Acrylic-based clear topcoat composition and its applications

Abstract

The present invention discloses an acrylic-based clear topcoat composition and its application, which includes a high-solid thermosetting hydroxyl acrylic resin, an acrylic resin containing epoxy groups, an acrylic resin containing acid anhydride groups, an etherified amino resin, a diurea compound-modified acrylic resin, additives and diluents. This clear topcoat composition is environmentally friendly, has high appearance and high performance, especially excellent acid resistance, and has strong adhesion to different systems.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and particularly to an acrylic-based clear topcoat composition and its application. Background Art

[0002] Varnish is made of resin and solvent, transparent or light yellow in color. The surface coated with varnish looks very shiny, and the forming time of varnish is short. After drying, it will not affect the color of the original object. When used in automotive painting, varnish is often used as the outermost coating, so there are high technical requirements for appearance and various properties such as weather resistance and chemical resistance.

[0003] Particularly, due to the changes in the natural environment, such as the increasing severity of acid rain, the application market has put forward higher requirements for the acid resistance and bird droppings resistance (the mechanism is similar to acid resistance) of varnish. Compared with two-component varnish of the hydroxyl-isocyanate crosslinking system, two-component varnish has problems such as high spraying equipment cost, complex maintenance process, and short coating service life. At present, the commonly used acrylic amino-based one-component varnish in the automotive painting market is very easy to hydrolyze due to the cleavage of ether bonds in an acidic environment, thus greatly reducing the acid resistance, which has always been a major weakness of conventional one-component varnishes.

[0004] On the other hand, to improve the painting efficiency, reduce energy consumption and material costs, and reduce the negative impact on the environment, automotive painting plants often use the same varnish to match different color paints. These color paints have different systems (three coats and two baking or three coats and one baking), and may also come from different suppliers. The common compatibility of varnishes is relatively narrow. When applied together with non-matching color paints, film defects such as poor adhesion and poor appearance are likely to occur.

[0005] In summary, it is necessary to provide a new one-component clear topcoat to overcome the above technical problems. The present invention combines the most commonly used acrylic amino-based one-component varnish on the market, improves the formula, and prepares an acrylic-based clear topcoat composition with greatly enhanced acid resistance. Summary of the Invention

[0006] In order to overcome the above technical problems in the prior art, the present invention provides an acrylic-based clear topcoat composition and its application.

[0007] The first object of the present invention is to provide an acrylic-based clear topcoat composition, which is environmentally friendly, has high appearance and high performance, especially excellent acid resistance, and strong adhesion to different systems.

[0008] The second object of the present invention is to provide an acrylic-based clear topcoat.

[0009] The third object of the present invention is to provide an application of an acrylic-based clear topcoat in the external coating of industrial products.

[0010] To achieve the above first object, the present invention adopts the following technical solutions:

[0011] An acrylic-based clear topcoat composition, comprising the following components in parts by weight:

[0012]

[0013] Further, the high-solid thermosetting hydroxy acrylic resin, the acrylic resin containing an epoxy group, and the acrylic resin containing an acid anhydride group are copolymers of acrylic monomers and other monomers containing carbon-carbon double bonds.

[0014] Further, the high-solid thermosetting hydroxy acrylic resin has at least one of the following characteristics:

[0015] (1) The number average molecular weight is 3000 to 5000;

[0016] (2) The hydroxyl value is 150 to 250 mgKOH / g;

[0017] (3) The acid value is 7.0 to 11.0 mgKOH / g; and / or

[0018] (4) The glass transition temperature is between -10°C and +35°C.

[0019] Further, the solid content of the high-solid thermosetting hydroxy acrylic resin is 80% by weight or more.

[0020] Further, the preparation method of the high-solid thermosetting hydroxy acrylic resin comprises the following steps:

[0021] A mixture of isobornyl methacrylate, styrene, n-butyl acrylate, 2-hydroxyethyl methacrylate, acrylic acid, and methyl methacrylate and an initiator are added to a solvent at a temperature of 130 to 140°C, and kept at a temperature of 130 to 140°C for 1 to 2 hours to obtain the high-solid thermosetting hydroxy acrylic resin.

