Digital printing process suitable for real wood surface of automotive trim

Abstract

The invention belongs to the field of automobile interior manufacturing, and discloses an automobile interior real wood surface digital printing process which comprises the following steps: S1, preparing a base material: selecting a wood veneer of 0.3-0.6 mm, cutting the wood veneer, polishing, spraying water for humidifying and mechanically leveling; the surface of the wood veneer is colored and sprayed with a transparent resin protection layer, then the surface of the protection layer is treated through a plasma surface treatment technology, and the surface energy and the chemical activity of the protection layer are improved; s3, digital printing: coating the surface of the treated protective layer with a bottom coating liquid, printing a pattern by using digital jet printing equipment, and then carrying out UV curing; s4, interior trim part forming, wherein the printed and cured wood veneer is attached to the automobile interior trim plastic base material at the temperature of 55-60 DEG C; and S5, surface layer protection: applying transparent protective finish paint on the surface of the laminated product. The process can solve the problems that the printing definition of an ink layer on the real wood surface of the existing automotive trim is low, and the ink layer is easy to peel, wrinkle and bloom in the processing or using process.

Description

Technical Field

[0001] This invention relates to the field of automotive interior manufacturing, and more particularly to a digital printing process suitable for real wood surfaces in automotive interiors. Background Technology

[0002] Real wood interior trim, with its natural and unique texture and luxurious feel, is widely used in mid-to-high-end automotive interiors. To meet the market demand for personalized interior customization, digital printing technology has been introduced into the surface decoration of real wood trim. Chinese patent application CN115990928A discloses a digital spraying finish for fully enclosed wood veneer wrapping. This process primarily addresses the problems of cracking and insufficient flexibility in 15-30mm thick wood veneer during the wrapping process. This technical solution fundamentally alters the physical properties of the wood veneer through complex chemical softening liquid immersion and hot-press penetration of self-healing shape memory polymer emulsion, forming a flexible protective layer with interconnected inner and outer layers, upon which digital printing is then performed.

[0003] However, when this process is directly applied to ultra-thin genuine wood veneer with a thickness of 0.3-0.6mm for automotive interiors, the following defects will exist: 1. Ultra-thin wood veneer itself already has sufficient flexibility and plasticity. Its technical bottleneck is not "crack resistance", but how to build a printing functional layer that can produce super strong adhesion to ink and withstand the extreme environment of automotive interiors on an extremely limited thickness. The complex chemical impregnation and overall modification scheme of CN115990928A may damage the inherent fiber structure of ultrathin wood veneer due to strong chemical reagents and high-pressure hot pressing processes, leading to reduced strength or deformation, and introducing the risk of excessive VOCs. 2. The protective layer of CN115990928A is essentially an inert, physically closed polymer layer. The resulting printing substrate has low surface energy and strong chemical inertness, making it unable to effectively bond and wet the ink. This results in weak interlayer adhesion. During the subsequent heat processing necessary for automotive interiors and in the simulated high temperature, cold, and humid aging environment, the printing ink layer is very easy to peel off, wrinkle, or bleed from the inert polymer substrate, resulting in an extremely low yield. It completely fails to meet the automotive industry's durability standards for parts that last for several years or even more than ten years. Summary of the Invention

[0004] This invention addresses the technical problems of ink layer peeling, wrinkling, and smudging in existing digital spraying technology for automotive interior wood trim, and proposes a digital printing process suitable for automotive interior wood surfaces.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A digital printing process suitable for real wood surfaces in automotive interiors includes the following steps: S1 Substrate Preparation: Select wood veneer with a thickness of 0.3-0.6mm, and perform cutting, sanding, water spraying for moisture conditioning and mechanical smoothing treatment on the wood veneer; S2 printing base surface construction: S21 Coloring and Protection: The wood veneer surface is painted and colored after it has been smoothed. After the paint dries, a transparent resin protective layer is sprayed onto the surface. S22 Surface activation: The surface of the resin protective layer is subjected to plasma treatment to clean and activate its surface; S3 Digital Printing: S31 Primer: Apply a primer liquid to the surface of the protective layer after plasma treatment; S32 Printing and Curing: Print a pattern on the primer using a digital inkjet printer and then UV cure it; S4 interior trim molding: The printed and cured wood veneer is bonded to the automotive interior plastic substrate at a temperature of ≤65℃; S5 Topcoat Protection: Apply a transparent protective topcoat to the surface of the bonded product.

