A low dielectric microporous film and a method for manufacturing the same

Abstract

The invention discloses a low dielectric microporous film and a manufacturing method thereof, which comprises the following steps: 1. Melting and plasticizing a thermoplastic liquid crystal polymer through an extruder, and extruding it into a film; 2. Pressing the liquid crystal polymer film obtained in the previous step with a support to obtain a composite; 3. Heating the liquid crystal polymer film composite obtained in the previous step to a certain temperature range and maintaining it for a certain time; 4. Separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film. The low dielectric microporous film obtained by the preparation process of the invention has uniformly distributed micropores and a small dielectric loss factor at high frequencies.

Description

Technical Field

[0001] The invention relates to a low-dielectric microporous film and a manufacturing method thereof, belonging to the technical field of polymer materials and also to the field of film production and processing. Background Art

[0002] With the full advancement of 5G technology applications and the further increase in communication frequencies, the use of low-dielectric-constant dielectric films as insulating substrates for circuit boards is an effective way to reduce interconnection delays, crosstalk, and energy consumption. Thermotropic liquid crystal polymer (LCP) film materials have low dielectric constants at high frequencies, low dielectric losses, and stable properties, making them irreplaceable in communication base stations and mobile terminals. At present, the dielectric constant of LCP films is generally between 3 and 4, which is still relatively high compared to fluorocarbon films such as polytetrafluoroethylene.

[0003] The present invention mainly develops a preparation process to solve the problem that the dielectric constant of LCP film is not low enough. The LCP film obtained by the preparation process has an extremely low dielectric constant. Summary of the invention

[0004] The dielectric constant of conventional liquid crystal polymer films can be slightly reduced by modification and process adjustment, but the reduction is limited. The purpose of the invention is to provide a low-dielectric microporous liquid crystal polymer film. By subjecting the liquid crystal polymer film to heat treatment and other processing techniques, pores are generated inside the liquid crystal polymer film, air is introduced, and its dielectric constant is reduced.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A method for manufacturing a low dielectric microporous film, the manufacturing method is as follows:

[0007] (1) Film forming step: melt plasticizing the thermoplastic liquid crystal polymer through an extruder and extruding it into a film; the film forming method may be extrusion casting film forming, extrusion blow molding film forming, or extrusion stretching film forming, etc.;

[0008] (2) Composite step: The liquid crystal polymer film obtained in the previous step is pressed together with the support to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, the upper layer and the lower layer are support layers, and the upper support layer and the lower support layer can be made of the same material or different materials. The support body and the liquid crystal polymer film are bonded together by physical action. The support body will not soften or deform during the subsequent heat treatment process;

[0009] (3) Heat treatment step: heating the liquid crystal polymer film composite obtained in the previous step to a temperature ranging from the liquid crystal polymer initial reaction temperature to a temperature 20°C higher than the melting temperature, and maintaining the temperature for a certain period of time; the heat treatment time is 10 minutes to 60 minutes;

[0010] (4) Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0011] During the preparation process, the liquid crystal polymer used is a wholly aromatic liquid crystal polyester or a wholly aromatic liquid crystal polyester amide, and its melting temperature is between 260°C and 360°C. A die with an inner diameter of 0.5 mm is used, and the temperature is increased by 10°C above the melting temperature for 1000 seconds. -1 The melt viscosity η measured by capillary rheometer at a shear rate of LCP Between 30-100Pa·s.

[0012] The support is a metal foil or a high temperature resistant polymer film.

[0013] A low-dielectric microporous film, wherein the equivalent circular diameter of the micropores is 5 to 50 microns and the porosity is 20% to 50%.

[0014] About 100 grams of liquid crystal polymer particles used in the present invention are heated to a certain temperature and maintained for 1 hour; the gas released by the particles after the particles are heated is collected and condensed. The temperature at which the collected volatile matter condensation amount reaches 0.2 grams is defined as the initial reaction temperature of the liquid crystal polymer.

