Pretreatment process special for electrostatic spraying of PA / PPO alloy and spraying method

Abstract

The invention provides a pretreatment process special for PA / PPO alloy electrostatic spraying and a spraying method. Plasma activation and chemical etching are combined, the surface resistivity is accurately controlled to be 104-106 ohms, the electrostatic adsorption performance is optimized, the spraying process adopts a multi-section temperature control ratio of preheating of a base material at the temperature of 80-120 DEG C, the electrostatic voltage of 60-80 kV and the atomization pressure of 0.3-0.5 MPa, and the surface resistivity is accurately controlled to be 10 < 4 >-10 < 6 > ohms. According to the process, the problems that the PA / PPO alloy is high in surface resistivity and poor in electrostatic adsorption are solved, the coating uniformity is improved, the adhesive force reaches the 5B level, and the process is suitable for electrostatic spraying scenes such as automobile engine parts and precise structural parts and has the advantages of being high in process compatibility, capable of saving energy and environmentally friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer material surface treatment and electrostatic spraying technology, and particularly relates to a pretreatment process and spraying method special for PA / PPO alloy electrostatic spraying. BACKGROUND

[0002] In modern automobile manufacturing industry, the electrostatic spraying process has become one of the key technologies for surface treatment of automobile parts due to its advantages of high efficiency, environmental protection, excellent coating quality and the like. The electrostatic spraying process can make coating particles charged and adsorbed on the surface of a workpiece under the action of an electrostatic field, so as to form a uniform and dense coating, thereby improving the appearance of the automobile parts and enhancing the corrosion resistance, wear resistance and other protective properties of the automobile parts.

[0003] PA / PPO alloy is a high-performance polymer material, which combines the good processability, chemical corrosion resistance and impact resistance of PA (polyamide) and the high-temperature resistance and dimensional stability of PPO (polyphenylene oxide), and is widely used in the field of automobiles, such as interior and exterior parts and some functional parts. From the material itself, the resistivity of the original surface of PA / PPO alloy is relatively high, which is usually far beyond the suitable range (10 4 -10 6 Ω) required for electrostatic spraying. The excessively high resistivity can cause the coating particles to be difficult to be uniformly and stably adsorbed on the surface of the alloy during the electrostatic spraying process, thereby causing defects such as uneven coating thickness, spraying leakage or accumulation, and seriously affecting the coating quality and protective properties.

[0004] The traditional electrostatic spraying pretreatment process, such as simple degreasing, rust removal and cleaning, can remove the oil stains and impurities on the surface of the PA / PPO alloy automobile parts to a certain extent, but has limited effect on adjusting the surface resistivity of the material and optimizing the electrostatic adsorption effect. The surface treatment technology cannot accurately control the surface resistivity, which leads to unstable electrostatic adsorption effect and poor coating uniformity. The spraying process parameters are not reasonably matched, which can easily cause problems such as uneven coating thickness and insufficient adhesion. In the curing process, a single curing method can easily cause internal stress in the coating, thereby causing defects such as coating cracking and pinholes, which seriously affect the product quality and service life.

[0005] Therefore, it is of urgent and important practical significance to develop a pretreatment process special for PA / PPO alloy automobile parts, which can accurately control the surface resistivity in the range of 10 4 -10 6 Ω to optimize the electrostatic adsorption, so as to improve the electrostatic spraying quality of the automobile parts and expand the application of PA / PPO alloy in the field of automobiles. SUMMARY

[0006] OBJECTIVE

[0007] The application aims to provide a PA / PPO alloy electrostatic spraying special pretreatment process and spraying method, which realizes accurate control of surface resistivity, improves electrostatic adsorption performance and coating quality by optimizing surface treatment, spraying process and curing technology, and solves the problems in the prior art.

[0008] The technical scheme of the application is as follows:

[0009] The PA / PPO alloy electrostatic spraying special pretreatment process comprises the following steps:

[0010] Plasma activation treatment: the PA / PPO alloy surface is activated by plasma gas, the plasma power is 100-300 W, and the treatment time is 5-15 min;

[0011] Chemical etching treatment: the PA / PPO alloy activated by plasma is immersed in a chemical etching solution for etching treatment, and the etching time is 30-120 s;

[0012] Post-treatment cleaning: the PA / PPO alloy surface after etching is ultrasonically cleaned with deionized water, and the cleaning time is 10-15 min, so that the surface resistivity is controlled to be 10 4 -10 6 Ω.m.

[0013] Further, the plasma gas is selected from one or more mixed gases of Ar, N2 and O2; in the plasma activation treatment, the total flow of the mixed gas is 30-50 sccm, and the treatment cavity pressure is 10-30 Pa.

