Colored varnish, preparation method thereof and preparation method of colored workpiece

Abstract

The invention provides colored varnish, a preparation method thereof and a preparation method of a colored workpiece. The colored varnish comprises a component A and a component B, based on 100 parts of the total mass of the component A, the component A comprises the following components: 30-35 parts of first resin, 13-20 parts of second resin, 2-3 parts of nanoscale black pigment, 1-2 parts of a dispersing aid, 3-4 parts of a leveling aid, 2-3 parts of an ultraviolet light absorber, 2-3 parts of a drying aid and 30-47 parts of a solvent, the first resin comprises acrylic resin, and the second resin comprises polyester resin; on the basis that the total mass of the component B is 100 parts, the component B comprises 60-85 parts of aliphatic isocyanate and 15-40 parts of an anhydrous diluent; the mass ratio of the component A to the component B is (2-4): 1. The colored varnish not only has the same color endowing function as colored paint, but also has good leveling property, glossiness, color saturation, tinting strength and weather resistance.

Description

Technical Field

[0001] The present application relates to the technical field of automobile coating, and in particular to a colored varnish, a preparation method thereof, and a preparation method of a colored workpiece. Background Art

[0002] With the continuous advancement of paint material technology by automotive original equipment manufacturers (OEMs), the function of clearcoat is no longer limited to providing gloss, appearance and weather resistance. It also needs to meet the high saturation requirements of vehicle body colors and have better performance.

[0003] However, existing clearcoats struggle to meet these requirements. Furthermore, the traditional automotive color coating process is complex, requiring multiple spraying (at least six times) and baking (at least five times). This baking process is energy-intensive and costly, resulting in poor appearance. Therefore, there is an urgent need to develop a new type of colored clearcoat material that can simplify the color coating process, reduce energy consumption and costs, while also improving appearance and weather resistance to meet the high standards of modern automotive manufacturing. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, an embodiment of the present application provides a colored varnish.

[0005] In addition, the embodiments of the present application also provide a method for preparing the aforementioned colored varnish and a method for preparing a colored workpiece using the colored varnish.

[0006] In a first aspect, an embodiment of the present application provides a colored varnish, which includes a component A and a component B; based on the total mass of the component A being 100 parts, the component A includes the following components: 30 to 35 parts of a first resin; 13 to 20 parts of a second resin; 2 to 3 parts of a nano-scale pigment; 1 to 2 parts of a dispersing aid; 2 to 3 parts of a drying aid; and 30 to 47 parts of a solvent; wherein the first resin includes an acrylic resin and the second resin includes a polyester resin; based on the total mass of the component B being 100 parts, the component B includes 60 to 85 parts of an aliphatic isocyanate and 15 to 40 parts of an anhydrous diluent; the mass ratio of the component A to the component B is (2 to 4):1.

[0007] In some possible embodiments, the average particle size of the nanoscale pigment is 5 nm to 100 nm; and / or The nano-scale pigment includes nano-scale carbon black.

[0008] In some possible embodiments, the dispersing aid includes at least one of an ionic dispersant, a non-ionic dispersant, a polymer dispersant, and a coupling agent.

[0009] In some possible embodiments, the resin further includes an amino resin; and / or The acrylic resin includes a hydroxyl-containing acrylic resin, and the hydroxyl value of the hydroxyl-containing acrylic resin is 76-182.

[0010] In some possible embodiments, the aliphatic isocyanate is an unsaturated isocyanate.

[0011] In some possible embodiments, the unsaturated isocyanate includes at least one of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (TMDI), and hydrogenated toluene diisocyanate (HTDI).

[0012] In some possible embodiments, the solvent includes at least one of a lipid solvent, an ether solvent, a polyol solvent, and an aromatic hydrocarbon solvent; and / or The component A further contains at least one of a leveling agent, an ultraviolet light absorber and an antioxidant.

[0013] In a second aspect, an embodiment of the present application further provides a method for preparing the aforementioned colored varnish, the preparation method comprising the following steps: pre-mixing a second resin, a dispersing aid and a solvent to form a resin system, adding a pigment to the resin system and mixing to obtain a mixture, wherein the second resin comprises a polyester resin; grinding the mixture to make the particle size of the pigment nanometer level, and then centrifuging to separate to obtain a supernatant; adding a first resin and a drying aid to the supernatant to obtain component A, wherein the first resin comprises an acrylic resin; mixing an aliphatic isocyanate and an anhydrous diluent to obtain component B; and mixing the component A and the component B to obtain the colored varnish.

[0014] On the third aspect, an embodiment of the present application also provides a method for preparing a colored workpiece, comprising: pre-treating the workpiece, then spraying sealant to obtain a pre-treated workpiece; and spraying the aforementioned colored varnish on the surface of the pre-treated workpiece, and then flash-drying, baking and polishing to obtain a colored workpiece.

[0015] In some possible embodiments, the surface of the colored workpiece includes a first area and a second area. After the step of obtaining the colored workpiece, the preparation method further includes: after shielding the first area of ​​the colored workpiece with a masking material, spraying the main color topcoat on the second area and pre-drying the sprayed main color topcoat to obtain a semi-finished workpiece; and removing the masking material, spraying a transparent varnish on the surface of the semi-finished workpiece and drying it to obtain the colored workpiece with color matching. Compared with the prior art, the colored varnish provided in the embodiment of the present application, by introducing nano-scale pigments, has a finer particle size and a more delicate texture than micron-scale pigments, so it has better leveling properties, can obtain high gloss and improve tinting power, has better clarity and distinctness of image and other appearance effects, and also has the same color-imparting function as the colored paint. Combined with a dispersing aid, it can improve the dispersion effect of the nano-scale pigment, prevent flocculation, and fully display the saturation of the pigment, thereby improving the gloss, saturation, tinting power and hiding power of the colored varnish. The present application also provides a method for coloring workpieces using the colored varnish, which can simplify the conventional double-layer coating spraying process of colored paint and varnish into a single-layer colored varnish spraying process, reducing the number of spraying and baking times, thereby simplifying the spraying process and the complexity of colored workpiece preparation, and reducing the thickness of the paint film, which can effectively improve the appearance and weather resistance, while also reducing paint consumption, energy consumption and the volatilization of volatile organic compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a process flow chart of a method for preparing a colored varnish provided in one embodiment of the present application.

