Background of the ϊnvention

The subject invention relates generally to a method of forming a synthetic material, which

simulates natural mineral substances such as stone and the like and, more particularly, to a method

of preparing and manufacturing a synthetic plastic material capable of being formed into useful

shapes. The subject invention also relates to the synthetic filler which is employed in a plastic

matrix, and which gives it the appearance of a mineral composition.

There currently exists a great need for synthetic materials which mimic the appearance of

natural stone and, in particular, granite. Such materials are commonly used in the manufacture

of flooring, tiles, countertops, sinks, architectural accoutrements, ornamental objects, and for

other purposes for which natural materials are used.

Today's acrylics are commonly available in clear or solid colors, although several

marbleized varieties are now on the market. Although the subject invention is particularly

advantageous for acrylic compositions, the aggregates or granules of the present invention can be

employed in any type of plastic matrix, including thermoset resins such as unsaturated polyester

resins and gel coat resins.

The compositions of the subject invention and, in particular, acrylic compositions made

in accordance with the present invention, may be used in manufacturing applications normally served by conventional acrylics. Such applications include, but are not limited to, products

requiring low electrical conductivity, good arc resistance and dielectric strength, and the ability

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to resist alkali solutions, weak acids, aliphatic hydrocarbons, saltwater, photographic solutions and

battery solutions.

Summary of the Invention

The subject invention relates to a specific type of non-mineral aggregate or granules

comprising a combination of thermoset and thermoplastic resins which can be suspended in a

plastic matrix to provide a mineral-like appearance.

The subject invention also provides a simulated mineral article which comprises the

dispersed phase (i.e., granules), suspended within a thermoplastic matrix. The granules and the thermoplastic matrix are visually distinguishable.

Detailed Description of the Invention

This section details various preferred embodiments of the subject invention. These

embodiments are set forth to illustrate the subject invention, but are not to be construed as limiting. A broad array of plastic compositions in accordance with the present invention are

described. Common to each of these plastic compositions is the suspension within a thermoplastic

matrix of granules that are composed of thermoset plastics and thermoplastics.

Thermoplastic resins employed in the present invention include, but are not limited to:

ABS (polymers produced by copolymerizing acrylonitrile, butadiene and styrene), olefin-modified

styrene-acrylonitrile, copolymer acetal homopolymer, acetal copolymer, ionomers, nitrile resins,

phenylene-based resins, poly(amide-imide), modified poly(phenylene ether), polybutylene,

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polycarbonate, aromatic polyester, thermoplastic polyester (e.g., poly(butylene terephthlalate),

poly(tetramethylene terephthlalate), or poly(ethylene terephthalate)), polypropylene, poly (ether

ketone), poly(ether mide), ethylene acid copolymer, ethylene-ethyl acrylate, ethylene-methyl

acrylate, ethylene-vinyl acetate, polyamide, poly(methylpentene), poly(phenylene sulfide), etc.,

and combinations thereof.

The preferred thermoplastic resins employed as matrix compositions in the present invention are the acrylic resins which are based on the use of acrylic and methacrylic esters as the

major monomer, in which the ester moiety contains from 1 to 18, and preferably from 1 to 6

carbon atoms, such as methyl methacrylate, butyl acrylate or ethyl acrylate. The acrylic resins,

as preferred in the present invention, may include additional monomers such as styrene, vinyl

acetate, acrylonitrile, acrylamide, and others well known in the art.

The thermoplastic matrix resins employed in the present invention are preferably employed

in fully polymerized form, which allows the resin to be directly fabricated by such well-known

techniques as extrusion, compression molding, or injection molding into the desired final form. The granules are preferably uniformly incorporated by dry or melt blending the thermoplastic resin

and the granules before final fabrication. A very uniform distribution of the granules in the matrix resin is obtained when a dry-blended mixture of matrix resin and granules is extruded into pellets

through a mixing extruder. The pelletized product allows for transportation and/or loading of any

further fabrication equipment. It is, however, also possible to employ liquid partially polymerized

liquid resins and uniformly mix the granules with the liquid resin and then complete the

polymerization. The latter method is used principally for thermoset resins.

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In addition to the granules, there may be optionally included in the thermoplastic matrix

resin such other additives as are called for by the particular end-use application contemplated for

the material. Thus, it may be desirable to include an antioxidant, a dye or pigment, additional

inorganic fillers, coupling agents, lubricating agents, antistatic agents, and any other additive

deemed to be useful in the contemplated end-use application. Such additives are well-known in

the art, and hence need no further elaboration. Of particular value to optimize the properties of

the compositions of the present invention are coupling agents that are compatible both with the

thermoplastic resin, as well as with the granule composition such as acrylic acid polymers

commercially available under the tradename "Joncryl 2630" or "Lotader. "

The thermoset matrix resins employed with the granules of the present invention are, in

general, unsaturated polyester resins and, in particular, neopentyl glycol resins with

polycarboxylic acids or anhydrides, such as phthalic acid or anhydride, and the class of resins

known as gel coat resins.