[0014] Further, the chemical etching solution is a H2SO4 solution with a mass fraction of 5-15% or a NaOH solution with a mass fraction of 5-10%; after the chemical etching treatment, the alloy surface forms a nanoscale groove structure with a depth of 10-30 nm, and the surface roughness Ra is 0.5-1.2 μm.

[0015] The PA / PPO alloy electrostatic spraying method provided by the application comprises the following steps:

[0016] Substrate preheating: the pretreated PA / PPO alloy is preheated at 85-110℃ for 10-15 min;

[0017] Electrostatic spraying: spraying is performed by using an electrostatic voltage of 65-75 kV and an atomization pressure of 0.35-0.45 MPa, and the coating solid content is 45-55%;

[0018] Temperature control: during the spraying process, the substrate temperature is controlled to be 70-90℃, and the environmental humidity is 40-60% RH;

[0019] Infrared-hot air combined curing: using a stepwise temperature rising program, the first stage is from 25℃ to 60℃, the temperature rising rate is 5℃ / min, then keeping for 10-15min, the second stage is from 60℃ to 120℃, the temperature rising rate is 3℃ / min, keeping for 15-20min, the third stage is from 120℃ to 180℃, the temperature rising rate is 2℃ / min, keeping for 20-30min, then naturally cooling to room temperature.

[0020] Further, the substrate preheating temperature is adjusted according to the PA content in the PA / PPO alloy: when the PA mass content is 60-70%, the preheating temperature is 95-110℃; when the PA mass content is 71-75%, the preheating temperature is 85-95℃.

[0021] Further, in the electrostatic spraying, the distance between the spray gun and the substrate is 200-300mm, the spraying speed is 300-500mm / s, and the spraying angle is 45°-90°.

[0022] Further, in the infrared-hot air combined curing, the infrared radiation wavelength is 2-4μm, the hot air circulating wind speed is 1-3m / s, and the oxygen content in the cavity during the curing process is ≤5%.

[0023] Further, the coating thickness after spraying is 40-60μm, and the surface resistivity uniformity deviation is ≤10%.

[0024] Further, the raw materials of the PA / PPO alloy include, by mass percentage: 60-75% of PA nylon, 20-40% of maleic anhydride grafted PPO, 5-8% of PPS, 2-5% of nanometer carbon tube, and 0.1-1% of additives. Further, the PA nylon is PA6T or PA9T.

[0025] Beneficial effects:

[0026] The present application provides a PA / PPO alloy electrostatic spraying special pretreatment process and spraying method, which can precisely control the surface resistivity to 10 4 -10 6 Ω, optimize the electrostatic adsorption performance, and improve the uniformity, adhesion, hardness, and heat deformation temperature of the PA / PPO alloy surface coating, which is suitable for electrostatic spraying scenes such as automobile engine parts and precision structural parts, and has the characteristics of strong process compatibility, energy saving, and environmental protection. DETAILED DESCRIPTION

[0027] The present application will be described below in conjunction with specific embodiments. It should be noted that the following examples are examples of the present application and are only used to illustrate the present application, but not to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0028] The chemical reagents used in the present application are all commercially available analytical pure unless otherwise specified. Among them, PA6T nylon is E630NK from Japan Mitsui Chemical; maleic anhydride grafted PPO is Shenghao Rubber and Plastic, grafting rate: 2%; PPS, i.e. polyphenylene sulfide, brand: 1140A4; carbon nanotube is carbon positive technology 100T; the coating used in the present application is NPD300-H powder coating from Liangbang.

[0029] The preparation of PA / PPO alloy parts includes the following steps:

[0030] S1: 7 kg of PA6T nylon, 2 kg of maleic anhydride grafted PPO (2% grafting rate), 0.5 kg of PPS, 0.4 kg of carbon nanotube, 0.05 kg of antioxidant 1010, and 0.05 kg of antioxidant 168 are prepared;

[0031] S2: The above materials are put into a co-rotating twin-screw extruder, PA6T nylon, maleic anhydride grafted PPO, and PPS are added from the main feeding port, and carbon nanotube, antioxidant 1010, and antioxidant 168 are added from the side feeding port. The barrel temperature is set to 300℃, and the screw rotation speed is 300rpm;

[0032] S3: The extrudate is cooled, granulated, and hot pressed using a mold to prepare PA / PPO alloy parts with a size of 120mm long x 15mm wide x 3mm thick.

