FR2618374A1 - PROCESS FOR THE MANUFACTURE OF RUBBER PRODUCTS BY VULCANIZATION BY MEANS OF IONIZING IRRADIATION - Google Patents

Abstract

Process for the production of rubber products, which consists in subjecting an unvulcanized rubber composition, comprising a sulfenamide-type vulcanization accelerator, to ionizing irradiation, typically by means of electron radiation, and to prepare thus an unvulcanized rubber composition or an unvulcanized rubber molded element whose vulcanization rate is controlled and used to produce a uniformly vulcanized rubber product.

Description

The present invention relates to a method for

  the manufacture of rubber products and, more particularly

  in particular, a process which makes it possible to manufacture pro-

  very uniformly vulcanized rubber compounds.

  In most of the usual methods for

  manufacture of vulcanized rubber products, we pro-

  generally yields by suitable molding of an uncured rubber composition mixed for example with sulfur, a vulcanization accelerator and other additives, and vulcanization of the resulting molded mass

  by pressure heating, followed by hardening.

  However, molded masses comprising uncured rubbers generally have a relatively low thermal conductivity so that, during the vulcanization of these masses, irregularities tend to occur between the degree of vulcanization reached in an interior part and that which is reached in an outer part of vulcanized molded parts, which has the consequence of producing a rubber product

  vulcanized which is not uniformly vulcanized in its to-

  tality. For example, in the manufacture of tires in which a plurality of structural elements, such as a carcass layer, a belt layer,

  a layer of sub-tread, an upper layer

  re rolling, etc., are successively superimposed and the resulting laminate is molded by heating in a mold, it takes a very long time before an element of

  structure of the tire, placed away from a structural element

  directly in contact with the heating surface of the mold, reaches a required vulcanized state and, therefore, differences in degree of vulcanization tend to occur among the laminated structural members. he

  this results in differences or irregularities in the quality

  quality and characteristics of the tires produced.

  In addition, the time required before the completion of the vul-

  pipe should be relatively long and a perfection-

  This is desirable from the point of view of production yield.

  As a result, we generally searched in di-

  for the rubber industry to obtain an improvement in uniformity or related to the uniformity of the vulcanization effect of rubber products and to reduce

  the time required for vulcanization.

  As a means of reducing the time required for vulcanization in the manufacture of products

  rubber, it has been proposed to increase the amount used

  of a vulcanization accelerator to be mixed in uncured rubber compositions and / or to use,

  mixed in these rubber compositions, an ac-

  vulcanization booster having a relatively high effect of accelerating vulcanization. However, in each of these proposed methods, there is a risk that,

  in the molding operation to transform a composite

  tion of uncured rubber into a molded part of the

  imposed configuration, for example by extrusion, calan-

  drage or the like, there begins a burn or that the vulcanized rubber products do not have satisfactory physical properties, and the means proposed are not very useful in practice. On the other hand, the rotary hardening is also known in which, for example, a sheet of rubber and a fabric coated with rubber which are not hardened are subjected to preheating by passage between heating rollers, but the sulfur then tends to form flowers and / or the adhesive power tends to decrease, so that the production yield in one or more

  following operations tends to degrade.

  In US Pat. Nos. 2,933,441 and 2,933,553, a method is proposed for shortening the time required for vulcanization in a mold, according to which, after molding an uncured rubber composition, heating and vulcanization are carried out. usual, then we apply irradiation to part of the product

  heated and vulcanized which has not reached a sufficient degree

  fisant of crosslinking. A method is also proposed for obtaining a vulcanized (pneumatic) product.

  homogeneously, according to which a material of constitution

  carcass or other parts of a tire,

  which are precured by irradiation by means of a ray-

  electron, are superimposed on another component of the tire, comprising an uncured rubber composition, and the resulting laminate is heated and vulcanized. However, these proposed methods

  consist essentially in the crosslinking of chai-

  nes of the high polymer constituting rubber by carbon-to-carbon bonds, by means of electron radiation. The inventors of the present invention have carried out extensive studies on effective methods of accelerating the vulcanization of uncured rubber compositions, using ionizing irradiation, to verify that the effect of ionizing irradiation on

  the rate of hardening or vulcanization of the

  uncured rubber positions vary when used

  reads different vulcanization accelerators, so that vulcanization can be accelerated in some cases but not in some other cases and, as a result

  from these studies, they resulted in the present invention.

