MXPA00002512A - Structured abrasives with adhered functional powders - Google Patents

Abstract

Coated abrasives suitable for very fine abrading applications can be obtained by depositing a layer of a formulation comprising abrasive grits, fillers, grinding aid, additives and a binder resin on a substrate in the form of a structured abrasive and then adhering to the surface of the structured abrasive a functional powder.

Description

ABRASIVES STRUCTURED WITH ADHERED FUNCTIONAL POWDERS BACKGROUND OF THE INVENTION This invention relates to the production of structure abrasives on substrates in a form useful for the fine finishing of substrates such as metals, wood, plastics and glass. It has been known for many years to propose depositing generally insulated structures such as protrusions and ridges of a mixture of a binder and abrasive material on a reinforcing material to form the so-called "structured abrasives". If the ridges or ridges have very similar heights on top of the reinforcement and then separate properly (perhaps after a slight coating operation), the use of the product will result in reduced surface scraping and improved surface smoothness. In addition, the spaces between the projections provide a route through which the burr generated by the abrasion can be dispersed from the work area and the coolant can circulate. In a conventional coated abrasive, the investigation of the polishing surface reveals that a comparatively small number of the abrasive grains of the surface in an active abrasive zone is in contact with the workpiece at the same time. As the surface wears out, this number increases, but utility can also be reduced ^^ AJSjtí ^ ^ g ^ j -i-M-l-t-ÍÍH-IIÍ-i - l-i-li -Ü of some of those abrasive grains enromando. The use of structured abrasives has the advantage that uniform protrusions wear out at essentially the same speed, so that a uniform rate of abrasion can be maintained for longer periods. In a certain sense, the abrasion work is distributed more evenly among a larger number of polishing points. In addition, since the projections contain many smaller particles of abrasive, the wear of a projection leaves uncovered new unused abrasive particles that are still unenlightened. One technique for forming such an arrangement of protrusions or isolated points that has been described is the description of rotogravure. The technique of rotogravure printing employs a roller to the surface from which a pattern of cells has been engraved. The cells are filled with the formulation and the roller is pressed against a surface and the formulation of the cells is transferred to the surface. In USP 5,014,468, a technique for producing structured abrasives is described. In the process, a binder / abrasive formulation is deposited from rotogravure cells on a roller, such that the formulation is placed in a series of structures surrounding an area devoid of abrasive. It is believed that this is the result of depositing less than the volume of the cell and only from the perimeter of each cell, which would leave the ring formations described.

The problem with the rotogravure process has therefore always been the retention of a useful shape to the projection. It has turned out to be very difficult to formulate an abrasive / binder mixture that is sufficiently flowable to be deposited and yet sufficiently non-flowable, so that it does not crush to an essentially uniform layer coating when deposited on a substrate. Chasman et al., In USP 4,773,920, stated that using a rotogravure coater, it is possible to apply a uniform pattern of ridges and valleys to the binder composition which, when cured, can serve as channels for the removal of lubricant and burr. However, beyond the mere affirmation of possibility, no details are given to show us how this can be done. In USP 4,644,703, Kaczmarck et al. they used a rotogravure roller in a more conventional manner to deposit an abrasive / binder formulation to deposit a layer that is then softened before a second layer is deposited by a rotogravure process on top of the softened first layer. There is no teaching about the nature of the final cured surface. In USP 5,014,468 (Ravipati et al.), It was proposed to use an abrasive / binder mixture having non-Newtonian flow properties and to deposit this mixture by a rotogravure technique on a film. In this procedure, the mixture was deposited from the edges of the rotogravure cells to produce a unique structure with ^^ z ¿¿£.

