JP2018167409A - Method of producing fiber-reinforced resin mold article - Google Patents

Abstract

To provide a fiber-reinforced resin mold article having high rigidity and being excellent in impact resistance.SOLUTION: An injection molder including a low shear type screw of a single flight is used in injection molding using a molding material containing carbon fiber resin pellets and glass fiber resin pellets, in which: both pellets each have a weight average lenth of 10 mm or longer; a combined percentage content of carbon fibers and glass fibers is 20 mass% or more and 50 mass% or less; a ratio of the glass fibers to a total amount of the carbon fibers and the glass fibers is 5 mass% or more and 15 mass% or less; and in the injection molding, L/D is 22 or more and a compression ratio is 1.6 or more and 1.8 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a fiber-reinforced resin molded product.

  Since carbon fibers are light and have high rigidity, they are used as reinforcing fibers for fiber-reinforced resin molded products. Such a fiber reinforced resin molded product can be manufactured by injection molding, but it is known that the reinforcing fiber breaks when kneading or molding the resin pellet containing the reinforcing fiber. Due to this breakage, the physical properties (strength, elasticity, conductivity, etc.) of the obtained fiber-reinforced resin molded product are lowered.

  On the other hand, in Patent Document 1, in order to suppress breakage of carbon fibers in the manufacturing process such as kneading and molding, carbon fibers having a specific crystal structure and having a specific crystal size are used. Have been described. Further, this document describes that glass fibers may be added to the pellets in addition to the carbon fibers as necessary.

JP 2010-77407 A

  Fiber reinforced resin molded products using carbon fibers as reinforcing fibers have higher flexural modulus than fiber reinforced resin molded products using glass fibers, and are expected to be applied to products that require high rigidity. . However, carbon fiber reinforced resin molded products are inferior in impact resistance compared to glass fiber reinforced resin molded products, and are disadvantageous for application to products that require impact resistance.

  Then, this invention makes it a subject to obtain the fiber reinforced resin molded product which is highly rigid and excellent in impact resistance.

  The present inventor has studied a fiber-reinforced resin molded article using both carbon fiber and glass fiber as reinforcing fiber. In the research, as a result of examining the strength and impact resistance of fiber reinforced resin molded products obtained by changing the blending ratio of carbon fiber and glass fiber, it was found that impact resistance was greatly improved by blending a small amount of glass fiber. I found it.

The manufacturing method of the fiber reinforced resin molded article disclosed here is a fiber reinforced resin molded article by injection molding using a molding material including carbon fiber resin pellets containing carbon fibers and glass fiber resin pellets containing glass fibers. A manufacturing method of
The weight average length of the fibers contained in each of the carbon fiber resin pellets and the glass fiber resin pellets is 10 mm or more,
The total content of the carbon fiber and the glass fiber in the molding material is 20% by mass to 50% by mass,
The ratio of the glass fiber to the total amount of the carbon fiber and the glass fiber is 5 mass% or more and 15 mass% or less,
An injection molding machine provided with a single flight low shear type screw having a ratio L / D of a screw length L to a diameter D of 22 or more and a compression ratio of 1.6 to 1.8. It is characterized by using.

  Thereby, a fiber reinforced resin molded article having high strength and high impact resistance can be obtained. A great feature is that the impact resistance is greatly improved by a small amount of glass fiber (the ratio of the glass fiber to the total amount of the carbon fiber and the glass fiber is 5 mass% or more and 15 mass% or less). In addition, since the amount of glass fiber is small, a decrease in strength from the case where the reinforcing fiber is only carbon fiber is suppressed, and the strength is relatively high despite the relative decrease in the amount of carbon fiber. Is maintained.

  Here, it is recognized that by reducing the compression ratio, the shearing force applied to the molding material in the compression part of the injection molding machine is reduced, and the damage received by the carbon fibers and glass fibers is reduced.