  A main object of the present invention

  is to provide a process for the manufacture of pro-

  - rubber products, which can allow vulcanization

  uniform in a relatively short time, prevents burning

  lure and the formation of flowers in the operation of

  lage of unvulcanized rubber compositions, in particular in an extrusion operation and a

  calendering operation, and provides a rubber product

  vulcanized cabbage having uniformity or regularity

  very remarkable with regard to the effect of vulcani-

  station. The object of the invention is also to provide

  molded parts of unvulcanized rubber, containing

  nant a vulcanization accelerator whose speed

  hardening or vulcanization can be advantageous

  controlled by exposure to ionizing radiation and which can be used advantageously for setting

  work of the process according to the invention.

  The process according to the invention is characterized in that at least one of the molded elements of unvulcanized rubber is prepared from an unvulcanized rubber composition which comprises a component of

  rubber, sulfur and vulcan accelerator

  sulfenamide type setting and speed

  vulcanization by exposure to ionizing radiation.

  Other objects and advantages of the invention

  will appear to those skilled in the art in the light of the

  detailed description below of its preferred modes of implementation, with reference to the accompanying drawings in which: FIG. 1 illustrates an example of rheometric curves making it possible to evaluate the vulcanization characteristics of rubber compositions; Figures 2 and 3 illustrate the relationship between the rate of hardening or vulcanization and the dose of electrons absorbed and the dose of Y-rays absorbed from a rubber composition used in an exemplary implementation of the invention; Figure 4 is a section of one half of a

  tire produced in accordance with the process of the invention

tion;

  Figure 5 illustrates the relationship between the posi-

  - relative position in the tire crown of Figure 4 and the relative absorbed electron dose; FIG. 6 illustrates the relationship between the degree of curing equivalence, indicating degrees of vulcanization at various locations between points a and b of the section of the tire of FIG. 4, and the relative position; and

  FIG. 7 is a section of one half of an example

full of automotive tires.

  The process according to the present invention is

  intended for the manufacture of a rubber product

  channeled, by heating a molded mass comprising a plurality of molded elements of unvulcanized rubber, by heat conduction for example from a mold

  and vulcanization of the molded mass.

  More specifically, the process according to the invention

  tion is intended for the manufacture of a rubber product

  vulcanized cabbage, including prior adjustment of the

  vulcanization braids of non-vulcanized rubber molded elements formed by extrusion, calendering and others,

  by means of ionizing irradiation such as

  ment of electrons, Y-rays and X-rays or, otherwise

  said, the preparation of each of the molded elements

  non vulcanized rubber in the form preferably of a

  element which has a vulcanization or hardening speed

  ment corresponding to the degree of heat supplied by a mold or the like when the molded mass comprising the rubber elements is molded during the vulcanization operation; then molding a combination of

  molded parts of unvulcanized rubber having vi-

  hardening braids set different, followed by

vulcanization.

  For or in the present invention, it is

  required that at least one of the molded rubber elements

  unvulcanized cabbage includes a rubber composition

  unvulcanized cabbage which contains a vulcan accelerator

  line of sulfenamide type and the speed of which

  cissement is set beforehand by means of an irra-

ionizing diation.

  If the contained vulcanization accelerator

  in the above unvulcanized rubber composition

  above does not have a sulfenamide-type vulcanization accelerator, so ionizing irradiation does not have much effect on the rate of vulcanization. By

  against, the sulfenation-type vulcanization accelerator

  mide, when subjected to ionizing irradiation, undergoes cleavage and decomposition in the unvulcanized rubber composition and generates an intermediate reaction product which acts to accelerate the rate of vulcanization and which can be used to control the

  vulcanization speed of rubber molded elements

unvulcanized cabbage.

