JP3439366B2 - Material burn prevention method in injection molding - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing burning of a material which is likely to occur when a synthetic resin is injection-molded by an in-line screw type injection device. [0002] An injection device generally called an in-line screw type is, as shown in FIG. 2, a plasticizing cylinder having a band heater (not shown) mounted on an outer periphery thereof. 1 has a structure in which a plasticizing screw 2 is provided so as to rotate and move forward and backward. The plasticizing cylinder 1 is provided with a nozzle member 12 at the tip of a plasticizing head 11 having a funnel-shaped inside, and a hopper 13 on the rear part of the cylinder. Further, the plasticizing screw 2 has a tip end surface having the plasticizing head 11.
A torpedo 21 formed in a conical shape corresponding to the inside of the torpedo is provided at a tip end, and has a ring valve 22 loosely fitted to a rear portion of the torpedo 21 and a seat ring 23 provided on an end face of the plasticizing screw. In such an injection device, the granular material resin stored in the hopper 13 is fed into the rear portion of the plasticizing cylinder 1 from the supply port 14 by the rotation of the plasticizing screw 2, and further forward by the rotation of the screw. Is transferred. In the course of this transfer, the material resin is melted and kneaded by shearing due to screw rotation and heating from the cylinder side, and the ring valve 22 is pushed open to open the plasticizing head 1.
1 and the torpedo 21. Further, the reaction force of the material transfer accompanying the screw rotation acts on the plasticized screw 2 as a resin pressure, whereby the plasticized screw 2 moves backward and the molten resin enters the plasticized head 11 on the screw front side. Will be accumulated.
That is, the set amount of the material resin is measured. When the above measurement is completed, the plasticizing screw 2
Moves forward with the rotation stopped, and presses the measuring resin by the torpedo 21. The resin pressure generated by this compression forcibly retreats the ring valve 22 until it comes into contact with the seat ring 23, prevents backflow of the metering resin into the screw gap, and further advances the plasticizing screw 2 to move the metering resin. Injection filling is performed from a nozzle member 12 to a mold (not shown). [0007] In plasticizing and measuring such a material resin, if even a very small portion of the material resin is in a state of being easily subjected to a large thermal history, a defect (black spot) called material burning due to carbonization of the resin may occur. Occurs in products. In particular, in the case of caps such as food packaging containers, the inclusion of black spots in a product is regarded as a fatal defect, and even fine black spots are excluded as defective products. [0008] The burning of the material due to the carbonization of the resin causes a small amount of resin that stays in the plasticizing cylinder for a long period of time due to an unpredictable cause, which is carbonized to burn the material. Cleaning by extraction is performed to prevent material burning. [0009] The standard for screw cleaning and removal cleaning is as follows.
In consideration of productivity, cleaning is performed once every two days and sampling cleaning is performed once.
It is performed once a month, but this does not solve all the burning of the material, and it has been difficult to reduce the mixed amount of the carbonized resin to 60 PPM or less. The present invention was conceived to solve the above-mentioned problem of burning of a material, and an object of the present invention is to determine the cause of carbonization of a resin in a plasticizing cylinder, and to take measures corresponding to the cause. It is an object of the present invention to provide a new method for preventing material burning in injection molding, which can significantly reduce material burning compared to the conventional method. According to the present invention, there is provided a plasticizing cylinder having a nozzle member at a tip of a plasticizing head and a hopper on a rear portion of the cylinder, and an inside of the plasticizing cylinder. Provided to be rotatable and retractable, in the injection molding of the resin by the injection device consisting of a plasticized screw located in the plasticizing head with the torpedo tip in the plasticizing head together with the ring valve, the contact surface of the plasticizing head with the molten resin The contact surface between the torpedo and the molten resin of the ring valve and the seat ring is subjected to CrN coating to reduce the stagnation of the contact surface due to the adhesion of the measuring resin. Of the molten resin is prevented, and the synergistic action of the CrN coating treatment and the W-Ni plating on the plasticizing head side causes the carbonization of the resin. Prevention of material burning due to liquefaction, and providing a powder removing device in the hopper, and removing in advance the fine particles or powdery resin that is susceptible to a large heat history at the time of plasticization in the powder removing device. Connect the antioxidant gas injection pipe, inject the antioxidant gas into the plasticizing cylinder from the hopper, and plasticize the resin in that gas atmosphere.
