JP7352462B2 - Resin film, thermoplastic carbon fiber prepreg, and manufacturing method thereof - Google Patents

Description

The present invention relates to a resin film for forming a thermoplastic carbon fiber prepreg by a film stacking method, a thermoplastic carbon fiber prepreg using the resin film, and a method for manufacturing the same.

Carbon fiber reinforced plastics are used in a wide range of fields, including automobiles, aircraft, and temporary civil engineering materials, due to their light weight, excellent strength, and high durability. Carbon fiber reinforced plastics include thermosetting carbon fiber reinforced plastics and thermoplastic carbon fiber reinforced plastics, depending on the properties of the resin to be impregnated. Among these, thermoplastic carbon fiber-reinforced plastics are particularly used as constituent materials for automobiles because of their short molding time and their ability to be recycled by heating.

Such thermoplastic carbon fiber reinforced plastics are manufactured using thermoplastic carbon fiber prepreg as an intermediate material. Thermoplastic carbon fiber prepreg is obtained by opening a tow (bundle) of carbon fibers and impregnating the carbon fibers with a thermoplastic resin.
Among prepregs, those made by opening carbon fiber tows (bundles) and aligning them in one direction are called unidirectional (UD) prepregs.

Conventionally, dry powder coating methods, pultrusion methods, mixed fiber methods, and film stacking methods are generally known as methods for producing thermoplastic carbon fiber prepregs.
Among these, the film stacking method is a method in which a resin film is laminated onto carbon fibers, and the carbon fibers are impregnated with a resin constituting the resin film by heating and pressurizing (see, for example, Patent Document 1). Additionally, prepregs using phenoxy resin as a thermoplastic resin are also generally known (see, for example, Patent Document 2).

International Publication No. 2016/18610 Japanese Patent Application Publication No. 2010-126694

However, in the polycarbonate resin prepreg disclosed in Patent Document 1, the resin film has a thickness of 100 μm or more, and the thick thickness reduces the carbon fiber content (Vf value) of the polycarbonate resin prepreg. Therefore, there was a problem in that it was difficult to increase the strength of the obtained polycarbonate resin prepreg.

Furthermore, in order to increase the carbon fiber content (Vf value) of the thermoplastic carbon fiber prepreg and increase its strength, it is necessary to reduce the thickness of the resin film. However, if the resin film is made thinner, heat shrinkage (neck-in) occurs in the TD (width direction) of the resin film when the resin film is impregnated with carbon fibers using the film stacking method, and the carbon fibers become closer to the center and the thermoplastic carbon There was a problem in that the physical properties of the fiber prepreg in the TD (width direction) varied.
Furthermore, when the resin film is made thinner, there is a problem that the resin film breaks when carbon fibers are impregnated with the resin film using a film stacking method, resulting in a lack of manufacturing stability.
Although Patent Document 2 includes descriptions of phenoxy resin and prepreg as thermoplastic resins, it does not include descriptions of properties such as the tear strength and heat shrinkage rate of resin films, which are important when manufacturing prepregs by the film stacking method. do not have.

The present invention was made in view of the above-mentioned circumstances, and it is possible to make a thin film, and when used in a thermoplastic carbon fiber prepreg, it is possible to increase the carbon fiber content and improve the strength. The present invention aims to provide a resin film for forming a thermoplastic carbon fiber prepreg, a thermoplastic carbon fiber prepreg using the same, and a method for manufacturing the same.

The present invention has the following aspects.
<1> A resin film for forming a thermoplastic carbon fiber prepreg by a film stacking method,
The resin film has a thickness of 8 μm or more and 55 μm or less, a tear strength in the width direction according to JIS 7128 of 28 mN or more, and a heat shrinkage rate in the width direction of less than 7% , and the resin film contains a phenoxy resin. resin film.
In addition, the method for measuring the heat shrinkage rate in the width direction in the present invention is to measure both ends of a resin film in the machine direction of 50 mm in TD (width direction) x 100 mm in MD (machine direction) along the width direction with an aluminum tape with a thickness of 0. .The length (mm) of the most shrunk part of the resin film in the TD (width direction) after fixing it on a 3mm SUS plate, putting it in an oven, and maintaining it at 100°C for 2 minutes with the damper opening 50%. was measured, and the shrinkage rate in TD (width direction) was calculated from the ratio to 50 mm.

