CA1100671A - Elastoplastic compositions of rubber and polyamide resin - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention provides an elastoplastic composition comprising a blend essentially free of low molecular weight phenol plasticizer of as thermoplastic crystalline polyamide in an amount sufficient to impart thermoplasticity up to 50 weight percent of the composition, wherein the polyamide in said blend retains at least 50% of its original crystallinity, b) rubber cross-linked to the extent that the gel content of the rubber is at least about 80 percent, wherein the rubber in said blend is in the form of small dispersed particles essenti-ally of the size of 50 microns or below and is a homopolymer of 1,3-butadiene, copolymer of 1,3-butadiene or isoprene or mix-tures thereo'. in an amount sufficient to impart rubberlike elasticity up to 80 weight percent of the composition provided that, when the amount of polyamide exceeds the amount of rubber, sufficient inert plasticiser is present to impart rubber-like elasticity to the composition which composition is process-able as a thermoplastic and is elastomeric. Elastoplastic com-positions of the invention are useful for making a variety of articles such as tires, hoses, belts, gaskets, moldings and molded parts . The compositions are useful for making articles by extrusion, injection molding and compression molding techni-ques and also for modifying thermoplastic resins.

Description

43-0969~

ELASTOP~ASTIC COMPOSITIONS OF RUBBER
AND POLYAMIDE RESIN
This invention relates to thermoplastic compositions and, more particularly, to thermoplastic elastomeric composi-tions comprising blends o~ polyamide resin and cross-linked rubber.
BACKGROUND OF THE IN~ENTION
Thermoplastics are compositions whlch can be molded or otherwise shaped and reprocessed at temperatures above their melting or softe~ing point. Thermoplastic elastomers (elastoplastics) are materials which exhibit both thermoplastic and elastomeric properties, i.e., the materials process as thermoplastics but have physical properties like elastomers.
Shaped articles may be formed from thermoplastic elastomers by extrusion, injection molding or compression molding without the time-consuming cure step required with conventional vulcanizates. Elimination of the time required to effect - vulcanization provides signiicant manufacturing advantages.
Further, thermoplastic elastomers can be reprocessed without

2~ the need for reclaiming and, in addition, many thermoplastics can be thermally welded.
Moldable thermoplastic compositions of nylon and cured rubber containing high proportions of nylon prepared ~rom scrap tire cord material are kno~n but such compositions are rigid nonelastomeric ma~erials of high stiffness and low alongation (Elgin/ U. S. patent 3,468,794)~ Moldable thermo-plas-tic compositions of nylon and curable rubber containing high proportions of rubber are known which compositions are cured in a mold (British patents 866,479 and 1,190,049 and French patent 1~ 592, 857), This inventlon concerns moldable -2~ r 7~L

thermoplastic elastomeric compositions of polyamide resin and cross-linked rubber.
SUMMARY OF_THE INVENTION
Elastoplastic compositions in accordance with this invention are compositions comprising blends of (a) thermo-plastic polyamide resin in an amount sufficient to impart thermoplasticity up to 50 ~eight percent of the composition, (b) rubber cross-linked to the ~xtent that the gel content of the rubber is at least about 80 percent, the rubber being a homopolymer of 1,3-butadiene, a copolymer of 1,3-butadiene copolymerized with styrene, vinyl pyridine, acrylonitrile, or methacrvlonitrile, or mixtures thereof, in an amo~t sufficient to impart rubberlike elasticity up to 80 weight percent of the composit.ion and~ tc) opt.ionally, polyamide resin plasticizer in an amount not exceeding the weight of resin, in which the total weight of the rubber and plasticizer does not exceed 80 weight percent of the composition, which compositions are processable as thermoplastics and are elasto-meric. Preferred compositions of the invention comprise blends in which the amount of xubber exceeds the amount of polyamide resin, particularly blends of (a) about 20-50 parts by weight of thermoplastic polyamide resin and (b) about . 80-50 parts by weight of rubber. More preferred compoæitions ; comprise blends of about 20-45 percent by weight of the resin and about 80-55 percent by weight of the rubber. The composi-tions are elastomeric and are processable as thermoplastics even though the rubber is cross-linked to a point where it is 80 percent insoluble in the usual organic solvents for the unvulcanized rubber and they retain thermoplasticity even when 30 the rubber is cross-linked to the extent that the rubber is sssentially completely insoluble. The indicated relative 43-0969A ~ ~ Q ~7 ~

proportions o~ polyami~e resin and rubber are necessary to provide sufficient rubbex ~o give elastomeric compositions and to provide sufficient resin to give thermoplasticity. When the amount of rubber exceeds abou~ 80 parts by weight per 100 parts total weiyht of resin and rubber, there is insufficient resin present to provide thermoplasticity~ When the quantity of rubber in the absence of polyamide resin plasticizer falls belcw about 50 parts by weight per 100 parts total weight of resin and rubber or when the quantity of resin exceeds 50 weight percent of the composition, hard, rigid compositions having reduced toughness are obtained. The blends of the invention are envisaged as comprising microsized particles of cross-linked rubber dispersed throughout a continuous resin matrix. Especially pre~erred compositions of the invention comprising cross-linked nitrile rubber are characterized by toughness, as repre~ented by TS2/E wherein TS is tensile strength and E is Young's modulus, o~ at least 50~ more than that of a similar composition containing no resin plasticizer but wherein the weight of resin exceeds the weight of rubber.
As indicated, the thermoplastic elastomers of the invention are rubbery compositions in which the rubber portion of the blend is cross-linked to a gel content o~ 80% or more or a cross-link density of 3 x 10-5 or more moles per milli-liter of rubber. The procadure appropriate for evaluating cross-link density depends upon the particular ingredients present in the blends. The properties of the compositionR can be improved by further cross-linking the rubber until it is essentially completely cured which state of cure is usually indicated by a gel content o~ 96~ or more. However, in thi~

connection, essentially complete gelation of say 96% or more i8 not always a necessary criterion of a fully cured product 43-0969~

