GB2350366A

GB2350366A - Latex for aggregate treatment

Info

Publication number: GB2350366A
Application number: GB0010448A
Authority: GB
Inventors: Gerald Owen Schulz
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1999-04-30
Filing date: 2000-04-28
Publication date: 2000-11-29
Anticipated expiration: 2020-04-28
Also published as: GB2350366B; FR2792943A1; BR0001644A; GB0010448D0; CA2301928A1

Abstract

An aggregate is coated with a latex composition by: (1) mixing the aggregate with latex to form a latex/aggregate mixture; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 66{C to about 232{C; and (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0.7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate. These latex compositions are made by adding 0.1 phr to about 5 phr of a sulfonate surfactant and about 0.1 phr to about 4 phr of a ethylene oxide/propylene oxide triblock polymer to conventional styrene-butadiene rubber latices made with fatty acid soaps.

Description

2350366 LATEX FOR AGGREGATE TREATMENT

Background of the Inventig-n

The first section of the Appian Way extending from Rome to Capua was built by about 300 B.C. Ultimately, more than 50, 000 miles of roadway was built in the Roman Empire and some of these roads were constructed with heavy stone. The importance of good roads and highways for military and commercial purposes has been appreciated since the time of the Roman Empire. However, not much progress was made in the art of road construction from the era of the Roman Empire until the development of motor vehicles, such as automobiles and trucks, in the early part of the twentieth century.

For centuries, stone blocks, wood blocks, vitrified brick and natural asphalt (bitumen) have been used to pave roads, driveways and highways. For instance, Louis XIV used an extensive amount of stone blocks to pave the entrance to his chateau at Versailles. However, until earlier in the twentieth century, paved streets and roadways were found almost exclusively in large cities. At the beginning of the automobile era, most rural roadway surfacing consisted of broken stone or gravel. Such roads were often rough, dusty and clearly inadequate for modern automobile and truck traffic.

Today, the United States has the most extensive highway system in the world with about 2,000,000 miles of paved road. Napoleon realized the importance of roadway systems and built such a system in France which today has the second most extensive system of paved roadways in the world, covering about 500,000 miles. Germany, Japan, Great Britain, India and Australia also currently have systems of paved roads which extend well over 100,000 miles. In addition to 2 these public roadways, there are countless paved driveways and parking lots all over the world.

Roads, highways, driveways and parking lots all over the world are frequently paved with asphalt concrete. Asphalt concrete pavements are highly desirable since they are dust-free, smooth and offer the strength required for modern automobile and heavy truck traffic. Asphalt concrete is generally made by mixing aggregate (sand and gravel or crushed stone) with the proper quantity of an asphalt cement at an elevated temperature. The hot asphalt concrete is then placed by a layering machine or paver on the surface being paved and thoroughly rolled before the asphalt concrete mixture cools. The asphalt concrete is normally applied at a thickness varying from about 25 to about 100 millimeters.

Asphalt concrete pavements can be made to be very smooth which offers outstanding frictional resistance as well as excellent ride characteristics for vehicles operating thereon. Such asphalt concrete pavement can also be repaired simply by adding additional hot asphalt concrete to holes and other types of defects which develop in the surface. Asphalt concrete pavements can also be upgraded easily by adding additional layers of hot asphalt concrete to old surfaces which are in need of repair.

Even though asphalt concrete offers numerous benefits as a paving material, its use is not troublefree. one major problem encountered with asphalt concrete pavements is the loss of the adhesive bond between the aggregate surface and the asphalt cement. This breaking of the adhesive bond between the asphalt cement and the aggregate surface is known as wstripping.n The stripping of asphalt binder from aggregate surfaces results in shorter pavement life O's- and necessitates the implementationknassive annual highway maintenance programs. Reduction of this stripping tendency is of great interest when trying to improve the condition of roads while lowering maintenance costs.

Over the years, various methods have been developed to reduce stripping tendencies. For instance, amines and lime are known to act as anti stripping agents and are frequently applied to the surface of the aggregate prior to mixing it with the asphalt cement in making asphalt concrete. United States Patent 5,219,901 discloses a technique for reducing stripping tendencies which involves coating the aggregate with a thin, continuous film of a waterinsoluble high molecular weight organic polymer, such as an acrylic polymer or a styrene-acrylic polymer.

