Preparation method of high-transmittance anti-yellowing self-adhesive film

Abstract

The invention relates to the technical field of protective films, in particular to a preparation method of a high-light-transmittance anti-yellowing self-adhesive film, which comprises the following steps: respectively preparing an outer-layer blending material, a middle-layer blending material and an inner-layer blending material, mixing low-density polyethylene, uncoiling master batch and an ultraviolet absorbent to form the outer-layer blending material, mixing the middle-layer blending material with a light stabilizer to form the inner-layer blending material, and mixing the inner-layer blending material with the outer-layer blending material to form the high-light-transmittance anti-yellowing self-adhesive film. And the inner-layer blending material is prepared by mixing a self-adhesive material and an antioxidant. Then feeding the three-layer blended material through a three-layer co-extrusion blow molding machine according to a specific proportion, controlling the corresponding heating temperature, carrying out co-extrusion molding to obtain a self-adhesive film blank, finally cooling the film blank to normal temperature in a specific temperature environment, standing, and slitting and rolling. According to the method, through the three-layer function partition design, auxiliaries in all the layers synergistically play a role, and the prepared self-adhesive film has high light transmittance, excellent anti-yellowing performance and stable mechanical performance and can meet the use requirements of various scenes.

Description

Technical Field

[0001] This invention relates to the field of protective film technology, and in particular to a method for preparing a high-transmittance, anti-yellowing self-adhesive film. Background Technology

[0002] Self-adhesive polyethylene protective film, also known as PE protective film, plays an irreplaceable role as a highly efficient and environmentally friendly surface protection material in industrial manufacturing, electronics, building decoration, and public health. Compared with traditional coated films, self-adhesive PE protective film achieves adhesive-free bonding by relying on the material's own viscoelastic properties, offering core advantages such as no residue risk, stable adhesion, low cost, and environmental friendliness, making it a mainstream protective material in the market. With the diversification of application scenarios and the refinement of functional requirements, the technological development of self-adhesive PE protective film shows three major trends: multi-layer co-extrusion structure, functional composite, and long-lasting performance. Its innovative design not only expands the material's application range but also demonstrates significant value in emerging fields.

[0003] Currently, PE self-adhesive film is widely used in the home appliance and building materials industries. However, home appliances and building materials covered with PE self-adhesive film will turn yellow and the performance of the protective film will deteriorate after long-term exposure to the outdoors or prolonged exposure to direct sunlight, which directly affects the customer's user experience.

[0004] Most self-adhesive film products currently on the market adopt a single-layer or simple multi-layer structure design, resulting in low integration of material functions. To achieve anti-yellowing properties, some products add additives such as UV absorbers and light stabilizers to the matrix material, but this is often done by mixing them throughout the entire layer. This method not only easily leads to uneven distribution of additives within the material, causing localized agglomeration and thus reducing film transmittance and affecting transparency requirements, but it may also weaken the individual functional effects of different additives due to interactions throughout the entire layer, making it difficult to form a highly efficient and synergistic anti-aging system. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a high-transmittance, anti-yellowing self-adhesive film. Through a three-layer functional partition design, the precise distribution and synergy of each partition are achieved, solving problems such as low transmittance due to full-layer mixing, poor anti-yellowing effect, easy thermal and oxidative aging and loss of adhesion of self-adhesive material, and difficulty in balancing mechanical and light transmittance properties. Specifically, this is achieved through the following technical solutions.

[0006] This invention discloses a method for preparing a high-transmittance, anti-yellowing self-adhesive film, which specifically includes the following steps: Step 1: Mix low-density polyethylene, uncoiled masterbatch, and ultraviolet absorber evenly using a mixer to obtain the outer layer blend for later use; Step 2: Mix low-density polyethylene and light stabilizer evenly using a mixer to obtain a middle layer blend for later use; Step 3: Mix the self-adhesive and antioxidant evenly using a mixer to obtain the inner layer blend for later use; Step 4: Add the outer layer blend, middle layer blend, and inner layer blend to the first, second, and third feed ports of the three-layer co-extrusion blow molding machine, respectively, and heat them to the set temperature so that each layer blend is in a molten state. Then, extrude the three molten blends simultaneously through the die head to obtain a three-layer self-adhesive film preform. Step 5: Transfer the self-adhesive film blank to an environment of 20-40℃ to cool to room temperature, let it stand for 1-2 hours, then cut and roll it up to obtain a high-transmittance, anti-yellowing self-adhesive film.

