esterifying samples with excess acetic anhydride. Excess acetic anhydride was converted by hydrolysis and titrated potentiometrically with standard potassium hydroxide. The volume difference of titrated potassium hydroxide between the blank (no reaction) and the sample corresponds to the acid content of the sample from which the hydroxyl number is calculated as the milligrams of potassium hydroxide required to neutralize the acid in 1 gram of the sample. The hydrolysis solution used in the determination is a mixture of dimethylformamide, pyridine and distilled water, and the acetylation reagent is a mixture of acetic anhydride and dichloroethane, wherein p-toluenesulfonic acid is used as a catalyst.

Suitable commercially available polyester polyols include Desmophen 800, Desmophen 670, Desmophen 1200, Italester MX 353, Setal 1603 BA-78.

The polyester polyol component may be present in an amount of at least 20 wt.%, at least 40 wt.%, at least 60 wt.%, or at least 80 wt.%, based on the total solids weight of the final resin (polysiloxane-modified polyurethane). The polyester polyol component may be present in an amount of up to 90 wt.%, up to 80 wt.%, or up to 70 wt.%, or up to 50 wt.%, based on the total solids weight of the resin. The polyester polyol component may also be present, for example, in the range of 20 to 90 wt.%, or 40 to 80 wt.%, or 60 to 70 wt.%, based on the total solid weight of the final resin.

As used herein, a coupling agent refers to a molecule comprising two or more functional groups reactive with other functional groups and capable of linking two or more monomer or polymer molecules via chemical bonds. The coupling agents in this disclosure can react with both polyols and polysiloxanes.

Isocyanate-functional silane coupling agents contain one or more isocyanate groups. Also, mixtures of silanes can be used as isocyanate functional silane coupling agents. Preferably, it further contains at least one alkoxy group OR attached to the Si atom. In a preferred embodiment, the silane coupling agent contains at least two and more preferably three alkoxy groups, and these alkoxy groups may be the same or different. Preferably, the silane coupling agent comprises an isocyanate group, optionally bonded to the Si atom via a linking moiety.

In a preferred embodiment, the silane coupling agent has the following formula: OCN-R ¹ -Si-(OR ² )(OR ³ )(OR ⁴ ) (I), wherein R ¹ is a covalent bond or a divalent linking part, and R ² , R ³ , and R ⁴ may be the same or different and are C1-C6 alkyl groups. The linking moiety is preferably a divalent C1-C6 alkyl group.

Preferably, R ¹ is a divalent alkyl group having 1-6 carbon atoms, more preferably 1-3 carbon atoms, still more preferably, R ¹ is propylidene-C ₃ H ₆ -. Preferably, R ² , R ³ and R ⁴ may be the same or different and are selected from the list consisting of methyl and ethyl. More preferably, the isocyanate functional silane coupling agent is selected from the list consisting of 3-(triethoxysilyl)propyl isocyanate, 3-(trimethoxysilyl)propyl isocyanate, 3-(triethoxysilyl)ethyl isocyanate, 3-(trimethoxysilyl)ethyl isocyanate and mixtures thereof. Even more preferably, the silane coupling agent is selected from 3-(triethoxysilyl)propyl isocyanate, 3-(trimethoxysilyl)propyl isocyanate and mixtures thereof. Suitable silane coupling agents include USi-SL25, USi-SL35 of Nanjing Union Silicon Chemical; KH550, KH560, KH570, KH792 of Zhejiang Feidian Chemical; DL602, DL171 of Jiangsu Chenguang Coincident Dose.

In the synthesis step (a), the molar ratio of the hydroxyl equivalent of the polyol to the isocyanate equivalent of the silane coupling agent may be at least 1.5:1, or at least 2:1, or at least 2.5:1, or at least 3:1, or at least 3.5:1, or at least 4:1, or at least 4.5:1, or at least 5:1, or at least 7.5:1 or at least 8:1. The molar ratio is preferably not higher than 10:1. Preferred molar ratios include 1.5:1 to 3.5:1, or 1.8:1 to 3.0:1, or 2.0:1 to 3.0:1. The excess hydroxyl equivalents ensure that at least some of the hydroxyl groups of the polyol remain unreacted during the reaction of the polyol with the silane coupling agent, which when used in a 2K coating composition can benefit the final cure of the coating composition.

