JP2013091170A - Double flight screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double flight screw capable of stably processing a molded article in which a miniaturized ultraprecise molding or high dimensional accuracy is required.SOLUTION: The double flight screw is used for an injection molding machine. A main flight and a sub-flight are arranged in a compression and melt zone of the screw which includes: a feed zone; the compression and melt zone; and a metering zone. A root diameter constant portion E in which the depth of a melt channel 13b is constant is formed on the bottom surface of the melt channel 13b divided by the sub-flight, that is, in front of the metering zone D. The screw includes a function with which a molding material transferred in the melt channel 13b is homogenized by the operation of the metering function in the root diameter constant portion E, and supplied to the metering zone D to be further homogenized.

Description

  The present invention relates to a thermoplastic resin screw in an injection molding machine, an extrusion molding machine, a blow molding machine, and the like, and more particularly, to a double flight screw with a main flight and a sub flight.

  In a thermoplastic resin screw used in an injection molding machine or the like, in order to improve plasticization efficiency and kneading efficiency, a sub flight as a sub flight is provided in a full flight screw as a main flight by a single thread screw screw. A barrier screw is used.

  In a barrier screw with this type of subflight in the middle of the screw in the longitudinal direction, the molten resin is immediately passed over the subflight and melted and kneaded in the melt channel. By promoting the above, uniform melting performance is improved. However, in general injection molding machines, the plasticization state due to the change in the effective screw length based on the reciprocating motion of the screw length may not be sufficient to maintain the repeatability of the dimensions and shape of the ultra-precise molded parts. is there.

  In view of the above-mentioned problems, the inventors of the present invention have improved the melt-kneading performance of plastics including general-purpose resins, engineering plastics, and super engineering plastics, and improving the homogenization of plasticity with a screw having a relatively short general length. A barrier screw capable of preventing defects of dimensional accuracy, fine burrs and shorts has been proposed (see Patent Document 1).

  Further, as a conventional double flight screw of this type, Patent Document 2 discloses a screw for a resin molding machine. As shown in FIG. 9, this screw 1 is a rod in which a flight is spirally wound around a shaft 2 of a rod-like body, and has a feed zone A, a compression zone B, a melt zone C, and a metering zone D. A multi-strip flight having a plurality of flights 3a, 3b, 3c is provided from fee zone A to compression zone B. The melt zone C is a double flight having a main flight 4 and a sub flight 5. The metering zone D includes a flight 6.

  FIG. 10 is a cross-sectional view showing an example of the double flight screw cut along the main flight 7 and the sub flight 8. The bottom surfaces of the compression zone B and the melt zone C are formed so as to gradually become deeper from the feed zone A side toward the metering zone D, and the metering zone is an inclined surface gradually becoming shallower from the front of the metering zone D. It is formed in a shape reaching D.

Japanese Patent No. 3170757 JP 2002-192597 A

  By the way, in recent years, expectations and demands for small precision molding have increased, and in narrow pitch connectors used in mobile phones etc. and multi-part liquid crystal polymer (LCP) thin base molding, LCP resin and Amodel It is not easy to secure dimensional accuracy by resin or other engineering plastic resin molding and to prevent fine burrs and shorts. Moreover, it is not easy to enable stable molding to be repeated for a long time.

  In recent years, there has been a proposal for a pre-plastic injection device (see Japanese Patent No. 3311999) as a response to such market needs, which is put into practical use in this market.

  On the other hand, not only in the small precision molding field, high dimensional accuracy may be required even for a large molded product such as a silicon wafer transfer container. In such a transfer container, for example, a wafer holding plate made of 25-stage PBT (polybutylene terephthalate) resin that stores silicon wafers requires high dimensional accuracy, but it is difficult to ensure dimensional accuracy, and the conventional yield is low. However, it is about 65%, which is not sufficient, and hinders production cost reduction.

  Therefore, the present invention can perform molding processing of small precision components such as narrow pitch connectors and products requiring high dimensional accuracy, and does not impair the stability of molding even after repeated use for a long time. The purpose is to provide a high-performance double flight screw that eliminates the drawbacks of inline screws.