[0022] Further, in the preparation method of the high-solid thermosetting hydroxy acrylic resin, the addition amounts of the respective components are as follows in parts by weight:

[0023]

[0024] Furthermore, the hydroxyl value of the epoxy group-containing acrylic resin is 30 to 80 mg KOH / g, the solid content is 68 to 73 wt% or more, the glass transition temperature is between 20°C and 50°C, the epoxy equivalent is 400 to 600 g / mol, and the number average molecular weight is 2,000 to 4,000.

[0025] Furthermore, the preparation method of the epoxy group-containing acrylic resin comprises the following steps:

[0026] A mixture of isobutyl methacrylate, styrene, n-butyl acrylate, 2-hydroxyethyl acrylate, isobornyl acrylate, and glycidyl methacrylate and an initiator are added to a solvent at a temperature of 170 to 190°C, and kept at 170 to 190°C for 0.5 to 1 hour, and then kept at 110 to 130°C for 1 to 2 hours to obtain the epoxy group-containing acrylic resin.

[0027] Furthermore, in the preparation method of the epoxy group-containing acrylic resin, the addition amounts of the respective components are as follows by weight parts:

[0028]

[0029] Furthermore, the solid content of the acid anhydride group-containing acrylic resin is 45 to 50 wt%, the number average molecular weight is 3,000 to 5,000, the glass transition temperature is between -35°C and +45°C, and the hydroxyl value is 0 mg KOH / g.

[0030] Furthermore, the preparation method of the acid anhydride group-containing acrylic resin comprises the following steps:

[0031] A mixture of maleic anhydride, styrene, n-butyl acrylate, isooctyl acrylate, isobornyl acrylate, acrylic acid, and cyclohexyl methacrylate and an initiator are added to a solvent at a temperature of 130 to 140°C, and kept at 130 to 140°C for 2 to 4 hours to obtain the acid anhydride group-containing acrylic resin.

[0032] Furthermore, in the preparation method of the acid anhydride group-containing acrylic resin, the addition amounts of the respective components are as follows by weight parts:

[0033]

[0034] Furthermore, the etherified amino resin is a butylated amino resin, preferably at least one selected from Neoresins SETAMINE US-146 BB-72, SETAMINE US-138 BB-70, and BASF LUWIPAL 018.

[0035] Furthermore, the solid content of the etherified amino resin is 70 wt% or more.

[0036] Further, the modification amount of the biurea compound in the biurea compound-modified acrylic resin is 3.2-4.2%.

[0037] Further, the auxiliary agent includes the following components in parts by weight:

[0038]

[0039]

[0040] Further, the ultraviolet light absorber is a benzotriazole ultraviolet light absorber. Preferably, the ultraviolet light absorber is selected from at least one of BASF Tinuvin 928, Tinuvin 384-2, Tinuvin 400, and Tinuvin 477.

[0041] Further, the light stabilizer is a sterically hindered amine light stabilizer. Preferably, the light stabilizer is selected from at least one of BASF Tinuvin 292 and Tinuvin 123, or a combination thereof.

[0042] Further, the silicone leveling agent is a polyester-modified polydimethylsiloxane silicone leveling agent. The silicone leveling agent cooperates with other components to achieve the best balance effect of reducing surface tension, improving smoothness and other properties. Preferably, the silicone leveling agent is selected from at least one of BYK-331, BYK-315, BYK-306, BYK-310, Tego-450, and BAYSILONE OL-17.

[0043] Further, the acrylate leveling agent is a non-reactive acrylate leveling agent. It synergistically acts with the silicone leveling agent to achieve the best appearance. Preferably, the acrylate leveling agent is selected from at least one of BYK-358N, TegoFlow-300, and Modaflow-2100.

[0044] Further, the auxiliary agent includes the following components in parts by weight:

[0045]

[0046] Further, the diluent is selected from at least one of butanol, butyl acetate, ethyl acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, mixed dibasic acid diester (DBE), and ethyl 3-ethoxypropionate (EEP). The selected diluent effectively reduces the viscosity of the varnish while avoiding compounds with greater environmental hazards such as xylene and toluene.

[0047] To achieve the second above-mentioned purpose, the present invention provides an acrylic clear topcoat varnish prepared from the acrylic clear topcoat varnish composition described in the first above-mentioned purpose.

[0048] To achieve the third above-mentioned purpose, the present invention provides the application of the acrylic clear topcoat varnish described in the second above-mentioned purpose in the external coating of industrial products.