The functional silane coupling agent may be present in an amount of at least 5 wt.%, at least 10 wt.%, at least 15 wt.%, or at least 20 wt.%, or at least 25 wt.%, or at least 30 wt.%, based on the total solids weight of the final resin (polysiloxane-modified polyurethane). The functional silane may be present in an amount of up to 50 wt.%, up to 40 wt.%, or up to 30 wt.%, or up to 20 wt.%, based on the total solids weight of the final resin. Functional silanes may also be present, for example, in the range of 10 to 50 wt.%, or 15 to 40 wt.%, or 20 to 30 wt.%, based on the total solids weight of the final resin.

The reaction between the hydroxyl group in the polyol and the isocyanate group in the silane coupling agent can be carried out in the presence of a catalyst. Conventional catalysts known in the art for this reaction can be used, such as metallic, acidic or basic catalysts. Preferably, the reaction is carried out in the presence of a metal catalyst such as an organotin compound. More preferably, the catalyst is dibutyltin dilaurate (DBTDL). Other metal catalysts such as stannous octoate, zirconium or titanium based catalysts may also be used. The use of a catalyst can help drive the reaction to completion. Preferably the reaction is allowed to proceed until no free NCO groups are detectable.

The catalyst may be used in an amount of at least 0.1 wt.%, at least 0.5 wt.%, at least 1 wt.%, or at least 3 wt.%, or at least 5 wt.%, or at least 10 wt.%, based on the total solids weight of the final resin. The catalyst may also be present, for example, in the range of 0.1 to 10 wt.%, or 0.5 to 5 wt.%, or 1 to 3 wt.%, based on the total solids weight of the final resin.

In the second synthesis step (b), the silane-grafted polyol obtained in the synthesis step (a) is subjected to a condensation reaction with a hydroxyl-functional polysiloxane to obtain a polysiloxane-modified polyurethane.

The hydroxy-functional polysiloxane is preferably a linear polysiloxane chain having the formula -(Si( ^R4 )( ^R5 )-O-) and two terminal OH groups. This is also known as silanol-terminated silicone oil. The groups R ⁴ and R ⁵ can be the same or different and are preferably selected from straight chain C1-C6 alkyl groups. More preferably, R ⁴ and R ⁵ are selected from methyl and ethyl, more preferably both R ⁴ and R ⁵ are methyl. Preferred hydroxy-functional polysiloxanes are dihydroxypoly(dimethylsiloxane) (DHPDMS).

Suitable hydroxy-functional polysiloxanes are commercially available as silanol-terminated polysiloxane oils with different viscosities, such as Andisil® OH 50,000 (50,000 cps), Andisil® OH 4,000 (4,000 cps), Andisil® OH 1,000 (1,000 cps), Andisil® OH 40 (40 cps).

In some embodiments, it may be desirable to use a mixture of at least two hydroxy-functional polysiloxanes having different viscosities. Particularly good results in soft feel properties are obtained when mixtures of polysiloxanes with viscosities above 20,000 cps at 25° C. and polysiloxanes with viscosities below 20,000 cps at 25° C. are used. More preferably, the mixture contains a first polysiloxane having a viscosity in the range of 25,000-80,000 cps at 25°C and a second polysiloxane having a viscosity in the range of 40-20,000 cps at 25°C. Preferably, both polysiloxanes in this embodiment are dihydroxypoly(dimethylsiloxane). Viscosity is usually provided by the supplier of silicone oil.

The functional polysiloxane may be present in an amount of at least 0.5 wt.%, at least 1 wt.%, at least 5 wt.%, or at least 10 wt.%, or at least 20 wt.%, or at least 30 wt.%, based on the total solids weight of the final resin. The polysiloxane may be present in an amount of up to 50 wt.%, up to 40 wt.%, or up to 25 wt.%, or up to 15 wt.%, based on the total solids weight of the final resin. Polysiloxane may also be present, for example, in the range of 0.5 to 50 wt.%, or 5 to 25 wt.%, or 10 to 15 wt.%, based on the total solids weight of the final resin.

In reaction step (b), the molar ratio of alkoxy groups present in the silane-grafted polyol to hydroxyl groups of the polysiloxane is preferably 1.5:1 or higher, 3:1 or higher, 5:1 or higher, 10:1 or higher, 100:1 or higher or even 1,000:1 or higher. The molar ratio can be as high as 1,000,000:1. The molar ratio may range from 1.5:1 to 1,000,000:1, or from 10:1 to 100,000:1, or from 1,000:1 to 10,000:1.