[0033] Example 1

[0034] The process of pretreatment of PA / PPO alloy parts includes the following steps:

[0035] Plasma activation treatment: Put the PA / PPO alloy parts into the plasma treatment cavity, and introduce Ar / O2 mixed gas (volume ratio 3:1, total flow rate 40sccm), control the cavity pressure to 20Pa, power 200W, and treat for 8min;

[0036] Chemical etching treatment: immerse the activated parts into a 10% H2SO4 solution by mass fraction, etch at 25℃ for 60s, etch out a groove with a depth of 20nm, and the average surface roughness Ra is 0.8μm;

[0037] Post-treatment cleaning: ultrasonic cleaning with deionized water for 12min to remove residual etching solution.

[0038] Spraying method, including the following steps:

[0039] Substrate preheating: preheat the pretreated PA / PPO alloy at 105℃ for 10min;

[0040] Electrostatic spraying: using electrostatic voltage 70 kV, atomization pressure 0.4 MPa, spray gun distance from substrate 250 mm, spraying at a speed of 400 mm / s, paint solid content 50%, spraying angle 45°;

[0041] Temperature control: substrate temperature maintained at 80°C during spraying, ambient humidity 50% RH;

[0042] Infrared-hot air combined curing: using a stepwise temperature program, the first stage from 25°C to 60°C, the heating rate 5°C / min, then maintaining for 10-15 min, the second stage from 60°C to 120°C, the heating rate 3°C / min, maintaining for 15 min, the third stage from 120°C to 180°C, the heating rate 2°C / min, maintaining for 20 min, infrared radiation wavelength 3 μm, hot air circulating air speed 2 m / s, oxygen content in the cavity during curing ≤3%, after natural cooling, coating thickness 50 μm, surface resistivity uniformity deviation 2%.

[0043] The pretreatment process and spraying method of the PA / PPO alloy parts of Examples 2-5 and Comparative Examples 1-3 are different from those of Example 1 in that the plasma activation treatment and / or chemical etching treatment and / or substrate preheating and / or electrostatic spraying, and the specific differences are shown in Table 1.

[0044] Table 1: Pretreatment process and spraying method parameters of Examples 2-5 and Comparative Examples 1-3

[0045]

[0046]

[0047]

[0048] After the pretreatment process of Examples 1-5 and Comparative Examples 1-3 is used to treat the PA / PPO alloy, the plasma activation treatment, chemical etching, post-treatment cleaning are carried out, the resistivity of the treated PA / PPO alloy parts is tested, then the PA / PPO alloy coating is prepared after spraying on the surface of the pretreated PA / PPO alloy parts, the coating thickness is 50 μm, the uniformity, adhesion, hardness, heat distortion temperature of the PA / PPO alloy coating are tested.

[0049] 1. Resistivity test: according to GB / T 1410-2006 "Test method for volume resistivity and surface resistivity of solid insulating materials", the surface resistivity of the PA / PPO alloy parts after surface treatment is tested.

[0050] 2. Electrostatic adsorption test: using adsorption force test method, the material to be tested is placed on the lower plate after cleaning and drying, a 10mm x 10mm x 50μm clean aluminum foil is placed on the center of the material surface; the upper plate is kept 10mm away from the material, 5kV high voltage is applied and kept for 10s, the material surface is charged and then disconnected; then the aluminum foil is in contact with the charged material and placed for 10s to ensure the adsorption force is stable; the material and aluminum foil are vertically separated at a speed of 1mm / s, and the force sensor records the maximum adsorption force (unit: mN) during separation; the same material is tested 3 times, and the average value of the maximum adsorption force is taken as the result.

[0051] 3. Coating uniformity test: according to GB / T 1743-1979 "Paint film gloss determination method", the coating surface defects are observed by visual observation, the observation is carried out under standard light source (D65, illumination 500-1000lux) at a distance of 500mm from the sample, and the following grade is scored: 5 grade: smooth surface, no visible defects; 4 grade: slight orange peel, defect area <5%; 3 grade: obvious orange peel, defect area 5-15%, evaluate the appearance uniformity.

[0052] 4. Adhesion test: according to ISO 2409 standard, the adhesion of the coating on the surface of the test piece is tested by grid method.

[0053] 5. Hardness test: according to GB / T 4340.1—2024 "Metallic materials Vickers hardness test Part 1: test method" for testing.

[0054] 6. Heat distortion temperature test: according to ASTM D648-19 "Determination of the heat distortion temperature of plastics under load", the ability of the PA / PPO alloy part material after surface treatment to resist heat distortion under 1.82MPa load is tested, the higher the temperature, the better the high temperature resistance.

