JP6480756B2 - Raw tread rubber design method and die plate design method using the same - Google Patents

Description

  The present invention relates to a raw tread rubber design method and a die plate design method using the same.

  Conventionally, various methods for designing the cross-sectional shape of raw tread rubber for use in a design tire in which the dimensions of the tread rubber after vulcanization molding are designed using a computer have been proposed. For example, in Patent Document 1, a three-dimensional tread rubber model having a predetermined length in the tire circumferential direction is created based on the dimensions of the tread rubber after vulcanization molding, and the tread rubber model is arranged in the tire width direction. After obtaining a plurality of divided bodies by dividing, a method of calculating the volume of each divided body and designing the cross-sectional shape of the raw tread rubber based on the volume distribution is disclosed.

JP 2002-137610 A

  The green tread rubber is affixed to the green tire body in the molding process, and the green tire thus completed is then vulcanized and molded with a mold. However, the design method disclosed in Patent Document 1 does not take into account the deformation of the raw tread rubber in the molding process or the rubber flow during the vulcanization molding. It was difficult to obtain a cross-sectional shape.

  The present invention has been devised in view of the actual situation as described above, and calculates the cross-sectional shape of the raw tread rubber that is optimal for the production of the design tire, so that the design of the cross-sectional shape of the raw tread rubber can be made efficient. The main purpose is to provide a method.

  The present invention is a method for designing the cross-sectional shape of a raw tread rubber used in a design tire in which the dimensions of a tread rubber after vulcanization are designed, and the dimensions of the tread rubber after vulcanization and Creating a three-dimensional first tread rubber model having a first length in the tire circumferential direction based on the tread rubber of the reference tire in which the cross-sectional shape of the raw tread rubber before vulcanization is designed; Dividing the first tread rubber model at a predetermined interval in the tire width direction to obtain a plurality of first divided bodies; calculating a volume of each first divided body; By dividing the volume of the first divided body by the first length, a step of calculating an average cross-sectional area of each first divided body, and a second length in the tire circumferential direction based on the tread rubber of the designed tire. 3D second tread rubber with thickness A step of creating a Dell; a step of dividing the second tread rubber model in the tire width direction at the intervals to obtain a plurality of second divided bodies; and a step of calculating a volume of each second divided body; Dividing the volume of each second divided body by the second length to calculate the average cross-sectional area of each second divided body; the average cross-sectional area of each second divided body; A step of taking a difference from an average cross-sectional area of each of the first divided bodies corresponding to the second divided body, and adding the difference to a cross-sectional shape of the raw tread rubber of the reference tire to obtain a raw tread of the designed tire And a step of calculating a cross-sectional shape of the rubber.

  In the raw tread rubber designing method according to the present invention, it is desirable that the tread rubber of the reference tire and the tread rubber of the designed tire have the same tread pattern.

  In the raw tread rubber designing method according to the present invention, the absolute value of the difference between the nominal width of the reference tire and the nominal width of the designed tire is preferably 10 mm or less.

  In the raw tread rubber designing method according to the present invention, the radial stretch (%) at the time of vulcanization molding of the reference tire is the same as the radial stretch (%) at the time of vulcanization molding of the designed tire. It is desirable that

  The die plate designing method of the present invention includes a prediction step of predicting die swell from physical properties of unvulcanized rubber used for the raw tread rubber of the designed tire, the predicted die swell, and the raw tread rubber. Determining a cross-sectional shape of a die plate for extruding the raw tread rubber of the designed tire based on a cross-sectional shape of the raw tread rubber of the designed tire calculated by a design method. Features.

In the die plate designing method according to the present invention, the physical properties of the unvulcanized rubber are expressed by the following formula (1) obtained by measuring in a frequency dispersion mode with a shear type elastic tester. It is desirable to include rate dependent constants.
η = Kγ ' ^n-1 (1)
Where η is the shear viscosity, γ ′ is the shear rate, K is an approximate constant, and n is a rate-dependent constant.

  In the die plate designing method according to the present invention, the die swell is preferably predicted by being decomposed into a component in the width direction of the raw tread rubber and a component in the thickness direction of the raw tread rubber.

  In the die plate design method according to the present invention, in the prediction step, the raw tread rubber of the design tire is divided into a plurality of regions in the width direction based on a shear rate of the raw tread rubber passing through the discharge port of the die plate. It is desirable to predict the die swell for each region.

  In the die plate designing method according to the present invention, in the prediction step, the raw tread rubber of the design tire is divided into a plurality of regions in the width direction based on a flow rate of the raw tread rubber discharged from the discharge port of the die plate. It is desirable to predict the die swell for each region.

