Polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient and preparation method thereof

Abstract

The invention belongs to the technical field of engineering plastics, and particularly relates to a polyphenylene sulfide-based composite material with an adjustable thermal expansion coefficient and a preparation method thereof. The composite material comprises the following components in parts by weight: 40-65 parts of polyphenylene sulfide resin, 10-45 parts of glass fibers, 8-50 parts of a positive thermal expansion coefficient ceramic filler, 22-50 parts of a negative thermal expansion coefficient ceramic filler and 0.1-2 parts of a surface modifier. The linear thermal expansion coefficient of the composite material is obviously lower than the thermal expansion coefficient of a single ceramic filler under the synergistic regulation of the mixed ceramic filler with positive and negative thermal expansion coefficients, and after modification and compounding, the raw materials have a synergistic effect, so that the composite material is excellent in mechanical property and heat resistance; and the thermal expansion coefficient value can be adjusted in a relatively large range.

Description

Technical Field

[0001] The present invention belongs to the technical field of engineering plastics, and particularly relates to a polyphenylene sulfide-based composite material with an adjustable thermal expansion coefficient and a preparation method thereof. Background Art

[0002] With the rapid development of 5G communication technology, the number of receiving and transmitting channels of 5G communication base stations has increased sharply. Due to factors such as the limited frequency band that the base station transceiver channels can occupy and the mutual influence between adjacent frequency bands, the cavity filters used in 5G base stations must have high frequency selectivity and temperature stability. Under normal circumstances, the main reason affecting the frequency stability of the cavity filter is the temperature drift. The working environment of the cavity filter in 5G base stations is relatively complex and needs to work within a wide temperature range. When the ambient temperature and the internal temperature change, the various structural components of the cavity filter will expand and contract with the temperature change, resulting in a change in its resonant frequency, and may cause an increase in the standing wave ratio, an increase in insertion loss, and a phase shift of the filter, that is, the temperature drift phenomenon. When the amplitude-phase change caused by the temperature drift exceeds a certain limit, it will affect the normal transmission of the signal. Therefore, it is necessary to perform temperature compensation on the cavity filter.

[0003] At present, there are mainly the following two temperature compensation schemes for cavity filters used in base stations: 1. Using materials with a small thermal expansion coefficient to prepare the cavity filter, so as to reduce the influence of the filter structure on temperature changes; 2. Using materials with different thermal expansion coefficients to match each other, so that the influence of ambient temperature changes on the filtering characteristics of the filter cancels each other out. The two schemes are usually used in combination. For example, Invar (with a thermal expansion coefficient of about 0.9 ppm / °C) with a small thermal expansion coefficient is used for the tuning screws in the cavity filter, aluminum alloy (with a thermal expansion coefficient of about 23 ppm / °C) is used for the outer shell cavity, and brass (with a thermal expansion coefficient of about 18 ppm / °C) is used for the resonant rod, and the overall temperature drift of the filter is reduced through structural optimization design. However, metal materials such as Invar and brass are expensive and heavy, which do not meet the requirements of lightweight, low cost, and large-scale production of 5G base station filters. Compared with metal materials, polyphenylene sulfide-based composite materials have the advantages of high temperature resistance, high strength, light weight, low cost, etc., and the injection molding technology is relatively mature, which can greatly reduce the large-scale manufacturing cost of cavity filters. However, the thermal expansion coefficient value of pure PPS plastic is relatively high, and its thermal expansion coefficient is still above 20 ppm / °C after being modified by traditional glass fiber. Therefore, it is urgent to solve the problem of further reducing its thermal expansion coefficient and realizing controllable adjustment within a certain range while ensuring the mechanical properties of the PPS modified plastic, so as to replace metal materials to reduce the weight of the cavity filter, reduce the cost, compensate for the influence of ambient temperature changes on the filtering characteristics of the filter, and meet the application requirements of the 5G communication field. Summary of the Invention

[0004] The object of the present invention is to provide a polyphenylene sulfide-based composite material with adjustable coefficient of thermal expansion and a preparation method thereof. By regulating the dosages of glass fiber and positive and negative coefficient of thermal expansion fillers, a polyphenylene sulfide-based composite material with excellent mechanical properties and heat resistance is obtained, and its linear coefficient of thermal expansion can be flexibly regulated within the range of 7-15 ppm / °C.

