WO1991009903A1

WO1991009903A1 - Thermoplastic elastomers based upon chlorinated or chlorosulfonated polyethylene and a crystalline olefin polymer

Info

Publication number: WO1991009903A1
Application number: PCT/US1991/000082
Authority: WO
Inventors: Oliver C. Ainsworth; Ronald L. Glomski
Original assignee: The Dow Chemical Company
Priority date: 1990-01-04
Filing date: 1991-01-04
Publication date: 1991-07-11
Also published as: EP0461252A4; ES2116287T3; DK0461252T3; JP2703113B2; DE69129516D1; US4978703A; DE69129516T2; CA2050354C; EP0461252A1; CA2050354A1; JPH04505034A; EP0461252B1

Abstract

A chlorinated or chlorosulfonated polyethylene is dispersed in a polyolefin and vulcanized, the vulcanizate is then dispersed into a thermoplastic chlorinated or chlorosulfonated polyethylene forming a partially cross-linked thermoplastic chlorinated or chlorosulfonated polyethylene vulcanizate having good interply adhesion, hot weld strength, processable on commercially available equipment, and crack resistance.

Description

THERMOPLASTIC ELASTOMERS BASED UPON

CHLORINATED OR CHLOROSULFONATED POLYETHYLENE

AND A CRYSTALLINE OLEFIN POLYMER

The present invention generally relates to thermoplastic elastomer compositions comprising blends of chlorinated or chlorosulfonated polyethylene (PE) and a crystalline olefin polymer. The present invention particularly relates to vulcanized chlorinated or chlorosulfonated PE blended with crystalline polyolefins and blended with either thermoplastic chlorinated or thermoplastic chlorosulfonated PE or mixtures thereof. The present invention also relates to the preparation of said compositions by dynamic vulcanization or by a sequential combination of dispersion of the vulcanized material and dispersion of the remaining chlorinated or chlorosulfonated PE. The present invention further relates to the use of a nonperoxide cure package to accomplish said dynamic vulcanization.

Thermoplastic elastomers, which can be processed and fabricated by methods used for thermoplastics and which do not require vulcanization to develop elastomeric properties, are known (see, for example, U.S. Patent No. 3,265,765 as well as Hartman et al., "Butyl Grafted to Polyethylene Yields Thermoplastic Elastomer," Rubber World, October 1970, pp. 59-64).

Dynamic vulcanization is a process whereby a blend of plastic, rubber and rubber curative is masticated while curing the rubber. The term "dynamic" indicates the mixture is subjected to shear forces during the vulcanization step as contrasted with "static" vulcanization wherein the vulcanizable composition is immobile (in fixed relative space) during vulcanization. One advantage of dynamic vulcanization is that elastoplastic (thermoplastic elastomeric) compositions can be obtained when the blend contains the proper proportions of plastic and rubber. Dynamic vulcanization processes are described in U.S. Patent Nos. 3,037,954; 4,104,210; 4,116,914; 4,141,863; 4,141,878; 4,173,556; 4,271,049; 4,287,324; 4,288,570; 4,299,931; 4,311,628 and 4,338,413.

Known dynamic vulcanization processes are believed to be somewhat unsuitable for making soft compositions because as the rubber level rises the resulting compositions become less fabricable. In other words, the compositions give poor extrudates and, sometimes, cannot be extruded at all. Accordingly, there is a need for processes for preparing soft, extrusion fabricable, thermoplastic elastomeric compositions.

U.S. Patent No. 4,130,535 discloses thermoplastic vulcanizates or blends of polyolefin resin and monoolefin copolymer rubber which are processable in the same manner as thermoplastics even though the rubber is fully cured. The thermoset state is avoided by simultaneously masticating and curing the blends. The blends comprise from 25 to 95 percent by weight of the resin and from 75 to 5 percent by weight of the rubber. Oil extended vulcanizates have a ratio of from 35 to 65 percent of the resin and from 65 to 35 percent of the rubber. Peroxide, azide and sulfur vulcanizing agents can be used to effect curing of the rubber. Typical monoolefin copolymer rubbers include saturated EPM (ethylene-propylene rubbers) or unsaturated EPDM (ethylene-propylene-diene terpolymer rubbers).

U.S. Patent No. 4,594,390 teaches that improved thermoplastic elastomer materials are obtained when a composition comprising polypropylene, an EPDM rubber, an extender oil and a curative is masticated at a shear rate of at least 2000 sec^-1. Suitable results -are obtained with shear rates of from 2500 to 7500 sec^-1.

U.S. Patent No. 4,207,404 discloses thermoplastic elastomer compositions prepared by dynamic vulcanization of blends of chlorinated PE and nylon in the presence of a peroxide vulcanizing agent.

U.S. Patent No. 3,806,558 discloses partially cured blends of a monoolefin copolymer rubber, such as those disclosed in U.S. Patent No. 4,130,535, and a polyolefin, usually PE or polypropylene. The blend is mixed with a small amount of curative, and subjected to curing conditions while working the mixture dynamically.

A. Y. Coran, R. P. Patel and D. Williams, in an article entitled "Rubber-Thermoplastic Compositions, Part V., Selecting Polymers for Thermoplastic Vulcanizates," Rubber Chemistry and Technology, Vol. 55, 116 (1982), describe approximately 100 thermoplastic vulcanizate compositions, based on 9 kinds of thermoplastic resins and 11 kinds of rubber. All compositions contain 60 parts of rubber and 40 parts of plastic.

