LCP film, its preparation method and application

Abstract

The application discloses a preparation method and application of LCP film and belongs to the technical field of polymer material processing. The preparation method of the LCP film is characterized by comprising the following steps: S1, melt extrusion; S2, mold preparation; S3, mold traction; S4, mold inflation; S5, film bubble flattening; and S6, film pressing, so that the LCP film is obtained. The preparation method combines the film blowing method and the calendering method, first utilizes the bidirectional rotating mold head with the outer mold body and the core rod having opposite rotating directions to regulate and control the molecular orientation arrangement structure in the LCP film, makes the LCP molecular structure form a woven net structure, avoids the problem that the longitudinal and transverse tensile properties are greatly different due to the LCP molecular orientation order, then through the pressing step, the double-layer LCP film is pressed into a single-layer LCP film, and the problems of poor film thickness uniformity and uneven film winding are solved.

Description

Technical Field

[0001] This invention belongs to the field of polymer material processing technology, and particularly relates to an LCP thin film, its preparation method and application. Background Technology

[0002] Liquid crystal polymers (LCPs), also known as liquid crystal polymers, are a new type of polymer material that generally transforms into a liquid crystal form under certain heating conditions. They are characterized by high molecular weight and ordered molecular orientation. Superior high-temperature resistance, weather resistance, dimensional stability, and good electrical properties are the core advantages of these specialty engineering plastics, leading to their widespread application in high-tech fields such as electronics, communications, and aerospace. The low water absorption and low dielectric loss properties of LCPs further solidify their core position in 5G mobile phone antenna film materials. Currently, there is no mature LCP film processing technology in China, mainly due to the high barriers to entry in producing LCP film raw materials and processing technologies.

[0003] Depending on the processing method, film forming methods mainly include calendering, casting, blown film, coating, and biaxial stretching. Each method has its own advantages and limitations. Currently, most processing methods for specialty engineering plastic films employ calendering or biaxial stretching. Calendering can effectively solve the problem of film thickness accuracy, but it cannot avoid the problem of uneven longitudinal and transverse properties, especially for crystalline or easily oriented specialty engineering plastics, which are almost impossible to produce as films. Biaxial stretching can effectively avoid the above-mentioned technical shortcomings, but its equipment structure is complex and has many moving parts.

[0004] Currently, the main methods for preparing LCP thin films include: 1) blown film method; 2) biaxial stretching method; 3) coating method; and 4) nonwoven fabric hot pressing method. However, all of the above methods have their shortcomings.

[0005] 1) Shortcomings of blown film method: Due to the easy orientation of LCP molecules, there is a large difference in the longitudinal and transverse tensile mechanical properties of the film. At the same time, due to the high rigidity of LCP film, the adhesion between films is poor, and wrinkles are easy to occur during the winding process, resulting in uneven film winding and poor film thickness uniformity. Chinese invention patent CN114274542A improves the film winding flatness by controlling the bubble temperature when the film reaches different positions, but it cannot solve the problems of large differences in longitudinal and transverse tensile properties and film thickness uniformity.

[0006] 2) Shortcomings of biaxial stretching method: Biaxial stretching method is an effective technical means to solve the problems of large differences in longitudinal and transverse tensile properties of film and uneven winding. However, its equipment structure is complex with many moving parts and high processing accuracy is required. Chinese invention patent CN113771324A uses asynchronous stretching process to prepare LCP film. Due to asynchronous stretching, the film is prone to cracking during the stretching process.

[0007] 3) Shortcomings of coating method: The coating method can solve the problem of film thickness uniformity, but it has problems such as solvent evaporation and low film strength.

[0008] 4) Shortcomings of the nonwoven fabric hot pressing method: Chinese invention patent CN112501954A adopts the nonwoven fabric hot pressing method, which solves the problems of film thickness uniformity and uneven winding relatively well. However, it has the problems of being unable to control the porosity of the nonwoven fabric after secondary hot pressing and the inability to achieve continuous production, resulting in low efficiency.

