MXPA99006382A - Rotogravure process for production of patterned abrasive surfaces - Google Patents

Abstract

Coated abrasives suitable for very fine abrading applications can be obtained by depositing formulations comprising abrasive grits, fillers, grinding aid, additives and a binder resin and in patterns on a surface using a rotogravure technique providing the viscosity is controlled such that the formulation deposited does not lose its shape prior to cure.

Description

PROCESSING OF ROTOGRAVED FOR THE PRODUCTION OF ABRASIVE SURFACES WITH PATTERNS BACKGROUND OF THE INVENTION This invention relates to the production of patterned abrasive surfaces on substrates in a form useful for fine finishing of substrates such as metals, wood, plastics and glass using a rotogravure process. The proposal for depositing insulated structures such as islands of a mixture of a binder and abrasive material on a backing material has been known for many years. If the islands have very similar heights on the backing and are properly separated (perhaps after a minor coating operation), then the use of the product will result in a reduced surface striation and improved surface smoothness. In addition, the spaces between the islands provide a route through which the grinding mud generated by the abrasion can be dispersed from the work area. In a conventional coated abrasive, the investigation of the abrasive surface reveals that a comparatively small number of the surface abrasive grains in an active abrasion zone are in contact with the workpiece at the same time. As the surface wears, this number increases but also the usefulness of certain abrasive grains can be reduced by the loss of roughness. The use of abrasive surfaces comprising a uniform arrangement of insulated islands has the advantage that the uniform islands wear out at essentially the same speed, whereby a uniform abrasion rate can be maintained for longer periods. In one sense, abrasion work is shared more evenly among a larger number of grinding points. Moreover, since the islands comprise many smaller abrasive particles, the erosion of an island reveals new and unused abrasive particles that have also lost harshness. One technique for forming said arrangement of isolated islands or points that has been described is that of rotogravure printing. The rotogravure printing technique employs a roller within a surface from which a pattern of cells has been printed. The cells are filled with the formulation and the roller is pressed against a surface and the formulation in the cells is transferred to the surface. Normally, the formation would flow later until there was no separation between the formulations deposited from any single cell. Finally, a layer of essentially uniform thickness can be obtained. By way of illustration, comparative examples C and D of the US patent. No. 5,152,917 describe a process in which the pattern obtained by a rotogravure process quickly lost all separation of the individual amounts deposited from the cells. In U.S. Patent No. 5,014,468, an abrasive / binder formulation was deposited from rotogravure cells on a roller in such a manner that the formulation was placed in a series of structures surrounding an abrasive-free area. It is believed that this is the result of depositing less than the full volume of the cell and only from the perimeter of each cell, which could leave the ring formations described. The problem with the rotogravure approach has therefore always been the retention of a useful form on the island. It has proved to be very difficult to formulate an abrasive / binder mixture that is sufficiently flowable to be deposited, but also sufficiently non-flowable so that it does not collapse to an essentially uniform layer coating when deposited on a substrate. Chasman et al., In U.S. Patent No. 4,773,920 disclose 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 grinding mud. Nevertheless, beyond the pure affirmation of possibility, no details are given that could teach how this can be carried out. In U.S. Patent No. 4,644,703, Kaczmarek et al. Use a rotogravure roller in a more conventional manner to deposit an abrasive / binder formulation on a layer which is then smoothed before a second layer is deposited by a process of rotogravure on the upper part of the first smoothed layer. There is no teaching of the nature of the final cured surface.

