FR2646443A1 - Fibre-reinforced plastic sheet and method for producing such a sheet - Google Patents

Abstract

The present invention relates to a fibre-reinforced plastic sheet 10 having a structure with a layer with a gradient in which the degree of aggregation of the reinforcing fibres varies continuously, and to a method for producing the said sheet by spreading out a mixture of fibres 1 which differ in the number of filaments aggregated over the zone of displacement of a conveyor belt 6 and then pressing the said mixture of fibres containing a resin. The fibre-reinforced plastic sheet of the invention has an excellent smooth appearance, excellent fluidity during moulding of an article, excellent fibre-filling capability in a portion of complex shape of an article, and excellent mechanical strength, and may be produced inexpensively.

Description

Technological background of the invention
Field of the Invention
The present invention relates to a fiber reinforced plastic sheet having a gradient layer structure according to
Which the degree of aggregation of the reinforcing fibers varies continuously as well as a process for the production of such a sheet.

Description of the prior art
Up to now, various plastic sheets have been developed, composed of thermoplastic resins and reinforcing fibers. They can be divided into the following groups. One of these groups is produced by mixing reinforcing fibers such as glass fibers with a thermoplastic resin in the molten state using the screw of an extruder and extruding the mixture into a sheet through a Another group is a laminate of a web of continuous fibers such as glass fibers and a sheet of fibers (Japanese patent publication examined No. 54-36193). Another group is a laminate of web of yarns of cut skeins or surfacing ply of staple fibers and a sheet of resin (Japanese patent publication examined No. 51-14557). Another group is produced by mixing chopped strand yarns such as glass fibers with resin powder with water in a slurry, dehydration, drying and pressing with heating to form a sheet (Japanese patent publication no Another group is produced by opening and mixing skeins of cut skeins with resin powder in a gas phase and pressing with heating the cotton-like mixture to form a sheet (Japanese patent publication examined no. 64-6227, Japanese patent publication no. examined no. 59-49929). Yet another group is produced by mixing a resin powder with unopened skein yarns, and pressing with heating to form a sheet (Japanese Patent Publication No. 51-20550).

However, in the first method using an extruder, since most of the fibers of
reinforcement is cut to a length of less than 1 mm by the extruder screw, the reinforcing effect of the thermoplastic resin, in particular impact resistance, is insufficient. The second method of laminating a sheet of fibers
continuous is the most common method. In this method, since the fibers are continuous, the fluidity of the fibers is insufficient in the molding process such as compression molding, using a mold having an arbitrary shape with heating. Therefore, when a complex shape such as a rib is molded, the length of the fibers filled in the rib is short. The third method of laminating a sheet of cut skein yarn or a surfacing sheet of Staple fiber is expensive because it uses the web as the starting material for the sheet. In addition, the fluidity of the fibers is lower in the sheet forming process, due to the bonding of the fibers by coating with a binder in order to maintain the web form of the web of chopped strand or the surfacing ply. In the method of mixing the strands of skeins cut with resin powder with water in a slurry, the strands of skeins are opened in water in monofilaments Consequently, discontinuous monofilaments about 7 to 50 mm in length are uniformly dispersed in the plastic sheet, and as a result, the articles molded from the sheet in an arbitrary shape have an excellent appearance. In addition, this method is excellent because the fibers are filled in the complex shaped portions. However, since the monofilaments are tangled together in the sheet, great resistance to flow occurs upon molding against the flow of fibers in an arbitrary shape together with a resin. high pressure is required for molding. In addition, insufficient injection loads occasionally occur due to the inferiority of the fluidity of the resin. Another problem with this method of mixing skeins cut in water concerns the low impact resistance due to the monofilaments. Due to the manufacturing method, the manufacturing cost is increased due to the process of dehydrating a large amount of water and the drying process. In the method of opening skein yarns cut in a gas phase, the staple fibers and a resin powder are used in a similar manner to the previous method, but it is different from the mixing process which is carried out in the gas phase. Therefore, the dehydration process and the drying process do not necessarily lead to a decrease in the number of steps. However, since the open threads are dispersed in a plastic resin, the plastic sheet has defects similar to those of the plastic sheet of the previous method, i.e. high resistance to flow, high molding pressure, low impact resistance etc. In addition, the open monofilaments are in the form of plug balls, and the monofilaments are randomly oriented in three dimensions in the mixture of resin powder and fibers.

