Patent Application
20220193865
The invention relates to a method for treating an abrasive article, where a release agent dispersion is applied at least to a surface of the abrasive article intended for grinding to produce a covering layer, where the release agent dispersion comprises at least one anti-adhesion agent. Furthermore, the invention relates to a corresponding abrasive article.
Methods for treating an abrasive article are already known, for example from U.S. Pat. Nos. 5,766,277 B and 2,768,886 B, and in these a release agent dispersion is applied at least to the surface of the abrasive article intended for grinding to produce a covering layer, where the release agent dispersion comprises at least one anti-adhesion agent.
The invention proceeds from a method for treating an abrasive article, in particular a coated abrasive article, where a release agent dispersion is applied at least to a surface of the abrasive article intended for grinding to produce a covering layer, where the release agent dispersion comprises at least one anti-adhesion agent.
An “abrasive article” is employed for the grinding or abrasive working of a workpiece, in which the material of the workpiece is mechanically removed in the form of swarf from the surface of the workpiece. The abrasive article is, in particular, a coated abrasive article. The abrasive article comprises an abrasive article substrate, in particular a flexible abrasive article substrate, having at least one layer. The abrasive article substrate can comprise, in particular, paper, paperboard, vulcanized fiber, foam, a polymer, a textile structure, in particular a woven fabric, formed-loop knitted fabric, drawn-loop knitted fabric, braid, nonwoven, or a combination of these materials, in particular paper and woven fabric, in one or more layers. The abrasive article substrate, in particular flexible abrasive article substrate, gives the abrasive article specific properties in respect of adhesion, elongation, tear strength and tensile strength, flexibility and stability. In a coated abrasive article, abrasive grains are fixed by means of a binder (often referred to as base binder) on the abrasive article substrate. By means of the binder, the abrasive grains are at least prefixed, in particular fixed, in particular in a desired orientation and/or distribution, on the abrasive article substrate. A person skilled in the art will know of suitable binders for fixing abrasive grains on the abrasive article substrate from the prior art. Such binders of the prior art are typically solvent-based adhesives such as polychloroprene. In addition to the binder as base binder, it is possible to use a further binder known as a covering binder which is applied, in particular, as a layer over the abrasive grains which have been fixed by means of the base binder on the abrasive article substrate. Here, the covering binder bonds the abrasive grains firmly to one another and firmly to the abrasive article substrate. Suitable covering binders, in particular, will be adequately known to a person skilled in the art from the prior art. Possible covering binders are, in particular, synthetic resins such as for example phenolic resin, epoxy resin, urea resin, melamine resin, polyester resin. In addition, further additives (“grinding additives”) can be provided in order to give the abrasive article specific properties. A person skilled in the art will be familiar with such additives.
Furthermore, alternative abrasive articles, such as for example bonded abrasive articles, are in principle also conceivable. Bonded abrasive articles are, in particular, typically synthetic resin-bonded parting and grinding disks, with which a person skilled in the art will be familiar. For synthetic resin-bonded parting and grinding disks, a composition is produced by mixing abrasive minerals together with fillers, pulverulent resin and liquid resin and this is then pressed to give parting and grinding disks of various thickness and diameters. In particular, the parting and grinding disks also comprise woven fabric layers composed of glass fibers. Curing of the composition typically occurs at about 180° C. In combination with the method of the invention, advantages according to the invention can also be achieved in the case of such abrasive articles.
The abrasive article has a surface intended for grinding, i.e. an abrasive surface, in particular on that side of the abrasive article on which the abrasive grains are fixed and optionally provided with a covering binder and/or a further additive. The abrasive surface of the abrasive article is moved over a workpiece to be worked during a grinding operation, so that a grinding effect is produced by the abrasive grains arranged on the abrasive surface. The abrasive article can in principle be present in various manufactured forms, for example as grinding disk or as grinding belt, as sheet, roller, strip or as abrasive article stock strip (e.g. in production).
The term “release agent dispersion” which is applied to the surface intended for grinding of the abrasive article refers to, in particular, a lubricant dispersion. The release agent dispersion is employed for application of materials present in the dispersion to the surface of the abrasive article, with these materials being present as fine, essentially insoluble particles in the dispersion medium (also: dispersion agent) of the release agent dispersion. In one embodiment, the release agent dispersion comprises water as dispersion medium. In an alternative embodiment, the dispersion medium can also be formed by ethanol, alcohol, an organic solvent or the like. The release agent dispersion is intended to be applied to the surface of the abrasive article and bring about formation of a covering layer on the surface.
