Coating system
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- PPG COATINGS TIANJIN
- Filing Date
- 2024-08-16
- Publication Date
- 2026-06-24
Smart Images
Figure PCTCN2024112742-FTAPPB-I100001 
Figure PCTCN2024112742-FTAPPB-I100002 
Figure PCTCN2024112742-FTAPPB-I100003
Abstract
Description
COATING SYSTEMTECHNICAL FIELD
[0001] The present invention relates to the field of coatings, and in particular to a coating system, especially a coating system with excellent color effects suitable for automobile coating.BACKGROUND
[0002] Metallic colors with high chroma, large color difference at different angles, and low particle glitter are increasingly favored by the automotive industry. To achieve such color effects, there are two main categories of coating technologies on the market.
[0003] The first method is to use colored clearcoat, but this technology cannot share clearcoat with other colors and requires an additional paint system. Moreover, the miscibility of clearcoat with an underlying metal layer is also easy to reduce the orientation effect of aluminum powder, reducing the color difference at different angles, and easy to produce uneven color defects.
[0004] The second method is a three-coat technology, that uses an ordinary transparent clearcoat, but sprays a colored transparent basecoat with only color paste on a metal layer to achieve a high chroma color effect. However, the miscibility between the upper layer and the underlying layer will cause a loss of color effect, and thus some paint manufacturers use a method of baking the underlaying layer before spraying the upper layer. However, this method requires adding an extra oven. It increases the energy usage and reduces the productivity, which is contrary to the current green and environmental protection policies.
[0005] In addition, to achieve the high chroma, some technologies need to partially color aluminum flakes by means of soaking, electroplating, or the like, increasing the complexity of technical implementation.SUMMARY
[0006] In view of the above technical problems, the inventors have conducted a lot of research and developed a coating system. This coating system can be applied using a wet-on-wet process, meanwhile does not need to color aluminum flakes or use a colored clearcoat, and provides excellent color effects to meet the performance requirements of coatings in automotive and other application fields.
[0007] The present invention provides a coating system, comprising: an underlying coat formed from a first coating composition comprising an effect pigment and a top coat formed from a second coating composition, the first coating composition and the second coating composition being cured simultaneously, wherein the underlying coat has a dry film thickness of 8 to 15 μm, the top coat has a dry film thickness of 4 to 8 μm, and the effect pigment has an aspect ratio of 60 to 200.
[0008] The present invention further discloses a coated substrate, comprising a substrate and the coating system applied on at least a part of the substrate.
[0009] The present invention further provides a method of coating a substrate, comprising: applying a first coating composition comprising an effect pigment to form an underlying coat, applying a second coating composition on at least a part of the underlying coat to form a top coat, and simultaneously curing the first coating composition and the second coating composition, wherein the underlying coat has a dry film thickness of 8 to 15 μm, the top coat has a dry film thickness of 4 to 8 μm, and the effect pigment has an aspect ratio of 60 to 200.
[0010] The features and advantages of the present invention will be particularly presented in details in the following description of the embodiments.DETAILED DESCRIPTION
[0011] In the present application, unless expressly stated otherwise, the use of a singular comprises a plural and the use of a plural comprises a singular. For example, although “a” resin is referred to herein, one or more of the specie can be used.
[0012] In this application, the terms “include, ” “comprise, ” and “contain” or the like are not intended to limit the invention to exclude any variations or additions. In addition, although the present invention has described the coating compositions, preparation methods, or the like with terms such as “comprise” , the coating compositions, preparation methods, or the like as detailed herein can further be described as “consist essentially of” or “consist of ... ” Herein, “consist essentially of” means that any additional components would not materially affect the properties of the coating layer formed from the coating composition.
[0013] In the present application, unless expressly stated otherwise, the use of “or” means “and / or” , even though “and / or” can be expressly used in some cases. Additionally, it should be understood that any numerical range described herein is intended to encompass all the sub-ranges contained therein. For example, a range of “1 to 10” is intended to comprise all the sub-ranges between the listed minimum value of 1 and the listed maximum value of 10 (including the endpoints) , namely, all the sub-ranges having a minimum value equal to or great than 1 and a maximum value equal to or less than 10.
[0014] Except those in the examples or otherwise expressly stated, it is to be understood that all numerical values representing amounts of components used in the specification and claims can be varied by the term “about” in all cases. Accordingly, the numerical parameters set forth in the following description and claims are approximations that can vary depending upon desired properties to be obtained by the present invention, unless otherwise indicated to be contrary. At the least, it is not to limit the application of the doctrine of equivalents to the scope of the claims, and each numerical parameter should at least be construed in terms of its number of significant digits and by applying ordinary rounding.
[0015] Although the numerical ranges and parameters describing the broad scope of the present invention are approximations, the numerical values listed in the particular Examples should be reported as precisely as possible. However, any numerical value inherently has a certain error, which is an inevitable result of the standard deviation derived from its corresponding measurement method.
[0016] The present invention relates to a coating system, comprising: an underlying coat formed from a first coating composition comprising an effect pigment and a top coat formed from a second coating composition, the first coating composition and the second coating composition being cured simultaneously, wherein the underlying coat has a dry film thickness of 8 to 15 μm, the top coat has a dry film thickness of 4 to 8 μm, and the effect pigment has an aspect ratio of 60 to 200.
[0017] The coating system according to the invention can be applied using a wet-on-wet process. The term “wet-on-wet” , also known as multiple-coating-and-one-baking, means that two or more coating layers are applied and then baked simultaneously, while the baking step of an intermediate coating layer is omitted. As will be understood by those skilled in the art, the multiple-coating-and-one-baking process comprises a flash-drying of each coating layer applied. The term “flash-drying” refers to a process of evaporating solvent in the coating composition.
[0018] In the coating system according to the present invention, the combination of a thinner top coat with a thicker underlying coat avoids appearance problems such as sagging and floating.
[0019] As used herein, the phrase “simultaneously curing / cured simultaneously” means that the first coating composition and the second coating composition are cured simultaneously to form films, and the first coating composition is not yet cured when the second coating composition is applied. The term “curing / cured” means that at least some components of the coating composition is polymerized and / or crosslinked, or dried to form a hardened coating film.