[0006] Using the above-mentioned scheme, this process fundamentally eliminates structural damage to ultra-thin wood veneer. It replaces the "softening solution soaking" with strong chemical reagents in existing technologies with a gentle "water spraying and mechanical leveling" method, and replaces high-temperature, high-pressure hot-pressing penetration with "low-temperature bonding" at ≤65℃, thus significantly reducing the risk of damage to wood veneer fiber strength, deformation, and VOCs exceeding standards. Next, it first sprays paint to seal the veneer pores during the coloring process, then sprays a protective layer to prevent ink penetration, followed by plasma surface activation. This achieves surface cleaning while significantly improving the micro-roughness and chemical activity of the protective layer surface. Then, the primer and the activated protective layer surface form a strong bond through both physical and chemical bonding. Next, UV curing further strengthens the chemical bond between the ink and the primer, ensuring the stability of the printed layer and solving the problems of easy ink peeling and wrinkling in traditional processes. Then, low-temperature bonding avoids high-temperature damage to the bonding structure between the ink and the substrate. Finally, a double-layer protective topcoat locks in the pattern and wood veneer texture, resulting in a finished product that can withstand temperatures down to -40℃. Even in extreme environments up to 80℃, it remains free from delamination and cracking, with ink adhesion reaching GT0 level, while simultaneously meeting the requirements for personalized printing and long-term durability of automotive interiors.

[0007] Preferably, in S1, the specific process of mechanical leveling is to place the wood veneer in a flat template and press it with a cylinder for 3.5-4.5 hours.

[0008] The above-mentioned method provides a lasting and stable physical shaping for ultra-thin wood veneers. Compared with the chemical softening method of the comparative patent, it can not only effectively eliminate the internal stress of the wood veneer and prevent rebound and deformation during subsequent processing, but also avoid the risk of damage to the wood veneer fiber structure caused by chemical treatment.

[0009] Preferably, in S21, the amount of paint applied is 31-39 g / m²; the resin protective layer is an acrylic resin protective layer with a thickness of 20-40 μm.

[0010] Using the above method, after the paint is sprayed, the pores of the wood veneer will be sealed, and after the protective layer is sprayed, a printing base with moderate thickness and stable performance will be formed.

[0011] Preferably, in S22, the plasma surface treatment technology is implemented using an atmospheric low-temperature plasma treatment machine with a plasma power of 800-1000W, using compressed dry air as the gas, and a processing speed of 30-40mm / s.

[0012] Using the above-mentioned method, compressed dry air is ionized in plasma, generating a variety of highly active particles including oxygen ions, nitrogen ions, electrons, and excited-state molecules. These active particles treat the protective layer surface through a dual action of physical bombardment and chemical modification: on the one hand, the impact of high-energy particles effectively removes surface oil and weak boundary layers, and forms microscopic pits through physical sputtering, increasing the surface area; on the other hand, and more importantly, active oxygen and other particles undergo a controllable and moderate oxidation reaction with polymer molecules on the protective layer surface, introducing a large number of oxygen-containing polar functional groups (such as hydroxyl and carboxyl groups) onto its surface, thereby significantly improving the chemical activity and surface energy of the protective layer surface. The combination of 800-1000W power and 0.2Mpa air pressure parameters used in this invention can precisely control the intensity of the process, ensuring effective cleaning, roughening, and activation while avoiding degradation of the protective layer or damage to the underlying wood veneer fiber structure due to over-treatment. This combination of physical and chemical modification provides excellent spreadability for the subsequent primer and creates a strong chemical bonding foundation, which is key to achieving ultra-high ink adhesion.

[0013] Preferably, in S31, the amount of the primer is 14-18 ml / m².

[0014] Using the above scheme, the above coating amount setting can ensure that the primer liquid uniformly covers the surface of the protective layer, filling the micro-pits etched by plasma without causing sagging due to excessive amount; the primer liquid formula can moderately wet the activated surface of the protective layer, helping the acrylic resin molecules to fully contact the polar functional groups on the surface of the protective layer, and undergo hydrogen bonding and esterification reactions. At the same time, the acrylic resin and the upper ink material are homologous, and the chemical bonding can be further enhanced through molecular compatibility, so that the bonding between ink and substrate is upgraded from "single physical interlocking" to "physical interlocking plus chemical adsorption" dual bonding. After high temperature testing, the ink still did not fall off, and the adhesion reached the GTO level.

[0015] Preferably, in step S32, the printing resolution of the digital inkjet printing equipment is 720×900 DPI; and the curing energy of the UV curing is 1800-2200 mJ / cm². 2 .

