Multilayer gradient function integrated pet matte composite release film and preparation method thereof

Abstract

This invention discloses a multilayer gradient functional integrated PET matte composite release film and its preparation method. The release film has a five-layer co-extruded biaxially stretched structure, comprising, from one side to the other: a surface functional coating, a first matte structural layer, a reinforcing core layer, a second functional layer, and a heat-sealing / treatment layer. The surface functional coating is formed by baking and curing a fluorosilicone copolymer release coating liquid; the first matte structural layer is composed of PET resin, matte PET resin, and permanent antistatic PET resin; the reinforcing core layer is composed of PET resin and nano-inorganic particle reinforcing masterbatch; the second functional layer is composed of PET resin, halogen-free flame-retardant PET resin, and antibacterial PET resin; and the heat-sealing / treatment layer is composed of low-melting-point PET copolymer or corona-treated PET. This invention also provides a method for preparing the release film. The release film prepared by this invention has a release force as low as 8-13 g / inch and exhibits excellent antistatic durability, flame retardancy (LOI≥27%), antibacterial properties (≥99%), and high matte effect (haze≥68%).

Description

Technical Field

[0001] This invention relates to the field of polymer film materials technology, and more specifically, to a multilayer gradient functional integrated PET matte composite release film suitable for electronic product labels, flexible circuit board lamination, medical packaging, and high-end decorative materials. This invention also relates to a method for preparing the PET matte composite release film. Background Technology

[0002] Release film, also known as peel-off film, release film, or anti-stick film, is a functional film that lies between an adhesive material and other substrates. Its core function is to provide necessary protection when in contact with specific pressure-sensitive adhesives or bonding agents, while allowing for easy peeling when needed, without adhesive transfer or residue. The performance of the release film directly affects the efficiency and yield of downstream processing steps such as die-cutting, lamination, and coating.

[0003] Currently, release films are widely used in numerous fields such as electronics, printing, packaging, pharmaceuticals, and automotive. Especially in the electronics industry, with the increasing prevalence of smartphones, wearable devices, and flexible displays, the performance requirements for release films are becoming increasingly stringent. For example, in the manufacturing process of flexible printed circuit boards (FPCs), release films are used to cover the bonding and protection between the film and the substrate, requiring them to prevent adhesive overflow and residue under high temperature and pressure, and to maintain stable peel force. In the field of electronic product labels, release films are not only required to have excellent release performance, but also to have a matte finish similar to frosted glass to reduce glare and enhance visual quality.

[0004] Traditional release films are mostly made by coating a layer of silicone release agent onto polyethylene terephthalate (PET) film. However, this traditional approach has several limitations. First, the adhesion between the silicone release agent and the PET substrate is limited. Under high temperature or long-term storage conditions, small-molecule silicone components can easily migrate to the film surface, and even transfer to the adhesive layer or electronic components in contact with it, causing "silicone contamination" and affecting subsequent printing, plating, or bonding processes. Second, ordinary PET films have high transparency and a gloss level typically above 90%, which can produce strong glare when used for electronic tags or decorative films, resulting in poor visual effects. Although matte PET films can be prepared by adding matting agents such as silica, relying solely on substrate matting often makes it difficult to balance the adhesion of the release coating with the uniformity of the matte effect.

[0005] To address these issues, the industry has explored various technologies. Multilayer co-extrusion technology has become a research hotspot due to its ability to composite materials with different properties onto a single film. For example, patent document CN203419392U discloses a five-layer co-extruded matte release film, whose structure includes an upper surface layer (release layer), an upper sub-surface layer (homogeneous layer), a core layer (homogeneous functional layer), a lower sub-surface layer (homogeneous layer), and a lower surface layer (matte release layer). This technology simplifies the production process through a one-step five-layer co-extrusion molding process and achieves a combination of release and matte effects. However, the release function of this solution mainly relies on the properties of the resins in the upper and lower surface layers, limiting the range of release force control. Furthermore, the functional definition of its "homogeneous functional layer" is somewhat vague, failing to clearly endow the film with multiple functions such as antistatic, flame retardant, or antibacterial properties.

[0006] Another patent document, CN213798447U, discloses an antistatic biaxially oriented nylon release film with a more complex structure, including a release layer, a base coating, an antistatic coating, and five co-extruded nylon substrate layers. This solution addresses static electricity issues by using a specialized antistatic coating; however, the nylon substrate is expensive, has high water absorption, and its heat resistance is inferior to PET, posing a risk of dimensional instability in certain high-temperature applications. Furthermore, the gradient design and synergistic effect of the functional layers in its multilayer structure still need optimization.