[0005] To achieve the above object, the present invention provides a polyphenylene sulfide-based composite material with adjustable coefficient of thermal expansion, which comprises 40-65 parts by weight of polyphenylene sulfide resin, 10-45 parts by weight of glass fiber, 8-50 parts by weight of positive coefficient of thermal expansion ceramic filler, 22-50 parts by weight of negative coefficient of thermal expansion ceramic filler, and 0.1-2 parts by weight of surface modifier.

[0006] The present invention realizes the regulation of the coefficient of thermal expansion of the composite material through the synergistic effect of introducing zirconium tungstate ceramic filler with negative coefficient of thermal expansion and boron nitride ceramic filler with positive coefficient of thermal expansion. Through the synergistic regulation of positive and negative thermal expansion fillers, during the thermal cycle: the positive expansion behavior of boron nitride offsets the inherent expansion of the polyphenylene sulfide resin / glass fiber composite substrate, and the negative expansion of zirconium tungstate further reduces the overall coefficient of thermal expansion. The synergistic effect of the two makes the coefficient of thermal expansion of the composite material lower than that of a single filler system.

[0007] As a further improvement of the present invention, the polyphenylene sulfide-based composite material comprises 50-60 parts by weight of polyphenylene sulfide resin, 30-40 parts by weight of glass fiber, 8-20 parts by weight of positive coefficient of thermal expansion ceramic filler, 22-40 parts by weight of negative coefficient of thermal expansion ceramic filler, and 0.1-2 parts by weight of surface modifier, and the addition amount of the negative coefficient of thermal expansion ceramic filler is 2-3 times the mass of the positive coefficient of thermal expansion ceramic filler, preferably 2.5-2.8 times. Research of the present invention shows that within the limited dosage ratio range, by adding positive and negative coefficient of thermal expansion ceramic fillers, the composite material has higher mechanical strength and lower coefficient of thermal expansion compared with a single filler with the same addition amount.

[0008] As a further improvement of the present invention, the positive coefficient of thermal expansion ceramic filler is boron nitride, and the negative coefficient of thermal expansion ceramic filler is zirconium tungstate.

[0009] As a further improvement of the present invention, the particle size of the positive coefficient of thermal expansion ceramic filler is 0.8 μm - 1.2 μm, and the coefficient of thermal expansion is 6 ppm / °C - 10 ppm / °C; and / or, the particle size of the negative coefficient of thermal expansion ceramic filler is 1 μm - 3 μm, and the coefficient of thermal expansion is -7.7 ppm / °C - -7.9 ppm / °C.

[0010] As a further improvement of the present invention, the polyphenylene sulfide resin is an injection-molding grade linear polyphenylene sulfide with an average molecular weight of 20,000 to 60,000, and more preferably 40,000. The tensile strength of the polyphenylene sulfide is above 80 MPa, the flexural strength is above 140 MPa, and the melting temperature is 280 °C. Its mechanical properties are good and it can be used in a high-temperature environment for a long time.

[0011] As a further improvement of the present invention, the glass fiber is an alkali-free chopped glass fiber with a circular cross-section, a diameter of 5 to 15 μm, and a chopped length of 2 to 4 mm; the linear thermal expansion coefficient of the glass fiber is 3 to 5 ppm / °C, and the thermal expansion coefficient is more preferably 3.3 ppm / °C; the tensile strength is 2000 to 3000 MPa, and the elastic modulus is 60 to 80 GPa. The tensile strength is more preferably 2400 MPa, and the elastic modulus is 72 GPa. In the present invention, by adding glass fiber modified with a surface modifier to the polyphenylene sulfide resin, the degree of combination between the glass fiber and the polyphenylene sulfide resin matrix is further improved. Glass fiber has a higher specific strength and modulus. Through the shearing action of the screw, it can be evenly dispersed in the matrix to transfer the load and play a role in structural support and improving the mechanical properties of the composite material. The glass fiber in the present invention has a negative effect on the thermal expansion performance of the composite material. The linear expansion coefficient in the axial direction of the glass fiber is small. As the temperature rises, the amplitude of the vibration of the particles in the glass fiber increases, and the average distance between atoms changes, affecting the thermal expansion performance of the polyphenylene sulfide-based composite material. In addition, a large number of interfaces and internal stresses formed in the polyphenylene sulfide matrix material due to the addition of glass fiber will also have an obstructive effect on the thermal expansion of the polyphenylene sulfide-based composite material.

