RU2795194C1 - Method for producing thermoplastic prepregs by applying thermoplastic polymeric binder to reinforcing fibrous materials using directional aerosol spraying - Google Patents

Abstract

FIELD: obtaining modern composite materials.

SUBSTANCE: methods for obtaining modern composite materials for the aerospace, chemical, oil industry, rocket and space technology, energy. Method for producing a thermoplastic prepreg includes applying a thermoplastic polymer binder to a reinforcing fibrous material by method of directional aerosol spraying, preliminary removal of moisture and lubricant, applying a sizing agent to the surface of reinforcing fibrous material, regulating the tension of the fibrous material, depositing the thermoplastic polymer binder in form of a powder on the reinforcing fibrous material using one or more nozzles for directional aerosol spraying, calendering of the reinforcing fibrous material impregnated with the thermoplastic polymer binder at a temperature from the glass transition temperature to the melting point of the polymer, while reinforcing fibrous material is a unidirectional or bidirectional fibrous material made of carbon, or basalt, or aramid fibres, electrically conductive or dielectric, without carrying out metallization operations or applying a conductive powder, and the thermoplastic polymer binder is polyether ether ketone, or polyphenyl sulphide, or polyamide.

EFFECT: obtaining prepregs with high physical and mechanical properties relative to the background with a uniform distribution of fibres in the plane of the tape, as well as in increasing the adhesive strength between the fibre and the polymer.

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Description

The invention relates to methods for obtaining modern composite materials for the aerospace, chemical, oil industry, rocket and space technology, energy.

The proposed solution relates to technological high-performance methods for producing thermoplastic prepregs based on thermoplastic polymer binders by directional aerosol spraying, including the use of tribostatic spraying. The thermoplastic polymer binder is polyphenylene sulfide, polyamide, polyether ether ketone, or other high-tech polymers in the form of powders with a preferred average particle size of 3 to 100 microns. Reinforcing fibrous materials are unidirectional tapes or bidirectional fabrics based on carbon, basalt or high-tech organic fibers.

The thermoplastic prepregs obtained by the method are intended for use in load-bearing structures, including engine elements, chemically resistant cylinders, pipeline elements or other structures that combine high strength properties, an allowable maximum operating temperature of up to 230-250 ° C and low weight (material density less than 1, 8 g/ ^cm3 ).

To obtain products from polymer composite materials with high physical and mechanical properties, resistance to aging and external influencing factors, prepregs based on a reinforcing filler and a polymeric thermosetting matrix are used as raw materials in modern industries. This type of prepregs is characterized by limited shelf life (no more than 6-12 months at a temperature of minus 18°C), fragility of the polymer matrix, limited possibilities for connecting product elements, irreversible changes in the structure and properties of the polymer matrix, and the impossibility of recycling products.

The advantages of thermoplastic prepregs obtained by the method in comparison with thermosetting prepregs widely used in engineering are the possibility of reversible melting of thermoplastic polymeric material (binder), welding of parts due to matrix melting, extended shelf life up to 15 years or more at a temperature of 20°C and above, partial reversibility of changes in material properties under the influence of external factors, the possibility of using thermoplastic polymer binders with a wide range of operating temperatures (from minus 120°C to plus 230°C).

From the prior art there are several ways to obtain thermoplastic prepregs using thermoplastic polymer binders:

1) Application in a fluidized bed;

2) Application of polymer melt using extruder technology;

3) Application from a suspension of a binder in a solvent.