  The sulphide-type vulcanization accelerator

  namide usable for the needs of the invention can

  be chosen in practice from N-cyclohexyl-2-benzothiazo-

  ryl sulphenamide, N-oxy-diethylene-2-benzothiazoryl sulphide

  namide, N-t-butyl-2-benzothiazoryl sulfenamide, N, N-dii-

  sopropyl-2-benzothiazoryl sulfenamide and N, N-dicyclohexyl-

2-benzothiazoryl bulfenamide.

  If, together with one of the sulfenamide-type vulcanization accelerators above, a different vulcanization accelerator is used, for example a thiuram-type vulcanization accelerator, a guanidine-type vulcanization accelerator and the like,

  this does not cause any harmful effect.

  The amounts to be combined of a rubber-like component constituting a main ingredient of the usable unvulcanized rubber composition

  in the present invention, a vulcan accelerator

  sulfenamide type which is an essential component

  sand according to the invention and sulfur vary according to the

  type of ionizing radiation, the dose of electrons absorbed

  the arrangement of a particular unvulcanized rubber composition in a rubber product to be obtained, and the type and combination formula of

  components mixed in the rubber composition.

  However, to give a hardening speed

  highly desirable rubber composition not vul-

  channeled and also to obtain a rubber product

  cauliflower having satisfactory physical properties, the sulfenamide-type vulcanization accelerator is preferably incorporated in an amount between 0.5

  and 3 parts by weight, and sulfur in a com-

  taken between 0.5 and 10 parts by weight, per 100 parts

  by weight of the rubber-like component.

  For the rubber component, you can use

  read, in addition to any of the various rubbers

  known vulcanizable natural materials, any of the

  synthetic sprouts such as styrene-butadiene rubber

  (SBR), isoprene rubber (IR), acrylonitrile rubber-

  butadiene (NBR), butadiene rubber (BR), butyl rubber (IIR), ethylene-propylene rubber (EPM, EPR), ethylene-propylene terpolymer (EPT, EPDM) etc. The unvulcanized rubber composition

  may also contain various additives which are mixed ha-

  usually in rubber compositions, for example reinforcing agents, fillers, antioxidants, carbon black, other pigments, etc. The unvulcanized rubber composition, suitably mixed with various additives indicated

  above based on a rubber product to fa-

  brickwork and -features required for this product, is formed or molded by -any of the known operations of extrusion, injection, calendering and the like so as to generate an unvulcanized rubber element having the desired shape and it is then subject to

  ionizing radiation represented by radiation from

  electrons, rays, and x-rays, preferably

electron radiation.

  For ionizing irradiation, electron radiation is preferably used, except for special cases in which the molded rubber element

  unvulcanized has a thickness which is very large.

  We can work by applying irra-

  ionizing ionization to an unvulcanized rubber composition which has not been formed into a molded mass or a molded element, then treatment of the rubber composition by a molding or forming operation

  to obtain a molded or formed element having the configuration

appropriate ration required.

  The degree of exposure or the dose of electrons absorbed varies according to the formulation of the unvulcanized rubber composition, in particular its content of sulfenamide-type vulcanization accelerator, the shape, the thickness and the position of the molded element or elements. in a rubber product to be manufactured, etc. However, in cases where electron radiation is used for ionizing irradiation, it is necessary to

  preferably carry out the irradiation at an access voltage

  leration of at least 100 kV and at an absorbed dose

  taken between 2 and 15 Mrad so as to obtain an element

  molded having the desired rate of cure or cure

  channeling. When using Y-rays, the absorbed dose should preferably be between 1 and 15 Mrad. If the acceleration voltage is lower or

  if the absorbed dose is smaller than the ranges

  favorite pectives above, it is impossible to obtain

  provide a sufficient effect of accelerating vulcanization by irradiation by means of electron or ray radiation and, if they exceed the preferred ranges

  above, there is a risk of manufacturing rubber products

  cabbage which does not have the satisfactory physical properties

  health. A first molded element of unvulcanized rubber, subjected to ionizing irradiation and having a vulcanization rate set as above, is suitably combined with a second element

  molded in unvulcanized rubber subjected to a dose of ir-

  absorbed radiation regulated and different and having a vulcanization speed different from that of the first