[0016] Using the above method, high resolution ensures the color richness and clarity of the printed pattern; appropriate UV curing energy ensures that the ink can be fully and quickly cured, forming a tough pattern layer.

[0017] As a preferred option, in S4, a vacuum airbag hot-pressing device is used for bonding, with a bonding pressure of 0.22-0.24 MPa and a pressure holding time of 8-10 minutes.

[0018] By adopting the above scheme, the vacuum airbag can better adapt to complex curved surfaces and ensure uniform pressure; the combined parameters can enable the wood veneer and plastic substrate to achieve full, tight and wrinkle-free bonding under relatively mild conditions, effectively preventing delamination.

[0019] Preferably, in step S4, the bonding temperature is 55-60°C.

[0020] Preferably, in S5, the transparent protective topcoat covers two layers, with each layer having a thickness of 15-20 μm.

[0021] Compared to single-layer thick coating, the above solution can produce a more uniform, denser protective film with lower internal stress, providing superior scratch resistance, UV resistance, and chemical corrosion resistance, ensuring that the pattern and wood veneer maintain their beauty during long-term use.

[0022] Preferably, in S4, the automotive interior plastic substrate is an ABS plastic substrate or a PC / ABS alloy plastic substrate.

[0023] This invention, by employing the above technical solutions, achieves significant technical effects: Firstly, this process fundamentally eliminates structural damage to ultra-thin wood veneer. It replaces the "softening solution soaking" with strong chemical reagents in existing technologies by using gentle "water spraying for humidification and mechanical leveling," and replaces high-temperature hot-pressing penetration with "low-temperature bonding" at 55-60℃. This significantly reduces damage to the wood veneer fiber strength, deformation, and VOCs. The risk of exceeding limits is addressed by employing coloring, a protective layer, and plasma treatment. First, the pores of the wood veneer are physically filled to prevent ink penetration. Then, surface activation is achieved through plasma, significantly improving the micro-roughness and chemical activity of the protective layer while cleaning the surface. Next, the primer and the activated protective layer surface form a strong bond through a combination of physical and chemical bonding. Following this, UV curing further strengthens the chemical bond between the ink and the primer, ensuring the stability of the printed layer and resolving the issues of easy ink peeling and wrinkling common in traditional processes. Next, low-temperature bonding is used to avoid high-temperature damage to the bonding structure between the ink and the substrate. Finally, a double-layer protective topcoat locks in the pattern and wood veneer texture. The resulting product remains free of delamination and cracking even in extreme environments ranging from -40℃ to 80℃, achieving GT0-level ink adhesion, while simultaneously meeting the requirements for personalized printing and long-term durability in automotive interiors. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of a digital printing process applicable to the real wood surface of automotive interiors according to the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0026] This embodiment provides a digital printing process suitable for real wood surfaces in automotive interiors. The specific steps and performance verification are as follows: S1. Substrate Preparation Select white ash veneer with a thickness of 0.5±0.05mm, or other suitable wood species such as maple. Use a fully automatic cutting machine to cut the veneer, and use a fully automatic sander to sand it to remove surface burrs and knots. Then use a high-pressure sprayer to evenly spray water on the surface of the veneer to adjust the humidity, until there is no water accumulation on the surface of the veneer.

[0027] The conditioned wood veneer is placed in a flat template and pressed with a cylinder for 4 hours to achieve a smoothing process. This step eliminates internal stress in the wood veneer through a purely physical method, avoiding damage to the fiber structure caused by chemical treatments. At the same time, it ensures that the substrate surface is flat and uniform, providing a stable foundation for subsequent pore sealing, coating adhesion, and pattern printing.

[0028] S2. Substrate Pretreatment S21 Coloring and Protection The smoothed wood veneer was sprayed with colored paint using a spray gun, with the spraying amount controlled at 35g / ㎡. After spraying, the wood veneer was placed in an environment of 25-35℃ for 8 hours to allow the paint to fully cure.

[0029] A transparent acrylic resin protective layer was sprayed onto the paint surface using a spray gun and then stored in an environment of 25-35℃ for 14 hours, eventually forming a transparent protective layer with a thickness of 32μm. Visual inspection showed that the protective layer surface was free of defects such as drips, pinholes, and bubbles.

[0030] This step involves coloring the wood veneer with paint. During the coloring process, the paint fills the pores of the wood veneer, preventing subsequent ink penetration and spread. At the same time, the transparent acrylic resin protective layer protects the natural texture of the wood veneer from damage and provides a structurally stable and uniform substrate for plasma treatment and ink adhesion.