  As a technical means for achieving the above object, a double flight screw according to the present invention comprises two flights having different spiral lead angles, and includes a feed zone, a compression and melt zone, and a metering zone. A subflight is disposed from an arbitrary position in the compression and melt zone to the front of the metering zone, and a cylindrical bottom surface is formed with a constant valley diameter of a part of the melt channel in the compression and melt zone. The formed valley diameter constant part is formed.

  The molding material heated and melted in the solid channel is transferred to the melt channel over the sub flight by the rotation of the screw, and scraped in the melt channel by the main flight. When the kneading and melting are promoted to reach the constant valley diameter portion, the portion is more uniformized by receiving the metering action of the portion.

  The double flight screw according to the invention of claim 2 is formed by gradually reducing the valley diameter so that the bottom surface of the compression and melt channels of the melt zone gradually becomes deeper toward the metering zone. It is characterized in that the above-described constant valley diameter portion in which a cylindrical bottom surface is formed with a constant valley diameter is formed in front of the zone.

  At the same time, the volume in the melt channel is designed to be approximately equivalent to the injection weight of the molded product, so that the next shot can be measured with the melted resin in the melt channel already melted in the melt channel metering zone and the tip metering zone. It becomes possible to measure via, and the molten resin temperature, viscosity, and kneading state are sufficiently uniformized.

  The molding material having the melt viscosity, the kneading degree, and the resin temperature made uniform by the metering action in the constant valley diameter portion is made more uniform in the molten state again in the subsequent metering zone.

  According to the double flight screw of the present invention, the molding material that has been kneaded and melted uniformly in the compression and melt zone before being fed to the metering zone is made uniform in the metering portion in the valley diameter constant portion. Since the molten state is made uniform by receiving the ring action, the measurement is performed in the subsequent metering zone, and the metering action is received again to promote the homogenization to be used for the molding process. For this reason, even if a screw reverse | retreats and the effective screw length for plasticization becomes short, a molded product becomes more uniform in a molten state. In addition, molding accuracy is greatly improved by uniformizing the molding material repeatedly, and high dimensional accuracy is required even for small precision molding such as narrow pitch connectors and large molded products such as silicon wafer transfer container parts. Therefore, it is possible to sufficiently cover the defects of the conventional in-line screw.

It is an expanded view of the resin transfer groove | channel (channel) of the double flight screw which concerns on this invention. (A) is sectional drawing along the PP line in FIG. 1, (b) is sectional drawing along the QQ line similarly. It is an external view of the double flight screw which concerns on this invention. Injection resin according to each of the double flight screw according to the present invention and the conventional double flight screw (conventional type having the shape of FIG. 3 but having no constant valley diameter in the melt channel and having the shape of the melt channel of FIG. 10). It is the figure which compared the temperature profile and has shown the case where a back pressure is zero. It can be said that the double flight screw of the new invention has a much better uniform melting performance. It can be said that it is the most important factor as a screw plasticizing function that influences the molding quality that the melting temperature is repeatedly made constant in a state where the back pressure is zero. It is the figure which compared the injection resin temperature profile by each of the double flight screw concerning this invention, and the conventional double flight screw, and has shown the case where a back pressure is 5 (kg / cm < ² >). A silicon wafer shipping container holding plate is formed by a conventional general-purpose screw, a conventional double flight screw, and a double flight screw according to the present invention using the double flight screw according to the present invention, and is mounted on a predetermined shipping container. It is a figure which shows the measurement point of a silicon wafer at the time of carrying out comparative measurement of the holding plate precision. It is a comparison table which shows the pass rate as a result of forming the left and right holding plates of a silicon wafer and mounting them on a shipping container and measuring the dimensions with a Nikon laser machine. Shows the molding machine, each screw, molding result and appearance quality judgment when molding 0.4mm narrow pitch connector (same mold with 8 pcs). It is a figure which shows an example of a double flight screw. It is a figure explaining the structure of the conventional double flight screw, and is a figure equivalent to Fig.2 (a).

