Abrasive tool making process – material – or composition – With synthetic resin
Reexamination Certificate
1998-12-22
2001-05-29
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With synthetic resin
C051S295000, C051S297000, C051S306000
Reexamination Certificate
active
06238449
ABSTRACT:
BACKGROUND
This invention is directed to an abrasive article having an abrasive coating containing a siloxane polymer.
U.S. Pat. No. 5,152,917 (Pieper et al.) reports abrasive articles which have a structured abrasive coating comprising a plurality of precisely shaped abrasive composites bonded to a backing. The precisely shaped abrasive composites can have a variety of geometric shapes and are formed of a plurality of abrasive particles dispersed in a cured binder.
Structured abrasives can be made in a variety of different coating processes such as reported in U.S. Pat. No. 5,304,223 (Pieper et al.), U.S. Pat. No. 5,435,816 (Spurgeon et al.), U.S. Pat. No. 5,672,097 (Hoopman et al.), and WO 97/12727 (Hoopman et al.). One method of making structured abrasive is to first coat an abrasive slurry (i.e., a plurality of abrasive particles dispersed in a binder precursor) onto a backing. The slurry-coated backing is then brought into contact with a production tool comprising a series of precisely shaped cavities. The cavities have essentially the inverse shape and dimensions of the desired abrasive composites. The abrasive slurry flows into the cavities of the production tool. Next, the binder precursor is exposed to conditions to cure the binder precursor to form an abrasive coating which is bonded to the backing.
The production tool may comprise a continuous thermoplastic sheet or belt that has the desired pattern of precisely shaped cavities embossed into the surface. For a variety of reasons, it is desirable to re-use the production tool multiple times before disposal. In order to re-use the production tool, the previously manufactured abrasive composites must cleanly separate from the cavities of the production tool. If residual portions of abrasive composites remain in the production tool, the cavities will be obstructed, thereby preventing subsequently coated slurry from completely filling the cavities. This may result in a malformed abrasive coating which does not have the desired precisely shaped surface and/or abrasive coating weight.
What is desired is a means to re-use a production tool many times, without adversely affecting the abrasive article formed therefrom.
SUMMARY
This invention pertains to abrasive articles and to methods of making abrasive articles. More particularly, this invention relates to structured abrasive articles having abrasive coatings comprising a reactive siloxane polymer. It has been found that the addition of a reactive siloxane polymer to a structured abrasive coating aids the release of the abrasive coating from the production tool.
In one aspect of this invention, an abrasive article is provided which comprises a backing having adhered to at least one major surface thereof a structured abrasive coating comprising a plurality of abrasive particles dispersed in a binder. The binder comprises the reaction product of a binder precursor and at least one reactive siloxane polymer which is capable of reacting with the binder precursor. Binder precursors include free radically curable materials (e.g., acrylates or methacrylates) and cationically curable materials such as vinyl ethers. The reactive siloxane polymer may be represented by formula (I) or formula (II):
Formula (I) is:
where n is 50 to 1000.
In formula (I), R
1
is:
where n
1
is an integer from 3 to 12 and where n
2
is an integer from 3 to 10.
R
2
is independently methyl, ethyl, or phenyl.
R
3
is:
an aliphatic group having from 1 to 10 carbon atoms,
an aromatic group, preferably having from 6 to 12 carbon atoms.
where n
1
is an integer from 3 to 12 and where n
2
is an integer from 3 to 10.
Formula (II) is:
In formula (II), X is:
where n
3
is an integer from 5 to 500 and where the terminal oxygen atom of X is connected to the Si atom of formula (II).
R
4
is independently methyl, ethyl, or phenyl.
R
5
is independently:
where n
4
is an integer from 3 to 12 and where n
5
is an integer from 3 to 10.
As used herein “reactive siloxane polymer” or “siloxane polymer” refers to any of the polymers represented by formula (I), formula (II) or a mixture thereof. The reactive siloxane polymers represented by formulas (I) and (II) have at least one functional group that is capable of reacting with the binder precursor. Therefore, the siloxane polymer reacts with the binder precursor and becomes chemically bound (i.e., through covalent chemical bonds) to the cured binder. Functional groups include alpha, beta-unsaturated carbonyl groups (i.e., acrylates, methacrylates, thioacrylates, thiomethacrylates) or vinyl ether groups.
The abrasive coatings of abrasive articles of the present invention are preferably formed by coating an abrasive slurry on a production tool having a surface with a plurality of precisely shaped recesses and then curing the abrasive slurry while the abrasive slurry is both being borne on a backing and filling the precisely shaped cavities. The abrasive slurry comprises abrasive particles, a binder precursor, a reactive siloxane polymer, and desired optional ingredients. The abrasive coating has a structured surface. As used herein “structured abrasive coating” or “structured” means an abrasive coating having a surface topography comprising a plurality of precisely-shaped abrasive composites arranged on a backing in a predetermined array, wherein each composite has a predetermined precise shape. The predetermined array may be random or non-random. As used herein “precisely-shaped” is used to describe abrasive composites having a three dimensional shape defined by relatively smooth surfaced sides that are bounded and joined by well-defined sharp edges having distinct lengths with distinct endpoints defined by the intersections of the sides.
The present invention also relates to a method of making an abrasive article, the method comprising the steps of:
(a) providing an abrasive slurry comprising a plurality of abrasive particles, a binder precursor and a reactive siloxane polymer of formulas (I) or (II) or a mixture thereof;
(b) providing a production tool, wherein the production tool has a plurality of precisely shaped cavities;
(c) applying the abrasive slurry into the cavities of the production tool such that the abrasive slurry is present between the production tool and a major surface of a backing;
(d) exposing the abrasive slurry to an energy source to initiate the cure of the binder precursor; and
(e) removing the abrasive article from the production tool.
Curing converts the abrasive slurry into an abrasive coating by converting the binder precursor into a cured binder. It is believed that the siloxane polymer aids in the release of the abrasive coating from the production tool. Release of the abrasive coating from the production tool is important since there is a tendency for small portions of the abrasive coating to stick to the production tool and to remain adhered to the inside of the cavities of the production tool after the abrasive article has been removed. This results in abrasive articles having malformed abrasive coatings and may reduce the number of times that the production tool may be reused, since it becomes clogged with debris from the abrasive coating. If the abrasive coating can be consistently removed cleanly from the production tool then the production tool may be reused many times.
In addition to aiding the release of an abrasive coating from a production tool, the siloxane polymer may reduce the tendency of the abrasive article to load. Loading refers to the tendency for debris generated from sanding to become lodged in between the abrasive particles or in between adjacent abrasive composites.
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patent: 4170481 (1979-10-01), Akama et al.
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Chou Yeun J.
Fraser Scott K.
Woo Edward J.
3M Innovative Properties Company
Marcheschi Michael
Pribnow Scott R.
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