Preparation process of strong-weak adhesive forming protective film

Abstract

This disclosure provides a process for preparing a strong-weak adhesive molded protective film. The process includes the following steps: coating an adhesive on one side of a base film; forming an outer film with a transparent portion and a light-shielding portion; applying a first photocurable adhesive to the light-shielding portion and a second photocurable adhesive to the transparent portion; attaching the side of the outer film coated with the first and second photocurable adhesives to the side of the base film opposite to the adhesive; and curing the film using a photocuring process. The adhesive strength of the cured first photocurable adhesive is greater than that of the cured second photocurable adhesive. The outer film and the base film are completely bonded together, avoiding physical interference caused by edge lifting during cold carving and transport, and eliminating the risk of displacement or detachment due to accidental pulling by external forces. The light-shielding portion blocks light to form a strong adhesive area, while the light-transmitting portion allows light to pass through to form a weak adhesive area, making the outer film and the base film easy to peel off.

Description

Technical Field

[0001] This disclosure relates to precision electronics manufacturing, and in particular to a process for preparing a strong and weak adhesive molding protective film. Background Technology

[0002] In the field of electronic component manufacturing, especially for precision parts such as glass covers, mobile phone back panels, and camera modules, cold carving is used to achieve high-precision cutting or chamfering. During cold carving, protective films are widely used to cover and protect the surfaces to prevent scratches, contamination, or physical damage during processing. Cold carving typically involves high-speed rotating tools, coolant scouring, and complex spatial movements, placing stringent requirements on the adhesion and stability of the protective film.

[0003] Most common protective films are single-layer pressure-sensitive adhesive structures, with limited bonding properties. This makes it difficult to simultaneously meet the dual requirements of stable adhesion without lifting during cold carving and easy peeling without residue after carving. If the overall adhesive strength of the protective film is too high, although it can maintain a firm fit during cold carving, peeling becomes difficult afterward, leading to tearing and adhesive residue, severely impacting product yield and production efficiency. To facilitate peeling, some protective films have handles on the edges. However, in actual cold carving, raised handles can not only physically interfere with the workpiece, affecting processing accuracy, but can also be accidentally pulled by external forces, causing the protective film to shift or detach, exposing the protective surface to the processing environment.

[0004] For example, the prior art document CN201720445981.X discloses a type of lift-up tear-off handle and its production device. The lift-up tear-off handle includes a base film and a tear-off base film. One end of the tear-off base film has an adhesive backing layer, which is double-sided adhesive. A single-sided adhesive tape is attached to the end of the tear-off base film opposite the adhesive backing layer. The adhesive backing layer is located on the lower surface of the tear-off base film, and the single-sided adhesive tape is located on the upper surface. The single-sided adhesive tape is rolled outwards, causing both ends of the tear-off base film to lift outwards. One end of the tear-off base film is attached to the base film through the adhesive backing layer. When this solution is used to protect surfaces of precision parts requiring cold carving, the lifting of the tear-off handle causes physical interference, and the tear-off handle is easily pulled by external force, leading to overall displacement or detachment of the protective film. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a process for preparing a strong and weak adhesive molding protective film that avoids interference caused by film layer lifting, prevents accidental pulling, and prevents easy-tear films.

[0006] The purpose of this disclosure is achieved through the following technical solution: A process for preparing a protective film using strong and weak adhesives includes the following steps: A base film is obtained, and an adhesive is coated on one side of the base film. A first coating area and a second coating area are formed on the portion of the base film opposite to the adhesive. An outer film is obtained, the outer film having a transparent portion and a light-shielding portion; a first photocurable adhesive is applied to the light-shielding portion, and a second photocurable adhesive is applied to the transparent portion; The outer film coated with the first and second photocurable adhesives is attached to the side of the base film opposite to the adhesive. This ensures that the first photocurable adhesive is correspondingly disposed in the first coating area, and the second photocurable adhesive is correspondingly disposed in the second coating area. A strong and weak adhesive protective film is obtained by curing through a photocuring process; wherein, the first photocurable adhesive blocks light through the light-shielding part to maintain an uncrosslinked or low crosslinked state to maintain the bonding strength, and the second photocurable adhesive reduces the bonding strength by initiating a crosslinking reaction through the light transmitted through the transparent part; the bonding strength of the first photocurable adhesive after curing is greater than the bonding strength of the second photocurable adhesive after curing.

[0007] In one embodiment, the first photocurable adhesive includes at least one of acrylate-based photocurable pressure-sensitive adhesives, polyurethane-based photocurable pressure-sensitive adhesives, and silicone-based photocurable pressure-sensitive adhesives; and / or, The second photocurable adhesive includes at least one of acrylate photocurable pressure-sensitive adhesive, polyurethane photocurable pressure-sensitive adhesive, and silicone photocurable pressure-sensitive adhesive.

[0008] In one embodiment, the photoinitiator content in the second photocurable adhesive is 0.5wt%-5.0wt%, and the photoinitiator content in the first photocurable adhesive is 0.1wt%-0.5wt%.

[0009] In one embodiment, the light-shielding portion and the transparent portion are integrally formed.