[0012] As a further improvement of the present invention, the surface modifier is a silane coupling agent, preferably KH550.

[0013] The present invention also provides a method for preparing a polyphenylene sulfide-based composite material with an adjustable thermal expansion coefficient as described in any one of the above, comprising the following steps:

[0014] S1. Weigh 40 to 65 parts by weight of polyphenylene sulfide resin, 10 to 45 parts by weight of glass fiber, 8 to 50 parts by weight of positive thermal expansion coefficient ceramic filler, 22 to 50 parts by weight of negative thermal expansion coefficient ceramic filler, and 0.1 to 2 parts by weight of surface modifier;

[0015] S2. First, use the surface modifier to perform surface treatment on the glass fiber, negative thermal expansion coefficient ceramic filler, and positive thermal expansion coefficient ceramic filler respectively, and then put them into a high-speed mixer together with the polyphenylene sulfide resin and stir at a speed of 500 rpm for 5 minutes to mix evenly;

[0016] S3. Add the mixed raw materials into a twin-screw extruder. After the mixture is melted and extruded, lead it out from the discharge port of the die head, cool it with water and then pelletize and dry it to obtain polyphenylene sulfide-based composite material particles with adjustable thermal expansion coefficient, and process and form them into polyphenylene sulfide-based composite materials.

[0017] Further, the polyphenylene sulfide-based composite material particles with adjustable thermal expansion coefficient can be injection molded using an injection molding machine after being dried by blowing at 120°C. The temperature distribution of each section of the injection molding machine is 310 - 320°C, and the mold temperature is 130 - 150°C. Preferably, the temperature distribution of each section of the injection molding machine is 320°C, and the mold temperature is 140°C.

[0018] As a further improvement of the present invention, the surface treatment in step S2 specifically includes:

[0019] (1) Weigh 1 - 2 wt% of silane coupling agent according to the amount of the material to be modified, dissolve it in absolute ethanol, and then add deionized water and ultrasonicate for 5 minutes to prepare a silane coupling agent solution; the mass ratio of the silane coupling agent to absolute ethanol is preferably 1:(8 - 12), preferably 1:10, and the mass ratio of deionized water to the silane coupling agent is 1:(3 - 5), preferably 1:4; the material to be modified is glass fiber, negative thermal expansion coefficient ceramic filler or positive thermal expansion coefficient ceramic filler;

[0020] (2) Take the material to be modified, dry it at 120°C for 2 hours, add it to absolute ethanol to make it completely impregnated, then drop it into the silane coupling agent solution, ultrasonicate for 30 minutes to mix evenly, use absolute ethanol to wash away the unreacted silane coupling agent on the surface of the material to be modified, and then dry it completely at 120°C for standby.

[0021] The present invention selects a silane coupling agent with a suitable proportion to perform surface modification on the additive material according to the characteristics of different inorganic additive materials. Preferably, the added mass of silane coupling agent KH550 for glass fiber is 1% of the mass of glass fiber. Preferably, the added mass of silane coupling agent KH550 for negative thermal expansion coefficient ceramic filler zirconium tungstate is 1.5% of the negative thermal expansion coefficient ceramic filler. Preferably, the added mass of silane coupling agent KH550 for positive thermal expansion coefficient ceramic filler boron nitride is 1.5% of the boron nitride ceramic filler.

[0022] As a further improvement of the present invention, the temperatures of the five zones of the twin-screw extruder starting from the feeding port are 285 - 295°C, 295 - 305°C, 295 - 305°C, 295 - 305°C, 295 - 305°C respectively, the temperature of the discharge port is 305 - 315°C, and the extrusion pressure at the discharge port is 18 - 22 MPa.