The release agent dispersion comprises at least one anti-adhesion agent, in particular as material present in the dispersion medium. Here, an “anti-adhesion agent” is an agent which prevents or reduces accumulation of swarf formed during a grinding operation. The anti-adhesion agent serves to prevent or reduce accumulation of swarf in the intermediate spaces between adjacent abrasion grains, which can lead, in particular, to blocking or clogging of the abrasive surface of the abrasive article. In particular, the anti-adhesion agent serves to prevent or reduce the effect in which swarf sinters together, sticks together or melts together under the action of the heat arising in a grinding process and melts on the abrasive surface of the abrasive article and in this way likewise leads to blocking or clogging of the abrasive surface of the abrasive article (as is often the case for, for example, polymers, polymer surface coatings or the like to be abrasively treated). In this way, a cutting capability and in particular an operating life (service life) of the abrasive article is advantageously improved. In this way, the anti-adhesion agent serves as a type of lubricant between abrasive article and workpiece surface to be worked during a grinding operation. In particular, such an anti-adhesion agent is often referred to as “stearate” in the literature about abrasive articles, even though it can comprise any materials which are useful for preventing the accumulation of swarf. For example, the anti-adhesion agent can comprise metal salts of fatty acids (for example zinc stearate or calcium stearate), salts of phosphate esters (for example potassium behenyl phosphate), phosphate esters, urea-formaldehyde resins, waxes, mineral oils, crosslinked silanes, crosslinked silicones, fluorinated chemicals and/or combinations thereof as constituent. Such anti-adhesion agents are often produced from fats in which a mixture of fatty acids is present. For example, an anti-adhesion agent—which is referred to as “stearate” in the literature—can also contain calcium salts of other fatty acids, for example palmitate, myristate or laurate. It is pointed out that such anti-adhesion agents are known to a person skilled in the art, for example from U.S. Pat. No. 5,766,277 B. The anti-adhesion agent typically does not dissolve in the dispersion medium of the release agent dispersion (for example water), so that a release agent dispersion containing the anti-adhesion agent is present. In this case, anti-adhesion agent particles, in particular very fine anti-adhesion agents particles, “float” in the dispersion medium of the release agent dispersion. In this sense, the anti-adhesion agent or the anti-adhesion agent particles is/are present as fine, essentially insoluble particles in the dispersion medium of the release agent dispersion.
According to the invention, the release agent dispersion comprises at least one film-forming agent, in particular a filming agent and/or a gap filling agent. According to the invention, the film-forming agent can be utilized to treat an abrasive article in such a way that no strips or streaks remain on its surface as residue of a coating with the anti-adhesion agent.
A “film-forming agent” refers to a substance which is suitable and is in particular also provided for producing bonding of individual anti-adhesion agent particles to the surface of the abrasive article and/or to close gaps between individual anti-adhesion agent particles on the surface of the abrasive article. This makes it possible to produce a layer, in particular uniform layer, or a film, in particular uniform film—the covering layer according to the invention—from the many individual anti-adhesion agent particles applied to the surface of the abrasive article. The covering layer advantageously no longer has individual anti-adhesion agent particles capable of refraction of light. In other words, no light-refracting residues which lead—depending on the position on the surface of the abrasive article—to a nonuniform or inhomogeneous appearance (such as for example streaks or strips on the surface) remain on the surface of the abrasive article after carrying out the method of the invention. Thus, a uniform covering layer which appears optically transparent (or in some cases also translucent) through to optically slightly opaque is produced on the surface of the abrasive article. In particular, a covering layer having—depending on the position on the surface of the abrasive article—a uniform or homogeneous refractive index is made possible.
On the basis of present-day knowledge, the production of a uniform film which appears optically transparent through to optically slightly opaque appears to be possible by means of partial dissolution and joining of neighboring anti-adhesion agent particles and/or by filling-up of gaps between neighboring anti-adhesion agent particles. A film-forming agent which brings about partial dissolution and joining of (two or more) neighboring anti-adhesion agent particles will in the context of the present text be referred to as “filming agent”. In particular, the filming agent brings about adhesive bonding and filming (i.e. film formation) of adjacent anti-adhesion agent particles. In particular, this partial dissolution, joining, adhesive bonding (may also be characterized as melting) and/or filming of adjacent anti-adhesion agent particles is made possible at advantageously low temperatures in the range from 0° C. to 100° C., in particular from 15° C. to 80° C., very particularly from 30° C. to 60° C. The filming agent thus acts in a manner analogous to an adhesive which partially dissolves the materials of objects to be joined in the surface region and subsequently dries. As a distinction from a filming agent, a film-forming agent which brings about the filling of gaps between neighboring anti-adhesion agent particles will be referred to as “gap filler”. A gap filler advantageously has a refractive index similar to that of the anti-adhesion agent particles, so that no or only very little refraction of light occurs at the places filled with gap filler between adjacent anti-adhesion agent particles and the gap filler thus likewise serves to produce an optically transparent (or sometimes also translucent) but homogeneous covering layer.