[0049] Furthermore, the industrial products include automobiles, automobile wheels, motorcycles, construction machinery, and light industrial products.

[0050] Compared with the prior art, the technical solution provided by the present invention has the following advantages:

[0051] The acrylic clear topcoat varnish composition provided by the present invention is a one-component clear varnish composition, which adopts the combination of a high-solid thermosetting hydroxyl acrylic resin, an acrylic ester containing an epoxy group, an acrylic resin containing an acid anhydride group, an etherified amino resin, and a diurea compound-modified acrylic resin, so that the obtained clear varnish composition and the corresponding products are environmentally friendly, have high appearance and high performance, especially excellent acid resistance, and have strong adhesion to different systems. Detailed Description of the Invention

[0052] The specific embodiments of the present invention will be described in detail below. However, it should be understood that the present invention is not limited to the embodiments described below, and the technical concept of the present invention can be implemented in combination with other known technologies or other technologies with the same functions as those known technologies.

[0053] In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of these features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0054] In the present invention, unless otherwise clearly defined and limited, the terms "installation", "connection", "connection", "fixation" and other terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] In this article, the "clear topcoat varnish" can be arranged on the primer coating and the coating above the toner and / or ink printed thereon, which can enhance the appearance performance of the substrate.

[0056] Unless clearly indicated to the contrary, each aspect or embodiment defined herein can be combined with any other one or more aspects or one or more embodiments. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature indicated as being preferred or advantageous.

[0057] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0058] In the case where the object of the present invention is clarified and explained by the following examples, the components of the composition are described in terms of parts by weight as a general standard. Unless otherwise specified, for the sake of simplicity, the "parts" described in the embodiments of the present invention have the same meaning as parts by weight.

[0059] Unless otherwise specifically stated, various raw materials of the present invention can be obtained commercially; or prepared according to conventional methods in the art. Unless otherwise defined or stated, all professional and scientific terms used in this application have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention.

[0060] For the experimental methods without specific conditions in the following specific embodiments and examples, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise stated, all parts are parts by weight, all percentages are weight percentages, and the molecular weight of the polymer mentioned is the number average molecular weight.

[0061] The present invention improves the deficiencies of conventional one-component varnishes in many performance aspects by introducing epoxy groups and anhydride groups into the hydroxyl-amine crosslinking system. The epoxy groups can react with the anhydride groups under baking conditions, and the hydroxyl groups generated after the epoxy ring opening can further react with the amino resin, making the varnish a multiple curing system, reducing the ether bond content in the system, improving the acid resistance, and at the same time improving other properties such as chemical resistance.

[0062] On the other hand, the introduction of epoxy groups and anhydride groups makes the varnish contain various different types of anchoring groups. These anchoring groups have different polarities and solubility parameters, making the varnish have a better adhesion effect on the underlying layer, so that the varnish can be matched with different color paint systems.

[0063] When the epoxy group reacts with the anhydride group, it is different from the conventional hydroxyl - amino reaction and does not eliminate small molecules. This reduces the shrinkage of the paint film, improves the appearance of the varnish, enables the varnish to have a good appearance when paired with different colored paint systems, and simultaneously reduces the VOC during coating baking.

[0064] In the embodiments of the present invention, the high - solid thermosetting hydroxyl - acrylic resin, the acrylic resin containing epoxy groups, and the acrylic resin containing anhydride groups are copolymers of acrylic monomers and other monomers containing carbon - carbon double bonds. Specifically, they are copolymers formed by free - radical copolymerization of acrylic monomers and other monomers containing carbon - carbon double bonds under the action of an initiator.

[0065] Among them, exemplary acrylic monomers include, but are not limited to, one or more selected from methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert - butyl acrylate, tert - butyl methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, 2 - ethylhexyl acrylate, 2 - ethylhexyl methacrylate, 3,3,5 - trimethylhexyl acrylate, 3,3,5 - trimethylhexyl methacrylate, octadecyl acrylate, octadecyl methacrylate, dodecyl acrylate, dodecyl methacrylate, cyclopentyl acrylate, cyclopentyl methacrylate, isobornyl acrylate, isobornyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, glycidyl acrylate, glycidyl methacrylate, hydroxyalkyl methacrylate, 2 - hydroxyethyl acrylate, 2 - hydroxyethyl methacrylate, 2 - hydroxypropyl acrylate, 2 - hydroxypropyl methacrylate, 3 - hydroxypropyl acrylate, 3 - hydroxypropyl methacrylate, 3 - hydroxybutyl acrylate, 3 - hydroxybutyl methacrylate, 4 - hydroxybutyl acrylate, 4 - hydroxybutyl methacrylate, condensation product of acrylic acid and glycidyl versatic acid, condensation product of methacrylic acid and glycidyl versatic acid, acrylic acid, and methacrylic acid.

