Spraying process for plastic treatment and application

Abstract

The invention belongs to the technical field of coatings, and discloses a spraying process for plastic treatment and application, and the spraying process comprises the following steps: preparing a liquid coating; spraying a liquid coating on the surface of the to-be-treated plastic, and curing to complete the spraying process; the liquid coating is prepared from the following raw materials in parts by weight: 50 to 65 parts of modified polyurethane resin, 8 to 12 parts of modified silicon dioxide aerogel, 2 to 5 parts of silane coupling agent, 1 to 3 parts of polyamide wax, 4 to 6 parts of pigment, 0.5 to 2 parts of flatting agent, 0.3 to 1 part of defoaming agent and 20 to 30 parts of water. According to the spraying technology for plastic treatment, through collaborative optimization design of all components of the liquid coating and precise matching of technological parameters, the combination stability of the coating and a plastic base material can be remarkably improved, the coating is endowed with excellent comprehensive use performance, the smoothness of the spraying process and the uniformity of the film forming quality can be guaranteed, and the spraying quality is improved. And the treatment requirements of different types of plastic base materials are met.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a spraying process and application for plastic treatment. Background Technology

[0002] In the rapid development of the automotive industry towards lightweighting and intelligentization, plastic parts, with their advantages of light weight, high molding efficiency, and significant cost benefits, have been widely used in automotive interiors, exteriors, and various functional components, including key components such as dashboard housings, bumpers, sensor housings, and battery pack covers for new energy vehicles. However, the inherent low surface energy and weak polarity of plastic materials present a difficult technical bottleneck for coating adhesion, becoming a core issue restricting the performance improvement of automotive plastic parts. During long-term use, automotive plastic parts must continuously withstand complex conditions such as driving vibration, alternating high and low temperature cycles, outdoor weathering, humid interior environments, and oil contamination. The coatings used in existing spraying processes are difficult to form a stable interface bond with the plastic substrate, leading to coating failures such as peeling, flaking, and cracking. This not only damages the appearance integrity of automotive parts but also accelerates the wear and aging of the substrate, thereby affecting the functional stability of the parts and potentially impacting the overall safety of the vehicle.

[0003] To improve the bonding effect between coatings and plastic substrates, existing technologies often involve adding conventional modifiers or ordinary fillers. However, these solutions have significant limitations: modifiers have a singular interface adjustment effect, only improving the bonding state locally and failing to consider the synergistic effect between the coating and the substrate, as well as among the components within the coating; ordinary fillers are prone to agglomeration due to poor dispersibility, affecting the storage stability of the coating and leading to a decline in film quality, resulting in problems such as uneven surface and inconsistent mechanical properties. Meanwhile, automotive parts have extremely stringent requirements for the comprehensive performance of coatings, demanding not only reliable adhesion but also excellent weather resistance, mechanical toughness, and surface smoothness to meet the sealing requirements of automotive assembly, the process compatibility of mass production, and the durability requirements of long-term use. Existing spraying processes and matching coatings are insufficient to fully meet these diverse requirements. Especially with the increasing standards for environmental friendliness and durability of components in new energy vehicles, the limitations of traditional technologies are becoming increasingly prominent, severely restricting the performance upgrade and application expansion of automotive plastic parts. Summary of the Invention

[0004] The present invention aims to improve at least one technical problem in the prior art.

[0005] This invention provides a spraying process for plastic treatment, comprising the following steps: Preparation of liquid coatings; The liquid coating is sprayed onto the surface of the plastic to be treated and cured to complete the spraying process. The raw materials of the liquid coating, by weight, include: 50-65 parts of modified polyurethane resin, 8-12 parts of modified silica aerogel, 2-5 parts of silane coupling agent, 1-3 parts of polyamide wax, 4-6 parts of pigment, 0.5-2 parts of leveling agent, 0.3-1 parts of defoamer, and 20-30 parts of water. The prepolymer of the modified polyurethane resin is obtained by reacting petroleum-based polyol, lignin hydroxymethyl furfural resin and diisocyanate. The modified silica aerogel is obtained by coating and modifying silica aerogel with a first coating layer, which is obtained by cross-linking and curing a prepolymer of urea-formaldehyde resin.

