A high-temperature resistant, low-climbing acrylic protective film and its preparation method

Abstract

This invention discloses a high-temperature resistant, low-climbing acrylic protective film and its preparation method. The protective film comprises a polyimide film layer, an acrylic adhesive layer, and a release film layer stacked sequentially. The acrylic adhesive layer is composed of the following raw materials in the indicated mass percentages: 40-60% acrylate soft monomers; 10-20% acrylate hard monomers; 5-15% functionalized monomers; 3-8% high-temperature modifier; 0.5-3% nanocellulose crystals; 1-5% ionic liquid; 0.5-3% crosslinking agent; 0.1-1% initiator; and the balance being solvent. This invention achieves comprehensive technical effects of high-temperature low climbing, stable peel force, and no adhesive residue by rationally designing a multi-component functionalized acrylic adhesive without relying on a high-cost silicone system.

Description

Technical Field

[0001] This invention relates to the field of protective film technology, and in particular to a high-temperature resistant, low-climbing acrylic protective film and its preparation method. Background Technology

[0002] Acrylic protective films are widely used for temporary protection of surfaces such as electronic components, metal sheets, and plastic products due to their advantages such as good initial tack, high transparency, excellent weather resistance, and low cost. In high-temperature processing processes such as semiconductor manufacturing, printed circuit board reflow soldering, metal heat treatment, and high-temperature spraying of automotive parts, the protective film needs to withstand high-temperature environments of 150~250℃ and be easily peeled off after the process, leaving no residue and not contaminating the protected surface.

[0003] However, traditional acrylic protective films generally suffer from three major problems under high-temperature conditions: First, the peel force increases dramatically. The moderate peel force at room temperature often increases significantly after high-temperature treatment, making it difficult to peel off or even damaging the protected surface. Second, the adhesive layer creeps. At high temperatures, the movement of adhesive molecular chains intensifies and the cohesive force decreases. The edge of the adhesive layer flows and expands towards the center of the protected material, increasing the contamination area. Third, adhesive residue remains. High temperatures cause damage to the adhesive layer structure or excessive softening. When peeling off, adhesive residue remains on the protected surface, directly affecting the yield of subsequent processes.

[0004] To address the aforementioned issues, some existing high-temperature protective films utilize silicone adhesives. While silicone protective films offer excellent temperature resistance, they also suffer from significant drawbacks: high cost; easy transfer of the adhesive layer (silicone oil migration), leading to contamination of the protected surface; peel strength heavily influenced by substrate surface energy, resulting in poor stability; and susceptibility to blistering or detachment under high temperature and humidity conditions. Therefore, the market urgently needs a protective film that combines the advantages of acrylic adhesives (high initial tack, high transparency, and low cost) with good temperature resistance.

[0005] In summary, existing acrylic protective films cannot simultaneously meet the requirements of high-temperature processing for peel strength stability, low creepage, and no residue. A key technical challenge in this field is how to enable acrylic adhesives to maintain sufficient cohesion to suppress creepage at high temperatures while also maintaining moderate interfacial adhesion to prevent a sharp increase in peel strength, without introducing a high-cost silicone system. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a high-temperature resistant, low-climbing acrylic protective film and its preparation method, thereby solving the problems of rapid increase in peel force and adhesive layer climbing of traditional acrylic protective films under high-temperature environments.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: The present invention provides a high-temperature resistant and low-climbing acrylic protective film, comprising a polyimide film layer, an acrylic adhesive layer and a release film layer stacked sequentially; The acrylic adhesive layer is composed of the following raw materials in the indicated mass percentages: 40-60% soft acrylate monomers; 10-20% hard acrylate monomers; 5-15% functionalized monomers; 3-8% high-temperature modifier; 0.5-3% nanocellulose crystals; 1-5% ionic liquid; 0.5-3% crosslinking agent; 0.1-1% initiator; and the balance being solvent.