In U.S. Patent No. 5,014,468, Ravipati et al., It was proposed to use an abrasive / binder mixture having non-Newtonian shear thickening flow properties and to deposit this mixture by a rotogravure technique on a film. In this process the mixture was deposited from the edges of the rotogravure cells to produce a unique structure with deposits of reduced thickness with a distance far from the areas surrounding the free surface of the mixture. If the cells are close enough to one another, the surface structures may seem intertwined. This product has proven to be very useful, particularly in ophthalmic operations. The procedure is very useful but has a potential problem of increasing the accumulation of material in the cells of the rotogravure roller, so that the deposition pattern may change slightly during a series of prolonged production. 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 approach has been to deposit the abrasive / binder mixture on a substrate surface and then impose a pattern comprising an arrangement of insulated islands on the mixture by curing the binder while in contact with a mold having the opposite of the surface with desired pattern. This approach is described in U.S. Patent Nos. 5,437,754; 5,378,251; 5,304,223 and 5,152,917. There are several variations on this subject, but all have the common feature that each island in the pattern is fixed by curing a binder in contact with a molding surface. This approach is also not without problems, since incomplete extraction of the mold often occurs, so instead of producing, for example, pyramids, forms of a volcano complete with a crater often appear. The present invention presents a technique for producing uniformly patterned shapes of an abrasive / binder combination that does not require an in-mold curing operation, or the selection of a binder / abrasive combination with specific non-Newtonian shear thickening characteristics. Therefore, the present invention provides a flexible and effective route for the production on a commercial scale of coated abrasives with a uniform arrangement of isolated mixed abrasive shapes. Said coated abrasives are well adapted to the treatment of a wide range of substrates to produce fine finishes and during extended periods of operation at a substantially uniform cutting speed.

GENERAL DESCRIPTION OF THE INVENTION The problem encountered with the use of rotogravure techniques to produce coated and patterned abrasive materials has always been the retention of a useful shape and pattern after the deposition of the formulation. Very often, the deposited shape loses its vertical dimensions and tends to run across the surface and join adjacent shapes. This problem is mentioned in Comparative Examples C and D of U.S. Patent No. 5,152,917 which was mentioned above. In U.S. Patent No. 5,014,468 the solution that was adopted was to use a formulation with a rheology of shear thickening causing the mixture to be deposited from the edges of the rotogravure cells to form the unique pattern described therein. It has now been found that if the low shear viscosity and the high shear viscosity are adequately controlled, it is possible to produce, using a rotogravure technique, abrasives coated with patterns and with several distinct patterns including defined points, connected points, lines or other patterns even when the formulation has a rheology of shearing thinning. The key is to formulate the binder / abrasive mixture to meet two conditions. The first condition is that the viscosity is relatively low under relatively high shear conditions (such as those experienced when the engraving cells are filled, a scalpel is passed over the engraving roller after filling the cells, and while transferring the material to a substrate in the space between the rotogravure roller and a rubber roller). In other words, the formulation must have a low viscosity for high shear stress to facilitate deposition of the coating on the substrate. The second condition is that the formulation has a high viscosity by low shear stress so as to avoid excessive flow and leveling when the formulation is on the substrate under low shear conditions before being cured. It is also highly desirable that the viscosity recovery time be short compared to the time between coating deposition and curing. Theoretical studies of the deposit pattern retention indicate that the surface tension is the driving force that leads to the flow (and consequently loss of the pattern) and the viscosity is the strength of resistance. In this way, the retention of the pattern will be favored by a low surface tension and high viscosity. However, with radiation curable binders such as those commonly used with the abrasive / binder formulations to which this invention relates primarily, the surface tension does not vary much and is generally in the range of about 30-40 dynes / cm. A fully formulated water-based abrasive / binder mixture generally also has a surface tension on the same scale. In this way, viscosity is the parameter of the most affected results that can be adjusted. Therefore, the present invention comprises a process for the production of a coated abrasive comprising a pattern of mixed abrasive / binder materials adhered to a backing material, said process comprising: (a) applying a layer of a gravure using a gravure technique; a formulation comprising abrasive grains (and optionally abrasion aid, fillers and additives), and a curable resin binder in a pattern of insulated structures, said formulation having a viscosity at a high shear rate of 103 sec. at 1, 000 cp.; (b) after deposition of the formulation on the backing material, increase the velocity of at least the surface layers of the deposited formulation to be above 4,000 cp at a low shear rate of 0.05 sec "1 so as to maintain the insulation of the structures, and (c) cure the binder component of the formulation to retain said pattern of insulated structures on said backing." The viscosity is measured here using a Bohlin VOR rheometer at the temperatures of coating that are typically around 15 ° C to 50 ° C. The key is that the formulation should have a reasonably low viscosity at the high shear conditions encountered during the filling of the rotogravure cells, scalpel down the roller to remove the excess formulation and deposition from the cells, but after the deposition the viscosity needs to be increased sufficiently quickly to prevent the flow of the formulation from destroying the insulation of the deposited structures. The insulation is not considered lost if the margins are touched in places but only if the structures are in contact with adjacent structures at all points around the margins and the depth of the formulation at the contact points is at least 10% of the maximum height of the contact structures on the backrest. A very suitable way to ensure the retention of the separation is to use a resin formulation having a thixotropic character, that is to say, exhibiting shear thinning behavior that depends on time. Said formulations quickly recover their high viscosity when the high shear conditions are removed.

