PREPREG, PREPARATION METHOD THEREOF AND FIBER REINFORCED COMPOSITE MATERIAL PREPARED THEREFROM

Abstract

The present disclosure relates to a prepreg, a preparation method thereof and a fiber-reinforced composite material prepared therefrom. The preparation method of a prepreg may include an aramid fiber base material with improved wettability to resin, can increase a thickness reduction rate during molding of the prepreg, has an appropriate resin content, and can provide a prepreg suitable for molding by an out-of-autoclave process. In addition, the prepreg may provide a fiber-reinforced composite material that exhibits a thin thickness and a high resin content even by an out-of-autoclave process, and shows high strength and low moisture absorption

Claims

1. A preparation method of a prepreg, comprising: a first laminating step of laminating a resin film on an aramid fiber base material and applying a pressure; and a second laminating step of applying a pressure to a laminate obtained from the first laminating step, wherein a lower pressure is applied at a lower temperature in the second laminating step than in the first laminating step.

2. The preparation method of a prepreg of claim 1, wherein the first laminating step is performed at a temperature of 80° C. to 90° C.

3. The preparation method of a prepreg of claim 1, wherein the first laminating step is to laminate a resin film on an aramid fiber base material and apply a pressure of 2.6 to 5 bar.

4. The preparation method of a prepreg of claim 1, wherein the second laminating step is performed at a temperature of 70° C. to 79° C.

5. The preparation method of a prepreg of claim 1, wherein the second laminating step is to apply a pressure of 1.5 to 2.5 bar to a laminate obtained from the first laminating step.

6. The preparation method of a prepreg of claim 1, wherein the first laminating step is to continuously supply the aramid fiber base material and the resin film at a feed rate of 0.1 to 1.5 m/min so that the resin film is laminated on both sides of the aramid fiber base material.

7. The preparation method of a prepreg of claim 1, wherein the aramid fiber base material is woven with aramid fibers of 1500 to 3500 deniers.

8. The preparation method of a prepreg of claim 1, wherein the resin film is cured at 90° C. to 130° C.

9. The preparation method of a prepreg of claim 1, wherein the resin film has an absolute viscosity of 5 to 10 Pa.Math.s at 70° C.

10. The preparation method of a prepreg of claim 1, wherein the resin film is formed from a thermosetting resin composition comprising an epoxy resin and a curing agent.

11. The preparation method of a prepreg of claim 10, wherein the epoxy resin comprises at least one selected from the group consisting of bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin, tetrabromobisphenol A diglycidyl ether, epoxy resin having a biphenyl skeleton, epoxy resin having a naphthalene skeleton, epoxy resin having a dicyclopentadiene skeleton, phenol novolac type epoxy resin, cresol novolac type epoxy resin, diaminodiphenylmethane type epoxy resin, diaminodiphenylsulfone type epoxy resin, aminophenol type epoxy resin, metaxylene diamine type epoxy resin, 1,3-bisaminomethyl cyclohexane type epoxy resin and isocyanurate type epoxy resin.

12. A prepreg prepared from the preparation method of a prepreg of claim 1.

13. The prepreg of claim 12, which has a resin content of 35 to 45 wt %.

14. A fiber-reinforced composite material, comprising an aramid fiber base material and a resin cured in a state of being impregnated in the aramid fiber base material, wherein a flexural strength measured according to ASTM D790 is 250 to 400 M Pa.

15. The fiber-reinforced composite material of claim 14, wherein a moisture absorption rate calculated by the following Equation 1 is 0 to 3 wt %:
Moisture absorption rate=Weight of sample after immersion−Weight of sample before immersion)/Weight of sample before immersion*100   [Equation 1] in the Equation 1, the weight of a sample before immersion is a weight before immersing the sample in distilled water, and the weight of a sample after immersion is a weight of the sample measured after being completely immersed in distilled water and taken out, wherein the weight is a value measured after primarily removing moisture from upper and lower portions and an edge of the sample with towel and secondarily removing moisture from the upper and lower portions with dry towel.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] Hereinafter, the function and effect of the present invention will be described in more detail with specific examples. However, these examples are for illustrative purposes only, and the invention is not intended to be limited by these examples.

EXAMPLE 1

Preparation of Prepreq

[0051] A plain-woven aramid fabric was woven using aramid yarn having about 3000 denier as warp and weft yarns.

[0052] Meanwhile, an epoxy resin film prepared by applying an epoxy resin composition available as SCP-510 from EZ Composite to a release paper in an application amount of about 80±10 g/m.sup.2, followed by drying was used as the resin film.