[0017] Figure 2 A process flow chart of a colored workpiece provided in one embodiment of the present application.

[0018] Figure 3 A schematic diagram of dividing the first area and the second area of ​​the colored workpiece surface provided in one embodiment of the present application.

[0019] Figure 4 A schematic diagram of the division of the first area and the second area of ​​the automobile body surface provided in one embodiment of the present application. DETAILED DESCRIPTION

[0020] The embodiments of the present application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0021] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of this application; the implementation methods of this application and the features in the implementation methods can be combined with each other unless there is a conflict; many specific details are set forth in the following description to facilitate a full understanding of this application, and the implementation methods described are only part of the implementation methods of this application, not all of the implementation methods.

[0022] Traditional spraying technology has many defects, such as: (1) complex process, high energy consumption for baking, and large amount of raw materials; (2) multiple spraying and baking are required, resulting in poor appearance; (3) poor durability, washability, scratch resistance and stone impact resistance of the formed paint film; (4) long process flow, large paint consumption and high volatile organic compound (VOC) emissions; (5) obvious steps between the two layers of paint film, affecting the appearance.

[0023] To this end, an embodiment of the present application provides a new type of colored varnish, which includes component A and component B, and the mass ratio of component A to component B is (2~4):1.

[0024] Wherein, based on the total mass of component A being 100 parts, component A includes the following components: 30-35 parts of the first resin; 13-20 parts of the second resin; 2~3 parts of nano-scale pigment; 1~2 parts of dispersing agent; 2~3 parts of drying aid; and 30-47 parts of solvent; The first resin includes acrylic resin, and the second resin includes polyester resin.

[0025] Based on 100 parts by weight of component B, component B includes 60 to 85 parts by weight of aliphatic isocyanate and 15 to 40 parts by weight of an anhydrous diluent.

[0026] First, nano-pigments are introduced into the tinted clearcoat. Compared to micron-sized pigments, nano-pigments have better leveling, gloss, and tinting strength due to their smaller particle size and finer texture. This allows the tinted clearcoat to not only impart color like a base coat, but also effectively improve its saturation, smoothness, gloss, and hiding power. After spraying the tinted clearcoat onto the vehicle body surface, the resulting paint surface exhibits superior visual clarity, gloss, and vividness, with superior appearance. Furthermore, due to the smaller particle size and greater tinting strength of nano-pigments, a small addition of nano-pigments can achieve the same or even greater tinting effect as micron-sized pigments. Specifically, the amount of nano-pigments is 2-3 parts per 100 parts by weight of component A. Furthermore, the high specific surface area and small size of nano-pigments enhance the interfacial bonding between the workpiece and the paint film, fill microscopic defects in the paint film, disperse internal stresses in the paint film, and increase film hardness, thereby effectively improving the paint film's scratch resistance and stone chip impact resistance.

[0027] However, because smaller pigment particles are more difficult to disperse, nano-pigments are more prone to aggregation, affecting the uniformity and stability of the paint film. Therefore, 1-2 parts of a dispersing aid are added to component A to improve the dispersibility of nano-pigments. Dispersing aids can deflocculate nano-pigments through steric stabilization. Dispersing aids also impart the same charge to nano-pigment particles. The repulsive force generated by these charges reduces particle flocculation, allowing the nano-pigment to be evenly dispersed in the tinted clearcoat, fully displaying the pigment's saturation and resulting in higher gloss, color saturation, tinting strength, and hiding power. For example, using black nano-scale pigments, the blackness of ordinary high-gloss black paint is about 307. After using nano-scale black pigments and dispersing additives in this application, the blackness of the obtained colored varnish can be as high as 352 (the blackness measurement method refers to DIN 55979, DIN5033-10, and DIN EN ISO 18314-3 standards, and is measured using color2viewPro in blackness mode 45° / 0°).

[0028] Therefore, the colored varnish can replace the conventional double-coat paint of colored paint and varnish, simplify the color matching process and reduce the thickness of the paint film. While ensuring the weather resistance of the paint film, it can effectively improve the appearance effect and reduce paint consumption, energy consumption and VOC volatilization.

[0029] In some embodiments, the average particle size of the nanoscale pigment can be 5 nm to 100 nm, which is beneficial for further improving the glossiness, color saturation and coating smoothness of the colored varnish. At the same time, the nanoscale pigment within this range can also be evenly dispersed using a dispersing aid. For example, the average particle size of the nanoscale pigment can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any value within a numerical range consisting of any two of the above values. Furthermore, the average particle size of the nanoscale pigment can be 10 nm to 20 nm.

[0030] In some embodiments, the nano-pigment may include nano-carbon black. Nano-carbon black has an extremely high specific surface area and a small particle size, providing strong hiding power and tinting strength. A small amount of nano-carbon black can achieve a deep black effect, reducing pigment usage, lowering costs, and reducing VOC emissions, thus meeting environmental requirements. Furthermore, nano-carbon black has excellent UV absorption properties, effectively reducing UV radiation damage and improving the weather resistance and service life of colored varnishes. Choosing nano-carbon black as a nano-black pigment not only meets appearance and performance requirements but also plays an important role in environmental protection and sustainable development.

[0031] As previously mentioned, selecting a dispersing aid that can reduce nano-pigment particle aggregation and impart uniform charge to all nano-pigment particles can meet the requirements of this application. Specifically, the dispersing aid introduces a uniform charge to the particle surface through ionization, thereby utilizing charge repulsion to prevent particle agglomeration and achieve uniform dispersion. For example, the dispersing aid may include at least one of an ionic dispersant, a nonionic dispersant, a polymeric dispersant, and a coupling agent. These dispersing aids can enhance the dispersion of nano-pigments, prevent flocculation, and fully develop the pigment's saturation, thereby improving the gloss, color saturation, and tinting strength of the colored varnish. Ionic dispersants stabilize the dispersion system through charge interactions (positive and negative ions); nonionic dispersants stabilize the dispersion system through non-charge interactions such as steric hindrance or hydrogen bonding; polymeric dispersants prevent particle aggregation through the steric hindrance of polymer chains, and polymeric dispersants can further be polymeric block copolymers; coupling agents can enhance the interfacial bonding between the particles and the matrix, enhancing the dispersion effect and promoting crosslinking between component A and component B. Furthermore, the dispersing aid includes an ionic dispersing aid and a non-ionic dispersing aid. Still further, the ionic dispersant may be an ionic carbon black dispersant, and the non-ionic dispersant may be a non-ionic carbon black dispersant.

