Double-drawing PBT release film and preparation method thereof

Abstract

The invention relates to the field of release films, and discloses a double-drawing PBT release film and a preparation method thereof.The preparation method comprises the steps that raw materials of nucleating agent master batch are mixed and subjected to melt extrusion, cooling forming and pelletizing, and the nucleating agent master batch is obtained; the nucleating agent master batch comprises the following raw materials: PBT resin, a nucleating agent and an antioxidant; the nucleating agent is selected from one or more of N-butyl potassium piromate, sodium montanate, aluminum adipate and sodium succinate; mixing release film raw materials, performing melt extrusion, and performing film casting to obtain a cast film; the release film is prepared from the following raw materials in parts by weight: 100 parts of PBT (Polybutylene Terephthalate) resin and 20 to 30 parts of nucleating agent master batch, the cast film is embossed and then sequentially subjected to longitudinal stretching, transverse stretching, heat setting and rolling, and then the double-drawn PBT release film with the thickness of 20-80 microns is obtained. By adding the specific nucleating agent and combining the two-way stretching process, the prepared PBT release film can improve the temperature resistance and dimensional stability of the product under the condition of low thickness.

Description

Technical Field

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

[0002] An FPC (flexible printed circuit board) is a circuit board made of a flexible copper clad laminate and is used as a medium for signal transmission in the connection of electronic products. It has the characteristics of high wiring assembly density, good bendability, light weight, and flexible process. PBT (polybutylene terephthalate) resin-based release films are an important product in the FPC market and are used for release protection during the FPC lamination process.

[0003] Currently, the thickness of the release film is generally in the range of 100μm to 200μm. For example, a PBT release film and its preparation method and application disclosed in Patent CN115011277B. The PBT release film includes a first film layer, a second film layer, and a third film layer arranged in sequence. Both the first film layer and the third film layer are 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 requirements, there is a trend for the release film to be gradually thinned. However, the lower the thickness of the PBT release film, the worse the release property and dimensional stability of the product. Developing a low-thickness PBT release film is a major challenge. Summary of the Invention

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

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a biaxially stretched PBT release film, comprising the following steps: (1) Mix the raw materials of the nucleating agent masterbatch, and after melting, extruding, cooling, forming, and pelletizing, obtain the nucleating agent masterbatch. By weight, the raw materials of the nucleating agent masterbatch include: 100 parts of PBT resin, 1 - 3 parts of nucleating agent, and 0.1 - 0.5 parts of antioxidant; the nucleating agent is selected from one or more of potassium N-butylpiperazide, sodium lignite, aluminum adipate, and sodium succinate; (2) Mix the raw materials of the release film, melt and extrude them, and cast them into a film to obtain a cast film. By weight, the raw materials of the release film include: 100 parts of PBT resin and 20 - 30 parts of nucleating agent masterbatch; (3)The cast film is longitudinally stretched, transversely stretched, and heat-set in sequence after embossing, and a double-stretched PBT release film with a thickness of 20 - 80 μm is obtained after winding.

[0007] During the high-temperature lamination process of the PBT release film with the FPC board, due to the low thickness, the PBT release film softens quickly, and the film surface is prone to being deeply indented into the surface structure of the FPC board under pressure, resulting in difficulty in peeling after cooling and a large amount of PBT film residue on the FPC board surface. In addition, PBT resin is an easily crystallizable plastic. Under the conventional cast extrusion process, PBT is prone to grow into spherulites with larger particle sizes, resulting in poor toughness of the material. Especially after the thickness decreases, the tensile properties are greatly reduced, and the film is extremely prone to breakage after high-temperature lamination. By adding a specific type of nucleating agent in the present invention, on the one hand, the growth of large-sized spherulites during the crystallization process can be inhibited, thereby forming fine and dense spherulites. The spherulites can grow regularly, with an increase in quantity and a decrease in size, to improve the tensile strength and toughness of the low-thickness film. On the other hand, the nucleation period can be shortened, and the crystallinity and crystallization temperature of the PBT release film can be increased. At the same time, the present invention adopts a biaxial stretching process, and the arrangement regularity of the polymer chains of the PBT release film is improved under high-temperature stretching, thereby further increasing the crystallinity of the PBT release film and improving the heat resistance and dimensional stability of the product. Therefore, the PBT release film of the present invention can have good heat resistance, dimensional stability, and release property at low thickness.