[0020] Suitably, the first coating composition and the second coating composition and optionally one or more additional coating compositions can be cured simultaneously. The additional coating composition (s) can form a coat under the underlying coat, and / or a coat on the top coat.
[0021] Suitably, the first coating composition and the second coating composition can be cured by heating. For example, the first coating composition and the second coating composition according to the present invention are curable at 140℃ within 20 min. The term “curable” means that the resulting coating layer has a MEK double wiping value of at least 50 times, suitably even at least 100 times, after baking at 140℃ for 20 min.
[0022] Suitably, the underlying coat formed from the first coating composition is subjected to flash-drying after applying the first coating composition and before applying the second coating composition. Suitably, the first coating composition, the second coating composition and / or optionally one or more additional coating compositions can be independently subjected to flash-drying at room temperature (e.g., 23℃) for 1 to 15 min.
[0023] As used herein, the term “dry film thickness” refers to the thickness of a fully cured coat formed from the coating composition. The “dry film thickness” can be measured by a commercially available film thickness gauge.
[0024] In the coating system of the present invention, the top coat can have a dry film thickness of 4 to 8 μm. For example, the top coat can have a dry film thickness of 4 μm, 5 μm, 6 μm, 7 μm or 8 μm. Suitably, the top coat can have a dry film thickness of 4 μm or more, 5 μm or more, or 6 μm or more, and / or 8 μm or less, or 7 μm or less. Suitably, the top coat can have a dry film thickness of 4 to 7 μm, or within any range between any two of the above values as endpoints.
[0025] In the coating system of the present invention, the underlying coat can have a dry film thickness of 8 to 15 μm. For example, the underlying coat can have a dry film thickness of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm. Suitably, the underlying coat can have a dry film thickness of 8 μm or more, 9 μm or more, 10 μm or more, or 11 μm or more, and / or 15 μm or less, 14 μm or less, 13 μm or less, or 12 μm or less. Suitably, the underlying coat can have a dry film thickness of 9 to 14 μm, 10 to 13 μm, or within any range between any two of the above values as endpoints.
[0026] In the coating system of the present invention, the first coating composition for forming the underlying coat comprises an effect pigment. The effect pigment refers to a pigment for providing the coating with a metallic effect, which can comprise an aluminum powder pigment and / or a mica powder pigment. The effect pigment can comprise an effect pigment with and / or without a surface treatment. The effect pigment without a surface treatment can be pre-envelopped with a passivator prior to use. Suitably, the passivator can comprise a phosphate-based resin with an acid value of 20 to 200 mgKOH / g. The acid value refers to milligrams of KOH required by neutralizing the free acid in 1 gram of resin.
[0027] Suitably, the pigment can comprise a silver dollar type effect pigment, e.g, a silver dollar type aluminum powder. The silver dollar type effect pigment refers to a flake-like effect pigment in the form of silver dollar. Suitably, the effect pigment can have an aspect ratio of 60 to 200, such as, an aspect ratio of 70 to 200, e.g., an aspect ratio of 100 to 200. The “aspect ratio” refers to the ratio of the diameter to the thickness of a pigment. Herein, the diameter is a D50 diameter that can be measured by a Synchronous Laser Diffraction and Dynamic Image Particle Analyzer using the following parameters: refractive index = 2.5, and light shading = 10～20%. Herein, the thickness can be determined by SEM and then calculated on D50 particles.
[0028] Suitably, the effect pigment can have a WCA of greater than 30,000 cm2 / g. The WCA refers to the water-covering area of an aluminum powder, that is, the area occupied by one gram of aluminum powder particles which are continuously arranged in a single layer of particles on water surface without any gap between particles. The WCA can be determined according to the GB / T 3173-1982 standard.
[0029] To obtain a higher FI (Flip-flop Index) value, the effect pigment can comprise those with a narrow particle size distribution. The particle size distribution can be expressed in a metric form as a cumulative particle size distribution curve, in which the percentages of particles smaller than a certain size are obtained, respectively, for example, D10 (the particle size corresponding to the cumulative particle size distribution number of 10%on volume basis) , D50 (the particle size corresponding to the cumulative particle size distribution number of 50%on volume basis) and D90 (the particle size corresponding to the cumulative particle size distribution number of 90%on volume basis) . As used herein, the narrow particle size distribution can be characterized by calculating the particle size span, i.e., (D90-D10) / D50. Suitably, the effect pigment can have a particle size span of less than 1.5.
[0030] To achieve a desired glitter effect, the effect pigment can have a D50 particle size of 5 to 25 μm, suitably a D50 particle size of 5 to 20 μm, such as a D50 particle size of 5 to 15 μm, or even a D50 particle size of 5 to 10 μm. Herein, the particle size can be measured by a Synchronous Laser Diffraction and Dynamic Image Particle Analyzer using the following parameters: refractive index = 2.5, and light shading = 10～20%.
[0031] The content of the effect pigment can be 5 wt%or more, 6 wt%or more, or 7 wt%or more, and / or 15 wt%or less, 13 wt%or less, or 10 wt%or less, based on the total solid weight of the first coating composition. The content of the effect pigment can be in a range of 5 to 15 wt%, 6 to 13 wt%, 7 to 10 wt%, or in any range between any two of the above values as endpoints, based on the total solid weight of the first coating composition. As used herein, the total solid weight of the first coating composition refers to a total residual weight after evaporation of solvent in the coating composition.
[0032] The content of the effect pigment can be 0.3 wt%or more, 0.5 wt%or more, or 1 wt%or more, and / or 5 wt%or less, 3 wt%or less, or 2 wt%or less, based on the total weight of the first coating composition. The content of the effect pigment can be in a range of 0.3 to 5 wt%, 0.5 to 3 wt%, 1 to 2 wt%, or in any range between any two of the above values as endpoints, based on the total weight of the first coating composition.
[0033] The first coating composition can further comprise an additional pigment, which refers to a pigment other than the effect pigment. Suitable pigments for the first coating composition can comprise inorganic pigments, such as carbon black, titanium white, iron red, etc., and / or organic pigments, such as azo-based, phthalocyanine-based, perylene-based pigments, etc.