[0032] It is understood that when the dispersing aid contains various types of dispersing aids such as ionic dispersants and polymer block copolymers, the dispersing effect is better due to the inclusion of various types of dispersing groups, and the dispersing aid is a hyperdispersant. The hyperdispersant can also bind to the surface of the pigment particles through the anchoring groups of the polymer block copolymer, forming a stable steric hindrance and enhancing the dispersibility of the pigment. Exemplarily, the hyperdispersant can include BYK-161 hyperdispersant.

[0033] The first resin and the second resin in component A are the main film-forming substances.

[0034] The first resin comprises 30-35 parts per 100 parts by weight of component A, which helps ensure film-forming properties in the colored clearcoat. The first resin comprises an acrylic resin, which is the primary film-forming substance in the clearcoat, providing the film's structural and mechanical properties. In high-performance industrial coatings such as automotive clearcoats, acrylic resin is a key component for coating durability and aesthetics.

[0035] Furthermore, based on 100 parts by weight of component A, the acrylic resin may be present in an amount of 10 to 35 parts, which is beneficial for improving the adhesion, weather resistance and chemical resistance of the colored varnish, and can also impart better hardness and wear resistance to the colored varnish.

[0036] In some embodiments, the acrylic resin may include a hydroxyl-containing acrylic resin having a hydroxyl value of 76 mg KOH / g to 182 mg KOH / g. The hydroxyl value refers to the hydroxyl (-OH) content in the resin molecule, expressed as milligrams of hydroxyl groups per gram of resin (mg KOH / g). Acrylic resins with higher hydroxyl values ​​(76-182) contain more hydroxyl groups, which can enhance crosslinking reactions with aliphatic isocyanates, forming a three-dimensional crosslinked network. This further improves the crosslink density, adhesion, and toughness of the tinted clearcoat, thereby further enhancing the car wash resistance, abrasion resistance, and stone chip impact resistance of the resulting tinted clearcoat film. It is understood that other types of acrylic resins may also be included.

[0037] In some embodiments, the resin may further include an amino resin, which can effectively improve the resin's wetting properties on nano-pigments (especially nano-carbon black), shorten the dispersion time of nano-pigments, improve preparation efficiency, and further improve the vividness of the colored and clear paint film.

[0038] Furthermore, based on 100 parts by weight of component A, the amino resin may be present in an amount of 5 to 20 parts, which is beneficial for improving the wetting performance of nano-pigments.

[0039] The second resin includes a polyester resin, which is primarily used in colored varnishes to improve the flexibility and impact resistance of the paint film. When used in combination with an acrylic resin, the polyester resin can further enhance the gloss of the paint film while also increasing its chemical and heat resistance. Specifically, the polyester resin may include at least one of a TGIC polyester resin, an HAA polyester resin, and a super-weather-resistant polyester resin. Based on 100 parts by weight of component A, the second resin is added in an amount of 13 to 20 parts.

[0040] Component A also contains 2-3 parts of a drying aid. This aid accelerates the curing process of the clearcoat and promotes a gradual polymerization reaction within the film, thereby shortening the drying time. This facilitates wet-on-wet application of the clearcoat with the sealant during overprinting, optimizes the clearcoat spraying process, and reduces spraying and baking times. Specifically, the drying aid can include a benzenesulfonic acid-based drying aid, which effectively catalyzes the gradual polymerization reaction.

[0041] The solvent in component A acts as a dissolving agent, helping to dissolve the acrylic resin, polyester resin, nanoscale black pigment, or other solid components in the colored varnish, allowing the colored varnish to be sprayed in a liquid form. The solvent also regulates viscosity, improving workability and leveling properties, making the colored varnish easier to spray evenly during application. Specifically, the solvent can include at least one of a lipid solvent, an ether solvent, a polyol solvent, and an aromatic hydrocarbon solvent.

[0042] Component A can also include a leveling agent. This agent improves the leveling properties of the tinted clearcoat, ensuring even leveling after spraying and reducing surface defects such as orange peel and brush marks. Specifically, the leveling agent can include at least one of an acrylic, silicone, or fluorine-based agent. These agents can improve the leveling properties of the tinted clearcoat by reducing surface tension. Based on 100 parts by weight of Component A, the leveling agent can be added in an amount of 3 to 4 parts to improve the leveling properties of the tinted clearcoat.

[0043] Component A may also include a UV absorber, a functional additive primarily used to absorb UV rays, reducing UV damage to the colored clearcoat, thereby improving the weather resistance and durability of the paint film. By absorbing UV light and converting it into harmless heat, the UV absorber reduces UV-induced yellowing, chalking, cracking, and other issues. The amount of UV absorber added may be 2-3 parts per 100 parts by weight of Component A.

[0044] Component A may also include an antioxidant, which inhibits free radical generation and chain oxidation reactions in the colored clearcoat, further reducing oxidative degradation, discoloration, and deterioration caused by heat, light, or chemicals. Antioxidants synergize with UV absorbers to more comprehensively protect the paint film, minimizing performance degradation caused by UV rays, high temperatures, or oxidation reactions. Based on 100 parts by weight of Component A, the antioxidant can be added in an amount of 2 to 5 parts.

[0045] Based on 100 parts by weight of Component B, Component B comprises 60-85 parts of an aliphatic isocyanate and 15-40 parts of an anhydrous diluent. The aliphatic isocyanate acts as a curing agent, cross-linking with the hydroxyl groups in Component A (the acrylic resin and polyester resin in Component A) to form a paint film with excellent chemical resistance, abrasion resistance, and mechanical strength. The anhydrous diluent adjusts the viscosity of the pigmented clearcoat, improves workability, and enhances the stability of the isocyanate.

[0046] In some embodiments, the aliphatic isocyanate may be an unsaturated isocyanate. The presence of unsaturated bonds further enhances the crosslinking density and toughness of the colored clearcoat, thereby improving the resulting paint film's resistance to car washes, scratches, and stone chip impacts. Specifically, the isocyanate includes at least one of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (TMDI), and hydrogenated toluene diisocyanate (HTDI).