[0007] In summary, current technologies still lack a PET-based release film that can achieve stable, low-migration release properties while effectively integrating multiple functions such as matte finish, antistatic properties, flame retardancy, and antibacterial properties through ingenious gradient structure design. In particular, how to solve the compatibility issue between the fluorosilicone release coating and the multilayer co-extruded substrate, and how to achieve functional synergy through interlayer material design, are the current bottlenecks in technological development. Summary of the Invention

[0008] In view of the shortcomings of the prior art described above, the primary objective of this invention is to provide a multilayer gradient functional integrated PET matte composite release film to solve the technical problems of unstable release force, easy silicone migration, single function, and difficulty in simultaneously achieving matte effect and mechanical properties in existing release films. Another objective of this invention is to provide a method for preparing the aforementioned multilayer gradient functional integrated PET matte composite release film. This method is simple, easy to industrialize, and produces a film with excellent comprehensive properties.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a multi-layer gradient functional integrated PET matte composite release film, characterized in that the release film is a five-layer co-extruded biaxially stretched structure, comprising, from one side to the other: a surface functional coating (1), a first matte structural layer (2), a reinforcing core layer (3), a second functional layer (4), and a heat-sealing / treatment layer (5). The five-layer structure is extruded in one step through a five-layer co-extrusion die to form a composite base film with functional gradients, and then a surface functional coating is applied to the surface of the base film.

[0010] The surface functional coating (1) is located on the outermost side of the film and is the interface layer that is in direct contact with the substrate. Its main function is to provide a stable and controllable release force, while giving the film surface good stain resistance and scratch resistance.

[0011] The surface functional coating (1) is formed by baking and curing a modified fluorosilicone release agent. Although traditional silicone release agents have moderate release forces, they suffer from the aforementioned migration problem. This invention introduces a fluorosilicone copolymer, which utilizes the extremely low surface energy of fluorine (typically below 20 mN / m) to significantly reduce the surface tension of the coating, thereby achieving a lower and more stable release force. At the same time, the introduction of siloxane segments ensures good adhesion and flexibility between the coating and the substrate.

[0012] In this invention, the thickness of the surface functional coating (1) is 0.5-3 micrometers. If the thickness is too thin, it is difficult to form a continuous and uniform coating, and the release force is unstable; if the thickness is too thick, it will not only increase the cost, but may also lead to a decrease in the cohesive strength of the coating and the risk of coating transfer.

[0013] The modified fluorosilicone release coating liquid has the following typical formulation composition by weight percentage: 15-25% fluorosilicone copolymer, 2-6% crosslinking agent, 1-4% nano-matte filler, and 65-80% solvent.

[0014] The fluorosilicone copolymer is a block copolymer containing both perfluoropolyether and polysiloxane segments in its molecular chain. The perfluoropolyether segments provide extremely low surface energy and excellent chemical inertness, while the polysiloxane segments provide good film-forming properties and reactivity with crosslinking agents. Such copolymers can be prepared by free radical polymerization or polycondensation reactions using existing technologies.

[0015] The crosslinking agent is used to react with active groups (such as hydroxyl and amino groups) in the fluorosilicone copolymer to form a three-dimensional network structure, thereby improving the cohesive strength and temperature resistance of the coating. Suitable crosslinking agents include, but are not limited to, isocyanate crosslinking agents, melamine-formaldehyde resin, and epoxy resin.

[0016] The nano-scale matte filler can not only adjust the gloss of the coating and assist in the matte effect, but also improve the wear resistance and hardness of the coating to a certain extent. Available nano-scale matte fillers include nano-silica, nano-alumina, nano-calcium carbonate, etc., with spherical silica with a particle size of 20-200 nm being preferred.

[0017] The solvent is used to dissolve and dilute the components and adjust the viscosity of the coating solution to suit the coating process. Available solvents include isopropyl ether, ethyl acetate, butanone, toluene, etc., or mixtures thereof. Considering environmental friendliness and coating safety, a mixture of isopropyl ether and ethyl acetate is preferred.

[0018] The first matte structural layer (2) is located below the surface functional coating (1) and is one of the core layers for achieving the matte effect and antistatic function of this invention. This layer is composed of PET resin, matte PET resin, and antistatic PET resin through melt blending. The weight percentages of each component are: PET resin 50-70%, matte PET resin 20-35%, and antistatic PET resin 5-15%. The thickness of this layer accounts for 10-20% of the total film thickness.

[0019] PET resin, as the base resin, provides basic film-forming properties and mechanical properties. The preferred PET resin is film-grade polyester chips with an intrinsic viscosity of 0.60-0.75 dL / g. Matte PET resin is key to achieving the matte effect. Matte PET resin typically refers to PET chips containing particles incompatible with PET (such as cross-linked PMMA microspheres or silica microparticles), or PET with certain crystal defects formed by copolymerization modification with a third monomer. During biaxial stretching, these particles or defects can induce fine interfacial peeling or scattering centers, thereby disrupting the surface smoothness of the film, producing diffuse reflection, and exhibiting a matte effect. In this invention, the amount of matte PET resin added needs to be precisely controlled: below 20%, the matte effect is not obvious, and the haze value is low; above 35%, it may lead to a decrease in the mechanical properties of the film and easy film breakage during stretching.

[0020] Antistatic PET resin is used to address the problems of electrostatic adsorption and electrostatic breakdown that easily occur in films during processing and use. This invention preferably uses PET chips containing a permanent antistatic agent. The permanent antistatic agent is a polyether amide block copolymer. This type of antistatic agent forms a microphase-separated structure with the PET matrix, creating fine conductive channels within the film and dissipating static charge through an ionic conductivity mechanism. Compared to traditional small-molecule quaternary ammonium salt antistatic agents, permanent antistatic agents are unaffected by environmental humidity and do not become ineffective or cause contamination due to migration; their antistatic effect is permanent. By directly introducing the antistatic function into the first matte structural layer, the process complexity and interlayer adhesion problems associated with separately coating an antistatic layer are avoided.