  In the raw tread rubber designing method of the present invention, a three-dimensional first tread rubber model is created based on the tread rubber of the reference tire, and a plurality of first divided bodies are obtained by dividing the first tread rubber model. The volume and average cross-sectional area of each first divided body are sequentially calculated. Similarly, a three-dimensional second tread rubber model is created based on the tread rubber of the designed tire, and a plurality of second divided bodies are obtained by dividing the second tread rubber model, and the volume of each second divided body. And the average cross-sectional area is calculated sequentially. Then, the difference between the average cross-sectional area of each second divided body and the average cross-sectional area of each corresponding first divided body is calculated, and the difference is added to the cross-sectional shape of the raw tread rubber of the reference tire. Thus, the cross-sectional shape of the raw tread rubber of the designed tire is calculated. In this way, the calculated cross-sectional shape of the raw tread rubber of the designed tire takes into account the deformation of the raw tread rubber in the molding process of the reference tire and the rubber flow in the vulcanization process. Therefore, the cross-sectional shape of the raw tread rubber optimum for the production of the design tire can be obtained by calculation, thereby reducing the number of trial productions and improving the efficiency of the raw tread rubber design.

  In the die plate design method of the present invention, the die swell predicted from the physical properties of the unvulcanized rubber used for the raw tread rubber of the designed tire, and the cross section of the raw tread rubber calculated by the raw tread rubber design method Based on the shape, the sectional shape of the die plate for extruding the raw tread rubber of the designed tire is determined. Since the physical properties of the unvulcanized rubber and the die swell are highly correlated, it is possible to predict the shape of the optimal die plate with high accuracy for extruding the raw tread rubber of the designed tire. Design can be made more efficient.

It is a perspective view of a computer which performs processing of this embodiment. It is a flowchart which shows an example of the process sequence of the design of the raw tread rubber which concerns on one Embodiment of this invention. FIG. 3 is a perspective view of a first tread rubber model of a reference tire created in a first model creation step of FIG. 2 and a second tread rubber model of a design tire created in a second model creation step. It is a perspective view which shows the volume of each 1st division body calculated at the 1st volume calculation process of FIG. It is a graph which shows the average cross-sectional area of each 1st division body calculated at the 1st cross-sectional area calculation process of FIG. It is a graph which shows the difference of the average cross-sectional area of each 2nd division body calculated by the difference process of FIG. 2, and the average cross-sectional area of each 1st division body. It is a figure which shows the cross-sectional shape of the raw tread rubber of the reference | standard tire of FIG. (A) is a figure which shows the cross-sectional shape of the raw tire of the design tire of FIG. 2, (b) is a figure which expands and shows a part. It is a flowchart which shows an example of the process sequence of the design of the die plate which concerns on one Embodiment of this invention. It is a graph which shows the relationship between n value of unvulcanized rubber, and the width direction component of a swell ratio. It is a graph which shows the relationship between n value of unvulcanized rubber, and the thickness direction component of a swell ratio. It is a graph which shows the relationship between the stress relaxation value of unvulcanized rubber, and the swell ratio of a cross-sectional area. It is a graph which shows the relationship between the Mooney viscosity of unvulcanized rubber, and the swell ratio of a cross-sectional area. (A) is sectional drawing of a raw tread rubber, (b) is a graph which shows distribution of the shear rate of the raw tread rubber which passes the discharge port of a die plate. It is a graph which shows the relationship between the n value of the unvulcanized rubber in the tread center part of raw tread rubber, and the die factor of the thickness direction. It is a graph which shows the relationship between the n value of the unvulcanized rubber in the tread middle part of raw tread rubber, and the die factor of the thickness direction. It is a graph which shows the relationship between the n value of the unvulcanized rubber in the tread shoulder part of raw tread rubber, and the die factor of the thickness direction. It is a graph which shows the relationship between the n value of the unvulcanized rubber in the tread edge part of raw tread rubber, and the die factor of the thickness direction. It is a perspective view which shows distribution of the raw tread rubber discharged from the discharge port of a die plate, and its flow velocity.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The design method of the raw tread rubber of the present embodiment is a method for designing the cross-sectional shape of the raw tread rubber used for the design tire in which the dimensions of the tread rubber after vulcanization molding are designed. A computer is preferably used.
(First embodiment)

  As shown in FIG. 1, the computer 1 includes a main body 1a, a keyboard 1b, a mouse 1c, and a display device 1d. The main body 1a is provided with an arithmetic processing unit (CPU), a ROM, a working memory, a storage device such as a magnetic disk, and disk drive devices 1a1, 1a2. Note that a processing procedure (program) for executing the design method of the present embodiment is stored in the storage device in advance.

  FIG. 2 shows a processing procedure of the raw tread rubber designing method according to the present embodiment. This design method is based on a standard tire that is designed based on the dimensions of the tread rubber after vulcanization molding and the cross-sectional shape of the raw tread rubber before vulcanization molding. Is how to design.

