JP6772787B2 - Die plate for rubber extruder - Google Patents

Description

The present invention relates to a mouthpiece of an extruder for extruding a rubber composition. More specifically, the present invention relates to improving the shape of the die plate included in the mouthpiece.

Tires are obtained by vulcanizing the low cover. This low cover is made of members such as carcass, tread, sidewall, bead, and belt. Usually, a tread is formed by winding a rubber sheet obtained by extruding a rubber composition into a ring shape. Extrusion is performed by an extruder with a base. This mouthpiece contains a die plate.

Japanese Unexamined Patent Publication No. 2014-205331 discloses a die plate having a retention portion. In this die plate, the stagnant portion can contribute to the good shape of the extruded rubber sheet ears (outer edges in the width direction).

JP-A-2014-205331

A typical rubber sheet for a tread has a cap layer, a base layer and an under tread layer. These layers are formed from different rubber compositions. A rubber sheet is formed by co-extruding and laminating a plurality of types of rubber compositions.

In extrusion using a conventional die plate, the rubber composition for the under tread layer may not be sufficiently spread close to the ears of the rubber sheet. With this rubber sheet, the width of the under tread layer is insufficient. In this case, a rubber sheet having inferior quality can be obtained. Rubber sheets of poor quality are discarded. Discard reduces the yield of raw materials.

Similar problems occur with various rubber sheets obtained by coextrusion other than the rubber sheet for tread.

An object of the present invention is to provide a die plate for coextrusion that can contribute to the high quality of a rubber sheet.

The die plate for a rubber extruder according to the present invention has an inflow side surface, a discharge side surface located downstream of the inflow side surface, a base surface located between the inflow side surface and the discharge side surface, and a flow path recessed from the base surface. It has a forming surface and a retention space forming surface located near the widthwise end of the flow path forming surface and having an opening on the inflow side surface. The center of the opening in the width direction is located inside the end of the flow path forming surface in the width direction.

Preferably, the distance between the center in the width direction of the opening and the end of the flow path forming surface is 2.0 mm or more.

Preferably, the retention space forming surface has a shape in which the cross-sectional area thereof gradually decreases from the opening toward the discharge side surface.

According to another viewpoint, the tire manufacturing method according to the present invention is:
(1) A step of extruding a rubber composition with an extruder having a base to obtain a rubber sheet.
(2) A process of assembling the rubber sheet with other rubber members to obtain a low cover.
And (3) includes a step of heating the low cover to cause a cross-linking reaction in the rubber. This mouthpiece has a die plate. This die plate includes an inflow side surface, a discharge side surface located downstream of the inflow side surface, a base surface located between the inflow side surface and the discharge side surface, a flow path forming surface recessed from the base surface, and this flow path. It has a retention space forming surface that is located near the widthwise end of the forming surface and has an opening on the inflow side surface. The widthwise center of this opening is located inward in the width direction with respect to the edge of the flow path forming surface.

In coextrusion using the die plate according to the present invention, each of the plurality of rubber compositions used for this extrusion is sufficiently spread to the edge of the rubber sheet. By this extrusion, a high quality rubber sheet can be obtained.

FIG. 1 is a perspective view showing a die plate according to an embodiment of the present invention. FIG. 2 is a front view showing the die plate of FIG. FIG. 3 is a rear view showing the die plate of FIG. FIG. 4 is a bottom view showing the die plate of FIG. FIG. 5 is a cross-sectional view taken along the line VV of FIG. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. FIG. 7 is a front view showing a part of the base including the die plate of FIG. 1-6. FIG. 8 is a cross-sectional view showing a part of the rubber sheet extruded from the base of FIG. 7. FIG. 9 is an enlarged view showing a part of the die plate of FIG.

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

The die plate 2 shown in FIGS. 1-6 has an inflow side surface 4, a discharge side surface 6, a base surface 8, a top surface 10, a flow path forming surface 12, and a retention space forming surface 14. The direction indicated by the arrow A1 in FIG. 1 is the extrusion direction of the rubber composition. The direction indicated by the arrow A2 in FIG. 1 is the width direction. As is clear from FIGS. 5 and 6, the cross-sectional shape of the die plate 2 is substantially rectangular except for the flow path forming surface 12 and the retention space forming surface 14. The material of the die plate 2 is metal. Typically, the die plate 2 is made of steel (carbon steel or alloy steel).

The inflow side surface 4 extends perpendicular to the extrusion direction A1. The discharge side surface 6 also extends perpendicular to the extrusion direction A1. The discharge side surface 6 is located downstream of the inflow side surface 4 in the extrusion direction. The base surface 8 is located between the inflow side surface 4 and the discharge side surface 6. The top surface 10 is also located between the inflow side surface 4 and the discharge side surface 6.