United States Patent 5,262,240 discloses an excellent technique for providing aggregate with a high level of resistance to stripping by water, which comprises: (1) mixing the aggregate with latex to form a latex/aggregate mixture which is comprised of from about 0.005 weight percent to about 0.5 weight percent dry polymer; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 660C to about 2320C; (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0.7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate to produce the coated aggregate.

The technique disclosed by United States Patent 5,262,240 can be used to treat most aggregates with excellent results. However, its use on some claybearing aggregates which undergo water absorption can result in a loss of compressive strength and modulus. This, of course, results in the asphalt concrete made therewith having less desirable physical characteristics. United States Patent Application Serial No. 09/103,592, filed on June 24, 1998, discloses that rubber latex containing a water-soluble divalent metal salt acts as an excellent anti-strip agent when applied to the surface of aggregate and that the use of such aggregates does not result in water absorption and reduced compressive strength and modulus. In addition to providing excellent anti- strip characteristics, the use of such latices does not present environmental or safety hazards. In such applications, the latex is applied to the surface of the aggregate and dried prior to mixing the aggregate with the asphalt cement used in making asphalt is concrete.

United States Patent Application Serial No. 09/103,592, more specifically discloses a latex that is particularly useful for coating aggregate to improve resistance to stripping by water, said latex being comprised of water, an emulsifier, a rubbery polymer and from about 1 phr to about 50 phr of a water-soluble salt of a divalent metal.

United States Patent Application Serial No. 09/103,592 also discloses a process for preparing asphalt concrete with comprises: (1) mixing the aggregate with latex to form a latex/aggregate mixture, wherein said latex is comprised of water, an emulsifier, a polymer and a water-soluble divalent metal salt; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 6611C to about 2321C; (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0.7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate to produce the coated aggregate; (4) mixing the coated aggregate with about 3 percent to about 8 percent asphalt based upon the total weight of the coated aggregate at a temperature of at least about 1070C; and (5) continuing to mix the coated aggregate with the asphalt to attain an essentially homogeneous asphalt concrete.

Conventional styrene-butadiene rubber latices made with fatty acid soaps lack stability in hard water. This is frequently a problem in commercial applications due to the inaccessibility of soft water sources at road construction sites. In other words, latices frequently need to be diluted with hard water prior to being used as an aggregate coating. in cases where hard water is used and instability results, clogs in hoses, lines and pumps frequently occur.

This is, of course, highly undesirable. Additionally, the occurrence of coagulation or creaming can reduce effectiveness by preventing good film formation on the surface of the aggregate. 20 Summary of the Invention It has been unexpectedly found that the stability of styrene-butadiene rubber latices in hard water and their resistance to creaming can be significantly 25 improved by adding from 0.1 phr (parts per 100 parts by weight of dry rubber) to 5 phr of a sulfonate surfactant. and 0.1 phr to 4 phr of an ethylene oxide/propylene oxide/ethylene oxide triblock polymer nonionic surfactant thereto. The hard water stability and resistance to creaming of conventional styrenebutadiene rubber latices made with fatty acid soap systems can be improved by the addition of the sulfonate surfactant and the ethylene oxide/propylene oxide/ethylene oxide triblock polymer thereto. Such latices can be diluted with hard water and then used to coat aggregate. This technique virtually eliminates clogs in hoses, lines and pumps caused by latex instability. Since creaming is also virtually eliminated, better film formation on the surface of the aggregate can also potentially be realized.

The present invention specifically discloses a styrene-butadiene latex having improved stability in hard water and good resistance to creaming, said styrene-butadiene latex being comprised of (1) water, (2) a styrenebutadiene rubber, (3) a fatty acid soap, (4) a sulfonate surfactant and (5) an ethylene oxide/propylene oxide/ethylene oxide triblock polymer, wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight of at least 8000. In cases where the latex is is being applied to clay-bearing aggregates which undergo water absorption, it is preferred for the latex to additionally contain a water-soluble divalent metal salt to prevent loss of compressive strength and modulus.

