Local pre-curing and gradient curing transfer printing method for multi-layer texture of shell

Abstract

The invention discloses a local pre-curing and gradient curing transfer printing method for shell multi-layer textures, which comprises the following steps: a base material pretreatment step: carrying out differentiation treatment according to the material of a base material, and sequentially carrying out degreasing, plasma activation, primer coating and curing on the metal base material; preparing a multi-layer composite transfer printing film; a local UV pre-curing step: selecting a corresponding type of mask to be attached to the surface of the strippable UV texture layer; a vacuum laminating step: laminating a transfer printing film with the pretreated base material; a vacuum hot-pressing compounding step: setting corresponding temperature, pressure and time parameters according to the type of the base material, and performing hot-pressing compounding; a stripping and gradient curing step: stripping the uncured areas of the base film and the strippable UV texture layer, and performing gradient curing in two stages of high-temperature deep curing; and a surface strengthening step: carrying out wear-resistant coating spraying and curing on the cured texture layer. Accurate transfer printing can be achieved, and wear resistance and stripping resistance are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of transfer printing, in particular to a local pre-curing and gradient curing transfer printing method for multi-layer textures of a shell. BACKGROUND

[0002] The market competition of 3C consumer electronics products is intensifying, and the differentiation decoration and functional requirements of the surface of the product shell are becoming more and more prominent. Among them, the UV transfer printing technology has become the mainstream scheme for decorating the surface of the shell due to its high texture restoration degree and high molding efficiency. However, the existing UV transfer printing technology still has some limitations. For example, the traditional process relies on roller pressing, which is only suitable for flat or simple regular substrates, and is difficult to adapt to precise transfer printing of curved surfaces, special shapes and already molded shells; when transferring local textures, the UV glue flowability is out of control, which can cause pattern deformation and edge overflow, and an additional edge cutting process is required, which can easily damage the shell; in multi-layer texture transfer printing, the stability of each layer is insufficient, and delamination and peeling can easily occur, and the wear resistance and weather resistance cannot meet the long-term use requirements. These defects limit its application in multi-layer texture decoration of complex curved shell, and cannot meet the high-quality requirements of market for appearance personalization, structural stability and service life of products. SUMMARY

[0003] The present application relates to the technical field of transfer printing, in particular to a local pre-curing and gradient curing transfer printing method for multi-layer textures of a shell.

[0004] To solve the above problems, the present application provides a local pre-curing and gradient curing transfer printing method for multi-layer textures of a shell. In order to achieve the above purpose, the technical scheme adopted by the present application to solve its technical problems is: A method for local pre-curing and gradient curing transfer of multi-layer textured shells includes: a substrate pretreatment step: differentiated treatment according to the substrate material, with metal substrates sequentially undergoing degreasing, plasma activation, primer coating, and curing; plastic substrates sequentially undergoing plasma activation, primer coating, and curing; and composite substrates undergoing zoned pretreatment followed by dehydration; a multi-layer composite transfer film preparation step: preparing a composite transfer film comprising, from top to bottom, a base film layer, a peelable UV texture layer, a release layer, a non-peelable UV texture layer, a functional interlayer, an electroplated reflective layer, a local adhesive layer, and a protective film layer; and a local UV pre-curing step: selecting a corresponding type... The mask is bonded to the surface of the peelable UV texture layer, and local pre-curing is performed using an LED-UV light source; Vacuum bonding step: The transfer film is bonded to the pre-treated substrate, and vacuuming and pressurizing are used to ensure that the transfer film and the curved surface of the substrate are completely bonded; Vacuum hot pressing bonding step: In a vacuum environment, hot pressing bonding is performed according to the corresponding temperature, pressure and time parameters set according to the substrate type; Peeling and gradient curing step: The uncured areas of the base film and the peelable UV texture layer are peeled off, and gradient curing is performed in two stages: low-temperature pre-curing and high-temperature deep curing; Surface strengthening step: A wear-resistant coating is sprayed and cured on the cured texture layer, and then the edges are trimmed.

[0005] As a further improvement of the present invention, the substrate is a metal substrate, a plastic substrate, or a metal-plastic composite substrate; the metal substrate includes aluminum, magnesium alloy, and aluminum-magnesium alloy, and plasma activation uses a mixture of argon and oxygen in a volume ratio of 3:1, with a processing power of 300W-500W and a time of 60 to 90 seconds; the plastic substrate includes PC, ABS, PMMA, and PC-PMMA composite materials, and plasma activation uses nitrogen, with a processing power of 200W-300W and a time of 40 to 60 seconds.

[0006] As a further improvement of the present invention, in the preparation step of the multilayer composite transfer film, the base film layer is a PET film with a thickness of 80μm-150μm; the peelable UV texture layer has a thickness of 5μm-15μm and a surface roughness ≤0.05μm; the non-peelable UV texture layer has a thickness of 5μm-15μm and is formed by imprinting with an impression roller; the partial adhesive layer is printed with an anilox roller with a thickness of 2μm-10μm and is coated only in the target area.

