Method for preparing thermoplastic prepreg and thermoplastic prepreg prepared thereby

Abstract

A method for preparing a high quality thermoplastic prepreg, includes: laminating a thermoplastic resin film having a crystallization degree in a range of 1 to 20% on at least one surface of a matrix fiber; and heating the laminate to a higher temperature than a melting point of the film, then, pressing the same. The method uniformly impregnates a matrix fiber with a thermoplastic resin, has a short curing cycle in the formation, and involves no random modification in alignment of fibers in the matrix fiber due to a low crystallization degree of the impregnated thermoplastic resin, thereby increasing rigidity of a formed product and enabling reduction of thickness. Thus produced prepreg has a low weight variation per unit area.

Claims

1. A method for preparing a thermoplastic prepreg, comprising: laminating a thermoplastic resin film having a crystallization degree in a range of 1 to 20% on at least one surface of a matrix fiber to give a laminate; and heating the laminate to a higher temperature than a melting point of the thermoplastic resin film, then, pressing the heated laminate, wherein the thermoplastic prepreg has a weight variation per unit area of 3-5%, said weight variation per unit area being determined by the following equation (I) or (II):
weight variation per unit area (%)=[(W0W1)/W0]100(I)
weight variation per unit area (%)=[(W1W0)/W0]100(II) wherein W0 is an average weight of 10 samples of the thermoplastic prepreg, and W1 is a weight of the samples which show the greatest difference from the average weight W0.

2. The method according to claim 1, wherein the thermoplastic resin film has a crystallization degree of 3 to 12%.

3. The method according to claim 1, wherein the thermoplastic resin film has a thickness of 3 to 100 m.

4. The method according to claim 1, wherein the thermoplastic resin film has a thickness of 7 to 65 m.

5. The method according to claim 1, wherein the pressing process is executed by pressing the laminate with a pressure of 10 to 150 kg/cm at a temperature as 30 to 100 C. higher than a melting point of the thermoplastic resin film.

6. The method according to claim 1, wherein a weight ratio of the matrix fiber:the thermoplastic resin film is adjusted to 40-90 wt. %:10-60 wt. %.

7. The method according to claim 1, wherein the thermoplastic resin film is one selected from a group consisting of a polyamide resin film, polypropylene resin film, polyester resin film, thermoplastic polyurethane resin film, polylactide resin film, polyethylene resin film, polybutylene terephthalate resin film, polyphenylene sulfide resin film, Teflon resin film and polyether ether ketone resin film.

8. A thermoplastic prepreg prepared by the method according to claim 1, wherein a matrix fiber is impregnated with a thermoplastic resin, wherein the thermoplastic prepreg has a weight variation per unit area of 3-5%, said weight variation per unit area being determined by the following equation (I) or (II):
weight variation per unit area (%)=[(W0W1)/W0]100(I)
weight variation per unit area (%)=[(W1W0)/W0]100(II) wherein W0 is an average of 10 samples of the thermoplastic prepreg, and W1 is a weight of the samples which show the greatest difference from the average weight W0.

9. The thermoplastic prepreg according to claim 8, wherein a content of thermoplastic resin ranges from 10 to 60% by weight to a total weight of the thermoplastic prepreg.

Description

BEST MODE

(1) Hereinafter, the present invention will be described in details.

(2) The method for preparing a thermoplastic prepreg according to the present invention is characterized by: laminating a thermoplastic resin film having a crystallization degree in a range of 1 to 20% on at least one surface of a matrix fiber; heating the laminate to a temperature higher than a melting point of the thermoplastic resin film, then, pressing the same.

(3) The crystallization degree of the thermoplastic resin film may range from 1 to 20%, and preferably, from 3 to 12%. If the crystallization degree is less than 1%, a discharge rate and a winding rate of the thermoplastic film are substantially not different from each other, hence causing several problems during cooling and winding of the film. If the crystallization degree exceeds 20%, heat shrinkage rapidly occurs in a high crystal drawn part when the thermoplastic resin film is heated, hence causing an occurrence of irregular impregnation phenomenon of the thermoplastic resin into the matrix fiber.

(4) The crystallization degree described above is a value measured by the following procedure.