[0008] Preferably, the nucleating agent is a mixture of sodium lignosulfonate and potassium N-butylpiperazide with a mass ratio of 5 - 10:2.

[0009] Preferably, the melt index of the PBT resin is 10 - 20 g / 10 min (250 °C, 2.16 kg).

[0010] Preferably, the antioxidant is one or a mixture of two of antioxidant 1076 and antioxidant 168.

[0011] Preferably, the temperature of the melt extrusion in step (1) is 160 - 280 °C.

[0012] Preferably, the temperature of the melt extrusion in step (2) is 150 - 300 °C.

[0013] Preferably, the thickness of the cast film obtained in step (2) is 150 - 300 μm.

[0014] Preferably, the draw ratio during the longitudinal stretching and transverse stretching in step (3) is 2.3 - 2.5 times, and the temperature during stretching is 60 - 280 °C.

[0015] Preferably, during the embossing in step (3), it passes through embossing by a rubber roll and a steel roll in sequence. The temperature of the rubber roll is 10 - 40 °C, and the temperature of the steel roll is 20 - 60 °C.

[0016] Preferably, the heat setting temperature in step (3) is 180 - 280°C, and the heat setting time is 20 - 200 s.

[0017] The present invention also provides a double - drawn PBT release film prepared by the above - mentioned preparation method.

[0018] Therefore, the present invention has the following beneficial effects: (1) Adding a specific type of nucleating agent to the raw materials can, on the one hand, improve the tensile strength and toughness of the low - thickness film, and on the other hand, increase the crystallinity and crystallization temperature of the PBT release film, thereby improving the heat resistance and dimensional stability of the product; (2) Adopting a biaxial stretching process can further increase the crystallinity of the PBT release film, improve the heat resistance and dimensional stability of the product, and enable the PBT release film to have good heat resistance, dimensional stability and release property at low thickness. Specific Embodiments

[0019] The following further describes the present invention in conjunction with specific embodiments.

[0020] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following examples are conventional methods in this field if not otherwise specified.

[0021] General Example: A preparation method of a double - drawn PBT release film includes the following steps: (1) Mix the raw materials of the nucleating agent masterbatch, and after melt - extrusion, cooling and forming into pellets, obtain the nucleating agent masterbatch; calculated by weight, the raw materials of the nucleating agent masterbatch include: 100 parts of PBT resin, 1 - 3 parts of nucleating agent, 0.1 - 0.5 parts of antioxidant; the nucleating agent is selected from one or more of potassium N - butylpiperazate, sodium lignite, aluminum adipate, and sodium succinate; (2) Mix the raw materials of the release film, then melt - extrude and cast into a film to obtain a cast film; calculated by weight, the raw materials of the release film include: 100 parts of PBT resin and 20 - 30 parts of nucleating agent masterbatch; (3) The cast film is embossed and then subjected to longitudinal stretching, transverse stretching, and heat setting in sequence, and after winding, a double - drawn PBT release film with a thickness of 20 - 80 μm is obtained.

[0022] As a specific embodiment, the nucleating agent is a mixture of sodium lignite and potassium N - butylpiperazate with a mass ratio of 5 - 10:2.

[0023] As a specific embodiment, the melt index of the PBT resin is 10 - 20 g / 10 min (250°C, 2.16 kg).

[0024] As a specific embodiment, the antioxidant is one or a mixture of two of antioxidant 1076 and antioxidant 168.

[0025] As a specific embodiment, the temperature of melt extrusion in step (1) is 160 - 280 °C.

[0026] As a specific embodiment, the temperature during melt extrusion in step (2) is 150 - 300 °C.

