KR102439566B1 - Manufacturing method of carbon fiber-reinforced PA6 composite by LFT process and long-fiber reinforced PA6 composite manufactured thereby - Google Patents

Abstract

The present invention relates to a manufacturing method of a carbon fiber-reinforced PA6 composite by an LFT process, which impregnates carbon fibers with a molten PA6 resin through the LFT process by supplying and filling the molten PA6 resin from an extruder into a die for resin impregnation, and then supplying the carbon fibers to the die, thereby improving the impregnability between the carbon fibers and the PA6 resin and physical properties of the carbon fiber-reinforced PA6 composite manufactured by the method.

Description

Manufacturing method of carbon fiber-reinforced PA6 composite by LFT process and long-fiber reinforced PA6 composite manufactured thereby}

The present invention relates to a method for manufacturing a carbon fiber reinforced PA6 composite by an LFT process, and by controlling the shape of a die for resin impregnation during the LFT process, the impregnation of the PA6 resin to the carbon fiber and the interfacial adhesion between the carbon fiber and the thermoplastic resin It relates to a method for manufacturing a carbon fiber reinforced PA6 composite by an LFT process that improves the properties of the carbon fiber reinforced PA6 composite and improves the physical properties of the carbon fiber reinforced PA6 composite.

Carbon fiber reinforced composites (CFRC) are a combination of high-strength carbon fibers as reinforcing fibers in a thermosetting or thermoplastic polymer matrix. It has been widely used as a lightweight material in various fields such as civil engineering/construction, wind turbine blades, military and defense industries, and thermosetting resins have been used for a long time as a matrix resin for carbon fiber reinforced composite materials.

Thermosetting resins not only have excellent mechanical and thermal properties after curing, but also have a very low viscosity before curing and have high impregnation properties for reinforcing fibers. Various types of fibers can be used. However, since thermosetting resins require a curing reaction, the molding cycle time increases, productivity decreases, and recycling is impossible, so it is difficult to apply them to various material fields.

Therefore, in recent years, there is no need for curing reaction, so the molding cycle time can be shortened, the productivity is high, and technology development using a recyclable thermoplastic resin is in progress. For example, PA6 resin, which is one of the thermoplastic resins, may be used as a matrix of a carbon fiber reinforced composite material as it has excellent mechanical and thermal properties such as abrasion resistance, corrosion resistance, low friction coefficient, heat resistance, and excellent toughness. However, these PA6 resins have a higher melt viscosity than general thermosetting resins, and thus have low compatibility with carbon fibers and low impregnation properties for carbon fibers. It was manufactured through extrusion and injection molding processes that go through melting and compounding steps.

However, when a carbon fiber reinforced composite is manufactured by extrusion or injection molding process, the carbon fiber is broken due to the screw action in the extruder, and the length of the carbon fiber is greatly reduced, resulting in a low fiber aspect ratio. In the case of manufacturing, it is difficult to realize high physical properties.

Therefore, long fiber thermoplastic (LFT) process technology is applied to increase the fiber aspect ratio by preventing the occurrence of breakage of carbon fibers and to manufacture fiber-reinforced thermoplastics with improved physical properties by supplementing the shortcomings of the thermoplastic resin matrix. do.

The LFT process is a thermoplastic composite material molding technology that uses long fibers (3mm to 25mm) and thermoplastic resin, and combines pultrusion and extrusion technology. The fibers are not damaged, cut, or pulverized during the process, and a relatively long reinforcing fiber state is maintained, thereby increasing the aspect ratio, and thus, the composite material prepared therefrom can exhibit significant improvement in physical properties.

U.S. Patent Publication No. 2013-0113133 (published on May 9, 2013) relates to a method for manufacturing a hybrid structure composite material reinforced with long fibers, wherein a resin for impregnation is injected into a passage through which fiber filaments pass, and long fibers It discloses manufacturing a composite material reinforced with a hybrid structure, and discloses PA, ABS, etc. as the impregnating resin, and discloses carbon fiber as a fiber filament. However, in the case of the prior document, the impregnating resin is supplied from a portion away from the fiber filament inlet, and is supplied at an angle of less than 90° with respect to the movement direction of the filament, so that the carbon fiber is impregnated with a resin such as PA, ABS, etc. There is a limit to

In addition, Korean Patent Application Laid-Open No. 1996-0033683 (published on October 22, 1996) relates to a method for manufacturing a long fiber reinforced thermoplastic composite material, wherein a molten resin is supplied from an extruder to a crosshead, and reinforcing fibers are used as the crosshead. After passing the roving to coat the fiber roving with a resin, moving it to an impregnation die to impregnate the resin applied to the roving between the fibers of the roving, manufacturing a long fiber reinforced thermoplastic composite material. have.

