Multilayer release film and method of manufacturing a multilayer release film

Abstract

The application discloses a multilayer release film, which comprises a release layer, an intermediate layer and a heat-resistant layer; the release layer is arranged on the outer layer of the multilayer release film, the material of the release layer comprises polyolefin resin, the melting point of the polyolefin resin is greater than 200 DEG C, and the dyne value of the polyolefin resin ranges from 15 to 30; the heat-resistant layer is arranged on the outer layer of the multilayer release film and is arranged opposite to the release layer, the material of the heat-resistant layer comprises polyester resin, the melting point of the polyester resin is greater than 200 DEG C, the dyne value of the polyester resin ranges from 35 to 55, and the elongation at break of the polyester resin is greater than 50%; the intermediate layer is arranged between the release layer and the heat-resistant layer, the two sides of the heat-resistant layer are in contact with the release layer and the heat-resistant layer respectively, and the material of the intermediate layer comprises the polyolefin resin of the release layer and the polyester resin of the heat-resistant layer. The multilayer release film has excellent tensile resistance and can prevent the multilayer release film from warping.

Description

Technical Field

[0001] This application relates to multilayer release films and methods for manufacturing the same, and particularly to multilayer release films for flexible printed circuit board (FPC) processing and methods for manufacturing the same. Background Technology

[0002] Flexible printed circuit boards (FPCs) significantly reduce the size and weight of electronic products, improving the ease of circuit board installation. FPCs are primarily composed of metal conductor foil, thermosetting adhesive, and an insulating base film, bonded together by hot pressing. However, several problems arise during the hot pressing process. Firstly, the softened thermosetting adhesive can overflow from the insulating base film and cover the surrounding metal conductor foil, preventing subsequent gold plating or chemical gold treatment of the metal conductor foil and hindering subsequent component soldering. Secondly, the high-temperature, high-pressure environment of FPC processing can easily cause the insulating base film to adhere to the pressing panel of the hot press, leading to damage or wrinkles in the FPC. To address these issues, a release film is placed between the pressing panel of the hot press and the FPC, and then peeled off after the pressing process. During processing, the release film serves to prevent adhesive overflow, provide protection, resist wrinkles, and facilitate easy peeling.

[0003] Release films with this structure include an upper layer, a middle layer, and a lower layer arranged sequentially. The upper and lower layers are primarily made of poly-4-methyl-1-pentene (TPX). TPX possesses excellent heat resistance and good peel performance, making the release film less prone to deformation during heating and allowing for smooth peeling. However, such release films still have the following problems:

[0004] First, TPX material is brittle and prone to cracking during stretching, exhibiting poor compressive strength and failing to meet the requirements of some FPC production processes. This is particularly true in FPC production, where the roll-to-roll process is commonly used, specifically referring to the bonding of FPC raw materials and release film in a "roll-to-roll" manner. In this roll-to-roll process, the release film, with TPX material on both sides, is extremely prone to breakage, significantly impacting FPC production efficiency.

[0005] Secondly, TPX material has a high melting point and high specific heat. Therefore, when using TPX material to produce and process release films, a large amount of energy is required, which increases production costs and is not conducive to energy conservation and emission reduction.

[0006] Secondly, TPX raw materials are expensive and scarce, mainly supplied by Japanese companies, making China vulnerable to supply bottlenecks. Furthermore, release film is closely linked to the development of my country's electronics industry. Therefore, TPX, a high-cost raw material heavily reliant on imports, is unsuitable for large-scale promotion and use, hindering the development of my country's electronics industry.

[0007] To address the above-mentioned technical problems, this invention is proposed. Summary of the Invention

[0008] This invention discloses a multilayer release film, comprising a release layer, an intermediate layer, and a heat-resistant layer. The release layer is disposed on the outer layer of the multilayer release film, and the material of the release layer includes a polyolefin resin with a melting point greater than 200°C and a dyne value ranging from 15 to 30. The heat-resistant layer is disposed on the outer layer of the multilayer release film, opposite to the release layer, and the material of the heat-resistant layer includes a polyester resin with a melting point greater than 200°C, a dyne value ranging from 35 to 55, and an elongation at break greater than 50%. The intermediate layer is disposed between the release layer and the heat-resistant layer, with both sides of the heat-resistant layer in contact with the release layer and the heat-resistant layer, and the material of the intermediate layer includes the polyolefin resin of the release layer and the polyester resin of the heat-resistant layer.

[0009] Furthermore, the polyolefin resin is selected from one or more combinations of TPX, ETFE, and PTFE.

[0010] Furthermore, the polyester resin is selected from one or more combinations of PBT, PET, and PC.

[0011] Furthermore, the ratio of the thickness of the heat-resistant layer to the thickness of the release layer is 1.1 to 5.

[0012] Furthermore, the ratio of the thickness of the heat-resistant layer to the thickness of the release layer is 1.5 to 3.

[0013] Furthermore, the heat-resistant layer includes a first heat-resistant surface and a second heat-resistant surface disposed opposite to the first heat-resistant surface, the second heat-resistant surface being in contact with the intermediate layer; regarding the surface properties of the first heat-resistant surface, using a method based on ISO 4287-1997, with a stylus having a front-end radius of 2μm and a cone angle of 60°, under the conditions of a measuring force of 0.75mN, a cutoff value of λs = 2.5μm, and λc = 0.8mm, the maximum height roughness Rz ranges from 5μm to 50μm, and the average width RSm of the roughness curve profile unit ranges from 30μm to 300μm.

