Composition comprising a mixture of organic peroxides including 1,3-1,4-bis (tert-butylperoxy isopropyl) benzene for the crosslinking of crosslinkable polymers

The present invention relates to a composition comprising a mixture of organic peroxides, as defined below, which is intended to be used in particular for the crosslinking, in particular for improving the crosslinking speed, of crosslinkable polymers, such as polymers. thermoplastics and / or elastomers.

The invention also relates to the use of a composition comprising a mixture of organic peroxides, as defined below, and at least one crosslinkable polymer for the manufacture of all or part of an article, preferably an article. belonging to the shoe industry.

The invention also relates to an article, preferably an article belonging to the safe footwear or groundsheet industry, all or part of which can be obtained by crosslinking the composition as defined above.

The crosslinking of crosslinkable polymers, in particular thermoplastic polymers and / or elastomeric polymers, generally gives a very wide variety of products, for example joints, pipes, articles belonging to the carpet industry, in particular for the carpet industry. cushioning / filling of carpets, articles belonging to the shoe industry, in particular soles, cables or insulation, advantageous thermomechanical properties, such as better elasticity and / or improved creep resistance.

Thus, the processes for preparing these products mainly use thermoplastic polymers and / or elastomers, such as copolymers of ethylene and vinyl acetate (EVA), various grades of polyethylene, polypropylene, natural rubber or silicone, which are crosslinked (or cured) under the action of crosslinking agents.

The crosslinking agents typically employed are organic peroxides, in particular dicumyl peroxide (DCP). For example, dicumyl peroxide, sold under the trade name Luperox® DCP, is conventionally used in the manufacture of articles belonging to the groundsheet industry and also to the safe footwear industry, in particular of soles, made from compositions which may be in the form of a foam containing copolymers of ethylene and of crosslinked vinyl acetate (EVA) or of crosslinked polyethylene as the main component.

Compositions comprising the polymers thus crosslinked are generally prepared by molding processes, such as an injection molding process or a compression molding process. The products or articles described above are therefore produced in suitable molds within which the crosslinking of the thermoplastic polymers and / or of the elastomers takes place.

However, the thermal decomposition of dicumyl peroxide during crosslinking most often generates the formation of acetophenone, as a by-product, which generates a strong odor, unpleasant and irritating to the respiratory tract and whose exposure repeated can be dangerous for operators.

More specifically, the compositions containing the polymers thus crosslinked exhibit this characteristic odor of acetophenone, which requires additional treatment in order to be able to mask it, or even to eliminate it.

In order to overcome the drawbacks caused by acetophenone, it has been proposed in the state of the art to replace dicumyl peroxide with other crosslinking agents, in particular 1, 3- 1, 4-bis (tert- butylperoxy isopropyljbenzene which is an organic peroxide sold under the trade name Luperox®L or Luperox Vul-Cup®R.

In fact, 1, 3- 1, 4-bis (tert-butylperoxy isopropyljbenzene has the advantage of efficiently crosslinking thermoplastic polymers and / or elastomers, in particular by leading to a good crosslinking density which makes it possible to ensure articles obtained with satisfactory thermomechanical properties. More specifically, if the crosslinking density is too low, the article or the product obtained is liable to exhibit, among other things, insufficient resistance to breaking and tearing. 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene is increasingly used in the manufacture of articles obtained from the crosslinking of rubber or polyolefin.

However, 1, 3 - 1, 4-bis (tert-butylperoxy isopropyl) benzene has a number of disadvantages compared to dicumyl peroxide.

Indeed, the crosslinking of polymers in the presence of 1, 3 - 1, 4-bis (tert-butylperoxyisopropyl) benzene during the molding processes must be carried out at higher temperatures, for example of the order of l 80 ° C, than those used for dicumyl peroxide, typically of the order of 70 ° C, in order to obtain similar productivity and production time which would be particularly satisfactory from an industrial point of view.

However, it has been found that operating at higher temperatures, on the order of 180 ° C, due to the thermal stability of 1, 3- 1, 4-bis (tert-butylperoxyisopropyl) benzene , can induce fouling problems of the manufacturing molds and have an impact on the quality of the articles obtained.

In fact, at these temperatures, the thermoplastic polymers and / or crosslinkable elastomers can degrade chemically, which can limit their crosslinking inducing, on the one hand, deposits of uncrosslinked polymer residues at the bottom of the manufacturing molds causing their fouling. and, on the other hand, articles whose properties are not satisfactory because their surfaces have not been fully crosslinked.

For example, at temperatures of the order of l 80 ° C, it has in particular been observed, on the one hand, that EVA tends to decompose chemically and to release small amounts of acetic acid and, on the one hand, on the other hand, that the oxygen inhibition rate is

accelerates. Thus the formation of acetic acid combined with the inhibition of oxygen will jointly interfere with the in situ generation of free radicals resulting from the decomposition of 1, 3- 1, 4-bis (tert-butylperoxyisopropylbenzene and therefore will , limit the crosslinking of the EVA. In this case, the surface of the article obtained is found not only insufficiently crosslinked but also yellow due to the decomposition of the EVA. In addition, the manufacturing molds are fouled by the sticky deposit of uncrosslinked EVA residues.