  This design method includes a first model creating step (# 1) for creating a first tread rubber model of a reference tire, and a first dividing step (# 2) for dividing the first model to obtain a plurality of first divided bodies. A first volume calculating step (# 3) for calculating the volume of each first divided body, a first cross sectional area calculating step (# 4) for calculating an average cross sectional area of each first divided body, and a design tire A second model creating step (# 5) for creating a second tread rubber model, a second dividing step (# 6) for dividing the second model to obtain a plurality of second divided bodies, and for each of the second divided bodies A second volume calculation step (# 7) for calculating the volume, a second cross-sectional area calculation step (# 8) for calculating an average cross-sectional area of each second divided body, an average cross-sectional area of each second divided body and each A difference step (# 9) for obtaining a difference from the average cross-sectional area of the first divided body and a cross-sectional shape R11 of the raw tread rubber of the reference tire are obtained. A step (# 10), in addition to the difference in cross-sectional shape of the raw tread rubber of the reference tire, cross calculation step of calculating the cross-sectional shape of the raw tread rubber design tires and (# 11).

  FIG. 3 shows the first tread rubber model 10 of the reference tire created in the first model creation step (# 1). The first tread rubber model 10 is a three-dimensional rubber model having a first length L1 in the tire circumferential direction, and is created on the computer 1 based on the tread rubber after vulcanization molding of the reference tire. The first tread rubber model 10 includes main grooves 12, 13, 14, sub-grooves 15, lug grooves 16, 17, slots 18, 19 and the like corresponding to the tread pattern of the reference tire.

  The first length L1 is determined according to the tread pattern of the reference tire. For example, when the reference tire is a tread pattern in which the same pattern is repeatedly formed in the tire circumferential direction, a length corresponding to one pitch length is desirable.

  In the first dividing step (# 2), the first tread rubber model 10 is divided at a predetermined interval w in the tire width direction, whereby a plurality of first divided bodies 11 are obtained. Since the first tread rubber model 10 is divided into a large number of first divided bodies 11 as the interval w is smaller, the calculation accuracy is improved. However, since the calculation becomes complicated, the interval w is the processing capability of the computer 1. It is decided according to.

  In the first volume calculation step (# 3), the volume of each first divided body 11 is calculated. FIG. 4 shows the volume V11 of each first divided body 11 calculated in the first volume calculation step (# 3). The volume V11 of each first divided body 11 reflects the volumes of the main grooves 12, 13, 14, sub-grooves 15, lug grooves 16, 17, slots 18, 19, etc., and the volume V11 of each first divided body 11 is reflected. This distribution has local unevenness.

  In the first cross-sectional area calculation step (# 4), the average cross-sectional area S11 of each first divided body 11 is calculated by dividing the volume V11 of each first divided body 11 by the first length L1. FIG. 5 shows the average cross-sectional area S11 of each first divided body 11 calculated in the first cross-sectional area calculating step (# 4). In FIG. 5, the average cross-sectional area S11 of each first divided body 11 is displayed as a line graph, but may be displayed as a bar graph.

  Through the above steps, the distribution of the average cross-sectional area S11 in the tire axial direction is obtained for the tread rubber of the reference tire.

  Also for the tread rubber of the design tire, in the second model creation step (# 5), the second division step (# 6), the second volume calculation step (# 7), and the second cross-sectional area calculation step (# 8), The distribution of the average cross-sectional area S12 in the tire axial direction is obtained by performing a calculation equivalent to.

  That is, in the second model creation step (# 5), a three-dimensional second tread rubber model 20 having a second length L2 in the tire circumferential direction shown in parentheses in FIG. In the second dividing step (# 6), a plurality of second divided bodies 21 are obtained by dividing the second tread rubber model 20 at intervals w. Furthermore, in the second volume calculation step (# 7) and the second cross-sectional area calculation step (# 8), the volume V21 and the average cross-sectional area S21 of each second divided body 21 are sequentially calculated.

  Next, in the difference step (# 9), the difference ΔS between the average sectional area S21 of each second divided body 21 and the average sectional area S11 of each first divided body 11 corresponding to each second divided body 21 is calculated. Calculated. In FIG. 6, the average cross-sectional area S21 of each second divided body 21 and the average cross-sectional area S11 of each first divided body 11 corresponding to each second divided body 21 are superimposed and displayed, and the difference ΔS is displayed. It is shown by hatching. Where the average cross-sectional area S21 is larger than the average cross-sectional area S11, the difference ΔS has a positive value, and when the average cross-sectional area S21 is smaller than the average cross-sectional area S11, the difference ΔS has a negative value.

  Then, as shown in FIG. 2, in # 10, a cross-sectional shape R11 of the raw tread rubber before vulcanization molding of the reference tire is obtained. FIG. 7 shows a cross-sectional shape R11 of the raw tread rubber before vulcanization molding of the reference tire. In this embodiment, the cross-sectional shape after extrusion of the raw tread rubber used for the reference tire is applied as the cross-sectional shape R11 of the raw tread rubber of the reference tire. The cross-sectional shape R11 of the raw tread rubber is preferably an optimal cross-sectional shape for manufacturing a reference tire as designed. Therefore, for example, when there is a difference between the design standard value of the thickness of the tread portion of the reference tire and the finished thickness, the correction necessary for obtaining the finished thickness of the tread portion of the reference tire as designed is corrected. It is desirable to use the applied cross-sectional shape R11.

