MXPA06007398A - Crosslinkable, expandable polymeric compositions - Google Patents

Abstract

The present invention is a crosslinkable, expandable polymeric composition comprising a free-radical crosslinkable polymer, a free-radical inducing species, a crosslinking-profile modifier, and a blowing agent. Preferably, the free-radical inducing species is a low temperature free-radical inducing species.

Description

METHODS OF THE INVENTION The present invention relates to expandable polymeric compositions that undergo cross-linking reaction by free radicals. DESCRIPTION OF THE PREVIOUS TECHNIQUE A number of expandable polymers can undergo reactions by free radicals. Some of these reactions are beneficial, such as cross-linking, at the desired cross-linking temperature, while others are harmful, such as premature cross-linking or degradation. There is a need to promote beneficial cross-linking reactions while minimizing the impact of harmful reactions. In general, the polymeric crosslinkable, expandable free radical polymer compositions are processed for re-binding purposes, the polymers and other ingredients are first melt processed and then subjected to a nominal cross-linking profile. The melt processing step occurs at a nominal melt processing temperature. The nominal cross-linking temperature profile has three temperature-related portions: (1) a portion of molding temperature; (2) a transition temperature portion; and (3) a portion of crosslinking temperature. Depending on the process, the molding temperature portion can be replaced by an extrusion temperature portion. The nominal melt processing temperature and the nominal cross-linking profile are directly related to the polymer and the free radical-inducing species (or the cross-linking agent) selected. Figure 1 shows a typical nominal cross-linking profile. To ensure that only the desired crosslinking reaction occurs, the melt processing temperature and the molding temperature are kept low, to avoid premature crosslinking. After the desired level of fusion processing has occurred, the expandable crosslinkable polymer composition is transferred to the mold or to the extruder. At the molding temperature, it is desirable to allow the expandable crosslinkable polymer composition to fill the mold and then further heat the composition without premature crosslinking. Additionally, it is desirable that the expandable crosslinkable polymer composition be uniformly heated before the crosslinking begins. From the molding temperature portion, the expandable crosslinkable polymer composition goes through a transition temperature portion until it reaches the nominal crosslinking temperature. If the free radical species is an organic peroxide, the nominal crosslinking temperature directly depends on the decomposition temperature of the peroxide. Accordingly, the temperature range of the transition temperature portion is determined by the nominal molding temperature at the lower end of temperature and by the nominal cross-linking temperature at the upper temperature end.

It is important to note that in some applications, fusion processing can occur in a single stage or in more than one stage. For example and as a single step, the components can be added separately to the hopper or to an extruder and are melt blended at a suitable melt processing temperature. An example of multi-stage fusion processing may include a first stage wherein the components are mixed at a temperature above the melting temperature of the polymer, but below the nominal melting temperature of the free radical-inducing species and a second step wherein the mixed composition is transferred to an extruder for further processing. As used herein, the term "melt processing temperature" is defined as a single-stage or multi-stage fusion processing technique. Because the rate of crosslinking increases gradually with temperature, the temperature difference (i.e., the transition temperature portion) between the melting temperature portion (i.e., the temperature of the initial molten polymer after its introduction into the mold) and the crosslinking temperature portion (ie to say, the temperature at which it is preferred to crosslink the polymer) can be very large, typically greater than about 60 grams Celsius for injection molded articles. For compression molded articles, the transition temperature range may exceed 140 degrees Celsius. While the crosslinking temperature changes according to the chosen free radical-inducing species, the corresponding temperature range of the transition temperature portion is generally unaffected. Therefore, a change in the crosslinking temperature (or of the free radical inducing species) typically requires a corresponding change in the molding temperature. Similarly, there is typically a corresponding change in the melt processing temperature. In addition to the crosslinking profile, other factors affect the uniformity of the crosslinking, the uniformity of the cell size and the cycle time for the expandable crosslinkable polymeric compositions to be transformed into articles of manufacture. These factors include the kinetics of the blowing agent and the geometry of the article (e.g. the general thickness and the thickness distribution). Understandably, the complexity of the geometry contributes significantly to the quality and properties of the resulting article. In accordance with the foregoing, there is a need for an expandable crosslinkable polymer composition, which produces uniformly cross-linked articles of manufacture. Also, there is a need for the resulting article of manufacture to have a uniform cell size. There is a need for an expandable crosslinkable polymer composition that is processable within suitable time cycles. Significantly, there is a need for an expandable crosslinkable polymer composition, which produces a uniformly crosslinked article of manufacture, with a uniform cell size, in a suitable cycle time, even when the article of manufacture has a complex geometry. Additionally, there is a need for an expandable crosslinkable polymer composition using a low temperature free radical inducing species as a replacement for the conventional free radical inducing species. Specifically, the low temperature free radical inducing species should have lower free radical initiation temperatures than the free radical inducing species conventionally used in the expandable crosslinkable polymer composition. More particularly, when the low temperature free radical producing species is an organic peroxide, it should have a lower decomposition temperature than the organic peroxides conventionally used in the expandable crosslinkable polymer composition. Additionally, it is desirable that the expandable crosslinkable polymer be useful in an improved process having higher melt processing temperatures than those conventionally used. In addition, the process should allow the expandable crosslinkable polymer to be molded at higher temperatures than conventionally used. All of these needs will be met without exceeding the level of premature crosslinking that is obtained with conventional expandable crosslinkable polymeric compositions and employing conventional processes for the preparation of articles of manufacture. It is also desirable not to exceed the level of premature crosslinking, nor to further minimize the level of premature crosslinking while operating at higher processing temperatures or under more rapid processing conditions. There is also a need for the temperature range of the transition temperature portion, is significantly smaller than that provided in conventional processes, also without adversely affecting premature crosslinking. A smaller temperature range will produce a faster process, because the transition heating of the expandable crosslinkable polymer composition is minimized. It is also desirable that the transition temperature portion increase as abruptly as possible and present a slope that tends to infinity. In addition, it is desirable that the crosslinking temperature portion have a slope as close to zero as possible. Each of these necessary improvements must be achieved without significantly modifying conventional fusion processing equipment or conventional crosslinking equipment. BRIEF DESCRIPTION OF THE INVENTION The present invention relates to an expandable crosslinkable polymer composition comprising a free radical crosslinkable polymer, a free radical inducing species. a cross-linking profile modifier and a blowing agent. Preferably, the free radical-inducing species is a low-temperature free radical-inducing species.