  molded part of unvulcanized rubber and / or of an ele

  molded from unvulcanized rubber which has not been

  subjected to irradiation, these elements then being

  the. Furthermore, in accordance with the present invention,

  the vulcanization speed of the rubber molded elements

  unvulcanized cabbage is preferably adjusted on the basis of the irradiation dose absorbed during the aforementioned ionizing irradiation, but it is also possible to adjust the vulcanization speed on the basis of the mixed amount of the vulcanization accelerator of

  sulfenamide type to be incorporated into the composition of rubber

  unvulcanized cabbage, or on the basis of both the amount

  mixture of the vulcanization accelerator and the

  absorbed dose of ionizing radiation during irradia-

tion.

  Molded rubber elements, the speed of which

  se vulcanization has been set to the desired value as indicated above are combined appropriately, so that their uniform or homogeneous vulcanization can

  be completed in as short a time as possible

  ble, given the type and shape of the rubber product to be manufactured and the structure of the vulcanization device such as a mold and a bladder, they are laminated and formed and can then be processed to - obtain the product rubber desired, by vulcanization

  performed by heating by conduction of heat

  them from the vulcanization device.

  We now describe in more detail

  the characteristics and advantages of the present invention

  tion, with reference to examples and comparative examples. In or for the present invention, the dose

  of absorbed electron radiation and the accelerating effect

  vulcanization ration are determined as follows.

  Absorbed Electron Radiation Dose The determinations are carried out using triacetyl cellulose FTR-125 (a product of Fuji Photo Film Co., Ltd. Japan) which is fixed on surfaces of

rubber sheets.

  Vulcanization Accelerating Effect

  Using a rheometer, the values are determined.

  their torque (daN.cm) of rubber compositions subjected to irradiation having the prescribed intensity

  and the prescribed absorbed dose of electron radiation.

  With reference to Figure 1, the torque values found

  are regularly reported on a 100 scale,

  between the maximum torque MH and the minimum torque ML. The ins-

  as long as the minimum torque ML is 5/100 is indicated

  qué par t5, the instant at which it amounts to 30/100 is indi-

  qué par t30 and the instant at which it rises to 95/100 is indicated by t95 in Figure 1 which represents a curve

  rheometric as determined above.

  Figure 2 is a curve obtained by transfer

  values of the curing or vulcani-

  sation (t30) determined for a rubber composition-

  cabbage used in an exemplary implementation of the present invention, as a function of the dose values

  of absorbed electron radiation. This figure 2 my-

  that when the absorbed dose increases, the value t30 decreases, that is to say that the vulcanization speed increases. On the other hand, the value t30 is a percentage value (%), taking as value 100 the curing speed of the rubber composition which has not been subjected to ionizing irradiation. EXAMPLES 1 to 3 and Comparative Examples 1 to 3 Rubber compositions are prepared by mixing a part by weight respectively of the

  various sulfenation-type vulcanization accelerators

  mide indicated in table 1 below, in the following composition: natural rubber 100 parts by weight carbon black (HAF) 45 parts by weight oil 6 parts by weight

sulfur 2.5 parts by weight.

  After kneading in a Bum- mixer

  bury type B, we transform each composition of

  rubber into a rubber sheet 1 mm thick-

  which is subjected to irradiation by means of a ray-

  electron of 500 kV and 5 Mrad. Care is taken to ensure that irradiated and non-irradiated samples of the rubber sheets

  follow an identical story, except that the first

  miers are subjected to ionizing irradiation while

the latter are not.

  The rheometric curves are determined at the

  times before and after irradiation with radiation from

  lectrons and the values found are also indi-

  listed in Table 1 below. In addition, in Table 1, each value indicated in parentheses

  under the heading "after irradiation" represents a

  their relative (index) respectively of the value t5,

  of the t30 value and the t95 value after irradia-

  tion, when we take their value t5 as 100,

  their corresponding t30 value and t95 value remain

  pectives before irradiation, as indicated in parentheses-

  its under the heading "before irradiation".