[0007] Preferably, in step 1, the mass ratio of low-density polyethylene, unwinding masterbatch, and ultraviolet absorber is 95%–99%: 1%–4%: 0.05%–0.5%.

[0008] Preferably, the ultraviolet absorber in step 1 is a compound of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and triazine-based ultraviolet absorbers in a molar ratio of 0.8–1.2:0.8–1.2:0.8–1.2.

[0009] Preferably, the unwinding masterbatch in step 1 contains 50% to 70% carrier resin, 25% to 45% opening agent, and 5% to 10% auxiliary agent; The carrier resin is linear low-density polyethylene or low-density polyethylene, the opening agent is dicalcium phosphate, and the auxiliary agent is stearic acid and silane coupling agent in equal mass ratio.

[0010] Preferably, the light stabilizer in step 2 is a hindered amine light stabilizer, and its addition amount accounts for 0.05% to 0.5% of the total mass of the middle layer.

[0011] Preferably, the self-adhesive material in step 3 is compounded from polyisobutylene, modified polyethylene, and thermoplastic elastomer in a molar ratio of 0.7-1.3:0.7-1.3:0.7-1.3.

[0012] Preferably, in step 3, the antioxidant is a compound of phenolic antioxidants, amine antioxidants, phosphite antioxidants and sulfide antioxidants in a molar ratio of 0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2, and the amount of antioxidant added accounts for 0.01% to 0.1% of the total mass of the inner layer.

[0013] Preferably, in step 4, the feed mass ratio of the first, second, and third feed inlets of the three-layer co-extrusion blow molding machine is 3-4:3-4:2-4.

[0014] Preferably, in step 4, the heating temperature of the outer layer blend is 150-200°C, the heating temperature of the middle layer blend is 160-230°C, and the heating temperature of the inner layer blend is 160-200°C.

[0015] After adopting the above technical solution, the beneficial effects of the present invention are: 1. Through a three-layer functional zoning design, the UV absorber is concentrated in the outer layer, the light stabilizer is distributed in the middle layer, and the antioxidant is placed in the inner layer, which realizes the precise distribution and synergistic effect of each functional additive, significantly improving the anti-yellowing performance and aging resistance of the self-adhesive film.

[0016] 2. The outer layer uses a specific ratio of unwound masterbatch and UV absorber to effectively inhibit UV intrusion while ensuring high light transmittance. The middle layer light stabilizer inhibits free radical chain reactions, and the inner layer antioxidant prevents thermal and oxidative degradation, thereby extending the overall service life of the film.

[0017] 3. The three-layer structure is based on a low-density polyethylene system with good compatibility. It has strong interlayer bonding, no interface separation, excellent mechanical properties, and maintains a high level of tensile strength and elongation.

[0018] 4. By using premixing and step-by-step feeding processes, the additives are ensured to be uniformly dispersed in the matrix, avoiding light scattering or uneven performance caused by local agglomeration, thus ensuring the overall light transmittance and functional stability of the film.

[0019] 5. The overall preparation process is simple and controllable, suitable for industrial production. The thickness of each layer and the proportion of additives can be adjusted according to actual needs, and it has good prospects for promotion and application flexibility. Detailed Implementation

[0020] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0021] This invention provides a method for preparing a high-transmittance, anti-yellowing self-adhesive film, specifically including the following steps: Step 1 Low-density polyethylene (LDPE), uncoiled masterbatch, and ultraviolet absorber are mixed evenly using a mixer to prepare the outer layer blend material.

[0022] In the above process, the mass ratio of low-density polyethylene, unwinding masterbatch, and ultraviolet absorber is 95%–99%: 1%–4%: 0.05%–0.5%.

[0023] The ultraviolet absorber is composed of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and triazine-based ultraviolet absorbers in a molar ratio of 0.8–1.2:0.8–1.2:0.8–1.2.

[0024] The unwinding masterbatch includes 50%–70% carrier resin, 25%–45% opening agent, and 5%–10% auxiliary agents. The carrier resin is linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE), the opening agent is dicalcium phosphate, and the auxiliary agents are stearic acid and silane coupling agent in equal mass ratios.

