CN116890427A - Injection molding device for directly injection molding fiber reinforced thermoplastic material - Google Patents

Abstract

The invention provides an injection molding device for directly injection molding a fiber reinforced thermoplastic material, which comprises a screw for eliminating maldistribution of reinforced fibers in a thermoplastic resin without applying excessive shearing action. The screw is disposed in a barrel of the injection molding machine, is rotatable and movable in a barrel axis direction, and is fed with a thermoplastic resin raw material through a hopper disposed upstream of the barrel, and is fed with reinforcing fibers through a fiber feeder disposed downstream of the barrel. The screw comprises: a first stage screw having a surface screw flight for melt-plasticizing the resin raw material; the second section of screw rod is connected with the first section of screw rod, and a mixer arranged at the tail end of the second section of screw rod is provided with a channel for forward conveying and reverse conveying of the molten resin; the screw head is arranged at the tail end of the screw and is provided with a pin structure; the molten material formed by the conveyed thermoplastic resin and the reinforced fibers is subjected to stirring and mixing effects exerted by the screw, so that the reinforced fibers are uniformly dispersed in the molten material.

Description

Injection molding device for directly injection molding fiber reinforced thermoplastic material

Technical Field

The invention relates to the technical field of injection molding, in particular to an injection molding device for directly injection molding a fiber reinforced thermoplastic material.

Background

The range of applications for fiber reinforced thermoplastic composite injection molded articles is increasing. The molding method of the fiber reinforced thermoplastic resin is generally to melt and plasticize the resin by a twin screw extruder, then impregnate the fiber into the molten resin to obtain master batch particles, and then make the master batch particles into products by an injection molding technology. However, the process of manufacturing the master batch is complex, and an intermediate link exists, so that the master batch is expensive. Therefore, an injection molding device capable of directly adding raw materials and directly performing injection molding on fiber reinforced thermoplastic resin without a granulating step is provided.

When the dispersion of the fibers in the thermoplastic resin is better, the reinforcing effect obtained by adding the fibers is better. In order to achieve uniform dispersion of the fibers, a method of enhancing the shearing force is generally adopted, but too strong a shearing force may cause severe breakage of the reinforcing fibers, decrease the length of the added fibers, and excessively short the effective fiber length in the final molded article, resulting in failure in the mechanical properties of the resulting article to satisfy the desired effect (EP 3098052 A1). Therefore, it is necessary to reduce the shearing force to prevent the fibers from being excessively cut, but the reinforcing fibers are not uniformly dispersed in the thermoplastic resin after the shearing action is reduced. The reinforcing fibers are easier to be blocked and difficult to be uniformly dispersed in the molten resin, and particularly, even if a quantitative feeder for forcibly adding fibers is added, the fiber blocks can not be eliminated, so that the uniform distribution in the reinforced fiber thermoplastic resin is ensured.

Disclosure of Invention

The purpose of the present invention is to innovate a fiber-reinforced thermoplastic resin injection molding device and a screw used in the injection molding device. Specifically, it is an object to provide an injection molding apparatus and a screw used in combination with the apparatus, which can disperse reinforcing fibers added to a molten resin more uniformly and ensure that the fibers are not excessively sheared to cause an excessively short effective fiber length in a molded article.

In order to achieve the above object, the present invention provides an injection molding apparatus for direct injection molding of a fiber-reinforced thermoplastic material, having a screw capable of rotating and axially moving in a barrel, the screw comprising: a first stage screw having a surface screw flight for melting the resin raw material supplied; the second section of screw rod is connected with the first section of screw rod, and a mixer is arranged at the tail end of the second section of screw rod; the screw head is arranged at the tail end of the screw and is provided with a pin structure; thermoplastic resin raw materials are added into a charging barrel through a hopper, reinforcing fibers are added into the charging barrel through a fiber feeder, molten resin is generated under the shearing action generated by rotation of a heating device and a screw, the conveyed molten material formed by the thermoplastic resin and the reinforcing fibers is subjected to stirring and mixing action by the screw to enable the fibers to be dispersed in the molten resin, uniform dispersion of the reinforcing fibers in a melt is ensured, and finally the screw is advanced for injection, so that the molten resin containing the reinforcing fibers enters a die cavity through a screw head and a nozzle to be molded to obtain a product.