One of the applications for chlorinated or chlorosulfonated PE vulcanizate blend compositions is in single ply roofing membranes. However, microbial action causes cracking or "alligatoring" in such membranes. While thermoplastic chlorinated or chlorosulfonated PE is easily fabricatable in sheet form, it tends to crack. While thermoset or vulcanized chlorinated or chlorosulfonated PE is more resistant to microbial cracking, it is less easily fabricatable. Therefore, a blend of the two would be advantageous for blending the features of both. However, it is not possible to partially cross-link or vulcanize one chlorinated or chlorosulfonated PE in the presence of another without also affecting the other.

It has now been found that chlorinated or chlorosulfonated PE, as well as various mixtures or blends blended or crosslinked with crystalline thermoplastic polyolefin polymers have features not known to previously available elastomeric compositions of the single polymers themselves or which skilled practitioners would be lead to employ.

The invention resides in a blend of a .thermoplastic elastomer material comprising from 35 to 50 parts of an amorphous chlorinated or chlorosulfonated PE and from 15 to 30 parts of a crystalline thermoplastic polyolefin polymer, said composition having a tension set value, at 100 percent elongation, of less than 50 percent, a decreased heat distortion temperature and decreased shrinkage at 80°C.

The invention further resides in a thermoplastic elastomeric composition having a tension set value, at 100 percent elongation, of less than 50 percent, which is resistant to environmentally induced cracking, said composition comprising a blend of from 35 to 45 parts by weight of an admixture of a crosslinked amorphous chlorinated or chlorosulfonated PE, and from 15 to 25 parts by weight a crystalline thermoplastic polyolefin resin, said crosslinking being carried out in the presence of a vulcanizing package comprising an inorganic base and an activator material selected from 2,5-dimercapto-1,3-thiadiazole or a derivative of 2,5- dimercapto-1,3,4-thiadiazole , said activator material being initially present in an amount of from 0.5 to 1.5 parts by weight, and the residue of said activator material being present in the composition.

The invention also resides in a blend of a thermoplastic elastomer, having therein a vulcanized elastomer, composition comprising a blend elastomer material of from 35 to 50 parts of a vulcanized chlorinated PE in admixture with from 15 to 30 parts of a crystalline thermoplastic polyolefin polymer, said admixture being further admixed with from 15 to 60 parts of a thermoplastic chlorinated or chlorosulfonated PE.

The invention additionally resides in a process for preparing a cross-linked blend of a thermoplastic elastomer material having a tension set value, at 100 percent elongation, of less than about 50 percent comprising the steps of: (a) forming a heat-plastified, substantially uniform admixture comprising an amorphous chlorinated or chlorosulfonated PE, a crystalline thermoplastic polyolefin polymer and an inorganic base; and (b) dispersing a vulcanizing material for the chlorinated or chlorosulfonated PE throughout the admixture to activate the vulcanizing material without substantially degrading any component of the composition and to cure substantially all of the chlorinated or chlorosulfonated PE, said vulcanizing material being selected from a derivative of 2,5-dimercapto-1,3,4- thiadiazole or a combination of 2,5-dimercapto-1,3,4- thiadiazole and an activator material.

The invention also resides in a process for preparing a blend of thermoplastic elastomer material having a tension set value, at 100 percent elongation, of less than about 50 percent from a blend of an amorphous chlorinated or chlorosulfonated PE and a crystalline thermoplastic polyolefin polymer which comprises forming a heat-plastified, substantially uniform admixture comprising said amorphous chlorinated or chlorosulfonated PE and said crystalline thermoplastic polyolefin polymer.

The materials of the invention suitably have a tension set value, at 100 percent elongation (ASTM D412), of less than about 50 percent. Materials having tension set values of greater than 50 percent are believed to be unsuitable for use as elastomers. Thus, another aspect of the present invention is a thermoplastic elastomeric composition resistant to environmentally induced cracking, in which the composition comprises a blend of from 10 to 75, preferably from 35 to 45, parts by weight of an admixture of a cross-linked amorphous chlorinated or chlorosulfonated PE and from 10 to 65, preferably from 15 to 25, parts by weight of a crystalline thermoplastic polyolefin resin, the cross-linking being carried out in the presence of a vulcanizing package initially present at from 0.5 to 1.5 parts by weight (the residue only being present in the composition) and from 15 to 60, preferably from 8 to 15,. parts by weight of a semicrystalline chlorinated or chlorosulfonated PE dispersed therethrough as the continuous phase, forming a partially cross-linked blend elastomer which is resistant to environmental cracking.

The crystalline thermoplastic polyolefin polymer is a solid, high molecular weight, resinous plastic material made by polymerizing olefins such as ethylene, propylene, butene-1, pentene-1, 4-methyl- pentene, and the like, by conventional processes. Illustrative polymers include low density PE (0.910 to 0.925 grams per cubic centimeter (g/cc)), medium density PE (0.926 to 0.940 g/cc) or high density PE (0.941 to 0.965 g/cc), whether prepared by high pressure processes or low pressure processes. Polyesters such as PE terephthalate may also provide suitable results. Particularly suitable polymers include the crystalline forms of polypropylene. Crystalline block copolymers of ethylene and propylene (which are plastics distinguished from amorphous, random ethylene-propylene elastomers) can also be used. Included among the polyolefin resins are the higher alpha-olefin modified PEs and polypropylenes (see,"Polyolefins," N. V. Boenig, Elsevier Publishing Co., N. Y. 1966).