Normally, at approximately 30 seconds the viscosity has recovered at least 50% of its value under low shear conditions and this is sufficient in many cases to avoid the loss of the insulation until the curing process has begun to increase the viscosity . In a manufacturing facility, the viscosity can be measured more conveniently with a Brookfield viscometer. Thus, a preferred method according to the invention comprises: (a) applying by a rotogravure technique a layer of a formulation comprising abrasive grains (and optionally abrasion aid, fillers and additives) and a resin binder curable in a pattern of isolated structures, said formulation has a Brookfield viscosity at a spindle speed of 60 rpm from 50,000 to 1,000 cp., (preferably 25,000 to 2,000 and more preferably from 15,000 to 5,000 cp.); (b) after deposition of the backing material, increase the viscosity, at a spindle speed of 6 rpm, of at least the surface layers of the deposited formulation from 150,000 to 5,000 cp., (preferably 50,000 to 7,000. cp., and most preferably 25,000 to 8,000 cp.); and (c) curing the binder component of the formulation to retain said pattern of isolated structures on said backing. The viscosity is affected by the temperature and the higher viscosities are at the temperature at which the formulation is applied in the above procedure. Typically, this is a temperature for example of about 15 ° C to 50 ° C. Viscosity is measured using a viscometer Brookfield model LVF 5X with a # 4 spindle. It is also desirable that the recovery time of the viscosity, ie the time for the low viscosity under high shear conditions to be reversed to the normal high viscosity when the shear conditions are removed, should be relatively short, such as less than 60 seconds and preferably less than 30 seconds. However, any formulation-even a non-trichotropic one-that has a high shear viscosity low in the above scale can be modified after deposition to quickly adjust the viscosity to the higher low shear viscosity level described above., so as to limit the flow that could tend to occur at the lowest viscosities at which the formulation is deposited. Nor is it necessary that the viscosity of the entire formulation be adjusted to the highest level. It is usually sufficient if the exposed outer layer quickly obtains the highest viscosity, since it acts as a skin to retain the shape of the structure even if the inner portion retains the lower viscosity for a longer period. Viscosity modification of at least the surface layers can be achieved by, for example, incorporating into the formulation a volatile solvent that is rapidly lost when the formulation is deposited on the backing material, perhaps with the help of increased room temperature or by a hot gas jet located. The increased temperature can of course also decrease the viscosity. Therefore, it is important to balance these effects to ensure that the result is an increasingly high viscosity. A factor that helps in this direction would be a tendency of the increased temperature to cause an accelerated curing. Another option would be to quickly adjust the temperature of the structure downwards so that the viscosity is increased. This can be done for example by passing the substrate with the formulation structures deposited thereon on a cooled roller and / or under a cold gas flow. Apart from adjusting the viscosity by changing the temperature or removing the liquid, it is possible to adjust the viscosity by increasing the solids content. Although this can not be done for the internal portion of the deposited formulation, this is not really necessary. It is sufficient that the surface layer achieve the highest viscosity to maintain the shape of the deposited pattern. In this way, sprinkling a finely divided powder on the surface of the structure will act to form a localized "skin" of higher viscosity on the structure, causing it to retain its shape until the curing makes the form permanent. The powder itself can be an abrasive, a filler or a powder material which confers advantageous properties, for example an abrasion aid such as potassium tetrafluoroborate, an anti-static agent such as graphite, an anti-filling agent such as stearate of zinc, a solid lubricant such as wax or any combination of said materials. This is in fact an advantageous and preferred aspect of the present invention. The process can also be aided by having the rotogravure roller heated and the surface on which the formulation is deposited cooled. However, the heating of the rotogravure roll should not be at a level such that the binder begins to cure and the viscosity increases as a consequence, in the case of thermally curable resin formulations.