Therefore when a sheet formed from the mixture is heated to a temperature higher than the melting point of the resin during molding, the sheet expands by the spring effect of the fibers, and a certain amount of fibers is projected from the surface. of the leaf which degrades its appearance. In the latter method of mixing a resin powder with unopened cut skein yarns, since unopened yarns are present around the surface of the sheet, the appearance of the molded article is inferior.

Summary of the invention
One of the objects of the invention is to solve the above-mentioned problems of the prior art in a collective manner and to provide a fiber-reinforced plastic sheet having an excellent appearance, excellent mechanical properties such as resistance to impact and fluidity in molding allowing the fibers to be filled in portions of complex shape, in an inexpensive manner.

 The present invention provides a fiber-reinforced plastic sheet and a method for obtaining such a sheet for achieving the object mentioned above.

 The fiber-reinforced plastic sheet comprises staple fibers of different reinforcement by the number of aggregation of filaments dispersed in a thermoplastic or thermosetting resin, said fibers being arranged in a gradient layer structure varying from a fiber layer having a large number of aggregation of filaments to a layer of fibers having a lower number of aggregation of filaments in a continuous manner.The process for producing a fiber reinforced plastic sheet which comprises separating the staple reinforcing fibers which are open or which have been opened to form a distribution of fibers different by the number of aggregation of filaments by spreading them over the displacement zone of a conveyor belt at an angle, with the exception of the vertical direction, in the direction of the displacement area together with a draft to form a gradient layer using the different that of the weight of each fiber, by superimposing or interposing a resin on or inside said gradient layer, and pressing the superimposed or interposed material with heating to form the fiber-reinforced plastic sheet.

Brief description of the drawings
Figure 1 is a schematic sectional view of a nonwoven fabric of fibers used for -the fiber reinforced plastic sheet according to the invention.

 Figure 2 is a schematic side view of an apparatus for producing the aforementioned fiber nonwoven fabric.

 Figure 3 is a schematic sectional view illustrating the superimposed state before pressing with heating to produce a fiber reinforced plastic sheet of the invention.

 Figures 4 to 6 show other apparatus for the production of a nonwoven fabric of fibers used for the fiber reinforced plastic sheet of the invention.

 Figure 7 is a perspective view of a molded article using a fiber-reinforced plastic sheet of the invention.

 Figure 8 is a schematic sectional view illustrating the superimposed state before pressing with heating to produce a fiber-reinforced plastic sheet of the invention.

 Figure 9 is a schematic side view of an apparatus for producing a fiber-reinforced plastic sheet of the invention by impregnating a molten resin into a nonwoven fabric of fibers by pressing with heating followed by cooling .

 Figure 10 is a schematic sectional view of two plastic sheets reinforced with fibers placed face to face, and Figure II is a schematic enlarged sectional view after they have been joined together.

 Figure 12 is a schematic side view of an apparatus for producing a fiber-reinforced plastic sheet of the invention, and Figure 13 is a schematic side view of an apparatus for joining two mentioned fiber-reinforced plastic sheets above arranged face to face.

 Figure 14 is a schematic sectional view of a laminated sheet containing two fiber-reinforced plastic sheets of the invention.

Detailed description of the invention
The fibers used as starting materials are discontinuous yarns known as cut skein yarns and a skein yarn is an aggregate of hundreds of thousands of single fibers.

A suitable length of the skein threads is usually 3 to 50 mm. When continuous strand yarns are used, they are cut to the length mentioned above. The type of fibers must necessarily have an appropriate thermal resistance to resist the pressing process of the superimposed material under heating, and is chosen in accordance with the use of the fiber-reinforced plastic sheet or the like. Examples of fibers include synthetic fibers such as glass fibers, carbon fibers, metallic fibers, asbestos fibers and aramid fibers, pulp, cotton and the like.

 A gradient layer varying from a fiber layer having a large number of aggregated filaments to a fiber layer having a lower number of continuously aggregated filaments can be produced as follows. First, we prepare yarns of skeins cut to the prescribed length (yarns of cut skeins). Cut skein yarns are used as the starting material as is, or are opened to a certain extent to form a distribution from the skein yarn itself or from the skein yarn suitably opened or considerably open to monofilament stage. The degree of openness is chosen in accordance with the required properties of the fiber-reinforced plastic sheet, but it is important that more than 30% by weight and preferably 50% by weight of the fibers do not consist of monofilaments. An appropriate amount of monofilaments is from 1 to 70% by weight, preferably 5 to 50X by weight. When the fibers have an appropriate distribution of the filament aggregation number, the fibers can be fed to the separation process. When the fibers are not open or insufficiently open, they are opened in the separation process using a rotary drum provided with needles or the like until a portion of the fibers is opened in the monofilament stage.