That is. FIG. 1 shows an injection apparatus which makes it possible to carry out the present invention. The injection apparatus has a funnel-shaped interior like the normal apparatus shown in FIG. Plasticizing head 11
A plasticizing screw 2 is rotatably and advancing and retracting inside a plasticizing cylinder 1 having a nozzle member 12 at a tip end thereof and a hopper 13 on a rear portion of the cylinder. The hopper 13 has an air removing hopper 15 for previously removing fine particles and powdery resin mixed in the granular material resin, and nitrogen as a gas for preventing oxidation of the molten resin in the plasticizing cylinder. A gas injection pipe 16 is provided. Further, the contact surface of the plasticizing head 11 with the molten resin is plated with W-Ni (tungsten-nickel) by the torpedo 21 at the tip of the plasticizing screw 2 and the molten resin of the ring valve 22 and the seat ring 23. The contact surfaces are each treated with a CrN (chromium nitride) coating, thereby increasing the surface smoothness of the contact surface, improving the slip of the molten resin, and preventing long-term stagnation due to adhesion. In the injection molding of the resin by such an injection device, fine particles or powdery resin, which is susceptible to a large thermal history at a volume ratio to the granular resin, are removed by the air removing hopper 15 before being stored in the hopper 13. The material resin having the uniform particle size is stored in the hopper. The material resin in the hopper is fed into the rear portion of the plasticizing cylinder 1 from the supply port 14 by the rotation of the plasticizing screw 2 as in the prior art, and is further melted and kneaded while being transferred to the front of the cylinder. Above torpedo 2
1 is metered into the plasticizing head 11 on the front. In the plasticizing process up to this measurement, the molten resin tends to stagnate on the contact surface with the molten resin in each part from the seat ring 23 to the torpedo 21 in the past. Of the molten resin is less likely to occur due to the CrN coating treatment, and the resin that has been carbonized due to the long-term high-temperature and high-pressure heat history due to the long-term residence is almost invisible even when the screw is cleaned. Therefore, the defective rate of the product due to burning of the material is significantly reduced as compared with the conventional case. Also on the plasticizing head side, the W-Ni plating on the contact surface reduces the stagnation due to the adhesion of the measuring resin, and the defective rate at which the carbonized resin is kneaded into the product as black spots due to the synergistic action with the screw side. Is incomparably lower than before. The reduction of the kneading defect rate is further improved by the removal of fine particles or powdery resin which is susceptible to a large heat history by the air dusting hopper 15, and material burning caused by long-term stagnation of the molten resin is caused. Most of them will be solved. However, material burning is not only long-term retention of molten resin,
In some cases, this is due to oxidation of the resin during plasticization, and material burning due to such other causes is difficult to solve only by surface treatment on the plasticizing head side or plasticizing screw side. The problem can be reduced by adopting the oxidation suppressing means. This is achieved by injecting an inert gas into the plasticizing cylinder 1 from the injection pipe 16 of the hopper 13 to replace the air between the granular resins with the inert gas and to confine the granular resin in an inert gas atmosphere. By melt-kneading.