[0047] Compared with the prior art, the colored varnish provided in the embodiments of the present application has the following beneficial effects: 1. The combined use of nano-pigments and dispersing aids allows the nano-pigments, which have a large specific surface area and small particle size, to be fully dispersed in the colored clearcoat. This not only imparts color to the clearcoat but also effectively improves its leveling, gloss, color saturation, tinting strength, and weatherability. The resulting paint film exhibits superior visual clarity, gloss, and vividness, while also exhibiting excellent washability, abrasion resistance, stone chip impact resistance, and weatherability. This colored clearcoat serves the dual purpose of a topcoat and a clearcoat, and can be used for direct single-spray coating or for multi-color spraying of workpieces.

[0048] 2. By adding drying aids, the curing process of the colored varnish can be accelerated, and the gradual polymerization reaction in the paint film can be promoted, thereby shortening the drying time. It is beneficial for the colored varnish to be applied in the spray process with the sealant for wet-on-wet construction, thereby optimizing the spraying process.

[0049] 3. By using acrylic resin with a higher hydroxyl value or unsaturated isocyanate alone, or using acrylic resin with a higher hydroxyl value and unsaturated isocyanate at the same time, the cross-linking reaction between acrylic resin and isocyanate can be promoted to form a three-dimensional cross-linking network, thereby improving the cross-linking density and toughness of the colored varnish, thereby improving the wash resistance, scratch resistance and stone chip impact resistance of the formed paint film.

[0050] 4. Reasonable proportions of the various components of the colored varnish can further improve the appearance and weather resistance of the colored varnish.

[0051] See also Figure 1 As shown, the embodiment of the present application provides a method for preparing the aforementioned colored varnish, which specifically includes the following steps: Step S11 : pre-mixing a second resin, a dispersing aid, and a solvent to form a resin system, adding a pigment to the resin system and mixing to obtain a mixture, wherein the second resin includes a polyester resin.

[0052] Specifically, a certain amount of polyester resin, dispersing aid, and solvent are added to a pre-dispersion kettle, dispersed at a speed of 2000 rpm to 2500 rpm for 5 to 10 minutes, and mixed evenly to form a resin system; then, pigment is slowly added to the resin system until completion, and then dispersed at high speed for 60 minutes to completely and evenly disperse the pigment in the resin system to obtain a mixture.

[0053] In some embodiments, the pigment may include carbon black. As a raw material of the pigment, the carbon black may be a product of nano-scale carbon black material particles, which need to be dispersed to the nanometer level.

[0054] Step S12: grinding the mixture to reduce the particle size of the pigment to nanometer level, and then centrifuging to separate and obtain a supernatant.

[0055] Specifically, the mixture can be ground using a sand mill, and micron-sized zirconium beads are required as the grinding medium. After grinding for about 20 hours, the mixture is measured using a nanoparticle size potentiometer (such as BeNano 90) with an accuracy range of 1nm~1000nm. Since the particle size of the grinding medium is small, conventional filtration cannot be used for separation, so centrifugal separation technology is used for separation.

[0056] In some embodiments, the average particle size of the ground pigment particles is 5 nm to 100 nm, indicating that the average particle size of the pigment added in step S1 has been ground to 5 nm to 100 nm, which is beneficial for improving the leveling, distinctness of image, and saturation of the colored varnish. The average particle size of the ground mixture can be measured using the nanoparticle size potentiometer described above.

[0057] Step S13: adding a first resin and a drying aid to the supernatant to obtain component A, wherein the first resin includes acrylic resin.

[0058] Specifically, after centrifugal separation is completed, the first resin and the drying aid are added according to the composition ratio of the colored varnish, and mixed to obtain component A. In addition, the viscosity of component A can be adjusted by adding solvent again.

[0059] In some embodiments, a functional additive may be added to the supernatant to further improve the spraying effect or weather resistance of the colored varnish. The functional additive may include at least one of a leveling agent, an ultraviolet light absorber, and an antioxidant.

[0060] Step S14: mixing the aliphatic isocyanate and the anhydrous diluent to obtain component B.

[0061] Specifically, the aliphatic isocyanate and the anhydrous diluent are mixed according to a ratio to obtain component B. The anhydrous diluent can adjust the viscosity of component B and stabilize the aliphatic isocyanate.

[0062] Step S15: Mix component A and component B to obtain a colored varnish.

[0063] Specifically, the component A obtained in step S13 and the component B obtained in step S14 are mixed evenly to obtain the aforementioned colored varnish in a construction state, wherein the mass ratio of component A to component B is (2-4):1.

[0064] Compared to the prior art, the preparation method of the colored varnish provided in the embodiments of the present application adds the steps of premixing, grinding, and particle size testing. By grinding, large-particle pigments are ground into nanoscale pigments, which helps control the pigment particle size and improve the dispersion of the pigment. In addition, the introduction of nanoscale pigments and dispersing aids into the colored varnish is beneficial for improving the leveling, gloss, color saturation, tinting strength, and weather resistance of the colored varnish. Furthermore, the preparation method is simple and efficient, which is conducive to the large-scale production of colored varnishes and has excellent commercial prospects.

[0065] See also Figure 2 As shown, the embodiment of the present application also provides a method for preparing a colored workpiece, which specifically includes the following steps: Step S21 , pre-treating the workpiece, and then spraying sealant to obtain a pre-treated workpiece.

[0066] Pretreatment may include electrophoresis and cleaning to polish and clean the workpiece surface. Specifically, the colored varnish of the embodiment of the present application can be used for surface decoration of automobiles, and the workpiece can be exemplarily an automobile body.

[0067] Compared to traditional two-tone car color coating processes, this application incorporates the pre-treatment of electrophoretic polishing and cleaning. The car body is electrophoretically polished and cleaned before the sealant is applied. After the sealant is applied, the car body is directly sprayed in the paint booth for the colored varnish, eliminating the need for polishing the sealed body. If the sealant is sprayed and then electrophoretic polishing and cleaning are performed, dust and impurities generated will adhere to the sealant, resulting in particles. Furthermore, the sealant can be easily scratched by operators during operation.

