JPH05200765A - Molding method of fiber-reinforced thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To manufacture efficiently a molded product whose plate thickness is thick by expansion molding of a fiber-reinforced thermoplastic sheet, by a method wherein air is circulated forcibly within an expanded sheet in a mold in a method of obtaining the molded product in a fixed form by compression- molding an expanded sheet into lower density than theroretical density. CONSTITUTION:A fiber-reinforced thermoplastic resin sheet 1 whose resin is expanded by causing the resin to be softened and melted by heating the sheet 1 is led onto a bottom force 3, a top force 2 is clamped down by a press machine and compressed into a form formed in the top and bottom forces 2, 3. At that time, trimmed scraps 7 are cut off by a shear edge 5. Then when an air suction pump 8 is operated and the air is sucked through a hole 4, since insides of a mold and hole 4 formed in the top and bottom forces 2, 3 become negative pressure, air 9 is streamed into them through a shear edge 5 and the air is circulated forcibly within the expanded sheet 1 of a porous molded product. Since the passing air takes away sensible heat of the expanded sheet 1, a molding time can be reduced drastically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a low-density, lightweight molded product by using a fiber-reinforced thermoplastic resin sheet, which is used for interior parts of automobiles, floor boards for trucks, etc.
The present invention relates to a method for molding a fiber-reinforced thermoplastic resin molded product for use as a substitute for plywood in civil engineering applications.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open No. 60-179234 discloses
A method is disclosed in which a solidified sheet of a thermoplastic synthetic resin in which reinforcing fibers are dispersed is heat-molded, and the matrix is expanded and expanded into the shape of a mold by the stress applied to the fibers to form a porous molded article. Further, in Japanese Unexamined Patent Publication No. 62-161529, a composite thermoplastic resin sheet is preheated, stress is removed to expand the sheet, and a molded product is molded in a compression molding die to obtain a molding density. Disclosed is a method for producing a partially different and highly versatile molded article.

According to the methods described in these publications, since the sheet thickness of the molded product can be increased by expanding the sheet to a low density, a highly rigid molded product can be manufactured. Further, by partially adjusting the interval between the molding dies, there is an advantage that the mounting portion of the molded product and the like are compressed to the theoretical density to increase the strength of the part where the molded product is present. Further, it is shown that these inventions are effective when applied to a fiber-reinforced thermoplastic resin sheet produced by a papermaking method.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the example of Japanese Patent No. 1529, a sheet having a thickness before expansion of about 2 to 4 mm is heat-molded to obtain a molded product having a thickness of about 4 to 6 mm. By increasing the plate thickness, high rigidity is obtained. Has been obtained.

However, if an attempt is made to obtain a molded product having a thickness larger than the above-mentioned plate thickness, the productivity will be extremely poor, and depending on the plate thickness, there will be a range in which production will be impossible. Since the reason is the molding of the thermoplastic resin, the resin is molten at the time of shaping, and after the shape becomes faithful to the mold, the resin is below the melting point, preferably below the glass transition point or the recrystallization temperature. In the following, it is necessary to lower the resin temperature to freeze the shape.

On the other hand, since the expansion molding method is a method of molding a fiber-reinforced thermoplastic resin sheet into a porous material, as the theory of heat conduction teaches, the substance containing air has a low thermal conductivity, and originally, Since this is a molding method in which it is difficult to cool a molded product, its drawbacks are apt to appear at a place where the plate thickness is large, which is a problem of the present invention.

For example, as the heat conduction equation teaches, the cooling time needs to be long in proportion to the square of the plate thickness. That is, in order to solidify a molded product having a thickness of about 4 to 6 mm to the center of the plate thickness, cooling on the order of 1 to 2 minutes is necessary.
Under this condition, in order to obtain a molded product having a plate thickness of about 3 times or more, the cooling time is on the order of 10 to 20 minutes, which is not a practical molding method. In addition, when the plate thickness is changed at a specific part of the molded product in order to optimize the rigidity of the molded product, the cooling rate changes greatly depending on the part, and there are disadvantages such as large distortion after molding. There is.

In order to increase the cooling rate by a conventionally known method, a method of lowering the mold temperature or a method of cooling the mold can be considered. However, when the mold temperature is low, the moment the heating sheet is placed in the mold. In addition, the resin near the surface of the sheet in contact with the mold becomes below the solidification point, the reinforcing fibers called freeze marks become fluffy surface defects, and the cooling rate itself also causes heat conduction in the expansion sheet. Because it becomes a neck,
Even if the mold is cooled, the effect is small and the cooling rate cannot be increased by an order of magnitude.

