CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of U.S. Patent Application Serial No.

08/656,645, filed 31 May 1996.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION This invention relates in general to roofing products such as shingles, laminated shingles and roll roofing. More specifically, the invention relates to roofing products having a protective and ornamental surface layer including naturally colored rock granules, and is useful in the production of asphalt shingles, laminated shingles or roll roofing for use in residential or commercial roofing applications.

BACKGROUND OF THE INVENTION A common method for manufacturing roofing products involves producing a continuous strip of roofing material and then cutting the material into individual shingles or into a suitable length to make roll roofing. In the production ofthe roofing material, a base sheet such as a glass fiber mat is typically passed through a coater containing molten asphalt. The asphalt saturates the base sheet and forms a tacky coating thereon. Subsequently, the coated base sheet is passed beneath one or more granule applicators which apply surface granules to portions ofthe sheet. Typically, the granules are dispensed from hoppers at a rate which can be controlled by making manual adjustments on the hoppers.

In the manufacture of colored shingles, two types of granules are often employed. Granules of relatively low cost are usually applied to the headlap portion of the shingle which is normally covered on the roof by an overlapping portion of an adjacent shingle, whereas colored granules of relatively higher cost are typically applied to the tab portion ofthe shingle which is normally exposed on the roof. To provide a color pattern of pleasing appearance on the tab or exposed portion, the colored granules are often provided in different colors. Usually a background color is formed of colored granules having a first color, and highlighted portions referred to as "blend drops" are formed of colored granules having a second color different from the first color.

The colored granules are usually produced by applying ceramic coating or paint to granules of mineral material, to control and provide consistency in performance and color ofthe granules. This approach allows granules of one color to be made consistently of mineral materials of different kinds from different sources. Unfortunately, the coloring process significantly increases the cost ofthe artificially colored rock granules in comparison to that of naturally colored rock granules. This adds to the direct manufacturing cost of roofing products made with the granules. The artificially colored rock granules also may experience problems such as fading, color shifting, spaulling, and loss of coating. Consequently, it would be desirable to be able to use naturally colored rock granules as at least a partial replacement for artificially colored rock granules on the exposed portion of roofing products.

SUMMARY OF THE INVENTION There has now been developed a roofing product in which the surface layer of granules includes naturally colored rock granules. The naturally colored rock granules come in a variety of attractive colors. They avoid problems associated with artificially colored granules such as fading, color shifting, spaulling, and loss of coating. In a first embodiment ofthe invention, the naturally colored rock granules are blended with artificially colored rock granules on the exposed portion ofthe roofing products. Roofing products surfaced with the blend including naturally colored rock granules can result in having a more natural appearance than products surfaced with artificially colored mineral granules alone. The naturally colored rock granules provide significant cost savings versus artificially colored rock granules, and the naturally colored granules can be used in existing manufacturing equipment. However, some colors of naturally colored rock granules are not available in large enough quantities for making the most desirable color patterns of roofing products. Thus, to achieve superior appearance, cost savings, and assurance of a suitable granule supply, as well as other benefits not set forth below, the naturally colored rock granules are advantageously blended with artificially colored rock granules in amounts of from about 2% to about 98% by weight ofthe blend. Also, from the standpoint of color and overall appearance, it has been found preferable for producing some desirable color patterns to blend artificially colored mineral granules with the naturally colored rock granules.

In a second embodiment ofthe invention, the surface layer ofthe exposed portion comprises a blend of at least three different kinds of granules, at least two of

which are naturally colored rock granules that have a translucency of not greater than about 30%.

In a third embodiment, the naturally colored rock granules are provided with a preferred particle size distribution in which the granules are finer sized than conventional, artificially colored roofing granules. At least about 2% by weight ofthe granules ofthe tab portion are naturally colored rock granules, and the granules ofthe tab portion have a particle size from about 1.2 mm to about 0.3 mm. Granules having this preferred particle size distribution dramatically reduce shading problems on the roofing products. The finer size granules also require less weight of granules to cover the surface ofthe roofing products, so that the cost ofthe granules and the roofing products is reduced. The reduced weight ofthe granules allows the use of additional asphalt on the roofing products to achieve improved weatherability.

