Automobile interior metal part spraying process based on high-adhesion water-based paint

Abstract

The invention discloses an automotive interior metal part spraying process based on a high-adhesion water-based paint, which comprises the following steps: firstly, carrying out alkali washing and acid washing treatment on a metal part, so that the metal surface is clean and micro roughness is formed; then carrying out chemical conversion treatment by adopting a water-based conversion solution containing amino silane and epoxy silane to form a compact and uniform conversion film on the metal surface; then water-based prime coat is sprayed on the surface of the conversion film, the thickness of a dry film is controlled to be 3-8 microns, and good substrate binding force is provided after heating; the preparation method comprises the following steps: firstly, spraying a water-based finishing coat taking hydroxy acrylic resin as a main body, adding a blocked isocyanate cross-linking agent, uniformly coating through an electrostatic spraying process, and finally curing under a sectional heating condition to obtain a coating with excellent durability; according to the present invention, the adhesion between the water-based paint and the metal base material is effectively improved, the durability of the paint film in the damp and hot salt mist environment is improved, the use of the organic solvent is reduced, and the advantages of environmental protection, low VOC emission and suitableness for industrial large-scale production are provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of surface coating technology for metal parts in automotive interiors, and specifically relates to a spraying process for metal parts in automotive interiors based on high-adhesion water-based paint. BACKGROUND

[0002] With the rapid development of the automotive industry, the demand for decoration and protection of metal parts in automotive interiors is increasing. Traditional solvent-based paint has mature application experience in metal part spraying, but it contains a high proportion of organic solvents, which will produce a large amount of volatile organic compound emissions during spraying and curing, affecting the construction environment and bringing environmental pressure. In recent years, water-based paint has gradually attracted attention due to its low VOC emissions, safety and environmental protection. However, in the application of metal parts in automotive interiors, there are still problems of insufficient adhesion and poor durability, especially in hot and humid and salt spray environments, the coating is prone to blistering and peeling, which is difficult to meet the use requirements of high-end interior parts.

[0003] The prior art usually improves adhesion by adding special additives or using physical polishing, but the effect is limited, and the process is complex and costly. On the other hand, some studies propose using phosphating or chromizing as a pretreatment method, but these methods have difficulties in wastewater treatment and environmental pollution problems, and have been gradually eliminated. Therefore, it is urgent to develop a spraying process that can maintain excellent adhesion in a water-based system while meeting the durability requirements to adapt to the development trend of green environmental protection and lightweight of automotive interior metal parts. SUMMARY

[0004] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0005] In view of the problems in the prior art, the present application is proposed.

[0006] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art and provide a spraying process for metal parts in automotive interiors based on high-adhesion water-based paint.

[0007] To solve the above technical problems, the present application provides the following technical scheme: a spraying process for metal parts in automotive interiors based on high-adhesion water-based paint, comprising the following steps: (1) Surface pretreatment of the metal substrate, including alkaline cleaning, acid cleaning and rinsing, to clean the substrate surface and form micro-roughness; (2) immerging the pretreated metal substrate into a conversion solution containing silane, controlling the silane concentration to be 0.5-1.5 mass percent, the pH value to be 3.5-5.0, and the treatment time to be 2-5 minutes, and then drying to form a conversion film with a thickness of 30-80 nanometers on the surface; (3) spraying a water-based primer on the surface of the conversion film, and the dry film thickness of the primer is 3-8 micrometers, and then heating and drying; (4) spraying a water-based topcoat on the surface of the primer layer, and the wet film thickness of the topcoat is 20-35 micrometers, and then curing by heating in stages, first heating at 80-95 DEG C for 3-6 minutes, and then heating at 110-120 DEG C for 10-15 minutes, and finally forming a topcoat layer with a dry film thickness of 15-25 micrometers.

[0008] As a preferred scheme of the automobile interior metal part spraying process based on the high adhesion water-based paint, in the step (1), the alkali washing adopts a sodium hydroxide solution with a concentration of 5-25 g / L, the temperature is 50-65 DEG C, and the time is 2-6 minutes; the acid washing adopts an acidic solution with a concentration of 5-15 g / L, and the treatment time is 1-3 minutes.

[0009] As a preferred scheme of the automobile interior metal part spraying process based on the high adhesion water-based paint, in the step (2), the silane is selected from amino silane, epoxy silane or a mixture thereof, and the substrate surface after silane treatment is dried by hot air or heated drying to form a uniform conversion film.

[0010] As a preferred scheme of the automobile interior metal part spraying process based on the high adhesion water-based paint, in the step (3), the water-based primer is selected from a water-based epoxy system, a water-based polyurethane system or a mixed system of the two.