[0053] While continuously supplying the aramid fabric, the epoxy resin film was continuously supplied so as to come into a contact with both sides of the aramid fabric. A feed rate of the aramid fabric and the resin film was controlled to about 0.5 m/min.

[0054] Then, a first laminating step was performed by applying a pressure of 3 bar to a resin film laminated on both sides of the aramid fabric with a pressure roller heated to 85° C. After that, a prepreg was prepared by impregnating the resin film in both sides of the aramid fabric through a second laminating step of applying a pressure of 2 bar to a laminate obtained in the first laminating step with a pressure roller heated again to 70° C.

COMPARATIVE EXAMPLE 1

Preparation of Prepreq

[0055] A prepreg was prepared in the same manner as in Example 1, except for performing a first laminating step of applying a pressure to the resin film laminated on both sides of the aramid fabric with a pressure roller heated to 85° C.; a second laminating step of applying a pressure to the resin film laminated on both sides of the aramid fabric with a pressure roller heated to 70° C.; and a third laminating step of applying a pressure to the resin film laminated on both sides of the aramid fabric with a pressure roller heated to 100° C. instead of the first and second laminating steps.

[0056] 10

[0057] Test Examples: Evaluation of Physical Properties of Prepreq

[0058] The physical properties of the prepregs prepared in Examples and Comparative Examples were evaluated by the method described below, and the results thereof are shown in table 1.

[0059] 1) Resin Content before Molding

[0060] A percentage of mass per unit of a resin film to mass per unit of a prepreg ((Mass per unit of prepreg−Mass per unit of aramid fabric)/Mass per unit of prepreg*100) was measured and defined as a resin content (unit: wt %).

[0061] 2) Thickness after Molding, Rate of Change in Thickness and Resin Content

[0062] Four prepregs were laminated in four layers and then sufficiently compressed with a roller. Then, the laminate was placed on a release-treated flat mold, and a release film was laminated. And, a breather serving as an air flow path inside a vacuum bag was laminated on the release film with or without the lamination of a caul plate (steel) having the same size as that of the prepreg having a thickness of 2 mm, and finally wrapped with the vacuum bag, followed by sealing with sealant. Then, a fiber-reinforced composite material was prepared by curing the prepreg while maintaining at 125° C. for 30 minutes under a vacuum pressure of 28 inchHg.

[0063] A thickness, a rate of change in thickness, and a resin content were measured, respectively for the fiber-reinforced composite material prepared by using the caul plate and the fiber-reinforced composite material prepared without the caul plate.

[0064] The thickness was measured by measuring a thickness at eight points of total four corners with two points for each corner of a sample, and then obtaining an average value thereof, the rate of change in thickness was calculated from a percentage of difference in thickness before and after molding to a thickness before molding (Difference in thickness before and after molding/Thickness before molding*100), and the resin content was measured by the method described above.

[0065] 3) Flexural Strength

[0066] A flexural strength of the fiber-reinforced composite material prepared by using the caul plate and the fiber-reinforced composite material prepared without the caul plate was measured with a universal tensile tester at a temperature of 23±2° C. according to ASTM D790.

[0067] 4) Moisture Absorption Rate

[0068] A moisture absorption rate of the fiber-reinforced composite material prepared by using the caul plate and the fiber-reinforced composite material prepared without the caul plate was measured by completely immersing a sample in distilled water. Then, the moisture absorption rate was calculated by substituting a weight before immersion and a weight after immersion in the following Equation 1.

Moisture absorption rate (wt %)=(Weight of sample after immersion−Weight of sample before immersion)/Weight of sample before immersion *100   [Equation 1]

[0069] At this time, the weight before and after immersion was measured after primarily removing moisture from upper and lower portions and an edge of the sample with towel (five sheets of Kimwipes, dry fabric, etc.) and secondarily removing moisture from the upper and lower portions again with dry towel to completely remove the moisture visually.

TABLE-US-00001 TABLE 1 Comparative Example 1 Example 1 Resin content before molding 39.78 wt % 40.44 wt % Caul Plate Thickness 2.49 mm 2.49 mm unused Rate of change in 2.46% Unmeasured thickness Resin content after 37.71 wt % 38.85 wt % molding Flexural strength 321.31 MPa 232.54 MPa Moisture absorption 1.637 wt % 3.461 wt % rate Caul Plate Thickness 2.37 mm 2.32 mm used Rate of change in 13.10%  2.52% thickness Resin content after 37.22 wt % 36.48 wt % molding Flexural strength 308.86 MPa 199.01 MPa Moisture absorption 1.581 wt % 4.102 wt % rate