Materials other than crystalline thermoplastic polymers can be used in conjunction with the amorphous chlorinated or chlorosulfonated PE provided such materials are mechanically compatible therewith. "Mechanically compatible", as used herein, means that the polymers form a two-phase mixture that does not undergo substantial delamination. Illustrative materials believed to meet this criterion include glassy polymers such as polycarbonates, styrene-acrylonitrile copolymers and terpolymers of acrylonitrile, butadiene and styrene.

The chlorosulfonated PE useful in this invention is typically a material having from 20 to 48 weight percent chlorine and from 0.4 to 3.0 weight percent sulfur. Typical preparations of chlorosulfonated PE are given in U.S. Patents 2,586,363 and 2,503,252.

Chlorinated PE starting materials suitable for purposes of the present invention are finely-divided particles which must meet four physical property criteria. First, the materials must have a weight average molecular weight of from 40,000 to 300,000.

Second, the materials must have a chemically combined chlorine content of from 20 to 48 percent by weight of polymer. Third, the materials must have a 100 percent modulus, measured in accordance with ASTM Test D-412, from 0.5 to 4.8 MPa. Fourth,, the materials must have a heat of fusion of from 0 to 15 calories per gram, preferably from 0 to 10 calories per gram.

Chlorinated PE materials meeting the aforementioned physical property criteria can be prepared by a chlorination procedure of the type disclosed in U.S. Patent No. 3,454,544.

Satisfactory chlorinated PE resins are readily obtained by a chlorination procedure which comprehends suspension chlorination, in an inert medium, of a finely divided, essentially linear PE or olefin interpolymer. The interpolymer contains at least about 90 mole percent ethylene with the remainder being one or more ethylenically unsaturated monomers polymerizable therewith. The polymer is first chlorinated at a temperature below its agglomeration temperature for a period of time sufficient to provide a partially chlorinated polymer having a chlorine content of from 2 to 23 percent chlorine, based on the total weight of polymer. This is followed by sequential suspension chlorination of the partially chlorinated polymer, in a particulate form, at a particular temperature. The particular temperature is, with respect to the olefin interpolymer, above its agglomeration temperature but at least about 2°C below its crystalline melting point. Sequential chlorination is continued for a period of time sufficient to provide a chemically combined chlorine content of up to about 48 percent by weight of polymer.

Useful ethylenically unsaturated monomers include nonaromatic hydrocarbon olefins having three or more carbon atoms such as propylene, butene-1,

1,4-hexadiene, 1,5-hexadiene, octene-1, 1 ,7-octadiene, 1,9-decadiene, and the like; substituted olefins such as acrylic acid, acrylic acid esters, and the like; alkenyl aromatic compounds such as styrene and its derivatives, and other known polymerizable materials.

The temperature at which chlorination normally leads to agglomeration of polymer particles depends to a large extent on the nature and molecular weight of the polymer to be chlorinated. In the case of crystalline and predominantly straight-chain PEs having a branching of the chains of less than one methyl group per 100 carbon atoms and a density of at least 0.94 g/cc, the temperature is above 95°C, preferably above 100°C, and more preferably about 110°C. In the case of- PEs having a relatively marked branching of the chains and a lower density, the temperature is lower, about 65°C.

The temperature employed in the sequential chlorination must be greater than that employed in the initial chlorination in order to prevent (a) retention of excessive undesirable crystallinity and (b) formation of nonuniformly chlorinated polymer. The temperature employed in the sequential chlorination must also be below the crystalline melting point of the polymer being chlorinated in order to prevent accelerated particle size growth and development of undesirable agglomeration of polymer particles.

After a polyolefinic material has been suspension chlorinated to a desired degree, it can easily be filtered from suspension in the inert suspending liquid, washed and dried to prepare it for subsequent use.

The present invention is not restricted to chlorinated PE resins prepared by suspension or slurry chlorination procedures. Solution chlorination and bulk, or fluidized bed, chlorination procedures may also be used provided the polymers produced thereby meet the aforementioned requirements with regard to chlorine content and residual crystallinity.

The thermoplastic elastomers or vulcanizates of the present invention are suitably cured with a cure package comprising an inorganic base and 2,5-dimercapto 1,3,4-thiadiazole or a derivative thereof. These cure packages are disclosed in U. S. Patent Nos. 4,128,510 and 4,288,576.

Peroxide cure packages are believed to be unsuitable for use in curing blends as disclosed herein, particularly where the crystalline olefin polymer is polypropylene. Physical properties and handling characteristics of the blends indicate either a lack of sufficient cross-linking or at least partial degradation of the polypropylene.

Illustrative derivatives of 2,5-dimercapto- 1,3,4-thiadiazole include:

wherein X is a substituent selected from hydrogen, -CRR'OH, -(CH₂-CH-O)_nH,

where m is an integer of from 2 to 10; n is an integer of from 1 to 5; R and R' are selected from hydrogen, alkyl groups containing from 1 to 8 carbon atoms, and aryl, alkaryl or aralkyl groups containing from 6 to 8 carbon atoms; R² is an alkyl group containing from 1 to 17 carbon atoms, an aryl group containing one or two rings, an alkaryl group containing from 7 to 14 carbon atoms, an aralkyl group containing from 7 to 8 carbon atoms or a cyclohexyl group; and R³ is an alkyl group containing from 1 to 8 carbon atoms. X' can be the same as X with the exception of hydrogen and Y is zinc, lead,

r

where R⁴ is an alkylene or alkenylene group containing from 1 to 8 carbon atoms, or a cycloalkylene, arylene or a alkarylene group containing from 6 to 8 carbon atoms; z is 0 or 1; and R⁵ is an alkylene group containing from 2 to 8 carbon atoms or a phenylene, methylphenylene or methylenediphenylene group.