[0009] Therefore, there is a need for a method to prepare LCP films that can solve the problems of large differences in longitudinal and transverse tensile properties, poor uniformity of film thickness, and uneven film winding. Summary of the Invention

[0010] In order to overcome the problems existing in the prior art, one of the objectives of the present invention is to provide a method for preparing LCP films, wherein the LCP films prepared by the method have small differences in longitudinal and transverse tensile properties, good uniformity in film thickness, and flat film winding.

[0011] The second objective of this invention is to provide an application of the above-mentioned method for preparing LCP films.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A first aspect of the present invention provides a method for preparing an LCP thin film, comprising the following steps:

[0014] S1. Melt extrusion: LCP raw material is melt extruded to obtain LCP melt;

[0015] S2. Mold preparation: LCP melt is passed into a bidirectional rotating die head to form a tubular mold blank with a woven mesh structure of LCP molecules; the bidirectional rotating die head includes an outer mold body and a mandrel, and the outer mold body and the mandrel rotate in opposite directions;

[0016] S3. Mold blank traction: Pull the tubular mold blank along the axial direction;

[0017] S4. Molding blank inflation: Gas is injected into the tubular molding blank to inflate it and obtain a cylindrical membrane bubble;

[0018] S5. Flattening the membrane bubble: Flatten the cylindrical membrane bubble to form a double-layer LCP film;

[0019] S6. Film lamination: The double-layer LCP film is laminated to obtain the LCP film.

[0020] This invention combines blow-blowing and calendering methods to further prepare a flat single-layer LCP film from a blown bilayer LCP film, significantly improving the film's flatness. It also enables the LCP molecular structure to form a woven mesh structure, avoiding the problem of large differences in longitudinal and transverse tensile properties caused by the ordered orientation of LCP molecules.

[0021] Preferably, in step S3, the traction speed of the mold blank is 3 to 10 m / min.

[0022] The traction speed of the mold blank needs to be maintained at a suitable level, that is, within the range of 3 to 10 m / min. Too fast or too slow will affect the molecular structure of LCP molecules in the mold blank, causing the network molecular structure formed in the bidirectional rotating die to deform. This will affect the difference in longitudinal and transverse tensile properties of the final monolayer LCP film, and will also affect the effect of eliminating film thickness non-uniformity during the pressing process, resulting in unsatisfactory thickness uniformity of the final film.

[0023] More preferably, in step S3, the traction speed of the mold blank is 4.5 to 9.5 m / min; even more preferably, it is 6 to 9 m / min.

[0024] Preferably, in step S6, the pressure of the film pressing is 3-10 MPa; more preferably 4-9 MPa; and even more preferably 5-8 MPa.

[0025] Preferably, in step S6, the film pressing time is 5 to 20 minutes; more preferably 6 to 15 minutes; and even more preferably 8 to 12 minutes.

[0026] In step S6, the film lamination temperature is selected based on the temperature at which the LCP raw material can be processed. The temperature at which the LCP raw material can be processed refers to a temperature 5–10°C above the melting point Tm of LCP.

[0027] In some specific embodiments of the present invention, the LCP raw material used is Japanese Factoring A950; in step S6, the film pressing temperature is 285-290°C.

[0028] In some specific embodiments of the present invention, the film lamination can be performed using a molding press or a pressing roller. Both molding press and pressing roller lamination can achieve the purpose of laminating a double-layer LCP film into a single-layer film. The difference between the two is that pressing roller lamination can achieve continuous production, while molding press lamination is an intermittent operation.

[0029] Preferably, after step S5 and before step S6, step S55 (film preheating) is also included.

[0030] Preferably, in step S55, the temperature at which the film is preheated is the viscosity flow temperature of the LCP raw material.

[0031] The film preheating temperature is set to be near the viscosity flow temperature of LCP, which makes the bilayer LCP film plastic, which is beneficial for subsequent lamination.

[0032] In some specific embodiments of the present invention, the LCP raw material is Japanese Factoring A950; in step S55, the preheating temperature of the film is 270-330°C; more preferably 280-320°C; and even more preferably 290-310°C.