In other words, the use of temperatures higher than those used to thermally decompose the dicumyl peroxide leads to a certain number of drawbacks which result in a loss of productivity, due to the need to wash regularly. clogged manufacturing molds, a reduction in their lifespan, due to the frequency of washing cycles of the manufacturing molds, and poor quality of the articles or products obtained, in particular of their surfaces which are notably yellowed during use of EVA.

In particular, in the case of EVA, the degradation of the desired thermomechanical properties may be accompanied by a lack of yellowing of the articles and the manufacturing molds may be clogged with a yellowish deposit of EVA.

The unsatisfactory properties of the articles obtained are more particularly observed in the manufacture of articles belonging to the field of footwear, in particular soft shoe soles, which is problematic because the properties of elasticity, resistance to creep and / or rigidity are highly sought after.

Thus, one of the objectives of the present invention is to provide a composition having good crosslinking properties, in particular by conferring a satisfactory crosslinking speed and density, in order to obtain an article endowed with thermomechanical properties suitable for the desired applications while at the same time. minimizing the fouling problems of manufacturing molds which may affect the productivity of the molding processes, the life of the manufacturing molds and the final properties of said article.

In other words, there is a real need to provide a composition capable of efficiently crosslinking crosslinkable polymers, in particular thermoplastic and / or elastomeric polymers, under operating conditions similar to those used for 1, 3- 1. , 4-bis (tert-butylperoxyisopropyl) benzene while minimizing the risk of clogging of the manufacturing molds.

In view of the foregoing, the object of the invention is more particularly to provide a composition intended to improve the crosslinking speed and / or the crosslinking density of crosslinkable polymers, in particular thermoplastic polymers and / or elastomeric polymers, such as than copolymers of ethylene and vinyl acetate, while reducing the risk of clogging of the manufacturing molds thereby prolonging their life.

The present invention therefore has in particular as an object a composition comprising at least one mixture of organic peroxides containing:

- 1, 3- 1, 4-bis (tert-butylperoxy isopropyljbenzene and

- at least one second organic peroxide having a half-life temperature at one (1) minute ranging from 130 to l 70 ° C, preferably ranging from 135 to l 65 ° C, and more preferably ranging from l 42 ° C to l 60 ° C.

The composition according to the invention thus has the advantage of efficiently crosslinking crosslinkable polymers, in particular by leading to a satisfactory crosslinking speed and density, while minimizing the risks of clogging of the manufacturing molds liable to affect productivity. molding processes, the life of the manufacturing molds and the final properties of the article obtained.

In other words, the composition according to the invention makes it possible to increase the speed and / or the crosslinking density of the crosslinkable polymers, in particular thermoplastic polymers and / or elastomeric polymers, in particular polyolefins, while reducing the fouling problems occurring in manufacturing molds.

More particularly, the composition according to the invention makes it possible in particular to improve the crosslinking speed of crosslinkable polymers, in particular thermoplastic polymers and / or elastomeric polymers, compared with the use of 1, 3- 1, 4-bis (tert-butylperoxyisopropyl) benzene alone.

The composition according to the invention has the advantage of specifically increasing the crosslinking speed of the crosslinkable polymers at the start of the crosslinking while inducing a good crosslinking density.

Thus the composition according to the invention makes it possible to reduce the problems of fouling of the manufacturing molds compared with the use of l, 3- l, 4-bis (tert-butylperoxyisopropyl) benzene alone.

The invention also relates to the use of the composition according to the invention as defined above for the crosslinking of one or more crosslinkable polymers, preferably one or more thermoplastic polymers and / or one or more elastomeric polymers.

In particular, the composition makes it possible to improve the speed and / or the crosslinking density of one or more crosslinkable polymers as defined above.

Likewise, the invention relates to a composition comprising at least the mixture of organic peroxides, as described above, and at least one crosslinkable polymer, preferably at least one thermoplastic polymer and / or at least one elastomeric polymer.

In this case, the composition further comprising at least one crosslinkable polymer is a crosslinkable composition, ie. that the mixture of organic peroxides is capable of crosslinking the crosslinkable polymer (s) at a given temperature by generating in situ free radicals capable of causing the crosslinking of said polymers.

Thus, the crosslinkable composition makes it possible to lead to crosslinked compositions resulting in good properties of the desired article with high productivity.

Likewise, the invention relates to a composition in the form of soft (or capable of generating soft) obtained by crosslinking the composition according to the invention further comprising one or more crosslinkable polymers.

In other words, the composition, obtained from the crosslinking of the mixture of organic peroxides as defined above and of the crosslinkable polymer (s), is a soft or generates soft.

Furthermore, the present invention also relates to a method of manufacturing all or part of an article, preferably an article belonging to the groundsheet or safe shoe industry, more preferably safe shoe, in particular soles. , comprising a step of crosslinking the crosslinkable composition according to the invention, ie further comprising at least one crosslinkable polymer.

The method according to the invention has the advantage of resulting in an article having good thermomechanical properties, in particular satisfactory elasticity and resistance to creep, and the surface appearance of which is improved.