[0034] In the first coating composition, the content of the pigment (including the effect pigment and optionally an additional pigment) can be represented by a pigment-to-binder ratio. The “pigment-to-binder ratio (P / B) ” refers to the solid weight ratio of the pigment (including the effect pigment and optionally an additional pigment) in the first coating composition to the binder (i.e., the film-forming resin) in the first coating composition. Suitably, the first coating composition has a P / B ratio of 0.02 to 0.3, such as a P / B ratio of 0.02 to 0.1.
[0035] The specific pigment as described above is beneficial to the underlying coat formed from the first coating composition to obtain a high FI value and a low glitter, while the low P / B ratio of the specific pigment in the first coating composition is beneficial to achieve good mechanical properties.
[0036] In addition, in the coating system according to the present invention, the formula design of the first coating composition and the second coating composition considers desired properties of the coating system.
[0037] The film-forming material in the first coating composition can comprise a high- Tg acrylic resin and a high-Tg polyurethane (PU) resin, wherein the high-Tg acrylic resin and the high-Tg PU resin are different from each other. Suitably, the weight ratio of the high-Tg acrylic resin and the high-Tg PU resin can be (10-80) : (5-50) , such as (30-50) : (10-30) . The combination of the high-Tg acrylic resin and the high-Tg PU resin forms a dense and stable coating structure, reducing the penetration of organic solvent from other coatings; and the selection of the film-forming resins imparts mechanical properties to the coating to meet various application requirements, while contributing to the orientation of the effect pigment in the first coating composition.
[0038] The acrylic resin refers to a polymer formed from (meth) acrylic monomer as its basic elements. The “basic element” means that the (meth) acrylic monomer accounts for at least 70 wt%of all monomers used for forming the polymer, such as at least 80 wt%, such as at least 90 wt%.
[0039] The high-Tg acrylic resin can have a glass transition temperature (Tg) of greater than 40℃, suitably a glass transition temperature of >40 to 150℃. The Tg can be determined by dynamic thermomechanical analysis (DMA) using a TA Instruments Q800 instrument, with the following measuring parameters: a frequency of 10 Hz, an amplitude of 5 mm, and a temperature ramp of -100℃ to 250℃. The Tg is determined as the peak of the tanδ curve according to ASTM D7028-2007.
[0040] Suitably, the high-Tg acrylic resin can have a hydroxyl value of 10 to 100 mg KOH / g, such as 20 to 80 mg KOH / g. The hydroxyl value refers to milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl group in 1 gram of resin. Suitably, the high-Tg acrylic resin can have an acid value of 1 to 70 mgKOH / g, such as an acid value of 10 to 50 mgKOH / g. The acid value refers to milligrams of KOH required by neutralizing the free acid in 1 gram of resin. Suitably, the high-Tg acrylic resin can have an average particle size on a volume basis of 100 to 5000 nm, such as, an average particle size on a volume basis of 500 to 3000 nm. The particle size can be measured by a Synchronous Laser Diffraction and Dynamic Image Particle Analyzer using the following parameters: refractive index = 2.5, and light shading = 10～20%.
[0041] Suitably, the high-Tg acrylic resin can be in the form of dispersion or emulsion with solid content of 20 to 60 wt%. The “solid content” refers to a percentage of the mass remaining after evaporation of dispersion / emulsion to the mass of the original dispersion / emulsion. The high-Tg acrylic resin dispersion / emulsion has a good film-forming ability and can be rapidly dried.
[0042] The content of the high-Tg acrylic resin can be 2 wt%or more, 3 wt%or more, or 4 wt%or more, and / or 15 wt%or less, 10 wt%or less, or 8 wt%or less, based on the total weight of the first coating composition. The high-Tg acrylic resin can be present in the coating composition in an amount of 2 to 15 wt%, suitably from 3 to 10 wt%, such as from 4 to 8 wt%, or in any range with any other combination of these endpoints, based on the total weight of the first coating composition.
[0043] The PU resin refers to the polymer having a repeating unit containing urethane group. The PU can comprise a polymer having at least 50 wt%of the organic units linked by urethane linkages, e.g., at least 70 wt%, such as at least 90 wt%of the organic units. Herein, the organic units comprise residues derived from one or more selected from the group consisting of simple glycols, such as, butylene glycol, polyester glycol, polyether glycol, and polycarbonate glycol.
[0044] The high-Tg PU resin can have a glass transition temperature (Tg) of greater than 30℃, suitably a glass transition temperature of >30 to 80℃. The Tg can be determined by dynamic thermomechanical analysis (DMA) using a TA Instruments Q800 instrument, with the following measuring parameters: a frequency of 10 Hz, an amplitude of 5 mm, and a temperature ramp of -100℃ to 250℃. The Tg is determined as the peak of the tanδ curve according to ASTM D7028-2007.
[0045] Suitably, the high-Tg PU resin can have a weight average molecular weight (Mw) of 2,000 to 200,000, such as a weight average molecular weight of 5,000 to 150,000. The Mw can be determined by gel permeation chromatography using appropriate standards such as polystyrene standards, and is given in g / mol.
[0046] Suitably, the high-Tg PU resin can be in the form of dispersion or emulsion with solid content of 20 to 60 wt%. The “solid content” refers to the percentage of the mass remaining after evaporation of dispersion or emulsion to the mass of the original dispersion or emulsion. When the PU resin is in the form of dispersion or emulsion, the Mw of the PU resin refers to the molecular weight of the portion of the dispersion or emulsion that is soluble in tetrahydrofuran. The high-Tg PU dispersion or emulsion has a fast-drying speed and good chemical resistance after the film formation.
[0047] The content of the high-Tg PU resin can be 1 wt%or more, 2 wt%or more, or 3 wt%or more, and / or 18 wt%or less, 15 wt%or less, or 10 wt%or less, based on the total weight of the first coating composition. The high-Tg PU resin can be present in the coating composition in an amount of 1 to 18 wt%, suitably from 2 to 15 wt%, such as from 3 to 10 wt%, or in any range with any other combination of these endpoints, based on the total weight of the first coating composition.
