ABRASIVE FORMULATION CONTAINING ORGANIC POLYMER PARTICLES

Field of the Invention

The invention relates to an abrasive fluid formulation containing organic polymeric particles. The formulation is useful in cleaning and polishing metals, plastic, glass, skin, ceramics and other materials. The polymer particles can be round or irregular in shape. The invention also relates to a method of adjusting polymer and particle characteristics including modulus, elasticity, morphology, molecular weight, Tg, degree of crosslinking, particle size and particle size distribution, to produce an abrasive fluid formulation having optimal cleaning and polishing properties for a given substrate.

Background of the Invention

Most abrasive media contain inorganic particles as the abrasive. Generally used inorganic abrasive particles include metal oxide particles such as the oxides of titanium, zirconium, aluminum, silicon, magnesium, germanium, chromium, and iron; nitride particles; silicon carbide particles; diamond particles; ceramic particles; metal pieces, and combinations thereof. One problem with these very hard abrasives is that they tend to produce scratching of the articles being cleaned. It is often desired to use a less abrasive media that provides a combination of a good level of scrubbing and also a good level of polishing, on a variety of different substrates. Polymeric particles offer many advantages over the very hard inorganic particles. The hardness of the polymer can be adjusted by the selection of parameters, such as monomers, molecular weight, and crosslinking. In addition, the modulus and elasticity can be varied by selection of monomers, glass transition of the polymer (Tg) and the degree of crosslinking. The particles are also easily recyclable, and are more environmentally friendly, especially when used in an aqueous-based formulation.

US 2001/0039322 describes the use of polymer particles in a chemical- mechanical polishing (CMP) process. The polymer particles contain polyvalent metallic ions.

US 2002/0173243 describes the use of low levels of polymeric particles in an aqueous CMP process. The polymeric polymers homo-, co- and ter-polymers; cross-

linked or uncross-linked; homogeneous, core-shell or hollow sphere. They have average molecular weights of at least 500,000, and Tgs of at least 25 ⁰ C. Particle size diameters are in the 5 to 5,000 nm range.

Organic polymer particles for use as abrasives in an fluid formulation must be strong enough to withstand multiple cleaning cycles. It is advantageous for the formulation to be recyclable. The polymer particles perform the dual function of scouring and polishing.

It has now been found that fluid abrasive formulations can be produced using organic polymer particles as the abrasive, in which the polymer particle parameters are selected for optimum polishing and cleaning properties. The particles will have an medium particle size of from 10 to 1000 microns.

Summary of the Invention

The invention relates to an fluid abrasive formulation having organic polymer particles with a median particle diameter of from 10 to 1000 microns. The polymer particles in the formulation are selected to have an effective Tg, degree of crosslinking, modulus, elasticity, morphology, and particle size distribution for optimal cleaning and polishing of a given substrate. The organic polymer particles are preferably suspended in an aqueous media. The particles may be round or irregular in shape.

The invention also relates to a method for cleaning and polishing a substrate using a fluid abrasive formulation having organic polymer particles with a mean particle diameter of from 10 to 1000 microns as the abrasive agent.

Detailed Description of the Invention

The invention provides a fluid-based abrasive formulation having organic polymeric particles. The particles are chosen to have a modulus, Tg, hardness, elasticity, particle size and particle size distribution to provide both good scrubbing and good polishing properties for a selected substrate.

PARTICLES

The organic polymer particles of the invention can be made of a thermoplastic or thermoset polymer. The particles may also be composed of a blend of two or more different polymer types and/or compositions. The term "polymer" as used herein is

used to mean homopolymers as well as copolymers in which "copolymers" means polymers formed from two or more monomers, including terpolymers, etc.. The copolymers can be random or block; heterogeneous or homogeneous, and may be of any morphology including but not limited to linear, branched, star, comb, and core- shell. The polymer particles may be uncrosslinked or crosslinked. Preferably the particles are insoluble in water.

The polymer particles may also be impact modified by the addition of from 0 to 100% by weight, based on the weight of the polymer matrix material, of impact modifiers. Useful impact modifiers include copolymers having soft and hard segements, including both linear and core-shell morphologies.

The organic polymer particles are made up of polymer chains that generally have an average molecular weight of greater than 50,000 g/mol, and preferably greater than 100,000 g/mol.

In one embodiment, the polymer particles are made of acrylic polymers. By "Acrylic", as used herein, includes polymers formed from alkyl methacrylate and alkyl acrylate monomers, and mixtures thereof. The alkyl methacrylate monomer is preferably methyl methacrylate, which may make up from 50 to 100 percent of the monomer mixture. 0 to 50 percent of other acrylate and methacrylate monomers or other ethylenically unsaturated monomers, included but not limited to, styrene, alpha methyl styrene, acrylonitrile, and crosslinkers may also be present in the monomer mixture. Other methacrylate and acrylate monomers useful in the monomer mixture include, but are not limited to, methyl acrylate, 2-ethyl hexyl acrylate and methacrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, iso-octyl methacrylate and acrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and methacrylate, methoxy ethyl acrylate and methacrylate, 2-ethoxy ethyl acrylate and methacrylate, dimethylamino ethyl acrylate and methacrylate monomers. Alkyl (meth) acrylic acids such as methyl acrylic acid and acrylic acid can be useful for the monomer mixture. The polymers may be made by methods known in the art including emulsion polyerization, suspension polymerization, bulk polymerization, and solution polymerization. The polymer particles may be formed by means known in the art, including but not limieted to: formed directly from the polymerization (suspension, emulsion); by coagulation of a polymer suspesension or emulsion; into a sheet or

other shape from the polymerization process, and ground into particles; or may be extruded to form strands that can be cut into pellets, hi one embodiment the polymer sheet is made by a bulk, cast process. The particles may be screened, or in other ways sorted to provide the desired particle sizes and particle size distribution. One skilled in the art would be able from the description herein to adjust the monomer mixtures, feed levels and feed rates, initiator level, reaction temperature, reaction time, level of crosslinker, and other process conditions to achieve the desired level of hardness, modulus, elasticity, Tg, morphology, molecular weight, particle size and particle size distribution in a manner to produce particles with characteristics suited to the final application.