In a fourth embodiment ofthe invention, the surface layer ofthe exposed portion comprises naturally colored rock granules selected from shale, siltstone, limestone and dolomite having a particle size from about 2.0 mm to 0.3 mm.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a schematic perspective view of apparatus for applying granules onto the surface of an asphalt roofing product in accordance with the invention.

Figure 2 is a schematic plan view of a continuous strip of roofing material made in accordance with the invention, after cutting the strip but prior to separating it into individual shingles.

Figure 3 is a schematic perspective view of a shingle made in accordance with the invention.

Figure 4 is an enlarged schematic sectional view of a shingle taken along line 4-4 of Figure 3.

Figure 5 is a schematic perspective view ofthe two parts of a laminated shingle made in accordance with the invention.

Figure 6 is a schematic perspective view ofthe laminated shingle formed by joining the two shingle parts of Figure 5. Figure 7 is a schematic perspective view of a laminated shingle including colored blend drop granules.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENT OF THE INVENTION Referring now to Figure 1, a base sheet 10 is provided to function as a reinforcing web for the roofing product. The base sheet is of a conventional type known for use in roofing products, such as a woven fabric or a nonwoven web of fibrous materials, for example, a nonwoven web or felt of glass fibers, synthetic organic fibers such as polyester fibers, natural organic fibers such as cellulose fibers, rag fibers, mineral fibers, mixtures of glass and synthetic fibers, or the like. Preferably the base sheet is a glass fiber mat. The base sheet is passed through coater 12 containing a liquid adhesive such as a bituminous mixture, which is preferably molten asphalt. The hot, liquid asphalt saturates the base sheet and forms a tacky coating on both sides thereof. If desired, the asphalt can contain a filler material such as calcium carbonate (limestone), silica, rock fillers, fly ash, mica, or other fillers known for use in asphalt roofing products. In an alternate embodiment ofthe invention, an outer layer of polymer- modified asphalt (not shown) is applied to the asphalt-coated base sheet. The resulting asphalt roofing product is heavier and has improved flexibility.

The base sheet with the tacky coating is then passed beneath a granule- dispensing device, preferably a granule blender 14, for the application of colored blend drop granules. The granules are applied as deposits on the upper surface ofthe tab portion ofthe sheet. The granules adhere to the coating and usually are partially embedded in the coating. The blender has a plurality of openings 16 formed therethrough. Hoppers 18 are positioned above the blender to feed blend drop granules into the openings. The hoppers are connected to storage bins 20 which contain the granules. The number of hoppers, storage bins and openings can be varied depending on the type of shingle product being manufactured. The rate, timing, size and shape of deposit ofthe blend drop granules can be adjusted by the blender. Blend compensators 22 are provided to coordinate the operation ofthe blender with the speed ofthe base sheet.

The base sheet is then passed beneath backfall hopper 24 for the application of colored background granules and headlap granules to the upper surface of the sheet. The backfall hopper has a center compartment 26 which deposits colored background granules on the base sheet. The colored background granules adhere to the asphalt coating on the tab portion ofthe roofing product, except on those parts already

covered with colored blend drop granules. Thus, the colored background granules form the background color ofthe tab portion ofthe base sheet. The backfall hopper also has a pair of side compartments 28 which deposit headlap granules on the headlap portion of the base sheet. Granules are fed to the different compartments by hoppers connected to storage bins (not shown).

Either blends of granules or single types of granules can be applied as colored blend drop granules, colored background granules, and headlap granules. The granules are usually blended before being supplied to the storage bins, but they can also be blended during the process of applying the granules to the base sheet. The types and blends of granules can be chosen depending on the particular shingle product being manufactured. The various types of granules applied to the base sheet will be discussed in more detail below.

Not all ofthe granules deposited on the coated base sheet adhere to the coating, particularly the colored background granules which are deposited on parts ofthe sheet already covered with colored blend drop granules. After deposition ofthe granules, the base sheet is turned around a drum 30 to invert the sheet and cause the non-adhered granules to drop off.