In the method for manufacturing structural thermoplastic carbon fiber (1) (RU 2556109), layers of carbon filler are placed in a heating cabinet and dried until moisture is completely removed. Under the pressure of compressed air, the polyphenylene sulfide binder is brought into a fluidized state and applied to the filler, followed by impregnation. The binder is preferably applied by electrostatic spraying. This ensures its uniform distribution on the filler, and, in addition, by setting a certain potential difference between the binder powder and the filler, it is possible to control the thickness of the applied binder layer. The impregnation of the filler should be carried out with a preliminarily fluidized binder, since this avoids the use of solvents for polyphenylene sulfide, which are harmful and at the same time adversely affect the quality of the resulting carbon fiber. The preliminary fluidization of the binder also ensures further uniform impregnation of the filler. From the layers of the obtained prepreg, a package is made up. The specified package is placed between the press plates, which, in order to prevent thermal-oxidative degradation of the binder, which can occur during further heating, must be preheated to a temperature of 10-30°C higher than the melting point of the binder.

The method according to the invention (2) (NZ Patent No. 204971) consists in impregnating the tapes with a molten thermoplastic binder with an organic solvent benzophenone. The use of a solvent makes it possible to reduce the viscosity of the binder, bringing it closer to the values of thermoplastics. The main operation is pulling the reinforcing filler through a container with a binder solution.

The disadvantages of this method include the difficulty of choosing the correct solvent for the binder: it must be thermally stable up to the melting point of the polymer binder, and the volatilization temperature of the solvent must be lower than the thermal degradation temperature of the resulting composition of materials. Solvent removal is an energy-consuming process, and the solvents used and implied by the method, for example, benzophenone, are highly toxic carcinogens. In addition, the complete removal of a high-boiling solvent before the onset of thermal degradation of the polymer is extremely difficult, and the residual solvent leads to the appearance of pores and a decrease in the physical and mechanical properties of the material.

A known method for producing thermoplastic prepregs (3) (Patent WO 2015121583), which makes it possible to manufacture prepregs with a thermoplastic matrix from one or more unidirectional tapes, obtaining them by pulling a reinforcing material (fibrous filler) through a fluidized layer of polymer, followed by calendering (rolling through several hot rolls in order to increase the degree of impregnation of the fibers with a binder and remove excess binder) using auxiliary systems for controlling parameters (gap between rolls, pressure on the tape, etc.). In the case of simultaneous production of several tapes, the method provides for the possibility of using several calenders.

The disadvantages of this method include the use of spheroidized powder with a narrow fractional composition from 40 to 60 microns, because the processes of spheroidization and selection of a narrow fraction are expensive and sharply increase the waste of the polymer binder, which leads to a reduced economic efficiency of the technology as a whole.

The disadvantages of this technology include the inability to use different types of thermoplastic polymer binder and reinforcing fibrous fillers (only carbon filler and polyphenylene sulfide binder are described), which limits the range of possible combinations of materials with unique characteristics for various operating conditions.

There is a known method for producing prepregs based on fibrous fillers and thermoplastic polymers (4) (Patent WO 2018115737), based on applying at least one thermoplastic polymer to one or more unidirectional tapes of fibrous material powder, and the particle size ratio in the powder d90/d10 can vary in range from 1.5 to 50, preferably from 2 to 10, and the ratio of the average particle size of the polymer powder (d50 by volume) to the diameter of the elementary fiber varies from 3 to 40, except in the case of applying a thermoplastic polymer from an aqueous suspension to carbon fiber, when the ratio of d50 to the diameter of the elementary fiber is from 3 to 8. The process eliminates the presence of electrostatic charging of the surface. As a filler in the process, ribbons of glass or carbon fibers, silicon carbide fibers, basalt, silicon oxide, natural fibers, preferably cotton, bamboo, silk or cellulose (preferably viscose), or amorphous thermoplastic fibers are used. The application method may include direct powder application, fluidized bed application, drawing through an aqueous suspension of polymer, or spraying with a spray gun or through a nozzle.

The method has a number of significant disadvantages:

- a narrow and regulated distribution of polymer powder particles by size is used, as well as a certain range of ratios of the average particle size of thermoplastic polymer powder to the diameter of a filler elementary fiber;

- application is possible only on unidirectional tapes (rovings), the use of bidirectional fillers is not provided;

- there is no possibility to control the amount of applied polymer powder.