Reducing thickness purposes with distance away from the areas surrounding the surface devoid of mixing. If the cells are sufficiently close to each other, the surface structures may appear intertwined. This product has proved to be very useful particularly in ophthalmic refinement operations. The procedure is very useful, but it has a potential problem with the increasing formation of material in the cells of the rotogravure roll such that the deposition pattern may change slightly during a prolonged production cycle. In addition, the nature of the process is such that it is limited to formulations containing relatively fine abrasive grains (usually less than 20 microns). Another method is provided for making structured abrasives, depositing an abrasive / binder mixture on a substrate surface and then putting on a pattern comprising an arrangement of insulated structures on the mixture, curing the binder while in contact with a mold having the reverse of the surface with pattern that is desired. This procedure is described in USP 5,437,754; 5,378,251; 5,304,233 and 5,152,917. There are several variations on this subject, but all have the common feature that each structure in the pattern is set by curing the binder while the mixed body is in contact with a mold surface. The present invention presents a technique for producing structured abrasives with particularly effective options that give rise to the most aggressive abrasion, which are well adapted to the treatment of a ^^^^^^^^^^^^^^^ t? »» ^ atg ^^^^^^^ j ^^ JWHMI ^ WB ^^^^^^^^^^^^^ t? j ^^^^^^^^^^^^^^^^^^ g ^^ extensive range of substrates, while being adapted to produce fine finishes during extended periods of operation at a substantially uniform cutting speed.

BRIEF DESCRIPTION OF THE INVENTION It has been found that a structured abrasive having a functional powder adhered to the surface provides a wide range of advantages over the structured abrasive alone. In the present application, the term "functional powder" is used to refer to finally divided material that modifies the abrasive qualities of the structured abrasives to which it is applied. This can be as simple as making the structured abrasive cut more aggressively or reduce the formation of burrs or static charge on the surface. Some functional powders may additionally serve as a release agent or barrier between the resin formulation and the embossing tool, reducing adhesion problems and allowing for improved release. Included under the heading of "functional powders" are the fine abrasive grains, the auxiliary polishing materials, the antistatic additives, the lubricating powders and the like. By "finely divided" it is meant that the individual particles of the powder have a mean particle size (D o). less than about 250 micrometers, such as from 1 to 150 micrometers and more preferably from 10 to 100 micrometers. ß ^^^ | ^ a & ^^^^ uÍS.-ei? b.