[0021] The reinforcing core layer (3) is the main structural support of the entire composite membrane, and plays a decisive role in the tensile strength, elastic modulus and thermal stability of the membrane.

[0022] This layer is composed of a blend of PET resin and toughening and reinforcing masterbatch. The toughening and reinforcing masterbatch is a PET composite material modified with nano-inorganic particles, with a weight percentage of 85-95% PET resin and 5-15% toughening and reinforcing masterbatch. This layer accounts for 40-60% of the total thickness and is the thickest of the five layers.

[0023] The introduction of nano-inorganic particles not only acts as a nucleating agent, increasing the crystallization rate and crystallinity of PET, thereby improving the rigidity and heat resistance of the film, but also induces microcracks and shear bands at the particle-matrix interface, absorbing impact energy and thus playing a toughening role. Commonly used nano-inorganic particles include nano-silica, nano-calcium carbonate, and nano-montmorillonite. Surface-organically modified nano-silica is preferred to improve its dispersibility in the PET matrix. The amount of toughening and reinforcing masterbatch added needs to be optimized: below 5%, the toughening and reinforcing effect is not obvious; above 15%, particle agglomeration may lead to increased film defects and abnormally high haze.

[0024] The second functional layer (4) is located on the other side of the reinforcing core layer. It mainly imparts flame retardant and antibacterial functions to the film, providing protection for the film in fields such as medical and electronic applications where safety and hygiene are highly required.

[0025] This layer is composed of a blend of PET resin, flame-retardant PET resin, and antibacterial PET resin. The weight percentages of each component are: 70-85% PET resin, 8-15% flame-retardant PET resin, and 5-12% antibacterial PET resin. This layer accounts for 10-20% of the total thickness.

[0026] Flame-retardant PET resin refers to PET chips containing flame-retardant elements. To comply with current environmental trends, this invention preferably uses halogen-free flame-retardant PET resin, such as copolymer or blended PET containing phosphorus-based flame retardants (e.g., DOPO derivatives). Phosphorus-based flame retardants promote char formation during combustion, creating a dense char layer that isolates heat and oxygen, thus achieving flame retardancy. By designing the flame-retardant layer in the middle and lower layers of the film, the surface functional layers can be protected from rapid damage upon exposure to fire, resulting in better flame-retardant performance. The amount of flame-retardant PET resin added should ensure that the limiting oxygen index (LOI) of the film reaches 26% or higher.

[0027] Antibacterial PET resin refers to PET chips containing antibacterial agents. These agents can be inorganic (such as silver ion zeolite or silver ion glass) or organic (such as chitosan or quaternary ammonium salts). Silver ion zeolite is preferred due to its good heat resistance and high safety. The amount of antibacterial PET resin added must ensure that the film maintains an antibacterial rate of greater than 99% against common bacteria such as Escherichia coli and Staphylococcus aureus.

[0028] The heat-sealing / treatment layer (5) is located in the innermost layer of the film, on the opposite side from the first matte structural layer. This layer is a designable interface layer whose function can be adjusted according to the specific application requirements of downstream customers. This layer is composed of low-melting-point PET copolymers (such as PETG, i.e., polyethylene terephthalate-1,4-cyclohexanediol ester), and its thickness accounts for 5-15% of the total thickness. PETG has a lower glass transition temperature and melting point than ordinary PET, thus having good heat-sealing performance. When the release film needs to be laminated with other substrates (such as cardboard, foam) by hot pressing, this heat-sealing layer can melt and bond under heating conditions, acting as an adhesive and eliminating the need for separate adhesive coating.

[0029] This layer can also be made of ordinary PET resin, but it undergoes online corona treatment to increase its surface tension to over 52 dyn / cm, so that users can perform secondary coating or printing later.

[0030] By setting this flexible functional layer, the release film of the present invention is no longer a product with a fixed function, but a platform-type technical solution that can be customized according to customer needs, significantly broadening its application scope.

[0031] This invention also provides a method for preparing the above-mentioned multilayer gradient functional integrated PET matte composite release film, the method comprising the following steps: Step 1: Preparation of Surface Functional Coating Solution The formulated amounts of fluorosilicone copolymer, crosslinking agent, and nano-sized matte filler are added to the solvent. First, pre-disperse the mixture at a low speed (e.g., 300-500 rpm), then transfer it to a high-speed disperser and disperse at 1000-2000 rpm for 30-60 minutes to ensure complete deagglomeration of the nanoparticles. Filter the dispersed mixture through a 200-400 mesh screen to remove undispersed agglomerates. Allow the filtered coating solution to stand for 2-4 hours to degas and set aside. The final coating solution should have a solid content of 20-30% and a viscosity of 50-200 cPs (25℃) to suit the microgravure coating process.