 Subsequently, a nonwoven fabric of fibers is formed using the threads of open cut skeins mentioned above.

This process is the most important for the invention. The threads of open cut skeins are delivered from part T: from a slot having a prescribed width with air, or preferably delivered by the centrifugal force of a rotary drum provided with needles. The open skein threads projected into the air fall in a layer on the area of movement of a conveyor belt located below. The projection angle to the area is not 900 o (vertical) and 10 to 80 are preferred. The thickness and weight per unit area of the layer can be controlled by changing the speed of movement of the conveyor belt, the delivery rate of the yarns of open cut skeins or the like. The nonwoven fabrics of fibers thus formed can be superimposed to form a multilayer.

 A resin powder can be dispensed by spraying on the upper side of the displacement zone between the position where the stacking of the open cut skein threads begins and the position where this stacking ends. When a necessary amount of the resin has been dispensed, the following method of superimposing a resin can be omitted.

 The conveyor belt displacement zone is preferably of the air passage type, such as a mesh conveyor or a SUNOKO conveyor (the displacement zone is formed by a drip grid or a rack), in order to stack the threads of cut skeins open evenly. When the movement zone of the conveyor belt is not of the air passage type, the threads of open cut skeins are possibly disturbed on the movement zone and do not form a uniform layer.

 Subsequently, a resin is superimposed on the nonwoven fabric of fibers. As a layering method, the resin powder or resin granules can be spread evenly on both sides of the nonwoven fabric, or preferably, resin sheets or the melted sheet-like resin are layered on both sides of the non-woven fabric. Then the superimposed material is pressed under the action of heat to achieve integration. The heating temperature must necessarily be higher than the melting point or the softening point. The type of resin is selected in accordance with the use of the fiber reinforced plastic sheet or the like, and includes various thermoplastic resins such as polyethylene resin, polypropylene resin, ethylene-propylene copolymer resin, ethylene vinyl acetate copolymer resin, ethylene ester acrylate copolymer resin , polyethylene terephthalate resin, polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polycarbonate resin, polyamide resin, polyacetal resin, methacrylic resin and mixture of resins containing them, and various thermosetting resins such as phenolic resin, melamine resin and urea resin e.

 A suitable ratio of resin to fiber is 100 parts by weight of the resin per 1 to 400 parts, preferably 5 to 200 parts by weight of the fiber.

 The thickness of the sheet is usually 1 to 10 mm. The sheet can also be used as a wall material, as a floor covering material, as a stamped sheet or the like in an arbitrary shape or as molded articles.

 In the manufacturing process, the threads of open cut skeins are projected at an arbitrary angle except for the vertical direction. The heavier fibers, i.e. the less open threads fall over a shorter distance and the lighter fibers, i.e. the more open threads fall over a longer distance Consequently, the each fiber fall position varies continuously according to its weight due to the degree of opening of the wire. Since the area of movement of the conveyor belt always moves in one direction, the projected fibers are arranged in a gradient layer structure in which the less open threads are arranged on the lower side and the more open threads are arranged on the upper side. The gradient layer material is a non-woven fabric having a low bonding force due to the entanglement of the fibers. Therefore, it can be used without binder coating or without needling treatment.

 In the sheet of the invention, the monofilaments or sufficiently open fibers are arranged around the surface of the sheet, and they are arranged parallel to the surface.

The arrangement parallel to the surface of the sheet means that the largest amount of fibers is deposited in an even layer during the formation of the nonwoven fabric and the fibers arranged in
The vertical direction, that is to say in the direction of the thickness of the nonwoven fabric are rare. Therefore, unopened or less open wires are not exposed to the surface of the molded articles. In addition, since the fibers are arranged in two dimensions parallel to the surface, the fibers are not expelled from the surface by the spring effect in the direction of the thickness of the sheet during heating before molding. Since the open fibers are dispersed uniformly in directions parallel to the surface, the sheet has an excellent smooth appearance compared to the above-mentioned conventional sheet containing buttons.