[0011] As a preferred scheme of the automobile interior metal part spraying process based on the high adhesion water-based paint, in the step (3), the solid content of the primer is 30%-40%, the wet film thickness is 6-12 micrometers, and the dry film thickness is obtained by heating at 80-90 DEG C for 3-6 minutes.

[0012] As a preferred scheme of the automobile interior metal part spraying process based on the high adhesion water-based paint, in the step (4), the water-based topcoat mainly comprises hydroxyl acrylate resin, and is matched with a blocked isocyanate crosslinking agent, and the amount of the crosslinking agent is 15%-30% of the solid mass of the resin.

[0013] As a preferred scheme of the automobile interior metal part spraying process based on the high adhesion water-based paint, in the step (4), the solid content of the topcoat is 35%-45%, the spraying mode is electrostatic spraying, the spraying voltage is 40-55 kilovolts, and the distance between the spraying gun and the workpiece is 180-220 millimeters.

[0014] As a preferred scheme of the automobile interior metal part spraying process based on high adhesion force water-based paint according to the present application, the metal substrate is selected from steel, aluminum alloy or magnesium alloy.

[0015] As a preferred scheme of the automobile interior metal part spraying process based on high adhesion force water-based paint according to the present application, the coating has a 0-level adhesion force in the cross-hatch test, and no blistering and peeling occurs after 240 hours under the condition of 40 DEG C and 95% relative humidity, and the corrosion expansion at the scratch is not more than 1 mm after 240 hours in a 5% salt spray solution.

[0016] As a preferred scheme of the automobile interior metal part spraying process based on high adhesion force water-based paint according to the present application, the coating has a hardness of H level or above, a smooth and flat paint film surface, and the properties of resistance to wet heat, salt spray and abrasion, and is suitable for industrialized spraying production of automobile interior metal parts.

[0017] The present application has the advantages that the present application improves the universality of water-based paint on different substrates such as steel, aluminum alloy and magnesium alloy; the coating shows stability under the conditions of wet heat and salt spray, and can withstand long-term corrosion and stress without peeling; the low-temperature segmented curing method ensures the dense crosslinking of the paint film and reduces energy consumption; at the same time, the whole process is environmentally friendly and chromium-free, meeting the requirements of the automobile industry for green manufacturing, and providing an efficient and sustainable spraying scheme for automobile interior metal parts. DETAILED DESCRIPTION

[0018] In order to make the above-mentioned objects, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the embodiments of the present application.

[0019] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from the description, and those skilled in the art can make similar generalizations without departing from the scope of the present application, so the present application is not limited to the specific embodiments disclosed below.

[0020] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor does it mean an embodiment that is separate or selectively excluded from other embodiments.

[0021] Embodiment 1 The present embodiment provides an automobile interior metal part spraying process based on high adhesion force water-based paint.

[0022] Specifically, the substrate is a cold-rolled steel interior part.

[0023] Further, the steel piece is first cleaned with an alkaline aqueous solution containing 15 g / L sodium hydroxide, the temperature is controlled at 55°C, and the treatment time is 5 minutes, so as to remove oil stains and impurities.

[0024] Subsequently, the steel piece is pickled in an 8 g / L dilute sulfuric acid solution for 1 minute, so as to remove the oxide layer and form a micro-rough structure on the surface, and then the steel piece is immersed in a conversion solution containing 1.0 wt% amino silane and 0.5 wt% epoxy silane, the pH is adjusted to 4.0, the treatment time is 3 minutes, and the steel piece is dried by hot air at 60°C, so as to form a uniform conversion film.

[0025] Further, the conversion film surface is sprayed with a water-based epoxy primer with a solid content of 35%, the wet film thickness is controlled at 8 microns, and after drying at 85°C for 5 minutes, a dry film thickness of 4 microns is formed.

[0026] Further, a water-based topcoat with a hydroxyl acrylate resin as the base material and containing 20 wt% blocked isocyanate crosslinking agent is sprayed, 1 wt% dispersant and 0.3 wt% leveling agent are added, the mixture is uniformly mixed, and then electrostatic spraying is performed, the spraying voltage is 45 kV, the spraying distance is 200 mm, and the wet film thickness is 30 microns.

[0027] After spraying is completed, the workpiece is first heated at 90°C for 5 minutes, and then cured at 115°C for 12 minutes, so as to obtain a topcoat layer with a dry film thickness of 20 microns.

[0028] Test results show that the coating has an adhesion of 0 level in the cross-hatch test, no blistering or peeling occurs in the 240-hour damp heat test, the scratch corrosion in the salt spray test is less than 1 mm, the coating surface is smooth and flat, and the coating has excellent durability and decorative effect.

[0029] Example 2 The present embodiment provides a spraying process for automobile interior metal parts based on high-adhesion water-based paint.

[0030] Specifically, the substrate is an aluminum alloy part for automobile interior.