While the base sheet is inverted, a back dusting material such as sand or talc is applied to the lower surface ofthe base sheet. The back dusting material is supplied from a back dusting applicator 32. The base sheet coated with asphalt and surfaced with granules is then fed through a series of standard operations such as cooling and weighing. The sheet is then subjected to a cutting operation to form an asphalt roofing product of this invention. The sheet can be cut into individual shingles, into parts to make laminated shingles, or into a suitable length for roll roofing. The product is then packaged and shipped.

Figure 2 illustrates the strip of roofing material 34 made by the process after the cutting step but before separating the strip into individual shingles. Each strip is divided into two lanes of asphalt roofing shingles 36. A shingle 36 separated from the strip is shown in more detail in Figure 3. The shingle includes a tab portion 38 which comprises three tabs 40. The tabs are defined by cut-outs 42. However, it is recognized that the tab portion does not necessarily have cut-outs. The tab portion is normally exposed when the shingle is installed on a roof. A surface layer of granules is adhered to the coating on the tab portion. Background granules 44 provide the background color of

the tab portion, and deposits of blend drop granules 46 provide areas of highlighted color on the tab portion. Certain types of naturally colored rock granules and/or artificially colored mineral granules may be preferred for use as colored background granules or blend drop granules. The shingle also includes a headlap portion 48. When rows of shingles are installed on a roof, the headlap portions ofthe shingles in each row are positioned beneath the tab portions ofthe shingles in an adjacent row. Thus, except for small strips ofthe headlap portion exposed through the cut-outs, the headlap portion ofthe shingle is normally covered when the shingle is installed on a roof. A surface layer of headlap granules 50 is adhered to the coating on the headlap portion.

As described above and illustrated in Figure 4, the shingle is comprised of several layers of material. The shingle includes a base sheet 10 of a glass fiber mat which functions as a reinforcing web for the shingle. The base sheet is saturated and coated with adhesive such as asphalt. An asphalt coating 52 is formed on the upper surface ofthe base sheet. A surface layer 44 of granules is adhered to the coating on the upper surface. A back coating 54 of asphalt is formed on the lower surface ofthe base sheet. A surface layer of back dusting material 56 such as sand is provided on the back coating.

While the production ofthe asphalt roofing product has been illustrated with respect to a preferred process, it will be understood that the product may be formed by any conventional manufacturing process. Although the illustrated process uses a strip of roofing material divided into two lanes of shingles, it is understood that the strip can also be a single lane or typically three or four lanes. The apparatus can be modified depending on the process, in a manner known to persons skilled in the art.

Figures 5 and 6 illustrate a preferred laminated asphalt shingle 58 in accordance with this invention. The laminated shingle is comprised of two parts, an overlay 60 and an underlay 62. The overlay includes a headlap portion 64 having a surface layer of headlap granules 66. The overlay further includes a tab portion 68 comprising four irregularly shaped tabs 70 in a sawtooth pattern. The tabs are defined by cutouts 72. The tab portion has a surface layer of colored background granules 74. The underlay 62 is adapted for positioning beneath the tab portion ofthe overlay. It is secured to the lower surface ofthe tab portion by adhesive or other means. The underlay has a surface layer of colored background granules 76. When the underlay 62 and overlay 60 are secured together as shown in Figure 6, exposed portions 78 ofthe underlay can be

seen through the cut-outs ofthe overlay. Usually the colored background granules 74 of the tab portion are a different color from the colored background granules 76 ofthe underlay. The resulting laminated shingle has a very attractive color pattern and a three- dimensional appearance when installed on a roof. Figure 7 illustrates another laminated asphalt shingle 80 having blend drop granules 82 deposited on the tab portion. The overlay has a surface layer of colored background granules 84, and the underlay has a surface layer of colored background granules 86.

In accordance with this invention, the granules used to surface the roofing products include naturally colored rock granules. The term "naturally colored rock granules" means rock granules or mineral granules that are colored in their natural state, not granules that are artificially colored. Specifically, the naturally colored rock granules are not painted or covered with a coating such as a ceramic material to impart color to the granules However, the naturally colored rock granules can be covered with a coating to provide other beneficial properties to the granules For example, additives such as a hydrophobic additive or a bonding enhancer can be applied to the natural rock granules. The term "colored" means all colors including black and white, and includes different shades of a color. The naturally colored rock granules are obtained by crushing natural rocks and/or minerals to a desired particle size according to any method known in the art. The granules can also be screened to adjust the particle size

Advantageously, the naturally colored rock granules used in this invention have excellent aesthetic and protective properties so that they are well suited for use on the exposed portion of a roofing product. The naturally colored rock granules come in a wide range of natural colors. The granules are preferably uniform in color on a consistent basis The good color properties ofthe granules allow for traditional as well as improved roof aesthetics The granules can be used as the background color ofthe exposed tab portion, or they can be used as blend drop granules to provide highlighted portions of contrasting color.