  By adopting a single flight, the flight of the molding material that applies a large force to the carbon fiber and glass fiber is reduced, and the shear of the molding material between the narrow flights is suppressed, resulting in breakage of the carbon fiber and glass fiber. Is recognized as being suppressed.

  It is recognized that plasticization and defibration of the resin pellets could be improved while suppressing breakage of the carbon fiber and glass fiber by increasing the supply part of the injection molding machine with L / D being 22 or more.

  The backflow prevention ring of the injection molding machine is preferably a co-rotating type that rotates together with the screw. This prevents a strong shearing force from being applied to the molding material between the screw head and the backflow prevention ring, which is advantageous for preventing breakage of the carbon fibers and glass fibers.

  According to the present invention, the weight average length of the fibers contained in each of the carbon fiber resin pellets and the glass fiber resin pellets is 10 mm or more, and the combined content of the carbon fibers and the glass fibers in the molding material is 20% by mass or more and 50%. The ratio of the glass fiber to the total amount of the carbon fiber and the glass fiber is 5 mass% or more and 15 mass% or less, and the ratio L / D of the screw length L to the diameter D is 22 or more in the injection molding. Since an injection molding machine equipped with a single flight low shear type screw having a compression ratio of 1.6 or more and 1.8 or less is used, a fiber-reinforced resin molded product having high strength and high impact resistance can be obtained. .

It is sectional drawing which shows the injection molding machine which concerns on embodiment of this invention. It is a side view which expands and shows the supply part of the screw of the injection molding machine. It is sectional drawing which expands and shows the backflow prevention ring part of the injection molding machine. The graph which shows the relationship with the glass fiber compounding ratio with the amount of puncture energy absorption in MD of a fiber reinforced resin molded product, and a bending elastic modulus. The graph which shows the relationship with the glass fiber compounding ratio with the puncture energy absorption amount and bending strength in MD of a fiber reinforced resin molded product. The graph which shows the relationship with the glass fiber compounding ratio with the puncture energy absorption amount and bending elastic modulus in TD of a fiber reinforced resin molded product. The graph which shows the relationship with the glass fiber compounding ratio with the puncture energy absorption amount and bending strength in TD of a fiber reinforced resin molded product.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

<Injection molding machine>
In the injection molding machine shown in FIG. 1, reference numeral 1 denotes a heating cylinder, and 2 denotes a low-shearing screw that is disposed in the heating cylinder 1 so as to be capable of rotating and reciprocating. Although not shown, the injection molding machine includes a hydraulic motor that rotates the screw 2 and an injection cylinder that drives the screw 2 forward and backward.

  A hopper 3 for feeding a molding material is provided on the proximal end side of the heating cylinder 1, and an injection nozzle 4 is provided on the distal end of the heating cylinder 1. A band heater as an external heater 5 is wound around the outer periphery of the heating cylinder 1. The injection nozzle 4 is connected to a runner 7 of a mold 6 for molding a fiber reinforced resin molded product. The mold 6 includes a fixed mold 6a having a runner 7 and a movable mold 6b. A cavity 8 is formed by the fixed mold 6a and the movable mold 6b.

  The screw 2 includes a screw body 11 and a screw head 12 coupled to the tip of the screw body 11. The screw main body 11 is a single flight type in which the flights 13 are formed by one line. The ratio L / D of the length (length from the material supply port 13 to the screw tip) L of the screw body 11 and the diameter D of the screw body 11 is 22 or more. The upper limit of the L / D ratio may be about 30, for example.

  The screw body 11 includes a supply unit 14, a compression unit 15, and a metering unit 16 in order from the proximal end side (upstream side) to the distal end side (downstream side). The supply unit 14 has a length that is 10 to 15 times the diameter D. As shown in FIG. 2, the screw groove depth (height of the flight 13) d of the supply unit 14 is constant over the entire length of the supply unit 14, and the groove depth d is larger than any pellet length of the molding material 17. large. The molding material 17 supplied from the hopper 3 to the supply unit 14 is sent to the compression unit 15 through the space separated by the flight 13 by the rotation of the screw 2 while being softened by receiving heat from the external heater 5. .

