JPH09300413A - Injection screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain flexibility required for the transfer of a material resin in a supply part and prevent adverse effects due to the residence of the material resin from occurring in a molding process by constituting a screw for the supply part and a compressing part of a fixed pitch section and a variable pitch section. SOLUTION: A supply part side and a compressing part side position across a distance equivalent to 0.4-0.5 of the length of the compressing part from the compression start point (a) of the compressing part of an injection screw is set as the first change point (b) and the second change point (c) of a screw pitch. In addition, the screw pitch P3 in a section C between a second change point (c) and a measuring part is set larger than the screw pitch P1 in a section A from the first change point (b) upto the rear end of the screw. The screw in a section B between both change points is given as to be of the variable pitch type and the screw pitch P2 is set gradually larger toward the second change point (c) from the first change point (b).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection screw equipped with a heating cylinder of an injection device used for molding synthetic resin.

[0002]

In an injection screw, a supply section, a compression section,
A measuring section is formed, and a screw (flight) having the same outer diameter is continuously formed over each section. In addition, the screw pitch is standardly set as Pitch (P) / Outer Diameter (D) = 1, but the screw pitch of each part is changed for the purpose of improving the plasticization efficiency.

The melting of the granular material resin in the heating cylinder is caused by both the heating by the band heater on the outer periphery of the cylinder and the shearing heat generation of the resin by the rotation of the screw, and the material dropped from the supply port into the groove of the rotating screw. The resin is sent while rubbing against each other into the cylinder heated by the band heater by the rotation of the screw, and starts heating and melting when it approaches the rear band heater away from the supply port.

The heat-melting occurs from the material resin on the outer side in contact with the inner wall of the cylinder, and reaches the material resin on the inner side in contact with the screw shaft while being transported through the supply section by the rotation of the screw. When the material resin is softened by heating and begins to melt on the surface side, viscosity and volume expansion occur in the material resin. The expansion coefficient of this volume varies depending on the material resin, but when the outer material resin expands in the screw groove of which the volume is limited, the inner material resin that is in contact with the screw shaft portion is pressed and becomes overcrowded, The mutual flexibility necessary for the transfer by rotation of the screw is lost and the screws are accumulated.

Such a tendency is remarkable in the resin having a large expansion coefficient, and the retention at the position where the heating and melting start is not only an obstacle to the transfer of the material resin continuously fed from the supply port, but also the screw of the screw. It is forced into the starting position of heating and melting by the rotating force, and the material density of the screw groove at that position is significantly increased. For this reason, the rotation resistance of the screw increases, so that a large screw rotation torque is required, and the material retention causes defects such as burning and discoloration of the molded product. Therefore, when injection-molding a resin such as an acrylic resin, if the phenomenon at the start position of heating and melting is not solved by some means, it will be molded like a resin with a small volume expansion or a resin that can be rubbed against each other smoothly. Has been difficult to do.

As a means for reducing the rotational torque during plasticization, the screw pitch in the supply section is set to P / D = 0.8 to
A material resin in which the volume is less likely to decrease during plasticization by setting a small value in the range of 1.0 or a large pitch of the screw of the measuring unit in the range of P / D = 1.0 to 1.3,
Or even material such as resin with high viscosity in the molten state,
It is known that the measurement unit can be moved smoothly.

However, this prior art does not mention the problem of material retention at the heating and melting start position, the compression start position, etc., and the screw pitch in the supply section is smaller than usual, or the screw in the metering section is smaller than usual. Even if the pitch is set to a large value, the pitch is constant and it does not solve the above phenomenon at the heating and melting start position or the compression start position, so it is suitable for injection molding of material resin such as acrylic resin. Has problems that are difficult to adopt.

The present invention has been conceived in order to solve the above-mentioned conventional problems, and an object thereof is to provide a screw of a supply part and a compression part by a constant pitch part and a variable pitch part. The flexibility required for the transfer of the material resin in the part can be secured, which allows the material resin to be transferred smoothly at the heating and melting start position and the compression start position, and a new injection that prevents adverse effects on molding due to material retention To provide a screw.