  Further, as shown in FIG. 8, in the cross-section calculation step (# 11), by adding a difference ΔS to the cross-sectional shape R11 of the raw tread rubber of the reference tire, the cross-sectional shape R21 of the raw tread rubber of the design tire is added. Is calculated. The difference ΔS includes fine irregularities due to errors during volume calculation in the first volume calculation step (# 3) and the second volume calculation step (# 7), etc. In some cases, fine irregularities are also generated in the sum of the surface shape R11 and the difference ΔS. In such a case, as shown in FIG. 8 (b), the cross-sectional shape R21 of the designed tire is deformed with a smooth outline in the width direction to such an extent that a large difference in local cross-sectional area distribution does not occur. May be configured.

  In this way, the calculated cross-sectional shape R21 of the raw tread rubber of the designed tire takes into account the deformation of the raw tread rubber in the molding process of the reference tire and the rubber flow in the vulcanization process. Therefore, the cross-sectional shape R21 of the raw tread rubber optimum for the production of the designed tire can be obtained by calculation, thereby reducing the number of trial productions and improving the design of the raw tread rubber.

  It is desirable that the tread rubber of the reference tire and the tread rubber of the designed tire have the same tread pattern. In such a case, the rubber flow at the time of vulcanization molding of the reference tire is equal to the rubber flow at the time of vulcanization molding of the design tire, so that the cross-sectional shape R21 of the raw tread rubber optimum for the production of the design tire is increased. Can be calculated accurately.

  The absolute value of the difference between the nominal width of the reference tire and the nominal width of the designed tire is preferably 10 mm or less. In such a case, the error of the difference ΔS becomes small, and the cross-sectional shape R21 can be calculated with higher accuracy.

  Furthermore, it is desirable that the radial stretch (%) at the time of vulcanization molding of the reference tire and the radial stretch (%) at the time of vulcanization molding of the designed tire are the same. In such a case, since the change in the thickness of the tread rubber during vulcanization molding is equivalent between the reference tire and the designed tire, the cross-sectional shape R21 can be calculated with higher accuracy.

  A method for designing a die plate for extruding a raw tread rubber having a cross-sectional shape R21 that is optimal for manufacturing a design tire will be described below.

  Generally, since raw tread rubber has viscoelasticity, it expands when extruded from a die, and the expansion rate is expressed by a swell ratio that is a ratio of a cross sectional area of the raw tread rubber and a cross sectional area of the die. . In the present embodiment, the swell ratio is considered by decomposing the raw tread rubber into the width direction component and the thickness direction component, and the die swell is predicted from the physical properties of the unvulcanized rubber used in the raw tread rubber. Design the cross-sectional shape. For example, a computer shown in FIG. 1 is used to design the cross-sectional shape of the die plate. Examples of the physical properties of the unvulcanized rubber include an n value that is a constant indicating the shear rate dependence of the unvulcanized rubber.

  FIG. 9 shows a processing procedure of the die plate design method according to the present embodiment. The method for designing the die plate includes a step of preparing a relational expression between the n value of the unvulcanized rubber and the swell ratio in the width direction (# 21), a step of predicting the die swell in the width direction (# 22), A step of determining the dimension in the width direction of the die plate (# 23), a step of preparing a relational expression between the n value of the unvulcanized rubber and the swell ratio in the thickness direction (# 24), and a die in the thickness direction A step of predicting the well (# 25), and a step of determining the dimension in the thickness direction of the die plate (# 26).

FIG. 10 shows the relationship between the n value of the unvulcanized rubber and the width direction component of the swell ratio. The n value is obtained by measuring in a frequency dispersion mode with a shear type elastic tester, and is represented by the following formula (1).
η = Kγ ' ^n-1 (1)
Where η is the shear viscosity, γ ′ is the shear rate, and K is an approximate constant.
Width direction component of the swell ratio, i.e. swell ratio S ₁ in the width direction is measured by extrusion test the raw tread each rubber having a respective n values (hereinafter, also applies to swell ratio S in the thickness direction).

As shown in FIG. 10, the preparation step of preparing a relational expression between swell ratio S ₁ of n values and a width direction of the unvulcanized rubber (# 21), the relational expression of the following formula (2) is obtained. Swell ratio S ₁ in the width direction is measured by extrusion test of the raw tread rubber.
S ₁ = n × A ₁ + B ₁ (2)
However, A ₁ and B ₁ are constants. Between the n value and the swell ratio S _{1 in the} width direction, a very strong correlation with a determination coefficient R ² of 0.95 is obtained, so that the die swell in the width direction can be predicted very accurately.

  In the prediction step (# 22) for predicting the die swell in the width direction, the n value of the unvulcanized rubber obtained in the above equation (1) is substituted into the above equation (2) to predict the die swell in the width direction. The

  In the step of determining the dimension in the width direction of the die plate (# 23), the dimension in the width direction of the die plate is determined based on the die swell in the width direction and the cross-sectional shape R21 of the raw tread rubber. That is, the dimension in the width direction of each part of the die plate is calculated by dividing the width of the corresponding portion in the cross sectional shape R21 of the raw tread rubber by the die swell in the width direction.