The naturally colored rock granules can be used by themselves as the surface layer on the exposed tab portion ofthe roofing products In a preferred embodiment ofthe invention, however, the naturally colored rock granules are blended with artificially colored mineral granules. As used herein, the term "blend" means only that both types of granules are present on the exposed portion ofthe roofing product; the

granules need not be intimately mixed or blended together. Accordingly, such blends include roofing products having one type of granule on a first portion ofthe exposed surface ofthe product and another type of granule on a second portion ofthe exposed surface, as well as those in which the two types of granules are intimately mixed. For example, such a blend would encompass a roofing product wherein the blend drop portion ofthe product is composed of artificially colored granules and the background portion is composed of naturally colored granules.

The blend of granules comprises, by weight: naturally colored rock granules in an amount within the range of from about 2% to about 98%, preferably from about 10% to about 98%, more preferably from about 20% to about 98%, more preferably from about 35% to about 98%, more preferably from about 50% to about 98%, and most preferably from about 70% to about 98%; and artificially colored mineral granules in an amount within the range of from about 2% to about 98%, preferably from about 2% to about 90%, more preferably from about 2% to about 80%, more preferably from about 2% to about 65%, more preferably from about 2% to about 50%, and most preferably from about 2% to about 30%.

The artificially colored mineral granules are obtained by crushing and screening natural rocks and/or minerals and then painting or coating the granules to impart a uniform color to the granules. Preferred artificially colored mineral granules are colored ceramic-coated mineral granules which are presently available from several different suppliers. Suitable granules include 3M Brand Roofing Granules available from Minnesota Mining and Manufacturing Co. of St. Paul, Minnesota, and ISP Brand Roofing Granules available from ISP Minerals Incorporated, Bound Brook, New Jersey. Other suitable granules are available from Bird and H B. Reed. As described above, the blend of granules advantageously includes from about 2% to about 98% naturally colored rock granules. Roofing products surfaced with the naturally colored rock granules can result in having a more natural appearance and a richer, truer color than products surfaced with 100% artificially colored mineral granules. Consumers may prefer the roofing products having naturally colored rock granules as being more environmentally friendly and natural, and less artificial. The naturally colored rock granules can be selected based on the type of rocks and/or the rock colors of a particular region ofthe country, so that the roofing products will have regional appeal. In addition, the naturally colored rock granules provide significant cost savings versus

artificially colored rock granules, and the granules can be used in existing manufacturing equipment.

The preferred blend of granules also includes at least about 2%, and preferably at least about 10% artificially colored rock granules. It has been found that some colors of naturally colored rock granules may not be available in large enough quantities for making the most desirable color patterns of commercial roofing products. For example, blue rocks are not found abundantly in nature, and most white natural rocks do not have the required opacity for good roofing granules. Thus, to achieve superior appearance, cost savings, and assurance of a suitable granule supply, the blend is advantageously provided with at least about 2% artificially colored rock granules. In addition, the use of this minimum amount of artificially colored rock granules helps to ensure that the appearance ofthe roofing products is at least as good as products made with 100% artificially colored rock granules. As discussed above, in many instances the use of a blend of artificially colored rock granules and naturally colored rock granules causes the roofing products to have a preferred more natural appearance.

From the standpoint of color and overall appearance, it has also been found that some color patterns of roofing products cannot be made with 100% naturally colored rock granules. Instead, at least a minimum amount of artificially colored rock granules must be blended with the naturally colored rock granules to achieve the desired color patterns. In some instances, from 1 to 4 different kinds of naturally colored rock granules are blended with from 1 to 4 different kinds of artificially colored rock granules to achieve the desire appearance. As used herein, different "kinds" of rock granules include both differences in color and/or differences in rock type. Different ranges of types and colors of granules can be used depending on the particular color pattern. In a preferred embodiment ofthe invention, the granules are a blend of at least three different kinds of granules, naturally colored.