The flow path forming surface 12 is recessed upward in FIG. 5 from the base surface 8. The flow path forming surface 12 extends from the inflow side surface 4 to the discharge side surface 6. In other words, the flow path forming surface 12 is open to the inflow side surface 4 and is also open to the discharge side surface 6. As shown in FIG. 2-4, the flow path forming surface 12 has two end Eds in the width direction A2. Each end Ed is also a boundary between the base surface 8 and the flow path forming surface 12. In this embodiment, the flow path forming surface 12 has a flat surface 16 and a pair of curved surfaces 18. Each curved surface 18 is located outside the flat surface 16 in the width direction. The shape of the curved surface 18 in front view is generally arcuate. The curved surface 18 is continuous with the flat surface 16. In the base 20 (see FIG. 7) described later, the flow path forming surface 12 forms a flow path for the rubber composition.

As is clear from FIG. 3, the residence space forming surface 14 is located in the vicinity of the end Ed of the flow path forming surface 12. As is clear from FIG. 6, the retention space forming surface 14 is continuous with the flow path forming surface 12. The retention space forming surface 14 is formed by cutting a base metal made of metal. Therefore, the shape of the retention space forming surface 14 is generally recessed. The retention space forming surface 14 is recessed from the inflow side surface 4, and is also recessed from the flow path forming surface 12. The retention space forming surface 14 is also referred to as “lining”. In the present embodiment, the shape of the retention space forming surface 14 is a part of a spherical surface.

The retention space forming surface 14 has an opening 22 on the inflow side surface 4. As is clear from FIGS. 4 and 6, the residence space forming surface 14 has a shape in which the cross-sectional area thereof gradually decreases from the opening 22 toward the discharge side surface 6. The retention space forming surface 14 does not reach the discharge side surface 6. A space for the rubber composition to stay is formed by the staying space forming surface 14.

FIG. 7 is a front view showing a part of the base 20 including the die plate 2 of FIG. 1-6. The base 20 has a holder 24 together with the die plate 2. FIG. 7 shows the discharge side surface 6 of the die plate 2. The base surface 8 of the die plate 2 is in contact with the holder 24. Due to this contact, a discharge port 26 is formed between the flow path forming surface 12 and the holder 24. The discharge port 26 is the end of the flow path of the rubber composition in the base 20.

In coextrusion using the base 20, a plurality of cylinders are connected to the base 20. A rubber composition is supplied to the base 20 from each cylinder. In other words, a plurality of types of rubber compositions are supplied to the base 20. These rubber compositions are laminated by the base 20 and discharged from the discharge port 26. A rubber sheet is obtained by this discharge. The method of extruding a plurality of rubber compositions from the base 20 is called coextrusion.

FIG. 8 is a cross-sectional view showing a part of the rubber sheet 28 extruded from the base 20 of FIG. 7. The rubber sheet 28 is for a tire tread. Rubber sheets for other parts of the tire may be extruded from the base 20.

The rubber sheet 28 has a cap layer 30, a base layer 32, an under tread layer 34, and a wing layer 36. The cap layer 30 is laminated on the base layer 32. The base layer 32 is laminated on the under tread layer 34. The wing layer 36 covers the ends of the cap layer 30, the base layer 32 and the undertread layer 34. In FIG. 8, the arrow W1 indicates the width of the undertread layer.

The rubber sheet 28 is assembled with other rubber members to form a low cover. This low cover is put into the mold. The low cover is pressurized and heated in the mold. The low cover rubber composition flows by pressurization and heating. The rubber undergoes a cross-linking reaction due to heating, and a tire is obtained. That is, the tire manufacturing method according to the present invention is
(1) A step of extruding a rubber composition with an extruder having a base 20 to obtain a rubber sheet 28.
(2) A step of assembling the rubber sheet 28 with another rubber member to obtain a low cover.
And (3) includes a step of heating the low cover to cause a cross-linking reaction in the rubber.

In the above step (1), the rubber composition stays in the staying space. By this retention, a rubber sheet 28 having a good ear shape can be formed.

FIG. 9 is an enlarged view showing a part of the die plate 2 of FIG. FIG. 9 shows the inflow side surface 4. In FIG. 9, the left side is the outside in the width direction, and the right side is the inside in the width direction. An opening 22 of a retention space forming surface 14 exists on the inflow side surface 4. In FIG. 9, reference numeral P1 indicates the outer end in the width direction of the opening 22, and reference numeral P2 indicates the inner end in the width direction of the opening 22. In the present embodiment, the outer end P1 coincides with the end Ed of the flow path forming surface 12. The opening 22 may have an outer end P1 that does not coincide with the end Ed of the flow path forming surface 12.

The width-direction distance between the straight line indicated by the reference numeral CL and the outer end P1 in FIG. 9 is equal to the width-direction distance between the straight line CL and the inner end P2. In other words, the straight line CL is a line representing the center of the opening 22 in the width direction. As is clear from FIG. 9, the width direction center line CL is located inside the end Ed of the flow path forming surface 12 in the width direction. At the retention space forming surface 14 where the opening 22 is located at this position, the rubber composition for the undertread layer 34 sufficiently flows into the space formed by the retention space forming surface 14. In the rubber sheet 28 obtained by the base layer 20, the rubber composition for the under tread layer 34 is sufficiently spread to the vicinity of the edge of the base layer 32. Therefore, a rubber sheet 28 including an undertread layer 34 having a sufficient width W1 (see FIG. 8) can be obtained. In coextrusion using this base 20, the defective rate of the rubber sheet 28 is small. In the tire in which the rubber sheet 28 is used, the tread can be sufficiently adhered to other rubber members (for example, belt, band, etc.).