[0066] Other types of monomers containing carbon-carbon double bonds, that is, non-acrylic monomers containing carbon-carbon double bonds. Exemplary other types of monomers containing carbon-carbon double bonds include, but are not limited to, those selected from styrene, methylpropylene, allyl alcohol, vinyl versatate, acrylonitrile, acrylamide, diacetone acrylamide, maleic anhydride, monomethyl maleate, monoethyl maleate, monon-propyl maleate, monoisopropyl maleate, monon-butyl maleate, monoisobutyl maleate, monotert-butyl maleate, monopentyl maleate, monohexyl maleate, monoethylhexyl maleate, dimethyl maleate, diethyl maleate, di-n-propyl maleate, diisopropyl maleate, di-n-butyl maleate, diisobutyl maleate, ditert-butyl maleate, dipentyl maleate, dihexyl maleate, diethylhexyl maleate, or one or more of them.

[0067] The initiator includes azo or peroxide initiators. Exemplary initiators include, but are not limited to, the following compounds known to those skilled in the art: azobisisobutyronitrile, azobisheptanenitrile, benzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-amyl peroxy-2-ethylhexanoate, 1,1-bis(tert-amylperoxy)cyclohexane, 1,1-bis(tert-amylperoxy)-3,3,5-trimethylcyclohexane, tert-butyl peroxybenzoate, tert-amyl peroxybenzoate, tert-amyl peroxyacetate, tert-butyl peroxy-3,5,5-trimethylhexanoate, ethyl 3,3-bis(tert-butylperoxy)butyrate, ethyl 3,3-bis(tert-amylperoxy)butyrate, dicumyl peroxide, tert-amyl hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, di-tert-amyl peroxide, or one or more of them.

[0068] In yet another specific embodiment of the present invention, a clear topcoat based on acrylic acid is provided. The clear topcoat is prepared from the high-solid clear topcoat composition based on acrylic acid provided in the first specific embodiment above.

[0069] In yet another specific embodiment of the present invention, the application of the clear topcoat provided in the second specific embodiment above in the external coating of industrial products is provided.

[0070] Among them, exemplary industrial products include, but are not limited to, automobiles (such as automobile bodies, automobile wheels), motorcycles, construction machinery, and light industrial products.

[0071] In a preferred example, the specific application includes:

[0072] First, apply the primer or intermediate coat to the substrate and cure it, apply the color coat to the substrate on which the primer or intermediate coat has been cured, then apply the clear coat composition to the surface of the uncured color coat, and finally cure the two parts of the coating simultaneously to obtain the multi-layer coating system, and the multi-layer coating system is a three-coat two-bake system.

[0073] Alternatively, first apply the primer or intermediate coat to the substrate, then apply the color coat to the surface of the uncured primer or intermediate coat, and then apply the clear coat composition to the surface of the uncured color coat. Finally, cure the three-part coating simultaneously to obtain the multi-coat finishing system, which is a three-coat one-bake system.

[0074] Alternatively, apply two layers of color coat to a substrate without primer and intermediate coat, then spray the clear coat composition on the surface of the second layer of color coat, and cure the three-part coating simultaneously to obtain the multi-coat finishing system, which is an Integrated Paint Processes (IPP) system.

[0075] The intermediate coat and / or color coat used in the three-coat two-bake, three-coat one-bake and IPP systems are waterborne coatings or solvent-based coatings, and the solids content during the application of the primer and / or color coat is between 25 and 55% by weight; the color coat is at least one of a single-color paint, a metallic paint or a pearl paint, is a waterborne color paint or a solvent-based color paint, and the film thickness after curing is 5 to 40 μm, further 5 to 30 μm.

