JPH10166412A - Molding method of thermoplastic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a molded form, molded by a mold, by a method wherein the temperature of grain group, consisting of thermoplastic material, is increased to a temperature immediately before melting while the grain group, having this temperature, is molten upon supplying into the mold or in the mold. SOLUTION: A kneading extruder 6 is equipped with hoppers 3, provided continuously on the upper surface of the vicinity of upstream end of a cylinder 1 having a cylindrical internal surface, heaters 13a-13n, wound around the cylinder 1, a full flighted screw 2, inserted into the cylinder 1, and a driving device 5, driving the screw 2. In this kneading and extruding machine 6, the heat generating amount of the heaters 13a-13n is controlled so that thermoplastic material is injected into a mold clamping mechanism 7 when the same material is softened and become a condition immediately before softened and molten. The screw 2, inserted into the cylinder 1, is full flighted type, in which a flight part 21 is wound spirally with the pitch of 26.3mm, for example, around the outer periphery of a column shaft unit 28, is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a thermoplastic material, and more particularly to a method for molding a thermoplastic material capable of improving the quality of a molded product.

[0002]

2. Description of the Related Art FIG. 7 is a sectional view showing an example of a conventional injection molding apparatus. This injection molding apparatus comprises a cylinder (1) having a simple cylindrical inner surface, a full flight screw (2) inserted into the cylinder (1), and the screw (2).
And a hopper (3) for supplying raw materials to the hopper.

A heater (12a) is provided on the outer periphery of the cylinder (1).
(12b) (12c) ··· are wound so that the inside of the cylinder (1) can be heated by the heater. A mold (71) is connected to the tip of the cylinder (1), and the resin injection hole (714) of the female mold (712) of the mold (71) is
The discharge port (11) at the tip of (1) is connected.

Next, the operation of the above-described injection molding apparatus will be described. In the above injection molding apparatus, the hopper (3) is filled with a thermoplastic material (8) such as a thermoplastic resin pellet,
Rotate screw (2) and heat (12a) (12b) (1
2c) Generate heat. Then, the thermoplastic material (8) is supplied into the cylinder (1) from the material supply port (31) connected to the lower end of the hopper (3), and is supplied to the preheating zone (14) → the melting zone ( 15) → The final zone (17) is sequentially transferred to the downstream side. When the thermoplastic material (8) passes through the melting zone (15), the heaters (12b) (12c)
The melt pool (82a) (82b) (82c) in which the molten resin is heated and melted by the generated heat gradually grows. Then, the resin in the molten state is supplied to the final zone (17) and stored in the storage section (10) at the tip of the cylinder (1). When the storage amount of the molten resin reaches the set amount, the screw (2) advances to the downstream side by a driving device (not shown), whereby the molten resin in the storage unit (10) is discharged from the discharge port (11). ) Is injected into a mold (71) and molded by the mold (71).

[0005]

When injection molding is performed using a thermoplastic material (8) that is significantly thermally degraded, it is necessary to shorten the time during which the thermoplastic material (8) is maintained in a high-temperature molten state. Is desirable. However, in the prior art described above, the time required for the thermoplastic material (8) to pass through the final zone (17), that is, the thermoplastic material (8) is
The time in which the thermoplastic material (8) is maintained in the hot state is relatively long since it is maintained in the hot molten state. Therefore, if the above-described conventional method of molding using the molten resin in the final zone (17) previously melted is applied to a molding operation using a thermoplastic material (8) that is significantly thermally degraded, the quality of the molded product is reduced. There is a fear that it will drop.

It is an object of the present invention to improve the quality of a molded product formed by a mold (71).