(5) <Procedure of Measurement of Crystallization Degree of Thermoplastic Resin Film>

(6) 5 mg of thermoplastic resin film was taken as a simple in an aluminum pan and measured using a differential scanning calorimeter. At first, after raising a temperature from room temperature to 260 C. at a rate of 10 C./minute under a nitrogen atmosphere (first run) and maintaining this temperature for 10 minutes, cooling to 20 C. at a rate of 10 C./minute and maintaining this temperature for 5 minutes, and then, raising the temperature again at a rate of 10 C./minute (second run), fusion peaks observed were divided into non-crystalline fusion peaks which existed in a temperature region of melting point (Tm)10 C., and crystalline fusion peaks which were observed in a glass temperature (Tc) region. In this regard, a heat capacity (Hm) at the melting point (Tm) and a heat capacity (Hc) at the glass temperature (Tc) were estimated from an area surrounded by a base line and peaks, with reference to a flat part at a high temperature side, followed by estimating a theoretical heat capacity (Hm, Zero) of 100% crystallized thermoplastic resin film. Thereafter, a degree of crystallization was calculated according to the following Equation.
Degree of crystallization (%)=[HmHc]/Hm, zero100

(7) Hm: Heat capacity at a melting point (Tm)

(8) Hc: Heat capacity at a glass temperature (Tc)

(9) Hm, zero: Theoretical heat capacity of 100% crystallized thermoplastic resin film

(10) The thermoplastic resin film may have a thickness of 3 to 100 m, and preferably, 7 to 65 m. If the thickness exceeds 100 m, the thermoplastic resin film is not uniformly molten at a contact part between the surface of the thermoplastic resin film and the surface of the matrix fiber to cause a difficulty in uniform impregnation of the thermoplastic resin into the matrix fiber. If the thickness is less than 3 m, the thermoplastic resin film may easily tear even by a small amount of external force, hence decreasing process ability.

(11) The present invention preferably includes laminating the thermoplastic resin film on at least one surface of a matrix fiber, heating the laminate to a temperature of 30 to 100 C. higher than a melting point of the thermoplastic resin film to endow flowability, and then, pressing the same at a pressure of 10 to 150 kg/cm.

(12) If the heating temperature and/or pressure are lower than the above ranges, the matrix fiber may not be sufficiently impregnated with the thermoplastic resin. If the pressure is higher than the above range, a part of the matrix fiber is ruptured to deteriorate physical properties of the prepreg, while the temperature is higher than the above range, the thermoplastic resin is oxidized to deteriorate physical properties thereof, thus not being preferable.

(13) It is preferable to adjust a weight ratio of the matrix fiber:the thermoplastic resin film to 40-90% by weight (wt. %):10-60 wt. %, so that process ability is improved and the matrix fiber is uniformly impregnated with the thermoplastic resin.

(14) If the weight ratio of the thermoplastic resin film exceeds 60 wt. %, a thickness of the film is excessively increased and the thermoplastic resin film is not uniformly molten at a contact part between the surface of the thermoplastic resin film and the surface of the matrix fiber, thus causing a difficulty in uniform impregnation of the thermoplastic resin into the matrix fiber. If the weight ratio of the thermoplastic resin film is less than 10 wt. %, the thickness of the film is excessively decreased and the thermoplastic resin film may easily tear even by a small amount of external force, thus decreasing process ability.

(15) The thermoplastic resin film may include, for example, a polyamide resin film, polypropylene resin film, polyester resin film, thermoplastic polyurethane resin film, polylactide resin film, polyethylene resin film, polybutylene terephthalate resin film, polyphenylene sulfide resin film, Teflon resin film, or polyether ether ketone film, or the like.

(16) The thermoplastic prepreg prepared according to the present invention may have a low weight variation per unit area since the thermoplastic resin is uniformly impregnated into the matrix fiber.

