WO1992005218A1

WO1992005218A1 - Method of manufacturing a nitrosamine-free rubber article

Info

Publication number: WO1992005218A1
Application number: PCT/US1991/005997
Authority: WO
Inventors: Robert R. Barnhart
Original assignee: Uniroyal Chemical Company, Inc.
Priority date: 1990-09-21
Filing date: 1991-08-22
Publication date: 1992-04-02

Abstract

This invention relates to the use of certain N-alkyl, N-benzyl, N-dibenzyl or N-cycloalkyl substituted bis(2-benzothiazolesulfen)amides as a curing accelerator for rubbery thermosettable polymers in a process of manufacturing rubber articles without generation of N-nitrosamine compounds in the manufacturing environment or article. The articles include tires, belts, hose and other rubber articles.

Description

METHOD OF MANUFACTURING

A NITROSAMINE-FREE RUBBER ARTICLE

FIELD OF THE INVENTION

This invention relates to the manufacture of tires and other rubber products without the emission of nitrosamines into the workplace. The environmental and health issues concerning nitrosamines may be eliminated by the use of the vulcanization accelerators which are the subject of this invention.

BACKGROUND OF THE INVENTION

Vulcanization may be defined as a reaction in the presence of heat where a chemical additive reacts with an elastomer to change it from a plastic, tacky solid to a thermoset, fixed solid with improved strength and elasticity, and increased hardness. The vulcanization reaction is one in which the polymeric rubber molecules are cross-linked by the vulcanizing agent to form a network of macromolecules having less mobility and which have the desired physical properties of a usable rubber product. The type of crosslinking (or vulcanizing) agent will vary with the type of rubber used and the properties desired. The most commonly used vulcanizing agent is sulfur, as it enters into reactions with the majority of the unsaturated rubbers to produce vulcanizates. Sulfur, in the presence of heat, reacts with adjoining olefinic bonds in the polymeric backbone chains or in pendant chains of two elastomeric molecules to form crosslinks between the molecular chains.

Vulcanization, as originally known, required long hours and elevated temperatures. Progress was made in speeding the process and improving the properties of the vulcanized product by using accelerators. Reduction in the time required for vulcanization is generally

accomplished by changes in the amounts and types of accelerators used.

A type of accelerator used widely with a sulfur vulcanizate system are sulfenamides. Sulfenamides give fast vulcanization (approximately 30 minutes) while providing delayed curing action. Examples of

sulfenamide accelerators include N-Cyclohexyl-2-Benzothiazole Sulfenamide (CBS), N-t-Butyl-2-Benzothiazole Sulfenamide (TBBS), N,N,-Dicyclohexyl-2-Benzothiazole Sulfenamide (DCBS), N,N-Diisopropyl-2-Benzothiazole Sulfenamide (DIBS), 2-(4-Morpholinylthio-)-Benzothiazole (MBS) and 2-(4-Morpholinyldithio)-Benzothiazole (MBDS).

A sulfur acceleration system consists of a

vulcanizing agent (sulfur), a primary accelerator (such as a sulfenamide), and optionally a secondary accelerator which activates the primary accelerator. Normally the ratio of primary accelerator to sulfur ranges from 1:4 in a fast curing elastomer (for example, natural rubber) to approximately 1:2 in a slower curing elastomer such as EPDM. A typical recipe follows:

Typical Recipe using Sulfur Acceleration System

SBR 100.00

ZINC OXIDE 3.00

STEARIC ACID 1.00

CARBON BLACK 50.00

MBT 1.00

SULFUR 1.75 The thiazoles, characterized by mercaptobenzothiazoles and its derivatives, are an important and widely used class of accelerators. The discovery of this type of compound dates back to the 1920's,

evidenced by US patent 1,544,687 to Goodyear which discloses 2-Mercaptobenzothiazole (MBT). This discovery has led to the family of delayed-action accelerators in wide use today.

2-Mercaptobenzothiazole is formed by reacting aniline with carbon disulfide and sulfur. The

derivatives are built up chemically through the mercapto group. By oxidation, it may be changed into the disulfide form. The most important derivatives are the sulfenamides, which have long scorch delays coupled with good cure rates.

The sulfenamides are formed by oxidation of a mixture of MBT and an amine. Alternatively,

N-chloroamine can be reacted with the sodium salt of MBT. The sulfenamines in commercial use are generally derived from secondary amines or from primary amines that are somewhat hindered.

When a sulfenamide accelerator in use in the rubber making process, spontaneous oxidation occurs via the reaction of the compound with the NO_χ present in ambient air. The formation of nitrosamines should be considered here. Their precursors are found in vulcanization accelerators and to a lesser degree in rubber fillers and additives.

As used throughout this specification and claims the term "nitrosamine" shall refer to N-nitroso-dimethyl- amine(NDaMA), N-nitroso-diethylamine(NDEA), N-nitroso- dibutylamine(NDBA), N-nitroso-morpholine(NMOR),

N-nitroso-methylamine(NMA), N-nitroso-ethylamine(NEA) and N-nitroso-isopropylamine(NPIP) collectively and or individually.