 As for the fluidity of the material in the molding process, it is determined by the fluidity properties of the resin such as the viscosity in the molten state and by the shape of the fiber such as the length and the degree of fiber opening. When comparing the sheet of the invention with the conventional sheets mentioned above in the case of the use of the same resin, in the sheet of the invention, since "the threads of skeins cut not open or less open are arranged inside, the flow resistance of the molten resin is low compared to conventional sheets in which most of the fibers are monofilaments, moreover, since no binder is used to maintain the shape of the nonwoven fabrics in the sheet of the invention, the fibers can move together.

 Regarding the filling property of the fibers in the complex shaped portions, in the sheet of the invention, since staple fibers having a length of 3 to 50 mm are used, the entanglement of the fibers is less than for conventional sheets using a web of continuous fibers. As a result, the fibers move together with the resin, and the fibers fill complex shaped portions such as ribs. The filling property is also superior to that of the conventional sheet using a binder.

 As regards the mechanical properties, in the sheet of the invention, the fibers used for the reinforcement have a length of 3 to 50 mm, and the length of the fibers is practically the same during the production of the sheet. This means that the aspect ratio of the length of fibers to the diameter of fibers is maintained at a high value. Therefore, the sheet of the invention has excellent mechanical strength, especially excellent impact resistance compared to the conventional sheet produced using an extruder. As far as impact resistance is concerned, it is known empirically that impact resistance when using threads of unopened cut skeins is greater than that in the case where monofilaments are used (see "PLASTICS", volume 17, n 19, page 10). This is thought to be due to the difference in the propagation of the shock energy and the absorption mechanism. In the sheet of the present invention, the fibers near the surface of the sheet are open, while the unopened threads remain inside. Thus, the impact resistance of the sheet of the invention is higher than that of conventional sheets of the open-wire type, due to the structure mentioned above. In addition, in conventional sheets using unopened skein threads alone as reinforcing material, the contact surface of the resin with the fibers is small, and it is known that the reinforcing effects, in particular the bending properties such as flexural strength and elastic flexural modulus, are lower. On the contrary, in the case of the sheet of the invention, since the open threads are arranged around the effective surface for the flexural properties, it has sufficient flexural strength.

 The sheet of the invention can be produced inexpensively for the reason that an inexpensive commercial product of cut skein yarns is used as a starting material, compared to conventional sheets using a sheet of nonwoven fabric of expensive fiber. The dehydration process and the drying process are not necessary, and the manufacturing process is simple which reduces the manufacturing cost.

Examples
Example 1
Cut skein threads ("FES-13-1252M", manufactured by Fuji Fiber Glass Co., Ltd.) having a fiber length of 13 mm, a fiber diameter of 11 un and an aggregated number of filaments 800 are placed in a Henschel mixer
("FM 75J #, manufactured by the firm Mitsui Miike Machinery Co., Ltd.), and stirred at a speed of rotation of the ZoSo blade of approximately 40 n of peripheral speed for 3 min. The glass fibers removed from the mixer are composed of about 5% by weight of monofilaments and about 50% by weight of unopened skein yarns, the remainder being in intermediate open states.

A nonwoven glass fiber fabric shown in
Figure 1 from the glass fibers mentioned above using a needle type machine of the unique type (from the firm
Chuo Menki Seisakusho) shown in Figure 2. The glass fibers 1 are placed on a conveyor belt 2 from the firm SUNOKO (the displacement zone is made of bamboo in the form of a drip grid or screen) of a uniformly, and supplied to a drum 5 furnished with needles rotating at 600 rpm via a wooden pressure roller 3 and a steel supply roller 4. The diameter of the drum provided with 'needles 5 is. 513 mm, and a sheet furnished with projection needles called card lining is wrapped around the surface. The glass fibers are opened by the projection needles and projected downwards by the centrifugal force of the drum 5 in the direction d 'a SUNOKO 6 bamboo conveyor belt moving in the direction of the arrow. The unopened threads fall just near the discharge portion 7 and the fibers in the intermediate opening states fall more to the right of the figure according to the degree of opening. The monofilaments and the sufficiently opened fibers fall on the rightmost part. Thus, the glass fibers are arranged in layers arranged in accordance with the degree of opening, and become entangled with one another inside these layers. The surface of the layer is slightly regulated by a contact roller 8 in stainless steel and pressed by a steel roller 9 to exit in the form of a non-woven fabric of glass fibers 10. The air is sucked through a duct 18 placed after the contact roller 8.