The present invention also specifically discloses a process for coating aggregate which is particularly useful in making asphalt concrete to provide the aggregate with a high level of resistance to stripping by water, which comprises: (1) mixing the aggregate with latex to form a latex/aggregate mixture, wherein said latex is comprised of water, a styrene-butadiene rubber, a fatty acid soap, a sulfonate surfactant and an ethylene oxide/propylene oxide/ethylene oxide triblock polymer having a number average molecular weight of at least 8000; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 660C to about 2320C; and (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0. 7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate to produce the coated aggregate.

The present invention further discloses a process for preparing asphalt concrete which comprises: (1) mixing the aggregate with latex to form a latex/aggregate mixture, wherein said latex is comprised of water, a styrene-butadiene rubber, a fatty acid soap, a sulfonate surfactant and an ethylene oxide/propylene oxide/ethylene oxide triblock polymer having a number average molecular weight of at least 8000; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 660C to about 232"C; (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0.7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate to produce the coated aggregate; (4) mixing the coated aggregate with about 3 percent to about 8 percent asphalt based upon the total weight of the coated aggregate at a temperature of at least about 1070C; and (5) continuing to mix the coated aggregate with the asphalt to attain an essentially homogeneous asphalt concrete.

Detailed Description of the Invention

The latex utilized in coating aggregate in accordance with this invention is the latex of a styrene-butadiene rubber (SBR). Such styrene- butadiene rubbers are comprised of repeat units which are derived from styrene monomer and 1,3-butadiene rubber. Such styrene-butadiene rubbers will typically be comprised of repeat units which are derived from about 1 to about 40 weight percent styrene and about 60 to about 99 weight percent butadiene. The styrenebutadiene rubber in the latex will typically contain from about 10 weight percent to about 30 styrene and from about 70 weight percent to about 90 weight percent butadiene. The styrene-butadiene rubber in the latex will more preferably contain about 15 weight percent to about 25 weight percent styrene and from about 75 weight percent to about 85 weight percent butadiene.

The styrene-butadiene rubber latex can be synthesized using a fatty acid soap system and conventional emulsion polymerization techniques. Such emulsion polymerizations generally utilize a charge composition which is comprised of water, styrene monomer, 1,3-butadiene monomer, an initiator and a fatty acid soap. Such polymerizations can be conducted over a very wide temperature range from about OOC to as high as about 1000C. Such emulsion polymerizations are typically conducted at a temperature which is within the range of about 50C to about GOOC.

The fatty acid soap used in such polymerizations may be charged at the outset of the polymerization or may be added incrementally or proportionately as the reaction proceeds. Normally, from about 2 phm (parts by weight per 100 parts by weight of monomer) to about 7 phm of the fatty acid soap will be charged into the polymerization medium. It is typically preferred for the polymerization medium to contain from about 4 phm to about 6 phm of the fatty acid soap.

The emulsion polymerizations used in synthesizing the styrene-butadiene rubber latex may be initiated using free radical catalysts, ultraviolet light or radiation. To insure a satisfactory polymerization rate, uniformity and a controllable polymerization, free radical initiators are virtually always used to initiate such emulsion polymerizations. Free radical initiators which are commonly used include the various 9 peroxygen compounds such as potassium persulfate, ammonium persulfate, benzoyl peroxide, hydrogen peroxide, di-t-butylperoxide, dicumyl peroxide, 2,4dichlorobenzoyl peroxide, decanoyl peroxide, lauroyl 5 peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butylhydroperoxide, acetyl acetone peroxide, methyl ethyl ketone peroxide, succinic acid peroxide, dicetyl peroxydicarbonate, t-butyl peroxyacetate, t-butyl peroxymaleic acid, t-butyl peroxybenzoate, tbutyl peroxymaleic acid, t-butyl peroxybenzoate, acetyl cyclohexyl sulfonyl peroxide, and the like; the various azo compounds such as 2-tbutylazo-2-cyanopropane, dimethyl azodiisobutyrate, azodiisobutyronitrile, 2-t-butylazo-i- is cyanocyclohexane, 1-t-amylazo-i-cyanocyclohexane, and the like; the various alkyl perketals, such as 2,2 bis-(t-butylperoxy)butane, ethyl 3,3-bis(t butylperoxy)butyrate, 1,1-di-(t butylperoxy)cyclohexane, and the like.

