A double-stretch PBT release film and its preparation method

Abstract

The present invention relates to the field of release films, and discloses a double-stretch PBT release film and a preparation method thereof, comprising the steps of: mixing raw materials of a nucleating agent masterbatch, and melt-extruding, cooling, forming, and pelletizing to obtain a nucleating agent masterbatch; the raw materials of the nucleating agent masterbatch include: PBT resin, a nucleating agent, and an antioxidant; the nucleating agent is selected from one or more of potassium N-butylpyraclostrobin, sodium montanate, aluminum adipate, and sodium succinate; after mixing the release film raw materials, melt-extrude and cast into a film to obtain a cast film; in parts by weight, the release film raw materials include 100 parts of PBT resin and 20 to 30 parts of nucleating agent masterbatch; the cast film is embossed, sequentially stretched longitudinally, stretched transversely, and heat-set, and wound to obtain a double-stretch PBT release film with a thickness of 20 to 80 μm. The present invention combines a biaxial stretching process with the addition of a specific nucleating agent to obtain a PBT release film that can improve the temperature resistance and dimensional stability of the product at a low thickness.

Description

Technical Field

[0001] The present invention relates to the technical field of release film materials, in particular to a double-stretched PBT release film and a preparation method thereof. Background Art

[0002] Flexible printed circuits (FPCs) are circuit boards made from flexible copper-clad laminates. They serve as a signal transmission medium for connecting electronic products and feature high wiring density, excellent flexibility, lightweight construction, and flexible manufacturing processes. PBT (polybutylene terephthalate) resin release film is a key product in the FPC market, used for release protection during the FPC lamination process.

[0003] Currently, the thickness of release films is generally in the range of 100μm to 200μm. For example, patent CN115011277B discloses a PBT release film, a preparation method, and an application thereof. The PBT release film includes a first film layer, a second film layer, and a third film layer arranged in sequence. The first film layer and the third film layer are both pure PBT film layers, and the second film layer is a modified PBT film layer. The total thickness of the release film is 110-130μm.

[0004] Due to product needs, release films tend to be made thinner. However, the lower the thickness of the PBT release film, the worse the release and dimensional stability of the product. The development of low-thickness PBT release films is a major challenge. Summary of the Invention

[0005] The present invention aims to overcome the problem in the prior art that the release properties and dimensional stability of the product are poor when the thickness of the PBT release film is low. A double-stretched PBT release film and a preparation method thereof are provided. By adding a specific nucleating agent and combining it with a biaxial stretching process, the prepared PBT release film can improve the temperature resistance and dimensional stability of the product at a low thickness.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a double-stretch PBT release film comprises the following steps:

[0008] (1) Mixing the raw materials of the nucleating agent masterbatch, and then melting, extruding, cooling, forming and pelletizing to obtain the nucleating agent masterbatch; the raw materials of the nucleating agent masterbatch include, by weight, 100 parts of PBT resin, 1 to 3 parts of nucleating agent, and 0.1 to 0.5 parts of antioxidant; the nucleating agent is selected from one or more of potassium N-butylpyraclostrobin, sodium montanate, aluminum adipate, and sodium succinate;

[0009] (2) mixing the release film raw materials, melt-extruding, and casting to form a film to obtain a cast film; in parts by weight, the release film raw materials include: 100 parts of PBT resin and 20-30 parts of nucleating agent masterbatch;

[0010] (3) After embossing, the cast film is sequentially stretched longitudinally, stretched transversely, and heat-set, and then rolled up to obtain a double-stretched PBT release film with a thickness of 20~80μm.

[0011] During the high-temperature pressing process between the PBT release film and the FPC board, the PBT release film softens quickly due to its low thickness. Under pressure, the film surface easily sinks into the surface structure of the FPC board, making it difficult to peel off after cooling, and a large amount of PBT film remains on the FPC board surface. In addition, PBT resin is an easily crystallized plastic. Under the conventional cast extrusion process, PBT easily grows into spherulites with larger particle sizes, resulting in poor toughness of the material. In particular, when the thickness becomes low, the tensile properties are greatly reduced, and the film is easily broken after high-temperature pressing. The present invention, through the addition of a specific type of nucleating agent, can, on the one hand, inhibit the growth of large-particle spherulites during the crystallization process, thereby forming spherulites with fine and dense particles. The spherulites can grow regularly, increase in number and become smaller in size, so as to improve the tensile strength and toughness of the low-thickness film; on the other hand, it can shorten the nucleation cycle and improve the crystallinity and crystallization temperature of the PBT release film. Furthermore, the present invention utilizes a biaxial stretching process, which improves the regularity of the polymer chains under high-temperature stretching, further increasing the film's crystallinity and enhancing the product's heat resistance and dimensional stability. Consequently, the present invention's PBT release film offers excellent heat resistance, dimensional stability, and release properties at a low thickness.