[0025] As the outer layer that comes into direct contact with the external environment, this step involves physical blending to uniformly disperse different functional components in a low-density polyethylene matrix. The synergistic effect of these components endows the outer layer with excellent UV aging resistance, good processing fluidity, and opening performance.

[0026] Low-density polyethylene has good optical properties, processing fluidity and flexibility, and is the basic matrix material for the outer layer, providing the basic physical structure and light transmission properties for the self-adhesive film.

[0027] The core function of unwinding masterbatch is to solve the adhesion problem of films during production, storage and use. Its carrier resin is LLDPE or LDPE, which has good compatibility with the outer matrix LDPE and can uniformly disperse the opening agent and auxiliary agents. The opening agent, dicalcium phosphate, forms tiny protrusions on the film surface to reduce the contact area and friction between films. Among the auxiliary agents, stearic acid can further reduce the surface tension of the film, while the silane coupling agent can improve the interfacial bonding force between dicalcium phosphate and the resin matrix.

[0028] Ultraviolet absorbers can selectively absorb ultraviolet rays in external light and convert them into harmless heat energy, thereby preventing the degradation of polymer materials by ultraviolet rays and delaying the yellowing and performance decline of films. Furthermore, different types of ultraviolet absorbers have slightly different wavelength ranges for absorbing ultraviolet rays, so by using them in combination, the anti-ultraviolet spectrum can be further broadened, thereby improving the anti-yellowing effect.

[0029] In this step, each component is added to the mixer in a specific ratio, and the solid particles are uniformly dispersed by mechanical stirring. This ensures that the functional components in the UV absorber and the unwound masterbatch are evenly distributed on the surface and in the gaps between the low-density polyethylene particles, laying the foundation for component homogenization during subsequent extrusion molding.

[0030] Step 2 Low-density polyethylene and light stabilizer are mixed evenly using a mixer and used as a middle layer blend for later use.

[0031] The amount of light stabilizer added accounts for 0.05% to 0.5% of the total mass of the middle layer.

[0032] Among them, the light stabilizer is a hindered amine light stabilizer.

[0033] In the process of mixing low-density polyethylene with light stabilizer, the light stabilizer is first mixed evenly with a small amount of low-density polyethylene, and then the remaining low-density polyethylene is added to complete the final mixing.

[0034] The middle layer, as a functional reinforcement layer of the self-adhesive film, mainly assists the outer layer in improving its anti-aging performance, while maintaining the structural stability and light transmittance of the film.

[0035] The low-density polyethylene is consistent with the outer matrix, ensuring better compatibility between the middle and outer layers and avoiding a decrease in interlayer strength due to material differences. At the same time, the high light transmittance and flexibility of low-density polyethylene ensure that the middle layer does not affect the overall optical and physical properties of the self-adhesive film.

[0036] In addition, the introduction of light stabilizers in the middle layer can work synergistically with the ultraviolet absorbers in the outer layer to form an anti-aging system. The main function of the ultraviolet absorbers in the outer layer is to absorb ultraviolet light, while the hindered amine light stabilizers do not directly absorb ultraviolet light. Instead, they inhibit free radical chain reactions by capturing free radicals such as hydroxyl and alkyl groups generated during the degradation of polymer materials, thus preventing further degradation of the materials.

[0037] In addition, hindered amine light stabilizers can decompose the highly destructive hydrogen peroxide produced during the oxidation process of materials into relatively stable and harmless substances, thereby interrupting the chain degradation reaction that leads to the decline in material performance. Furthermore, the nitrogen and oxygen free radicals in hindered amine light stabilizers are constantly regenerated and can work repeatedly, thus providing long-term anti-aging effects.

[0038] In this step, low-density polyethylene and hindered amine light stabilizers are added to a mixer and uniformly dispersed by mechanical stirring. Since the amount of light stabilizer added is extremely low, in order to avoid its agglomeration, the light stabilizer is usually premixed with a small amount of low-density polyethylene first, and then mixed with a large amount of low-density polyethylene to ensure that the light stabilizer is fully dispersed in the middle layer blend and to avoid the decrease in film transmittance due to excessively high local concentration.

[0039] Step 3 The self-adhesive material and antioxidant are mixed evenly using a mixer and used as the inner layer blend material.

[0040] The self-adhesive material is composed of polyisobutylene, modified polyethylene, and thermoplastic elastomer in a molar ratio of 0.7-1.3:0.7-1.3:0.7-1.3.