Additionally, the present invention includes an improved process for preparing an expandable crosslinkable article of manufacture. Examples of suitable processes include injection molding, compression molding, extrusion and thermoforming processes. An expandable crosslinkable manufacturing article manufactured from the improved process composition is also considered as part of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a nominal cross-linking temperature profile for a combination of polymeric composition crosslinkable by free radicals and a free radical-inducing species. Figure 2 shows a cross-sectional view of a shoe sole made from an expandable crosslinkable polymer composition, containing a short half-life free radical inducing species, representing the present invention. DESCRIPTION OF THE INVENTION The term "conventional free radical-inducing species" as used herein, means, in the absence of a cross-linking profile modifier, a free radical-inducing species that is selected to minimize premature cross-linking and facilitate reasonable times of crosslinking cycles.

In addition to other factors, when the conventional free radical species is an organic peroxide, the selection is based on the nominal decomposition temperature of the peroxide and its half-life at various processing / cross-linking temperatures.

The term "nominal decomposition temperature" as used herein with respect to organic peroxides, means the temperature at which 90% of the peroxide decomposes in a period of 12 minutes. The term "fusion induction time" as used herein, means the amount of time necessary for the torque value of the polymer composition, measured with a moving die rheometer (RDM), to be increased by 0.04. pounds-inch above the minimum torque, at a melt processing temperature of the polymer composition, at 100 cycles per minute and an arc of 0.5 degrees. At the nominal melt processing temperature, the melting induction time is called the nominal melting induction time (to.0 n-fUsióp) or the time to start an increase in torque (t¡n¡cio) - If the Fusion induction time is a longer period at the nominal melt processing temperature, the period of time is referred to as "improved melting induction time". Also, if the period of time equivalent to the nominal fusion induction time is achievable at a higher melt processing temperature, the period of time is referred to as the "enhanced fusion induction period". The term "mold induction time" as used herein, means the time required for the torque value of a polymer composition, measured with a moving die rheometer (RDM), to be increased by 0.04 pounds. inch above the minimum torque, at a molded temperature of the polymer composition, at 1 00 cycles per minute and an arc of 0.5 degrees. At the nominal molding temperature, the mold induction time is called the nominal mold induction time (t0.o4n-moide). If the mold induction time is a longer period at the nominal molding temperature, the period of time is called "improved mold induction time". Also, if a period of time equivalent to the mold induction time is achieved at a higher molding temperature, the period of time is called "improved mold induction time". The present invention is an expandable crosslinkable polymer composition comprising (a) a free radical crosslinkable polymer; (b) a low temperature free radical inducing species; (c) a cross-linking profile modifier and (d) a blowing agent. In the absence of the crosslinking temperature profile modifier, a combination of the free radical crosslinkable polymer and a conventional free radical inducing species, has a nominal melt processing temperature and achieves a nominal melt induction time at the nominal melt processing temperature. It is noted that the melt processing temperature can be raised by increasing the cutting energy when using extrusion equipment. Achieving desirable fusion induction times when the cutting energy contributes to the melt processing temperature is within the scope of the present invention. The combination of the free-radical crosslinkable polymer and the conventional free radical-inducing species also has a nominal cross-linking profile comprising (a) a nominal molding temperature portion, (b) a transition temperature portion, and (c) ) a portion of nominal cross-linking temperature. The combination achieves a nominal molding induction time at the nominal molding temperature. When nominal processing conditions are used, the combination is processed at its nominal processing speed. A variety of polymers crosslinkable by free radicals is useful in the present invention. In addition, many polymers that have hitherto not been suitable for free radical crosslinking are useful in the present invention. Notably, polymers having a high melting temperature are now suitable for free radical crosslinking. In particular, the present invention is useful with free radical crosslinking polymers having a melting temperature equal to or greater than about 130 degrees Celsius or a short nominal induction time. For example, the present invention is particularly useful for combinations of a free radical crosslinkable polymer and a free radical inducing species having a nominal induction time of less than about 5 minutes or even less than about one minute. Preferably, the free radical crosslinkable polymer is based on hydrocarbons. Suitable hydrocarbon-based polymers include ethylene / propylene / diene monomers, ethylene / propylene gums, ethylene / alpha-olefin copolymers, ethylene homopolymers, propylene homopolymers, ethylene / unsaturated ester copolymers, ethylene / styrene interpolymers, halogenated polyethylenes, copolymers of propylene, rubber or natural rubber, styrene / butadiene rubber, styrene / butadiene / styrene block copolymers, styrene / ethylene / butadiene / styrene copolymers, polybutadiene rubber, butyl rubber, chloroprene rubber, chlorosulfonated polyethylene gum, ethylene / diene copolymers and nitrile rubber, and mixtures thereof. With respect to the appropriate ethylene polymers, free-radical crosslinkable polymers are generally classified into four main groups: (1) highly branched; (2) heterogeneous linear chain; (3) homogeneously branched linear; and (4) substantially linear homogeneously branched. These polymers can be prepared with Ziegler-Natta catalysts, single-site metallocene or vanadium-based catalysts, or single-site catalysts of restricted geometry. Highly branched ethylene polymers include low density polyethylene (LDPE). These polymers can be prepared with a free radical initiator at high temperatures and high pressure. Alternatively, they can be prepared with a coordination catalyst at high temperatures and relatively low pressures. These polymers have a density between about 0.910 and about 0.940 grams per cubic centimeter, measured according to ASTM D-792. Straight chain heterogeneous ethylene polymers include linear chain low density polyethylene (LDPE), ultra low density polyethylene (BD PEU), very low density polyethylene (LDPE) and high density polyethylene (HDPE). The straight chain low density ethylene polymers have a density between about 0.850 and about 0.940 grams per cubic centimeter and a melt index between about 0.01 and about 100 grams per 10 minutes, measured according to ASTM 1238, condition I. Preferably, the melt index is between about 0.1 and about 50 grams per 10 minutes. Also, preferably the PEBDL is an interpolymer of ethylene and one or more alpha-olefins having from 3 to 1 8 carbon