[0012] Preferably, the nucleating agent is a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 5 to 10:2.

[0013] Preferably, the PBT resin has a melt index of 10-20 g / 10 min (250° C., 2.16 kg).

[0014] Preferably, the antioxidant is one of antioxidant 1076 and antioxidant 168, or a mixture of the two.

[0015] Preferably, the temperature of the melt extrusion in step (1) is 160-280°C.

[0016] Preferably, the temperature during melt extrusion in step (2) is 150-300°C.

[0017] Preferably, the thickness of the cast film obtained in step (2) is 150-300 μm.

[0018] Preferably, the stretching ratio during the longitudinal stretching and the transverse stretching in step (3) is 2.3 to 2.5 times, and the temperature during stretching is 60 to 280°C.

[0019] Preferably, in step (3), the embossing is performed sequentially through a rubber roller and a steel roller, the temperature of the rubber roller is 10-40°C, and the temperature of the steel roller is 20-60°C.

[0020] Preferably, the heat setting temperature in step (3) is 180-280°C, and the heat setting time is 20-200s.

[0021] The present invention also provides a double-stretched PBT release film prepared using the above preparation method.

[0022] Therefore, the present invention has the following beneficial effects:

[0023] (1) Adding a specific type of nucleating agent to the raw materials can improve the tensile strength and toughness of low-thickness films on the one hand, and on the other hand, it can increase the crystallinity and crystallization temperature of the PBT release film, thereby improving the temperature resistance and dimensional stability of the product;

[0024] (2) The biaxial stretching process is used to further increase the crystallinity of the PBT release film, improve the temperature resistance and dimensional stability of the product, and enable the PBT release film to have good temperature resistance, dimensional stability and release properties at a low thickness. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific embodiments.

[0026] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0027] Overall embodiment:

[0028] A method for preparing a double-stretch PBT release film comprises the following steps:

[0029] (1) Mixing the raw materials of the nucleating agent masterbatch, and then melting, extruding, cooling, forming and pelletizing to obtain the nucleating agent masterbatch; the raw materials of the nucleating agent masterbatch include, by weight, 100 parts of PBT resin, 1 to 3 parts of nucleating agent, and 0.1 to 0.5 parts of antioxidant; the nucleating agent is selected from one or more of potassium N-butylpyraclostrobin, sodium montanate, aluminum adipate, and sodium succinate;

[0030] (2) mixing the release film raw materials, melt-extruding, and casting to form a film to obtain a cast film; in parts by weight, the release film raw materials include: 100 parts of PBT resin and 20-30 parts of nucleating agent masterbatch;

[0031] (3) After embossing, the cast film is sequentially stretched longitudinally, stretched transversely, and heat-set, and then rolled up to obtain a double-stretched PBT release film with a thickness of 20~80μm.

[0032] As a specific embodiment, the nucleating agent is a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 5 to 10:2.

[0033] As a specific embodiment, the melt index of the PBT resin is 10-20 g / 10 min (250° C., 2.16 kg).

[0034] As a specific embodiment, the antioxidant is one of antioxidant 1076 and antioxidant 168, or a mixture of the two.

[0035] As a specific embodiment, the temperature of the melt extrusion in step (1) is 160-280°C.

[0036] As a specific embodiment, the temperature during melt extrusion in step (2) is 150~300℃.

[0037] As a specific embodiment, the thickness of the cast film obtained in step (2) is 150-300 μm.

[0038] As a specific embodiment, the stretching ratio during longitudinal stretching and transverse stretching in step (3) is 2.3 to 2.5 times, and the temperature during stretching is 60 to 280°C.

[0039] As a specific embodiment, in step (3), the embossing is performed sequentially through a rubber roller and a steel roller, the temperature of the rubber roller is 10-40°C, and the temperature of the steel roller is 20-60°C.

[0040] As a specific implementation manner, the heat setting temperature in step (3) is 180-280° C., and the heat setting time is 20-200 s.

[0041] Example 1:

[0042] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0043] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0044] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0045] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0046] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0047] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.4 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0048] Example 2:

[0049] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0050] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0051] (2) After mixing 70 parts by weight of PBT resin and 30 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0052] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0053] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0054] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.4 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0055] Example 3:

[0056] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0057] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared, wherein the extrusion temperature was controlled in the range of 160°C to 280°C; the nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 10:2;

[0058] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0059] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 160 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0060] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0061] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being wound into a film; the longitudinal and transverse stretching ratios were set to 2.3 times, the stretching temperature was 100 °C, the heat-setting temperature was 230 °C, and the time was 100 s; the thickness of the final wound finished film was 30 μm.

