High-adhesion powder coating for surface of die-casting aluminum base material and preparation method of high-adhesion powder coating

Abstract

The invention discloses a high-adhesive-force powder coating for the surface of a die-casting aluminum base material and a preparation method of the high-adhesive-force powder coating, relates to the technical field of metal surface treatment, and aims to solve the problems that when the powder coating is sprayed on the surface of the die-casting aluminum base material, the adhesive force is insufficient, a pretreatment process is not environment-friendly and surface defects exist. The coating is composed of 240g of epoxy resin, 360g of polyester resin, 26g of an auxiliary agent, 180g of a pigment, 20g of an adhesion auxiliary agent and 174g of a filler. The epoxy resin is bisphenol A type epoxy resin with the epoxy equivalent of 450 to 550 g / mol; the polyester resin is carboxyl polyester resin with an acid value of 30-40 mgKOH / g; the auxiliary agent is prepared from 12g of an acrylic leveling agent, 5g of a polyether modified silicone defoaming agent, 4g of a high molecular weight segmented copolymer dispersing agent, 2g of a hindered phenol antioxidant and 3g of nano titanium dioxide, and the nano titanium dioxide and the acrylic leveling agent have a synergistic effect.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and more particularly to a high-adhesion powder coating on the surface of a die-cast aluminum substrate and a preparation method thereof. Background Art

[0002] In the field of modern industrial manufacturing, die-cast aluminum is widely used in industries such as automobiles, 3C, and aerospace due to its advantages of light weight, high strength, and easy molding. However, as the market's requirements for product quality continue to increase, the shortcomings of its surface coating technology have gradually been exposed. Among them, problems such as insufficient adhesion, environmentally unfriendly pre-treatment processes, and surface micropore defects are particularly prominent, seriously restricting the development of the industry.

[0003] First, traditional powder coatings have poor adhesion to die-cast aluminum surfaces, with a cross-cut test grade of only 1-2. Under external impact and environmental changes, the coating with poor adhesion will peel off quickly.

[0004] Furthermore, the currently commonly used chromating or phosphating pre-treatment processes, although they can improve the bonding performance of the coating, bring serious pollution. The chromium used in chromating is highly toxic and will pollute the soil and water bodies. The discharge of phosphorus-containing wastewater produced by phosphating will cause eutrophication of water bodies.

[0005] Finally, due to the influence of the die-casting molding process, there are a large number of micropores on the surface of die-cast aluminum. During painting, the air in the micropores cannot be discharged when the paint is cured, resulting in pinholes and bubbles in the coating, which not only affects the appearance but also reduces the protective performance.

[0006] In view of this, we propose a high-adhesion powder coating for the surface of a die-cast aluminum substrate and a preparation method thereof. Summary of the Invention

[0007] The purpose of the present invention is to provide a high-adhesion powder coating for the surface of a die-cast aluminum substrate and a preparation method thereof, aiming to solve the problems of insufficient adhesion, environmentally unfriendly pre-treatment process and surface defects of existing powder coatings when sprayed on the surface of a die-cast aluminum substrate.

[0008] To solve the above technical problems, the present invention provides the following technical solution: a high-adhesion powder coating for the surface of a die-cast aluminum substrate, wherein 1000g of the powder coating comprises 240g of epoxy resin, 360g of polyester resin, 26g of additive, 180g of pigment, 20g of adhesion promoter, and 174g of filler;

[0009] The epoxy resin is a bisphenol A epoxy resin with an epoxy equivalent weight of 450-550 g / mol;

[0010] The polyester resin is a carboxyl polyester resin with an acid value of 30-40 mgKOH / g;

[0011] The auxiliary agent is composed of 12g of acrylic leveling agent, 5g of polyether modified silicone defoamer, 4g of high molecular weight block copolymer dispersant, 2g of hindered phenol antioxidant and 3g of nano titanium dioxide, and the nano titanium dioxide and acrylic leveling agent act synergistically;

[0012] The adhesion promoter is composed of 18g of an organic compound containing phosphoryl and silane groups and 2g of nano-alumina, and the nano-alumina enhances the bonding strength between the adhesion promoter and the substrate and the coating;

[0013] The filler is a mixture of precipitated barium sulfate and talc powder in a mass ratio of 3:2, which is pretreated with a coupling agent and mixed with 5g of graphene nanosheets.