<2> The resin film according to <1>, wherein the difference in the heat shrinkage rate in the width direction with respect to the heat shrinkage rate in the machine direction is less than 10%.
The method for measuring the heat shrinkage rate in the machine direction in the present invention is to After fixing it on a 0.3 mm thick SUS plate with aluminum tape, putting it in an oven, and maintaining it at 100°C for 2 minutes with the damper opening 50%, the most contracted part of the resin film in MD (machine direction) The length (mm) was measured, and the MD (machine direction) shrinkage rate was calculated from the ratio to 50 mm.

<3> A thermoplastic carbon fiber prepreg characterized in that carbon fibers are impregnated with the resin film described in <1> or <2> .

<4> A method for producing a thermoplastic carbon fiber prepreg, comprising a step of impregnating carbon fibers with the resin film according to <1> or <2> .

According to the present invention, there is provided a resin film for forming a thermoplastic carbon fiber prepreg that can be made into a thin film and that can increase the carbon fiber content of the thermoplastic carbon fiber prepreg to improve its strength. It is possible to provide a thermoplastic carbon fiber prepreg and a method for producing the same.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of the manufacturing method of the thermoplastic carbon fiber prepreg of this invention.

The following definitions of terms apply throughout the specification and claims.
MD (machine direction) is the extrusion direction (longitudinal direction) of the strip-shaped resin film. Moreover, TD (width direction) is a direction perpendicular to MD (flow direction) along the resin film surface.

Hereinafter, a resin film according to an embodiment of the present invention and a thermoplastic carbon fiber prepreg using the same will be described. It should be noted that the embodiments shown below are specifically explained in order to better understand the gist of the invention, and unless otherwise specified, the embodiments are not intended to limit the invention.

(resin film)
The resin film of the present invention is arranged on one side and the other side of sheet-like carbon fibers to form a thermoplastic carbon fiber prepreg by a film stacking method, and can be selected from various thermoplastic resins. I can do it.

Specific examples of resin films include polyamide resins such as nylon 6 (registered trademark), nylon 66 (registered trademark), and aromatic nylon (registered trademark), polycarbonate resins, polyolefin resins such as polyethylene and polypropylene, polyphenylene sulfide resins, and epoxy resins. Examples include sheet materials such as phenoxy resin, polyester resin, polysulfone resin, polyether ether ketone resin, polyimide resin, polystyrene resin, and ABS resin, which are made by increasing the molecular weight of resin into a linear chain.
Further, the resin film of the present invention is manufactured by, for example, an inflation method, a T-die extrusion method, a calender method, or the like.
When manufacturing by the inflation method, a molten thermoplastic resin is extruded from a ring die and formed into a continuous tube shape. The resin film of the present invention can be produced by feeding compressed air into this tube-shaped resin from the inside to gradually expand it to a film of a predetermined width, and then taking it between the nip rolls of a take-off machine.

When manufacturing a resin film by the above-mentioned inflation method, the film is formed to a target thickness while the resin temperature at the exit of the ring die is higher than the glass transition temperature by, for example, 60°C or more, and then the film is kept in its shape. The compressed air volume and take-up speed are adjusted so that the air is gradually cooled. The take-up speed is not too high, preferably 10 m/min or more and less than 30 m/min, more preferably 10 to 20 m/min. When the take-up speed is 10 m/min or more and less than 30 m/min, the MD (machine direction) stretching and orientation of the resin film can be controlled, and thermal shrinkage is less likely to occur.

