JPH04163020A - Method and apparatus for extrusion molding of rubber - Google Patents

Abstract

PURPOSE:To diminish the swelling of formed rubber member by a method wherein low frequency vibration, the plane of vibration of which is nearly normal to the discharging direction and the wavelength of which is specified, is given to the inner surface discharge head. CONSTITUTION:At the extrusion molding of green rubber composition, the composition is pressurized at the discharge port 4 of an extruder 1 by the screw 3 of the extruder and then discharged in the preform 8 of a discharge head 5 so as to compress the section of the rubber composition to the direction of the center line Y-Y in the preformer 8 in order to reduce the crosssectional area as a whole though the composition is enlarged to the direction X-X, resulting in increasing the pressure in the composition. The preformer 8 is elastically supported by dampers 11 so as to be vibrantly supported to an outer shell 9 in order to be vibrated to the direction Y-Y in the plane of vibration nearly normal to the extrusion direction by the low frequency vibration of 5-100Hz, which is applied by shakers 13. The direction of vibration is not limited in the plane normal to the extrusion direction, but some vibrational components in the extrusion direction are allowed to be present.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for extrusion molding a long unvulcanized sheet-like rubber member used as a constituent member in tire manufacturing, and an extrusion molding method used therein. Regarding equipment.

[Conventional technology]

During tire manufacturing, green tires are manufactured by sequentially wrapping long sheet-like rubber members such as tread rubber, sidewall rubber, bead filler, etc. onto the scraps on a tire assembly drum, and then vulcanizing in a mold. Each of the long sheet-like rubber members made of unvulcanized rubber used in this tire assembly process is formed by extruding an unvulcanized rubber composition into a predetermined cross-sectional shape using an extrusion molding device. Manufactured by

This extrusion molding device does not attach a die with a predetermined cross-sectional shape directly to the discharge port of the extruder, but instead creates a structure between the circular cross-section discharge port of the extruder and the die, while reducing the cross-sectional area from the circular cross-section to the predetermined cross-sectional shape of the die. A sheet-like rubber having a predetermined cross-sectional shape is manufactured by interposing a discharge head having an inner cross-sectional shape that gradually changes continuously to a nearly flat cross-sectional shape and sufficiently increasing the pressure of the rubber introduced into the mouthpiece.

On the other hand, JP-A-52-4558 and JP-A-52-4
Publication No. 559 discloses a method of reducing extrusion pressure by applying ultrasonic vibrations that vibrate in the discharge direction, that is, the axial direction of the die, to the die of an extrusion molding device for unvulcanized rubber, thermoplastic synthetic resin, etc. .

[Problem to be solved by the invention]

The cylindrical rubber discharged from the extruder's circular cross-section discharge port is
For example, in order to uniformly extrude sheet rubber with a flat cross-sectional shape such as sidewall rubber, it is necessary to increase the extrusion pressure at the nozzle to an extremely high level. That is, the ratio of the cross-sectional area of the exit to the population needs to be 1/4 to 1/7. However, when a rubber composition with high viscoelasticity is extruded under high pressure, a large residual strain occurs during extrusion, and in order to alleviate the residual stress, the extruded rubber sheet contracts in the extrusion direction, resulting in an increase in cross-sectional area. , a so-called swell phenomenon occurs.

When the dimensional accuracy of the rubber members constituting the tire decreases due to the swell phenomenon, the quality of manufactured tires varies, and the uniformity of the tire also deteriorates.

The rate at which the cross-sectional area of extruded rubber members increases due to this swell phenomenon is due to variations in the quality of the raw materials and the dispersion state of carbon black in the rubber composition, even if the same brand of raw materials are used as raw materials for the rubber composition. It varies greatly depending on the standing time after kneading the rubber composition, the temperature, cross-wire conditions, the temperature of the extruder, and differences in the mechanical and thermal history that the rubber composition undergoes after kneading and before extrusion.

When mass producing sheet-like rubber materials constituting tires, variations in these conditions are unavoidable, and it is extremely difficult to always produce extruded rubber of the same size. In order to reduce variations in the molded dimensions of rubber parts, we aim to keep quality as constant as possible by strictly controlling the rubber cross-wire conditions, storage conditions of the kneaded rubber composition, and mixing rubber compositions with different lofts. There is a need. Furthermore, it is necessary to inspect the extruded rubber during the extrusion process and adjust the extruder, and there is a problem in that the extrusion process requires skilled manpower.

Therefore, an object of the present invention is to provide a method for extruding extrusion-molded sheet rubber with a small swell, and an extrusion device used therefor.

[Means to solve the problem]

In order to achieve the above object, as a result of extensive research, the present inventor has determined that the discharge head interposed between the extruder and the nozzle has a direction approximately perpendicular to the discharge direction and a direction in which the swell is intended to occur after extrusion molding. The present inventors have discovered that the swell of extruded rubber can be reduced by applying low-frequency vibrations in a direction that substantially coincides with the above, and have completed the present invention.