[0014] Preferably, the acrylic leveling agent is a fluorine-containing acrylic ester copolymer, the polyether chain segment molecular weight of the polyether-modified silicone defoamer is 1000-2000, the hindered phenol antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the number of blocks of the high molecular weight block copolymer dispersant is not less than 3.

[0015] Preferably, the particle size of the precipitated barium sulfate in the filler is 0.5-1.5 μm, and the particle size of the talc powder is 1-2 μm.

[0016] Preferably, the graphene nanosheets have a sheet thickness of 3-10 nm, a sheet diameter of 5-20 μm, and a carbon content of ≥98 wt%.

[0017] A method for preparing a high-adhesion powder coating for a die-cast aluminum substrate surface, the method being used to prepare any of the above-mentioned high-adhesion powder coatings for a die-cast aluminum substrate surface, the method comprising the following steps:

[0018] S1. Weigh the materials, including 240 g epoxy resin, 360 g polyester resin, 26 g additive, 180 g pigment, 20 g adhesion agent, and 174 g filler;

[0019] S2. Material mixing: The weighed epoxy resin, polyester resin, additives, pigments, adhesion promoters and fillers are placed in a high-speed mixer, and mixed at a speed of 800-1000 r / min for 10-15 min to obtain a mixed material;

[0020] S3, melt extrusion, the mixed material is fed into a twin-screw extruder for melt extrusion, the extruder temperature is set to 100-110°C in zone 1, 120-130°C in zone 2, 130-140°C in zone 3, 140-150°C in zone 4, and the screw speed is 150-200 r / min;

[0021] S4, cooling and pressing, cooling the extruded material through a cooling roller, and then pressing it into a sheet material;

[0022] S5, crushing and screening, crushing the flaky material, and then sieving it through a 180-200 mesh screen to obtain a powder coating;

[0023] S6. Powder coating spraying: immerse the die-cast aluminum substrate to be sprayed with powder coating in an aqueous solution containing 2-5wt% silane coupling agent, treat it at 40-60°C for 5-10 minutes, then wash and dry it with water or use an alkaline detergent to clean the substrate at 50-70°C for 5-15 minutes, then wash and dry it with water, and then use electrostatic spraying equipment to spray the powder coating on the treated surface of the die-cast aluminum substrate.

[0024] Preferably, in the above step S1, the epoxy resin and polyester resin are symmetrically taken before vacuum drying, with a vacuum degree of -0.08MPa to -0.095MPa, a drying temperature of 80-90°C, and a drying time of 2-3h to remove moisture and low-boiling point impurities in the raw materials and improve the purity and stability of the resin.

[0025] Preferably, in the above step S2, the mixed materials are further subjected to ultrasonic dispersion treatment, with an ultrasonic frequency of 20-40 kHz, an ultrasonic power of 300-500 W, and a treatment time of 5-10 min, so that the materials are dispersed more evenly and the mixing effect of the materials is enhanced.

[0026] Preferably, in the above step S5, a combination of air flow pulverization and mechanical pulverization is adopted, wherein the flaky material is first pulverized into 50-80 meshes by a mechanical pulverizer, and then further pulverized into 180-200 meshes by an air flow pulverizer.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention forms a chemical chelate bond between an organic compound containing phosphoryl and silane groups and the aluminum atoms on the surface of the die-cast aluminum substrate, combined with nano-alumina, to significantly improve the interface bonding strength and impact resistance of the coating and the substrate, solve the problem of coating peeling caused by insufficient adhesion, and adopt silane treatment or alkaline cleaning to avoid the emission of chromium and phosphorus, making the pretreatment process environmentally friendly. In addition, through the gradient particle size filling effect of precipitated barium sulfate and talcum powder, combined with the gas diversion function of graphene nanosheets, the micropores on the surface of the die-cast aluminum are filled and the air is guided to be discharged when the coating is cured, thereby solving the micropore defects.

[0029] 2. In the present invention, the epoxy resin and the polyester resin react to form dense crosslinks, making the coating both flexible and hard. The fluorine-containing acrylic leveling agent and nano-titanium dioxide synergistically reduce the surface tension of the coating, promote melt leveling, and eliminate defects such as orange peel. The polyether-modified silicone defoamer matches the polarity of the resin and efficiently breaks down microbubbles during the twin-screw extrusion stage. The high molecular weight block copolymer dispersant stabilizes the pigment particles through the steric hindrance effect, avoiding uneven hue caused by flocculation and improving the uniformity of the coating.