Likewise, another object of the invention relates to the article, all or part of which is obtained by the method described above, i .e. by crosslinking the composition according to the invention further comprising one or more crosslinkable polymers.

Other characteristics and advantages of the invention will emerge more clearly on reading the description and the examples which follow.

In what follows, and unless otherwise indicated, the limits of a domain of values ​​are included in this domain.

The expression "at least one" is equivalent to the expression "one or more".

Composition for crosslinking

As indicated above, the composition according to the invention comprises 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene and at least one second organic peroxide having a half-life temperature at one minute ranging from 130 to 1. 70 ° C, preferably ranging from 135 ° C to 165 ° C, and more preferably ranging from 142 ° C to 160 ° C.

The term “organic peroxide” is understood to mean an organic compound, that is to say one containing carbon, comprising at least one -OO- group (two oxygen atoms linked by a single covalent bond).

During the crosslinking process, the organic peroxide decomposes at its unstable 0-0 bond to free radicals. These free radicals allow the creation of crosslinking bonds.

1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene is an organic peroxide sold under the trade name Luperox®F or Luperox Vul-Cup®R by the company Arkema.

Preferably, 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene is present in the composition in a content ranging from 1 to 80% by weight, preferably in a content ranging from 30 to 70% by weight , more preferably in a content ranging from 40% to 70% by weight, relative to the total weight of the composition.

The second organic peroxide has a half-life temperature at one minute ranging from l 30 ° C to l 70 ° C, preferably ranging from l 35 ° C to l 65 ° C, and more preferably ranging from l 42 ° C to l. 60 ° C.

The term "half-life temperature at one minute" represents the temperature at which half of the organic peroxide has decomposed in a given time of one minute. Conventionally, the "one minute half-life temperature" is measured in n-decane or n-dodecane.

Preferably, the second organic peroxide is chosen from the group consisting of dialkyl peroxides, aryl peroxides, peroxyesters, monoperoxycarbonates, diacyl peroxides, diperoxyketals, hemipercetal peroxides, cyclic peroxides and mixtures thereof.

More preferably, the second organic peroxide is chosen from the group consisting of peroxyketals.

By way of example of peroxyesters, mention may be made of t-butyl peroxy-2-ethylhexanoate (Luperox® 26), tertbutylperoxyisobutyrate (Luperox® 80); t-butyl peroxyacetate (Luperox® 7), t-amyl peroxyacetate (Luperox® 555), t-butyl perbenzoate (Luperox P), t-amyl perbenzoate (Luperox TAP), tertbutylperoxy-3,5,5 -trimethylhexanoate (Luperox® 270) and tertamylperoxy-3,5,5-trimethylhexanoate (Luperox® 570).

By way of example of monoperoxycarbonates, mention may be made of OO-t-butyl l- (2-ethylhexyl) monoperoxycarbonate (Luperox® TBEC), OO-t-amyl l- (2-ethylhexyl) monoperoxycarbonate (Luperox® TAEC), OO-tert-amyl peroxyisopropyl monoperoxycarbonate (TAIC) and OO-tert-butyl peroxy isopropyl monoperoxycarbonate (TBIC).

By way of example of hemipercetal peroxide, mention may be made of 1,1-dimethylpropyll-methoxycyclohexylperoxide (Luperox® V10).

By way of example of diperoxyketals, mention may be made of 1,1-di- (t-butylperoxy) -3,3,5-trimethylcyclohexane (Luperox® 231), 1,1-di- (t-amylperoxy) -3 , 3,5-trimethylcyclohexane (Luperox® 531), 1-1-ditertbutylperoxycyclohexane (Luperox® 331), 2,2-di (tert-amylperoxy) butane (Luperox® 520), 2,2-di (tert -butylperoxy) butane (Luperox® 220) and their mixture.

Even more preferably, the second organic peroxide is 1,1 '-di- (t-butylperoxy) -3,3,5-trimethylcyclohexane sold under the trade name Luperox® 231.

Preferably, the second organic peroxide is present in the composition in a content ranging from 20 to 99% by weight, preferably in a content ranging from 30 to 70% by weight, preferably in a content ranging from 30 to 60% by weight. weight, relative to the total weight of the composition.

Advantageously, the weight ratio between the second organic peroxide, preferably chosen from the group consisting of peroxyketals, and 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene is greater than or equal to 0.25, preferably greater than 0.4.

Advantageously, the weight ratio between the second organic peroxide, preferably chosen from the group consisting of peroxyketals, and 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene is less than or equal to 2, preferably less than or equal to 1, 5.

Preferably, the weight ratio between the second organic peroxide, preferably chosen from the group consisting of peroxyketals and 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene varies in the range from 0.4 to 1 , 5.

Controlling the weight ratio within the ranges indicated above makes it possible to obtain an increase in the crosslinking speed of the polymers while ensuring good crosslinking density.

Preferably, the composition according to the invention further comprises at least one nitroxide.