[0010] In one embodiment, the light-shielding part is at least one of a black light-shielding film, a semi-permeable film, a metal coating, and an ink layer, and the ultraviolet light transmittance of the light-shielding part is less than 5%.

[0011] In one embodiment, the ultraviolet light transmittance of the transparent portion is greater than 85%.

[0012] In one embodiment, the photocuring process uses ultraviolet light irradiation with an energy of 500 mJ / cm². 2 -3000mJ / cm 2 .

[0013] In one embodiment, curing is performed using a photocuring process, including the following steps: With a first light intensity of 500 mJ / cm2 -700mJ / cm 2 The second photocurable adhesive is pre-cured to partially cross-link the second photocurable adhesive, thereby forming a pre-shaped second photocurable adhesive; Then, with a second light intensity of 1000 mJ / cm 2 -3000mJ / cm 2 Full exposure is performed to further crosslink the second photocurable adhesive to the target viscosity reduction level, while the first photocurable adhesive remains uncrosslinked or only minimally crosslinked due to the light-shielding part.

[0014] In one embodiment, the base film is at least one of PET film, PI film and PO film, and the outer film is at least one of PET film or TPU film.

[0015] In one embodiment, the thickness of the first and second photocurable adhesives after curing is 5μm-50μm; the thickness of the base film is 25μm-100μm; and the thickness of the outer film is 25μm-100μm.

[0016] Compared with the prior art, this disclosure has at least the following advantages: In the aforementioned process for preparing the strong and weak adhesive protective film, during cold carving and transfer, the outer film and the bottom film are completely bonded together through the first and second UV-curable adhesives. This ensures that there is no relative sliding or lifting between the outer and bottom films, preventing physical interference with cutting tools, fixtures, or automated equipment after the film edges lift. It also eliminates the risk of the protective film shifting or falling off due to accidental pulling of the lifted portion by external force. By blocking light through the light-shielding part, the first UV-curable adhesive maintains high bonding strength, whether cross-linked or not. By allowing light to pass through the light-transmitting part, the cross-linking reaction of the second UV-curable adhesive reduces the bonding strength, forming a weak adhesive bonding area. The increased cohesive strength and tensile strength of the outer film through the cross-linking reaction make the transparent part of the outer film easy to peel from the bottom film, avoiding breakage or adhesive residue during the peeling process. The easy peeling design of the light-transmitting part and the step structure formed between the transparent parts of the bottom film and the outer film constitute the stress point for peeling, thus achieving a convenient and efficient peeling operation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1This is a flowchart illustrating the process steps for preparing a strong and weak adhesive molding protective film according to one embodiment. Figure 2 for Figure 1 The diagram shows the structure of a protective film formed by strong and weak adhesives. Detailed Implementation

[0019] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0020] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments: Please see Figure 1 As shown, this is a process for preparing a strong-weak adhesive molded protective film according to an embodiment of the present invention, which includes the following steps: S101, Obtain a base film, apply adhesive to one side of the base film, and form a first coating area and a second coating area on the portion of the base film opposite to the adhesive. S103, an outer film is obtained, the outer film having a transparent portion and a light-shielding portion, a first photocurable adhesive is applied to the light-shielding portion, and a second photocurable adhesive is applied to the transparent portion; S105, the side of the outer film coated with the first photocurable adhesive and the second photocurable adhesive is attached to the side of the bottom film away from the adhesive, so that the first photocurable adhesive is correspondingly disposed in the first coating area and the second photocurable adhesive is correspondingly disposed in the second coating area. S107, a strong and weak adhesive protective film is obtained by photocuring process; wherein, the first photocurable adhesive is shielded from light by the light-shielding part to maintain an uncrosslinked or low crosslinked state, and the second photocurable adhesive is subjected to a crosslinking reaction by light transmitted through the transparent part, thereby reducing the bonding strength; the bonding strength of the first photocurable adhesive after curing is greater than the bonding strength of the second photocurable adhesive after curing.

[0023] Understandably, the base film adheres to the protective surface through an adhesive layer, and it does not shift during the cold carving process. The outer film and the base film are kept in complete adhesion through a first and a second UV-cured adhesive, ensuring that there is no relative sliding or lifting between the outer and base films during cold carving and transportation. This avoids interference problems that may be caused by film lifting, as the edges of the lifted film can easily interfere with the cutting tools, fixtures, or automated equipment during cold carving, resulting in decreased processing accuracy or equipment failure. It also prevents the lifted part from being accidentally pulled by external force, causing the entire protective film to shift or fall off, ensuring continuous and stable coverage of the protective surface by the base film and guaranteeing the smooth progress of the cold carving process.