[0048] The film-forming resin in the first coating composition can further comprise a polyester resin. The polyester resin refers to a polymer produced by the polyesterification of polyol and polyacid, where the polyol is a compound containing two or more hydroxyl groups per molecule, and the polyacid is a compound containing two or more carboxyl groups per molecule.
[0049] Suitably, the polyester resin can have a hydroxyl value of 10 to 100 mgKOH / g, such as a hydroxyl value of at least 20 to 80 mgKOH / g. The hydroxyl value refers to milligram (s) of potassium hydroxide (KOH) equivalent to the hydroxyl groups in 1 gram of resin. Suitably, the polyester resin can have an acid value of 1 to 100 mg / g, such as an acid value of at 10 to 70 mg / g. The acid value refers to milligrams of KOH required by neutralizing the free acid in 1 gram of resin.
[0050] The content of the polyester resin can be 0.1 wt%or more, or 0.5 wt%or more, and / or 5 wt%or less, or 3 wt%or less, based on the total weight of the first coating composition. The polyester resin can be present in the coating composition in an amount of 0.1 to 5 wt%, suitably from 0.5 to 3 wt%, or in any range with any other combination of these endpoints, based on the total weight of the first coating composition.
[0051] The film-forming resin in the first coating composition can further comprise a melamine formaldehyde (MF) resin. The MF resin can be crosslinked with the high-Tg acrylic resin, the high-Tg PU resin and / or the polyester resin to improve the film-forming ability of the first coating composition and promote the curing. The MF resin can be one MF resin or a combination of different MF resins. In the MF resin or the combination of MF resins, the molar ratio of the sum of the imino and hydroxymethyl functional groups to the alkoxy functional group is 5 / 80 to 50 / 50.
[0052] The MF resin can be 1 wt%or more, or 3 wt%or more, and / or 15 wt%or less, or 10 wt%or less, based on the total weight of the first coating composition. The MF resin can be present in the coating composition in an amount of about 1 to 15 wt%, suitably from 3 to 10 wt%, or in any range with any other combination of these endpoints, based on the total weight of the first coating composition.
[0053] The first coating composition can further comprise a solvent. The solvent can comprise water and optionally an organic solvent. Suitably, the organic solvent can comprise alcohol and / or ether organic solvents. The content of the solvent can be 40 to 70 wt%, based on the total weight of the first coating composition.
[0054] The first coating composition can further comprise one or more additional auxiliary components of: thickener, wetting aid, anti-pinhole additive, curing catalyst, defoaming agent, ultraviolet absorber, light stabilizer, adhesion promoter, surface leveling agent, pH adjuster, substrate wetting agent, and filler, etc. When these auxiliary components are present, each auxiliary component is present in an amount of 10 wt%or less based on the total weight of the first coating composition.
[0055] The first coating composition according to the present invention can be a waterborne coating composition. As used herein, the “waterborne” means that the solvent of the coating composition comprises at least 50 wt%of water based on the total weight of the solvent.
[0056] The first coating composition according to the present invention can have a low VOC content of less than 420 g / L. As used herein, the term “VOCs (volatile organic compounds) ” refers to any organic compounds having a boiling point at or below 250℃ (482°F) as measured under standard atmospheric pressure of 101.3 kPa. Organic solvents are usually the main source of VOCs. The VOC value can be a VOC value determined in water-free manner, which can be obtained by detecting the contents of various organic compound ingredients in the composition by gas chromatography, followed by adding up the contents of the various ingredients.
[0057] Suitably, the first coating composition according to the present invention has a solid content of greater than 10 wt%and no greater than 17 wt%. The “solid content” refers to the solid content in the coating composition, which can be obtained by determining the percentage of the residual weight after the solvent of the composition has been fully evaporated to the total weight of the coating composition.
[0058] The first coating composition according to the present invention can be a one-component (1K) coating composition. The “one-component (1K) ” means that all of the film-forming resin (i.e., the binder) , pigment / filler, solvent and / or auxiliaries of the coating composition are packaged in a single container, and thus it has advantages of convenience of storage and use, etc.
[0059] The film-forming material in the second coating composition can comprise an acrylic resin, a PU resin, an amine resin, and optionally a polyester resin. Suitably, the weight ratio of the acrylic resin, the PU resin, the amine resin and the polyester resin can be (5-50) : (5-30) : (3-40) : (0-15) . The combination of film-forming resins provides desired mechanical properties and high chroma of the coating formed from the second coating composition without affecting the FI value and low glitter of the undercoat of the first coating composition in the coating system of the present invention.
[0060] The acrylic resin refers to the polymer having (meth) acrylic monomer as its basic element. The “basic element” means that the (meth) acrylic monomer accounts for at least 70 wt%of all monomers used for forming the polymer, such as at least 80 wt%, such as at least 90 wt%.
[0061] The acrylic resin can have a hydroxyl value of 20 to 200 mg KOH / g, such as 20 to 80 mg KOH / g. The hydroxyl value refers to milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl group in 1 gram of resin. Suitably, the acrylic resin can have an acid value of 10 to 50 mgKOH / g. The acid value refers to milligrams of KOH required by neutralizing the free acid in 1 gram of resin. Suitably, the acrylic resin can have an average particle size of 100 to 3,000 nm, such as, an average particle size of 500 to 2,000 nm. The particle size is a volume average particle size that can be measured by a Synchronous Laser Diffraction and Dynamic Image Particle Analyze using the following parameters: refractive index = 2.5, and light shading = 10～20%. Suitably, the acrylic resin can have a weight average molecular weight (Mw) of 1,000 to 2,0000, such as a weight average molecular weight of 5,000 to 10,000. The Mw can be determined by gel permeation chromatography using appropriate standards such as polystyrene standards, and is given in g / mol.
[0062] Suitably, the acrylic resin can be in the form of dispersion or emulsion with a solid content of 10 to 50 wt%. The “solid content” refers to the percentage of the mass remaining after evaporation of solvent in the dispersion / emulsion to the mass of the original dispersion / emulsion. When the acrylic resin is in the form of dispersion or emulsion, the Mw of the acrylic resin refers to the molecular weight of the portion of the dispersion or emulsion that is soluble in tetrahydrofuran. The acrylic resin dispersion / emulsion has a high transparency and good stability, and can provide high application performance, such as excellent color uniformity and high anti-sagging performance.