[0068] Step S22: spraying colored varnish on the surface of the pretreated workpiece, and then flash-drying, baking and polishing to obtain a colored workpiece.

[0069] Since the colored varnish of the present application has the combined effects of colored paint and varnish, the resulting paint film performance can meet the paint film performance requirements.

[0070] In conventional processes, after the sealant is sprayed, it is necessary to bake it once to ensure that the sealant is fully cured and achieves the required performance before painting can be carried out. The baking process is time-consuming and energy-consuming, which not only increases production costs but also prolongs the production cycle. The colored varnish provided in this application has the ability to wet-to-wet with the sealant, so the spray sealant is placed afterward, and the sealant does not need to be baked or other operations. The colored varnish is directly sprayed when the sealant is not fully cured, so that the two layers of coating are cured at the same time in a wet state, and then flash-dried, baked and polished together. This method can not only shorten production time, but also reduce energy consumption, while also improving the adhesion and appearance quality of the paint film. Specifically, baking the sealant and colored varnish together can save a set of glue baking ovens.

[0071] Moreover, in this step, since the colored varnish prepared above is used, the colored varnish has the same ability to give the car body color as the colored paint, and also has good leveling, glossiness, color saturation, tinting strength and weather resistance. Therefore, the conventional color paint and varnish double-layer spraying color mode can be simplified to the colored varnish single-coat spraying. Under the same hiding power requirement, the conventional color paint and varnish double-layer spraying requires a color paint coating film thickness of 15μm±2μm, and a varnish film thickness of 50μm±5μm to ensure good hiding power and aging resistance. The colored varnish of the present application only requires 45μm~55μm to achieve the same paint film performance index requirements such as hiding power and weather resistance. The single coating and the reduction of film thickness can not only effectively reduce the paint consumption and VOC volatilization during the spraying operation, but also simplify the process, save energy and equipment. Specifically, a set of spray booths and spray paint equipment, as well as a set of color paint pre-baking furnaces can be reduced.

[0072] In some embodiments, the flash-drying temperature after spraying the colored varnish can be 21°C~30°C, and the flash-drying time can be 5min~10min, which is beneficial to improving the painting efficiency and reducing the phenomenon of colored varnish sagging or dripping, thereby improving the quality and adhesion of the coating film.

[0073] In some embodiments, the baking temperature can be 120°C to 150°C, and the baking time can be 20 minutes to 60 minutes. For example, the baking conditions can be baking at 140°C for 20 minutes or baking at 150°C for 10 minutes. In the traditional color matching process, after the color paint flashes off, it needs to be pre-baked at 80°C for 8 minutes and then baked at 145°C for 25 minutes with the varnish to achieve complete curing of the coating film and ensure the relevant coating film properties. The colored varnish and color matching process provided in this application can improve the spraying cycle, shorten the baking time, reduce the energy consumption of flash drying, and reduce the energy consumption of drying.

[0074] In some embodiments, the sealant's wet-on-wet spraying capability with colored varnishes can be further enhanced by optimizing the sealant's wetting agents (e.g., polyether-modified wetting agents), leveling agents (e.g., polysiloxanes), plastic materials (e.g., dibasic phthalates), and pigment-to-binder ratio. Drying aids can also be added to the sealant to accelerate its drying process.

[0075] It's important to note that since the sealant isn't baked separately, you can test the sealant's baking temperature while the clearcoat is baking to ensure the sealant dries to meet product performance requirements. Also, it's best to apply the clearcoat within 12 hours of applying the sealant to prevent moisture absorption and potential quality issues.

[0076] In some embodiments, before spraying the aforementioned colored varnish onto the surface of the pretreated workpiece, a conventional black topcoat may be sprayed onto the pretreated workpiece, and then the colored varnish may be sprayed onto at least a portion of the workpiece to produce a colored workpiece. This can reduce the amount of black topcoat and colored varnish sprayed individually, thereby enhancing color saturation and achieving a deeper black effect.

[0077] In some embodiments, as Figure 3 As shown, the surface of the colored workpiece includes a first area and a second area. After the step of obtaining the colored workpiece, the preparation method may further include steps S23 and S24 to perform color matching on the colored workpiece.

[0078] Step S23 , after masking the first area of ​​the colored workpiece with a masking material, spraying a main color topcoat on the second area and pre-drying the sprayed main color topcoat to obtain a semi-finished workpiece.

[0079] Specifically, a masking material is used to shield the first area of ​​the colored workpiece (i.e., the overprinting area) to protect the overprinting area that does not require the primary color. The primary color topcoat is then sprayed on the second area (i.e., the primary color area) and pre-dried to achieve a two-color coating. This overprinting method has been optimized, reversing the order of spraying the clearcoat and topcoat used in traditional processes: instead of spraying the primary color topcoat first and then the clearcoat, the overprinting area is first sprayed with the colored clearcoat. Therefore, when spraying the primary color in step S23, only the overprinting area needs to be shielded, reducing the area required for masking material and thus reducing the number of operators and material consumption during the masking process.

[0080] It's important to note that when spraying the primary color on a car, the door must be opened, and other operations must be performed. Therefore, when using masking material, care must be taken to ensure that the material is applied in a manner that does not affect subsequent painting operations. Furthermore, vehicle body quality requirements must be met, such as ensuring clear color separation lines in the visible area after opening the door, and free of paint scratches.

[0081] In some embodiments, a low-temperature shielding film may be used for shielding, which helps to reduce costs.

[0082] Step S24 , removing the masking material, spraying transparent varnish on the surface of the semi-finished workpiece and drying it to obtain a colored workpiece.

[0083] Specifically, the masking material is removed, and conventional transparent varnish is sprayed on the surface of the semi-finished workpiece and dried. This step can effectively solve the step problem between the paint films caused by the two sprayings (spraying of colored varnish and spraying of main color topcoat) and improve the texture of the paint film.

[0084] See also Figure 4 The workpiece can be, for example, a car body, wherein the pink area is the first area and the remaining area is the second area. The above method can achieve efficient color matching of the car body.

[0085] Compared with the prior art, the method for preparing a colored workpiece provided in the embodiment of the present application has the following beneficial effects: 1. The paint film formed by using the aforementioned colored varnish exhibits excellent appearance effects such as better visual clarity, glossiness and brightness, and also has good washability, abrasion resistance, stone chip impact resistance, weather resistance, etc.