It is preferable to keep the blow ratio (resin film diameter/ring die diameter) as low as 1.5 to 6.0 by adjusting the amount of compressed air. If the blow ratio is in the range of 1.5 to 6.0, it is possible to control the stretching and orientation of the resin film in the TD (width direction) and MD (machine direction). Direction) heat shrinkage is less likely to occur.

In addition, when the resin film of the present invention is also produced by T-die extrusion, the cylinder temperature and die temperature of a 20 to 80 mmφ single-screw or twin-screw extruder equipped with a T-die with a lip width of 1 mm should be adjusted to the temperature of the thermoplastic resin. The thermoplastic resin was charged into an extruder, melted and kneaded at a screw rotation speed of 5 to 50 rpm, and extruded from a T-die. Thereafter, this extruded product is taken off at a chill roll temperature of 10 to 50°C and a take-up speed of 10 m/min or more and less than 30 m/min to obtain a resin film with a thickness of 8 to 55 μm.

When impregnating carbon fibers with a resin film using the film stacking method, preliminary impregnation is performed at a temperature near the melting point and glass transition point of the resin film, and then main impregnation is performed. For example, phenoxy resin has a glass transition point of 105°C, and is pre-impregnated at 100°C, which is close to that temperature. If the temperature exceeds 100°C, the resin film will break, and if the temperature is lower than that, the preliminary impregnation will be insufficient. If heat shrinkage (neck-in) occurs in the TD (width direction) of the resin film at 100°C, the carbon fibers will move toward the center of the thermoplastic carbon fiber prepreg, which may cause variations in physical properties within the plane. . Therefore, dimensional stability of the resin film is required. The dimensional stability of the resin film is evaluated, for example, by heating it for 2 minutes in an oven with an internal temperature of 100° C. and measuring the heat shrinkage rate.

The heat shrinkage rate in the TD (width direction) of the resin film is preferably at least less than 7%, more preferably less than 5%, and even more preferably less than 3%. If the heat shrinkage rate in the TD (width direction) is less than 7%, heat shrinkage (neck-in) will not occur in the TD (width direction) of the resin film, and the carbon fibers will be closer to the center of the thermoplastic carbon fiber prepreg. There is no.

The MD (machine direction) heat shrinkage rate of the resin film is preferably less than 15%, more preferably less than 10%. Further, the difference in heat shrinkage rate in TD (width direction) with respect to heat shrinkage rate in MD (machine direction) of the resin film is preferably less than 10%, more preferably less than 6%.

If the MD (machine direction) heat shrinkage rate is less than 15%, and the difference in the TD (width direction) heat shrinkage rate from the MD (machine direction) heat shrinkage rate is less than 10%, the thickness of the thermoplastic carbon fiber prepreg This eliminates molding defects when thermoplastic carbon fiber reinforced plastics are molded by laminating thermoplastic carbon fiber prepregs. In addition, the yield during the production of thermoplastic carbon fiber prepreg is improved, increasing production efficiency.

When impregnating carbon fibers with a resin film using the film stacking method, if the tear strength of the resin film is low, the resin film may break during the impregnation process. For this reason, impregnating workability of the resin film is required. The impregnation workability of the resin film is evaluated by measuring the tear strength.

The tear strength of the resin film in TD (width direction) according to JIS K7128 (Tear strength testing method for plastic films and sheets) is preferably at least 28 mN or more, more preferably 50 mN or more.

When the tear strength of the resin film in the TD (width direction) is 28 mN or more, the resin film does not break during the impregnation step of impregnating carbon fibers with the resin film using the film stacking method.

If the resin film is thick, the fiber content of the thermoplastic carbon fiber prepreg will decrease, making it impossible to obtain the necessary strength when made into carbon fiber reinforced plastic. Therefore, the fiber content of the thermoplastic carbon fiber prepreg is evaluated by measuring the thickness of the resin film.