The base 20 is particularly effective in so-called cold extrusion. Cold extrusion means extrusion in which the temperature of the rubber composition immediately after ejection is 50 ° C. or lower.

In FIG. 9, the arrow L indicates the distance between the widthwise center CL of the opening 22 and the end Ed of the flow path forming surface 12. From the viewpoint of the quality of the rubber sheet 28, the distance L is preferably 2.0 mm or more, and particularly preferably 3.0 mm or more. The distance L is preferably 15 mm or less.

As described above, on the inflow side surface 4, the position of the outer end P1 of the opening 22 coincides with the position of the end Ed of the flow path forming surface 12. The position of the outer end P1 may be outside the position of the end Ed of the flow path forming surface 12 in the width direction. The widthwise distance between the position of the outer end P1 and the position of the end Ed of the flow path forming surface 12 is preferably 0.0 mm or more. This distance is preferably 15 mm or less.

In this embodiment, the shape of the opening 22 is an arc. It is the radius of this arc that is indicated by the reference numeral R in FIG. The radius R is preferably 5 mm or more and 25 mm or less, and particularly preferably 10 mm or more and 20 mm or less.

What is indicated by the arrow W2 in FIG. 9 is the width of the opening 22. The width W2 is preferably 5 mm or more and 25 mm or less, and particularly preferably 10 mm or more and 20 mm or less.

In FIG. 4, the arrow Dp indicates the depth of the retention space forming surface 14, and the arrow T indicates the thickness of the die plate 2. The ratio of the depth Dp to the thickness T (Dp / T) is preferably 0.5 or more, and particularly preferably 0.7 or more. This ratio (Dp / T) is preferably 0.95 or less.

Hereinafter, the effects of the present invention will be clarified by Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.

[Example 1]
The die plates shown in FIGS. 1-7 and 9 were prepared. This die plate has a retention space forming surface. The shape of the retention space forming surface is a part of a spherical surface. On this retention space forming surface, the radius R of the opening is 15 mm, the distance L is 2.0 mm, the width W2 is 14 mm, and the ratio (Dp / T) is 0.9.

[Examples 2 and 3 and Comparative Example 2]
Die plates of Examples 2 and 3 and Comparative Example 2 were obtained in the same manner as in Example 1 except that the distance L was as shown in Table 1 below.

[Comparative Example 1]
A die plate of Comparative Example 1 was obtained in the same manner as in Example 1 except that the retention space forming surface was not provided.

[Extrusion]
A rubber sheet for the tread was extruded from an extruder equipped with a base having each die plate. This rubber sheet had a cap layer, a base layer, an under tread layer and a wing layer. The shape of the ear of this rubber sheet was visually determined. Further, the width W1 of the under tread layer in this rubber sheet was measured. These results are shown in Table 1 below.

As shown in Table 1, the rubber sheets obtained from the die plates of the examples are excellent in quality. From this evaluation result, the superiority of the present invention is clear.

The die plate described above can be applied to coextrusion of various rubber sheets.

2 ... Die plate 4 ... Inflow side surface 6 ... Discharge side surface 8 ... Base layer 12 ... Flow path forming surface 14 ... Retention space forming surface 20 ... Mouthpiece 22 ... Opening 24 ... Holder 26 ... Discharge port 28 ... Rubber sheet 30 ... Cap layer 32 ... Base layer 34 ... Under tread layer 36 ... Wing layer

Claims (3)

(1) by coextrusion multiple rubber composition in an extruder having a die to obtain a rubber sheet step,
(2) A process of assembling the rubber sheet with other rubber members to obtain a low cover.
And (3) the step of heating the low cover to cause a cross-linking reaction in the rubber is included.
The above base has a die plate,
The die plate has an inflow side surface, a discharge side surface located downstream of the inflow side surface, a base surface located between the inflow side surface and the discharge side surface, a flow path forming surface recessed from the base surface, and this flow path. It has a retention space forming surface that is located near the widthwise end of the forming surface and has an opening on the inflow side surface.
The center of the opening in the width direction is located inside the end of the flow path forming surface in the width direction .
The shape of the opening is an arc
The residence space forming surface, toward the discharge side through the opening, its height is gradually decreased, to have a shape that its cross-sectional area decreases gradually, the tire manufacturing process. The manufacturing method according to claim 1, wherein the distance between the center in the width direction of the opening and the end of the flow path forming surface is 2.0 mm or more. The manufacturing method according to claim 1 or 2, wherein a tread rubber sheet having a cap layer, a base layer and an under tread layer can be obtained in the above step (1).

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