The N-nitroso compounds are formed by the reaction of a substance containing secondary amino groups and a nitrosating agent derived from the oxides of nitrogen (NO_χ) or nitrite salts. A specific example of this can be shown by the following reaction:

O

MBS ACCELERATOR

N-NITROSOMDRPHOLINE

Government agencies, such as OSHA and NIOSH in the United States, have been concerned about worker level of exposure to nitrosamines in many industries, including rubber manufacture. In the October 30, 1989 issue of Rubber and Plastics News, OSHA was reported to be considering the mandatory elimination of nitrosamines in the workplace. Later issues of this publication discuss further ramifications and controversy over this

subject. The United Rubber Workers union has sought the regulation of nitrosamines in the workplace since 1978.

The results of this controversy are not known at the time of this writing, but nitrosamine exposure in the workplace, particularly to rubber workers, is a definite concern. The nitrosamines thus produced by certain sulfenamide accelerators are an undesirable byproduct and there is a desire by both government agencies and the rubber industry to eliminate them. Another important concern of the rubber

vulcanization process is scorch, which may be defined as premature vulcanization. It is considered to be

extremely important in defining processibility limits (as stated, for example in Rubber Technology, 3rd

Edition, Morton, 1987) and is an additional aspect of the current invention.

Continuous measurement of viscosity at processing temperatures will indicate the time available for further processing. A good stock will have a scorch time slightly longer than the equivalent of the maximum heat it may accumulate during processing.

Of the previously mentioned sulfenamide

accelerators in current use, N-Cyclohexyl-2-Benzothiazole-Sulfenamide (CBS) and N-t-butyl-2-Benzothiazole-Sulfenamide (TBBS) have poor scorch safety, as will be seen in the following description and examples. 2-(4-Mόrpholinothio)benzothiazole (MBS) is known to exhibit the a level of scorch safety which is very desireable in many rubber compounds.

The problem of nitrosamine generation is present, however, using MBS. Therefore, it is an object of the invention to virtually eliminate the generation of nitrosamines in making various rubber articles using a vulcanization process employing curing temperatures above 275°F.

A further object of this invention is to produce articles using a rubber compound which possesses scorch safety equivalent to that of MBS while eliminating the generation of nitrosamines. The compounds of the current invention will also be shown to have other desirable cure properties which will produce cured rubbers equivalent to currently manufactured rubbers without the aforementioned generation of nitrosamines.

THE ACCELERATORS OF THE INVENTION

The aforesaid objects of the invention may be achieved by utilizing as the primary accelerator in the elastomeric composition, the accelerators of this invention which can be depicted as follows:

where R represents a C³ to C⁹ branched, linear or cyclo- alkyl group, such as, but not limited to isopropyl, isobutyl, cyclohexyl, tert-butyl, tert-amyl, t-octyl as well as representing an aryl group, for example benzyl or dibenzyl.

This class of compound is not new. Two early patents to Messer (US 2,321,305 and US 2,321,306, June

8, 1943) describe the vulcanization accelerators of this invention. Examples are given of reaction products of 1,1'-dithio bis(benzothiazole) and aniline or ethyl amine. Although these examples produce vulcanization accelerators, they are described only in non-black, low temperature cured (274°F) natural rubber compositions. The unique utility of this invention, the elimination of nitrosamine generation in a method for making specific rubber articles such as tires, belts, hose, roofing sheeting, was not recognized or appreciated in these publications.

U.S. Patents 2,873,277 and 2,889,331 to Sundholm describe alternate processes to manufacture the N-alkyl and N-cycloalkylbis(2-benzothiazolesulfen) amides of structure (I). They are incorporated in natural rubber test formulations which were cured at 250°F. They contain no implicit or explicit teaching of utility in the method of producing the non-nitrosamine containing rubber articles of the invention, particularly tires.

Examples of later work dealing with bis

(2-Benzothiazolsulfenamides) include a Chemical

Abstracts reference to Fedorov et al (CA83(8) : 61146n) on vulcanization of butadiene-nitrile rubbers in the presence of new accelerators based on sulfenamides and bis (sulfenamides). This reference differs significantly from the instant invention as it refers to nitrile rubbers specifically and discusses the influence of these accelerators on rubber properties, and not on the nitrosamine-free curing process for specific rubber articles. Another Russian reference is to CA82 (24) : 157542u, in which the reversion of natural rubber vulcanization is reduced by the use of sulfenamide accelerators. In CA72(8) : 32951p Fel'dshtein et al discuss di(2-benzo- thiazole) sulfenamide accelerators. The advantages listed include longer induction times and high reaction rates of crosslinking during vulcanization.