[0031] S22 Plasma Surface Modification The surface of the acrylic resin protective layer is treated using plasma treatment equipment. Equipment parameters include: plasma power 900W, processing speed 35mm / s, compressed dry air (CDA) gas type, gas pressure 0.2Mpa, and processing height 8mm. During the treatment process, the power output and processing speed can be set to ensure no damage to the veneer surface.

[0032] This treatment combines physical bombardment with chemical activation, which effectively enhances the surface chemical activity of the protective layer while cleaning the surface and increasing its micro-roughness, thus providing an excellent bonding foundation for the subsequent primer.

[0033] S3. Digital Printing S31 Primer Coating A primer was applied to the surface of the protective layer after plasma treatment. The primer used was Marlebo, model P5, and the application rate was controlled at 16 ml / ㎡. The wood veneer coated with the primer was placed in a natural environment to dry. When the ambient temperature was 30℃, the drying time was only 5 minutes. When the temperature was below 20℃, the drying time was extended to 15-30 minutes. After drying, the primer surface was inspected by visual and tactile means, and there were no drips, bubbles, or stickiness. The surface was stable.

[0034] S32 Pattern Printing and Curing A high-precision printer with a resolution of 720×900 DPI was used, employing MARBAO UV printing ink (model DUV-DLE-MF_PI_GB_0519) to print a pre-set customized pattern onto the base coat surface. During the printing process, a visual recognition function was activated to intelligently align the pattern according to the actual shape of the wood veneer, ensuring no pattern offset. Testing showed that the deviation between the pattern edge and the pre-set position was ≤0.1mm, meeting the precision requirements for automotive interior decoration.

[0035] The printed pattern is cured using a UV-LED lamp. Parameter settings: curing energy 2000 mJ / cm². 2 The lamp spacing is 20mm, and the curing time is 30 seconds. After curing, the ink layer surface is not sticky or wrinkled, forming a stable pattern layer.

[0036] UV instant curing technology can quickly lock in ink components, preventing ink diffusion and smudging, while enhancing the chemical bond between ink molecules and the base layer, significantly improving the abrasion resistance and stability of the pattern layer.

[0037] S4. Adhesion process A vacuum airbag thermoforming machine (model TM2680DA) was used to align the printed wood veneer with the complex curved plastic substrate. The process parameters were set as follows: pressure 0.23 MPa, temperature 60℃, and holding time 10 minutes. The machine was then started to complete the bonding process. After bonding, the sample showed no wrinkles or delamination, and the wood veneer and plastic substrate were tightly bonded.

[0038] Vacuum airbag hot pressing technology can be adapted to complex curved substrates. The low-temperature bonding process ensures that the ink layer does not peel off or wrinkle, and the uniform pressure makes the wood veneer bond more firmly to the substrate.

[0039] S5. Surface Protection and Performance Testing Two layers of transparent acrylic resin varnish are applied to the surface of the printed pattern after lamination, with the thickness of each varnish layer controlled at 15-20μm. The sample is then placed in an environment of 25-35℃ for 15 hours to form a scratch-resistant and UV-resistant protective layer.

[0040] Compared to a single-layer thick coating, a double-layer thin-coat clear varnish produces a more uniform coating and reduces internal stress.

[0041] To verify the performance of the finished product, multiple tests were conducted on the sample, and the results are shown in the table below: Table 1: Environmental adaptability and reliability test results Experimental Project Test Standards Test conditions Technical Requirements Experimental results Heat-resistant storage TL52321-2016 80°C, 48h No delamination, no obvious visible changes on the product surface; grid cutting: Gt0-1 No obvious visible changes were observed on the product surface. GT0-1 Low temperature resistance TL52321-2016 -40°C, 48h No defects such as deformation, delamination, or cracking; color and gloss remain unchanged. No obvious visible changes Climate change experiment PV1200 8 cycles No deformation, delamination, or cracking; no change in color or gloss. No defects; stable color Condensate constant temperature test TL52321-2016 40°C, 100%RH, 48h It exhibits no defects such as deformation, delamination, or cracking, maintains consistent color and gloss, and meets the coating mesh cutting requirements (Gt0-1). No obvious visible changes were observed on the product surface. GT0-1 Ink adhesion test TL52321-2016 Stroke pattern (1mm spacing) No ink peeling, adhesion rating ≥GT1 No shedding, grade GT0 Scratch resistance ISO15184-2017 500g load, rubbed with steel wool 10 times No obvious scratches on the surface No visible scratches, and no significant change in gloss. As shown in Table 1, the samples prepared by this process did not exhibit defects such as delamination, cracking, or wrinkling after high-temperature, low-temperature, humid-heat, and harsh climate alternation tests, and the ink adhesion reached the highest GTO level. This fully demonstrates that the printing substrate formed by the combination of plasma treatment and primer coating, combined with the low-temperature bonding process, can solve the technical problems of easy ink layer peeling and wrinkling in traditional processes, and meet the stringent requirements of automotive interior materials for long-term reliability.