DESCRIPTION OF THE DRAWINGS Figure 1 shows an example of the viscosity variation with respect to the shear rate of an abrasive suspension formulation of this invention. As shown, the variation in the viscosity of the conditions of high shear at low shear stress is very marked. Similarly, as shown in Figure 2, the recovery of the viscosity upon removal of the high shear conditions is such that more than 50% of the low shear viscosity is recovered once the conditions of high shear stress they are removed. With these rheological characteristics, deposited coating formulations retain the rotogravure pattern with the separation between individual depositions. Figures 3 and 4 illustrate the coated patterns of an abrasive formulation according to this invention that is cured immediately after the arrangement vs. with a delay of 40 minutes between deposition and curing. This demonstrates that in contrast to the smeared patterns of Comparative Examples C and D in U.S. Patent No. 5,152,917, an abrasive slurry formulation with a rheology suitably formulated in accordance with this invention can retain its defined pattern even up to 40 minutes after the deposition before the binder is finally cured and fixed by UV rays.

DETAILED DESCRIPTION OF THE INVENTION The deposition can be in any desired pattern and will be largely determined by the size and distribution of the cells on the rotogravure roll. The hexagonal, tetragonal, triangular and quadrangular cell shapes are quite adequate, although others can also be used. It is possible, for example, to make the cells in the form of grooves (for example tri-helical grooves) cut on the roller surface. This is commonly a very advantageous configuration and can be adapted to produce a diagonal striking pattern that is both very distinctive and also very effective for abrasion. The number of cells per unit length can also vary, although with a higher cell density the volume of the cells is preferably smaller to maximize the separation between the contents of the cell after deposition on the surface. If the cells are located very close together, it is possible to cause the deposited formulations to run together by design to produce an essentially continuous line. Other designs are also very suitable, including isolated points or groups of points. The deposited points tend to be round but the deposition technique, including the speed of the rotogravure roll and the method by which the cells are filled, can cause the shape of the deposited point to be different from the round one. In this way, the point can have the shape of a crest or have a "comet tail". In some cases these forms may have certain advantages but are generally not preferred. Therefore, it is preferred to adjust the printing pressure and the circumstances under which the rotogravure roller contacts the surface of the substrate to which the formulation will be applied to ensure that defined round spots of a deposited formulation are obtained. The abrasive component of the formulation can not be any of the available materials known in the art, such as alpha alumina, (fused or concreted ceramic), silicon carbide, fused alumina / zirconia, cubic boron nitride, diamond and the like, as well as the combination of them. In applications for which this type of product is primarily designed, the preferred abrasive is alumina and particularly fused alumina. The abrasive particles useful in the typical invention and preferably have an average particle size of from 1 to 150 microns and more preferably from 1 micron to 80 microns.

The proportion of abrasive in the formulation is determined, of course, in part by the viscosity limitations set forth above and by the type of application. However, in general the amount of abrasive present provides about 10 to about 90%, preferably 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 an electron beam, UV radiation or visible light, such as the acrylated oligomers of acrylated epoxy resins, acrylated urethanes and polyester acrylates and acrylated monomers which they include mono-acrylated, multi-acrylated monomers and thermally curable resins such as phenolic resins, urea / formaldehyde resins and epoxy resins, as well as mixtures of said resins. In fact, it is commonly desirable to have a radiation curable component present in the formulation that can be cured relatively quickly after the formulation has been deposited to add to the stability of the deposited form, as well as a thermally curable resin. In the context of this application, it is understood that the term "radiation curable" encompasses the use of visible light, ultraviolet (UV) light and electron beam radiation as the agent that will cause curing. In some cases, the functions of thermal curing and the functions of radiation curing can be provided by different functionalities in the same molecule. This is commonly a desirable aspect.