[0041] The amount of antioxidant added accounts for 0.01% to 0.1% of the total mass of the inner layer.

[0042] The antioxidant is composed of phenolic antioxidants, amine antioxidants, phosphite antioxidants, and sulfide antioxidants in a molar ratio of 0.8–1.2:0.8–1.2:0.8–1.2:0.8–1.2.

[0043] The inner layer, as the layer in direct contact between the self-adhesive film and the adhered object, must possess good self-adhesion, compatibility, and resistance to heat and oxygen aging.

[0044] Self-adhesive is a polymer material with a low glass transition temperature and high flexibility. Its molecular chain segments are highly mobile and can make close contact with the surface of the object to be bonded under certain pressure. It generates self-adhesion through van der Waals forces, hydrogen bonds and other interactions, ensuring that the self-adhesive film can be firmly adhered to the surface of the object to be bonded.

[0045] The main function of antioxidants is to inhibit the thermo-oxidative aging of self-adhesive materials during processing and use, avoid molecular chain breakage or cross-linking caused by degradation of self-adhesive materials, ensure the long-term stability of the inner layer's self-adhesiveness, and meet the usage requirements of self-adhesive films.

[0046] During the above steps, since the self-adhesive has strong adhesion, a step-by-step mixing method can be adopted. First, the antioxidant is pre-mixed with a small amount of self-adhesive, and then added to a large amount of self-adhesive to ensure that the antioxidant is evenly distributed in the self-adhesive and to avoid oxidation degradation of the self-adhesive during high-temperature processing due to the absence of antioxidant in some areas.

[0047] In addition, during the mixing process of self-adhesive and antioxidant, it is necessary to control the temperature and stirring speed. On the one hand, this will prevent the self-adhesive from clumping due to excessive temperature, and on the other hand, it will ensure that the antioxidant can be evenly dispersed in the adhesive matrix to avoid agglomeration.

[0048] Step 4 The outer layer blend, middle layer blend, and inner layer blend are fed into the first, second, and third feed ports of a three-layer co-extrusion blow molding machine, respectively. The outer layer, middle layer, and inner layer blends are heated to 150–200°C, 160–230°C, and 160–200°C, respectively. The three molten blends are simultaneously extruded through the die head to obtain a three-layer self-adhesive film preform.

[0049] The first, second, and third feed inlets are fed in a mass ratio of 3-4:3-4:2-4.

[0050] In the above steps, the outer, middle, and inner layer blends are melted and plasticized in different extruders, and then the three molten material flows are compounded, extruded, and shaped through a three-layer co-extrusion die to finally obtain a three-layer film preform. Through the three-layer co-extrusion blow molding process, the functions of the outer, middle, and inner layers are organically combined to prepare a three-layer integrated self-adhesive film preform, so that the film has comprehensive properties such as anti-yellowing, high light transmittance, and self-adhesion.

[0051] In addition, the heating temperature of each layer is precisely controlled during the process to ensure that the three melts are temperature matched during lamination, avoiding poor interlayer bonding due to temperature differences. By precisely controlling the feeding ratio of each layer, the product thickness is made uniform, avoiding problems such as interlayer delamination, excessive thickness deviation, and film defects.

[0052] Step 5 The self-adhesive film blank obtained in step 4 is transferred to an environment of 20-40°C and cooled to room temperature. After standing for 1-2 hours, it is slit and rolled up to obtain a high-transmittance, anti-yellowing self-adhesive film.

[0053] During the above steps, after the self-adhesive film preform comes out of the blow molding machine, there is still some residual heat inside, and the molecular chain arrangement is not yet completely stable. Transferring it to an environment of 20-40°C to cool it to room temperature can fully relax the molecular chains inside the film and stabilize the crystal structure, thus avoiding dimensional shrinkage or performance changes in the film during subsequent processing or use due to residual heat.

[0054] To facilitate a further understanding of the present invention, several embodiments and comparative examples are given below.

[0055] Example 1 This embodiment provides a method for preparing a high-transmittance, anti-yellowing self-adhesive film, which specifically includes the following steps: Step 1 Linear low-density polyethylene, low-density polyethylene, dicalcium phosphate, stearic acid, and silane coupling agent are prepared in a mass ratio of 5:5:6:1:1 to form an open-coil masterbatch. Benzophenone-3, cresoltrazolium trisiloxane, and octyltriazine ketone are compounded in a molar ratio of 1:1:1 to form an ultraviolet absorber. Low-density polyethylene, open-coil masterbatch, and ultraviolet absorber are mixed evenly in a mass ratio of 96:3.5:0.5 using a mixer to prepare an outer layer blend for later use.