US 3,875,177 to Maison presents a process for the manufacture and purification of bis(benzothiazyl- sulfene) amides by reacting a benzothiazylsulfenamide with an acid anhydride. The reaction product is used in a rubber formulation and data representing the Mooney Scorch times for impure and pure samples are presented, and are essentially the same. The art is concerned with a process and does not describe their use in a

non-nitrosamine process for making rubber articles.

It is an object of this invention to provide such a non-nitrosamine generating process for making rubber articles using sulfur vulcanization systems. A further object of this invention is to have the accelerator possess a high degree of scorch safety for optimal processing. A still further object of this invention to provide a process by which to incorporate this

accelerator into the compounding of rubbers. This resulting process will be one that will not pose the health risks and concerns of the currently used

accelerators while producing a cured rubber product equivalent to the state-of-the-art, exhibiting optimal scorch safety and cure time.

These objects, and other additional benefits and advantages will become more apparent from the following description and accompanying examples.

DETAILED DESCRIPTION OF THE INVENTION

This invention is directed to a specific method of using the class of compounds of the general formula(I):

where R is a C³ to C⁹ branched or linear alkyl, a C³ to C⁹ cycloalkyl, or a substituted or non-substituted aryl moiety. Compounds of this genus are claimed to be suited for use as primary delayed action accelerators for sulfur vulcanization of rubber. The following examples will show that these compounds function as accelerators comparable to the current sulfenamides in use without the generation of objectionable byproducts, such as nitrosamines.

The compounds of the invention are most

advantageously utilized as accelerators to cure highly unsaturated polymers such as natural or synthetic elastomers. Representative of the highly unsaturated polymers which may be employed in the practice of this invention are diene elastomers. Such elastomers will typically possess an iodine number of between about 100 and about 250, although highly unsaturated rubbers having a higher or a lower (i.e., of 50-100) iodine number may also be employed. Illustrative of the diene elastomers which may be utilized are polymers based on conjugated dienes such as 1,3-butadiene; 2-methyl-1,3- butadiene; 1,3-pentadiene; 2,3-dimethyl-1,3-butadiene; and the like, as well as copolymers of such conjugated dienes with monomers such as styrene, alpha-methylsty- rene, acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate and the like. Preferred highly

unsaturated rubbers include natural rubber, cis-polyiso- prene, polybutadiene, poly(styrene-butadiene),

polychloroprene and poly(acrylonitrile-butadiene).

Moreover, mixtures of two or more highly unsaturated rubbers may be employed. Also, mixtures of the highly unsaturated rubbers with elastomers having lesser unsaturation such as EPDM, EPR, butyl or halogenated butyl rubbers are also within the contemplation of the invention.

The second critical cure compound is sulfur, preferably in elemental form such as the commonly used rhombic crystalline form called rubber makers' sulfur or spider sulfur. It is employed at any suitable level, such as between .25 to about 3.5 parts per hundred of rubber hydrocarbon. More preferred is below about 2.5, and most preferred below about 2.0 PHR. The mixing of the composition of this invention may be accomplished by any suitable means including an internal mixer, a transfer mixer, and extruder or an open mill. Independent of the method of mixing the composition, the method of curing may be chosen from the many conventionally known methods including open steam, autoclave, press or mold curing, liquid salt bath, hot air, microwave, UHF or infared vulcanization. The method of forming the article into the desired shape is largely dependent upon the mixing and curing method chosen. Some representative methods are mold forming, extrusion, roller head die forming, die cutting, hand lay-up and in the case of tires, belts and hoses

virtually all of these methods are used at some point in the complex method of manufacturing. The forming step can possibly occur after the curing step in such

articles as die cut gaskets, rubberbands and others.

The highly unsaturated polymers to be protected may be formulated in conventional manner with the many usual compounding ingredients, in addition to the critical primary accelerator of Compound (I), for example, vulcanizing agents, secondary accelerators, activators (zinc oxide, stearic acid, zinc stearate), tackifiers, processing aids , retarders, antiozonants, antioxidants, plasticizing oils and softeners, particulate fillers including but not limited to: reinforcing pigments, talc, clay, silicas, whiting, calcium carbonate and carbon blacks. The primary accelerator compounds of the invention may be added to a unsaturated polymer at a level of from .1 to about 5 parts by weight per hundred parts by weight of rubber hydrocarbon (hereinafter PHR). For these purposes the polymer is assumed to be one or more natural or synthetic rubbers. A more preferred addition level is about 0.25 to about 4 parts PHR. The most preferred level is from about 0.5 to about 3 parts PHR. When the compounds of the invention are used in

combination with other non-nitrosamine forming secondary accelerators they may be added in a blend which is additive to the ranges set forth above. The compounds of the invention may be blended with the other secondary accelerators at ratios ranging from 1:3 to 3:1. More preferred is a ratio range of 2:3 to 3:2. These ratios are meant to indicate the percentages are 40:60 to 60:40 where in all cases the compounds of the invention are the first number of each ratio. It should be noted that in certain applications and with certain other

accelerators, the PHR ranges of accelerators listed above may be varied in order to obtain the optimal protection. Reasonable experimentation must be

undertaken in order to optimize the ratios and overall levels of the blend when the compounds of the invention are blended with other conventional antioxidants and antiozonants.