atoms, preferably from 3 to 8 carbon atoms. Preferred comonomers include 1-butene, 4-methyl-1-pentene, 1-hexene and 1-ketene. The ultra low density polyethylene and the very low density polyethylene are known interchangeably. These polymers have a density between about 0.870 and about 0.910 grams per cubic centimeter. High density ethylene polymers are generally homopolymers with a density between about 0.941 and about 0.965 grams per cubic centimeter. Homogeneously branched linear ethylene polymers include homogeneous P EB DL. The uniformly branched / homogeneous polymers are those polymers in which the comonomer is randomly distributed in a given interpolymer molecule and where the interpolymer molecules have a similar ethylene / comonomer ratio in that interpolymer. Homogeneously branched substantially linear ethylene polymers include (a) olefin homopolymers of 2 to 20 carbon atoms, such as ethylene, propylene and 4-methyl-1-pentene, (b) interpolymers of ethylene with at least one alpha- olefin of 3 to 20 carbon atoms, an acetylenically unsaturated monomer of 2 to 20 carbon atoms, a diolefin of 4 to 18 carbon atoms or combinations of the monomers, and (c) interpolymers of ethylene with at least one of alpha -olefins of 3 to 20 carbon atoms, diolefins or acetylenically unsaturated monomers, in combination with other unsaturated monomers. These polymers generally have a density of between about 0.850 and about 0.970 grams per cubic centimeter. Preferably, the density is between about 0.85 and about 0.955 grams per cubic centimeter, more preferably between about 0.850 and 0.920 grams per cubic centimeter. The ethylene / styrene interpolymers useful in the present invention include substantially random interpolymers prepared by the polymerization of an olefin monomer (eg, ethylene, propylene or alpha-olefin monomer) with an aromatic vinylidene monomer, a vinylidene monomer hindered aliphatic or a cycloaliphatic vinylidene monomer. Suitable olefin monomers contain from 2 to 20, preferably from 2 to 12 and more preferably from 2 to 8 carbon atoms. Preferred monomers include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene. Most preferred are ethylene and a combination of ethylene with propylene or alpha-olefins of 4 to 8 carbon atoms. Optionally, the polymerization components of ethylene / styrene interpolymers may also include ethylenically unsaturated monomers, such as rigid ring olefins. Examples of rigid ring olefins include norbornene and norbornenes substituted with alkyl radicals of 1 to 10 carbon atoms or aryl of 6 to 10 carbon atoms. The ethylene / unsaturated ester copolymers useful in the present invention can be prepared by conventional high pressure techniques. The unsaturated esters may be alkyl acrylates, alkyl methacrylates or vinyl carboxylates. The alkyl groups may have from 1 to 8 carbon atoms and preferably from 1 to 4 carbon atoms. The carboxylate groups can have from 2 to 8 carbon atoms and preferably from 2 to 5 carbon atoms. The portion of the copolymer attributed to the ester comonomer may be in the range of about 5 to about 50 weight percent, based on the weight of the copolymer, and is preferably in the range of about 15 to about 40 weight percent . Examples of the acrylates and methacrylates are ethyl acrylate, methyl acrylate, methyl methacrylate, t-butyl acrylate, n-butyl acrylate, n-butyl methacrylate and 2-ethylhexyl acrylate. Examples of vinyl carboxylates are vinyl acetate, vinyl propionate and vinyl butanoate. The melt index of the ethylene / unsaturated ester copolymers may be in the range of about 0.5 to about 50 grams per 10 minutes. Halogenated ethylene polymers useful in the present invention include fluorinated, chlorinated and brominated olefin polymers. The olefin base polymer can be a homopolymer or an interpolymer of olefins having from 2 to 18 carbon atoms. Preferably, the olefin polymer will be an interpolymer of ethylene with propylene or an alpha-olefin monomer of 4 to 8 carbon atoms. Preferred alpha-olefin comonomers include 1-butene, 4-methyl-1-pentene, 1 -hexene and 1-ketene. Preferably, the halogenated olefin polymer is chlorinated polyethylene. Examples of propylene polymers useful in the present invention include propylene homopolymers and copolymers of propylene with ethylene or other unsaturated comonomer. The copolymers also include terpolymers, tetrapolymers, and the like. Typically, polypropylene copolymers comprise units derived from propylene in an amount of at least about 60 weight percent. Preferably, the propylene monomer is at least about 70 percent by weight of the copolymer and more preferably at least about 80 percent by weight. Suitable natural rubbers in the present invention include high molecular weight isoprene polymers. Preferably, the natural rubber will have an average degree of polymerization of about 5000 and a broad molecular weight distribution. Useful styrene / butadiene rubbers include random copolymers of styrene and butadiene. Typically, these gums are produced by free radical polymerization. The styrene / butadiene / styrene block copolymers of the present invention are a separate phase system. The styrene / ethylene / butadiene / styrene copolymers useful in the present invention are prepared from the hydrogenation of styrene / butadiene / styrene copolymers. The polybutadiene rubber useful in the present invention is preferably a 1,4-butadiene homopolymer. Preferably, the butyl rubber of the present invention is a copolymer of isobutylene and isoprene. Isoprene is typically used in an amount of between about 1.0 and about 3.0 weight percent. For the present invention, polychloroprene gums, are generally polymers of 2-chloro-1,3-butadiene. Preferably, the gum is produced by an emulsion polymerization. Additionally, polymerization can occur in the presence of sulfur, to incorporate crosslinking in the polymer. Preferably, the nitrile rubber of the present invention is a random copolymer of butadiene and acrylonitrile. Other polymers crosslinkable by free radicals include silicone rubber and fluorocarbon gums. Silicone gums include gums with a siloxane structure of the form -Si-O-Si-O-. Fluorocarbon gums useful in the present invention include copolymers or terpolymers of vinylidene fluoride, with a cure site monomer to allow free radical crosslinking. Useful free radical inducing species include organic peroxides and free radical initiators of the Azo type. Organic peroxides can be added by direct injection. These free radical-inducing species can be used in combination with other free radical initiators, such as bicumerous, oxygen and air. Oxygen-rich environments can also initiate useful free radicals. The organic peroxides useful in the present invention have a lower nominal decomposition temperature than the organic peroxides conventionally used in practice. For example, when compared to di (tert-butylperoxyisopropyl) benzene as a conventional organic peroxide, tert-butyl peroxybenzoate is a desirable peroxide for use in the present invention. Notably, di (tert-butylperoxyisopropyl) benzene has a nominal decomposition temperature of 175 degrees Celsius (ie, the temperature at which 90% of the peroxide decomposes in a period of 12 minutes) and a half-life of 94 minutes at 140 degrees Celsius, while tert-butyl peroxybenzoate has a nominal decomposition temperature of 140 degrees Celsius and a half-life of 4.4 minutes at 140 degrees Celsius. Preferably, the free radical-inducing species is present in