Inorganic basic materials suitable for use in conjunction with derivatives of 2,5-dimercapto-1,3,4- thiadiazole include materials such as metal oxides and hydroxides and their salts with weak acids, such as, for example, magnesium hydroxide, magnesium oxide, calcium oxide, calcium hydroxide, barium oxide, barium carbonate, sodium phenoxide and sodium acetate. These basic materials also serve as heat stabilizers for the chlorinated or chlorosulfonated PE. Thus, they are beneficially admixed with the chlorinated or chlorosulfonated PE before the polymer blend is converted to a heat-plastified admixture rather than in conjunction with the thiadiazole derivative. Additional basic material may, if desired, be added together with the thiadiazole derivative. Other basic materials may also be used so long as they do not promote degradation of one of the components of the blend or deactivate the vulcanizing materials. The Basic material is preferably magnesium oxide or magnesium hydroxide.

Basic or activator materials suitable for use in conjunction with 2 , 5-dimercapto- 1 , 3 , 4-thiadiazole include (1) amines having a boiling point above 110°C, and a pK value below 4.5; (2) salts of amines having pK values below 4.5 with acids having pK values above 2.0;

(3) quaternary ammonium hydroxides and their salts with acids having pK values above 2.0; (4) diphenyl- and ditolyl-guanidines; and (5) the condensation product of aniline and at least one mono-aldehyde containing from 1 to 7 carbon atoms, in combination with at least an equal amount of an inorganic base. The term "pK value" refers to the dissociation constants of bases and acids in aqueous solution. Representative values are shown in the Handbook of Chemistry and Physics, 45th Edition, The Chemical Rubber Co., page D-76 (1964). As noted in the preceding paragraph, a certain amount of a basic material such as magnesium oxide or magnesium hydroxide must also be present to heat-stabilize the chlorinated or chlorosulfonated PE.

The plasticizing material is suitably selected from trimellitate esters, phthalate esters, aromatic oils and polyesters of dicarboxylic acids containing from 2 to 10 carbon atoms. The plasticizing material is desirably trioctyl trimellitate.

The ingredients save for the vulcanizing material are mixed at a temperature sufficient to soften the crystalline thermoplastic polymer or, more commonly, at a temperature above its melting point if the polymer is crystalline at ordinary temperatures. Blending is carried out for a time sufficient to form a generally uniform blend of the components. It is accomplished by any one of a number of conventional techniques, for example, in an internal mixer, two-roll mill or extruder. After the resin and rubber are intimately mixed, the vulcanizing material is added. Heating and masticating the blend components at vulcanization temperatures are generally adequate to complete curing in a few minutes. If shorter vulcanization times are desired, higher temperatures may be used, provided they are low enough to preclude substantial degradation of the chlorinated or chlorosulfonated PE.

Suitable vulcanization temperatures range from about the melting temperature of the crystalline thermoplastic polymer (about 130°C in the case of PE and about 175°C in the case of polypropylene) to 250°C or more. Typically, the range is from 150°C to 225°C. A preferred range of vulcanization temperatures is from 180°C to 200°C. Thermoplastic vulcanizates are beneficially prepared by continuously mixing the compositions, after the vulcanizing material is added, until vulcanization is complete.

If desired from an economic point of view, completion of vulcanization may be accomplished by static vulcanization provided that sufficient curing by dynamic vulcanization has occurred before static vulcanization begins. If insufficient dynamic vulcanization occurs, an unprocessable thermoset vulcanizate may be obtained.

The chlorinated or chlorosulfonated PE dispersed into the vulcanized admixture can be the same as that used in the vulcanization step or different. The primary difference being that the subsequently added chlorinated or chlorosulfonated PE is thermoplastic and not a cross-linked material. Therefore, the finally added chlorinated or chlorosulfonated PE can be either amorphous or semicrystalline, with the latter being preferred. It must also meet the four physical property criteria mentioned hereinabove for the chlorinated or chlorosulfonated PE to be vulcanized. Preferably, the chlorine content can range from 25 to 48 percent based on the total polymer weight, with a more preferred chlorine content being from 32 to 44 weight percent based on the total polymer weight. The heat of fusion, measured by differential scanning calorimetry, for the thermoplastic chlorinated or chlorosulfonated PE is in the range of from 0.2 to 16 cal/g, with 5 to 11 cal/g being preferred. The residual sodium chloride can range from 0.05 to 0.5 weight percent based on the total weight of the resin, with from 0.1 to 0.4 being more preferred.

In a most preferred aspect, the chlorinated or chlorosulfonated PE useful in the second dispersion step is prepared from a high density PE interpolymer having a bimodal melt index. In one preferred aspect, the interpolymer useful in this invention is ethylene copolymerized with propylene, butene-1, or isobutylene, and more preferably with butene-1.

Still more preferably the interpolymer feedstock for the thermoplastic chlorinated PE used in the second dispersion has a primary stage melt index of from 0.25 to 10.35 I₅ value, and a density of from 0.948 to 0.952 g/cc. This polyolefin is used to prepare a chlorinated PE having from 32.5 to 35.5 weight percent chlorine and a heat of fusion ranging from 5 to 11 cal/g.

The properties of the thermoplastic vulcanizates of this invention can be modified, either before or after vulcanization, by adding ingredients which are conventional in the compounding of chlorinated or chlorosulfonated PE elastomers, polyolefin resins and blends thereof. Skilled artisans will recognize, however, that chlorinated or chlorosulfonated PE compounding additives generally must be added before vulcanization if they are to have an effect upon the chlorinated or chlorosulfonated PE. The timing of addition is not as critical for addition of ingredients to the thermoplastic portion of the materials of the present invention.