The resin binder formulation may also comprise a non-reactive thermoplastic resin which can improve the self-sharpening characteristics of the mixed abrasive materials deposited by increasing its erosion capacity. Examples of said thermoplastic resin include polypropylene glycol, polyethylene glycol and polyoxypropylene-polyoxyethene 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: metal carbonates such as calcium carbonate, sodium carbonate; silicas such as quartz, glass spheres, 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. In the abrasive suspension formulation, it may comprise an abrasion aid to increase the abrasive efficiency and cutting speed. A useful abrasion aid may be of inorganic base, such as halide salts, for example sodium cryolite, potassium tetrafluoroborate, etc; or of organic base, such as chlorinated waxes, for example polyvinyl chloride. The abrasion aids that are preferred in this formulation are cryolite and potassium tetrafluoroborate with a particle size ranging from 1 micron to 80 microns, and more preferably from 5 microns to 30 microns. The weight percentage of the abrasion aid varies from 0% to 50% and more preferably 10-30%.

The abrasive suspension formulations of this invention may also comprise additives which include: coupling agents, such as silane coupling agents, for example A-174 and A-1100 available from Osi Specialties, Inc., titanate and zircoaluminates; anti-static agents, such as graphite, carbon black and the like; suspending agent, such as fumed silica, for example Cab-O-Sil M5, Aerosil 200; anti-filling agents, such as zinc stearate; lubricants such as wax; wetting agents; colorants; dispersants and defoamers. The backing material on which the formulation is deposited can be a fabric (woven, nonwoven or hairy), paper, plastic film, metal foil or combination thereof. In general, products made in accordance with the present invention find their greatest utility in the production of fine abrasion materials and therefore a very smooth surface is preferred. In this way, finely calendered paper, plastic film or a cloth with a smooth surface coating is usually the substrate that is preferred for the deposition of the mixed formulations according to the invention. The invention will be described more fully with respect to certain specific embodiments which are understood to have nothing more for purposes of illustration only and do not imply any necessary limitation of the scope of the invention.

Abbreviations To simplify the presentation of the data, the following abbreviations will be used: Binding components Ebecryl 3600, 3700 acrylated epoxy oligomers available from UCB Radcure Chemical Corp. TMPTA trimethylolpropane triacrylate available from Sartomer Company, Inc. HDODA 1,6-hexanediol diacrylate available from Sartomer Co., Inc. V-PYROL vinylpyrrolidone available from GAF Corp. ICTA isocyanurate triacrylate available from Sartomer Co., Inc. TRPGDA tripropylene glycol diacrylate available from Sartomer Co., Inc. Kustom KS-201 acrylate monomer gel available from Kustom Service Inc.

Photoinitiators and additives Irgacure 651 a photoinitiator available from Ciba-Geigy Company. Speedeure ITX 2-isopropylthioxanthone available from Acetate Chemical Corp.

Speedeure EDB ethyl 4-dimethylaminobenzoate available from Aceto Chemical Corp. KR-55 titanate coupling agent available from Kenrich Petrochemicals. FC-171 fluorocarbon surfactant available from 3M Company BYK-A510 foam suppressor available from Mallinckrodt Corp. A-1100 aminopropyltriethoxysilane available from Osi Specialties, Inc. SOLOX isopropyl alcohol available from EM Science. Coloring 9R-75 violet quinacridone UV, a dispersion available from Penn Color. Pluronic 25R2 polyoxypropylene-polyoxyethylene block copolymer available from BASF Corp .. Cab-O-Sil M5 fumed silica from Cabot Corporation. ATH S3 aluminum trihydrate from Alcoa.

Grano FU .... A 03 merged with 3 micras of Fujimi. T FRPL AI2O3 merged Treibacher (grade indicated by the number "P-"). TB BFRPLCC AI2O3 fused and heat treated with Treibacher ceramic coating (grade indicated by the number "P-").

Abrasion aid KBF4 potassium tetrafluoroborate with an average particle size of 20 microns available from Solvay, Inc ..