[0056] Step 2 Low-density polyethylene and bis(2,2,6,6-tetramethyl-4-piperidine) sebacate were mixed evenly in a mixer at a mass ratio of 99.5:0.5 and used as a middle layer blend for later use.

[0057] Step 3 Polyisobutylene, modified polyethylene, and thermoplastic elastomer are compounded in a molar ratio of 1:1:1 to form a self-adhesive material. Bisphenol A, diphenylamine, trinonylphenyl phosphite, and dilauryl thiodipropionate are compounded in a molar ratio of 1:1:1:1 to form an antioxidant. The self-adhesive material and the antioxidant are mixed evenly in a mixer at a mass ratio of 99.9:0.1 and used as the inner layer blend material for later use.

[0058] Step 4 The outer layer blend, middle layer blend, and inner layer blend are fed into the first, second, and third feed ports of a three-layer co-extrusion blow molding machine at a mass ratio of 3.5:3.5:3. The outer, middle, and inner layer blends are heated to 170°C, 200°C, and 180°C, respectively. The three molten blends are then extruded simultaneously through the die head to obtain a three-layer self-adhesive film preform.

[0059] Step 5 The self-adhesive film blank obtained in step 4 was transferred to an environment of 30°C and cooled to room temperature. After standing for 1.5 hours, it was slit and wound up to obtain a high-transmittance, anti-yellowing self-adhesive film.

[0060] Example 2 This embodiment is based on Example 1, but the addition ratio of each component in step 1 is adjusted, specifically as follows: Step 1 Linear low-density polyethylene, low-density polyethylene, dicalcium phosphate, stearic acid, and silane coupling agent are prepared in a mass ratio of 5:5:6:1:1 to form an open-coil masterbatch. Benzophenone-3, cresoltrazolium trisiloxane, and octyltriazine ketone are compounded in a molar ratio of 1:1:1 to form an ultraviolet absorber. Low-density polyethylene, open-coil masterbatch, and ultraviolet absorber are mixed evenly in a mass ratio of 98:1.8:0.2 using a mixer to prepare an outer layer blend for later use.

[0061] The remaining steps are exactly the same as in Example 1.

[0062] Example 3 This embodiment is based on Example 1, but the addition ratio of each component in step 2 is adjusted, specifically as follows: Step 2 Low-density polyethylene and bis(2,2,6,6-tetramethyl-4-piperidine) sebacate were mixed evenly in a mixer at a mass ratio of 99.8:0.2 and used as a middle layer blend for later use.

[0063] The remaining steps are exactly the same as in Example 1.

[0064] Example 4 This embodiment is based on Example 1, but adjusts the addition ratio of each component in step 3, specifically as follows: Step 3 Polyisobutylene, modified polyethylene, and thermoplastic elastomer are compounded in a molar ratio of 1:1:1 to form a self-adhesive material. Bisphenol A, diphenylamine, trinonylphenyl phosphite, and dilauryl thiodipropionate are compounded in a molar ratio of 1:1:1:1 to form an antioxidant. The self-adhesive material and the antioxidant are mixed evenly in a mixer at a mass ratio of 99.95:0.05 to prepare the inner layer blend material for later use.

[0065] The remaining steps are exactly the same as in Example 1.

[0066] Example 5 This embodiment is based on embodiment 1, but adjusts the ratio of the first, second, and third feed inlets in step 4, specifically as follows: Step 4 The outer layer blend, middle layer blend, and inner layer blend are fed into the first, second, and third feed ports of a three-layer co-extrusion blow molding machine at a mass ratio of 4:4:2. The outer, middle, and inner layer blends are heated to 170°C, 200°C, and 180°C, respectively. The three molten blends are then extruded simultaneously through the die head to obtain a three-layer self-adhesive film preform.

[0067] The remaining steps are exactly the same as in Example 1.