[0042] Table 2: Surface Properties and Functional Test Results Experimental Project Test Standards method Technical Requirements Experimental results Color difference stability test GB / T 11186.3-2009 D65 light source, 10° viewing angle After heat resistance / low temperature resistance / climate alternation, ΔE ≤ 1.5 ΔE≤1.2 Gloss test GB / T 9754-2007 60° angle of incidence Initial gloss deviation ≤ 5 GU; post-weathering deviation ≤ 8 GU Deviation ≤ 3GU Scratch resistance test ISO 15184-2017 500g load, 10 cycles of steel wool friction No obvious scratches after scratching; gloss change ≤10%. No visible scratches, variation ≤5% Xenon lamp aging test PV 1303 5 cycles No visible change compared to the original state; gray registration level ≥ 4. No significant change, level 4-5 Table 2 shows that the color difference ΔE of the printed patterns on the decorative parts treated with this process is far superior to the standard requirements after weather resistance testing, demonstrating excellent color stability. Meanwhile, the excellent scratch resistance and UV resistance ensure that the products maintain their exquisite appearance and feel even after long-term use.

[0043] The test results above show that the sample in this embodiment meets and exceeds the technical requirements of automotive interior parts in terms of environmental adaptability, ink adhesion, and surface durability.

[0044] The fact that it remained defect-free under various extreme environments demonstrates that the combination of paint and protective layer effectively improved the stability of the wood veneer, and that the low-temperature bonding process ensured the integrity of the ink layer.

[0045] The ink adhesion reached GT0 level, indicating that the combination of plasma treatment and primer coating can achieve super strong interlayer adhesion.

[0046] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A digital printing process suitable for real wood surfaces in automotive interiors, characterized in that, Includes the following steps: S1 Substrate Preparation: Select wood veneer with a thickness of 0.3-0.6mm, and perform cutting, sanding, water spraying for moisture conditioning and mechanical smoothing treatment on the wood veneer; S2 printing base surface construction: S21 Coloring and Protection: The wood veneer surface is painted and colored, and after the paint dries, a transparent resin protective layer is sprayed on the surface. S22 Surface activation: The surface of the resin protective layer is subjected to plasma treatment to clean and activate its surface; S3 Digital Printing: S31 Primer: Apply a primer liquid to the surface of the protective layer after plasma treatment; S32 Printing and Curing: Print a pattern on the primer using a digital inkjet printer and then UV cure it; S4 interior trim molding: The printed and cured wood veneer is bonded to the automotive interior plastic substrate at a temperature of ≤65℃; S5 Topcoat Protection: Apply a transparent protective topcoat to the surface of the bonded product.

2. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S1, the specific process of mechanical leveling is to place the wood veneer in a flat template and press it with a cylinder for 3.5-4.5 hours.

3. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S21, the amount of paint applied is 31-39 g / m²; the resin protective layer is an acrylic resin protective layer with a thickness of 20-40 μm.

4. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S22, the plasma surface treatment technology is implemented using an atmospheric low-temperature plasma treatment machine with a plasma power of 800-1000W, using compressed dry air as the gas, and a processing speed of 30-40mm / s.

5. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S31, the amount of the primer is 14-18 ml / m².

6. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S32, the printing resolution of the digital inkjet printing equipment is 720×900 DPI; the curing energy of the UV curing is 1800-2200 mJ / cm². 2 .

7. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S4, a vacuum airbag hot-pressing device is used for bonding, with a bonding pressure of 0.22-0.24 MPa and a pressure holding time of 8-10 minutes.

8. The digital printing process for automotive interior wood surfaces according to claim 7, characterized in that: In S4, the bonding temperature is 55-60℃.

9. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S5, the transparent protective topcoat covers two layers, with each layer having a thickness of 15-20 μm.

10. The digital printing process for automotive interior wood surfaces according to claim 1, characterized in that: In S4, the automotive interior plastic substrate is an ABS plastic substrate or a PC / ABS alloy plastic substrate.

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