[0009]

SUMMARY OF THE INVENTION According to the present invention according to the above object, there is provided a plurality of band heaters on the outer periphery of a cylinder having a nozzle at the tip thereof, and a heating port is provided in the cylinder upper wall at the rear of the band heater. An injection screw that is installed in the cylinder so that it can rotate and move back and forth.The effective screw length from the rear end to the front end is divided into a supply part, a compression part, and a measuring part in order, and a screw flight with the same outer diameter is continuously formed over each part. In the injection screw described above, the positions on the supply unit side and the compression unit side, which are separated from the compression start point of the compression unit by a distance corresponding to 0.4 to 0.5 of the compression unit length, are the first change points of the screw pitch. And the second change point, the pitch of the screw in the section C extending from the second change point to the measuring section is made larger than the pitch of the screw in the section A from the first change point to the rear end of the screw. Constant, and formed by sequentially set larger pitch towards the section second change point from the first change point as a variable pitch screw for B between the two changes, is that.

Further, according to the present invention, the position corresponding to the end portion on the supply port side of the rear band heater of the supply section at the most forward position of the screw is divided into the front and rear of the section A as the start point of the heating and melting of the material resin, and the start point thereof. From the rear end of the screw to the rear end of the screw, the pitch of the screw in the rear part A ₁ is P ₄ /D=0.7 to
While set in the range of 0.73, P ₅ /D=0.8~0 from the start point provided variable pitch interval A ₃ between the pitch of the screw of the front section A ₂ to the first change point. The range is set to 85 and the pitch of the screw in the section C extending from the second change point to the measuring section is set to the range of P ₃ /D=1.0 to 1.2.

In such a structure, the screw before and after the compression start point has a variable pitch in which the pitch is gradually increased from the first change point to the second change point, and the screw groove has a small volume. Since the volume of the material resin is gradually expanded, even if the volume of the material resin is expanded by heating and melting, the expansion is absorbed by the continuous expansion of the volume of the screw groove.

For this reason, the flexibility of the materials and resins necessary for the screw rotation transfer is ensured, the over-condensation of the semi-molten material near the compression start point is prevented, and the rotation resistance of the screw due to the over-congestion of the material disappears. The screw rotation torque as in the above is not required, overheating due to retention is also prevented, and defects such as burning and discoloration do not occur in the molded product.

The position corresponding to the end of the rear band heater of the supply section on the side of the supply port is divided into front and rear as the starting point of heating and melting of the material resin, and the screw pitch of the rear section A ₁ of the section is set small. In the configuration in which the pitch of the screw of the front portion A ₂ of the section is set to be larger than that of the rear side of the section by providing the variable pitch section A ₃ therebetween, even if the volume of the granular material resin expands rapidly at the start point, The expansion is absorbed by the screw groove on the front side of the section where the volume is expanded, the screw rotation resistance due to the overcrowding of the material at the heating and melting start position is also eliminated, the biting noise is reduced with acrylic resin, etc., and overheating due to retention is also prevented. As a result, defects such as burning and discoloration do not occur in the molded product. In addition to acrylic resin, bite of material resin such as liquid crystal polyester (LCP) and contained plastic is improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In FIG.
c, the measuring portion Lm, which is formed by continuously forming the screw (flight) 2 having the same outer diameter over the respective portions.

A heating cylinder 3 is provided with three sets of band heaters 5, 6 and 7 in the order of a front part, an intermediate part and a rear part on the outer periphery of a cylinder having a nozzle at the tip, and on the cylinder behind the band heaters. A material resin supply port 4 is formed in the wall.

The injection screw 1 uses the end of the rear band heater 7 provided near the supply port 4 on the supply port side as a starting point M for heating and melting the material resin.
The granular material resin fed to the supply port 4 is plasticized while being pressure-fed from the supply portion Lf to the measuring portion Lm at the tip by rotation, and at the same time, is metered into the tip of the heating cylinder 3. The plasticized material pressure causes it to retract to the set position.

The pitch of the screw 2 is such that the supply portion Lf,
The compression unit Lc and the measuring unit Lm are different. In the embodiment shown in FIG. 1, the positions on the supply section Lf side and the compression section Lc side, which are separated from the compression start point a of the compression section Lc by a distance corresponding to 0.4 to 0.5 of the compression section length, are respectively set. A first change point b and a second change point c of the screw pitch, and a section B between them
The screw has a variable pitch to prevent the material resin from staying near the start of compression.