Examples of suitable additives include various carbon blacks, alumina, silica, titanium, dioxide, calcium carbonate, colored pigments, clays, zinc oxide, stearic acid, accelerators, vulcanizing agents, sulfur, stabilizers, antioxidants, antidegradants, adhesives, tackifiers, plasticizers, processing aids such as lubricants and waxes, prevulcanization inhibitors, discontinuous fibers such as glass fibers and wood cellulose fibers, and extender oils. The amounts used depend, at least in part, upon the quantities of other ingredients in the composition and the properties desired from the composition. Minor amounts of other saturated and unsaturated polymers such as alpha-olefins may be added to reduce the cost or modify the properties of the composition.

Aromatic, naphthenic and paraffinic extender oils provide satisfactory results so long as they are used in amounts which do not exceed their limits of compatibility with chlorinated or chlorosulfonated PE. Suitable extender oils are identified in Rubber World Blue Book, Materials and Compounding Ingredients for Rubber (1975), pages 145-190. The quantity of extender oil added depends upon the properties desired. The upper limit, which depends upon the compatibility of a particular oil and blend ingredients, is exceeded when excessive exudation of extender oil occurs. Typically, from 5 to 150 parts by weight extender oil are added per

100 parts by weight of chlorinated or chlorosulfonated PE, preferably, from 30 to 125 parts by weight, with from 70 to 100 parts by weight being most preferred.

Thermoplastic elastomeric vulcanizates prepared as described herein are useful for making a variety of articles such as tires, hoses, belts, gaskets, moldings and molded parts. They are particularly useful for making articles by extrusion, injection molding and compression molding techniques. They are most preferably used for roofing membranes. They also are useful for further modifying thermoplastic resins in general and polyolefin resins in particular. The vulcanizates are suitably blended with thermoplastic resins using conventional mixing equipment. The properties of the modified resin depend upon the amount of vulcanizate blended. Generally, the amount of vulcanizate is sufficient to provide from 5 to 25 parts by weight of chlorinated PE per 100 parts by weight of the modified resin.

The following examples are for purposes of illustration only and are not to be construed as limiting the scope of the present invention. All parts and percentages are by weight unless otherwise specified. Arabic numerals are used to identify examples representing the present invention whereas alphabetic characters are used to designate comparative examples.

Sample Preparation

A 1450 cc capacity Banbury mixer is used to provide initial melt compounding of all blends and, when appropriate, curative components are added and activated to obtain at least partial curing of said blends. Further mixing and, if needed, completion of curing takes place when the contents of the Banbury mixer are placed on a heated two-roll mill. Curing can also be completed in a static cure oven.

Single Banbury Mix Procedure

A Banbury mixer is loaded with the chlorinated or chlorosulfonated PE, which is to be dynamically vulcanized, fillers and stabilizers and the semicrystalline thermoplastic polyolefin. The load factor in the Banbury mixer is about 70 percent. The materials are melt blended in the mixer for about 5 minutes or until the melt temperature is above the melting temperature of the thermoplastic polyolefin employed. The cure package for the chlorinated or chlorosulfonated PE is then added and mixing is continued for 3 minutes at 350°F to 401°F (176.7°C to

204.4°C). After the curative for the chlorinated PE is exhausted, the thermoplastic chlorinated or chlorosulfonated PE is added together with its associated fillers and stabilizers. This final loading brings the Banbury load factor to 85 percent. The mixing is continued at melting temperature for 2 minutes. Then the Banbury mixer is unloaded and the admixture is formed into sheets on a compression mold and preheated to about 400°F (204.4°C) at 25 tons of pressure (38.5 hectobars) and the results of the physical properties determined according to standarized test procedures.

Multiple Step Banbury Mix Procedure

1. A rubber masterbatch is prepared by adding chlorinated or chlorosulfonated PE, crystalline thermoplastic polymer, stabilizers, fillers, plasticizers and other additives to the Banbury mixer while it is operating at moderate speed (about 90 revolutions per minute (rpm)). Cooling water is circulated through the front and rear rotors, right and left sides and fixed sections of the Banbury mixer. As noted hereinabove, the base to be used in conjunction with the vulcanizing material can also function as the stabilizer. The amounts of masterbatch components are not sufficient to give an 85 percent load factor in the mixing cavity. Mixing continues for from 2.5 to 5 minutes at which time the temperature of the contents reaches from the melting point up to about 350°F (about 176.7°C) maximum.

2. Components to be used in vulcanizing the blend (also known as the "cure package") are added and mixing is continued at about 50 rpm for a period of about 3 minutes at a temperature of from 340°F to 400°F (171.1°C to 204.4°C). The temperature is controlled by varying the mixer speed. The melt mix is sheeted on a two-roll mill and sliced into strips for feed to a second Banbury mixer.

3. In the second Banbury mix, the vulcanizate made in the second step is added with a thermoplastic chlorinated or chlorosulfonated PE, additional fillers and stabilizers to the Banbury mixer which is operated at a set temperature of from 350°F to 400°F (about 176°C to 204.4°C). Mixing of the thermoplastic CPE with the vulcanizate continues for about 3 minutes with temperature control as in step 2. This period of time is generally sufficient to completely blend the thermoplastic component of the blend with the vulcanizate resulting in the thermoset chlorinated or chlorosulfonated PE rubber particles being dispersed in a thermoplastic matrix of polyolefin and chlorinated or chlorosulfonated PE.