However, in the case of the prior literature, the reinforcing fiber roving supplied to the crosshead must be preheated before feeding to the crosshead, and furthermore, the reinforcing fiber roving is not impregnated with the molten resin in the crosshead, but is primarily reinforced at the crosshead. After the resin is coated on the fiber roving, it is moved to an impregnation die, and the resin applied to the roving in the impregnation die is impregnated between the fibers of the roving, thereby reducing process efficiency and productivity.

Long fiber reinforced thermoplastic composites using this LFT process affect not only the fiber composition, fiber length, fiber orientation, and matrix properties, but also the interfacial adhesion between the fibers and the matrix, and physical properties depending on the manufacturing method.

As an example, in pultrusion molding of fiber-reinforced thermoplastic prepreg materials (Composites Part B 89 / p.328-339 (2016), Daekyung Seo), a cross-head extrusion die is used when manufacturing a thermoplastic matrix prepreg product, but the cross - Disclosed is the production of prepregs by feeding the resin in a direction perpendicular to the fibers passing through the head extrusion die.

However, when the prepreg is manufactured by extruding the resin in a direction perpendicular to the fiber in the cross-head die, the permeability of the resin to the fiber is insufficient, so there is a limit in improving the physical properties of the composite material.

Therefore, the present invention is to improve the problems of the conventional carbon fiber reinforced composite material manufacturing by LFT, to prevent damage to the fiber, and to significantly improve the impregnation property of the resin to the fiber, carbon fiber reinforced by LFT to improve the physical properties of the composite material However, it provides an invention in which the PA6 resin impregnation method for carbon fiber during the LFT process is different to prepare a PA6 composite material.

US Patent Publication No. 2013-0113133 (published date: 2013.05.09) Korean Patent Publication No. 1996-0033683 (published date: October 22, 1996)

Pultrusion molding of fiber-reinforced thermoplastic prepreg materials (Composites Part B 89 / p.328-339 (2016), Daekyung Seo)

The present invention improves the impregnation property of the PA6 resin to the carbon fiber by controlling the shape of the die for resin impregnation of the LFT process in the production of the carbon fiber reinforced PA6 composite material by the LFT process, and through this, the carbon fiber and the PA6 resin The first task is to provide a method for manufacturing a carbon fiber reinforced PA6 composite material by the LFT process that improves physical properties such as interfacial adhesive properties, tensile strength, flexural modulus, and impact strength.

In addition, the present invention makes a second solution to provide a carbon fiber reinforced PA6 composite manufactured by the method for manufacturing a carbon fiber reinforced PA6 composite by the LFT process.

In order to solve the above problems, in the method of manufacturing a carbon fiber reinforced PA6 composite by the LFT process, (a) the molten PA6 resin from the extruder is extruded into a resin impregnation die, and the inside of the resin impregnation die filling with molten PA6 resin; (b) drawing carbon fibers from one end of a die for resin impregnation filled with the molten PA6 resin to the other end to prepare a towpreg impregnated with the molten PA6 resin; and (c) cooling the towpreg impregnated with the molten PA6 resin to produce a solid towpreg;

In one embodiment, before cooling the towpreg impregnated with the PA6 resin melted in step (c), the method may further include pressing.

In one embodiment, the resin impregnation die may be a crosshead-die in which the molten PA6 resin and the carbon fiber move together in the same horizontal direction and the carbon fiber is impregnated with the molten PA6 resin. have.

In addition, the present invention provides a carbon fiber-reinforced PA6 composite prepared by the manufacturing method of the carbon fiber-reinforced PA6 composite by the LFT process.

In one embodiment, the carbon fiber reinforced thermoplastic composite material includes carbon fiber and polyamide 6 (PA6) resin, a tensile strength of 195 to 250 MPa, a tensile modulus of 8.0 to 15 GPa, and a flexural strength of 250 to 300 MPa, and may have a flexural modulus of 13 to 25 GPa.