The closest technical solution is a method and installation for the manufacture of tape from reinforcing threads impregnated with a polymeric binder material (5) (Patent RU 2703213). The continuous tape is formed by unidirectional fibers of inorganic material, has a constant width along its entire length. The method includes assembling a ribbon from filaments fed from spools with adjustable tension, centering the ribbon along the machine axis, adjusting the strand width, and depositing a polymer on the strand using electrostatic powder application. In this case, the mass fraction of the polymer is from about 20 to about 75%. Next, the polymer is melted, the width and thickness of the tape are calibrated, and the tape is collected on a reel for storage.

The disadvantages of this technical solution are:

- if it is necessary to use a non-conductive fibrous material, the technology involves complication in the form of introducing additional metallization operations or applying a conductive powder;

- lack of a technical solution for the manufacture of bidirectionally reinforced polymer composite materials, the need to use only threads as a fibrous filler, which limits the possibility of obtaining polymer composite materials based on finished tapes and fabrics;

- the lack of a technical solution for removing and applying sizing compositions from the fibrous material, which does not allow you to adjust the adhesive strength between the fibrous material and the polymeric binder and limits the range of possible combinations of materials;

- the lack of a technical solution for stitching two or more continuous fibrous materials to obtain a single material with a length exceeding the length of the feedstock.

This technical solution was applied as the basis for the present method of applying thermoplastic polymer binder powder to continuous reinforcing fibrous materials. The polymeric thermoplastic prepregs obtained by the method are further used as prepregs for the manufacture of load-bearing structures.

The objectives of the proposed solution are:

- increasing the versatility and manufacturability of the process of applying thermoplastic polymer powders of various chemical compositions, such as polyphenylene sulfide, polyamide, polyetheretherketone and other high-tech polymers, to any unidirectional and bidirectional reinforcing fibrous materials, both electrically conductive and dielectric, without additional metallization by spraying;

- the introduction of the possibility of removing the lubricant previously applied to the raw fibrous material and applying a special coupling agent to increase the adhesion of the thermoplastic polymer material to the continuous fibrous filler;

- providing the possibility of stitching two or more continuous fibrous materials, if necessary, to obtain a single material with a length exceeding the length of the original fibrous filler.

The tasks set are solved in a method for producing thermoplastic prepregs by applying a thermoplastic polymeric binder to reinforcing fibrous materials by the method of directed aerosol spraying, including the regulation of the tension of fibrous materials, their grounding, deposition of a polymer powder on a reinforcing fibrous material using one or more powder sprayers, calendering of reinforcing fibrous materials, impregnated with a thermoplastic polymer binder at a temperature from the glass transition temperature to the melting temperature of the polymer, and characterized in that moisture and lubricant are preliminarily removed from the reinforcing fibrous materials and a coupling agent is applied that increases the level of adhesion between the reinforcing fibrous material and the thermoplastic polymer, and the application of powders of different chemical composition thermoplastic polymers is possible on any unidirectional and bidirectional fibrous materials, both electrically conductive and dielectric, without the need for additional operations. Polyphenylene sulfide, polyamide, polyetheretherketone or other high-tech polymers with a preferred particle size of 3 to 100 µm are used as thermoplastic polymer powders. Fibrous fillers are unidirectional tapes or bidirectional webs with a width of at least 5 mm made of carbon, basalt or high-tech organic fibers. Removal of the original lubricant and moisture from the surface of the fibrous filler occurs in one stage.

The method is implemented in the technological scheme, which includes the following operations:

Operation 1. Raw fibrous material in the form of a unidirectional tape or bidirectional fabric, for example, fabrics with the type of weaving of twill or chintz, is unwound to ensure an optimal and evenly distributed level of tension of the reinforcing fibrous material over the cross section, as well as the direction of movement of the reinforcing fibrous material strictly parallel to the installation axis . The necessary and sufficient level of tension is determined experimentally from the condition of the absence of sagging of the reinforcing fibrous material.