an amount of between about 0.1 and about 10 pch (parts per hundred parts of rubber by weight), preferably between about 0.5 and about 5.0 pch. And still more preferably, between 1.0 and about 4 pch. Preferably, the free radical-inducing species is present in an amount sufficient to achieve a crosslinking density at least as high as that achieved in the presence of the cross-linking profile modifier. Useful examples of the crosslinking profile modifier are free radical inhibitors such as (i) stable organic free radicals derived from hindered amines, (i) iniferters, (iii) organometallic compounds, (iv) arylazoxy radicals and (v) nitrous compounds. The selection of modifiers of the cross-linking temperature profile is based on determining whether the modifier will impart at least an induction time 5 times larger than the nominal induction time. Preferably, the crosslinking temperature profile modifier is present in an amount of between about 0.01 and about 5.0 pch. More preferably, it is present in an amount between about 0.05 and about 3.0 pch, and still more preferably, between about 0.1 and about 3.0 pch. The crosslinking profile modifier, when added to the combination and blowing agent, may allow the resulting expandable crosslinkable polymer composition to achieve an improved melting induction time at the nominal melt processing temperature. The improved fusion induction time would be sufficient to allow the melt processing of the expandable crosslinkable polymer composition, before the crosslinking begins. The crosslinking profile modifier may also allow the resulting expandable crosslinkable polymer composition, achieve an improved fusion induction time at temperatures higher than the nominal melt processing temperature. The crosslinking profile modifier may allow the expandable crosslinkable polymer composition to achieve an improved mold induction time at the nominal molding temperature. The improved mold induction time would be sufficient to allow uniform heating of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved mold induction time is at least 5 times larger than the nominal mold induction time. More preferably, the improved mold induction time is at least 10 times greater than the nominal mold induction time. Still more preferably, the improved mold induction time is at least 15 times larger. Preferably, the crosslinking profile modifier allows the resulting expandable crosslinkable polymer composition to achieve an improved mold induction time at temperatures higher than the nominal molding temperature. More preferably, the improved mold induction time would be sufficient to allow uniform heating of the expandable crosslinkable polymer composition at temperatures higher than the nominal molding temperature. Preferably, the crosslinking profile modifier allows uniform heating at the crosslinking temperature. Preferably, the modifier of the crosslinking profile makes it possible to achieve a curing speed at least as fast as that which is achieved in the absence of the crosslinking profile modifier. Preferably, the expandable crosslinkable polymer composition of the invention can be processed to obtain an article of manufacture at a speed at least 20 percent faster than the conventional composition (the nominal processing speed). Preferably, improvements in speed occur without having an unfavorable impact on crosslink density, uniformity of crosslinking or uniformity of cell size, in the resulting article of manufacture. Stable organic free radicals, derived from suitable hindered amines, include 2,2,6,6-tetramethyl piperidinyloxy (TEMPO) and its derivatives. Preferably, the stable organic free radicals derived from hindered amines are bis-TEMPOs, oxo-TEMPO, 4-hydroxy-TEMPO, an ether of 4-hydroxy-TEMPLE, TEMPO bound to a polymer, PROXYL, DOXYL, butyl-N -oxyl-di-tertiary, dimethyl-diphenyl-pyrrolidin-1-oxoyl, 4-phosphonooxy-TEM PO or a metal complex with TEMPO. Even more preferably, the stable organic free radical derived from hindered amines is a bis-TEMPO or 4-hydroxy-TEMPO. An example of a bis-TEM PO is bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate. Iniferters are compounds capable of initiating and terminating free radical reactions. They are also capable of reversibly finishing polymer chains in growth. When the crosslinking temperature profile modifier is an iniferter, it is preferably selected from the group consisting of tetraethylthiuram disulfide, benzyl N, N-diethyldithiocarbamate, dithiocarbamates, polythiocarbamates and S-benzyl dithiocarbamate. The crosslinking temperature profile modifier and the low temperature free radical inducing species can be combined with the free radical crosslinkable polymer in a variety of ways, including direct composition, direct immersion and direct injection. The blowing agent can be a chemical or physical blowing agent. Preferably, the blowing agent will be a chemical blowing agent. An example of a useful chemical blowing agent is azodicarbonamide. Preferably, the blowing agent will be a chemical blowing agent with its activation temperature within the nominal cross-linking temperature profile. Preferably, when the blowing agent is a chemical blowing agent, it is present in an amount of between about 0.05 and about 6.0 pch. Preferably, it is present between about 0.5 and about 5.0 pch, still more preferably, between about 1.5 and about 3.0 pch. The expandable crosslinkable polymeric composition may also contain an organic crosslinker modifier that does not have a double bond, wherein the organic crosslinker modifier and the crosslinking temperature profile modifier synergistically (a) suppresses the crosslinking speed of the polymer crosslinkable by free radicals, at temperatures lower than the nominal curing temperature of the free radical-inducing species and (b) improve the cross-linking density at the nominal curing temperature of the free radical-inducing species. Preferably, the organic crosslinker modifier is tris (2,4-di-ferf-butylphenyl) phosphite, poly [[6 - [(1, 1, 3,3-tetramethylbutyl) amino] -s-triazine-2,4 -diyl] [2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [2,2,6,6-tetramethyl-4-piperidyl) imino)], 2 (2'-hydroxy-3 ', 5'-di-ery-amylphenyl) benzotriazole or mixtures thereof. The expandable crosslinkable polymer composition may also contain a non-polar additive, wherein the additive improves the crosslinking performance, without contributing to the migration of the crosslinking temperature profile modifier, to the surface of an article of manufacture manufactured from the crosslinkable polymer composition. Preferably, the non-polar additive is decadiene or polybutadiene. The expandable crosslinkable polymer composition may also contain a curing enhancer or a co-agent to improve the crosslinking performance of the free radical-inducing species, without increasing the amount of free radical-inducing species. The improvement of the crosslinking performance can include the curing speed and the degree of curing. The addition of a curing enhancer is particularly useful when the free radical crosslinkable polymer is a chlorinated polyethylene. Useful curing enhancers include polyvinyl agents and certain monovinyl agents, such as dimers of alpha-methylstyrene, allyl pentaerythritol (or pentaerythritol triacrylate), triallyl cyanurate (CTA), TAIC, 4-allyl-2-methoxyphenyl allyl ether and 1, 3-di-isopropenylbenzene. Other useful curing enhancers include compounds having the following chemical structures.