[0007] As a further improvement of the present invention, in the local UV pre-curing step, the mask is a stainless steel laser-cut mask or a quartz glass photolithography mask; the LED-UV light source wavelength is 365nm, the pre-curing energy is 600mJ / cm²-800mJ / cm², the time is 8 to 12 seconds, the degree of curing is controlled at 60%-70%, and the hardness of the cured area is ≥2H.

[0008] As a further improvement of the present application, the vacuum lamination step uses a profiling jig with exhaust grooves, vacuum extraction to a vacuum degree of ≤-0.09 MPa, holding for 10-15 seconds, then pressurization to form a pressure difference of 0.1-0.2 MPa, lamination time of 15-20 seconds.

[0009] As a further improvement of the present application, in the vacuum hot-pressing composite, the hot-pressing temperature of the metal substrate is 130-160°C, the pressure is 0.5-0.8 MPa, and the time is 60-90 seconds; the hot-pressing temperature of the plastic substrate is 100-130°C, the pressure is 0.3-0.5 MPa, and the time is 40-60 seconds; the hot-pressing temperature of the metal-plastic composite substrate is 120-140°C, the pressure is 0.4-0.6 MPa, and the time is 50-70 seconds.

[0010] As a further improvement of the present application, in the peeling and gradient curing step, the low-temperature pre-curing temperature is 70-80°C, a LED-UV light source with a wavelength of 365 nm is used, and the curing time is 20-25 seconds; the high-temperature deep-curing temperature is 90-110°C, a LED-UV light source with a wavelength of 385 nm is used, and the curing time is 30-35 seconds.

[0011] As a further improvement of the present application, in the surface strengthening step, the wear-resistant coating is a nano-silicon oxide coating or a UV-curable wear-resistant coating, and the coating thickness is 2-5 μm; the nano-silicon oxide coating is cured by baking at 80°C for 15-20 minutes, and the UV-curable wear-resistant coating is cured by a LED-UV light source with a wavelength of 365 nm and an energy of 1200-1500 mJ / cm² for 15-20 seconds.

[0012] As a further improvement of the present application, in the multi-layer composite transfer film, the functional interlayer is a nano-silicon coating or a polyurethane elastomer, and the thickness is 2-5 μm; the electroplated reflective layer is silicon oxide or aluminum-zinc alloy, and the thickness is 100-200 nm; the local adhesive layer is a polyurethane acrylate adhesive, and the solid content is 40-50%.

[0013] As a further improvement of the present application, the multi-layer texture includes one or more combinations of CD texture, dynamic optical texture, carbon fiber texture, and AG texture.

[0014] The beneficial technical effects of the local pre-curing and gradient curing transfer method for the multi-layer textured shell of the present application are: By implementing differential pretreatment on different material substrates, combining vacuum lamination and vacuum hot-pressing composite processes, the curved surface, irregularly shaped, and formed shells of metal, plastic, and composite materials can be effectively adapted. It breaks through the limitation of traditional transfer technology which is only applicable to flat or simply regular substrates, and widens the application range of transfer technology.

[0015] By means of local UV pre-curing and local adhesive layer design of multi-layer composite transfer film, the texture transfer area can be accurately controlled, pattern deformation and edge overflow caused by un-cured UV glue flow can be avoided, no additional edge cutting process is needed, both the accuracy of local texture transfer and the edge damage of the shell are avoided.

[0016] Finally, by means of staged gradient curing and surface strengthening treatment, the full cross-linking and bonding of each texture layer and the texture layer and the substrate are promoted, and the wear resistance of the texture layer is improved, effectively solving the problems of easy delamination and peeling in multi-layer texture transfer, prolonging the service life of the transferred decoration and ensuring the structural stability of the product. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating any inventive labor.

[0018] Figure 1 is a flow chart of an embodiment of the present application. DETAILED DESCRIPTION

[0019] The content of the present application will be further described in detail below in combination with specific embodiments: In order to achieve the purpose of the present application, the substrate pretreatment step: according to the material of the substrate, the metal substrate is sequentially subjected to degreasing, plasma activation, primer coating and curing. The plastic substrate is sequentially subjected to plasma activation, primer coating and curing. The composite substrate is subjected to dehydration treatment after partition pretreatment. The multi-layer composite transfer film preparation step: a composite transfer film is prepared, which includes from top to bottom a base film layer, a peelable UV texture layer, a release layer, a non-peelable UV texture layer, a functional interlayer, an electroplated reflective layer, a local adhesive layer and a protective film layer. The local UV pre-curing step: a corresponding type of mask is attached to the surface of the peelable UV texture layer, and LED-UV light source is used for local pre-curing. The vacuum lamination step: the transfer film and the pretreated substrate are laminated, vacuumized and pressurized to completely laminate the transfer film and the curved surface of the substrate. The vacuum hot pressing composite step: in a vacuum environment, the corresponding temperature, pressure and time parameters are set according to the type of the substrate for hot pressing composite. The peeling and gradient curing step: the uncured area of the base film and the peelable UV texture layer is peeled off, and gradient curing is carried out in two stages of low temperature pre-curing and high temperature deep curing. The surface strengthening step: wear-resistant coating is sprayed on the cured texture layer and then the edge is trimmed.