[0024] Understandably, the first photocurable adhesive in the first coating area blocks light through the light-shielding part of the outer film, preventing it from receiving enough energy to initiate a cross-linking reaction. It remains in a non-cross-linked or low-cross-linked state, maintaining high fluidity and interfacial wetting ability in its molecular chains. This allows it to fully adhere to the surface of the object being coated, forming strong interfacial adhesion and maintaining high adhesive strength after curing. The second photocurable adhesive layer in the second coating area allows light to pass through the transparent part of the outer film, directly irradiating the second photocurable adhesive layer. This triggers a cross-linking polymerization reaction between the prepolymer and monomers initiated by the photoinitiator in the second photocurable adhesive. The cross-linking reaction sacrifices the fluidity and interfacial wetting ability of the adhesive layer's molecular chains, significantly reducing interfacial adhesion. The cross-linking network gives the adhesive layer higher cohesive strength, ensuring complete and residue-free detachment upon peeling. This transforms the high-adhesion-strength second photocurable adhesive into a weak adhesive bonding area with low adhesion strength and high tensile strength after sufficient light exposure. It is understood that the second coating area and the first coating area are formed on the part of the base film, so that a stepped structure is formed between the base film and the outer film. The stepped structure forms the stress point for tearing the film at the edge of the transparent part. Combined with the low peel force characteristics of the weak adhesive bonding area of ​​the transparent part, the operator can easily separate the transparent part from the base film directly from the step.

[0025] In the aforementioned process for preparing the strong and weak adhesive protective film, during cold carving and transfer, the outer film and the bottom film are completely bonded together through the first and second UV-curable adhesives. This ensures that there is no relative sliding or lifting between the outer and bottom films, preventing physical interference with cutting tools, fixtures, or automated equipment after the film edges lift. It also eliminates the risk of the protective film shifting or falling off due to accidental pulling of the lifted portion by external force. By blocking light through the light-shielding part, the first UV-curable adhesive maintains high bonding strength, whether cross-linked or not. By allowing light to pass through the light-transmitting part, the cross-linking reaction of the second UV-curable adhesive reduces the bonding strength, forming a weak adhesive bonding area. The increased cohesive strength and tensile strength of the outer film through the cross-linking reaction make the transparent part of the outer film easy to peel from the bottom film, avoiding breakage or adhesive residue during the peeling process. The easy peeling design of the light-transmitting part and the step structure formed between the transparent parts of the bottom film and the outer film constitute the stress point for peeling, thus achieving a convenient and efficient peeling operation.

[0026] Furthermore, in one embodiment, before applying adhesive to one side of the base film, the following step is also included: A skin-feel surface is formed on one side of the base film by surface coating, embossing, or plasma treatment. In this embodiment, the skin-feel surface is located on the side of the base film opposite to the adhesive. The second cured adhesive adheres to the skin-feel surface of the base film, providing the base film side with a comfortable touch, anti-slip properties, and fingerprint resistance. After surface coating, embossing, or plasma treatment, the skin-feel surface forms a micro-nano-level texture or a low surface energy modified layer, reducing the actual contact area and interfacial bonding force between the second photocurable adhesive and the base film. This makes it easier to achieve interfacial separation in the weak adhesive areas after cross-linking and curing, further reducing the initial peel force and improving the smoothness of film removal.

[0027] Furthermore, in one embodiment, after obtaining the outer film, which has a transparent portion and a light-shielding portion, applying a first photocurable adhesive to the light-shielding portion, applying a second photocurable adhesive to the transparent portion, and before attaching the side of the outer film coated with the first and second photocurable adhesives to the side of the base film opposite to the adhesive, the following step is further included: The outer film coated with the first and second UV-curable adhesives undergoes a pre-drying treatment to control the residual solvent content of the first and second UV-curable adhesives to below 0.5%, and to form a micro-adhesive surface on the surfaces of the first and second UV-curable adhesives. In this embodiment, the pre-drying treatment uses a hot air circulating oven at a temperature of 40℃-80℃ for 1-5 minutes. The low solvent residue effectively avoids defects such as bubbles and pinholes caused by the evaporation of residual solvents during subsequent UV curing, ensuring the density and uniformity of the adhesive layer structure, thereby improving the performance stability of the cured adhesive layer and reducing the evaporation of residual solvents during cold carving or subsequent processes. The formation of a suitable micro-adhesive surface on the surfaces of the first and second UV-curable adhesives provides temporary positioning and pre-fixation when the outer film is bonded, preventing relative sliding or displacement before subsequent UV curing processes.

[0028] Furthermore, in one embodiment, before attaching the outer film to the side of the base film opposite to the adhesive, the method further includes the step of: The side of the substrate film facing away from the adhesive is subjected to corona treatment or plasma treatment to improve the adhesion between the first and second photocurable adhesives and the substrate film. In this embodiment, corona treatment or plasma treatment can effectively increase the polarity of the substrate film surface, increase surface energy, and improve its wetting properties. After treatment, a fine uneven structure is formed on the substrate film surface and active functional groups are introduced, thereby significantly enhancing the physical anchoring and chemical bonding between the first and second photocurable adhesives and the substrate film, improving interfacial adhesion, and enhancing overall adhesion. The improved interfacial adhesion ensures that the first and second photocurable adhesives can firmly adhere to the substrate film surface during subsequent photocuring and cold carving processes, avoiding delamination, bubbling, or delamination caused by poor bonding between the adhesive layer and the substrate film interface. The improved wetting properties also allow the photocurable adhesive to spread more evenly during coating, reducing coating defects, further improving the consistency of the adhesive layer thickness and coating yield, and enhancing adhesion.