  In the present embodiment, by substituting the n value obtained by the above equation (1) into the above equation (2), the die swell in the width direction is predicted very accurately. Accordingly, it is possible to predict the dimension in the width direction of the die plate that is optimal for extruding the raw tread rubber of the designed tire with extremely high accuracy, and the design of the die plate can be made more efficient.

11 shows the relationship between the swell ratio S ₂ of the n value and the thickness direction is shown. In preparation step of preparing a relational expression between swell ratio S ₂ of n values in the thickness direction of the unvulcanized rubber (# 24), the relational expression of the following formula (3) is obtained.
S ₂ = n × A ₂ + B ₂ (3)
However, _{A 2} and _{B 2} are constants. Since a very strong correlation with a determination coefficient R ² of 0.94 is obtained between the n value and the swell ratio S _{2 in} the thickness direction, a die swell in the thickness direction is predicted very accurately.

  In the prediction step (# 25) of predicting the die swell in the thickness direction, the n value of the unvulcanized rubber obtained in the above equation (1) is substituted into the above equation (3), and the die swell in the thickness direction is is expected.

  In the step of determining the dimension in the thickness direction of the die plate (# 26), the dimension in the thickness direction of the die plate is determined based on the die swell in the thickness direction and the cross-sectional shape R21 of the raw tread rubber. . That is, the dimension in the thickness direction of each part of the die plate is calculated by dividing the thickness of the corresponding portion in the cross sectional shape R21 of the raw tread rubber by the die swell in the thickness direction.

  In the present embodiment, by substituting the n value obtained by the above equation (1) into the above equation (3), the die swell in the thickness direction is predicted very accurately. Accordingly, it is possible to predict the dimension in the thickness direction of the die plate that is optimal for extruding the raw tread rubber of the designed tire with extremely high accuracy, and the design of the die plate can be made more efficient.

  In the design of the die plate, as described above, the swell ratio is decomposed into the width direction and the thickness direction of the raw tread rubber, and the dimensions in the width direction and the thickness direction of the die plate are calculated with separate relational expressions. It is desirable to do. However, the dimension in the width direction and the dimension in the thickness direction of the die plate may be calculated by the same relational expression using the swell ratio of the cross-sectional area.

  Furthermore, the stress relaxation value or Mooney viscosity may be applied as the physical property of the unvulcanized rubber used for predicting the die swell.

FIG. 12 is shown the relationship between the swell ratio S ₃ of the stress relaxation value r and the cross-sectional area of the unvulcanized rubber. In the step of preparing a relational expression between swell ratio S ₃ of the stress relaxation value r and the cross-sectional area of the unvulcanized rubber, the following relational expression (4) is obtained.
S ₃ = r × A ₃ + B ₃ (4)
However, _{A 3} and _{B 3} are constants. A strong correlation with a determination coefficient R ² of 0.65 is also obtained between the stress relaxation value r and the cross-sectional area swell ratio S ₃ . Therefore, by using the stress relaxation value r of the unvulcanized rubber, it becomes possible to predict the dimension in the thickness direction of the die plate suitable for extruding the raw tread rubber of the designed tire, and the die plate design is made more efficient. it can.

Figure 13 shows the relationship between the swell ratio S ₄ Mooney viscosity m and the cross-sectional area of the unvulcanized rubber. In the step of preparing a relational expression between swell ratio S ₄ Mooney viscosity m and the cross-sectional area of the unvulcanized rubber, the following relational expression (5) is obtained.
S ₄ = m × A ₄ + B ₄ (5)
However, _{A 4} and _{B 4} are constants. A correlation with a coefficient of determination R ² of 0.34 is also obtained between the Mooney viscosity m and the cross-sectional area swell ratio S ₄ . Therefore, by using the Mooney viscosity m of the unvulcanized rubber, it becomes possible to predict the dimension in the thickness direction of the die plate suitable for extruding the raw tread rubber of the designed tire, and the die plate design can be made efficient. .
(Second Embodiment)

Hereinafter, a die plate design method according to the second embodiment of the present invention will be described.
FIG. 14 shows a cross-sectional view of the raw tread rubber extruded using the die plate and the distribution of the shear rate (velocity gradient) of the raw tread rubber passing through the discharge port of the die plate. 14A and 14B, the positions in the width direction of the raw tread rubber are described so as to correspond to each other. Note that a value calculated by CFD (Computational Fluid Dynamics) analysis is applied to the shear rate.

  In general, organic polymer materials such as rubber have entanglement of molecular chains. The entanglement of molecular chains is easily loosened by shearing during flow. When the raw rubber passes through the extruder tube, the extrusion head, and the discharge port of the die plate, the shear rate of the rubber in the vicinity of the wall surface increases, thereby loosening the entanglement of the molecular chains and increasing entropy. . Thereafter, the raw rubber discharged from the discharge port of the die plate tries to return to the original entangled state so as to reduce entropy, and a swell phenomenon occurs. The inventor has developed the above theory after intensive research, and the die swell of raw tread rubber depends on the shear rate of the raw tread rubber, and the larger the shear rate of the raw tread rubber, the more swell tends to occur. And gained knowledge.