The emulsion polymerization system used in the synthesis of the latex can be treated at the desired degree of conversion with shortstopping agents, such as hydroquinone or a combination of the sodium salt of N,N-dimethyl dithiocarbamate with N,N-diethyl hydroxylamine. Typical stabilizing agents and standard antioxidants can also be added to the latex. In cases where the latex is being applied to claybearing aggregates which undergo water absorption, it may be advantageous for a water-soluble divalent metal salt to also be added to the latex to prevent loss of compressive strength and modulus. The divalent metal salt will typically be a calcium or magnesium salt. Some representative examples of water-soluble divalent metal salts that can be utilized include calcium chloride, magnesium chloride and magnesium sulfate.

The divalent metal salt will typically be added to the latex while the latex is being agitated.

In such cases, from about 1 phr to about 50 phr of the divalent metal salt will be added to the latex.

It is typically preferred for the latex to contain from about 4 phr to about 30 phr of the divalent metal salt. It is normally more preferred for the latex to contain from about 5 phr to about 10 phr of the divalent metal salt.

It is normally desirable to reduce the pH of the latex to below about 9 prior to addition of the divalent metal salt to improve latex stability. This can be accomplished by adding an acid, such as sulfuric acid, to the latex. In many cases, it will is be preferred to adjust the pH of the latex to below about 8 prior to addition of the divalent metal salt.

In accordance with this invention, from about 0.1 phr to 5 phr of a sulfonate surfactant and from about 0.1 phr to about 4 phr of an ethylene oxide/propylene oxide/ethylene oxide block terpolymer will be added h latex. It is typically preferred to add 1 phr to 3 phr of the sultonate surfactant and 0.4 phr to 2 phr of the ethylene oxide/propylene oxide/ethylene oxide block terpolymer to the styrene-butadiene latex. It is typically more preferred to add 1.5 phr to 2.5 phr of the sulfonate surfactant and 0.8 phr to 1.2 phr of the ethylene oxide/propylene oxide/ethylene oxide block terpolymer to the styrene-butadiene latex.

Some representative examples of sulfonate surfactants that can be employed include: alkane sulfonates, esters and salts (such as alkylchlorosulfonates) and alkylsulfonates with the general formula:

RS03H wherein R is an alkyl group having from 1 to 20 carbon atoms; sulfonates with intermediate linkages such as ester and esterlinked sulfonates such as those having the formula:

RCO0C2H4SO3H and ROOC-CH2-SO3H wherein R is an alkyl group having from 1 to 20 carbon atoms such as dialkyl sulfosuccinates; ester salts with the general formula:

0 0 11 11 C-CH-CHrC-O-R 503Na wherein R is an alkyl group having from 1 to 20 carbon atoms, alkarylsulfonates in which the alkyl groups contain preferably from 10 to 20 carbon atoms (e.g., dodecylbenzenesulfonates, such as sodium dodecylbenzenesulfonate) and alkyl phenol sulfonates.

Disulfonated surfactants having the structural formula:

0 R S03 X+ S03 X+ wherein R represents a linear or branched alkyl group containing from about 6 to about 16 carbon atoms and wherein X represents a metal ion, such as a sodium ion, have proven to be excellent surfactants for making the latex used in the practice of this invention. Such surfactants are sold by The Dow Chemical Company as Dowfax7' anionic surfactants.

The ethylene oxide/propylene oxide/ethylene oxide triblock polymers that can be used are of the structural formula:

C H3 HO -4CH2CH20xCH2CHO4-Y--4CH2CH20+x- H These triblock polymers will typically have a number average molecular weight of at least 8000. The triblock polymer will typically have a number average molecular weight which is within the range of about 10,000 to about 20,000. It is normally preferred for the triblock polymer to have a number average molecular weight which is within the range of 10,500 to 16,000. It is typically more preferred for the triblock polymer to have a number average molecular weight which is within the range of 11,000 to 14,000.