[0020] The beneficial effects of the above technical scheme are: suitable for the surface decoration of the shell of consumer electronic products such as mobile phones, smart wearable devices, notebook computers, and automotive interior parts. This involves multiple materials such as metal, plastic, and metal-plastic composite, especially for the precise transfer printing needs of multi-layer textures of curved shells. Through targeted pretreatment, multi-layer transfer film customization, local pre-solidification, vacuum lamination, hot pressing, gradient solidification, and surface strengthening, the whole process achieves high-precision and high-adhesion decorative effects.

[0021] First, the metal substrate such as aluminum, magnesium alloy, and aluminum-magnesium alloy needs to be pretreated to improve the surface activity. First, perform degreasing treatment, for example, preferably use an alkaline degreasing agent with a concentration of 5% to 8%, soak in a temperature environment of 50°C to 60°C for 10 to 15 minutes, and completely remove the oil stains and impurities on the surface of the substrate. After degreasing, use a low-temperature plasma treatment device for activation treatment, adjust the device power to 300 to 500 W, select argon and oxygen as the treatment gas, the volume ratio of the two is three to one, the treatment distance is controlled at 5 to 8 mm, and the treatment time is 60 to 90 seconds. Through this treatment, the surface energy of the substrate can be improved to 40 dynes or more, and the surface oxide layer can be effectively removed. Then, a special primer is applied, a polyurethane epoxy composite primer is selected, the solid content is 35% to 45%, the viscosity is between 20 mPa·s and 30 mPa·s, and a micro-concave coating method is used for uniform coating, the coating thickness is 6 to 10 μm. After coating, place the substrate in a constant temperature oven at 80 to 90°C and bake for 20 to 25 minutes to allow the primer to fully cure and form a dense cross-linked primer layer, which provides a stable bridge for the subsequent combination of the texture layer and the metal substrate.

[0022] The pretreatment process of plastic substrates such as PC, ABS, PMMA, and PC-PMMA composite is relatively simple. For example, use a low-temperature plasma treatment device for activation, select nitrogen as the treatment gas, and improve the surface energy of the substrate to 38 dynes or more to improve the inertness of the plastic substrate surface. Then, apply an acrylic primer with a solid content of 25% to 35% and a viscosity of 15 to 25 mPa·s using a screen roller coating method with a coating thickness of 4 to 8 μm. Then, place the substrate in a constant temperature oven at 60 to 70°C and bake for 15 to 20 minutes to promote the physical adsorption and chemical combination of the primer and the plastic substrate, and improve the adhesion of the subsequent transfer printing layer.

[0023] The metal-plastic composite substrate combined with the aluminum alloy frame and the PC back plate needs to adopt a partitioned pretreatment scheme. The metal area is executed according to the pretreatment process of the metal substrate, and the plastic area follows the pretreatment steps of the plastic substrate, so that the areas of different materials can be treated specifically. After the treatment of each area is completed, the whole substrate is placed in a vacuum oven at 50°C for 10 minutes to remove the residual moisture on the surface, so that no bubbles or other defects caused by the presence of moisture in the subsequent transfer process, and the consistency of the overall transfer effect is ensured. The equipment used in the pretreatment process includes a low-temperature plasma treatment machine, a micro-concave coating machine, a screen roller coating machine, a constant temperature oven and a vacuum oven. The power of the low-temperature plasma treatment machine can be adjusted in the range of 100W to 600W, the coating accuracy of the micro-concave coating machine and the screen roller coating machine can reach ±0.5μm, the temperature control accuracy of the constant temperature oven is ±2°C, and the vacuum degree of the vacuum oven can reach -0.08MPa or below.

[0024] The customization of the multi-layer composite transfer film is the core of realizing local precise positioning and multi-layer texture effect. The eight-layer composite structure from top to bottom is adopted in the present application, and the selection of each layer material, thickness control and preparation process are all precisely designed. The uppermost layer is the base film layer, which selects PET film as the supporting material with a thickness of 80μm to 150μm. The surface is treated with release treatment, the release force is controlled at 0.8N / 25mm to 1.2N / 25mm, and the light transmittance is not less than 92%. Its main role is to support the functional layers below, and can be easily peeled off after transfer, and at the same time protect the lower texture layer from damage during preparation, transportation and storage.

[0025] The peelable UV texture layer below the base film layer is composed of polyurethane acrylate oligomer, trimethylolpropane triacrylate, photoinitiator and diluent, and the coating thickness is 5μm to 15μm. This layer is prepared by comma blade coating, the surface texture is designed as a high-gloss mirror surface with a roughness of not more than 0.05μm, and the core function is to realize texture positioning through local pre-curing. The pre-cured area remains structurally intact during the subsequent peeling process, while the non-pre-cured area is peeled off with the base film, thereby accurately retaining the target texture area.

[0026] The peelable UV texture layer below the base film layer is composed of polyurethane acrylate oligomer, trimethylolpropane triacrylate, photoinitiator and diluent, and the coating thickness is 5μm to 15μm. This layer is prepared by comma blade coating, the surface texture is designed as a high-gloss mirror surface with a roughness of not more than 0.05μm, and the core function is to realize texture positioning through local pre-curing. The pre-cured area remains structurally intact during the subsequent peeling process, while the non-pre-cured area is peeled off with the base film, thereby accurately retaining the target texture area.