 The structure of the glass fiber nonwoven fabric 10 thus formed is shown schematically in FIG. 1. The fibers open up to the monofilament stage 11 are in the layer on the upper side of the nonwoven fabric 10 and the unopened threads 13 are in the bottom side layer. The fibers in the intermediate opening states 12 are arranged in accordance with the degree of opening between the two layers to form a continuously varying layer. The nonwoven fabric shown in Figure 1 is not a 3-layer structure but a gradient-layer structure whose number of aggregated filaments varies continuously.

The speed of movement of the conveyor belts
SUNOKO 2,6 can be arbitrarily fixed and it can be 50 cm / min for the conveyor belt 2 and 100 cm / min for the conveyor belt 6. The weight per surface of the nonwoven fabric 10 is approximately 500 g / m2.

 Four sheets of nonwoven fabric 10 and five sheets of polypropylene film tPP) (melt index MI = 10, manufactured by the firm Mitsui Petrochemical Industries Co., Ltd.) are alternately superimposed as shown in FIG. 3. The superimposed material is previously heated by a heating press at 2000C for 3 min, then prepared at 40 kg / cm2 (3920 KPa) for 5 min with heating. This composite sheet is transferred to a press and then pressed at 40 kg / cm2 (3920 KPa) at ordinary temperature for 5 min. The thickness of the fiber-reinforced plastic sheet thus produced is 4 mm, and the content of glass fibers is 40% by weight.

Example 2
Five types of cut skein yarn (FES-13-1252M ',
manufactured by Fufi Fiber Glass Co., Ltd. having
different aggregated filament numbers are mixed evenly
to obtain a mixture composed of 50% by weight of yarns having a
number of aggregated filaments of 800, 30% by weight of yarns having a
number of aggregated filaments of 400, 10% by weight of yarns having a
number of aggregated filaments of 100.5% by weight of yarns having a
number of aggregated filaments of 50 and 5% by weight of yarns having a
number of aggregated filaments of 10. A nonwoven fabric of
the same way as in Example 1.

Instead of the polypropylene film 14, spread the same
quantity of polypropylene powder t "J 900P, manufactured by the
Mitsui Petrochemical Industries Cc., Ltd.) and we are preparing a
4 mm thick fiber reinforced plastic sheet
same as in example 1.

Example 3
Preparing a nonwoven fabric using the apparatus
shown in Figure 4. This device is the same as that
used in Example 1 except that a hopper 15 of resin powder
is provided after the needle drum 5. The powder-
polypropylene (J 900P ') 17 is spread over the fiber layers of
glass through holes 16 with a diameter of 1.5 mm. In sight
to obtain a uniform distribution, the hopper 15 is vibrated by a
vibrator (not shown).

Nonwoven fabric containing poly powder
propylene is pressed by a heating press under heating and
then by a cold press. The pressing conditions are the same as in Example 1. The thickness of the plastic sheet
reinforced with fibers thus produced is 1 mm, and the content of
glass fiber is 40% by weight.

Example 4
Preparing a nonwoven fabric using the apparatus
shown in Figure 5. This device is the same as that used in
example 1 except that the direction of feeding of the glass fibers and the direction of rotation of the needle drum 5 have been reversed. The layered structure of the nonwoven fabric is reversed, that is to say that the monofilaments are deposited in a layer on the lower side and the unopened threads are deposited in a layer on the upper side.

Example 5
The same mixture of glass fibers as that used in
Example 1 is discharged through a nozzle 21 of a blower 20 having a rotary blade (1000 rpm) together with air in
the direction of a SUNOKO 6 bamboo conveyor belt at an angle of about 450 (Figure 6). The width of the nozzle 21 is almost the same as that of the bamboo strap from SUNOKO. The glass fibers forming the nonwoven fabric are more open than those placed in the blower 20. The layered structure is similar to that shown in FIG. 1.

Comparative example 1
In the apparatus of FIG. 6, the angle of the nozzle 21 is fixed vertically with respect to the conveyor belt of
SUNOKO 6, and a nonwoven fabric is produced in the same manner as in Example 5. The nonwoven fabric has a random structure in which the monofilaments, the unopened threads and the threads in the intermediate open states are mixed.