4. The contents of the Banbury mixer are removed and sheeted on a cooled two-roll mill. This final rolling is done to cool the melt and prepare the sheets which are used to prepare samples for testing. The contents of the mill in the form of a sheet are fed to a dicer which produces uniformly diced pieces of chlorinated PE/crystalline thermoplastic or chlorosulfonated PE/crystalline thermoplastic dispersed in thermoplastic chlorinated or chlorosulfonated PE or the milled sheets or blankets are compression molded in a 400°F (204.4°C) press (3 minutes preheat, 3 minutes pressed) at 25 tons (38.5 hectobars), and 3 minutes cooled under pressure. The physical properties are determined in accordance with standard tests.

Test Procedures

The following American Society for Testing and Materials (ASTM) tests are used to characterize the physical properties of materials prepared in accordance with the above procedure:

Specific Gravity ASTM Method D792

Hardness ASTM Method D2240

Tensile Strength ASTM Method D412

Elongation ASTM Method D412

Modulus ASTM Method D412

Tension Set ASTM Method D412

Compression Set ASTM Method D395B

Oil Resistance ASTM Method D471

Heat Resistance ASTM Method D573 Because a crucial test of the applicability of proposed membrane materials is the resistance to cracking caused by microbial species, a test procedure has been devised for determining, on an accelerated basis, whether the sample sheet will resist cracking. The test procedure is a Dextran adhesion and cracking test. It attempts to simulate the attachment and shrinking of microbial colonies on single ply roofing membranes.

In the adhesion and cracking test, five 0.3 milliliter drops of a 2.5 weight percent aqueous solution of Dextran (Dextran, 5,000,000 to 40,000,000 molecular weight, Catalog No. D5501, from Sigma Chemical Company) are placed on the sample sheet. The sheet is then subjected to light from heat lamps, such as Gro-Lamp's (55°C to 60°C) for from 3 to 5 hours or dried in a forced-air oven at 80°C to 85°C for 1 hour, until the solution is dried and only Dextran flakes remain. After allowing the sample sheet to cool to room temperature, a piece of pressure sensitive adhesive tape, such as 3M's Scotch™ Brand Magic™ Tape, is pressed over the flakes and pulled off at a consistent rate. The number of flakes adhering to the tape indicates the extent of adhesion of Dextran to the sample surface. Because adherence is a prerequisite to cracking, the more flakes are removed the lower is the tendency to crack, or alligator, as it is known in the art. A rating of 5 means all flakes are removed.

After the adherence test, the remaining Dextran is washed off the sample sheet and new Dextran drops are applied, dried by the same procedure and then rewetted with a similar size drop of distilled water and dried again. The rewetting and drying cycle is repeated four times, before washing and rating the samples for cracks. The appearance of the sample is reported according to the depth and width of cracks. The crack depth is a logarithmic scale from 4 to 0, with 4 having essentially no surface deformation and 0 being mostly extended through the entire sample. Because it is logarithmic a rating of 1.5 indicates more than twice the damage of a 3 rating. The cracks are also rated as to type. Thus, a surface crack (s) indicates surface peeling, layering, and microcracks; a wide crack (w) can be superficial or deep; and a sharp crack (sp) indicates a narrow, penetrating type of crack. The surface cracks are mainly cosmetic and can range from 4 to 3 in penetration depth;. wide cracks sometimes penetrate deep and can range from 4 to 1.5; sharp cracks can penetrate entirely through the membrane and can range from 4 to 0.

Further, the samples can be exposed to UV radiation in a Xenotest 1200 unit from Heraeus, Inc., West Germany, in order to simulate the effect of sunlight on the cracking process. UV light also promotes photo oxidation and, therefore, Dextran adhesion. Thus, the UV exposure causes those samples which show little initial Dextran adhesion to experience similar deforming forces. Again correlation with field tests is pending. However, in evaluating samples, experience has shown that the removal of more flakes in the tape test after the same UV exposure time or the need for longer UV exposure in order to cause similar adhesion, indicates a lower tendency toward alligatoring. Examples 1-10 and Comparative Examples A-J

In a Banbury mixer the various formulations given were mixed according to the general procedure described above. After mixing, sample sheets were prepared and tested for Shore hardness, melt viscosity and Dextran adhesion and cracking. Each formulation also contained the following fillers, stabilizers, pigments, processing aids, etc.

A. Marinco H, (magnesium hydroxide used as activator for vulcanization), Calgon

Corporation, 5 phr.

B. Tetrasodium pyrophosphate, antioxidant or inhibitor, from Monsanto Company, 5 phr.

C. Irganox™ 1010, antioxidant, Ciba-Geigy Corp.; 2 phr.

D. Irganox™ 1076, antioxidant, Ciba-Geiby Corporation; 2 phr.

E. Weston™ 619, antioxidant, Borg Warner Chemical Company 4 phr.

F. Omycarb™ UF, calcium carbonate filler, Omya Inc., 20 phr.

G. Tiθ2 Type R960, filler, SCM Chemicals, 10 phr.

H. HiSil 233,hydrated amorphous silica as filler, PPG Industries, Inc., 5 phr.

I. Sanitizer 711, di (C7-C9-C11 alkyl phthalate, Monsanto Company, 100 phr. J. Echo-S, mercapto-thiadiazole derivative vulcanizers, Hercules, Inc., 3 phr.