The upstream, downstream, front end, and rear end used in the present invention are based on the direction in which the screw conveys the molten resin.

The present invention is preferably applied to an injection molding method in which the reinforcing fiber feeding position is downstream of the resin raw material feeding position.

The kneading structure in the screw of the present invention may be provided as a disk-shaped kneader.

Preferably, the disc-shaped mixer is arranged at the tail end of the second section of the screw rod and consists of a first groove-shaped spiral structure, a second groove-shaped spiral structure, an annular channel and a disc-shaped structure.

Preferably, the first groove-like helical structure is arranged on a disc-like structure, preferably in a number of more than 3. The bottom of the first groove-shaped spiral structure is tangent to the annular channel, and forms a channel for forward flow of molten resin with the inner wall of the charging barrel, and the processing depth of the channel is preferably the same as the depth of the spiral groove of the second section screw metering section, namely, the processing depth is 0.03-0.04D. The spiral direction of the first groove-shaped spiral structure is the same as the spiral direction of the second section screw thread, and the spiral lead angle is larger than the spiral lead angle of the second section screw thread but smaller than 45 degrees.

Preferably, the second groove-shaped spiral structures are arranged on the disc-shaped structure, the number of the second groove-shaped spiral structures is the same as that of the first groove-shaped spiral structures, a molten resin countercurrent passage is formed with the inner wall of the charging barrel, and the machining depth of the second groove-shaped spiral structures is preferably half that of the first groove-shaped spiral structures, namely, the machining depth is 0.015-0.02D. The spiral direction of the second groove-shaped spiral structure is opposite to that of the first groove-shaped spiral structure, and the values of the spiral lift angles are the same.

Preferably, the annular channels are located between adjacent disc-like structures. The processing depth is preferably the same as the groove depth of the metering section of the second section screw, namely the processing depth is 0.03-0.04D, and the width is preferably one third to one half of the width of any disc-shaped structure.

Preferably, the screw head is mounted at the tail end of the screw, a pin structure is configured on the screw head, the pin structure is arranged on a channel formed by the screw head and the rubber ring and is in annular configuration, and the cross section of the pin structure can be in a round shape, a rectangular shape or a diamond shape.

The invention provides an injection molding device applying the screw, which comprises: a feed cylinder, on which a nozzle for melt injection and a heating device for melting the resin raw material are arranged; a screw provided inside the cylinder and rotatable and movable along a cylinder axis direction; a mixer provided at the end of the screw; a hopper that adds a thermoplastic resin raw material into the barrel; and a fiber feeder provided downstream of the hopper for adding reinforcing fibers into the barrel.

In addition, the invention provides an injection molding method using the screw, wherein thermoplastic resin raw material is added to a charging barrel at an upstream hopper, reinforcing fibers are added to the charging barrel at a downstream fiber feeder, a melt with uniformly distributed reinforcing fibers is obtained under the functions of melting, plasticizing and mixing of the screw, and finally, the injection molding is performed to obtain a fiber reinforced thermoplastic material product, wherein the charging barrel is provided with the screw which can rotate and move along the axis direction of the charging barrel.

The invention provides an injection molding device for directly injection molding a fiber reinforced thermoplastic material. The apparatus includes a screw for eliminating maldistribution of reinforcing fibers in a thermoplastic resin without applying excessive shearing.

Drawings

Fig. 1 is a schematic view of an injection molding apparatus according to the present embodiment.

Fig. 2 is a schematic view of a fiber feeder according to the present embodiment.

Fig. 3 is a schematic view of a screw with a disk-shaped kneader according to this embodiment.

Fig. 4 is a schematic perspective view of a disk-shaped kneader according to this embodiment.

Fig. 5 is a schematic view showing the development of the disk mixer according to the present embodiment in the circumferential direction.