[0029] In one embodiment, the first photocurable adhesive includes at least one of acrylate photocurable pressure-sensitive adhesive, polyurethane photocurable pressure-sensitive adhesive, and silicone photocurable pressure-sensitive adhesive; and / or, the second photocurable adhesive includes at least one of acrylate photocurable pressure-sensitive adhesive, polyurethane photocurable pressure-sensitive adhesive, and silicone photocurable pressure-sensitive adhesive. In this embodiment, acrylic photocurable pressure-sensitive adhesives have the advantages of fast curing speed, wide adjustable range of adhesion performance, and relatively low cost; polyurethane photocurable pressure-sensitive adhesives have excellent flexibility, weather resistance, and resilience, making them suitable for applications with high impact resistance requirements; silicone photocurable pressure-sensitive adhesives have excellent high and low temperature resistance, dielectric properties, and release characteristics, making them suitable for applications with stringent requirements for weather resistance and electrical performance; for strong adhesive areas, acrylic or polyurethane adhesives with high initial tack can be selected to provide a reliable anchoring effect between the outer film and the bottom film; for weak adhesive areas, similar or complementary adhesives with significant tack reduction after crosslinking and obvious improvement in cohesive strength can be selected, so that the adhesive layer can be completely separated from the bottom film without residue when peeling.

[0030] In one embodiment, the photoinitiator content in the second photocurable adhesive is 0.5wt%-5.0wt%, and the photoinitiator content in the first photocurable adhesive is 0.1wt%-0.5wt%. In this embodiment, by differentiating the photoinitiator content in the first and second photocurable adhesives, precise control of the photocuring response in the strong and weak adhesive regions is achieved. The second photocurable adhesive has a higher photoinitiator content, so when light passes through the transparent part of the outer film and irradiates the first coating area, sufficient free radicals or cationic active centers can be generated in the adhesive layer, initiating a full and rapid crosslinking polymerization reaction between the prepolymer and the monomer. The high content of photoinitiator ensures the thoroughness of the cross-linking reaction, significantly reducing the interfacial adhesion of the second UV-curable adhesive while significantly improving the cohesive strength. This reliably achieves the characteristics of a weak adhesive with low bond strength and high tensile strength. The lower content of the first UV-curable adhesive, combined with the shielding effect of the outer film, means that even if stray light passes through the shielding part, the low content of photoinitiator is unlikely to trigger a significant cross-linking reaction. This ensures that the first UV-curable adhesive remains uncrosslinked or in a low-crosslinked state. At the same time, it ensures the stability of the adhesive layer during coating, drying, and storage, avoiding unexpected curing caused by ambient light exposure. This reliably maintains the characteristics of a strong adhesive with high bond strength. The differentiated photoinitiator content allows the strong and weak adhesive regions to achieve different degrees of cross-linking under the same light conditions. This avoids stringent requirements on process parameters such as light intensity and time, reduces batch-to-batch differences caused by equipment fluctuations or environmental changes, and ensures the consistency and reliability of product performance in mass production.

[0031] In one embodiment, after curing by a photocuring process, the adhesive strength of the second photocurable adhesive decreases to 20%-60% of the maximum adhesive strength achieved during its curing and cross-linking process, while the adhesive strength of the first photocurable adhesive remains above 80% of the maximum adhesive strength achieved during its curing and cross-linking process. In this embodiment, the adhesive strength of the second photocurable adhesive is controlled within the range of 20%-60% of the maximum adhesive strength, allowing the weak adhesive areas to be easily peeled off after cold carving, avoiding the risk of accidental detachment during cold carving or transportation due to excessively low adhesive strength; the adhesive strength of the first photocurable adhesive remains above 80% of the maximum adhesive strength, ensuring that the strong adhesive areas have sufficient and stable anchoring force during cold carving. The high retention rate of adhesive strength allows the edges and key areas of the outer film to adhere firmly to the base film, effectively resisting external forces such as vibration, cutting force, and coolant erosion generated during cold carving.

[0032] In one embodiment, the light-shielding portion and the transparent portion are integrally formed. In this embodiment, by employing a selective processing technology on a single base film, the light-shielding portion and the transparent portion are formed in the same continuous film layer, ensuring precise correspondence between the light-shielding portion and the first coating area, and between the transparent portion and the second coating area. This eliminates the need for secondary lamination or alignment adjustments, improving the yield and consistency of the strong-weak adhesive molding protective film. In one embodiment, the light-shielding part is at least one of a black light-shielding film, a semi-permeable film, a metal coating, and an ink layer, and the ultraviolet light transmittance of the light-shielding part is less than 5%. In this embodiment, the black light-shielding film and semi-permeable film effectively block the penetration of curing light by utilizing the light absorption characteristics of the substrate itself; the metal coating provides excellent light-shielding effect through a dual mechanism of high reflection and high absorption; the ink layer reduces ultraviolet light transmittance through the light absorption effect of dark pigments; controlling the ultraviolet light transmittance to below 5% improves the reliability of light-shielding performance and process tolerance; specifically, by selecting a transparent base film as the bottom layer, a light-shielding coating is applied to the transparent base film through printing or composite coating to obtain an integrally formed light-shielding part and transparent part; using a multi-layer co-extrusion extrusion equipment, the light-shielding material and transparent material are melted and plasticized separately, and the interlayer distribution and width ratio of the two materials during the extrusion process are controlled through the co-extrusion die; after extrusion, the material is cooled and shaped to obtain an integral film material with alternating transparent and light-shielding parts; a uniform metal coating is formed on the surface of the transparent base film through vacuum evaporation or magnetron sputtering technology.