K. Vanax™ 808, condensation product of analine and buteraldehyde, R.T. Vanderbilt Co., Inc., 59 phr.

L. Ultranox™ 626, antioxidant, Borg Warner Chemical.

Other additives which may be used in the place of or in addition to various of the above-listed materials are given as follows:

M. ERL 422, chemical and heat stabilizer, Union Carbide Corporation;

N. Mark 1117,1 chemical aand heat stabilizer, Argus Chemical Corporation;

0. TBABr, tetrabutylammonium broide vulcanization accelerator, Nobel Chemicals; and

P. Vanchem™ DMTD, 25-dimercapto-1,3,4-thiadiazole vulcanizer, R. T. Vanderbilt Company, Inc.

The following Tables give the results of the Examples of this invention and the comparative experiments.

As seen in the above results of tests in which a chlorosulfonated PE alone was subjected to the tests in Comparative Example A along with examples of various aspects of this invention, the present materials had much improved heat distortion and initial weld strength. Further, the examples of this invention shrank considerably less than did the chlorosulfonated PE per se. Further, improvement is noted in the tendency to crack over the comparative material.

Example 1 1

In another procedure, the chlorinated PE, stabilizer and filler package and PE according to the following percentages were added to a Banbury mixer and the Multiple Banbury Mix Procedure was used.

Weight Percent of

Total Formulation Vulcanizate chlorinated PE, heat of fusion 8-9, 25 % chlorine 39 .59

Marinco H (MgOH₂) 2.06 trisodium polyphosphate 1.98

Irganox 1010 (antioxidant) 0.79

Weston 619 (antioxidant) 1.58

Omycarb UF (CaCO₃) 7.92 TiO₂ Type R960 9. 90

Ultra low density crystalline

PE 20.04

The materials are dispersed by mixing at 90 rpm under a ram pressure of 35 psig (241.3 kilopascals) for

150 seconds at a maximum temperature of 340°F (171.1°C).

Then the cure package was added, including 0.65 weight percent based on the total resin composition of 2,5- dimercapto-1,3,4-thiadiazole and tetrabutyl ammonium bromide, 0.46 weight percent. The chlorinated PE was dynamically cured in the Banbury mixer at 50 rpm and at a temperature of from 340°F to 360°F (171.1°C to 182.2°C) for 1.5 minutes. To the Banbury mixer was then added the following chlorinated PE including a filler and stabilizer package, the percentages are weight percent based on the total composition weight.

Thermoplastic chlorinated PE, heat of fusion 6-9, 35% chlorine 9.92

Mark 1117 (stabilizer) 0.20 ERL 4221 (stabilizer) (stabilizer) 0.10

629A Wax 0.15

Ultranox 622 (antioxidant) 0.07

Irganox 1076 (antioxidant) 0.05

Stearic Acid 0.09

Omycarb UF (CaCO₃ filler) 1.98

TiO₂ Type R960 (filler) 2.48

The vulcanized chlorinated PE dispersed in the thermoplastic PE was then dispersed in the added thermoplastic chlorinated PE under Banbury conditions of 50 rpm, 100 seconds mixing time at a maximum temperature of 365°F (185°C). The dispersed matter polymer was discharged onto a hot two-roll mill and sheeted for additional dispersion and fed from the mill to a dicer. The diced thermoplastic vulcanizate was then compression molded into sheets at 400°F (204.4°C) at 25 tons of pressure (38.5 hectobars). Table III following gives the physical properties obtained. Table I II

Physical Properties of Chlorinated PE Thermoplastic Vulcanizate

Hardness, Shore A 85

Ultimate Tensile, psi (kPa) 1175 (8096)

Elongation, % 364 100% Modulus, psi (kPa) 903 (6222)

200% Modulus, psi (kPa) 1052 (7248)

The thermoplastic vulcanizate produced in

Example 11 was made into a single-ply roofing membrane and tested in the field. After six months, it passed the weathering test without cracking or "alligatoring". It also had excellent seam welding, interply adhesion, and was produced on commercial processing equipment.

Claims

1. A blend of a thermoplastic elastomer material comprising from 35 to 50 parts of an amorphous chlorinated or chlorosulfonated polyethylene (PE) and from 15 to 30 parts of a crystalline thermoplastic polyolefin polymer, said composition having a tension set value, at 100 percent elongation, of less than 50 percent, a decreased heat distortion temperature and decreased shrinkage at 80°C.

2. A thermoplastic elastomeric composition having a tension set value, at 100 percent elongation, of less than 50 percent, which is resistant to environmentally induced cracking, said composition comprising a blend of from 35 to 45 parts by weight of an admixture of a crosslinked amorphous chlorinated or chlorosulfonated PE, and from 15 to 25 parts by weight a crystalline thermoplastic polyolefin resin, said crosslinking being carried out in the presence of a vulcanizing package comprising an inorganic base and an activator material selected from 2,5-dimercapto-1,3- thiadiazole or a derivative of 2,5-dimercapto-1,3,4- thiadiazole , said activator material being initially present in an amount of from 0.5 to 1.5 parts by weight, and the residue of said activator material being present in the composition.

3. The composition of Claim 2, including a plasticizing material selected from trimellitate esters, phthalate esters, butyloleate, aromatic oils, and polyesters of dicarboxylic acid, said plasticizing material being present in an amount of up to 30 parts by weight of the total weight of the composition.

4. The composition of Claim 2 or 3, wherein the crystalline thermoplastic polymer is ultra low density PE or polypropylene, and the plasticizing material is trioctyl trimellitate.

5. A blend of a thermoplastic elastomer, having therein a vulcanized elastomer, composition comprising a blend elastomer material of .from 35 to 50 parts of a vulcanized chlorinated PE in admixture with from 15 to 30 parts of a crystalline thermoplastic polyolefin polymer, said admixture being further admixed with from 15 to 60 parts of a thermoplastic chlorinated or chlorosulfonated PE.