[0033] Preferably, in step S55, the preheating time of the film is 3 to 10 minutes; more preferably 3 to 8 minutes; and even more preferably 4 to 6 minutes.

[0034] Preferably, step S6 is followed by step S7, which involves film winding.

[0035] Preferably, in step S7, the film winding is performed using constant torque winding.

[0036] Preferably, in step S7, the torque for winding the film is 0.16 to 0.26 N·m.

[0037] The magnitude of the traction force during film winding plays a crucial role in the flatness of the film. When the traction force during film winding exceeds 40% of the rated torque of the motor, it can easily lead to film breakage and distortion of the film plane, resulting in winding wrinkles.

[0038] Preferably, in step S2, the rotational speed of the bidirectional rotating die head is 5–20 r / min; more preferably 6–15 r / min; and even more preferably 8–12 r / min.

[0039] Preferably, in step S5, the thickness of a single layer of the bilayer LCP film is 0.08–0.12 mm; more preferably, it is 0.09–0.11 mm.

[0040] Preferably, in step S6, the thickness of the LCP film is 0.1 to 0.15 mm; more preferably, it is 0.11 to 0.13 mm.

[0041] In some specific embodiments of the present invention, the LCP film is prepared using a specific apparatus, which includes an extruder, a bidirectional rotating die, an air valve, a sizing sleeve, a herringbone plate, a traction clamping roller, a preheating oven, a pressing device, and a winding roller connected in sequence.

[0042] Preferably, the device further includes a thickness gauge; the thickness gauge is preferably an ultrasonic thickness gauge. The thickness gauge detects whether the film thickness variation is within a set tolerance range. If the variation exceeds the tolerance, the film thickness is controlled by adjusting the pressing force of the pressing device and the speed of the winding roller.

[0043] In some specific embodiments of the present invention, the method for preparing LCP thin films includes the following steps:

[0044] S1. Melt extrusion: LCP raw material is melt-extruded in an extruder to obtain LCP melt;

[0045] S2. Mold preparation: LCP melt is passed into a bidirectional rotating die head to form a tubular mold blank with a woven mesh structure of LCP molecules; the bidirectional rotating die head includes an outer mold body and a mandrel, and the outer mold body and the mandrel rotate in opposite directions;

[0046] S3, Mold blank traction: The tubular mold blank is pulled along the axial direction to the traction clamping roller;

[0047] S4. Mold blank inflation: Gas is injected into the tubular mold blank using an air valve to inflate it, resulting in a cylindrical film bubble with an outer diameter that matches the inner diameter of the shaping sleeve.

[0048] S5. Flattening the membrane bubble: The cylindrical membrane bubble is pulled to the herringbone plate and flattened to form a double-layer LCP film;

[0049] S55. Film preheating: The double-layer LCP film is preheated in a preheating oven;

[0050] S6. Film lamination: The preheated double-layer LCP film is pulled to the lamination device and laminated to obtain the LCP film;

[0051] S7. Film winding: Use a winding roller to wind up the LCP film.

[0052] Preferably, after step S6 and before step S7, step S65, thickness measurement, is also included: using a thickness gauge to detect the film thickness.

[0053] A second aspect of the present invention provides an LCP film prepared by the preparation method described in the first aspect of the present invention, wherein the LCP film satisfies at least one of the following requirements:

[0054] 1) The ratio of longitudinal tensile strength to transverse tensile strength is 1 to 1.5;

[0055] 2) The average thickness is 100–140 μm;

[0056] 3) The standard deviation of the thickness is 1–5 μm;

[0057] 4) The coefficient of variation for thickness is 1–12%;

[0058] 5) The film flatness rate is 90-100%.

[0059] Preferably, the ratio of the longitudinal tensile strength to the transverse tensile strength of the LCP film is 1.05 to 1.4; more preferably, it is 1.1 to 1.3.

[0060] Preferably, the average thickness of the LCP film is 110–135 μm; more preferably, it is 120–130 μm.