[0006] The spraying process for plastic treatment provided in this application addresses the technical challenges of low surface polarity and poor coating adhesion in plastics through the synergistic effect of various components, while simultaneously endowing the coating with excellent comprehensive performance. Modified polyurethane resin serves as the base material for the coating, while petroleum-based polyols provide good flexibility and film-forming properties. Lignin-based hydroxymethylfurfural resin introduces a bio-based structure to enhance compatibility with other components. Diisocyanate constructs a stable molecular framework through cross-linking reactions. These three components together form the basic support of the coating, ensuring the continuity of resin film formation and laying the foundation for subsequent bonding with other components. Modified silica aerogel, after being coated with urea-formaldehyde resin, not only overcomes its tendency to agglomerate but also forms a physical interweaving and weak chemical interaction with the modified polyurethane resin. The porous structure of the aerogel enhances the coating's weather resistance and toughness, while the urea-formaldehyde resin coating strengthens the bond with the resin matrix. Together, they improve the structural stability and mechanical properties of the coating. Silane coupling agents, as key interface modifiers, can react with the active groups of modified polyurethane resin and the hydroxyl groups on the surface of modified silica aerogel on one end, and form chemical bonds with the active sites on the surface of plastic substrates on the other end. This establishes a stable chemical bridge between the components and the substrate, effectively solving the interfacial bonding problem between different substances and significantly improving the adhesion between the coating and the plastic. Polyamide wax, by adjusting the rheological properties of the coating, can prevent the sedimentation of modified silica aerogel and pigments during storage and application, and suppress sagging after spraying, ensuring uniform coating thickness. It provides a stable application and film-forming environment for other components to fully function, synergistically ensuring the storage stability and film quality of the coating with aerogel and pigments. Pigments not only impart the desired appearance and color to the coating, but their particles can also form a physical barrier within the coating. Combined with the porous structure of the aerogel, this further enhances the coating's resistance to the external environment. Leveling agents improve the spreadability of coatings on plastic surfaces, reduce defects such as pinholes and craters during film formation, and synergistically optimize film formation with polyamide wax, ensuring a smooth and even coating surface without affecting the bonding strength between components. Defoamers eliminate air bubbles generated during coating formulation and spraying, preventing them from solidifying and forming pores, thus ensuring coating density. Together with leveling agents, they enhance film quality, enabling modified polyurethane resin, aerogel, and other components to bond tightly to form a continuous and dense coating structure. Water, as a dispersion medium, provides a uniform mixing environment for all components, allowing for full contact and synergistic effects, ensuring suitable fluidity of the coating during application, guaranteeing smooth spraying and uniform coating. All components work together, each fulfilling its specific function, forming a complete synergistic system from base film formation, interfacial bonding, performance enhancement to application assurance. Ultimately, the sprayed plastic coating possesses strong adhesion, good mechanical properties, excellent weather resistance, and stable storage and application performance, meeting practical application requirements.

[0007] In some preferred embodiments, the mass ratio of the petroleum-based polyol, the lignin hydroxymethyl furfural resin, and the diisocyanate is (40-60):(20-30):(15-25).

[0008] In some preferred embodiments, the petroleum-based polyol is one of polypropylene carbonate diol, polypropylene oxide diol, polytetrahydrofuran diol, polyethylene adipate diol, and polybutylene adipate diol.

[0009] In some preferred embodiments, the mass ratio of the silica aerogel to the urea-formaldehyde resin prepolymer is 10:(4-6).

[0010] In some preferred embodiments, the silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane.

[0011] The preparation of the above-mentioned liquid coating includes the following steps: The modified polyurethane resin and the water were stirred and mixed at a speed of 800 r / min-1000 r / min to obtain mixture A; Add the modified silica aerogel and the pigment to the mixture A, and stir and mix at a speed of 1500 r / min-2000 r / min to obtain mixture B; The silane coupling agent, the polyamide wax, the leveling agent, and the defoamer are added to the mixture B, and stirred at a speed of 500 r / min-800 r / min to obtain the liquid coating.