The thickness of the resin film is preferably at least 8 μm or more and 55 μm or less, more preferably 10 μm or more and 30 μm or less. When the thickness of the resin film is 8 μm or more, the diameter of the carbon fiber is 5 to 10 μm, so when thermoplastic carbon fiber prepreg is manufactured, the carbon fiber can be sufficiently impregnated with the resin constituting the resin film, and the carbon Resin shortages such as voids between fibers do not occur. When the thickness of the resin film is 55 μm or less, the carbon fiber content (Vf value) when producing a thermoplastic carbon fiber prepreg will be 50 to 60%, and the strength will be high.

(Thermoplastic carbon fiber prepreg)
The thermoplastic carbon fiber prepreg of the present invention can be obtained, for example, by feeding carbon fibers into an opening/impregnating machine and sandwiching the fibers between the resin films of the present invention to impregnate the carbon fibers with resin.

By using the resin film of the present invention as a matrix resin, the thickness of the resin film is thin in the range of 8 μm or more and 55 μm or less, so it is possible to increase the carbon fiber content (Vf value) of the thermoplastic carbon fiber prepreg and improve the strength. Highly thermoplastic carbon fiber prepreg can be achieved.

In addition, since the heat shrinkage rate in the TD (width direction) of the resin film of the present invention is less than 7%, when producing a thermoplastic carbon fiber prepreg, the resin film will undergo a large heat shrinkage and the carbon fibers will move closer to the center. It is possible to suppress variations in the physical properties of the thermoplastic carbon fiber prepreg in the width direction, and to realize a thermoplastic carbon fiber prepreg with uniform properties in the plane. Then, the yield during production of thermoplastic carbon fiber prepreg can be improved, and the cost of thermoplastic carbon fiber prepreg can be reduced.

Furthermore, by setting the TD (width direction) tear strength of the resin film of the present invention to 28 mN or more, breakage of the resin film is suppressed during the production of thermoplastic carbon fiber prepreg, and production is improved, which is an advantage of production by the film stacking method. Taking advantage of the high speed, thermoplastic carbon fiber prepreg can be manufactured stably and with high productivity.

(Method for manufacturing thermoplastic carbon fiber prepreg)
FIG. 1 is a schematic diagram showing a method for manufacturing a thermoplastic carbon fiber prepreg of the present invention.
In the method for manufacturing thermoplastic carbon fiber prepreg of the present invention, a sheet-like carbon fiber CS is fed out toward a plate heater 12 by a supply roller pair 11 of a fiber opening/impregnation machine 10, and one side of this carbon fiber CS and other The resin films RF1 and RF2 of the present invention are respectively superimposed on the surfaces. This laminate is then held between the first pair of rollers 13 and the second pair of rollers 14 and passed through the plate heater 12 . As a result, the resin films RF1 and RF2 of the laminate are softened and impregnated into the carbon fibers CS. Thereby, the thermoplastic carbon fiber prepreg P of the present invention can be obtained.

Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.
Resin films of Examples of the present invention and conventional comparative examples were verified.
(Examples 1 to 6)
Phenoxy resin was made into a resin film using the inflation method. Specifically, the molten resin is extruded from a ring die and formed into a continuous tube shape, and compressed air is sent in from the inside to gradually expand the film to a predetermined width, which is then pulled between the nip rolls of a take-off machine and taken off to a thickness of 10 μm. A resin film of ~50 μm was obtained. The film is formed to the target thickness while the resin temperature at the ring die exit is 60°C or more higher than the glass transition temperature, and then the compressed air volume and take-up speed are adjusted so that the film is slowly cooled while maintaining its shape. did. The volume of compressed air was adjusted so that the blow ratio (resin film diameter/ring die diameter) was 1.5 to 6.0, and the take-up speed was in the range of 12 to 20 m/min. Then, the obtained resin film and carbon fiber tow are supplied to a fiber opening/impregnation machine 10 as shown in FIG. Got prepreg.