That is, the columnar unvulcanized rubber composition discharged from the outlet of the extruder is heated between the outlet and the die until the cross-sectional shape of the outlet changes to a shape close to the flat cross-sectional shape of the extrusion die. In a method for forming a long sheet-like rubber member, the elongated sheet-like rubber member is molded into a predetermined cross-sectional shape through the die, by passing through a discharging head interposed in the discharge head, the cross-sectional shape is continuously changed and the cross-sectional area is reduced, and the elongated sheet-like rubber member is formed into a predetermined cross-sectional shape through the mouthpiece. The gist of this invention is a rubber extrusion molding method characterized by reducing the swell of a molded rubber member by applying low frequency vibrations of 5 to 100 Hz in a direction substantially perpendicular to the discharge direction to the inner surface of the head.

Another invention includes an extruder having a discharge port with a circular or square cross-sectional shape, a discharge head connected to the discharge port, and an extrusion molding die connected to the outlet of the discharge head, The discharge head consists of an outer shell and a cylindrical preformer that is held inside the outer shell by a damper so that it can vibrate elastically with a gap, and the cross-sectional shape of the preformer is the same as that of the discharge port of the extruder. The cross-sectional shape of the inlet is changed continuously from the cross-sectional shape of the inlet that substantially matches the cross-sectional shape of the die to the flat cross-sectional shape of the outlet that is close to the cross-sectional shape of the die, and the cross-sectional area is continuously reduced in the extrusion direction. The preformer
The gist is an extrusion molding apparatus equipped with a low frequency vibrator mounted on the outer surface in a direction substantially perpendicular to or slightly inclined to the extrusion direction of the preformer.

Next, the content of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view of an example of an extrusion molded INM used in the rubber extrusion molding method of the present invention, and FIG. 2 is a sectional view taken along line AA in the direction perpendicular to the cross section of FIG. (1) is a screw type extruder, with a screw (
3), and its rotation pressurizes the rubber composition at high pressure and extrudes it.

A discharge head (5) is fixed to the discharge port (4) of the extruder (1), and a molding die (
7) is installed. The discharge head (5) has a double structure of an inner preformer (8) and an outer shell (9),
A narrow gap α between the preformer (8) and the outer shell (9)
has. A damper (manufactured by Co., Ltd.) that also serves as a spacer is inserted into both ends of the gap ill. As shown in FIG.
It has a circular cross-sectional shape with the same diameter as 4), and the interval between its inner surfaces narrows toward the exit in the cross section shown in Figure 1, but widens in the cross section perpendicular to this in Figure 2. ing. Therefore, the cross-sectional shape of the inner surface of the intermediate part of the preformer (8) in the direction perpendicular to the discharge direction is an ellipse as shown in FIG. The cap (7) as shown in Figure 3C
It has a shape close to the cross-sectional shape of , and is formed to be larger than the internal dimension of the entrance of the cap (7).

An arbitrary cross-sectional shape of the die (7) is selected depending on the cross-sectional shape of the rubber member to be extruded. - It may have an elongated rectangular shape with a certain width, or it may have a wedge-shaped cross-section like filler rubber.

A part of the gap α1 between the preformer (8) and the outer shell (9) is widened at two locations, and a vibrator (2) consisting of a low frequency vibrator is fitted into each of the two locations. The vibration exciter (1) is installed at both ends of the short axis of the elliptical cross section of the middle part of the preformer (8). In other words, among the two mutually perpendicular center lines x-xSy-y in the cross section perpendicular to the discharge direction at the middle part of the preformer (8), the inner diameter of the preformer (8) is in the direction of the shorter one. A pair of vibration exciters (2) are arranged at opposing positions on the center line Y-Y.

Instead of a pair of vibration exciters (to), a plurality of pairs of vibration exciters 0 may be arranged at symmetrical positions with respect to the center lines XX and YY. For example, four vibration exciters (2) can be arranged at symmetrical positions with respect to the rain center line.

If each vibrator ■ is placed on the same side across the center line The preformer (8) side vibrates in opposite phase and in synchronization with each other, with the outer shell (9) as a reference.

The appropriate frequency of low frequency vibration applied to the preformer (8) by the vibrator surface is 5 to 100&. If it is less than 57, the effect of reducing swell will be small, and if it exceeds 100,07, it will be undesirable as it will cause unpleasant noise and have a large impact on the working environment.

The amplitude of the excited preformer (8) is 0.5 to 5 m
m is appropriate. If the amplitude is less than 0.5 mm, the effect of reducing swell is small, and if the amplitude exceeds 5 fi, there is a risk that the ejection head (5) may be damaged.

The cap (7) attached to the outlet (i) of the preformer (8) is formed so that its diameter narrows in the vertical direction from the inlet toward the outlet.

[Effect]

When extrusion molding an unvulcanized rubber composition using the extrusion molding apparatus of the present invention, pressure is applied at the discharge port (4) of the extruder by the screw (3) of the extruder (1), and the discharge head ( 5)
is discharged into the preformer 03). Within the preformer (8), the cross section of the rubber composition is compressed in the center line Y-Y direction and expanded in the XX direction, but the cross-sectional area as a whole is reduced, and therefore the pressure is increased.