[0032] Step 2: Preparation of each layer of mixture According to the formulation of the first matte structural layer, reinforcing core layer, second functional layer, and heat-sealing / treatment layer, PET resin chips and corresponding functional masterbatches (matte masterbatch, antistatic masterbatch, reinforcing masterbatch, flame-retardant masterbatch, antibacterial masterbatch, heat-sealing masterbatch, etc.) are fed into a mixer for mechanical mixing to ensure uniform distribution of each component. The mixing time is generally 10-20 minutes. The mixed material is then sent to a dehumidifying drying tower for deep drying. The drying conditions are typically: temperature 120-150℃, time 3-6 hours, dew point below -40℃. The moisture content of the dried material should be controlled below 50ppm to prevent hydrolytic degradation during extrusion.

[0033] Step 3: Melt co-extrusion and biaxial stretching The five dried mixtures are separately fed into five single-screw or twin-screw extruders. The temperature of each extruder is independently controlled according to the material characteristics, generally between 260-290℃. After the materials are melted and plasticized in the extruders, the precisely metered melt is conveyed to a five-layer co-extrusion distributor. The distributor combines the five melt streams according to a set layer thickness ratio (controlled by the extruder speed) and then enters the T-die. After being extruded from the die, the melt is rapidly cooled on the quench rolls to form a cast sheet. The thickness of the cast sheet is controlled by the die opening and the air knife pressure.

[0034] The cast film then enters the biaxial stretching process. First, longitudinal stretching occurs: the cast film is heated on preheating rollers to above the glass transition temperature of PET (approximately 80-90°C), and then stretched using rollers with different speed differences, typically with a stretch ratio of 3.0-4.0 times. The longitudinally stretched film then enters the transverse stretching machine. Inside the transverse stretching machine, the film is first heated in the preheating zone, and then transversely stretched by gradually expanding guide rails in the stretching zone, typically with a stretch ratio of 3.0-4.0 times. The stretched film undergoes heat setting in the high-temperature setting zone to eliminate internal stress and improve dimensional stability. The heat setting temperature is generally 200-230°C. Finally, the film is cooled in the cooling zone to obtain a five-layer co-extruded biaxially oriented base film.

[0035] Step 4: Online Coating and Post-treatment Before the base film production line is wound up, an online coating station is set up. Using a micro-gravure coating roller or a slit coating head, the surface functional coating liquid prepared in step one is uniformly coated on one side of the first matte structural layer (2) of the base film. Micro-gravure coating technology has the advantages of precise coating amount, good coating uniformity, and no influence from substrate tension fluctuations.

[0036] The coated film is then placed in a multi-temperature zone oven for baking and curing. This invention preferably employs a gradient temperature curing process. For example, the first temperature zone is 80-90℃, primarily to remove solvent; the second temperature zone is 100-110℃ to promote the initial cross-linking reaction; and the third temperature zone is 120-140℃ to ensure full cross-linking and curing of the coating. The total baking time is controlled within 10-40 seconds. Gradient temperature increases prevent rapid solvent evaporation, which could lead to pinholes or orange peel defects on the coating surface, ensuring the density and uniformity of the coating.

[0037] After curing, the film is stretched and trimmed, and finally wound into a large roll by a winding machine. According to customer requirements, the large roll can be slit and packaged to obtain the final product.

[0038] The beneficial effects of this invention are: Compared with existing technologies, the multilayer gradient functional integrated PET matte composite release film and its preparation method provided by this invention have the following outstanding advantages: 1. Functional gradient integration, resulting in significant synergistic effects. This invention abandons the traditional single-layer or simple multi-layer structure, creatively designing a five-layer gradient structure: "surface functional coating - first matte structural layer - reinforcing core layer - second functional layer - heat-sealing / treatment layer". Each layer undertakes a clear and different core function: the surface coating specializes in release lining; the first layer combines matte finish and antistatic properties; the core layer focuses on mechanical reinforcement; the second layer integrates flame retardancy and antibacterial properties; and the bottom layer is responsible for heat sealing or treatment adaptation. This "specialized" gradient design allows each function to be achieved with an optimized material system and layer thickness ratio, avoiding performance compromises or mutual interference caused by piling all functions into the same layer, thus achieving synergistic effects.

[0039] Excellent release properties, completely solving the persistent problem of silicon migration. Using a self-designed fluorosilicone copolymer as the main resin for the release coating fundamentally solves the migration problem of traditional silicone release agents. The fluorine segments in the fluorosilicone copolymer endow the coating with extremely low surface energy (down to 15 mN / m), allowing the release force to be easily controlled at an extremely low level of 5-15 g / inch, with stable release force and minimal fluctuations. Simultaneously, the excellent heat resistance and chemical stability of fluorosilicone materials ensure that they maintain their surface properties even after high-temperature pressing or long-term storage, eliminating the risk of silicon residue contamination of electronic components.

[0040] The matte effect is no longer achieved solely through matting powder in the coating. Instead, it utilizes the bulk scattering of a large amount of matte PET resin in the first matte structural layer, combined with the auxiliary matting effect of nano-scale matte fillers in the coating, to achieve a three-dimensional matte effect from the inside out. This matte effect is uniform, delicate, and natural, like frosted glass. It not only eliminates glare visually but also has a unique, delicate sandy feel, making it ideal for high-end electronic product labels and decorative materials.

