Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-12-12
2002-03-26
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S843000, C524S845000
Reexamination Certificate
active
06362275
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
NA
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
NA
BACKGROUND OF THE INVENTION
The present invention relates to aldehyde resins having low amounts of free aldehydes. More particularly the present invention relates to aldehyde resins formed in the presence of an amino acid. In the invention aldehyde resins refer to resins derived from the reactions of a phenol, urea, melamine or a mixture thereof and an aldehyde. Examples of aldehyde resins include phenol formaldehyde resins, urea formaldehyde resins, melamine formaldehyde resins, melamine-urea-formaldehyde resins, and the like. These resins are well known in the art.
Phenol formaldehyde resins were the first true synthetic resins to gain commercial acceptance early in the twentieth century. These phenolic resins are the product of the reaction between phenol and formaldehyde. Novalacs are acid catalyzed phenol formaldehyde resins where typically an excess of phenol used. Resoles are the base catalyzed reaction product of phenol and an excess of formaldehyde. In commercial production resoles are normally processed to a workable viscosity; then subsequently polymerized to high molecular weight polymers by simple heating. Urea formaldehyde resins are typically prepared by the condensation of urea and formaldehyde at a pH of between 4 and 7 and at a temperature close to boiling point. Melamine formaldehyde and melamine-urea-formaldehyde resins undergo condensation reactions with an aldehyde in a manner analogous to that of urea. U.S. Pat. No. 5,681,917 discloses a method of making melamine-urea-formaldehyde resins and is herein incorporated by reference.
A problem that exists with aldehyde resin systems is the amount of free formaldehyde that exists in the resins both during storage and upon cure. Formaldehyde is considered toxic and a carcinogen. The American Conference of Governmental and Industrial Hygienists has lowered its TLV to 0.3 ppm. Due to these health concerns much effort has been expended attempting to obtain aldehyde resins with reduced free formaldehyde levels.
An abstract of Japanese patent application 60149638 discloses the use of polyvinyl alcohol to reduce the odor from free formaldehyde in foams produced from resole type phenol-formaldehyde resins. U.S. Pat. No. 3,917,558 discloses the use of nitro compounds such as nitromethane to reduce the concentration of free formaldehyde in phenol-formaldehyde resins. U.S. Pat. No. 5,705,537 discloses the addition of a proteinaceous material, cysteine, glutamic acid, glycine, isoleucine, lysine, phenylalanine, serine tryptophan or mixtures thereof to a phenolic foam composition consisting of a phenol formaldehyde resole resin. The reference discloses the addition of the aldehyde reducing agent to the already formed resin. The use of melamine, urea and sodium sulfite have also been suggested for use as scavengers for formaldehydes. Some reduction in free formaldehyde concentration was noted in uncured resins where these scavengers were used, however during curing at high temperatures free formaldehyde levels increased over precure levels.
There are no suggestions in the art to utilize amino acids and in particular glycine to reduce the free formaldehyde in aldehyde resins by adding the amino acids to the reaction mixture of the aldehyde resin.
BRIEF SUMMARY OF THE INVENTION
The present invention describes aldehyde resins having reduced free formaldehyde. Particularly the invention relates to the use of amino acids to effectively reduce the amount of free aldehyde in the resins. More particularly the invention relates to the use of glycine as a component in aldehyde resins to reduce the free formaldehyde in aldehyde resins. The use of glycine in aqueous aldehyde resin systems also provides the added benefit of increased water tolerance over time.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
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DETAILED DESCRIPTION OF THE INVENTION
The present invention describes aldehyde resins having reduced amounts of free formaldehyde and methods of making the resins. In addition when glycine is added to the reaction mixture of an aqueous aldehyde resin system the resin especially resoles exhibit increased water tolerance over time.
The aldehyde resins for which amino acids will function to reduce free aldehyde include those aldehyde resins known in the art such as phenol formaldehyde, urea formaldehyde, melamine formaldehyde or melamine-urea-formaldehyde.
Phenols used in the preparation of phenol formaldehyde resins include one or more of the phenols which have heretofore been employed in the formation of phenolic resins and are not substituted at either the two ortho positions or at one ortho position and the para position. Such unsubstituted positions are necessary for the polymerization reaction.
Any one or all of the remaining carbon atoms of the phenol ring can be substituted. The nature of the substituent can vary widely and it is only necessary that the substituent not interfere with the polymerization of the aldehyde with the phenol at the ortho and/or para position. Substituted phenols employed in the formation of phenolic resins include alkyl substituted phenols, aryl substituted phenols, cyclo-alkyl substituted phenols, aryloxy substituted phenols, and halogen substituted phenols. The foregoing substituents can contain from 1 to 26 carbon atoms and preferably from 1 to 12 carbon atoms.
Specific examples of suitable phenols include 2,6-xylenol, o-cresol, p-cresol, 3,5-xylenol, 2,3,4-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol. Multiple ring phenols such as bisphenol A are also suitable.
The urea used to prepared urea formaldehyde resins is available in many forms. Solid urea, such as prill, and urea solutions, typically aqueous solutions are commonly available.
The melamine used in the preparation of melamine and melamine urea formaldehyde resins may be totally or partially replaced with other aminotriazine compounds. Other aminotriazine compounds include substituted melamines, cycloaliphatic guanamines or mixtures thereof. Substituted melamines include alkyl melamines and aryl melamines which can be mono-, di- or tri-substituted. Examples of alkyl substituted include monomethyl melamine, dimethyl melamine, trimethyl melamine, monoethyl melamine and 1-methyl-3-propyl-5-butyl melamine. Examples of aryl substituted melamine include monophenyl melamine and diphenyl melamine.
Aldehydes used to react with the phenol, urea, melamine and combinations thereof have the general formula RCHO wherein R is a hydrogen or hydrocarbon radical having from 1 to 8 carbon atoms. Examples of aldehydes reacted with the phenol, urea, melamine or mixtures thereof include any of the aldehydes heretofore employed in the formation of aldehyde resins such as formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde, paraformaldehyde and benzaldehyde.
Suitable catalysts used to promote the reaction of the phenol, urea, melamine and mixtures thereof and the aldehyde are also present. Novalak type phenolic resins are typically prepared in the presence of strong acids such as sulfuric acid, sulfonic acid, oxalic acid or occasionally phosphoric acid. Novalak type resins may also be prepared using divalent metal catalysts containing Zn, Mg, Mn, Cd, Co, Pb, Cu, and Ni. Resole type phenolic resins are generally prepared in the presence of basic catalysts such as NaOH, Ca(OH)
2
and Ba(OH)
2
. Other basic catalysts such as triethyl amine may be used to prepare resoles. The catalysts may be used alone or as mixtures. The catalysts used in urea, melamine and melamine-urea formaldehyde resins are well known in the art.
Typically, a dual catalyst system is used to prepare urea, melamine, and melamine-urea resins. Initially the reaction is carried out in the presence
Mani Ramanathan
Robbins Warren L.
Ashland Inc.
Cain Edward J.
Connaughton Martin
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