After filling the molten PA6 resin in the resin impregnation die according to the present invention, carbon fibers are passed through the resin impregnation die to produce a carbon fiber reinforced PA6 composite, the carbon fibers are evenly distributed between the PA6 resin matrix As a result, interfacial adhesion properties are improved, and there is no resin-impregnated carbon area or the range of the area is significantly reduced, so physical properties such as tensile strength, flexural strength, and flexural modulus are improved.

Figure 1 (a) shows a T-type type of resin impregnation die of the LFT process according to an embodiment of the present invention and a towpreg manufacturing process according thereto, Figure 1 (b) is an embodiment of the present invention It shows a die for resin impregnation of the I-type type of the LFT process and the towpreg manufacturing process accordingly.
Figure 2 (a) shows the manufacturing of the towpreg according to the T-type resin impregnation die of the LFT process according to an embodiment of the present invention and a process for pressing the same, and Figure 2 (b) is the present invention. It shows the manufacturing of the towpreg according to the I-type resin impregnation die of the LFT process according to an embodiment and the process of pressing the same.
3 is a view showing an injection molding process according to an embodiment of the present invention.
4 is a graph showing (a) tensile strength and (b) tensile modulus of carbon fiber/PA6 composite material injection-molded according to an embodiment of the present invention.
5 is a graph showing (a) flexural strength and (b) flexural modulus of a carbon fiber/PA6 composite material injection-molded according to an embodiment of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is those well known and commonly used in the art.

In the present specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

1 (b) is a view showing the shape of the resin impregnation die of the LFT process according to an embodiment of the present invention and the manufacturing process of the carbon fiber reinforced PA6 composite material according thereto, and the present invention will be described in detail with reference to this.

In one aspect, in a method for manufacturing a carbon fiber reinforced PA6 composite by an LFT process, (a) extruding a molten PA6 resin from an extruder with a resin impregnation die, and molten PA6 inside the resin impregnation die filling with resin; (b) drawing carbon fibers from one end of a die for resin impregnation filled with the molten PA6 resin to the other end to prepare a towpreg impregnated with the molten PA6 resin; and (c) cooling the towpreg impregnated with the molten PA6 resin to produce a solid towpreg;

In the present invention, in the step (a), the PA6 resin is put into the hopper of the extruder and melted, and then the molten PA6 resin is supplied to the resin impregnation die connected to the extruder head to determine the total internal length of the resin impregnation die. Filling with the molten PA6 resin.

The PA6 resin has 6 carbons in the repeating unit of the molecular chain structure including the amide (-CONH-) group in polyamide (PA), and contains 10 to 20% of water in caprolactam. It can be prepared by polymerization by adding pressure and heat. In PA6, both the N-H bond and the C-O bond have polarity, and N and O are negatively charged. This polarity helps to form double bonds between the molecules of PA6. This double bond is a hydrogen bond, which restricts the movement of PA6 molecules with each other and consequently increases the tensile strength. In addition, the molecular chain of PA6 forms a flat laminated structure by hydrogen bonding with the surrounding molecular chains to have high crystallinity. Therefore, PA6 has excellent properties such as high crystallinity, excellent properties and toughness, low gas permeability, fatigue resistance, weather resistance, and heat resistance, as well as excellent processability, making it an engineering plastic with high industrial utility. In particular, since PA6 has excellent wear resistance, corrosion resistance, and low coefficient of friction, PA6 having such excellent mechanical and thermal properties can be used as a matrix of carbon fiber reinforced composites.

In the present invention, step (b) is a step of producing a towpreg impregnated with the molten thermoplastic resin by drawing carbon fibers from one end of the die for resin impregnation filled with the molten PA6 resin to the other end.

Specifically, in step (b), carbon fibers are supplied to the resin impregnation die filled with the molten PA6 resin so that the carbon fibers come into contact with the molten PA6 resin throughout the entire section of the resin impregnation die and move to draw out the other end of the resin impregnation die. Accordingly, the contact time and contact area between the carbon fiber and the molten PA6 resin in the resin impregnation die are increased, so that the environment in which the molten PA6 resin can penetrate the carbon fiber continues for a long time, and the molten PA6 resin A towpreg with improved resin impregnation property is prepared.

