A method for making a low-porosity continuous fiber-reinforced thermoplastic resin article

Abstract

The application discloses a preparation method of a low-porosity continuous fiber reinforced thermoplastic resin product. First, a continuous fiber reinforced thermoplastic resin preform is prepared, and the preform is sealed and vacuumized. Then, the preform after being sealed and vacuumized is placed in a container full of inert gas and having a heating function, and the pressure in the container is kept at least 0.5 MPa. After a stepwise temperature rising and falling, a product with a porosity of less than 1.5% is prepared. The application uses inert gas to press the continuous fiber reinforced thermoplastic resin product, which can ensure that the product is uniformly pressed in all directions, and can also protect the thermoplastic resin from pyrolysis at high temperature.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and particularly relates to a method for preparing low-porosity continuous fiber reinforced thermoplastic resin products. Background Technology

[0002] Continuous fiber reinforced thermoplastic resin materials have become a research hotspot both domestically and internationally in recent years due to their environmentally friendly and recyclable advantages. Continuous fiber reinforced thermoplastic resin composites require the thermoplastic resin to be above its melting point to be manufactured into various products. However, during the manufacturing process, the high melt viscosity of the thermoplastic resin in its molten state makes it difficult to achieve good wetting between the molten resin and the fibers. Furthermore, gases trapped inside the material cannot escape due to the excessive viscosity of the thermoplastic resin melt, thus forming pores within the continuous fiber reinforced thermoplastic resin products. The presence of pores leads to a decrease in product performance, consequently affecting service life and safety.

[0003] Chinese patent CN104441695A discloses a method for preparing low-porosity PPS / CFF thermoplastic composite materials. This invention employs a melt molding process and can produce products with a porosity of less than 2%. However, this invention still uses a traditional molding process, in which thermoplastic resins are prone to pyrolysis in air. Furthermore, this method cannot achieve the low-porosity target for products with a thickness exceeding 50 mm. Summary of the Invention

[0004] To overcome the problems in the prior art, the present invention provides a method for preparing a low-porosity continuous fiber reinforced thermoplastic resin product. During the preparation process, the gas inside the product is discharged, reducing the porosity of the product. Furthermore, the thermoplastic resin does not undergo high-temperature decomposition during the high-temperature process, thus preventing a decrease in resin performance.

[0005] To solve the above-mentioned technical problems, the present invention proposes the following technical solution:

[0006] This invention provides a method for preparing a low-porosity continuous fiber reinforced thermoplastic resin product, comprising the following steps:

[0007] S1. Prepare a preform from continuous fiber-reinforced thermoplastic resin;

[0008] S2. Place the preform prepared in step S1 into the casing, and then seal the casing after evacuating it.

[0009] S3. Place the sealed package in a device with a pressurization and heating function, fill the device with inert gas, set the pressure and stepped temperature, and obtain a low-porosity continuous fiber reinforced thermoplastic resin product after treatment.

[0010] This invention first prepares a preform from continuous fiber-reinforced thermoplastic resin, then places the preform in a vacuum-sealed enclosure. Inert gas is then introduced into the equipment, and after setting the pressure and temperature, the inert gas is used to apply pressure to the continuous fiber-reinforced thermoplastic resin product. This not only ensures uniform pressure in all directions but also protects the thermoplastic resin from pyrolysis at high temperatures. The enclosure provides shape to the product, while the vacuum helps expel internal gas, reducing porosity. Due to the low thermal conductivity of gas, setting a stepped temperature helps the product heat evenly under gas conditions, preventing uneven temperature distribution throughout the product.

[0011] As an optional implementation, in the preparation method provided by the present invention, in step S3, the stepped temperature is to heat to above the melting point of the thermoplastic resin for the first heat preservation, and then cool down to above the glass transition temperature of the thermoplastic resin for the second heat preservation.

[0012] In this invention, a first heat treatment is performed at a temperature above the melting point to allow the thermoplastic resin to impregnate the fiber bundles. A second heat treatment is then performed when the temperature is lowered to below the melting point but above the glass transition temperature. This serves two purposes: first, to control the crystallinity of the crystalline thermoplastic resin; and second, to ensure that the resin exhibits a rubbery state within this temperature range, and to eliminate internal pores by increasing pressure.

[0013] As an optional implementation, in the preparation method provided by the present invention, the first heat preservation time is 15-30 min, and the second heat preservation time is 60-120 min.