[0030] 3. The present invention removes moisture and low-boiling-point impurities from the raw materials by vacuum drying the epoxy resin and polyester resin, avoids hydrolysis and degradation, ensures the purity and stability of the resin, and combines high-speed mixing with ultrasonic dispersion technology to achieve uniform dispersion of nano-components such as nano-alumina and graphene nanosheets, avoiding the filler agglomeration problem in traditional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic flow diagram of the preparation method of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] Example 1

[0034] Weigh 240g of epoxy resin, 360g of polyester resin, 26g of additives, 180g of pigment, 20g of adhesion promoter and 174g of filler. It should be noted that the epoxy resin and polyester resin before symmetry should be vacuum dried with a vacuum degree of -0.08MPa, a drying temperature of 80°C and a drying time of 2h to remove moisture and low-boiling impurities in the raw materials and improve the purity and stability of the resin. Then put the weighed epoxy resin, polyester resin, additives, pigment, adhesion promoter and filler into a high-speed mixer, mix them at a speed of 800r / min for 10min to obtain a mixed material, and perform ultrasonic dispersion treatment on the mixed material. The frequency is 20kHz, the ultrasonic power is 300W, and the processing time is 5min, so that the materials are dispersed more evenly and the mixing effect of the materials is enhanced. The mixed materials are then sent to a twin-screw extruder for melt extrusion. The extruder temperature is set to 100°C in zone 1, 120°C in zone 2, 130°C in zone 3, and 140°C in zone 4. The screw speed is 150r / min. The extruded material is then cooled by a cooling roller and then pressed into a sheet material. Then, a combination of airflow crushing and mechanical crushing is adopted. The sheet material is first crushed to 50 mesh by a mechanical crusher, and then further crushed to 180 mesh by an airflow crusher, and then sieved through a 180-mesh screen to obtain a powder coating.

[0035] It should be noted that when spraying powder coating, the die-cast aluminum substrate to be sprayed with powder coating should be immersed in an aqueous solution containing 2-5wt% silane coupling agent, treated at 40-60℃ for 5-10 minutes, then washed and dried, or the substrate should be cleaned with an alkaline detergent at 50-70℃ for 5-15 minutes, then washed and dried, and then the powder coating should be sprayed on the treated surface of the die-cast aluminum substrate using electrostatic spraying equipment to avoid the emission of chromium and phosphorus and achieve environmentally friendly spraying.

[0036] Example 2

[0037] This embodiment is basically the same as the first embodiment, except that 240g of epoxy resin, 360g of polyester resin, 26g of auxiliary agent, 180g of pigment, 20g of adhesion promoter and 174g of filler are weighed. It should be noted that the epoxy resin and polyester resin before symmetry are vacuum dried with a vacuum degree of -0.095MPa, a drying temperature of 90°C and a drying time of 3h to remove moisture and low-boiling impurities in the raw materials and improve the purity and stability of the resin. Then, the weighed epoxy resin, polyester resin, auxiliary agent, pigment, adhesion promoter and filler are put into a high-speed mixer, mixed at a speed of 1000r / min for 15min to obtain a mixed material, and the mixed material is subjected to Ultrasonic dispersion treatment, ultrasonic frequency of 40kHz, ultrasonic power of 500W, treatment time of 10min, so that the materials are dispersed more evenly and the mixing effect of the materials is enhanced, and then the mixed materials are sent to a twin-screw extruder for melt extrusion, the extruder temperature is set to 110℃ in zone 1, 130℃ in zone 2, 140℃ in zone 3, and 150℃ in zone 4, the screw speed is 200r / min, and then the extruded material is cooled by a cooling roller and then pressed into a sheet material, and then a combination of air flow crushing and mechanical crushing is adopted. The sheet material is first crushed to 80 mesh by a mechanical crusher, and then further crushed to 200 mesh by an air flow crusher, and then sieved through a 200-mesh screen to obtain a powder coating.