[0068] Comparative Example 1 This comparative example involves swapping the outer and middle layers in Example 1 and adjusting the blending heating parameters accordingly. Specifically: Step 1 Linear low-density polyethylene, low-density polyethylene, dicalcium phosphate, stearic acid, and silane coupling agent are prepared in a mass ratio of 5:5:6:1:1 to form an open-coil masterbatch. Benzophenone-3, cresoltrazolium trisiloxane, and octyltriazine ketone are compounded in a molar ratio of 1:1:1 to form an ultraviolet absorber. Low-density polyethylene, open-coil masterbatch, and ultraviolet absorber are mixed evenly in a mass ratio of 96:3.5:0.5 using a mixer to prepare a middle layer blend for later use.

[0069] Step 2 Low-density polyethylene and bis(2,2,6,6-tetramethyl-4-piperidine) sebacate were mixed evenly in a mixer at a mass ratio of 99.5:0.5 and used as the outer layer blend material for later use.

[0070] Step 4 The outer layer blend, middle layer blend, and inner layer blend are fed into the first, second, and third feed ports of a three-layer co-extrusion blow molding machine at a mass ratio of 3.5:3.5:3. The outer, middle, and inner layer blends are heated to 200°C, 170°C, and 180°C, respectively. The three molten blends are then extruded simultaneously through the die head to obtain a three-layer self-adhesive film preform.

[0071] The remaining steps are exactly the same as in Example 1.

[0072] Comparative Example 2 In this embodiment, UV absorbers, light stabilizers, and antioxidants are added to the outer, middle, and inner layers, and the total amount is the same as in Example 1, specifically: Step 1 A UV absorber is prepared by compounding benzophenone-3, cresoltrazol trisiloxane, and octyltriazine in a molar ratio of 1:1:1. A light stabilizer is prepared by compounding bisphenol A, diphenylamine, trinonylphenyl phosphite, and dilauryl thiodipropionate in a molar ratio of 1:1:1:1. An antioxidant is prepared by uniformly mixing the UV absorber, light stabilizer, and antioxidant in a mass ratio of 35:35:6.

[0073] Step 2 Linear low-density polyethylene, low-density polyethylene, dicalcium phosphate, stearic acid, and silane coupling agent are prepared in a mass ratio of 5:5:6:1:1 to form an unwinding masterbatch. Low-density polyethylene, unwinding masterbatch, and additives are mixed evenly in a mass ratio of 96:3.5:0.5 using a mixer to prepare the outer layer blend material.

[0074] Step 3 Low-density polyethylene and additives were mixed evenly in a mixer at a mass ratio of 99.5:0.5 and used as a middle layer blend for later use.

[0075] Step 4 Polyisobutylene, modified polyethylene, and thermoplastic elastomer are compounded in a molar ratio of 1:1:1 to form a self-adhesive material. The self-adhesive material and additives are mixed evenly in a mixer at a mass ratio of 99.9:0.1 to prepare the inner layer blend material for later use.

[0076] Step 5 The outer layer blend, middle layer blend, and inner layer blend are fed into the first, second, and third feed ports of a three-layer co-extrusion blow molding machine at a mass ratio of 3.5:3.5:3. The outer, middle, and inner layer blends are heated to 170°C, 200°C, and 180°C, respectively. The three molten blends are then extruded simultaneously through the die head to obtain a three-layer self-adhesive film preform.

[0077] Step 6 The self-adhesive film blank obtained in step 5 was transferred to an environment of 30°C and cooled to room temperature. After standing for 1.5 hours, it was slit and rolled up to obtain a high-transmittance, anti-yellowing self-adhesive film.

[0078] Comparative Example 3 This comparative example is based on Comparative Example 1, with adjustments made to the amount of adjuvants used in steps 2, 3, and 4, specifically: Step 2 Linear low-density polyethylene, low-density polyethylene, dicalcium phosphate, stearic acid, and silane coupling agent are prepared in a mass ratio of 5:5:6:1:1 to form an unwinding masterbatch. Low-density polyethylene, unwinding masterbatch, and additives are mixed evenly in a mixer in a mass ratio of 95.5:3.5:1 to serve as the outer layer blend material.

[0079] Step 3 Low-density polyethylene and additives are mixed evenly in a mixer at a mass ratio of 99:1, and used as a middle layer blend for later use.

[0080] Step 4 Polyisobutylene, modified polyethylene, and thermoplastic elastomer are compounded in a molar ratio of 1:1:1 to form a self-adhesive material. The self-adhesive material and additives are mixed evenly in a mixer at a mass ratio of 99.8:0.2 to prepare the inner layer blend material for later use.