[0014] As an optional implementation, in the preparation method provided by the present invention, the temperature range of the second heat preservation is Tg~(Tm+10~20), where Tg represents the glass transition temperature of the thermoplastic resin and Tm represents the melting temperature of the thermoplastic resin.

[0015] In this invention, the resin only becomes fluid above its glass transition temperature during the second heat treatment; below the glass transition temperature, the resin remains in a glassy state and lacks fluidity. Setting the maximum temperature 10-20°C above the melting point helps reduce energy consumption and protects the resin from high-temperature decomposition.

[0016] As an optional implementation, in the preparation method provided by the present invention, the heating rate is 5-10℃ / min and the cooling rate is 5-10℃ / min.

[0017] In this invention, the cooling rate can be clearly defined for crystalline thermoplastic resins, which is beneficial for controlling the crystallinity of the resin.

[0018] As an optional implementation, in the preparation method provided by the present invention, in step S3, the pressure is set to be no less than 0.5 MPa. Setting the pressure to be greater than 0.5 MPa allows for good impregnation of the thermoplastic resin fibers.

[0019] Preferably, the pressure is set to 5-300 MPa.

[0020] As an optional implementation, in the preparation method provided by the present invention, in step S3, the pressure is increased to 9-20 MPa after heating and increased to 20-90 MPa after cooling.

[0021] As an optional implementation, in the preparation method provided by the present invention, the sleeve is a rigid sleeve or a flexible sleeve, wherein the rigid sleeve is one of a stainless steel sleeve, an aluminum alloy sleeve or a copper sleeve, and the flexible sleeve is a rubber sleeve or a polyimide film sleeve.

[0022] As an optional implementation, in the preparation method provided by this invention, the vacuum degree inside the casing is not less than 0.01 MPa. Setting the vacuum degree inside the casing to be greater than 0.01 MPa can effectively remove gas from the preform. Below this vacuum degree, gas cannot be effectively removed.

[0023] Preferably, the vacuum degree inside the casing is 0.06-0.1 MPa.

[0024] As an optional implementation, in the preparation method provided by the present invention, the thermoplastic resin is one of polyether ether ketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), and liquid crystal polymer (LCP).

[0025] As an optional implementation, in the preparation method provided by the present invention, the thickness of the preform is 5 mm or more.

[0026] As an optional implementation, in the preparation method provided by the present invention, in step S3, the device with the function of pressurizing and heating is a hot isostatic pressing device. After the processing is completed, when the temperature of the isostatic pressing device drops to below 80°C, the pressure is released and the product is taken out.

[0027] As an optional implementation, in the preparation method provided by the present invention, in step S1, a preform is prepared by molding or welding.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] In this invention, thermoplastic resin material is melt-impregnated onto fibers under an inert gas atmosphere. This prevents the thermoplastic resin from decomposing at high temperatures, thus avoiding a decrease in resin performance. Simultaneously, the inert gas transmits pressure, ensuring consistent pressure across the product in all directions. For thicknesses exceeding 50 mm, the porosity can be controlled below 1.5%. Detailed Implementation

[0030] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with the specification and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1

[0034] PEEK carbon fiber unidirectional prepreg tape is cut to the required size and laminated according to the layup design requirements, with 100 layers. Each layer of prepreg tape is bonded together using a welding process. The laminated prepreg tape is placed inside a polyimide film sheath, and a vacuum pump is used to evacuate the sheath to 0.06 MPa, then the vacuum nozzle is sealed.

[0035] The workpiece to be encapsulated is placed in the high-pressure furnace of a hot isostatic press and filled with inert gas. The initial pressure of the hot isostatic press is set to 2 MPa, the heating rate is 5℃ / min, the temperature is increased to 340℃, the pressure is increased to 10 MPa, and the temperature is held for 15 min. Then the temperature is reduced to 250℃, the pressure is increased to 20 MPa, and the temperature is held for 120 min. The temperature is reduced to 80℃, the gas is recovered, the pressure is released, and the encapsulation is removed. The encapsulation is removed to obtain a 30 mm thick PEEK product with low porosity.

[0036] Example 2

[0037] The PEEK film and carbon fiber woven fabric were cut to the required size and alternately stacked for a total of 401 layers, so that the upper and lower surfaces were PEEK films. Each layer was bonded together using a welding process. The stacked preform was placed in an aluminum sheath, and the sheath was evacuated to 0.09 MPa using a vacuum pump. The vacuum nozzle was then sealed.

