Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D11/00—Constructional features of flexible abrasive materials; Special features in the manufacture of such materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/001—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as supporting member
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
  • B24D3/20—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially organic
  • B24D3/28—Resins or natural or synthetic macromolecular compounds

Definitions

• This invention relates to novel coated abrasives, and, in particular, to a lapping material in sheet form.
• “Lapping”, as the term is used in this specification, means working a particulate abrasive material against the surface of a workpiece until an exceedingly fine, mirror-like finish is imparted thereto.
• the objective sought is the attainment of a very smooth surface finish, while retaining a high degree of dimensional control, so that the resulting product will conform to very precise size standards.
• the lapping of surfaces from their original state to the final finish is a progressive operation, involving the use of a series of abrasives ranging from relatively coarse at the beginning through successively finer sizes to the end.
• results secured depend upon a number of factors, such as the properties of the abrasive employed, the pressure with which the abrasive is forced against the workpiece, the pattern of movement preserved in the contact of the workpiece with the abrasive particles and other considerations.
• U.S. Patent 4,288,233 describes lapping pads for ophthalmic lenses. While the lapping material of this invention is useful, the components thereof, i.e. diamonds, and the method of making it, i.e. metal plating, are expensive. Furthermore the lapping0227394 materials described therein are not flexible.
• U.S. Patent 4,255,164 discloses a glass fining sheet suited for finishing rough ground vitreous surfaces to provide a surface finish which may be readily polished comprising a flexible, conformable backing sheet bearing a microcellular abrasive granule-resin matrix which, under use conditions and in the presence of an aqueous flow, generates a fining slurry.
• the fining sheet is prepared by coating a flexible conformable backing sheet with a foamed liquid abrasive granule-resin coating composition comprised of liquid curable binder material, abrasive fining granules, and sufficient compatible solvent to provide a coatable composition.
• the coating provides a cellular layer which releases the fining abrasive granules at a controlled rate under use conditions.
• the released granules perform the actual abrading.
• the sheet of this patent appears to be another means of preparing a fining slurry.
• the invention involves a method of preparing a coated abrasive which is especially useful as a lapping material.
• the method comprises the steps of:
• the curable binder is preferably curable by radiation, and it may also be curable by thermal energy.
• the abrasive grains are of a size typically used for lapping; i.e., they can have an average particle size of up to about 35 micrometers.
• the backing is preferably primed to promote adhesion between it and the cured binder.
• the coatable composition does not require a solvent, although a solvent may be used, if desired, for some purposes.
• the method of this invention is low in cost due to the savings derived from eliminating the solvent and solvent removal steps.
• this invention involves a coated abrasive suitable for use as a lapping material comprising a backing, lapping size abrasive grains, and a binder which adheres said grains to the backing.
• the coated abrasive of this invention exhibits high endurance for extended periods of use.
• the coated abrasive can be die cut to shape, if desired, e.g., for specialty microfinishing apparatus.
• curable binder means the flowable or coatable composition from which the binder is prepared by means by free-radical polymerization;
• binder or “cured binder” means the dry, polymerized coating which adheres the abrasive grains to the backing.
• the backing should be sufficiently strong to support the binder and abrasive grains therein under contemplated use conditions. It should be sufficiently flexible to allow mounting thereof on the surfaces of lapping tools. Because most lapping operations require the use of water or oil or both, it is preferred that the backing be water-resistant and oil-resistant. it is also preferred that the backing be smooth and of uniform caliper so the lapping film can be used successfully for finishing high precision articles.
• Materials suitable for the backing include water-resistant paper and polymeric films. If polymeric film is to be used as a backing, it should preferably have a primed surface to promote adhesion between the backing and the binder.
• the preferred primer for the purposes of this invention is ethylene acrylic acid as described in U.S. Patent 3,188,265, incorporated herein by reference. Alternatively polymeric film having a roughened surface can provide excellent adhesion between the backing and binder.
• the preferred backing material is polyester, e.g. polyethylene terephthalate, which has been oriented and heat set and primed with ethylene acrylic
• the backing should be sufficiently thick to provide sufficient strength to bear the coating, but not so thick as to adversely affect flexibility.
• the backing should have a thickness of less than about 10 mils, and a thickness of 2 to 3 mils is preferred.
