FR2618380A1 - METHOD FOR MANUFACTURING RADIAL TIRES FOR MOTOR VEHICLES, WITH PARTIAL CROSS-LINKING OF THE BELT REINFORCEMENT LAYER BY MEANS OF IONIZING RADIATION - Google Patents

Abstract

Method for manufacturing radial tires for motor vehicles, comprising a layer 6a, 6b for reinforcing the belt 5 of the tire. The belt reinforcement layer is prepared in a state of partial crosslinking, by exposure to ionizing radiation. The tires obtained have better uniformity.

Description

The present invention relates to a method of

  manufacture of radial tires for automobiles.

  We already know that the level of uniformity represented

  felt by the variation in radial force (VFR) of pneuma-

  Radial ticks for automobiles, which influences the generation of noise or vibration during the movement of automobiles at high speed, varies according to a deformation which occurs during vulcanization in the connection part. formed by superimposing the two ends of a belt reinforcement layer, during the manufacture of tires. More precisely,

  in a radial tire composed of a part of a wheel

  ment, side walls, beads, a carcass, a belt and at least one reinforcing layer of the belt layers, the belt reinforcing layer is disposed between the belt and the rolling part, ends of the belt, so that

  cover part of the edge at each end of the

  belt patches around the entire circumference of the tire

  than. Two parts of longitudinal ends are superimposed

  the belt reinforcement layer, one on top of the other, to form a connection as shown more

  high, which has an effect not only on the characteristics

  belt layer reinforcement ticks but also

  uniformity of the tire and generates a

  noise or vibration when moving at high speed

size of cars.

  The inventors of the present invention are

  are interested in the rubber hardening technique

  cabbage by means of electron radiation, as proposed in US Patent No. 4,221,253, and they have carried out extensive studies to establish a manufacturing process

  radial tires using the technique below

  hardening rubber and can avoid the decrease in uniformity which may be caused by the connecting part of the reinforcing layers of

  belt, in order to successfully complete the present in-

  vention. The subject of the present invention is a method for manufacturing radial tires for automobiles,

  that you can prevent overlapping width

  The mutually superimposed end parts of the belt reinforcement layer in the connection part will undergo significant variation before

  and after vulcanization, so we can get a tire-

  radial automotive material which has a level of uniformity

  satisfactory and which does not generate noise and

  bration when moving at high speed.

  According to the present invention, this object

  jectif is achieved by a method of the above type, characterized in that the belt reinforcement layer is prepared in a state of partial crosslinking, by

  exposure to ionizing radiation.

  Other objects and advantages of the invention

  will appear in the light of the detailed description

  below of its preferred embodiments, not li-

  mitatives, with reference to the attached drawings in the-

which:

  Fig. 1 is a section through one half of a tire

  radial tick for an automobile produced in accordance with the method of the present invention;

  Fig. 2a and 2b are partial sections illus-

  trant the connection part of a layer of reinforcement

  belt ment of a conventional tire, before and after vulcanization, respectively; and Fig. 3 is a curve illustrating the level

uniformity of the tire.

  As shown in Figure 1, in a tire-

  radial material consisting of a rolling part 1, of

  two side walls 2, two beads 3, a car-

  breakage 4 comprising at least one carcass layer available

  placed radially between the two beads 3, a belt and at least one belt reinforcing layer (in the example illustrated, layers 6a and 6b) for the layers of the belt 5, the reinforcing layers 6a and 6b belt are placed between the belt 5 and the wearing course 1, at the respective ends of the belt 5, and they overlap the prescribed width at the respective ends of the layers of the belt 5, on

  the entire circumference of the tire.

  As shown in Figure 2a, the extremi

  longitudinal tees of the belt reinforcement layer

  re 6a (6b) are then placed in mutual overlap to form a connection part -7 having the prescribed overlap width Wl, and the end parts

  are joined and fixed together in this state before vul-

  channeling. As can also be seen in Figure 2a,

  the belt reinforcement layer 6a (6b) is composed

  reinforced with a layer of rope reinforcement 8 and layers of unvulcanized rubber 9 covering the outside

  the layer of rope 8. We superimpose, over the entire circumference

  ference of the belt 5 and of the belt reinforcement layer 6a (6b) comprising the coating layers 9 of unvulcanized rubber, the rolling part 1 made of an unvulcanized rubber and preparation is made

  a raw tire in a tire manufacturing mold

  matic. The green tire thus formed is vulcanized by application of heat and pressure, from

  inside the mold, to obtain a final tire.