The compounds of the invention may be used in elastomeric mixtures in combination with antiozonants used to protect against static ozone attack. The antiozonants which may be utilized include any of the commonly recognized paraphenylenediamine class of materials.

An accelerator of this invention can be synthesized advantageously by the following procedure, which was used to synthesize N-cyclohexyl Bis(2-Benzothia- zole) sulfenamide. This synthesis example is provided to illustrate a method of making compounds of this class and is not meant limit the scope of this invention in any way.

EXAMPLE 1

Preparation of N-cyclohexyl-bis(2-Benzothiazole)sul fenamide

(NCBBS)

A 3-liter, 4-necked round bottom flask equipped with a mechnaical stirrer, a gas frit, a thermometer and a reflux condenser was -charged with 274.0 g (1.0 mol) of 97% pure N-cyclohexyl-2-benzothiazole sulfenamide

(commercially available accelerator known by the

tradename Delac S, from Uniroyal Chemical Co.) and 104.4 g of toluene. The stirred suspension was bubbled with nitrogen gas and was warmed to 34°C. HCl gas (18.3 g, 0.50 mol) was added subsurface through the gas frit over a 28 minute period.

Progress of the reaction was followed by high performance liquid chromatography by observing the loss of the monosulfenamide peak and the growth of the bissulfenamide peak. During the addition, the solution temperature exothermed to 45°C and a light colored solid percipitated from the solution. The solution was then purged with nitrogen for two minutes.

The solid, cyclohexylamine hydrochloride, was filtered and then washed twice with 50 ml of toluene. The combined filtrate and washings were concentrated to one half volume by evaporating the solvent on a rotary evaporator. An equal volume (650 ml) of hexane was added to the concentrated toluene solution to precipitate an off-white solid. The product was filtered, washed with hexane, and dried in a 60°C oven.

A total of 197.4 g of product was isolated. The melting point was 129-131°C. A weight percent assay of 95.3% was determined for this material based on high performance liquid chromatography. Structure of the compound was confirmed by infrared spectra.

Example 2

Preparation of N-tert-Octylbis(2-Benzothiazolesul fen) amide

(NTO)

In a 500-milliliter four-necked round-bottomed flask equipped with a thermometer, a mechanical stirrer, a condenser, and a subsurface gas addition tube was placed a solution of 88.2 grams (0.3 mole) of

N-tert-octyl-2-benzothiazylsulfenamide in 400 ml of toluene. The temperature of the solution was adjusted to 15°C and 5.5 grams (0.15 mole) of anhydrous hydrogen chloride gas was bubbled in over a half hour period keeping the temperature at 15°C. The reaction mixture was held an additional 15 minutes at 15°C. The

insoluble tert-octylamine hydrochloride was filtered off and washed with a small amount of cold toluene. The filtrate was concentrated to 200 ml and cooled to 10°C. The title compound precipitated and was removed by filtration. The melting point of the

N-tert-octylbis(2-benzothiazolesulfen) amide was found to be 102-104°C, and the yield was 53.7%. Structure of the compound was confirmed by infrared spectroscopy.

Relative area HPLC analysis of the product showed it to br 95.8% pure. Example 3

Preparation of N-Isopropylbis(2-benzothiazolesulfen) amide

(NIB)

The procedure of Example 2 was repeated except on a

0.115 molar scale with N-isopropyl-2-benzothiazylsul- fenamide as the starting material. The resulting

product, N-isopropylbis(2-benzothiazolesulfen) amide, had a melting point of 103-105°C, and the yield was 44.7%.

Structure of the compound was confirmed by infrared spectroscopy.

Relative area HPLC analysis of the product showed it to be 96.5% pure. Example 4

Preparation of N-tert-Amylbis(2-benzothiazolesulfen) amide

(NTA)

The procedure of Example 2 was again repeated on a 0.27 molar scale, with N-tert-amyl-2-benzothiazylsul- fenamide. The product, N-tert-amylbis(2-benzothiazole- sulfen) amide, was found to have a melting point of

122-124°C. The infrared spectrum was consistent with the structure. Relative area HPLC analysis of the product showed it to be 94.6% pure.

Employing the products of Examples 1 through 4, the following rubber blends were prepared, tested for Mooney Scorch (ASTM Method D1646), Cure Meter Data, (ASTM

Method D2084) and percent nitrosamine generation by both an extraction and an airspace method, the details of which will be given.

Using the ingredients indicated in Table 1 (which are listed in parts per hundred rubber by weight), several rubber compositions were compounded in the following manner: Elastomers, carbon black, zinc oxide, and stearic acid in the amounts listed in Table 1 were charged in a Banbury mixer and blended at #2 speed with water on at full temperature and power. Details of the mixing procedures can be found in ASTM Methods D3184, D3185, and D3187 for masterbatches 1,2, and 3,

respectively.