Step 2. Reinforcing fibrous material, carbon, basalt or organic, to remove moisture and lubricant is subjected to heating to a certain temperature for a certain period of time to remove moisture from the fibrous material and, if necessary, pre-applied lubricant, if it does not provide the required level of adhesion between the reinforcing fibrous filler and the thermoplastic polymer binder.

Table 1 shows the data of the experiment on removing moisture and oiling from samples of fibrous fillers in an oven at 250°C for 120 seconds to determine the minimum heating time. For the experiment, a carbon fabric of the UT-3K-Sarzha2/2-200-100 brand with a lubricant based on a mixture containing 20-80% vinyl monomer with glycide groups and 80-20% of an amine, and a basalt fabric of the BT-11p brand with a lubricant on the basis of based on diamide-formaldehyde resin. During the experiment, it was found that to remove moisture and sizing from BT-11p basalt fabric, it is sufficient to heat it at 250°C for 30 s.

Operation 3. A special sizing is applied to the fibrous material, the composition of which is selected specifically for each pair of reinforcing fibrous material / thermoplastic polymer matrix, which increases adhesion between materials. The sizing composition is selected for each pair of fibrous filler/thermoplastic polymeric binder experimentally or on the basis of literature data.

For example, for a pair of basalt thread/polyamide, AGM-9 sizing can be applied, in work (6), to improve adhesion at the border of the basalt fiber of polyamide, gamma-aminopropylethoxysilane was used, which is sold under the brand name AGM-9 and consists of two isomers of gamma-aminopropyltriethoxysilane : gamma-aminopropyltriethoxysilane and beta-aminoisopropyltriethoxysilane. (Khandelwal S., Rhee K.Y. Recent advances in basalt-fiber-reinforced composites: Tailoring the fiber-matrix interface // Composites Part B: Engineering. - 2020. - T. 192. - C. 108011 - article about the active component of the corresponding coupling agent ).

Operation 4. The application of thermoplastic polymer binder powder to the reinforcing fibrous material is carried out by the method of directional aerosol spraying, including the use of tribostatic spraying using sprayers (using nozzles). The application method is selected depending on the reinforcing fibrous material used, for example, for electrically conductive carbon fiber materials, the directional aerosol spraying method is used, together with the tribostatic method. The amount of applied thermoplastic polymer binder is adjusted depending on the required filling volume within the range of 30% to 60%, which, as is known from the prior art, corresponds to the optimal strength of the resulting thermoplastic prepregs. For example, for a pair of carbon thread/polyphenylene sulfide, the volume ratio of the components is 50/50, which is within the optimal range. The particle size of the polymer powder can vary over a wide range of 3-100 µm. It has been experimentally established that the use of smaller particles leads to an increase in powder losses due to the formation of stable aerosols, an increase - to a slowdown in the melting of thermoplastic polymer powder, the risk of clogging the nozzle nozzle; entrainment of polymer particles to dumps due to spraying losses (losses to entrainment in the recovery system).

Step 5. The reinforcing fibrous material with the thermoplastic polymer binder powder applied to the surface is heated for a certain period of time until a temperature above the melting point but below the polymer degradation temperature is reached to ensure uniform impregnation throughout the volume of the fibrous material. For example, heating a tape using polyphenylene sulfide to a temperature of 315°C for 60 seconds. For the carbon/PPS pair, the experimental temperature versus time dependence is shown in FIG. 2.

Step 6. The impregnated reinforcing fibrous material at a polymer temperature above the melting point passes through a continuous pressing device to obtain a certain thickness of the tape and increase the degree of impregnation of the reinforcing fibrous material with polymer. Typical equivalent pressing pressure is 10-25 MPa.