  Table 1 shows that, compared to the rubber compositions used in Comparative Examples 1 to 3 and containing a vulcanization accelerator other than an accelerator of the sulfenamide type,

  any of the rubber compositions used

  in examples 1 to 3 containing an accelerator

  vulcanization of sulfenamide type in accordance with the pre-

  The invention does not necessarily have much larger t5, t30 and t95 values, both before and after exposure to electron radiation. However, as a result of electron irradiation, while the

  values t5, t30 and t95 do not undergo a sub-change

  stantiel in the case of comparative examples 1 to 3, the corresponding values decrease a lot and the vulcanization speed therefore increases in the case of the examples

  1 to 3. (See Table 1 on page 13).

EXAMPLE 4

  Figure 4 is a section of one half of a

  typical large tire. On this fi-

  gure, we see an upper tread 1, a

  side wall 2, a bead 3, a carcass 4 comprising

  so many carcass layers 4-1, 4-2 and 4-3, a belt

  ture 5 and an interior covering 6. These marks designate

  also the same elements in figure 7.

  A raw tire is manufactured, in order to obtain a tire having a large dimension of 3000-51 and a structure as shown in FIG. 4, as follows. A number of molded rubber elements (such as rubber sheets, rubber coated fibrous material, etc.) are used including

  rubber compositions not vulcanized in the

  which is incorporated a vulcanization accelerator of sulfenamide type according to the present invention. We

TABLE 1

  Accelerator Before Before vulcanization Irradiation Irradiation Example Mmin / Mmax Comparative (daN-cm) 12.2 / 29.0 15.6 / 31.8 2-mercaptobenzot5 1.30 (100) 1.35 (104) thiazole thiazole t30 2.02 (100) 2.10 (104) t95 3.82 (100) 3.82 (100) EXAMPLE 'i Mmin / Mmax (daN-cm) 13.0 / 40.8 16.8 / 41, 6 Ncyclohexyl-2- t 2.17 (100) 1.68 (77) benzothiazoryl sulfeamide a30t 2.80 (100) 2.18 (78) sulfnamide t 30 '' t95 3.52 (100) 2.90 (82 ) t95 EXAMPLE 2 Mmin / Mmax (daN-cm) 15.2 / 44.2 19.0 / 44.8 N-oxydiethylene- t 2.63 (100) 2.97 (79) 2-benzothiazoryl sulfenamide 3 sulfenamide t30 3, 52 (100) 2.73 (78) t95 4.67 (100) 3.80 (81) t TABLE 1 (Continued) Accelerator before After vulcanization Irradiation Irradiation EXAMPLE 3 Mmin / Mmax (daN-cm) 15.4 / 47.4 19.2 / 48.0 Nt-butyl-2- t- 2.43 (100) 2.00 (82) benzothiazory] eulfothiaidoryl t30 3.32 (100) 2.72 (82) sulfenamide t95 4, 27 (100) 3.67 (86) Comparative Mmin / Mmax example (daN-cm) 17.6 / 41.4 21.4 / 42.2 2 diphenyl- t 1.22 (100) 1.27 (104) guanidine guanidine t30 2.20 (100) 2.25 (102) t95 7.45 (100) 7.53 (101) Example Mmin / Mmax Comparative (daN-cm) 11.0 / 28.8 14.2 / 31.6 3 dibenzothiazoryl t 1 , 52 (100) 1.62 (107) disulfide ds dt3Q 2.30 (100) 2.33 (101) t95 4.23 (100) 4.23 (100) c \

* t95 -.

Co __

  subjects the molded rubber elements to irradiation

  electrons and we superimpose them

  in such a way that the relationship between the position re-

  lative and the relative absorbed dose, represented by the curve in FIG. 5, is satisfied, in accordance with the change in relative position between position a of

  inner lining and position b of the upper end

  lower of the tread, in the section of the

  central tread of the tread in FIG. 4. The raw tire is vulcanized in an ordinary mold

  made up of molded rubber elements

  his. With regard to the respective parts of the tire other than the central crown part, when necessary, the same relationship is observed between the relative position and the relative absorbed dose.

  than in the central crown part. The degree of vul-

  pipe obtained in the region between positions a and b of the section in FIG. 4 of the tire constructed as described above is indicated in FIG. 6, which illustrates the relationship between the relative position, between position a of the inner lining and position b of the upper end of the tread in the central crown portion, and the degree of equivalence of

  hardening. In Figure 6, the hardening regions

  excessive are indicated by hatching. We see

  in FIG. 6 that a correct degree of vulcanization is obtained

  sation at any point between positions a and b and that a

  uniform vulcanization is carried out. There is also

  curing time is reduced.