[0014] Furthermore, regarding the surface properties of the second heat-resistant surface, using a method based on ISO 4287-1997, and employing a stylus with a front-end radius of 2 μm and a cone angle of 60°, under the conditions of a measuring force of 0.75 mN, a cutoff value of λs = 2.5 μm, and λc = 0.8 mm, the maximum height roughness Rz ranged from 0.8 μm to 24 μm, and the average width RSm of the roughness curve profile unit ranged from 50 μm to 600 μm.

[0015] Furthermore, the maximum height roughness Rz of the first heat-resistant surface ranges from 20 μm to 40 μm.

[0016] Furthermore, the thickness of the release layer is 10μm to 50μm.

[0017] Furthermore, the thickness of the release layer is 20μm to 40μm.

[0018] Furthermore, the thickness of the intermediate layer is 10μm to 200μm.

[0019] Furthermore, the material of the intermediate layer can also be selected from ethylene, α-olefin-(meth)acrylate copolymers, mixtures of polyethylene terephthalate copolymerized with 1,4-cyclohexanediol, and mixtures of α-olefin polymers and α-olefin-(meth)acrylate copolymers such as ethylene.

[0020] Furthermore, the ratio of the thickness of the heat-resistant layer to the maximum height roughness Rz of the first heat-resistant surface ranges from 1.2 to 5.

[0021] Furthermore, the ratio ranges from 1.5 to 3.

[0022] The foregoing summary does not include an exhaustive list of all aspects of the invention. It is contemplated that the invention encompasses all systems and methods that can be implemented by all suitable combinations of the aspects outlined above and those disclosed in the detailed embodiments below and specifically pointed out in the claims filed with this patent application. Such combinations have specific advantages not specifically set forth in the foregoing summary. Attached Figure Description

[0023] The embodiments are illustrated in the accompanying drawings by way of example rather than limitation, and similar reference numerals in the drawings indicate similar elements. It should be noted that embodiments referred to as "a" or "an" in this disclosure are not necessarily the same embodiments.

[0024] Figure 1 A schematic diagram of the multilayer release film of the present invention is shown;

[0025] Figure 2 A schematic diagram of the multilayer release film of the present invention is shown from a side view.

[0026] Figure 3 A schematic diagram of some steps in the production process of the multilayer release film of the present invention is shown. Detailed Implementation

[0027] In this section, several embodiments of the invention will be explained with reference to the accompanying drawings. Where the shape, relative position, and other aspects of the components described in the embodiments are not explicitly defined, the scope of the invention is not limited to the components shown, which are for illustrative purposes only. Furthermore, while many details are set forth, it should be understood that some embodiments of the invention can be practiced without these details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the understanding of this description.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Spatially related terms, such as “below,” “under,” “down,” “above,” “above,” etc., may be used herein for convenience in describing the relationship of one element or feature to one or more other elements or features, as illustrated in the accompanying drawings. It should be understood that spatially relative terms are intended to cover different orientations of the device during use or operation other than those shown in the accompanying drawings. For example, if the device in the drawings is flipped, an element described as “below” or “under” other elements or features may then be oriented “above” other elements or features. Thus, the exemplary term “below” can cover both the orientations above and below. The device may be oriented in other ways (e.g., rotated 90 degrees or otherwise), and the spatially relative descriptive terms used herein are interpreted accordingly.

[0029] As used herein, the singular forms “a,” “the,” etc., are intended to include the plural forms as well, unless the context otherwise indicates. It should be further understood that the terms “comprising” and / or “including” define the presence of a feature, step, operation, element, and / or component, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or collections thereof.

[0030] The terms “or” and “and / or” as used herein should be interpreted as inclusive or refer to any one or any combination thereof. Therefore, “A, B, or C” or “A, B, and / or C” means “any one of the following: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition only arise when the combination of elements, functions, steps, or behaviors is inherently mutually exclusive to some extent.

[0031] The release film of the present invention comprises a release layer 101, an intermediate layer 102, and a heat-resistant layer 103.

[0032] Release layer

[0033] The release layer 101 is disposed on the outer layer or outer side of the release film and is a film layer that contacts the FPC surface during FPC production. The thickness of the release layer in the release film of the present invention is 10 μm to 50 μm, and more specifically, 20 μm to 40 μm. When the thickness of the release layer is above the lower limit of the above data range, the mechanical strength of the release layer can be improved, reducing breakage during heating and pressurization. When the thickness of the release layer is below the upper limit of the above data range, the amount of release layer material used can be reduced, thus reducing costs.

[0034] The release layer of the present invention may optionally include polyolefin resins, such as poly-4-methyl-1-pentene resin (TPX, also known as polymethylpentene resin), ethylene-tetrafluoroethylene copolymer (ETEF), polytetrafluoroethylene (PTEF), etc. The release layer of the present invention may include one type of polyolefin resin, or a combination of two or more polyolefin resins.

[0035] The polyolefin resin of the release layer of the present invention has a dyne value of 15 to 30. A lower dyne value means lower adhesion. The release layer of the present invention uses the above-mentioned polyolefin resin to improve the peel performance of the release film.

[0036] In the above materials, the main component of the release layer of the present invention is preferably TPX. TPX has good heat resistance and peelability. When the main component of the release layer is TPX, the release performance and thermal stability of the release film can be improved.

[0037] Furthermore, the polyolefin resin of the release layer of the present invention has a melting point greater than 200°C. During the FPC fabrication process, the FPC needs to be heated and pressurized to improve the adhesion between the metal traces, pads, and insulating base film. Using the polyolefin resin of the present invention ensures that the shape and physical state of the release layer itself do not change during the heating and pressurization process of the FPC. This guarantees the release properties of the release layer while preventing thermal deformation that could transfer wrinkles and other defects to the FPC surface.

[0038] As an optional embodiment, in addition to the polyolefin resins mentioned above, the release layer of the release film of the present invention may also contain various additives such as antioxidants, slip agents, anti-blocking agents, antistatic agents, pigments, stabilizers, fluororesins, epoxy rubber, titanium dioxide, calcium carbonate, and talc.

[0039] The release layer of the release film of the present invention provides good peeling performance, so that the release film can be easily peeled off from the FPC surface after the hot pressing process is completed.

[0040] heat-resistant layer

[0041] The heat-resistant layer 103 is a film layer that comes into contact with the hot press panel of the hot press machine during the hot pressing process of FPC production.

[0042] The composition of the heat-resistant layer of the present invention differs from that of the release layer, and may optionally include polyester resins, such as one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), polypropylene terephthalate (PTT), polyethylene terephthalate (PHT), and syndiotactic polystyrene (SPS).

[0043] The polyester resin of this invention has a melting point greater than 200°C. During FPC fabrication, the FPC needs to be heated and pressurized to improve the adhesion between the metal traces, pads, and insulating base film. Using the polyester resin of this invention ensures that the shape and physical state of the heat-resistant layer remain unchanged during the heating and pressurization process, preventing the heat-resistant layer from adhering to the hot press plate due to heat.

[0044] The lower limit of the dyne value of the polyester resin of the present invention includes 30, 35, and 40, and the upper limit of the dyne value of the polyester resin of the present invention includes 50, 55, and 60. When the dyne value of the polyester resin selected for the heat-resistant layer is below the above-mentioned upper limit, the adhesion between the heat-resistant layer and the hot press plate can be reduced, preventing the heat-resistant layer from adhering to the hot press plate after hot pressing. The heat-resistant layer is usually a film layer that comes into contact with the hot press plate and conveying devices such as conveyor belts and conveyor rollers. When the dyne value of the polyester resin selected for the heat-resistant layer is above the above-mentioned lower limit, misalignment between the heat-resistant layer and other object surfaces can be avoided during transportation and conveying, improving the control accuracy of the release film production and processing.

[0045] While the polyolefin resin used in the release layer of this invention has good release properties, it is relatively brittle and prone to cracking and wrinkling during processing or peeling. The polyester resin used in the heat-resistant layer of this invention has an elongation at break greater than 50%, optionally greater than 100%, and further optionally greater than 150%. When the elongation at break of the heat-resistant layer is above these values, the heat-resistant layer has better mechanical properties and can withstand greater mechanical pressure and tensile length, thereby ensuring that the release film of this invention does not suffer mechanical damage during processing, transportation, and use, avoiding breakage of the release layer due to its brittleness, and improving the yield of both the release film itself and the FPC.

[0046] The thickness of the heat-resistant layer is set according to the thickness of the release layer. The thickness of the release layer is set as 'a', and the thickness of the heat-resistant layer is set as 'b'. The ratio of the heat-resistant layer thickness 'b' to the release layer thickness 'a' ranges from 1.1 to 5, further from 1.5 to 4, and even further from 2 to 3. When the ratio of the heat-resistant layer thickness to the release layer thickness is above the lower limit of the above range, the tensile strength of the release film can be further improved, the mechanical properties of the release film can be increased, the breakage of the release film can be reduced, and the number of wrinkles generated on the release layer during the heating and pressurization process can be reduced.

[0047] Because the heat-resistant layer is in direct contact with the hot press plate, its film temperature is often higher than that of the release layer. Furthermore, since the heat-resistant layer and the release layer use different materials, their thermal deformation coefficients also differ. Under these circumstances, the deformation along the length direction caused by heating in the heat-resistant layer and the release layer will differ significantly. This difference will lead to warping of the multilayer release film, affecting the processing efficiency and yield of the FPC. Setting the ratio of the heat-resistant layer thickness to the release layer thickness above the lower limit can, on the one hand, increase the material mass of the heat-resistant layer relative to the release layer. With the specific heat capacity and the amount of heat received by the heat-resistant layer remaining constant, increasing the mass of the heat-resistant layer will reduce its temperature rise, thereby reducing its deformation and decreasing the difference in deformation between the heat-resistant layer and the release layer under heating conditions. On the other hand, a thicker heat-resistant layer itself can improve the rigidity of the release film. This increased rigidity can further reduce the possibility of warping in multilayer release films.

[0048] Setting the ratio of the heat-resistant layer thickness to the release layer thickness below the upper limit not only reduces the thickness of the heat-resistant layer to save costs, but also allows the roughness-improving embossing on the embossing roller to be directly imprinted onto the other side during the process of embossing one side of the heat-resistant layer, thereby improving the production efficiency of the release film.

[0049] The heat-resistant layer of the present invention includes a first heat-resistant surface 1031 and a second heat-resistant surface 1032 disposed opposite to the first heat-resistant surface. The first heat-resistant surface is in contact with the hot-press plate during the FPC hot pressing process, and the second heat-resistant surface is in contact with the intermediate layer. The term "relatively disposed" as used in this specification includes the positional relationship of two layered structures, objects, or surfaces that are not on the same plane being stacked or disposed on each other, as well as the positional relationship between two or more different surfaces of the same layered structure or object. As long as the two layered structures, objects, or surfaces are not on the same plane and have a relative positional relationship, it is acceptable. Whether other objects are sandwiched between such structures, objects, or surfaces, or the angles between them, are not limited.

[0050] Regarding the surface properties of the first heat-resistant surface, using a method based on ISO 4287-1997, and employing a stylus with a front-end radius of 2 μm and a cone angle of 60°, under conditions of a measuring force of 0.75 mN, a cutoff value λs = 2.5 μm, and λc = 0.8 mm, the lower limit of the maximum height roughness Rz can be 0.8 μm, 1.2 μm, 1.6 μm, or 2.4 μm; the upper limit of the maximum height roughness Rz can be 15 μm, 18 μm, 21 μm, or 24 μm. As an optional embodiment, the range of the maximum height roughness Rz of the first heat-resistant surface of the release film heat-resistant layer of the present invention is 0.8 μm to 24 μm, optionally 1.2 μm to 18 μm, and also optionally 2.4 μm to 15 μm. Rz is defined as the maximum height roughness; per unit sampling range, Rz characterizes the parameter representing the peak-to-valley spacing of the material surface.