Description of the reference numerals

10. Screw rod

11. First section screw

11A charging section

11B compression section

11C metering section

12. Second section screw

12A charging section

12B compression section

12C metering section

13. First segment of screw thread

14. Second-stage screw thread

15. Mixing device

15a first groove-like structure

15b second groove-like structure

15c annular channel

15d disk structure

16. Rubber cushion ring

17. Rubber ring

18. Glue passing head

20. Charging barrel

21. Heater

22. Nozzle

30. Hopper

40. Plasticizing motor

50. Injection cylinder

60. Metering feeder

70. Fiber feeder

F reinforcing fiber

Detailed Description

The present invention will be described in detail below based on embodiments shown in the drawings

The upstream, downstream, and front and rear ends used in the present invention are based on the direction in which the screw conveys the molten resin.

First, the structure of the injection molding apparatus of the present invention will be described. Fig. 1 is a schematic view showing the structure of an injection molding apparatus provided with a plasticizing screw for injection molding. The injection molding device is provided with: screw 10, barrel 20, hopper 30, plasticizing motor 40, injection cylinder 50, nozzle 22. The screw 10 is disposed inside the barrel 20, and the hopper 30 is disposed on the upper portion of the barrel 20. The rear part of the screw 10 is connected with a plasticizing motor 40, and the plasticizing motor 40 drives the screw 10 to rotate. The injection cylinder 50 is connected with the screw 10 and the plasticizing motor 40, and can drive the screw 10 and the plasticizing motor 40 to advance and retreat.

The plasticizing operation of the injection molding apparatus according to the present embodiment will be described below with reference to fig. 1 and 2.

First, in the injection molding apparatus, the injection cylinder 50 drives the screw 10 to retreat together with the plasticizing motor 40, and at the same time, the heater 21 heats the cylinder 20, and the plasticizing motor 40 drives the screw 10 to rotate. Pellets of thermoplastic resin, which may be selected from polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyamide (PA), polyethylene terephthalate (PMMA), and acrylonitrile-butadiene-styrene (ABS), etc., are added to the cartridge 20 through the hopper 30 according to the production requirements of the finished product. Long fibers, such as glass fibers, carbon nanofibers, etc., and natural fibers, such as bamboo or pulp, may be added to the cartridge 20 via the fiber feeder 70. The length of the fibers is preferably 2mm or more, more preferably about 6 to 12 mm.

The plasticizing motor 40 rotates the screw 10 to feed forward the thermoplastic resin pellets fed through the hopper 30, and the thermoplastic resin pellets are melted and plasticized by the combined action of the compression section 11B of the first-stage screw 11 and the heater 21, pass through the metering section 11C, and are fed to the feeding section 12A of the second-stage screw 12.

The continuous fibers F are cut to a desired length and then fed into the barrel 20 through the fiber feeder 70, and the feeding elements in the fiber feeder 70 may be of a single screw structure or a double screw structure, and the fiber feeder of the single screw structure is shown in the present invention. The added fibers are mixed with the molten resin passing through the metering section 11C of the first-stage screw 11 in the charging section 12A of the second-stage screw 12, transported together and stored downstream of the screw 10, and when the amount for one shot is stored, the screw 10 stops rotating and retreating, completing the plasticizing process.

Fig. 2 shows a schematic front view of the screw 10. The screw 10 is a two-stage screw similar to a vented screw, and includes: a first-stage screw 11, and a second-stage screw 12 connected to the first-stage screw 11. The first section screw 11 has feeding section 11A, compression section 11B and metering section 11C in proper order from the upstream to the downstream, and the second section screw 12 has feeding section 12A, compression section 12B and metering section 12C in proper order from the upstream to the downstream, wherein the end of metering section 12C is provided with mixer 15. The flights 13 on the first stage screw 11 and the flights 14 on the second stage screw are helical along the screw circumferential surface.

FIG. 3 is an enlarged perspective view of the front end of a screw with a mode A kneader. In the present embodiment, the kneader 15 is composed of four structures, namely, a first groove-like spiral structure 15a, a second groove-like spiral structure 15b, an annular channel 15c, and a disk-like structure 15d. The first groove-shaped spiral structure 15a and the second groove-shaped spiral structure 15B are arranged on the disc-shaped structure 15d, the spiral direction of the first groove-shaped spiral structure 15a is the same as the spiral direction of the thread 14 of the compression section 12B, and the spiral angle is larger than the thread angle of the thread 14 but smaller than 45 degrees; the spiral direction of the second groove-shaped spiral structure 15b is opposite to that of the first groove-shaped spiral structure 15a, and the values of the spiral angles are the same. The annular channels 15c are located between adjacent disc-like structures 15d.