The screw pitch P ₂ of the section B is the screw pitch P ₃ of the section C extending from the second change point c to the measuring section Lm, and the screw pitch P ₂ of the section A from the first change point b to the rear end of the screw. By setting the pitch larger than the pitch P _{1, the} pitch is gradually increased from the first change point b toward the second change point c, so that even if the volume of the material resin expands due to heating and melting, the expansion is caused by the screw groove. It is absorbed by the continuous expansion of the volume of the resin, and the flexibility of the materials and resins necessary for the transfer by the screw rotation near the compression start point is secured, which allows the transfer of the semi-molten material smoothly. As a result, overcrowding near the compression start point is prevented.

Incidentally, preferable screw pitches of respective parts are shown below. P ₁ /D=0.7 to 0.85, P ₂ /D=(0.7-1.0) to (0.85-1.
2), P3 _{= /} D ₌ 1.0 to 1.2,

In the embodiment shown in FIG. 2, the material resin is also prevented from staying near the starting point M of the heating and melting of the supply section Lf, and the section A is defined by the starting point M as a boundary. It is divided into front and rear, the pitch P ₄ of the screw in the rear part A ₁ of the section serving as the material receiving section is set small, and the pitch P ₅ of the screw in the front part A ₂ of the section is set to a variable pitch section A _{3 having} a length of about 1 pitch. Is provided so that the volume expansion of the granular resin material can be absorbed.

The pitch of the screw at the rear portion A ₁ of the section is P
_{4 /} D = 0.7 to 0.73, and the screw pitch in the section front part A ₂ is P ₅ /D=0.8 to 0.
It is set in the range of 85, and both screws are connected in series via the screw of the pitch variable section A ₃ . Then, in succession to the screw having the pitch P ₅ , the screw 2 in the section B from the first change point b continues to the second change point c while changing the pitch of the screw largely in the same manner as in the case of FIG. The screw is formed and connected to the screw in the section C in which the pitch of the screw is set in the range of P ₃ /D=1.0 to 1.2.

Although not shown in the drawing, the starting point M is not limited to one point, and the screw in the section A ₁ which becomes the material receiving portion facing the supply port 4 is selected depending on the material resin, screw design, injection stroke and the like. Since the lengths are naturally different, the start point M can be set with a certain width in the front and back accordingly. However, the setting range of the first change point is preferably a range from the start point M to the position before and after the start point corresponding to 1.0 to 1.5 pitches.

In such a screw configuration, the section A is
Due to the limitation of the screw pitch of (1), the amount of the material resin intruded from the supply port 4 is reduced to some extent. However, due to the expansion of the screw pitch from the starting point M and the expansion of the screw pitch due to the variable pitch of the section B extending from the supply part Lf to the compression part Lc, the volume expansion of the material resin increases with the progress of heating and melting. Are absorbed, and the material resin is prevented from being overcrowded in the vicinity of the heating and melting start position and the compression start position due to volume expansion.

As a result, even in the case of the material resins that have become less slippery due to softening in the semi-molten state, the screws are smoothly transported by rotation, and there is no retention at the heating and melting start position and the compression start position. . Then, the material resin is sheared by the screw rotation from the compression start point a, and is melted and kneaded (plasticized) by the shearing heat generation and the external heating to be transferred to the metering section L _m and metered in the cylinder tip. .

[0025]

EXAMPLE The screw pitch in each section in the embodiment shown in FIG. 1 is as follows. Screw outer diameter 40mm Section C (P ₃ ) Section B (P ₂ ) Section A (P ₁ ) 40mm 40-32mm 32mm

The screw pitch of each section in the embodiment shown in FIG. 2 is as follows. Screw outer diameter 42mm section C (P ₃₎ section B (P ₂₎ section A (P ₅₎ change portion _{(P 4) 42mm 42-35mm 35mm 35-30mm} 30mm

[Brief description of drawings]

FIG. 1 is a side view of a first embodiment of an injection screw according to the present invention.

FIG. 2 is likewise a side view of the second embodiment.