The following Table 1 discloses preferred blends of naturally colored rock granules and artificially colored mineral granules for making different shingle colors. The blends of granules provide a more natural look on the shingles than 100% artificially colored mineral granules.

Table 1 Naturally Colored Colored Ceramic-Coated

Shingle Color Rock Granules Rock Granules

Gray with Red Dark gray diabase 40-65%, Red 5-15%, pref. 6% pref. 53%;

Light gray diabase 30-50%, pref. 41% Light Gray and White Dark gray diabase 5-10%, White 30-55%, pref. 45% pref 5%; Light gray diabase 40-65%, pref. 50%

Green and White Green greenstone 50-70%, White 30-50%, pref. 41% pref. 59%

Green and Black Dark gray diabase 30-50%, Green 50-70%, pref. 64% pref. 36%

The following Table 2 discloses other preferred blends of naturally colored rock granules and artificially colored rock granules for making different shingle colors.

Table 2 Naturally Colored Colored Ceramic-Coated Shingle Color Rock Granules Rock Granules Medium Gray Dark gray diabase 60-80%, Dark gray 10-30%, pref. 20% pref. 70%;

Light gray diabase 5-15%, pref. 10% Grayish Brown Dark gray diabase 30-50%, Taupe 20-35%, pref. 29%; pref. 36%; Dark brown 15-30%,

Light gray diabase 5-20%, pref. 21% pref. 14%

Dark Brown Brown rhyolite 45-60%, Light and dark black 40-55%, pref. 53% pref. 47%

Reddish Brown Brown rhyolite 30-50%, Buff, light brown and red 50- pref. 40% 70%, pref. 60%

Brown with Red Brown rhyolite 25-45%, Taupe, buff, and dark gray 55- pref 35% 75%, pref. 65%

Brownish Black Brown rhyolite 50-65%, Reddish brown, buff and dark pref 56% gray 35-50%, pref 44% Brown Brown rhyolite 40-60%, Reddish brown, buff and dark pref 50% gray 40-60%, pref. 50% In the above blends, the colored ceramic-coated mineral granules can be

3M Brand Roofing Granules in standard 3M colors The colors ofthe naturally colored rock granules are defined by their Hunter L, a*, and b* colors as measured by a Hunter Colorimeter The Hunter color system is well known to persons skilled in the art. A complete technical description can be found in an article by R S Hunter, "Photoelectric

Color Difference Meter", J. ofthe Optical Soc. of Amer., 48, 985-95 (1958) The following Table 3 discloses the Hunter colors of some typical roofing shingles

Table 3 Shingle Color L al bl

Dark Gray 15-30 -15-1 1 -5

Light Gray 45-55 -15-0 1 -2

Medium Gray 25-40 -15-2 2- 10

Brown 20-30 2-4 4-7 Dark Brown 18-30 0-6 2-5

Green 35-50 -5- 1 3-7

Dark Green 20-30 -5- 1 0-5

Light Tan 35-45 5- 10 15-20

Red 23-32 15-20 10- 18 Black 15-35 -05-1 0-1

The following Table 4 discloses the Hunter colors of some naturally colored rock granules

Table 4

Granule Color Rock Tvpe L a* bl

Green greenstone 25-35 -12-0 2-8

Red slate, shale 20-40 4-18 3-15

Buff limestone, rhyolite 35-60 5- 15 15-25

Brown rhyolite 20-35 3-12 5-10

Gray diabase 25-55 -2.5-2 3-5

White limestone, dolomite 50-70 -2-0 0-5

Black diabase, basalt 15-30 0-5 -2-2 In another embodiment ofthe invention, the granules used to surface the roofing product are provided with a preferred particle size distribution in which the granules are finer sized than conventional roofing granules. As discussed below, the granules can be 100% naturally colored rock granules, or they can be blends of naturally colored rock granules with some amounts of artificially colored mineral granules. Preferably, the granules ofthe exposed tab portion have a particle size from about 1.2 mm to about 0.3 mm. More preferably, the granules have the particle size distribution shown in Table 5 as measured by U.S. Sieve Series according to ASTM Method No. D-451:

Table 5

Screen Opening Weight Percent Preferred Wt. % Mesh No. Size of Granules of Granules

Retained on 16 Mesh 1.19 mm 10-20 14.00

Retained on 20 Mesh 0.84 mm 40-55 50.00

Retained on 30 Mesh 0.59 mm 20-35 28.00

Retained on 40 Mesh 0.42 mm 3- 13 6.00 Pass Through 40 Mesh — 0-2 1.00

The granules having the preferred particle size distribution provide several advantages over conventional roofing granules. When conventional roofing granules are processed for application onto a roofing product, large and small sized granules have a tendency to separate from one another. As a result, the granules are segregated on the surface ofthe roofing product into areas of large granules and areas of small granules.

This causes a problem known as "shading" in which different areas ofthe roofing product have a different shade of color caused by the different granule size. Shading is generally not desirable on roofing products from an aesthetic standpoint. By using granules having

the above-defined particle size distribution, the average granule size is closer to the size of the smallest granules. This has been found to reduce the shading problem on roofing products, even when the granules undergo segregation during processing.

Another advantage is that the finer sized granules require less weight of 5 granules to cover the surface ofthe roofing products. As a result, the cost ofthe granules and the roofing products is reduced. Because roofing products are sold at a standard weight according to applicable building codes, the reduced weight ofthe granules allows the use of additional asphalt on the roofing products. The increased asphalt is expected to improve the weathering ability ofthe roofing products.

10 A common problem with roofing products is that the roofing granules tend to come loose from the asphalt, for example in a bundle of roofing shingles prior to use. Advantageously, the finer sized roofing granules of this invention may be less prone to coming loose from the asphalt ofthe roofing product.

Roofing products in accordance with this invention can be made using

15 100% naturally colored rock granules as well as blends of naturally colored rock granules and artificially colored rock granules. However, certain properties ofthe naturally colored rock granules are significant for providing good properties in roofing products, whether the naturally colored rock granules are used alone or in blends. For example, the chemical composition ofthe rock is important. The chemical composition controls the constituent 0 mineralogy and color ofthe rock, and affects the weatherability ofthe rock, the granules shape, and the resistance ofthe rock to ultraviolet light. One ofthe basic functions of roofing granules is to protect the asphalt ofthe roofing product from the ultraviolet rays ofthe sun. The amount of ultraviolet rays transmitted through the natural rock granules is measured by a percent translucency. Preferably the natural rock granules used in the 5 products ofthe invention have a translucency of not greater than about 30% according to ASTM Method D1866. Rocks that are high in iron, magnesium and/or calcium tend to be more UV resistant. Additionally, the grain size ofthe natural rock granules can also have a significant impact on the translucency. Generally, the smaller or finer the grain size, the more opaque, or less translucent, the granule. Consequently, the chemical composition is 0 of lesser importance with finer grained rocks.

The hardness ofthe rock is another significant property for providing good roofing granules. The hardness ofthe rocks is determined by their mineralogy. Rocks containing a high content of silicates are usually relatively hard. One type of preferred

rock is a fine-grained aphanitic igneous rock with a silica content from about 47% to about 71% by weight The term "aphanitic" means the grains are not clearly visible to the naked eye Another preferred type of rock is medium- to coarse-grained phanevitic igneous rock with a silica content of about 41-50% by weight, such as diabase, gabbro and ultramafic rocks. Harder rocks are more resistant to breakdown during processing and handling Preferably the natural rock granules have not more than about 3% breakdown during processing. Harder rocks also have improved weatherability. Preferably the natural rock granules have an average Mohs hardness greater than about 3, more preferably, greater than about 5. The natural rock granules must also be non-brittle so that they are not susceptible to breaking down in the raw material handling process, such as shipping and conveying through the plant process