  On the other hand, in Figure 6, the curves in-

  indicated by the numbers 1 to 4 in a respective circle

  are envelope lines defined by the degree of pro-

  increase in vulcanization as a function of the time elapsed in a case without irradiation and these lines show that

  vulcanization tends to be late in some part

  intermediate between positions a and b. Zone A indicated by hatching inclined upward and to the right is an area of excessive hardening in the case where irradiation is not carried out, while zone B indicated by hatching inclined upward and towards left is an area of excessive hardening in the event that irradiation is performed. In addition, the dotted line represents the lower limit of equivalence.

  hardening required for the vulcanization of each

  gion in the crown portion of the tire.

  A more detailed description is given below

tire manufacturing.

  From non-vulcanized rubber compositions

  pipelines comprising N-oxy-diethylene-2-benzothiazoryl sulfenamide as a vulcanization accelerator and a

  unvulcanized rubber composition based on natural rubber and / or diene rubber as type component

  rubber, molded elements are prepared

  rubber; such as rubber sheets, a ma-

  rubber coated fibrous material, etc., for forming

  tion of a carcass layer divided into two layers, a belt layer, a tread underlayment and a

  upper wearing course divided into three layers.

  The rubber molded layers are subjected to an ir-

  radiation by means of electron radiation,

  to the specifications below, then laminated to form a raw tire which is vulcanized in a

ordinary mold.

  Carcass layer: Inner layer: 500 kV, 1 Mrad Outer layer: 500 kV, 2 Mrad Belt layer: 500 kV, 4 Mrad Underlayment: 750 kV, 5 Mrad Top bearing layer: Layer. inner: 750 kV, 3 Mrad Intermediate layer: 750 kV, I Mrad

  Outer layer: no irradiation.

  - The molded rubber elements for the carcass layer and the belt layer are calendered then

  subjected to irradiation by electron radiation, tan-

  say that in the case of molded rubber elements for the underlayment and the upper wearing course which have a sheet thickness greater than

  that of the carcass layer and the belt layer

  re, irradiation is applied to the leaves of the composition

  sition of rubber, which are then molded on a drum

bour.

  The hardening time of the tire is found to be

  material thus obtained, with a large dimension of 3000-51,

  is reduced by about 25% compared to the curing time

  ment of a comparable tire made from

  elements which have not been subjected to irradiation at the mo-

  yen of electron radiation. It is also found that the tire produced in accordance with the process of

  present invention has a value representing the

  tire reliability expressed in tonnes.km / hour, which

is improved by 8%.

  An explanation is given below

  the above value, called TKPH (tonne.km/hour). When-

  that a tire operates under a constant load and at a constant speed, the temperature of the tire

  finally reaches a point of equilibrium and this temperature

  equilibrium measurement should preferably be as low as

  possible, from the point of view of the durability of the tire.

  So when you set a certain critical temperature,

  the product of a load on the tire and a

  tire rolling size, for which the temperature

  above critical ture is reached, is taken as

  their TKPH which represents the durability of the tire.

  A larger TKPH (tonne.km/hour) value corresponds to

  greater durability of tires.

EXAMPLE 5

  A fibrous material coated with rubber is prepared.

  chouc, which includes 1500 D / 2 polyester fiber ropes and an unvulcanized rubber composition having the following combination formula: natural rubber / SBR 80/20 parts by weight carbon black (HAF) 45 parts by weight oil 6 parts by weight sulfur 2.5 parts by weight antioxidant 1 part by weight N-oxydiethylene-2-benzothiazoryl

sulfenamide 1 part by weight.