6. A process for preparing a cross-linked blend of a thermoplastic elastomer material having a tension set value, at 100 percent elongation, of less than about 50 percent comprising the steps of:

(a) forming a heat-plastified, substantially uniform admixture comprising an amorphous chlorinated or chlorosulfonated PE, a crystalline thermoplastic polyolefin polymer and an inorganic base; and

(b) dispersing a vulcanizing material for the chlorinated or chlorosulfonated PE throughout the admixture to activate the vulcanizing material without substantially degrading any component of the composition and to cure substantially all of the chlorinated or chlorosulfonated PE, said vulcanizing material being selected from a derivative of 2, 5-dimercapto-1,3,4- thiadiazole or a combination of 2,5-dimercapto-1,3,4- thiadiazole and an activator material.

7. The process of Claim 6, wherein the heat- plastified admixture further comprises a plasticizing material compatible with the amorphous chlorinated or chlorosulfonated PE, said plasticizing material being selected from trimellitate esters, phthalate esters, aromatic oils, and polyesters of dicarboxylic acid.

8. The process of Claim 6 or 7, wherein the inorganic base is selected from basic metal oxides and hydroxides and their salts with weak acids.

9. The process of Claim 8, wherein the inorganic base is selected from magnesium oxide, magnesium hydroxide, barium carbonate, barium oxide, calcium oxide, and calcium hydroxide.

10. The process of Claim 7 or 8, wherein the heat-plastified, substantially uniform admixture is formed in at least two sequential steps comprising:

(a) forming the heat-plastified, substantially uniform admixture by mixing the amorphous chlorinated or chlorosulfonated PE, the plasticizing material and the inorganic base to heat plastify the chlorinated or chlorosulfonated polyethylene with substantially no degradation thereof; and

(b) dispersing the thermoplastic polyolefin polymer throughout the admixture while heating said admixture to a temperature above the polymer's crystalline melting point but below a temperature at which substantial degradation of the chlorinated or chlorosulfonated PE occurs.

11. The process of Claim 10, wherein the temperature in step (a) is from 27°C to 149°C, and wherein the temperature in step (b) is from 121°C to 218°C.

12. The process of Claims 6 to 11, wherein the vulcanizing material comprises 2,5-dimercapto-1,3,4- thiadiazole and an activator material selected from (1) amines having a boiling point above 110°C and a pK value below 4.5; (2) salts of amines having pK values below 4.5 with acids having pK values above 2.0; (3) quaternary ammonium hydroxides and their salts with acids having pK values above 2.0; (4) diphenyl- and ditolyl-guanidines; and (5) the condensation products of aniline and at least one mono- -aldehyde containing 1 to 7 carbon atoms in combination with at least an equal amount of an inorganic base.

13. The process of anyone of Claims 6 to 11, wherein the vulcanizing material is a derivative of 2,5- dimercapto-1,3,4-thiadiazole selected from:

wherein X is a substituent selected from hydrogen, —CRR'OH, —(CH₂--CH—O)_nH,

where m is an integer of from 2 to 10; where n is an integer of from 1 to 5, R and R' are selected from hydrogen, alkyl groups containing from 1 to 8 carbon atoms, and aryl, alkaryl or aralkyl groups containing from 6 to 8 carbon atoms; R² is an alkyl group containing from 1 to 17 carbon atoms, an aryl group containing one to two rings, an alkaryl group containing from 7 to 14 carbon atoms, an aralkyl groups containing from 7 to 8 carbon atoms or a cyclohexyl groups; R³ is an alkyl group containing from 1 to 8 carbon atoms; X' is the same as X with the exception of hydrogen ; and Y is selected from zinc, lead,

where R⁴ is selected from alkylene and alkenylene groups containing from 1 to 8 carbon atoms and cycloalkylene, arylene or alkarylene groups containing from 6 to 8 carbon atoms; z is 0 or 1; and R⁵ is an alkylene group containing from 2 to 8 carbon atoms, or a phenylene, methylphenylene or methylenediphenylene group.

14. The process of any one of Claims 7 to 13, wherein the amorphous chlorinated or chlorosulfonated PE comprises 100 parts by weight, the plasticizing material comprises from 0 to 150 parts by weight, and the crystalline thermoplastic polyolefin polymer comprises from 12 to 150 parts by weight.

15. The process of Claim 10, including the step of:

(c) dispersing in the vulcanized admixture prepared in step (b), a chlorinated or chlorosulfonated PE free from additional vulcanizing material to produce a molten partially cross-linked blend of a thermoset chlorinated or chlorosulfonated PE in a thermoplastic chlorinated or chlorosulfonated PE.

16. The process of Claim 15, in which the chlorinated or chlorosulfonated PE dispersed in step (c) into the vulcanized admixture is a semicrystalline chlorinated or chlorosulfonated PE.

17. A process for preparing a blend of thermoplastic elastomer material having a tension set value, at 100 percent elongation, of less than about 50 percent from a blend of an amorphous chlorinated or chlorosulfonated PE and a crystalline thermoplastic polyolefin polymer which comprises forming a heat- plastified, substantially uniform admixture comprising said amorphous chlorinated or chlorosulfonated PE and said crystalline thermoplastic polyolefin polymer.

18. The process of Claim 17, including a plasticizing material selected from trimellitate esters, phthalate esters, butyloleate, aromatic oils, and polyesters of dicarboxylic acid.