The second step (b) is preferably carried out in the presence of a catalyst for the condensation reaction. Conventional catalysts known in the art for this reaction can be used, such as metallic, acidic or basic catalysts. Preferably, the reaction is carried out in the presence of a metal catalyst (eg, an organotin compound such as dibutyltin dilaurate or dibutyltin bis(acetylacetone)). More preferably, the catalyst is dibutyltin dilaurate (DBTDL).

The condensation catalyst may be used in an amount of at least 0.1 wt.%, at least 0.5 wt.%, at least 1 wt.%, or at least 3 wt.%, or at least 5 wt.%, or at least 10 wt.%, based on the total solids weight of the final resin. The condensation catalyst component may be used, for example, in the range of 0.1 to 10 wt.%, or 0.5 to 5 wt.%, or 1 to 3 wt.%, based on the total solid weight of the final resin.

The polysiloxane-modified polyurethane obtained from the above parts preferably has a number average molecular weight Mn of at least 1,000, or at least 1,500, or at least 2,000, or at least 3,000 or at least 5,000. Mn can be up to 1,000,000, or up to 100,000, or up to 10,000. For example, the Mn of the polysiloxane-modified polyurethane can be in the range of 1,000 to 1,000,000, or 1,500 to 10,000, or 2,000 to 5,000. Mn can be determined by gel permeation chromatography (GPC) using polystyrene standards with tetrahydrofuran as mobile phase.

The hydroxyl value of the polysiloxane-modified polyurethane is at least 30 mg KOH/g. Preferably, its hydroxyl number is at least 50 mg KOH/g, or at least 100 mg KOH/g, or at least 150 mg KOH/g, or at least 200 mg KOH/g, or at least 250 mg KOH/g. The hydroxyl value is preferably not higher than 300 mg KOH/g. In some embodiments, the polysiloxane-modified polyurethane has a hydroxyl value in the range of 30 to 300 mg KOH/g, 50 to 250 mg KOH/g, or 100 to 150 mg KOH/g. The OH value can be determined by esterifying a sample with excess acetic anhydride as described above.

Preferably, the polysiloxane-modified polyurethane does not have carboxyl functional groups. The acid value is preferably 0 mg KOH/g.

In some embodiments, the polysiloxane-modified polyurethane may still have some unreacted alkoxy-OR groups (eg, -OR ² , -OR ³ and/or -OR ⁴ ) after the synthesis step (b). If the polyurethane is used in a 2K composition, these groups can participate in the curing reaction with the hardener. In addition, these alkoxy groups can also react with substrates (such as glass, metal, plastic) to provide better adhesion of the polymer to the substrate. For example, for glass, -OR groups can interact with -Si-OH groups on the surface; for metals, such as Al, it can interact with Al-O groups on the surface.

In another aspect, the present invention provides a coating composition comprising the above polysiloxane-modified polyurethane.

The coating compositions are provided as two-component (2K) coating compositions. Handling of two-component coating compositions generally requires mixing the reactive components together shortly before application to avoid the reactive components. The term "shortly before application" is well known to those skilled in the handling of two-component coating compositions. The period of time during which the ready-to-use coating composition can be prepared before actual use/application depends, for example, on the pot life of the coating composition. Pot life is the time that once the interacting components of the coating composition are mixed, the coating composition can still be processed or applied properly and a coating of unimpaired quality can be achieved.

The coating composition of the present invention preferably comprises the above-mentioned polysiloxane-modified polyurethane in the first component A and the hardener in the second component B.

The polysiloxane-modified polyurethane may be present in an amount of at least 10 wt.%, at least 15 wt.%, at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 40 wt.%, or at least 50 wt.%, based on the total solids weight of the coating composition. In some embodiments, the coating composition may comprise up to 70 wt.%, up to 60 wt.%, or up to 50 wt.%, or up to 30 wt.% polysiloxane-modified polyurethane based on the total solids weight of the coating composition. For example, the coating composition may comprise 10 to 70 wt.%, or 20 to 50 wt.%, or 25 to 30 wt.% of the polysiloxane-modified polyurethane based on the total solids weight of the coating composition.