In FIG. Figure 1 shows an optical electron microscopy image of a tape sample based on basalt fibers and polyphenylene sulfide. Impregnation result: polymer and fibers are evenly distributed.

Step 7. The impregnated reinforcing fibrous material, a thermoplastic prepreg, is wound onto a spool for storage.

In the continuous production of thermoplastic prepregs, the belt speed depends on the particle size of the thermoplastic polymer binder powder, the temperature and time required to remove moisture and pre-applied lubricant, melt and impregnate the reinforcing fibrous material with polymer. The continuous production speed can be from 0.1m/min to 10m/min.

Examples of a specific implementation:

Example 1. Obtaining a prepreg - a unidirectional reinforced tape based on a carbon filler and a polyphenylene sulfide (PPS) polymer matrix.

To obtain a unidirectional reinforced tape based on carbon filler and PPS, carbon fiber UMT49-12K-EP (hereinafter referred to as CF) with a width of 10 mm, a length of 1000 m and a thermoplastic polymer powder (material based on PPS brand DIC V-100-C (hereinafter TM ) with a characteristic size of the main fraction from 5 to 40 µm). The fiber was heated to 250°C ± 1°C for 60 seconds to remove the sizing. The application was carried out by the tribostatic method. HM was sprayed from two sprayers located above and below the tape. Then, the CF with the applied HM was heated for 60 seconds to a temperature of 315°C ± 1°C. Continuous pressing system, which consists of two or three calenders, with a gap of 0.2 mm, heated to 310°C ± 0.5°C. The CF with the deposited HM passes between the calenders, continuously pressing the HM into the CF. The whole process was carried out at a belt speed of 2 m/min. within 500 minutes. As a result, 1000 meters of unidirectional reinforced tape based on carbon filler and PPS polymer matrix were obtained.

Example 2. Obtaining a prepreg - a unidirectional reinforced tape based on a basalt filler and a PPS polymer matrix.

According to example 1, it differs in that basalt fiber of the brand RB(D) 18-1200-041M with a width of 10 mm, a length of 2000 m was used as a fibrous filler. Operations according to the example according to p. 1, with the following differences: the shaft was not grounded, TM was sprayed from one top atomizer.

Example 3. Obtaining a prepreg - a bidirectional reinforced fabric based on carbon fabric and a PPS polymer matrix.

According to example 1, it differs in that carbon fabric of the brand UT-3K-Sarzha2 / 2-200-100 with a width of 500 mm, a length of 50 m in the amount of 2 pieces is used as a fibrous filler. The operations were performed similarly to item 1 with the following differences: TM was sprayed from six sprayers (three upper, three lower), the second one was hemmed to the end of one fabric without interrupting the process.

Example 4. Obtaining a prepreg - a bidirectional reinforced fabric based on a basalt fabric and a PPS polymer matrix.

According to example 2, it differs in that BT-11p brand basalt fabric with a width of 500 mm and a length of 550 m was used as a fibrous filler. The operations were carried out similarly to paragraph 2, only TM was sprayed from three sprayers.

Example 5. Obtaining a prepreg - a unidirectional reinforced tape based on a basalt tape and a polyamide (PA-12) polymer matrix.

According to example 2, it differs in that PA-12 was used as a thermoplastic material. The factory lubricant based on diamide-formaldehyde resin was removed at a temperature of 250°C for 1 min and a special sizing composition (AGM-9) was applied for the best interaction between the fibrous filler and the polymer matrix. The CM coated with HM was heated to 220°C ± 1°C for 60 seconds. The calenders were heated to 220°C ± 0.5°C.

Example 6. Obtaining a prepreg - a unidirectional reinforced tape based on a carbon tape and a polyetheretherketone (PEEK) polymer matrix.

According to example 1, it differs in that PEEK brand PEEK-1000 was used as a thermoplastic material, HC coated with TM was heated to 380°C ± 1°C for 60 seconds. The calenders were heated to 380°C ± 0.5°C.