This resin impregnation die is a crosshead-die mounted vertically with respect to the extruder, and the inlet and outlet directions of the molten PA6 resin into the resin impregnation die are different, but the resin impregnation die The direction of movement toward the discharge of the molten PA6 resin in the die and the carbon fiber passing through it is the same.

Specifically, as shown in FIG. 1(b), the molten PA6 resin is supplied to a resin impregnation die connected to an extruder, that is, a crosshead-die, and the entire length of the crosshead-die is molten PA6 resin. The carbon fiber enters the resin impregnation die filled with the molten PA6 resin and is drawn toward the discharge part in the same horizontal direction as the molten PA6 resin, so that the molten PA6 resin in the carbon fiber is The impregnated and impregnated, towpregs are prepared.

The _towpreg produced by the above process and discharged from the resin impregnation die is in a somewhat flexible state, and as shown in FIG. It is possible to further improve the impregnability and interfacial adhesion properties of the molten PA6 resin to the fiber.

In step (b), the carbon fibers are continuously supplied to the resin impregnation die and are tows made of untwisted continuous filament bundles. The tow size is not limited, but may be 1K to 60K, preferably 1K to 24K, where 'K' represents the number of filaments in the carbon fiber tow, and 1K tow is made of 1,000 thin fiber filaments. it means.

In addition, the carbon fiber may be a PAN (polyacrylonitrile)-based, pitch-based or rayon-based carbon fiber, preferably a PAN-based carbon fiber.

In the present invention, step (c) is a step of preparing a solid towpreg by cooling the towpreg impregnated with the molten PA6 resin. Since the above process is carried out by the generally known LFT process, it is not specifically described, and the LFT series of processes (a) to (c) above are for continuous supply of carbon fiber and molten PA6 resin by extrusion and drawing. The tow pregs produced in this way may be stored in a bobbin so as not to be entangled with each other, or may be cut and manufactured in the form of pellets.

The pellets prepared according to the present invention contain 20 to 45% by weight of carbon fibers based on the total weight of the pellets. When the carbon fiber content is less than 20% by weight, it is not possible to expect sufficient improvement of the properties of the carbon fiber-reinforced PA6 composite material. Alternatively, it may act as an impurity to impair the physical properties of the carbon fiber reinforced PA6 composite. Therefore, in the pellet, the carbon fiber is included in an amount of 20 to 45% by weight, preferably 25 to 35% by weight.

In addition, the aspect ratio of the pellets is 3 to 20. When the aspect ratio of the pellets is less than 3, the length of the pellets is too short, so it is difficult to effectively increase the mechanical properties in the composite. There may be problems limiting the effectiveness.

Therefore, preferably, the aspect ratio of the pellets is 5 to 15.

In addition, the pellet may be molded by injection molding or compression, and the towpreg cutting, pellet manufacturing, injection molding or compression may be performed by a generally known process, so the process is not specifically described.

The carbon fiber-reinforced PA6 composite prepared according to this method, including carbon fiber and PA6 resin, has a tensile strength of 195 to 250 MPa, a tensile modulus of 8.0 to 15 GPa, and a flexural strength of 250 to 300 MPa, and the flexural strength is 250 to 300 MPa. The modulus of elasticity may be 13 to 25 GPa.

The carbon fiber reinforced PA6 composite material is prepared by using a crosshead-die in the LFT process according to the above method to prepare a resin-impregnated towpreg, but the crosshead-die is first filled with a molten PA6 resin, and then the crosshead -A tow preg is produced by passing carbon fibers through a die, and the impregnation property of PA6 resin to carbon fibers is improved.

Accordingly, the carbon fiber-reinforced PA6 composite material does not have a carbon region impregnated with the PA6 resin or has a small region range, and the carbon fibers are evenly distributed between the PA6 resin matrix, so that the carbon fiber and the PA6 resin interfacial adhesion characteristics are improved.

Therefore, when a load is applied from the outside, the carbon fiber-reinforced PA6 composite material receives a relatively small load than the initially applied load as the load is uniformly transmitted to the neighboring carbon fiber and resin matrix, and tensile strength, tensile modulus of elasticity, flexural strength , the flexural modulus is improved.