[0063] The content of the acrylic resin can be 5 wt%or more, 8 wt%or more, or 10 wt%or more, and / or 30 wt%less, 25 wt%or less, or 20 wt%or less, based on the total weight of the second coating composition. The acrylic resin can be present in the coating composition in an amount of 5 to 30 wt%, suitably from 8 to 25 wt%, such as from 10 to 20 wt%, or in any range with any other combination of these endpoints, based on the total weight of the second coating composition.
[0064] The PU resin refers to the polymer having a repeating unit containing urethane groups. The PU can comprise a polymer having at least 50 wt%of the organic units linked by urethane linkages, e.g., at least 70 wt%, such as at least 90 wt%of the organic units. Herein, the organic units comprise residues derived from one or more selected from the group consisting of simple glycol, such as, butylene glycol, polyester glycol, polyether glycol, and polycarbonate glycol.
[0065] The PU resin can have an average particle size of 100 to 1,000 nm, such as, an average particle size of 100 to 600 nm. The particle size is a volume average particle size that can be measured by a Synchronous Laser Diffraction and Dynamic Image Particle Analyze using the following parameters: refractive index = 2.5, and light shading = 10～20%.
[0066] Suitably, the PU resin can be in the form of dispersion or emulsion with a solid content of 20 to 60 wt%. The “solid content” refers to the percentage of the mass remaining after evaporation of solvent in the dispersion or emulsion to the mass of the original dispersion or emulsion. The PU dispersion or emulsion is combined with a suitable co-solvent to form a transparent coating, which not only increases the pigment chroma of the coating to ensure excellent color vividness even with a low film thickness, but also can avoid an uneven color caused by the erosion of the upper clearcoat wet film, as well as provides excellent adhesion, stone impact resistance, moisture resistance, and weather resistance.
[0067] The content of the PU resin can be 5 wt%or more, 8 wt%or more, or 10 wt%or more, and / or 30 wt%or less, 25 wt%or less, or 20 wt%or less, based on the total weight of the second coating composition. The content of the PU resin can be 5 to 30 wt%, suitably 8 to 25 wt%, such as 10 to 20 wt%, or in any range with any other combination of these endpoints, based on the total weight of the second coating composition.
[0068] The amine resin can be an MF resin or a combination of different MF resins. Suitably, the amine resin comprises a methoxylated MF resin. In the MF resin or the combination of MF resins, the molar ratio of the sum of the imino and hydroxymethyl functional groups to the alkoxy functional group is 5 / 80 to 60 / 50.
[0069] The amine resin can be 3 wt%or more, or 5 wt%or more, and / or 15 wt%or less, or 10 wt%or less, based on the total weight of the second coating composition. The amine resin can be present in the coating composition in a range of about 3 to 15 wt%, suitably 5 to 10 wt%, or in any range with any other combination of these endpoints, based on the total weight of the second coating composition.
[0070] The polyester resin refers to the polymer produced by the polyesterification of polyol and polyacid, where the polyol is a compound containing two or more hydroxyl groups per molecule, and the polyacid is a compound containing two or more carboxyl groups per molecule. Suitably, the polyester resin can comprise an unsaturated polyester resin. The unsaturated polyester resin can comprise an unsaturated double bond. Alternatively, the polyester resin can comprise a hyper-branched polyester resin.
[0071] Suitably, the polyester resin can have a hydroxyl value of 10 to 80 mgKOH / g. The hydroxyl value refers to milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl groups in 1 gram of resin. Suitably, the polyester resin can have an acid value of 10 to 50 mg / g. The acid value refers to milligrams of KOH required by neutralizing the free acid in 1 gram of resin. Suitably, the polyester resin can have a weight average molecular weight (Mw) of 5,000 to 80,000. The Mw can be determined by gel permeation chromatography using appropriate standards such as polystyrene standards, and is given in g / mol.
[0072] The polyester resin can be 0 wt%or more, or 5 wt%or more, and / or 20 wt%or less, or 15 wt%or less, based on the total weight of the second coating composition. The polyester resin can be present in the coating composition in a range from about 0 to 20 wt%, suitably 5 to 15 wt%, or in any range with any other combination of these endpoints, based on the total weight of the second coating composition.
[0073] The second coating composition can further comprise a pigment. Suitable pigments for the second coating composition can comprise inorganic pigments, such as carbon black, titanium white, iron red, etc., and / or organic pigments, such as azo-based, phthalocyanine-based, perylene-based pigments, etc. Suitably, the pigment can comprise highly transparent organic pigments such as P.R. 179 Perylene Red, Monolite 3RX-H Indolinone Blue, Heliogen Blue 1 6960 Titanium Blue. The second coating composition can be free of an effect pigment.
[0074] In the second coating composition, the pigment content can be represented by a pigment-to-binder (P / B) ratio. The “pigment-to-binder ratio (P / B) ” refers to the solid weight ratio of the pigment in the second coating composition to the binder (i.e., the film-forming resin) in the second coating composition. Suitably, the second coating composition can have a P / B ratio of 0.05 to 0.3, such as a P / B ratio of 0.1 to 0.2.
[0075] The second coating composition can further comprise a solvent. The solvent comprises water and optionally an organic solvent. Suitable organic solvents for the second coating composition can comprise ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monobutyl ether, isopropyl alcohol, ethanol, isooctyl alcohol, and / or n-propanol. The solvent should be selected to have good compatibility with the resin so that the formed film has a high transparency, e.g., the color difference between the coated region on a blade applied with coating and baked and the uncoated region on the blade without coating is less than 0.2. For example, the solvent can comprise water and ethylene glycol monobutyl ether. The organic solvent can serve as a good co-solvent for the resin for use to achieve good compatibility with the system, thereby improving the transparency of the coating film, improving the dispersion of pigments, and improving the color chroma. The content of the solvent can be 50 to 80 wt%based on the total weight of the second coating composition.