[0033] In one embodiment, the ultraviolet light transmittance of the transparent portion is greater than 85%. In this embodiment, an ultraviolet light transmittance greater than 85% means that during the photocuring process, most of the ultraviolet light energy can pass through the transparent portion of the outer film and effectively irradiate the second photocurable adhesive layer in the second coating area. High transmittance ensures that the photoinitiator receives sufficient light energy to generate a sufficient number of free radicals or cationic active centers, initiating a full and uniform crosslinking polymerization reaction between the prepolymer and monomer, saturating the crosslinking degree in the weak adhesive area, thereby achieving the effect of low adhesive strength and high tensile strength. The high ultraviolet light transmittance of the transparent portion allows for full crosslinking of the second photocurable adhesive under lower light intensity or shorter light duration, reducing the dependence of the photocuring process on equipment energy output, widening the process window, and reducing the problem of uneven curing caused by light attenuation. Therefore, in large-area irradiation scenarios, the light energy received by different parts of the weak adhesive area tends to be consistent, ensuring the uniformity of product performance and batch stability. The transparent part and the light-shielding part are integrally formed on the same outer film, forming a differentiated optical structure with high light transmittance and low light transmittance. Under the same photocuring process, the weak adhesive area receives sufficient light energy to achieve complete cross-linking, while the strong adhesive area is basically unaffected by light due to the blocking of the light-shielding part. Thus, the differentiated control of the performance of strong and weak adhesives can be achieved simultaneously in the same process step.

[0034] In one embodiment, the photocuring process uses ultraviolet light irradiation with an energy of 500 mJ / cm². 2 -3000mJ / cm 2 In this embodiment, the irradiation energy is controlled above 500 mJ / cm², ensuring that the second photocurable adhesive in the second coating area receives sufficient ultraviolet light energy. This allows the photoinitiator in the second photocurable adhesive to be fully excited, initiating a complete crosslinking polymerization reaction between the prepolymer and the monomer. This significantly reduces interfacial adhesion and effectively enhances cohesive strength, enabling the weak adhesive area to achieve the performance target of low adhesive strength and high tensile strength. The irradiation energy is controlled below 3000 mJ / cm² to avoid problems such as embrittlement or yellowing caused by excessive curing of the adhesive layer due to excessive energy. Furthermore, the effective shielding of the outer film ensures that the stray or transmitted light energy received by the first photocurable adhesive in the first coating area is insufficient to trigger significant crosslinking, thus keeping the first photocurable adhesive in an uncrosslinked or low-crosslinked state and maintaining its strong adhesive properties with high adhesive strength.

[0035] In one embodiment, curing is performed using a photocuring process, including the following steps: With a first light intensity of 500 mJ / cm 2 -700mJ / cm 2 The second photocurable adhesive is pre-cured to partially cross-link the second photocurable adhesive, thereby forming a pre-shaped second photocurable adhesive; Then, with a second light intensity of 1000 mJ / cm 2 -3000mJ / cm 2 Full exposure is performed to further crosslink the second photocurable adhesive to the target viscosity reduction level, while the first photocurable adhesive remains uncrosslinked or only minimally crosslinked due to the light-shielding part.

[0036] In this embodiment, in the first stage, 500 mJ / cm 2 -700mJ / cm 2 The second photocurable adhesive is pre-cured under low light intensity to achieve partial cross-linking and initial shaping. The pre-cured adhesive layer forms a stable preliminary network structure, providing a uniform reaction basis for further cross-linking during subsequent full exposure, ensuring the consistency and controllability of the final cross-linking degree; the second stage uses 1000mJ / cm 2 -3000mJ / cm 2 Full exposure to high light intensity allows the second UV-curable adhesive to further crosslink to the target viscosity reduction level. High-energy exposure ensures that the photoinitiator in the second UV-curable adhesive is fully excited, and the crosslinking reaction reaches a saturated state, significantly reducing the interfacial adhesion to the target range. At the same time, the crosslinking network gives the adhesive layer higher cohesive strength and tensile strength, ensuring that the adhesive layer detaches completely without residue upon peeling. Through phased control of pre-curing and full exposure, problems such as excessively rapid, uneven, or over-crosslinking that may occur due to a single high-energy exposure are avoided, allowing the adhesion strength in the weak adhesive area to be more precisely controlled within the target range. During the two-stage exposure process, the light-blocking part continuously and effectively blocks light, further reducing the potential impact of stray light or edge light transmission on the first UV-curable adhesive, ensuring stable and reliable performance in the strong adhesive area.