because of differences in molecular weiyht, molecular weight distribution and other variables among diene ru~bers which influence the gel determination. Determination of the cross-link density of the rubber is an alterncltive means of deter-mining state of cure of the vulcanizates but must be determi~ed indirectly because the presence of the resin interferes with the determination. Accordingly~ the same rubber as present in the blend is txeated under conditions - with respect to time, temperature, and amount of curative which result in a ~ully cured product as demonstrated by its cross-link density, and such cross-link density is assigned to the blend similarly treated. In general, a cross-link density of about 7 x 10-5 or more moles (number of cross-links divided by Avogadro's number) per milliliter of rubber is representative of the ~alues for ully cured nitrile rubber, however, this value may be as low as about 5 x 1~-5 especially for polybutadiene rubber or polybutadiene-styrene rubber.
An effect of curing the composition is the very substa~tial improvement in tensile properties which improvement directly relates to its practical uses. Surpxisingly~ such high strength elastomeric compositions are still thermoplastic as contrasted to thermoset elastomers.
Vulcanizable rubbers, although thermoplastic in the unvulcanized state, are normall~ classified as th~rmosets because they undergo the process of thermosetting to an unprocessable state. The products of the instant invention, although processable~ are prepared from blends of rubber and resin which are treated under time and temperature conditions to cross-link th rubber or are treated with curatives in amounts and under time and temperatuxe condi~ions known to give cured pxoducts from static cures of the rubber in molds 43-0969A ~ 7~

and, indaed, the rubber has undergone gelation to the extent characteristic of rubber subjected to a similar treatment alon~.
Thermosets are avoided in the compositions of the invention by simultaneously masticating and curing the blends. Thus, the thermoplastic compositions of the invention are preerredly prepared by blending a mixture of rubber, polyamide resin, - and curatives when required, then masticating the blend at a temperature sufficient to efect cross-link formation, using conventional mas~icating equipment, for example, Banbury mixer, Brabender mixer, or certain mixing extxuders. The resin and rubber are mixed at a temperature sufficient to soften the polyamide resin or, more commonly, at a temperature above its melting point if the resin is crystalline at ordi~ary tempera-tures. After the resin and rubber are intimately mixed, ~ curative is added if needed. Heating and masticating at `~ vulcanization temperatures are generally adequate to complete the cross-link formation in a few minutes or less, but if shorter times are desired, higher temperatures may be used.
A suitable range of temperatures for cross-link ormation is ~0 from about the melting temperature of the polyamide resin to the decomposition temperature of the rubber which range commonly is rom about 150C to 270C with the maximum temperature varying somewhat depending on the type of rubber, the presence of antidegradants and the mixing time. Typically the ra~ge is from about 160~C to 250C. A preferred range of temperatures is from about 180C to about 230C. ~o obtain thermoplastic compositions, it is important that mixing con-tinues without interruption until cross-linking occurs. If appreciable cross-linking is allowed after mixing has stopped, a thermoset unprocessable composition may be obtainecl. A few simple experiments within the skill of the art utilizing 43-0969A ~ 7~

available rubbers and curative systems will suffice to deter-mine their applicability for the preparation of the improved products of this invention.
Methods other than the dynamic vulcanization o rubber/resin blends can be utilized to prepare compositions of the invention. For example, the rubber can be fully vulca~ized in the absence of th~ resin, either dynamically or statically, po~dered, and mixed with the resin at a temperature above the melting or softeniny point of the resin. Provided that the ; 10 cross-linked rubber particles are small, well dispersed and in an appropriate concentration, the compositions within the in~ention are easily obtained by blending cross-linked rubber and re~in. Accordingly, the term "blend" herein means a mixture comprising well dispersed small particles of cross-linked rubber. A mixture which is outside o~ the invention because it contains poorly dispersed or too large rubb~r particles can be comminuted by cold milling (to reduce -particle size to below about 50~) preferredly below 20~ and more preferredly to below 5~. After sufficient comminution or pulverization, a composition of the invention is obtained.
Frequently, the case o poor dispersion or too large rubber particles is visibly obvious to the naked eye and observabls in a molded sheet. This is especially true in the absence of pigments and fillers. In such a case, pulverization and remolding gives a sheet i~ which aggregates of rubber particles or large particles are no~ obvious or are far less obvious to the naked eye and mechanical properties are greatly improved.
The compositions of the invention are all processable in an internal mixer, to products which, upon transferring at

3~ temperatures above the softening or crystallizing points of the resin phases, to the rotating rolls of a rubber mill, orm i67~

continuous sheets. The sheets are reprocessable in the inter-nal mixer, ~fter reaching temperatures above the softening or melting points of the resin phases. The material is again transformed ko the plastic state ~molte,n state of the resin phase) but upon passing the molten product through the rolls of the rubber mill a co~tinuous sheet again forms. In addition, a sheet of thermoplastic composition of this invention can be cut into pieces and compression molded to give a single smooth sheet with complete knitting or fusion between the pieces. It is in the foregoing sense that "thermoplastic"
will be herein understood. In addition, the elastoplastic compositions of the invention are fur~her processable to the extent that articles may b0 formed therefrom by extrusion or injection molding.
Where the determination of e~tractables is an appro-priate measure of the state of cure, the improved elasto-plastic compositions are produced by cross-linking the blends to the extent that the composition contains no more than about twenty percent b~ weight of rubber extractable at room tempera-2Q ture by a solvent which dissolves the uncured rubber, and preferably to the extent that the composition contains less than four percent by weight extractable and more preferably less than two percent b~ weigh~ ex~ractable. In general, with nonself-curing rubber, the less extractables the better are the pro-perties, whereas, with self-curing rubber, respectable proper-ties are obtained with extractables as high as twenty percent, but with either nonself-curing rubber or self-curinq rubber the more preferable compositions comprise low quantities o extract-able rubber. Gel content reported as percent gel is determined by the procedure of U. S~ patent 3,203,937 which comprises determi~ing the amount of insoluhle polymer by soaking the 67~