[0012] In some preferred embodiments, the thickness of the liquid coating sprayed is 60μm-80μm.

[0013] In some preferred embodiments, the curing temperature is 80℃-100℃ and the time is 20min-30min.

[0014] In some preferred embodiments, the plastic to be treated is subjected to electrostatic dust removal before the liquid coating is sprayed.

[0015] The present invention also provides the application of the above-described spraying process for plastic treatment in the treatment of automotive plastic parts.

[0016] The beneficial effects of this invention are as follows: The spraying process for plastic treatment provided by this invention, through the synergistic optimization design of each component of the liquid coating and the precise matching of process parameters, not only significantly improves the bonding stability between the coating and the plastic substrate, giving the coating excellent comprehensive performance, but also ensures the smoothness of the spraying process and the uniformity of film quality, adapting to the treatment needs of different types of plastic substrates. Simultaneously, the introduction of bio-based components in the process embodies the concept of green and environmentally friendly development, reducing dependence on traditional petroleum-based raw materials, and aligning with the current trend of green transformation and upgrading in the industrial sector. Furthermore, this process has good compatibility for large-scale production, a simple and controllable operation process, and can be widely applied to surface treatment scenarios for various plastic parts, especially in the treatment of automotive plastic parts, where it can fully leverage its advantages to help improve product quality and service life, demonstrating significant technological innovation and industrial promotion value. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0018] Example 1 A spraying process for treating plastics includes the following steps: Preparation of liquid coatings; Electrostatic dust removal is performed on the plastic to be processed; The liquid coating (70 μm thick) is sprayed onto the surface of the plastic to be treated and cured (at a temperature of 90 °C for 25 min) to complete the spraying process.

[0019] The raw materials of the above-mentioned liquid coating, by weight, include: 58 parts modified polyurethane resin, 10 parts modified silica aerogel, 3 parts silane coupling agent (γ-aminopropyltriethoxysilane), 2 parts polyamide wax, 5 parts pigment, 1.2 parts leveling agent (BYK-333), 0.6 parts defoamer (BYK-094), and 25 parts deionized water.

[0020] The modified polyurethane resin prepolymer is obtained by reacting polypropylene carbonate diol (molecular weight 1200), lignin hydroxymethyl furfural resin (obtained by reacting alkali lignin (molecular weight 1500) and hydroxymethyl furfural in an alkaline solution (pH=9) at 80℃ for 4 hours) with diphenylmethane diisocyanate in a mass ratio of 50:25:20; the preparation of the modified polyurethane resin includes the following steps: under a nitrogen atmosphere Polypropylene carbonate diol was mixed with lignin-hydroxymethylfurfural resin, heated to 70°C and stirred for 30 min, then diphenylmethane diisocyanate was added and the reaction was continued for 2.5 h to obtain a prepolymer; the temperature was lowered to 45°C, a chain extender (2,2-dimethylolpropionic acid) was added and reacted for 1.5 h, then triethylamine was added to neutralize for 10 min, and finally deionized water was slowly added at 1800 r / min for 35 min to emulsify, followed by degassing under reduced pressure for 25 min to obtain modified polyurethane resin.

[0021] The modified silica aerogel is obtained by coating silica aerogel with a first coating layer, which is obtained by cross-linking and curing a urea-formaldehyde resin prepolymer. The mass ratio of silica aerogel to urea-formaldehyde resin prepolymer is 10:5. The preparation of modified silica aerogel includes the following steps: the silica aerogel is vacuum dried at 110℃ for 5h to remove adsorbed water, cooled and mixed with molten (85℃-95℃) urea-formaldehyde resin prepolymer in proportion, and then hydrochloric acid (the amount of hydrochloric acid is 0.8% of the sum of the mass of silica aerogel and urea-formaldehyde resin prepolymer) is added as a catalyst. The mixture is heated to 90℃ and stirred for 3h. After cooling to room temperature, it is pulverized (the particle size is controlled to be 5μm), washed 3 times with anhydrous ethanol, and dried at 95℃ for 6h to obtain modified silica aerogel.