The nitroxide is preferably chosen from the group consisting of 2,2,6,6-tetramethyl-1 -piperidinyloxy (generally sold under the trade name TEMPO), 4-hydroxy 2,2,6, 6-tetramethyl-1 -piperidinyloxy (generally sold under the trade name 4-hydroxy-TEMPO), 4-methoxy 2,2,6,6-tetramethyl-1 piperidinyloxy (generally sold under the trade name 4-methoxy-TEMPO), 4-oxo-2 , 2, 6, 6-tetramethyl- 1 -piperidinyloxy (commonly called 4-oxo-TEMPO), 2, 2, 5, 5 tetramethyl- 1 -pyrrolidinyloxy, bis (1 -oxyl- 2, 2, 6, 6 tetramethylpiperidin-4-yl) sebacate (marketed under the trademark CXA 5415 by the company Ciba Specialty Chemical), 1 -piperidinyloxy-4,4'- (1, l Odioxo 1, l 0-decanediyl) bis (oxy)) bis (2,2,6,6-tetramethyl-) (commonly known as di-TEMPO sebacate),

2,2,6,6-tetramethyl-4-hydroxypiperidin-1 -oxyl monophosphonate and 3 -carboxy-2,2,5,5-tetramethylpirrolidinyloxy (commonly referred to as 3-carboxyproxyl).

Preferably, the nitroxide is 4-hydroxy 2, 2,6,6-tetramethyl-1 -piperidinyloxy (4-hydroxy-TEMPO) or 1 -piperidinyloxy-4,4'- (1, 10-dioxo l, 10-decanediyl) bis (oxy)) bis (2,2,6,6-tetramethyl-) (di-TEMPO sebacate).

More preferably still, the nitroxide is 4-hydroxy

2,2, 6, 6 - tetramethyl-1 -piperidinyloxy (4-hydroxy-TEMPO).

Advantageously, the weight ratio between the second organic peroxide and the nitroxide is greater than or equal to 1, preferably varies in the range going from 1 to 50, more preferably varies in the range going from 5 to 20, and even more preferably in a range ranging from 8 to 13.

According to a preferred embodiment, the composition according to the invention comprises 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene, a second organic peroxide chosen from the group consisting of peroxyketals and at least one nitroxide corresponding to 4-hydroxy 2, 2, 6, 6-tetramethyl-1 -piperidinyloxy (4-hydroxy-TEMPO).

According to this embodiment, the second organic peroxide is preferably 1,1'-di- (t-butylperoxy) -3, 3, 5 -trimethylcyclohexane.

The composition thus defined corresponds to a composition intended for the crosslinking of one or more crosslinkable polymers.

In particular, the composition thus defined corresponds to a mixture comprising 1, 3 - 1, 4-bis (tert-butylperoxy isopropyl) benzene and at least one second organic peroxide having a half-life temperature at one minute ranging from 130 to l 70 ° C, preferably ranging from l 35 ° C to l 65 ° C, and more preferably ranging from l 42 ° C to l 60 ° C.

Thus the mixture has all the characteristics of the composition intended for crosslinking.

Preferably, the mixture further comprises at least one nitroxide.

Crosslinkable composition

The present invention also relates to a composition according to the invention comprising a composition as defined above and in addition one or more crosslinkable polymers.

The composition thus defined corresponds to a crosslinkable composition.

In particular, the composition thus defined comprises the mixture defined above and in addition one or more crosslinkable polymers.

More preferably, the crosslinkable polymer (s) is (are) chosen from the group consisting of thermoplastic polymers, elastomeric polymers and mixtures thereof.

Preferably, the crosslinkable polymer (s) is or are polyolefins.

For the purposes of the present invention, the term “polyolefin” is understood to mean a polymer derived from an olefin, for example ethylene, propylene, butene, hexene, and the like.

For the purposes of the present invention, the term “derivative of” means that the units of the main chain of the polymer and / or of the adjacent chains (or pendant chains) of the polymer result from the polymerization or the copolymerization of the monomers from which the polymer is made.

For the purposes of the present invention, the term “elastomeric polyolefin” (POE) means an elastomeric polymer derived from an olefin, for example ethylene, propylene, butene, hexene, and the like.

For the purposes of the present invention, the term “elastomer” is understood to mean a polymer capable of undergoing uniaxial deformation at room temperature, preferably of at least 20% for a period of fifteen minutes, and of returning to its initial shape, preferably with a residual strain of less than 5% compared to its initial shape, when this stress is no longer exerted.

The thermoplastic and / or elastomeric polymers used in the composition according to the invention can be defined as

natural or synthetic polymers which have a thermoplastic and / or elastomeric character and which can be crosslinked (cured) under the action of a crosslinking agent. In Rubber World, "Elastomer Cros slinking with Diperoxyketals", October 1983, pages 26-32, and in Rubber and Plastic News, "Organic Peroxides for

Rubber Cros slinking ", September 29, 1980, pages 46-50, describes the crosslinking action and crosslinkable polymers. Polyolefins which are suitable for the present invention are described in Modern Plastics Encyclopedia 89, pages 63-67, 74-75 .