In one embodiment of the method, the film-forming agent comprises at least one constituent which is suitable for partially dissolving anti-adhesion agent particles. The constituent can, for example, be selected from a list, where the list comprises at least organic acids, alcohols, amines, phosphanes, lactic acid, acetic acid, salts of lactic acid, salts of acetic acid, in particular ammonium salts of lactic acid (ammonium lactate) or ammonium salts of acetic acid (ammonium acetate), polyethylenimine, polyethylene glycol, urea and mixtures thereof. Polyethylenimine in particular has good properties as film-forming agent, in particular as filming agent, since it becomes solid and does not diffuse after treatment of the abrasive article, in particular does not diffuse into the abrasive article. Polyethylene glycol has been found to be an advantageous gap filler. Urea, which is partially dissolved by one of the abovementioned film-forming agents, is likewise suitable as good gap filler.
In an embodiment of the method, the release agent dispersion contains at least one surfactant. Surfactants which are able to achieve good leveling, i.e. good spread, of the release agent dispersion on the surface of the abrasive article while the abrasive article is being treated in the method of the invention are particularly suitable. A surfactant leads to an advantageous equalization of amounts of release agent dispersion applied to the surface if the release agent dispersion is not applied homogeneously over the surface (self-leveling). This equalization occurs by flow of the release agent dispersion.
In an embodiment of the method, the release agent dispersion is applied to the surface of the abrasive article at a temperature of the abrasive article in the range from 0° C. to 100° C., in particular from 15° C. to 80° C., very particularly from 30° C. to 60° C. In particular, a temperature of above 0° C. leads to evaporation of the dispersion medium water, with the anti-adhesion agent and the film-forming agent remaining on the surface of the abrasive article—where a gap filler fills gaps between anti-adhesion agent particles and/or a filming agent partially dissolves and joins adjacent anti-adhesion agent particles—and the optically homogeneous covering layer being formed in this way. The higher the temperature selected, the more quickly does evaporation of the dispersion medium occur. On the other hand, heating of the abrasive article to a high temperature is costly and complicated in terms of manufacturing technology. In one embodiment of the method, the release agent dispersion is applied to the surface of the abrasive article during the production process of the abrasive article, in particular after a process step of heating the abrasive article, very particularly before a process step for cooling the abrasive article. Accordingly, it is sufficient in order to maintain the proposed temperatures to treat the abrasive article in the still-hot state during or immediately after manufacture thereof—during which heating to typically above 70-140° C. is carried out in order to cure the binder. Here, heating means heating of the abrasive article to significantly above room temperature, i.e. above 30° C., in particular above 50° C., very particularly above 70° C. According to the invention, residual heat still present in the abrasive article can be utilized and it is not necessary to reheat the abrasive article in a heating oven in a (further) process step of after-treatment. Here, “production process” means the sequence of process steps which serve to manufacture and provide the abrasive article. In an embodiment, these process steps can be formed by (1) application of base binder to an abrasive article substrate, (2) sprinkling of abrasive grains onto the abrasive article substrate covered with base binder, (3) curing of the base binder, (4) application of a covering binder, (5) drying and/or curing of the resulting abrasive article by heating of the abrasive article, (6) cooling of the abrasive article and (7) finishing (stamping or laser cutting) of the abrasive article. According to the invention, the release agent dispersion can be applied to the surface of the abrasive article during the production process of the abrasive article, in particular after the process step (5) of heating to effect drying and/or curing of the abrasive article (also: drying process step), very particularly before the cooling process step (6) for the dried/cured abrasive article and the residual heat present in the abrasive article can be utilized in this way. Furthermore, the method of the invention can be integrated in this way into an existing process chain of the production process and a corresponding process facility, for example into an existing manufacturing plant, without further, in particular complicated, machines or restructuring being necessary in the process chain and/or process facility. In particular, no separate heating oven is therefore required and/or no double utilization of an existing heating oven for drying/curing (in process step (5)) and for later reheating in order to treat the abrasive article is necessary for carrying out the method. In one embodiment, the release agent dispersion can be applied directly “in-line” onto an abrasive article stock strip (referred as stock strip) moving through a manufacturing plant and which has previously been heated for drying and curing of the binder, with the dispersion medium water of the release agent dispersion evaporating and filming of the surface occurring to form the covering layer.