[0086] 2. Using the aforementioned colored clearcoat simplifies the conventional two-layer spraying pattern of color paint and clearcoat to a single-layer spraying pattern of colored clearcoat, reducing paint film thickness. This single coating and reduced film thickness not only effectively reduce paint consumption and VOC emissions during the spraying process, but also simplifies the process, saving energy and equipment.

[0087] 3. Colored varnish and sealant can be applied wet-on-wet, reducing the number of spraying and baking times, shortening production time, reducing energy consumption, and improving the adhesion and appearance quality of the paint film.

[0088] 4. This method improves the color sequence for overlay spraying, reversing the traditional order of clearcoat and topcoat application: Instead of spraying the primary color topcoat first and then the clearcoat, the overlay area is first sprayed with the colored clearcoat, followed by the larger primary color area with the primary color topcoat. This allows only the overlay area to be masked when the primary color topcoat is applied, reducing the area of ​​masking material required and the number of operators and auxiliary material consumption required during the masking process.

[0089] The above-mentioned colored varnish, its preparation method and the preparation method of the colored workpiece are further described below through specific examples.

[0090] Example 1 A colored varnish comprises component A and component B, with the mass ratio of component A to component B being 3:1. Component A, based on 100 parts by mass, comprises the following: 32 parts of an acrylic resin having a hydroxyl value of 146 mg KOH / g (a first resin), 15.8 parts of a polyester resin (a second resin), 2.8 parts of nano-carbon black having an average particle size of 12 nm, 1.5 parts of an ionic dispersant, 0.5 parts of a coupling agent, 1 part of an organosilicon leveling agent, 2.5 parts of an acrylic leveling agent, 2 parts of an ultraviolet light absorber, 2 parts of a drying aid, and 39.9 parts of an organic solvent. Component B, based on 100 parts by mass, comprises the following: 70 parts of an unsaturated aliphatic isocyanate and 30 parts of an anhydrous diluent.

[0091] The specific preparation method comprises the following steps, wherein the raw materials are added in the same proportion as the components of the above-mentioned colored varnish: Step S11: pre-mixing a polyester resin, a dispersing aid, and a solvent to form a resin system, and adding carbon black to the resin system to obtain a mixture.

[0092] Step S12: Grind the mixture to make the particle size of the pigment nanometer level, specifically the average particle size of the particles is 12 nm, and then centrifuge to separate and obtain a supernatant.

[0093] Step S13: adding a hydroxyl-containing acrylic resin, a drying aid, a leveling aid and an ultraviolet light absorber to the supernatant to obtain component A.

[0094] Step S14: mixing the aliphatic isocyanate and the anhydrous diluent to obtain component B.

[0095] Step S15: Mix component A and component B to obtain a colored varnish in a construction state.

[0096] The prepared colored varnish is applied to a method for preparing a colored workpiece, the method specifically comprising the following steps: In step S21 , the workpiece is pre-treated by electrophoresis and cleaning, and then sprayed with sealant to obtain a pre-treated workpiece.

[0097] In step S22, the surface of the pre-treated workpiece is sprayed with the aforementioned colored varnish using an electrostatic rotary cup sprayer, such as an IRB1000 atomizer from ABB, and then flash-dried, baked, and polished to obtain a colored workpiece.

[0098] Step S23, the surface of the colored workpiece includes a first area and a second area. After masking the first area of ​​the colored workpiece with a masking material, the second area is sprayed with a main color topcoat and the sprayed main color topcoat is pre-dried to obtain a semi-finished workpiece.

[0099] Step S24 , removing the masking material, spraying transparent varnish on the surface of the semi-finished workpiece and drying it to obtain a colored workpiece.

[0100] Example 2 The difference between Example 2 and Example 1 is that Example 2 uses carbon black with an average particle size of 70 nm as a nanoscale black pigment and uses BYK-161 hyperdispersant for dispersion. The preparation method of the remaining colored varnish is the same as that of Example 1 and is not described in detail here.

[0101] Example 3 Example 3 differs from Example 1 in that, in Example 3, the first resin in Component A comprises 27 parts acrylic resin and 5 parts amino resin. The remaining methods for preparing the colored varnish and the colored workpiece are the same as in Example 1 and are not further described here.

[0102] Example 4 The preparation method of the colored varnish and the colored varnish in Example 4 is the same as that in Example 1 and will not be described in detail here.

[0103] The difference between Example 4 and Example 1 is that the method for preparing the colored workpiece in Example 4 only includes the following steps: In step S21 , the workpiece is pre-treated by electrophoresis and cleaning, and then sprayed with sealant to obtain a pre-treated workpiece.

[0104] In step S22, the colored varnish is sprayed onto the surface of the pretreated workpiece by using an electrostatic rotary cup. The electrostatic rotary cup can be an IRB1000 atomizer of ABB Company, and then flash-dried, baked and polished to obtain a colored workpiece.

[0105] During the preparation process, the colored varnish of this embodiment is directly applied on the electrophoretic coating of the workpiece after spraying the sealant. The colored varnish has the combined effects of colored paint and varnish, and the resulting paint film performance can meet the paint film performance requirements.

[0106] Example 5 The preparation method of the colored varnish and the colored varnish in Example 5 is the same as that in Example 1 and will not be described in detail here.

[0107] The difference between Example 5 and Example 1 is that the preparation method of the colored workpiece in Example 5 is different from that in Example 1.

[0108] The method for applying the prepared colored varnish to a colored workpiece specifically comprises the following steps: In step S21 , the workpiece is pre-treated by electrophoresis and cleaning, and then sprayed with sealant to obtain a pre-treated workpiece.

[0109] In step S22, a conventional black topcoat is sprayed onto the surface of the pretreated workpiece and pre-dried. The colored clearcoat is then sprayed onto the surface of the conventional black topcoat using an electrostatic rotary cup, such as an ABB IRB1000 atomizer. Flash drying, baking, and polishing are then performed to obtain a colored workpiece that has not been sprayed with the clearcoat.

[0110] Step S23: spraying transparent varnish on the surface of the colored workpiece and drying it.

