BINDERS AND PIGMENT, COMPOSITE SHEETS INCLUDING SAME,

AND METHODS OF MAKING SAID COATED PARTICLES

This invention relates to inorganic paniculate materials coated with non- silicon containing organic binder and pigment. Such particles find use, for example, as roofing granules.

Prime roofing granules have long been used in the asphalt shingle industry to provide the shingle with long-term weathering tolerance, such as protection of the asphalt from exposure and degradation by ultraviolet (UV) light, and to provide color to the roofing material and, ultimately, a roof. It is this protection against UV degradation which extends the life of the asphalt shingle and consequently the effective life of the roof.

Also, when shingles are applied to a roof, generally the lower half of a shingle overlays the upper half of the shingle below on the roof. The granules on the upper half of the lower shingle are the so-called headlap granules. It is known to employ the headlap granules on upper portions of asphalt roofing shingles to add shingle weight and help prevent undue interbonding or sticking between stacked asphalt shingles to thus permit facile separation of individual shingles from the stack during roofing operations. The headlap granules on the shingle are generally completely protected from the environment, except for minor exposures at granules located beneath narrow alignment slits cut in the bottom portion of the overlaying shingle. These alignment slits typically extend in a direction parallel to the short lateral sides of the shingle. While the headlap granules may not need to display the same rigorous tolerance to long-term weathering exposure as prime granules, the granules nonetheless must provide worthy pigment and asphalt bonding capabilities. For this reason, it is imperative that once the roofing granules, whether they be prime granules or headlap granules, are embedded into the asphalt shingle, they remain firmly adhered thereon in order to serve their respective functions. One factor which affects the extent of adhesion between the roofing granules and the asphalt (or other adhesive) surface is the coating on the granule

itself. Historically, this coating is typically a clay: silicate ceramic which has been insolubilized on the rock surface by heating to modestly high temperatures via a kiln. Clay-silicate ceramic coated granules may also contain a variety of inorganic pigments which add color. Coatings produced in this way are often highly porous and can leach out a variety of acidic or basic materials upon contact with moisture. In addition, their surfaces are often highly charged, making the granules less compatible with asphalt than a neutral surface. Weakly acidic species are commonly added following kiln firing to neutralize any surface charge. Such neutralization processes (referred to in the art as "pickling") are expensive and may cause premature corrosion of granule processing equipment.

One solution to this problem is to simply heat the roofing granules to much higher temperatures (e.g., 900°F, 482°C) to yield a more completely "cured" granule coating. While more appealing from an equipment corrosion standpoint, higher temperatures tend to require slower production rates as well as increased energy consumption. Silicones are also usually added to roofing granules after such kiln-firing as a post-treatment step both to increase the wettability of the granule into asphalt and provide water repellency. Roofing granules which are highly alkaline or lack water repellency may adhere to the asphalt less than optimally.

Current methods of manufacturing roofing granules, outlined above, are not without drawbacks. For instance, because of the elevated temperatures used in the kiln, normally required to "cure" the ceramic coating, the use of heat-sensitive organic pigments to impart color on roofing granules is practically impossible. Although lower temperature kiln processes have been developed to accommodate this limitation, excessive amounts of acidic pickle solution are required at the end of the process to accomplish this objective.

U.S. Patent Application Serial No. 08/424,594 which is a continuation of U.S. Patent Application No. 08/136,584, filed October 14, 1993, describes one proposed solution allowing for the use of heat-sensitive organic pigments because of low temperature processing involved. The 08/424,594 application describes coated granules that are inorganic particles, which may be porous or substantially devoid of void space, coated with organometallic polymeric binders and, preferably,

an organic pigment. Further, the organometallic polymeric binder is the reaction product of water with at least one component of a binder precursor composition. The preferred water reactive organic polymers are described as those derived from the condensation reaction of an alkyl methacrylate and an alkoxysilylalkyl- methacrylate, which provide silyl groups on the molecule.

In general, after being binder-coated and optionally colored, roofing granules and the like are typically coated with a solution of silicone and oil to reduce dust formation, to provide water repellency, and to promote adhesion of the granules to asphalt. The silicone/oil solution typically contains a petroleum oil and a mixture of various silicones. Typically, the silicones are polymeric derivatives of dimethyl-siloxane. After the silicone/oil treatment, the roofing granules are applied to an asphalt substrate.

Prior to the present invention, another problem existed with respect to attempts to recover waste oiled granules for reuse. Waste oiled granules have an undesirable off-color due to the presence of a residue from the original silicone treatment performed on the granules. Further, the oily waste granules recovered during manufacturing and from shingles and the like also were not susceptible to recoating by alkali silicate binders due to the presence of the silicone residue on the granule surfaces from the original silicone treatment. Further, the incineration of the old granule coating by high heat to permit recoating is not a desirable option due to pollution concerns associated with the generated burn-off exhaust.

The present invention provides pigment-coated granular material and a method of making the same. The novel granular material avoids certain of the problems noted above. The granular material of the present invention comprises inorganic particles coated with binder and pigment, said binder comprising a non- silicon containing organic binder selected from polyalkyl(meth)acrylate or polyvinyl acetate. The present invention effectively avoids and eliminates the need to use any inorganic alkali metal silicate binder as an independent component of the granule coating and also avoids the need to synthesize silicon-containing groups in the organic binder that is employed.

As used herein, the following terms, in either their singular or plural forms, have meanings as set forth below:

"Granular material" means material composed of small solid particles having in bulk flowable properties. "Inorganic particles" means particles that do not contain carbon, excepting carbonates.

"Prime granule" means granules which are deployed on construction products in a manner so as to be left directly exposed to environmental conditions, such as sunlight, air, and rain. "Headlap granule" means granules which are deployed in building construction asphalt shingles, in the main, so as to be intimately covered by the underside of a partly superposed sheet of a shingle, except allowing for minimal noncoverage at regions situated beneath narrow alignment or aesthetic slits cut in the superposed shingle. Therefore, headlap granules, as incorporated into shingle products, generally are not directly exposed to environmental conditions.

"Non-silicon containing polyalkyl(meth)acrylate" means a polymer having no silicon-containing groups in the backbone or as pendant groups in a polymer molecule having a repeating unit of formula (A):

wherein X is a hydrogen atom or a methyl group, and R is an alkyl group having 1 to 10 carbon atoms. In one preferred embodiment, the "R" group in formula (A) represents an alkyl group having 1-4 carbon atoms. Preferably, the poly(meth)acrylate binder is constituted by at least 95% by weight up to 100% by repeat unit (A), noninclusive of the terminal ends of the polymer. The terminal ends of the polyacrylate also do not include a silicon-containing group. "Silicon-containing group" means a silicon atom-containing moiety in the backbone or as a pendant group of a polymeric molecule.

"Non-silicon containing polyvinyl acetate" means a polymer having the segment (B):

The terminal ends of the polyvinyl acetate do not include a silicon- containing group. "Binder" means a material having the ability to hold solid substances together.