specimen for ~8 hours in a solvent for the rubber at room temperature and weighing the dried residue and making suitable corrections based upon knowledge of the composition. Thus, corxected initial and final weights are obtained by sub-tracting rom the initial weight, the weight of soluble com-ponents, other than the rubber, such as extender oils, plasticizers and components of the resin soluble in organic solvent. Any insoluble pigments, fillers, e~c., are subtracted rom bo~h the initial and final weights.
To employ cross-link density as the measure of the state of cure which characterizes the improved elastoplastic compositions, the blends are cross-linked to the extent which corresponds to cross-linking the same rubber as in the blend statically cross-li.nked under pressure in a mold with such amounts of the same curative if present as in the blend and under such conditions of time and temperature to give an efective cross-link density greater than about 3 x 10 moles per milliliter of rubber and preferably greater than about 5 x 10-5 or even more preferredly 1 x 10-4 moles per milliliter of rubber. The blend is then dynamically cross-linked under similar conditions twith the same amount of curative, when present, based on the rubber content of the blend~ as was required for the rubber alone. The cross-link density so determined may be regarded as a measure of the amount of vulcanization which gives the improved thermoplastics.
~owever, it s~ould not be assumed, from the fact that the amount of curative is based on the rubber content o the blend and is that amount which gives with the rubber alone the - aforesaid cross-link density that the curative does not react with the resin or that there is no reaction between the xesin and rubber. There may be highly significant react:ions involved _g_ ' 7~

but of limited extent. However, the assumption that the cross-link density determined as described provides a useful approxi-mation of the cross~link density of the elastoplastic co~lposi~
tions is consistent with the thermoplastic properties and with the fact that a large proportion of the resin can be removed from the composition by extraction with a solvent for the resin such as formic acid.
The cross-link density of the rubber is determined by equilibrium solvent swelling using the Flory-Rehner e~uation, ~. Rubber Chem. and Tech., 30, p. 329. The appropria~e ~uggins solubility paxameters ~or rubber-solvent pairs used in the calculation were obtained from the review article by Sheehan and Bisio, J. Rubber Chem. & Tech., 39, 149. If the extracted gel content o the vuJcanized rubber is low, it is necessary to use the correction of Bueche wherein the term vl/3 is multiplied by the gel fraction (% gel/100). The cros~-link density is half the effec~ive network chain density v deter-mined in the absence of resin. The cross-link density of the vulcanized blends will, therefore, be hereinafter understood to refer to ~he value determined o~ the same rubber as in the blend in the manner descxibed. Still more preferred compo~itions meet both of the aoredescribed measures oi state of cure, namely, by estimation of cros~-link density and percent of rubber extraatable.
Rubber satisfactory for the practice of the invention comprise essentially random noncrystalline, rubbery polymer selected from the group consisting of a homopolymer of 1,3-blltadiene, a copolymer of 1,3-butadiene copolymerized with styrene, vinyl pyridine, acrylonitrile~ or methacrylonitrile, or mixtures o~ said homopolymer with one or more o said co-polymers or mixtures of two or more said copolymers.

Commercially available rubbers suitable for the practice of the invention are described in Rubber World Blue Book, 1975 Edition, Materials and Compounding Ingredients for Rubber as follows: Nitrile Rubb~r, pages 416-430~ Polybutadiene Rubber, pages 431-432, and Styrene Butadiene R~ber, pages 452-460.
Copolymers of l,3-butadiene and about 15-60% acrylonitrile commonly called nitrile rubber are preferred. Both nonsel-curing and self-curing nitrile rubbers are suitable in the practice of the invention. Nonself-curing nitrile rubbers as the name implies requires ~he presence of curatives to cross-link the rubber under processing temperatures to the extent that the gel content of the rubber is at least about 80 per-aent or more. Sel-curing nitrile as the ~ame indicates will cross-link under processing temperatures in the absence of curatives (other than curatives which may be inherently pre-sent) to the extent that the gel content of th~ rubber is at least about 80 percent or more. Compositions of the invention comprising blends in which the rubber component is self-curing - nitrile rubber generally exhibit superior tensile strengths and consequently are preferred. Blends comprising self~curing nitrile rubber may be cross-linked further by the use of convantional curatives as hereinafter described which use generally results in a further increase in the tensile strength of the resulting composition.
Whether a nitrile rubber is self-curing or nonsalf-curing is not depend~nt on acrylonitrile content or Mooney Viscosity but appears to be an inherent property of cextain r~bbers. A convenient means or dete~mining whether a nitrile rubber i~ sel-curing compris2~ mas~icating the r~ber a~

225C in a Brabender mixer and observing its tendency to scorch. Self-curing nitrile rubbers generally scorch under --11~
. , the a~oresaid conditions within 2-8 mihutes, whereas, nonself-curing rubbers generally may be subjected to the aforesaid treatment for twenty minutes or more without scorching.
Scorching as used above means the rubber loses i~ ability to maintain a continuous fluid mass in the mixer but instead crumbles into discrete particles with some of the particulate crumbs discharging from the ~hroat of the mixer if the ram is lifted while mixing is continued. The scorched rubber or the rubber having been masticated for twenty minutes as des-cribed is dumped from mixer, compxession molded at 230C~or five minutes, and the gel content determined by extraction in dichloromethane at room temperature. A self-curing rubber will have a gel content of about 80 percent or more (weight extractable of 20 peraent or less) whereas, a nonself-curing rubber will have a gel content of less than 80 percent.
Suitable thermoplastic polyamide (nylon) resins com-prise crystalline or resinous, high molecular weight solid polymers having recurring amide units within the polymer chain.
Polyamide resins may be prepared by polymerization of one or more epsilon lactams such as caprolactam, pyrrolidione, lauryllactam and aminoundecanoic lactam and by condensation of dibasic acids and diamines Both fiber-forming and molding grade nylons are suitable. Examples of such resins axe poly-caprolactam (nylon-6), polylauryllactam (nylon 12), poly-hexamethyleneadipicamide (nylon-6l6), polyhexamethyleneaze-laicamide ~nylon-6,9), polyhexamethylenesebacicamide (nylon 6,10), polyhexamethyleneisophthalamide (nylon-6,IP) and the condensation product of ll-aminoundecanoic acid (nylon ll).
Additional exc~mples of satisfactory polyamide resins (especially those having a softening point below 275C) are described in Kirk-Othmer, Encyclopedia of Chemical Technolo~ V. lO,page 919, ~,~