(Comparative Examples 1 to 3)
Resin films were molded in the same manner as Examples 1 to 6, but Comparative Example 1 had a thickness of 5 μm, and Comparative Example 3 had a thickness of 60 μm. Moreover, in Comparative Example 2, the tear strength in TD (width direction) is 25.4 mN, which is less than 28 mN. In addition, in Comparative Example 1, the thickness was too thin (5 μm) and a resin film could not be formed.
Table 1 shows the conditions and evaluation results of Examples and Comparative Examples.

"Evaluation method"
(1) Heat shrinkage rate The heat shrinkage rate in TD (width direction) is the heat shrinkage rate in TD (width direction) of a resin film of 50 mm in TD (width direction) x 100 mm in MD (machine direction) when both ends of MD (machine direction) are measured along TD (width direction). The resin was fixed on a 0.3 mm thick SUS plate with aluminum tape, placed in an oven (manufactured by ESPEC, model: PHH-201M), and kept at 100°C for 2 minutes with the damper opening 50%. The length (mm) of the most shrunk portion in the TD (width direction) of the film was measured, and the shrinkage rate in the TD (width direction) was calculated from the ratio to 50 mm. The number of tests was 10 times.

The heat shrinkage rate in MD (machine direction) is the TD of a resin film of 50 mm MD (machine direction) x 100 mm TD (width direction) when fixing the resin film on a 0.3 mm thick SUS plate with aluminum tape. (width direction) along the MD (machine direction), measure the length (mm) of the most contracted part in MD (machine direction) of the resin film, and calculate the ratio to 50 mm in MD (machine direction). ) was measured in the same manner as the heat shrinkage rate in the TD (width direction), except that the shrinkage rate in the TD (width direction) was calculated.

(1-1) Evaluation of MD: 15% or more was rated as ×, 10% or more and less than 15% was rated as ○, and less than 10% was rated as ◎.
(1-2) Evaluation of TD: 7% or more was marked as ×, 3% or more and less than 7% was marked as ○, and less than 3% was marked as ◎. Note that because there are problems such as neck-in during impregnation, the TD heat shrinkage rate is set as a higher evaluation standard than the MD heat shrinkage rate.
(1-3) Evaluation of |MD-TD|: 10% or more is ×, 6% or more and less than 10% is ○, and less than 6% is ◎.
(1-4) Evaluation of dimensional stability: As a comprehensive evaluation of the evaluations (1-1) to (1-3), it was evaluated as good ◎, fair ○, and poor ×.

(2) Tear strength The MD and TD tear strengths of the obtained resin film were measured in accordance with JIS K7128 (Tear strength test method for plastic films and sheets).
(2-1) Evaluation of impregnation workability: TD tear strength of less than 28 mN was evaluated as ×, 28 mN or more and less than 50 mN was evaluated as ○, and 50 mN or more was evaluated as ◎.

(3) Thickness The thickness of the resin film was measured.
(3-1) Evaluation of fiber content: The thickness of the resin film was evaluated as × if it was thicker than 50 μm, ○ if it was 25 μm or more and 50 μm or less, and ◎ if it was less than 25 μm.

10...Fiber opening/impregnation machine 11...Supply roller pair 12...Plate heater 13...First roller pair 14...Second roller pair

Claims (4)

A resin film for forming a thermoplastic carbon fiber prepreg by a film stacking method,
The thickness is 8 μm or more and 55 μm or less, the tear strength in the width direction according to JIS 7128 is 28 mN or more, and the heat shrinkage rate in the width direction is less than 7%,
The resin film is characterized in that the resin film contains phenoxy resin . The resin film according to claim 1, wherein the difference in heat shrinkage rate in the width direction with respect to heat shrinkage rate in the machine direction is less than 10%. A thermoplastic carbon fiber prepreg characterized in that carbon fibers are impregnated with the resin film according to claim 1 or 2 . A method for producing a thermoplastic carbon fiber prepreg, comprising the step of impregnating carbon fibers with the resin film according to claim 1 or 2 .

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