[0031] First, the substrate is cleaned with a 20 g / L sodium hydroxide solution, the temperature is 60°C, and the time is 4 minutes, so as to remove surface oxides and residual impurities.

[0032] Further, after rinsing with deionized water, the substrate is pickled with a 10 g / L dilute nitric acid solution for 2 minutes, so as to remove alkali etching residues and level the surface.

[0033] The treated aluminum part is placed in a conversion solution containing 0.8 wt% amino silane and 0.5 wt% epoxy silane, the pH is 4.5, the time is 4 minutes, and after drying by hot air at 70°C, a silane conversion film with a thickness of about 50 nm is formed.

[0034] An aqueous polyurethane primer with solid content of 38% was sprayed on the surface of the conversion film, with a wet film thickness of 10 microns, and dried at 80°C for 4 minutes to obtain a dry film of 5 microns.

[0035] Subsequently, an aqueous acrylic topcoat with solid content of 40% was sprayed, containing 25 wt% blocked isocyanate crosslinker, 0.8 wt% dispersant and 0.2 wt% leveling agent, with an electrostatic spraying voltage of 50 kV and a spraying distance of 180 mm, and a wet film thickness of 28 microns. After spraying, it was heated at 85°C for 4 minutes and then cured at 110°C for 15 minutes to form a compact topcoat layer of 18 microns.

[0036] The test results showed that the coating remained intact in a humid and hot environment, with no significant corrosion propagation in the 240-hour salt spray test, and the surface hardness of the coating reached H level, with excellent wear resistance and weather resistance, indicating that this process is also applicable to aluminum alloy interior parts.

[0037] Example 3 This example provides a spraying process for automotive interior metal parts based on high adhesion water-based coatings.

[0038] Specifically, the substrate is a magnesium alloy automotive interior part.

[0039] The magnesium alloy has high surface activity and is prone to oxidation and corrosion, so during pretreatment, it is alkaline washed with 12 g / L sodium hydroxide solution at a temperature of 50°C for 3 minutes to remove oil stains and part of the oxidation film; then it is acid washed with 10 g / L dilute sulfuric acid solution for 1 minute to further activate the surface.

[0040] Subsequently, the magnesium part is immersed in a conversion solution containing 1.2 wt% amino silane and 0.6 wt% epoxy silane, with a pH value of 3.8, for 5 minutes, and after drying at 65°C, a uniform conversion film is formed, improving its corrosion resistance and bonding performance.

[0041] Further, an aqueous epoxy-polyurethane composite primer with a solid content of 32% is sprayed on the surface of the conversion film, with a wet film thickness of 9 microns, and dried at 85°C for 5 minutes to obtain a dry film of 4 microns.

[0042] An aqueous topcoat with hydroxy acrylic as the main body, containing 18 wt% blocked isocyanate crosslinker, and adding 0.5 wt% defoamer and 0.2 wt% leveling agent, is sprayed thereon, with a spraying voltage of 42 kV, a spraying distance of 220 mm, and a wet film thickness of 25 microns.

[0043] After staged heating, it is first heated at 90°C for 5 minutes and then at 115°C for 13 minutes to obtain a topcoat layer with a dry film thickness of 17 microns.

[0044] The coating adhesion reaches 0 level, no corrosion expansion of the magnesium matrix is found in the salt spray test, and no blistering and loss of luster of the paint film after the damp heat test, and the surface is smooth and glossy. The results show that the process is also suitable for magnesium alloy substrates, and can significantly improve the coating durability thereof.

[0045] In summary, the above embodiments are directed to three typical automotive interior metal parts of steel, aluminum alloy and magnesium alloy.

[0046] Firstly, the surface pretreatment process makes the metal surface clean and forms a micro rough structure through alkaline washing and acid washing, thereby increasing the mechanical embedding force.

[0047] Specifically, a silane chemical conversion film is used, which is a thin layer containing silicon-oxygen bonds and organic functional groups, can chemically combine with the metal matrix, and at the same time reacts with the water-based primer resin to form a "bridge" effect, greatly improving the interfacial bonding strength. Compared with traditional phosphating or chromizing treatment, silane conversion is not only environmentally friendly, but also can form a stable and dense film layer at a lower concentration, which is suitable for water-based coating systems.

[0048] Secondly, the primer layer plays a role of connecting the previous and the next, and the polar groups in the molecular structure of the primer can interact with the silane conversion layer, while providing a uniform surface to facilitate the wetting and spreading of the topcoat.

[0049] By controlling the solid content and film thickness of the primer, it can not only fully cover the conversion film, but also avoid stress concentration caused by excessive thickness, so as to balance the bonding strength and flexibility. The epoxy primer and the polyurethane primer each have its own advantages, the epoxy system has strong adhesion, the polyurethane system has good flexibility, and the combination of the two can balance the hardness and ductility.