[0081] The remaining steps are exactly the same as those in Comparative Example 1.

[0082] According to the steps and methods in the above embodiments and comparative examples, corresponding self-adhesive film samples were prepared, and the transmittance and yellowing resistance of each self-adhesive film sample were tested. The tensile strength and elongation of each self-adhesive film sample were also measured.

[0083] Among them, the transmittance was measured by spectrophotometry according to the GB / T 2410-2008 standard, measuring the transmittance in the 380-780nm wavelength range.

[0084] Yellowing resistance testing determines the yellowing resistance of a sample by measuring the color difference before and after UV aging. Aging tests are conducted according to GB / T 14522-2008 standard, using a yellow index meter. Specific parameters are as follows: The UV lamp used for UV aging was UVA-313, with an irradiance of 0.71 W / m². 2 During the irradiation process, a cycle consists of 4 hours of light exposure at 60°C plus 4 hours of cooling at 50°C, with a total cycle time of 300 hours to complete the test. The yellow index YI of the corresponding samples before and after UV aging is measured, and the yellowing index ΔYI is calculated by subtracting the values.

[0085] Tensile strength and elongation were tested using a tensile testing machine. The strength data and elongation at fracture were recorded. The strength data at fracture is the tensile strength, and the ratio of the elongation data to the original sample size is the elongation.

[0086] The samples from each embodiment and comparative example were tested using the above detection and measurement methods, and the results are shown in the table below:

[0087] Analyzing the above data, we can draw the following conclusions: Regarding light transmittance, Examples 1 to 5 all adopted a three-layer functional partition design. The outer and middle layers are based on high-transmittance LDPE, and the UV absorbers, light stabilizers, and antioxidants added to each layer are uniformly dispersed through premixing and other processes. There is basically no problem of light transmittance reduction caused by local agglomeration, and the light transmittance is maintained above 92%.

[0088] In Comparative Example 1, because the outer and middle layers were swapped, the middle layer, which originally contained a light stabilizer, became the outer layer. This caused slight light scattering due to the light stabilizer's distribution on the surface. Furthermore, when the outer layer, which originally contained a UV absorber, became the middle layer, the UV absorber absorbed light internally, resulting in a decrease in transmittance to 85.6%. In Comparative Examples 2 and 3, because various additives were added to each layer, there were slight interactions between the additives, which increased light scattering and absorption. Therefore, their transmittance was lower than that of the example. Comparative Example 3 had a higher amount of additives, and its transmittance was slightly lower than that of Comparative Example 2.

[0089] Regarding resistance to yellowing, in Examples 1-5, the outer layer UV absorber and the middle layer light stabilizer form a synergistic anti-aging system, which can effectively inhibit UV damage and free radical chain reactions. Therefore, the color difference change value ΔYI after UV aging and heat aging is relatively small.

[0090] In Example 2, the absorption capacity of ultraviolet light was weakened due to the reduced amount of ultraviolet absorber added to the outer layer, resulting in a higher ΔYI than in Example 1. In Example 3, the ability to inhibit free radical reactions decreased due to the reduced amount of light stabilizer added to the middle layer, resulting in a slightly higher ΔYI than in Example 1. In Example 4, although the reduced amount of antioxidant added to the inner layer mainly affected the inner layer's resistance to thermo-oxidative aging, a small amount of free radicals diffused to the middle and outer layers, leading to a slightly higher ΔYI than in Example 1. In Example 5, the increased proportion of the outer and middle layers resulted in a thicker anti-aging functional layer and a better anti-yellowing effect, resulting in a slightly lower ΔYI than in Example 1.

[0091] In Comparative Example 1, due to the functional misalignment between layers, the outer light stabilizer could not effectively absorb ultraviolet rays, and the middle ultraviolet absorber had a weak ability to inhibit internal free radicals, resulting in the failure of the anti-aging system and a significant increase in ΔYI. In Comparative Example 2, due to the mixed addition of additives, the synergistic effect was weakened, the anti-aging ability decreased, and ΔYI was higher than that of the Example. In Comparative Example 3, due to the increased amount of additives, although the anti-aging ability was improved to some extent, the interaction between additives was intensified, and the anti-aging system in some areas was unbalanced, resulting in ΔYI lower than that of Comparative Example 1 but higher than that of the Example.