[0041] Through the design of the second functional layer, the release film of this invention simultaneously possesses high levels of flame retardancy (UL94 V-0 rating) and antibacterial properties (antibacterial rate >99%). This allows it to be safely used in the interiors of electronic products with stringent fire safety requirements, as well as in medical packaging applications with demanding hygiene conditions. The application of permanent antistatic technology ensures the film's electrostatic protection capability in low-humidity environments.

[0042] The heat-sealing / treatment layer design provides the product with great flexibility, allowing it to be customized into heat-sealing or corona-treated types according to customer needs without altering the main process. The entire production process does not involve solvent-based adhesives and produces no harmful emissions. The entire film is made of PET-based material, free of difficult-to-separate dissimilar materials, and can be completely recycled and granulated after use, achieving material recycling and aligning with the green and environmentally friendly industry trend. Detailed Implementation

[0043] To explain in detail the technical content, structural features, objectives, and effects of the present invention, further explanation is provided below in conjunction with the embodiments.

[0044] In the following examples, all resins and additives used were commercially available industrial products or could be prepared by known methods. The test methods for each performance parameter are as follows: Thickness test: Electronic thickness gauge was used, and the test was conducted according to GB / T 6672-2001 standard.

[0045] Release force test: Referring to GB / T 25256-2010 "Determination of release force of optical functional film release film", TESA 7475 test tape was used to perform a 180° peel test at a speed of 300 mm / min in an environment of 23℃±2℃ and 50%±5% RH.

[0046] Surface resistance test: Refer to GB / T 1410-2006 "Test methods for volume resistivity and surface resistivity of solid insulating materials", and use a high resistance meter to test at a voltage of 500V.

[0047] Limiting Oxygen Index (LOI) Test: The test was conducted in accordance with GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test".

[0048] Antibacterial rate test: Referring to GB / T 31402-2015 "Test method for antibacterial properties of plastic surfaces", Escherichia coli (ATCC 25922) was used as the test species, and the antibacterial rate was tested after 24 hours.

[0049] Haze test: Refer to GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics" and use a haze meter for testing. Example 1

[0050] This embodiment provides a multilayer gradient functional integrated PET matte composite release film with a total thickness of 100 micrometers. Its specific structure and fabrication parameters are as follows: 1. Structure and composition of each layer Surface functional coating: 1.5 micrometers thick. Coating composition (weight percentage): 20% fluorosilicone copolymer (perfluoropolyether-polydimethylsiloxane block copolymer), 4% HDI trimer crosslinking agent, 2% nano-silica (40nm particle size), 74% isopropyl ether. Coating solids content: 22%, viscosity: 120 cPs.

[0051] First matte structural layer: 15 micrometers thick. Composition (weight percentage): 65% PET resin (intrinsic viscosity 0.68 dL / g), 25% matte PET resin (containing 15% cross-linked PMMA microspheres), and 10% antistatic PET resin (containing 20% ​​polyether amide block copolymer).

[0052] Reinforced core layer: 50 micrometers thick. Composition (weight percentage): 90% PET resin (intrinsic viscosity 0.68 dL / g), 10% nano-silica reinforced masterbatch (containing 30% surface-modified nano-silica).

[0053] Second functional layer: 20 micrometers thick. Composition (weight percentage): 78% PET resin (intrinsic viscosity 0.68 dL / g), 12% halogen-free flame-retardant PET resin (containing 8% DOPO derivative), and 10% antibacterial PET resin (containing 5% silver ion zeolite).

[0054] Heat-sealing / treatment layer: 15 micrometers thick. Composition (weight percentage): 100% low-melting-point PET copolymer (PETG, glass transition temperature 80°C).

[0055] Preparation method Preparation of coating solution: Add fluorosilicone copolymer and nano silica to isopropyl ether according to the formula amount, disperse in a high-speed disperser at 1500 rpm for 45 minutes, then add HDI trimer, stir for 10 minutes, filter through a 300-mesh filter, and let stand for 2 hours to remove bubbles.

[0056] Drying of the mixture: The raw materials of each layer are premixed in a mixer for 10 minutes, and then sent to a dehumidifying drying tower and dried at 130°C for 4 hours to reduce the moisture content to less than 50 ppm.

[0057] Co-extrusion and stretching: The five dried mixtures are added to five extruders (temperature settings: zone 1 260℃, zone 2 270℃, zone 3 280℃, zone 4 280℃), and extruded through a five-layer co-extrusion distributor (layer thickness ratio controlled by design) and a T-die (die temperature 280℃). The extruded material is then cast onto a quench roll (quench roll temperature 25℃). The cast material is first stretched 3.3 times at 85℃ by a longitudinal stretching mill, and then enters a transverse stretching mill, preheated at 100-120℃, stretched at 110℃ with a stretch ratio of 3.5 times, and heat-set at 220℃ to obtain the base film after cooling.