"Pigment" means a fine insoluble white, black, or colored material. The binder for the granular material comprises a water-based physically drying system, viz. an emulsifiable polyalkyl-(meth)acrylate or polyvinyl acetate, devoid of silicon-containing groups or atoms. This binder is applied on the granule surfaces in emulsion form as preformed polymer solids dispersed in an aqueous medium. Upon drying the binder emulsion, the water vehicle is volatized leaving polymer solids as an adherent coating containing the pigment on the granule surfaces. The present invention allows for the use of organic pigments because the non-silicon containing polyalkyl(meth)acrylate or polyvinyl acetate binder may be processed at a relatively low temperature to coat the granules. Therefore, one advantage of the present invention is that the binder emulsion can be dried on the granules at a relatively low temperature of only about 90 to 120°C, although even room temperature drying also is feasible to volatize the water from the binder emulsion if longer drying periods are tolerable.

An additional advantage of low temperature processible binder is the reduction in energy expenditures per ton of granules produced without seriously affecting the rate of production. In particular, the binder employed in the granules of this invention colorable is a less energy-intensive process than the conventional inorganic (sodium) silicate process. Further, the use of the polyacrylate or polyvinyl acetate binder employed in the granules of this invention with pigments has been

found to provide brighter colored granules, which are deeper in tone than prior colored granules made using inorganic binders that are insolubilized by relatively high temperature or acid process. Also, low temperature processing tends to render usable granule rock which may otherwise be unusable by avoiding the tendency of granule rock to fracture at elevated temperatures. In addition, the binder coated on the inorganic particles of the inventive granules shows less staining than standard granules coated with sodium silicate pigment binder. Further, granules produced according to this invention have been shown to exhibit better adhesion to asphalt and other adhesive substrates than ceramic-coated granules. Better granule adhesion to the asphalt surface decreases the probability of granule loss and subsequent premature degradation of a shingle due to UV light. Further yet, the binders of the invention dry clear, require no organic solvents, and can well-disperse pigments such as carbon black. Also, the binders used in this invention impart adequate water repellency to the coatings formed on the inventive binder-coated granules. The discovery that water repellency property is not unduly hindered even without providing silicon-containing groups in the molecules of the binder translates into significant cost and time advantages otherwise associated with incorporating such silicon functionality and the like. While silicone oils may be added later during processing as a separate physical coating to the previously binder-coated granules of this invention for optimal water repellency, it has been discovered that, even in that circumstance, less silicone oil is needed in this regard than for conventional inorganic alkali metal silicate binder-coated granules. Also, the granules of the invention generate less dust than that observed from conventional granules coated with inorganic alkali metal silicate binder. Another advantage of the invention is that the non-silicon containing polyacrylate or polyvinyl acetate binder has also been found to be suitable not only for coloring fresh granules but also for recoloring "waste" granules, i.e., reclaimed oiled granules. For example, waste or previously oiled granules can be rejuvenated by recoloring, e.g., with carbon black pigment, using the binding system described herein based on either the polyalkyl(meth)acrylate or polyvinyl acetate binder. In

one embodiment, these rejuvenated granules can be used as headlap granules of an asphalt shingle.

In one further embodiment, the alkyl(meth)acrylate or vinyl acetate segments of the binder molecule represent the principal (i.e., typically greater than 50% up to 100% by weight) solid component of the binder. In one embodiment, the binder can be provided as a homopolymer or copolymer of vinyl acetate as long as the vinyl acetate is the principal component of the binder molecule.

In an alternate embodiment, the binder can be provided as a homopolymer or a copolymer of acrylate, or as a physical blend of different homopolymers and/or copolymers of acrylates. The alkyl(meth)acrylate polymer comprises chain segments or repeating units formed from one type or different types of alkyl(meth)- acrylate monomers. These alkyl(meth)acrylate monomers typically are esters of acrylic or methacrylic acids involving R groups per the aforesaid formula (A) preferably having 1-10 carbon atoms; although R may contain any number of carbons as long as water dispersibility is maintained. That is, the polyalkyl-

(meth)acrylate should remain dispersible in an aqueous medium to form an emulsion therewith without precipitation.

In any event, a binder including butyl (meth)acrylate has been found to be particularly suitable. For instance, one preferred binder is based on a copolymer of butyl(meth)acrylate and methyl (meth)acrylate monomers in a weight ratio of about 40:60 to 60:40, respectively. Another preferred binder is based on a physical blend of butyl (meth)acrylate and methyl (meth)acrylate homopolymers in a ratio, by weight, of about 40:60 to 60:40, respectively.

It is possible to add adjuvants, such as a surfactant or wet adhesion promoter, such as an nonylphenol polyethylene glycol adduct, to the polyacrylate or polyvinyl acetate binder used in the present invention to the extent that the additive does not chemically react with other components of the granule or have an adverse effect on the granule or impair its ultimate use.

Methods of making the inventive coated granules are another aspect of the invention. The general method comprises coating inorganic particles with non-

silicon containing polyalkyl(meth)acrylate or polyvinyl acetate binder and pigment. More particularly, this method comprises the steps of:

(a) dispersing a binder composition comprising a non-silicon containing organic binder selected from polyalkyl(meth)acrylate or polyvinyl acetate into an aqueous medium to provide a binder emulsion;

(b) providing inorganic granules;

(c) combining pigment with at least one of the binder emulsion and the inorganic particles;

(d) combining the inorganic granules with the binder emulsion to yield binder-coated granules; and

(e) exposing the binder-coated granules to conditions sufficient to dry the binder emulsion.

It will be recognized by those skilled in the art that various steps (a)-(d) may be performed in any convenient sequence of plural steps and in any convenient manner or simultaneously as a single step; for example, steps (a) or (b) may be reversed or carried out simultaneously; or steps (a)-(d) may be combined. All of these method embodiments are considered within the invention.

The "exposing" step (e) preferably comprises heating the binder coated granules to moderate temperatures for a time sufficient to dry the binder solution to a substantially solid mass of material left as a thin coating or surface layer on the granules, for example, temperatures ranging from about 90°C to about 120°C and times preferably ranging from about 10 to about 60 minutes. These relatively low binder drying temperatures afforded by the binder used in this invention, yields significant savings in energy costs and heating equipment. In fact, the binder of the present invention can be allowed to dry at room temperature (about 25°C) over a period of 6-24 hours; although for practical production line requirements,, low temperature heating at 90 to 120°C to effect drying of the binder is preferred.

Another aspect of the invention is a composite sheet material suitable for use in building material, the composite sheet comprising a backing, the backing at least partially coated with an adhesive (preferably asphalt), the adhesive, in turn, at least partially coated with the inventive coated granules.

Other aspects and advantages of the invention will become apparent from the description of preferred embodiments which follows.

The useful binder coatings for the granules of the invention are formed from aqueous binder emulsions comprising an aqueous emulsion of a non-silicon containing organic binder selected from polyalkyl(meth)acrylate or polyvinyl acetate organic polymer solids as binder polymer solids, and an aqueous medium such as deionized water. This emulsion, after any and all dilutions are completed before its usage in granule coating in this invention, generally comprises from about 70% to about 90% by weight of an aqueous liquid vehicle and from about 30% to about 10% by weight of binder polymer solids.

In setting the lower and upper amounts for the water and binder solids content of the binder emulsion, it is important that the amount of water is raised to a level adequate to disperse the binder throughout the granules. If too much water is employed, the binder can become overly dispersed such that inadequate amounts of binder solids are coated upon the surfaces of the granules to sustain a pigment coating.