[0076] In a preferred example, the acrylic-based clear topcoat satisfies the following conditions when in use:

[0077] 1) During spraying, the application viscosity is 33 ± 2 seconds with a No. 4 Ford cup;

[0078] 2) The one-time spray film thickness of the clear coat is 30 to 50 μm;

[0079] 3) The flash-off conditions of the clear coat are at 20 to 30 °C and 60 to 70% humidity for 5 to 10 minutes; and / or

[0080] 4) The final baking and film-forming conditions of the clear coat are 145 ± 5 °C for 20 to 30 minutes.

[0081] Term Explanation

[0082] As used herein, the term "glass transition temperature" or "Tg" refers to the temperature at which or above which a glassy polymer will undergo segmental motion of the polymer chains.

[0083] As used herein, the term "hydroxyl value" represents the number of milligrams of KOH per gram.

[0084] Hereinafter, the technical solutions of the present invention will be described in conjunction with some specific embodiments:

[0085] Preparation of high-solid thermosetting hydroxy acrylic resin: Hydroxy acrylic resin A

[0086] Add the following solvents: 800 parts of butyl acetate and 400 parts of propylene glycol monomethyl ether acetate into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen conduit, and a reflux condenser;

[0087] Heat the reaction system to 130 - 140 °C;

[0088] When the reaction temperature is stable, add the following premix of monomers: 425 parts of isobornyl methacrylate, 300 parts of styrene, 1750 parts of n-butyl acrylate, 1750 parts of 2-hydroxyethyl methacrylate, 50 parts of acrylic acid, and 950 parts of methyl methacrylate, gradually and uniformly into the reaction vessel through a pump, maintaining the reaction temperature between 130 and 140 °C during the process, controlling the rate to ensure that the reaction mixture is added dropwise within 2 - 4 hours;

[0089] Meanwhile, add the following initiator mixture, specifically: 200 parts of tert-butyl peroxy-2-ethylhexanoate Kayaester O (purchased from AkzoNobel) and 159 parts of di-tert-amyl peroxide Luperox DTA (purchased from Arkema), into the reaction vessel at the same rate as the above premix of monomers through another pump and pipeline;

[0090] After adding all the above reactants, continue to keep warm at 130 - 140 °C for 1 - 2 hours to terminate the reaction, obtaining a hydroxy acrylic resin A with a solid content of 80 ± 1%, a hydroxyl value of 155 mg KOH / g, a glass transition temperature (Tg) of 22 °C, and a molecular weight of about 3500.

[0091] Preparation of acrylic resin containing epoxy group: Acrylic resin B

[0092] Add the following solvents: 100 parts of butyl acetate and 200 parts of S-100 solvent into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen conduit, and a reflux condenser, and pressurize to 0.2 mPa;

[0093] Heat the reaction system to 170 °C;

[0094] When the reaction temperature is stable, add the following premix of monomers: 60 parts of isobutyl methacrylate, 250 parts of styrene, 60 parts of n-butyl acrylate, 110 parts of 2-hydroxyethyl acrylate, 170 parts of isobornyl methacrylate, and 400 parts of glycidyl methacrylate, gradually and uniformly into the reaction vessel through a pump, maintaining the reaction temperature between 170 and 175 °C during the process, controlling the rate to ensure that the reaction mixture is added dropwise within 2 - 4 hours;

[0095] At the same time, the following initiator mixture, specifically: 4 parts of tert-amyl peroxy-2-ethylhexanoate Luperox 575 (purchased from Arkema) and 28 parts of di-tert-amyl peroxide Luperox DTA (purchased from Arkema), were added to the reaction vessel at the same rate as the above-mentioned premix of monomers through another pump and pipeline;

[0096] After the above reactants were added, the temperature was kept between 170 and 175 °C for 1 to 2 hours to terminate the reaction, obtaining an acrylic resin B containing epoxy groups with a hydroxyl value of 30 to 80 mg KOH / g, a solid content of 68 to 73 wt% or more, a glass transition temperature between 20 °C and 50 °C, an epoxy equivalent of 400 to 600 g / mol, and a molecular weight of 2000 to 4000.