[0007]

Means for Solving the Problems According to a first aspect of the present invention, which is adopted to solve the above-mentioned problem, a method is described in which “a group of particles made of a thermoplastic material is brought to a temperature immediately before melting, and When it is supplied to the mold or melted in the mold. "

The above means operates as follows. When the particles of the thermoplastic material adjusted to the temperature just before melting are supplied to the mold or melted in the mold, the thermoplastic resin is compared with the case where the thermoplastic material is molded using a thermoplastic material that has been melted in advance. The time during which the material is maintained in the hot molten state can be shortened.

Specifically, the temperature immediately before the melting is defined as “at a temperature equal to or higher than the softening point of the thermoplastic material and lower than the melting point”.
Yes, by keeping the thermoplastic material at this temperature condition, it can be brought to a state just before melting. The thermoplastic material may be a metal such as aluminum, in addition to the case where the thermoplastic material is “thermoplastic synthetic resin”.

[0010]

As described above, according to the first to third aspects of the present invention, the time during which the thermoplastic material is maintained at a high temperature in a molten state can be shortened, so that the thermoplastic material (8)
Is suppressed, and a high quality molded product is obtained.

[0011]

Next, an embodiment of the present invention will be described. [Overall Configuration] FIG. 1 is a longitudinal sectional view of an injection molding apparatus for explaining an embodiment of the present invention. In FIG. 1, a kneading extruder (6) for heating and kneading a thermoplastic material and a mold clamping at the tip thereof are shown. It consists of a mechanism (7).

Hereinafter, the configuration of each unit will be described. [Kneading extruder (6)] The kneading extruder is a hopper connected to the upper surface near the upstream end of a cylinder (1) having a cylindrical inner surface.
(3) and a heater (1) wound around the outer circumference of the cylinder (1).
3a) to (13n), a full-flight screw (2) inserted into the cylinder (1), and a driving device (5) for driving the screw (2). Further, in this kneading extruder, when the thermoplastic material (8) to be described later is softened and becomes a state immediately before melting, the above-mentioned heaters (13a) to () are injected into the mold clamping mechanism (7). 13n) is controlled.

Next, details of each of the above components will be described. * Regarding the cylinder (1) * The cylinder (1) is formed in a simple cylindrical shape, and the inner diameter of the downstream end is narrowed to form the discharge port (11). A material supply port (31) communicating with the inside of the hopper (3) is formed in the upper wall near the upstream end of the cylinder (1). In this embodiment, the inner diameter of the cylinder (1) is
It is set to 32.2 mm. * About hopper (3) * Inside the hopper (3) connected to the material supply port (31) formed on the upper wall near the upstream end of the cylinder (1), pellets or powder of thermoplastic synthetic resin An additive (80) such as a thermoplastic material (8) and a coloring material for coloring the same is supplied from a supply device (not shown). * About screw (2) * Screw (2) inserted into cylinder (1) is cylindrical shaft part.
A full flight type in which flight portions (21) are spirally wound at a pitch of 26.3 mm on the outer periphery of (28) is employed, and a spiral shape is provided between each adjacent flight portion (21). Groove (23)
It has become. The groove portion (23) is formed so as to be wound around the cylindrical shaft portion (28) 27 times, whereby a groove portion (23) having 27 pitches is formed. The range of the first pitch portion to the fifth pitch portion near the upstream portion (near the end on the material supply port (31) side) in the groove portion (23) is a preheating for preheating the thermoplastic material (8). A zone (14), a range from the sixth pitch portion to the fourteenth pitch portion is a softening zone (16) for softening the thermoplastic material (8), and further a fifteenth pitch portion to a twenty-seventh pitch portion. The range of the pitch portion is the final zone (1) for supplying the softened thermoplastic material (8) to the mold clamping mechanism (7) side.
7), and zones are divided into predetermined ranges.

Next, the screw shape and the like of the preheating zone (14) will be described. In the preheating zone (14), the outer periphery of the flight part (21) wound around the cylindrical shaft part (28) is
(1) is substantially in contact with the inner surface of the flight portion (21), and the boundary between the outer periphery of the flight portion (21) and the inner surface of the cylinder (1) is in a state where the thermoplastic material (8) is not allowed to enter. ing.