The SBR masterbatches were mixed in a temperature range of 280-300°F. The accelerators for the SBR masterbatches were mixed as follows: initially the product of masterbatch #1 was added. In 0.5 minutes the accelerator was added and 1.0 minute the sulfur was added. The mixture was discharged after 2 minutes. The stock temperature was in the 210 to 240°F range

The natural rubber masterbatches were mixed at #2 speed with water on full as described above. The natural rubber masterbatches were mixed at the 260-300°F range. The accelerators were added as described above. The stock temperature was in the 170-200°F range.

The nitrile rubber masterbatches were mixed as above, with the masterbatches mixed in the 280-300° range. The accelerators were added as described above. The stock temperature was in the 200-230° range during mixing.

The master batches made in this fashion were then cured using various accelerators, again listed in Table 1, to evaluate the physical properties and other

characteristics of the cured samples.

The compounded stocks were mixed with curatives and accelerators in a Banbury Mix at #1 speed, with water on full. Accelerators were added in a small B Banbury following the previous final mixing cycle to the tire model masterbatch. The tire sulfur was added at the 1.0 minute interval. The final batch was discharged after one additional minute of mixing. The stocks developed temperatures of 90-104°C during the two minute mix. The stocks were sheeted off a two roll laboratory mill to the proper gauge for testing. Results of this testing are given in Table 2.

Notes for Table 1

(1) SBR 1502-Ameripol-Synpol cold styrene butadiene polymer containing 23.5% εtyrene, mixed acid emulsifier, nonstaining stabilizer and salt/acid coagulant.

(2) Budene 1207 - Goodyear high cis content

polybutadiene rubber

(3) Standard Malaysian rubber-CV viscosity stabilized high quality grade rubber prepared from typical rubber smoked sheets. (4) Paracril (TM) BJ, Uniroyal Chemical Company

(5) Kadox 911C, C.P. Hall, French process zinc oxide, surface treated

(6) Emory H-400 grade stearic acid

(7) N-299 Carbon Black, ASTM N299 high structure, high modulus, general purpose traed carbon black.

(8) Flexone 7P (TM) Uniroyal Chemical Company

(9) Sundex 8125, Sun Refining Co., high aromatic (84%) petroleum oil, ASTM D2226 Type 1.

(10) Sunproof Improved (TM), Uniroyal Chemical Co., blend of paraffin and micro crystalline waxes with a melting point of 60-65°C.

(11) Delac S (TM) Uniroyal Chemical Co.

(12) Delac NS (TM) Uniroyal Chemical Co.

(13) Delac MOR (TM) Uniroyal Chemical Co.

(14) Product of Example 1:

N-Cyclohexylbis(2-benzothiazole) sulfenamide

(15) N-Isopropyl bis (2-benzothiazole) sulfenamide

(16)N-tert-Octyl bis (2-benzothiazole)sulfenamide

(17) N-tert-Amyl bis (2-benzothiazole) sulfenamide

(18) Tire sulfur, Stauffer Chemical, 99.5% min elemental sulfur

Notes for Table 2: NMOR (N-Nitroso Morpholine)

NDMA (N-Nitroso Dimethyl Amine) ND (None Detected) The above data indicate the relative advantages of the experimental bis (sulfenamide) accelerators of the instant invention. The processing safety of the uncured stocks was measured by the Mooney Scorch Test (ASTM D1646).

In these data MBS, 2-(morpholinothio)benzothiazole, is used as the industry standard. MBS is widely favored over TBBS ( N-t-butyl-2-benzothiazolesulfenamide) or CBS (N-cyclohexyl-2-benzothiazole sulfenamide) because of its better processing safety with less chance of scorchy rough processing stocks. For this reason, the Scorch rating of the forumulations using MBS are given a rating of 100, and is considered the standard.

It can be seen that the formulations using NCB (Examples D, H, J, and L) and NIB (Example M)

accelerators are in the same processing safety class as MBS (Examples C,G, I, and K) and superior to TBBS

(Examples B, F, and N), which is also a commerciallly used accelerator.

Experimental accelerators NTA (Example P) and NTO (Example O) are better in scorch safety than TBBS but not equivalent to MBS. The experimental accelerators of the instant invention do not generate nitrosamines in any detectable amount, as can be seen by the data of Table 2.

Another critical property in rubber is cure strength. The method used to determine cure strength is using a cure meter as decribed in ASTM Method D2084. The maximum torque data correlates well with the cured 300% modulus figures from cured tensile slabs.

Both the cure meter data and the 300% modulus data from cured tensile specimens are presented in Table 2. These data show that the experimental accelerators of this invention, NCB, NIB, NTO, and NTA are similar to that of the industry standard, MBS. It is emphasized that none of these accelerators generate nitrosamines, and do possess the necessary vulcanizing and processing safety characteristics for the manufacture of rubber.