[0097] Preparation of acrylic resin containing anhydride group: Acrylic resin C

[0098] The following solvents: 200 parts of S-100 solvent and 100 parts of propylene glycol methyl ether acetate were added to a reaction vessel equipped with a stirrer, a thermometer, a nitrogen conduit, and a reflux condenser;

[0099] The reaction system was heated to 130 to 140 °C;

[0100] When the reaction temperature was stable, the following premix of monomers: 100 parts of maleic anhydride, 110 parts of styrene, 70 parts of n-butyl acrylate, 70 parts of isooctyl acrylate, 10 parts of isobornyl acrylate, 10 parts of acrylic acid, and 95 parts of cyclohexyl methacrylate were gradually added to the reaction vessel at a constant speed by a pump. During the process, the reaction temperature was maintained between 130 and 140 °C, and the rate was controlled to ensure that the reaction mixture was added dropwise within 2 to 3 hours;

[0101] At the same time, the following initiator mixture, specifically: 45 parts of tert-butyl peroxy-2-ethylhexanoate Kayaester O (purchased from AkzoNobel) was added to the reaction vessel at the same rate as the above-mentioned premix of monomers through another pump and pipeline;

[0102] After the above reactants were added, the temperature was kept between 130 and 140 °C for 0.5 hour.

[0103] Then, the following initiator mixture, specifically: 5 parts of tert-butyl peroxy-2-ethylhexanoate Kayaester O (purchased from AkzoNobel) was added to the reaction vessel through a pump and pipeline within 0.5 hour;

[0104] After the above reactants were added, the temperature was kept between 130 and 140 °C for 1 hour.

[0105] The reaction is terminated to obtain an acid anhydride group-containing acrylic resin C with a solid content of 45-50% by weight, a molecular weight of 3000-5000, a glass transition temperature between -35°C and +45°C, and a hydroxyl value of 0 mg KOH / g.

[0106] Preparation of acrylic-based clear topcoat paint

[0107] Example 1: Clear topcoat 1

[0108] The formulation of the topcoat varnish coating in this example is shown in Table 1 below. Its preparation method includes the following steps:

[0109] 1) Ethylene glycol monobutyl ether acetate, mixed dibasic acid diester (DBE), ethyl 3-ethoxypropionate (EEP) and butyl acetate are successively added to the main cylinder a and stirred for 10 minutes at a rotation speed of 200-400 rpm;

[0110] 2) TINUVIN 292, TINUVIN 384-2, BYK 358N and BYK 310 are successively added to the main cylinder a at a rotation speed of 300-500 rpm, and after the addition, stirring is continued for 30 minutes;

[0111] 3) Hydroxyl group-containing acrylic resin A, epoxy group-containing acrylic resin B and acid anhydride group-containing acrylic resin C are successively added to the main cylinder a at a rotation speed of 300-500 rpm, and after the addition, stirring is continued for 20 minutes;

[0112] 4) SETALUX 91796 SS-69 is added to the main cylinder a at a rotation speed of 300-500 rpm, and after the addition, stirring is continued for 30 minutes;

[0113] 5) SETAMINE US-138 BB-70 is successively added to the main cylinder a at a rotation speed of 300-500 rpm, and after the addition, stirring is continued for 30 minutes;

[0114] 6) The varnish in the main cylinder a is diluted to the appropriate viscosity described in Table 1 using an appropriate amount of n-butanol and DBE to obtain the topcoat varnish 1.

[0115] Table 1: Composition of the coating formulations of Example 1 and Comparative Example 1

[0116]

[0117] Comparative Example 1: Topcoat varnish C1

[0118] The preparation method is the same as that of Example 1, except that in step 3), the epoxy group-containing acrylic resin B and the acid anhydride group-containing acrylic resin C are not added and replaced with an equal amount of solid content of hydroxyl group-containing acrylic resin A.

[0119] Comparative Example 2: Topcoat Clear Varnish C2

[0120] Use the clear varnish with model number O-3300 (purchased from Nippon Paint), which is a conventional acrylic amino single-component topcoat clear varnish, without epoxy groups and anhydride groups.

[0121] Comparative Example 3: Topcoat Clear Varnish C3

[0122] Use the Starlight clear varnish purchased from BASF, which is a conventional acrylic amino single-component topcoat clear varnish, without epoxy groups and anhydride groups, and contains blocked isocyanate resin.

[0123] Comparative Example 4: Topcoat Clear Varnish C4

[0124] The preparation method is the same as that of Example 1, except that the acrylic resin C containing anhydride groups in step 3) is not added, and is replaced with hydroxy acrylic resin A with the same solid content.