  When subjected to pressure and heat as

  indicated above, the raw tire expands radially-

  ment outwards and the unvulcanized rubber softens and creeps, due to the rise in temperature, and it is fixed by pressure on the internal surface of the mold. Then there is a thermal contraction of the rope reinforcing layer 8 in the part

  connection 7 in which the ends longitu-

  dinales of the belt reinforcement layer 6a (6b) are overlapped, so that the width of the connection part 7, which was W1 before vulcanization as shown in FIG. 2a, decreases to a value W2 after the vulcanization as illustrated in Figure 2b. When the width of the connection part 7 of the belt reinforcement layer 6a (6b) decreases as described above, the level of uniformity (VPR) of the vulcanized tire decreases. If the width W1 of the

  connection part before vulcanization is insufficient

  health, it may even happen that the width W2 of the par-

  connection tie becomes zero after vulcanization

  and the belt reinforcement layer 6a (6b) does not

  folds more reinforcement function.

  The level of uniformity (VFR) described here for

  the tires is determined by inflating a pneuma-

  tick finished at the prescribed inflation pressure, mounting of the tire rotation axis parallel to the rotation axis of a steel rotating drum, and pressing

  of the tire with the prescribed load perpendicular-

  lying on the drum. The level of consistency-is represented

  by the variation of the load in the perpendicular direction

  circular, produced on the rotation shaft of the drum,

  this variation representing the characteristic of uniform

  load mate in the circumferential direction

  tire. With reference to Figure 3, if the diff-

  4P20 reference between the upper peak P23 and the lower peak

  P24 of the load variation curve 22 increases, this means that the variation in radial force VFR is greater and that the quality of the tire decreases. If you mount tires with a high VFR value on an automobile and then drive the automobile

  noise or vibration disadvantages at high speed

tion tend to occur.

  The present invention is characterized in that

  that in the manufacture of a tire by laminate

  cation of the constituent elements, such as tread, side walls, beads, carcass, belt placed between the carcass and the tread, and reinforcement layer of the belt, all these elements

  being in the unvulcanized state, then by molding and vulcanizing

  nization, we prepare the belt reinforcement layer

  in a partially hardened state by exposure to a ra-

ionizing yonnement.

  For the purposes of the present invention,

  although ionizing radiation can be a ray-

  of electrons or Y rays, we prefer to use

ences radiation of electrons.

  Rubber for rubber composition

  usable for or in the present invention is -before-

  suitably a natural rubber or a rubber of the type

diene.

  Can be incorporated into the composition rubber

  chouteuse any additive usually mixed with the compounds

  rubber for tire manufacturing, such as

  than sulfur, vulcanization accelerators, reinforcement agents

  forcing, fillers, plasticizers, antioxidants, etc. The belt reinforcing layer is prepared, using the rubber composition and reinforcing cords comprising organic fibers such as nylon, polyester fibers and aramid fibers of the type

"Kevlar" supplied by Du Pont.

  According to the present invention, it is

  necessary to submit the reinforcing layer beforehand

  belt cement to an ionization irradiation, then to superimpose the belt reinforcement layer on the

  other components of the tire or, more

  shear, to the belt layer and mold the stra-

  resulting tire to obtain a green tire which is vulcanized by heating under pressure in a mold

  vulcanization. More specifically, in accordance with the

  Vention, an element is used for the belt reinforcement layer which is subjected beforehand to ionizing irradiation and the rate of vulcanization of the rubber composition which it contains is thus

  set, so that the change can be avoided or eliminated

  undesirable adjustment of the width of the connecting part

  during vulcanization and molding of the tire

raw tick.

  Although the conditions for irradiation with ionizing radiation, in particular electron radiation, of the belt reinforcing layer may vary more or less depending for example on the formulation of the rubber composition in the reinforcing layer belt as well as the shape, thickness and other characteristics of the belt reinforcement layer, the irradiation is preferably carried out at an acceleration voltage of at least

  kV and at an absorbed dose of ionizing radiation including

  taken between 2 and 10 Mrad. If the acceleration voltage

  and the absorbed dose do not reach the respective ranges

  ves preferred above, it becomes difficult to avoid or eliminate the variation in width of the connecting part before and after vulcanization and we can not then obtain an improvement in the level of uniformity

  (VFR). On the other hand, if the acceleration voltage and the do-

  get absorbed exceed the respective preferred ranges above, the physical properties of the rubber in the

  belt strengthening layer tend to degrade.

  The internal pressure in the bladder, placed in the mold in which the green tire, the belt of which is reinforced by the belt reinforcement layer, is vulcanized by heating under pressure, should preferably be at least 10 daN / cm2. There is a decrease in the width of the connection part,

  because of vulcanization, because the strings of reinforcement-

  may undergo thermal contraction when the rubber coating becomes fluid in the part

  connection at the time of vulcanization. Therefore

  quent, when it is difficult to creep the rubber coating in the connection part, thanks to its partial crosslinking prior to exposure to electron radiation, we can obtain a more efficient transfer to the connection part, the retaining force of the connection part between the mold and the bladder, so that the reduction in width of the connection part at the time of vulcanization can be avoided.