[0076] The second coating composition can further comprise one or more additional auxiliary components of: thickener, wetting aid, pinhole aid, curing catalyst, defoaming agent, ultraviolet absorber, light stabilizer, adhesion promoter, surface leveling agent, pH adjuster, substrate wetting agent, and filles, etc. When these auxiliary components are present, each auxiliary component is present in an amount of 10 wt%or less based on the total weight of the second coating composition.
[0077] The second coating composition according to the present invention can be a waterborne coating composition. As used herein, the “waterborne” means that the solvent of the coating composition comprises at least 50 wt%of water based on the total weight of the solvent.
[0078] The second coating composition according to the present invention can have a low VOC content of less than 420 g / L. As used herein, the term “VOCs (volatile organic compounds) ” refers to any organic compounds having a boiling point at or below 250℃ (482°F) as measured under standard atmospheric pressure of 101.3 kPa. Organic solvents are usually the main source of VOCs. The VOC value can be a VOC value determined in water-free manner, which can be obtained by detecting the contents of various organic compound ingredients in the composition by gas chromatography, followed by adding up the contents of the various organic compound ingredients.
[0079] Suitably, the second coating composition according to the present invention can have a solid content of 10 to 30 wt%. The “solid content” refers to the solid content in the coating composition, which can be obtained by determining the percentage of the residual weight after the solvent of the composition has been fully evaporated to the total weight of the coating composition.
[0080] The second coating composition according to the present invention can be a one-component (1K) coating composition. The “one-component (1K) ” means that all of the film-forming resin (i.e., the binder) , pigment / filler, solvent and / or adjuvants of the coating composition are packaged in a single container, and thus it has advantages of convenience of storage and use, etc.
[0081] The coating system according to the present invention can have a high FI value. Suitably, the coating system according to the present invention can have an FI value of at least 12.The method for determining the FI value is described in detail in the Examples section below.
[0082] The coating system according to the invention can have a low G value. The G value represents the glitter intensity of a coating, where: the smaller the G value, the lower the glitter intensity; and the larger the G value, the higher the glitter intensity. Suitably, the coating system according to the invention can have a G value of not more than 6. The method for determining the G value is described in detail in the Examples section below.
[0083] The coating system according to the invention can have a high chroma. The chroma, also called color saturation, is represented by the saturation. The higher the saturation, the brighter the color, and the lower the saturation, the grayer the color. The saturation can be calculated by where a and b are parameters based on the L*a*b color system specified in JIS Z 8729. Suitably, the coating system according to the present invention can have a chroma of at least 110.
[0084] The present invention further discloses a coated substrate, comprising a substrate and the coating system applied on at least a part of the substrate. Suitably, the substrate can comprise metal. The substrate can or cannot be subjected to pre-treatment and / or pre-coating. For example, the substrate can be a substrate coated with a primer. The primer can be baked prior to the application of the coating system of the current invention. Alternatively, the substrate can be a substrate coated with a functional basecoat layer. As used herein, the “functional basecoat layer” refers to the layer formed from a functional basecoat composition, which functions similar to a primer composition, and constitutes a wet-on-wet system with the coating system of the current invention.
[0085] The underlying coat in the coating system can be obtained by applying the first coating composition using any standard method known in the art. The top coat in the coating system can be obtained by applying the second coating composition using any standard method known in the art. Standard methods known in the art can comprise, but are not limited to, spraying, dipping, roller coating, brushing, etc.
[0086] The present invention further provides a method of coating a substrate: applying a first coating composition comprising an effect pigment to form an underlying coat, applying a second coating composition on at least a part of the underlying coat to form a top coat, and simultaneously curing the first coating composition and the second coating composition, wherein the underlying coat has a dry film thickness of 8 to 15 μm, the top coat has a dry film thickness of 4 to 8 μm, and the effect pigment has an aspect ratio of 60 to 200.
[0087] Suitably, the first coating composition and the second coating composition can be cured by baking at 140℃ for 20 to 60 min. Suitably, the underlying coat formed from the first coating composition is subjected to flash-drying after applying the first coating composition and before applying the second coating composition. Suitably, the first coating composition and the second coating composition can be independently subjected to flash-drying at room temperature (e.g., 23℃) for 1 to 15 min.
[0088] The method of coating a substrate can further comprise: applying a clearcoat composition on at least a part of the top coat, and simultaneously curing the first coating composition, the second coating composition and the clearcoat composition.
[0089] Suitably, the method of coating a substrate can further comprise: before applying the first coating composition, applying a primer composition on at least a part of the substrate and then curing said primer composition.
[0090] Alternatively, the method of coating a substrate can further comprise: before applying the first coating composition, applying a functional basecoat composition on at least a part of the substrate, and simultaneously curing the functional basecoat composition, the first coating composition, the second coating composition and the clearcoat composition.
[0091] The functional basecoat layer can be cured simultaneously with the first coating composition, the second coating composition, and optionally the clearcoat composition.
[0092] EXAMPLES
[0093] The following examples are provided to further illustrate the present invention, but should not be construed to limit the present invention to the details of the examples. All parts and percentages in the following examples are by weight, unless otherwise stated.
[0094] First Coating Composition
[0095] The first coating compositions 1-6 (C1-6) were prepared according to the ingredients and amounts listed in Table 1 below by steps of: (1) sequentially adding the acrylic resin, the PU resin, and the polyester resin to a stirring tank under stirring; (2) adding the pH adjuster to adjust the mixture in step (1) to pH 8.2-8.7, and adding an appropriate amount of deionized water to adjust the system viscosity; (3) adding the defoaming agent, the wetting agent, the MF resin, and a part of the rheological aid into the mixture in step (2) under stirring; (4) mixing the aluminum powder effect pigment with the passivator and the solvent in a separate stirring tank so that the aluminum powder was evenly dispersed; (5) grinding the pigment with some resin, solvent, and dispersing agent into a nanometric color paste; (6) adding the aluminum powder premix in step (4) and the nanometric color paste in step (5) into the mixture prepared in step (3) under stirring; and (7) adding the remaining rheological aid to the mixture in step (6) , and adding the pH adjuster to adjust the system to pH 8.2-8.7.