When the expandable crosslinkable polymer composition contains a curing enhancer, it is present in an amount less than about 5.0 pch. Preferably, it is present in an amount of between about 0. 1 and about 4.0 pch, even more preferably, between about 0.2 and about 3.0 pch. The expandable crosslinkable polymer composition may also contain catalysts to increase the formation of free radicals. Suitable examples of catalysts include tertiary amines, cobalt naphthenate, manganese naphthenate, vanadium pentoxide and quaternary ammonium salts. Other additives are useful in the expandable crosslinkable polymer composition of the present invention. These additives include burn inhibitors, antioxidants, fillers, clays, processing aids, carbon black, flame retardants, peroxides, dispersing agents, waxes, coupling agents, mold release agents, light stabilizers, metal deactivators, plasticizers, antistatic agents, bleaching agents, nucleating agents, other polymers and dyes. The expandable crosslinkable polymer composition may have a high filler content. Other suitable non-halogenated flame retardant additives include alumina trihydrate, magnesium hydroxide, red phosphorus, silica, alumina, titanium oxides, melamine, calcium hexaborate, alumina, carbon nanotubes, wollastonite, mica, silicone polymers, phosphate esters, hindered amine stabilizers, ammonium octamolybdate, hardening compounds, melamine octamolybdate, fluxes, hollow glass microspheres, talc, clay, organo-modified clay, zinc borate, antimony trioxide and expandable graphite. Suitable halogenated flame retardant additives include decabromodiphenyl oxide, decabromodiphenylethane, bis- (tetrabromophthalimide) ethylene and decloran plus. In another alternative embodiment, the present invention is an expandable crosslinkable polymer composition comprising a free radical crosslinkable polymer, a short half-life free radical inducing species, a crosslinking profile modifier and a blowing agent. When activated at a specific temperature, a short-lived free radical producing species has a shorter half-life than the free radical-inducing species conventionally used with a combination of the free-radical crosslinkable polymer and blowing agent , when used as an expandable crosslinkable polymer composition. The conventionally selected free radical-inducing species is selected to minimize premature cross-linking and facilitate reasonable cross-linking cycle times, while the short-lived free-radical-inducing species is not selected to avoid premature cross-linking. Preferably, the short half-life free radical-inducing species will have a half-life at least 20% shorter than the conventional free-radical-inducing species when activated at approximately the same temperature. Preferably, the short-lived free radical-inducing species will have a half-life at least 30% shorter, and still more preferably, at least 50% shorter. The modifier of the crosslinking profile, when added to the free radical crosslinkable polymer, the short half-life free radical inducing species and the blowing agent, may allow the resulting expandable crosslinkable polymer composition to reach a melting induction time improved to the nominal fusion processing temperature. The improved fusion induction time would be sufficient to allow the melt processing of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved fusion induction time is at least 5 times longer than the nominal fusion induction time. More preferably, the improved fusion induction time is at least 10 times longer than the nominal fusion induction time. Even more preferably, the improved fusion induction time is at least 15 times greater. Also, preferably, the crosslinking profile modifier allows the resulting expandable crosslinkable polymer composition to achieve an improved melting induction time at temperatures higher than the nominal melt processing temperature. Also, the crosslinking profile modifier may allow the expandable crosslinkable polymer composition to achieve an improved mold induction time at the nominal molding temperature. The improved mold induction time would be sufficient to allow uniform heating of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved mold induction time is at least 5 times longer than the nominal mold induction time. More preferably, the improved mold induction time is at least 10 times greater than the nominal mold induction time. Even more preferably, the improved mold induction time is at least 15 times greater. Preferably, the crosslinking profile modifier allows the resulting expandable crosslinkable polymer composition to achieve an improved mold induction time at temperatures higher than the nominal molding temperature. The replacement of the conventionally selected free radical-inducing species by the short-lived free radical-inducing species also allows the cross-linking speed to be increased to approximately the same cross-linking temperature. Preferably, the expandable crosslinkable polymer composition of the invention can be processed to obtain an article of manufacture at a rate at least 20 percent faster than the conventional composition. Preferably, the composition of the invention can reach process speeds at least 40 percent faster. Still more preferably, speed improvements occur without having an unfavorable impact on the crosslink density, uniformity of crosslinking or uniformity of the cell size, of the resulting article of manufacture. In another embodiment, the present invention is an expandable crosslinkable article of manufacture, prepared from the expandable crosslinkable polymer composition of the invention, which comprises a free radical crosslinkable polymer, a low temperature free radical inducing species, a modifier of the cross-linking profile and a blowing agent. Preferably, the size of the foamed cells is substantially uniform. Also preferably, the crosslinking is substantially uniform. In another embodiment, the present invention is an expanded crosslinked article of manufacture, prepared from the expandable crosslinkable polymer composition of the invention, which comprises a free radical crosslinkable polymer, a short lived free radical inducing species, a modifier of the cross-linking profile and a blowing agent. Preferably, the size of the foamed cells is substantially uniform. Also preferably, the crosslinking is substantially uniform. In another embodiment, the present invention is an improved process for preparing an expandable crosslinkable article of manufacture. The process comprises the steps of (a) melt processing an expandable crosslinkable polymer composition, (b) molding the composition to form the article of manufacture, and (c) crosslinking and expanding the composition to obtain a shaped article of manufacture. The composition comprises a free radical crosslinkable polymer, a low temperature free radical inducing species, a blowing agent and a crosslinking profile modifier. The present invention also includes the article of manufacture manufactured from this improved process. To a comparable average life, a low temperature free radical producing species has a nominal decomposition temperature, lower than that of the free radical inducing species conventionally used with a combination of the free radical crosslinkable polymer and the blowing agent, when used as crosslinkable expandable polymer composition. The conventionally selected free radical-inducing species is selected to minimize premature cross-linking and facilitate reasonable cross-linking cycle times, while the low-temperature free radical-inducing species is not selected to prevent premature cross-linking. In the absence of the crosslinking profile modifier, a combination of the free radical crosslinkable polymer and the conventionally selected free radical inducing species has a nominal melt processing temperature and reaches a nominal melting induction time at the processing temperature. of nominal fusion. The combination of the free radical crosslinkable polymer and the conventionally selected free radical inducting species also has a nominal crosslinking profile comprising (a) a nominal molding temperature portion (b) a nominal transition temperature portion y ( c) a nominal crosslinking temperature portion. The combination achieves a nominal mold induction time at the nominal molding temperature. The crosslinking profile modifier, when added to the free radical crosslinkable polymer, the low temperature free radical inducing species and the blowing agent, may allow the expandable crosslinkable polymer composition to reach an improved melting induction time at the temperature of nominal fusion processing. The improved fusion induction time would be sufficient to allow the melt processing of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved fusion induction time is at least 5 times longer than the nominal fusion induction time. More preferably, the improved melting induction time is at least 10 times greater than the nominal melting induction time. Even more preferably, the improved fusion induction time is at least 15 times greater. Also preferably, the crosslinking profile modifier allows the resulting expandable crosslinkable polymer composition to achieve an improved melting induction time at temperatures higher than the nominal melt processing temperature. According to the above, in the improved process, the composition can be melt processed at a temperature higher than the nominal melt processing temperature. Also, the crosslinking profile modifier can allow the resulting expandable crosslinkable polymer composition to achieve a better induction time of the mold at the nominal molding temperature. The improved molding induction time would be sufficient to allow uniform heating of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved mold induction time is at least 5 times longer than the nominal mold induction time. More preferably, the improved mold induction time is at least 10 times greater than the nominal mold induction time. Even more preferably, the improved mold induction time is at least 1.5 times greater. Preferably, the crosslinking profile modifier allows the expandable crosslinkable polymer composition to achieve an improved mold induction time at temperatures higher than the nominal molding temperature. In accordance with the above, in the improved process, the composition can be molded at a temperature higher than the nominal molding temperature. The replacement of the conventionally selected free radical-inducing species, by the low temperature free radical inducing species, it also allows to lower the crosslinking temperature up to the low nominal decomposition temperature. Preferably, the expandable crosslinkable polymer composition can be processed to obtain an article of manufacture, at a rate at least 20 percent faster than the nominal composition. Preferably, the composition of the invention can reach processing speeds at least 40 percent faster. Even more preferably, the improvements in speed occur without having an unfavorable impact on the crosslink density, the uniformity of crosslinking or the uniformity of the cell size, of the resulting article of manufacture. In another embodiment, the present invention is an improved process for preparing an expanded article of manufacture. The process comprises the steps of (a) melt processing an expandable crosslinkable polymer composition, (b) molding the composition to shape the article of manufacture and (c) crosslinking and expanding the composition to obtain a shaped article of manufacture. The composition comprises a free radical crosslinkable polymer, a short half-life free radical inducing species, a blowing agent and a crosslinking profile modifier. The present invention also includes the article of manufacture manufactured from this improved process. When activated at approximately the same temperature, a short-lived free-radical-inducing species has a shorter half-life than that of the free radical-producing species conventionally used with a combination of the free radical-crosslinkable polymer and the free-radical agent. blown, when used as an expandable crosslinkable polymer composition. The conventionally selected free radical-inducing species is selected to minimize premature cross-linking and facilitate reasonable cross-linking cycle times, while the short-lived free-radical-inducing species is not selected to avoid premature cross-linking. In the absence of the crosslinking profile modifier, a combination of the free-radical crosslinkable polymer and the conventionally selected free radical-inducing species has a nominal melt processing temperature and achieves a nominal melting induction time at the processing temperature of nominal merger. The combination of the free-radical crosslinkable polymer and the conventionally selected free radical-inducing species also has a nominal cross-linking profile comprising (a) a nominal molding temperature portion, (b) a nominal transition temperature portion y ( c) a nominal crosslinking temperature portion. The combination achieves a nominal mold induction time at the nominal molding temperature. The crosslinking profile modifier, when added to the free radical crosslinkable polymer, the short half-life free radical inducing species and the blowing agent, may allow the resulting expandable crosslinkable polymer composition to achieve an improved melting induction time. , at the nominal fusion processing temperature. The improved fusion induction time would be sufficient to allow the melt processing of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved fusion induction time is at least 5 times longer than the nominal fusion induction time. More preferably, the improved melting induction time is at least 10 times greater than the nominal melting induction time. Even more preferably, the improved melting induction time is at least 1.5 times greater. Also, preferably, the crosslinking profile modifier allows the resulting expandable crosslinkable polymer composition, achieve an improved fusion induction time at temperatures higher than the nominal melt processing temperature. Accordingly, in the improved process, the composition can be melt processed at a temperature higher than the nominal melt processing temperature. Also, the crosslinking profile modifier may allow the resulting expandable crosslinkable polymer composition to achieve an improved mold induction time at the nominal molding temperature. The improved mold induction time would be sufficient to allow uniform heating of the expandable crosslinkable polymer composition, before the crosslinking begins. Preferably, the improved mold induction time is at least 5 times longer than the nominal mold induction time. More preferably, the improved mold induction time is at least 10 times greater than the nominal mold induction time. Even more preferably, the improved mold induction time is at least 15 times greater. Preferably, the crosslinking profile modifier allows the resulting expandable crosslinkable polymer composition to achieve an improved mold induction time at temperatures higher than the nominal molding temperature. Accordingly, in the improved process, the composition can be molded at a temperature higher than the nominal molding temperature. The replacement of the conventionally selected free radical-inducing species by the short-lived free radical-inducing species also allows the cross-linking speed to be increased to approximately the same cross-linking temperature. Preferably, the expandable crosslinkable polymer composition of the invention can be processed to obtain an article of manufacture at a rate at least 20 percent faster than the conventional composition. Preferably, the composition of the invention can reach process speeds at least 40 percent faster. Even more preferably, improvements in speed occur without having an unfavorable impact on crosslink density, uniformity of crosslinking or uniformity of cell size, of the resulting article of manufacture. Among other applications, the present invention is particularly useful in footwear, automotive, furniture, foam and upholstery applications. Particularly useful articles of manufacture manufactured from the present invention include shoe soles, shoe soles of multiple components (including polymers of different densities and types), window seals, gaskets, profiles, durable articles, inserts for flat tires , construction panels, foams for entertainment and sports equipment, foams for energy management, foams for handling acoustics, insulation foams and other foams.