  The compression part 15 is a section where the screw groove depth gradually decreases. The molding material 17 is compressed by the rotation of the screw 2 in the compression unit 15, plasticized and melted by receiving a large shearing force and heat, and sent to the metering unit 16 as a molten resin. The metering unit 16 is formed with a small screw groove depth so that the molten resin can be stored in the resin reservoir in front of the screw 2.

  The compression ratio of the screw 2 (the ratio of the volume per pitch of the grooves of the supply unit 14 and the metering unit 16) is 1.6 or more and 1.8 or less.

  As shown in FIG. 3, a backflow prevention ring 18 having a co-rotating structure is provided on the back of the screw head 12. The backflow prevention ring 18 is fitted to a coupling shaft 19 that couples the screw body 11 and the screw head 12 so as to be able to advance and retreat with a gap. On the outer periphery of the base end portion of the screw head 12, a groove 21 opened in the base end surface of the head 12 is formed at a circumferential interval, and a protrusion 22 protruding forward from the backflow prevention ring 18 in the groove 21. Are engaged. By this engagement, the backflow prevention ring 18 rotates with the screw 2.

<Molding of fiber reinforced resin molded products>
-About molding materials-
In the molding of a fiber reinforced resin molded product, as the molding material 17, carbon fiber resin pellets (long fiber pellets) formed by impregnating a carbon fiber bundle extending in the pellet length direction and glass fibers extending in the pellet length direction are used. Glass fiber resin pellets (long fiber pellets) formed by impregnating a bundle with resin are used. The length of the two kinds of pellets is 10 mm or more. Carbon fiber resin pellets and glass fiber resin pellets, which are long fiber pellets, have the same length as the pellet length, and therefore the weight average length of the fibers is 10 mm or more. The pellet length is preferably 15 mm or less (the weight average length of the fibers is 15 mm or less).

  PP (polypropylene) having an MFR (temperature 230 ° C., load 2.16 kg) of 9 g / 10 min to 65 g / 10 min may be adopted as the matrix resin for each of the carbon fiber resin pellets and glass fiber resin pellets. preferable.

  The carbon fiber resin pellets and glass fiber resin pellets have a combined content of carbon fibers and glass fibers in the molding material 17 of 20% by mass to 50% by mass (preferably 30% by mass to 50% by mass), Mixing is performed so that the ratio of the glass fiber to the total amount of the carbon fiber and the glass fiber is 5% by mass or more and 15% by mass or less, and the mixture is put into the hopper 3.

-Effect of the ratio of glass fiber to the total amount of carbon fiber and glass fiber on the strength and impact resistance of molded products-
A plurality of types of molding materials having different carbon fiber blending ratios were prepared using carbon fiber resin pellets and glass fiber resin pellets. The total content of carbon fibers and glass fibers in each molding material was 40% by mass. Puncture energy absorption amount, bending elastic modulus and bending strength of MD (direction in which the molten resin flows in the mold) and TD (direction perpendicular to MD) of the fiber reinforced resin molded products by these molding materials were measured.

  As carbon fiber resin pellets, PP-CF40-11 (L8) manufactured by Daicel with a carbon long fiber / PP = 40/60 mass ratio was used, and as glass fiber resin pellets, glass long fiber / PP = 40/60 mass was used. LR24A manufactured by Nippon Polypro Co., Ltd. was used. Table 1 shows the physical properties of these resin pellets.

  As the injection molding machine, a low shear type screw shown in Table 2 was used.

  The measurement results are shown in FIGS. 4 to 7, “puncture E” is an abbreviation for “puncher energy”, “CF” is an abbreviation for “carbon fiber”, and “GF” is an abbreviation for “glass fiber”.