[0061] Preferably, the standard deviation of the thickness of the LCP film is 1.5 to 5 μm; more preferably, it is 2 to 5 μm.

[0062] Preferably, the coefficient of variation of the thickness of the LCP film is 1.5 to 11%; more preferably, it is 1.8 to 10%.

[0063] Preferably, the LCP film has a flatness of 95-100%; more preferably, it has a flatness of 98-100%.

[0064] A third aspect of the present invention provides an application of the LCP thin film described in the second aspect of the present invention in the fields of electronics, communications, and aerospace.

[0065] Preferably, the communication field is the 5G communication field; more preferably, the 5G communication field is the field of antenna film materials for 5G communication.

[0066] The beneficial effects of this invention are:

[0067] The preparation method of this invention combines blown film and calendering methods. First, a bidirectional rotating die head with an outer mold body and a mandrel rotating in opposite directions is used to control the molecular orientation and arrangement structure in the LCP film, so that the LCP molecular structure forms a woven mesh structure, avoiding the problem of large differences in longitudinal and transverse tensile properties caused by the ordered orientation of LCP molecules. Then, through a pressing step, the double-layer LCP film is pressed into a single-layer LCP film, which solves the problems of poor film thickness uniformity and uneven film winding.

[0068] Specifically, compared with the prior art, the present invention has the following advantages:

[0069] 1. This invention introduces a bidirectional rotating die head. The outer die body and the mandrel of this rotating die head rotate in opposite directions, which can apply a circumferential flow field to the LCP melt. Under the extrusion pressure, the LCP melt simultaneously participates in the upward flow field. The superposition of the two motions forms a spiral upward composite flow field. Therefore, under the action of the composite flow field, the LCP molecular chains are oriented along the spiral direction, forming a woven mesh-like structure on the molecular structure of the tubular preform, thereby solving the problem of large differences in longitudinal and transverse tensile properties of LCP films. Furthermore, by controlling the traction force of the preform, the woven mesh structure is kept undeformed during the preparation process, which is also beneficial for pressing. The final LCP film has small differences in longitudinal and transverse tensile properties and good thickness uniformity.

[0070] 2. The present invention uses a pressing step to heat-press two layers of film into a single layer of film with a specific thickness, thereby eliminating the unevenness of film thickness caused by uneven die head gap, and eliminating the wrinkles formed on the double-layer film at the traction pressure roller.

[0071] 3. The present invention also controls the tension on a single-layer film by controlling the traction force during film winding, thereby solving the problem of uneven film winding. Attached Figure Description

[0072] Figure 1 This is an apparatus for preparing LCP films in the examples and comparative examples. In the apparatus, 1-extruder; 2-air valve; 3-sizing sleeve; 4-cylindrical film bubble; 5-herringbone plate; 6-traction clamping roller; 7-preheating oven; 8-double-layer LCP film; 9-pressing device; 10-film support roller; 11-heat insulation box; 12-guide roller; 13-ultrasonic thickness gauge; 14-single-layer LCP film; 15-winding roller; 16-tubular preform; 17-bidirectional rotating die.

[0073] Figure 2 This is a photograph of the LCP film prepared in Example 1.

[0074] Figure 3 This is a photograph of the LCP thin film prepared in Comparative Example 2.

[0075] Figure 4 This is a photograph of the film at the winding roller during the winding process of Comparative Example 3.

[0076] Figure 5 This is a photograph of the film after it was unwound in Comparative Example 3. Detailed Implementation

[0077] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described herein are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0078] It should be noted that the particulate LCP used in the embodiments and comparative examples of the present invention is Japanese Factoring A950.