[0051] When the maximum height roughness Rz of the first heat-resistant surface is above the lower limit, the first heat-resistant surface is less likely to adhere to the hot press plate, thus improving the release properties between the heat-resistant layer and the hot press plate. When the maximum height roughness Rz of the first heat-resistant surface is below the upper limit, the process can effectively impart unevenness within this parameter range while ensuring that the surface of the first heat-resistant surface has a certain degree of flatness.

[0052] The imprint ratio is defined as the ratio of the thickness of the heat-resistant layer (in μm) to the maximum height roughness Rz of the first heat-resistant surface (in μm). For the release film of this invention, the imprint ratio ranges from 1.2 to 5, further from 1.3 to 4, and even further from 1.5 to 3. Roughness is typically formed on the first heat-resistant surface by embossing with an embossing roller, that is, the raised and recessed areas on the surface of the embossing roller are transferred to the surface of the first heat-resistant surface, thereby forming roughness on the first heat-resistant surface. When the imprint ratio of the release film is above the aforementioned lower limits of 1.2, 1.3, and 1.5, the thickness of the heat-resistant layer is greater than the maximum height roughness Rz of the first heat-resistant surface. Simultaneously, since the heat-resistant layer uses a ductile material, perforation of the heat-resistant layer during the embossing roller process can be avoided. When the imprinting ratio of the release film is below the upper limit of 5, 4, or 3, the thickness of the release film is within a suitable range relative to the roughness of the first heat-resistant surface, and is not too thick. This allows the unevenness of the first heat-resistant surface to be smoothly imprinted onto the second heat-resistant surface while the first heat-resistant surface is rolled to produce roughness. With this setting, roughness can be produced on both the first and second heat-resistant surfaces in one rolling process during the processing of the heat-resistant layer, thus improving production efficiency.

[0053] Because the raw materials need to be heated during the production of release film, the intermediate layer of the release film has a certain degree of fluidity under this heated state. By creating irregularities on the second heat-resistant surface and pressing the heat-resistant layer and the intermediate layer together, the flowing intermediate layer material can fill the spaces between the irregularities on the second heat-resistant surface, thereby increasing the contact area between the intermediate layer and the second heat-resistant surface and making the adhesion between the intermediate layer and the second heat-resistant surface stronger. Regarding the properties of the second heat-resistant surface, using the method based on ISO 4287-1997, and using a stylus with a front-end radius of 2μm and a cone angle of 60°, under the conditions of a measuring force of 0.75mN, a cutoff value λs = 2.5μm, and λc = 0.8mm, the lower limit of the average width RSm of the roughness curve profile unit can be 10μm, 30μm, or 60μm; the upper limit of the RSm value can be 300μm, 400μm, or 500μm. The average width RSm of the roughness curve profile unit of the second heat-resistant surface of the release film heat-resistant layer of the present invention ranges from 10 μm to 500 μm, optionally from 30 μm to 400 μm, and also optionally from 60 μm to 300 μm.

[0054] The average width RSm of the roughness curve profile unit reflects the spacing between the bumps and recesses on the second heat-resistant surface. When RSm is greater than the upper limit, the spacing between the bumps and recesses on the second heat-resistant surface is larger, which means there are fewer bumps and recesses per unit area. In this case, the effect of increasing the contact surface area between the heat-resistant layer and the intermediate layer by setting the roughness, thereby improving adhesion, is smaller. If RSm is less than the lower limit, the spacing between the bumps and recesses on the second heat-resistant surface is smaller, and there are more bumps and recesses per unit area. When the heat-resistant surface and the intermediate layer are laminated, the material of the intermediate layer, which is in a relatively flowing state, cannot fully fill the gaps between the bumps and recesses on the second heat-resistant surface, thus reducing the adhesion between the second heat-resistant surface and the intermediate layer. When the average width RSm of the roughness curve profile unit of the second heat-resistant surface is between the lower and upper limits disclosed in this invention, the adhesion performance between the second heat-resistant surface and the intermediate layer is optimal, avoiding separation between the heat-resistant layer and the intermediate layer during the release film peeling process.

[0055] Intermediate layer

[0056] The intermediate layer is a film layer located between the release layer and the heat-resistant layer. The intermediate layer can be a single layer or multiple layers.

[0057] In most existing FPC boards, the copper foil is bonded to an insulating base film using thermosetting adhesive. Circuit traces are then formed through exposure and development processes, creating gaps between the traces and pads. During the FPC hot-pressing process, the thermosetting adhesive between the insulating base film and the copper foil becomes more fluid due to heat, causing some to overflow and adhere to the copper foil, resulting in an uneven surface. If the thermosetting adhesive adheres to pads or other locations, it can easily cause poor soldering or detachment of electronic components, leading to defective products.

[0058] The intermediate layer of the release film of this invention has a certain degree of fluidity after being heated. During the FPC hot pressing process, under the action of the intermediate layer, the multi-layer release film of this invention can fill the gaps between circuit traces and pads, and also cover the circuit traces and pads, preventing the flowing thermosetting adhesive from overflowing and adhering to the circuit traces or pads. In addition, the intermediate layer of this invention also serves to adhere the release layer and heat-resistant layer disposed on both sides of the intermediate layer, preventing the release layer or heat-resistant layer from detaching from the intermediate layer when covering or peeling off the release film.