[0027] As a specific embodiment, the thickness of the cast film obtained in step (2) is 150 - 300 μm.

[0028] As a specific embodiment, the draw ratios during longitudinal and transverse drawing in step (3) are 2.3 - 2.5 times, and the temperature during drawing is 60 - 280 °C.

[0029] As a specific embodiment, during embossing in step (3), it passes through an embossing roller and a steel roller in sequence. The temperature of the embossing roller is 10 - 40 °C, and the temperature of the steel roller is 20 - 60 °C.

[0030] As a specific embodiment, the heat setting temperature in step (3) is 180 - 280 °C, and the heat setting time is 20 - 200 s.

[0031] Example 1: A method for preparing a double - drawn PBT release film, the steps are as follows: (1) After uniformly mixing 100 parts by weight of PBT resin (melt index is 18 g / 10 min), 2 parts by weight of a nucleating agent, and 0.2 parts by weight of antioxidant 1076, adding them to a twin - screw granulator, and after melt extrusion, cooling, forming, and pelletizing, a nucleating agent masterbatch is prepared, wherein the extrusion temperature is controlled within the range of 160 °C - 280 °C; the nucleating agent is a mixture of sodium lignite and N - butyl piperazine potassium with a mass ratio of 8:2; (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of the nucleating agent masterbatch, drying in a blast drying oven at 110 °C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) After melt - extruding the above - dried mixture, laminating and casting into a film at the die head to obtain a cast film with a thickness of 180 μm; wherein the processing temperature of the extruder is set at 150 °C - 300 °C, and the die head temperature is set at 260 °C; (4) The cast film is embossed by passing through an embossing roller and a steel roller, wherein the temperature of the embossing roller is set at 25 °C, and the temperature of the steel roller is set at 40 °C; (5) The cast film after embossing is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film; the longitudinal and transverse stretching ratios are set to 2.4 times, the stretching temperature is 100 °C; the heat setting temperature is 230 °C, and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0032] Example 2: A method for preparing a double-drawn PBT release film, the steps are as follows: (1) After uniformly mixing 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of a nucleating agent, and 0.2 parts by weight of antioxidant 1076, add them to a twin-screw granulator. After melt extrusion, cooling, and pelletizing, a nucleating agent masterbatch is prepared, and the extrusion temperature is controlled within the range of 160 °C to 280 °C; the nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 8:2; (2) Mix 70 parts by weight of PBT resin and 30 parts by weight of the nucleating agent masterbatch, and dry them in a forced-air oven at 110 °C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) After melt-extruding the above-mentioned dried mixture, laminate and cast it into a film at the die head to obtain a cast film with a thickness of 180 μm; the processing temperature of the extruder is set to 150 °C to 300 °C, and the die head temperature is set to 260 °C; (4) The cast film is embossed by a rubber roll and a steel roll, where the temperature of the rubber roll is set to 25 °C and the temperature of the steel roll is set to 40 °C; (5) The cast film after embossing is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film; the longitudinal and transverse stretching ratios are set to 2.4 times, the stretching temperature is 100 °C; the heat setting temperature is 230 °C, and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0033] Example 3: A method for preparing a double-drawn PBT release film, the steps are as follows: (1) After uniformly mixing 100 parts by weight of PBT resin (melt index of 18 g / 10 min), 2 parts by weight of a nucleating agent, and 0.2 parts by weight of antioxidant 1076, add them to a twin-screw granulator. After melt extrusion, cooling, and pelletizing, a nucleating agent masterbatch is prepared, and the extrusion temperature is controlled within the range of 160 °C to 280 °C; the nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 10:2; (2) Mix 80 parts by weight of PBT resin and 20 parts by weight of the nucleating agent masterbatch, and dry them in a forced-air oven at 110 °C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) The dried mixture mentioned above is melt-extruded and then laminated and cast into a film at the die head to obtain a cast film with a thickness of 160 μm. The processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C. (4) The cast film is embossed by a rubber roller and a steel roller. The temperature of the rubber roller is set at 25°C, and the temperature of the steel roller is set at 40°C. (5) The embossed cast film is successively longitudinally stretched, transversely stretched, heat-set and then wound into a film. The longitudinal and transverse stretch ratios are set at 2.3 times, and the stretching temperature is 100°C. The heat-setting temperature is 230°C, and the time is 100 s. The thickness of the finally wound finished film is 30 μm.