The polyalkyl(meth)acrylate can be a homopolymer or copolymer, or physical mixtures thereof, comprising chain segments or repeat units of alkyl(meth)acrylates of basic formula (A); although the only limit on the number of carbons thought to exist in this regard is the retention of water dispersibility The repeat units A of the poly(meth)acrylates used in the binder of the present invention have the following basic formula:

wherein X is a hydrogen atom or a methyl group, B represents a hydrogen atom or non-silylated substituent thereof, and R is an alkyl group having 1 to 10 carbon atoms. Neither Segment (A), nor the terminal groups of the polymer, can include a silicon-containing group. The silicon-containing group that is eliminated and

avoided in the polymeric binder used in the present invention of this invention, includes, for example, a silyl group (-SiH ₃ ), a silyenyl radical (-SiH ₂ -), a siloxy group (-OSiH ₃ ), a silicone group (-Si(R ₂ )O-), a siloxanyl group

I I

(— Si — O — Si — O-) where x is an integer of one or more. More typicallv, the

I I esters of the acrylic or methacrylic acids used in formula (A) involve "R" groups having 1-4 carbon atoms. Preferably, the poly(meth)acrylate binder is constituted by at least 95% by weight up to 100% by repeat unit (A), noninclusive of the terminal ends of the polymer. In any event, a binder including butyl (meth)acrylate has been found to be particularly suitable. For instance, one preferred binder is based on a copolymer formed of butyl (meth)acrylate and methyl (meth)acrylate monomers in a ratio, by weight, of about 40:60 to 60:40, respectively. Another preferred binder is based on a physical blend of butyl (meth)acrylate and methyl(meth)acrylate homopolymers in a ratio, by weight, of about 40:60 to 60:40, respectively. Another useful binder polymer solids composition comprises, by weight, 47% methyl (meth)acrylate, and 53% butyl (meth)acrylate. Yet another useful binder polymer solids composition comprises, by weight, 35% methyl methacrylate, 11% butyl (meth)acrylate, and 55% ethyl acrylate. Commercially available dispersions of acrylic (co)polymers which are suitable as the binder emulsion used in coating the granules of the present invention, include those available under the trade designations "RHOPLEX-R AC-2235" and "RHOPLEX-R AC-2234", both available from Rohm & Haas Company, Philadelphia, Pennsylvania. "RHOPLEX-R AC-2235" and "RHOPLEX-R AC-2234" dispersions are obtained in aqueous dispersion form with about 46-47% polymer solids/53-54% water content. For purposes of formulating the binder emulsions used in coating the granules in this invention, these "RHOPLEX" emulsions are diluted with an approximately equal amount of deionized water. That is, a binder emulsion is formed comprising 40-60% by weight of "RHOPLEX" emulsion in combination with 60 to 40% by weight deionized water as a diluent. This dilution arrives at a binder emulsion having 20% to 30% by weight

polyacrylate resin solids. Thereafter, this binder emulsion is ultimately combined with the pigment before the coating is applied to the granule surfaces and dried to eliminate the water vehicle. Where the granules are intended for exposed surface of composite roofing and siding sheets, such as shingles, approximately equal amounts of binder emulsion containing 20 to 30% by weight resin solids, after all dilution is completed, and pigment are combined. That is, the diluted binder emulsion is mixed with pigment(s) in amounts of 40 grams to 60 grams diluted binder emulsion for every 60 grams to 40 grams by weight pigment, respectively, for granule coating applications relating to preparing granules intended for exposed shingle surfaces, and the like.

Another useful source of polyacrylate as the organic binder used in this invention is commercially available under the trade designation "RES 1019" from Rohm & Haas Company, Philadelphia, Pennsylvania, which is an acrylate copolymer emulsion containing about 50% by weight binder solids. The "RES 1019" is further diluted with deionized water to the extent necessary to provide a 10% to 20% resin solids emulsion. Also, the "RES 1019" preferably is further formulated before use in this invention for coating granules by mixing MgCl ₂ (34% by weight) with the "RES 1019" in a approximately equivalent amounts by weight MgCl ₂ with respect to the the amount of polyvinyl acetate solids. The addition of the MgCl ₂ acts to clarify the binder coating. If the MgCl ₂ is not used in conjunction with the "RES 1019", the dried coating is undesirably cloudy or milky.

The non-silicon containing polyvinyl acetate which can be alternately used as the organic granule binder in this invention means a polymer having the segment (B):

The terminal ends of the polyvinyl acetate do not include a silicon- containing group. A suitable polyvinyl acetate emulsion for the granule coating is a 10% to 20% resin solids by weight emulsion. A commercially available source of

polyvinyl acetate in emulsion form can be obtained under the trade designation "AEROSPRAY A70" (60% by weight resin solids) from American Cyanamid Company. The "AEROSPRAY A70" is further diluted with deionized water to the extent necessary to provide a 10% to 20% resin solids emulsion. Also, the "AEROSPRAY A70" is further formulated before use in this invention for coating granules by mixing MgCl ₂ (34% by weight) with the "AEROSPRAY A70" in approximately equivalent amounts by weight MgCl ₂ with respect to the amount of polyvinyl acetate emulsion. The MgCl ₂ acts to impart clarity to the dried binder coating. The organic binder of the present invention is selected without need or concern for providing silicon-containing groups, such as the types mentioned supra, on the alkyl(meth)acrylate or polyvinyl acetate polymer molecules. Therefore, the binder of the present invention effectively excludes the presence of such silicon- containing groups. Also, inorganic alkali metal silicates or hydrated alumino- silicates are not used as separate component of the granule coating binder of the invention, which permits the use of relatively low drying temperatures, i.e., 90° to 120°C, for the binder coating. The relatively low temperatures required for drying the binder and fixing the pigment in the granule coating is attributable to the particular polymeric binders employed that are described herein. It is within the scope of the invention that substituents other than silicon- containing groups may be attached to the organic binder polymer in place of one or more of the active hydrogen atoms present in segments (A) or (B) described herein. Examples of such substituents and groups include fluorine, and chlorine atoms, alkyl, alkenyl, aryl, carboalkoxy, carbamides, alkoxy, carboxyl, nitrile, pyrrolidinone, carboxylic acid groups and the like.

It will be understood that binder compositions useful in the present invention may contain effective amounts of additives, such as surfactants, ultraviolet light absorbers, light stabilizers, acid neutralizers and oxidation stabilizers. For example, certain surfactants or wet adhesion promoters can be employed in the binder emulsion. The incorporation of a surfactant in the binder composition may be desirable because its presence may allow water to be mixed

more uniformly throughout the binder precursor mixture and it may allow for more complete coverage of the inorganic particles. The surfactant is employed in an amount sufficient to maintain a dispersion of the binder solids in the aqueous medium. Surfactants useful in the practice of the present invention include anionic, cationic, and non-ionic surfactants. Preferred are commercially available non-ionic surfactants including but are not limited to a nonylphenol polyethylene glycol adduct, polyethylene oxide, polyethylene oxide nonylphenyl monoether, and propylene oxide - ethylene oxide block copolymers. The surfactant as used is present in relatively minor residual amount of the binder emulsion, i.e., less than 1.0% by weight of the binder emulsion.