[0023] Preferably, the temperatures of the five zones of the twin-screw extruder starting from the feeding port are 290 °C, 300 °C, 300 °C, 300 °C, 300 °C respectively, the temperature of the discharging port is 310 °C, and the extrusion pressure at the discharging port is 20 MPa.

[0024] The present invention provides a specific application of the polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient can replace the metal components of antennas, power dividers, combiners, and filters in 5G communication devices, preferably the key metal components of cavity filters in 5G communication base stations, to achieve temperature compensation of the filters.

[0025] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0026] 1. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient provided by the present invention is prepared by adding glass fibers and mixed ceramic fillers with positive and negative thermal expansion coefficients with optimized proportions into a polyphenylene sulfide resin matrix. The inorganic fillers are surface-modified, and the interaction between the components is closer. Under the synergistic regulation of the mixed ceramic fillers with positive and negative thermal expansion coefficients, it can ensure excellent mechanical properties, and the linear thermal expansion coefficient is lower than that of a single filler system, and can be flexibly regulated in the range of 7-15 ppm / °C, and can be used to achieve temperature compensation of cavity filters for 5G base stations. Compared with the existing polyphenylene sulfide engineering plastics, the polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient provided by the present invention not only has improved mechanical properties, but also its linear thermal expansion coefficient can be reduced to 7 ppm / °C by adjusting the compounding ratio of the mixed ceramic fillers with positive and negative thermal expansion coefficients, and it can still maintain basic performance at a high temperature of 250 °C, greatly broadening the application scenarios of the polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient.

[0027] 2. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient provided by the present invention has good injection molding processing performance, lower cost with mixed fillers, and higher economic benefits. It can not only greatly reduce the weight of the cavity filter, but also achieve high temperature stability of the resonance characteristics of the cavity filter, thus helping to realize large-scale replacement of the key metal components (such as tuning screws, resonance rods, metal cavities, etc.) of cavity filters for 5G communication base stations to promote the development of 5G construction.

[0028] 3. By controlling the dosage ratio of the ceramic fillers with positive and negative thermal expansion coefficients, the present invention can make the synergistic effect of the two more significant, and obtain a composite material with a lower thermal expansion coefficient and better mechanical properties.

[0029] 4. In the present invention, glass fibers modified with a surface modifier are added to the polyphenylene sulfide resin, further improving the bonding degree between the glass fibers and the polyphenylene sulfide resin matrix. Glass fibers have higher specific strength and modulus. Through the shearing action of the screw, they can be evenly dispersed in the matrix to transfer loads and play a role in structural support and improving the mechanical properties of the composite material. At the same time, glass fibers have a negative effect on the thermal expansion performance of the composite material. The linear expansion coefficient of the glass fiber in the axial direction is small. As the temperature rises, the amplitude of the vibration of the particles in the glass fiber increases, and the average distance between atoms changes, affecting the thermal expansion performance of the polyphenylene sulfide-based composite material. Furthermore, it can cooperate with ceramic fillers with positive and negative thermal expansion coefficients to regulate its comprehensive performance. Detailed Embodiments

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] In the specific embodiments provided by the present invention, the experimental technical means used are all conventional experimental methods unless otherwise specified. The raw materials and reagents used can be purchased through commercial channels unless otherwise specified. The cross-section of the glass fiber used in each embodiment is circular, with a diameter of 10 μm and a chopped length of 3 mm. The polyphenylene sulfide resin is an injection-grade linear polyphenylene sulfide with an average molecular weight of 40,000 and a melting temperature of 280 °C. The particle size of zirconium tungstate is 1 μm to 3 μm, and the particle size of boron nitride is 0.8 μm to 1.2 μm.