In this embodiment, the cylindrical shaft portion (2
The diameter of 8) is set to 21.1 mm in the first pitch portion,
The width is set to 21 mm in the second to fourth pitch portions, and is set to 21.4 mm in the fifth pitch portion. or,
The diameter including the flight part (21) (the outer diameter of the screw (2))
The distance is set to 39.1 mm in the entire first to fifth pitch portions.

Next, the screw shape of the softening zone (16) will be described. In the softening zone (16), a gap (26) allowing passage of the thermoplastic material (8) is provided between the outer periphery of the flight portion (21) wound around the cylindrical shaft portion (28) and the inner surface of the cylinder (1). ) Is formed. In this embodiment, the diameter of the cylindrical shaft portion (28) is 2 in the sixth pitch portion to the ninth pitch portion.
It is set to change in the order of 2.2 mm, 23 mm, 23.7 mm, and 24.4 mm, and is set to 25.2 mm in the tenth pitch part to the twelfth pitch part, the thirteenth pitch part and the first pitch part.
In the 4-pitch section, the distance is set to 26.4 mm. The diameter including the flight portion (21) is set to 29.8 mm in the sixth pitch portion to the eleventh pitch portion, and is set to 29.8 mm in the twelfth pitch portion to the fourteenth pitch portion.
The pitch is set to 31.2 mm. Therefore, the inner surface of the cylinder (1) having an inner diameter of 32.2 mm and the flight portion
The gap (26) on the outer periphery of (21) is set to 1.2 mm in the sixth to eleventh pitch portions, and is set to 0.5 mm in the twelfth to fourteenth pitch portions. Then, the thermoplastic material (8) can pass through the gap (26) having the above dimensions formed on the outer periphery of the flight portion (21) and the inner surface of the cylinder (1). The plastic material (8) can move between adjacent pitch grooves (23).

FIG. 2 shows the screw in the softening zone (16).
FIG. 3 is an enlarged view of a boundary portion between (2) and a cylinder (1). Cylinder
Between the inner surface of (1) and the outer periphery of the flight portion (21) of the screw (2), the gap (2) allowing the passage of the thermoplastic material (8)
6) is formed, and a guide surface (27) is formed so as to be inclined from the surface on the downstream side (left side in FIG. 2) of the flight portion (21) to the outer peripheral portion thereof. The inclination angle θ of the guide surface (27) with respect to the center axis of the screw (2) is set to 15 degrees in this embodiment, and the outermost peripheral portion of the flight portion (21) and the tip of the guide surface (27) The radial distance L of the portion (271) is set to 0.6 mm. In addition, the guide surface (27)
Is continuously formed on the outer periphery of the flight portion (21) over the entire softening zone (16).

Next, the screw shape and the like of the final zone (17) will be described. In the last zone (17), cylindrical shaft (28)
The outer periphery of the flight portion (21) wound around is substantially in contact with the inner surface of the cylinder (1).
The boundary between the outer periphery of (21) and the inner surface of the cylinder (1) is in a state in which the intrusion of the thermoplastic material (8) is not allowed.

In this embodiment, the cylindrical shaft (2
The diameter of 8) is 27 in the 15th to 17th pitch portions.
mm, the pitches are set to 26.5 mm and 19.3 mm in the 18th and 19th pitch sections, respectively, set to 19.1 mm in the 20th and 21st pitch sections,
21.1 mm and 24.6 mm in the pitch section and the 23rd pitch section
, And 25 in the 24th pitch section to the 27th pitch section.
is set to mm. The diameter including the flight portion (21) is 3 in the entire range of the 15th pitch section to the 27th pitch section.
It is set to 1.9 mm. * Regarding heaters (13a) to (13n) * The outer peripheral surface of cylinder (1) is surrounded by heaters (13a) to (13n) that are wound at predetermined intervals from the upstream to the downstream end. The heat value of each of the heaters (13a) to (13n) can be set to an appropriate value individually.