[0027] Below the release layer is a non-peelable UV texture layer, serving as the core decorative layer after transfer. Its material consists of polyurethane acrylate oligomer, dipentaerythritol hexaacrylate, photoinitiator, optical pigments, additives, and diluents, with a coating thickness ranging from 5μm to 15μm. The texture of this layer is formed using an impression roller embossing process with an embossing pressure of 0.2MPa to 0.3MPa. Various texture types, such as CD patterns, dynamic optical patterns, and carbon fiber patterns, can be embossed according to requirements. Slit coating is used, achieving a coating accuracy of ±1μm. This layer permanently bonds to the substrate after transfer, and the addition of optical pigments imparts rich dynamic optical effects, enhancing the product's differentiated competitive advantage.

[0028] Beneath the non-peelable UV texture layer lies a functional interlayer. Preferably, this interlayer is a nano-silicon coating or a polyurethane elastomer, with a coating thickness of 2μm to 5μm, prepared using a microgravure coating method, and a solid content of 20% to 25%. The nano-silicon coating has a particle size controlled between 50nm and 100nm. Its main function is to isolate the non-peelable UV texture layer from the underlying electroplated reflective layer, preventing the two materials from interpenetrating and affecting the effect. Simultaneously, it enhances the overall structural flexibility, allowing the transfer film to better adapt to the curved shape of the shell, ensuring that no texture breakage or film peeling occurs during the transfer process.

[0029] Below the functional interlayer is an electroplated reflective layer, which uses silicon oxide or aluminum-zinc alloy as the coating material. The coating thickness is 100nm to 200nm and is prepared by vacuum evaporation. This enhances the optical reflection effect of the texture layer, makes the multi-layer texture present a three-dimensional sense of layering, and improves the visual impact of the product appearance.

[0030] Beneath the electroplated reflective layer is a localized adhesive layer, using a polyurethane acrylate adhesive with a solid content of 40% to 50% and a coating thickness of 2μm to 10μm, prepared using anilox roller printing. The mesh count of the anilox roller is selected based on the coating thickness. This layer can be printed with localized patterns such as logos and decorative strips as needed, providing adhesion only in the target area. There is no adhesive layer in non-target areas, and it peels off along with the base film after transfer, eliminating the need for additional edge trimming and effectively preventing damage to the edges of the already formed casing.

[0031] The bottom layer is a protective film, made of PE film with a thickness of 20μm to 30μm. It is laminated onto the surface of the local adhesive layer using a laminating machine at a pressure of 0.1MPa to 0.2MPa. Its function is to protect the local adhesive layer from contamination during transportation and storage, ensuring stable adhesion during transfer printing. The equipment used in the transfer film preparation process includes a slot coater, a comma blade coater, a gravure coater, an embossing machine, a vacuum evaporation machine, an anilox roller printer, and a laminating machine.

[0032] The core purpose of local UV pre-curing is to achieve selective curing of the peelable UV texture layer through mask shielding, control the fluidity of the uncured area, avoid pattern deformation during subsequent lamination, and ensure the precise positioning of the local texture. Different types of masks are selected according to the complexity of the texture pattern. For simple patterns such as LOGO and decorative strips, stainless steel laser cutting masks with a thickness of 0.1mm to 0.2mm can be selected, with a positioning accuracy of ±0.1mm. For complex patterns or fine textures, quartz glass photolithography masks with a thickness of 1mm to 2mm are selected, with a positioning accuracy of ±0.01mm.

[0033] After the mask is prepared, the protective film layer of the multi-layer composite transfer film is peeled off, and the mask is attached to the surface of the peelable UV texture layer. During the attachment process, a CCD visual positioning system is used to assist alignment, ensuring that the mask and the pattern of the local adhesive layer are accurately overlapped, with a positioning accuracy of ±0.03mm. The attachment pressure is controlled at 0.1MPa to 0.2MPa to ensure that the mask and the transfer film are tightly attached without gaps, avoiding UV light leakage during pre-curing, which can cause mis-curing in non-target areas.

[0034] Pre-curing uses LED-UV light source with a wavelength of 365nm, and the pre-curing time is 8 to 12 seconds, ensuring that the target area of the peelable UV texture layer is cured to 60% to 70%, which retains a certain adhesion to avoid breaking during peeling, and effectively controls the fluidity. The pre-curing process is carried out in a nitrogen protection environment, with oxygen content controlled at 500ppm or below, to avoid UV light attenuation in air and ensure uniform curing.

[0035] After pre-curing, effect verification is required. The hardness of the peelable UV texture layer is tested using a Shore hardness tester, and the hardness of the cured area should be 2H or higher, while the hardness of the uncured area should not exceed 0.5H. At the same time, 3M adhesive tape is used for adhesion test. After peeling off the adhesive tape, the UV glue in the uncured area should be adhered to the adhesive tape, while the cured area should not have adhesion, ensuring that the pre-curing effect meets the requirements of subsequent processes. The equipment used in this process includes LED-UV curing machine, CCD visual positioning system and Shore hardness tester, among which the energy accuracy of the LED-UV curing machine is ±50mJ / cm².

[0036] The core of vacuum suction positioning and attachment is to ensure that the transfer film is completely attached to the curved shell without air bubbles or wrinkles, laying a foundation for subsequent hot pressing and compounding. The pre-processed curved shell is placed in a profiling jig, which is customized according to the shape of the shell. The material is aluminum alloy, with a surface roughness of not more than 0.8μm. The jig surface is uniformly provided with exhaust grooves with a width of 0.1mm to 0.2mm and a pitch of 5mm to 8mm, ensuring that air can be easily exhausted during the attachment process. The shell is fixed by positioning pins on the jig, with a positioning accuracy of ±0.05mm, to avoid displacement during attachment.

[0037] The protective film layer of the release transfer film is peeled off, and the partial adhesive layer is directed towards the surface of the shell. The aligned edge positioning line is manually positioned. The shell after being attached is placed in the vacuum attachment machine together with the transfer film. After closing the mold cavity, the vacuum program is started, and the vacuum degree in the mold cavity is extracted to-0.09 MPa or below, and maintained for 10-15 seconds, to fully exhaust the air between the transfer film and the shell. Then, compressed air is introduced to form a pressure difference of 0.1-0.2 MPa, so that the transfer film is completely attached to the curved surface of the shell under the action of pressure, and the attachment time is 15-20 seconds. The sequence of vacuum extraction and pressure increase must be strictly followed during the attachment process to avoid air bubbles caused by air residues. The exhaust grooves of the profiling tool should be densely distributed in areas with large curvature to ensure smooth exhaust and flat attachment effect.

[0038] The vacuum hot pressing composite promotes the full infiltration and cross-linking of the non-peeling UV texture layer, functional interlayer, electroplated reflective layer, and substrate surface primer layer through the synergistic effect of temperature and pressure, significantly improving the bonding force between the layers. The hot pressing parameters are differentiated according to the type of substrate. The hot pressing temperature of metal substrates is controlled at 130-160°C, the hot pressing pressure is 0.5-0.8 MPa, and the hot pressing time is 60-90 seconds. The hot pressing temperature of plastic substrates is 100-130°C, the hot pressing pressure is 0.3-0.5 MPa, and the hot pressing time is 40-60 seconds. The hot pressing temperature of metal-plastic composite substrates is 120-140°C, the hot pressing pressure is 0.4-0.6 MPa, and the hot pressing time is 50-70 seconds. The whole hot pressing process is carried out in a vacuum environment, and the vacuum degree in the mold cavity is maintained at-0.09 MPa or below to avoid air bubbles or oxidation during hot pressing.

[0039] The temperature control accuracy of the vacuum hot press used is ±2°C, and the pressure accuracy is ±0.05 MPa, which can accurately control the stability of the hot pressing parameters. During the hot pressing process, the temperature softens the partial adhesive layer and the primer, accelerates the molecular diffusion speed, promotes the chemical cross-linking reaction, and improves the flexibility of the non-peeling UV texture layer, making it better adapt to the curved surface shape. The role of pressure is to ensure that each functional layer is in close contact with the substrate, eliminating gaps and improving physical adsorption. After hot pressing, a preliminary effect verification is performed by gently peeling off the edge of the base film with your hand. The texture layer in the target area should be tightly bonded to the substrate without falling off or warping, ensuring that the hot pressing composite effect meets the requirements.

[0040] Peeling and gradient post-curing are key steps to ensure the precise retention of the texture layer and the stability of the structure. After hot pressing is completed, first, the temperature of the cavity of the vacuum hot press is reduced to 60-80°C, the vacuum and pressure in the cavity are released, and the shell is taken out. Starting from the edge of the shell, slowly peel off the base film and the peelable UV texture layer at an angle of 180 degrees to the surface of the shell along the peeling direction of the base film, and the peeling speed is controlled at 5-10 mm / s to ensure a smooth peeling process and avoid tearing of the texture layer caused by too fast peeling. The uncured area of the peelable UV texture layer will be peeled off with the base film, and the non-peelable UV texture layer, functional interlayer and electroplated reflective layer in the target area are completely retained on the substrate surface, forming a precise local texture.

[0041] After peeling, gradient post-curing is performed in two stages. The first stage is low-temperature pre-curing, the shell is placed in the first curing zone of the double-section UV curing machine, the temperature is controlled at 70-80°C, and a LED-UV light source with a wavelength of 365 nm is used. The second stage is high-temperature deep curing, the shell is transferred to the second curing zone, the temperature is raised to 90-110°C, and a LED-UV light source with a wavelength of 385 nm is switched on to promote the crosslinking between the layers and make the curing degree reach 95% or above. After curing is completed, the shell is naturally cooled to room temperature, about 30-40°C, to avoid sudden cooling which may cause stress concentration and affect the structural stability of the texture layer.

[0042] Surface strengthening treatment can significantly improve the wear resistance, scratch resistance and weather resistance of the texture layer. In the present application, plasma spraying wear-resistant coating is combined with UV curing. First, plasma spraying is performed, and nano-silicon oxide wear-resistant coating or UV-curable wear-resistant coating is selected as the spraying material. The particle size of the nano-silicon oxide wear-resistant coating is 20-50 nm. To ensure uniform coating of the texture layer surface without leakage and sagging, electrostatic spraying is used to make the coating particles uniformly adhere to the surface of the texture layer by electrostatic adsorption.

[0043] After spraying, strengthening post-curing is performed. If nano-silicon oxide coating is selected, the shell is placed in an 80°C constant temperature oven for 15-20 minutes to make the coating fully densified. If UV-curable wear-resistant coating is selected, a LED-UV light source with a wavelength of 365 nm is used, the curing energy is 1200-1500 mJ / cm², and the curing time is 15-20 seconds.

[0044] Finally, edge trimming is performed, and laser cutting equipment is used to precisely trim the slight overflow of the texture layer edge. After trimming, the edge is gently polished with sandpaper to ensure that the shell edge feels smooth, without burrs or edges. After the strengthening process, performance verification is required. The wear resistance is evaluated by steel wool testing. After 1000 hours of testing, the texture layer has no yellowing, cracking, or peeling, ensuring that the product maintains good appearance and performance during long-term use.

[0045] The following further illustrates the feasibility and practical application effect of the process of the present application through three different application scenarios. The process parameters of each embodiment are optimized based on the general process described above to ensure that they are suitable for specific product requirements.

[0046] Example one is a local LOGO multi-layer texture transfer printing of an aluminum alloy mobile phone back cover. The substrate used is a 5052 aluminum alloy stamping mobile phone back cover with a surface curvature of 3-5 mm. The surface has been anodized, and the oxide layer is 10 μm thick. The texture design is a local LOGO texture, and the multi-layer structure uses a combination of surface AG wear-resistant texture, middle dynamic optical texture, and bottom silicon oxide reflective layer to create a three-dimensional and rich visual effect.

[0047] The specific process implementation process is as follows: the substrate pretreatment stage, first, alkaline degreasing, select the concentration of 6% alkaline degreasing agent, soak in 55℃ temperature environment for 12 minutes. Subsequently, plasma activation, equipment power 400W, the volume ratio of argon and oxygen is three to one, the processing distance is 6mm, the processing time is 70 seconds. Then, polyurethane epoxy composite primer is coated, micro concave coating method is adopted, the thickness is 8μm. Finally, in the constant temperature oven at 85℃, baking for 22 minutes. The transfer film customization stage, the base film selects the PET film with a thickness of 120μm, the peelable UV texture layer has a thickness of 10μm, the release layer has a thickness of 2μm, the non-peelable UV texture layer is dynamic optical texture, the thickness is 10μm, the functional interlayer is nano-silicon coating, the thickness is 3μm, the silicon oxide reflection layer has a thickness of 150nm, the local adhesion layer is printed into a LOGO shape by a screen roller, the thickness is 5μm, and the protective film selects the PE film with a thickness of 25μm. The local pre-curing stage, a stainless steel laser cutting mask with a thickness of 0.15mm is used, and after being attached through a CCD visual positioning system, an LED-UV light source is used for pre-curing, the wavelength is 365nm, the time is 10 seconds, and after curing, the hardness of the cured area is 2H, and the hardness of the uncured area is 0.5H. The vacuum lamination stage, the shell is positioned in a profiling jig, and after the PE protective film is peeled off, it is placed in a vacuum laminating machine, the vacuum degree is-0.095MPa, the pressure is 0.15MPa, and the lamination time is 18 seconds. The vacuum hot pressing stage, the temperature is 145℃, the pressure is 0.6MPa, the time is 70 seconds, and the vacuum degree is-0.095MPa. The peeling and gradient curing stage, after cooling at 70℃, the base film is peeled off at a speed of 8mm / s, the first stage curing temperature is 75℃, the wavelength is 365nm, the energy is 1100mJ / cm², and the time is 22 seconds. The second stage curing temperature is 100℃, the wavelength is 385nm, the energy is 1700mJ / cm², and the time is 32 seconds. The surface strengthening stage, the nano-silicon oxide coating is sprayed by plasma, the thickness is 3μm, and the last step is to trim the edge in a laser cutting machine.

[0048] The effect verification result of this embodiment is as follows: the LOGO edge positioning is accurate, and there is no offset deformation phenomenon. The adhesion is evaluated by the cross hatch test, the grid spacing is 1mm, the adhesive tape is pasted three times, and the falling area is not more than 0.5%. The wear resistance is tested by steel wool, and there is no scratch after wiping 500 times under a load of 500g, and the hardness reaches 4.5H. In terms of optical effect, the dynamic optical texture presents gradient color at different angles, the silicon oxide reflection layer effectively improves the brightness, the AG surface layer reduces the reflection, and the overall visual effect is excellent.

[0049] Example two is a PC and PMMA composite smart watch shell full wrap texture transfer. The substrate is a PC and PMMA composite material with a thickness of 1.8 mm and a curved surface curvature of 2 mm to 4 mm, used for a smart watch middle frame. The texture design is a full wrap carbon fiber texture, and the multi-layer structure is a surface UV wear-resistant texture, a middle carbon fiber texture, and a bottom aluminum-zinc alloy reflective layer, achieving a unified overall decorative effect.