[0037] In one embodiment, the base film is at least one of PET film, PI film, and PO film, and the outer film is at least one of PET film or TPU film. In this embodiment, the PET film is made of polyethylene terephthalate, which has excellent mechanical strength, dimensional stability, and temperature resistance, and can maintain stable support during cold carving, without easily deforming or shrinking; the PI film is made of polyimide, which has higher temperature resistance and excellent chemical corrosion resistance, and is suitable for applications with high requirements for coolant and cutting fluid tolerance or high processing temperature in cold carving processes. PI film also has good flexibility and dimensional stability, and performs well in protective film products with high temperature processing or high flexibility requirements; the PO film is made of polyolefin, which has advantages such as low cost, good flexibility, and low density, and is suitable for protective film products that are cost-sensitive or have high flexibility requirements; the TPU film is made of thermoplastic polyurethane, which has excellent flexibility, elastic recovery ability, and wear resistance when used as an outer film, and is suitable for applications that require the outer film to have a certain degree of extensibility or impact resistance.

[0038] Furthermore, in one embodiment, a cross-linked coating area is formed between the second coating area and the first coating area. The outer film has a curing portion corresponding to the cross-linked coating area. A UV cross-linked curing adhesive is applied to the curing portion. When the outer film is adhered to the side of the base film away from the adhesive, the UV cross-linked curing adhesive is disposed in the cross-linked coating area. The UV transmittance of the curing portion is greater than 50%, and the adhesive strength of the UV cross-linked curing adhesive is improved after photocuring. In this embodiment, the adhesive strength of the UV cross-linked curing adhesive is improved after photocuring, enabling it to provide additional anchoring force during cold carving. The strengthening effect of the UV cross-linked curing adhesive further ensures that the protective film does not shift, warp, or wrinkle during cold carving. By setting three different types of UV curing adhesives on the same protective film, fine-tuning of the performance of different areas on the same protective film is achieved. The performance differentiation of the three curing adhesives can be completed simultaneously in a single photocuring process, eliminating the need for multiple coatings or multi-step curing, making the process simple and efficient.

[0039] Furthermore, in one embodiment, the UV crosslinking adhesive is at least one of acrylate-based UV-curable structural adhesives, polyurethane-based UV-curable structural adhesives, and epoxy acrylate-based UV-curable adhesives. In this embodiment, the acrylate-based UV-curable structural adhesive exhibits significantly improved cohesive strength and interfacial adhesion after curing, making it suitable for crosslinking coating areas with high adhesion requirements and effectively enhancing the interfacial bonding between strong and weak adhesive areas. The polyurethane-based UV-curable structural adhesive, after curing, possesses both good impact resistance and maintains a certain degree of flexibility, making it suitable for crosslinking coating areas requiring stress buffering or dynamic load bearing, avoiding interfacial failure due to brittle fracture. The epoxy acrylate-based UV-curable adhesive has extremely high crosslinking density and cohesive strength, excellent heat resistance and chemical corrosion resistance, making it suitable for crosslinking coating areas with extremely high strength requirements or harsh operating environments. It is understandable that the first and second UV-curable adhesives are pressure-sensitive adhesives, which initially have pressure-sensitive tack. The UV cross-linking adhesive has lower initial tack. If structural adhesive is used in the weak adhesive area, it may not have sufficient initial tack before curing and cannot stably adhere to the outer film before UV curing. If pressure-sensitive adhesive is used in the transition area, the bond strength improvement after curing is limited and cannot achieve the ideal reinforcement effect.

[0040] Furthermore, in one embodiment, a transition coating portion is provided between the transparent portion and the cured portion, and the transition coating portion is coated with a UV crosslinking curable adhesive; the light transmittance of the corresponding area of ​​the transition coating portion along the direction from the transparent portion to the cured portion is gradient-distributed, and the light transmittance is 50% to 85%. In this embodiment, the crosslinking degree of the transition coating portion near the cured portion is higher, and the bonding strength is significantly improved; the crosslinking degree of the transition coating portion near the transparent portion is lower, and the bonding strength changes gradually, thereby forming a continuous gradient distribution of bonding strength. This avoids the performance abrupt change caused by the direct transition from a weak bonding area to a strong bonding area, thereby eliminating stress concentration points at the interface, avoiding local stress concentration caused by excessive performance differences, and improving the structural stability and integrity of the protective film during cold carving and peeling.

[0041] In one embodiment, the thickness of the first and second photocurable adhesives after curing is 5μm-50μm; the thickness of the base film is 25μm-100μm; and the thickness of the outer film is 25μm-100μm. In this embodiment, the thickness of both the first and second photocurable adhesives is 5μm-50μm, ensuring reliable initial adhesion and preventing insufficient energy penetration during photocuring due to excessive adhesive thickness, which could affect the uniformity of crosslinking in weak adhesive areas. The bottom film thickness is greater than 25μm to ensure sufficient mechanical strength and dimensional stability during cold carving, effectively resisting external forces and preventing excessive deformation or tearing. The bottom film thickness is less than 100μm to ensure good flexibility and conformability. The outer film thickness is greater than 25μm to ensure sufficient mechanical strength and tensile strength, maintaining structural integrity during bonding, photocuring, and cold carving, effectively protecting the internal adhesive structure. The outer film thickness is less than 100μm, as excessive thickness would lead to light energy attenuation and prevent excessive step height between the outer and bottom films, which could affect the overall bonding smoothness.