 A deflector is arranged following the nozzle 21 of the apparatus of FIG. 6 and a # nonwoven fabric is produced in the same manner as in example 5. The current of glass fibers is disturbed by the deflector , and the nonwoven fabric has a random structure but a gradient layer structure similar to that shown in Figure 1 could not be obtained.

 Subsequently, various properties of a fiber-reinforced plastic sheet of the invention prepared in Example 6 are compared to those of conventional fiber-reinforced plastic sheets prepared in Comparative Examples 2 to 6.

Example 6
A nonwoven fabric 10 is prepared in the same manner as in
Example 1 except that the speed of movement of the conveyor belt 6 is lowered to 50 cm / min. The weight per surface of the 2 nonwoven fabric is approximately 1000 g / m2. Two sheets of nonwoven fabric 10 and three sheets of polypropylene film 14 (MI = 40, manufactured by Mitsui Petrochemical Industries Co., Ltd.) are alternately superimposed as shown in Figure 8, and a fiber-reinforced plastic sheet 4 mm thick is prepared in the same manner as that used in Example 1.

Comparative example 2
Two sheets of tablecloths of skeins of cut skeins 2 ("CM 9005FAS", weight per surface 900 g / m, manufactured by the firm
Asahi Fiber Glass Co., Ltd.), two sheets of g / n2 surfacing plies ("3605E", 100, manufactured by the same company) and five sheets of polypropylene film 14 are superimposed in the following order: polypropylene, surfacing ply, polypropylene film, cut skein yarn web, polypropylene film, cut skein yarn web, polypropylene film, surfacing web and polypropylene film. The superimposed material is pressed with the heating press and then with the cold press to form a plastic sheet reinforced with fibers 4 minutes thick. The respective sheets contain an organic binder.

Comparative example 3
Cut glass fibers ("FES-13-0874G", from the firm
Fufi Fiber Glass Co., Ltd.) 13 mm in length of fiber containing a water-soluble sizing agent are mixed with the powdered polypropylene powder ("J 900", MI = 40, passing through a sieve of 0.149 mm of mesh opening, from the firm Mitsui
Petrochemical Industries Co., Ltd.) and a small amount of synthetic pulp ("SWP E620", from the firm Mitsui Petrochemical
Industries Co., Ltd.) - in water using a homomixer.The cut glass fibers are opened in the monofilament stage to form a uniform mixture with the polypropylene powder The mixture is transformed into a sheet by the paper making method, then dehydrated and dried. The sheet is pressed with a heat press and then with a cold press to form a fiber-reinforced plastic sheet.

Comparative example 4
The cut glass fibers C "FES-13-1252M") and the polypropylene powder ("J 900") are placed in a Henschel mixer ("FM75J"), and mixed by the ZoSo stirring blade at a peripheral speed 40 m / min for 5 min. The cut glass fibers are opened in a pilling form and a cotton-like mixture is obtained in which the polypropylene powder adheres to the fibers. The mixture is made into a sheet, and pressed with a heat press and then with a cold press to form a plastic sheet reinforced with fibers.

Comparative example 5
The cut glass fibers ("FES-13-1252M") are mixed lightly with the polypropylene powder ("J 900") using a ribbon mixer under control so that the cut glass fibers are not not open. The mixture is made into a sheet, and a fiber-reinforced plastic sheet is prepared in a similar manner.

Comparative example 6
A commercial stamping sheet A is used as the comparative material containing a web of continuous glass strands as the reinforcing material. The ply of threads is formed by a needling process.

 With regard to the strength of each fiber-reinforced plastic sheet, the tensile strength, the flexural strength, the elastic modulus in bending and the Izod impact resistance are compared. As a molding test, each sheet is cut into pieces of 4 x 130 x 130 mm, and each pair of pieces is heated to 2100C. The pieces are superimposed, and placed in a mold having a structure with shear edges. Then, they are molded by compression molding in the form shown in Figure 7. The molded article has dimensions of 150 x 150 x 25 mm, and its thickness is 3 mm. The mold temperature is 300C and the pressing time is 30 s. The molded article is evaluated in terms of appearance by visual observation, minimum pressure to achieve Molding in the form of Figure 7 without loss of capacity filling and filling capacity of the fibers in the rib portion. The glass fiber content of all fiber-reinforced plastic sheets is fixed at 40% by weight.