The present invention also comprises a process for the production of a structured abrasive comprising a pattern of mixed abrasive / binder bodies adhered to a reinforcing material, said method comprising: (a) depositing a suspension formulation comprising abrasive grains (and optionally fillers, auxiliary polishing materials and other additives) and a curable resin binder on a substrate in a continuous or pattern manner, (b) imposing a pattern on the suspension formulation to form a structured abrasive; and (c) adhering the coating of a functional powder to the pattern surface of the structured abrasive. The key to this procedure is the adhesion of the functional powder to the surface of the structured abrasive. This can be achieved by the application of the powder to the surface of the structured abrasive before the curing of the binder has been completed and the binder is still in a state in which a powder applied thereto is permanently fixed when the curing is complete. . Alternatively, an adhesive coating can be applied to the surface of a fully cured structured abrasive to provide a means of adhering a functional powder to the surface of the structured abrasive. The powder can be applied in the form of a single layer on top of the mixed body of abrasive / binder or in several layers with layers ? - > - ^ - k-i-fii-tk-. ^ "? Imtm ita ^ intermediate of the adhesive to retain the powders in position. For example, one layer could be a fine abrasive powder and the second an auxiliary polishing material. The powder itself can be an abrasive or a variety of powdered materials, or a combination of the foregoing, conferring advantageous properties. Some usable abrasives such as functional powder may consist of any type of abrasive grain and grain size which in some cases may differ from that of the grain used in the adhesive formulation and may result in unique polishing characteristics. The dust functional can also consist of any of the family of auxiliary polishing materials, antistatic additives, any kind of filter and lubricants. The deposition of the functional powder layers can be done using a variety of conventional deposition methods. These methods include gravity coating, electrostatic coating, aspersion, vibratory coatings, etc. The deposition of variable powders can occur simultaneously or in an orderly manner to create a mixed structure before embossing. The adhesive, if one is used, can be of the same or different type from that which is present in the abrasive / binder formulation. !already. «-a» * --.- ^ ^. «^ K .. -. ^ - ^ W-M - ^^ »» - ^ DETAILED DESCRIPTION OF THE INVENTION The formation of the structured abrasive surface can be any of those known in the art, in which a mixed body 5 in abrasive suspension and a binder precursor is cured, while in contact with a reinforcement and a production tool, so that they are adhered on a surface to the reinforcement and the precise form of the inner surface of the tool of production has been imposed on the other surface. Such a procedure is described, for example, in documents USPP 5,152,917; 5,304,223; 5,378,251; and 5,437,254, all of which are incorporated herein by reference. Alternative forming methods, including rotogravure coating, are described in USPP 5,014,468 and 4,773,920 and these are also incorporated by reference in this application. The surface of the structured abrasive can have any desired pattern and this is largely determined according to the intended purpose of the coated abrasive product. It is possible for example to cause the surface to be formed with crests and alternating valleys oriented in any desired direction. Alternatively, the surface can be provided with a plurality of mixed shapes of shoulder that may be separated and connected and be either identical or different from the adjacent shapes. Very typically, the abrasives of the structure have substantially identical conformations in predetermined patterns across the surface of the abrasive íg g t fe aáli ^ s-coated. Such conformations can be in the form of pyramids with square or triangular bases or they can have more rounded conformations without defined edges where the adjacent planes are located. The rounded shapes can be circular in cross section or be elongated depending on the deposition conditions and the desired use. The regularity of the conformations depends to a certain degree on the desired application. More closely spaced conformations, for example more than about 1000 per square centimeter, are favored for finishing or fine polishes, while more aggressive cutting is favored for more widely spaced shapes. The abrasive component of the formulation may be any of the available materials known in the art such as alpha / alumina (fused or concreted ceramic), silicon carbide, fused alumina / zirconium oxide, cubic boron nitride, diamond and the like, as well as the combination thereof. The abrasive particles useful in the invention typically and preferably have an average particle size of 1 to 150 microns and more preferably 1 to 80 microns. In general, however, the amount of abrasive present provides from about 10 to about 90% and preferably from about 30 to about 80%, of the weight of the formulation. The other main component of the formulation is the binder. This is a curable resin formulation selected from radiation curable resins, such as those curable using electron beam, UV radiation or ^ a ^^^^^^^^^^^ visible light, such as acrylated oligomers of acrylic epoxy resins, urethanes and acrylated polyester acrylates and acrylated monomers including mono-acrylated, multi-acrylated monomers, and thermally curable resins such as resins phenolic, urea / formaldehyde resins and epoxy resins, as well as mixtures of such resins. In fact, it is often convenient to have a radiation curable component present in the formulation that can be cured relatively quickly after it is deposited in the formulation in order to increase the stability of the deposited conformation. In the context of this application, the term "radiation curable" is understood to encompass the use of visible light, ultraviolet (UV) light and electron beam radiation as the agent that causes curing. In some cases, thermal curing works and the functions of radiation curing can be provided by different functionalities of the same molecule. This is often a desirable expedient. The resin binder formulation may also comprise a non-reactive thermoplastic resin which can enhance the self-sharpening characteristics of the deposited mixed abrasive bodies by enhancing the wear capability. Examples of such thermoplastic resin include polypropylene glycol, polyethylene glycol and polyoxypropylene-polyoxyethylene block copolymer, etc. Fillers can be incorporated into the abrasive suspension formulation to modify the rheology of the formulation and the hardness and rigidity of the cured binders. Examples of useful fillers include: carbonates w ^ & ^ & ! Ü ^ flttgfc. ^^^^^ fe¡S fe¡ ^ g ^ metal such as calcium carbonate, sodium carbonate, silicas such as quartz, glass globules, glass bubbles; silicates such as talc, clays, calcium metasilicate; metal sulfate such as barium sulfate, calcium sulfate, aluminum sulfate; metal oxides such as calcium oxide, aluminum oxide; and aluminum trihydrate. The abrasive suspension formulation from which the structured abrasive is formed may also comprise an auxiliary polishing material to increase polishing efficiency and cutting speed. Useful auxiliary polishing material can be inorganic base, such as halide salts, for example sodium cryolite, potassium tetrafluoroborate, etc; to the organic base, such as chlorinated waxes, for example polyvinyl chloride. The preferred polishing auxiliary materials in this formulation are cryolite and potassium tetrafluoroborate with a particle size ranging from 1 to 80 microns and most preferably from 5 to 30 microns. The weight percentage of the polishing auxiliary material varies from 0 to 50% and most preferably from 10 to 30%. The abrasive / binder suspension formulations used in the practice of this invention may further comprise additives including: coupling agents, such as silane coupling agents, for example A-174 and A-1100 obtainable from Osi Specialties, Inc., organotitanates and zircoaluminates; antistatic agents, such as graphite, carbon black and the like; suspending agents, viscosity modifiers such as fumed silica, for example Cab-O-Sil M5; agents of anticargas, such as zinc stearates; lubricants such as wax, wetting agents, dyes; fillers; viscosity modifiers; dispersants; and foaming eliminators. Depending on the application, the functional powder deposited on the surface in suspension can impart unique polishing characteristics to the abrasive products. Examples of functional powders include: 1) abrasive grains - all types and sizes of grain; 2) fillers - calcium carbonate, clay, silica or wollastonite, aluminum trihydrate, etc; 3) auxiliary polishing materials-KBF, cryolite, halide salt, halogenated hydrocarbons, etc; 4) anti-caking agent - zinc stearate, calcium stearate, etc; 5) antistatic agents - carbon black, graphite, etc; 6) Lubricants - waxes, PTFE powder, polyethylene glycol, polypropylene glycol, polysiloxanes, etc. The reinforcement material on which the formulation is deposited can be a fabric (woven, non-woven, or shaggy), paper, plastic film or sheet metal. Generally, products made in accordance with the present invention find their greatest utility in producing fine polishing materials and a very smooth surface is therefore preferred. Thus, the finely glazed paper, the plastic film or a fabric with a Soft surface coating is usually the preferred substrate for the deposition of the mixed formulations according to the invention. The invention will be described more broadly with respect to certain specific embodiments which are understood to be for the purposes of illustration only and do not imply any necessary limitation on the scope of the invention.