[0008] Furthermore, the thickness of the polyimide film layer is 20-30 μm, the thickness of the acrylic adhesive layer is 8-12 μm, and the thickness of the release film layer is 45-55 μm.

[0009] Preferably, the nanocellulose crystals are surface-modified nanocellulose crystals with a particle size of 50-200 nm and an aspect ratio of 10-50.

[0010] Preferably, the ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0011] Preferably, the acrylate soft monomer is selected from at least one of isooctyl acrylate, n-butyl acrylate, and ethyl acrylate; the acrylate hard monomer is selected from at least one of methyl methacrylate, methyl acrylate, and styrene.

[0012] Preferably, the functionalized monomer is an acrylate monomer containing a carboxyl group, a hydroxyl group, an epoxy group, or an amino group, including at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, and glycidyl methacrylate.

[0013] Preferably, the high-temperature resistant modifier is at least one of silicone-modified acrylate, fluorinated acrylate, or high-temperature resistant silicone resin.

[0014] Furthermore, the protective film has a 180° peel force of 8-12g / 25mm after being attached to a steel plate at room temperature for 20 minutes. After being heat-treated at 200℃ for 2 hours and left at room temperature for 2 hours, the 180° peel force is less than 30g / 25mm, and the peel force increase rate is less than 150%.

[0015] Another aspect of the present invention provides a method for preparing a high-temperature resistant, low-climbing acrylic protective film, which includes the following steps: (1) Preparation of acrylic adhesive: acrylate soft monomers, acrylate hard monomers, functional group monomers, high temperature resistant modifiers, nanocellulose crystals, ionic liquids and some solvents are mixed evenly, an initiator is added, and the mixture is reacted at 60-85℃ for 4-8 hours to obtain an acrylate copolymer solution; the temperature is lowered to below 40℃, a crosslinking agent and the remaining solvent are added, and the mixture is stirred evenly to obtain acrylic adhesive; (2) Coating: The acrylic adhesive is coated onto the polyimide film; (3) Drying: Dry the coated polyimide film in an oven at 80-120℃ for 1-3 minutes to allow the solvent to evaporate; (4) Lamination: The release film is laminated with the dried acrylic adhesive layer to obtain a protective film semi-finished product; (5) Curing: Curing the semi-finished protective film at 40-60℃ for 3-7 days to obtain the high temperature resistant and low climbing acrylic protective film.

[0016] Further, the initiator in step (1) is at least one of benzoyl peroxide, azobisisobutyronitrile, or diisopropyl peroxide dicarbonate; the solvent is at least one of ethyl acetate, toluene, or acetone; and the dry adhesive thickness in step (2) is controlled to be 8-12 μm.

[0017] The beneficial effects of this invention are as follows: (1) After the nanocellulose crystals in the acrylic adhesive layer of the present invention are uniformly dispersed in the adhesive layer, they can construct a three-dimensional physical cross-linking network in the acrylic polymer matrix due to their high crystallinity, high modulus and nanoscale size. This network hardly affects the flexibility of the molecular chain at room temperature, ensuring moderate initial tack and peel force; while in high temperature environment, the network can effectively restrict the thermal movement of polymer molecular chains, inhibit the macroscopic flow and creep of the adhesive layer, thereby fundamentally preventing the phenomenon of the adhesive layer edge climbing towards the center of the protected material, and preventing the problem of residual adhesive caused by excessive decrease in cohesion.

[0018] (2) The introduction of ionic liquid into the acrylic adhesive layer of this invention not only improves the interfacial compatibility between nanocellulose crystals and the acrylate matrix, avoiding the agglomeration of nanocellulose crystal fillers and defects in the adhesive layer, but also dynamically regulates the viscoelastic behavior of the adhesive at high temperatures through the electrostatic interaction between its anions and cations and the polar groups of the polymer. This regulating effect prevents the adhesive layer from experiencing a sharp increase in interfacial adhesion due to excessive softening of the molecular chains under high-temperature conditions, thus avoiding the problem of a surge in peel force. At the same time, the extremely low vapor pressure and excellent thermal stability of the ionic liquid itself ensure that it will not volatilize or migrate during high-temperature processing, maintaining a stable regulating function over a long period of time.