(17) In order to determine the weight variation per unit area of the thermoplastic prepreg, 10 samples having the same unit area were taken from the thermoplastic prepreg and subjected to measurement of an average weight (W0) of these 10 samples, then, a weight (W1) of the samples which exhibited the greatest difference from the average weight was substituted for Equation I or II below.
Weight variation per unit area (%)=[(W0W1)/W0]100(I)
Weight variation per unit are (%)=[(W1W0)/W0]100(II)

(18) The thermoplastic prepreg prepared according to the present invention has a structure of the matrix fiber impregnated with the thermoplastic resin, and a content of thermoplastic resin in a range of 10 to 60 wt. % to a total weight of the thermoplastic prepreg.

(19) Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples. However, these examples are only given as preferred embodiments of the present invention and not construed to limit the scope of the present invention to be protected.

EXAMPLE 1

(20) After laminating a polyester resin film having a crystallization degree of 4% and a thickness of 10 m on an upper surface of a carbon fiber fabric (matrix fiber), the laminate was heated until a temperature of the polyester resin film reached 300 C., followed by pressing the same at a pressure of 20 kg/cm, thereby preparing a thermoplastic prepreg.

(21) Herein, a weight ratio of the carbon fiber fabric:polyester resin film was adjusted to 85 wt. %:15 wt. %.

(22) The prepared thermoplastic prepreg had a weight variation per unit area of 3%, and this demonstrated that the polyester resin was uniformly impregnated into the carbon fiber fabric.

(23) Further, an interlayer adhesiveness between the carbon fiber fabrics (matrix fibers) included in the prepared thermoplastic prepreg was excellent as high as 55.5 MPa.

EXAMPLE 2

(24) After laminating a polyethylene resin film having a crystallization degree of 8% and a thickness of 50 m on an upper surface of an aramid fabric (matrix fiber), the laminate was heated until a temperature of the polyethylene resin film reached 200 C., followed by heating and pressing the same at a pressure of 80 kg/cm, thereby preparing a thermoplastic prepreg.

(25) Herein, a weight ratio of the aramid fabric:polyethylene resin film was adjusted to 70 wt. %:30 wt. %.

(26) The prepared thermoplastic prepreg had a weight variation per unit area of 3%, this demonstrated that the polyethylene resin was uniformly impregnated into the aramid fabric.

(27) Further, an interlayer adhesiveness between the aramid fabrics (matrix fibers) included in the prepared thermoplastic prepreg was excellent as high as 62.8 MPa.

EXAMPLE 3

(28) After laminating a polyamide 6 resin film having a crystallization degree of 19% and a thickness of 90 m on an upper surface of a carbon fiber non-woven fabric (matrix fiber), the laminate was heated until a temperature of the polyamide 6 resin film reached 260 C., followed by pressing the same at a pressure of 130 kg/cm, thereby preparing a thermoplastic prepreg.

(29) Herein, a weight ratio of the carbon fiber non-woven fabric:polyamide 6 resin film was adjusted to 45 wt. %:55 wt. %.

(30) The prepared thermoplastic prepreg had a weight variation per unit area of 5%, this demonstrated that the polyamide 6 resin was uniformly impregnated into the carbon fiber non-woven fabric.

(31) Further, an interlayer adhesiveness between the carbon fiber non-woven fabrics (matrix fibers) included in the prepared thermoplastic prepreg was excellent as high as 50.4 MPa.

COMPARATIVE EXAMPLE 1

(32) After laminating a polyester resin film having a crystallization degree of 30% and a thickness of 10 m on an upper surface of a carbon fiber fabric (matrix fiber), the laminate was heated until a temperature of the polyester resin film reached 320 C., followed by pressing the same at a pressure of 20 kg/cm, thereby preparing a thermoplastic prepreg.

(33) Herein, a weight ratio of the carbon fiber fabric:polyester resin film was adjusted to 30 wt. %:70 wt. %. The prepared thermoplastic prepreg had a weight variation per unit area of 18%, and this demonstrated that the polyester resin was non-uniformly impregnated into the carbon fiber fabric.

(34) Further, an interlayer adhesiveness between the carbon fiber fabrics (matrix fibers) included in the prepared thermoplastic prepreg was reduced as low as 35.8 MPa.

INDUSTRIAL APPLICABILITY

(35) The thermoplastic prepreg prepared by the present invention may be applied to materials for helmets or materials for automobile parts, which are composed of fiber-reinforced composite materials.