EXAMPLES The following non-limiting examples illustrate the invention. Test Methods The following test methods were used to evaluate the non-limiting examples: (1) Density The density was measured in accordance with ASTM D-792. The test samples were prepared by cutting three 2.1 x 2.3 cm specimens from a solid molded article. Afterwards, each sample was conditioned by a minimum of 12 hours before the test, preferably 7 days or more after production. The conditioning occurred at 23 ± 2 degrees Celsius and a humidity of 50 ± 1%. Each sample was weighed dry. Then, a rate of distilled water was placed on the scale and then the balance was taken. The test samples were added to the water and weighed again. The density was calculated by dividing the dry weight between the wet weight. The values are reported in grams per cubic centimeter. (2) Hardness Hardness (Asker C) was measured in accordance with the standard ASTM D-2240. Each sample was conditioned for a minimum of 12 hours before the test, preferably 7 days or more after its production. The conditioning occurred at 23 + 2 degrees Celsius and at a humidity of 50 + 1%. The test samples had a minimum thickness of 6 mm.

The tests were carried out at the conditioning conditions and at a minimum distance of 12 mm from any edge of the sample. When the sample was peeled, measurements were made with the shell on top of the plate and centered. The hardness scale was measured approximately 10 seconds after applying the pressure. The average of 5 measurements was reported, where the 5 measurements were taken in different positions on the specimen, at a separation of at least 6 mm between each measurement site. (3) Gel level The gel level (percent of gels) was measured in accordance with ASTM D-2765, Procedure A. The solvent was xylene.