Moreover, in the case of the carbon fiber-reinforced PA6 composite, PA6, which has a relatively low viscosity among thermoplastic resins, is used as a matrix to further improve the flowability and permeability of the matrix resin to carbon fibers, and the composite manufactured through this has a high viscosity Compared to the case of using a resin having a resin as a matrix, physical properties such as tensile strength, tensile modulus of elasticity, flexural strength, and flexural modulus can be more remarkably improved.

Hereinafter, the present invention will be described in more detail by way of Examples, but the present invention is not limited by the Examples.

<Example>

ingredient

(1) carbon fiber

The PAN-based carbon fiber (carbon fiber, 12K, T700 grade) used as the reinforcing fiber of the carbon fiber-reinforced PA6 composite is manufactured by Toray Advanced Materials (Korea) and has a density of 1.8 g/cm ³ , The tensile strength was about 4,900 MPa and the tensile modulus was about 230 GPa, and it was supplied in the form of a continuous fiber wound on a cylindrical bobbin for the LFT process.

(2) Matrix resin - PA6

Polyamide 6 (PA6) resin (KN136) used as a matrix for carbon fiber reinforced PA6 composite is an engineering plastic with excellent physical properties, manufactured by Kolon Plastics (Korea), has a pellet shape, and has a density of 1.14 g/cm ³ , The tensile strength is about 80 MPa, the flexural strength is about 130 MPa, the flexural modulus is about 2,950 MPa, the Izod impact strength is about 60 J/m, and the heat deflection temperature is about 65°C, and the melt flow index (260) °C, 5 kg) is 127.3 g/10 min.

Since the PA6 resin has excellent flowability, it can be expected to exhibit high resin impregnation properties when using the PA6 resin to prepare a composite material by an LFT process.

LFT pellet manufacturing

A lab-scale LFT device that combines a single-screw extruder (Ø20) and a pulling machine manufactured by Bautek (Korea) was used to manufacture the resin-impregnated carbon fiber towpreg. LFT pellet production using this is carried out by the following LFT pellet manufacturing method, I-type, MI-type, T according to the resin type impregnated in the carbon fiber according to the die shape through which the carbon fiber tow passes. -type and MT-type were prepared, respectively.

(LFT pellet manufacturing method)

According to the LFT process, continuous carbon fiber tow in the form of a bobbin passes through a die connected to the extruder head, and PA6 pellets fed through the hopper of the extruder are melted inside the extruder and the die connected to the extruder by screw rotation. The molten resin was impregnated into a continuous carbon fiber tow that was extruded into a furnace and passed through a die connected to the extruder head.

The resin-impregnated towpreg was cooled through a water bath while being pulled by a drawing machine. The towpreg thus prepared was wound and stored on a cylindrical bobbin so as not to become entangled with each other.

The towpreg was cut to a length of 12 mm using a pelletizer developed by ACE C&TECH (Korea) to prepare LFT pellets.

The carbon fiber content compared to the resin was calculated by dividing the weight of the carbon fiber tow of 10 cm length by the weight of the carbon fiber of the same length impregnated with the resin and then multiplying by 100%.

In addition, in order to remove the influence of moisture in the LFT pellet manufacturing process, PA6 pellets and carbon fiber bobbins dried for 12 hours in a drying oven at 80°C were used respectively, and the screw rotation speed of the extruder and the speed of the drawing machine were adjusted by adjusting the LFT Pellets were prepared.

(1) I-type and MI-type LFT pellets

In the process of impregnating the molten resin into the continuous carbon fiber tow, as shown in FIG. 1(b), the LFT pellets are prepared according to the LFT process, after filling with the molten PA6 resin extruded by the cross-die. , by supplying continuous carbon fiber to the cross-die, the carbon fiber and the molten PA6 resin in the cross-die moved horizontally in the same direction, and the towpreg impregnated with the molten PA6 resin in the carbon fiber tow was prepared. , the pellets thus prepared were named I-type.

In addition, as shown in FIG. 2(b), the LFT pellets prepared by further including the step of pressing the prepared towpreg before cooling were named MI-type.

(2) T-type

According to the LFT process, LFT pellets are prepared, but as shown in FIG. 1(a), the molten resin is passed through an extruder head connected to a cross-die, perpendicular to the carbon fiber tow passing through the cross-die. A towpreg was prepared in which the carbon fiber tow was impregnated with a molten resin by extruding it in a round shape in the phosphor direction. The pellets thus prepared were named T-type.