[0034] Example 4: A method for preparing a double-stretched PBT release film, the steps are as follows: (1) 100 parts by weight of PBT resin (melt index is 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 are uniformly mixed and then added to a twin-screw granulator. After melt-extrusion, cooling and forming into pellets, a nucleating agent masterbatch is prepared. The extrusion temperature is controlled within the range of 160°C to 280°C. The nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 6:2. (2) 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch are mixed and then dried in a blast drying oven at 110°C until the moisture content of the masterbatch is lower than 0.02 wt%. (3) The dried mixture mentioned above is melt-extruded and then laminated and cast into a film at the die head to obtain a cast film with a thickness of 190 μm. The processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C. (4) The cast film is embossed by a rubber roller and a steel roller. The temperature of the rubber roller is set at 25°C, and the temperature of the steel roller is set at 40°C. (5) The embossed cast film is successively longitudinally stretched, transversely stretched, heat-set and then wound into a film. The longitudinal and transverse stretch ratios are set at 2.5 times, and the stretching temperature is 100°C. The heat-setting temperature is 230°C, and the time is 100 s. The thickness of the finally wound finished film is 30 μm.

[0035] Comparative Example 1: A method for preparing a double-stretched PBT release film, the steps are as follows: (1) After uniformly mixing 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, add them to a twin-screw granulator. After melt extrusion, cooling, forming, and pelletizing, a nucleating agent masterbatch is obtained, where the extrusion temperature is controlled within the range of 160°C to 280°C; the nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 8:2; (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, dry them in a forced-air oven at 110°C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) After melt-extruding the above-mentioned dried mixture, laminate and cast it into a film at the die head to obtain a cast film with a thickness of 150 μm; the processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C; (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set at 25°C and the temperature of the steel roller is set at 40°C; (5) The embossed cast film is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film; the longitudinal and transverse stretching ratios are set at 2.2 times, and the stretching temperature is 100°C; the heat setting temperature is 230°C, and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0036] Comparative Example 2: A method for preparing a biaxially stretched PBT release film, the steps are as follows: (1) After uniformly mixing 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, add them to a twin-screw granulator. After melt extrusion, cooling, forming, and pelletizing, a nucleating agent masterbatch is obtained, where the extrusion temperature is controlled within the range of 160°C to 280°C; the nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 8:2; (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, dry them in a forced-air oven at 110°C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) After melt-extruding the above-mentioned dried mixture, laminate and cast it into a film at the die head to obtain a cast film with a thickness of 200 μm; the processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C; (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set at 25°C and the temperature of the steel roller is set at 40°C; (5) The cast film after embossing is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film; the longitudinal and transverse stretching ratios are set to 2.6 times, and the stretching temperature is 100 °C; the heat setting temperature is 230 °C, and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0037] Comparative Example 3: A method for preparing a double-stretched PBT release film, the steps are as follows: (1) After uniformly mixing 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, add them to a twin-screw granulator. After melt extrusion, cooling, and pelletizing, a nucleating agent masterbatch is prepared, and the extrusion temperature is controlled within the range of 160 °C to 280 °C; the nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 8:2; (2) After mixing 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch, dry them in a forced-air oven at 110 °C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) After melt-extruding the above-mentioned dried mixture, laminate and cast it into a film at the die head to obtain a cast film with a thickness of 240 μm; the processing temperature of the extruder is set to 150 °C to 300 °C, and the die head temperature is set to 260 °C; (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; (5) The cast film after embossing is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film; the longitudinal and transverse stretching ratios are set to 2.8 times, and the stretching temperature is 100 °C; the heat setting temperature is 230 °C, and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0038] Comparative Example 4: A method for preparing a double-stretched PBT release film, the steps are as follows: (1) After uniformly mixing 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, add them to a twin-screw granulator. After melt extrusion, cooling, and pelletizing, a nucleating agent masterbatch is prepared, and the extrusion temperature is controlled within the range of 160 °C to 280 °C; the nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 8:2; (2) After mixing 90 parts by weight of PBT resin and 10 parts by weight of nucleating agent masterbatch, dry them in a forced-air oven at 110 °C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) The above-mentioned dried mixture is melt-extruded and then laminated and cast into a film at the die head to obtain a cast film with a thickness of 180 μm; the processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C; (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set at 25°C and the temperature of the steel roller is set at 40°C; (5) The embossed cast film is successively longitudinally stretched, transversely stretched, heat-set and then wound into a film; the longitudinal and transverse stretch ratios are set at 2.4 times, and the stretching temperature is 100°C; the heat-setting temperature is 230°C and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0039] Comparative Example 5: A method for preparing a biaxially stretched PBT release film, the steps are as follows: (1) 100 parts by weight of PBT resin (melt index is 18 g / 10 min) is dried in a blast oven at 110°C until the moisture content of the masterbatch is lower than 0.02 wt%; (2) The above-mentioned dried PBT resin is melt-extruded and then laminated and cast into a film at the die head to obtain a cast film with a thickness of 180 μm; the processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C; (3) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set at 25°C; the temperature of the steel roller is set at 40°C; (4) The embossed cast film is successively longitudinally stretched, transversely stretched, heat-set and then wound into a film; the longitudinal and transverse stretch ratios are set at 2.4 times, and the stretching temperature is 80 - 180°C; the heat-setting temperature is 230°C and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0040] Comparative Example 6: A method for preparing a PBT release film, the steps are as follows: (1) 100 parts by weight of PBT resin (melt index is 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 are uniformly mixed and then added to a twin-screw granulator. After melt-extrusion, cooling and forming, and pelletizing, a nucleating agent masterbatch is prepared, where the extrusion temperature is controlled within the range of 160°C to 280°C; the nucleating agent is a mixture of sodium lignite and N-butylpiperazine potassium with a mass ratio of 8:2; (2) 80 parts by weight of PBT resin (specific manufacturer, grade and melt index) and 20 parts by weight of nucleating agent masterbatch are mixed and dried in a blast oven at 110°C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) The above-mentioned dried mixture is melt-extruded and then laminated and cast into a film at the die head to obtain a cast film with a thickness of 30 μm; the processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C; (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set at 25°C; the temperature of the steel roller is set at 40°C; (5) The embossed cast film is heat-set and then wound into a film; the heat-setting temperature is 230°C and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0041] Comparative Example 7: A method for preparing a biaxially stretched PBT release film, the steps are as follows: (1) 100 parts by weight of PBT resin (melt index is 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 are uniformly mixed, then added to a twin-screw granulator, and after melt-extrusion, cooling and forming into pellets, a nucleating agent masterbatch is prepared, where the extrusion temperature is controlled within the range of 160°C to 280°C; the nucleating agent is sodium lignite; (2) 80 parts by weight of PBT resin and 20 parts by weight of nucleating agent masterbatch are mixed and dried in a forced-air oven at 110°C until the moisture content of the masterbatch is lower than 0.02 wt%; (3) The above-mentioned dried mixture is melt-extruded and then laminated and cast into a film at the die head to obtain a cast film with a thickness of 180 μm; the processing temperature of the extruder is set at 150°C to 300°C, and the die head temperature is set at 260°C; (4) The cast film is embossed by a rubber roller and a steel roller, where the temperature of the rubber roller is set at 25°C and the temperature of the steel roller is set at 40°C; (5) The embossed cast film is successively longitudinally stretched, transversely stretched, heat-set and then wound into a film; the longitudinal and transverse stretch ratios are set at 2.2 times, and the stretching temperature is 100°C; the heat-setting temperature is 230°C and the time is 100 s; the thickness of the finally wound finished film is 30 μm.