  Based on the knowledge described above, in this embodiment, a preparation step (# 24) for preparing a relational expression between the n value of the unvulcanized rubber and the swell ratio S in the thickness direction shown in FIG. In the prediction step (# 25) for predicting the direction die swell, it is desirable to consider the shear rate of the raw tread rubber passing through the discharge port of the die plate as a swell factor.

  More specifically, in the preparation step (# 24), the raw tread rubber is divided into a plurality of regions in the width direction based on the shearing speed of the raw tread rubber passing through the discharge port of the die plate. A relational expression between the n value of the unvulcanized rubber and the swell ratio S in the thickness direction is prepared. In the prediction step (# 25), the n value of the unvulcanized rubber is substituted into the relational expression, and the die swell in the thickness direction is predicted.

  For example, in this embodiment, as shown in FIG. 14, the shear rate of the raw tread rubber is large in the tread center portion Tc and the tread shoulder portion Ts, and the shear rate of the raw tread rubber is medium in the tread middle portion Tm. The shear rate of the raw tread rubber is minimal at the tread edge portion Te. Accordingly, in this example, the raw tread rubber is divided into seven regions in the width direction, that is, a plurality of regions of the tread center portion Tc, the tread middle portion Tm, the tread shoulder portion Ts, and the tread edge portion Te. The division | segmentation number of raw tread rubber can be set arbitrarily. As the number of divisions increases, a higher correlation is obtained between the physical properties of the unvulcanized rubber and the die swell. In this example, for example, the raw tread rubber is divided into the seven regions by comparing the shear rate of the raw tread rubber with the threshold values TH1 and TH2.

15 to 18 show the relationship between the n value of the unvulcanized rubber and the swell ratios Sc, Sm, Ss and Se in the respective regions of the tread center portion Tc, the tread middle portion Tm, the tread shoulder portion Ts, and the tread edge portion Te. Is shown. In each figure, the vertical axis indicates the die factor (ratio between the thickness in the thickness direction of the die plate and the thickness of the raw tread rubber) corresponding to the reciprocal of the swell ratio S. In the preparation step (# 24), the following relational expressions (6) to (9) are obtained for each region.
Sc = n.times.Ac + Bc (6)
Sm = n * Am + Bm (7)
Ss = n × As + Bs (8)
Se = n × Ae + Be (9)
However, Ac, Am, As, Ae and Bc, Bm, Bs, Be are constants.

  Further, in the prediction step (# 25) for predicting the die swell in the thickness direction, the n value of the unvulcanized rubber obtained by the above equation (1) is substituted into the above equations (6) to (9), and the thickness A vertical die swell is predicted.

  According to the design method of this die plate, paying attention to the fact that the swell of raw tread rubber depends on the shear rate of raw tread rubber, and considering the shear rate as a swell factor, the physical properties of unvulcanized rubber An even higher correlation is obtained between swell and die swell. Thereby, it becomes possible to predict the shape of the optimal die plate for extruding the raw tread rubber of the designed tire with higher accuracy, and the design of the die plate can be made more efficient.

  FIG. 19 shows the raw tread rubber extruded using a die plate and the distribution of the flow velocity thereof. In addition, the value calculated by CFD analysis is applied to the flow velocity of the raw tread rubber.

  The raw tread rubber 30 is discharged from the discharge port 41 of the die plate 40. The inventor has found that the flow velocity V of the raw tread rubber 30 discharged from the discharge port 41 is not uniformly distributed, and is large at, for example, the tread center portion Tc and the tread shoulder portion Ts. And in the extrusion process of raw tread rubber 30, in order to control sagging and meandering of raw tread rubber 30, the extrusion speed of raw tread rubber 30 is set according to the place where the flow velocity in discharge port 41 is the largest. . As a result, as shown by the two-dot chain line in the drawing, the rubber at the portion where the flow velocity is small is discharged from the discharge port 41 while being pulled and contracts in the thickness direction. The inventor has developed the above theory after earnest research, and the die swell of the raw tread rubber 30 depends on the flow velocity V of the raw tread rubber 30 discharged from the discharge port 41. The knowledge that it is hard to occur is obtained.

  Based on the knowledge described above, in this embodiment, a preparation step (# 24) for preparing a relational expression between the n value of the unvulcanized rubber and the swell ratio S in the thickness direction shown in FIG. In the prediction step (# 25) for predicting the direction die swell, the flow velocity V of the raw tread rubber 30 discharged from the discharge port 41 may be considered as a swell factor.

  More specifically, in the preparation step (# 24), the raw tread rubber 30 is divided into a plurality of regions in the width direction based on the flow velocity V of the raw tread rubber 30 discharged from the discharge port 41, and each region is divided. A relational expression between the n value of the unvulcanized rubber and the swell ratio S in the thickness direction is prepared. The division into each region can be performed, for example, by comparing the flow velocity V with a threshold value (not shown) as in FIG. In the prediction step (# 25), the n value of the unvulcanized rubber is substituted into the relational expression, and the die swell in the thickness direction is predicted.