Ultraviolet light absorbers, light stabilizers, and antioxidants may be desirable to provide acceptable product lives by improving the stability of the binder. Compounds useful for these purposes in the invention include, for example, substituted benzophenones, benztriazoles, phenols, sebacates, and the like. Preferred light stabilizers are sebacates, especially hindered amine sebacates such as the light stabilizer presently known under the trade designation TINUVIN 123, which has the generic chemical formula bis-(l-octyloxy-2,2,6,6-tetramethyl-4- piperidinyl) sebacate. Preferred ultraviolet light absorbers are substituted benzotriazoles such as that presently known under the trade designation TINUVIN 384, which is 3-(2H-benzotriazol-2-yl)-5-( 1 , 1 -dimethylethyl)-4-hydroxy- benzenepropanoic acid. Both compounds are available from Ciba-Geigy Corp., Ardsley, NY. The stabilizers, if used, generally and preferably are present at a weight percentage ranging from about 1% to about 5%, based on weight of acrylate binder. Also, small amounts of neutralizers, preferably ammonia, can be added to the binder emulsion before coating the granules to neutralize acidity such as from residual acrylic monomers present in the emulsion. The presence of residual acrylic monomers in the binder emulsion generally should be minimized to below 0.5% by weight, preferably less than 0.05% by weight. The amount of ammonia added to the binder emulsion generally should be no greater than 0.1% by weight.

The core material of the granules to be coated by the binder employed in the present invention include raw inorganic particles or recovered (waste) roofing granules. These recovered roofing granules can comprise an inorganic particle previously coated with an inorganic or organic binder. Also, these recovered granules may be dry or oily. Examples of waste core granules include Wausau headlap base and Wausau Greystone.

The core material, in general, may be porous or substantially devoid of void space. The inorganic particles used as or in the core material can be, for example, of weather-resistant mineral rock such as greenstone, nepheline syenite, common gravel, slate, gannister, quartz, quartzite, greystone, argiUite, coal slag, copper slag, nickel slag, and the like. Suitable recovered granules for use as the core material are granules such as disclosed in U.S. Patent No. 5,009,511, which are made from recycled materials. Typical inorganic particles used for making either prime or headlap roofing granules have sizes ranging from about 425 to 1300 micrometers. The use of somewhat larger or smaller inorganic particles or recycled granules is within the scope of the present invention, provided the inorganic particles or recovered granules have a size permitting, or still permitting, their function as a roofing granule.

The general method of making the granules of the invention comprises coating inorganic particles with non-silicon containing organic binder selected from polyalkyl(meth)acrylate binder or polyvinyl acetate, and pigment. More particularly, this method comprises the steps of:

(a) dispersing a binder composition comprising a non-silicon containing organic binder selected from polyalkyl(meth)acrylate or polyvinyl acetate into an aqueous medium to provide a binder emulsion;

(b) providing inorganic granules;

(c) combining pigment with at least one of the binder emulsion and the inorganic particles;

(d) combining the inorganic granules with the binder emulsion to yield binder-coated granules; and (e) exposing the binder-coated granules to conditions sufficient to dry the binder emulsion.

It will be recognized by those skilled in the art that various steps (a)-(d) may be performed in any convenient sequence of plural steps and in any convenient manner or simultaneously as a single step; for example, steps (a) or (b) may be reversed or carried out simultaneously; or steps (a)-(d) may be combined. All of these method embodiments are considered within the invention.

The "exposing" step (e) preferably comprises heating the binder coated granules to moderate temperatures for a time sufficient to dry the binder solution to a substantially solid mass of material left as a thin coating or surface layer on the granules, for example temperatures ranging from about 90°C to about 120°C and times preferably ranging from about 10 to about 60 minutes. These relatively low binder drying temperatures afforded by the binder used in this invention, yield significant savings in energy costs and heating equipment. In fact, the binder of the present invention can be allowed to dry at room temperature (about 25°C) over a period of 6-24 hours; although for practical production line requirements, low temperature heating at 90 to 120°C to effect drying of the binder is preferred.

The pigments used in this invention to impart a hue to the surfaces of the granules can be organic or inorganic varieties well known in the field. Exemplary pigments include carbon black, titanium oxide, chromium oxide, yellow iron oxide, phthalocyanine green and blue, ultramarine blue, red iron oxide, metal ferrites, and mbrtures thereof. Examples of suitable organic pigments can be found in the Raw Material Index, Pigment Section, National Paint & Coating Assoc, Washington DC, 1985 ed. A dispersant is typically and preferably used to disperse the carbon black or other fine particle size pigments used in the invention. One such dispersant is the sodium salt of sulfonated naphthalene-formaldehyde condensate known under the trade designation "Blancol N", available from Rhone-Poulenc Surfactants & Specialities, Cranbury, NJ.

Although the pigments can be added separately to either the granules or binder before mixing these components together, it is preferred to premix the pigments with the dry granules with thorough mixing such that the pigments are well-dispersed and cover the granules, before admixture with the binder emulsion. The dispersion of pigments can be maximized and facilitated, if desired, by the

addition of a paniculate dispersant, such as clay, to the pigments. The amount of paniculate clay dispersant added in this regard is approximately 20% by weight of the weight of prime or nonwaste granules. For granules intended for nonexposed applications, such as for headlap granules, calcined clay can be optionally added in an amount of up to about 2 grams per 1,000 grams of granules. Alternatively, in a different embodiment of this invention, the desired pigment material can be added and dispersed in the emulsion of binder polymer solids before coating the granules with the binder emulsion. The mixture of pigments and binder emulsion may be optionally agitated and or warmed to facilitate emulsion maintenance. Mechanical stirring of the mixture of polymer solids, water and pigment is prefened and heating of the mixture at temperatures up to and including the boiling point of the aqueous liquid vehicle is prefened. Formation at temperatures above the boiling point of the aqueous liquid, attainable for example in a sealed reactor, may also be useful. In any event, as general requirements of the method of coating the raw roofing granules with the acrylate or vinyl acetate binder, the following conditions should be followed. Preferably, the raw granules are preheated at a temperature between 90 and 120°C to aid in drying the binder coating.

Separately, for the acrylate resin derived from "RHOPLEX" sources, such as described herein, it is further mixed and dispersed in an aqueous solution to form a more dilute emulsion generally resulting in an amount of about 20% to 30% by weight binder solids/( water + binder solids). It is possible to employ lower amounts of acrylate solids in the binder emulsion, such as, as low as about 10%-20% by weight, where the "RES 1019" polyacryalate copolymer is used. The polyvinyl acetate emulsion, such as derived from the "AEROSPRAY A70" formulation commercially available and described herein, generally is used in an amount of about 10% to 20% by weight binder solids; the amount of binder solids can be adjusted within this range, if desired, by appropriate water dilution.