[0042] Furthermore, in one embodiment, after the outer film is laminated, a pressing process is performed first, followed by the photocuring process. The pressing pressure is 0.1 MPa-1.0 MPa, and the pressing temperature is 25℃-60℃. In this embodiment, by applying a uniform pressure of 0.1 MPa-1.0 MPa, the photocurable adhesive layer between the outer film and the base film is allowed to flow and spread fully, and air bubbles at the interface are squeezed out or compressed. The viscosity of the adhesive layer is appropriately reduced by the pressing temperature, enhancing its wettability and flowability, further promoting complete contact at the interface. After the pressing process, the laminated interface is flat and free of air bubbles, providing a uniform light transmission path for subsequent photocuring and avoiding light scattering or uneven curing caused by air bubbles. The synergistic effect of the pressing pressure and temperature ensures that the adhesive layer achieves a uniform thickness distribution and an ideal interface wetting state before curing, improving the preparation quality and product consistency of the strong and weak adhesive molded protective film.

[0043] Furthermore, in one embodiment, after the photocuring process is completed, the following step is also included: The protective film formed by the strong and weak adhesives is subjected to an aging treatment, placed at a temperature of 40℃-60℃ for 24h-72h. In this embodiment, the cohesive strength of the first photocurable adhesive is further stabilized, and the internal stress generated during the photocuring process is eliminated. In this embodiment, the first UV-curable adhesive remains in a non-crosslinked or low-crosslinked state during the UV curing process due to the shielding of the light-shielding part. Placed at a moderate temperature of 40℃-60℃ for 24-72 hours, it provides sufficient thermal energy to the adhesive molecular chains, allowing them to slowly relax to a more stable conformational state. This stabilizes the cohesive structure of the adhesive layer. After aging treatment, the bonding strength fluctuation range of the first UV-curable adhesive is significantly reduced, ensuring that the strong adhesive area maintains stable and reliable anchoring force during cold carving. The second UV-curable adhesive and the UV crosslinking adhesive undergo a rapid crosslinking polymerization reaction during UV curing. This crosslinking process generates volume shrinkage and internal stress, which may cause the protective film to warp. By aging at 40℃-60℃, the residual stress in the crosslinking network is released and homogenized through chain segment rearrangement and local structural relaxation, reducing internal stress and thus improving the performance stability, long-term reliability, and product yield of the strong and weak adhesive molded protective film.

[0044] like Figure 2As shown, in one embodiment, the strong-weak adhesive molded protective film 10 includes a base film 100, a strong-weak adhesive layer 200, and an outer film 300 stacked sequentially. One side of the base film 100 has an adhesive layer for adhering to the protective surface. A portion of the base film 100 opposite to the adhesive layer has a second coating area 102 and a first coating area 101. The outer film 300 has a light-shielding portion 210 and a light-transmitting portion 320. The strong-weak adhesive layer 200 includes a first photocurable adhesive layer 210 and a second photocurable adhesive layer 220. The first photocurable adhesive layer 210 is disposed in the second coating area 102, and the second photocurable adhesive layer 220 is disposed in the first coating area 101. The light-transmitting portion 320 is correspondingly disposed in the second coating area 102, and the light-shielding portion 210 is correspondingly disposed in the first coating area 101. In this embodiment, after the outer film 300 is attached to the bottom film 100, the light-transmitting part 320 precisely covers the second coating area 102, and the light-shielding part 210 precisely covers the first coating area 101. The light-transmitting part 320 allows ultraviolet light to pass through, so that the second photocurable adhesive in the second coating area 102 is fully cross-linked, achieving the weak adhesive characteristics of low bonding strength and high tensile strength. The light-shielding part 210 blocks ultraviolet light, so that the first photocurable adhesive in the first coating area 101 remains uncross-linked or low-cross-linked, maintaining the strong adhesive characteristics of high bonding strength. After the outer film 300 is attached, a stepped structure is naturally formed between the light-transmitting part 320 of the outer film 300 and the bottom film 100 due to the difference in adhesive layer thickness, which facilitates the film peeling operation.

[0045] like Figure 2 As shown, in one embodiment, the outer film 300 further includes a curing section 330, which is disposed between the light-transmitting section and the light-shielding section 210. The strong and weak adhesive layer 200 further includes a UV crosslinking curing adhesive layer 230, which is correspondingly disposed in the curing section 330. In this embodiment, the strong and weak adhesive layer 200 forms a sandwich structure of a first photocurable adhesive layer 210, a UV crosslinking curing adhesive layer 230, and a second curing adhesive layer 220. This structure enhances the interfacial bonding temperature and provides strong resistance to external interference through synergistic effects. The first photocurable adhesive layer 210 remains uncrosslinked or in a low-crosslinked state, providing high adhesive strength. The UV crosslinking curing adhesive layer 230 has increased adhesive strength after photocuring, enabling it to provide additional anchoring force during cold carving. The second photocurable adhesive layer 220 has significantly decreased adhesive strength and significantly increased cohesive strength after full crosslinking, achieving low peel force and high tensile strength, ensuring easy peeling and no residue after cold carving.