In addition, the pellets prepared by pressing the prepared towpreg as shown in FIG. 2(a) before entering the cooling water bath were named MT-type.

In the preparation of the T-type and I-type LFT pellets, the LFT process conditions and the carbon fiber content of the LFT pellets prepared accordingly are shown in Table 1 below.

Barrel Temperature (℃) Thermoplastic Resin Zone 1 Zone 2 Head Die PA6 160 200 260 260 Thermoplastic Resin Cross-die type screw speed
(rpm) pulling speed
(rpm) carbon fiber
(wt%) PA6 T-type 6.8 4.1 30-33 I-type 4.9 3.8

Manufacture of injection molded carbon fiber/PA6 composite material

The carbon fiber/PA6 LFT pellets of each pellet type (T-type, I-type, MT-type and MI-type) prepared above were subjected to an injection molding process to prepare a carbon fiber/PA6 composite material according to each pellet type. .

Before performing the injection molding process, each type of LFT pellets were dried in a drying oven at 80° C. for 12 hours to remove the effect of moisture. The injection molding process was performed using an injection molding machine (PRO-WD 80) manufactured by Dongshin Hydraulics (Korea), and injection molding was performed according to the conditions shown in FIG. 3 and Table 2 below.

In addition, the composite material according to each pellet type manufactured by the injection molding process was prepared in the form of a specimen for performing the following characteristic analysis.

Table 2 below shows the injection molding conditions of the carbon fiber/PA6 composite material by the carbon fiber/PA6 LFT pellet, which was made by the injection molding machine of FIG. 3 .

Barrel Temperature (℃) Mold Temperature (℃) Cooling time (s) zone 1 zone 2 zone 3 Nozzle 90 20 280 270 260 280 Molding Process conditions Parameter Injection 1 Injection 2 Injection 3 Injection 4 Injection 5 holding
Pressure1 holding
Pressure2 holding
Pressure3 Pressure
(kg/cm2) 50 50 50 55 55 20 20 20 Speed (%) 35 30 30 30 30 25 Time(s) 4.0 4.0 4.0 4.0 4.0 5.0 1.0 1.0 Position
(mm) 48.0 38.0 23.0 21.0 18.0

Characterization

(1) Tensile test

4 shows the results of (a) tensile strength and (b) tensile modulus of carbon fiber/PA6 composite material manufactured through the injection molding process. The tensile strength and tensile modulus were tested by the following method.

(Test method for tensile strength and modulus of elasticity)

The tensile test of the composite material was performed using a universal testing machine (UTM, AG-50kNX) of Shimadzu JP (Japan). According to ASTM-D638, the length is about 165 mm, the width is about 12.5 mm, and the thickness is about 3 mm. A specimen having a dog-bone shape was used. The load cell used was 50 kN, the crosshead speed was 5 mm/min, and the gauge length was 100 mm. Tensile strength and tensile modulus were obtained from the average values of 10 specimens per composite material.

In the case of the carbon fiber / PA6 composite material of Figure 4, the tensile strength in T-type, MT-type, I-type, and MI-type is about 151, 196, 201, and 210 MPa (Figure 4(a)), respectively. , the tensile modulus of elasticity are about 8.2, 8.4, 8.9, and 9.2 GPa (Fig. 4(b)), respectively, and the tensile strength and tensile modulus of the composite material are T-type, depending on the degree of resin impregnation for carbon fibers in LFT pellets. Composite materials manufactured with MT-type, I-type, and MI-type LFTs improved in that order.

In the T-type carbon fiber/PA6 composite material and the MT-type carbon fiber/PA6 composite material, there was a region of carbon fiber that was not properly impregnated with resin, and the dispersibility of the carbon fiber was not good. As such, when the carbon fibers in the composite material are not evenly distributed in the resin matrix, the load applied from the outside is not evenly transmitted between the resin matrix and the carbon fibers constituting the composite material, thereby providing a cause of lowering the resistance to load. In addition, microdefects such as voids and defects may exist around carbon fibers that are not impregnated with resin. At this time, the discontinuity between the carbon fiber and the resin matrix causes failure, and consequently reduces the tensile strength and tensile modulus of the composite material.