[0032] Example 1

[0033] This example provides a polyphenylene sulfide-based composite material with an adjustable thermal expansion coefficient, and its raw material ratio is as follows by weight:

[0034] 60 parts of polyphenylene sulfide resin

[0035] 40 parts of glass fiber

[0036] 22 parts of zirconium tungstate

[0037] 8 parts of boron nitride

[0038] 0.85 part of silane coupling agent KH550

[0039] Example 2

[0040] This example provides a polyphenylene sulfide-based composite material with an adjustable thermal expansion coefficient, and its raw material ratio is as follows by weight:

[0041] 60 parts of polyphenylene sulfide resin

[0042] 40 parts of glass fiber

[0043] 29 parts of zirconium tungstate

[0044] 11 parts of boron nitride

[0045] 1 part of silane coupling agent KH550

[0046] Example 3

[0047] This example provides a polyphenylene sulfide-based composite material with an adjustable coefficient of thermal expansion. The raw material ratio is as follows by weight parts:

[0048] 60 parts of polyphenylene sulfide resin

[0049] 40 parts of glass fiber

[0050] 36 parts of zirconium tungstate

[0051] 14 parts of boron nitride

[0052] 1.15 parts of silane coupling agent KH550

[0053] Comparative Example 1

[0054] This comparative example provides a polyphenylene sulfide-based composite material. The raw material ratio is as follows by weight parts:

[0055] 60 parts of polyphenylene sulfide resin

[0056] 40 parts of glass fiber

[0057] 30 parts of boron nitride

[0058] 0.85 part of silane coupling agent KH550

[0059] Comparative Example 2

[0060] This comparative example provides a polyphenylene sulfide-based composite material. The raw material ratio is as follows by weight parts:

[0061] 60 parts of polyphenylene sulfide resin

[0062] 40 parts of glass fiber

[0063] 40 parts of boron nitride

[0064] 1 part of silane coupling agent KH550

[0065] Comparative Example 3

[0066] This comparative example provides a polyphenylene sulfide-based composite material. The raw material ratio is as follows by weight parts:

[0067] 60 parts of polyphenylene sulfide resin

[0068] 40 parts of glass fiber

[0069] 50 parts of boron nitride

[0070] 1.15 parts of silane coupling agent KH550

[0071] Comparative Example 4

[0072] This example provides a polyphenylene sulfide-based composite material with an adjustable coefficient of thermal expansion, and its raw material ratio is as follows by weight parts:

[0073] 60 parts of polyphenylene sulfide resin

[0074] 40 parts of glass fiber

[0075] 30 parts of zirconium tungstate

[0076] 0.85 parts of silane coupling agent KH550

[0077] Comparative Example 5

[0078] This example provides a polyphenylene sulfide-based composite material with an adjustable coefficient of thermal expansion, and its raw material ratio is as follows by weight parts:

[0079] 60 parts of polyphenylene sulfide resin

[0080] 40 parts of glass fiber

[0081] 40 parts of zirconium tungstate

[0082] 1 part of silane coupling agent KH550

[0083] Comparative Example 6

[0084] This example provides a polyphenylene sulfide-based composite material with an adjustable coefficient of thermal expansion, and its raw material ratio is as follows by weight parts:

[0085] 60 parts of polyphenylene sulfide resin

[0086] 40 parts of glass fiber

[0087] 50 parts of zirconium tungstate

[0088] 1.15 parts of silane coupling agent KH550

[0089] Comparative Example 7

[0090] This example provides a polyphenylene sulfide-based composite material with an adjustable coefficient of thermal expansion, and its raw material ratio is as follows by weight parts:

[0091] 60 parts of polyphenylene sulfide resin

[0092] 40 parts of glass fiber

[0093] 0.4 part of silane coupling agent KH550

[0094] The specific preparation steps of the polyphenylene sulfide-based composite materials provided in the above examples and comparative examples are as follows:

[0095] (1) Weigh polyphenylene sulfide resin, glass fiber, negative thermal expansion coefficient ceramic filler, positive thermal expansion coefficient ceramic filler, and surface modifier according to the above weight ratio.