  For example, in the present embodiment, as shown in FIG. 19, the flow velocity V is large in the tread center portion Tc and the tread shoulder portion Ts, the flow velocity V is medium in the tread middle portion Tm, and the flow velocity V in the tread edge portion Te. Minimal. Therefore, in this example, the raw tread rubber 30 is divided into seven regions in the width direction, that is, a plurality of regions of the tread center portion Tc, the tread middle portion Tm, the tread shoulder portion Ts, and the tread edge portion Te. Similarly to the above, the division | segmentation number of the raw tread rubber 30 can be set arbitrarily. As the number of divisions increases, a higher correlation is obtained between the physical properties of the unvulcanized rubber and the die swell. In dividing each region, the shear rate described above may be considered together with the flow velocity V.

  Similarly to FIGS. 15 to 18, in the preparation step (# 24), the relational expressions (6) to (9) are obtained for each region.

  Further, in the prediction step (# 25) for predicting the die swell in the thickness direction, the n value of the unvulcanized rubber obtained by the above equation (1) is substituted into the above equations (6) to (9), and the thickness A vertical die swell is predicted.

  According to the design method of this die plate, paying attention to the fact that the swell of raw tread rubber depends on the flow velocity V of the raw tread rubber 30 discharged from the discharge port 41, the flow velocity V is considered as a swell factor. Therefore, an even higher correlation can be obtained between the physical properties of the unvulcanized rubber and the die swell. Thereby, it becomes possible to predict the shape of the die plate 40 optimal for extruding the raw tread rubber 30 of the designed tire with higher accuracy, and the design of the die plate 40 can be made more efficient.

  The raw tread rubber designing method and die plate designing method of the present invention have been described in detail above, but the present invention is not limited to the above-described specific embodiments, and can be implemented in various forms. The

  Using the raw tread rubber designed based on the specifications shown in Table 1, 15 tires of comparative examples and examples were each prototyped, and the suitability of the finished thickness of the tread rubber to the design value was tested. Each tire of the comparative example and the example is arranged on both outer sides of the tire equator and extends in the tire circumferential direction, and a pair of center main grooves, and is arranged on the outer side in the tire axial direction of the center main groove and continues in the tire circumferential direction. By providing a pair of extended shoulder main grooves, a center land portion between the pair of center main grooves, a pair of middle land portions between the center main groove and the shoulder main grooves, and a tire shaft of the shoulder main grooves It has a tread portion that is divided into a pair of shoulder land portions located on the outer side in the direction. Measurement Each tire was measured for the thickness of the tread rubber in the center land portion, the middle land portion, and the shoulder land portion at four cross-sections on the tire circumference. The results are expressed as a rate that the finished thickness is within a range of ± 0.5 mm with respect to the design value, and the larger the value, the closer the finished thickness is to the design value.

  As can be seen from Table 1, it was confirmed that the design method of the raw tread rubber of the example significantly improved the design accuracy of the cross-sectional shape of the raw tread rubber compared to the comparative example.

  Using the die plates of the comparative examples and examples determined based on the die swell predicted from the specifications in Tables 2 to 4, raw tread rubber was extruded and a tire using them was molded.

  The physical properties of the unvulcanized rubber used for predicting the die swell in the examples were measured by the following methods.

<Mooney viscosity>
According to the Mooney viscosity measurement method based on JIS K6300, the unvulcanized rubbers of the blends A, B and C were measured under a temperature condition of 130 ° C.
<Stress relaxation value>
After measurement of the Mooney viscosity, the rotation of the rotor was stopped and a decrease in the viscosity of the rubber was measured over 2 minutes. The measuring machine and the rubber sample were used continuously after the Mooney viscosity was measured. The obtained data was plotted on a graph with time (seconds) on the horizontal axis and Mooney viscosity on the vertical axis, and the slope of the exponential approximate curve when expressed in a log-log graph was used as the stress relaxation value.
<N value>
Using a shear type viscoelasticity tester (device name “ARES”, manufactured by T.A. Instruments Co., Ltd.), “shear rate (1 / s) obtained by measuring under the following conditions in the measurement mode of frequency dispersion. ”Is plotted on the horizontal axis, and“ shear stress (Pa · s) ”is plotted on the vertical axis, and the n value indicated by y = ax ⁿ + b of the exponential approximation curve when expressed in a log-log graph is used.
Frequency: 100 → 0.1 rad / sec or 15.9 → 0.0159 Hz
Distortion: 0.5%
Temperature: 80 ° C, 100 ° C, 120 ° C, 140 ° C

<Rolling index of raw tread rubber>
In the process of extruding raw tread rubber, the weight of the extruded raw tread rubber was measured, and the yield of the conforming product was calculated except for those judged to be out of design tolerance due to excess or deficiency in weight. The yield of each example was displayed as an index with the yield index of Example 1 as 100 by the following formula.
(Capacity index) = (Capacity of each product (%))
/ (Applicable product yield of Example 1 (%)) × 100
As a result, the larger the numerical value, the better the yield of the conforming product and the better.