[0019] (3) The introduction of high-temperature resistant modifier in the acrylic adhesive layer of the present invention further reduces the surface energy of the adhesive layer, weakens the interfacial interaction between the adhesive and the surface of the protected material at high temperature, and reduces the risk of increased peel force due to interfacial diffusion or chemical bonding enhancement.

[0020] The high-temperature modifier, nanocellulose crystals, and ionic liquid work together with the cross-linking network to ensure that the acrylic protective film of this invention maintains a balance between cohesion and interfacial adhesion even after high-temperature processes (such as reflow soldering and metal heat treatment). The adhesive layer does not exhibit significant edge creep, and the peel force increases only moderately, far from being difficult to peel or damaging the protected surface. Furthermore, the protected surface remains clean and free of adhesive residue after peeling. In addition, the use of a polyimide film as the substrate further enhances the heat resistance and dimensional stability of the entire film structure, preventing substrate deformation at high temperatures from interfering with the adhesive layer's performance.

[0021] In summary, this invention achieves comprehensive technical effects such as high temperature and low creepage, stable peel force, and no adhesive residue by rationally designing multi-component functionalization of acrylic adhesives without relying on high-cost silicone systems. It can reliably meet the stringent requirements of high-temperature processing processes for temporary protective films in electronic components, metal products, and other products. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a high-temperature resistant, low-climbing acrylic protective film and its preparation method. The protective film comprises a polyimide film layer, an acrylic adhesive layer, and a release film layer stacked sequentially. Exemplarily, the thickness of the polyimide film layer can be 20–30 μm, the dry adhesive thickness of the acrylic adhesive layer can be 8–12 μm, and the thickness of the release film layer can be 45–55 μm, for example, 25 μm, 10 μm, and 50 μm respectively. This thickness combination can balance heat resistance, adhesion performance, and processing adaptability.

[0024] The acrylic adhesive layer is composed of the following raw materials in the indicated mass percentages: 40-60% soft acrylate monomers, 10-20% hard acrylate monomers, 5-15% functionalized monomers, 3-8% high-temperature modifier, 0.5-3% nanocellulose crystals, 1-5% ionic liquid, 0.5-3% crosslinking agent, 0.1-1% initiator, and the balance being solvent. The soft acrylate monomers are preferably at least one of isooctyl acrylate, n-butyl acrylate, or ethyl acrylate, used to provide initial tack and flexibility; the hard acrylate monomers are preferably at least one of methyl methacrylate, methyl acrylate, or styrene, used to adjust the glass transition temperature and cohesive strength; the functionalized monomers are preferably acrylate monomers containing carboxyl, hydroxyl, epoxy, or amino groups, such as at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, or glycidyl methacrylate, used to provide crosslinking reaction sites. The high-temperature modifier is preferably at least one of silicone-modified acrylate, fluorinated acrylate, or high-temperature resistant silicone resin, to reduce surface energy at high temperatures and improve thermal stability. The nanocellulose crystals are preferably surface-modified products with a particle size controlled between 50 and 200 nm and an aspect ratio of 10 to 50. This helps to form a three-dimensional physical cross-linked network in the adhesive layer, inhibiting the flow and creep of the adhesive layer at high temperatures. The ionic liquid is preferably at least one of 1-ethyl-3-methylimidazolium acetate or 1-butyl-3-methylimidazolium hexafluorophosphate, utilizing its low volatility, high stability, and electrostatic / hydrogen bonding interactions to improve component compatibility and dynamically regulate viscoelastic behavior at high temperatures. The cross-linking agent is used to chemically react with functionalized monomers to form a chemical cross-linked network, improving the cohesive strength of the adhesive layer. Exemplarily, the cross-linking agent can be an isocyanate cross-linking agent (such as toluene diisocyanate adduct, hexamethylene diisocyanate trimer), an epoxy cross-linking agent, or a metal chelate cross-linking agent. The initiator is used to initiate the free radical polymerization reaction of the acrylate monomers. For example, the initiator may be selected from at least one of peroxides (such as benzoyl peroxide), azo compounds (such as azobisisobutyronitrile), or diisopropyl peroxide dicarbonate.