By way of example of polymers and / or elastomers, mention may be made of linear low density polyethylene, low density polyethylene (LDPE), high density polyethylene (HDPE), chlorinated polyethylene, ethylene terpolymers. propylene-diene (EPDM), ethylene-vinyl acetate copolymers (EVA), ethylene propylene copolymers,), ethylene and butene copolymers, silicone rubber, natural rubber (NR), polyisoprene (IR), polybutadiene (BR), acrylonitrile-butadiene copolymers (NBR), styrene-butadiene copolymers (SBR), chlorosulfonated polyethylene or fluoroelastomers, copolymers of ethylene and (meth) acrylate , copolymers of ethylene and of glycidyl methacrylate and mixtures thereof.

According to one embodiment, the crosslinkable polymers lack chlorine functional groups and carboxylic acid functional groups, preferably free of halogen functional groups and carboxylic acid functional groups.

Preferably, the crosslinkable polymers are chosen from the group consisting of copolymers of ethylene and of vinyl acetate (EVA), of copolymers of ethylene and of butene, of polyethylene, of rubber and their mixtures.

Preferably, the crosslinkable polymers are chosen from the group consisting of:

- copolymers of ethylene and vinyl acetate (EVA),

- a mixture comprising the copolymers of ethylene and vinyl acetate (EVA) and polyethylene with rubber,

- a mixture comprising the copolymers of ethylene and vinyl acetate (EVA) and the copolymers of ethylene and butene.

More preferably, the crosslinkable polymers are chosen from the group consisting of polyethylene, copolymers of ethylene and vinyl acetate (EVA) and mixtures thereof.

More preferably, the crosslinkable polymers are copolymers of ethylene and vinyl acetate (EVA).

The amount of vinyl acetate can vary from 0.1 to 50% by weight, in particular from 5 to 50% by weight, more particularly from 10 to 50%, in particular from 15 to 45% by weight relative to the total weight. of the copolymer.

The copolymers of ethylene and vinyl acetate (EVA) can be modified by methods known in the art, including modification with unsaturated carboxylic acids and their derivatives, such as maleic acid or maleic anhydride.

Preferably, the copolymers of ethylene and of vinyl acetate exhibit a melt flow index (Melt Flow Index) ranging from 0.1 to 60 g / 10 minutes.

The melt flow index (MFI) of ethylene vinyl acetate copolymers is measured according to the methods commonly used to characterize thermoplastic materials to obtain information on extrudability as well as pos material shaping possibilities such as those described in standard ASTM D 1238, standard NF T5 1-016 or standard ISO 1 133.

The MFI values ​​referred to are determined according to ASTM D 1238 at a temperature of 190 ° C under a load of 2.16 kg (units expressed in g / 10 minutes).

Polyethylene can include homopolymers and copolymers such as linear low density polyethylene, low density polyethylene (LDPE), high density polyethylene (HDPE), chlorinated polyethylene, ethylene propylene diene terpolymers ( EPDM).

According to one embodiment, the crosslinkable polymers can be chosen from the group consisting of copolymers of ethylene and vinyl acetate or a mixture containing polyethylene, rubber or an ethylene / butene copolymer.

The mixture of organic peroxides as defined above preferably represents between 0.5 to 5 parts and advantageously between 1 and 3 parts per 100 parts by weight of polymer.

The composition according to the invention can also comprise one or more reinforcing fillers chosen from the group consisting of silica, calcium carbonate, kaolin and their mixtures, preferably kaolin or a mixture of calcium carbonate and silica, more preferably kaolin.

The reinforcing fillers can be present in the composition in a content ranging from 1 to 60%, in particular from 10 to 50% by weight, relative to the total weight of the composition.

The composition according to the invention can also comprise at least one organic peroxide different from the mixture of organic peroxides defined above.

Preferably, the composition is free from an organic peroxide different from the mixture of organic peroxides defined above.

use

In accordance with the present invention, the composition as described above is used for the crosslinking of at least one crosslinkable polymer as defined above, preferably chosen from the group consisting of polyethylene, copolymers of ethylene and of acetate. vinyl (EVA) and mixtures thereof.

Thus, the present invention relates to the use of a composition as defined above for the crosslinking of a crosslinkable polymer (s) as defined above.

In other words, the present invention relates in particular to the use of the mixture as defined above for the crosslinking of a crosslinkable polymer (s) as defined above.

More preferably, the crosslinkable polymers are chosen from the group consisting of copolymers of ethylene and vinyl acetate (EVA).

The term “crosslinking” is understood to mean the formation of a three-dimensional network by the creation of bonds between the molecules of crosslinkable polymers. The use according to the invention is therefore preferably carried out in the context of a crosslinking process, during which the crosslinking takes place.

In particular, the composition according to the invention is used to increase the crosslinking speed of at least one crosslinkable polymer as defined above, preferably a crosslinkable polymer chosen from the group consisting of copolymers of ethylene and of acetate. vinyl (EVA).

Furthermore, the composition according to the invention makes it possible to lead to a good crosslinking density.