The polyoxypropylene block in the triblock polymer will typically have a number average molecular weight which is within the range of about 2,000 to about 12,000 and will more typically have a number average molecular weight which is within the range of 2,500 to 8,000. The polyoxypropylene block in the triblock polymer will preferably have a number average molecular weight which is within the range of 3,000 to 6,000. The polyoxypropylene block in the triblock polymer will more preferably have a number average molecular weight which is within the range of 3,500 to 4,500.

The polyoxyethylene blocks in the triblock polymer will typically comprise 50 weight percent to 90 weight percent of the total weight of the triblock polymer (the polyoxypropylene blocks will, of course, comprise the remaining 10 weight percent to 50 weight percent of the triblock polymer). The polyoxyethylene blocks in the triblock polymer will preferably comprise 60 weight percent to 80 weight percent of the total weight of the triblock polymer with the polyoxypropylene blocks comprising the remaining 20 weight percent to 40 weight percent of the triblock polymer. The polyoxyethylene blocks in the triblock polymer will preferably comprise 70 weight percent to 75 weight percent of the total weight of the triblock polymer with the polyoxypropylene blocks comprising the remaining 25 weight percent to 30 weight percent of the triblock polymer. It is preferred for the triblock polymer to have a HLB (hydrophilic/lipophilic balance) number which is within the range of about 18 to about 26. It is more preferred for the triblock polymer to have a HLB number which is within the range of 18 to 23.

Standard aggregate can be utilized in the practice of this invention. The aggregate is essentially a mixture containing rocks, stones, crushed stone, gravel and/or sand. The aggregate will typically have a wide distribution of particle sizes ranging from dust to golf ball size. The best particle size distribution varies from application to application. However, the use of the styrenebutadiene rubber latices as anti-stripping agents in accordance with this invention is applicable to all aggregate particle size distributions.

The aggregate is coated with the styrene- butadiene rubber latex in the first step of carrying out the process of this invention. The latex used will typically have a solids content within the range of about 2 percent to about 45 percent (based on weight). It is more typical for the latex to have a solids content within the range of about 5 to about 30 weight percent with it generally being preferred for the latex to have a solids content which is within the range of about 10 weight percent to about 20 weight percent. Because the styrene-butadiene latex of this invention is stable in hard water, it can be diluted with hard water to the desired solids content.

The styrene-butadiene latex can be simply sprayed onto the aggregate. It is, of course, also possible to coat the aggregate with the latex by slurrying it with the latex or by actually dipping it into the latex. The amount of latex applied will be sufficient for the latex/aggregate mixture to contain from about 0.005 weight percent to about 0.5 weight percent dry polymer, based upon the weight of the aggregate. It is preferred for the latex/aggregate mixture to contain from 0.01 to 0.2 weight percent polymer and is more preferred for it to contain from 0.05 to 0.1 weight percent polymer. in any case, after the latex is thoroughly applied to the aggregate, the aggregate will be dried to a moisture content which is below about 0.7 weight percent. This can be accomplished by heating the aggregate to an elevated temperature. The aggregate will typically be heated to a temperature which is within the range of about 150OF (660C) to about 45011F (2 3211C). It is typically preferred to heat the aggregate to a temperature which is within the range of about 200OF (930C) to 400OF (2040C). It is generally most preferred to heat the aggregate to a temperature which is within the range of about 300OF (1490C) to about 350OF (1770C). As the water in the latex evaporates, a polymer film forms and crosslinks on the surface of the aggregate to produce a coated aggregate surface.

The coated aggregate can be dried utilizing standard equipment which is used in plants which are designed to make asphalt concrete. For instance, the aggregate which has been coated with latex can be dried in a conventional drying drum or in a conventional drum mixer. After the aggregate has been dried, it is then mixed with an appropriate amount of asphalt cement. As a general rule, from about 3 weight percent to about 8 weight percent of the asphalt will be mixed with the coated aggregates, based upon the total weight of the coated aggregates. It is more typical for from about 5 weight percent to about 6 weight percent of the asphalt to be added to the coated aggregate, based upon the total weight of the coated aggregate.