  An ionizing irradiation of 500 kV and 3 Mrad is applied to the part of the rubber-coated fibrous material corresponding to a part folded back into the respective beads of the carcass layer, and a tire for an automobile is produced (tire size 165SR13) having a structure as shown in FIG. 7. On the other hand, a tire is made of a size and a structure comparable to those of the above tire, using for the carcass layer the same fibrous material coated with rubber

  as above but not subject to irradiation.

  The curing time of the tires is compared.

  respective ticks and we find that, if we take as

  their 100 the tire hardening time in the

  case without irradiation, the curing time of the pneuma-

  tick in the case of irradiation by electromagnetic radiation

  trons according to the present invention is 94. It can be seen that the hardening time is significantly reduced in

the case of the latter tire.

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

  unvulcanized rubber, by exposure to rayon

  ionizing ion, typically electron rays and y rays, and the process of the invention makes it possible to obtain a uniformly vulcanized rubber product, with high productivity and a reduced curing time. In particular, when a rubber product

  includes various molded rubber elements

  nized, for example in the case of tires, it is possible to adjust the vulcanization speed of each molded rubber element and to standardize the degree of vulcanization of the rubber product as a whole, by irradiation

  ionizing according to the invention, which makes it possible to manufacture

  quer rubber products with remarkable quality and performance. The process according to the invention

  is therefore of great industrial importance.

  When used in the present invention

  Y-rays which have relatively high permeability

  Vee, rubber elements which have a thickness of several millimeters or more, or a laminated rubber element comprising a plurality of layers, can be vulcanized uniformly in a short period of time, and this vulcanization can be carried out without risk of burns. and flower formation. The process according to the invention therefore applies to the manufacture of a large

  variety of rubber products.

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

this one.

Claims (7)

Claims   1. Process for manufacturing a rubber product   chouc, which includes heating a molded mass,   formed from a plurality of molded elements of unvulcanized rubber, by heat conduction from a mold for example, and the vulcanization of the molded mass, characterized in that at least one of the elements is prepared   molded from unvulcanized rubber from a composite   tion of unvulcanized rubber which comprises a composition   rubber type, sulfur and a sulfenamide type vulcanization accelerator, and whose   rate of vulcanization by ionizing irradiation.   2. Method according to claim 1, character-   laughed at in the fact that at least two of the soft elements are prepared   unvulcanized rubber sheeting, from unvulcanized rubber compositions which are irradiated with   different absorbed doses of ionizing radiation.   3. Method according to claim 1, character-   laughed at in the fact that at least two of the soft elements are prepared   strips of unvulcanized rubber, from compositions   of unvulcanized rubber which contain quanti-   tees different from the vulcanization accelerator of the sufenamide type.   4. Method according to any one of the claims   cations 1 to 3, characterized in that the sulfenamide-type vulcanization accelerator is at least one compound   chosen from the group comprising N-cyclohexyl-2-benzothia-   zoryl sulfenamide, N-oxydiethylene-2-benzothiazoryl sul-   fenamide, N-t-butyl-2-benzothiazoryl sulfenamide, N, N-   diisopropyl-2-benzothiazoryl sulfenamide and N, N-dicyclo-   hexyl-2-benzothiazoryl sulfenamide.   5. Method according to any one of the res-   previous indications, characterized in that the component   rubber type is a rubbery mixture of   with natural rubber as an essential ingredient   and at least one substance chosen from sty rubber   reene-butadiene, isoprene rubber, acrylic rubber   nitrile-butadiene, rubber butadiene, rubber   butyl, ethylene-propylene rubber, and ter- ethylene-propylene polymer.   6. Method according to any one of the claims.   previous cations, characterized in that for ionizing irradiation an electron radiation is used whose acceleration voltage is at least 100 kV, the irradiation being carried out at an absorbed dose included between 2 and 15 Mrad.   7. Process according to any one of the claims.   previous cations, in which the rubber product is a tire comprising an upper wearing layer (1), a rolling underlay, a belt layer (5) and a carcass layer (4) which are   layered in this order, characterized in that one applies   that, to an element constituting the underlayment or the belt layer and / or to an element constituting   a folded-down part of the carcass layer in fillers   respective relets (3) of the tire, an absorbed dose   ionizing irradiation greater than that applied   than to the elements constituting the other layers of the tire tick.