[Explanation of reference numerals] 1 injection screw 2 screw (flight) 3 heating cylinder 4 supply port 7 rear band heater

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[Procedure amendment]

[Submission date] May 12, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction contents]

The melting of the granular material resin in the heating cylinder is caused by both the heating by the band heater on the outer periphery of the cylinder and the shearing heat generation of the resin by the rotation of the screw, and the material dropped from the supply port into the groove of the rotating screw. The resin is sent into the cylinder heated by the band heater while being rubbed against each other by the rotation of the screw, and starts to be heated and melted when it approaches the rear band heater away from the supply port.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

The heat-melting occurs from the material resin on the outer side in contact with the inner wall of the cylinder, and reaches the material resin on the inner side in contact with the screw shaft while being transported through the supply section by the rotation of the screw. When the material resin is heated and softened to start melting on the inner peripheral surface side of the heating cylinder, the material resin becomes viscous and expands in volume. The expansion coefficient of this volume differs depending on the material resin, but when the material resin on the outer side (the inner surface of the heating cylinder) expands in the screw groove with a limited volume, the inner material that is in contact with the screw shaft and has not yet been heated. The resin is pressed and becomes over-consolidated, and the mutual flexibility necessary for the transfer by rotation of the screw is lost and the resin stays.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

Such a tendency is remarkable in the resin having a large expansion coefficient, and the retention at the position where the heating and melting start is not only an obstacle to the transfer of the material resin continuously fed from the supply port, but also the screw of the screw. It is forced into the starting position of heating and melting by the rotating force, and the material density of the screw groove at that position is significantly increased. For this reason, the rotation resistance of the screw increases, so that a large screw rotation torque is required, and the material retention causes defects such as burning and discoloration of the molded product. Therefore, in injection molding of resin such as acrylic resin, if the phenomenon at the start position of heating and melting is not solved by some means, molding such as resin with small volume expansion or resin with smooth mutual friction is performed. It is difficult to do.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

The position corresponding to the end of the rear band heater of the supply section on the side of the supply port is divided into front and rear as the starting point of heating and melting of the material resin, and the screw pitch of the rear section A ₁ of the section is set small. In the configuration in which the pitch of the screw of the front portion A ₂ of the section is set to be larger than that of the rear side of the section by providing the variable pitch section A ₃ therebetween, even if the volume of the granular material resin expands rapidly at the start point, The expansion is absorbed by the screw groove on the front side of the section where the volume is expanded, the screw rotation resistance due to the overcrowding of the material at the heating and melting start position is also eliminated, the biting noise is reduced with acrylic resin, etc., and overheating due to retention is also prevented. As a result, defects such as burning and discoloration do not occur in the molded product. In addition to acrylic resin, bite of material resin such as liquid crystal polyester (LCP) and oil-impregnated plastic is improved.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

Although not shown in the drawing, the starting point M is not limited to one point, and the screw in the section A _{1 which} is the material receiving portion facing the supply port 4 is selected by the material resin, screw design, injection stroke, or the like. Since the lengths are naturally different, the start point M can be set with a certain width in the front and back accordingly. However, the setting range of the first change point is preferably a range from the start point M to the position before and after the start point corresponding to 1.0 to 1.5D.

[Procedure correction 6]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

[Procedure amendment 7]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

[Fig. 2]

Claims (2)

[Claims] 1. An injection rotatably and reciprocally provided in a heating cylinder provided with a plurality of band heaters on the outer periphery of a cylinder having a nozzle at its tip, and a supply port formed in the cylinder upper wall at the rear of the band heater. With a screw, from the rear end to the tip of the effective screw length, supply unit, compression unit,
In an injection screw in which a screw flight having the same outer diameter is continuously formed over each part of the measuring part, the compression screw length from the compression start point a of the compression part is 0.4 to
Positions on the supply section side and the compression section side that are separated by a distance corresponding to 0.5 are respectively a first change point b and a second change point c of the screw pitch, and a section C extending from the second change point c to the measuring section. The screw pitch P ₃ is set to be larger than the screw pitch P _{1 in} the section A from the first change point b to the rear end of the screw, and the screw in the section B between the two change points is set as a variable pitch. Pitch P from b toward the second change point c
An injection screw characterized by increasing ₂ sequentially. 2. The position corresponding to the supply port side end of the rear band heater of the supply section Lf at the most advanced position of the screw is divided into the front and rear of the section A as the start point M of heating and melting of the material resin, and the start point M From the rear end of the screw to the rear end of the screw, the pitch of the screw in the rear part A ₁ is P ₄ /D=0.7 to 0.
While setting the range to 73, the first change point b from the start point M
The pitch of the screw in the front section A ₂ is set in the range of P ₅ /D=0.8 to 0.85 by providing the variable pitch section A ₃ between them, and extends from the second change point c to the measuring section. Section C
The screw according to claim 1, wherein the pitch of the screw is set in the range of P ₃ /D=1.0 to 1.2.