[0059] The thickness of the intermediate layer in this invention is 10 μm to 200 μm, further, 20 μm to 180 μm, and even further, 30 μm to 150 μm. When the thickness of the intermediate layer is above the lower limit, it can fully utilize its function of filling the gaps in the FPC after heating, thereby improving the performance of the anti-overflow adhesive. When the thickness of the intermediate layer is below the upper limit, it can improve the thermal conductivity of the release film, allowing the heat from the hot press plate to be quickly conducted to the FPC plate, thus improving production efficiency.

[0060] The intermediate layer of this invention comprises the same materials as the release layer and the heat-resistant layer. Since identical materials have better compatibility, the intermediate layer uses materials that are the same as those used in the release layer and the heat-resistant layer. This improves the adhesion between the intermediate layer and the release layer and the heat-resistant layer, preventing peeling between them. Specifically, the intermediate layer of this invention comprises polyolefin resins and polyester resins.

[0061] Optionally, the intermediate layer material may also include engineering plastic resins such as polyethersulfone and polyphenylene sulfide. Additionally, the intermediate layer material may also include mixtures of ethylene, α-olefin-(meth)acrylate copolymers, mixtures of polyethylene terephthalate copolymerized with polybutylene terephthalate and 1,4-cyclohexanediol, and mixtures of α-olefin polymers with α-olefin-(meth)acrylate copolymers such as ethylene. Examples include mixtures of ethylene and ethylene-methyl methacrylate copolymer (EMMA), mixtures of polypropylene (PP) and ethylene-methyl methacrylate copolymer (EMMA), and mixtures of polybutylene terephthalate (PBT) and polypropylene (PP) and ethylene-methyl methacrylate copolymer (EMMA).

[0062] When the intermediate layer material includes the above-mentioned substances, its melting point is relatively low. Therefore, the intermediate layer has better fluidity under heating. On the one hand, better fluidity can further improve the adhesive resistance of the release film. On the other hand, during the processing of the release film, since the intermediate layer acts as a backing layer for the heat-resistant layer when the heat-resistant layer is embossed by rollers, the softer and more fluid the intermediate layer is, the more completely it can imprint the roughness and unevenness of the first heat-resistant surface of the heat-resistant layer, further improving the adhesion between the intermediate layer and the heat-resistant layer.

[0063] The multilayer release film of the present invention takes into account both peel performance and tensile strength during hot pressing, while reducing warping of the release film itself and reducing separation between the film layers, thus greatly reducing time and material costs.

[0064] Methods for preparing multilayer release films

[0065] like Figure 3 As shown, the method for preparing the release film of the present invention includes: adding the materials of the release layer 101, the intermediate layer 102, and the heat-resistant layer 103 into a co-extrusion device, such as a multi-die co-extrusion device, extruding and molding the above layers respectively using the co-extrusion device, and stacking the film layers in the order of release layer, intermediate layer, and heat-resistant layer.

[0066] Next, two pressure rollers 201 and 202 are used to press the stacked film layers together. The first pressure roller 201 is in contact with the release layer and is used to apply pressure to the release layer. The second pressure roller 202 is in contact with the heat-resistant layer and is used to apply pressure to the heat-resistant layer. Under the relative pressure of the release layer and the heat-resistant layer, the release layer, the intermediate layer and the heat-resistant layer can press each other together to form a multi-layer release film structure.

[0067] The first pressure roller 201 of this invention is a rubber roller. The rubber roller can provide a certain cushioning performance to prevent the release layer from breaking or wrinkling under force, so as to obtain a smoother and more complete release layer surface and ensure that the FPC surface will not have defective products due to defects in the release layer surface.

[0068] The second pressure roller 202 of the present invention is a rigid roller. For the multilayer release film of the present invention, the rigid roller can easily impart unevenness to the heat-resistant layer to form roughness. Furthermore, through the cooperation of the rigid roller and the rubber roller, since the rubber roller is relatively soft, when the rubber roller acts as a backing, the unevenness imparted by the rigid roller to the first heat-resistant surface of the heat-resistant layer can be well imprinted onto the second heat-resistant surface, thereby setting roughness on the second heat-resistant surface, increasing the contact area between the intermediate layer and the second heat-resistant surface, and improving the adhesion between the intermediate layer and the second heat-resistant surface.

[0069] Temperature control is implemented for both rigid rollers and rubber rollers. This control can be achieved by installing water channels, resistance wires, or other temperature control devices inside the rigid rollers and / or rubber rollers. The surface temperature of the rigid rollers and rubber rollers is controlled by adjusting parameters such as the water temperature in the water channels or the current in the resistance wires. There are no restrictions on the method used to control the surface temperature of the rigid rollers / rubber rollers. Since the surface temperature of the rigid rollers and rubber rollers is usually lower than the processing temperature of the release film material, they serve to cool the release film material. Therefore, the surface temperature of the rigid rollers and rubber rollers is often referred to as the "cooling temperature."

[0070] In one embodiment of the manufacturing method of the multilayer release film of the present invention, the temperature of the rubber roller in contact with the release layer is above 20°C, optionally above 25°C, and optionally above 30°C. Simultaneously, the temperature of the rubber roller is below 120°C, optionally below 100°C, and optionally below 80°C. The temperature range of the rubber roller is 20°C to 120°C, optionally 25°C to 100°C, and optionally 30°C to 80°C. When the temperature of the rubber roller is above the aforementioned lower limit, the influence of room temperature on the roller temperature can be minimized. If the temperature of the rubber roller is too low, in the case of a higher room temperature, the room temperature will heat the rubber roller, which is detrimental to the temperature control of the rubber roller. At the same time, a higher cooling temperature can prevent wrinkles and blistering on the surface of the release layer caused by a large difference between the cooling temperature of the rubber roller and the production temperature of the release layer. When the temperature of the rubber roller is below the above-mentioned upper limit, the cooling rate of the multilayer release film can be increased, thereby increasing production efficiency. Since the rubber roller is in direct contact with the release layer of the release film, when the temperature of the rubber roller is below the above-mentioned upper limit, the molecular chains of the polymer material of the release layer tend to be arranged in a disordered manner, reducing the brittleness of the release layer and reducing the possibility of cracking and wrinkling of the release layer during production and use.