Backups ... film for mylar ophthalmic applications of 76.2 microns. B ... film for work applications with metal Mylar of 127 microns. C ... weight J polyester fabric with a surface extrusion coating with a thickness of 75 microns of Surlyn *. D ... weight J polyester fabric with an extrusion coating of 50 micron thick Surlyn surface. F ... polyester fabrics J weight phenolic finish F755. * Surlyn is an ionomeric SURLYN 1652-1 resin from Du Pont.

Formulations: TABLE 1 Procedure for preparing the formulation The monomer and / or oligomer components were mixed for 5 minutes using a high-shear mixer at 1000 rpm. This binder formulation was then mixed with any initiators, wetting agents, defoaming agents, dispersants, etc. and mixing was continued for a further 5 minutes at the same stirring speed. Then the following components were added, slowly and in the order indicated, with five minutes of agitation at 1500 rpm between additions: suspending agents, abrasion aids, fillers and abrasive grain. After the addition of the abrasive grain the agitation speed was increased to 2,000 rpm and continued for 15 minutes. During this time the temperature was carefully monitored and the stirring speed was reduced to 1,000 rpm if the temperature reached 40.6 ° C. Then the temperature and viscosity were recorded.

Fixing the engraving coating The fixing of the coating included a rubber roller with a Shore A hardness of 75 and a scalpel was used to make an angle with respect to the tangent at the contact point of 55-75 °. An engraving roll rotates in a coating container to fill the formulation in the cells. The engraving roller carrying the filled cells then passes under the scalpel to remove the excess formulation and then in contact with the substrate while passing under the rubber roller that acts to extract the formulation from the cells and deposit it on the backing material .

Curing After the pattern is deposited on the substrate, the patterned substrate passes to a curing station. When the curing is thermal, adequate means are provided. When curing is activated by photoinitiators a light source can be provided. If UV curing is used, two 300-watt sources are used: a bulb D and a bulb H with a dosage controlled by the speed at which the patterned substrate passes under the sources. The coated standards and the relevant viscosities are shown in the following tables 2 and 3. "HEX" indicates hexagonal cells; "QUAD" indicates square cells and "TH" indicates patterns of trihelical lines. The raised hexagonal crest patterns are typical of those according to the prior art U.S. Patent No. 5,014,468. "Defined" points "indicates that the defined points were triangular. Note that all the examples with the viscosity within the scale established above exhibited a defined pattern with separation between individual depositions.

TABLE 2 TABLE 3 The 17 HEX hexagonal engraving pattern comprises cells of 559 microns deep with equal sides of 1000 microns at the top and 100 microns at the bottom.

The helical pattern 10 TH comprises a continuous channel cut to 45 ° towards the axis of the roller that has a depth of 699 microns and an upper opening width with a width of 2500 microns. The 10 QUAD quadrangular pattern comprises square cells with a depth of 420 microns, an upper side dimension of 2340 microns and a lower side dimension of 650 microns. It was found that, when the engraving roller deposits "dots", the shape of the dots can be influenced by the rotating speed of the engraving roller and by the pressure exerted by the rubber roller. A very high speed or a very high pressure between the rubber roller and the engraving roller tends to distort the shape out of the round to the triangular and can even lead to the connection of adjacent points. However, under ideal conditions, which will vary according to the formulation, the hardness and pressure of the rubber roller on the engraving roller, the engraving pattern and the deposition rate, the ideal "dot" pattern is round. Curing was started using UV radiation at approximately 30 seconds of deposition of the formulations. The examples described above were subjected to abrasion tests using a modified 121 Fss ring test procedure. In each case a 6.4 cm x 152.4 cm band was used and was moved at a speed of 1524 smpm. The band was placed in contact with a 304 stainless steel ring work piece, (17.8 cm D.E., 15.2 cm D. and 3.1 cm wide) at a pressure of 69 KN / m2. The contact wheel behind the band was a rubber wheel with a flat surface of 17.8 cm with a hardness of 60 durometers.

The work piece moved at a speed of 3 smpm. Ten rings were previously roughened to an initial Ra of 50.

Abrasion intervals of one minute were followed by measurements of cut amount, workpiece temperature and surface finish.