[0096] (2) Inorganic fillers such as glass fiber, negative thermal expansion coefficient ceramic filler, and positive thermal expansion coefficient ceramic filler need to be surface-treated with a surface modifier. Then, the inorganic fillers such as glass fiber, negative thermal expansion coefficient ceramic filler, and positive thermal expansion coefficient ceramic filler are mixed evenly with the polyphenylene sulfide resin, and the mixture is added into the feeding port of a twin-screw extruder. After the mixture is melted and extruded, it is led out from the outlet of the die head, cooled by water, and pelletized to obtain the polyphenylene sulfide-based composite material particles with adjustable thermal expansion coefficient. Among them, the melting and extrusion temperature distribution of each screw section of the twin-screw extruder is 290 - 310 °C, the temperatures of the five zones starting from the feeding port are 290 °C, 300 °C, 300 °C, 300 °C, 300 °C respectively, the temperature of the outlet is 310 °C, and the extrusion pressure at the outlet is 20 MPa.

[0097] The surface treatment includes: preparing a coupling agent solution. Weigh 1 wt% of the silane coupling agent according to the amount of glass fiber used and dissolve it in anhydrous ethanol. The mass ratio of the silane coupling agent to anhydrous ethanol is 1:10. Then, deionized water with a mass ratio of 1:4 to the silane coupling agent is added, and after ultrasonic treatment for 5 minutes, a coupling agent solution is prepared.

[0098] Surface modification of inorganic fillers. Take the glass fiber, dry it at 120 °C for 2 hours, then add it to anhydrous ethanol to make it completely impregnated, and then dropwise add the coupling agent solution and ultrasonic for 30 minutes. After mixing evenly, use anhydrous ethanol to wash away the unreacted silane coupling agent on the surface of the inorganic filler, and place the modified inorganic filler at 120 °C to dry completely for standby.

[0099] The modification methods of boron nitride and zirconium tungstate are the same as those of glass fiber, and the amount of silane coupling agent used is 1.5 wt% of their mass.

[0100] (3) The obtained polyphenylene sulfide-based composite material particles with adjustable thermal expansion coefficient are dried in a blast dryer at 120 °C and then can be injection-molded using an injection molding machine. The temperature distribution of each section of the injection molding machine is 310 - 320 °C, and the mold temperature is 130 - 150 °C. Preferably, the temperature distribution of each section of the injection molding machine is 320 °C, and the mold temperature is 140 °C.

[0101] Performance test:

[0102] The following performance tests were carried out on the polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient obtained by injection molding according to the above embodiments:

[0103] The tensile strength and elongation at break were tested according to the method for determining the tensile properties of plastics in ISO 527-1-2012, and the tensile rate was 5 mm / min.

[0104] The flexural strength and modulus were tested according to the methods for determining the flexural properties of plastics in ASTM D790&ISO178.

[0105] The coefficient of thermal expansion was tested for the heat distortion temperature of the sample according to the thermomechanical analysis method of plastics in ISO 11359-2-1999, and the measurement temperature range was from room temperature to 250 °C.

[0106] The results of the performance tests are shown in the following table.

[0107] Index Tensile strength Elongation at break Flexural strength Flexural modulus Coefficient of thermal expansion Unit MPa ％ MPa MPa ppm / ℃ Example 1 136 1.52 230 11183 15 Example 2 128 1.47 219 12968 12 Example 3 119 1.34 212 14625 7 Comparative example 1 142 1.70 229 11354 20 Comparative example 2 139 1.64 223 14189 18 Comparative example 3 123 1.52 208 16096 16 Comparative example 4 129 1.25 231 10893 17 Comparative example 5 126 1.31 224 11169 14 Comparative example 6 115 1.22 214 12892 8 Comparative example 7 145 2.33 245 8824 27

[0108] In Examples 1 to 3, the polyphenylene sulfide / glass fiber composite substrate was synergistically modified with mixed ceramic fillers of modified zirconium tungstate and modified boron nitride with different compounding ratios. In Comparative Examples 1 to 3, the polyphenylene sulfide / glass fiber composite substrate was modified with different contents of modified boron nitride fillers. In Comparative Examples 4 to 6, the polyphenylene sulfide / glass fiber composite substrate was modified with different contents of modified zirconium tungstate fillers.