[0071] In one embodiment of the manufacturing method of the multilayer release film of the present invention, the temperature of the rigid roller in contact with the heat-resistant layer is higher than the temperature of the rubber roller in contact with the release layer. Specifically, the temperature of the rigid roller in contact with the heat-resistant layer is above 60°C, optionally above 70°C, and alternatively above 80°C. The temperature of the rigid roller is below 150°C, optionally below 120°C, and alternatively below 100°C. The temperature range of the rigid roller is 60°C to 150°C, optionally from 70°C to 120°C, and alternatively from 80°C to 100°C. The release layer and heat-resistant layer of the multilayer release film of the present invention are made of different materials, and the coefficients of thermal expansion of the materials of the release layer and heat-resistant layer are different. Furthermore, the coefficient of thermal expansion of polyester resin is generally greater than that of polyolefin resin. Therefore, the release film of the present invention may experience warping due to thermal expansion and contraction during subsequent application. When the temperature of the rigid roller is above the lower limit, the cooling time is increased. Since some molecular chains of the polymer material rearrange during cooling to form an ordered structure, increasing the cooling time of the heat-resistant layer allows the rearranged molecular chains to become more dominant, thus making the thermal expansion coefficient of the heat-resistant layer closer to that of the release layer, further mitigating the warping of the release film of this invention. When the temperature of the rigid roller is below the upper limit, cooling efficiency is improved, and energy consumption is reduced.

[0072] In the manufacturing process of the multilayer release film of this invention, the rubber roller and the rigid roller move at a linear speed of 10 m / min to 50 m / min, optionally 15 m / min to 45 m / min, and alternatively 20 m / min to 30 m / min. When the linear speed of the roller is below the upper limit, the heat-resistant layer can be maintained at a higher temperature for a longer period of time, which is beneficial for the orderly rearrangement of the molecular chains of the heat-resistant layer material and reduces the warping of the release film. When the linear speed of the roller is above the lower limit, production efficiency can be improved. The linear speed of the rubber roller and the rigid roller is kept consistent, that is, after the above-mentioned rolling process, the lengths of the release layer and the heat-resistant layer of the multilayer release film of this invention are consistent. When the temperature continues to decrease, since the coefficient of thermal expansion of the heat-resistant layer is greater than that of the release layer, the change in length of the heat-resistant layer is also greater than that of the release layer. In this case, the multilayer release film is prone to warping, reducing the usability of the product.

[0073] After the main production process of the release film is completed, the next step includes winding the multilayer release film for easy storage. The multilayer release film of this invention is wound with the release layer on the outside and the heat-resistant layer on the inside. In this winding method, the length of the heat-resistant layer is relatively shorter than the length of the release layer, which reduces warping of the multilayer release film. This is because, for the multilayer release film of this invention, although the coefficient of thermal expansion of the heat-resistant layer is usually greater than that of the release layer, the coefficient of thermal expansion of the heat-resistant layer is usually smaller than that of the intermediate layer, and the thickness of the intermediate layer is usually thicker. Therefore, when the release film cools, the intermediate layer shrinks more than the heat-resistant layer, leading to warping. In the production method of the release film of this invention, winding the release film with the release layer on the outside and the heat-resistant layer on the inside is equivalent to placing the intermediate layer on the periphery of the heat-resistant layer, physically lengthening the intermediate layer and reducing the length difference between the intermediate layer and the heat-resistant layer, thereby reducing warping of the release film.

[0074] Implementation examples and evaluation

[0075] Implementation Example 1:

[0076] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is a mixture of PBT and TPX. The release layer has a thickness of 6 μm, and the heat-resistant layer has a thickness of 30 μm. The maximum height roughness Rz of the first heat-resistant surface is 10 μm, and the imprint ratio is 3.

[0077] Implementation example 2:

[0078] The release film consists of a multilayer release layer made of PTEF, a heat-resistant layer made of PET, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PTEF and PET. The release layer has a thickness of 10 μm, and the heat-resistant layer has a thickness of 13 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 0.65.

[0079] Implementation example 3:

[0080] The release film consists of a multilayer release layer made of ETEF, a heat-resistant layer made of PC, and an intermediate layer with a thickness of 100 μm, which is a mixture of PBT and TPX. The release layer has a thickness of 20 μm, and the heat-resistant layer has a thickness of 40 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 2.

[0081] 4th implementation example:

[0082] The release film consists of a multilayer release layer made of TPX, a heat-resistant layer made of PET, and an intermediate layer with a thickness of 100 μm, which is a mixture of PBT and TPX. The release layer has a thickness of 30 μm, and the heat-resistant layer has a thickness of 80 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 4.

[0083] 5th implementation example:

[0084] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is a mixture of PBT and TPX. The release layer has a thickness of 40 μm, and the heat-resistant layer has a thickness of 60 μm. The maximum height roughness Rz of the first heat-resistant surface is 10 μm, and the imprint ratio is 6.

[0085] Implementation example 6:

[0086] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is a mixture of PBT and TPX. The release layer has a thickness of 25 μm, and the heat-resistant layer has a thickness of 100 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 5.

[0087] Implementation example #7:

[0088] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is made of a mixture of PBT and TPX. The release layer has a thickness of 60 μm, and the heat-resistant layer has a thickness of 72 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 3.6.

