JP2004249517A - Extruder for thin-walled rubber and extrusion method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extruder for a thin-walled rubber capable of extruding and molding the thin-walled rubber of good quality having appearance free from wrinkles, and an extrusion method using it. <P>SOLUTION: The extruder 1 for the thin-walled rubber for extruding and molding a sheetlike thin-walled rubber is equipped with a first die 61 having a cross-sectional shape corresponding to that of the thin-walled rubber and the second die 62 arranged just on the upstream side of the first die 61 and having a cross-sectional shape for uniformizing the flow velocity distribution in the width direction of the molded thin-walled rubber. The second die 62 has a cross-sectional shape becoming large in cross-sectional height toward the outside in the width direction of the thin-walled rubber. Further, the extruder is equipped with a screw 2 for sending a rubber material to the first and second dies 61 and 62 and the gear pump 3 arranged on the leading end side of the screw 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thin rubber extruder and a thin rubber extrusion method for extruding a sheet-like thin rubber.
[0002]
[Prior art]
In extruding a rubber having a predetermined cross-sectional shape, a rubber extruder to be manufactured has been known for a long time. As a basic configuration thereof, a screw extruder is provided, and the supplied rubber material is kneaded and plasticized. The kneaded rubber material is fed into a die head, and rubber is extruded from a die having a predetermined cross-sectional shape. For example, in the case of producing a rubber constituting a tread portion of a pneumatic tire, the tread rubber is extruded and formed using a die head corresponding to a cross-sectional shape of the tread portion. By winding this rubber around a forming drum, a rubber layer of tread rubber is formed. Alternatively, a strip rubber having a small sectional area is extruded. In the case of a strip rubber, it is wound around a forming drum to form a rubber layer having a predetermined sectional shape.
[0003]
[Problems to be solved by the invention]
The problems of such a rubber extruder (extrusion method) are as follows. The rubber extruded from the rubber extruder is thick and not thin rubber. The thin rubber refers to, for example, rubber formed into a sheet having a thickness of 0.3 to 1 mm level.
[0004]
However, when such a thin rubber is extruded and formed from the die head, a thin rubber having a wrinkled appearance is formed. The reason why such wrinkles are formed is that the flow velocity of the rubber material in the width direction of the thin rubber is not constant.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thin rubber extruding apparatus and method capable of extruding high quality thin rubber having no wrinkles in appearance.
[Means for Solving the Problems]
To solve the above problems, the thin rubber extruder according to the present invention,
A thin-walled rubber extruder for extruding a thin rubber in a sheet form,
A first die having a cross-sectional opening corresponding to the cross-sectional shape of the thin rubber;
A second die disposed just upstream of the first die and having a cross-sectional shape such that the flow velocity distribution in the width direction of the thin rubber to be molded is made uniform.
[0005]
According to the thin rubber extruder, the first die and the second die are provided, and the cross-sectional opening of the first die has a shape corresponding to the cross-sectional shape of the thin rubber. Further, a second die is disposed immediately upstream of the first die, and the second die has a cross-sectional shape that makes the flow velocity distribution uniform. Theoretically, the flow velocity increases as the cross-sectional area decreases, and decreases as the cross-sectional area increases. Therefore, in consideration of this point, the cross-sectional shape of the second die can be set so that the flow velocity distribution becomes constant. As a result, it is possible to provide a thin rubber extruder capable of extruding high quality thin rubber having no wrinkles in appearance.
[0006]
As a preferred embodiment of the present invention, the second die has a cross-sectional shape formed such that the cross-sectional height increases as going outward in the width direction of the thin rubber.
[0007]
In the case of a rubber extruder, the flow velocity tends to increase near the die head as it goes outward in the width direction of the flow path. Therefore, the flow velocity distribution can be made constant by increasing the cross-sectional height (ie, increasing the cross-sectional area) as going outward in the width direction. Thereby, it is possible to extrude a thin rubber having no wrinkles formed in appearance.
[0008]
As another preferred embodiment of the present invention, one provided with a screw for feeding a rubber material into the first die and the second die, and a gear pump disposed at a tip side of the screw.
[0009]
Extrusion molding of a thin rubber requires a high molding pressure. Therefore, a high molding pressure can be realized by feeding the rubber material using a gear pump.