With the ten rings a total of 10 minutes of abrasion was carried out with each band and the total cut and the average surface finish Ra, Rtm as well as the temperature of the work piece were reported. Ra is the arithmetic mean of deviation of the roughness profile from the midline and Rtm is the weighted average of the deepest tears. Both Ra and Rtm values are in units of millimicrons. The results are shown in table 4. Comparative example C-1 uses a commercial fine abrasive product available from Norton Company under the designation R245 with fused alumina abrasive grains P-400. R245 does not carry a patterned surface.

TABLE 4 The standard coated samples give a much higher total cut, while offering a cooler cut than the conventional coated R245 abrasive.

The second example set followed the same test procedure, except that the rings were made rough previously to an initial Ra of 1,778. The results are shown in table 5. Comparative example C-2 uses a commercial fine abrasive product available from Norton Company under the designation R245 with fused alumina abrasive grains P-302. R245 does not carry a patterned surface.

TABLE 5 Again, both 10Q and 10TH pattern abrasives in several different backings outperform conventional bare-faced coated abrasives in full cut and colder cut, while providing acceptable surface finishes. In the following series of tests, the same test procedure as described above was used, with the difference that 20 rings were made previously rough to an initial Ra of 1,778 and a total of 20 minutes were carried out in each band. abrasion time. The initial cut was also reported after the first minute of abrasion. The results are shown in table 6.

TABLE 6 Example 13-a indicates that the band was the same as that used in example 13, except that the band was pre-coated before use. This clearly improved the initial cut (after the first minute of abrasion) and the smoothness of the surface, but had some cost in the total short time obtained. Example 13-b shows the effect of omitting the auxiliary abrasion component (KBF4) of the formulation, ie with 70% by weight of aluminum oxide grain P320 (T) and without any KBF4 in the suspension. The initial cut of Example 13-b remained low even after the pre-coating step before the test. Example 16 shows a lower initial and total cut, but a finer surface finish can be obtained with a different resin formulation. In the following set of abrasion examples, the effect of an additional coating of powder material on the coated abrasive suspension is demonstrated. The same test procedure as described above was followed with 20 rings made harsh previously to an initial Ra of 2.032. The Ra and Rtm values were measured only after the first minute, the tenth minute interval and the twenty minute abrasion. The Ra and Rtm reported are the average of these three readings. The initial cut was also reported after the first minute of abrasion. The results are shown in table 7.

TABLE 7 Example 14 shows that the trihelical pattern abrasive 10 with a suspension formulation using heat treated aluminum oxide grains (BFRPLCC) and KBF4 abrasion aid exhibited a much higher cut and cold cut than those of comparative example C -2. Example 14-a is the same as example 14, except that an additional layer of abrasive grains of BFRPLCC was applied on the patterned abrasive suspension followed by UV curing. This improves the initial cut (after a minute of abrasion) and the surface finish, but decreases the overall cut. This compromise between the initial cut and the total cut can be eliminated if a powder mix of BFRPLCC grain and KBF4 abrasion aid was applied instead of grains only on the surface of the patterned abrasive suspension followed then by UV curing. As shown in example 14-b, an additional powder coating of the grain / auxiliary abrasion mixture (ratio 2 to 1 by weight) significantly improved the initial cut while maintaining full cut and a finer surface finish. This approach is in fact a preferred aspect of this invention. The following set of examples shows how the addition of a non-reactive thermoplastic polymer affects the performance of patterned abrasives.

Example 13-c in Table 8 is the same as Example 13 in Table 6, except that an additional powder coating of FRPL / KBF4 mixture (weight ratio) was applied on the surface of the abrasive suspension. 2: 1). Note that with everything else being equal, the addition of Pluronic 25R2, a non-reactive polyoxypropylene-polyoxyethylene block copolymer, significantly improved the total cut (example 25 against example 26 and example 24 against example 13-c) in both cases, with and without additional surface powder coating.