[0046] Compared with the prior art, this disclosure has at least the following advantages: In the aforementioned process for preparing the strong and weak adhesive protective film, during cold carving and transfer, the outer film and the bottom film are completely bonded together through the first and second UV-curable adhesives. This ensures that there is no relative sliding or lifting between the outer and bottom films, preventing physical interference with cutting tools, fixtures, or automated equipment after the film edges lift. It also eliminates the risk of the protective film shifting or falling off due to accidental pulling of the lifted portion by external force. By blocking light through the light-shielding part, the first UV-curable adhesive maintains high bonding strength, whether cross-linked or not. By allowing light to pass through the light-transmitting part, the cross-linking reaction of the second UV-curable adhesive reduces the bonding strength, forming a weak adhesive bonding area. The increased cohesive strength and tensile strength of the outer film through the cross-linking reaction make the transparent part of the outer film easy to peel from the bottom film, avoiding breakage or adhesive residue during the peeling process. The easy peeling design of the light-transmitting part and the step structure formed between the transparent parts of the bottom film and the outer film constitute the stress point for peeling, thus achieving a convenient and efficient peeling operation.

[0047] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A process for preparing a protective film formed by strong and weak adhesives, characterized in that, Includes the following steps: A base film is obtained, and an adhesive is coated on one side of the base film. A first coating area and a second coating area are formed on the portion of the base film opposite to the adhesive. An outer film is obtained, the outer film having a transparent portion and a light-shielding portion; a first photocurable adhesive is applied to the light-shielding portion, and a second photocurable adhesive is applied to the transparent portion; The outer film coated with the first and second photocurable adhesives is attached to the side of the bottom film away from the adhesive, so that the first photocurable adhesive is correspondingly disposed in the first coating area and the second photocurable adhesive is correspondingly disposed in the second coating area. A strong and weak adhesive protective film is obtained by curing through a photocuring process; wherein, the first photocurable adhesive blocks light through the light-shielding part to maintain an uncrosslinked or low crosslinked state to maintain the bonding strength, and the second photocurable adhesive reduces the bonding strength by initiating a crosslinking reaction through the light transmitted through the transparent part; the bonding strength of the first photocurable adhesive after curing is greater than the bonding strength of the second photocurable adhesive after curing.

2. The preparation process of the strong / weak adhesive molded protective film according to claim 1, characterized in that, The first photocurable adhesive includes at least one of acrylate photocurable pressure-sensitive adhesives, polyurethane photocurable pressure-sensitive adhesives, and silicone photocurable pressure-sensitive adhesives; and / or, The second photocurable adhesive includes at least one of acrylate photocurable pressure-sensitive adhesive, polyurethane photocurable pressure-sensitive adhesive, and silicone photocurable pressure-sensitive adhesive.

3. The preparation process of the strong / weak adhesive molded protective film according to claim 2, characterized in that, The photoinitiator content in the second photocurable adhesive is 0.5wt%-5.0wt%, and the photoinitiator content in the first photocurable adhesive is 0.1wt%-0.5wt%.

4. The preparation process of the strong / weak adhesive molded protective film according to claim 1, characterized in that, The light-shielding part and the transparent part are integrally formed.

5. The preparation process of the strong / weak adhesive molded protective film according to claim 4, characterized in that, The light-shielding part is at least one of a black light-shielding film, a semi-permeable film, a metal coating, and an ink layer, and the ultraviolet light transmittance of the light-shielding part is less than 5%.

6. The preparation process of the strong / weak adhesive molded protective film according to claim 4, characterized in that, The ultraviolet light transmittance of the transparent part is greater than 85%.

7. The preparation process of the strong / weak adhesive molded protective film according to claim 1, characterized in that, The photocuring process uses ultraviolet light irradiation with an irradiation energy of 500 mJ / cm². 2 -3000mJ / cm 2 .

8. The preparation process of the strong / weak adhesive molded protective film according to claim 7, characterized in that, Curing is achieved through a photopolymerization process, including the following steps: With a first light intensity of 500 mJ / cm 2 -700mJ / cm 2 The second photocurable adhesive is pre-cured to partially cross-link the second photocurable adhesive, thereby forming a pre-shaped second photocurable adhesive; Then, with a second light intensity of 1000 mJ / cm 2 -3000mJ / cm 2 Full exposure is performed to further crosslink the second photocurable adhesive to the target viscosity reduction level, while the first photocurable adhesive remains uncrosslinked or only minimally crosslinked due to the light-shielding part.

9. The preparation process of the strong / weak adhesive molded protective film according to claim 1, characterized in that, The bottom film is at least one of PET film, PI film and PO film, and the outer film is at least one of PET film or TPU film.

10. The preparation process of the strong / weak adhesive molded protective film according to claim 1, characterized in that, The thickness of the first and second photocurable adhesives after curing is 5μm-50μm; the thickness of the base film is 25μm-100μm, and the thickness of the outer film is 25μm-100μm.

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