On the other hand, due to recent global environmental problems, it is becoming difficult to obtain timber, and a substitute for it has been demanded. Wood is lightweight and has high rigidity, and it is very difficult to substitute it with a general resin, but a molded product obtained by expanding the fiber-reinforced thermoplastic resin sheet is lightweight and has high rigidity. It can meet your needs. However, as substitutes for wood, those used for floor boards such as trucks, construction and civil engineering materials, etc. are often required to be thick molded products with a plate thickness of about 15 mm or more due to high rigidity and high strength. The present invention provides a method for efficiently producing a molded product having a large plate thickness by expansion molding of this fiber reinforced thermoplastic resin sheet.

[0010]

According to the present invention, a sheet made of a fiber reinforced thermoplastic resin is heated to melt and soften the resin, thereby removing the stress of the reinforcing fiber in the sheet and expanding the sheet. In a method of compression-molding a sheet to a density smaller than the theoretical density of the fiber-reinforced thermoplastic resin in a molding die to obtain a molded article of a predetermined shape, air is forced into the expanded sheet in the die. The present invention provides a method for molding a fiber-reinforced thermoplastic resin sheet, which is characterized in that

[0011]

According to the present invention, a fiber-reinforced thermoplastic resin sheet is heated to melt and soften the resin to remove stress of the reinforcing fibers in the sheet, thereby expanding the sheet into a molding die. In the method of compression-molding to a density smaller than the theoretical density of the fiber-reinforced thermoplastic resin to obtain a molded article of a predetermined shape, in the mold, air is forced to flow in the expanded sheet. The formed sheet-like material can be directly cooled and solidified. Further, even if the plate thickness is large, it can be cooled regardless of the thickness, and the time required for molding can be greatly reduced.

Further, in the case of obtaining a thicker porous molded article, it is efficient to stack and mold a plurality of sheet-like materials which have been heated and expanded, but conventionally there is a difficulty in terms of cooling speed. However, according to the present invention, since the sheet-like material is directly cooled by forcibly circulating the air in the expansion sheet, it becomes more effective as the thickness of the porous molded article increases.

The composite material used as the raw material for the sheet made of the fiber-reinforced thermoplastic resin sheet is basically composed of the fibrous reinforcing material and the thermoplastic resin.

(A) Thermoplastic resin Examples of the thermoplastic resin include polyolefin such as polyethylene and polypropylene, polyvinyl chloride, polystyrene, ABS resin, polyamide, polyoxymethylene, acrylic resin, polyester, polycarbonate, polyphenylene ether, polyether sulfone. Any thermoplastic resin such as polysulfone, polyetherimide, polyetheretherketone, or modified products or blends thereof can be applied.

Among these, it is desirable to use a crystalline resin whose heat resistance (eg, heat distortion temperature) is significantly improved by the fibrous reinforcing material. Specific examples of such a crystalline resin include polyethylene, polypropylene, polyamide, polyester and the like, but especially polypropylene,
It is preferable to use polyamide.

The thermoplastic resins used for the above composite materials may be the same, may be the same type and have some different physical properties, or may be completely different. Examples of the form of the thermoplastic resin material used for the composite material include pellets, powders, flakes, fibers and films, and the following composite material production methods, for example, the following stacking method, impregnation method, and dispersion method. Since it depends on the manufacturing method, the most suitable one is selected.

(B) Reinforcing Fibers Reinforcing fibers include relatively short fibers such as natural fibers such as pulp and wood powder, inorganic fibers such as glass fibers, carbon fibers and metal fibers, and synthetic fibers such as aramid fibers. Although fibers and mixtures thereof can be mentioned, glass fibers having a diameter of 3 to 20 μm and a length of 3 to 80 mm are particularly preferably used.

Further, when the length of the reinforcing fibers constituting the fiber-reinforced thermoplastic resin sheet is 3 to 80 mm, the expansion based on the elastic modulus of the reinforcing fibers is easily achieved by heating the sheet material. If the length of the reinforcing fiber is less than 3 mm, the stress of the fiber is small, and thus the case where it does not expand to a desired plate thickness occurs. On the other hand, if the length of the reinforcing fiber exceeds 80 mm, it is difficult to open the fiber, and there is a problem that uniform dispersion is impaired.

The reinforcing fibers constituting the fiber reinforced thermoplastic resin sheet are used in a proportion of 20% to 70% by weight. If the amount of this reinforcing fiber is less than 20%, the reinforcing effect of the fiber will be insufficient and the amount of expansion during heating will be insufficient. On the other hand, when the amount of the reinforcing fibers exceeds 70%, the adhesive bonding of the reinforcing fibers with the resin becomes insufficient, and the desired strength cannot be achieved.

The following method may be mentioned as a method for producing the sheet. Stacking method Spraying thermoplastic resin powder on the mat of fiber reinforced material,
A method of stacking or laminating a thermoplastic resin film immediately after extrusion molding on the mat and laminating with a roll (Japanese Patent Publication No. 61
No. 14926). Impregnation Method A method in which an aqueous dispersion of resin powder is poured from the top of the mat or the mat is immersed in the aqueous dispersion to impregnate the mat with the resin (European Patent No. 56703). A dry or wet dispersion method in which a reinforcing material and a resin powder are stirred and mixed in air or water and then shaped into a mat by paper making or the like (Japanese Patent Laid-Open Nos. 63-158228 and 62-29711).
No. 3, JP-A-2-51536).

In view of the fact that the composite material used as a raw material in the present invention is preferably a dispersion method, it is preferable that the thermoplastic resin material is in the form of powder, and especially the particle size is 1 mm. The following powders are preferred. The form of the resin material used is slightly different depending on each form of the composite material to be formed, but the form is appropriately selected according to the manufacturing method of the composite material. For example, pellets are generally used in the extrusion coating method, and powders are generally used in the fluidized bed coating method.

Additives, fillers, colorants, foaming agents, cross-linking agents and the like can be further added to the thermoplastic resin material depending on the purpose of use. Among these, when a sheet manufactured by a papermaking method by a wet method is used, since the voids of the sheet after expansion are close to open cells, forced flow of air into the expanded sheet can be performed smoothly and uniformly. ..

The molding method of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a cross-sectional explanatory view showing an example of a method for obtaining a porous expanded product according to the present invention, in which 1 is a fiber-reinforced thermoplastic resin sheet during expansion molding, and 2 and 3 are a pair. It is preferable that the dies 4 are a plurality of holes for air suction drilled in the die 3, and the setting positions of the holes 4 are provided on the back surface side of the molded product. 5 is a shear edge for cutting the molded product from the blank sheet, 6 is a spacer for adjusting the plate thickness of the molded product, 7 is trim scraps cut by the shear edge, and 8 is air suction for circulating air through the expansion sheet. A pump, 9 indicates the flow direction of the air in the hole 4. Of the above, a plurality of holes 4 for air suction,
The shear edge 5 and the spacer 6 function as the opening in the present invention.

Explaining the sheet forming procedure, the sheet 1 made of the fiber reinforced thermoplastic resin of the forming blank is heated to soften and melt the resin to expand the sheet 1 and guide the sheet 1 to the lower mold 3 and then to the upper part. The mold 2 is tightened by a press machine and compressed into the shape formed in the upper and lower molds 2 and 3 as shown in FIG.

At this time, the trim scrap 7 is cut by the shear edge 5. After that, when the air suction pump 8 is operated and air is sucked through the holes 4, the inside of the molds formed in the upper and lower molds 2 and 3 and the holes 4 become negative pressure, so that the air 9 flows in from the shear edge 5 and the porosity increases. Inflatable sheet 1 which is a quality molded product
Air is forcibly circulated therein, and the passing air carries away the sensible heat of the expansion sheet 1, so that it can be cooled. Therefore, the molding time can be greatly shortened as compared with the conventionally known molding methods.

FIG. 2 is a cross-sectional explanatory view of another example of the method for obtaining a porous expansion-molded product according to the present invention. In the figure, 10 is a hole for blowing air, and the air blowing device 11 is operated at room temperature or The air adjusted to a selected temperature not lower than the melting point of the resin and not lower than room temperature is sent into the molds 2 and 3. The flow of air is indicated by arrow 9 and flows through the cross-sectional direction of the expanded molding 1 and is expelled by the holes 4. A part of the introduced air is also discharged from the gap between the molds 2 and 3.

In the present invention, since air is supplied through a part of the opening provided in the mold, that is, the air is provided at the end of the mold or inside the mold depending on the shape characteristics of the molding mold. Since air is supplied from the opening composed of multiple air introduction holes, heating molding to prevent fluffing of fibers on the surface of the molded product and improve the surface quality especially by setting the mold temperature higher Even if the above is adopted, the porous molded article can be cooled efficiently, so that the molding time can be substantially shortened, and further the cooling can be carried out uniformly according to the shape characteristics of the molded article. Further, since the temperature of the air supplied through the opening 4 provided in the mold is adjusted to be not higher than the melting point of the resin of the sheet and not lower than room temperature,
It is possible to adjust the mold temperature to a temperature below the temperature at which the resin of the expansion sheet solidifies without cooling too much.

Moreover, it is possible to uniformly control the cooling rate difference that is inevitably generated based on the shape characteristics.
The molding strain can be dispersed by making the cooling rate difference generated from the shape characteristic into a smooth cooling rate difference. Furthermore,
When air is taken in through a part of the opening 4 provided in the mold, the mold can be cooled efficiently even by heat molding in which the mold temperature is set to be high as in the case of the air supply, and the shape characteristics of the molded product are improved. It can be cooled accordingly.

[0029]

[Example] MFR as a thermoplastic resin is 150 g / 10
60% by weight of propylene resin and 40% of glass fiber having a glass fiber length of 13 mm were added to the reinforcing fiber, and a fiber-reinforced thermoplastic resin sheet was manufactured by a papermaking method. As the blank sheet of the molded product, a sheet having a plate thickness of 2 to 4 mm was used, in which bubbles in the sheet were expelled and consolidated to a theoretical density. Before the blank sheet was introduced into the molding die, the central portion of the plate thickness was heated under the condition of the melting point of propylene resin (about 167 ° C.) or higher.

Table 1 shows the results of forming porous expansion-molded articles of various thicknesses using the blank sheet. As the molding time, only the holding time of the mold necessary for freezing the shape of the molded product is shown in the table, and the blank charging time and the molded product removal time are excluded. Further, Nos. 1 to 5 are based on the present invention, and Nos. 6 to 10 are conventional methods.

[0031]

[Table 1]

[0032]

In the expansion molding method, when a molded product having a large plate thickness is obtained, the conventional method has a solidification time of about the square of the plate thickness for shape freezing, but in the present invention, it is cooled in a very short time. Since it can be solidified, the production time can be greatly shortened. In addition, since the conventional method requires a long molding time, it is impractical if the solidification time is taken up to the point where the solidification temperature of the resin is actually lowered to the center of the plate thickness. I don't get it. Therefore, the molded products taken out of the mold cannot be stacked and stored until the shape retention is secured, and the handling becomes complicated, and if external force is applied for some reason, the products deform and become defective. However, in the present invention, since the molded product after taking out is almost constant from the surface to the center of the plate thickness, it has excellent shape stability. In order to improve the surface quality of the molded product, even if the mold temperature is set high, the air circulation method inside the molded product according to the present invention allows the molding to be performed in a short time regardless of the mold temperature. The industrial value of the present invention is great.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view showing an example of a method for obtaining a porous expanded product according to the present invention.

FIG. 2 is a cross-sectional explanatory view of another example of the method for obtaining a porous expansion-molded product according to the present invention.

[Explanation of symbols]

1 Fiber reinforced thermoplastic resin sheet in expansion molded product 2, 3 Pair of molds 4 Air suction holes 5 Shear edge for cutting molded product from blank sheet 6 Spacer for adjusting plate thickness of molded product 7 By shear edge Cut trim scraps 8 Air suction pump 9 Arrow indicating the air flow direction 10 Hole for blowing air 11 Air feeding device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadamichi Nozawa 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Nippon Steel Corporation Advanced Technology Research Laboratories (72) Inventor Akihiro Murata 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Corporation Advanced Technology Research Center

Claims (2)

[Claims] 1. A sheet obtained by expanding a sheet of a fiber reinforced thermoplastic resin by heating the sheet to melt and soften the resin to remove stress of the reinforcing fibers in the sheet, and to expand the sheet in a molding die. In the method for obtaining a molded product of a predetermined shape by compression molding to a density smaller than the theoretical density of the fiber-reinforced thermoplastic resin, air is forced to flow in the expanded sheet in the mold. A method for forming a fiber-reinforced thermoplastic resin sheet. 2. The method for molding a fiber-reinforced thermoplastic resin sheet according to claim 1, wherein air is taken in through a part of an opening provided in the mold.