Examples of rocks having preferred chemical compositions, grain size and hardness are (1) the igneous rocks having an average grain size less than about 0.3 mm such as basalt, andesite, bacite and rhyolite, (2) the igneous rocks having an average grain size greater than 0 3 mm such as diabase, gabbro and ultramafic rocks, (3) the metamorphic rocks having an average grain size less than about 2 0 mm such as amphibolite, greenstone, argillite, slate, hornfels, phyllite and gneiss, and (4) sedimentary rocks containing organic contaminants and clay minerals such as shale, siltstone, limestone and dolomite. In one preferred embodiment ofthe invention, the granules have a translucency of not greater than about 30% as a result ofthe constituent minerals having a high degree of secondary chemical alteration such as chloritization, sericitization or saussuritization Other preferred natural rock granules comprise course grained plagioclase feldspars having an Ab or albite content from 0% to about 40% and an An or anorthite content from about 60% to 100% These rocks are more UV resistant, and are darker and more desirable The natural rock granules can also comprise course grained potassium feldspar mineral fragments.

The size ofthe natural rock granules is another important property. The size ofthe granule affects the appearance ofthe rock, with a larger rock granule giving more appearance of texture on the roofing product In one embodiment ofthe invention, the rock granules are capable of screening to achieve size grade from No 10 to No. 12 according to ASTM Method No. D-451 These sizes balance the texture ofthe granules with their coverage ofthe roofing product. In fine grained rocks, the granules may be composed of multiple grains and minerals. In coarse grained rocks, the granules will tend

to be single mineral grains when crushed. This may result in increased variability. Preferred fine grained rocks are the igneous rocks having an average grain size less than about 0.3 mm, such as basalt, andesite, dacite and rhyolite, the metamorphic rocks having an average grain size less than about 2.0 mm such as slate, phyllite, argillite, gneiss and greenstone; and sedimentary rocks such as shale, siltstone, limestone and dolomite. Preferred coarse grained rocks are the igneous rocks having an average grain size of from greater than about 0.3 mm to about 8.0 mm such as diabase and gabbro, and the metamorphic rocks having an average grain size greater than 2.0 mm such as amphibolite, greenstone and gneiss. It has been found that the size ofthe natural rock granules also affects the color ofthe granules. The smaller the rock granule, the lighter the color ofthe base rock. As a result, the color ofthe rock granules can be adjusted by grinding the rock to different particle sizes. A roofing product can be provided with portions of lighter color and darker color by applying finer sized granules and larger sized granules to different portions ofthe product

Another significant property ofthe natural rocks is their fracture or cleavage which determines the shape ofthe granules. Desired cleavage is flaky to prismatic. Cleavage in one direction results in a flat or flaky shape. Cleavage in two directions results in elongated rectangular blocks or cubes. The cleavage is mineralogy dependent for coarser grained rocks. The cleavage is structure dependent for metamorphic rocks. Preferred granules are predominantly minerals having basal or prismatic cleavage, and preferably are comprised of minerals having at least about 80% basal or prismatic cleavage. A basal cleavage means one prominent direction of cleavage and is found in metamorphic rocks such as slate, phyllite or schist. A prismatic cleavage has a blocky or cubic texture resulting from two prominent directions of cleavage at some angle relative to one another. The shape ofthe granules can be selected to improve other performance characteristics, such as to reduce shading problems. Round and cubic granules are good for eliminating shading. The shape ofthe granules will also affect how they pack together on the surface ofthe roofing product The density ofthe natural rock granules is another important property.

The density ofthe granules affects shipping weight, shingle weight, and quantity of granules applied to a shingle Ifthe granules are less dense, more asphalt could be used on the roofing products to improve weatherability. A wide variety of different rocks are

available having high and low densities. A rock that is more mafic and/or has a lower silica content usually has a higher density. Preferably the average density ofthe natural rock granules is greater than about 2.5 g/cm ³ .

Another significant property of the natural rock granules is their resistance to weathering. Rocks that have a high resistance to weathering are preferred so that the granules retain their protective properties and do not change color over the life ofthe roofing product (as much as 20-40 years for shingles). The granules must not fracture due to a freeze thaw mechanism or break apart In general, rocks that are rich in quartz are very resistant to weathering, while rocks that are rich in iron or magnesium are easily weathered. The grain size and the cleavage also affect weathering. In general, preferred rocks are hard, silica-rich and fine grained Preferred rocks include diabase, basalt, intermediate volcanics, argillite, slate, greenstones, and metabasalt Chemically altered igneous and metamorphic rocks, such as by chloritization, sericitization, saussuritization or serpentinization, are believed to be very resistant to weathering Preferred natural rock granules are resistant to weathering due to a high degree of secondary chemical weathering ofthe constituent silicate mineral.