[0050] The specific process implementation process is as follows: substrate pretreatment stage, low temperature plasma activation is adopted, equipment power is 250 W, and nitrogen is used as the treatment gas. Then, an acrylic primer is coated by a screen roller. The transfer film customization stage, the base film is selected to be a PET film with a thickness of 100 pm, the peelable UV texture layer has a thickness of 8 pm, the release layer has a thickness of 1.5 pm, the non-peelable UV texture layer is a carbon fiber texture with a thickness of 8 pm, the functional interlayer is a polyurethane elastomer with a thickness of 4 pm, the aluminum-zinc alloy reflective layer has a thickness of 180 nm, the local adhesive layer is coated on the whole surface with a thickness of 6 pm, and the protective film is selected to be a PE film with a thickness of 20 pm. The local pre-curing stage, since the full wrap texture is adopted, a mask is not needed, and LED-UV pre-curing is directly performed, with a wavelength of 365 nm, an energy of 650 mJ / cm², a time of 9 seconds, and a curing degree of 65%. The vacuum lamination stage, after positioning by a profiling jig, the PE protective film is peeled off, and then the vacuum lamination machine is used, with a vacuum degree of -0.09 MPa, a pressure of 0.1 MPa, and a lamination time of 15 seconds. The vacuum hot pressing stage, with a temperature of 125 °C, a pressure of 0.4 MPa, a time of 55 seconds, and a vacuum degree of -0.09 MPa. The peeling and gradient curing stage, after cooling at 65 °C, the base film is peeled off at a speed of 10 mm / s, the first stage curing temperature is 70 °C, the wavelength is 365 nm, the energy is 1000 mJ / cm², and the time is 20 seconds. The second stage curing temperature is 95 °C, the wavelength is 385 nm, the energy is 1500 mJ / cm², and the time is 30 seconds. The surface strengthening stage, electrostatic spraying of a UV-cured wear-resistant coating with a thickness of 3 pm is performed, LED-UV curing is adopted with a wavelength of 365 nm and a time of 18 seconds, and finally the edges are mechanically polished by sandpaper.

[0051] The effect verification results of this example are as follows: the texture layer is completely laminated to the curved surface shell without bubbles, wrinkles, and edge overflow. The wear resistance is tested by steel wool, and no scratches are found after 500 times of wiping under a load of 500 g, and the hardness reaches 5H. The weather resistance is tested by ultraviolet aging, and no yellowing or cracking is found after 1000 hours, and the carbon fiber texture remains clear and complete.

[0052] Example three is a magnesium alloy and ABS composite notebook computer shell composite texture transfer, the substrate is a composite structure of magnesium alloy frame and ABS backplane, the magnesium alloy area has a curvature of 5mm to 8mm, and the ABS area is a plane. The texture design is a combination of magnesium alloy frame CD texture, ABS backplane AG and dynamic optical composite texture, realizing differentiated decoration effect in different areas.

[0053] The specific process implementation process is as follows: substrate pretreatment stage, the magnesium alloy area is first subjected to alkaline degreasing, concentration 7%, 58°C soaking for 14 minutes. Subsequently, plasma activation, equipment power 450W, argon and oxygen volume ratio three to one, treatment distance 7mm, time 80 seconds. Coating polyurethane epoxy primer, thickness 9μm. Baking in constant temperature oven for 24 minutes. The ABS area is activated by plasma, the equipment power is 280W, nitrogen is used as the treatment gas, the treatment distance is 5mm, and the time is 55 seconds. Coating acrylic primer, thickness 5μm. Baking in constant temperature oven at 68°C for 16 minutes. The whole substrate is baked in a vacuum oven at 50°C for 10 minutes to remove moisture. The transfer film customization stage, the base film is selected as a PET film with a thickness of 150μm, the peelable UV texture layer has a thickness of 12μm, the release layer has a thickness of 2μm, the non-peelable UV texture layer is a combination of CD texture and AG and dynamic optical composite texture, with a thickness of 12μm, the functional interlayer is a nano-silicon coating layer with a thickness of 3μm, the silicon oxide reflection layer has a thickness of 200nm, the local adhesive layer is printed on the corresponding area by a screen roller, with a thickness of 8μm, and the protective film is selected as a PE film with a thickness of 30μm. Local pre-curing stage, quartz glass photomask is used, and after positioning by a CCD visual positioning system, LED-UV pre-curing is performed with a wavelength of 365nm. Vacuum lamination stage, after positioning by a profiling jig, the PE protective film is peeled off, and then the vacuum lamination machine is used with a vacuum degree of-0.095MPa, a pressure of 0.2MPa, and a lamination time of 20 seconds. Vacuum hot pressing stage, temperature 135°C, pressure 0.5MPa, time 65 seconds, vacuum degree-0.095MPa. Peeling and gradient curing stage, after cooling at 75°C, the base film is peeled off at a speed of 7mm / s, the first stage curing temperature is 80°C, the wavelength is 365nm, the energy is 1200mJ / cm², and the time is 25 seconds. The second stage curing temperature is 105°C, the wavelength is 385nm, the energy is 1600mJ / cm², and the time is 35 seconds. Surface strengthening stage, plasma spraying of nano-silicon oxide coating layer, thickness 4μm, baking in constant temperature oven at 80°C for 20 minutes, finally trimming the edge with a laser cutting machine with a power of 18W.