[0058] Online coating and winding: Before the base film enters the winding station, the coating liquid is applied to the surface of the first matte structural layer using a micro-gravure coating method. The coated film enters a three-stage drying oven: the first stage at 90℃ / 10 seconds, the second stage at 110℃ / 10 seconds, and the third stage at 130℃ / 10 seconds. After curing, it is pulled, trimmed, and wound to obtain the finished product. Example 2

[0059] This embodiment is basically the same as Embodiment 1, except that the composition of the first matte structural layer and the thickness of the surface functional coating are adjusted.

[0060] Surface functional coating: thickness adjusted to 2.5 micrometers.

[0061] First matte structural layer: The composition is adjusted (by weight percentage): 70% PET resin, 20% matte PET resin, and 10% antistatic PET resin.

[0062] The remaining layers and preparation processes are the same as in Example 1. Example 3

[0063] This embodiment is basically the same as Embodiment 1, except that the composition of the reinforcing core layer and the function of the heat-sealing / treatment layer are adjusted.

[0064] Reinforcing core layer: The composition was adjusted (by weight percentage): 88% PET resin and 12% nano-calcium carbonate reinforcing masterbatch. Heat-sealing / treatment layer: The material was changed to ordinary PET resin, and corona treatment was performed before winding to achieve a surface tension of 54 dyn / cm. The remaining layers and preparation processes were the same as in Example 1. Example 4

[0065] This embodiment is basically the same as Embodiment 1, except that the composition and total thickness of the second functional layer are adjusted. Second functional layer: Composition adjusted (by weight percentage): 70% PET resin, 15% halogen-free flame-retardant PET resin, 15% antibacterial PET resin. Total thickness: Adjusted to 150 micrometers, with the thickness of each layer increasing proportionally. The remaining composition and preparation process are the same as in Embodiment 1. Example 5

[0066] This embodiment is basically the same as Embodiment 1, except that the formulation of the surface functional coating liquid and the curing process are adjusted.

[0067] Surface functional coating: The composition of the coating solution was adjusted to (by weight percentage): 15% fluorosilicone copolymer, 6% isocyanate crosslinking agent, 3% nano-alumina, and 76% ethyl acetate / isopropyl ether mixed solvent (1:1). Curing process: The baking temperature was adjusted to 80℃ / 15 seconds for the first stage, 100℃ / 15 seconds for the second stage, and 120℃ / 10 seconds for the third stage. The remaining layers and preparation processes were the same as in Example 1.

[0068] Comparative Example 1 (Commercially available ordinary three-layer co-extruded matte release film) This comparative example uses a commercially available three-layer co-extruded PET matte release film product from a well-known company as a comparison sample. This product represents a relatively mature matte release film technology solution currently on the market.

[0069] 1. Product Structure The comparative product has a three-layer co-extruded structure, consisting of a surface layer, a middle layer, and an inner layer, with a total thickness of 100 micrometers and a thickness ratio of 1:2:1 for the three layers.

[0070] 2. Composition of each layer Surface layer (release layer): 25 micrometers thick, composed of 80% ordinary PET resin and 20% matte PET resin, without added antistatic functional components. This layer is coated with a silicone release agent, with a coating thickness of approximately 2 micrometers.

[0071] Intermediate layer: 50 micrometers thick, composed of 100% ordinary PET resin, without any added functional additives.

[0072] Inner layer (non-release surface): 25 micrometers thick, composed of 100% ordinary PET resin.

[0073] 3. Release coating The surface is coated with a solvent-based silicone release agent, the main components of which are vinyl-terminated polydimethylsiloxane, hydrogen-containing silicone oil crosslinking agent, and platinum catalyst. The solid content is about 15%, the dry coating weight is about 0.8 g / m², and the baking and curing temperature is 120℃ for 30 seconds.

[0074] 4. Preparation process The conventional three-layer co-extrusion biaxial stretching process is adopted: after each layer of raw material is dried separately, it is melted and plasticized by three extruders, and then extruded into a casting through a three-layer co-extrusion distributor into a T-die. The base film is obtained by longitudinal stretching (stretch ratio 3.2 times), transverse stretching (stretch ratio 3.5 times), and heat setting (220℃). Then, an organosilicon release agent is coated by offline coating, and after baking and curing, it is wound up and slit.

[0075] 5. Performance Characteristics This product has a matte finish (haze approximately 45%), moderate release force (approximately 25g / inch), and low production cost, making it suitable for general applications such as labels and protective films. However, it has the following drawbacks: ① The silicone in the release coating is prone to migration, which may cause silicone contamination after high-temperature pressing; ② It lacks antistatic properties, and its surface resistivity is as high as 10¹⁰. 5 ③ With a strength of Ω / sq or higher, it is prone to electrostatic adsorption during processing; ④ It lacks dual flame retardant and antibacterial functions, limiting its application areas; ⑤ The matte effect is mainly achieved through the surface resin, resulting in a single effect and generally poor uniformity.

[0076] Comparative Example 2 (Five-layer co-extruded functional release film) This comparative example refers to the five-layer co-extrusion structure described in existing technical documents (such as CN203419392U), and combines the common design of commercially available functional release films to construct a release film with a five-layer structure but without adopting the gradient functional integration technology of this invention, in order to verify the inventiveness of the structure of this invention.