[0010]
In order to solve the above problems, the method for extruding a thin rubber according to the present invention,
Kneading the rubber material with a screw and sending it out,
Passing the rubber material fed by the screw through a second die having a cross-sectional shape such that the flow velocity distribution in the width direction of the thin rubber to be molded is made uniform.
Extruding the rubber material that has passed through the second die from the first die having a cross-sectional opening corresponding to the cross-sectional shape of the thin rubber.
[0011]
As a preferred embodiment of the present invention, the second die has a cross-sectional shape formed such that the cross-sectional height increases as going outward in the width direction of the thin rubber.
[0012]
As another preferred embodiment of the present invention, a gear pump is arranged at the tip end side of the screw, and has a step of sending out a rubber material kneaded by the gear pump.
The operation and effect of the method for extruding thin rubber with such a configuration are as described above.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of a thin rubber extruder according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a cross-sectional configuration of the extrusion device.
[0014]
1, a screw extruder 2, a gear pump 3, a first flow path 4, a second flow path 5, and a die head 6 are provided in this order from the right side. The screw extruder 2 kneads and plasticizes a rubber material supplied from a rubber material supply port (not shown) and extrudes the rubber material forward. The gear pump 3 is composed of a pair of gears, and further kneads and plasticizes the rubber material supplied from the screw extruder 2 and sends out a certain amount of the rubber material toward the front flow path. The first flow path 4 and the second flow path 5 are arranged in front of the gear pump 3, and the first flow path 4 has a predetermined large cross-sectional area. In the second flow path 5, the cross-sectional area of the flow path gradually decreases.
[0015]
FIG. 2 is an enlarged view showing details of the die head 6 (holder for holding the die). The first die 61 is disposed at the most distal end in the flow direction of the die head 6, and the second die 62 is disposed immediately upstream of the first die 61. A thin rubber is extruded from the die head 6. Here, the term “thin” refers to a material having a thickness of about 5 mm or less. In particular, it refers to one having a thickness of about 0.05 mm to 0.2 mm. Such a thickness is considered to be suitable, for example, for manufacturing an inner liner of a pneumatic tire, and also convenient for forming rubber layers having various cross-sectional shapes. A rubber layer having various cross-sectional shapes can be formed by appropriately winding a thin rubber (rubber sheet) around a forming drum.
[0016]
FIG. 3 is a view of the first die 61 as viewed from the front. The shape of the opening 61a is determined according to the cross-sectional shape of the sheet-like thin rubber to be formed. Therefore, the shape of the opening 61a is formed in a horizontally long rectangle.
[0017]
4 and 5 show the structure of the second die 62. FIG. The second die 62 is provided to make the flow velocity distribution of the rubber material along the width direction of the formed thin rubber constant. When unevenness occurs in the flow velocity distribution, wrinkles are formed on the external surface of the extruded rubber, and desired quality cannot be obtained. Therefore, the second die 62 is arranged to keep the flow velocity distribution constant. FIG. 4 shows the structure of the second die according to the first embodiment. (A) is a front view, (b) is a side sectional view, (c) is a rear view, and (d) is a plan sectional view. The shape of the opening 62a is not formed in a rectangular shape in order to make the flow velocity distribution constant. The cross-section height is set to be the smallest at the center in the width direction, and the cross-section height becomes higher toward the outside in the width direction. Also, in the second embodiment shown in FIG. 5, the section height is set to be higher toward the outside in the width direction. The shapes of the first die 61 and the second die 62 are set according to changes in the size, material, and the like of the thin rubber to be extruded.
[0018]
A third flow path 63 is also formed inside the die head 6 and is connected to the second flow path 5. The third channel 63 is formed in a concave portion. When the first die 61 and the second die 62 are arranged (replaced), the dies 61 and 62 are detached from the right side in FIG. It should be noted that no particular means is required for fixing the dies 61 and 62. When the rubber material is extruded, pressure acts from the right side in FIG. 2, so that the dies 61 and 62 always exert pressure so as to be pressed to the left side in FIG. 2. Since only the dies 61 and 62 are replaced, it is not necessary to replace the entire die head. Therefore, it is possible to easily cope with a change in specifications. Further, the cross-sectional shape of the second die 62 is a two-dimensional curve (the cross-sectional shape of any part is the same in the flow direction of the rubber material), and manufacture is easy.