[0092] Regarding strength performance, in Examples 1 to 5, the three-layer material has good compatibility, and the additives are uniformly dispersed without damaging the molecular chain structure. Therefore, the tensile strength is maintained at 18.2 to 19.0 MPa, and the elongation is maintained at 505% to 525%.

[0093] Because the amount of a single additive was adjusted in Examples 2-4, the impact on the molecular chain structure of the material was small, so the mechanical properties were similar to those of Example 1. In Example 5, due to the increased proportion of the outer and middle layers, the overall structure of the material was more stable, and the tensile strength and elongation were slightly higher than those of Example 1.

[0094] Due to the functional change between layers, the interlayer bonding force of Comparative Example 1 decreased slightly, and the reduced anti-aging ability led to slight degradation of the material, resulting in a significant reduction in mechanical properties. In Comparative Examples 2 and 3, due to the mixed addition of additives, some additives had a slight cross-linking effect on the molecular chains, and the uneven distribution of additives between layers affected the bonding force, so the mechanical properties were lower than those of the Example. Furthermore, Comparative Example 3 had a higher amount of additives, and the cross-linking and interface effects were more obvious, resulting in slightly lower mechanical properties than Comparative Example 2.

[0095] The embodiments described above are not exhaustive, nor do they limit the invention to any specific embodiments. Clearly, many modifications and variations can be made based on the above description. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing a high-transmittance, anti-yellowing self-adhesive film, characterized in that, Includes the following steps: Step 1: Mix low-density polyethylene, unwinding masterbatch, and ultraviolet absorber evenly using a mixer to obtain the outer layer blend for later use; Step 2: Mix low-density polyethylene and light stabilizer evenly using a mixer to obtain a middle layer blend for later use; Step 3: Mix the self-adhesive and antioxidant evenly using a mixer to obtain the inner layer blend for later use; Step 4: Add the outer layer blend, middle layer blend, and inner layer blend to the first, second, and third feed ports of the three-layer co-extrusion blow molding machine, respectively, and heat them to the set temperature so that each layer blend is in a molten state. Then, extrude the three molten blends simultaneously through the die head to obtain a three-layer self-adhesive film preform. Step 5: Transfer the self-adhesive film blank to an environment of 20-40℃ to cool to room temperature, let it stand for 1-2 hours, then cut and roll it up to obtain a high-transmittance, anti-yellowing self-adhesive film.

2. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, In step 1, the mass ratio of low-density polyethylene, unwinding masterbatch, and ultraviolet absorber is 95%–99%: 1%–4%: 0.05%–0.5%.

3. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, In step 1, the ultraviolet absorber is a compound of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and triazine-based ultraviolet absorbers in a molar ratio of 0.8–1.2:0.8–1.2:0.8–1.

2.

4. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, The unwinding masterbatch in step 1 contains 50%–70% carrier resin, 25%–45% opening agent, and 5%–10% auxiliary agent. The carrier resin is linear low-density polyethylene or low-density polyethylene, the opening agent is dicalcium phosphate, and the auxiliary agent is stearic acid and silane coupling agent in equal mass ratio.

5. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, In step 2, the light stabilizer is a hindered amine light stabilizer, and its addition amount accounts for 0.05% to 0.5% of the total mass of the middle layer.

6. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, The self-adhesive material in step 3 is composed of polyisobutylene, modified polyethylene, and thermoplastic elastomer in a molar ratio of 0.7-1.3:0.7-1.3:0.7-1.

3.

7. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, In step 3, the antioxidant is a compound of phenolic antioxidants, amine antioxidants, phosphite antioxidants and sulfide antioxidants in a molar ratio of 0.8-1.2:0.8-1.2:0.8-1.2:0.8-1.2, and the amount of antioxidant added accounts for 0.01% to 0.1% of the total mass of the inner layer.

8. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, In step 4, the feed mass ratio of the first, second, and third feed inlets of the three-layer co-extrusion blow molding machine is 3-4:3-4:2-4.

9. The method for preparing the high-transmittance, anti-yellowing self-adhesive film according to claim 1, characterized in that, In step 4, the heating temperature of the outer layer blend is 150-200℃, the heating temperature of the middle layer blend is 160-230℃, and the heating temperature of the inner layer blend is 160-200℃.

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