[0038] The embodiments disclosed in the present invention are preferred embodiments, but are not limited to them. Ordinary technicians in this field can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. As long as they do not deviate from the spirit of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A high-adhesion powder coating for the surface of a die-cast aluminum substrate, characterized in that: The powder coating, based on 1000 g, consists of 240 g of epoxy resin, 360 g of polyester resin, 26 g of additive, 180 g of pigment, 20 g of adhesion promoter and 174 g of filler; The epoxy resin is a bisphenol A epoxy resin with an epoxy equivalent weight of 450-550 g / mol; The polyester resin is a carboxyl polyester resin with an acid value of 30-40 mgKOH / g; The auxiliary agent is composed of 12g of acrylic leveling agent, 5g of polyether modified silicone defoamer, 4g of high molecular weight block copolymer dispersant, 2g of hindered phenol antioxidant and 3g of nano titanium dioxide, and the nano titanium dioxide and acrylic leveling agent act synergistically; The adhesion promoter is composed of 18g of an organic compound containing phosphoryl and silane groups and 2g of nano-alumina, and the nano-alumina enhances the bonding strength between the adhesion promoter and the substrate and the coating; The filler is a mixture of precipitated barium sulfate and talc powder in a mass ratio of 3:2, which is pretreated with a coupling agent and mixed with 5g of graphene nanosheets.

2. The high-adhesion powder coating for die-cast aluminum substrate according to claim 1, characterized in that: The acrylic leveling agent is a fluorine-containing acrylic ester copolymer, the polyether chain segment molecular weight of the polyether-modified silicone defoamer is 1000-2000, the hindered phenol antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the number of blocks of the high molecular weight block copolymer dispersant is not less than 3.

3. The high-adhesion powder coating for die-cast aluminum substrate according to claim 1, characterized in that: The particle size of the precipitated barium sulfate in the filler is 0.5-1.5 μm, and the particle size of the talc powder is 1-2 μm.

4. The high-adhesion powder coating for die-cast aluminum substrate according to claim 1, characterized in that: The graphene nanosheets have a sheet thickness of 3-10 nm, a sheet diameter of 5-20 μm, and a carbon content of ≥98 wt%.

5. A method for preparing a high-adhesion powder coating for a die-cast aluminum substrate surface, the method being used to prepare a high-adhesion powder coating for a die-cast aluminum substrate surface according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: S1. Weigh the materials, including 240 g epoxy resin, 360 g polyester resin, 26 g additive, 180 g pigment, 20 g adhesion agent, and 174 g filler; S2. Material mixing: The weighed epoxy resin, polyester resin, additives, pigments, adhesion promoters and fillers are placed in a high-speed mixer, and mixed at a speed of 800-1000 r / min for 10-15 min to obtain a mixed material; S3, melt extrusion, the mixed material is fed into a twin-screw extruder for melt extrusion, the extruder temperature is set to 100-110°C in zone 1, 120-130°C in zone 2, 130-140°C in zone 3, 140-150°C in zone 4, and the screw speed is 150-200 r / min; S4, cooling and pressing, cooling the extruded material through a cooling roller, and then pressing it into a sheet material; S5, crushing and screening, crushing the flaky material, and then sieving it through a 180-200 mesh screen to obtain a powder coating; S6. Powder coating spraying: immerse the die-cast aluminum substrate to be sprayed with powder coating in an aqueous solution containing 2-5wt% silane coupling agent, treat it at 40-60°C for 5-10 minutes, then wash and dry it with water or use an alkaline detergent to clean the substrate at 50-70°C for 5-15 minutes, then wash and dry it with water, and then use electrostatic spraying equipment to spray the powder coating on the treated surface of the die-cast aluminum substrate.

6. The method for preparing a high-adhesion powder coating on the surface of a die-cast aluminum substrate according to claim 5, characterized in that: In the above step S1, the epoxy resin and polyester resin are symmetrically taken and vacuum dried at a vacuum degree of -0.08 MPa to -0.095 MPa, a drying temperature of 80-90°C, and a drying time of 2-3 hours to remove moisture and low-boiling point impurities in the raw materials and improve the purity and stability of the resin.

7. The method for preparing a high-adhesion powder coating on the surface of a die-cast aluminum substrate according to claim 5, characterized in that: In the above step S2, the mixed materials are further subjected to ultrasonic dispersion treatment, with an ultrasonic frequency of 20-40 kHz, an ultrasonic power of 300-500 W, and a treatment time of 5-10 min, so as to make the materials more evenly dispersed and enhance the mixing effect of the materials.

8. The method for preparing a high-adhesion powder coating on the surface of a die-cast aluminum substrate according to claim 5, characterized in that: In the above step S5, a combination of air flow pulverization and mechanical pulverization is adopted. The flaky material is first pulverized into 50-80 meshes by a mechanical pulverizer, and then further pulverized into 180-200 meshes by an air flow pulverizer.

Images