[0079] Specifically, the LCP films in the embodiments and comparative examples of the present invention are obtained through... Figure 1 The apparatus shown is prepared using the following method:

[0080] After the LCP granules are melted and plasticized into a high-temperature melt in extruder 1, they flow through the transition section and through the annular die of the self-made bidirectional rotating die head 17 to form an inner diameter. outer diameter The tubular preform 16 is simultaneously pulled upwards to the traction clamping roller 6 using a special tool. Under the action of the traction roller, the preform continues to move upwards and passes sequentially through the preheating oven 8, the pressing device 9, the guide roller 12, the thickness gauge 13, and finally reaches the winding roller 15. The air valve 2 is opened to introduce an appropriate amount of air, which inflates the preform to form a cylindrical film bubble 4 with an outer diameter consistent with the inner diameter of the shaping sleeve 3. When the film bubble moves upwards under the action of the traction roller and passes through the herringbone plate 5, the cylindrical film bubble is flattened to form a double-layer LCP film 8. After the double-layer film passes through the preheating oven 7 and the film temperature rises to a certain temperature, it is then calendered by the pressing device 9 to press the double-layer LCP film into a single-layer LCP film 14. An ultrasonic thickness gauge 13 detects the thickness of the single-layer LCP film. When the film thickness exceeds the set tolerance range, the signal is fed back to the PLC, which then controls the pressing device to adjust the film pressing force and the winding speed of the take-up roller 15 to control the film thickness. The take-up roller 15 uses constant tension winding during the film winding process. The specific preparation steps are as follows:

[0081] Step a) Melt preparation, using a diameter of A screw extruder with a length-to-diameter ratio of 28:1 melts and plasticizes granular LCP material into a fluid high-temperature melt under the combined action of heat generated by the cast aluminum heater and shear heat generated by the screw rotation.

[0082] Step b) Film preform preparation: The high-temperature melt flows through the annular flow channel of a self-made bidirectional rotating die in the transition section, forming a tubular film preform. Since the mandrel of the self-made bidirectional rotating die rotates in the opposite direction to the outer die, a circumferential flow field is applied to the LCP melt. Under the extrusion pressure, the LCP melt simultaneously participates in the upward flow field. The superposition of these two motions forms a spiral upward composite flow field. Therefore, under the action of the composite flow field, the LCP molecular chains orient along the spiral direction, forming a woven mesh-like structure on the molecular structure of the tubular film preform, thus solving the problem of large differences in longitudinal and transverse tensile properties of LCP films. Under the action of the bidirectional rotating die, a woven mesh structure can be formed. By adjusting the rotation speed of the die, different weaving angles can be formed.

[0083] Step c) Inflate the membrane preform: Open the air valve and let air into the tubular membrane preform. The air inflates the tubular membrane preform until its outer diameter is consistent with the inner diameter of the shaping sleeve. Then close the air valve and keep the pressure inside the membrane bubble constant. The tubular membrane preform becomes a cylindrical membrane bubble.

[0084] Step d) Flattening the membrane bubble: The cylindrical membrane bubble moves upward under traction and automatically folds into a planar double-layer LCP film after passing through the herringbone process. After obtaining the double-layer LCP film, it can be directly wound and stored using a winding roller, or subsequent steps can be performed directly. Constant torque winding is used, with a torque of 0.16–0.26 N·m.

[0085] Step e) Film preheating: The double-layer LCP film is preheated in an oven with the oven temperature set at a specific temperature. The film temperature rises to near the LCP viscosity temperature, making the double-layer LCP film plastic.

[0086] Step f) Film lamination: The preheated bilayer LCP film, near its viscous flow temperature, passes through the lamination device. Due to the plasticity and viscosity of the bilayer LCP film, under the pressure of the lamination device, the bilayer LCP film is laminated into a single-layer LCP film. The thickness of the single-layer LCP film decreases while its width increases. The lamination process eliminates wrinkles formed at the traction pressure rollers and removes film thickness inconsistencies, while preserving the woven mesh structure formed inside the bidirectional rotating die channel. The lamination device in this step can be a lamination roller assembly or a molding press. Both lamination roller and molding presses achieve the goal of laminating a bilayer LCP film into a single-layer film. The difference lies in the operation: lamination rollers allow for continuous production, while molding presses operate intermittently.