The granules employed in the compositions of the present invention comprise blends of thermoplastic and thermoset resins in which the blending of the resins is accomplished prior to the

final cross-linking of the thermoset resin, which changes it from a flowable, fluid material, into

a rigid fixed structure. Substantially all thermoset resins are available in a partially polymerized,

fluid, low molecular weight version in which additives can be incorporated uniformly into the

resin. In forming the granules employed in the present invention up to 20% by weight of the total

resin composition of a thermoplastic resin is blended into a partially polymerized thermoset resin.

The thermoplastic resin can be included either in the form of a resin, or in the form of a monomer,

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which is polymerized simultaneously with the final polymerization of the thermoset resin. When

included in the form of a resin, it is necessary for the thermoplastic resin to be soluble in the fluid

thermosetting resin, in order to accomplish the benefits of the invention. Where the granules are

formed using the monomer of a thermoplastic resin, it is also necessary for the monomer to be

soluble in the fluid thermoset resin in order to achieve the uniform distribution of the subsequently

formed thermoplastic resin, in the subsequently cross-linked thermoset resin. The best results of

uniform distribution of the granules in the thermoplastic resin matrix, which results in the superior performance of the compositions of the present invention, is achieved when the thermoplastic resin

in the granules is the same as, or compatible with, that of the matrix. The term compatible is here

defined as permitting the melt or solution blending of the two resins into a uniform composition

on a molecular basis.

The preferred thermoset resins employed in forming the granules are unsaturated polyester

and unsaturated acrylic resins, which are cross-linked through further reaction with a vinyl

monomer. The unsaturated polyesters are obtained by the condensation of a dicarboxylic acid with

a diol. The acids principally used in the formation of the polyester are phthalic acid and

anhydride, isophthalic acid, adipic or azelaic acid, either alone or in combination. The diols

principally used in the formation of the polyester comprise principally glycols having from 2 to

8 carbon atoms, such as neopentyl glycol, 1,4-butanediol, ethylene glycol, diethylene glycol,

dispropylene glycol, 1,6-hexanediol, and others. The required unsaturation is normally

accomplished by adding an unsaturated dicarboxylic acid to the formation of the unsaturated

polyester, such as maleic acid or anhydride, fumaric acid and itaconic acid. At times, it may also

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be desirable to add an unsaturated monocarboxylic acid, such as methacrylic or acrylic acid, to

the condensation reaction. Unsaturated acrylic resins are formed by the polymerization of a

monounsaturated acrylic monomer with a polyunsaturated monomer, such as alkylene diacrylates

and dimethacrylates, trimethylol propane triacrylates and methacrylates, N,N'-methylene

diacrylamide and dimethacrylamide, divinylbenzene and divinyl toluene.

The unsaturated thermoset resins are normally cross-linked by polymerization with liquid

vinyl monomers. Such monomers are preferably vinyl aromatic monomers, such as styrene, or

acrylic monomers, as have been enumerated hereinabove, and particularly methyl methacrylate.

In addition, it may also be desirable to include acrylic acid, or methacrylic acid as comonomers

to promote the bonding of the granules to the matrix resin.

The foregoing description, however, is not intended to exclude other types of thermoset

resins from use in forming the granules employed in the present invention. As long as the

partially polymerized thermoset resin is in liquid form, and able to dissolve in that form, the thermoplastic resin desired to be combined with the thermoset resin, or dissolve the vinyl

monomer of the thermoplastic resin and cause its polymerization during the final cross-linking of the thermoset resin, such thermoset resin can be employed in forming the granules used in the

present invention. Examples of such resins are saturated polyester resins, cross-linkable with epoxy resins and cross-linkable polyurethane or polyurea resins.

In one preferred embodiment of forming the granules employed in the present invention, the vinyl monomer system which causes the cross-linking of the thermoset resin is also employed

to form the thermoplastic component. The formation of the thermoplastic resin component is

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achieved by increasing the quantity of the vinyl monomer beyond that which is consumed in the

cross-linking reaction. The amount of vinyl monomer consumed in the cross-linking reaction will

depend on the reactivity of the unsaturated thermoset resin, and the polymerization conditions such

as the amount of initiator and polymerization temperature. Generally speaking, the amount of

vinyl monomer consumed in the cross-linking reaction when there is excess monomer present will

vary from 40% to 65% by weight of the total composition and, therefore, in order to form the

thermoplastic component of the granules, it is necessary to increase the concentration of the monomer to above 40% to 65% . The exact point at which the thermoplastic resin is formed is best established experimentally by careful extraction of the thermoplastic resin from the granules

after the cross-linking reaction. The presence of the thermoplastic resin can also be established

through IR or NMR analyses, depending on the nature of the resin involved.

