Abrasive tool making process – material – or composition – With synthetic resin
Reexamination Certificate
2001-09-28
2003-06-03
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With synthetic resin
C051S307000, C051S308000, C051S309000, C051S295000, C051S293000
Reexamination Certificate
active
06572666
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods of making abrasive articles in which abrasive particles are bonded to a substrate by a binder. In particular the invention relates to methods of making coated abrasive and nonwoven, fibrous abrasive articles.
RELATED ART
Conventional coated abrasive articles have an abrasive layer of abrasive particles and binder attached to a backing material. In one common form the abrasive layer includes make and size layers of binder. Such coated abrasive articles are typically made by applying a the make layer (e.g., a resin) onto a major surface of the backing material, at least partially embedding abrasive particles into the make layer, at least partially solidifying (e.g., curing) the make layer, applying the size layer (e.g., a resin) over the abrasive particles and make layer, and solidifying (e.g., curing) the size layer. One function of the size layer is to improve the retention of the abrasive particles to the backing material.
Coated abrasive articles optionally further include other layers known in the art, including presize, backsize, tie, and supersize layers Functions of additional layers include providing a grinding aid, lubricant, or antistat.
Conventional nonwoven abrasive articles are typically made of nonwoven webs constituted of a network of synthetic fibers or filaments which provide surfaces upon which abrasive particles are adhesively attached by a binder.
Nonwoven abrasive articles have employed a “make” coat of resinous binder material in order to secure the abrasive particles to the fiber or filament surface backing as the particles are oriented on the backing or throughout the lofty fibrous mat. A “size” coat of resinous binder material also has been applied over the make coat and abrasive grains in order to anchor and reinforce the bond of the abrasive particles to the backing or fibrous mat. A conventional sequence of fabrication steps for making nonwoven abrasive articles involves: first applying the make coat and abrasive particles to the backing or lofty fibrous mats; partially curing the make coat; applying the size coat; and finally, the make and size coats are fully cured.
In another known process for the production of nonwoven abrasive articles a pre-bond coat is applied to the fibrous mat followed by a make coat which contains abrasive particles. The pre-bond coat may be applied by roll coating and the make coat by spraying each side of the web.
Binder resin used to make the abrasive articles are frequently the same or similar to avoid compatibility problems potentially associated with the use of dissimilar resins. Exemplary details regarding binders for abrasive articles can be found, for example, in U.S. Pat. No. 5,980,597 (Loughlin) and U.S. Pat. No. 5,478,908 (Hesse et al.). Thermally curable binders are one type of resin that has been used to make coated abrasives and nonwoven fibrous abrasive articles as they tend to provide abrasive articles having excellent properties (e.g., enhanced heat resistance). Conventional thermally curable resins include phenolic resins, urea formaldehyde resins, urethane resins, melamine resins, epoxy resins, and alkyd resins. Among these, phenolic resins have been used extensively to manufacture abrasive articles because of their thermal properties, availability, low costs and ease of handling. To render the resin precursors coatable, obtain the proper coating viscosities, and obtain defect free coatings, solvents are commonly added to the uncured resins.
There are two basic types of conventional phenolic resins: resole and novolac phenolic resins. Novolac phenolic resins are characterized by being acid catalyzed and having a ratio of formaldehyde to phenol of less than one, typically between 0.5:1 to 0.8:. Acidic catalysts suitable for novolac phenolic resins include sulfuric, hydrochloric, phosphoric, oxalic, and p-toluene sulfonic acids. Novolac phenolic are thermoplastic resins and in the cured form are brittle solids. Novolac phenolic resins are typically reacted with other chemicals to form a crosslinked solid. Resole phenolic resins are characterized by being alkaline catalyzed and having a ratio of formaldehyde to phenol of greater than or equal to one, typically from 1:1 to 3:1. Alkaline catalysts suitable for resole phenolic resins include sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide, organic amines, or sodium carbonate. Resole phenolic resins are thermosetting resins and in the cured form exhibit excellent toughness, dimensional stability, high strength, hardness, and heat resistance.
In formulating the phenolic resins, the monomers currently used in greatest volume are phenol and formaldehyde. Other noteworthy starting materials are the alkyl-substituted phenols, including cresols, xylenols, p-tert-butyl-phenol, p-phenylphenol and nonylphenol. Diphenols e.g. resorcinol (1,3-benzenediol and bisphenol-A (bis-A or 2,2-bis(4-hydroxyphenyl)propane) are employed in smaller quantities for applications requiring special properties.
In the production of adhesive coatings for nonwoven abrasive articles, one standard starting phenolic resin composition is a 70% solids condensate of a 1.96:1.0 formaldehyde: phenol mixture with 2% potassium hydroxide catalyst added based on the weight of phenol. The phenolic component of the phenolic resin is typically solid and requires the addition of solvent to render it soluble to react with the formaldehyde. The phenolic resin composition is typically 25 to 28% by weight water and 3 to 5% by weight propylene glycol ether to reduce the viscosity of the resin. Before this resin is used as a make or size coat, (i.e. to make it coatable), further viscosity reduction is often achieved using VOC (i.e. a volatile organic compound). A conventional phenolic resin make coat may contain up to 40% by weight of a VOC, such as isopropyl alcohol to reduce viscosity and make the phenolic compatible with resin modifiers (flexibilizers), while a size coat might contain up to 20% % by weight of a VOC, such as diethylene glycol ethyl ether. Unreacted phenol and formaldehyde in the final, cured resin also contribute to VOC.
To reduce emissions of VOC, progress has been made to modify suitable resin systems to replace organic solvents with water (see, e.g., U.S. Pat. No. 5,178,646 (Barber et al.) and U.S. Pat. No. 5,306,319 (Krishnan et al.)).
Although bisphenol/formaldehyde resin systems may have acceptable VOC levels, the use of these resins as make, size and pre-bond coats in abrasive articles does not provide abrasive articles having performance characteristics equivalent to abrasive articles having make, size and pre-bond coats of phenol/formaldehyde resins, particularly when coarse abrasive particles are used.
SUMMARY OF THE INVENTION
In one aspect, the present invention an abrasive article (e.g., a coated abrasive article or a nonwoven abrasive article) comprising abrasive particles bonded to a substrate by a bond system, wherein at least a portion of the bond system comprises a reaction product of components comprising a resole phenolic resin and a bisphenol/formaldehyde resin.
In another aspect, the present invention comprises an abrasive article comprising abrasive particles bonded to a substrate by a bond system, wherein at least a portion of the bond system is derived by curing a mixture of a resole phenolic resin and a bisphenol/formaldehyde resin.
In yet another aspect, the abrasive article comprises abrasive particles bonded to a substrate by a bond system wherein at least a portion of the bond system comprises polymeric material preparable by combining components comprising a resole phenolic resin and a bisphenol/formaldehyde resin.
In some embodiments of the present invention, the abrasive article is a coated abrasive comprising a backing material, a make coat having abrasive grains therein, and a size coat over the abrasive grains, wherein at least one of the make coat or size coat comprises the bond system. In other embodiments of the present invention, the abrasive article is a nonwoven abrasive
Ball Alan R.
Lambert Karen E.
Maljean Sandrine
Nettleship David A.
3M Innovative Properties Company
Allen Gregory D.
Marcheschi Michael
LandOfFree
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