On the other hand, in the composite material, carbon fibers are evenly dispersed and there is no area of carbon fiber impregnated with resin or the area is relatively small between I-type carbon fiber/PA6 composite material and MI-type carbon fiber/PA6 composite material. In this case, when an external load is applied, the load is efficiently transferred between the adjacent carbon fiber and the resin matrix, and the tensile strength and tensile modulus of the composite material are improved as the load is relatively smaller than the initially applied load.

This is because the PA resin has a very low viscosity, which is advantageous for the dispersion of carbon fibers in the composite material.

(2) Flexural test

5 shows (a) flexural strength and (b) flexural modulus of each type of carbon fiber/PA6 composite material manufactured by injection molding each type of LFT pellets. Flexural strength and flexural modulus were measured by the following method.

(Measurement of flexural strength and flexural modulus)

A three-point bending test of the composite material was performed using a universal testing machine (UTM, AG-50kNX) of Shimadzu JP (Japan). According to ASTM-D790, a specimen having a bar shape having a length of about 125 mm, a width of about 12.5 mm, and a thickness of about 3 mm was used. The load cell used was 50 kN, the crosshead speed was 5.1 mm/min, the span-to-depth ratio was 32:1, and the support span was 96 mm. Flexural strength and flexural modulus were obtained from the average values of 10 specimens per composite material.

In the case of the carbon fiber / PA6 composite material of FIG. 5, the flexural strengths of T-type, MT-type, I-type, and MI-type are about 184, 242, 253, and 280 MPa (Fig. 5(a)), respectively. , the flexural modulus is about 12.5, 13.1, 14.5, and 16.6 GPa (Fig. 5(b)), respectively, and the composite material is T-type, MT-type, I-type, and MI depending on the degree of resin impregnation in the LFT pellets. Flexural strength and flexural modulus were improved in the order of -type composite material.

In general, in fiber-reinforced composite materials, the interfacial properties between the reinforcing fibers and the polymer matrix play a very important role in the flexural strength and flexural modulus of the composite material. In the T-type and MT-type carbon fiber/PA6 composite materials, there were carbon fiber bundles that did not form an interfacial bond with the resin. The carbon fiber regions not impregnated with these resins act as voids and defects, and a stress concentration region is formed to lower the flexural strength and flexural modulus of the composite material. In addition, the carbon fibers are not well dispersed in the resin matrix, and the resin matrix existing between the carbon fibers is formed too thick or thin, so that the load cannot be evenly distributed, resulting in fracture of the composite material.

On the other hand, in the I-type and MI-type carbon fiber/PA6 composite materials, the carbon fibers are evenly distributed between the resin matrix, so that the load applied from the outside is effectively transmitted to the neighboring carbon fibers and matrix, and the load is dispersed, resulting in the flexural strength of the composite material. and flexural modulus were improved.

Claims (5)

In the manufacturing method of the carbon fiber reinforced PA6 composite material by the LFT process,
(a) extruding the molten PA6 resin from the extruder into a resin impregnation die, and filling the inside of the resin impregnation die with the molten PA6 resin;
(b) drawing carbon fibers from one end of a die for resin impregnation already filled with the molten PA6 resin to the other end to prepare a towpreg impregnated with the molten PA6 resin; and
(c) manufacturing a solid towpreg by cooling the towpreg impregnated with the molten PA6 resin;
The method of claim 1,
Before cooling the towpreg impregnated with the molten PA6 resin in step (c), the method for producing a carbon fiber reinforced PA6 composite by the LFT process, characterized in that it further comprises the step of pressing.
The method of claim 1,
The resin impregnation die is a crosshead-die in which the molten PA6 resin and the carbon fiber move together in the same horizontal direction and the carbon fiber is impregnated with the molten PA6 resin, LFT Manufacturing method of carbon fiber reinforced PA6 composite material by the process.
A carbon fiber-reinforced PA6 composite material prepared by the method of any one of claims 1 to 3.
5. The method of claim 4,
The carbon fiber reinforced thermoplastic composite material includes carbon fiber and polyamide 6 (PA6) resin, has a tensile strength of 195 to 250 MPa, a tensile modulus of 8.0 to 15 GPa, a flexural strength of 250 to 300 MPa, and a flexural modulus of elasticity Carbon fiber reinforced PA6 composite, characterized in that the 13 to 25 GPa.

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