[0089] Implementation Example 8:

[0090] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is a mixture of PBT and TPX. The release layer has a thickness of 30 μm, and the heat-resistant layer has a thickness of 15 μm. The maximum height roughness Rz of the first heat-resistant surface is 10 μm, and the imprint ratio is 1.5.

[0091] Implementation example #9:

[0092] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is made of a mixture of PBT and TPX. The release layer has a thickness of 30 μm, and the heat-resistant layer has a thickness of 24 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 1.2.

[0093] 10th Implementation Example:

[0094] A multilayer release film is used, with the release layer made of TPX, the heat-resistant layer made of PBT, and the intermediate layer having a thickness of 100 μm. The intermediate layer is made of a mixture of PBT and TPX. The release layer has a thickness of 30 μm, and the heat-resistant layer has a thickness of 210 μm. The maximum height roughness Rz of the first heat-resistant surface is 20 μm, and the imprint ratio is 10.5.

[0095] Evaluation of the correlation between the imprinting ratio and the imprinting effect on the second heat-resistant surface:

[0096] An embossing roller was selected, and a rubber roller was used to bond the release layer, while a steel roller was used to bond the first heat-resistant surface of the heat-resistant layer. The co-extruded release layer, intermediate layer, and heat-resistant layer were rolled at a linear speed of 15 m / min. The temperature of the rubber roller was 30°C, and the temperature of the steel roller was 90°C. Then, the first heat-resistant surface was given the maximum height roughness Rz described in the previous example. After preparation, the release film sample was left to stand at room temperature for 24 hours. The heat-resistant layer and intermediate layer were then peeled off, and the roughness of the second heat-resistant surface in contact with the intermediate layer was measured. If the maximum height roughness Rz of the second heat-resistant surface was greater than 0.8 μm, it was considered that there was an embossing; if the maximum height roughness of the second heat-resistant surface was less than 0.8 μm, it was considered that there was no embossing. If a perforation appeared on the heat-resistant layer, it was recorded as a perforation.

[0097] Evaluation of warp angle:

[0098] Take a 10cm x 10cm release film sample and let it stand at room temperature (20℃) for 72 hours. Take a side view photograph of the release film sample to obtain its side profile. Then, connect the highest point of the sample profile to the center point of the sample and calculate the angle between the line and the horizontal plane. This angle is the warpage angle of the sample. If the warpage angle of the release film sample is below 3°, it meets the requirements of industrial applications, and the sample is considered to have passed the warpage performance test.

[0099] Table 1

[0100]

[0101] Based on the above test results, when the imprinting ratio between the thickness of the heat-resistant layer and the maximum height roughness Rz of the first heat-resistant surface is between 1.2 and 5, the unevenness can be directly imprinted onto the second heat-resistant surface while simultaneously creating an uneven surface on the first heat-resistant surface, and perforation of the heat-resistant layer can be avoided.

[0102] Based on the above test results, when the thickness ratio between the heat-resistant layer and the release layer is above 1.1, the warpage angle of the release film sample is less than 3°, indicating good warpage performance, which can meet the requirements of industrial applications.

[0103] 11th Implementation Example:

[0104] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 0.8 μm and an RSm of 30 μm.

[0105] 12th Implementation Example:

[0106] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 3 μm and an RSm of 20 μm.

[0107] Implementation example 13:

[0108] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 5 μm and an RSm of 1000 μm.

[0109] Implementation example 14:

[0110] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 8 μm and an RSm of 100 μm.

[0111] 15th Implementation Example:

[0112] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 12 μm and an RSm of 200 μm.

[0113] 16th Implementation Example:

[0114] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 15 μm and an RSm of 300 μm.

[0115] Implementation example 17:

[0116] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 24 μm and an RSm of 200 μm.

[0117] Implementation example 18:

[0118] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 20 μm and an RSm of 300 μm.

[0119] 19th Implementation Example:

[0120] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has an Rz of 0.5 μm and an RSm of 500 μm.

[0121] Implementation example #20:

[0122] The release film consists of a release layer made of TPX, a heat-resistant layer made of PBT, and an intermediate layer with a thickness of 100 μm, which may be a mixture of PBT and TPX. The release layer has a thickness of 10 μm, the heat-resistant layer has a thickness of 30 μm, and the second heat-resistant surface of the heat-resistant layer has a radius of 30 μm (Rz) and a radius of 100 μm (RSm).

[0123] Peel strength test of heat-resistant layer:

[0124] To test the peel force between the heat-resistant layer and the intermediate layer, the multilayer release film was first cut into strips 50 mm wide. The peel force test method followed the People's Republic of China National Standard GB / T2792-2014. Specifically, under standard test conditions of 23°C and 50% relative humidity, one side of the multilayer release film from Examples 11-20 was fixed to a flat fixture with adhesive. A PFG-2504 tensile tester was used to clamp the free end of the heat-resistant layer away from the fixture, and the tester was fixed to a displacement device. The displacement device moved the tester at a constant speed of 5.0 ± 0.2 mm / s, peeling off 30 mm of the heat-resistant layer. The tester reading was taken when the movement reached a constant speed. The angle of the tester's movement was 180° with the intermediate layer, i.e., the peel angle was 180°. Each sample was tested three times, and the average value was taken as the peel force (in gf) between the heat-resistant layer and the intermediate layer for that example.

[0125] If the peel force obtained from the above test is greater than 30gf, it is considered that there is a large adhesion between the heat-resistant layer and the intermediate layer, which can effectively prevent the separation of the heat-resistant layer and the intermediate layer during use.