Example 7. Obtaining a prepreg - a bidirectional reinforced fiber based on an organic fabric and a PPS polymer matrix.

According to example 1, it differs in that aramid fabric of the SVM brand is used as a fibrous material, and PPS is used as a thermoplastic material. The fiber was heated to 250°C ± 1°C for 60 seconds, the shaft was not grounded, the CF with the deposited HM was heated to 315°C ± 1°C for 60 seconds. The calenders were heated to 315°C ± 0.5°C.

As a result, prepregs with physical and mechanical characteristics are given in Table 2.

The effectiveness of the sizing composition was evaluated on the material obtained in example 5 in terms of the adhesive strength between the fiber and the polymer by the hanging drop method (7) (P.J. Herrera-Franco, L.T. Drzal. Comparison of methods for the measurement of fiber/matrix adhesion in composites // Composites, 1992, Vol. 23, No. 1.), data are given in Table 3.

Thus, the implementation of the production method according to the proposed method provides for the production of thermoplastic prepregs involves the use of a universal method of directional aerosol spraying of thermoplastic polymer binders on a wide range of reinforcing fibrous materials with the possibility of preliminary removal of a regular lubricant and application of the required sizing agent, and the granulometric composition of the thermoplastic polymer binder powder can vary in wide limits. The method makes it possible to obtain prepregs with high physical and mechanical properties relative to the prior art (tensile strength up to 1172 MPa) with a uniform distribution of fibers in the plane of the tape.

Information sources:

1. Patent RU 2556109, Published on 07/10/2015, IPC C08J 5/10.

2. Patent NZ No. 204971 A, Published 09.10.1986, IPC C08J 5/042, B29B 15/122, C08J 3/18, C08K 5/0016, B29B 15/14, B29C 70/52, B29K 2105/0094.

3. Patent WO No. 2015121583, Published on August 20, 2015, IPC B29B 15/12, B29C 70/50, B29K 101/12.

4. Patent WO 2018115737, Published on June 28, 2018, IPC B29B 15/12, B29K 101/12.

5. Patent RU No. 2703213 Published on 10/15/2019 Bull. No. 29, IPC V29V 15/12, V29S 70/08.

6. Khandelwal S., Rhee K.Y. Recent advances in basalt-fiber-reinforced composites: Tailoring the fiber-matrix interface // Composites Part B: Engineering. - 2020. - T. 192. - C. 108011.

7.P.J. Herrera-Franco, L.T. Drzal. Comparison of methods for the measurement of fiber/matrix adhesion in composites // Composites, 1992, Vol. 23, no. 1.

Claims (3)

1. A method for producing a thermoplastic prepreg by applying a thermoplastic polymeric binder to a reinforcing fibrous material by directional aerosol spraying, including preliminary removal of moisture and a lubricant, applying a sizing to the surface of a reinforcing fibrous material, regulating the tension of the fibrous material, depositing a thermoplastic polymeric binder in the form of a powder on the reinforcing fibrous material using one or more nozzles for directional aerosol spraying, calendering of a reinforcing fibrous material impregnated with a thermoplastic polymer binder at a temperature from the glass transition temperature to the melting temperature of the polymer, characterized in that the reinforcing fibrous material is a unidirectional or bidirectional fibrous material made of carbon or basalt , or aramid fibers, electrically conductive or dielectric, without carrying out metallization operations or applying a conductive powder, and the powder of a thermoplastic polymer binder is polyether ether ketone, or polyphenyl sulfide, or polyamide. 2. The method according to claim 1, characterized in that in the case of an electrically conductive reinforcing fibrous material, the deposition is carried out by tribo- or electrostatic directional aerosol deposition, and in the case of a dielectric, directional aerosol deposition. 3. The method according to p. 1, characterized in that the removal of the lubricant and moisture from the surface of the fibrous filler occurs in one stage.

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