[0042] Comparative Example 8: A method for preparing a biaxially stretched PBT release film, the steps are as follows: (1) 100 parts by weight of PBT resin (melt index is 18 g / 10 min), 2 parts by weight of nucleating agent and 0.2 parts by weight of antioxidant 1076 are uniformly mixed, then added to a twin-screw granulator, and after melt-extrusion, cooling and forming into pellets, a nucleating agent masterbatch is prepared, where the extrusion temperature is controlled within the range of 160°C to 280°C; the nucleating agent is potassium N-butylpiperazide; (2) Mix 80 parts by weight of PBT resin 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 0.02 wt%. (3) Extrude the above-mentioned dried mixture through melting and then laminate and cast it into a film at the die head to obtain a cast film with a thickness of 180 μm. The processing temperature of the extruder is set at 150°C - 300°C, and the die head temperature is set at 260°C. (4) Pass the cast film through a rubber roller and a steel roller for embossing. The temperature of the rubber roller is set at 25°C, and the temperature of the steel roller is set at 40°C. (5) The embossed cast film is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film. The longitudinal and transverse stretching ratios are set at 2.2 times, and the stretching temperature is 100°C. The heat setting temperature is 230°C, and the time is 100 s. The thickness of the finally wound finished film is 30 μm.

[0043] Comparative Example 9: A method for preparing a biaxially stretched PBT release film, the steps are as follows: (1) Uniformly mix 100 parts by weight of PBT resin (melt index is 18 g / 10 min), 2 parts by weight of nucleating agent, and 0.2 parts by weight of antioxidant 1076, add them to a twin-screw granulator, and after melting extrusion, cooling and forming, and pelletizing, obtain a nucleating agent masterbatch, wherein the extrusion temperature is controlled within the range of 160°C - 280°C. The nucleating agent is a mixture of nano-silica and calcium oxide with a mass ratio of 1:1. (2) Mix 80 parts by weight of PBT resin 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 0.02 wt%. (3) Extrude the above-mentioned dried mixture through melting and then laminate and cast it into a film at the die head to obtain a cast film with a thickness of 180 μm. The processing temperature of the extruder is set at 150°C - 300°C, and the die head temperature is set at 260°C. (4) Pass the cast film through a rubber roller and a steel roller for embossing. The temperature of the rubber roller is set at 25°C, and the temperature of the steel roller is set at 40°C. (5) The embossed cast film is successively subjected to longitudinal stretching, transverse stretching, heat setting, and then wound into a film. The longitudinal and transverse stretching ratios are set at 2.4 times, and the stretching temperature is 100°C. The heat setting temperature is 230°C, and the time is 100 s. The thickness of the finally wound finished film is 30 μm.

[0044] Test the performance of the PBT release films prepared in the above examples and comparative examples, and the results are shown in Table 1.

[0045] Among them, the method for determining whether the film-forming property is qualified: whether there are burrs, warped edges, holes, white dots, black dots, and wrinkles on the appearance after film formation; the crystallinity and crystallization temperature are tested by a differential scanning calorimeter (DSC); the method for determining the release property: after the TPX release film is laminated with the FPC board, all 80 small squares on the FPC board are peeled off from the release film without residual glue marks, which is self-releasing, otherwise it is non-self-releasing; the method for testing the glue resistance value: the overflow length of the epoxy glue on the FPC board after lamination is observed by a confocal microscope.