Four heaters (13a) to (13n) are provided in a range corresponding to the first to eighteenth pitch portions in the groove portion (23) of the screw (2). Capacity is 2
It is set to 0 KW / H. Also, from the 19th pitch section
Two heaters are provided in the range corresponding to the 22nd pitch section, and the heat value of each is set to 2 KW / H. Further, in the range corresponding to the 23rd to 27th pitch sections, two heaters are provided. And each heating value is 2KW / H
Is set to * About drive device (5) * Next, the configuration of the drive device (5) will be described.

The driving device (5) includes a motor (51), a speed reducer (52) for transmitting the rotation of the motor (51) to the screw (2), and a screw (5).
(2) is constituted by an injection cylinder (53) for moving back and forth in the axial direction. [Regarding the mold clamping mechanism (7)] Next, the mold clamping mechanism (7) will be described.

The mold clamping mechanism (7) comprises a die set (77) attached to the tip of the cylinder (1) of the kneading extruder (6) and a mold (71) fixed thereto. . Die set
(77) is a movable plate (7) guided and moved by four guide posts (76a) (76b) and the guide posts (76a) (76b).
It is composed of 3). The movable plate (73) slidably penetrates through the fixed plate (74).
3) Driven by.

The mold (71) is composed of a male mold (711) fixed to the movable plate (73) and a female mold (712) combined therewith and fixed to the fixed plate (75). I have.
The resin injection hole (714) of the female mold (712) is connected to a discharge port (11) at the tip of a cylinder (1) constituting a kneading extruder. [Regarding the Actual Operation] Next, the operation of the injection molding apparatus will be described.

Pellets (2 to 3 mm in this embodiment)
The thermoplastic material (8) and the additive (80) in the form of particles of a synthetic resin with a size of) are supplied to the screw (2) side from the hopper (3) in a uniform ratio, and the motor (51) is rotated. In addition, heater (1
3a) to (13n) generate heat. Also, male mold (711) of mold (71)
And the female mold (712) are kept in a combined state. The thermoplastic material (8) supplied from the hopper (3)
The material is supplied through a material supply port (31) to a first pitch portion of a spiral groove (23) formed on the outer periphery of (2), and this is supplied to a screw.
Preheating zone (14) → softening zone (16) by the feed action of (2)
→ The final zone (17) → is sequentially transferred to the downstream side.

In the preheating zone (14), the heaters (13a) (13
b) The thermoplastic material (8) is pre-heated by the generated heat, and the pre-heated thermoplastic material (8) is transferred to the softening zone (16). In this preheating zone (14), screw
The thermoplastic material (8) or the like that is filled in the groove (23) of (2) does not enter the boundary between the outer periphery of the flight part (21) and the inner surface of the cylinder (1), and the gap between adjacent pitches Never move with. As described above, in the preheating zone (14), the outer periphery of the flight section (21) is substantially in contact with the inner surface of the cylinder (1).

When the thermoplastic material (8) etc. preheated in the preheating zone (14) is supplied to the softening zone (16), the thermoplastic material (8) etc. 13c) ・
..The thermoplastic material is further continuously heated at
(8) and the like are stirred, whereby each pellet of the thermoplastic material (8) is heated to a temperature higher than the softening point and lower than the melting point.