This suppresses oxidation due to oxygen in the air, which is likely to be caused by melt-kneading under high temperature and high pressure, so that even if fine particles or powdery resin which is susceptible to a large heat history is mixed, the initial stage caused by oxidation is caused. The material is prevented from burning due to carbonization, and a certain effect is achieved. The following table shows the black spot kneading defect rate in the case of the present invention and the conventional case, and the material resin is polyethylene. Note that an apparatus having both functions of mixing and dusting was used as the air dusting hopper. Nitrogen gas was used as an antioxidant gas. Defective rate (PPM) Reduction rate (%) Screw cleaning Conventional (no treatment) 60.0 0 1 time / 2 days Nitrogen atmosphere 10.0 83 None, CrN coating 1.0 90 None, Air dedusting hopper 1 0.0 0 no and W-Ni plating 0.550 no As described above, the reduction of the defective rate was most remarkable in the above, and finally the above conditions, that is, the plasticizing head side was subjected to W-Ni plating. With the synergistic effect of this, it is possible to reduce and prevent material burning due to long-term stagnation to a value close to perfection, and even if fine black spots are mixed in due to material burning, it is a fatal defect as a product Cap for food packaging containers Even in the case of molding of a kind, it is possible to carry out the molding operation without frequently performing screw cleaning as in the related art. The combined use of the above or the above means further improves the material burning prevention effect, and also prevents the material burning due to oxidation in the melt-kneading in a nitrogen atmosphere, so that the effect is remarkable and the molding efficiency is improved. It can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic explanatory view of an injection apparatus that can be employed for implementing a method for preventing material burning in injection molding according to the present invention. FIG. 2 is a schematic explanatory view of a normal injection device. [Description of Signs] 1 Plasticizing cylinder 2 Plasticizing screw 11 Plasticizing head 12 Nozzle member 13 Hopper 14 Supply port 15 Air dedusting hopper 16 Nitrogen gas injection pipe 21 Torpedo 22 Ring valve 23 Seat ring

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Suzuki 180, Oshita-shi, Oji, Komaki-shi, Aichi Prefecture Within Nihon Crown Cork Co., Ltd. Resin Kogyo Co., Ltd. (72) Inventor Hideyoshi Miyasaka Nagano Prefecture, Hanishina-gun, Sakajo-cho, 2110 Nanjo, Nashiro Resin Kogyo Co., Ltd. In-house (56) References JP-A-9-70863 (JP, A) JP-A-6-226802 (JP, A) JP-A-10-146873 (JP, A) JP-A-11-28725 (JP, A) JP-A-7-80893 (JP, A) JP-A-8-66938 (JP, A) JP-A-6-15708 (JP, A) JP-A-6-246803 (JP, A) JP-A-10-108 36935 (JP, A) JP-A-10-193418 (JP, A) JP-A-11-314259 (JP, A) JP-A-55-60323 (JP, U) Patent 2844697 (JP, B2) (58) Fields investigated (Int. .7, DB name) B29B ^7/ 00-7/94 B29C 45/00-45/84 B29C 47/00-47/96

Claims (1)

(1) A plasticizing cylinder having a nozzle member at a tip of a plasticizing head and a hopper on a rear portion of the cylinder, and a rotatable and retractable inside of the plasticizing cylinder. In the injection molding of a resin by an injection device comprising a plasticizing screw having a torped end at the tip together with a ring valve in a plasticizing head, a contact surface of the plasticizing head with a molten resin is W-Ni plated. Treatment to reduce the stagnation due to the adhesion of the metering resin to the contact surface, while applying a CrN coating treatment to the contact surface between the torpedo and the molten resin of the ring valve and the seat ring to adhere the molten resin to the contact surfaces. The stagnation is prevented, the CrN coating treatment and W on the plasticizing head side
-Prevent burning of the material due to carbonization of the resin by synergistic action with Ni plating, and provide a powder removing device in the hopper, and in the powder removing device, fine granules or powders which are susceptible to a large heat history during plasticization. Removing the resin in advance and connecting the antioxidant gas injection pipe to the hopper, injecting the antioxidant gas into the plasticizing cylinder from the hopper, and plasticizing the resin in the gas atmosphere. A method for preventing material burning in injection molding, characterized in that: