CA2085441C - Fiber reinforced thermoplastic resin shaped article and its preparation - Google Patents

Abstract

The present invention is directed to a fiber reinforced thermoplastic resin shaped article prepared by supplying a preheated fiber reinforced thermoplastic resin sheet between upper and lower molds, positioning the upper and lower molds so that clearance between the upper and lower molds when the mold clamping is completed is larger than the thickness of the unpreheated fiber reinforced thermoplastic resin sheet. A
molten thermoplastic resin is supplied in a recess provided in at least one of the upper and lower molds through a resin passage provided in the mold so that a portion formed from the molten thermoplastic resin in the recess is integrated by fusion with a portion formed from the fiber reinforced thermoplastic resin sheet. The article is light-weight and also has a rib, a boss or any other projection.

Description

Fiber Reinforced Thermoplastic Resin Shaped Article and its Preparation The present invention relates to a fiber reinforced thermoplastic resin shaped article and a method for preparing said article. The article of the present invention has excellent strength reinforced by fibers and is light weight.
It can be prepared with a rib, a boss or any other projection and is suitably utilized as a vehicle part or the like.
One of the known methods for preparing a fiber reinforced resin shaped article comprises heating and pressing a fiber reinforced thermoplastic resin sheet to prepare a product.
Depending on the type of reinforcing fiber, this method is classified into two types. One of them comprises mixing monofilaments each having a medium fiber length of from several millimetres to 100 mm with thermoplastic resin powder under wet or dry conditions, forming a fiber reinforced thermoplastic resin sheet using a heating roll press, preheating the sheet and then pressing the sheet to obtain a fiber reinforced thermoplastic resin shaped article (cf., for example, US Patent No. 4,645,565 corresponding to Japanese Patent Kokai Publication No. 28135/1982). The other comprises extruding a molten thermoplastic resin on a mat consisting of long fibers, laminating them, forming a fiber reinforced thermoplastic resin sheet with rollers, and. preheating and pressing the sheet to obtain a fiber reinforced thermoplastic resin shaped article.
When the fiber- reinforced thermoplastic resin sheet is preheated to press it, the sheet expands in the thickness direction. The shE_et is supplied between upper and lower molds, clamp clearance is set at a distance greater than the thickness of the unheated reinforced thermoplastic resin sheet. The sheet is pressurized and cooled to obtain a shaped article having a larger thickness than that of the unheated fiber reinforced thermoplastic resin sheet, namely a shaped article having a larger volume than that of the unheated fiber reinforced thermoplastic resin sheet. Hereinafter, this is referred to as "expansion shaping". US Patent No. 4,670,331 (corresponding to Japanese Patent Kokai Publication No.
179234/1985) discloses a method comprising conducting the expansion shaping in this way to obtain a fiber reinforced thermoplastic resin shaped article having a large volume, and thus being light in weight.
In the expansion shaping, a flat sheet made of a fiber reinforced thermoplastic resin is preheated, and supplied and pressurized between upper and lower molds to form a sheet having a larger thickness than that of the original unpreheated fiber reinforced thermoplastic resin sheet.
Accordingly, even if a recess is provided in the mold to give a rib, a boss or some other projection to the sheet, the preheated fiber reinforced thermoplastic resin sheet is merely pressurized mainly in the sheet thickness direction between the molds, and the sheet does not flow along a mold surface so that the recess is never or insufficiently filled with the fiber reinforced thermoplastic resin sheet. Accordingly, it is difficult to mold a fiber reinforced thermoplastic resin shaped article having a rib, a boss or some other projection.
An object of the present invention is the development of a shaped article having a rib, a boss or other projection by the expansion shaping of a fiber reinforced thermoplastic resin sheet.
The present invention provides a method for preparing a fiber reinforced thermoplastic resin shaped article comprising the steps of preheating a fiber reinforced thermoplastic resin sheet to expand it in the thickness direction, supplying the expanded sheet between a first mold and a second mold, and then pressurizing and cooling the sheet under the condition that clearance between the first mold and the second mold when mold clamping is completed is larger than the thickness of the original unheated fiber reinforced thermoplastic resin sheet, characterized in that a molten thermoplastic resin is supplied in a recess provided in at least one of the first and second molds through a resin passage provided in the mold so that a portion formed from the molten thermoplastic resin in the recess is integrated by fusion with a portion formed from the fiber reinforced thermoplastic resin sheet.
The method according to the present invention produces a fiber reinforced thermoplastic resin shaped article having a rib, a boss or other projection attached thereto with sufficient bonding ;strength. The shaped article is light weight resulting from the expansion shaping.
In drawings that illustrate preferred embodiments of the present invention:
Figs. 1 and 2 are cross-sectional views of a mold assembly used according to the present invention, showing different operative positions, respectively, and Fig. 3 is a cross-sectional view of a modified form of the mold assembly uaed according to the present invention.
Specific examples of the reinforcing fiber used in the fiber reinforced th~armoplastic resin sheet include inorganic fibers, for example, glass fibers, carbon fibers, and metal (e. g. stainless steal) fibers; organic fibers, for example, aramid fibers and; mixtures of inorganic and organic fibers.
In particular, glass fibers are economical and give a high reinforcing effect. The diameter of the fiber is usually from 1 to 50 Vim, preferalbly from 3 to 25 ~,m. The length of the fiber is usually at least 5 mm, preferably from 5 to 50 mm from the viewpoint of the reinforcing effect.
The matrix resin reinforced by the fiber in the fiber reinforced thermoplastic resin sheet may be any one of the thermoplastic resins usually used in extrusion molding, injection molding, press molding or the like. Specific examples of the matrix resin are polyethylene, polypropylene, polystyrene, acrylonitrile/styrene/butadiene terpolymer, polyvinyl chloride, polyamide, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, styrene/acrylonitri:le copolymer, mixtures thereof, and a polymer alloy containing them.
The fiber reinforced thermoplastic resin sheet may be a sheet formed by a paper making method from fibers each having a medium length and thermoplastic resin powder under wet or y dry conditions, or a sheet formed by laminating and impregnating a lone fiber mat with a molten thermoplastic resin through heating rollers.
The molten thE~rmoplastic resin, which is supplied in the recess of the mold through the resin passage provided in the mold so as to form the rib, the boss or other projection on the shaped article,, may be a thermoplastic resin having good thermal fusion to i:he matrix resin of the fiber reinforced thermoplastic resin sheet. The molten thermoplastic resin may be the same as or analogous to the matrix resin. The molten thermoplastic resin may contain fibers.
Hereinafter, i~he present invention will be described in detail by making reference to the attached drawings.
Fig. 1 is a cross-sectional view of a mold assembly used according to the present invention. An upper mold 1 is attached to an uppE~r platen of a pressing machine which moves up and down. The ;shaping surface of the upper mold is represented by 2 and the vertical internal surface of the upper mold is reprE~sented by 3. A lower mald 4 is attached to a fixed lower platE~n of the pressing machine. The shaping surface of the lower mold is represented by 5. The vertical internal surface 3 of the upper mold slides on a vertical external surface 6 of the lower mold. A recess for forming a rib is represented by 7 and a recess for forming a boss is represented by 8. A resin passage is represented by 9 and a resin feed outlet .is represented by 10. An end 11 of the resin passage is connected with a resin supplying apparatus (not shown) to supply a molten thermoplastic resin in a desired amount and pressure. A stopper is represented by 12 and a preheated fiber reinforced thermoplastic resin sheet is represented by 13.
The fiber reinforced thermoplastic resin sheet is preheated in an oven or the like at a temperature at which it is easy to handle i~he resin sheet for positioning it on the lower mold and it .is easy to mold the resin sheet without thermal degradation. Then, the resin sheet is positioned on the lower mold.
F