As in the case of the matrix resin, pigments, fillers, coupling agents and other additives

may be blended into the partially polymerized thermoset resin to achieve the desired end effect.

In the formation of mineral like compositions, the addition of an inorganic filler to the granule

forming composition is of particular importance. The concentration of such additive can vary

significantly, but is preferably in the range of 5% to 75% weight of the granule composition.

Suitable fillers useful in the subject invention include, but are not limited to, magnesium dioxide, aluminum trihydrate (ATH), powdered quartz, powdered glass, silica, powdered calcium

carbonate, diatomacious earth, gypsum, clay minerals, such as china clay, illite, montmorillonite,

bentonite and pyrophyllite, powdered chalk, marble, limestone, aluminum stearate, mullite,

calcium silicate, anhydrite, boracite and borax. One filler which has been found to be particularly

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useful is miniature glass bubbles (cenospheres). These small glass bubbles have a low relative

density by virtue of the air trapped within, and are readily introduced into a molten plastic

composition. Other desirable fillers include magnesium dioxide, which has a desired density, as

well as fire retardancy and fumed silica, which has a relatively low density. The fillers of the

present invention further are useful to equalize the densities of both the granules and the matrix,

which improves the stable distribution of the granules in the matrix. Thus, by adding a lighter or

a heavier filler, it is possible to obtain equal densities in both the matrix resin and the granule

composition.

After the completion of the thermosetting reaction, the granular aggregate is comminuted

to a size suitable for distribution in the thermoplastic resin matrix. The particle size will depend on the desired appearance of the resulting composition, but generally the granules are ground to

pass screen sizes of 4800 to 75 microns.

The concentration of the granules in the thermoplastic resin matrix varies from 2% to 65%

by weight of the total composition, and depends on the utility of the application. Thus, normally,

where a mineral-like appearance is desired, the concentration of the granules will be closer to the middle range of the concentration.

The pelletized version of the compositions of the present invention can be further fabricated

by extrusion, injection molding, or compression molding into sheet or board, articles or laminates

on such substrates as wood to provide shower enclosures, household fixtures, interior and exterior

walls and countertops, to name just a few of the possible applications.

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The formation of the compositions of the present invention are further illustrated by the

following examples, which are, however, not to be construed as limiting the scope of the invention here claimed.

Example 1 - Formation of Granules

The 500 g of a commercially available unsaturated isophthalic-neopentyl glycol resin

(Polylite 31-212-00 sold by Reichhold Chemical), containing 40% by weight of the total

composition styrene monomer was added 30g of methyl methacrylate and an additional 30g of

styrene to form the thermoplastic component. The further polymerization of this composition was

initiated by the addition of 1.68g of a peroxide initiator (commercially available as Perkadox 16), and the addition 5.60g of an antioxidant (commercially available as Triganox 121 BB75). The

resin was cured by heating the composition at 150° C in a metal tray for 45 minutes. The resulting slabs were pulverized in a grinder to pass an 75 micron mesh screen. Extraction with methylene chloride demonstrated the presence of thermoplastic polymer in the granules.

Example 2 - Formation of Granules With Commercial Additives

To 350 parts of an isophthalic anhydride, neopentl glycol unsaturated polyester resin,

available commercially from Advanced Coating as densified resin 380, having a viscosity of

500cps and containing 45% by weight of styrene is added 20 parts of styrene, 600 parts of finely

divided (20 microns) commercially available alumina trihydrate, 30 parts of pigment and a cross-

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linking catalyst comprising: (1) a mixture of 7.5 parts of t-butylperoxy-2-ethyl hexanoate and 1-t-

butylperoxy-3,3,5 trimethyl cyclohexane commercially available as Triganox KSM and (2) 2.5

parts of di (4-t butyl cyclohexyl) peroxydicarbonate commercially available as Perk-16.

After uniformly mixing, the resulting composition is loaded into an open mold and cured

in an over at 300°F. After curing, the slabs are crushed to a size to pass a 4800 micron mesh

screen, but retained by a 140 micron mesh screen. The crushed material is then ready for incorporation into a thermoplastic or thermosettable resin.

Example 3 - Simulated Mineral Composition

A high flow polymethyl methacrylate resin commercially available from Rohm & Haas

Co., is fed into a twin-screw extruder containing eight sections including feeding, heating,

compression, blending and metering sections having attached thereto a strand die at 80% of the

full capacity of the extruder. Just before the end of the last blending section, 20% of the full

capacity of the extruder of the granules of Example 2 are incorporated into the molten polymethyl

methacrylate. The polymer is then extruded at 500° F through the strand die, cooled and cut into

pellets.

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