[0062] Example 4:

[0063] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0064] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared, wherein the extrusion temperature was controlled in the range of 160°C to 280°C; the nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 6:2;

[0065] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0066] (3) The dried mixture was melt-extruded and then cast at a die to obtain a cast film with a thickness of 190 μm; wherein the processing temperature of the extruder was set at 150°C to 300°C, and the die temperature was set at 260°C;

[0067] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0068] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being wound into a film; the longitudinal and transverse stretching ratios were set to 2.5 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0069] Comparative Example 1:

[0070] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0071] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0072] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0073] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 150 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0074] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0075] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.2 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0076] Comparative Example 2:

[0077] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0078] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0079] (2) 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch were mixed and dried in a blast oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0080] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 200 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0081] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0082] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being wound into a film; the longitudinal and transverse stretching ratios were set to 2.6 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0083] Comparative Example 3:

[0084] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0085] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0086] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0087] (3) The dried mixture was melt-extruded and then cast at a die to obtain a cast film with a thickness of 240 μm; wherein the processing temperature of the extruder was set at 150°C to 300°C, and the die temperature was set at 260°C;

[0088] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0089] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being wound into a film; the longitudinal and transverse stretching ratios were set to 2.8 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled film was 30 μm.

[0090] Comparative Example 4:

[0091] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0092] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0093] (2) After mixing 90 parts by weight of PBT resin and 10 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0094] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0095] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0096] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.4 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0097] Comparative Example 5:

[0098] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0099] (1) 100 parts by weight of PBT resin (melt index 18 g / 10 min) was dried in a blast oven at 110°C until the moisture content of the masterbatch was less than 0.02 wt%;

[0100] (2) The dried PBT resin is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0101] (3) The cast film is embossed by a rubber roller and a steel roller, wherein the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0102] (4) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being wound into a film; the longitudinal and transverse stretching ratios were set to 2.4 times, the stretching temperature was 80-180 °C, the heat-setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled film was 30 μm.

[0103] Comparative Example 6:

[0104] A method for preparing a PBT release film, comprising the following steps:

[0105] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:2.

[0106] (2) Mix 80 parts by weight of PBT resin (specific manufacturer, brand and melt index) and 20 parts by weight of nucleating agent masterbatch, and dry them in a forced air oven at 110°C until the moisture content of the masterbatch is less than 0.02wt%;

[0107] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 30 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0108] (4) The cast film is embossed by a rubber roller and a steel roller, wherein the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0109] (5) The embossed cast film is heat-set and then rolled into a film; the heat-setting temperature is 230°C and the time is 100 seconds; the thickness of the final rolled film is 30 μm.

[0110] Comparative Example 7:

[0111] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0112] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw pelletizer. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was obtained. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was sodium montanate.

[0113] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0114] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0115] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0116] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.2 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0117] Comparative Example 8:

[0118] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0119] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw granulator. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was obtained. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was potassium N-butylpyraclostrobin.

[0120] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0121] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0122] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0123] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.2 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0124] Comparative Example 9:

[0125] A method for preparing a double-stretch PBT release film, comprising the following steps:

[0126] (1) 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 were uniformly mixed and added into a twin-screw pelletizer. After melt extrusion, cooling, molding and pelletizing, a nucleating agent masterbatch was prepared. The extrusion temperature was controlled in the range of 160°C to 280°C. The nucleating agent was a mixture of nano-silica and calcium oxide in a mass ratio of 1:1.

[0127] (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, the mixture was dried in a forced air oven at 110°C until the moisture content of the masterbatch was less than 0.02wt%;

[0128] (3) The dried mixture is melt-extruded and then cast at a die to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150°C to 300°C, and the die temperature is set at 260°C;

[0129] (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set to 25°C and the temperature of the steel roller is set to 40°C;

[0130] (5) The embossed cast film was sequentially stretched longitudinally, stretched transversely, and heat-set before being rolled into a film; the longitudinal and transverse stretching ratios were set to 2.4 times, the stretching temperature was 100 °C, the heat setting temperature was 230 °C, and the time was 100 s; the thickness of the final rolled finished film was 30 μm.

[0131] The properties of the PBT release films prepared in the above examples and comparative examples were tested, and the results are shown in Table 1.