As used herein, a hardener refers to a molecule comprising two or more functional groups reactive with other functional groups and capable of linking two or more monomer or polymer molecules via chemical bonds. It should be understood that the coating composition of the present invention can be cured by the reaction between the functional groups of the final polysiloxane-modified polyurethane and the functional groups of the hardener to form a coating. "Curing" refers to bond formation, which results in the formation of a crosslinked coating. Curing can occur upon application of an external stimulus, preferably heat.

The hardener in the present invention comprises groups reactive with groups present in the polysiloxane-modified polyurethane.

In particular, the hardener comprises at least one isocyanate. Non-limiting examples of isocyanates include polyfunctional isocyanates (polyisocyanates), such as linear, branched, and/or cyclic polyisocyanates. Examples of polyfunctional polyisocyanate include aliphatic diisocyanate such as hexamethylene diisocyanate and isophorone diisocyanate; and aromatic diisocyanate such as toluene diisocyanate and 4,4′-diphenylmethane diisocyanate. The polyisocyanates can be blocked or unblocked. Examples of other suitable polyisocyanates include isocyanurate trimers, allophanates, and uretdiones of diisocyanates. Suitable polyisocyanates are well known in the art and are widely used commercially. Examples of commercially available isocyanates include DESMODUR® N 3300A, DESMODUR® Z 4470BA, DESMODUR® N 3790, and DESMODUR® N 3900, which are commercially available from Bayer Corporation.

When an isocyanate-containing hardener is used, the molar ratio of -NCO groups in the hardener to hydroxyl groups in the polysiloxane-modified polyurethane can be, for example, 1:1 or higher, 1.5:1 or higher, 2:1 or higher, 2.5:1 or higher, 3:1 or higher, or 4:1 or higher. Mole's ratio is preferably up to 10:1. The molar ratio can be, for example, in the range of 1:1 to 10:1, or 1.5:1 to 5:1, or 1:1 to 3:1. The molar ratio can be achieved by using corresponding mixing ratios of the first component (comprising the polyurethane) and the second component (comprising the hardener) of the coating composition.

The hardener can be present in an amount of at least 20 wt.%, at least 40 wt.%, at least 60 wt.%, or at least 80 wt.%, based on the total solids weight of the coating composition. The hardener may be present in an amount of up to 90 wt.%, up to 70 wt.%, or up to 50 wt.%, or up to 30 wt.%, based on the total solids weight of the coating composition. The hardener may be present, for example, in the range of 20 to 90 wt.%, or 40 to 70 wt.%, or 60 to 65 wt.%, based on the total solids weight of the coating composition.

The coating composition may further comprise a catalyst for the reaction between the polysiloxane-modified polyurethane and the hardener. Catalysts can be acidic or basic. Metal catalysts are preferably used. Suitable catalysts include organotin catalysts such as DBTDL. The catalyst may be present in an amount of at least 0.1 wt.%, at least 0.5 wt.%, at least 1 wt.%, or at least 3 wt.%, or at least 5 wt.%, based on the total solids weight of the coating composition. The catalyst may be present, for example, in the range of 0.1 to 10 wt.%, or 0.5 to 5 wt.%, or 1 to 3 wt.%, based on the total solids weight of the coating composition.

The coating composition can be water-based or solvent-based. Preferably, the coating composition is solvent-based. Solventborne is a coating composition that contains an organic solvent as the main liquid phase when preparing and/or applying the coating composition. "Major liquid phase" means that the organic solvent accounts for at least 50 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.%, and even 100 wt.% in some embodiments, of the liquid phase. Typically, solvent-borne coating compositions contain 20 to 80% by weight of organic solvent, based on the total weight of the coating composition. Optionally, the coating composition may also contain up to 15% by weight, preferably less than 5% by weight, of water, based on the total weight of the coating composition. In some embodiments, the coating composition may preferably be non-aqueous (contains no water).

Examples of suitable organic solvents include alcohols (e.g., ethanol, isopropanol, n-butanol, n-propanol), esters (e.g., ethyl acetate, propyl acetate), aromatic solvents (e.g., toluene), ketone solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diacetone alcohol); aliphatic hydrocarbons; chlorinated hydrocarbons (e.g. _{, CH2Cl2} ); ethers (e.g., diethyl ether, tetrahydrofuran) and mixtures thereof. Preferred organic solvents include butyl acetate, methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), and methoxypropyl acetate (PMA) or mixtures thereof.

The solid content of the coating composition of the present invention may be in the range of 10 to 90 wt.%, preferably 25 to 75 wt.%, more preferably 40 to 65 wt.%.