[0019]
The second flow path 5 is formed inside the die adapter 50. The die head 6 is fastened to the die adapter 50 by screws. In the case of rubber, unlike resin, the viscosity is high. Therefore, unlike resin, it is generally considered difficult to extrude rubber into a thin wall. Therefore, in the present invention, the gear pump 3 is used as the extrusion device 1. By using the gear pump 3, a high extrusion pressure can be realized, and thin rubber can be extruded from the narrow opening 61a.
[0020]
<Example>
Next, the result of actually extruding thin rubber will be described. First, CR rubber was used as a rubber material. The characteristics of this CR rubber are as follows.
[0021]
Mooney viscosity = 32ML (1 + 4) 100 ° C
Mooney viscosity is based on JIS K 6300.
Apparent viscosity = 600 Pa · sec (1000 sec ⁻¹ : 95 ° C., L / D = 5) The apparent viscosity is measured by a capillary rheometer test (based on ASTM D 1703).
Die swell = 41% (1000 sec ⁻¹ : 95 ° C., L / D = 5)
Die swell is the ratio of strand diameter / capillary diameter. (See ASTM D 3835)
Here, L / D is the ratio of the diameter to the length of the capillary.
[0022]
FIG. 6 is a diagram showing the external surface of the rubber when the thin rubber is extruded and formed without the second die 62. Since the flow velocity distribution in the width direction is not constant, the surface has irregularities and wrinkles are formed. FIG. 7 shows an example in which thin rubber is molded in a state where the first die 61 shown in FIG. 3 and the second die 62 shown in FIG. 4 are provided. Although there are no irregularities on the surface, wrinkles remain at both ends in the width direction. FIG. 8 shows an example in which thin rubber is molded in a state where the first die 61 shown in FIG. 3 and the second die 62 shown in FIG. 5 are provided. Wrinkles are eliminated, and high quality rubber can be molded. In this way, by providing the second die 62 having an appropriate structure, it is possible to make the flow velocity distribution constant and to extrude the thin rubber having a clean surface with no wrinkles on the surface.
[0023]
<Another embodiment>
Another embodiment of the mounting structure of the first die and the second die will be described. In the case of the die head 60 shown in FIGS. 1 and 2, in order to exchange the first die 61 and the second die 62, it is necessary to remove the die head 6 from the die adapter 5. Alternatively, the first die 61 may be detachable from the front side of the die head 6. That is, the first die 61 may be configured to be attached from the front side with screws. Thereby, the replacement operation is further facilitated.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a cross-sectional configuration of a thin rubber extruder. FIG. 2 is an enlarged view showing details of a die head. FIG. 3 is a view showing a shape of a first die. FIG. FIG. 5 shows the structure of the second die according to the second embodiment. FIG. 6 shows the structure of the second die according to the second embodiment. FIG. 6 shows the structure of the experimental result. FIG. 7 shows the structure of the experimental result. Diagrams [Description of symbols]
DESCRIPTION OF SYMBOLS 1 Thin rubber extruder 2 Screw extruder 3 Gear pump 6 Die head 61 First die 61a Opening 62 Second die 62a Opening

Claims (6)

A thin rubber extruder for extruding a sheet-like thin rubber, comprising:
A first die having a cross-sectional opening corresponding to the cross-sectional shape of the thin rubber;
A second die disposed immediately upstream of the first die and having a cross-sectional shape such that the flow velocity distribution in the width direction of the thin rubber to be molded is made uniform. . The thin rubber extruder according to claim 1, wherein the second die has a cross-sectional shape such that a cross-sectional height increases as going outward in a width direction of the thin rubber. The thin rubber extruder according to claim 1 or 2, further comprising: a screw for feeding a rubber material into the first die and the second die; and a gear pump disposed on a tip side of the screw. apparatus. A thin rubber extrusion method for extruding a sheet-like thin rubber, the method comprising:
Kneading the rubber material with a screw and sending it out,
Passing the rubber material fed by the screw through a second die having a cross-sectional shape such that the flow velocity distribution in the width direction of the thin rubber to be molded is made uniform.
Extruding the rubber material that has passed through the second die from a first die having a cross-sectional opening corresponding to the cross-sectional shape of the thin rubber. The method for extruding a thin rubber according to claim 4, wherein the second die has a cross-sectional shape such that a cross-sectional height increases as going outward in a width direction of the thin rubber. The method for extruding a thin rubber according to claim 4 or 5, wherein a gear pump is disposed on a tip end side of the screw, and the method includes a step of sending out the rubber material kneaded by the gear pump.

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