[0046] Table 1: Performance test results of PBT release film

[0047] It can be seen from the results in Table 1 that the PBT release films prepared by the method of the present invention in Examples 1 to 4 can have good release properties and glue resistance properties at a low thickness of 30 μm. From the test data of Examples 1, 2 and Comparative Example 4, the addition of the nucleating agent helps to improve the crystallization and crystallization temperature of the release film, thereby improving the release performance of the release film, but further increasing the addition amount has little effect on the performance. From the data comparison of Example 1 and Comparative Examples 1, 2, and 3, it can be seen that the draw ratio during biaxial stretching has a greater impact on the crystallinity and release property of the release film. When the draw ratio is small, it is not conducive to the improvement of crystallinity. If the draw ratio is too large, it will cause a decrease in release property or even film breakage. In Comparative Example 5, no film can be formed during biaxial stretching without adding a nucleating agent, indicating that the nucleating agent in the present invention plays a crucial role in the crystallization process, changing the homogeneous nucleation of the original PBT release film to heterogeneous nucleation, refining the grain structure, and improving the film-forming performance during biaxial stretching. In Comparative Example 6, no biaxial stretching is performed, and the crystallinity and thermal stability of the release film are reduced compared with those in the examples, resulting in unqualified release performance. In Comparative Example 7, only sodium lignite is used as the nucleating agent, and no film can be formed during biaxial stretching; in Comparative Example 8, only potassium N-butylpiperazide is used as the nucleating agent, and the release property of the release film is unqualified; in Comparative Example 9, an inorganic nucleating agent is used instead of the organic nucleating agent of the present invention, and the nucleation effect is poor, and no film can be formed during biaxial stretching, indicating that the type of nucleating agent has a greater impact on the performance of the release film.

[0048] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a double-drawn PBT release film, characterized in that, It includes the following steps: (1) Mix the raw materials of the nucleating agent masterbatch, and after melting, extruding, cooling and forming into pellets, the nucleating agent masterbatch is obtained; By weight, the raw materials of the nucleating agent masterbatch include: 100 parts of PBT resin, 1 - 3 parts of nucleating agent, 0.1 - 0.5 part of antioxidant; the nucleating agent is selected from one or more of potassium N-butylpiperazide, sodium lignite, aluminum adipate, and sodium succinate; (2) Mix the raw materials of the release film, melt and extrude them, and cast them into a film to obtain a cast film; by weight, the raw materials of the release film include: 100 parts of PBT resin and 20 - 30 parts of nucleating agent masterbatch; (3) After the cast film is embossed, it is successively longitudinally stretched, transversely stretched, and heat-set, and after winding, a biaxially stretched PBT release film with a thickness of 20 - 80 μm is obtained.

2. The preparation method of the double-drawn PBT release film according to claim 1, characterized in that, The nucleating agent is a mixture of sodium lignite and potassium N-butylpiperazide with a mass ratio of 5 - 10:

2.

3. The preparation method of the double-drawn PBT release film according to claim 1, characterized in that, The melt index of the PBT resin is 10 - 20 g / 10min.

4. The preparation method of the double-drawn PBT release film according to claim 1, characterized in that, In step (1), the temperature of the melt extrusion is 160 - 280 °C.

5. The preparation method of the double-drawn PBT release film according to claim 1, characterized in that, In step (2), the temperature during the melt extrusion is 150 - 300 °C.

6. The preparation method of the double-drawn PBT release film according to claim 1, characterized in that, The thickness of the cast film obtained in step (2) is 150 - 300 μm.

7. The preparation method of the double-drawn PBT release film according to claim 1 or 6, characterized in that, In step (3), the draw ratio during the longitudinal stretching and transverse stretching is 2.3 - 2.5 times, and the temperature during the stretching is 60 - 280 °C.

8. The preparation method of the double-drawn PBT release film according to claim 1, characterized in that, In step (3), during the embossing, it successively passes through a rubber roller and a steel roller for embossing. The temperature of the rubber roller is 10 - 40 °C, and the temperature of the steel roller is 20 - 60 °C.

9. The preparation method of the double-drawn PBT release film according to claim 1 or 8, characterized in that, The heat-setting temperature in step (3) is 180 - 280 °C, and the heat-setting time is 20 - 200 s.

10. A double-drawn PBT release film, characterized in that, It is prepared by using the preparation method according to any one of claims 1 - 9.

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