and E cx~lo~eaia of Polyme_ Science and ~echnolo~y, ol. 10, pages 392-414. Commercially availc~ble thermoplastic poly~mide resin may be advantageously used in the pr~ctice of the inven-tion,with linear polyamide resins having a softening point or melting point between 160-230C being preferred.
Moreover, the particular results obtained`by the aforedescribed dync~mic curing process are a function of the particular rubber curing system selected. The cura~ives and the cuxati~e systems conventionally used to vulcanize~diene -rubbers are utilizable for preparing the improved ~hermoplas-tics of the invention. Any curative or curative system appli-cable for vulcanization of diene rubbers may be used in the practice of the invention, for example, peroxide, azide, quinoid or accelerated sulfur vulcanization systems. The combi~ation of a maleimide and a peroxide or disulfide accelerator can be used. For satisfactory curatives and cura-tive systems~ reference is made to columns 3-4 of U. S.
patent 3,806,558. Sufficient quantities of curatives are used to achieve essentially complete cure of the rubber as determined by *he increase in tensile strength, by the cross~link density, by the sol content (percent extractables), or combination thereof. Excessive quantities of curatives should be avoided because quantities well beyond the amount nece~sary to fully cure ~he rubber can result in diminution of properties, for example, a re~uction in ultimate elongation. Peroxide curatives are advantageously used in reduced quantities in conjunction with other curatives such as sulfur or bismaleimide providing the total c~mount of curatives i3 -sufficient to vulcanize fully - 3~ the rubber. ~igh energy raaiation is als~ utilizcible as the curative means~

$s~

6~
~ 43-0969A

.
Curative systems comprising phenylene bis-maleimide are espe~ially recommended. Also, part:icularly recommended are efficient or semi-efficient sulfur curative systems which comprise high accelerator-sulfur ratio~ as contrasted with conventional sulfur curative systems wherein ~he amount of sulfur exceeds the amount of the accelerator.
One aspect o the invention comprises adding a polyamide resin plasticizer to the blend which plas~icizer extends the range of proportions of resin in ~he composition while retaining elastoplasticity. For example, without resin plasticizer the weight of resin cannot exceed the weight of rubber without losing rubberlike elasticity, whereas, with resin plasticizer the weigh~ of resin may exceed the weight of rubber so long as the amount of resin does not com-prise more than 50 weight percent of the total composition and the weight of plasticizer does not exceed the weight of resin.
Generally, the quantity of polyamide resin plasticizer when present is between 10-30 weight percent of the total composi-tion. Any polyamide resin plasticizer may be used. Sulfon-amide plasticizers comprise an important class of polyamideresin plasticizer~, for example, N-butyl benz~lsulfonamide N-cyclohexyl-p-toluenesulfonamide, o,p-toluenesulEonamide, N-ethyl o,p-toluenesulfonamide and N-ethyl-o-toluenesul~on-amide.
Another aspeck of the invention comprises adding a rubber antide~radant to the blend prior to dynamic vulcaniza-tion. The presence of a r~ber antidegradant protects the blend rom thermal and/or oxidative degradation res~lting in compositions with superior properties. Preferredly, the rub~er antidegxadant is added early in the mixing cycle,and more pre~erredly, for greater effectivenes6 the antidegradant ;7~1L

is masterbatched with the rubber and a portion of the rubber-antidegradant masterbatch is mixed with the resin. The resin then melts and after complete mixing, the composition is dynamically cured as described above. E'or suitable rubber antidegradants, refer to Rubber World Blue Book, supra, pages 107-140.
The properties of the elastoplastic compositions of this invention may be modi~ied, either before or after ~ulcani-2ation, by addition of ingredients which are co~ventional in the compounding of diene rubber, polyami~e resin and blends thereof. Examples of such ingredients include carbon black, silica, titanium dioxide, colored pigments, clay, zinc oxide~
stearic acid, accelerators, vulcanizing agents, sulfur, stabilizers, antidegradants, processing aids, adhesives, tackifiers, rubber plasticizers, wax, prevulcanization inhi-bitors, discontinuous ~ibers such as wood cellulose fibers and extender oils. The addition o~ carbon black, rubber plasticizer or both, preferably prior to d~namic vulcanization, are particularly recommended. Preferredly, the carbon black and/or rubber plasticizer is masterbatched with the rubber and the masterbatch is mixed with the resin. Carbon black improves the tensile strenyth and rubber plasticizer can impro~e the resistance to oil swell, heat stability~ hysteresis, cost and ; permanent set of the elastoplastic compositions. Aromatic, naphthenic and parafinic extender oils are plastici~ers for polybutadiene and butadiene-vinylaxene type rubbers. Plasti-ciæers can also improve processability. For suitable extender oils, refer to Rubber World Blue Book, supra, pages 145-190.

The quantity of ex~ender oil added depends upon the properties desired, with the upper limit depending upon ~he compatibility of the particular oil and blend ingredients which limit is 67~

exceeded when excessive exuding of extender oil occ~rs.
Typically, 5-75 parts by weight extender oil are added per 100 parts by weight of rubber and polyamide resin. Commonly about 10 to 60 parts by weight of extender oil are added per 100 parts b~ weight o rubber in the bllend with guantities of about 20 to 50 parts by weight of extender oil per 100 parts by weight of rubber being preferred. Typical addition~ of carbon black comprise about 20-100 parts by weight o carbon black per 100 parts by weight o rubber and usually about 25-60 parts by weight carbon black per 100 parts total weight of rubber and extender oil. The amount of carbon black which can be used depends, at least in part, upon the type of black and the amount of extender oil to be used. The amount of extender oil depends, at least in part, upon the type of rubber.
High viscosity rubbers are more highly oil extendable. If nitrile rubber is used, polyvinylchloride-typa plasticizers are commonly used in place of extender oils.
Elastoplastic compositions o the invention are useful for making a variety o articles such as tires, hoses, belts, gaskets, moldings and molded parts. They are particularly u~eul for making articles by extrusion, injection molding and compression molding technigues. ~hey also are useful ~or modifying thermoplastic resins, in particular, polyamide resins.
The compositions of the invention are blended with thsrmo-plastic resins using conventional mixing equipmentO The properties o the modified resin depend upon the amount of elastoplastic composition. Generally, the amount is such that the modi~ied rasin contains about 5 to 50 parts by weight of rubber per about 95 to 50 parts total weight of resin.
The stress s~rain properties of ~he compositions are determined in accordance with the test procedures set orth in 7~

