Abrasive article with seamless backing

Details Abrasive article with seamless backing Abrasive article with seamless backing

1998-09-15

2002-10-15

Watkins, III, William P. (Department: 1772)

Stock material or miscellaneous articles

Structurally defined web or sheet

Continuous and nonuniform or irregular surface on layer or...

C428S149000, C428S423100, C051S295000, C051S297000, C442S063000, C442S164000, C442S167000

Reexamination Certificate

active

06465076

ABSTRACT:

BACKGROUND
The present invention relates to seamless backings for seamless coated abrasive articles. Additionally, this invention relates to methods of preparing seamless backings and seamless coated abrasive articles.
Backings or substrates used in coated abrasive articles are typically made of paper, polymeric materials, cloth, non-woven materials, vulcanized paper, or combinations of these materials. Many of these materials provide unacceptable backings for certain applications because they do not have sufficient strength, flexibility, or impact-resistance. In addition, some of these materials age too rapidly which is unacceptable. Furthermore, some of the materials are sensitive to liquids that are used as coolants and cutting fluids. Accordingly, early failure and poor functioning can occur in certain applications.
In a typical manufacturing process, a coated abrasive article is made by feeding a preformed backing in a continuous web form through a series of coating and curing steps wherein binder layers and abrasive particles are applied. The coated web is then converted into a desired construction, such as a sheet, disc, belt or the like. One useful construction of a coated abrasive article is an endless coated abrasive belt (i.e., a continuous loop of coated abrasive material). In order to form such an endless belt, the web form is typically cut into an elongate strip of a desired width and length. The ends of the elongate strip are then joined together to create a “joint” or a “splice”. Two types of splices are common in endless abrasive belts. These are the “lap” splice and the “butt” splice.
Although endless coated abrasive belts containing a splice in the backing are widely used in industry today, these products suffer from some disadvantages which can be attributed to the splice. For example, the splice is generally thicker than the rest of the coated abrasive belt, even though the methods of splicing generally used involve attempts to minimize this variation in the thickness along the length of the belt. This can lead to a region on the workpiece with a “coarser” surface finish than the remainder of the workpiece, which is highly undesirable, especially in high precision grinding applications. For example, wood with areas having a coarser surface finish will stain darker than the remainder of the wood. Also, the splice can be the weakest area or link in the coated abrasive belt. In extreme cases the splice may break prematurely before full utilization of the coated abrasive belt, which leads not only to waste, but potential hazard. Belts have therefore often been made with laminated liners or backings to give added strength and support. Such belts can be relatively expensive and, under certain conditions, can be subject to separation of the laminated layers. In addition, abrading machines that utilize a coated abrasive belt may have difficulty in properly tracking and aligning the belt because the splice creates a discontinuity in the coated abrasive belt. Furthermore, the spliced area can be undesirably more stiff than the remainder of the belt, and belts including such a splice may put undesirable “chatter” marks on the workpiece. Finally, the splice in the belt backing adds considerable expense in the manufacturing process of coated abrasive belts.
There are known processes for producing seamless abrasive belts. For example, Ball (U.S. Pat. No. 2,404,207) discloses belts produced by a method that utilizes a carrier belt that is rotated around support rolls. A comb removes a carded membrane from a stripper roll to thereby deposit the carded membrane upon the rotating carrier belt. Accordingly, layers of carded membrane are incrementally deposited around a peripheral surface of the carrier belt as the carrier belt is rotated around the support rolls. The carded membrane can be comprised of fibrous materials such that layers of fibrous materials form a web about the carrier belt. A pressure roll is used to compact the web and impregnate the web with an adhesive binder material. Abrasive particles can also be distributed upon the carrier belt through two different control hoppers.
PCT International Publication No. WO 93/12911, published Jul. 8, 1993, discloses coated abrasives using fiber reinforced polymeric backings. In producing the backing, the fibers are engulfed by a polymer and the polymer is then solidified or cured, depending on the polymer's chemistry. Abrasive particles are then adhered to the backing by a subsequent resin coating applied to the backing (sometimes referred to as a “make” coating), typically a resole phenolic resin. The procedures for making the fiber reinforced backings are essentially batch procedures.
U.S. Pat. No. 5,681,612 (Benedict et al.) reports methods for preparing endless, flexible, seamless abrasive backings containing an organic binder material and a fibrous material embedded therein. The preferred method of forming endless, seamless abrasive backings in Benedict et al. is a batch process. The circumference of the belt. The backing binder precursor is coated onto the periphery of the drum and is solidified by exposure to an energy source (e.g., thermal or radiation energy). Before the backing can be removed from the drum, the binder precursor must be sufficiently cured or polymerized so that the binder precursor retains its shape (i.e., does not flow substantially) when removed from the drum.
In Benedict et al., preferred organic binder materials are thermosetting resins such as epoxy resins, urethane resins, polyester resins, or flexible phenolic resins. The most preferred resins are epoxy resins and urethane resins, at least in part because they exhibit acceptable cure rate, flexibility, thermal stability, strength and water resistance. Although these binder materials exhibit acceptable cure rates for thermally cured systems, they typically require a thermal cure on the drum for at least 20 minutes. Since the method of making endless, seamless abrasive backings is a batch process, the production rate is proportional to the time it takes to cure the binder precursor on the drum. For this reason, it is desirable to provide faster method of producing endless, seamless abrasive backings. In addition, it is desirable to provide a backing binder which has improved performance, for example, a decreased sensitivity to water and increased thermal resistance.
SUMMARY
The present invention provides seamless backings for seamless coated abrasive articles (i.e., coated abrasive belts or loops) which have improved properties over known seamless backings. For example, the backing binder of a seamless backing of the present invention is more resistant to water (i.e., a lower water absorption) than conventional backing binders. In addition, the backing binder can be cured very quickly by exposure to radiation energy (e.g., ultraviolet light) allowing seamless backings of the present invention to be rapidly manufactured.
In one aspect, the present invention provides a seamless backing in the form of a belt (i.e., having a length, a width, a first and second generally parallel side edges, a first major exterior surface, and a second major interior surface). The seamless backing includes a backing binder comprising an interpenetrating polymer network formed by the polymerization of a backing binder precursor. The backing binder precursor includes:
(i) an aromatic polyisocyanate prepolymer;
(ii) a polyol curative;
(iii) an acrylated urethane; and
(iv) at least one polymerization agent.
The seamless backing further includes at least one fibrous reinforcing material which is engulfed within the backing binder. The term “seamless” means that the backing has a substantially uniform thickness or caliper throughout. That is, it is free from thickened areas resulting from distinct splices or joints. This does not preclude, however, splices and/or gaps in a fibrous reinforcing material embedded within the backing. The term “engulfed” means that the fibrous reinforcing material is essentially completely encapsulated or embedded within the backing

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