[0015] During the heat treatment of the liquid crystal polymer film, the liquid crystal polymer is still slowly reacting and polycondensing, and produces acetic acid as a byproduct. Due to the presence of the upper and lower supports, the acetic acid is vaporized at high temperature, but cannot escape from the film quickly, but causes the film to form holes. By controlling the heat treatment temperature and time, the porosity and hole diameter in the liquid crystal polymer film can be controlled, and then the dielectric properties of the prepared microporous liquid crystal polymer film can be controlled. The present invention is realized based on such a discovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of a liquid crystal polymer film composite;

[0017] Figure 2 This is a microstructure photo of the microporous film;

[0018] Figure 3 This is a microscope structure photo of a perforated liquid crystal polymer film. DETAILED DESCRIPTION

[0019] The liquid crystal polymer used in the present invention is a liquid crystal polyester or liquid crystal polyester amide prepared using aromatic compounds as raw material monomers, preferably a fully aromatic liquid crystal polyester or polyester amide prepared using only aromatic compounds as raw material monomers. It has repeating units represented by formula (1) to formula (6):

[0020] (1): -O-Ar1-CO-

[0021] (2): -CO-Ar2-CO-

[0022] (3):-O-Ar3-O-

[0023] (4): -O-Ar4-NH-

[0024] (5): -CO-Ar5-NH-

[0025] (6): -NH-Ar6-NH-

[0026] In the formula, Ar1 to Ar6 each independently represent a phenylene group, a naphthylene group or a biphenylene group.

[0027] In the film forming process, one liquid crystal polymer composed of the above repeating units may be used, or two or more liquid crystal polymers composed of the above repeating units may be used. When two or more liquid crystal polymers are used, each of the liquid crystal polymers must meet the above requirements for melting temperature and melt viscosity.

[0028] The liquid crystal polymer used in the present invention can also be compounded with other thermoplastic polymers to be used as a polymer composite material. Examples of the other thermoplastic polymers include polyarylate, polyphenylene ether, polyetheretherketone, polyetherimide, polyimide, polyamide, polyphenylene sulfide, polycarbonate, etc. The compounding amount of these thermoplastic polymers varies according to the type, and generally does not exceed 25% of the total amount of the polymer composite material. For the other added thermoplastic polymers, it is better that the melting temperature is as close as possible to the liquid crystal polymer used, and the melt viscosity is also similar to that of the liquid crystal polymer used.

[0029] The liquid crystal polymer or liquid crystal polymer composite material used in the present invention may further contain additives such as lubricants, antioxidants, and heat stabilizers.

[0030] The liquid crystal polymer film used in the present invention can be obtained by extruding the liquid crystal polymer into a film, and the known film forming methods that can be used include extrusion casting, extrusion blow molding, or extrusion stretching.

[0031] The liquid crystal polymer film after extrusion is subjected to a lamination step to obtain a liquid crystal polymer film composite. The liquid crystal polymer film composite is a three-layer structure, the middle layer is a liquid crystal polymer film layer, the upper layer and the lower layer are support layers, and the upper support layer and the lower support layer can be the same material or different materials. Lamination can be performed by known roller pressing or static hot pressing, and the lamination temperature is preferably 30°C below the melting temperature of the liquid crystal polymer to the melting temperature.

[0032] The support used in the liquid crystal polymer film composite can be selected from metal foil or high temperature resistant polymer film. Examples of the metal foil used include copper, gold, silver, nickel, aluminum, etc., among which copper and aluminum are preferred, and aluminum is particularly preferred. Examples of the polymer film used include polyimide, polyetheretherketone, polytetrafluoroethylene, etc.

[0033] During the heat treatment of the obtained liquid crystal polymer film composite, the heat treatment temperature used is in the range of the resin initial reaction temperature to 20°C higher than the melting temperature. The heating equipment used can use a well-known hot air circulation oven, a vacuum oven, a heating channel, etc. The above-mentioned heating channel can use a crawler, a traction roller, etc. to guide the liquid crystal polymer composite to move inside the heating channel, and the heating device used can use infrared heating, hot roller heating, ceramic plate heating, etc. The heating time is about 10 minutes to 60 minutes.

[0034] After the heat treatment, the upper support layer and the lower support layer of the liquid crystal polymer film composite are removed and separated to obtain a liquid crystal polymer microporous film. The separation can be directly carried out by physical peeling; if the support is a metal foil, etching can also be used.