In any event, the emulsion of acrylate resin or polyvinyl acetate is then blended with the granules and mixing is continued until the granules are completely coated thereby. The mixer conditions should be moist enough to allow the pigment (derived from either the binder emulsion or as premixed with the granules) and

binder to uniformly coat the granules. The amount of pigment added to either the granules or binder emulsion will vary in kind and amount depending on the ultimate use desired for the coated granule. For example, in the case of coated granule intended for use on the outer exposed surface of a shingle, the amount of pigment added is approximately equal in weight to the amount of binder emulsion (binder solids and aqueous vehicle) ultimately employed. Therefore, for exterior shingle usage, the amount of granule pigment used is in the range of about 10 to about 6.5 times the amount of the polyacrylate or polyvinyl acetate resin solids per se included in the aqueous binder emulsion upon coating of the granules. In contrast, if the granule is intended for use as a headlap granule, the amount of pigment, such as carbon black, is lowered to an amount approximately equivalent to the total amount of polyacrylate or polyvinyl acetate binder solids present in the binder emulsion upon coating of the granules.

Also, as will be understood, the steps of heating the granules, adding the dry pigments, and adding the polyacrylate or polyvinyl acetate resin emulsion can be performed sequentially or combined. The mixer discharge preferably should not exceed 2% moisture by weight. Then, the binder-coated granules are air dried with air heated to 93 °C until the binder coating is dried. The dryer heat source should be indirect and consist of a high volume of air, such as forced air at approximately 20 CFM (i.e., about 0.57 m ³ /min). The air drying temperature should not exceed about 120°C. If the temperature exceeds 120°C, a colored granule binder coating tends to become extremely tacky and the integrity of the binder coating on the granule may be lost. After drying, the binder-coated granules are then subjected to an adhesion treatment, such as described below, to yield granules which are ready for incorporation into construction materials such as asphalt shingles.

Suitable adhesion agents are compounds capable of promoting the adhesion of binder-coated roofing granules to an asphalt-based substrate. Preferred adhesion agents are hydrophobic in nature, and do not significantly alter the color of the roofing granules. The adhesion agent should be compatible with the binder and the surfaces of the roofing granules. Such adhesion agents include silicones other than those having long-chain hydrocarbon groups. Preferred silicones are described in

E. Schamberg, Adhesion, v. 29(11), pp. 20, 23-27 (1985), as well as in U.S. Pat. Nos. 4,486,476; 4,452,961; 4,537,595; and 4,781,950. These kinds of silicones can be purchased under the trade designations "TEGOSIVIN", particularly "TEGOSrVIN HL100", from Goldschmidt Chemical Corporation, Hopewell, Virginia. Other suitable adhesion agents are described in U.S. Patent No. 5,240,760, which is incorporated herein by reference in this regard.

The adhesion agent is employed on the roofing granule surfaces to an extent sufficient to promote granule adhesion to an asphalt-based substrate. An oil is typically mixed with the adhesion agent to assist spreading the adhesion agent over the surfaces of the roofing granules, and also helps reduce dust formation. This oil is typically one of three petroleum oils: (1) paraffinic oils; (2) naphthenic oils: and (3) aromatic oils, or a mixture thereof. Paraffinic and naphthenic oils are preferred due to their more favorable flash points compared to aromatic oils. Particularly preferred is slate oil, such as that available from Cross Oil & Refining Co. Inc., Smackover, AR.

In general, the silicones are applied to roofing granules at about 0.01 to 5 lbs. per ton of granules (5X10 ^" to 0.25 weight percent), and the oil is applied at a rate of about 1 to 10 pounds per ton of granules (0.05 to 0.5 weight percent). When the adhesion agent is a "TEGOSIVIN" silicone, the adhesion agent is employed in the oil at about 1 to 5 weight percent, preferably about 2 to 4% by weight of the mixture of the two components.

The silicone and oil should be used in amount that permits an adequate quantity of granules to be sufficiently coated with a thin film of the treatment composition, but not to such an extent that the quality of the shingle is compromised. Such a "thin film" preferably is continuous, extends over at least 50% of the granule surfaces, and is between about 5 to about 25 micrometers in thickness.

Also, it will be understood that other additives may be introduced into the roofing granule composition. For example, oleic acid can be used in granule treatment to promote adhesion and control dust. In addition, roofing granules can

also be treated with a water-soluble inorganic copper compound to prevent algicidal growth, such as described in U.S. Patent No. 3,528,842.

After treatment in the post-treatment stage with silicone and oil, the granules are removed and then can be shipped to a location where the granules are subsequently placed on an asphalt substrate. An asphalt substrate typically includes a base mat covered with an asphalt that is filled with a mineral filler or stabilizer. An asphalt is a cementitious material having bitumens as a main constituent. A filler is typically powder form (approximately 44 to 200 micrometers), and is included in the range of from 0 to 70 percent by weight of the total asphalt composition. Examples of asphalt fillers include limestone, dolomite, nepheline syenite, or ground shale.

Asphalt-based roofing materials are formed by providing an asphalt substrate, and applying roofing granules to at least a portion of the substrate. An asphalt substrate is typically formed by the following steps: (a) mixing a molten asphalt and a heated filler in a mixer; (b) conveying paper, felt, or a glass fiber available under the trade designation "FIBERGLASS" mat or web through a coating apparatus which coats the mat with the filled molten asphalt (typically by means of coating rolls). Roofing granules may be applied to the substrate, for example, by dropping the paniculate onto a hot asphalt surface of the asphalt substrate.

After the granules are applied, the coated mat is cooled, for example, by spraying water onto the hot asphalt surface. Typically, a release layer is then applied to the backside of the coated mat, and a sealer is applied to a portion of the mat. To form a shingle, the mat is cut to the appropriate shape. Shingles may be attached to the roof in any conventional manner. For example, the shingles may be nailed or stapled to the roof. Such methods of attaching shingles are well known to those skilled in the art, and therefore should need no further description herein.

Objects and advantages of this invention are further illustrated by the following test methods and examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit the invention.

Test Methods

Water Repellency Test

The hydrophobicity of the inventive granules was determined in accordance with the following test. Approximately 25 grams of finished granules to be tested were placed dry in a PYREX #9800 test tube of size 15 cm x 1.7 cm diameter. While covering the mouth of the test tube with a finger, the tube was inverted, the finger removed such that the granules were allowed to slowly escape so as to form a small conical pile on a surface 2-3 cm from the mouth of the tube. The top of the pile was then indented with the round base end of the test tube so as to form a concave surface (depression) which was used to receive 3 drops of distilled water. By visual observation, the time required for the bead of water to break up and sink down through into the granules was recorded.

Asphalt Wettability Test (Reverse Wettability)

This test was used to determine the completeness of distribution of the adhesion treatment on roofing granules. An asphalt soft enough to pour readily at 15.5°C is used. The asphalt was made by adding 13 parts of a Mid-Continent 130°F (54.4°C) melt point saturant to 10 parts by weight of oil having a Saybolt \iscosity of 635. The mixture was heated with stirring at a temperature not higher than 250°F (121°C) until the asphalt was thoroughly dissolved in the oil. The mixture was allowed to cool to room temperature (about 20°C) before using in the test.

To about 10 grams of granules in a 100 ml beaker were added about 50 ml of water. With a suitable spatula about 2 grams of the asphalt was placed into the granule-water mixture and constantly stirred for 1 minute to encourage coating of the granules with asphalt. While the whole mass of granules and asphalt was under water and after cessation of stirring, the percentage of total granule surface area coated by the asphalt was visually estimated. After 5 minutes, the mass of granules was observed again and the percentage of total granule surface area coated by asphalt was again visually estimated. The lower of the above two estimates was

reported as the asphalt wettability % value. In terms of % wettability, a rating of "100" is the target since that indicates that the entire exposed surface of each granule has been wet out by the asphalt.