[0109] By comprehensively analyzing the performance test data in Table 1, it can be seen that the linear thermal expansion coefficient of the polyphenylene sulfide / glass fiber composite substrate modified with modified boron nitride filler is between 16 and 20 ppm / °C. The thermal expansion coefficient of modified boron nitride is 8.9 ppm / °C, which shows a negative effect on the thermal expansion performance of the composite material, but the thermal expansion coefficient is still relatively high and cannot meet the requirements for replacing metal components in 5G communication equipment. In Example 3, the linear thermal expansion coefficient of the polyphenylene sulfide / glass fiber composite substrate modified with a mixture of modified zirconium tungstate and modified boron nitride ceramic fillers can be reduced to a minimum of 7 ppm / °C. Compared with the unmodified polyphenylene sulfide / glass fiber composite substrate in Comparative Example 7, the thermal expansion coefficient is relatively decreased by 74.1%. When the total amount of ceramic fillers added is the same, the thermal expansion coefficient of the composite material modified with a mixture of zirconium tungstate and boron nitride ceramic fillers in Example 3 is 7 ppm / °C, which is lower than that of the composite materials using a single zirconium tungstate or boron nitride filler (Comparative Examples 3 and 6). This shows that although the thermal expansion coefficient of boron nitride is higher than that of zirconium tungstate, when a part of zirconium tungstate is replaced by boron nitride in a certain proportion, in the system of the present invention, the composite material has a lower thermal expansion coefficient and better mechanical properties. The thermal expansion coefficient of the composite material modified with a mixture of zirconium tungstate and boron nitride ceramic fillers in Example 2 is 12 ppm / °C, which is decreased by 14.3% and 33.3% respectively compared with the thermal expansion coefficients of the composite materials using a single zirconium tungstate filler and a single boron nitride filler (Comparative Examples 5 and 2).

[0110] The present invention realizes the precise optimization of the thermal expansion coefficient of polyphenylene sulfide-based composite materials by simultaneously adding a certain proportion of mixed ceramic fillers with positive and negative thermal expansion coefficients. The synergistic regulation effect of the mixed ceramic fillers makes the thermal expansion coefficient of the polyphenylene sulfide-based composite materials significantly lower than that of the single filler system. Since the cost of boron nitride is lower than that of zirconium tungstate, using mixed fillers for modification has higher economic benefits. Compared with other commercial polyphenylene sulfide engineering plastics, the preparation cost of the polyphenylene sulfide-based composite materials with adjustable thermal expansion coefficient provided by the present invention is relatively low, and it has reached the level of commercial polyphenylene sulfide in terms of various mechanical properties, and can replace metal components in 5G communication applications. Moreover, compared with other commercial polyphenylene sulfide engineering plastics, the linear thermal expansion coefficient of the polyphenylene sulfide-based composite materials with adjustable thermal expansion coefficient provided by the present invention can be flexibly regulated in the range of 7 to 15 ppm / °C, and still can stably maintain a relatively low linear thermal expansion coefficient in a high-temperature (250 °C) environment, with a small size deformation at high temperature, which is suitable for the normal working requirements of cavity filters in 5G base stations in a high-temperature environment.

[0111] The above test results show that the present invention comprehensively uses modification means to improve the mechanical properties, linear thermal expansion coefficient, etc. of the polyphenylene sulfide-based composite material, so that the obtained polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient can replace various metal components in the 5G communication field, especially in cavity filters, so as to meet the requirements of lightweight and cost reduction of 5G communication equipment and promote the development of 5G construction.

[0112] It should be noted that the functions of the above various additive materials in the polyphenylene sulfide-based composite material of the present invention are not only to improve the performance in a certain aspect, nor is the improvement of a certain aspect the function of a single additive material. For example, the reduction of the thermal expansion coefficient of the composite material is the result of the combined action of zirconium tungstate ceramic filler, boron nitride ceramic filler and glass fiber.

[0113] It is easy for those skilled in the art to understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient, characterized in that: The invention comprises, by weight, 40 to 65 parts of polyphenylene sulfide resin, 10 to 45 parts of glass fiber, 8 to 50 parts of ceramic filler with positive thermal expansion coefficient, 22 to 50 parts of ceramic filler with negative thermal expansion coefficient, and 0.1 to 2 parts of surface modifier.

2. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to claim 1, characterized in that: The invention comprises 50-60 parts of polyphenylene sulfide resin, 30-40 parts of glass fiber, 8-20 parts of ceramic filler with positive thermal expansion coefficient, 22-40 parts of ceramic filler with negative thermal expansion coefficient, and 0.1-2 parts of surface modifier by weight, and the added amount of the ceramic filler with negative thermal expansion coefficient is 2-3 times the mass of the ceramic filler with positive thermal expansion coefficient.

3. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to claim 1 or 2, characterized in that: The positive thermal expansion coefficient ceramic filler is boron nitride, and the negative thermal expansion coefficient ceramic filler is zirconium tungstate.

4. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to claim 1 or 2, characterized in that: The particle size of the positive thermal expansion coefficient ceramic filler is 0.8um to 1.2um, and the thermal expansion coefficient is 6ppm / ℃ to 10ppm / ℃; And / or, the particle size of the negative thermal expansion coefficient ceramic filler is 1 um to 3 um, and the thermal expansion coefficient is -7.7 ppm / °C to -7.9 ppm / °C.

5. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to claim 1 or 2, characterized in that: The polyphenylene sulfide resin is an injection-molding grade linear polyphenylene sulfide with an average molecular weight of 20,000 to 60,000.

6. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to claim 1 or 2, characterized in that: The glass fiber is an alkali-free chopped glass fiber with a circular cross-section, a diameter of 5 to 15 μm, and a chopped length of 2 to 4 mm; And / or, the linear thermal expansion coefficient of the glass fiber is 3-5 ppm / °C, and the tensile strength is 2000-3000 MPa.

7. The polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to claim 1 or 2, characterized in that: The surface modifier is a silane coupling agent, preferably KH550.

8. A method for preparing a polyphenylene sulfide-based composite material with adjustable thermal expansion coefficient according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Weigh 40-65 parts of polyphenylene sulfide resin, 10-45 parts of glass fiber, 8-50 parts of ceramic filler with positive thermal expansion coefficient, 22-50 parts of ceramic filler with negative thermal expansion coefficient, and 0.1-2 parts of surface modifier by weight; S2, firstly use a surface modifier to perform surface treatment on the glass fiber, the ceramic filler with a negative thermal expansion coefficient, and the ceramic filler with a positive thermal expansion coefficient, and then put them into a high-speed mixer and mix them evenly with the polyphenylene sulfide resin; S3, adding the mixed raw materials into a twin-screw extruder, and after the mixed materials are melted and extruded, they are water-cooled and then pelletized and dried to obtain polyphenylene sulfide-based composite material particles with adjustable thermal expansion coefficient, and processed and molded to obtain polyphenylene sulfide-based composite materials.

9. The preparation method according to claim 8, characterized in that: The surface treatment in step S2 specifically includes: (1) weighing a silane coupling agent according to 1-2 wt% of the amount of the material to be modified and dissolving it in anhydrous ethanol, and then adding deionized water to prepare a silane coupling agent solution; the mass ratio of the silane coupling agent to the anhydrous ethanol is preferably 1:(8-12), and the mass ratio of the deionized water to the silane coupling agent is 1:(3-5); the material to be modified is glass fiber, a ceramic filler with a negative thermal expansion coefficient, or a ceramic filler with a positive thermal expansion coefficient; (2) After drying the material to be modified, add it to anhydrous ethanol to completely immerse it, then drop it into the silane coupling agent solution and mix it evenly with ultrasound, then use anhydrous ethanol to wash away the unreacted silane coupling agent on the surface of the material to be modified, and then dry it for later use.

10. The preparation method according to claim 8, characterized in that: The five zone temperatures of the twin-screw extruder starting from the feed port are 285-295°C, 295-305°C, 295-305°C, 295-305°C, 295-305°C, respectively; the discharge port temperature is 305-315°C; and the discharge port extrusion pressure is 18-22MPa.