[0035] The liquid crystal polymer microporous film obtained by the above steps has a porosity of 20% to 50%, and a micropore equivalent circle diameter of about 1 to 50 microns. The porosity calculation method is as follows:

[0036]

[0037] The present invention is further described below by way of examples and comparative examples. Without violating the spirit of the present invention, the present invention should not be limited to the contents specifically shown in the following examples.

[0038] Product performance test method:

[0039] The present invention uses a differential scanning calorimeter (DSC, TA Company, USA) to test the melting point (T m ), and the test was performed according to ASTM D3418. The present invention uses a capillary rheometer (RH 2200, Malvern, UK) to test the melt viscosity (MV), and the test is performed according to ASTM D3835.

[0040] Embodiment 1:

[0041] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K260, Pulite) was melted and plasticized, extruded through a ring die with a gap of 50 μm and a diameter of 50 mm, and blown into a film. The film blowing ratio was 5.5 and the pulling speed was 1 m / s;

[0042] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, and the upper and lower layers are both aluminum foils. The lamination temperature is 240°C.

[0043] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 275° C. in an oxygen-free oven and keep it for 50 minutes;

[0044] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0045] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0046] Embodiment 2:

[0047] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 μm and a diameter of 50 mm, and blown into a film. The film blowing ratio was 5.5 and the pulling speed was 1 m / s;

[0048] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, and the upper and lower layers are both aluminum foils. The lamination temperature is 260°C.

[0049] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 240° C. in an oxygen-free oven and keep it for 40 minutes;

[0050] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0051] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0052] Embodiment 3:

[0053] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite) was melted and plasticized, extruded through a ring die with a gap of 50 μm and a diameter of 50 mm, and blown into a film. The film blowing ratio was 6 and the pulling speed was 1 m / s;

[0054] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, the upper layer is the polyimide film, and the lower layer is the copper foil. The lamination temperature is 270°C.

[0055] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 275° C. in an oxygen-free oven and keep it for 30 minutes;

[0056] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0057] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0058] Embodiment 4:

[0059] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite) was melted and plasticized, extruded through a ring die with a gap of 50 μm and a diameter of 50 mm, and blown into a film. The film blowing ratio was 6 and the pulling speed was 1 m / s;

[0060] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is a liquid crystal polymer film layer, and the upper and lower layers are both polyimide films. The lamination temperature is 280°C.

[0061] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 300° C. in an oxygen-free oven and keep it for 20 minutes;

[0062] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0063] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0064] Embodiment 5:

[0065] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K335, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 microns and a diameter of 50 mm, and blown into a film. The film blowing ratio was 4 and the pulling speed was 1 m / s;

[0066] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is a liquid crystal polymer film layer, and the upper and lower layers are both polyimide films. The lamination temperature is 300°C.

[0067] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 330° C. in an oxygen-free oven and keep it for 15 minutes;

[0068] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0069] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0070] Embodiment 6:

[0071] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K345, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 microns and a diameter of 50 mm, and blown into a film. The film blowing ratio was 4 and the pulling speed was 1 m / s;

[0072] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, the upper layer is the polyimide film, and the lower layer is the aluminum foil. The lamination temperature is 315°C.

[0073] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 335° C. in an oxygen-free oven and keep it for 15 minutes;

[0074] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0075] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0076] Comparative Example 1:

[0077] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 microns and a diameter of 50 mm, and blown into a film. The film blowing ratio was 5 and the pulling speed was 1 m / s;

[0078] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, and the upper and lower layers are both aluminum foils. The lamination temperature is 260°C.

[0079] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 220° C. in an oxygen-free oven and keep it for 480 minutes;

[0080] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0081] Since the heat treatment temperature is lower than the initial reaction temperature of the resin, no micropores are generated in the treated liquid crystal polymer film. Other properties of the liquid crystal polymer film are shown in Table 1.

[0082] Comparative Example 2:

[0083] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 microns and a diameter of 50 mm, and blown into a film. The film blowing ratio was 5 and the pulling speed was 1 m / s;

[0084] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, and the upper and lower layers are both aluminum foils. The lamination temperature is 260°C.