  Hereinafter, the double flight screw according to the present invention will be specifically described based on the illustrated preferred embodiment. In addition, the same code | symbol is attached | subjected about the site | part same as the conventional structure shown in FIG. 9 and FIG.

  FIG. 3 is a view showing the outer shape of the double flight screw 10 according to the present invention, and FIG. 1 is a development view of the double flight screw 10. As shown in FIG. 3, the main flight 11 is spirally wound around the shaft 2, and a feed zone A, a compression and melt zone M, and a metering zone D are formed in this order. In the compression and melt zone M, a sub flight 12 having a lead angle larger than that of the main flight 11 is formed to form a double flight zone. 2 is a cross-sectional view of the compression and melt zone M, (a) is a cross-sectional view taken along the line P-P shown in FIG. 1, and (B) is a cross-sectional view taken along the line Q-Q. The secondary flight 12 rises from the front of the main flight 11 at the start of the compression and melt zone M, and the channel formed by the main flight 11 is divided into a primary solid channel 13a on the upstream side and a secondary side on the downstream side. Separated into melt channel 13b. The outer peripheral end of the main flight 11 has a gap of about 0.03 to 0.05 with respect to the inner peripheral surface of the cylinder barrel 15. The outer diameter of the subflight 12 is smaller than the outer diameter of the main flight 11, and the subflight A suitable gap through which the melt film passes is formed at the outer peripheral end of the flight 12 and the inner peripheral surface of the cylinder barrel 15. Therefore, the molding material supplied to the solid channel 13a is transferred to the melt channel 13b through this gap by the rotation of the screw 10 in the arrow R direction.

  As shown in FIG. 2A, the bottom surface of the melt channel 13b gradually decreases from the upstream side to the downstream side of the compression and melt zone M, that is, gradually increases from the outer peripheral surface of the main flight 11. It is formed on an inclined surface. And in the downstream part of this bottom face, a constant valley diameter E where the depth does not change is provided. The shaft 2 gradually increases in diameter from the downstream end portion of the valley diameter constant portion E so as to reach the metering zone D.

  On the other hand, as shown in FIG. 2 (b), the bottom surface of the solid channel 13a gradually increases from the upstream side to the downstream side of the compression and melt zone M, that is, gradually becomes shallower from the outer peripheral surface of the main flight 11. It is formed in the inclined surface so that it may become.

  In the double flight screw 10 configured as described above, the molding material supplied to the feed zone A is pushed by the main flight 11 by the rotation of the screw 10 in the direction of the arrow R and transferred to the compression and melt zone M. The molding material is supplied to the solid channel 13a in the compression and melt zone M, and is heated and melted in the solid channel 13a. The molding material is melted and melted as a melt film, passed through a gap formed between the outer peripheral surface of the sub flight 12 and the inner peripheral surface of the cylinder barrel 15, and scraped from the inner wall of the barrel by the main flight 11, and melt channel 13b. Stored and transported inside. In the melt channel 13b, kneading and melting are further promoted to adjust the molding material to an appropriate state. The molding material that has been transferred through the melt channel 13b and has reached the constant valley diameter portion E is subjected to metering action at this portion because the bottom surface of the melt channel 13b is at a constant depth. Furthermore, the molten state and melting temperature are made uniform.

  Thereafter, the melt is transferred from the melt channel 13b to the metering zone D, and the molten state is made uniform, and is injected from a nozzle (not shown) of the cylinder barrel 15.

4 and 5 show the injection resin temperature profile of the plasticized resin by the double flight screw 10 according to the present invention and the same temperature profile by the conventional double flight screw, and FIG. the case of a kg / cm ^2), FIG. 5 shows the case where the grant back pressure of 5 (kg / cm ^2). The experiment was conducted on a screw having an outer diameter D = 100 mm, and the conditions were as follows.
(1) Resin PP (Noblen MA4)
(2) Temperature conditions NH250 / 250/250/250/230 ℃
(3) Weighing stroke 250mm (2.5D equivalent)
(4) Soak time 1: 2
(5) Screw rotation speed 128rpm

  In both FIG. 4 and FIG. 5, the graph of (a) is the result of the conventional double flight screw, and the graph of (b) is the result of the double flight screw according to the present invention. The experiment was conducted for a plurality of shots with the same number of shots under any conditions. As shown in these figures, the repeated melting temperature at any back pressure is determined by the double flight screw according to the present invention. It was confirmed that the uniform performance was higher.