Asphalt is defined by ASTM as a dark brown to black cementitious material in which the predominant constituents are bitumens that occur in nature or are obtained in petroleum processing. Asphalts characteristically contain very high molecular weight hydrocarbons called asphaltenes. These are essentially soluble in carbon disulfide as well as aromatic and chlorinated hydrocarbons. Bitumen is a generic term defined by ASTM as a class of black or dark-colored (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons, of which asphalts, tars, pitches and asphaltites are typical. ASTM further classifies asphalts or bituminous materials as solids, semisolids or liquids using a penetration test for consistency or viscosity. In this classification, solid materials are those having a penetration at 250C under a load of 100 grams applied for 5 seconds, of not more than 10 decimillimeters (I millimeter).

Semi-solids are those having a penetration at 250C under a load of 100 grams applied for 5 seconds of more than 10 decimillimeters (1 millimeter) and a penetration at 250C under a load of 50 grams applied for 1 second of not more than 35 millimeters. Semi- solid and liquid asphalts predominate in commercial practice today.

Asphalts are usually specified in several grades for the same industry, differing in hardness and viscosity. Specifications of paving asphalt cements generally include five grades differing in either viscosity level at 600C or penetration level. Susceptibility of viscosity to temperatures is usually controlled in asphalt cement by its viscosity limits at a higher temperature such as 1350C and a penetration or viscosity limit at a lower temperature such as 250C. For asphalt cements, the newer viscosity grade designation is the mid-point of the viscosity range. Table I below shows the ASTM grading is system for AC-2.5, AC-5, AC-10, AC-20 and AC-40.

The asphalt materials which may be used in the present invention are those typically used for road paving, repair and maintenance purposes. Petroleum asphalts are the most common source of asphalt cements. Petroleum asphalts are produced from the refining of petroleum and used predominantly in paving and roofing applications. Petroleum asphalts, compared to native asphalts, are organic with only trace amounts of inorganic materials. The asphalt cements that may be used in the present invention have an ASTM grade of AC-2.5, AC-5, AC-10, AC-20 and AC-40.

The preferred asphalt cements include AC-5, AC-10 and AC-20 with AC-5 and AC-10 being the most preferred grades.

The coated aggregate is mixed with the asphalt to attain an essentially homogeneous asphalt concrete.

The coated aggregate is mixed with the asphalt cement utilizing conventional techniques and standard equipment. For instance, the coated aggregate can be dried and mixed with asphalt to produce asphalt concrete on a continuous basis in a standard mixer.

The asphalt concrete made by the process of this invention can then be used to pave roads, highways, exit ramps, streets, driveways, parking lots, airport runways or airport taxiways utilizing conventional procedures. However, pavements made utilizing the asphalt concretes of this invention are far less susceptible to stripping than conventional asphalt concrete surfaces. Additionally, such asphalt concrete pavements are believed to be less susceptible to oxidative degradation. This is because the rubber coating on the aggregate prevents oxidative degradation of the asphalt which can be catalyzed by the aggregate.

This invention is illustrated by the following examples which are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

g2jarlple In this series of experiments, various surfactants were added toPliopaves styrene-butadiene latex having a solids content of 70.8 percent in an attempt to improve calcium ion resistance (hard water resistance). In the procedure used, 2 phr of Dowfaxs 8390 sulfonate surfactant and 1 phr of the nonionic surfactant identified in Table I were added to a series of 8- ounce (237 milliliter) glass bottles containing 100 grams of the SBR latices. In some cases, additional deionized water was mixed into the latex to reduce viscosity. The glass bottles were capped and subsequently placed in a oven that was maintained at a temperature of 500C.

The nonionic surfactants evaluated included Triton X-305 octylphenoxypolyethoxyethanol, Triton X- octylphenoxypolyethoxyethanol, Natrosol hydroxyethyl cellulose, Klucel hydroxypropyl cellulose, Aqualon Cellulose Gum sodium carboxymethyl cellulose, Pluronic P105 polyethylene oxide/polypropylene oxide/polyethylene oxide triblock polymer, PluronicO F108 polyethylene oxide/polypropylene oxide/polyethylene oxide triblock polymer and PluronicO F127P polyethylene oxide/polypropylene oxide/polyethylene oxide triblock polymer.