FIG. 3 is a softening zone for explaining a state where each pellet of the thermoplastic material (8) and the additive (80) are stirred.
It is a principal part enlarged view of (16) part. The feed force of the flight portion (21) acts on all the thermoplastic materials (8) and the like contained in the n-th pitch portion of the groove portion (23), and these are transferred to the downstream side in the left direction in FIG. . However, the pellets of the thermoplastic material (8) located near the inner surface of the cylinder (1)
(21), and a gap (26) is formed between the outer circumference of the flight section (21) and the inner circumference of the cylinder (1). The pellet group located at the point does not move downstream, and only the pellets of the thermoplastic material (8) completely located within the groove (23) are
As shown by (84), the wafer is transferred to the (n + 1) th pitch portion on the downstream side. On the other hand, in the (n + 1) th pitch portion, the pellets of the thermoplastic material (8) located near the inner surface of the cylinder (1) are the same as the pellets of the thermoplastic material (8) transferred from the nth pitch portion. It moves relatively in the direction of arrow (85) in the figure.
As shown in FIG. 4, the pellets of the thermoplastic material (8) abutting on the guide surface (27) of the flight section (21) are
Move in the direction running up (27) (the direction of the arrow in the figure),
It is carried toward the gap (26) between the outer periphery of the flight section (21) and the cylinder (1). As a result, not only the thermoplastic material (8) located at the outer peripheral portion of the screw (2) but also the thermoplastic material (8) carried to the gap (26) at the guide surface (27). The density of the raw material in the gap (26) increases, and a part of the density is spouted vigorously into the n-th pitch portion. The pellets are compressed and flattened when they enter a gap (26) having a smaller dimension, and thereafter are vigorously ejected to the n-th pitch portion. In general, the rotational speed of the screw (2) is large (in this embodiment, it is set to 280 rpm), so that a large centrifugal force acts on the thermoplastic material (8), and as a result, the screw (2) The pressure on the outer periphery of 2) is high, and the screw (2)
Since the amount of the thermoplastic material (8) carried to the gap (26) on the outer periphery increases, the pressure in the gap (26) increases.
Therefore, the pellets of the thermoplastic material (8) are vigorously ejected from the high pressure gap (26) to the n-th pitch portion. Accordingly, the thermoplastic material (8) and the like located in the n-th pitch portion are stirred by the ejected thermoplastic material (8), and the arrangement position of each pellet of the thermoplastic material (8) in the pitch portion is changed. The exchange movement of the pellets occurs so that they are interchanged with each other, and this phenomenon is caused by the grooves (23) in the entire softening zone (16).
Occurs within. Then, the entire thermoplastic material (8)
As a result of being stirred in 3), all the thermoplastic materials (8) uniformly absorb the heat from the heaters (13c) ... on the outer periphery of the cylinder (1), and thereby the thermoplastic material (8) The temperature of each pellet is all heated to the same temperature and supplied to the final zone (17).

Also, a heater (13c) in the softening zone (16)
.. Are appropriately set, and thereby,
Each particle of the thermoplastic material (8) supplied from the softening zone (16) to the final zone (17) is adjusted to a temperature just before melting. That is, the surface layer (87) of each pellet of the thermoplastic material (8)
(See FIG. 5) only becomes slightly viscous,
An additive (80) such as a coloring material adheres to the surface layer (87). Further, as shown in FIG. 6, the thermoplastic material (8) supplied from the softening zone (16) to the final zone (17) has a surface layer (87a) (87b) of each adjacent pellet (8a) (8b). ) Are slightly adhered to each other.
a) (8b) is bonded in a semi-molten state immediately before melting.

In order to bring each pellet of the thermoplastic material (8) supplied to the final zone (17) into a state immediately before melting, each heater having the above-mentioned heat generating capacity is used, and a polypropylene of 40 kg / H is used. When processing pellets, the first pitch part ~
The heater temperature in the 18th pitch section may be set to 230 ° C, and the heater temperature in the 19th to 27th pitch sections may be set to 200 ° C. In this case, the temperature of each pellet supplied to the mold (71) is set to its softening point (about 140 ° C.) and melting point (about 170 ° C.).
C.) (about 160 ° C. in this embodiment). The temperature of the pellet is desirably as close to the melting point (about 170 ° C.) as possible.