[0087] Step g) Thickness measurement: Use an ultrasonic thickness gauge to check whether the film thickness variation is within the set tolerance range. If the deviation is out of tolerance, adjust the pressing force of the pressing roller group and the speed of the winding roller to control the film thickness.

[0088] Step h) Film winding: The single-layer LCP film is wound up by a winding roller. The winding adopts constant torque winding with a torque of 0.16 to 0.26 N·m.

[0089] Example 1

[0090] This example provides a method for preparing LCP thin films, which combines blown film method and calendering method. The specific steps are as follows:

[0091] Using screw diameter A dedicated screw extruder with a length-to-diameter ratio of 28 is used. The barrel section temperatures are set to 260℃, 300℃, and 300℃ respectively. Granular LCP is melted and plasticized into a high-temperature melt. The high-temperature melt passes through an annular flow channel of a bidirectional rotating die with a speed of 10r / min and two temperature zones set to 290℃ and 290℃ respectively, forming the outer diameter. A 0.4mm thick tubular preform moves upward at a speed of 8.5m / min under the traction force of the traction roller. The air valve is opened, allowing air to enter the preform, which inflates into a cylindrical bubble with an outer diameter matching the inner diameter of the shaping sleeve. Simultaneously, the air valve is closed while maintaining constant pressure. Cylindrical film bubbles are flattened into planar double-layer LCP films after passing through a herringbone plate. Each LCP film layer is 0.1±0.015mm thick. The double-layer LCP film is wound into a roll by a winding roller with constant torque, ranging from 0.16 to 0.26 N·m. The double-layer LCP film is then placed in an oven at 300℃ for 5 minutes. It is then pressed together using a molding press with preheated upper and lower molds at 290℃. The mold clamping force is maintained at 5 MPa for 10 minutes. After cooling to room temperature, the mold is opened, and the 0.12mm thick LCP film is removed and wound up again using a winding roller with constant torque, ranging from 0.16 to 0.26 N·m.

[0092] Example 2

[0093] This example provides a method for preparing LCP thin films, which combines blown film method and calendering method. The specific steps are as follows:

[0094] Using screw diameter A dedicated screw extruder with a length-to-diameter ratio of 28 is used. The barrel section temperatures are set to 260℃, 300℃, and 300℃ respectively. Granular LCP is melted and plasticized into a high-temperature melt. The high-temperature melt passes through an annular flow channel of a bidirectional rotating die with a speed of 10r / min and two temperature zones set to 290℃ and 290℃ respectively, forming the outer diameter. A 0.4mm thick tubular preform moves upward at 7m / min under the traction force of the traction roller. The air valve is opened, allowing air to enter the preform, which inflates into a cylindrical bubble with an outer diameter matching the inner diameter of the shaping sleeve. Simultaneously, the air valve is closed while maintaining constant pressure. Cylindrical film bubbles are flattened into planar double-layer LCP films after passing through a herringbone plate. Each LCP film layer is 0.1±0.015mm thick. The double-layer LCP film is wound into a roll by a winding roller with constant torque, ranging from 0.16 to 0.26 N·m. The double-layer LCP film is then placed in an oven at 300℃ for 5 minutes. It is then pressed together using a molding press with preheated upper and lower molds at 290℃. The mold clamping force is maintained at 5 MPa for 10 minutes. After cooling to room temperature, the mold is opened, and the 0.12mm thick LCP film is removed and wound up again using a winding roller with constant torque, ranging from 0.16 to 0.26 N·m.

[0095] Comparative Example 1

[0096] This example provides a method for preparing LCP thin films using the blown film method and a non-rotating die. The specific steps are as follows:

[0097] Using screw diameter A dedicated screw extruder with a length-to-diameter ratio of 28 is used, with barrel temperatures set at 260℃, 300℃, and 300℃ respectively. Granular LCP is melted and plasticized into a high-temperature melt. This high-temperature melt then passes through a non-rotating die (without applied power to the mandrel or die) at a temperature set at 295℃ to form the outer diameter. A 0.28mm thick tubular preform moves continuously upward at a speed of 5.2m / min under the traction force of the traction roller. Air is introduced into the preform through the air valve, inflating it into a cylindrical bubble with an outer diameter matching the inner diameter of the shaping sleeve. Simultaneously, the air valve is closed while maintaining constant pressure. The cylindrical film bubble is flattened into a planar double-layer LCP film after passing through the herringbone plate. The double-layer LCP film is then wound into a roll by the rotating winding roller. The winding roller uses constant torque winding with a torque of 0.16 to 0.26 N·m.