[0111] Comparative Example 1 A conventional varnish comprises component A and component B, with the mass ratio of component A to component B being 3.3:1. Component A, based on 100 parts by mass, comprises 53 parts of acrylic resin, 3 parts of ultraviolet light absorber, and 34 parts of solvent. Component B, based on 100 parts by mass, comprises 65 parts of isocyanate and 35 parts of anhydrous diluent.

[0112] The specific preparation method comprises the following steps, wherein the raw materials are added in the same proportion as the components of the conventional varnish: Step S11: premixing a polyester resin and a solvent to form a resin system, and adding an acrylic resin, a leveling agent, and an ultraviolet light absorber to the resin system to obtain component A.

[0113] Step S14: mixing the isocyanate and the anhydrous diluent to obtain component B.

[0114] Step S15: Mix component A and component B to obtain a conventional varnish.

[0115] The prepared conventional varnish is applied to a conventional color matching process, which specifically includes the following steps: Step S21 , spraying sealant on the vehicle body to seal and dry it, and then performing electrophoresis and cleaning pretreatment on the vehicle body.

[0116] Step S22: spraying and pre-drying the cleaned vehicle body with a primary color topcoat.

[0117] Step S23: spraying conventional varnish, followed by flash drying, baking and polishing.

[0118] Step S24: After masking the second area of ​​the vehicle body with a masking material, the first area is sprayed with a color-matching paint and pre-dried.

[0119] Step S25: spray conventional varnish again, perform flash drying, baking and polishing, and then remove the masking material.

[0120] The following performance tests were performed on the paint films formed by the preparation methods of the varnishes and colored workpieces obtained in Examples 1-5 and Comparative Example 1.

[0121] 1. Appearance performance test: (1) Surface orange peel long wave test (Lw, wavelength 1.2~12mm): BYK-Gardner orange peel meter can be used to measure the smoothness of the paint film surface by reflected light to obtain the Lw value.

[0122] (2) Short wave test (Sw, wavelength 0.2~1.2mm): BYK-Gardner orange peel meter can be used to measure the smoothness of the paint film surface by reflected light to obtain the Sw value.

[0123] (3) Distinctness of Image (DOI) test: BYK-Gardner's orange peel meter is used to evaluate the DOI of the paint film. The instrument calculates the clarity of the image by measuring the light reflected from the paint film surface.

[0124] (4) Gloss test: Use a gloss meter to measure the intensity of light reflected from a surface. Based on a measurement angle of 20°, the specific gloss value is obtained, usually in GU (Gloss Units).

[0125] 2. Paint film performance test: (1) Adhesion (grid): Use a handheld grid knife to make the multi-blade cut perpendicular to the sample plane; cut to the substrate with even pressure and a steady, non-vibrating technique; adjust the 90° position and repeat the above operation on the multi-cut incision to form a grid pattern; use a soft-bristled brush to gently brush the two diagonals of the grid pattern backward 5 times and forward 5 times; place the tape parallel to one set of cutting lines, and then use your fingers to flatten the tape on the grid area. The length of the tape must be at least 20mm longer than the grid; within 5 minutes of applying the tape, hold the dangling end of the tape and tear off the tape steadily within (0.5-1.0) seconds at an angle as close to 60° as possible.

[0126] (2) Adhesion (high-pressure water impact): Condition the sample at a temperature of (23±2)°C and a relative humidity of (50±5)% for at least 24 hours. Use a marking tool to create two 0.5mm lines on the sample to create initial paint damage. The markings should be made to the substrate, at right angles to ensure they intersect. The markings should extend beyond the test area. Each marking should be approximately 60mm long. Maintain a vertical distance of 100±3mm between the nozzle and the test surface. Adjust the water pressure to 12±0.3MPa, control the flow rate at 15.0±0.3 L / min, and maintain a water temperature of 50±5°C. Apply the water spray at a rate of 1 spray per second for 30 seconds. The water spray should be directed from the center of rotation of the nozzle tube across the test surface at a deviation angle of 5.6° (±20mm).

[0127] (3) Adhesion (scratch): Use a folding knife to scratch the painted surface. The contact angle between the blade and the surface coating should be about 45 degrees. Place your thumb nail vertically on the scratch and try to remove the paint here with your fingernail.

[0128] (4) Wipe resistance: At 6.6cm 2 A force of 9N is applied to the surface of the paint film. Driven by a robotic arm, the paint film is reciprocated at a linear motion rate of 60 times / min within a distance of 12 cm. 2400-grit silicon carbide sandpaper is rubbed back and forth on the paint film 15 times to test the gloss retention rate of the paint film.

[0129] (5) Resistance to gravel impact: Select hard, wear-resistant natural stone with a density of (2.7±0.05) g / cm³ and containing no limestone or crushed rock. Place it in the gravel impact tester. Adjust the air pressure in the gravel impact tester to (0.14±0.007) MPa (20 psi±1 psi). Place the test panel on the plate frame and secure it with the trailing edge bracket, with the coated surface perpendicular to the gravel throwing mechanism. Within 0.5-1 minute, all the gravel enters the impact airflow, completing the gravel impact test.

[0130] (6) Resistance to bird droppings: Select appropriate serum albumin and artificial guano solution; drop 0.2 mL of artificial guano solution onto the sample, then seal the test panel in the area where the guano solution was added with a lid; place the sample in a constant temperature and humidity chamber at (50±1)°C and a relative humidity of (30±5)% for 1 hour; remove the sample, clean the surface with tap water to remove the artificial guano solution, and wipe it clean with a soft dry cloth. Observe the surface condition of the sample and then rate it.

[0131] (7) Weather resistance: Natural Exposure: Place the test panels in a dedicated, industry-recognized airing facility, such as the Q-Lab Weathering Services test facility in Miami, Florida, USA, or the Qionghai Atmospheric Test Station in Hainan, China. The test panels should be mounted on an exposure rack, oriented toward the equator. The rack should be positioned at a 5° angle to the horizontal, and the test panels should be fully exposed. Flushing the site every three months is recommended. The exposure time is typically set for a specified number of months, but can also be set to the time required to reach a pre-specified amount of solar radiation. Changes in color, gloss, adhesion, and other properties of the test panels before and after exposure are measured.