A suitable preheating temperature depends on the fiber reinforced thermop7_astic resin sheet. The preheating temperature is higher by about 10 to 100°C, preferably from 20 to 60°C, than the melting point of the matrix resin. For example, the fiber reinforced thermoplastic resin sheet is preheated at a temperature of from 200 to 250°C, when the reinforcing fiber is a glass fiber and the matrix resin is polypropylene. When the preheating temperature is lower than the above lower limit, the expansion is insufficient. When it is higher than the above upper limit, the fiber, reinforced thermoplastic resin sheet is thermally degraded and handling is difficult.
For example, when a glass fiber reinforced polypropylene sheet of 2 mm in thickness is heated at 200 to 250°C, the sheet expands to a thickness of 6 mm. Then, when the sheet is compressed into a :shaped article having a thickness of 4 mm, the shaped article is obtained in an expansion coefficient (the thickness of t:he shaped article/the thickness of the original unpreheate:d fiber reinforced thermoplastic resin sheet) of 2.0 (4 mm/2 mm).
As shown in Fig. 1, the preheated fiber reinforced thermoplastic resin sheet is positioned on the shaping surface 5 of the lower mold and then the upper mold 1 is moved downward. Since the internal surface 3 of the upper mold slides on the external surface 6 of the lower mold so that the upper and lower molds are closed together, the softened fiber reinforced thermoplastic resin sheet does not flow out of the molds. When the upper mold 1 is further moved downward, the lowest end of the upper mold 1 abuts against the stopper 12 so that the downward movement of the upper mold 1 is terminated (cf. Fig. 2). During the closure of the molds, the fiber reinforced thermopl~~astic resin sheet 13 is compressed between the shaping surfacs- 2 of the upper mold and the shaping surface 5 of the lower mold. In Fig. 2, the height of the stopper 12 is selecaed so that clearance between the shaping surface 2 of the upper mold and the shaping surface 5 of the lower mold is large=r than the thickness of the original f preheated fiber reinforced thermoplastic resin sheet.
Temperatures of the upper and lower molds are the same or different and are usually from 10 to 120°C, preferably from 30 to 100°C. The temperature of the molten thermoplastic resin fed in the mold is higher by usually from 20 to 150°C, preferably from 30 to 100°C than the melting point of the molten thermoplastic resin.
At the time of or before or after the upper mold 1 reaches the lowest position shown in Fig. 2, a desired amount of the molten thermoplastic resin is supplied from the resin feed outlet 10 through the resin passage 9 and fills in the recesses 7 and 8 of the lower mold to form the rib and boss.
The rib and the boss of the shaped article are formed and integrated by fusion with a portion formed from the fiber reinforced thermoplastic resin sheet. The molten thermoplastic resin is supplied preferably after the upper mold 1 reaches the lowest position. This provides an article having good appearance and shape. For sufficient fusion, preferably, the thermoplastic resin supplied from the resin feed outlet 10 is analogous to and has high thermal fusion bonding strength to the matrix resin of the fiber reinforced thermoplastic resin sheet. Since the preheating temperature of the fiber reinforced thermoplastic resin sheet is limited from the viewpoint ~of the degradation and handling, the thermoplastic resin preferably has a higher temperature than that of the fiber reinforced thermoplastic resin sheet. It is advantageous to enlarge openings 16 of the recesses 7 and 8 of the mold to form the rib, the boss and the like, as shown in Fig. 3.
When the recess 7 has a volume remarkably different from that of the recess .B, a regulator mechanism may be employed to control the cross-section area of each resin feed outlet 10 to regulate the amount of the resin supplied into each recess.
The regulator mechanism may be of a type capable of selectively opening and closing each resin feed outlet 10 to adjust the length of time over which the resin is supplied.
With this regulator mechanism, the filling of the resin into each recess can be advantageously improved.
A skin material may be laminated on the fiber reinforced thermoplastic resin sheet in the mold assembly.
The present invention will be illustrated by the following Examples which should not be construed to limit the present invention.
Example 1 A fiber reinforced thermoplastic resin sheet of 2.0 mm in thickness (manufaci~ured by K-PLASHEET Corp., Japan) prepared by a paper making method under a wet condition was used.
Glass fibers (30% by weight) of 12-13 mm in an average length were used as the reinforcing fibers and polypropylene was used as the matrix resin. The fiber reinforced thermoplastic resin sheet was preheated at 210°C in an oven and then immediately positioned on the :shaping surface of the lower mold as shown in Fig. 1. The upper mold was moved downward. Then, compression was commenced and simultaneously a molten thermoplastic resin was supplied in recesses of the lower mold from the resin feed outlet through the resin passage.
Polypropylene (SUM:CTOMO NOBLEN* AX 568 manufactured by Sumitomo Chemical Company, Ltd., Melt index: 65) was used as the molten thermop_Lastic resin and was supplied at 240°C.
The molding was conducted under the following conditions:
the surfaces 2 and 5 of the upper and lower molds were at temperatures of 60"C and 50°C, respectively, pressing pressure (horizontal projeci~ion plane) was 40 kg/cm2 and the height of the stopper 12 was adjusted to give a shaped article of 3.0 mm in thickness at thEa sheet portion thereof excluding the rib and boss. A fiber reinforced thermoplastic resin shaped article having an expansion coefficient of 1.5, to which the rib and boss were i:ully fused, was obtained.
Example 2 The same procedure as in Example 1 was repeated except that a sheet having a glass fiber content of 40% by weight and a thickness of 3.0 mm which was prepared by impregnating a * Trademark _$_ glass long fiber mat with molten polypropylene was used as the fiber reinforced thermoplastic resin sheet, and the height of the stopper was adjusted to give a shaped article of 5.0 mm in thickness at the sheet portion thereof excluding the rib and boss. A fiber reinforced thermoplastic resin shaped article having an expansion coefficient of 1.7, to which the rib and boss were fully fused, was obtained.

Claims (5)

1. A method for preparing a fiber reinforced thermoplastic resin shaped article comprising the steps of preheating a fiber reinforced thermoplastic resin sheet to expand it in the thickness direction, supplying the expanded sheet between the first mold and the second mold, and then pressurizing and cooling the sheet under the condition that clearance between the first mold and the second mold when mold clamping was completed is larger than the thickness of the original unheated fiber reinforced thermoplastic resin sheet, characterized in that a molten thermoplastic resin is supplied in a recess provided in at least one of the first and second molds through a resin passage provided in the mold so that a portion formed from the molten thermoplastic resin in the recess is integrated by fusion with a portion formed from the fiber reinforced thermoplastic resin sheet.

2. The method according to claim 1, wherein the preheating temperature is higher by about 10 to 100°C than the melting point of the resin of the fiber reinforced thermoplastic resin sheet.

3. The method according to claim 1, wherein the recess of one of the first and second molds is outwardly flared to open toward the other mold.

4. The method according to claim 1, wherein an opening/closing mechanism is provided at a resin feed outlet of the resin passage.

5. A fiber reinforced thermoplastic resin shaped article prepared by the method according to claim 1.