ASTM D638 and ASTM D1566. An approximate toughness is calcu~
lated by an abbreviated Griffith equation (TS)2/E (TS= tensile strength, E=Young's modulus). For a detailed analysis, refer to Fracture, edited by ~O Liebowitz, published by Academic Press, New York, 1972, Ch. 6, Fracture of Elastomers by A~ N.
Gent. The compositions are elastomeric, processc~ble as thermo-plastics and reprocessable without the need for reclaiming in - contrast to ordinary thermoset vulcaniza~es. The term "elastomeric" as used herein and the claims means a composition which possesses the property of forcibly retracting within one minute to less than 60~ of its original length after being stretched at room temperature to twice its length and held for one minute before release. The aforesaid definition closely parallels the ~e~inition for rubber as defined by ASTM Standards, V. 28, p. 756 (D1566) which states:

"A rubber in its modified state, free of diluents, retracts within 1 min. to less than 1~5 times its original length after being stretched at room temperature t20 to 27C) to twice its length and held for 1 min. before release."
Especially preferred compositions of the invention are rubbery compositions having tension set values of about 50~ or less.
More preferred compositions are rubbery compositions having a Shore D hardness of 60 or below or a 100~ modulus of 160 Kg./cm2 or less or a Young's modulus below 2000 Kg./cm2.

A typical procedure for the preparation of elasto-plastic compo~itions of the invention comprises mixing, in the indicated proportions, rubber and polyamide resin in a Brabender mixer with an oil bath temperature as indicated for 3~ a time sufficient~ usually be~ween 2-6 minutes, to melt the resin and to form a blend. Hereinafter, mix temperature will be understood to be the temperature oE -the oil bath with the realization that the actual temperature of the mixture may vary~ Curatives are added, if needed~ ~o cross-link the rubber, and mixing is continued until the maximum Brabender consistency is reached, usually between 1-5 minutes,and for an additional two minutes thereaf-ter. The order of mixing can vary but all the ingredients should be added and mixed before substantial vulcanization occurs. The vulcanized but thermo-pla~tic composition is removed, sheeted on a mill (or sheete~
by compression in a press), returned to the Brabender and mixed at the same temperature for two minutes. The material is again sheeted and then compression molded at 200-270C and cooled below 100C under pressure before removal. Properties of the molded~sheet are measured and recorded. The aforesaid procedure is followed in the examples below unless stated otherwise.
Ingredients used to illustrate the invention are N'~(1,3-dimethylbutyl)-N'-(phenyl)-p-phenylenediamine ~Santoflex ~ 13 antidegradant), Polymerized 1,2-dihydro-2,2,4-trimethylquinoline (Flectol ~H antidegradant), m-phenylene bis-maleimide (HVA-2), 2-(morpholinothio)-benzo-thiazole, (Santocure ~- MOR accelerator), tetramethyl-thiuram disulfide (TMTD), and 2-bis-benzothiazyl disulide (MBTS); All ingredients including resin and rubber shown in the Tables are in parts b~ weight.
The data of Table I illustra~e compositions of the invention ¢omprising 66.7 parts by weight nitrile rubber and 33.3 parts by weight polyamide resin. The polyamide resin is Nylon 6,9, poly(hexamethyleneazelaicamide) m.p. 210C which is a condensation product of hexame~hylenediamine and azelaic acid or esterO The nitrile rubber designa~ed A is a nonself-67~

curing copolymer of l,3-butadiene and 41 weiyht percent acrylonitrile haviny a Mooney Viscosity (ML ~ 4) of 60. The nitrile rubber designated B is a self-curing copolymer of 1,3-butadiene and 41 weight percent acrylonitrile having a Mooney Viscosity (ML 1 -~ 4) of 80. Nitrile ru~,ber B when heated alone at 225 C self-cures (scorches within 5 minutes) to the extent that the gel content of the rubber is about 85 percent, (15 waight percent of the rubber is extractable in dichloro-methane).
Elastoplastic compositions are prepared in accordance to the typical pxocedure described above with a Brabender temperature of 210C and mixing speed of 80 rpm. A rubber antidegradant (0.67 parts by weight Flectol ~) is added prior to adding cura~ive (HVA-2). Compositions Stocks 1 and 7 con-tain no curative, whereas, in Stocks 2-6 and 8-12, the amount of curative, HVA-2, is varied.
The data show that the properties of the compositions - containing nonself-curing rubber are significantly improved with ~he addition of curative. An improvement of 100~ or moxe in tensile strength (TS), is obtained with th~ addition of 0.67 part by weight of curative, and the properties continue to increase with increasing curative level. Toughness, (TS)2/E, increases upon addition of curative and continues to improve up to 5.33 parts by weight of curative. Stock 7 illus-trates a composition of the invention prepared with self-cuxing nitrile rubber which composition exhibits excellent properties having especially high toughness. The addition of curative re-sults in only slightly s~ronger but substantially more rigid compositions. The toughness o~ the compositions decreases with increasing curative level.

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Elastoplastic compositions of the invention comprising 15 different nonself-curing nitrile rubbers are illustrated in Table II. The polyamide resin is the same as in Table I and compositions are prepared in the same ma~ner. All compositions contain 66.7 parts by rubbar, 33.3 parts by weight Nylon-6,9, 0.67 parts Flectol ~1 with the cured comp~sitions containing in addition 0.67 parts by weight HV~-2. The acrylonitrile (AN~
content and Mooney Viscosity of the nitrile rubber are shown in the table. The odd numbered stocks are controls containing 1~ antidegxadan~ but no curative and the even numbered s~ocks ; illustrate compositions o the invention in which the rubber is cross-linked by masticating with curative at 210C for 6-8 minutes. The compositions are comprèssion molded into sheets about 2-3 mm ~hick at 255C and cooled under pressure before removal. The gel content (weight percent insoluble in methylene-chloride) of the compositions conkaining no curative were - determined with the same rubber and under similar conditions but in the absence of resin. The cross-link density of the compositions containing curative is greater than 7 x lO 5 moles per milliliter of rubber. The data show that addition of curative resu]ts in a substantial increase in tensile strength, generally, lO0 percent or more. The compositions containing cured rubber also have greater resistance to oil swell. The percent oil swell represents the dimensional increase in a specimen soaked in #3 oil at 150C for 48 hours.
The data indicate that compositions of the invention may be prepared from all nitrile rubbers, regardless of the acrylonitrile content or Mooney Viscosity of the rubber.