Each sample was ground in such a way that the particles could pass through a U.S. mesh screen. No. 30, but could not pass through a U.S. mesh screen No. 60. One gram of the samples was mixed with 1750 ml of xylene. 51 grams of an antioxidant was added to the mixture. The antioxidant used was 2,2'-methylenebis (4-methyl-6-tert-butylphene!) Cyanox 2246, commercially available from Cytec Industries, Inc. The mixture was boiled for 12 hours. The gels were subjected to extraction and placed in a vacuum oven at less than 28 mm of mercury and at 150 degrees Celsius for 12 hours.

The gels were cooled for 1 hour in a desiccator. Then they were weighed. The analysis was carried out in duplicate. (4) Expansion ratio In a mold, two points were marked with a separation of 10 mm. Then, the example material was taken out of the mold and the distance between the points was immediately measured. After 30 minutes, the distance between the points was measured again; this value was divided by 10 and was reported as the expansion ratio. (5) Shrinkage Shrinkage (in percent) was measured according to SATRA PM-70. The test samples were prepared by cutting three 150 x 25 x 5 mm specimens from a solid molded article. Surface cuts were made on the samples at 25 mm from each edge, on the side measuring 150 mm. Subsequently, each sample was conditioned for a minimum of 12 hours before the test, preferably 7 days or more after its production. The conditioning occurred at 23 ± 2 degrees Celsius and at a humidity of 50 ± 1%. After at least 3 hours of conditioning, the length between the cuts was measured on the side measuring 150 mm. After conditioning, the test samples were placed in a furnace at 50 ± 2 degrees Celsius for 24 hours or at 70 ± 2 degrees Celsius for 4 hours. Subsequently, the samples were subjected to the conditioning conditions for 30 minutes. Then the length of the samples was measured. (6) Compression Compression (in percent) was measured in accordance with ASTM D-3574. The test samples were prepared by cutting 5 circles with a diameter of 2.8 cm and a thickness of 9.4 mm from a solid molded article. Three samples were analyzed per test. Later, the samples were conditioned for a minimum of 12 hours before the test, preferably 7 days or more after production. The conditioning occurred at 23 ± 2 degrees Celsius and humidity of 50 ± 1%. After conditioning, the test samples were compressed to 50 ± 1% of their original thickness. In a period of 15 minutes, with the compression applied, the samples were placed in an oven at 50 + 2 degrees Celsius for 6 hours. Then, the samples were subjected to the conditioning conditions for 40 minutes. Then the thickness of the samples was measured. (7) Tear by separation Tear by separation was measured in accordance with SATRA TM-65. The test samples were cut to dimensions of 25 x 75 x 5 mm. A 16 mm deep cut was made in the center thereof. Subsequently, each sample was conditioned for a minimum of 12 hours before the test, preferably 7 days or more after its production. The conditioning occurred at 23 ± 2 degrees Celsius and at a humidity of 50 ± 1%. The separation speed was set at 100 mm / min. The measurements were reported in kilograms per centimeter.