L*a*b* Scan Color Matching Test

Since color is the first stimulus that the consumer perceives, resulting in an immediate evaluation of roofing granule quality, color consistency is one of the principal quality attributes of roofing granules. To determine the color of roofing granules, a machine known under the trade designation "HunterLab LabScan Spectrocolorimeter" model 6000 was used. A sample preparation device, which is described in U.S. Pat. No. 4,582,425, was used to prepare the samples.

The spectrocolorimeter is designed to measure the reflectance color of objects. The spectrocolorimeter measuring geometry used was 0°/45°. This geometry provided for viewing the samples similar to normal visual evaluation, with 0° illumination, or perpendicular illumination of the sample, in 45° viewing of the sample. 45° circumferential viewing effectively excludes the specular (glossy) reflectance. This geometry essentially eliminated the effect of the sample directionality or granule texture.

As explained in the HunterLab LabScan Spectrocolorimeter brochure, light from a halogen lamp passes through a series of filters and lenses to simulate D65 daylight and eliminate heat, and is focused on the sample in a circular pattern. (Roofing granular color was read in "Illuminant D65", which represents daylight with a conelated color temperature of approximately 6500° Kelvin.) Light diffusely reflected from the sample is collected by sixteen fiber optic bundles staged circumferentially at 45° to the sample. The light input from all stations was averaged to eliminate errors caused by sample texture and directionality, and was then directed onto the circular variable filter which was spun continuously, separating the light into its component wavelengths. The separated light was picked up by a single photo detector, and then fed to a personal computer via an analog-to-digital converter. The computer processes measurement data at 10 nanometer intervals across the visual spectrum, from 400 to 700 nanometers.

For the color determination tests, the 10° CIE Standard Observer (CIE stands for the commission International de lΕclairage, an international commission on illumination). The "Standard Observer" is the spectral response characteristic of the average observer defined by the CIE. Two such sets of data are defined, the 1931 data for the 2° visual field (distance viewing) and the 1964 data for the annular 10° visual field (approximately arms length viewing). A much better agreement with the average visual assessment can be obtained by making use of the 10° standard observer, and thus this was the observer used in these tests. For each color granule tested, a sample was scanned by the spectrocolorimeter. This scan produced a numerical description of the colored sample, a fingerprint, which never changes. However, since it does not consider the lighting condition and the observer, the CIE L*a*b* does not completely describe the visual appearance of the color. A mathematical means of translating fingerprints into a set of three numbers (XYZ), tristimulus values, was developed. The tristimulus values describe color as a normal observer sees it under a specific lighting condition.

Because the tristimulus values (XYZ) do not provide either uniform or logical estimates of perceived color intervals or color relationships, scales based on the CIE standard observer were transformed into the "opponent-colors" theory of color vision. The 1976 CIE L*a*b* is one such transformation. The opponent- colors theory maintains that the interaction between the eye and the brain decodes the experience of a color into three specific signals. One of these signals is lightness- darkness (L*), one is red-green (a*), and one is yellow-blue (b*). This color system was chosen for use in these tests because it is believed to be understandable by both the color scientist and the novice. Thus all instrument color readings were taken on a HunterLab LabScan Spectrocolorimeter, in Illuminant D65, with 10° observer, in 1976 CIE L*a*b* color space. All Comparative Example granules in the Examples which follow were read after an oil had been removed from the granules. The oil removal procedure is described in the following test procedure. After the granules were deoiled, the granule preparation procedure of U.S.

Pat. No. 4,582,425 was used. Briefly, this procedure consisted of loading a layout

sample dish by slightly overfilling the dish with granules, compressing the granules into the dish with the flat surface of a layout tray, using only vertical pressure and no circular action. The loaded sample dish in each test was positioned on the layout device, matching the configuration, so that the sample dishes were in the locked position. A roll carriage was then gently lowered onto the sample dish, after which the roller is pulled back and forth across the surface on the face of the granules. It was found that twice across the surface produced the desired smooth, even, flat, and undented surface necessary for precise color readings. Excess granules fall over the sample dish edge. The prepared granule sample dish was then placed into the instrument sample port. The sample surface was first examined to insure that the sample has not "popped" and lost its smooth level surface.

Two complete spectrocolorimeter readings (scans) were taken, completely emptying and repeating the layout procedure each time. The procedure was repeated until two readings consistent with each other to within less than 0.3 unit range were obtained. If not, the procedures were repeated with more attention to detail. All samples presented to the spectrocolorimeter for color difference determination were at ambient temperature (hot granules give inaccurate color readings, as well as wet granules). After deoiling the granules in accordance with the procedure explained below, the granules were in all cases read within four hours of deoiling. (Samples left in an uncontrolled condition may exhibit unwanted changes, and samples that have been deoiled and then left standing for a long period of time are not acceptable for spectrocolorimeter readings.)

In interpreting the results from the spectrocolorimeter, the opponent-color scales give measurements of color in units of approximate visual uniformity throughout the color solid. L* measures lightness and varies from 100 for perfect white, to zero for black, approximately as the eye would evaluate it. a* and b*, the chromaticity dimensions, give understandable designations of color as follows: a* measures redness when plus, grey when zero, and greenest when minus; and b* measures yellowness when plus, grey when zero, and blueness when minus.

Acceptable opponent color scales for the granules of the present invention are when

all three of L*, a* and b* are within +/- 1.5 of the standard black roofing granules, more preferably within +/- 0. 5 of the L*, a* and b* measures of the standard roofing granules. The difference in the measured opponent color scale value from the coπesponding standard value is reported in terms of ΔL*, ,Δa*, and Δb*. For purposes of the application, the standard values determined for the no.

51 black granules were L*= 19.92, a*=0.19, and b*=0.59. The standard values determined for no. 9300 white granules were L*=68.49, a*=-0.58, and b*=0.21, and the standard values determined for no. 8 blue granules were L*=46.37, a*=-6.97, and b*=-19.2.

Deoiling Procedure for Comparative Examples

As explained previously, oil is frequently added to roofing granules as an adhesion medium between the asphalt and granule as well as for reducing dust generation during processing of the granules. For quality control, exposed color is the most critical feature; therefore, the exposed color must be assimilated through the deoiling process. The deoiling procedure uses the following equipment: deoiling funnel,

1,1,1 -trichloroethane,

100 milliliter beakers, distilled water, vent hood, vented oven, screens (Tyler 14 and 20), timer, screen brush, one-gallon can, stirring rod, and white paper towels.