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43-0969A ~ 67~

Elastoplas~ic compositions of the inve~tion comprising 8 different self-curing rubbers are illustrated in Table III. The odd numbered stocks contain 66.7 parts by weight nitrile rubber, 33.3 parts by weight nylon 6,9 and 0.67 parts by weight Flectol H. The even numbered stocks contain the same ingredients as the odd numbered stocks but, in additionr contain 0.67 parts by weight HVA-2. All stocks are masticated in a Brabender mixer at 210~C for a total mix time of 6-8 minutes via the typical procedure as explained above. The compositions are compression molded into sheets about 2-3 mm thick at ~55C and cooled under pressure beEore removal. The gel content (weight percent insoluble in methylenechloride) of the compositions contain-ing no curative were determined with the same rubber and under similar conditions but in the absence of resin. The cross-link density of the compositions containing curative is greater than 7 x 10 5 moles per milliliter of rubber.
The data indicate that the self-curing rubbers give thermo-plastic elastomeric compositions having excellent properties without curatives. The addition of curative increases the tensile strength, modulus and Youngls modulus. The properties ; of the compositions are similar regardless of the acrylo-nitrile content or Mooney Viscosity of the nitrile rubber in the blend~

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The data o Table IV illustrate compositions com-prising different proportions of nitrile ru~ber and poly-amide resin. The nitrile r~ber is a self-curing rubber containing 43 weight percent acrylollitrile having a Mooney Viscosity of 95. The polyamids res:Ln is Nyl~n 5,9. The procedure for preparing the c~mpositions is the same as in ~ables I-III. The data show that tensile strength and modulus decrease with increasing proportion of rubber.
The data further show that the toughness, (TS)2/E', of tha compositions are essentially the same up to 40 parts by weight rubber with a substantial jump in toughness when the amount of rubber is 50 parts by weight and from that point on touyhness increases with rubber content.

. .

-26~-~ 43-0969A 1~0~671 TABLE IV
' Nitrile 20 30 40 50 60 66.7 70 75 80 rubber . Nylon 80 70 60 50 40 33.3 30 25 20 - 6,9 Flectol H 0~2 0.3 0.4 O.S 0.6 0.67 0.7 0.75 0.8 H~A-2 0.2 0.3 0.4 O.S 0.6 0.67 0.7 0.75 0.8 mix ~peed, 80 80 80 80 80 80 80 80 80 rpm - mix temp, 210 210 210 210 210 210 210 210 210 ' Ult. ten- 358 300 252 234 219 202 190 180 lS4 sile strength, Kg. /cm2 lOQ% mod- 308 271 214 160 129 108 135 94 75 ulus,Kg./cm2 Youngls 6311 ~204 3533 1959 1232 785 654 463 228 Modulus, Kg./cm2 Ult.Elon- 240 240 260 300 320 320 190 240 250 gation,%
(TS) /E, 20 21 18 28 39 52 55 70 104 Kg . /cm~
tension 86 83 73 58 44 33 32 21 16 set,~

:

i7~

Elastoplastic compositions of the invention contain-ing dif~erent polyamide resins are illus-trated in Ta~le V.
The polyamide resin is poly~hexamethyleneisophthalamide) m.p.
220C, Nylon IP, in Stocks 1 and 2; poly(caprolactam~ mOp.
21~C, Nylon 6, in Stocks 3 and 4, copolymer of Nylon 6 and Nylon 6,6, m.p. 243C, Nylon 6-6,6 in Stock 5; and poly-hexamethyleneadipicamide, m.pO 264C, Nylon 6,6 in Stocks 6 and 7. The compositions are prepared by the typical procedure.
TABLE V

Nitrile rubber 601 601 601 66.71 602 603 603 Nylon IP 40 40 Nylon 6 - - 40 33.3 Nylon 6-6,6 - - - - 40 Nylon 6,6 - - - - - 40 40 A-2 0 2 2 0067 û.6 - 1.2 ~ntidegradant o.64 o.64 0.64 - o.65 1~25 1 25 mixing temp,C 220 220 220 220 250 270 270 UTS, K~O/cm2 179 271 218 219 159 74 216 2Q 100% modulus,Kg./cm2 162 217 177 136 143 - 184 Young's modulus, 1707 3341 1687 1034 1546 822 3305 Kg./cm2 Ult. Elongation, % 150 190 180 260 140 70 180 (TS)2~E, Kg./cm2 19 22 28 46 16 7 14 Shore D hardness - - 43 46 40 55 - tension set, ~ - - - 31 49 - 45 1 Self-cuxing nitrile rubber, acrylonitrile content 43 wt.~, Mooney Uisc~ 95.
2 Nonself-curing nitrile rubber, acrylonitrile content 45 wt.~, Mooney Visc. 600 Cure system includes 0.15 pa:rts MBTS.
- 3 Nonself-cuxing nitrile rubber, acrylonitrile content 39 wt. %, Mooney Vi~cosi ty 5 0 .
4 Santoflex 13 5 Flectol H