[0022] The preparation of the above-mentioned liquid coating includes the following steps: The modified polyurethane resin and deionized water were mixed in a high-speed mixer at a speed of 900 r / min for 25 min to obtain mixture A. Add modified silica aerogel and pigment to mixture A, and stir at 1800 r / min for 45 min to obtain mixture B; Add silane coupling agent, polyamide wax, leveling agent and defoamer to mixture B, and stir at 650 r / min for 15 min to obtain liquid coating.

[0023] Example 2 A spraying process for treating plastics includes the following steps: Preparation of liquid coatings; Electrostatic dust removal is performed on the plastic to be processed; The liquid coating (60 μm thick) is sprayed onto the surface of the plastic to be treated and cured (at a temperature of 85°C for 28 min) to complete the spraying process.

[0024] The raw materials of the above-mentioned liquid coating, by weight, include: 55 parts modified polyurethane resin, 11 parts modified silica aerogel, 4 parts silane coupling agent (γ-glycidyl etheroxypropyltrimethoxysilane), 1.5 parts polyamide wax, 4.5 parts pigment, 1 part leveling agent (BYK-333), 0.8 parts defoamer (BYK-094), and 28 parts deionized water.

[0025] The modified polyurethane resin prepolymer is prepared by reacting polypropylene glycol (molecular weight 1000), lignin hydroxymethyl furfural resin (obtained by reacting alkali lignin (molecular weight 1500) and hydroxymethyl furfural in an alkaline solution (pH=9) at 80℃ for 4 hours) with diphenylmethane diisocyanate in a mass ratio of 45:28:22. The preparation of the modified polyurethane resin includes the following steps: under a nitrogen atmosphere, polypropylene glycol and lignin hydroxymethyl furfural resin are mixed, heated to 70℃ and stirred for 30 minutes, then diphenylmethane diisocyanate is added, and the reaction is continued for 2.5 hours to obtain the prepolymer. The temperature is lowered to 45℃, a chain extender (2,2-dimethylolpropionic acid) is added and reacted for 1.5 hours, then triethylamine is added for neutralization for 10 minutes, and finally deionized water is slowly added at 1800 r / min for emulsification for 35 minutes, followed by degassing under reduced pressure for 25 minutes to obtain the modified polyurethane resin.

[0026] The modified silica aerogel is obtained by coating silica aerogel with a first coating layer, which is obtained by cross-linking and curing a urea-formaldehyde resin prepolymer. The mass ratio of silica aerogel to urea-formaldehyde resin prepolymer is 10:4.5. The preparation of modified silica aerogel includes the following steps: the silica aerogel is vacuum dried at 110℃ for 5h to remove adsorbed water, cooled and mixed with molten (85℃-95℃) urea-formaldehyde resin prepolymer in proportion, and then hydrochloric acid (the amount of hydrochloric acid is 0.8% of the sum of the mass of silica aerogel and urea-formaldehyde resin prepolymer) is added as a catalyst. The mixture is heated to 90℃ and stirred for 3 hours. After cooling to room temperature, it is pulverized (the particle size is controlled to be 5μm), washed 3 times with anhydrous ethanol, and dried at 95℃ for 6h to obtain modified silica aerogel.

[0027] The preparation of the above-mentioned liquid coating includes the following steps: The modified polyurethane resin and deionized water were mixed in a high-speed mixer at a speed of 1000 r / min for 20 min to obtain mixture A. Add modified silica aerogel and pigment to mixture A, and stir at 2000 r / min for 40 min to obtain mixture B; Add silane coupling agent, polyamide wax, leveling agent and defoamer to mixture B, and stir at 600 r / min for 15 min to obtain liquid coating.

[0028] Comparative Example 1 A spraying process for plastic treatment differs from Example 1 in that the prepolymer of the modified polyurethane resin is obtained solely from the reaction of polypropylene carbonate diol and diphenylmethane diisocyanate in a mass ratio of 75:25. Everything else is the same as in Example 1.