Abbreviations To simplify the presentation of data, the following abbreviations will be used: Polymer component Ebecryl 3605, 3700- acrylated epoxy oligomers obtainable from UCB Radcure Chemical Corp. TMPTA- Triacrylated trimethylol propane obtainable from Sartomer Company, Inc. ICTA- triacylated isocyanurate obtainable from Sartomer Co., Inc. TRPGDA- diacrylated tripropylene glycol obtainable from Sartomer Co., Inc.

Binder components Darocure 1173- photoinitiator obtainable from Ciba-Geigy Company Irgacure 651- photoinitiator obtainable from Ciba-Geigy Company 2-Methylimidazole - catalyst from BASF Corp. Pluronic 25R2 - block copolymer from poxipropylene-polyoxyethylene obtained from BASF Corp. KBF - material auxiliary polish with particle size medium of approximately 20 μm, obtainable from Solvay Cab-O-Sil M5- Wet silica from Cabot Corporation FRPL-Al203 melt from Treibacher (P320 or P1000: grade indicated by the "P-number"). Calcined AI2O3 (40 μm) from Microabrasives Corporation Reinforcements 76 micron Mylar film for ophthalmic applications 127 micron Mylar film for metalworking applications Suriyn-coated J-weight polyester fabric Suriyn is a DUPLON 1652 SURLYN ionomer recirculator.

TABLE I Abrasive suspension formulations Procedure for the preparation of the formulation The monomers and / or the components of the formulation were mixed together oligomer for 5 minutes, using a high shear mixer at 1000 rpm. This binder formulation was then mixed with any initiators, wetting agents, foaming removal agents, dispersants, etc. and mixing was continued for 5 more minutes at the same agitation speed. The following were added components, slowly and in the order indicated with the stirring of 5 minutes at 1500 rpm between the additions: suspending agents, auxiliary polishing materials, fillers and abrasive grain. After the addition of abrasive grain, the stirring speed was increased to 2000 rpm and the gg? j £ gjg ^^^^^^^^^ j ^^ g ^ á ^ j3 ^ ígs ^^^^^^^ for 15 minutes. During this time, the temperature was carefully monitored and the stirring speed was reduced to 1000 rpm if the temperature reached 40.6 ° C.

DEPOSITION OF THE FORMULATION The resin formulation was coated to a variety of conventional substrates listed previously. In the cases cited, the abrasive suspension was applied using a knife coating with the gap set to desired values. The coating was made at temperatures environment.