Table I

Nonionic Water Solids Lower Layer Surfactant Added Content (8 days) (g) ('116) Tr ton X-305 0 70 5 Triton X-165 0 70 3 Natrosol 41.6 50 20 Klucel 18 60 25 :malon Cellulose 41.6 50 20 PluronicIll P105 0 70 20 PluronicO F108 18 60 0 PluronicO F127P 18 60 0 Separation into two layers occurred relatively rapidly in most of the samples shown in Table 1.

Examinations after 8 days showed separations in all but two of the samples. These were the samples where the Pluronice F108 polyoxyethylene-polyoxypropylene- polyoxyethylene and the Pluronicc F127P polyoxyethylene-polyoxypropylene-polyoxyethylene were used as the nonionic surfactant. The latex samples made with the Pluronicc F108 surfactant and the Pluronicc F127P surfactant showed no evidence of creaming after being maintained at SOOC for 50 days.

Calcium ion resistance was determined by the slow addition of 50 mls of a 0.555 percent calcium chloride solution (0.1 N solution) to IbO g of latex. Then, the latex was filtered and rinsed on a 100 mesh (149 micron) screen and dried. Coagulum was reported as a percentage of latex solids. Both samples exhibited resistance to calcium ions with the sample made with the PluronicO F127P exhibiting much better resistance to calcium ions. In fact, samples made with PluronicO F127P exhibited a calcium ion resistance of up to 0.015 percents solids.

PluronicO F127P surfactant has a molecular weight of 12,600, an HLB number of 18-23, a polyoxypropylene block molecular weight of 4000 and contains about 71 percent polyoxyethylene blocks. Pluronics F108 surfactant has a molecular weight of 14,600, an HLB number of >24, a polyoxypropylene block molecular weight of about 3200 and contains about 80 percent polyoxyethylene blocks. PluronicO P105 surfactant has a molecular weight of 6,500, an HLB number of 12-18, a polyoxypropylene block molecular weight of about 3200 and contains about 55 percent polyoxyethylene blocks.

While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.

Claims

CLAIMS:

1. A styrene-butadiene latex having improved stability in hard water and good resistance to creaming, said styrene-butadiene latex being comprised of (1) water, (2) a styrene-butadiene rubber, (3) a fatty acid soap, (4) a sulfonate surfactant and (5) an ethylene oxide/propylene oxide/ethylene oxide triblock polymer, wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight of at least 8000.

2. A styrene-butadiene latex as specified in claim 1 wherein the sulfonate surfactant is present at is a level which is within the range of about 0.1 phr to about 5 phr, and wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer is present at a level which is within the range of about 0.1 phr to about 4 phr.

3. A styrene-butadiene latex as specified in claim 2 wherein the latex contains from about 2 phr to about 7 phr of the fatty acid soap.

4. A styrene-butadiene latex as specified in claim 3 wherein the styrene-butadiene rubber contains repeat units that are derived from about 10 weight percent to about 30 weight percent styrene and from about 70 weight percent to about 90 weight percent 1,3-butadiene.

5. A styrene-butadiene latex as specified in claim 4 wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a propylene oxide block that has a number average molecular weight which is within the range of 2,000 to 12,000.

6. A styrene-butadiene latex as specified in claim 5 wherein propylene oxide block in the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a molecular weight that represents from 10 weight percent to 50 weight percent of the total molecular weight of the triblock polymer.

7. A styrene-butadiene latex as specified in.claim 6 wherein the sulfonate surfactant is present at 10 a level which is within the range of about 1 phr to about 3 phr, and wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer is present at a level which is within the range of about 0.4 phr to about 2 phr. is

8. A styrene-butadiene latex as specified in claim 7 wherein the latex contains from about 4 phr to about 6 phr of the fatty acid soap.

9. A styrene-butadiene latex as specified in claim 8 wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight which is within the range of 10,000 to 20,000.