The coating composition may further comprise customary additives. For example, additives such as matting agents to reduce gloss, improve scratch resistance, control viscosity and enhance soft touch properties. Matting agents can be inorganic and/or organic particles such as silica, wax-treated silica, fumed silica, polysiloxane microbeads, metal oxides, micronized waxes, polyether condensates, polyamide microbeads, polyurethane microbeads, and combinations thereof. Examples of commercially available matting agents include EVONIK Acematt 3600, EVONIK Acematt 3300, EVONIK Acematt 3400, KMP 601, KMP 600, KMP 602. The matting agent may be present in an amount of at least 1 wt.%, or at least 4 wt.%, or at least 8 wt.%, or at least 15 wt.%, or at least 20 wt.%, or at least 30 wt.%, based on the total solids weight of the coating composition. The matting agent may be present, for example, in an amount of 1 to 30 wt.%, or 4 to 20 wt.%, or 8 to 15 wt.%, based on the total solids weight of the coating composition.

Other examples of additives that may be used in the coating compositions of the present invention include pigments, abrasion resistant particles, flow and surface control agents, thixotropic agents, organic solvents, organic co-solvents, reactive diluents, reaction inhibitors, and others.

The invention further provides a method of coating a substrate comprising applying a coating composition of the invention to a substrate and curing the coating composition to obtain a coated substrate.

The coating compositions of the present invention can be applied to a wide range of substrates, including metallic and non-metallic substrates. Suitable substrates include aluminum, aluminum alloys, polycarbonate acrylonitrile butadiene styrene (PC/ABS), polycarbonate, polyacrylate, polyolefin, polyamide, polystyrene, polyamide, glass, wood, stone, and the like.

The coating compositions of the present invention may be applied to a substrate by any suitable method known in the art, such as spraying, electrostatic spraying, dipping, rolling, brushing, electrophoretic coating, and the like. The coating composition of the invention may be applied to achieve a dry film thickness of, for example, 10 μm to 100 μm, 20 μm to 70 μm or 40 μm to 60 μm.

Curing of the coating composition can be carried out at ambient conditions (eg, room temperature). Room temperature is understood here to mean 15 to 30°C. Curing can be accelerated by external stimuli, for example by heating. Preferably, the coated substrate is heated at a temperature in the range of 40-100°C, more preferably 60-90°C. Conventional methods can be used, such as placing in an oven.

The coating compositions of the present invention can be used as a single layer applied directly to a substrate or in a multilayer system (for example, in combination with a primer and/or basecoat).

The coating composition of the present invention can be used in various coating industries, such as consumer electronics, automobiles, packaging, wood floors and furniture, glass and windows, sports equipment.

The invention further provides a coated substrate coated with a coating obtained by curing the coating composition on the substrate. Coatings formed from the coating compositions of the present invention have excellent general properties including adhesion, hardness, abrasion resistance, scratch resistance, weather resistance and UV resistance. In addition, the coating also has soft feeling properties.

Importantly, the coatings formed from the coating compositions of the present invention have good stain resistance and ease of cleaning, as will be apparent from the examples. For example, a series of chemicals, including sunscreen, dish soap, Fantastic Cleaner, mustard, alcohol, olive oil, blush, and hand cream, were applied to the coated white panels and soaked for up to 168 hours at room temperature for extended periods before the chemicals were removed. By comparing the coated surface before and after immersion, it was observed that the coated substrates according to the invention showed no discoloration or peeling. In addition, the coating also meets the requirements of adhesion and wear resistance.

Without wishing to be bound by a particular theory, it is believed that the unique combination of properties of the polyurethane-based coatings described above is due to their unique structure in which different segments from polyols, silane coupling agents, and polysiloxanes are combined in an advantageous manner. This achieves the best balance of soft feel, antifouling and mechanical properties.

example The invention will be elucidated with reference to the following examples. All parts and percentages are by weight unless otherwise indicated.

Desmophen® 800 - highly branched polyester polyol from Covestro, hydroxyl number: 283 mg KOH/g.

Desmophen® 670 - slightly branched hydroxy-functional polyester from Covestro, hydroxyl number: 142 mg KOH/g.

Italester MX 353 - saturated polyester ex Galstaff Mutiresine, hydroxyl number: 102 mg KOH/g.