The analytical procedures, both extraction and headspace, for determining nitrosamine content in elastomers can be described as follows:

EXTRACTION PROCEDURE: Approximately 5 grams of the rubber sample (accurately weighed) is diced, placed in an extraction thimble, capped with cotton and placed in a Soxhlet extractor. This extractor is fitted onto a pre-weighed 250 ml Florence flask filled with 75 ml of methanol. No boiling chip is used. The top of the Soxhlet extractor is fitted with a condenser and the methanol is heated with a heating mantle until reflux.

After 24 hours, the flask is cooled to room temperature and any methanol remaining in the Soxhlet extractor is quantitatively transferred to the Florence flask. The volume of the methanol is reduced to 10-15 ml by rotary evaporation (37°C with in-house vacuum). The flask containing the methanol extract is now re-weighed, knowing the weight and density of methanol allows for the volume to be calculated. 1.5-2.0 ml of the methanol extract is dispensed through a 0.45 micron filter into a sampling vial and analyzed by Gas

Chromatography and Thermal Energy Analysis (GC-TEA).

The GC conditions consist of a column of 10%

Carbowax, 2% Potassium Hydroxide (KOH), 2.0 meters, 80/100 mesh, Helium flow of 20 ml/min, initial

temperature of 80°C, initial time of 1 minute, ramp of 4 deg/min, final temp of 180°C, and a final time of 5 minutes.

Results are reported as ppb nitrosamine in the rubber. A standard mixture of 5 nitrosamines produces a chromatogram with the following approximate retention times: N-Nitrosodimethylamine-9 min; N-Nitrosodiethyl- amine-10min; N-Nitrosodipropylamine-13 min; N-Nitroso- dibutylarnine-15 min; N-Nitrosomorpholine-22 min.

HEADSPACE ANALYSIS PROCEDURE: Approximately 5 grams of the rubber sample (accurately weighed) is diced and placed in a headspace analysis vial. The vial is fitted ontoa Tekmar headspace analyzer unit and heated to the desired temperature, typically 160°C (the curing temperature for the rubber). Compressed air is allowed to flow over the sample (2.0 L/min) and through a

Thermedics air sampling cartridge for 15 minutes. The tubing leading from the Tekmar headspace analyzer to the air sampling cartridge is cooled in an ice bath, since it wa found that the performance of the cartridge

degrades at elevated temperatures. The air sampling cartridge efficiently removes all nitrosamines from the air and allows any nitrosamines that may form inside the cartridge to escape.

After the sampling time is completed, the

nitrosamines are eluted from the cartridge with

approximately 3 ml of a 75% CH₂C₁₂/25% CH₃OH (v/v) mixture. Nearly 1.5 ml is needed to fill the dead volume of the cartridge while the remainder is dispensed into a sampling vial. The dispensed amount should be accurately known. The eluent is analyzed by GC-TEA using the same conditions outlined previously in the extraction technique.

UTILITY IN DYNAMIC RUBBER ARTICLES

The accelerator of Compound (I) can be most

advantageously used as a component in any or all of the layers of a rubber article having an elastomeric body. The following sections describe particular rubber articles which are most advantageously produced using the materials of the invention. In the wide variety of industrial rubber products which will be discussed, many, many different types of rubbers are utilized encompassing all of those previously disclosed as useful in the invention. It is to be noted that compound(I) of the invention can be utilized to enhance the cure properties while eliminating the generation of

nitosamines of any polymer system which is being used in any conventional construction of the particular rubber article. TIRES

Tires of this invention are made by utilizing

Examples L,M,O,or P as the rubber compound for the tread composition. Compound I may be most advantageously used in a nitrosamine-free tire as a component of any or all of the thermosetting rubber-containing portions of the tire. These components include: the toroidal rubber carcass with a plurality of layers of thermosetting rubber compounds therein and a plurality of layers of reinforcing materials positioned within said carcass; an overlying tread; sidewall; shoulder; chafer; bead stock; inner liner and all other elastomeric portions of a truck, passenger or off-road vehicle tire. These components typically contain more than one thermosetting rubber polymer in a blend which must be protected from nitrosamine generation. The non-nitrosamine generating secondary accelerators may also be used in such a tire along with Compound (I).