The crosslinking density is related to the number of bridge bonds per unit constituting the polymer. It can be determined by a rheometric measurement, for example using a rheometer. For example, it can be determined according to standard ASTM D 5289A using a rheometer of the RPA 2000 or MDR type, at a temperature of l 60 ° C, with an oscillation amplitude of 0.5 °, a frequency of scillation of 1.667 Hz, from discs of the sample to be tested of 3.5 cm in diameter and 4.8 cm 3 in volume.

Depending on the crosslinking systems, adjusting the temperature to a different value may be appropriate.

The measurement is carried out during the crosslinking of the test sample which is initiated at the same time as the measurement, by placing the sample in a preheated test cavity. It makes it possible to obtain a rheometric curve representing the change in the viscoelastic torque resulting from the deformation imposed on the composition to be tested as a function of time. In the context of the present application, the crosslinking density is defined directly by the difference between the maximum torque MH and the minimum torque ML, and is expressed in dN m.

The minimum torque ML corresponds to the minimum value of the torque measured during the crosslinking (at the start of the test).

The maximum torque MH corresponds to the torque value at the end of the measurement. Preferably, the duration of the test is adjusted so that the crosslinking is essentially complete at the end of this period, the torque then reaching a plateau. A suitable time for the test is for example 60 minutes. However, this duration can be adapted as a function of the actual duration provided for the manufacture of a given part, from the crosslinkable polymer composition, and at a given temperature.

The crosslinking speed is evaluated by the value T90 corresponding to the time necessary to reach 90% of the maximum torque, which is obtained using the rheometric measurement described above. The lower the T90, the faster the crosslinking speed.

According to a particular embodiment, the crosslinking speed obtained with the composition according to the invention comprising the mixture of organic peroxides as described above is greater than the crosslinking speed which is obtained under the same conditions with a composition comprising the 1, 3- 1, 4-bis (tert-butylperoxy isopropyljbenzene as crosslinking agent.

Preferably, the crosslinking speed during the crosslinking process is greater than 1, 1 times, 1, 2 times, 1, 3, 1, 4 times or 1.5 times the crosslinking speed which is obtained in the same. conditions with a composition comprising 1, 3- 1, 4-bis (tert-butylperoxy isopropyljbenzene as a crosslinking agent.

By "same conditions with a composition comprising the

1.3 - 1, 4-bis (tert-butylperoxy isopropyl) benzene as crosslinking agent ”means a crosslinking carried out with the same parameters (the same time, the same temperature, etc.) and from the same composition, except for the fact that it comprises 1, 3- 1.4-bis (tert-butylperoxy isopropyl) benzene as crosslinking agent instead of the mixture of organic peroxides as defined above.

Thus, the composition according to the invention makes it possible in particular to increase the crosslinking speed relative to a composition comprising 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene as organic peroxide used as agent for crosslinking.

In particular, the invention relates to the use of a composition as defined above for the manufacture of all or part of an article, in particular a soft article. Preferably, said article belongs to the industry of safe shoes and floor mats, more preferably said article belongs to the industry of safe shoes, and more preferably is a sole of safe shoes.

Composition in the form of soft

As indicated above, the invention relates to a composition in soft form obtained from the crosslinking of the composition according to the invention as defined above, further comprising one or more crosslinkable polymers, preferably chosen from the group consisting of polyethylene, copolymers of ethylene and vinyl acetate (EVA) and mixtures thereof.

More preferably, the crosslinkable polymers are chosen from the group consisting of copolymers of ethylene and vinyl acetate (EVA).

Thus the composition in soft form corresponds to the crosslinked composition according to the invention.

For the purposes of the present invention, the term “composition in the form of a soft” is understood to mean that the composition is a soft or is capable of generating a soft.

Preferably, the composition in the form of a foam comprises at least one copolymer of ethylene and crosslinked vinyl acetate.

In other words, in the case of this preferred embodiment, the composition is a soft comprising at least one copolymer of ethylene and crosslinked vinyl acetate.

Preferably, the copolymer of ethylene and vinyl acetate is present in a content ranging from 70 to 99% by weight, particularly in a content ranging from 72 to 98% by weight, and even more preferably in a content ranging from 75 to 95% by weight, relative to the total weight of the composition.

The composition in soft form can comprise at least one organic or inorganic blowing agent.

Preferably, the organic swelling agent can be chosen from the group consisting of azodicarbonamide, G azobisisobutyronitrile, diazoaminobenzene, NN-dimethyl-N, N-dinitrosoterephthalamide, N, N-dinitrosopentamethylene-tetramine, P -toluene sulfonyl hydrazide and p. p'-oxybis (benzenesulfonyl hydrazide), 4,4'-oxybis benzene sulfonyl hydrazide; p-toluene sulfonyl semicarbizide, barium azodicarboxylate, butylamine nitrile, ammonium trihydrazino triazine bicarbonate, sodium bicarbonate, and mixtures thereof.

Preferably, the inorganic blowing agent can be selected from the group consisting of ammonium bicarbonate, sodium bicarbonate and mixtures thereof.

Crosslinking process

The present invention also relates to a process for crosslinking at least one crosslinkable polymer comprising a step of crosslinking at least one crosslinkable polymer as defined above, in the presence of the composition for crosslinking as defined above.