DBTDL - Dibutyltin dilaurate

Silane USi-SL25 - 3-(triethoxysilyl)propyl isocyanate from Nanjing Union Silicon Chemical

Andisil® OH 50,000 - Silanol-terminated polysiloxane oil, 50,000 cps, available from AB Specialty Silicones

Andisil® OH 4,000 - Silanol-terminated polysiloxane oil, 4,000 cps, available from AB Specialty Silicones

Acematt® 3600 - matting agent based on polymer-treated precipitated silica, available from Evonik Industries AG

MIBK - Methyl Isobutyl Ketone

MEK - Methyl Ethyl Ketone

PMA - Propyl Methoxyacetate

BYK® 3700 - polysiloxane based surface additive, commercially available from Byk

BYK® 306 - Surface additive containing silicone, commercially available from Byk

Desmodur® N 3790 BA - polyisocyanate (high functional HDI trimer) available from Covestro, supplied as 90% solids in n-butyl acetate

Desmodur® N 3300 BA - polyisocyanate (HDI isocyanurate) available from Covestro, supplied as 90% solids in n-butyl acetate

KMP 600 - Lubricant based on fine particle mixed polysiloxane powder, commercially available from Shin-Etsu

Examples 1-10: Preparation of polysiloxane-modified polyurethane Example 1 : First, 200 g of Desmophen® 800, 74 g of butyl acetate and 1 g of DBTDL were stirred at 60° C., and 66 g of Silane USi-SL25 was added dropwise into the solution under nitrogen for about 30 min. Then, the temperature was raised to 80°C for about 1 hour and the reaction was continued until no free NCO was detected. Next, 40 g of Andisil® OH 50,000 and 175 g of butyl acetate were added to the reaction solution at 80°C. The temperature was then raised to 120°C for about 4.5 hours and the reaction was allowed to proceed. Finally, 465 g of butyl acetate was added to the system and the system was cooled to 50°C. The product was filtered using 50 μm filter paper and stored in a container. The obtained resin had a Mn of about 2818 and a polydispersity index (PDI) of 22.806, as determined by GPC. The OH value was about 50 mg KOH/g as determined by the esterification method described above.

Example 2-10 : The synthesis method is the same as that of Example 1. The compounds used in the synthesis and their amounts (in parts by weight) are listed in Table 1. Examples 1-3 used polyester polyols with different hydroxyl values. Examples 1, 4 and 5 have different NCO/OH ratios. Examples 1, 6, 7 and 8 have different OH functional silicone oils. Compared with Example 1, the catalyst content of Examples 9 and 10 was changed. Table 1

Example 11: Preparation of coating from Example 1 A coating composition based on the resin obtained in Example 1 was prepared using the components listed in Table 2 (by weight %). Mix the compounds in the order listed in the table to obtain component A and component B respectively.

Components A and B were mixed at a molar ratio NCO/OH of 1.97. Leave the mixture for 30 minutes. The solution was filtered through a 50 μm filter paper and then sprayed onto a white polycarbonate/acrylonitrile butadiene styrene (PC/ABS) plate. The coated panels were allowed to evaporate excess solvent for 5 minutes at ambient temperature and then placed in a heated oven at 80°C for 2 hours. The dry film thickness of the coating is about 40-60 μm. Table 2

The general properties of the coatings prepared according to Example 11 were tested. The test methods and results are shown in Table 3. table 3 As can be seen from the table, the general properties of the obtained coatings are excellent and pass all tests.

The antifouling properties of the coating prepared in Example 11 were evaluated using different chemicals listed in Table 4. The results are listed in Table 4 and shown in Figure 1 . Figure 1 contains photographs of substrates with and after removal of chemicals. Table 4 It can be seen from the tables and figures that the coating of the present invention has excellent antifouling properties.

Examples 12-20: Preparation of coatings from Examples 2-10 Coating compositions were formulated in the same manner as Example 11, but using the polysiloxane-modified polyurethane from Examples 2-10. Abrasion (RCA), antifouling and soft feeling test results are listed in Table 5. table 5

Slightly worse means still acceptable, but not as good as Pass. Generally means still acceptable, but not as good as Good.