[0098] Comparative Example 2

[0099] This example provides a method for preparing LCP thin films using the blown film method and a bidirectional rotating die head. The specific steps are as follows:

[0100] Using screw diameter A dedicated screw extruder with a length-to-diameter ratio of 28 is used. The barrel section temperatures are set to 260℃, 300℃, and 300℃ respectively. Granular LCP is melted and plasticized into a high-temperature melt. The high-temperature melt passes through an annular flow channel of a bidirectional rotating die with a speed of 10r / min and two temperature zones set to 290℃ and 290℃ respectively, forming the outer diameter. A 0.4mm thick tubular preform moves upward at a speed of 8.5m / min under the traction force of the traction roller. The air valve is opened, allowing air to enter the preform, which inflates into a cylindrical bubble with an outer diameter matching the inner diameter of the shaping sleeve. Simultaneously, the air valve is closed while maintaining constant pressure. The cylindrical film bubble is flattened into a planar double-layer LCP film after passing through the herringbone plate. The double-layer LCP film is then wound into a roll by the rotating winding roller. The winding roller uses constant torque winding with a torque of 0.16 to 0.26 N·m.

[0101] Comparative Example 3

[0102] This example provides a method for preparing an LCP film. The difference from Example 1 is that, in this example, when the single-layer LCP film is wound up with a winding roller, the winding roller uses constant torque winding with a torque of 0.26 N·m or more.

[0103] Performance testing

[0104] 1) Tensile strength: The longitudinal (MD) tensile strength and transverse (TD) tensile strength of the film are tested according to GB / T 1040.3-2006 standard. The longitudinal direction refers to the direction perpendicular to the film, and the transverse direction refers to the direction parallel to the film.

[0105] 2) Thickness uniformity: The thickness of the film was measured at different locations, with 70 measurements taken. The average thickness μ, standard deviation σ, and coefficient of variation CV were calculated. The specific calculation formulas are as follows:

[0106]

[0107] The thickness of the thin film is n = 70 in this embodiment and the comparative example.

[0108] 3) Film flatness ratio ω: also known as effective area percentage. The specific measurement steps are as follows: Randomly select 3 films of 180mm×220mm. If it is a two-layer film, cut it into one film. Divide the film into 16 squares of 4×4 at equal intervals in both the longitudinal and transverse directions. Record the number of squares with dents, wrinkles, and creases, n. The film flatness ratio ω can be calculated. The calculation formula is as follows:

[0109]

[0110] The test results are shown in Table 1.

[0111] Table 1 Test results of the examples and comparative examples

[0112]

[0113]

[0114] Comparative analysis of Examples 1 and 2 shows that the traction speed during the traction of the tubular mold blank needs to be maintained at a suitable level. Too fast or too slow a speed will affect the molecular structure of LCP molecules in the mold blank, causing deformation of the network molecular structure formed in the bidirectional rotating die head. This affects the difference in longitudinal and transverse tensile properties of the final monolayer LCP film and also affects the elimination of film thickness inhomogeneity during the lamination process, resulting in unsatisfactory film thickness uniformity. In Examples 1 and 2, the traction speed was maintained at a suitable level, therefore the LCP films obtained had small differences in longitudinal and transverse tensile properties and good film thickness uniformity. A physical image of the LCP film obtained in Example 1 is shown below. Figure 2 As shown, where Figure 2 The numerical markers indicate the locations where the thickness was measured; a total of 70 measurements were taken. From Figure 2 As can be seen, the LCP film obtained in Example 1 has a relatively smooth surface. The few dents are caused by the precision of the equipment, such as the surface quality of the parts. No wrinkles appeared on the film surface, and the smoothness rate can reach 100%.