[0126] Table 2

[0127]

[0128]

[0129] According to Table 2, when the maximum height roughness Rz of the second heat-resistant surface is 0.8 μm to 24 μm and the average width of the roughness curve profile unit is 50 μm to 600 μm, during the preparation of the multilayer release film, the flowing intermediate layer can penetrate into the gap between the concave and convex surfaces of the second heat-resistant surface, increase the contact area, improve the bonding strength between the heat-resistant layer and the intermediate layer, and improve usability.

[0130] Implementation examples 21-30:

[0131] The temperature of the cooling roller used to prepare the multilayer release film of the present invention was changed. The temperature of the roller was controlled at 20°C, the linear speed was 15 m / min, the release layer was made of TPX, the heat-resistant layer was made of PBT, and the intermediate layer was a mixture of PBT and TPX. The resulting intermediate layer had a thickness of 100 μm, the release layer had a thickness of 10 μm, and the heat-resistant layer had a thickness of 30 μm. The temperature of the rigid roller during the preparation process was also changed. In Examples 21 to 30, the rigid roller temperatures were set to 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 120°C, and 150°C, respectively.

[0132] The degree of warping of the sample was evaluated using the aforementioned warping angle evaluation method.

[0133] Table 3

[0134] Serial Number Rigid roller temperature Sample warp angle 21 20℃ 9.3° 22 30℃ 8.7° 23 40℃ 6.5° 24 50℃ 5.1° 25 60℃ 2.7° 26 70℃ 2.8° 27 80℃ 2.3° 28 90℃ 1.9° 29 120℃ 1.5° 30 150℃ 1.3°

[0135] According to Table 3, the higher the temperature of the rigid roller, the longer the cooling time of the heat-resistant layer, and the more fully the ordered arrangement of the polymer material molecular chains. When the temperature of the rigid roller is between 60℃ and 150℃, the thermal deformation difference between the heat-resistant layer and the release layer of the multilayer release film produced is small, the warpage of the example is small, and it is industrially usable.

[0136] This invention is not limited to the specific materials, structures, processes, and parameters shown. Any technical solution employing a similar approach and achieving similar effects should be considered within the scope of protection of this invention. Regarding the parameter ranges disclosed in this specification and the parameter ranges described in the claims, due to various objective and subjective factors such as measurement errors, material feeding errors, and formula design, and given the limited space in this specification, it should be considered that parameter ranges with upper and lower limit deviations within 30% that achieve the same or similar functions as the corresponding parameter ranges are within the scope of protection of this invention.

Claims

1. A multilayer release film, comprising a release layer, an intermediate layer, and a heat-resistant layer; The release layer is disposed on the outer layer of the multilayer release film. The material of the release layer includes polyolefin resin, the melting point of the polyolefin resin is greater than 200°C, and the dyne value of the polyolefin resin ranges from 15 to 30. The heat-resistant layer is disposed on the outer layer of the multilayer release film and is disposed opposite to the release layer. The material of the heat-resistant layer includes polyester resin, the melting point of the polyester resin is greater than 200°C, the dyne value of the polyester resin is in the range of 35 to 55, and the elongation at break of the polyester resin is greater than 50%. The intermediate layer is disposed between the release layer and the heat-resistant layer, and both sides of the intermediate layer are in contact with the release layer and the heat-resistant layer, respectively. The material of the intermediate layer includes the polyolefin resin of the release layer and the polyester resin of the heat-resistant layer. The ratio of the thickness of the heat-resistant layer to the thickness of the release layer is 1.1 to 5; The heat-resistant layer includes a first heat-resistant surface and a second heat-resistant surface disposed opposite to the first heat-resistant surface, wherein the second heat-resistant surface is in contact with the intermediate layer; Regarding the surface properties of the first heat-resistant surface, using a method based on ISO4287-1997, and employing a stylus with a front-end radius of 2 μm and a cone angle of 60°, under the conditions of a measuring force of 0.75 mN, a cutoff value of λs = 2.5 μm, and λc = 0.8 mm, the maximum height roughness Rz ranges from 5 μm to 50 μm, and the average width RSm of the roughness curve profile unit ranges from 30 μm to 300 μm. Regarding the surface properties of the second heat-resistant surface, using a method based on ISO4287-1997, and employing a stylus with a front-end radius of 2 μm and a cone angle of 60°, under the conditions of a measuring force of 0.75 mN, a cutoff value of λs = 2.5 μm, and λc = 0.8 mm, the maximum height roughness Rz ranged from 0.8 μm to 24 μm, and the average width RSm of the roughness curve profile unit ranged from 50 μm to 600 μm. The ratio of the thickness of the heat-resistant layer to the maximum height roughness Rz of the first heat-resistant surface ranges from 1.2 to 5.

2. The multilayer release film according to claim 1, characterized in that: The polyolefin resin is selected from one or more of TPX, ETFE, and PTFE.

3. The multilayer release film according to claim 2, characterized in that: The polyester resin is selected from one or more of PBT, PET, and PC.

4. The multilayer release film according to claim 1, characterized in that: The ratio of the thickness of the heat-resistant layer to the thickness of the release layer is 1.5 to 3.

5. The multilayer release film according to claim 1, characterized in that: The maximum height roughness Rz of the first heat-resistant surface ranges from 20 μm to 40 μm.

6. The multilayer release film according to claim 1, characterized in that: The thickness of the release layer is 10μm to 50μm.

7. The multilayer release film according to claim 6, characterized in that: The thickness of the release layer is 20μm to 40μm.

8. The multilayer release film according to claim 1, characterized in that: The thickness of the intermediate layer is 10μm to 200μm.

9. The multilayer release film according to claim 1, characterized in that: The ratio of the thickness of the heat-resistant layer to the maximum height roughness Rz of the first heat-resistant surface ranges from 1.5 to 3.

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