Next, the improvement in yield due to the improvement in dimensional accuracy of the holding plate (groove plate) of the silicon wafer shipping container will be described. The screw used for comparison has a screw diameter of 60 mm.
1) Conventional type screw: General-purpose screw A with a short subflight in the metering zone,
2) A double flight screw B having the structure shown in FIG. 10 except that the secondary melt channel similar to FIG.
3) Invention screw C having the structure shown in FIGS. 1 to 3 in a double flight screw according to the present invention,
Was used.
Using each of these screws A to C, a silicon wafer holding plate (left and right) for housing a silicon wafer having a diameter of 300 mm was formed by an all-electric motor EC350-i19A molding machine.
As shown in FIG. 6, 25 silicon wafers with a diameter of 300 mm are mounted on the shipping container equipped with the left and right holding plates and mounted on a Nikon laser measuring machine. FIG. 7 shows the results (yield) obtained by measuring the heights of each of the four points a and d with a Nikon laser machine. Measurement points are measured from 25 to (28) wafer planes a to d from 44mm to 284mm height from the reference plane. The tolerance of the wafer mounting height of each step of the groove plate is +0 of each step height from the reference plane. .45mm to -0.45mm. The degree of the groove pitch of the 25 steps of the left and right holding plates affects the dimensional accuracy of the shipping container.

  From the measurement results shown in FIG. 7, it can be determined that the yield is highest when the C screw is used, that is, the machining accuracy by the double flight screw according to the present invention is the best.

  Next, narrow pitch connector molding was performed using a screw diameter 16 with a hybrid vertical molding machine (VH40-i4.0YV), and the result is shown in FIG. The type of the screw used is the above-described general-purpose screw A of A) and the invention screw C of C). The molded connector was a resin LCP (polyplastic: Vectra E471i) with a connector pitch of 0.4 mm (8 pieces). At the same time, this narrow-pitch connector was also molded in a 40-ton type pre-plastic injection machine molding machine, and the results of the comparison were also shown in the same figure.

In FIG. 8, the barrel temperature, the injection speed, the back pressure, the filling time, etc. are described as the optimum conditions for the two in-line screws and the pre-plastic injection machine. Screw A is a conventional full flight screw for LCP, screw C is a double flight screw according to the present invention, and for comparison, a 40-ton molding machine of the same class equipped with a pre-plastic type injection device proven in the narrow pitch connector market. Posted.
Screw A has been used exclusively for LCP resin molding in the past, but this 0.4 narrow-pitch connector molding does not eliminate fine shorts and burrs, which will trigger the development of the double flight screw (screw C) according to the present invention. .
Screw A and screw C are φ16, pre-plus screw is φ14 (with φ12 plunger), mold temperature is 100 ° C, and barrel temperature is optimum. Only screw C can be molded at a lower temperature of 340 ° C.
The injection pressure rise response at the time of molding the connector of each machine is 36 ms. With the screw A and C molding machines VH40-i0.4YV with hydraulic mold clamping device and electric servo motor driven injection device, while pre-plastic injection device machine is accumulator It is extremely fast with 18ms by the hydraulic servo.
Also, the filling time (injection speed) is the optimum condition for obtaining the best quality.
In the appearance quality judgment, the results of evaluating the presence or absence of fine burrs and shorts by continuous operation for 4 hours or more are indicated by ○ and ×.
With screw A, short-circuits could not be resolved even at a high temperature of 360 to 370 ° C., and fine burrs were randomly generated. On the other hand, in the screw C according to the present invention, fine burrs and short-circuits were relatively easily eliminated, and stable molding could be performed. Results The barrel temperature adopted by the new double flight screw of the screw C according to the present invention was 340 ° C., and the molding temperature of the pre-molded injection device machine for the non-defective product was slightly higher at 360 ° C.