[0132] Artificial accelerated aging: In a xenon lamp aging test chamber, perform a cyclic test on the sample for 3000 hours (3000 hours requirement) according to the following steps: Step 1: Light off, black mark temperature 38°C, test chamber temperature 38°C, relative humidity 95±5%; Step 2: Turn on the light, light intensity 0.55, black mark temperature 70℃, test chamber temperature 47℃, relative humidity 50±5%; Step 3: Turn on the light, light intensity 0.55, black mark temperature 70℃, test chamber temperature 47℃; Step 4: Turn on the light, light intensity 0.55, black mark temperature 70℃, test chamber temperature 47℃, relative humidity 50±5%.

[0133] The relevant test results of Examples 1-5 and Comparative Example 1 are shown in Table 1 and Table 2.

[0134] The above results show: The results in Table 1 show that the appearance of the paint films formed by the colored varnishes and the methods for preparing colored workpieces provided in Examples 1-5 of the present application is superior to the traditional color matching process in Comparative Example 1. Among them, Examples 1-5 performed well in the Lw and Sw tests, with Lw and Sw values ​​lower than those of Comparative Example 1, indicating that Examples 1-5 are visually smoother, brighter, and clearer, improving the aesthetics of the paint films. The DOI values ​​of Examples 1-5 are all higher than those of Comparative Example 1, indicating that the paint film surfaces of Examples 1-5 are smoother and flatter, capable of reflecting clearer images, and improving the accuracy and aesthetics of the visual effects. The gloss test results of Examples 1-5 show that their glossiness is higher than that of Comparative Example 1, indicating that the paint films of Examples 1-5 have higher surface gloss. The improvement in the appearance performance of the paint film shows that the colored varnish provided in the embodiments of the present application, due to the combined use of nano-pigments and dispersing aids, makes the colored varnish not only have the same color-imparting function as the colored paint, but also can effectively improve the leveling, glossiness, color saturation, tinting strength and weather resistance of the colored varnish. After spraying the colored varnish onto the surface of the vehicle body, the paint film formed presents excellent appearance effects such as better visual clarity, glossiness and brightness.

[0135] The results in Table 2 show that the paint films formed by the colored varnishes and the methods for preparing colored workpieces provided in Examples 1-5 of this application exhibit superior overall performance compared to the conventional coloring process (Comparative Example 1), with significant improvements in abrasion resistance and stone chip impact resistance. In weather resistance testing, the paint films of Examples 1-5 exhibited improved color retention and minimal surface damage after prolonged exposure to harsh environments (such as strong UV rays, humidity, and temperature fluctuations), demonstrating improved aging resistance, UV resistance, and corrosion resistance. These results demonstrate that the colored varnishes of Examples 1-5 possess excellent adhesion (resistance to scratches, high-pressure water impact, and abrasions), abrasion resistance, stone chip impact resistance, bird droppings resistance, and weathering resistance, meeting the high standards required of varnishes in modern automotive and industrial manufacturing.

[0136] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A colored varnish, characterized in that The colored varnish comprises component A and component B; based on 100 parts by weight of component A, component A comprises the following components: 30-35 parts of the first resin; 13-20 parts of the second resin; 2~3 parts of nano-scale pigment; 1~2 parts of dispersing agent; 2~3 parts of drying aid; as well as 30-47 parts of solvent; Wherein, the first resin comprises acrylic resin, and the second resin comprises polyester resin; Based on 100 parts by weight of the component B, the component B comprises 60 to 85 parts by weight of an aliphatic isocyanate and 15 to 40 parts by weight of an anhydrous diluent; The mass ratio of the component A to the component B is (2-4):

1.

2. The colored varnish according to claim 1, characterized in that The average particle size of the nanoscale pigment is 5nm to 100nm; and / or The nano-scale pigment includes nano-scale carbon black.

3. The colored varnish according to claim 1, characterized in that The dispersing aid includes at least one of an ionic dispersant, a non-ionic dispersant, a polymer dispersant and a coupling agent.

4. The colored varnish according to claim 1, characterized in that The first resin further comprises an amino resin; and / or The acrylic resin includes a hydroxyl-containing acrylic resin, and the hydroxyl value of the hydroxyl-containing acrylic resin is 76-182.

5. The colored varnish according to claim 1, characterized in that The aliphatic isocyanate is an unsaturated isocyanate.

6. The colored varnish according to claim 5, characterized in that The unsaturated isocyanate includes at least one of hexamethylene diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate and hydrogenated toluene diisocyanate.

7. The colored varnish according to claim 1, characterized in that The solvent includes at least one of a lipid solvent, an ether solvent, a polyol solvent and an aromatic hydrocarbon solvent; and / or The component A further contains at least one of a leveling agent, an ultraviolet light absorber and an antioxidant.

8. A method for preparing a colored varnish according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: Premixing a second resin, a dispersing aid, and a solvent to form a resin system, and adding a pigment to the resin system to obtain a mixture, wherein the second resin comprises a polyester resin; Grinding the mixture to reduce the particle size of the pigment to nanometer level, and then centrifuging to obtain a supernatant; adding a first resin and a drying aid to the supernatant to obtain component A, wherein the first resin comprises an acrylic resin; mixing an aliphatic isocyanate and an anhydrous diluent to obtain a B component; and The A component and the B component are mixed to obtain the colored varnish.

9. A method for preparing a colored workpiece, characterized in that: include: The workpiece is pre-treated, and then sprayed with sealant to obtain a pre-treated workpiece; as well as A colored varnish is sprayed on the surface of the pretreated workpiece, and then flash-dried, baked and polished to obtain a colored workpiece, wherein the colored varnish is the colored varnish according to any one of claims 1 to 7 or the colored varnish prepared by the preparation method of the colored varnish according to claim 8.

10. The method for preparing a non-ferrous workpiece according to claim 9, wherein: The surface of the colored workpiece includes a first area and a second area. After the step of obtaining the colored workpiece, the preparation method further includes: After masking the first area of ​​the colored workpiece with a masking material, spraying a main color topcoat on the second area and pre-drying the sprayed main color topcoat to obtain a semi-finished workpiece; and The masking material is removed, and a transparent varnish is sprayed on the surface of the semi-finished workpiece and dried to obtain the colored workpiece.

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