[0055] Table 2: Test results

[0056]

[0057]

[0058] From the data in Table 2, it can be seen that the pretreatment process combining plasma activation and chemical etching can synergistically regulate the surface resistivity of PA / PPO alloy, and also significantly improve the electrostatic adsorption force, making the uniformity, adhesion, hardness and heat resistance of the coating significantly improved; in Example 4, the adsorption force is reduced due to the absence of electrostatic assistance in air spraying, but the pretreatment guarantees the basic performance; in Example 5, the performance such as thermal deformation temperature and Vickers hardness is reduced due to the slight adjustment of preheating temperature, which does not achieve the expected effect; in Comparative Example 1, no chemical etching treatment is performed, and in Comparative Example 2, no plasma activation treatment is performed, which leads to a performance decline due to insufficient pretreatment; in Comparative Example 3, the traditional degreasing process is used, and due to the inability to modify the surface, the performance does not meet the standards, which proves the necessity of the new pretreatment process.

[0059] The present application can also be embodied in other various embodiments without departing from the spirit and essence of the present application, and those skilled in the art can make various corresponding changes and modifications according to the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A PA / PPO alloy pretreatment process for electrostatic spray coating, characterized in that, The method comprises the following steps: Plasma The PA / PPO alloy surface is activated by a plasma gas, the plasma power is 100-300 W, and the treatment time is 5-15 min; The PA / PPO alloy activated by the plasma is immersed in a chemical etching solution for etching treatment, and the etching time is 30-120 s; Post-treatment cleaning: The surface of the etched PA / PPO alloy is cleaned by ultrasonic cleaning with deionized water, the cleaning time is 10-15 min, and the surface resistivity is controlled at 10 4 -10 6 Ω.m.

2. The PA / PPO alloy electrostatic spray pre-treatment process of claim 1 wherein, The plasma gas is selected from one or more of Ar, N2 and O2 mixed gas; in the plasma activation treatment, the total flow of the mixed gas is 30-50 sccm, and the treatment cavity pressure is 10-30 Pa.

3. The PA / PPO alloy electrostatic spray finishing pretreatment process according to claim 1, characterized in that, The chemical etching solution is a H2SO4 solution with a mass fraction of 5-15% or a NaOH solution with a mass fraction of 5-10%; after the chemical etching treatment, the alloy surface forms a nanoscale groove structure with a depth of 10-30 nm, and the surface roughness Ra is 0.5-1.2 μm.

4. An electrostatic spraying process based on the PA / PPO alloy according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: Substrate preheating: the pretreated PA / PPO alloy is preheated at 85-110 ℃ for 10-15 min; Electrostatic spraying: spraying is performed by using an electrostatic voltage of 65-75 kV and an atomization pressure of 0.35-0.45 MPa, and the coating solid content is 45-55%; Temperature control: during the spraying process, the substrate temperature is controlled to be 70-90 ℃, and the environmental humidity is 40-60% RH; Infrared-heat air combined curing: a stepwise temperature rising program is adopted, the first stage is from 25 ℃ to 60 ℃ at a rate of 5 ℃ / min, then kept for 10-15 min, the second stage is from 60 ℃ to 120 ℃ at a rate of 3 ℃ / min, kept for 15-20 min, the third stage is from 120 ℃ to 180 ℃ at a rate of 2 ℃ / min, kept for 20-30 min, and then naturally cooled to room temperature.

5. The PA / PPO alloy electrostatic spray process of claim 4 wherein, The substrate preheating temperature is adjusted according to the PA content in the PA / PPO alloy: when the PA mass content is 60-70%, the preheating temperature is 95-110 ℃; when the PA mass content is 71-75%, the preheating temperature is 85-95 ℃.

6. The PA / PPO alloy electrostatic spray process of claim 4 wherein, In the electrostatic spraying, the distance between the spray gun and the substrate is 200-300 mm, the spraying speed is 300-500 mm / s, and the spraying angle is 45°-90°.

7. The PA / PPO alloy electrostatic spray process of claim 4 wherein, In the infrared-heat air combined curing, the infrared radiation wavelength is 2-4 μm, the hot air circulating wind speed is 1-3 m / s, and the oxygen content in the cavity during the curing process is ≤5%.

8. The PA / PPO alloy electrostatic spray process of claim 4 wherein, The coating thickness after the spraying is 40-60 μm, and the surface resistivity uniformity deviation is ≤10%.

9. The PA / PPO alloy electrostatic spray process of claim 4 wherein, The raw materials of the PA / PPO alloy include, by mass percentage: 60-75% of PA nylon, 20-40% of maleic anhydride grafted PPO, 5-8% of PPS, 2-5% of nanometer carbon tube, and 0.1-1% of additives.

10. The PA / PPO alloy electrostatic spray process of claim 4 wherein, The PA nylon is PA6T or PA9T.

Images