FIG. 4 is a schematic view showing the circumferential development of a specific structure of the kneader in order to explain the embodiment A. The first groove-like spiral structure 15a is recessed inward from the surface of the disk-like structure 15D, the bottom of the recess is tangent to the annular channel 15C, and the processing depth is preferably the same as the screw groove depth of the metering section 12C, that is, the processing depth is 0.03-0.04D, and more preferably, the number is more than 5, wherein the term "recess" is not limited to the processing manner and the cross-sectional shape thereof, the cross-section thereof may be semicircular, U-shaped, trapezoidal or rectangular, the maximum size of the cross-section thereof in the circumferential direction should be more than pi D/2n, wherein D is the inner diameter of the cylinder 20, and n is the number of the first groove-like structures 15a, and if less than pi D/2n, the channel flow cross-sectional area on the disk-like structure is too small to cause accumulation of the fiber-reinforced thermoplastic resin molten material, causing the molten resin to spray at the fiber feeder 70. The second groove-shaped spiral structure 15b is recessed inward from the disc-shaped structure 15D to the surface, the machining depth is preferably half of the machining depth of the first groove-shaped spiral structure 15a, namely, the machining depth is preferably 0.015-0.02D, the number of the second groove-shaped spiral structures is preferably more than 3, and more preferably, the number of the second groove-shaped spiral structures is the same as that of the first groove-shaped spiral structures 15a, wherein the term of "recess" is not limited to the machining mode and the cross-sectional shape, the cross-section of the second groove-shaped spiral structure can be semicircular, U-shaped, trapezoid or rectangular, the cross-sectional size of the second groove-shaped spiral structure is preferably one fourth of the cross-sectional size of the first groove-shaped structure 15a or less, and if the cross-sectional size is too large, the counterflow materials are excessive, and the forward conveying of the materials is not facilitated; the annular channels 15C are located between adjacent disk-like structures 15d, preferably having a depth equal to the depth of the grooves of the metering section 12C, and preferably having a width of one third to one half of the width of any one disk-like structure 15d, and if the width is below this ratio, which is detrimental to the dispersion of the fibers, the ratio is above which would result in too much material flowing in the circumferential direction, which is detrimental to the material transport.

In the present invention, when the molten resin fed from the upstream side and mixed with the fiber mass which has not completed the unwinding passes through the kneader 15, the molten resin is dispersed and passed through the plurality of first groove-like spiral structures 15a, passed through the first disk-like structures in the direction a shown in fig. 4, and enters the annular passage 15c. The rotation of the screw 10 drives a part of the molten resin containing the fiber bundles to move in the annular passage 15C in the direction C shown in fig. 4; a portion of the dispersion enters the first grooved helical structure 15a of the next disc-like structure and is conveyed downstream; a further portion of the second grooved helix 15B, which diverges into the last disc-like structure, moves in the direction B shown in fig. 4, forming a return flow for upstream transport. The molten resin which flows back returns to the upstream position and enters the inside of the wound reinforcing fiber block, so that the winding condition of the reinforcing fiber block is weakened, and the winding block of the reinforcing fiber is decomposed due to the impact of the molten resin which flows back and the higher energy content of the molten resin, so that the winding is unwound, and the fiber dispersion is promoted. The disk-shaped mixer of the invention can split the molten resin containing the reinforcing fibers for a plurality of times and form countercurrent flow, so that the reinforcing fibers can be fully unwound and dispersed in the molten resin.

According to the above preferred embodiment, the mixer 15 is disposed on the downstream side of the screw 10 and has a length in the range of 0.5D to 1.2D, the number of disc structures should be 3 to 6, and if the number is less than 3, the split and reverse flow conditions are weakened, resulting in a decrease in the degree of dispersion of the reinforcing fibers in the molten thermoplastic resin; on the other hand, when the number is more than 6, the number of times of the division of the molten material mixed with the reinforcing fibers is excessive, which results in an increase in the number of times of shearing of the fibers by the screw and a decrease in the fiber length.