  On the other hand, in or for the present invention

  tion, the abovementioned absorbed dose or, more particularly, the absorbed dose of electron radiation is determined using triacetyl cellulose FTR-125 (a product of

  Fuji Photo Film Co., Ltd, Japan), which is attached to the

rubber sheet faces.

  The present invention will now be described in more detail, with reference to examples and to

comparative examples.

  EXAMPLES 1 to 5 and Comparative Examples 1 to 4: A rubber composition is prepared by

  kneading and grinding of a mixture having the formula below

  afterwards, in a Bumbury type B mixer: natural rubber 50 parts SBR (styrene-butadiene rubber) 30 parts BR (butadiene rubber) 20 parts carbon black (GPF) 60 parts oil 5 parts sulfur 3 parts vulcanization accelerator 1; 5 part All the parts indicated above are by weight.

  A belt reinforcement layer is prepared

  re by coating of nylon reinforcement cords with

  the rubber composition obtained above.

  The reinforcing layer is irradiated

  belt forcing with electron radiation, at absorbed dose values indicated in the table

  1 below, then laminate each layer

  belt reinforcement che on the belt, followed by the lamination of the other constituent elements to prepare raw tires having a structure like

shown in Figure 1.

  We vulcanize raw tires in a mold

  vulcanization, under different vulcani-

  sation also indicated in table 1 below, to obtain respective finished tires having

  one dimension of 195 / 60R14. We determine the level of

  formality (VFR) of each finished tire and the results

  of these determinations are reported in Table 1.

?

TABLE 1

  Internal pressure Dose VFR index absorbed bladder (daN / cm2) (Mrad) (%)

Example

comparison: 1 5 0 102

2 5 4 100

3 10 0 100 *

Example: 1 10 4 90

Example

  comparison: 4 20 0 99 Example: 2 20 2 87

3 20 4 79

4 20 8 72

5 20 12

  * = standard In table 1 above, the VFR values are coefficients when the value found for the tire of Comparative Example 3 is taken as 100 (standard). A smaller value corresponds

at a more advantageous VFR value.

  Table -1 shows that the tires have

  as a belt reinforcement layer subjected to partial crosslinking by ionizing irradiation has a relatively small VFR value and therefore satisfactory uniformity. We also see that the internal pressure

  of the bladder at the time of vulcanization should preferably

rence to be at least 10 daN / cm2.

  In addition, in addition to electron radiation, short wavelength electromagnetic waves, such as t-rays, are also suitable for

  provide the same result as electron radiation.

  As described above, in accordance with the process of the present invention, a

  belt reinforcement layer, for or in tires-

  automotive radials, to electrical irradiation

  trons and the process thus effectively provides a solution

  tion to the problem of the decrease in uniformity, the cause of which is related to the connection part in which the ends of the belt reinforcement layer overlap, without appreciably modifying the operations

  usual tire manufacturing.

  In accordance with the process of the invention, difficult operations are avoided, such as the prior execution of a junction by means of an adhesive at the location

  of the connection, the execution at this location of a

  turing and / or performing a coating of a vul-

  piping, which are usually performed as mo-

  yen to remove the reduction in uniformity due to the connection part as described above (see for example Japanese utility model application publication No. 611817162). Consequently, thanks to the invention, the tires can be produced with a high production yield. In addition, it is no longer necessary to ensure that the connection part does not become too rigid, which is the case when the connection part is coated with an adhesive or when

  sews' at the connection point.

  It is understood that modifications of detail can be made in the form and the implementation of the method according to the invention, without departing from the scope thereof. 1 1

Claims (3)

Claims   1. Process for the manufacture of pneumatic tires   dials for automobiles, which comprises laminating a rolling part (1), two side walls   (2), two beads (3), a carcass (4) comprising   both at least one carcass layer disposed between the   two beads, a belt (5) arranged between the   bearing and carcass, and a layer of reinforcement   belt forcing (6a, 6b) to reinforce the belt, all these elements being in the unvulcanized state, then the molding and vulcanization of the resulting laminate,   characterized in that the reinforcing layer is prepared   belt belt (6a, 6b) in a crosslinking state   partial, by exposure to ionizing radiation.   2. Method according to claim 1, charac-   terized in that the ionizing radiation is a ray-   electron radiation, the irradiation being carried out at an acceleration voltage of at least 100 kV and at an absorbed dose of electron radiation between 2 and Mrad.   3. Method according to claim 1 or 2, characterized in that the laminate in the unvulcanized state   is molded and vulcanized in a mold in which the   internal pressure of a bladder is set to a value of at least minus 10 daN / cm2.