A sample of oiled granules was first screened to mesh size -14/+20. The screened sample was then placed in a 100 milliliter beaker, the granules filling up to 50 milliliters of a beaker. The beaker was then filled to the rim with 1,1,1-

trichloroethane. The granules and trichloroethane were then allowed to sit undisturbed for about five minutes. The granules and trichloroethane were then poured into a deoiling funnel and the solvent drained without stirring into a one- gallon can. Next, the funnel was filled with distilled water to the rim and stirred while draining, being sure to collect all solvent and water for proper disposal. The remaining granule samples in the funnel were placed on a white paper towel and dried in a vented oven. The temperature of the oven depended on how long the result can be waited for. At temperatures ranging from about 80°C to about 110°C, the samples merely needed to be taken out when dry. (At temperatures above 110°C, the samples must be closely watched and removed as soon as possible when dry or the color can be affected. Too long a drying time at a temperature below about 80°C can result in some "blooming" which will also affect spectrocolorimeter results.) The temperature of the drying oven used for these examples was 150°C. Finally, the dried granules were cooled on paper towels to room temperature on a table top prior to making any color determinations.

The staining property for a given sample of granules is calculated as the value of Δsb* - ΔsL*. Each of Δsb* and Δ _S L* is determined by measuring the initial day (0 hour) values for each of parameters b* and L* and remeasuring each value four days (96 hours) later. Then the difference in measurement values for each parameter b* and L* is calculated to determine Δ _s b* and ΔsL*. The four-day staining property is calculated as Δsb* - ΔsL*.

Adhesion Tests (Dry and Wet Pick Tests)

The pick test is a practical test to predict the adhesive characteristics of roofing granules to roofing asphalt. In general, sized granules are dropped into hot asphalt and later, when the asphalt is cooled, the granules are picked out of the asphalt. The granule surface which has been in contact with the asphalt is observed for the amount of asphalt adhering. If the surface is well coated with asphalt, the granule has a good "dry" pick test. Anything above 60% coverage of the contact surface is considered satisfactory. The effect of water upon adhesion is obtained by submerging the asphalt-granule combination under water for a set periods of time

and again observing the percent contact surface covered by asphalt. For an 18-hour wet test, values above 30% are considered excellent and values above 10% are considered satisfactory.

I. Preparation of Granule

The granules to be tested, which are the polymer coated granules of the invention, were prepared by screening full grade granules through a #588 ton cap or a Tyler No. 12 screen and only the granules left on the screen were employed for the pick tests (for #9 grade, use -10 and ton cap).

II. Preparation of Asphalt

A regular Mid-Continent coating asphalt was prepared by heating asphalt at 350°F (177°C) in a 4 liter can having a loosely fitted cover until the asphalt was fluid enough to pour, with removal of any skin formation before pouring. The asphalt was poured in narrow strips onto a release paper and allowed to cool to form the pick test asphalt. Any charred asphalt was then removed by picking it from the strips of cooled asphalt.

III. Procedure of Pick Test 5 grams of the pick test asphalt was removed from the release paper and placed in a can having a diameter of about 6 cm. The asphalt and can were then heated in a dispatch oven at 177°C with full circulation of air for 10 minutes. The can and heated asphalt were then removed from the oven and the can tapped on a hard surface once to remove air bubbles. Before the heated asphalt cooled, the screened granules were sprinkled from a height of about 30.5 cm or more and the can tapped on a hard surface three times to help embed the granules. The can, asphalt and granules were then allowed to cool to room temperature (about 0.5 hour).

The granules were first picked out of the cooled asphalt on a dry basis, picking out only the most well embedded granules. These granules are physically picked out of the asphalt by any convenient hand-held implement and turned over

for examination to estimate the area that pulls asphalt that was originally embedded in the asphalt. The estimate uses a scale of 0-10, with 0 meaning no asphalt clung to the granule and ten meaning that the part of the granule embedded in the asphalt was completely covered. Ten granules were picked out of the asphalt for each of the two different reading times (i.e., dry (0 hours) and 18 hours (wet)) and their total read in percent.

For the wet pick test, the procedure was to soak the granule covered asphalt in the same can for 18 hours under 0.64 cm distilled water at room temperature, and granules picked again. When picking granules, it is sometimes noted that the asphalt has a tendency to crack or break around the granule. When this happened, the result was ignored and additional granules were picked. In some cases, especially the wet pick tests, the can was held next to a microscope light for about 10 seconds (on the lid) and 12-13 seconds (on the bottom) to slightly warm the asphalt and prevent cracking.

Surface Alkalinity or Acidity Test (15 Minute)

Distilled water was brought to boil in a Florence flask and then 100 ml of the boiling distilled water was poured into a clean 250 ml Erienmeyer flask. The Erienmeyer flask had previously been boiled free of soluble alkali. Then 25 grams of the coated granules and 3 drops of phenophthalein solution were added to the boiling water and boiled gently for exactly 15 minutes. The concentration of the phenolphthalein solution should be 5 grams of phenolphthalein in a liter of isopropyl alcohol. Five to ten glass beads may be added to prevent "popping". Then, the water was decanted into a clean 250 ml Erienmeyer flask with care taken to leave the granules in the original Erienmeyer flask. The granules were rinsed once with 10 ml of cold distilled water from a wash bottle dispenser. The rinse water was added to the previously decanted granule solution while still leaving the granules in the original Erienmeyer flask. Then, if the solution was pink, titration was performed immediately while the decanted solution was still hot with 0.1 N H ₂ SO to the colorless end point. The number of ml of 0.1 N H ₂ SO necessary to reach the end point was designated the "alkalinity number". A lower alkalinity number is

prefened over a higher alkalinity number. On the other hand, if the solution was colorless, titration was performed immediately while the decanted solution was still hot with 0.1 N NaOH to the first tinge of pink color. The number of ml of 0.1 N NaOH necessary to reach the end point was designated the "acidity number". A lower acidity number is preferred over a higher acidity number.

Examples

Synthesis of Roofing Granules Using organic Binders Example 1

This Example demonstrated one prefened inventive method of making a coated granule having an organic, heat-sensitive pigment therein. The granules were pigmented, as described below, to provide grade no. 9300 white granules. More particularly, for Example 1 representing the invention, a 1 kilogram sample of raw mineral rock particulate of nepheline syenite having a particle size which is 98% +35 mesh Tyler (> 425 micrometers) was placed in a mechanical stirring pot and preheated with air at 93 °C. Then, 30 grams of white pigments were added to the heated granules, and the entire mixture was stored vigorously until the pigments had become well dispersed on the surfaces of the granules. Then, 5 grams of deionized water was then added to the pigmented raw rock and the granules were blended until all surfaces had been wetted. Then, 15 grams of "RHOPLEX AC-2234" obtained from Rohm & Haas Company, Philadelphia, Pennsylvania, comprising approximately 7 grams of acrylate copolymer resin solids, approximately 8 grams water, a maximum of 0.03 g ammonia, and less than 0.015 grams individual residual monomers, was dispersed into and mixed with 15 grams of deionized water to form a resulting diluted emulsion having approximately 7 grams acrylate copolymer solids dispersed in 23 grams water. The resulting binder emulsion was added, by pouring, to the heated granules and pigment and mixed thoroughly. The colored mineral granules were then transfened to a shallow aluminum pan and placed in a 93°C oven for 30 minutes to set the coating. The binder coated granules were coated with an adhesion agent prepared as a mixture of "TEGOSIVIN 100"

silicone obtained from Goldschmidt Chemical Company, Hopewell Virginia and naphthenic oil, where the application rate of silicone was 0.1 kg/metric ton granules and the application rate of the oil was 4.0 kg/metric ton of granules.