[0054] The effect verification results of this example are as follows: the combined texture transitions naturally, the CD texture is clear and regular, and the AG and dynamic optical composite texture presents a three-dimensional gradient effect. The texture layer does not fall off or warp, and maintains good structural stability and appearance integrity.

[0055] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for local pre-curing and gradient curing transfer of multi-layer textured shells, characterized in that, include: Substrate pretreatment steps: Different treatments are carried out according to the substrate material. Metal substrates are successively degreased, plasma activated, coated with primer and cured. The plastic substrate is sequentially subjected to plasma activation, primer coating, and curing; The composite substrate undergoes dehydration treatment after zonal pretreatment; Multilayer composite transfer film preparation steps: Prepare a composite transfer film from top to bottom, consisting of a base film layer, a peelable UV texture layer, a release layer, a non-peelable UV texture layer, a functional interlayer, an electroplated reflective layer, a local adhesive layer, and a protective film layer. Local UV pre-curing step: Select the corresponding type of mask and attach it to the surface of the peelable UV texture layer, and use an LED-UV light source for local pre-curing; Vacuum lamination step: The transfer film is laminated to the pretreated substrate, and vacuuming and pressurizing are applied to make the transfer film and the curved surface of the substrate completely bonded. Vacuum hot pressing lamination steps: In a vacuum environment, hot pressing lamination is performed according to the corresponding temperature, pressure and time parameters set according to the substrate type. Peeling and gradient curing steps: Peel off the uncured areas of the base film and the peelable UV texture layer, and perform gradient curing in two stages: low-temperature pre-curing and high-temperature deep curing; Surface strengthening steps: Apply a wear-resistant coating to the cured textured layer and cure it, then trim the edges.

2. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: The substrate is a metal substrate, a plastic substrate, or a metal-plastic composite substrate; The metal substrate includes aluminum, magnesium alloy, and aluminum-magnesium alloy. The plasma activation uses a mixture of argon and oxygen in a volume ratio of 3:1, with a processing power of 300W-500W and a time of 60 to 90 seconds. The plastic substrate includes PC, ABS, PMMA, and PC and PMMA composite materials. The plasma activation uses nitrogen gas with a processing power of 200W-300W and a time of 40 to 60 seconds.

3. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: In the preparation step of the multilayer composite transfer film, the base film layer is a PET film with a thickness of 80μm-150μm; the peelable UV texture layer has a thickness of 5μm-15μm and a surface roughness of ≤0.05μm; the non-peelable UV texture layer has a thickness of 5μm-15μm and is formed by imprinting with an imprinting roller. The local adhesive layer is printed using an anilox roller, with a thickness of 2μm-10μm, and is applied only to the target area.

4. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: In the local UV pre-curing step, the mask is a stainless steel laser-cut mask or a quartz glass photolithography mask; the LED-UV light source wavelength is 365nm, the pre-curing energy is 600mJ / cm²-800mJ / cm², the time is 8 to 12 seconds, the degree of curing is controlled at 60%-70%, and the hardness of the cured area is ≥2H.

5. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: In the vacuum bonding step, a conformal fixture with an exhaust groove is used to evacuate to a vacuum degree of ≤-0.09MPa and maintain it for 10 to 15 seconds. Then, pressure is applied to form a pressure difference of 0.1MPa-0.2MPa, and the bonding time is 15 to 20 seconds.

6. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 2, characterized in that: In the vacuum hot pressing composite process, the hot pressing temperature of the metal substrate is 130℃-160℃, the pressure is 0.5MPa-0.8MPa, and the time is 60 seconds to 90 seconds. The hot-pressing temperature of the plastic substrate is 100℃-130℃, the pressure is 0.3MPa-0.5MPa, and the time is 40 seconds to 60 seconds; The hot-pressing temperature of the metal-plastic composite substrate is 120℃-140℃, the pressure is 0.4MPa-0.6MPa, and the time is 50 seconds to 70 seconds.

7. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: In the peeling and gradient curing steps, the low-temperature pre-curing temperature is 70℃-80℃, using an LED-UV light source with a wavelength of 365nm, and the curing time is 20 to 25 seconds; the high-temperature deep curing temperature is 90℃-110℃, using an LED-UV light source with a wavelength of 385nm, and the curing time is 30 to 35 seconds.

8. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: In the surface strengthening step, the wear-resistant coating is a nano-silica coating or a UV-cured wear-resistant coating, with a coating thickness of 2μm-5μm. The nano-silica coating is cured by baking at 80℃ for 15-20 minutes, and the UV-curable wear-resistant coating is cured for 15 to 20 seconds by an LED-UV light source with a wavelength of 365nm and an energy of 1200mJ / cm²-1500mJ / cm².

9. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: In the multilayer composite transfer film, the functional interlayer is a nano-silicon coating or a polyurethane elastomer with a thickness of 2μm-5μm; the electroplated reflective layer is silicon oxide or an aluminum-zinc alloy with a thickness of 100nm-200nm; and the local bonding layer is a polyurethane acrylate adhesive with a solid content of 40%-50%.

10. The method for local pre-curing and gradient curing transfer of multi-layer textured shell as described in claim 1, characterized in that: The multi-layered texture includes one or more combinations of CD texture, dynamic optical texture, carbon fiber texture, and AG texture.

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