• the abrasive grains can be any abrasive grain conventionally used for lapping processes.
• Abrasives suitable for the lapping film of this invention include iron oxide, silicon carbide, silicon nitride, silicon boride, diamond, aluminum oxide, chromic oxide, and alumina and magnesia spinel ceramic prepared in accordance with U.S. Patent 4,314,827, referred to by the trademark Cubitron(l), commercially available from Minnesota Mining and Manufacturing Company, St. Paul, MN.
• the size range of the grains can range from about 0.2 to about 35 micrometers, the preferred range being from about 1 to about 20 micrometers. It is preferred that for a given lapping film, the grain size range be as narrow as possible, because a small number of excessively large grains can result in scratches on the workpiece surface. An excessive number of fine grains, however, will not result in this problem.
• the curable binder is curable by free-radical polymerization, preferably by radiation-initiation or generation of free-radicals.
• Sources of radiation that are useful for the process of the present invention include ultraviolet, visible, y-radiation, X-rays, and electron beam, with electron beam being most preferred.
• the curable binder can also be cured by thermal energy in the presence of an appropriate catalyst.
• Suitable curable binders for use in this invention comprise radiation-curable monomers, and, optionally, reactive diluents.
• the curable binder may also contain conventional additives, for example, wetting agents, lubricants, dispersing agents, fillers, and coupling agents.
• Radiation-curable monomers that are useful in this invention contain at least two ethylenically unsaturated moieties therein, e.g. acrylic (such as hexane diol diacrylate), methacrylic (such as hexane diol dimethacrylate).
• acrylic such as hexane diol diacrylate
• methacrylic such as hexane diol dimethacrylate
• Radiation-curable monomers that are preferred include oligomers selected from urethane acrylates and methacrylates, isocyanurate acrylates and methacrylates, polyester-urethane acrylates and methacrylates, and epoxy acrylates and methacrylates.
• One class of oligomers that are preferred for the compositions for preparing the binders can be represented by the general formula: where
• ZOH represents an aliphatic group having at least one acrylate functional group therein.
• Z can be represented by the structural formula wherein R', R" and x are as defined above.
• DBTDL represents dibutyl tin dilaurate, a catalyst
• the cyclic trimer of hexamethylene diisocyanate is commercially available from Mobay Chemical Corp. and 2,2,4-trimethylhexamethylene isocyanate is commercially available from Thorson Chemical.
• a coupling agent be included with the monomer in order to promote adhesion between the abrasive grains and the cured binder. Improved adhesion between cured binder and abrasive grains inhibits the grains from being loosened and removed from the binder during lapping operations, thus enhancing the durability of the lapping film.
• a preferred coupling agent is -methacryloxypropyl trimethoxy silane commercially available from Dow Corning Corp. under the trade designation Z6030 and Union Carbide Corp. under the trade designation A-174.
• the amount of coupling agent ranges from about 0.1 to about 10% by weight, preferably from about 1.5 to about 5% by weight, based on weight of abrasive grains.
• Reactive diluents suitable for the present invention include mono- or multifunctional acrylates and methacrylates such as hexane diol diacrylate (HDDA), pentaerythritol triacrylate (PET 3 A), pentaerythritol tetraacrylate (PET 4 A), trimethylolpropanetriacrylate (TMPTA), -hydroxyethylmethacrylate (HEMA), tetrahydrofuran acrylate (THF-A) the preferred specie.
• HDDA hexane diol diacrylate
• PET 3 A pentaerythritol triacrylate
• PET 4 A pentaerythritol tetraacrylate
• TMPTA trimethylolpropanetriacrylate
• HEMA -hydroxyethylmethacrylate
• THF-A tetrahydrofuran acrylate
• the reactive diluent serves to reduce the viscosity of the composition for preparing the binder, thus improving the coatability of the composition, and to modify the hardness of the cured binder.
• the ratio of monomer to reactive diluent is 85:15 to 25:75, more preferably, the ratio is 75:25 to 35:65, and most preferably, the ratio is 65:35 to 45:55.
• the cured binder can have a Knoop hardness, as measured on a Tukon® indentation tester, from about 1 to about 50.
• the Knoop hardness preferably ranges from about 7 to about 25.
• the cured binder should be compatible with the backing and primer thereon, i.e. the binder should be free of fisheyes, craters, voids, and orange-peels when coated and cured.
• the coated abrasive of this invention can vary with respect to product requirements. Depending upon the function of the coated abrasive, the user can specify hardness of cured binder and size of abrasive grains. For example, ophthalmic pads are characterized by a very hard resin combined with a relatively coarse mineral. Disc burnishing films are characterized by softer resin and finer mineral.
• the coated abrasive of this invention can be prepared by applying the curable binder and abrasive grains suspended therein onto the backing to form a coating and then curing the thus-applied coating by free-radical polymerization.
• the following method has been found to be useful in preparing the coated abrasive.
• the dry mineral grains first be treated with coupling agent. After the mineral grains are treated with coupling agent, they are then heat set in an oven. Typically, heat setting is conducted at 60°C-100°C for 1-1/2 to 2-1/2 hours.