[0025] The protective film obtained in this way has a 180° peel force of 8-12g / 25mm after being attached to a steel plate for 20 minutes at room temperature; after heat treatment at 200℃ for 2 hours and then placed at room temperature for 2 hours, the 180° peel force is less than 30g / 25mm, the peel force increase rate is less than 150%, and there is almost no climbing at the edge of the adhesive layer and no adhesive residue after peeling. It can well adapt to high-temperature processing processes such as reflow soldering and metal heat treatment.

[0026] The present invention also provides a method for preparing the above-mentioned protective film, specifically including the following steps: First, prepare the acrylic adhesive by mixing acrylate soft monomers, hard monomers, functional group monomers, high temperature modifiers, nanocellulose crystals, ionic liquids and some solvents evenly, adding an initiator, and reacting at 60-85℃ for 4-8 hours to obtain an acrylate copolymer solution. Then, cool the solution to below 40℃, add a crosslinking agent and the remaining solvent, and stir evenly to obtain the acrylic adhesive. The prepared acrylic adhesive was then coated onto a polyimide film, with the dry adhesive thickness controlled to be 8–12 μm. Next, the coated film is dried in an oven at 80–120°C for 1–3 minutes to allow the solvent to evaporate. The release film is then laminated with the dried adhesive layer to obtain a protective film semi-finished product; Finally, the semi-finished product is aged at 40-60℃ for 3-7 days to allow the cross-linking reaction to proceed fully and the performance to stabilize, thus obtaining the high-temperature resistant and low-climbing acrylic protective film.

[0027] For example, the initiator in the above preparation method can be at least one of benzoyl peroxide, azobisisobutyronitrile, or diisopropyl peroxide dicarbonate, and the solvent can be at least one of ethyl acetate, toluene, or acetone. This preparation method features mild process conditions and controllable operation, making it suitable for industrial production.

[0028] To better illustrate the technical solution of this invention, the specific formulations of several embodiments and comparative examples are given below, as shown in Table 1. It should be noted that the amounts of each component in Table 1 are by mass, with the solvent amount being the balance, ensuring that the total number of all components (including the solvent) is 100 parts. In each embodiment and comparative example, the ionic liquid is selected from 1-ethyl-3-methylimidazolium acetate; the crosslinking agent is an isocyanate crosslinking agent (such as toluene diisocyanate adduct); the initiator is benzoyl peroxide; and the solvent is ethyl acetate.

[0029] Table 1 The protective films prepared in each embodiment and comparative example were subjected to performance tests, and the results are shown in Table 2 below.

[0030] Table 2 Examples 1-4 all contain nanocellulose crystals, ionic liquids, and high-temperature modifiers. They exhibit moderate peel strength at room temperature (9.8-10.5 g / 25 mm), and the peel strength after high temperature is controlled at 20.8-24.3 g / 25 mm. The rate of rise is less than 150%, the climbing height does not exceed 0.5 mm, and there is no residue, demonstrating excellent high-temperature stability.

[0031] In contrast, Comparative Examples 1-3, lacking at least one of nanocellulose crystals or ionic liquids, exhibited significantly increased peel strength after high temperatures, with an increase rate exceeding 210%, and more pronounced issues with peel height and residual adhesive. Comparative Example 4, lacking both high-temperature modifiers and nanocellulose and ionic liquids, showed the worst performance.