[0077] 1. Product Structure The comparative product has a five-layer co-extrusion structure, consisting of, from top to bottom: upper surface layer, upper secondary surface layer, core layer, lower secondary surface layer, and lower surface layer, with a total thickness of 100 micrometers and a thickness ratio of 1:1.5:3:1.5:1.

[0078] 2. Composition of each layer Top layer (release surface): 10 micrometers thick, composed of 85% ordinary PET resin and 15% matte PET resin, without added antistatic agent. This layer is coated with a conventional silicone release agent, with a coating thickness of approximately 1.5 micrometers.

[0079] Top layer: 15 micrometers thick, composed of 95% ordinary PET resin and 5% antistatic masterbatch. The antistatic masterbatch is PET chips containing small-molecule quaternary ammonium salt antistatic agents.

[0080] Core layer: 40 micrometers thick, composed of 90% ordinary PET resin and 10% toughening masterbatch. The toughening masterbatch is PET chips containing 5% nano-calcium carbonate.

[0081] Next surface layer: 20 micrometers thick, composed of 100% ordinary PET resin.

[0082] Bottom layer: 15 micrometers thick, composed of 100% ordinary PET resin, corona treatment is performed before winding to improve surface tension.

[0083] 3. Release coating Similar to Comparative Example 1, a solvent-based silicone release agent was used, the main components of which were vinyl-terminated polydimethylsiloxane, hydrogen-containing silicone oil crosslinking agent, and platinum catalyst. The solid content was about 15%, the dry coating weight was about 0.8 g / m², and the baking curing temperature was 120℃ for 30 seconds.

[0084] 4. Preparation process The process employs a five-layer co-extrusion biaxial stretching process: after drying the five raw materials separately, they are melted and plasticized by five extruders, and then extruded into a casting through a five-layer co-extrusion distributor into a T-die. The base film is obtained by longitudinal stretching (stretch ratio 3.3 times), transverse stretching (stretch ratio 3.5 times), and heat setting (225℃). Then, an organosilicon release agent is applied by offline coating, and after baking and curing, it is wound up and slit.

[0085] 5. Performance Characteristics Compared to Comparative Example 1, this product has the following improvements: ① It adopts a five-layer structure, allowing for individual control of the function of each layer; ② A small-molecule antistatic agent is added to the sub-layer, providing a certain antistatic effect; ③ Nanoparticles are added to the core layer, improving mechanical properties; ④ The lower layer undergoes corona treatment, facilitating subsequent composite processing. However, the following shortcomings still exist: ① The release coating still uses a traditional silicone system, posing a migration risk; ② The antistatic agent is a small-molecule type, easily migrating and precipitating, resulting in a short-lasting antistatic effect; ③ No dedicated flame-retardant or antibacterial functional layers are provided, failing to meet special application requirements; ④ The matte effect still mainly relies on the upper surface resin, with limited effectiveness; ⑤ There is a lack of synergistic design between the functional layers, resulting in low functional integration.

[0086] Performance Testing and Results Analysis The release film samples prepared in Examples 1-5 and Comparative Examples 1-2 were placed in a standard environment (23℃±2℃, 50%±5% RH) for 24 hours, and then various performance tests were performed. The test results are summarized in Table 1.

[0087] Table 1: Performance test results of each embodiment and comparative example

[0088] Discussion of Results: 1. Release Performance: As can be clearly seen from the data in Table 1, the release forces of Examples 1-5 of this invention are all controlled at an extremely low level of 8-13 g / inch, and the values ​​are stable. This is due to the excellent low surface energy characteristics of the fluorosilicone copolymer coating. In contrast, the release forces of Comparative Examples 1 and 2 are as high as 25 g / inch and 22 g / inch, respectively, which are significantly higher than those of this invention. This indicates that the fluorosilicone coating of this invention has a significant advantage in reducing release force compared to traditional organosilicon coatings or release layers directly composed of resin.

[0089] 2. Antistatic properties: The surface resistivity of all embodiments of the present invention is within 10¹⁰. 0 The surface resistivity is between -10¹¹ Ω / sq, meeting the standard for antistatic materials (typically required to be less than 10¹² Ω / sq). This is achieved by adding a permanent antistatic agent to the first matte structural layer, resulting in a long-lasting effect. The surface resistivity of both Comparative Example 1 and Comparative Example 2 is greater than 10¹² Ω / sq. 5 Ω / sq, belonging to insulators, is extremely prone to electrostatic adsorption and electrostatic discharge, and cannot meet the antistatic requirements of electronic product processing.

[0090] 3. Flame Retardant Performance: The limiting oxygen index (LOI) of all embodiments of the present invention is greater than 26%, with Example 4 reaching 31%, indicating that the material has a certain degree of self-extinguishing property and belongs to the category of flame-retardant materials. The LOI of the comparative examples is only 21-22%, belonging to the category of flammable materials. This demonstrates that the halogen-free flame-retardant PET resin introduced into the second functional layer does indeed exert a good flame-retardant effect.