Application of functional powders and embossing Prior to embossing, the surface layer of the suspension was modified with abrasive grains with the same particle size or more fine than that used in the formulation. Sufficient deposited to form a single layer adhered by the uncured binder component. Excess powder was removed from the layer by vibration. The application of the powder was by a conventional vibratory screening method. Once the substrate was coated with the formulation in After the suspension was uncured and the functional powder was applied, an embossing tool was used for the desired pattern to impart the desired shape to the abrasive resin and the grain formulation. This embossing configuration included a steel reinforcement roller that provided the necessary support ^ during the application of pressure by the steel embossing roller. A wire brush configuration was used to remove any dry residue or loose grains left in the cells after the tool had split its impression to the modified viscosity formulation.

Curing After the pattern was embossed to the modified viscosity layer, the substrate of the embossing tool was removed and passed to a curing station. If the curing is thermal, appropriate means are provided. If the curing is activated by photoinitiators, a source of reversion can be provided. If UV curing is used, two 300-watt sources are used: a bulb D and a bulb H with the dosage controlled by the speed at which the pattern substrate passed under the sources. In the case of the matrix of the experiments listed in Table 2, curing was by UV light. In the case of formulation I, however, the UV curing was immediately followed by a thermal cure. This curing process will be inadequate to ensure final dimensional stability. In this first example, the lid was embossed with a roller that had cells engraved thereon in a hexagonal pattern 17. This produced the pattern of protrusions in a hexagonal shape. In each one, the abrasive grain was sprinkled on the surface to serve as a functional powder. In a first example, the abrasive sprinkled on the surface was P1000 and in a second example it was P320. In each case, the abrasive / binder formulation was formulation I. In the second example, the embossed roll was engraved with a hexagonal pattern 17 with 3-helical roll surface. The same coating technique was used. In a third example, the pattern engraved on the embossing roller was pyramid 45 with the formulation I giving a pattern of isolated pyramids with a square base. The surface was modified by applying grain of P1000 on the same formulation used in the first and second experiments. In all three experiments, the structures on the embossed surface were essentially unchanged from the time of embossing until the moment when the binder component was completely cured. Additional examples were also carried out, similar in shape but variants in formulation and abrasive content, as listed in table 1. In all cases, the manufacturing process is identical to the first three examples; however, variations were made in the resin composition and the functional powders.

TABLE 2 The hexagonal emboss roll pattern 17 comprised cells 559 microns deep with equal sides of 1000 microns at the top and 100 microns at the bottom. The trihelical pattern 25 comprised a continuous channel cut at 45 degrees to the axis of the roller having a depth of 508 microns and width of openings greater than 750 microns. The trihelical pattern 40 comprised a continuous channel cut at 45 degrees to the axis of the roller having a depth of 335 microns and an opening width of 425 microns. The pyramidal pattern 45 comprised cells in the form of an inverted pyramid, with a square base with a depth of 221 microns and a lateral dimension of 425 microns.

Polishing tests Several of the listed samples were subjected to two main forms of polishing test with the data listed in tables 3-5. The first test consisted of the Schieffer tests up to 600 revolutions with 3.63 kg. of constant load on a hollow, piece of work of stainless steel 304 with 2.79 cm of external diameter that gives an effective pressure of polish of 1.63 kg / cm2. The pattern abrasive was cut into 11.43 cm diameter discs and mounted to a steel reinforcement plate. Both the reinforcement plate and the workpiece rotate clockwise, turning the reinforcement plate to 195 RPM and rotating the piece of work at 200 RPM. Note was taken of the weight loss of the work piece every 50 revolutions and a total was obtained at the end of 600 revolutions. The second test method consisted of a test of microabrasive rings. In this test, the modular cast iron rings (4.45 cm outside diameter, 2.54 cm inner diameter and 2.54 cm wide) were previously roughened using a conventional 60 micron film product and then polished to 4.22 kg./ cm2 with the pattern abrasive. The 2.54 cm wide abrasive was first selected and held against the work piece with rubber shoes. The workpiece was rotated at 100 RPM and oscillated perpendicular to a speed of 125 oscillations per minute. All the polishing was done in a bath lubricated with undiluted OH200 oil. The weight loss was recorded every 10 revolutions and the total was obtained at the end of the test.