[0029] Comparative Example 2 A spraying process for plastic treatment differs from Example 1 in that the modified silica aerogel is replaced with unmodified silica aerogel. Otherwise, it is the same as Example 1.

[0030] Comparative Example 3 A spraying process for plastic treatment differs from Example 1 in that the raw materials of the liquid coating do not contain silane coupling agents, and the weight of deionized water is adjusted to 28 parts. Everything else is the same as in Example 1.

[0031] Comparative Example 4 A spraying process for plastic treatment differs from Example 1 in that the modified silica aerogel is replaced with nano-silica (5 μm particle size). Everything else is the same as in Example 1.

[0032] Comparative Example 5 A spraying process for treating plastics differs from Example 1 in that the liquid coating does not contain polyamide wax. Otherwise, it is the same as Example 1.

[0033] According to the spraying processes of Examples 1-2 and Comparative Examples 1-5, the coatings formed on the plastics after the spraying process were tested. The test items and standards are as follows: Adhesion: Assess according to GB / T 9286-1998, and grade (0 is the best, 5 is the worst). Weather resistance: Tested according to GB / T 1865-2009, color difference ΔE was tested after xenon lamp aging for 1000h; Abrasion resistance: Tested according to GB / T 1768-2021, under the condition of 1000r / 500g, and the weight loss was recorded; Water resistance: Refer to GB / T 1733-1993. After immersing in boiling water for 24 hours, observe the appearance and evaluate the standard (no abnormality / whitening / wrinkling / peeling). Appearance flatness: Observed under a 10x magnifying glass, the evaluation criteria are (no shrinkage cavities, runs / slight shrinkage cavities / obvious runs and shrinkage cavities).

[0034] The test results are shown in Table 1.

[0035] Table 1 Referring to the data in Table 1, the prepolymer reaction raw materials of the modified polyurethane resin in Comparative Example 1 liquid coating did not contain lignin hydroxymethylfurfural resin, and the properties of its coating were significantly inferior to those of the Example. The Example, through the synergistic polymerization of lignin hydroxymethylfurfural resin with petroleum-based polyols and diisocyanates, formed a more stable polyurethane resin matrix, which not only resulted in a tighter bond between the coating and the plastic substrate but also improved overall weather resistance and abrasion resistance. In contrast, Comparative Example 1, lacking modification and optimization of the bio-based component (lignin hydroxymethylfurfural resin), suffered from insufficient compatibility between the resin and other components, leading to decreased adhesion, poorer weather resistance, and weakened abrasion resistance due to insufficient molecular structural support.

[0036] Comparative Example 2 used unmodified silica aerogel instead of modified silica aerogel, without urea-formaldehyde resin coating treatment, and its performance differed significantly from that of the examples. In the examples, the modified silica aerogel was coated with urea-formaldehyde resin, which improved its dispersibility and formed a stable physical interweaving and chemical interaction with the modified polyurethane resin, constructing a dense coating structure. In contrast, the unmodified aerogel in Comparative Example 2 was prone to agglomeration and had weak interfacial bonding with the resin matrix, which not only led to a significant decrease in adhesion but also resulted in insufficient coating density, slight whitening of water resistance, poor weather resistance, and significantly deteriorated wear resistance due to its loose structure.

[0037] In Comparative Example 3, no silane coupling agent was added to the liquid coating. In the example, the silane coupling agent acts as an interface bridge, connecting the modified polyurethane resin and the modified silica aerogel at one end and forming a chemical bond with the plastic substrate at the other end, thus achieving synergistic bonding between the components. However, due to the lack of this key interface modifier, the bonding force between the coating and the substrate, as well as between the components within the coating, was significantly weakened in Comparative Example 3. Not only was the adhesion level significantly reduced, but the integrity of the coating structure was also insufficient, and the weather resistance, abrasion resistance, and water resistance all deteriorated to varying degrees, exhibiting whitening and wrinkling phenomena.