[0096] Table 1. First Coating Compositions
[0097] a. with solid content of 20 to 35 wt%, Tg of greater than 40℃, hydroxyl value of 10 to 100 mgKOH / g, acid value of 1 to 70 mgKOH / g, and average particle size of 100 to 2,000 nm;
[0098] b. with solid content 30 to 40 wt%, Tg of less than 10℃, Mw of 2,000 to 200,000, hydroxyl value of 10 to 100 mgKOH / g, acid value of 1 to 50 mgKOH / g, and average particle size of 100 to 2,000 nm;
[0099] c. with solid content of 30 to 40 wt%, Tg of greater than 40℃, and Mw of 10,000 to 150,000;
[0100] d. with solid content of 35 to 45 wt%, Tg of 10℃, and Mw of 2,000 to 150,000;
[0101] e. with solid content of 35 to 75 wt%, hydroxyl value of 10 to 100 mgKOH / g, and acid value of 1 to 100 mg KOH / g;
[0102] f. with solid content of 75 to 85 wt%, and molar ratio of imino plus hydroxymethyl functional groups to alkoxy functional group of 5 / 80 to 50 / 50;
[0103] g. alcohol and alcohol ether solvents;
[0104] h. perylene red and carbon black pigments;
[0105] i. silver dollar-type silica-coated aluminum powder, with D50 of 8 to 12 μm, aspect ratio of 150, and WCA of ～40,000 cm2 / g;
[0106] j. silver dollar-type silica-coated aluminum powder, with D50 of 8 to 12 μm, aspect ratio of 50, and WCA of ～20,000 cm2 / g;
[0107] k. silver dollar-type silica-coated aluminum powder, with D50 of 15 to 20 μm, aspect ratio of 50, and WCA of ～10,000 cm2 / g;
[0108] l. from BYK;
[0109] m. from BYK;
[0110] n. with acid value of 20 to 200 mgKOH / g;
[0111] o. comprising a silicate thickener and another thickener selected from the group consisting of acrylic thickener, PU thickener, polyamide wax thickener, and polyurea thickener, wherein a weight ratio of the silicate thickener to the other thickener is 0.2 to 5;
[0112] p. from DOW; and
[0113] q.Nonionic wetting and dispersing agent.
[0114] The second coating compositions 7-11 (C7-11) were prepared according to the ingredients and amounts listed in Table 2 below by steps of: (1) sequentially adding the acrylic resin, the PU resin, and the polyester resin to a stirring tank under stirring; (2) adding the pH adjuster to adjust the mixture in step (1) to pH 8.2-8.7, and adding an appropriate amount of deionized water to adjust the system viscosity; (3) adding the defoaming agent, the wetting agent, the MF resin, and a part of the rheological aid into the mixture in step (2) under stirring; (4) grinding the pigment with some resin, solvent, and dispersing agent into a nanometric color paste; (5) adding the nanometric color paste in step (4) into the mixture prepared in step (3) under stirring; and (6) adding the remaining rheological aid to the mixture in step (5) , and adding the pH adjuster to adjust the system to pH 8.2-8.7.
[0115] Table 2. Second Coating Compositions
[0116] a. with solid content of 20 to 35 wt%, hydroxyl value of 20 to 100 mgKOH / g, acid value of 10 to 50 mgKOH / g, and average particle size of 500 to 2,000 nm;
[0117] b. with solid content of 30 to 40 wt%, hydroxyl value of 10 to 20 mgKOH / g, acid value of 1 to 30 mgKOH / g, and average particle size of 100 to 1,000 nm;
[0118] c. with solid content 30 to 40 wt%, particle size 100 to 1,000 nm, and Mw 10,000 to 150,000;
[0119] d. with solid content 35 to 45 wt%, particle size 1,000 to 2,000 nm, and Mw 2,000 to 150,000;
[0120] e. with solid content of 35 to 75 wt%, hydroxyl value of 10 to 80 mgKOH / g, and acid value of 10 to 50 mgKOH / g;
[0121] f. methoxylated amine resin, with solid content of 75 to 85wt%, and molar ratio of imino plus hydroxymethyl functional groups to alkoxy functional group of 5 / 80 to 50 / 50;
[0122] g. ethylene glycol monobutyl ether;
[0123] h. perylene red and carbon black pigments;
[0124] i. from BYK;
[0125] j. from BYK;
[0126] k. comprising a silicate thickener and another thickener selected from the group consisting of acrylic thickener, PU thickener, polyamide wax thickener, and polyurea thickener, wherein a weight ratio of the silicate thickener to the another thickener is 0.2 to 5;
[0127] l. from DOW; and
[0128] m. Nonionic wetting and dispersing agent.
[0129] Performance Tests:
[0130] A coating system comprising an underlying coat formed from the first coating composition and an top coat formed from the second coating composition was prepared by steps of: spraying a functional basecoat composition (developed by PPG) on a metal substrate (pre-treated and pre-coated) to form a coat; flash-drying the coat at room temperature for 5 min; applying the first coating composition onto at least part of the coat to form the underlying coat; flash-drying the underlying coat at room temperature for 1 minute; applying the second coating composition onto at least part of the underlying coat to form an top coat; flash-drying the top coat at room temperature for at least 3 min, and pre-baking at 80℃ for at least 5 min; applying a clearcoat composition (acommercially available two-component clearcoat) onto at least part of the top coat; and simultaneously curing the functional basecoat composition, the first coating composition, the second coating composition, and the clearcoat composition.
[0131] The coating systems obtained from the first coating compositions C1-6 and the second coating compositions C7-11 were subjected to the following performance tests:
[0132] 1-FI value: referring to the color brightness at various angles. The greater the FI value, the greater the difference between the color brightness at small angle and large angle, and the more the mirror effect.
[0133] As used herein, the brightness value (L) was tested at 15°, 45° and 110° by a commercially available BYK colorimeter, and then the FI value was calculated by the formula of:
[0134] FI = 2.69 * (L*15°-L*110°) 1.11 / (L*45°) 0.86
[0135] 2-G value: representing the glitter intensity of color under a light source. The smaller the G value, the lower the glitter intensity, and the closer to a delicate mirror effect. As used herein, the G value was measured by a commercially available BYK colorimeter.
