Abrasive tool making process – material – or composition – With synthetic resin
Reexamination Certificate
2002-09-12
2004-01-27
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With synthetic resin
C051S307000, C051S308000, C051S309000, C051S295000
Reexamination Certificate
active
06682574
ABSTRACT:
RELATED APPLICATION
This application claims priority from British Application Number 0122153.0, filed Sep. 13, 2001.
FIELD OF INVENTION
This invention relates to a catalyzed urea formaldehyde binder for use in abrasive articles, a method of making the binder, abrasive articles made therewith and in particular to coated abrasive articles and to a method of making coated abrasive articles.
DISCUSSION OF RELATED ART
Coated abrasive articles generally contain an abrasive material, typically in the form of abrasive grains, bonded to a backing via of one or more adhesive layers. Such articles usually take the form of sheets, discs, belts, bands, and the like, which can be adapted to be mounted on pads, wheels or drums. Abrasive articles can be used for sanding, grinding or polishing various surfaces of, for example, steel and other metals, wood, wood-like laminates, plastic, fiberglass, leather or ceramics.
The backings used in coated abrasive articles are typically made of paper, polymeric materials, cloth, vulcanized fiber or combinations of these materials. A common type of bond system includes a make coat, a size coat, and optionally a supersize coat. The make coat typically includes a tough, resilient polymer binder that adheres the abrasive particles to the backing. The size coat, which also typically includes a tough resilient polymer binder that may be the same as or different from the make coat binder, is applied over the make coat and abrasive particles to further reinforce the particles. The supersize coat, including one or more antiloading ingredients or perhaps grinding aids, may then be applied over the size coat if desired.
In a typical manufacturing process, a coated abrasive article is made in a continuous web form and then converted into a desired construction, such as a sheet, disc, belt, or the like. Binders for the purpose of adhering the abrasive granules to the backing include the traditional phenolic resins, urea-formaldehyde resins, hide glue, varnish, epoxy resins, and polyurethane resins, or more recently a class of radiation cured crosslinked acrylate binders; see, e.g., in U.S. Pat. No. 4,751,138 (Tumey, et al.) and U.S. Pat. No. 4,828,583 (Oxman, et al.).
High performance coated abrasive articles have traditionally used phenolic size resins. Such resin systems suffer from the disadvantage that they require high temperatures for a prolonged time for optimum curing. This prevents the use of such resins with some polymeric backings either because they will not withstand the cure temperature or because the high cure temperature may result in dimensional instability of the coated sheet, e.g., curling upon cooling to ambient temperature. Additional disadvantages are that phenolic resins tend to be more expensive and have more undesirable emissions compared to urea-formaldehyde resin systems.
Urea formaldehyde (UF) was first patented for use as an adhesive for coated abrasives by 3M Company (“3M”) in the mid 1930's (Great Britain Pat. No. 419,812). Since that time a number of different coated abrasive products have been made with acid catalyzed UF resins. Today, the two most common catalysts used with UF resins are aluminum chloride (AlCl
3
) and ammonium chloride (NH
4
Cl).
Urea-aldehyde resins have enjoyed great success in coated abrasives. However, the need to reduce the use of solvents and unreacted reactants which contribute to release of volatile organic hydrocarbons (VOC) in the process of making coated abrasives and the need to increase the quality of the abrasives while maintaining or increasing their level of performance are challenging the industry.
When aluminum chloride is used as the catalyst, a higher temperature than normal must be used to cure the urea-aldehyde resin, which in turn leads to curling of edges of the coated abrasive. Also, the gel time, pot life and peak exotherm temperatures are all dependent on the concentration of the aluminum chloride. Consequently, there is a trade-off between aluminum chloride concentration and curing conditions, especially with low free-aldehyde UF resins.
Unlike aluminum chloride catalysis, the gel time, pot life and peak exotherm temperatures are all independent of the ammonium chloride concentration. However, the activity (ability of the catalyst to catalyze the reaction) of ammonium chloride is dependent on the free formaldehyde concentration in the binder precursor composition. With low free aldehyde resins, the ammonium chloride does not activate the condensation reaction very readily until a sufficient temperature is reached. However, as mentioned above, increased temperature tends to curl the edges of the coated abrasive and does not render performance improvements.
U.S. Pat. No. 5,611,825 (Engen, et al.) reports coated abrasives comprising a backing coated on at least one major surface thereof with an abrasive coating comprising a binder and abrasive particles. The binder is comprised of a solidified urea-aldehyde resin, the solidified urea-aldehyde resin being derived from a binder precursor comprising a urea-aldehyde resin having a low free aldehyde content and a co-catalyst. The co-catalyst is a catalyst consisting essentially of a Lewis acid, preferably aluminium chloride or an organic amine salt or an ammonium salt, preferably ammonium chloride. Preferred linear organic amine salts are those selected from the group of compounds having the general formula:
(X
31
)
+
H
3
N(CH
2
)
n
NH
3
+
(Y
−
)
wherein X and Y are halide atoms that may be the same or different and n is an integer ranging from about 3 to about 10. An example of such a linear organic amine salt found useful is the dichloride salt of hexamethylene diamine, obtained by the acidification of an aqueous solution of hexamethylene diamine with hydrochloric acid (HCl). One branched chain organic amine salt found useful is that known under the trade designation “DYTEK-A,” available from E. I. duPont de Nemours & Co., Wilmington, Del., which is commonly known as 2-methyl-pentamethylene diamine.
Although urea-formaldehyde resins have been used as make, size and supersize resins in coated abrasives they are generally not able to match the performance of coated abrasive made with phenol-formaldehyde resins.
SUMMARY OF THE INVENTION
It has now been found that certain urea formaldehyde resin systems can provide comparable performance to phenol formaldehyde resins when used in the production of coated abrasives. According to the present invention there is provided a coated abrasive article comprising a backing having at least one major surface, a plurality of abrasive grains bonded to at least a portion of the one major surface of the backing by at least one binder, wherein the binder comprises an urea formaldehyde resin precursor cured in the presence of a sole catalyst which consists essentially of at least one salt of an acid with a diamine of the formula:
H
2
N—R—NH
2
in which R is an alkylene group of 3 to 10 carbon atoms, wherein the acid is selected from the group consisting of hydrochloric, citric, nitric, sulphuric, acetic, phosphoric and combinations thereof.
In a further aspect, the invention provides a method of making a coated abrasive which comprises coating a major surface of a backing with a plurality of abrasive grains and a binder comprising a urea formaldehyde resin precursor solution and a solution of a sole catalyst which consists essentially of at least one salt of an acid with a diamine of the formula:
H
2
N—R—NH
2
in which R is an alkylene group of 3 to 10 carbon atoms, wherein the acid is selected from the group consisting of hydrochloric, citric, nitric, sulphuric, acetic, phosphoric and combinations thereof, and curing the urea formaldehyde resin precursor. Curing is typically accomplished by heating at a temperature of at least 60° C., preferably at a temperature in the range of about 75° C. to 140° C., or a temperature in the range of 80° C. to 90° C. for 40 minutes or less, or at a temperature in the range of 115° C. to 125° C. for less than 10 minutes.
In a further aspect, the invention prov
Carter Christopher J.
Darwood Richard J.
Stubbs Roy
3M Innovative Properties Company
Allen Gregory D.
Marcheschi Michael
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