• the coupling agent can be mixed in the curable binder along with the dry mineral grains.
• the grains of abrasive mineral are added to the curable binder under conditions of high-shear mixing.
• the composition is then applied, preferably by means of conventional coating equipment, to the backing.
• the viscosity of the composition determines the ease of coating.
• the viscosity of the composition can range from about 200 to about 5,000,000 centipoise at 25°C, preferably about 2000 to about 500,000. At higher temperatures, more viscous compositions can be used. For example, a composition having a viscosity of 30,000 centipoise at 25°C can be coated fairly easily at 50°C.
• Rotogravure coating is preferred for the reason that the rotogravure coater can impart a uniform pattern of ridges and valleys to the binder composition, which, after the composition is cured, can serve as channels for flow of lubricants and for removal of abraded material.
• the coating is then cured by means of free-radical polymerization.
• the free-radical polymerization is initiated by actinic radiation, preferably electron beam.
• actinic radiation preferably electron beam.
• other sources of radiation such as ultraviolet, visible, and gamma, are also suitable with appropriate catalyst.
• Thermal initiation is also suitable with an appropriate catalyst.
• solvents are not required to be added to the curable binder to facilitate coating thereof onto the backing. This has the advantage of avoiding troublesome solvent removal problems.
• an inert solvent can be employed along with the monomers, reactive diluents, and coupling agent of the curable binder.
• ophthalmic pads were prepared and tested.
• the testing procedures were designated as (a) first fine, (b) second fine, and (c) single fine. These testing procedures are designed to measure the amount of material removed and the character of finish imparted to a plastic CR-39 lens.
• First fine samples were prepared and tested according to the following procedure:
• the backside of the material to be tested was laminated with a pressure-sensitive adhesive.
• An ophthalmic test daisy was die cut with a standard die. The test daisy was mounted on a 2.12 diopter spherical lapping block. The lapping block was mounted on a Coburn Rocket lapping machine. The initial thickness of the lens was measured, and then the lens was clamped over the lapping block, air pressure was set at 20 psi. The lens and lapping blocks were flooded with water. A one minute test was run at settings of "medium” and "20 mm top stroke". The lens was removed and final thickness measured. Finish was measured with a Surtronic 3 instrument.
• Second fine samples were prepared and tested according to the same procedure, the only difference being that the test was run for two minutes, instead of one minute, and a 6.25/8.25 diopter lapping block was used.
• the contents of the second vessel were charged to the reaction vessel over a 30 minute period in such a manner, with cooling, that the reaction temperature is maintained at about 70°C.
• 2.3 equivalents of pentaerythritoltriacrylate (“Sartomer”) was added to the reaction vessel over a 15 minute period. Heat was applied to maintain a reaction temperature of 70-80°C until the reaction was complete as determined by % NCO.
• the contents of the second vessel were charged to the reaction vessel over a 30 minute period in such a manner, with cooling, that the reaction temperature was maintained at about 70°C.
• 5.0 equivalents of pentaerythritoltriacrylate (“Sartomer") was added to the reaction vessel over a 15 minute period. Heat was applied to maintain a reaction temperature of 70-80°C until the reaction was complete as determined by % NCO.
• the coated abrasive of the present invention exhibited improved results according to the second fine test procedure, as the cut was dramatically increased while finish and abrasive wear continued to be acceptable.
• This example demonstrates the preferred combination of monomer, reactive diluent, coupling agent, and abrasive grain.
• the monomers, and reactive diluents were blended, and abrasive grains pretreated with gamma-methacryloxypropyltrimethoxysilane coupling agent (Z6030) was introduced into the mixture.
• Dyes were also utilized in the mixtures so that the size of the abrasive grains in each run could be identified.
• the ratios of ingredients are set forth in Table III.
• compositions were knife coated at 1 mil thickness on ethylene acrylic acid primed polyethylene terephthalate film.
• the coated film was subjected to electron beam radiation at 250 Kev, 8 Mrad.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
• Paints Or Removers (AREA)

Applications Claiming Priority (2)

Publications (3)

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Family Applications (1)

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Cited By (8)

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Citations (8)

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• 1986
  • 1986-11-18 CA CA000523191A patent/CA1263240A/fr not_active Expired
  • 1986-12-12 DE DE8686309714T patent/DE3679048D1/de not_active Expired - Fee Related
  • 1986-12-12 EP EP86309714A patent/EP0227394B1/fr not_active Expired - Lifetime
  • 1986-12-15 JP JP61298591A patent/JP2655570B2/ja not_active Expired - Fee Related
  • 1986-12-15 KR KR1019860010720A patent/KR950001983B1/ko not_active IP Right Cessation

Patent Citations (8)

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