[0050] Furthermore, the topcoat layer adopts a two-component system crosslinked by hydroxy acrylate and blocked isocyanate, the paint film after crosslinking is dense and tough, has good chemical resistance and weather resistance, and through the synergistic effect of dispersing agent and leveling agent, the topcoat forms a uniform paint film during the spraying process, reducing pinholes and orange peel. The electrostatic spraying process not only improves the utilization rate of the coating, but also makes the coating thickness more uniform, further ensuring the overall performance of the coating.

[0051] Finally, the segmented curing process ensures the performance of the coating system. In the pre-baking stage, the main purpose is to remove water and residual solvent, so as to avoid the generation of bubble defects during high-temperature curing; in the final curing stage, the temperature and time are controlled to make the resin and crosslinking agent fully react, forming a three-dimensional crosslinked network, so as to obtain a dense and tough paint film structure. The segmented curing strategy takes into account both low energy consumption and high performance, and is suitable for continuous operation of industrial production lines.

[0052] From the performance, the embodiments of the three kinds of substrates all pass the cross-hatch, damp heat, salt spray and other tests, and the coating shows excellent adhesion and durability.

[0053] It should be noted that the above examples are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced, without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A spraying process for automotive interior metal parts based on high-adhesion water-based coatings, characterized in that: Includes the following steps: (1) Surface pretreatment of the metal substrate, including alkaline washing, acid washing and rinsing, to clean the surface of the substrate and form micro-roughness; (2) Immerse the pretreated metal substrate in a conversion solution containing silane, control the silane concentration to be 0.5-1.5% by mass, the pH value to be 3.5-5.0, the treatment time to be 2-5 minutes, and then dry to form a conversion film with a thickness of 30-80 nanometers on the surface; (3) A water-based primer is sprayed onto the surface of the conversion film, the dry film thickness of which is 3-8 micrometers, and then dried by heating; (4) Spray water-based topcoat onto the surface of the base layer, with a wet film thickness of 20-35 micrometers. After segmented heating and curing, first heat at 80-95℃ for 3-6 minutes, then heat at 110-120℃ for 10-15 minutes, and finally form a topcoat layer with a dry film thickness of 15-25 micrometers.

2. The automotive interior metal parts spraying process based on high-adhesion water-based coatings as described in claim 1, characterized in that: In step (1), the alkaline washing uses a sodium hydroxide solution containing 5-25 g / L, at a temperature of 50-65℃, for 2-6 minutes; the acid washing uses an acid solution containing 5-15 g / L, for 1-3 minutes.

3. The automotive interior metal parts spraying process based on high-adhesion water-based coatings as described in claim 1, characterized in that: In step (2), the silane is selected from aminosilane, epoxysilane or a mixture thereof, and the substrate surface after silane treatment is dried by hot air or heating to form a uniform conversion film.

4. The automotive interior metal parts spraying process based on high-adhesion water-based coatings as described in claim 1, characterized in that: The waterborne primer in step (3) is selected from waterborne epoxy system, waterborne polyurethane system or a mixture of both.

5. The automotive interior metal parts spraying process based on high-adhesion water-based coatings as described in claim 1, characterized in that: In step (3), the solid content of the primer is 30%~40%, the wet film thickness is 6~12 micrometers, and the dry film thickness is obtained by heating at 80~90℃ for 3~6 minutes.

6. The automotive interior metal parts spraying process based on high-adhesion waterborne coatings as described in claim 1, characterized in that: The water-based topcoat in step (4) is mainly composed of hydroxyl acrylic resin, combined with a blocked isocyanate crosslinking agent, and the amount of crosslinking agent is 15% to 30% of the resin solid mass.

7. The automotive interior metal parts spraying process based on high-adhesion water-based coatings as described in claim 1, characterized in that: In step (4), the solid content of the topcoat is 35%~45%, the spraying method is electrostatic spraying, the spraying voltage is 40~55 kV, and the distance between the spray gun and the workpiece is 180~220 mm.

8. The automotive interior metal parts spraying process based on high-adhesion waterborne coatings as described in claim 1, characterized in that: The metal substrate is selected from steel, aluminum alloy or magnesium alloy.

9. The automotive interior metal parts spraying process based on high-adhesion waterborne coatings as described in claim 1, characterized in that: The coating achieved an adhesion rating of 0 in the cross-cut test, exhibited no blistering or peeling after 240 hours at 40°C and 95% relative humidity, and showed no more than 1 mm of erosion at the scratch site after 240 hours in a 5% salt spray solution.

10. The automotive interior metal parts spraying process based on high-adhesion waterborne coatings as described in claim 1, characterized in that: The resulting coating has a hardness of H or higher, a smooth and even surface, and is resistant to damp heat, salt spray, and wear. It is suitable for the industrial spraying production of metal parts for automotive interiors.