[0125] Comparative Example 5: Topcoat Clear Varnish C5

[0126] The preparation method is the same as that of Example 1, except that the acrylic resin B containing epoxy groups in step 3) is not added, and is replaced with hydroxy acrylic resin A with the same solid content.

[0127] Application of the topcoat clear varnish

[0128] Test Example 1

[0129] Formation of the coating film

Adopt the three-coat two-bake process

[0130] On the passivated steel plate treated with zinc phosphate, apply the cationic electrophoretic coating PN-310 (purchased from Nippon Paint) until the dry coating film thickness reaches 20 μm, heat it at 160 °C for 30 minutes to cure it and then cool it to form a cured electrophoretic coating film. Then, spray the topcoat clear varnishes prepared in the foregoing examples and comparative examples on this electrophoretic coating film by using the three-coat two-bake process described above. The relevant other coatings are shown in Table 2 below. Then, conduct various index tests according to the content of Table 3.

[0131] Table 2: Formulations and construction conditions of each coating used in the three-coat two-bake process in Test Example 1

[0132]

[0133]

[0134] Table 3 Indexes of detection items

[0135]

[0136] The topcoat clear varnishes of Example 1 and Comparative Examples 1-5 were spray-coated and film-formed under the three-coat two-bake process, and the results of detecting various indexes are summarized in Table 4. After using the acrylic resin containing epoxy groups and anhydride groups, the three-dimensional interpenetration and compactness of the polymer chain segments after crosslinking and curing become higher, and the properties such as gasoline resistance, water resistance, and damp heat are significantly improved compared with the acrylic-amine system. The ether bonds in the system are reduced, and the acid resistance under harsh conditions is significantly improved. When the epoxy group and the anhydride group form a film, no small molecules volatilize, the shrinkage of the paint film is reduced, and the appearance is also better than that of the comparative example. At the same time, after film formation, the ester bond groups make it easier to recoat the colored paint and the clear varnish, and the recoat adhesion is better than that of the comparative example.

[0137] In Comparative Example 4, since the acrylic resin C containing anhydride groups was not used, the crosslinking degree of the acrylic resin B containing epoxy groups was insufficient, so the properties such as acid resistance were worse than those of the topcoat clear varnish in Example 1.

[0138] Similarly, in Comparative Example 5, since the acrylic resin B containing epoxy groups was not used, the crosslinking degree of the acrylic resin C containing anhydride groups was also insufficient, so the properties such as acid resistance were worse than those of the topcoat clear varnish in Example 1.

[0139] Table 4 Detection Results of Each Example and Comparative Example (Three-Coat Two-Bake Process)

[0140]

[0141] Test Example 2

[0142] Formation of the paint film

Adopt the three-coat one-bake process

[0143] On the passivated steel plate treated with zinc phosphate, the electrophoretic coating PN-310 (cationic electrophoretic coating manufactured by Nippon Paint) was applied until the dry film thickness reached 20 μm, and then it was heated at 160 °C for 30 minutes to be cured and then cooled to form a cured electrophoretic coating film. After that, all the examples and comparative examples were sprayed on this electrophoretic coating film by using the three-coat one-bake process described above. The relevant other coatings are as shown in Table 5 below. Then, various index tests were carried out according to the content of Table 3.

[0144] Table 5 Formulations and Construction Conditions of Each Coating Used in the Three-Coat One-Bake Process in Test Example 2

[0145]

[0146] The results are as described in Table 6, showing the same trend as in Test Example 1. Since the three-coat one-bake process is a more demanding wet-on-wet painting process, the film thicknesses of the primer surfacer and the basecoat become thinner, and the appearance and performance results show greater advantages. It is worth noting that in the three-coat one-bake system, the epoxy group has strong permeability and anchoring to the lower layer, and the adhesion of the clearcoat 1 containing the epoxy group is better than that of each comparative example.

[0147] Table 6 Test Results of Example 1 and Comparative Examples 1-5 (Three-Coat One-Bake Process)

[0148]

[0149]

[0150] The multiple-curing clearcoat composition based on acrylic resin of the present invention is more environmentally friendly, has good workability, high appearance, high performance, especially acid resistance, and good compatibility with different systems. It is particularly suitable for automotive exterior painting, and also suitable for the exterior painting of automotive wheels, motorcycles, construction machinery, light industrial products, etc.