The particles produced can be of any shape - such as cylindrical or irregular, though they are generally round, having median diameters of from 10 to 1,000 microns and preferably 20 to 300 microns. The particle size can be matched to the substrate to be cleaned and/or polished, wherein the smallest particles should be smaller than the smallest dimension of the substrate, to a particle size large enough for cleaning and polishing the larger surfaces. While not being bound by any particular theory, it is believed that a broad particle size distribution allows the small particles to effectively clean and polish small crevices in the substrate, while the larger particles would effectively clean and polish the larger surfaces of the substrate. By "broad" particle size distribution is meant that at least 50% of the particles are outside the range that is +/- 25% of the median particle size.

In one embodiment, the polymer particles are made irregular, through grinding or other means, to provide a rougher particle surface to aid in cleaning of the substrate.

FORMULATION

The organic polymer particles of the invention are formulated into a fluid- based formulation. More than one type/size of particles can be blended into the formulation. The formulation could be organic-solvent based, provided the solvent does not significantly dissolve the polymer particles.

For environmental and handling purposes, a preferred formulation of the invention is an aqueous-based formulation. By "aqueous-based", as used herein, is meant that the primary liquid is water. Small amounts of other miscible solvents, such as alcohols, could also be present. The fluid-based abrasive formulation contains

the polymer particles suspended in a liquid by means known in the art, such as by agitation, sonication, the use of suspending, gelling or thickening additives, or a combination thereof. The abrasive formulation could be in the form of an emulsion or an aqueous gel. The level of polymer particles in the liquid will vary, based on the final application, however the polymer particles are generally used at a level of from 1 to 75 weight percent, preferably from 5 to 60 weight percent, based on the total abrasive formulation. In some applications, as in fluid for cleaning hard metal surface, the formulation preferably contains 30 to 60 weight percent of the abrasive particles. In addition to the polymer particles and liquid(s), other adjuvants may be present in the media, including, but not limited, to UV absorbers, lubricants, antioxidants, pigments, dyes, buffers, thickeners, and biocides. In the case of a cosmetic formulation, cosmetic additives such as emulsifiers, aloe, skin softeners, vitamins may also be present. The abrasive formulation could also contain inorganic abrasive particles. In one embodiment, the abrasive formulation is adjusted to a low pH of from 1 to 5. The acidic media aid in the cleaning and polishing by etching the surface of the substrates. In some cases, the etching by an acidic media is the prime cleaning method, with the abrasive polymer particles serving the role of cleaning up the residue of any etching, then further polishing the substrate. In the case of an abrasive formulation for use on skin, hair, teeth, nails or other body part, the pH is adjusted to minimize irritation.

In one embodiment, the abrasive formulation is used as a lapping solutions for the cleaning and polishing of stainless steel parts.

SUBSTRATES

The aqueous-based abrasive media can be used to clean and polish substrates as hard as stainless steel, and as soft as a baby's skin. Substrates and articles that can be cleaned and polished by using the abrasive formulation o the invention include, but are not limited to, any metal or metallic alloys, plastics, skin, glass and ceramic. In one embodiment, the abrasive media of the invention is used in a cosmetic formulation for the cleaning of skin, scalp, or teeth. In another embodiment, stainless steel parts are cleaned by an acidic formulation of the polymer abrasive media.

USES

Since the usage level and particle properties can be easily adjusted to meet a large variety of end use applications, it is possible for one in the art to imagine many different uses, based on the information provided herein, for the organic polymer particle abrasive formulations of the invention. Some uses include: a cosmetic formulation for cleansing skin,

- a contact lens solution to remove proteins and dirt from contacts,

- a lapping fluid for the polishing and cleaning of stainless steel and other hard metal machine parts,

- as a formulation for nail polish removal

- car wash solution

- all-purpose cleaner (tiles, countertops, furniture, floors, etc) Toilet bowl cleaner One advantage of using organic polymer particles in the formulation, is the possibility of recycling the polymer particles. In the process of cleaning and polishing a substrate, the polymer particles cause extraneous material (dirt, grime, oils, hazardous materials, ect. from in-use substrates; extra substrate material from newly manufactured substrate pieces) to be removed from the substrate. The used formulation containing a carrier fluid, organic polymer particles and extraneous material can then be separated and recycled. Organic polymer particles can advantageously be separated based on their unique properties, including but not limited to thermal properties, specific gravities, size, and selective solubility in organic solvents. The organic polymer particles can then be reused in a new cleaning polishing formulation.

Examples

An acrylic polymer with a Rockwell hardness of M-100, as measured using ASTM Method D785 on a 0.236" thick sheet, and a flexural modulus of elasticity of 450 kpsi, as measured using ASTM Method D790, is made by a cast polymerization process and then ground. The granulated acrylic particles have a median size of 75 microns, and 57% of the particles are outside of the range +/- 25% of the median particle size. The particles are added to an aqueous solution with a pH between 2.8- 3.0 at a level of 50% by weight, and suspended in the solution with agitation.

Stainless steel articles to be cleaned are submerged in the solution and agitated until they are clean. The articles are then removed from the bath and rinsed to remove any of the residual cleaning solution. The cleaning solution can then be used to clean more parts.