[0091] 4. Antibacterial Properties: All embodiments of this invention exhibit an antibacterial rate exceeding 99% against *Escherichia coli*, demonstrating excellent antibacterial activity. This is a result of the antibacterial PET resin in the second functional layer. The comparative examples, lacking antibacterial components, have an antibacterial rate of 0 and do not possess antibacterial function.

[0092] 5. Matte Finish: The haze values ​​of all embodiments of the present invention are above 65%, reaching a maximum of 72%, exhibiting an excellent matte frosted effect. This is due to the synergistic effect of the high content of matte PET resin in the first matte structural layer and the nano-matte filler in the surface coating. The haze of Comparative Example 1 is only 45%, with a mediocre matte finish; the haze of Comparative Example 2 is 60%, which, although it also has a certain matte finish, is inferior to that of the present invention.

[0093] In summary, the multi-layer gradient functional integrated PET matte composite release film provided by this invention, through a unique five-layer gradient structure design and an innovative material system, successfully integrates multiple functions such as low release force, antistatic properties, flame retardancy, antibacterial properties, and high matte finish into one. Its comprehensive performance is far superior to existing products, and it can meet the increasingly demanding and diversified needs of high-end electronics, medical, and decorative fields.

[0094] The above are merely preferred embodiments of the present invention and do not limit the implementation methods and protection scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, should be included within the patent protection scope of the present invention.

Claims

1. A multi-layer gradient functional integrated PET matte composite release film, characterized in that, The release film is a five-layer co-extruded biaxially stretched structure, which includes, from one side to the other, a surface functional coating (1), a first matte structural layer (2), a reinforcing core layer (3), a second functional layer (4), and a heat-sealing / treatment layer (5); the five-layer structure is extruded in one step through a five-layer co-extrusion die.

2. The multi-layer gradient functional integrated PET matte composite release film according to claim 1, characterized in that, The surface functional coating (1) is formed by baking and curing a modified fluorosilicone release coating liquid, with a thickness of 0.5-3 micrometers; the modified fluorosilicone release coating liquid comprises, by weight percentage: 15-25% fluorosilicone copolymer, 2-6% crosslinking agent, 1-4% nano-matte filler, and 65-80% solvent.

3. The multi-layer gradient functional integrated PET matte composite release film according to claim 1, characterized in that, The first matte structural layer (2) is composed of a blend of PET resin, matte PET resin and antistatic PET resin, with the following weight percentages: PET resin 50-70%, matte PET resin 20-35%, and antistatic PET resin 5-15%; the thickness of this layer accounts for 10-20% of the total film thickness.

4. The multi-layer gradient functional integrated PET matte composite release film according to claim 1, characterized in that, The reinforcing core layer (3) is composed of PET resin and toughening masterbatch. The toughening masterbatch is a PET composite material modified with nano-inorganic particles, and its weight percentage is 85-95% PET resin and 5-15% toughening masterbatch. The thickness of this layer accounts for 40-60% of the total thickness.

5. The multi-layer gradient functional integrated PET matte composite release film according to claim 1, characterized in that, The second functional layer (4) is composed of a blend of PET resin, flame retardant PET resin and antibacterial PET resin, with the following weight percentages: 70-85% PET resin, 8-15% flame retardant PET resin and 5-12% antibacterial PET resin; the thickness of this layer accounts for 10-20% of the total thickness.

6. The multi-layer gradient functional integrated PET matte composite release film according to claim 1, characterized in that, The heat-sealing / treatment layer (5) is composed of low-melting-point PET copolymer, and its thickness accounts for 5-15% of the total thickness.

7. The multi-layer gradient functional integrated PET matte composite release film according to claim 2, characterized in that, The fluorosilicone copolymer is a block copolymer containing perfluoropolyether segments and polysiloxane segments.

8. The multi-layer gradient functional integrated PET matte composite release film according to claim 3, characterized in that, The antistatic PET resin is PET chips containing a permanent antistatic agent, and the permanent antistatic agent is a polyether amide block copolymer.

9. A method for preparing a multilayer gradient functional integrated PET matte composite release film as described in any one of claims 1-8, characterized in that, Includes the following steps: a. Preparation of surface functional coating solution: Fluorosilicone copolymer, crosslinking agent, and nano-sized matte filler are added to solvent, dispersed evenly, and then filtered to remove bubbles; b. Preparation of each layer mixture: The resin raw materials used for the first matte structural layer, the reinforcing core layer, the second functional layer, and the heat-sealing / treatment layer are premixed with the corresponding functional masterbatch and dried respectively; c. Melt co-extrusion and biaxial stretching: The dried mixture of each layer is added to the extruder, and then extruded into a casting through a T-die via a five-layer co-extrusion distributor. After biaxial stretching and shaping, a five-layer co-extruded biaxially stretched base film is obtained. d. Online coating and post-treatment: On the base film production line, the surface functional coating liquid prepared in step a is coated on the surface of the first matte structural layer (2), and then wound up after baking and curing.

10. The preparation method according to claim 9, characterized in that, The baking and curing process described in step d uses a gradient heating process, with a baking temperature of 80-140℃ and a time of 10-40 seconds.

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