<Index of occurrence of non-conforming tires>
The finished thickness of the tread rubber of the vulcanized tire was measured, and the incidence of nonconforming products that deviated from the design tolerance was calculated. The occurrence index of the non-conforming tire in each example was displayed as an index with the non-conforming tire occurrence index of Example 1 as 100 by the following formula.
(Generation index of non-conforming tire) = (Non-conforming tire occurrence rate (%) of Example 1)
/ (Non-conforming tire occurrence rate in each case (%)) x 100
As a result, the larger the numerical value, the less the occurrence of nonconforming tires.

<Decision coefficient R ² >
A coefficient of determination showing the correlation between the physical properties of the unvulcanized rubber used for prediction and the predicted die swell was calculated. As the result, the larger the numerical value, the stronger and better the correlation.

  As is apparent from Tables 2 to 4, it was confirmed that the design accuracy of the die plate design method of the example was significantly improved as compared with the comparative example.

10 first tread rubber model 11 first divided body V11 volume S11 average sectional area 20 second tread rubber model 21 second divided body V21 volume S21 average sectional area ΔS difference # 1 first model creation process # 2 first divided process # 3 First Volume Calculation Step # 4 First Cross Section Calculation Step # 5 Second Model Creation Step # 6 Second Division Step # 7 Second Volume Calculation Step # 8 Second Cross Section Calculation Step # 9 Difference Step # 11 Cross Section Calculation Process # 24 Preparation Process # 25 Prediction Process

Claims (9)

A method for designing a cross-sectional shape of a raw tread rubber used for a design tire in which a dimension of a tread rubber after vulcanization molding is designed,
Based on the tread rubber of the reference tire in which the dimensions of the tread rubber after vulcanization molding and the cross-sectional shape of the raw tread rubber before vulcanization molding are designed, a three-dimensional tire having a first length in the tire circumferential direction. Creating a first tread rubber model;
Dividing the first tread rubber model at a predetermined interval in the tire width direction to obtain a plurality of first divided bodies;
Calculating the volume of each first segment;
Calculating an average cross-sectional area of each first divided body by dividing the volume of each first divided body by the first length;
Creating a three-dimensional second tread rubber model having a second length in the tire circumferential direction based on the tread rubber of the designed tire;
Dividing the second tread rubber model at the intervals in the tire width direction to obtain a plurality of second divided bodies;
Calculating the volume of each second divided body;
Calculating an average cross-sectional area of each second divided body by dividing the volume of each second divided body by the second length;
Taking a difference between an average cross-sectional area of each of the second divided bodies and an average cross-sectional area of each of the first divided bodies corresponding to each of the second divided bodies;
And adding the difference to the cross-sectional shape of the raw tread rubber of the reference tire to calculate the cross-sectional shape of the raw tread rubber of the design tire.   2. The raw tread rubber designing method according to claim 1, wherein the tread rubber of the reference tire and the tread rubber of the designed tire have the same tread pattern.   The method for designing a raw tread rubber according to claim 1 or 2, wherein an absolute value of a difference between a nominal width of the reference tire and a nominal width of the designed tire is 10 mm or less.   The radial stretch (%) at the time of vulcanization molding of the reference tire and the radial stretch (%) at the time of vulcanization molding of the designed tire are the same. How to design raw tread rubber. A prediction step of predicting die swell from the physical properties of the unvulcanized rubber used for the raw tread rubber of the design tire;
The raw tread rubber of the designed tire based on the predicted die swell and the cross-sectional shape of the raw tread rubber of the designed tire calculated by the design method according to claim 1. And a step of determining a cross-sectional shape of the die plate for extruding the die plate. 6. The die plate according to claim 5, wherein the physical properties of the unvulcanized rubber include a rate dependent constant of shear viscosity represented by the following formula (1) obtained by measurement in a frequency dispersion mode with a shear type elastic tester. Design method.
η = Kγ ' ^n-1 (1)
Where η is the shear viscosity, γ ′ is the shear rate, K is an approximate constant, and n is a rate-dependent constant.   The die plate design method according to claim 5 or 6, wherein the die swell is predicted by being decomposed into a component in a width direction of the raw tread rubber and a component in a thickness direction of the raw tread rubber.   In the prediction step, the raw tread rubber of the designed tire is divided into a plurality of regions in the width direction based on the shear rate of the raw tread rubber passing through the discharge port of the die plate, and the die swell is divided into each region. The method for designing a die plate according to any one of claims 5 to 7, which is to be predicted. In the prediction step, the raw tread rubber of the design tire is divided into a plurality of regions in the width direction based on the flow velocity of the raw tread rubber discharged from the discharge port of the die plate, and the die swell is divided into each region. The method for designing a die plate according to any one of claims 5 to 7 , which is to be predicted.

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