Examples 11, 12 and 13 used different polysiloxane-modified polyurethanes synthesized from different polyester polyols with different hydroxyl values. Example 13 uses the resin obtained in Example 3, which is based on the polyester polyol Italester MX 353 with a hydroxyl number of 102 mg KOH/g. Although it gave a soft and smooth feel, the coating was too soft to pass the RCA and antifouling tests. The inventors believe that too low OH value of the polyol in the synthesis step (a) leads to low crosslink density, which in turn contributes to the softness of the coating.

Experiment with different silane coupling agent levels. In Example 15, relatively less silane coupling agent was used than, for example, Example 14. The inventors believe that this reduces the cross-linking density of the coating to some extent, resulting in slightly poorer wear and stain resistance. Also, it is thought that the poorer slippery feel may be due to the less dense surface structure.

Different catalyst contents were also tried. Example 19 uses less catalyst than Example 20. The inventors believe that lower catalyst amounts slow down the condensation reaction, which can lead to resins with lower molecular weight and poorer desirable film forming properties in coatings.

The inventors further believe that the polysiloxane chains in the polyurethane resin are hydrophobic and have a great influence on the antifouling properties of the polymer and thus the final coating. The silicone oils used in resin synthesis usually contain chains of different lengths and thus have different viscosities. Example 17, which used relatively more polysiloxane oil with a relatively higher viscosity in the synthesis, resulted in oil slicks being observed on the coating surface. This can be attributed to excess silicone oil, some of which may not have reacted to form the resulting polymer. Example 18 achieved excellent results using a mixture of low and high viscosity silicone oils.

Examples 21-26: Preparation of coatings based on Example 1 Coatings based on polysiloxane-modified polyurethane obtained in Example 1 were prepared using various other components to improve performance. The preparation method is the same as in Example 11, and the ingredients are listed in Table 6. Table 6

Compared with Example 11, in Example 21 half of the Acematt® 3600 was replaced by KMP 600, while in Example 22 the same amount of KMP 600 was added. The result is that the coating of Example 21 has a smoother feel, which can be explained by the smaller particle size of the additive. However, too high an amount of matting powder seems to give a rougher surface structure, resulting in a sticky feel and poorer stain resistance (Example 22).

In Examples 23 and 24, the kind and amount of hardening agent were varied. However, as can be seen from the table, this does not adversely affect the properties. Thus, coatings with desired properties can be obtained by using different hardeners.

In Example 25, the catalyst content was reduced, which is believed to slow curing and/or result in an incompletely cured coating with poorer properties.

In Example 26, the solids content was increased to 30 wt.%, which resulted in a structurable but slightly less slippery coating.

Figure 1 Antifouling evaluation of coatings prepared according to Example 11 on substrates using different chemical substances.

Claims (9)

A 2K coating composition comprising a polysiloxane-modified polyurethane and a hardener, wherein the polysiloxane-modified polyurethane can be obtained by a method comprising the steps of: a) reacting a polyol with an isocyanate-functional silane coupling agent to obtain a silane-grafted polyol, b) condensing the silane-grafted polyol with a hydroxyl-functional polysiloxane to obtain the polysiloxane-modified polyurethane, wherein the polysiloxane-modified polyurethane has at least 30 mg KOH /g of hydroxyl value, and wherein the hardener contains at least one isocyanate. The coating composition according to claim 1, wherein the polyol is polyester polyol. The coating composition according to claim 1 or 2, wherein the polyol has a hydroxyl value higher than 105 mg KOH/g. The coating composition according to claim 1 or 2, wherein the isocyanate-functional silane coupling agent is selected from 3-(triethoxysilyl)propyl isocyanate, 3-(trimethoxysilyl)propyl isocyanate and mixtures thereof. The coating composition according to claim 1 or 2, wherein the hydroxy-functional polysiloxane is dihydroxy poly(dimethylsiloxane). The coating composition of claim 1 or 2, wherein the polysiloxane-modified polyurethane has a number average molecular weight Mn in the range of 2,000 to 5,000, as determined by gel permeation chromatography using polystyrene standards and tetrahydrofuran as the mobile phase. A method of coating a substrate comprising applying the coating composition according to any one of claims 1 to 6 to a substrate, and curing the coating composition to obtain a coated substrate. A coated substrate, which can be obtained by the method as claimed in claim 7. The coated substrate of claim 8, wherein the substrate is selected from the list consisting of aluminum, aluminum alloy, polycarbonate acrylonitrile butadiene styrene (PC/ABS), polycarbonate, polyacrylate, polyolefin, polyamide, polystyrene, glass, wood, and stone.