TABLE 8 In a further set of experiments evaluating the abrasion efficiency of the products according to the invention, certain of the products were tested on a Coburn model 5000 machine that is designed to perform the Coburn I ophthalmic test procedure (505 Tpw -2FM). The test included polishing a CR-39 plastic lens that had a diameter of 6.4 cm and an espresso of 317.5 cm. The lens is oscillated at 1725 rpm and the abrasive carrier sheet, which has a Mylar support of 127 microns, is set to oscillate while making contact with the lens surface under an applied pressure of 138 KN / m2. The lens had received a first finishing treatment and the proven application in the series of comparisons was a second finishing operation. In the results shown in Table 9, the abrasion was not continued for two minutes. In Table 10, the data was obtained after repeated abrasion intervals of 30 seconds and the cumulative cut is reported after 1, 5 and 10 minutes.

TABLE 9 TABLE 10 From the above data in Table 9, it can be seen that a smooth coating without the etching pattern shows a cut and just a poor surface. It is also clear that the frequency and type of pattern is important. C-3 is a successful commercial product available from Norton Co. under the designation Q-135. However, it is comfortably outperformed by the products that carry the defined point patterns. The last point is made again in Table 10, which shows that the pattern of defined points continues to grind effectively long after the product with high hexagonal ridge pattern has ceased to be effective. All the formulations in the two previous paintings used the same resin formulation and the same abrasive grains with a size of 3 microns.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the production of a coated abrasive comprising a pattern of mixed abrasive / binder products adhered to a backing material, said method comprising: (a) applying by means of a rotogravure technique, a layer of a formulation comprising a mixture of abrasive grains and a curable resin binder in a pattern of insulated structures, said formulation has a viscosity at a shear rate of 103 sec "1 of 10,000 to 1,000 cp. (b) after the deposition of the formulation on the backing material, causing it to increase the viscosity of at least the surface layers of the deposited formulation to maintain the isolation of the structures and (c) curing the binder component of the formulation to retain said pattern of isolated structures on said support

2. The method according to claim 1, wherein the formulation is of a thixotropic nature. a and has a viscosity at a shear rate of 0.05 sec "1 of at least 4,000 cps.

3. The process according to claim 1, wherein it is caused to increase the viscosity of the deposited formulation, at least in part, by a change in temperature.

4. The method according to claim 1, wherein the formulation comprises a volatile component and is caused to increase the viscosity of the deposited formulation, at least in part, by removing at least a portion of the component. volatile formulation.

5. The process according to claim 1, wherein it is caused to increase the viscosity of the deposited formulation, at least in part, by the addition of a powder to the surface of the deposited structures.

6. A method according to claim 5, wherein the powder is selected from the group consisting of abrasive grains, abrasion aids, inert fillers, anti-static agents, lubricants, anti-filling agents and mixtures thereof. .

7. A process according to claim 6, wherein the powder is an abrasive grain selected from the group consisting of alumina, fused alumina / zirconia, silicon carbide, cubic boron nitride, diamond and mixtures thereof.

8. A process according to claim 6, wherein the powder is an abrasion aid selected from the group consisting of cryolite, potassium tetrafluoroborate and mixtures thereof.

9. A process according to claim 1, wherein the abrasive grain is selected from the group consisting of alumina, fused alumina / zirconia, silicon carbide, cubic boron nitride, diamond and mixtures thereof.

10. - A method according to claim 1, wherein the formulation also comprises one or more additives selected from the group consisting of abrasion aids, inert fillers, antistatic agents, lubricants, anti-filling agents and mixtures thereof.

11. A process according to claim 10, wherein the formulation comprises an abrasion aid selected from the group consisting of cryolite, potassium tetrafluoroborate and mixtures thereof.

12. A process according to claim 1. , wherein the binder resin comprises a thermally curable component.

13. A process according to claim 1, wherein the binder resin comprises a component curable by ultraviolet radiation.

14. A process according to claim 1, wherein the binder comprises a non-reactive thermoplastic component.

15. A method according to claim 1, wherein the formulation is extended in a pattern that is selected from defined points and defined lines.

16. A coated abrasive made by a process substantially as described in claim 15.

17. A coated abrasive made by a process substantially as described in claim 1.

18. A coated abrasive made by a process substantially of according to claim 8.

19. - A coated abrasive made by a process substantially in accordance with claim 12.

20. A coated abrasive made by a process substantially in accordance with claim 17.