[0151] Unless otherwise specified, the qualifiers such as "first" and "second" appearing in this article are not intended to limit the time sequence, quantity, or importance, but merely to distinguish one technical feature in the technical solution of the present invention from another technical feature. Similarly, the qualifier such as "a" appearing in this article is not intended to limit the quantity, but to describe a technical feature that has not appeared in the foregoing. Similarly, the modifiers such as "about" and "approximately" appearing before a numeral in this article usually include this number, and their specific meanings should be understood in combination with the context. Similarly, unless it is a noun modified by a specific quantity word, it should be regarded as including both the singular form and the plural form in this article, that is, in this technical solution, it can include a single such technical feature or a plurality of such technical features.

[0152] What is described in this specification is only the preferred specific embodiments of the present invention. The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Any technical solution that can be obtained by those skilled in the art according to the concept of the present invention through logical analysis, reasoning, or limited experiments should be within the scope of the present invention.

Claims

1. An acrylic-based clear topcoat composition, characterized in that, Comprising the following components in parts by weight: The high-solid thermosetting hydroxy acrylic resin has the following characteristics: (1) The number-average molecular weight is 3000 - 5000; (2) The hydroxyl value is 150 - 250 mg KOH / g; (3) The acid value is 7.0 - 11.0 mg KOH / g; (4) The glass transition temperature is between -10°C and +35°C; and (5) The solid content of the high-solid thermosetting hydroxy acrylic resin is above 80% by weight; The epoxy group-containing acrylic resin has the following characteristics: (1) The hydroxyl value is 30 - 80 mg KOH / g; (2) The solid content is 68 - 73% by weight or more; (3) The glass transition temperature is between 20°C and 50°C; (4) The epoxy equivalent is 400 - 600 g / mol; and (5) The number-average molecular weight is 2000 - 4000; The acid anhydride group-containing acrylic resin has the following characteristics: (1) The solid content is 45 - 50% by weight; (2) The number-average molecular weight is 3000 - 5000; (3) The glass transition temperature is between -35°C and +45°C; (4) The hydroxyl value is 0 mg KOH / g; By weight, the addition amounts of the components for preparing the high-solid thermosetting hydroxy acrylic resin are: By weight, the addition amounts of the components for preparing the epoxy group-containing acrylic resin are: By weight, the addition amounts of the components for preparing the acid anhydride group-containing acrylic resin are:

2. The acrylic-based clear topcoat composition according to claim 1, characterized in that, The preparation method of the high-solid thermosetting hydroxy acrylic resin comprises the following steps: adding a mixture of isobornyl methacrylate, styrene, n-butyl acrylate, 2-hydroxyethyl methacrylate, acrylic acid, and methyl methacrylate and an initiator into a solvent at a temperature of 130 - 140°C, and keeping the temperature at 130 - 140°C for 1 - 2 hours to obtain the high-solid thermosetting hydroxy acrylic resin.

3. The acrylic-based clear topcoat composition according to claim 1, characterized in that, The preparation method of the epoxy group-containing acrylic resin comprises the following steps: Adding a mixture of isobutyl methacrylate, styrene, n-butyl acrylate, 2-hydroxyethyl acrylate, isobornyl acrylate, and glycidyl methacrylate and an initiator into a solvent at a temperature of 170 - 190°C, keeping the temperature at 170 - 190°C for 0.5 - 1 hour, and then keeping the temperature at 110 - 130°C for 1 - 2 hours to obtain the epoxy group-containing acrylic resin.

4. The acrylic-based clear topcoat composition according to claim 1, characterized in that, The preparation method of the acid anhydride group-containing acrylic resin comprises the following steps: Adding a mixture of maleic anhydride, styrene, n-butyl acrylate, isooctyl acrylate, isobornyl acrylate, acrylic acid, and cyclohexyl methacrylate and an initiator into a solvent at a temperature of 130 - 140°C, and keeping the temperature at 130 - 140°C for 2 - 4 hours to obtain the acid anhydride group-containing acrylic resin.

5. An acrylic-based clear topcoat varnish prepared from the acrylic-based clear topcoat varnish composition according to any one of claims 1 - 4.

6. The application of the acrylic-based clear topcoat varnish according to claim 5 in the external coating of industrial products.

Images