[0115] In contrast, Comparative Example 1 did not use a bidirectional rotating die to process the LCP melt, thus failing to form a woven network structure of LCP molecules and failing to press the double-layer LCP film together. The resulting film had a high MD / TD value, indicating that the film's strength in the MD direction was too high and its strength in the TD direction was too weak, making it extremely easy to tear along the TD direction. Comparative Example 1's film exhibited significant differences in longitudinal and transverse tensile properties, poor thickness uniformity, and low film flatness.

[0116] Although Comparative Example 2 used a bidirectional rotating die to process the LCP melt, it did not press the bilayer LCP film together, resulting in a film with poor flatness. A physical image of the bilayer LCP film obtained in Comparative Example 2 is shown below. Figure 3 As shown, the film surface exhibits numerous dents, wrinkles, and creases. (This is achieved through...) Figure 2 and Figure 3 The comparison shows that Example 1 can significantly eliminate wrinkles by pressing, resulting in a film with high flatness.

[0117] Furthermore, the magnitude of the winding roller traction force has a significant impact on the film flatness. When the torque of the winding roller traction force exceeds 0.26 N·m, it can easily lead to film breakage and film plane distortion, resulting in winding wrinkles. In Comparative Example 3, the torque of the winding roller traction force exceeds 0.26 N·m, and the resulting LCP film is shown in the physical image below. Figure 4 and Figure 5 As shown, Figure 4 This is a photograph of the film at the take-up roller during the winding process. As can be seen, the film at the take-up roller is wrinkled and the surface is uneven. Figure 5 The image shows the unfolded film after being wound up. As can be seen, the surface of the unfolded film is not smooth and exhibits a planar twisted state.

Claims

1. A method for preparing an LCP thin film, characterized in that, Includes the following steps: S1. Melt extrusion: LCP raw material is melt extruded to obtain LCP melt; S2. Mold preparation: LCP melt is passed into a bidirectional rotating die head to form a tubular mold blank with a woven mesh structure of LCP molecules; the bidirectional rotating die head includes an outer mold body and a mandrel, and the outer mold body and the mandrel rotate in opposite directions; S3. Mold blank traction: Pull the tubular mold blank along the axial direction; S4. Molding blank inflation: Gas is injected into the tubular molding blank to inflate it and obtain a cylindrical membrane bubble; S5. Flattening the membrane bubble: Flatten the cylindrical membrane bubble to form a double-layer LCP film; S6. Film lamination: The double-layer LCP film is laminated to obtain the LCP film; In step S3, the traction speed of the mold blank is 6~9m / min; In step S6, the pressure for film pressing is 3~10MPa; The process includes step S55, film preheating, after step S5 and before step S6. In step S55, the film preheating temperature is the viscous flow temperature of the LCP raw material. Step S6 is followed by step S7, which involves film winding. The film winding is performed using constant torque winding. In step S7, the torque of the film winding is 0.16~0.26 N·m.

2. The preparation method according to claim 1, characterized in that, The preheating time for the film is 3-10 minutes.

3. The preparation method according to claim 1, characterized in that, In step S2, the rotational speed of the bidirectional rotating mold head is 5~20 r / min.

4. The preparation method according to claim 1, characterized in that, In step S5, the single layer of the bilayer LCP film is 0.08~0.12mm thick; And / or, in step S6, the thickness of the LCP film is 0.1~0.15mm.

5. The LCP thin film prepared by the method according to any one of claims 1 to 4, characterized in that, The LCP film meets the following requirements: 1) The ratio of longitudinal tensile strength to transverse tensile strength is 1~1.5; 2) The average thickness is 100~140μm; 3) The standard deviation of the thickness is 1~5μm; 4) The coefficient of variation for thickness is 1-12%; 5) The flatness of the film is 90~100%.

6. The application of the LCP thin film according to claim 5 in the fields of electronics, communications, and aerospace.

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