TABLE 3 Schieffer tests of FRPL P320 grain abrasives in the suspension formulation (500 revolutions) TABLE 4 Schieffer tests of standard abrasives with 400 μm grains of AI2O3 calcined in the suspension formulation (600 revolutions) TABLE 5 Ring tests for micro-termination applications (50 revolutions at 4.22 kg / cm2) fifteen Table 3 clearly shows the effect of the type of functional powder and pattern. With the pyramid 45 (P320 in the formulation and P1000 as the functional powder) as the control, using a larger hexagonal forming pattern 17 the same resin and functional powder formulation resulted in a slight increase in the total cut. In all cases in which P1000 was replaced with a rougher P320 grade, it was ^ k *** - * - ~ ^^^ ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Even more of the cut In addition, the trihelicoidal pattern worked better than the hexagonal pattern. In the final case in which the functional powder consisted of a mixture of KBF4 and P320, the cut was markedly increased. From this data set it can be clearly seen that the type of pattern coupled with the type of functional powder clearly alters the characteristics of the polish. In Table 4, the pattern abrasives were compared with Comparative Example C-1, a conventional 40 μm grain micro-grinding abrasive with the factory name of Q151 from Norton Co. It can be seen in both pattern abrasives, which the total cut significantly increased with respect to the conventional product by working the tri-helical material 25 better than the tri-helical 40. In table 5, the 40 μm standard abrasives were compared in a micro-termination application. Again, compared to comparative example C-1, the conventional abrasive product with the factory name Q151 from Norton Co., and the pattern abrasive demonstrates an improvement in the total cut. In general, the previous patterns worked well in the applications of abrasive tests, generating effective abrasion from the beginning. ffifiírn r -M Km M- ~ "HÜr -wflffpH

Claims (16)

NOVELTY OF THE INVENTION CLAIMS

1. A process for the production of a structured coated abrasive comprising a pattern of mixed bodies of abrasive / binder adhered to a reinforcing material, said method comprising: forming a substrate of mixed abrasive bodies on a material, comprising each mixed body a cured binder 10 at least partially and abrasive particles dispersed therein, and adhering a functional powder selected from the group consisting of abrasives, fillers, auxiliary polishing materials, antistatic powders, powders and mixtures thereof to the surface of such mixed bodies. abrasives.

2. A method according to claim 1, further characterized in that the mixed abrasive bodies are arranged in a regular configuration and comprise a partially cured binder, in such a way that the functional powder applied to the structured abrasive adheres thereto and subsequently complete the curing of the binder.

3. A process according to claim 1, further characterized in that a second binder material is applied on the structured abrasive surface and the functional powder is applied to the second binder which subsequently hardens. ^^ M «fejgg8 ^^^^^ g gg | ^ BÉ | ^^^ g

4. - A method according to claim 1, further characterized in that the functional powder has an average particle size of 1 to 150 micrometers.

5. A process according to claim 1, further characterized in that the binder comprises a curable resin by reaction or thermally, or a combination of the above.

6. A process according to claim 1, further characterized in that the resin of the binder comprises a non-reactive thermoplastic component.

7. A process according to claim 1, further characterized in that the abrasive comprises from about 10 to 90%, the weight of the formulation.

8. A process according to claim 1, further characterized in that the abrasive grain of the group consisting of cerium, alumina, fused alumina / zirconia, silicon carbon, cubic boron nitride and diamond is selected.

9. A process according to claim 1, further characterized in that the formulation also comprises one or more additives selected from the group consisting of auxiliary polishing materials, inert fillers, antistatic agents, lubricants, anti-fouling agents and mixtures thereof .

10. A process according to claim 9, further characterized in that the formulation comprises an auxiliary polishing material selected from the group consisting of cryolite, potassium tetrafluoroborate and mixtures thereof.

11. A method according to claim 3, further characterized in that the second binder is the same as the binder used to produce the structured abrasive.

12. A coated abrasive that is prepared by a process according to claim 1.

13. A coated abrasive that is prepared by a process according to claim 2. 10

14. A coated abrasive that is prepared by a process according to claim 3.

15. A coated abrasive that is prepared by a process according to claim 4.

16. A coated abrasive that is prepared by a method according to claim 5.