The control method of the fiber feeder 70 according to the present embodiment is a simple on/off method, and the rotational speed of the spiral structure in the fiber feeder 70, that is, the fiber feeding speed is constant. The content of the reinforcing fibers in the thermoplastic resin is adjusted by adjusting the rate of addition of the thermoplastic resin pellets by the doser 60 at the hopper. When the content of the reinforcing fiber is more than 10%, the conveying resistance of the molten resin containing the reinforcing fiber in the kneader 15 becomes large, and the pressure at the fiber inlet is increased due to clogging, resulting in an overflow phenomenon. The mass fraction of the reinforcing fiber in the present invention is preferably 10% to 50%, more preferably 15% to 45%.

Claims (3)

1. An injection molding apparatus for direct injection molding of fiber reinforced thermoplastic material, the apparatus comprising a screw; the screw is arranged in the injection molding machine charging barrel, can rotate and move along the axis direction of the charging barrel, adds thermoplastic resin raw materials through a hopper arranged at the upstream of the injection molding device charging barrel, and adds reinforcing fibers through a fiber feeder arranged at the downstream of the injection molding device charging barrel;

characterized in that the screw comprises:

a first stage screw having a surface screw flight for melt-plasticizing the resin raw material;

the second section of screw rod is connected with the first section of screw rod, a mixer is arranged at the tail end of the second section of screw rod, stirring and mixing effects are applied to molten materials formed by the conveyed thermoplastic resin and the reinforced fibers, so that the reinforced fibers are uniformly dispersed in the molten materials, and the mixer is provided with channels for conveying the molten resin in the forward direction and the reverse direction;

the screw head is arranged at the tail end of the screw;

the mixer is arranged at the tail end of the second section of screw rod and consists of a first groove-shaped spiral structure, a second groove-shaped spiral structure, an annular channel and a disc-shaped structure;

the first groove-shaped spiral structures are arranged on the disc-shaped structures, and the number of the first groove-shaped spiral structures is more than 3; the bottom of the first groove-shaped spiral structure is tangent to the annular channel, and forms a channel for forward flow of molten resin with the inner wall of the charging barrel, and the processing depth of the channel is the same as the depth of the spiral groove of the second section of screw metering section; the spiral direction of the first groove-shaped spiral structure is the same as the spiral direction of the second section screw thread, and the spiral lead angle is larger than the spiral lead angle of the second section screw thread but smaller than 45 degrees;

the second groove-shaped spiral structures are arranged on the disc-shaped structure, the number of the second groove-shaped spiral structures is the same as that of the first groove-shaped spiral structures, a molten resin countercurrent passage is formed with the inner wall of the charging barrel, and the machining depth of the second groove-shaped spiral structures is half of that of the first groove-shaped spiral structures; the spiral direction of the second groove-shaped spiral structure is opposite to the spiral direction of the first groove-shaped spiral structure, and the values of the spiral lift angles are the same;

the annular channels are positioned between adjacent disc-shaped structures; the processing depth is the same as the screw groove depth of the second section screw metering section, and the width is one third to one half of the width of any disc-shaped structure.

2. An injection molding apparatus for direct injection molding of fiber reinforced thermoplastic material according to claim 1, wherein said screw head is mounted at the end of said screw and is provided with a pin structure disposed in an annular configuration in a channel defined by the screw head and the stripper rubber.

3. The injection molding apparatus for direct injection molding of a fiber-reinforced thermoplastic material according to claim 1, comprising:

a feed cylinder, on which a nozzle for melt injection and a heating device for melting the resin raw material are arranged;

a screw provided inside the cylinder and rotatable and movable along a cylinder axis direction;

the screw head is arranged at the tail end of the screw and is provided with a pin structure;

a mixer provided at the end of the screw;

a hopper that adds a thermoplastic resin raw material into the barrel;

and a fiber feeder provided downstream of the hopper for adding reinforcing fibers into the barrel.