In other words, the step of crosslinking at least one crosslinkable polymer is carried out by bringing said crosslinkable polymer into contact with the composition for crosslinking as defined above.

More preferably, the crosslinkable polymers are chosen from the group consisting of copolymers of ethylene and vinyl acetate (EVA).

Preferably, the crosslinking temperature is between 140 ° C and 210 ° C, preferably between 150 and 190 ° C, and more preferably between 165 and 190 ° C.

Preferably, the crosslinking step takes place for a period ranging from 2 to 10 minutes, preferably for a period ranging from 3 to 8 minutes.

Thus, the composition according to the invention makes it possible to implement a process for crosslinking crosslinkable polymers at temperatures which can range up to 190 ° C. without degrading them or clogging the mold in which the crosslinking takes place.

Manufacturing process of all or part of an article

The present invention also relates to a process for manufacturing all or part of an article, preferably an article belonging to the shoe industry, comprising a step a) of crosslinking the composition as defined above.

Preferably, the manufacturing process according to the invention is a molding process, in particular injection molding.

Preferably, the manufacturing process according to the invention comprises a step b) of injection molding of the composition obtained following the crosslinking.

In particular, the manufacturing process according to the invention makes it possible to lead to a composition in the form of soft which is injected by molding in order to form all or part of an article, preferably an article belonging to the footwear industry. safe.

Preferably, the method according to the invention also comprises the shaping of the composition in the form of soft to result in all or part of the article.

Item

The invention also relates to an article, all or part of which is obtained by the method described above.

Preferably, the article is a soft article.

Preferably, the article belongs to the groundsheet or safe shoe industry, preferably safe shoe, more preferably the article is a shoe sole.

Even more preferably, the sole is chosen from the group consisting of an insole, a midsole or an outer sole.

Example:

The following example serves to illustrate the invention without, however, being limiting in nature.

1. Compositions tested

The following compositions were prepared from the ingredients indicated in Table 1 below. The amounts are given in part per hundred parts (phr) of ethylene vinyl acetate (EVA) copolymer.

Luperox® L = 1, 3- 1, 4-bis (tert-butylperoxy isopropyl) benzene

Luperox® 23 1 = 1,1-di- (t-butylperoxy) -3, 3, 5 -trimethylcyclohexane OH-tempo = 4-hydroxy 2,2,6,6-tetramethyl-1 -piperidinyloxy

The compositions were thus prepared in a Haake internal mixer at a temperature of 35 ° C for a period of 15 minutes, using a stirring speed of 50 rpm.

The polymer mixture is then passed through an open mill set at a temperature of 25 ° C to produce sheets approximately 2mm thick.

Samples of about 2 to 3 grams of the above compositions are placed in a plate on a moving die rheometer (MDR) supplied by GOTECH, which is capable of measuring the curing properties of the samples and includes software for analyzing. the results . Each of the samples is placed in a temperature-controlled cavity between two dies, the lower of which oscillates so as to apply cyclic stress or strain to the sample while the upper die is connected to a torque sensor to measure the response. torque of the sample to deformation.

Stiffness is recorded continuously as a function of time. The stiffness of the sample increases as vulcanization occurs.

This device is capable of providing, among others, calculated values ​​of ML (minimum torque), MH (maximum torque), and T90 (time to obtain 90% of the total crosslink density) as defined by international standards (ASTM D5289 and IS O 6502).

The crosslinking density is defined directly by the difference between the maximum torque MH and the minimum torque ML and is expressed in dN .m.

The MDR is operated at a temperature of 180 ° C and 185 ° C with an oscillation amplitude (degree of strain) of 0.5 ° applied to the sample for 30 min.

2. Results

The crosslinking density and the crosslinking speed of the different compositions were thus evaluated. The results are shown in Table 2 below:

In order to minimize, or even eliminate, the problems associated with the fouling of manufacturing molds, it is important to increase the crosslinking speed of the polymer while maintaining the same crosslinking density (MH-ML).

Compositions A, B and C according to the invention make it possible to reduce the crosslinking time (T90) compared with comparative composition D containing the Luperox® F product alone while leading to a similar crosslinking density.

In other words, the mixture of organic peroxides according to the invention makes it possible to induce faster crosslinking during crosslinking (T90) while maintaining a similar crosslinking density (MH-ML) compared to a composition containing Luperox ® F as a crosslinking agent.

CLAIMS

1. Composition comprising at least one mixture of organic peroxides containing 1,3-1, 4-bis (tert-butylperoxy isopropyl) benzene and at least one second organic peroxide having a half-life temperature at one minute ranging from 130 to 170 ° C, preferably ranging from 135 to 165 ° C, and more preferably ranging from 142 ° C to 160 ° C.

2. Composition according to claim 1, characterized in that the second organic peroxide is chosen from the group consisting of dialkyl peroxides, aryl peroxides, peroxyesters, monoperoxycarbonates, diacyl peroxides, diperoxyketals, peroxides. hemipercetals, cyclic peroxides, and mixtures thereof, and preferably diperoxyketals.