 The results are grouped in Table 1.

Table 1
Unit Example Comparative example
6 2 3 4 5 6
Fiberglass length mm 13 50 13 13 13 Continuous
Glass content% by weight 40 40 40 40 40 40 2
Strength at kgf / mm 9.0 8.0 9.0 8.0 7.0 9.0 tensile MPa 90 80 90 80 70 90
Resistance to kgf / mn2 15.0 12.0 14.0 12.0 10.0 12.0 bending MPa 150 120 140 120 100 120
Elastic modulus kgf / mm2 600 450 550 550 400 550 in flexion MPa 6000 4500 5500 5500 4000 5500
Izod impact resistance with notched test piece kgf.cm/cm 90 60 30 40 60 90
Smooth condition - ABACCB
Fiber exhibition 2 - AABDDC
Moldability (fluidity) - BCDDBB
Table 1 (continued)
Unit Example Comparative example
6 2 3 4 5 6
Minimum pressure * imale kgf / cm2 70 100 200 160 70 70 molding 3 MPa 7 10 20 16 7 7
Fiber filling capacity in ribs - ADAABD
1 A ... Excellent, B -. good, C ... slightly lower,
D ... lower;
2 less exposure and better projection of fibers;
3 value in relation to the projected surface (150 x 150 mm) of
the article molds.

 As shown in Table 1, the fiber reinforced plastic sheet of the present invention is superior to all conventional fiber reinforced plastic sheets. In the sheet of the invention, the expensive glass fiber webs are not used unlike Comparative Examples 2 and 6, and the dehydration process and the drying process are not necessary. Therefore, the sheet of the invention can be produced inexpensively.

Example 7
A nonwoven fabric of glass fibers of about 1000 g / m2 of weight per surface is prepared in the same manner as in Example 6. The structure is similar to that shown in Figure 1. Using an apparatus shown in FIG. 9, the molten polypropylene in the form of a sheet 14 is bonded on the two
sides of the nonwoven fabric 10 by pressing. Polypropylene is
prepared by modification of polypropylene ("J170, from the firm
Nippon Petrochemicals Co., Ltd.) and has an MI of 60.

The thickness of the resin in the two layers is approximately
0.8 mm. Polypropylene 14 is extruded in sheet form to
from a T-die 27 from the extruders 26 arranged on the
top and bottom sides of the nonwoven fabric 10 on each
pressure roller 22. Each pressure roller 22 is heated to a temperature above about 1000C, and the outer side is also heated by an infrared heater
distant 23, so that the molten polypropylene does not solidify before being pressed on the nonwoven fabric. The sheet of nonwoven fabric 10 moves continuously from the left side of FIG. 9. The molten polypropylene is bound on both sides of the nonwoven fabric during its passage between the pressure rollers 22, and cooled by the air blown through the air duct 24. The fiber-reinforced plastic sheet 25 thus produced at a thickness of approximately 2.5 mm contains polypropylene impregnated on
both sides of non-woven glass fiber fabric, and handling is possible.

 The sheet 25 is cut into pieces of about 30 x 30 cm, and the reverse sides of the two sheets are placed face to face as shown in Figure 10. The pair of sheets is completely impregnated and degassed by a method similar to that of Example 1 to form a laminated sheet about 4 mm thick. A section of the laminate is shown schematically in Figure 11. The polypropylene is impregnated on the sheet, and the monofilaments 11 are gathered on the outside and the unopened threads 13 are gathered in the central portion.

 In the method of this example, since the expensive resin sheet is not used, the cost of the fiber reinforced plastic sheet can be further lowered.

 The fiber-reinforced plastic sheet described above can be produced continuously, for example using the apparatus shown in Figures 12 and 13.

 In this apparatus, open glass fibers 1 are transported by a conveyor belt 28, and opened by an opener 29. The open fibers are transported pneumatically in a feeding device 30, and fed to a needle drum rotating quantitatively 5 by through a feed roller 4. The glass fibers are arranged in a gradient layer structure similar to Example 1 to form a nonwoven fabric of glass fibers 10 and the molten polypropylene is bonded to both sides of the nonwoven fabric. Then, it is pressed by a double belt press 21, and the sheet of fiber-reinforced plastic sheet 25 thus produced is wound around a take-up roller. The front portion of the double belt press comprises heating devices, and the resin is further impregnated by heating to a temperature above the melting point of the resin. On the other hand, the rear portion includes cooling devices, and the resin is solidified by cooling. Subsequently, as shown in FIG. 13, two rolls of the sheet of fiber-reinforced plastic sheet are placed face to face and delivered. The opposite sides are heated to melt the resin by far infrared heaters 32 and bonded by passing through a pair of pressure rollers 33. The bonded sheet is cooled during its movement, and cut to the length prescribed by the using a knife 34.