[0032] The above results indicate that there is a significant synergistic effect between nanocellulose crystals and ionic liquids, and neither can be dispensed with. When used together with a high-temperature modifier, it achieves a comprehensive effect of low climbing at high temperatures, low peel strength increase, and no residue.

[0033] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0034] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-temperature-resistant low-climbing acrylic protective film, characterized in that, It includes a polyimide film layer, an acrylic adhesive layer, and a release film layer stacked sequentially; The acrylic adhesive layer is composed of the following raw materials in the indicated mass percentages: 40-60% soft acrylate monomers; 10-20% hard acrylate monomers; 5-15% functionalized monomers; 3-8% high-temperature modifier; 0.5-3% nanocellulose crystals; 1-5% ionic liquid; 0.5-3% crosslinking agent; 0.1-1% initiator; and the balance being solvent.

2. The high-temperature-resistant low-climbing acrylic protective film according to claim 1, characterized in that, The thickness of the polyimide film layer is 20-30 μm, the thickness of the acrylic adhesive layer is 8-12 μm, and the thickness of the release film layer is 45-55 μm.

3. The high-temperature-resistant low-climbing acrylic protective film according to claim 1, characterized in that, The nanocellulose crystals are surface-modified nanocellulose crystals with a particle size of 50-200 nm and an aspect ratio of 10-50.

4. The high-temperature-resistant low-climbing acrylic protective film according to claim 1, characterized in that, The ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium hexafluorophosphate.

5. The high-temperature-resistant low-climbing acrylic protective film according to claim 1, characterized in that, The acrylate soft monomers are selected from at least one of isooctyl acrylate, n-butyl acrylate, and ethyl acrylate; the acrylate hard monomers are selected from at least one of methyl methacrylate, methyl acrylate, and styrene.

6. The high-temperature-resistant low-climbing acrylic protective film according to claim 1, characterized in that, The functionalized monomer is an acrylate monomer containing a carboxyl group, a hydroxyl group, an epoxy group, or an amino group, including at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, and glycidyl methacrylate.

7. The high-temperature-resistant low-sag acrylic protective film according to claim 1, wherein The high-temperature resistant modifier is at least one of silicone-modified acrylate, fluorinated acrylate, or high-temperature resistant silicone resin.

8. The high-temperature resistant, low-creep acrylic protective film according to claim 1, characterized in that, The protective film has a 180° peel force of 8-12g / 25mm after being attached to a steel plate at room temperature for 20 minutes. After being heat-treated at 200℃ for 2 hours and left at room temperature for 2 hours, the 180° peel force is less than 30g / 25mm and the peel force increase rate is less than 150%.

9. A method for preparing a high-temperature resistant, low-climbing acrylic protective film as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Preparation of acrylic adhesive: acrylate soft monomers, acrylate hard monomers, functional group monomers, high temperature resistant modifiers, nanocellulose crystals, ionic liquids and some solvents are mixed evenly, an initiator is added, and the mixture is reacted at 60-85℃ for 4-8 hours to obtain an acrylate copolymer solution; the temperature is lowered to below 40℃, a crosslinking agent and the remaining solvent are added, and the mixture is stirred evenly to obtain acrylic adhesive; (2) Coating: The acrylic adhesive is coated onto the polyimide film; (3) Drying: Dry the coated polyimide film in an oven at 80-120℃ for 1-3 minutes to allow the solvent to evaporate; (4) Lamination: The release film is laminated with the dried acrylic adhesive layer to obtain a protective film semi-finished product; (5) Curing: Curing the semi-finished protective film at 40-60℃ for 3-7 days to obtain the high temperature resistant and low climbing acrylic protective film.

10. The preparation method according to claim 9, characterized in that, The initiator in step (1) is at least one of benzoyl peroxide, azobisisobutyronitrile, or diisopropyl peroxide dicarbonate; the solvent is at least one of ethyl acetate, toluene, or acetone; and the dry adhesive thickness in step (2) is controlled to be 8-12 μm.

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