The flexor (8) is elastically supported by Damper Co., Ltd., and is supported so as to be able to vibrate with respect to the outer shell (9), and a vibration is applied from a vibration exciter 0 arranged in the Y-Y direction. Due to low frequency vibration, Y-
It vibrates in the Y direction. The vibration direction is not limited to within a plane perpendicular to the extrusion direction, and there may be a slight vibration component in the extrusion direction.

The compressive strain in the rubber composition to be molded is relaxed, and the
) The residual strain in the molded rubber extruded from the rubber is reduced.

Therefore, the swell phenomenon of the molded unvulcanized sheet rubber is almost eliminated.

In the extrusion molding apparatus of the present invention, unlike conventional extrusion molding apparatuses, ultrasonic vibrations are not applied along the extrusion direction, but low frequency vibrations are applied in a direction substantially perpendicular to the extrusion direction, so that the extrusion pressure can be reduced. The drop is small, the rubber can be discharged into the mouthpiece (7) under high pressure, and the rubber can be accurately molded into a predetermined flat shape.

〔Example〕

A nozzle (7) having a substantially trapezoidal inner cross-section with a height of 10 m and a width of 150 m is attached to the ejection head (5) having the cross-sectional shape shown in Figs. 1 and 2, and the preformer ( 8
) was applied with low frequency vibration. A tread rubber member was extruded by extruding a rubber composition having a Mooney viscosity of 60 while varying the frequency of the applied low-frequency vibration and keeping the amplitude of the preformer (8) constant at 1 part.

The extruded rubber sheet was immediately cut into a length of 40 cm, and after being left for 20 hours, a 100 m long section was cut from the longitudinal center of the rubber sheet and its weight was measured. The weight per unit length when low frequency vibration is not applied is set as 100, and the weight when low frequency vibration of various frequencies is applied is expressed as a rubber weight index, and the obtained measurement results are used as the rubber weight index. Shown in Figure 4.

As is clear from Figure 4, the frequency of low frequency vibration is 20
In the range of ~100&, as the frequency increases, the rubber weight index decreases, that is, the weight of the rubber per unit length of the tread rubber member extruded using the same die (7) after being left to stand decreases. Therefore, it can be seen that the higher the frequency of the applied vibration, the smaller the swell.

〔Effect of the invention〕

According to the rubber extrusion molding method and apparatus of the present invention, it is possible to easily produce a raw rubber sheet having an accurate predetermined size, and the molded rubber member has a small swell, and therefore the variation in its size is small, and its size is small. As a result, the quality of tires manufactured using it is stabilized and uniformity is improved.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of the extrusion molding apparatus of the present invention, FIG. 2 is a plane sectional view taken along the line DD, and FIG.
In the sectional views, b is a BB sectional view, and C is a CC sectional view. FIG. 4 is a graph showing the relationship between the swell of an extruded rubber member and the amplitude of the preformer. (1) Extruder, (2) Barrel, (3)
screw, (4) discharge, (5) discharge head, (6) outlet, (7) mouthpiece,
(8) Preformer-1 (9) Outer shell,
αQ gap, damper, ■
Inlet, side shaker. Patent applicant: Toyo Rubber Industries, Ltd. Agent: Yoshiyuki Koyama, patent attorney Figure 3 Y Figure 1

Claims (3)

[Claims] (1) The columnar unvulcanized rubber composition discharged from the discharge port of the extruder is changed from the cross-sectional shape of the discharge port to a shape close to the flat cross-sectional shape of the extrusion die. A method for forming a long sheet-like rubber member, in which the cross-sectional shape is continuously changed and the cross-sectional area is reduced at the same time by passing through a discharge head interposed in between, and the elongated sheet-like rubber member is formed into a predetermined cross-sectional shape through the die. A rubber extrusion molding method characterized in that the swell of a molded rubber member is reduced by applying low frequency vibration of 5 to 100 Hz in a direction substantially perpendicular to the discharge direction to the inner surface of the discharge head. (2) The rubber extrusion molding method according to claim 1, wherein the sheet-like rubber member is a tire component such as tread rubber, sidewall rubber, or filler rubber. (3) An extruder having a discharge port having a circular or square cross-sectional shape, a discharge head connected to the discharge port, and an extrusion molding die connected to the outlet of the discharge head, the discharge head being It consists of an outer shell and a cylindrical preformer that is held in the inner side of the outer shell by a damper so that it can vibrate elastically with a gap, and the cross-sectional shape of the preformer is the same as the cross-sectional shape of the discharge port of the extruder. The preform is formed so that the cross-sectional shape of the inlet that substantially matches the cross-sectional shape of the outlet changes continuously to the cross-sectional shape of the outlet that is flat close to the cross-sectional shape of the die, and the cross-sectional area thereof continuously decreases in the extrusion direction. An extrusion molding device equipped with a low-frequency vibrator that vibrates on the outer surface of the preformer in a direction substantially perpendicular to or slightly inclined to the extrusion direction of the preformer.