  When FIG. 4 (MD puncture energy absorption amount and bending elastic modulus) and FIG. 5 (MD puncture energy absorption amount and bending strength) are seen, the bending elastic modulus increases with the increase in the glass fiber content. In addition, the bending strength decreases substantially linearly. However, when the blending ratio of the glass fiber is 5% by mass or more and 15% by mass or less, the bending elastic modulus and the bending strength decrease rate from zero glass fiber blending amount are less than 5%, regardless of the addition of the glass fiber. It can be seen that high strength is maintained.

  On the other hand, impact resistance is greatly improved with a small amount of glass fiber. That is, when the glass fiber content is 5% by mass or more, the impact resistance is improved by about 1.4 times compared to when the glass fiber content is zero. When the blending ratio of the glass fiber exceeds 20 masses, the improvement in impact resistance accompanying the increase in the blending ratio is slow.

  Next, looking at FIG. 6 (puncture energy absorption amount and bending elastic modulus at TD), the bending elastic modulus at TD gradually decreases as the glass fiber blending ratio increases. Even when the blending ratio of the glass fiber is 15 masses, the rate of decrease in the flexural modulus from zero glass fiber blending amount is only a few percent. Looking at FIG. 7 (Puncture energy absorption amount and bending strength at TD), the bending strength at TD is almost the same even when the blending ratio of glass fiber is increased. The change in impact resistance associated with the increase in the glass fiber blending ratio in TD has substantially the same characteristics as in the MD case.

  From the above results, it can be seen that the impact resistance can be greatly increased without greatly reducing the strength of the fiber-reinforced resin molded product by adding a small amount of glass fiber.

  Here, the effect of adopting the low shear type screw is as follows. By adopting the single flight 13, it is possible to reduce overriding of the molding material in which a large force is applied to the carbon fiber and the glass fiber. Further, it is possible to prevent a large force from being applied to the carbon fiber and the glass fiber between narrow flights. By reducing the compression ratio, the shearing force applied to the molding material at the compression portion is reduced, and damage to the carbon fiber and glass fiber is reduced. By increasing the groove depth d of the supply unit 14, the breakage of the carbon fiber and the glass fiber when the resin pellet bites into the screw is suppressed. Since there is no mixing head that promotes defibration, the carbon fibers and glass fibers are not strongly damaged. Since the L / D ratio is large (because the supply unit 14 is long), defibration proceeds without giving strong damage to the carbon fibers and glass fibers. Since the backflow prevention ring 18 rotates together with the screw, the damage received when the carbon fiber and the glass fiber pass through the flow path between the screw head 12 and the backflow prevention ring 18 is reduced. Since the flow path 20 between the screw head 12 and the backflow prevention ring 18 is enlarged, the molding material easily passes through the flow path 20 and the damage received by the carbon fiber and the glass fiber is reduced.

DESCRIPTION OF SYMBOLS 1 Heating cylinder 2 Screw 11 Screw main body 12 Screw head 14 Supply part 15 Compression part 16 Weighing part 17 Molding material 18 Backflow prevention ring

Claims (2)

A method for producing a fiber-reinforced resin molded article by injection molding using a molding material comprising carbon fiber resin pellets containing carbon fibers and glass fiber resin pellets containing glass fibers,
The weight average length of the fibers contained in each of the carbon fiber resin pellets and the glass fiber resin pellets is 10 mm or more,
The total content of the carbon fiber and the glass fiber in the molding material is 20% by mass to 50% by mass,
The ratio of the glass fiber to the total amount of the carbon fiber and the glass fiber is 5 mass% or more and 15 mass% or less,
An injection molding machine provided with a single flight low shear type screw having a ratio L / D of a screw length L to a diameter D of 22 or more and a compression ratio of 1.6 to 1.8. A method for producing a fiber-reinforced resin molded product, comprising using In claim 1,
A method for producing a fiber-reinforced resin molded product, wherein the backflow prevention ring of the injection molding machine is a co-rotating type that rotates together with the screw.

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