Example compositions Four compositions were evaluated. The following components were used to prepare the compositions: (a) Elvax 460 ™ ethylene / vinyl acetate copolymer, containing 18 weight percent vinyl aceate, with a melt index of 2.5 grams per 10 minutes, available in the trade at DuPont; (b) di (tert-butylperoxyisopropyl) benzene Perkadox 1440 ™, with a nominal decomposition temperature (temperature at which 90% of the peroxide decomposes in a period of 12 minutes) of 175 degrees Celsius, with a half-life of 94 minutes at 140 degrees Celsius, being available commercially from Akzo Nobel Chemicals BV; (c) Trigonox C / 50D ™ tert-butyl peroxybenzoate, with a nominal decomposition temperature of 140 degrees Celsius, an average travel of 4.4 minutes at 140 degrees Celsius and commercially available from Akzo Nobel Chemicals BV; (d) TAC 70 ™ triallyl cyanurate, commercially available from Akzo Nobel Chemicals BV; (e) 4-hydroxy-TEMPO, commercially available in A. H. Marks; (f) Azodicarbonamide AZO AZ130 ™, commercially available in Crompton Uniroyal; (g) zinc oxide; (h) zinc stearate; and (i) calcium carbonation. Each composition contained 100 pch of Elvax 460 ™ ethylene / vinyl acetate copolymer, 2.40 pch of AZO AZ130 ™ azodicarbonamide, 2.00 pch of zinc oxide, 0.1 pch of zinc stearate and 5.00 pch of calcium carbonate. The amounts of the remaining components are shown in Table 1. Table 1 The exemplified formulations were evaluated using a normal shoe sole mold, 8 mm thick. The formulations were subjected to a molding temperaure of 106 degrees Celsius and a crosslinking temperature at 80 degrees Celsius. The material exemplified as Comparative Example 1 showed poor control of cell size and deformation, and a curing time of at least 360 seconds. While, after 300 seconds, the material exemplified as Comparative Example 2 showed poor dimensional stability and a gel content comparable to that of Comparative Example 1 after 360 seconds. After 300 seconds, the materials exemplified as Example 3 showed no deformation and showed good dimensional stability. Figure 2 is representative of a cross-sectional view of a shoe sole made from the expandable crosslinkable polymer composition of Example 3.

To determine the minimum time required to produce flat and non-deformed articles with Comparative Examples 1 and 2 and with Example 3, the compositions were crosslinked at 175 degrees Celsius or 180 degrees Celsius and evaluated after certain time limits. The minimum time to produce (1) a flat and non-deformed shoe sole or (2) a convex and deformed shoe sole was determined. Table 2 shows the result of the study. Table 2 Several general properties of the exemplified formulations were determined. These properties are reported in Table 3.

Table 3 -1 ^

Claims (20)

1. CLAIMS 1. An expandable crosslinkable polymer composition, comprising: (a) a free radical crosslinkable polymer; (b) a low temperature free radical inducing species; (c) a crosslinker profile modifier; (d) a blowing agent.
2. 2. The expandable removable polymer composition of claim 1, wherein the blowing agent is selected from the group consisting of chemical blowing agents and physical blowing agents.
3. 3. The expandable crosslinkable polymer composition of claim 1, wherein the blowing agent is a chemical blowing agent having its activation temperature within the nominal cross-linking temperature profile.
4. 4. The expandable crosslinkable polymer composition of claim 1, wherein the crosslinking profile modifier is present in an amount sufficient to permit uniform heating of the expandable crosslinkable polymer composition when the latter is heated.
5. The expandable crosslinkable polymer composition of claim 1, wherein the crosslinking profile modifier allows to achieve a curing speed at least as fast as that which is achieved in the absence of the crosslinking profile modifier.
6. 6. The expandable crosslinkable polymer composition of claim 1, wherein the free radical inducing species is present in a sufficient amount, to achieve a crosslinking density at least as high as that which is reached in the absence of the crosslinking profile modifier.
7. 7. The expandable crosslinkable polymer composition of claim 1, further comprising a curing enhancer, which is present in an amount sufficient to achieve a crosslink density, at least as high as that which is achieved in the absence of the profile modifier. reticulation.
8. 8. An expanded cross-linked manufacturing article, prepared from the expandable crosslinkable polymer composition of claim 1.
9. 9. The expanded cross-linked article of claim 8, wherein the size of the foamed cells is substantially uniform.
10. 10. The expanded crosslinked article of claim 8, wherein the crosslinking is substantially uniform. eleven .
11. An expandable crosslinkable polymeric composition comprising: (a) a free radical crosslinkable polymer; (b) a species that induces free radicals of short half-life; (c) a crosslinker profile modifier; and (d) a blowing agent.
12. 12. An improved process for preparing an expanded crosslinked manufacturing article, comprising the steps of: (i) melt processing an expandable crosslinkable polymer composition comprising: (1) a free radical crosslinkable polymer, (2) a radical inducing species low temperature free, - (3) a blowing agent, and (4) a crosslinking profile modifier. (ii) molding the expandable crosslinkable polymer composition to give it the shape of the article of manufacture; and (iii) crosslinking and expanding the expandable crosslinkable polymer composition to obtain an article of manufacture. The improved process of claim 12, wherein the crosslinking profile modifier is present in an amount sufficient to allow uniform heating of the expandable crosslinkable polymer composition during the molding step. 14. An improved process for preparing an expanded crosslinked manufacturing article, comprising the steps of: (i) melt processing an expandable crosslinkable polymer composition comprising: (1) a free radical crosslinkable polymer, (2) a species short-lived free radical-inducing agent, (3) a blowing agent, and (4) a cross-linking profile modifier, (i) molding the expandable crosslinkable polymer composition to give it the shape of the article of manufacture; and (iii) crosslinking and expanding the expandable crosslinkable polymer composition to obtain an article of manufacture. 15. The improved process of any of claims 12 to 14, for preparing an expanded crosslinked article of manufacture, wherein the melt processing occurs at a temperature greater than the nominal melt processing process. 16. The improved process of any of claims 12 to 15, for preparing an expanded cross-linked article of manufacture, wherein the molding occurs at a temperature greater than the nominal molding temperature. The improved process of any of claims 12 to 16, wherein the process is developed at least about 20 percent faster than the nominal processing speed. 1 8. An expanded cross-linked manufacturing item, prepared in accordance with the process of any of the Claims 12 to 17. 1 9. The expanded cross-linked article of manufacture according to claim 18, wherein the article is a shoe sole. The expanded cross-linked article of manufacture according to claim 19, wherein the article is a multi-component shoe sole,