[0136] 3-Chroma: representing the degree of color saturation. The higher the saturation, the brighter the color; and the lower the saturation, the grayer the color. Herein, the saturation can be calculated by where a and b are parameters based on the L*a*b color system specified in JIS Z 8729, which can be measured by a commercially available BYK colorimeter.
[0137] Other Mechanical Properties
[0138] Adhesion test: performed with reference to the GB / T 9286-2021 standard;
[0139] Moisture resistance test: performed with reference to the GB / T 1740-2007 standard; and
[0140] Aging resistance test: performed with reference to the GB / T 1865-2009 standard.
[0141] Table 3. Results of Performance Tests
[0142] It can be seen from the above test results that the Examples 1-3 with specific formulas (such as resins and aluminum powder) in combination and specific film thickness to give high FI value, low G value, high chroma, and excellent mechanical properties. By comparison, in the Comparative Example 1, the first coating composition do not utilize suitable aluminum powder , and fails to achieve a high FI value and high chroma; in the Comparative Example 2, the first coating composition contain the aluminum powder with large particle size to give high FI, but it has high G value (i.e., relatively high glitter) and low chroma associated with low aspect ratio and poor hiding power of the aluminum powder, meanwhile the second coating composition has a higher film thickness; and in the Comparative Example 3, the first coating composition adopts a method of forming an underlying coat with ultra-low solid- content and ultra-low film thickness to obtain high FI, which needs high aluminum powder content; although the color is somewhat improved, the adhesion, moisture resistance, and aging resistance are below standards.
[0143] Although the particular aspects of the present invention have been illustrated and described, it is obvious to persons skilled in the art that many other variations and modifications can be made without departing the spirit and scope of the present invention. Thus, the accompanying claims are intended to encompass all of these variations and modifications falling within the scope of the present invention.
Claims
1.A coating system, comprising: an underlying coat formed from a first coating composition comprising an effect pigment and a top coat formed from a second coating composition, the first coating composition and the second coating composition being cured simultaneously, wherein the underlying coat has a dry film thickness of 8 to 15 μm, the top coat has a dry film thickness of 4 to 8 μm, and the effect pigment has an aspect ratio of 60 to 200.2.The coating system of claim 1, wherein the effect pigment has a WCA of greater than 30,000 cm2 / g.3.The coating system of claim 1 or 2, wherein the effect pigment comprises a silver dollar type effect pigment.4.The coating system of any one of claims 1-3, wherein the first coating composition has a Pigment / Binder ratio of 0.02 to 0.3.5.The coating system of any one of claims 1-4, wherein the content of the effect pigment is 5 to 15 wt%based on the total solid weight of the first coating composition.6.The coating system of any one of claims 1-5, wherein the first coating composition comprises a high-Tg acrylic resin and a high-Tg polyurethane (PU) resin, and the high-Tg acrylic resin has a Tg of >40℃, and the high-Tg PU resin has a Tg of >30℃.7.The coating system of claim 6, wherein the weight ratio of the high-Tg acrylic resin to the high-Tg PU resin is (10-80) : (5-50) .8.The coating system of claim 6 or 7, wherein the high-Tg acrylic resin has a hydroxyl value of 10 to 100 mg KOH / g, an acid value of 1 to 70 mg KOH / g, and an average particle size of 100 to 5,000 nm.9.The coating system of any one of claims 6-8, wherein the high-Tg PU resin has a weight average molecular weight of 5,000 to 200,000 g / mol.10.The coating system of any one of claims 1-9, wherein the second coating composition comprises an acrylic resin, a PU resin, an amine resin and optionally a polyester resin.11.The coating system of claim 10, wherein the weight ratio of the acrylic resin, the PU resin, the amine resin and to the polyester resin is (5-50) : (5-30) : (3-40) : (0-15) .12.The coating system of claim 10 or 11, wherein the acrylic resin has an average particle size of 100 to 3,000 nm, a weight average molecular weight of 1,000 to 20,000 g / mol, a hydroxyl value of 20 to 200 mg KOH / g, and an acid value of 10 to 50 mg KOH / g.13.The coating system of any one of claims 10-12, wherein the PU resin has an average particle size of 100 to 1,000 nm.14.The coating system of any one of claims 1-13, wherein the second coating composition comprises a solvent, wherein the solvent comprises water and ethylene glycol monobutyl ether.15.The coating system of any one of claims 1-14, wherein the second coating composition has a Pigment / Binder ratio of 0.05 to 0.3.16.The coating system of any one of claims 1-15, wherein the first coating composition and / or the second coating composition is waterborne.17.The coating system of any one of claims 1-16, wherein each of the first coating composition and the second coating composition has a VOC content of less than 420 g / L.18.A coated substrate, comprising a substrate and the coating system of any one of claims 1-17 applied on at least a part of the substrate.19.The coated substrate of claim 18, wherein the substrate comprises a metal.20.The coated substrate of claim 18 or 19, wherein the substrate comprises a substrate already coated with a primer layer or a functional base coating layer.21.A method of coating a substrate, comprising:applying a first coating composition comprising an effect pigment to form an underlying coat,applying a second coating composition on at least a part of the underlying coat to form a top coat, andsimultaneously curing the first coating composition and the second coating composition,wherein the underlying coat has a dry film thickness of 8 to 15 μm, the top coat has a dry film thickness of 4 to 8 μm, and the effect pigment has an aspect ratio of 60 to 200.22.The method of claim 21, further comprising:applying a clearcoat composition on at least a part of the top coat to form a clearcoat, and simultaneously curing the first coating composition, the second coating composition and the clearcoat composition.23.The method of claim 21 or 22, further comprising:before applying the first coating composition, applying a primer composition on at least a part of the substrate and then curing the primer composition.24.The method of claim 21 or 22, further comprising:before applying the first coating composition, applying a functional basecoat composition on at least a part of the substrate, and simultaneously curing the functional basecoat composition, the first coating composition, the second coating composition and optionally the clearcoat composition.