43-0959A ~ ~ ~ 7 1 Thermoplastic elastomeric compositions oE the inven-tion containing styrene-butadiene rubber are illustrat~d in Table VI. The rubber is a cold polymexized butadiene-styrene rubber having a target bound styrene of 23.5% and nominal Mooney Viscosity of 52. The composikio}ls, in which the relative proportions of rubber and polyamide resin are varied, are prepared by the typical procedure as previously describad.
The data indicate that stronger, more r:igid compositions are obtained as the proportion o~ n~lon increases. Contrary to the results obtained with nitrile rubber, increasing the proportion of SBR-rubber does not improve toughness.
TABLE VI
_ 2 3 4 5 6 SBR-1502 80 75 70 66.7 60 50 Nylon 6,9 20 25 30 33.3 40 50 H~A-2 0.8 0.75 0.7 0.67 0.6 0.5 Flectol H 0.8 0.75 0.7 0.67 0.6 0.5 mix speed,rpm 80 80 80 80 80 80 mix temp., C 210 210 210 210 210 210 molding temp.,C 255 255 255 255 255 255 Ult. tensile strength, 63 6g 86 109 149 187 Kg./cm2 lOO~mo~ulus, 52 60 75 89 109 152 Kg./cm Young's modulus, 239 341 534 664 966 1600 Kg./cm2 Ult. Elong , % 140 130 140 160 200 200 (TS)2fE, 17 14 14 18 23 22 Kg./cm2 :

43-0969A ~ ~O ~67~

Compositions of the invention containing polybuta-diene rubber are illustrated in Table VII. The compositions are prepared by the typical procedure.

TABLE ~II

Polybutadiene Rubberl 66.7 Polybutadiene Rubber2 - 66.7 Nylon 6,9 33.3 33.3 Flectol H 0.67 0.67 HVA-2 0.67 0.67 mix speed, rpm 80 80 mix temp~, C 210 210 Ul tensile strength, 98 110 Kg./cm2 100% modulus, Kg./cm2 91 94 Young's modulus, Kg./cm2 845 743 20.
Ult. ~lvng., % 120 150 (TS)2/E, Kg./cm2 11 16 1 Nonstaining polybutadiene rubber, 98% cis content, Mooney Viscosity of 41.
2 Nonstaining, solution polymerized, polybutadiene rubber.

.

43-0969A ~ 7~

Compos.itions o the invention containing polyamide resin plasticizer are illustrated in TahIe VIII~ The com~
positions are prepared in a Bxabender mixer by the typical pro-cedure. The polyamide resin, nitrile ru~ber and plastici zer are added simultaneously at a mixing temperature of 215C. The mixing speed is 150 rpm until the resin is melted and the blend is then mixed at 80 rpm for 5 minutesO In stocks con-taining curative, the curative is added after 2 minutes of the 80 rpm cycle. Specimens are molded at 225-230C. All parts by weight~
T~BLE VIII
l 2 3 ~ 5 6 Nitrile rubberl 40 40 40. 40 40 40 Nylon 6,9 60 60 60 60 60 60 Flectol H 0.4 0.4 0.4 0.4 0.4 0.4 Antidegradant N-ethyl IP- ~ 20 20 30 40 toluenesulfonamide ~VA~2 - 0.4 - 0.4 0.4 0.4 Ult. t~n. str., 257 301 193 243 217 164 20 Kg./cm lO0~ m~dulus, 228 233 144 157 133 117 Kg./cm ~oung'~ modulus, 3905 4509 1490 1748 1451 1300 : Kg.~cm (TS)2/E, Kg./cm2 17 29 25 34 32 21 : Ult. Elong., % 210 300 250 310 340 280 : Shore D hardness 61 61 49 50 45 43 tension set, % 68 73 51 56 53 52 1 Sel-curing nitrile rubber, acrylonitrile content 43 wt %, Mooney Vi~cosity 95.
30.

The data indicate that stiff, hard, nonelastomeric compositions (Stocks 1 and 2) containing resin as the major componPnt may be modified by addition of resin plasticiæer to give flexible, soft, tougher elastomeric compositions (Stocks 3-6) with Young's modulus less than 2000 Kg./cm2, Shore D hardness of 50 or less and tension set of less than 60%-TABLE IX

Nitrile rubberl 60 60 60 60 Nylon2 6-6,6 40 40 40 40 Zinc oxide ~ 3 Stearic acid - 0.3 - -TMTD - 1.2 Santocure ~OR - 0.6 Sulfur - 0.12 HVA 2 - - 1.8 MBTS - - O.45 Peroxide3 ~ ~ ~ 0 3 20 TS, Kg./cm2 32 85 87 81 100% M~ Kg./cm~ 25 '75 38 62 ~oung's modulus, Kg~/cm2 63 348 65 174 Ult. Elongation, % 290 160 310 220 (TS)2/E, Kg./cm2 16 21 116 38 Tension set, % 72 15 51 31 5hore D hardness 17 35 28 32 1 Nonself-curing nitrile rubber, acrylonitrile content 39 wt~
Mooney Viscosity 50, gel ~ontent under cure conditions ~ans curative 65%.
: 30 2 Copolymer of Nylon 6 and Nylon 6,6 m.p. 160C.

- 3 2,5-Dimethyl-2,5-bis(t-butylperoxy)hexane ~90% act.ive).

43-0969A ~ 7~

Compositions of the invention with sulfur and peroxide curative systems are illustrated in Table IX. The compositions are prepared b~ the typical procedure except khe mixing tempera-ture is 180C and the mixing speed is 150 xpm until the nylon re~in is melted after which ~he mixing speed is 80 rpm. The molding tempera~ure is 220C. Stock 1 is a control containing no curative. S~ock 2 illustrates a composition prepared with an accelerated sulfur curative system. Stock 3 illustrates a composition made using an activated m-phenylene bis-maleimide curative system. Stock 4 illustrates a composition with a peroxide curative. The compositions of Stocks 2, 3 and 4 are thermoplastic elastomers and exhibit improved properties.
Although the invention has been illustrated by typical examples, it is not limited thereto. Changes and modi ications of the examples of the invention herein chosen for purposes of di~closure can be made which do not constitute departure from the spirit and scope of the invention.
'~

Claims (35)

The embodiments of the invention in which and ex-clusive prperty or privilege is claimed are defined as follows:

1. An elastoplastic composition comprising a blend essentially free of low molecular weight phenol plasticizer of a) thermoplastic crystalline polyamide in an amount sufficient to impart thermoplasticity up to 50 weight percent of the com-position, wherein the polyamide in said blend retains at least 50% of its original crystallinity, b) rubber cross-linked to the extent that the gel content of the rubber is at least about 80 percent, wherein the rubber in said blend is in the form of small dispersed particles essentially of the size of 50 microns or below and is a homopolymer of 1,3-butadiene, co-polymer of 1,3-butadiene or isoprene or mixtures thereof, in an amount sufficient to impart rubberlike elasticity up to 80 weight percent of the composition provided that, when the amount of polyamide exceeds the amount of rubber, sufficient inert plasticizer is present to impart rubberlike elasticity to the composition which composition is processable as a thermoplastic and is elastomeric.