Belts

Belts of the invention are made using Examples D or J for the belt elastomeric body. Among the various types of belts manufactured in the rubber industry, the power transmission belts are the types which are most improved using the materials and compounds described in this invention. The power transmission type generally described as a V-belt, as well as various positive drive and timing type belts, can be greatly improved by using these compositions. Rubber compounds which have

exhaustively been described earlier and which contain compounds of structure (I) can be most beneficially used on the exterior surfaces of the belt structure. In V-belts, power transmission and timing belts they can replace the neoprene in the lower pulley engaging areas of the belt alternatively described as cushion stock, compression stock or pulley cover, depending on the belt structure. In order to better understand the utility in power transmission belts, a general description of the belt structure should be useful. The power transmission belt has an elastomeric body which forms the majority of the belt. There is a geometrically defined neutral axis of most belts which pass over a plurality of pulleys. That neutral axis simply indicates that the area above the neutral axis is in tension when going over a pulley, and the area below the neutral axis plane is described as being in compression. Therefore, a typical power transmission belt would have a tension section and a compression section which are separated by the neutral axis plane. The major longitudinal reinforcements are completely conventional in the art are layers of cords, or fabric or steel cable which lie approximately on the neutral axis plane. The power transmission belt is comprised of one or more rubber compounds having either the same or different polymeric base rubbers. As indicated, the exterior envelope layers of a power transmission belt can be most beneficially enhanced using the rubber compounds of the invention. Also, the compression section which undergoes considerable flexing during the life of a belt can benefit from the enhanced resistance provided by use of compound (I) and,

particularly, when an EPDM rubber is further

incorporated with the unsaturated diene-type rubber composition. These areas have conventionally utilized a neoprene (polychloroprene) base rubber which can now be replaced using lower cost, higher oil and solvent resistant polymers such as NBR and NBR in blends with other polymers such as SBR, natural rubber, EPDM, etc. Since the rubber composition used in the elastomeric body of the power transmission belt must be capable of embedding within it a plurality of layers of various types of reinforcing materials, adhesion of the rubber stocks to the adjacent layers is absolutely critical to the success of a belt building manufacturing operation. It is has been found that excellent adhesion levels can be achieved using the materials of the invention.

Conveyor Belting

Conveyor belts of the invention are made using

Examples D or H. Conveyor belts are used in a wide variety of environments and carry an infinite variety of payload. A conveyor belt is generally comprised of an elastomeric body formed of one or more rubber compounds having embedded in the elastomeric body a plurality of reinforcements in a position between an upper cover and a lower cover. It is the cover materials that can most advantageously utilize the rubber compositions using the compound(I) with various synthetic and natural rubbers. Details on specific types of constructions in conveyor belts can be gleaned from Rubber Manufacturers

Association (RMA) specifications which deal with many types and constructions of conveyor belts. Such

conventional structure and materials will not be recited in detail here and it is assumed that one of ordinary skill in the art can incorporate through reasonable trial and error the rubber polymers cured with the accelerator compound(I). Air Springs

One of the most difficult a plications in the industrial rubber products industry is the fluid spring, commonly called an air spring, which is used to either actuate or vibration dampen a particular mechanical device. Two basic types of air springs are the

bellows-type and rolling lobe. A type of rolling lobe called a sleeve type is used in air adjustable shock absorbers for vehicles. The structures differ but in physical characteristics only, not in function. The materials required are very similar for both rolling lobe and bellows type air springs. During the useful life of an air spring, it may cycle millions and

millions of times during which the internal air pressure will be varied causing deflection of the elastomeric sleeve or diagram of the air spring. A typical air spring is constructed using an upper and a lower retainer which are rigid structures through which air can be injected or exhausted from a pneumatic working chamber formed by the flexible member which spans the gap between the upper and lower retainers. This fabric reinforced, air impervious membrane is formed into either a straight sleeve or a molded bellows form and air tightly attached to the upper and lower retainers to form the pneumatic working cavity therebetween. The exact structrual similarities and differences between rolling lobe and bellows air spring are well known in the art and only generates structural detail on rolling lobe and bellows air springs is felt to be necessary to enable one skilled in the art to make optimum use of our invention. The fabric reinforced, air impervious membrane is the elastomeric body are made using Example H.

Hose

A hose of the invention is made using Example J as the outer cover. The vast variety of hose products will not be described at length except to indicate that the elastomeric components of most hose applications can benefit by utilization of the compounds of the invention in at least a portion of the elastomeric body of the hose. A hose, of course, has an outer cover which is resistant to the environment in which the hose operates and an inner tube or liner which resists the particular fluid or material being conveyed within the hose.

Between those two layers are positioned a plurality of reinforcement materials, which may be bias laid fabric, woven, or knitted fiber or filled rubber composite materials. Such hose constructional details will not be reviewed in depth but incorporation by reference is made to the Rubber Manufacturers Association (RMA) hose specifications which deal at length and in depth with the constructional details of the various hose

structures. It is the selection of materials with which this invention is concerned and, therefore, it is sufficient to describe that the conventionally used unsaturated and lesser unsaturation rubbers can be improved in the many ways which have been previously described in this specification.

Many other rubber articles can benefit from the characteristics of the compound of structure (I) and these may include gaskets, bushings, motor mounts, window seals, weatherstripping, bridge bearing pads, rubber roofing membranes, geophysical membranes such as pond liners, shoe soles and heels, expansion joints, vibration joints, oil field parts and many other rubber articles.

In view of the many changes and modifications that may be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the

protection afforded the invention.