3. Composition according to claim 1 or 2, characterized in that the second organic peroxide is chosen from the group consisting of l, 1'-di- (t-butylperoxy) -3,3,5-trimethylcyclohexane,

1.1-di- (t-amylperoxy) -3,3,5-trimethylcyclohexane, 1-1-ditertbutylperoxycyclohexane, 2,2-di (tert-amylperoxy) butane,

2.2-di (tert-butylperoxy) butane and mixtures thereof, preferably is I, G -di- (t-butylperoxy) -3,3,5-trimethylcyclohexane.

4. Composition according to any one of the preceding claims, characterized in that the weight ratio between the second organic peroxide and 1,3-1, 4-bis (tert-butylperoxy isopropyl) benzene is greater than or equal to 0.25 , preferably greater than 0.4, and even more preferably varies in the range from 0.4 to 1.5.

5. Composition according to any one of the preceding claims, characterized in that the weight ratio between the second organic peroxide and 1,3-1, 4-bis (tert-butylperoxy isopropyl) benzene is less than or equal to 2, from preferably less than or equal to 1.5.

6. Composition according to any one of the preceding claims, characterized in that it further comprises at least one nitroxide.

7. Composition according to claim 6, characterized in that the nitroxide is chosen from the group consisting of 2, 2,6,6-tetramethyl-1 -piperidinyloxy, 4-hydroxy 2,2,6, 6-tetramethyl- 1 -piperidinyloxy, 4-methoxy 2, 2, 6, 6-tetramethyl- lpiperidinyloxy, 4-oxo-2, 2, 6, 6-tetramethyl- 1 - piperidinyloxy, 2, 2, 5, 5 tetramethyl- 1 -pyrrolidinyloxy, bis (1 -oxyl- 2, 2, 6, 6 tetramethylpiperidin-4-yl) sebacate, l -piperidinyloxy-4,4'- (l, l 0dioxo l, l 0-decanediyl) bis (oxy )) bis (2,2,6,6-tetramethyl-), 2, 2, 6, 6 -tetramethyl -4- hydroxypiperidine- 1 -oxyl monophosphonate and 3-carboxy-2, 2,5, 5-tetramethylpirrolidinyloxy .

8. Composition according to claim 5 or 6, characterized in that the nitroxide is 4-hydroxy 2, 2, 6, 6-tetramethyl-1 -piperidinyloxy (OH-Tempo) or l -piperidinyloxy-4,4'- (1,1 0-dioxo 1, 10-dec anediyl) bis (oxy)) bis (2,2, 6, 6-tetramethyl-), preferably is 4-hydroxy 2, 2, 6, 6-tetramethyl- 1 -piperidinyloxy (OH-Tempo).

9. Composition according to any one of claims 5 to 7, characterized in that the weight ratio between the second organic peroxide and the nitroxide is greater than or equal to 1, preferably varies in the range from 1 to 50 and more preferably in the range from 5 to 20, and more preferably in a range from 8 to 13.

10. Composition according to any one of the preceding claims, characterized in that it further comprises one or more crosslinkable polymers.

1 1. Composition according to Claim 10, characterized in that the crosslinkable polymer (s) is (are) chosen from the group consisting of thermoplastic polymers, elastomeric polymers and mixtures thereof.

12. Composition according to claim 10 or 1 1, characterized in that the crosslinkable polymer (s) is or are chosen from the group consisting of linear low density polyethylene,

low density polyethylene (LDPE), high density polyethylene (HDPE), chlorinated polyethylene, ethylene propylene diene terpolymers (EPDM), ethylene vinyl acetate (EVA) copolymers, copolymers of ethylene propylene, silicone rubber, natural rubber (NR), polyisoprene (IR), polybutadiene (BR), acrylonitrilebutadiene copolymers (NBR), styrene-butadiene copolymers (SBR), chlorosulfonated polyethylene or fluoroelastomers, ethylene and methyl (meth) acrylate copolymers, ethylene and glycidyl methacrylate copolymers, and mixtures thereof.

13. Composition according to any one of claims 10 to 12, characterized in that the crosslinkable polymer (s) is or are chosen from the group consisting of polyethylene, copolymers of ethylene and of vinyl acetate ( EVA) and mixtures thereof, preferably copolymers of ethylene and vinyl acetate (EVA).

14. Composition according to any one of the preceding claims, characterized in that it further comprises one or more reinforcing fillers chosen from the group consisting of silica, calcium carbonate, kaolin and their mixtures, preferably kaolin. or a mixture of calcium carbonate and silica, more preferably kaolin.

15. Use of a composition as defined according to any one of claims 1 to 9 and 14 for the crosslinking of one or more crosslinkable polymers as defined (s) according to any one of claims 10 to 13.

16. Use according to claim 15, for increasing the crosslinking rate of one or more crosslinkable polymers as defined (s) according to any one of claims 10 to 13.

17. A method of manufacturing all or part of an article comprising a step of crosslinking a composition as defined according to any one of claims 10 to 13.

18. Use of a composition as defined according to any one of claims 10 to 14 for the manufacture of all or part of an article, preferably a soft article.

19. An article or part of which is obtained by means of the process as defined in claim 17.