[0085] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 330° C. in an oxygen-free oven and keep it for 20 minutes;

[0086] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0087] Since the heat treatment temperature exceeds the melting point of the liquid crystal polymer used by 30°C, the micropores generated in the liquid crystal polymer film are too large to cause perforation in the film. Other properties of the liquid crystal polymer film are shown in Table 1.

[0088] Comparative Example 3:

[0089] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 microns and a diameter of 50 mm, and blown into a film. The film blowing ratio was 5 and the pulling speed was 1 m / s;

[0090] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, and the upper and lower layers are both aluminum foils. The lamination temperature is 260°C.

[0091] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 300° C. in an oxygen-free oven and keep it for 5 minutes;

[0092] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0093] Due to the long heat treatment time, the micropores generated in the liquid crystal polymer film are too large, resulting in perforation of the film. Other properties of the liquid crystal polymer film are shown in Table 1.

[0094] The properties of the finished liquid crystal polymer microporous film are shown in Table 1.

[0095] Comparative Example 4:

[0096] 1. Film forming step: Use a single screw extruder to extrude the thermoplastic liquid crystal polymer ( K280, Pulite Company) was melted and plasticized, extruded through a ring die with a gap of 50 microns and a diameter of 50 mm, and blown into a film. The film blowing ratio was 5 and the pulling speed was 1 m / s;

[0097] 2. Lamination step: The liquid crystal polymer film obtained in the previous step and the aluminum foil with a thickness of 25 microns are laminated by a static press to obtain a composite body, which is divided into three layers, the middle layer is the liquid crystal polymer film layer, and the upper and lower layers are both aluminum foils. The lamination temperature is 260°C.

[0098] 3. Heat treatment step: heat the liquid crystal polymer film composite obtained in the previous step to 300° C. in an oxygen-free oven and keep it for 480 minutes;

[0099] 4. Separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film.

[0100] Due to the long heat treatment time, the micropores generated in the liquid crystal polymer film are too large, resulting in perforation of the film. Other properties of the liquid crystal polymer film are shown in Table 1.

[0101] Table 1 Properties of liquid crystal polymer microporous films

[0102]

[0103]

Claims

1. A method for manufacturing a low dielectric microporous film, characterized in that: The preparation steps are as follows: (1) Film forming step: melt plasticizing the thermoplastic liquid crystal polymer through an extruder and extruding it into a film; the film forming method is extrusion casting film forming, extrusion blow molding film forming or extrusion stretching film forming; (2) a composite step: the liquid crystal polymer film obtained in the previous step is pressed together with a support to obtain a composite, wherein the composite is divided into three layers, the middle layer is a liquid crystal polymer film layer, the upper layer and the lower layer are support layers, and the upper support layer and the lower support layer are made of the same material or different materials; the support and the liquid crystal polymer film are bonded together by physical action; and the support will not soften or deform during the subsequent heat treatment process; (3) Heat treatment step: heating the liquid crystal polymer film composite obtained in the previous step to a temperature ranging from the liquid crystal polymer initial reaction temperature to a temperature 20°C higher than the melting temperature, and maintaining the temperature for a certain period of time; the heat treatment time is 10 minutes to 60 minutes; (4) separation step: separating the support from the heat-treated liquid crystal polymer film composite to obtain a finished liquid crystal polymer low dielectric microporous film; The liquid crystal polymer used is a wholly aromatic liquid crystal polyester or a wholly aromatic liquid crystal polyester amide, and its melting temperature is between 260℃ and 360℃. A die with an inner diameter of 0.5mm is used, and the temperature is 10℃ above the melting temperature for 1000sec. -1 The melt viscosity η measured by capillary rheometer at a shear rate of LCP Between 30-100 Pa·s; 100 grams of liquid crystal polymer particles are heated to a certain temperature and maintained for 1 hour; the gas released by the particles after heating is collected and condensed; the temperature heated to when the amount of condensed volatile matter collected reaches 0.2 grams is defined as the starting reaction temperature of the liquid crystal polymer.

2. The method for manufacturing a low dielectric microporous film according to claim 1, characterized in that: The support is a metal foil or a high temperature resistant polymer film.

3. A low dielectric microporous film, characterized in that: The low dielectric microporous film is prepared by the manufacturing method of claim 1; the equivalent circular diameter of the micropores is 5 to 50 microns, and the porosity is 20% to 50%.

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