Thus, the thermoplastic material immediately before melting
(8) is stored in the final zone (17), and is kept warm just before melting. When the storage amount reaches the set amount, the injection cylinder (53) operates to advance the screw (2) forward by a predetermined stroke. Then this screw (2)
As a result, the thermoplastic material (8) stored at the tip of the cylinder (1) is compressed and its internal pressure rises, and the thermoplastic material (8) becomes 2 by the pressure increase and shear insulation between the materials.
The temperature is raised by about 0 deg. Then, the thermoplastic material (8) is brought into a molten state by the temperature rise at this time, and the molten resin is injected into the mold (71) from the discharge port (11). As a result, injection molding is completed and the piston rod (7
13) is retracted, the male mold (711) and the female mold (712) are separated, and the molded product is taken out.

In this apparatus, the temperature of each pellet of the thermoplastic material (8) is uniformly heated to the same temperature in the softening zone (16) and supplied to the final zone (17). (8) The discharge port is
The quality of the kneaded material discharged from (11) is improved. The thermoplastic material (8) stored at the tip of the cylinder (1) is
(71) due to the pressure increase when injected into the thermoplastic material
This is temporarily melted by raising the temperature of (8),
Since the resin in the molten state is molded by the mold (71), the time during which the thermoplastic material (8) is maintained in the high-temperature molten state is short. Therefore, it is already in the molten state when transferred to the final zone (17),
The thermoplastic material (8) is less likely to be thermally degraded, and the quality of the molded product is further improved, as compared with the above-described conventional one in which (8) is maintained in a molten state at a high temperature.

In the above embodiment, the thermoplastic material (8) is melted at the discharge pressure when the thermoplastic material (8) immediately before melting is injected into the mold (71). The mold (71) may be heated above the melting point of (8), and the mold (71) may be cooled immediately after the thermoplastic material (8) is injected into the mold (71). In the above embodiment, the case of injection molding has been described. However, the present invention can be applied to the case of other molding such as extrusion molding and blow molding.

Further, in the above embodiment, the case of molding using thermoplastic synthetic resin pellets has been described.
A metal such as aluminum may be heated to a state immediately before melting, supplied into a mold and heated under pressure to thereby form a die-cast product. still,
In the above embodiment, the additive (80) such as a coloring material is kneaded with the thermoplastic material (8) and molded, but only the thermoplastic material (8) is melted and supplied to the mold (71). In this case, the present invention can be applied.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an injection molding apparatus illustrating an embodiment of the present invention.

FIG. 2 shows the cylinder (1) in the softening zone (16) shown in FIG.
Enlarged view illustrating the boundary between the flight and the flight section (21)

FIG. 3 shows the thermoplastic material in the softening zone (16) shown in FIG.
Illustration showing behavior of (8)

FIG. 4 is a schematic view for explaining the behavior of the thermoplastic material (8) in contact with the guide surface (27) and the portion of the flight portion (21) appearing in FIG.

FIG. 5: Thermoplastic material (8) treated in softening zone (16)
Diagram explaining the state of particles

FIG. 6 is an explanatory view in which particles of the thermoplastic material (8) in FIG. 5 are in an adhesive state.

FIG. 7 is an explanatory view of a conventional example.

[Explanation of symbols]

 (1) ・ ・ ・ Cylinder (2) ・ ・ ・ Screw (3) ・ ・ ・ Hopper (6) ・ ・ ・ Kneading extruder (7) ・ ・ ・ Molding mechanism (8) ・ ・ ・ Plastic material (21 )···Flight

Claims (3)

[Claims] 1. A method for molding a thermoplastic material in which particles of a thermoplastic material are brought to a temperature immediately before melting, and the particles at the temperature are supplied to a mold or melted in a mold. 2. The method for molding a thermoplastic material according to claim 1, wherein the temperature immediately before the melting is a temperature equal to or higher than a softening point of the thermoplastic material and lower than a melting point. 3. The method for molding a thermoplastic material according to claim 1, wherein the thermoplastic material is a thermoplastic synthetic resin.