Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-01-08
2004-11-16
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C523S145000, C524S594000
Reexamination Certificate
active
06818707
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a low cost binder composition comprising a blend of a thermosetting spray dried phenolic resole resin and a phenolic crystalline compound having two or more hydroxyphenyl groups. The binder, among other uses, finds utility in the preparation of molding compounds.
BACKGROUND OF THE INVENTION
Commercially, the phenolic powder molding industry is dominated by novolac powders. Thermosetting phenolic novolac molding powders are prepared in 5 distinct steps:
(1). Reacting phenol with aqueous formaldehyde under strongly acidic conditions.
(2). Distilling the reaction mixture to remove excess phenol and water.
(3). Flaking the hot phenolic novolac melt on a cold flaker belt into a handleable solid.
(4). Grinding the resulting solid thermoplastic novolac flake into a powder.
(5). Blending the novolac powder with powdered hexamethylenetetramine (hexa) to make it thermoset.
Thermosetting, mainly compression molded articles, are then produced by compounding the novolac-hexa powders into a wide variety of fillers, e.g., friction compounds like barytes for automotive brake pads, abrasive compounds like alumina for grinding wheels, refractory aggregates like magnesia and graphite for refractory bricks, glass fibers and fillers for automotive engine intake manifolds, inert fillers like calcium carbonate for lamp cement pastes, and in many other matrixes for articles that require good modulus retention at elevated temperatures. Also, the excellent adhesive properties of novolac molding powders make them useful for compounding with glass and textile fibers for automotive acoustical insulation, wood fiber for automotive interior door panels, textile fibers for automotive interior package trays, and wood flour for toilet seat moldings, etc.
Novolac powders are particularly suitable for making thermoset molding compounds as they: are free flowing and easily blended with other fibrous, granular or powdered components, including hexa; are resistant to sintering; have excellent hot flow characteristics since the powder melts with good fluidity at mold temperature, and flows, to wet out the matrix and fill voids before it thermosets; can be molded with short cycles; have excellent heat resistance and dimensional stability; have a very low flame smoke rating; and are low in cost.
Novolac molding powders, however, do suffer from one significant problem, mainly, the liberation of odiferous hexa decomposition products, such as trimethylamine and ammonia, during the high temperature molding process. High odor is particularly objectionable in articles molded for automotive interior components.
It is an object of this invention to provide novel thermosetting adhesive compositions.
It is another object of the present invention to provide a novel molding powder that retains some or all of the advantages described above for the novolac-hexa powders while producing molded articles that do not contain objectionable odors.
These objects are achieved by using a blend of a spray dried resole resin with a phenolic crystalline compound having two or more hydroxyphenyl groups.
DESCRIPTION OF THE PRIOR ART
Phenolic resole resins are prepared with an excess of formaldehyde and are therefore thermosetting and, unlike thermoplastic novolacs which are prepared with an excess of phenol, do not require compounding with hexamethylenetetramine (hexa, a formaldehyde source) to become thermosetting. The thermosetting, temperature sensitive nature of phenolic resoles, however, makes them much more difficult to prepare in solid form versus phenolic novolacs. Converting the resole to solid form requires significant heat input to remove the large amounts of water added from the aqueous formaldehyde used to make the resole. Too much temperature exposure may advance the resole to a state that renders it useless as a molding powder.
The fundamentally simpler and less expensive nature of phenolic resoles, often described as “one step” or “one stage” resins versus the “two step” or “two stage” (compounding with hexamine) novolacs, however, has fostered the description, in the prior art, of many different minimal heat input drying techniques for the preparation of solid phenolic resole resin molding powders, including:
(1). U.S. Pat. No. 5,047,275 of September 1991; U.S. Pat. No. 4,950,433 of August 1990 and U.S. Pat. No. 5,019,618 of May, 1981, all by S. Chiu which describe improving spray dryability of a low advanced phenol-formaldehyde resin by inclusion of a water soluble boron oxo compound.
(2). U.S. Pat. No. 4,708,967 of November 1987 by Ferentchak, et al. describes a centrifugal atomizer having a porous sintered metal filter ring, producing hollow resin particles.
(3). U.S. Pat. No. 4,626,569 of December 1986 by Waitkus, et al. example XXa, describes the solid pan cooling method, where substantially all of the water is removed by distillation and the hot, approx. 90 E C., molten thermosetting composition is discharged very quickly from the reaction vessel into thin layers in cooling pans where it cools rapidly forming a grindable solid, while retaining enough hot flow character to function as a molding powder.
(4). U.S. Pat. No. 4,542,204 of September 1985 by Shibahara, et al. describes dispersing the hot condensate in cold water with mechanical dewatering.
(5). U.S. Pat. No. 4,424,300 of January 1984 by O. Udvary, et al. describes spray drying by the spinning disc atomization process.
(6). U.S. Pat. No. 4,419,477 of December 1983 by Saeki, et al. in preparation example 2 describes a solid resole resin prepared by dehydration with distillation and rapid solid pan cooling.
(7). U.S. Pat. No. 4,414,378 of November 1983 by Koyama, et al. describes a reaction in dilute aqueous solution where a solid, reactive and fusible resole resin particle forms directly from a phenol formaldehyde reaction catalyzed with hydrochloric acid.
(8). U.S. Pat. No. 4,317,901 of March 1982 by H. Cosway, describes additions of polyvalent cationic precipitants with mechanical dewatering.
(9). U.S. Pat. No. 4,206,095 of July 1980 by J. Wynstra, et al. describes an aqueous suspension of a particulate resole with mechanical dewatering.
(10). U.S. Pat. No. 4,182,696 of January 1980 by Wynstra, et al. describes a precipitation and mechanical dewatering process.
(11). U.S. Pat. No. 4,098,770 of July 1978 by Berchem et al. describes a spray drying process.
Of the above methods only the spray drying techniques, such as described by Berchem, et al., Udvardy, et al., Ferentchak, et al., and S. Chiu, set forth hereinabove, all of which are incorporated herein by reference in their entirety, have reasonable economics and have gained significant commercial importance such as for use as adhesives in wood composite boards.
Thermosetting spray dried resoles, however, while having enough flow to function well as adhesives, do not have sufficient hot flow to function as molding powders, also referred herein simply as binders. Additionally, the spray dried resoles cause sticking in the molding equipment which, among other shortcomings, interferes with the flow of the molten binder. Resoles formulated to have better flow characteristics, such as those prepared by the method of Waitkus, may form sticky agglomerated masses in the hot air conveyance equipment and may sinter after cooling to a solid mass over a short period of time in their storable container due to inadequate moisture removal. The solid pan cooling method described by Waitkus while having the capability to produce material with acceptable hot flow has poor economics, as batch sizes must be kept small due to the requirement for very rapid discharge of the hot, molten thermosetting resole from the reaction vessel.
Several inventors have reported on improving the hot flow properties of solid phenolic resoles prepared via the solid pan cooling method by admixing the solid resole with phenolic novolac resins, including:
(1). U.S. Pat. No. 4,426,484 of January 1984 by Saeki, et al. which describes mixing a solid resole with a resorcinol novolac solid resin to improve cure
Borden Chemical, Inc.
Cantor & Colburn LLP
Yoon Tae H.
LandOfFree
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