Still another significant property ofthe natural rocks is their reflectance or absorption/conductance of incident light and heat. Preferred roofing granules provide radiation abatement, in that they reflect light and do not absorb and conduct heat. Preferably each type of natural rock granule applied to a roofing product is uniform in color to provide a consistently good appearance, and specifically to reduce problems of shading Also, preferably, the composition of each type of natural rock granule applied to a roofing product is relatively uniform.

The natural rock granules must be able to adhere to the coating asphalt. They should not be hygroscopic, because the absorption of moisture would loosen the bond between the granule and the asphalt. Artificially colored rock granules usually require the application of silicone and/or oils to obtain good adhesion to the asphalt. These materials are often not required for natural rock granules to obtain good adhesion, so that costs can be reduced and the granules are more environmentally friendly. The natural rock granules should not react chemically with the asphalt, to cause any significant changes in the granules or asphalt or to loosen the bond between the materials.

Certain color patterns of roofing products such as shingles have not previously been achieved by the use of 100% artificially colored rock granules. Preferred blends of naturally colored rock granules according to this invention will provide such color patterns. For example, shiny black colored shingles can be made using from about 20% to about 35% (preferably about 29%) dark gray diabase rock granules, and from about 65% to about 80% (preferably about 71%) shiny black coal slag granules. Green and black colored shingles can be made using from about 30% to about 50% (preferably about 36%) dark gray diabase rock granules, and from about 50% to about 70% (preferably about 64%) natural green greenstone rock granules. Some kinds of naturally colored rock granules have different shades of color within the individual rock granules. This provides the capability of using fewer different kinds of rock granules to obtain different preferred blends of colors on the roofing products. Also, the different colors of an individual kind of rock can provide the effect of blend drops without requiring the use of different rocks. For example, a rock can be used that is various shades of gray to provide a blended appearance. Other rocks, such as rhyolite, come in several different colors such as brown and gray.

It has been found that various desired colors for roofing granules can be obtained by using natural rock granules having certain mineral contents. Although white colored rocks having sufficient opacity to be suitable for roofing granules are relatively difficult to find in nature, in one preferred embodiment, the granules have a natural white color due to a mineral composition comprising at least about 90% by weight calcium-rich limestone or dolomite. Similarly, it is relatively difficult to find suitable red colored rocks in nature. However, suitable granules can be naturally colored red due to a content of from about 40% to about 50% of potassium feldspar. Preferred red colored rocks are some igneous rocks including rhyolites, some metamorphic rocks such as slate, and sedimentary rocks such as shale and siltstone.

In another preferred embodiment, the granules have a natural dark color (e.g., black, dark green, dark gray, or dark brown) resulting from at least about 40% by weight ferromagnesian silicate mineral content. A preferred dark rock is basalt. The granules can also be naturally colored black due to at least about 80% by weight ofthe mineral group amphibole. Preferred rocks include high grade metamorphic rock, metamorphosed shale, and metamorphosed basalt. The granules can also be naturally

colored green as a result of chlorite alteration ofthe ferramagnesian minerals ofthe granules. Usually basalt metamorphoses to a greenstone.

Naturally colored rock granules also provide an advantage over artificially colored mineral granules in terms of temperature ofthe granules. During their manufacture, artificially colored mineral granules are heated to cure their coating. The granules remain hot during subsequent shipping and storage. Ifthe granules are not allowed to cool sufficiently prior to their use, when they are applied to the roofing products, the hot granules sink into the asphalt excessively so that more granules are required to provide adequate coverage. Additionally, the temperature ofthe granules may also be non-uniform such that some sink into the asphalt more than others, resulting in a non-uniform appearance on the roofing product. In contrast, naturally colored rock granules are received cooler and do not need to be cooled prior to application to the roofing products so that they do not sink too far into the asphalt. As a result, fewer granules are required to provide good coverage ofthe roofing product, so that cost is reduced. Also, the appearance ofthe granules is more uniform on the surface.

The principle and mode of operation of this invention have been described in its preferred embodiment. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope.