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
2001-12-06
2004-06-22
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S330400, C525S330500, C525S385000, C525S386000, C523S102000
Reexamination Certificate
active
06753383
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for removing free aldehydes from compositions containing them.
2. Background Art
Aldehydes, and especially formaldehyde, are known irritants. Furthermore, some aldehydes, for example formaldehyde and acetaldehyde, are considered possible carcinogens. The latter are among the most important industrial chemicals, are widely used and reacted, but are also inadvertently released.
Formaldehyde, for example, is frequently used in the production of woodbase materials as a phenol-formaldehyde resin or a melamine-formaldehyde resin. Woodbase materials employing such resins as adhesives or binders regrettably release formaldehyde into the environment after production. Owing to its high volatility, formaldehyde is also frequently to be found in the offgas of a variety of industrial processes. For example, when textiles are treated with formaldehyde derivatives such as dimethyloldihydroxyethyleneurea (DMDHEU) or other methylol-functional compounds, they will release a not inconsiderable portion of the chemically-bound formaldehyde into the environment as free formaldehyde. As a further example, houses built with formaldehyde-releasing materials may release formaldehyde into the rooms through the masonry. One method of addressing this problem is presented in DE 19809479 A1, which describes a method for remediating formaldehyde-polluted interiors through the use of sheep's wool.
Polymer dispersions are frequently prepared using formaldehydic compounds as fungicides, monomers or polymerization initiators. As a result, the ready-produced dispersion will contain major amounts of formaldehyde which can be released in later use. For example, it is known to use polymer dispersions as binders for consolidating and coating fibrous structures such as wovens, nonwovens and waddings comprised of textile fiber, textile yarns, or woodbase materials. The polymer dispersions are frequently copolymer dispersions of (meth)acrylate or vinyl ester copolymers which contain self-crosslinking comonomer units with N-methylol or N-methylol ether functions to improve strength. The copolymers customarily contain up to 10% by weight of units derived from N-methylol(meth)acrylamide (NMAA). A disadvantage of these binders is the release of formaldehyde due to hydrolytic cleavage of the N-methylol functionality.
Various strategies are proposed in the literature for reducing the level of free formaldehyde in polymer dispersions. These strategies generally utilize alternative, formaldehyde-free initiator systems, for example ascorbic acid. Such systems are capable of lowering the formaldehyde content by up to 80%, but have the disadvantage that they are very costly. The dispersions thus produced, however, can be produced and processed using conventional formulations and equipment.
EP-0778290 (U.S. Pat. No. 5,744,418) describes a process in which formaldehydic polymerizable initiator systems are replaced by aldehydes masked by bisulfite. When no HCHO-containing monomers are used, this leads to almost HCHO-free dispersions (<3 ppm HCHO).
U.S. Pat. No. 5,585,438, DE-A 3328456 (AU 8431608), U.S. Pat. No. 5,071,902, EP-A 0488605 (U.S. Pat. No. 5,143,954) and U.S. Pat. No. 5,326,814 disclose the use of N-methylolacrylamide as a crosslinker with conventional initiator systems, but with further addition of low molecular weight components as formaldehyde traps or acceptors to reduce free formaldehyde. The compounds chosen for use as formaldehyde traps react quickly and very quantitatively with formaldehyde to form harmless derivatives. Urea compounds, acetoacetates, dicyandiamide, and imidazoles have found application here. However, these formaldehyde scavengers work only over a limited pH range, lack stability in storage, or may have to be added in large quantities. Formaldehyde reductions of above 90% are achieved through use of such scavengers. The dispersions thus produced can likewise be produced and processed using conventional formulations and equipment. However, the scavenger may be responsible for adverse effects, for example discoloration in the course of the subsequent crosslinking or else an increased toxicity of the compounds added.
SUMMARY OF THE INVENTION
The present invention provides a process for reducing free aldehyde in aldehyde-containing or aldehyde-generating compositions without causing adverse consequences such as for example unpleasant odors, increased toxicity, or discoloration. These and other objects are surprisingly achieved by addition of thioamine compounds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention accordingly provides a process for reducing free aldehydes in dispersions, suspensions, emulsions or solutions, which comprises including therein thioamines of the general formula I or II:
where Y and Z are each a divalent organic radical of at least two carbon atoms and R
1
is an organic alkyl or aryl radical of 1 to 15 carbon atoms or hydrogen, or mixtures thereof.
Preference is given to compounds of the formula III or IV or their salts or esters:
where R
1
is an organic alkyl radical of up to 5 carbon atoms, an aryl radical, or hydrogen, R
2
is —(COO)
a
—E or —(CONH)
a
—E, where a is 0 or 1 and E is an organic radical of up to 10 carbon atoms or hydrogen, R
3
is a monovalent organic radical of up to 10 carbon atoms or hydrogen, R
4
and R
5
represent organic radicals of up to 10 carbon atoms or hydrogen and may be bonded to each other, subject to the proviso that R
4
and R
5
together must contain at least one carbon atom, and n is 0 or 1.
Particular preference is given to compounds of the formula III or IV or their salts or esters where R
1
is hydrogen or acetyl, R
2
is —COOH or hydrogen, R
3
is hydrogen, R
4
is hydrogen or methyl, R
5
is —COOH, —COOR, —CH
2
—COOR, —CH
2
—CN, optionally substituted aromatic, and n is 0 or 1.
These compounds include, for example but not by limitation, L-cysteine, D-cysteine, D,L-cysteine, N-acetylcysteine, cysteamine, homocysteine or their salts, esters or amides thereof and also their addition products (aminothioacetals or aminothioketals) with glyoxylic acid and pyruvic acid and their esters and amides, benzaldehyde, salicylaldehyde, vanillin, anisaldehyde, piperonal, acetophenone, cinnamaldehyde, citral, glucose, fructose, acetoacetate ester and acetylacetone. These naturally occurring amino acid derivatives are particularly safe toxicologically.
In the process according to the invention, free aldehyde present or being formed in dispersions, suspensions, emulsions or solutions is effectively bound by chemical reaction according to the general equation (1):
Surprisingly, the equilibrium of the reaction is distinctly on the side of the bound aldehyde even in the presence of water, so that this reaction can be used for removing aldehydes in water-containing systems. In this context, the compounds of the general formula I have the advantage that they are capable of binding aldehydes very quickly by chemical reaction. However, some of the compounds of the general formula I have the disadvantage that they are readily oxidizable (cysteine for example).
Permanent reduction of free aldehyde, for example in polymer dispersions, is thus not always attainable through use of compounds of the formula I, for example cysteine, alone. However, permanent reduction of free aldehydes is attainable by using compounds of the general formula II alone or in admixture with compounds of the general formula I. This is because compounds of the general formula II, being the stable storage form of compounds of the formula I, cannot be oxidized and can react with the free aldehyde as per the general equation (2):
In addition to the bound aldehyde, the latter reaction produces a compound which is itself an aldehyde or ketone. However, these can be selected so that they have no unwanted odor, and/or are nontoxic. Representative examples are pyruvic acid and acetoacetate ester. The latter compound is especially advantageous in that it in turn can act as an
Doering Wolfgang
Schaefer Oliver
Stohrer Juergen
Brooks & Kushman P.C.
Consortium fuer Elektrochemische Industrie GmbH
Sastri Satya
Wu David W.
LandOfFree
Removal of free aldehydes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Removal of free aldehydes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Removal of free aldehydes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3365379