Claims

1. A method of manufacturing a nitrosamine-free rubber article having an elastomeric body comprising the steps of:

(i) mixing a thermosettable elastomeric composition comprised of (a) 100 parts by weight of at least one highly unsaturated rubbery polymer; (b) 10 to 500 parts of at least one particulate selected from the group consisting of carbon black, whiting, clay, pigment, silica, and talc; (c) 0.25 to 3.50 parts of sulfur; and (d) 0.1 to 5.0 parts of a compound of structure (I):

where R is a C³ to C⁹ branched or linear alkyl, a C³ to C⁹ cycloalkyl, or a substituted or non-substituted aryl, all parts are by weight; and

(ii) forming said elastomeric composition into the shape of said elastomeric body;

(iii) curing said elastomeric composition into said nitrosamine-free rubber article at a temperature and for a time sufficient to cure said composition.

2. A method according to claim 1 wherein said curing step is carried out a temperature avove 275°F.

3. A method according to claim 1 wherein R of said compound (I) is isopropyl, isobutyl. cyclohexyl, tert-butyl, tert-amyl, t-octyl, benzyl or dibenzyl.

4. A method according to claim 1 wherein said R of said compound (I) is cyclohexyl, benzyl or dibenzyl.

5. The method according to claim 1 wherein said elastomeric body is the form of a tire.

6. The method according to claim 1 wherein said elastomeric body is a airspring.

7. The method according to claim 1 wherein said elastomeric body is a conveyor belt.

8. The method according to claim 1 wherein said elastomeric body is the form of a rubber roofing membrane.

9. The method according to claim 1 wherein said article is a hose.

10. The method according to claim 1 wherein said elastomeric body is the form of a weather strip.

11. The method according to claim 1 wherein said elastomeric body is a shoe sole.

12. The method according to claim 1 wherein said elastomeric body is a shoe heel.

13. A method according to claim 1 wherein said highly unsaturated rubbery polymer is selected from the group consisting of natural rubber, cis-polyisoprene, polybutadiene, poly(styrene-butadiene), polychloroprene and poly(acrylonitrile-butadiene), ethylene-propylene-diene rubber, ethylene-propylene rubber, butyl rubber and halogenated butyl rubber.

14. A method of eliminating the spontaneous generation of nitrosamine compounds in a high

temperature vulcanization process for the curing of thermosetting elastomer compositions comprising:

mixing a thermosettable elastomeric composition comprised of (a) 100 parts by weight of at least one highly unsaturated rubbery polymer; (b) 10 to 500 parts of at least one particulate selected from the group consisting of carbon black, whiting, clay, pigment, silica, and talc; (c) 0.25 to 2.25 of sulfur or sulfur donor compounds; and (d) 0.1 to 5.0 parts of a compound of structure (I):

curing said elastomeric composition at a

temperature above 275°F for a time sufficient to cure said composition.

15. In a high temperature vulcanization process for the curing of thermosetting elastomer compositions at a temperature in excess of 275°F, said composition comprising (a) at least one highly unsaturated rubbery polymer; (b) at least one particulate selected from the group consisting of carbon black, whiting, clay, pigment, silica, and talc; (c) sulfur; and (d) a primary accelerator:

wherein the improvement consists of eliminating the formation of nitrosamine compounds during vulcanization above 275°F by utilizing as the primary accelerator from about 0.1 to about 5.0 parts per hundred rubber by weight of a compound of structure (I):

where R is a C³ to C⁹ branched or linear alkyl, a C³ to C⁹ cycloalkyl, or a substituted or non-substituted aryl

16. A tire essentially free of nitrosamine

compounds having a toroidal rubber carcass with an overlying tread portion and a sidewall portion, said carcass comprising:

a plurality of layers of thermosetting rubber compounds therein; and

a plurality of layers of reinforcing materials positioned within said carcass, at least one of said plurality of thermosetting rubber compounds being composed of (a) 100 parts by weight of at least one highly unsaturated rubbery polymer; (b) 10 to 500 parts of at least one particulate selected from the group consisting of carbon black, whiting, clay, pigment, silica, and talc; (c) 0.25 to 3.50 of sulfur or sulfur donor compounds; and (d) 0.1 to 5.0 parts of a compound of structure (I):

where R is a C³ to C⁹ branched or linear alkyl, a C³ to C⁹ cycloalkyl, or a substituted or non-substituted aryl, all parts are by weight.

17. A tire according to claim 16, wherein

substantially all of said thermosetting rubber compounds are cured with either compound (I) or one or more of a non-nitrosamine forming secondary accelerator.

18. A tire according to claim 16, wherein said one highly unsaturated rubbery polymer is selected from the group consisting of natural rubber, cis-polyisoprene, polybutadiene and poly(styrene-butadiene).

19. A tire according to claim 18 further

comprising an elastomer having lesser unsaturation than said highly unsaturated rubbery polymer, said elastomer being selected from the group consisting of EPDM, EPR, butyl rubber and halogenated butyl rubber.