  That is, in the general-purpose screw A, molding is performed at a molding barrel temperature of 360 to 370 ° C., but minute shorts and burrs are unstable, whereas the invention screw C can easily prevent these defects. Inventive screw C was able to perform short- and burr-free molding at a barrel temperature 20 ° C. lower than that of general-purpose screw A, making it easy to mold good products. Invention screw C demonstrated sufficient capability in terms of uniform melting and kneading performance required for forming thin-walled narrow pitch connectors. In addition, the barrel temperature can be greatly lowered, the physical properties of the resin such as strength can be maintained and improved, and the product strength can be increased. Moreover, decomposition | disassembly of the staying resin in a barrel can be suppressed by the fall of resin temperature, and as a result, drooling can be suppressed and the effect which makes a shaping | molding operation easy was also confirmed.

The pre-plastic injection machine shown in Fig. 8 performs stable non-defective molding, but does not reciprocate the screw A of this machine. It is a pre-plastic plastic screw at a fixed position. Has a superior advantage. In addition, an accumulator hydraulic servo is provided in the injection hydraulic source, and the pressure response during injection is as fast as 18 ms. These synergistic effects make the molding machine compatible with thin-wall narrow pitch connector molding.
On the other hand, the injection device of this machine (with screws A and C) is 36ms. (Actual machine monitor value), which is twice as long as the above pre-pla machine due to the general-purpose electric servo, which is disadvantageous for forming a thin, narrow-pitch connector. In spite of this, the adoption of C's new double flight screw makes it possible to obtain an equivalent molded product at a barrel temperature 20 ° C. lower than the pre-plastic injection machine. Although it was possible to achieve stable molding of the narrow-pitch connector, which was not possible with conventional in-line screws, it seems that these can be evaluated as a significant effect of the new double flight screw design.

  The general-purpose screw A required 7 MPa for the back pressure, whereas the invention screw C could be molded at 6 MPa and prevented drooling. That is, it can be determined that the invention screw C has sufficient uniform melting and kneading performance, even though the back pressure is low. Furthermore, it can be presumed that the uniform quality and dimensions can be ensured repeatedly due to the metering effect of the melt channel.

In addition, it seems that the above-mentioned pre-plastic injection machine has been advanced by imparting repeated stability such as melting, kneading, injection molding performance, etc. by a combination of two shafts of a pre-plus screw and an injection plunger. However, it is thought that it is a great improvement that the same stable molding performance was able to be demonstrated in the narrow pitch connector molding which could not be done by the conventional single-shaft inline screw by devising and developing a new double flight screw.
This is considered to prove that the uniform melting and kneading performance required for highly stable molding with an in-line screw has been greatly improved.

  According to the double flight screw according to the present invention, a stable melting temperature, a molten state, and a kneaded state can be ensured repeatedly, which contributes to a stable molding process of the product. Expected to be used for narrow pitch connectors, LED thin-walled bases, various engineering plastics with high dimensional accuracy, electronic and mobile phone parts, etc., which were difficult to achieve with conventional in-line screw general-purpose injection molding machines.

10 Double flight screw
11 Main flights
12 Subflight
13a solid channel
13b melt channel
15 Cylinder barrel A Feed zone M Compression and melt zone D Metering zone E Constant valley diameter

Claims (2)

It consists of two flights with different lead angles in a spiral shape, and has a feed zone, a compression and melt zone, and a metering zone, from any position in the compression and melt zone to the front of the metering zone Arrange subflights,
A double flight screw characterized by forming a constant valley diameter portion having a cylindrical bottom surface with a constant valley diameter of a part of the melt channel of the compression and melt zones. Formed by gradually reducing the valley diameter so that the bottom surface of the compression and the melt channel of the melt zone gradually becomes deeper toward the metering zone,
2. The double flight screw according to claim 1, wherein the constant valley diameter portion having a cylindrical bottom surface formed with a constant valley diameter is formed in front of the metering zone.

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