Example 8
A reinforced sheet in one direction composed of a roving of continuous glass fibers arranged in one direction, impregnated with polypropylene is prepared according to the method described in Example of Japanese patent publication no. Exam. 59-14924 . The thickness of the sheet is approximately 1 mm and the glass fiber content is approximately 40% by weight.

 Furthermore, a nonwoven glass fiber fabric having a surface area weight of about 500 g / m2 is prepared and the polypropylene is impregnated in the fabric, according to the same method as in Example f, to produce a sheet. fiber reinforced plastic about 1 mm thick having a gradient layer structure.

 Two glass fiber reinforced plastic sheets mentioned above are overlapped so that the unopened wire sides face each other, and the two outer sides are overlapped by reinforced sheets in one direction as shown in Figure 14. The superimposed material is 2 o pressed by a heating press at 40 kg / cm2 (3920 KPa) at 200 C for 5 min and then by a cold press at 40 kg / cm2 (3920 KPa) for 5 min. The thickness of the laminated sheet is approximately 4 mm, and the glass fiber content is approximately 40% by weight. The laminated sheet has a tensile strength of 25 kg / mm 2 (250 MPa), a flexural strength of 30 kg / mm2 (300 MPa) and an elastic flexural modulus of 1100 kg / mm2 (11000 MPa), in the direction of reinforcement.

 As shown in this example, molded articles having high strength in one direction and good flowability during processing can be produced by combining the fiber reinforced plastic sheet of the invention with the reinforced sheet in one direction, and are suitable as reinforcing elements for a bumper for an automobile or the like.

Example 9
CFES-13-1252M cut skein threads, from the firm
Fuji Fiber Glass Co., Ltd.) are placed uniformly in a cotton opener (# KF-3 ', from Chuo Menzai Seisakusho), and the threads are partially open. The diameter of the opener cylinder is 466 mm and the rotation speed is 600 rpm. The surface of the cylinder has several needles in projection. The threads pass twice through the cotton opener, and a mixture of glass fibers composed of about 5% by weight of monofilaments, about 50% by weight of unopened threads and the remainder being in the states of 'intermediate opening is obtained.

 The glass fiber mixture is treated in the same manner as in Example 1 to produce a nonwoven fabric of glass fibers shown in Figure 1.

Claims (6)

 1. A fiber-reinforced plastic sheet, characterized in that it comprises discontinuous reinforcing fibers different in the number of aggregated filaments, dispersed in a thermoplastic or thermosetting resin, said fibers being arranged in a structure with a gradient layer varying from a layer of fibers having a large number of aggregated filaments has a layer of fibers having a lower number of continuously aggregated filaments.  2 The fiber reinforced plastic sheet according to claim 1, characterized in that more than 30% by weight of said fibers have a number of aggregated filaments greater than 1.  3. The fiber reinforced plastic sheet according to claim 1, characterized in that the layer of fibers having a smaller number of aggregated filaments is arranged on the two outer sides of the sheet and the layer of fibers having the greater number of aggregated filaments is placed in the center of the sheet.  4. A process for producing a fiber reinforced plastic sheet, characterized in that it comprises the separation of the discontinuous reinforcing fibers which are being opened or which have been opened to form a different fiber distribution by the number of filaments aggregated by spreading them over the displacement zone of a conveyor belt at an angle, except for the vertical direction, directed towards the displacement zone together with a stream of air to form a gradient layer using the difference in the weight of each fiber, the superposition or interposition of a resin on or inside said gradient layer, and the pressing of the superimposed or interposed material with heating to form the fiber-reinforced plastic sheet.  5. The method according to claim 4, characterized in that said resin to be superposed is in the form of a sheet, a powder, of granules or is in the molten state.  6. The method according to claim 4, characterized in that said displacement zone has the capacity to let air pass.