2. The composition of claim 1 containing inert plasti-cizer in an amount not exceeding the weight of polyamide in which the total weight of the rubber and inert plasti-cizer does not exceed 80 weight percent of the composition.

3. The composition of claim 2 in which the inert plasti-cizer is selected from the group consisting of phthalate plasticizers, adipate plasticizers, phosphate plasticizers, glycolate plasticizers, sulfonamide plasticizers, trimellitate plasticizers and polymeric type permanent plasticizers.

4. The composition of claim 3 in which the plasticizer is a sulfonamide plasticizer.

5. An elastoplastic composition comprising a blend essentially free of low molecular weight phenol plasticizer, of a) about 20 - 50 parts by weight of thermoplastic crys-talline polyamide, wherein the polyamide in said blend retains at least 50% of its original crystallinity and b) about 80 - 50 parts by weight of rubber per 100 parts total weight of poly-amide and rubber, wherein the rubber in said blend is in the form of small dispersed particles essentiallly of the size of 50 microns or below and is cross-linked to the extent that the gel content of the rubber is at least about 80 percent, the rubber being a homopolymer of 1,3-butadiene, a copolymer of 1,3-butadiene or isoprene copolymerized with vinylarene monomer or vinyl nitrile monomer or mixtures thereof, which composition is processable as a thermoplastic and is elasto-meric.

6. The composition of claim 5 containing inert plasti-cizer in an amount not exceeding the weight of polyamide in which the total weight of the rubber and plasticiser does not exceed 80 weight percent of the composition.

7. The composition of claim 6 in which the plasticizer is selected from the group consisting of phthalate plasticizer, adipate plasticizers, phosphate plasticizers, glycolate plasti-cizers, sulfonamide plasticizers, trimellitate plasticizers and polymeric type permanent plasicizers.

8. The composition of claim 7 in which the plasticizer is a sulfonamide plasticizer.

9. The composition of claim 6 wherein the polyamide has a melting point between 160°-230°C.

10. The composition of claim 5 in which the rubber is cross-linked to the extent that the composition contains no more than about four percent by weight of rubber extract-able at room temperature or that the cross-link density deter-mined on the same rubber as the composition is greater than about 3 x 10-5 moles per ml of rubber.

11. The composition of claim 10 in which the rubber is cross-linked to the extent that the cross-link density of the rubber is at least about 5 x 10-5 moles per ml.

12. The composition of claim 10 which contains no more than about four percent by weight of rubber extractable.

13. The compostion of claim 11 in which the rubber is a copolymer of 1,3-butadiene and acrylonitrile.

14. The composition of claim 13 in which the polyamide is a crystalline linear polyamide.

15. The composition of claim 5 prepared by masticating the blend at cross-linking temperature until the rubber is cross-linked.

16. The compostion of claim 14 in which the blend com-prises about 20 to about 45 parts by weight polyamide and about 80 to about 55 parts by weight rubber.

17. The compostion of claim 16 having a tensile strength at least 50% higher than that of the composition containing noncross-linked rubber.

18. The composition of claim 13 in which the polyamide is a crystalline linear polylactam.

19. The composition of claim 18 in which the polyamide is polycaprolactam.

20. The composition of claim 12 in which the rubber is a homopolymer of 1,3-butadiene.

21. The composition of claim 20 in which the blend comprises about 20 to about 45 parts by weight polyamide and about 80 to about 55 parts by weight rubber.

22. The composition of claim 21 having a tensile strength at least 50% higher than that of the same composition containing noncross-linked rubber.

23. The composition of claim 5 in which the rubber is self-curing nitrile rubber.

24. The composition of claim 14 in which the particle size is below 20 microns.

25. The composition of claim 1 containing 10 - 30 weight percent inert plasticizer.

26. The composition of claim 5 containing 10 - 30 weight percent inert plasticizer.

27. An elastoplastic composition consisting essentially of a blend of about 20 - 50 parts by weight of thermoplastic crystalline polyamide wherein the polyamide in said blend re-tains at least 50% of its original crystallinity and about 80 - 50 parts by weight of rubber per 100 parts total weight of polyamide and rubber wherein the rubber in said blend is in the form of small dispersed particles essentially of the size of 50 microns or below and is a homopolymer of 1,3-butadiene or copolymer of 1,3-butadiene or isoprene or mixtures thereof and is cross-linked to the extent that the gel content is at least about 80 percent, which composition is processable as thermo-plastic and is elastomeric.

28. The composition of claim 27 in which the blend contains about 20 - 45 parts by weight of thermoplastic crystalline polyamide and about 80 - 55 parts by weight of rubber per 100 parts total weight of polyamide and rubber, the rubber being a copolymer of 1,3-butadiene copolymerized with vinyl nitrile monomer.

29. The composition of claim 28 in which the vinyl nitrile monomer is acrylonitrile.

30. The composition of claim 29 which contains a phenolic compound having a molecular weight of at least 200.

31. A modified thermoplastic crystalline polyamide prepared by blending said polyamide and elastoplastic com-position of claim 27 in an amount such that the modified polyamide contains about 5 to 50 parts by weight of rubber per about 95 to 50 parts total weight of polyamide.

32. The polyamide of claim 31 in which the elastoplastic composition contains about 20 to 50 parts by weight of thermo-plastic crystalline polyamide and 80 to 50 parts by weight of rubber per 100 parts total weight of polyamide and rubber.

33. The polyamide of claim 32 in which the rubber of the elastoplastic composition is a copolymer of 1,3-butadiene and acrylonitrile.

34. The polyamide of claim 33 in which the polyamide is linear polyamide having a melting point between 160° to 230°C.

35. The polyamide of claim 34 in which the polyamide is polycaprolactam.