10. A styrene-butadiene latex as specified in claim 9 wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a propylene oxide block that has a number average molecular weight which is within the range of 2,500 to 8,000.

11. A styrene-butadiene latex as specified in claim 10 wherein propylene oxide block in the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a molecular weight that represents from 20 weight percent to 40 weight percent of the total molecular weight of the triblock polymer.

12. A styrene-butadiene latex as specified in claim 11 wherein the sulfonate surfactant is present at a level which is within the range of about 1.5 phr to about 2.5 phr, and wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer is present at a level which is within the range of about 0.8 phr to about 1.2 phr.

13. A styrene-butadiene latex as specified in claim 12 wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number is average molecular weight which is within the range of 10,500 to 16,000.

14. A styrene-butadiene latex as specified in claim 13 wherein the ethylene oxidelpropylene oxide/ethylene oxide triblock polymer has a propylene oxide block that has a number average molecular weight which is within the range of 3,000 to 6,000.

15. A styrene-butadiene latex as specified in claim 14 wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight which is within the range of 11,000 to 14,000.

16. A styrene-butadiene latex as specified in claim 15 wherein propylene oxide block in the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a molecular weight that represents from 25 weight percent to 30 weight percent of the total molecular weight of the triblock polymer.

17. A styrene-butadiene latex as specified in claim 15 wherein the styrene-butadiene rubber contains repeat units that are derived from about 15 weight percent to about 25 weight percent styrene and from 5 about 75 weight percent to about 85 weight percent 1,3-butadiene.

18. A process for coating aggregate which is particularly useful in making asphalt concrete to provide the aggregate with a high level of resistance to stripping by water, which comprises: (1) mixing the aggregate with latex to form a latex/aggregate mixture, wherein said latex is comprised of water, a styrene-butadiene rubber, a fatty acid soap, a sulf'onate surfactant, an ethylene oxide/propylene oxide/ethylene oxide triblock polymer having a number average molecul ar weight of at least 8000; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 660C to about 2320C; (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0.7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate to produce the coated aggregate.

19. A process for preparing asphalt concrete which comprises: (1) mixing the aggregate with latex to form a latex/aggregate mixture, wherein said latex is comprised of water, a styrene-butadiene rubber, a fatty acid soap, a sulfonate surfactant and an ethylene oxide/propylene oxide/ethylene oxide triblock polymer having a number average molecular weight of at least 8000; (2) heating the latex/aggregate mixture to a temperature which is within the range of about 660C to about 2320C; (3) maintaining the latex/aggregate mixture at said elevated temperature for a time which is sufficient to reduce the moisture content of the latex/aggregate mixture below about 0. 7 weight percent and to allow the polymer in the latex to crosslink on the surface of the aggregate to produce the coated aggregate; (4) mixing the coated aggregate with about 3 percent to about 8 percent asphalt based upon the total weight of the coated aggregate at a temperature of at least about 1070C; and (5) continuing to mix the coated aggregate with the asphalt to attain an essentially homogeneous asphalt concrete.

20. A process as specified in claim 19 wherein the sulfonate surfactant in the latex is present at a level which is within the range of about 0.1 phr to about 5 phr, wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer in the latex is present at a level which is within the range of about 0.1 phr to about 4 phr, wherein the fatty acid soap in the latex is present at a level which is within the range of about 2 phr to about 7 phr and wherein the ethylene oxide/propylene oxide triblock polymer has a propylene oxide block that has a number average molecular weight which is within the range of 2,000 to 12,000.

21. A styrene-butadiene latex substantially as hereinbefore described in the last, or next-last, sample of the foregoing Example.

22. Asphalt concrete comprising aggregate coated with a styrene-butadiene 5 latex according to anyone of claims 1 to 17 or21.

23. Asphalt concrete whenever prepared by the process of claim 19 or claim 20.

24. Asphalt concrete pavement made from the asphalt concrete of claim 22 or 10 claim 23.

25. Coated aggregate whenever produced by the process of claim 19.

26. Aggregate coated with a latex according to any one of claims 1 to 17 or 2 1.