Furthermore, the covering layer produced by application of the release agent dispersion to the surface of the abrasive article can be dried in the process step for cooling the abrasive article by means of an air stream in such an embodiment of the method. Here, the cooling effect exerted on the abrasive article is reinforced and drying of the covering layer is at the same time accelerated.
The release agent dispersion can be applied to the surface of the abrasive article by means of doctor blade coating, rolling-on, printing, brushing or the like. In one embodiment of the method, the release agent dispersion is applied to the surface of the abrasive article by means of pulsed spraying. Pulsed spraying—i.e. repeated spraying with brief interruptions (intermittent spraying)—assists metering because the pressure and, associated therewith, droplet formation of the release agent dispersion applied to the surface of the abrasive article remain constant. Furthermore, the amount of release agent dispersion sprayed on can be altered in a simple way by varying the opening time of the spray valve (for example by changing the opening time from 10 milliseconds to 50 milliseconds per impulse). In particular, an otherwise necessary cleaning of adhesive boat and application roller(s) can be avoided in the cleaner process operation of spraying compared to a rolling of a solution onto the surface of the abrasive article as is known from the prior art.
In an embodiment of the method, the release agent dispersion has a solids content in the range from 20% to 60%, in particular from 25% to 50%, very particularly from 30% to 40%. The values according to the invention are advantageous solids contents for processing the release agent dispersion. A particularly high solids content makes it possible to achieve a high density of anti-adhesion agent particles sprayed on the surface of the abrasive article. On the other hand, a low solids content (i.e. a low-viscosity or fluid property) allows particularly good meterability and processability by means of the spray valves (spray nozzles), because these do not block. Furthermore, a release agent dispersion having a low solids content which has been sprayed onto the surface can distribute more readily on or over the surface (by flowing). In one embodiment, the solids content can be 33%.
The invention also provides an abrasive article which has been treated by a method according to the invention.
The invention is explained in more detail in the following description on the basis of embodiments depicted in the drawings. The drawings, the description and the claims contain numerous features in combination. A person skilled in the art will also advantageously look at the features individually and assemble them to give useful further combinations. Identical reference numerals in the figures denote identical elements.
The figures show:
The abrasive article 10 has been treated by the method according to the invention for treating an abrasive article 10, by a further covering layer 30 being applied to the surface 28 intended for grinding of the abrasive article 10. The application of the covering layer 30 is carried out by use of the method 100 according to the invention, cf.
In a first method step 102, a release agent dispersion comprising at least one anti-adhesion agent is provided. In this embodiment, the release agent dispersion further comprises a surfactant. This release agent dispersion here comprises, for example, water as dispersion medium, a stearate, in particular a calcium stearate, as anti-adhesion agent. The release agent dispersion here has a solids content in the range from 30% to 40%, for example 35%.
In method step 104, the release agent dispersion provided is admixed with at least one film-forming agent. Admixing is carried out, in particular, by blending or stirring the mixture of release agent dispersion and film-forming agent. The film-forming agent comprises, in particular, a filming agent and/or a gap filler. In an embodiment, the film-forming agent is a mixture of lactic acid and polyethylene glycol. In method step 106, the release agent dispersion which has been admixed with the film-forming agent is applied to the at least one surface 28 of the abrasive article 10. Application is carried out in this embodiment by pulsed spraying onto the surface 28 of the abrasive article 10 using at least one atomizer nozzle (not shown in more detail here). The pulsed spraying is carried out here by repeated intermittent spraying at an average frequency of 20 Hz, with valve opening times of about 20 milliseconds.
In process step 202, an abrasive article substrate 22, for example composed of vulcanized fiber, is provided. In process step 204, a base binder 24 is applied to the abrasive article substrate 22, for example by doctor blade coating or rolling-on. In process step 206, abrasive grains are sprinkled, for example by means of electrostatic sprinkling as is known from the prior art, onto the abrasive article substrate 22 which has been covered with base binder. In process step 208, the base binder 24 is firstly cured and subsequently coated in process step 210 with a covering binder 26, in particular by rolling-on or brushing-on. In process step 212, the abrasive article 10 obtained in this way is dried/cured (in particular the covering binder 26 is also cured) by conveying it through a heating oven and thus heating it. The heating oven is, for example, heated to 120° C. In parallel to these process steps 202 to 212, the method steps of the method 100 according to the invention can be carried out, in particular carrying out the method steps 102 to 104, as depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 220 672.4 | Nov 2018 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/081588 | 11/18/2019 | WO | 00 |