[0038] The workpiece to be encapsulated is placed in the high-pressure furnace of a hot isostatic press and filled with inert gas. The initial pressure of the hot isostatic press is set to 1 MPa, the heating rate is 5℃ / min, the temperature is increased to 350℃, the pressure is increased to 9 MPa, and the temperature is held for 20 min. Then the temperature is reduced to 250℃, the pressure is increased to 20 MPa, and the temperature is held for 120 min. The temperature is then reduced to 80℃, the gas is recovered, the pressure is released, and the encapsulation is removed. The encapsulation is removed to obtain a 60 mm thick PEEK product with low porosity.

[0039] Example 3

[0040] The PI film and carbon fiber fabric are cut to the required size and alternately stacked for a total of 41 layers, so that the upper and lower surfaces are PI films. Each layer is bonded and fixed using a welding process. The stacked preform is placed in a copper sheath, and a vacuum pump is used to evacuate the sheath to 0.08 MPa, and the vacuum nozzle is sealed.

[0041] The workpiece to be encapsulated is placed in the high-pressure furnace of a hot isostatic press and filled with inert gas. The initial pressure of the hot isostatic press is set to 5 MPa, the heating rate is 10℃ / min, the temperature is increased to 360℃, the pressure is increased to 20 MPa, and the temperature is held for 30 min. Then the temperature is reduced to 320℃, the pressure is increased to 80 MPa, and the temperature is held for 60 min. The temperature is reduced to 80℃, the gas is recovered, the pressure is released, and the encapsulation is removed. The encapsulation is removed to obtain a low-porosity PI product.

[0042] Comparative Example 1

[0043] PEEK film and carbon fiber woven fabric are cut to the required size and alternately stacked for a total of 401 layers, with the upper and lower surfaces being PEEK film. The cut pieces are placed in a metal mold, which is then placed on the heating table of a molding machine. The temperature is raised to 340℃ and held at 0.5MPa for 30 minutes, then the pressure is increased to 8MPa and held at 8MPa for 10 minutes. The temperature is then lowered to 80℃, and the product is demolded to obtain the finished product.

[0044] Performance testing: The tensile properties, flexural properties and porosity of Examples 1-3 and Comparative Example 1 were tested according to the following standards.

[0045] ISO 14125 Determination of flexural properties of fiber-reinforced plastic composites.

[0046] ISO 527-5 Test conditions for unidirectional fiber reinforced plastic composites.

[0047] JC / T Test Method for Void Content of Fiber Reinforced Plastics

[0048] The test results are shown in Table 1 below:

[0049] Table 1: Performance Test Results

[0050]

[0051]

[0052] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-porosity continuous fiber reinforced thermoplastic resin product, characterized in that, Includes the following steps: S1. Prepare a preform from continuous fiber-reinforced thermoplastic resin; S2. Place the preform prepared in step S1 into the casing, and then seal the casing after evacuating it. S3. Place the sealed package in a device with a pressurization and heating function, fill the device with inert gas, set the pressure and stepped temperature, and obtain a low-porosity continuous fiber reinforced thermoplastic resin product after treatment. The stepped temperature is achieved by first holding the temperature above the melting point of the thermoplastic resin at a pressure of 9-20 MPa for 15-30 min, then cooling the temperature below the melting point of the thermoplastic resin but above the glass transition temperature for a second holding at a pressure of 20-90 MPa for 60-120 min.

2. The method for preparing low-porosity continuous fiber reinforced thermoplastic resin products according to claim 1, characterized in that, The heating rate is 5-10℃ / min, and the cooling rate is 5-10℃ / min.

3. The method for preparing low-porosity continuous fiber reinforced thermoplastic resin products according to claim 1, characterized in that, The sheath can be a rigid sheath or a flexible sheath. The rigid sheath can be a stainless steel sheath, an aluminum alloy sheath, or a copper sheath. The flexible sheath can be a rubber sheath or a polyimide film sheath. The vacuum degree inside the sheath is not less than 0.01 MPa.

4. The method for preparing low-porosity continuous fiber reinforced thermoplastic resin products according to claim 1, characterized in that, The thermoplastic resin is one of polyetheretherketone, polyimide, polyetherimide, polyphenylene sulfide, and liquid crystal polymer.

5. The method for preparing low-porosity continuous fiber reinforced thermoplastic resin products according to claim 1, characterized in that, In step S3, the equipment with the function of pressurizing and heating is a hot isostatic pressing equipment. After the process is completed, when the temperature of the hot isostatic pressing equipment drops below 80°C, the pressure is released and the product is taken out.

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