Comparative Example A

In Comparative Example A, standard granules for grade no. 9300 white granules were prepared. This comparative example shows certain quality results for white ceramic (inorganic binder) coated raw rock treated with oil and silicone (standard product), respectively. That is, this comparative sample of granules was prepared using sodium silicate as binder and a high-temperature firing process to insolubilize the colored granule coating. Namely, 1.0 kg of nepheline syenite granules were preheated to 427 to 538°C and heating at such temperature continued as the granules were mixed with the 1.5 grams white pigment in a mixer and thoroughly mixed, then placed in a kiln for about 30 minutes, then cooled to room temperature. This data was included so that a comparison could be drawn between cunent production material and the organic polymeric binder-coated granules of this invention.

Example 2 Binder-coated pigmented granules were prepared in the same manner as

Example 1, except that the 15 grams white pigment was replaced by 15 grams of carbon black to provide a grade no. 51 black pigmented sampling of granules.

Cmnarative Example B In Comparative Example B, standard granules of grade no. 51 black were prepared. These comparative granules were prepared in the same manner as Comparative Example A, except that the 1.5 grams white pigment was replaced by 1.5 grams of carbon black as a black pigment agent.

Example 3

Binder-coated pigmented granules were prepared in the same manner as Example 1, except that the 15 grams white pigment was replaced by 15 grams of blue pigment to provide a grade no. 8 blue grade sampling of granules.

Comparative Example C

Comparative granules were prepared in the same manner as Comparative Example A, except that the 1.5 grams white pigment was replaced by 1.5 grams of blue pigment agent to provide standard grade no. 8 blue granules.

Table 1 indicates results obtained for the inventive granules of Examples 1-3 and the Comparative Examples A-C made following the above respective procedures.

Table 1

ΔL* Water Asphalt Pick Test

Δa* Repellency Wettability Pick Test 18 hr. Wet

Example Δb* (min) (%) Dry (g) (g)

1 +0.5 >60 100 72 51 +0.1 -0.25

A std. >60 100 53 15 std. std.

2 -0.3 >60 100 64 43 -0.2 +0.3

B std. 30 100 41 12 std. std.

3 -1.2 >60 100 81 51

-0.5 0.0

C std. >60 100 73 33 std. std.

Also, the 4-day staining property (Δ _s b*-Δ _S L*) was investigated for the granules of each of Example 1 and Comparative Example A. Example 1 had a staining value of 1.33, which was significantly superior to the staining value of 5.36 observed for Comparative Example A. The results summarized in Table 1 show that the granules of the present invention coated with the organic acrylate polymer, as compared to the comparison granules which employed an inorganic metal silicate binder system, have superior dry and wet pick property for all cases and superior water repellency in the case of Example 2. In addition to the results summarized in Table 1, it also was visually observed that the deoiled sample of granules of Examples 1 and 3 displayed noticeably less color change when deoiled as compared to the granules of Comparative Examples A and C. The coated roofing granules of all of Examples 1, 2 and 3 displayed adequate water repellency despite the lack of silicon-containing groups in the polyacrylate binder molecules employed in the granule coatings.

Example 4

This Example demonstrated another prefened inventive method of making a coated granule having an organic, heat-sensitive pigment therein. The granules were pigmented, as described below, so as to provide grade no. 11 black granules for headlap applications.

More particularly, a 1 kilogram sample of raw mineral rock particulate of type Wausau (Wisconsin) Greystone having a particle size which was 98% -r35 mesh Tyler (> 425 micrometers) was placed in a mechanical stirring pot. Then, 2 grams of carbon black pigments and 2 grams of calcined clay were added to the heated granules, and the entire mixture was stirred vigorously until the pigments had become well dispersed on the surfaces of the granules. Then, 4 grams of "RES 1019" emulsion (50% by weight resin solids) obtained from Rohm & Haas Company, Philadelphia, Pennsylvania, comprising approximately 2 grams of acrylate copolymer resin solids and approximately 2 grams water, was dispersed into and mixed with 9 grams of deionized water to form a resulting diluted emulsion having

approximately 2 grams acrylate copolymer solids dispersed in 11 grams water. 2 grams of MgCl was added to the emulsion with mixing. The resulting binder emulsion was added, by pouring, to the heated granules and pigment and mixed thoroughly for four minutes. Then the coated granules were dried by directing ambient air at room temperature (about 25°C) at the surface of the emulsion in the mixer by means of an air-blowing gun having the trade name "MASTER HEAT GUN" available from Master Appliance Corp., Racine, Wisconsin, for a duration adequate to evaporate all water in the coatings on the granules such that the coated granules were dry to the touch. Then, the colored mineral granules were then transfeπed to a shallow aluminum pan and placed in a 100°C oven for 2 hours. The coated granules were subjected to a 15 -minute surface alkalinity and acidity test and showed an acidity number value of approximately 0.01 for this test (i.e., one drop of 0.1 N NaOH changed the solution from colorless to faint pink in color). This result indicated that coated granules had been produced having a firmly bonded pigment coating.

Example S

This Example demonstrated yet another prefeαed inventive method of making a coated granule having an organic, heat-sensitive pigment therein. The granules were pigmented, as described below, so as to provide grade no. 11 black granules for headlap applications.

More particularly, for Example 5 representing the invention, a 1 kilogram sample of raw mineral rock particulate of type Wausau (Wisconsin) Greystone having a particle size which is 98% +35 mesh Tyler (> 425 micrometers) was placed in a mechanical stirring pot. Then, 2 grams of carbon black pigments and 2 grams of calcined clay were added to the heated granules, and the entire mixture was stured vigorously until the pigments had become well dispersed on the surfaces of the granules. Then, 3.3 grams of "AEROSPRAY A70" emulsion (60% by weight resin solids) obtained from American Cyanamid Company, comprising approximately 2 grams of polyvinyl acetate polymer resin solids and approximately 1.3 grams water, was dispersed into and mixed with 10 grams of deionized water to

form a resulting diluted emulsion having approximately 2 grams polyvinyl acetate copolymer solids dispersed in 11.3 grams water. 2 grams of MgCl ₂ was added to the emulsion with mixing. The resulting binder emulsion was added, by pouring, to the heated granules and pigment and mixed thoroughly for four minutes. Then the coated granules were dried by directing ambient air at room temperature (about 25°C) at the surface of the emulsion in the mixer by means of a heat gun having the trade name "MASTER HEAT GUN", which was obtained from Master Appliance Corp., Racine, Wisconsin, for a duration adequate to evaporate all water in the coatings on the granules such that the coated granules were dry to the touch. Then, the colored mineral granules were then transfeπed to a shallow aluminum pan and placed in a 100°C oven for 2 hours. Coated granules were obtained having a firmly bonded pigment coating. The coated granules were subjected to a 15-minute surface alkalinity and acidity test and showed an acidity number value of approximately 0.01 for this test (i.e., one drop of 0.1 N NaOH changed the solution from colorless to faint pink in color). This result indicated that coated granules had been produced having a firmly bonded pigment coating.

Various modifications and change to this invention will become apparent to those skilled in the art. Those skilled in the art will appreciate that the invention is not limited to the specific examples and materials described herein.