[0038] In Comparative Example 4, ordinary nano-silica was used instead of modified silica aerogel. The modified silica aerogel in the example, thanks to the good compatibility between the urea-formaldehyde coating layer and the resin, as well as the performance enhancement brought by its own porous structure, synergistically improved the overall performance of the coating with other components. In contrast, the ordinary nano-silica in Comparative Example 4 was not coated and modified, had poor dispersibility and could not form an effective bond with the resin, resulting in many weak points in the coating. Consequently, the adhesion, weather resistance, abrasion resistance and water resistance were not as good as those in the example, and slight cratering and whitening occurred.

[0039] The liquid coating of Comparative Example 5, which did not contain polyamide wax, exhibited performance defects primarily in appearance smoothness and abrasion resistance, contrasting sharply with the superior performance of the Examples. The polyamide wax in the Examples effectively prevented sagging after spraying by adjusting the rheological properties of the coating, while also enhancing the stability of the coating structure and contributing to improved abrasion resistance. In contrast, Comparative Example 5, lacking the thickening and anti-sagging effects of polyamide wax, showed significant sagging defects after spraying, and the insufficient dispersion stability of the fillers within the coating resulted in a decrease in abrasion resistance. Although water resistance and weather resistance were not significantly affected, its overall performance was still inferior to that of the Examples.

[0040] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A spraying process for treating plastics, characterized in that, Includes the following steps: Preparation of liquid coatings; The liquid coating is sprayed onto the surface of the plastic to be treated and cured to complete the spraying process. The raw materials of the liquid coating, by weight, include: 50-65 parts of modified polyurethane resin, 8-12 parts of modified silica aerogel, 2-5 parts of silane coupling agent, 1-3 parts of polyamide wax, 4-6 parts of pigment, 0.5-2 parts of leveling agent, 0.3-1 parts of defoamer, and 20-30 parts of water. The prepolymer of the modified polyurethane resin is obtained by reacting petroleum-based polyol, lignin hydroxymethyl furfural resin and diisocyanate. The modified silica aerogel is obtained by coating and modifying silica aerogel with a first coating layer, which is obtained by cross-linking and curing a prepolymer of urea-formaldehyde resin.

2. The spraying process for plastic treatment according to claim 1, characterized in that, The mass ratio of the petroleum-based polyol, the lignin hydroxymethyl furfural resin and the diisocyanate is (40-60):(20-30):(15-25).

3. The spraying process for plastic treatment according to claim 1, characterized in that, The petroleum-based polyol is one of polypropylene carbonate diol, polypropylene oxide diol, polytetrahydrofuran diol, polyethylene adipate diol, and polybutylene adipate diol.

4. The spraying process for plastic treatment according to claim 1, characterized in that, The mass ratio of the silica aerogel to the urea-formaldehyde resin prepolymer is 10:(4-6).

5. The spraying process for plastic treatment according to claim 1, characterized in that, The silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane.

6. The spraying process for plastic treatment according to claim 1, characterized in that, The preparation of the liquid coating includes the following steps: The modified polyurethane resin and the water were stirred and mixed at a speed of 800 r / min-1000 r / min to obtain mixture A; Add the modified silica aerogel and the pigment to the mixture A, and stir and mix at a speed of 1500 r / min-2000 r / min to obtain mixture B; The silane coupling agent, the polyamide wax, the leveling agent, and the defoamer are added to the mixture B, and stirred at a speed of 500 r / min-800 r / min to obtain the liquid coating.

7. The spraying process for plastic treatment according to claim 1, characterized in that, The thickness of the liquid coating sprayed is 60μm-80μm.

8. The spraying process for plastic treatment according to claim 1, characterized in that, The curing temperature is 80℃-100℃, and the time is 20min-30min.

9. The spraying process for plastic treatment according to claim 1, characterized in that, Before spraying the liquid coating, the plastic to be treated is subjected to electrostatic dust removal.

10. The application of the spraying process for plastic treatment as described in any one of claims 1-9 in the treatment of automotive plastic parts.

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