[0132] Among them, the method for judging whether the film forming property is qualified is: whether the appearance of the film after formation contains burrs, warping, holes, white spots, black spots, and wrinkles; the crystallinity and crystallization temperature are tested by differential scanning calorimetry (DSC); the method for judging the release property is: after the TPX release film is pressed onto the FPC board, all 80 small squares on the FPC board are peeled off from the release film, and there is no residual offset printing, which means it is self-releasing, otherwise it is non-self-releasing; the method for testing the adhesive resistance value is: the confocal microscope is used to observe the overflow length of the epoxy adhesive on the FPC board after pressing.

[0133] Table 1: PBT release film performance test results

[0134]

[0135] From the results in Table 1, it can be seen that the PBT release films prepared by the method of the present invention in Examples 1 to 4 can have good release properties and adhesive resistance at a low thickness of 30μm. From the test data of Examples 1, 2 and Comparative Example 4, the addition of a nucleating agent helps to increase the crystallization and crystallization temperature of the release film, thereby improving the release performance of the release film, but further increasing the amount of addition has little effect on the performance. From the comparison of the data of Example 1 and Comparative Examples 1, 2, and 3, it can be seen that the stretch ratio during biaxial stretching has a great influence on the crystallinity and release properties of the release film. A small stretch ratio is not conducive to the improvement of crystallinity, and an excessive stretch ratio will cause a decrease in release properties or even film breakage. Comparative Example 5 cannot form a film during biaxial stretching without adding a nucleating agent, indicating that the nucleating agent in the present invention plays a vital role in the crystallization process, transforming the PBT release film from the original homogeneous nucleation to heterogeneous nucleation, refining the grain structure, and improving the film-forming performance during biaxial stretching. In Comparative Example 6, biaxial stretching was not performed, resulting in lower crystallinity and thermal stability of the release film than in the examples, resulting in unqualified release performance. In Comparative Example 7, sodium montanate alone was used as a nucleating agent, but film formation failed during biaxial stretching. In Comparative Example 8, potassium N-butylpyraclostrobin was used alone as a nucleating agent, resulting in unqualified release performance. In Comparative Example 9, an inorganic nucleating agent was used instead of the organic nucleating agent of the present invention, resulting in poor nucleation and failure to form a film during biaxial stretching. This indicates that the type of nucleating agent significantly affects the performance of the release film.

[0136] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a double-stretched PBT release film, characterized in that: The steps include: (1) Mixing the raw materials of the nucleating agent masterbatch, and then melting, extruding, cooling, forming and pelletizing to obtain the nucleating agent masterbatch; The raw materials of the nucleating agent masterbatch include, by weight, 100 parts of PBT resin, 1 to 3 parts of nucleating agent, and 0.1 to 0.5 parts of antioxidant; the nucleating agent is a mixture of sodium montanate and potassium N-butylpyraclostrobin in a mass ratio of 5 to 10:2; (2) mixing the release film raw materials, melt-extruding, and casting to form a film to obtain a cast film; in parts by weight, the release film raw materials include: 100 parts of PBT resin and 20-30 parts of nucleating agent masterbatch; (3) After embossing, the cast film is sequentially stretched longitudinally, stretched transversely, and heat-set, and then rolled up to obtain a double-stretched PBT release film with a thickness of 20-80 μm; the stretching ratio during longitudinal stretching and transverse stretching is 2.3-2.5 times, and the temperature during stretching is 60-280 °C.

2. The method for preparing a double-stretch PBT release film according to claim 1, wherein: The nucleating agent is a mixture of sodium montanate and potassium N-butylpyrazone in a mass ratio of 8:

2.

3. The method for preparing a double-stretch PBT release film according to claim 1, wherein: The melt index of the PBT resin is 10-20 g / 10 min.

4. The method for preparing a double-stretched PBT release film according to claim 1, wherein: The temperature of the melt extrusion in step (1) is 160-280°C.

5. The method for preparing a double-stretched PBT release film according to claim 1, wherein: The temperature during melt extrusion in step (2) is 150-300°C.

6. The method for preparing a double-stretched PBT release film according to claim 1, wherein: The thickness of the cast film obtained in step (2) is 150-300 μm.

7. The method for preparing a double-stretched PBT release film according to claim 1, wherein: During the embossing in step (3), the rubber roller and the steel roller are used for embossing in sequence, the temperature of the rubber roller is 10-40°C, and the temperature of the steel roller is 20-60°C.

8. The method for preparing a double-stretched PBT release film according to claim 1 or 7, wherein: The heat setting temperature in step (3) is 180~280℃, and the heat setting time is 20~200s.

9. A double-stretch PBT release film, characterized in that: The method is prepared according to any one of claims 1 to 8.

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