Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Reexamination Certificate
1999-06-22
2001-03-13
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
C528S243000, C528S245000, C528S256000, C528S266000, C528S495000, C525S491000, C525S532000, C428S425300, C428S436000, C428S502000, C428S505000
Reexamination Certificate
active
06201095
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a dialkoxyethanal-melamine type resin that is lower in color, as measured by the Gardner color scale. The addition of a small amount of formaldehyde, relative to the dialkoxyethanal, before the reactants are acidified has been found to minimize the generation of color.
BACKGROUND OF THE INVENTION
Melamine-formaldehyde resins and phenol formaldehyde resins are known to give off formaldehyde in some applications. The emission of formaldehyde from these resins has become an issue as environmental concerns have been heightened. This has caused interest in non-formaldehyde or lower formaldehyde thermosetting resin technologies.
U.S. Pat. No. 5,539,077 discloses a resin composition which is the reaction product of an amine derivative chosen from melamine, glycolurile or their mixtures with a C
1
to C
8
dialkoxyethanal, the reaction product then being mixed and reacted with a polyol.
U.S. Pat. No. 5,691,426 discloses a binder comprising a mixture of a formaldehyde-based resin with a resin substitute comprising the reaction product of an amine derivative chosen from melamine, glycolurile or their mixtures with 1 or 2 moles of a C
1
to C
8
dialkoxyethanal, the reaction product being mixed, and preferably reacted, with a polyol. A paper entitled “Non-Formaldehyde Thermosetting Technology” by W. C. Floyd presented at INDA TEC '97 which is sponsored by INDA (Association of the Nonwoven Fabric Indrustry), discusses the benefits of blend technology of U.S. Pat. No. 5,691,426 in reducing the formaldehyde emissions while maintaining or improving properties of the blend as compared to formaldehyde based resins.
SUMMARY OF THE INVENTION
A resin composition low in color can be prepared by reacting an amine derivative selected from melamine, acetylene diurea and their mixtures with dialkoxyethanal and a small amount of formaldehyde. This can be further reacted with polyols and other components. Having the formaldehyde present in the mixture of the amine derivative and dialkoxyethanal prior to the time the pH is adjusted below 7 and heat is applied has been found to dramatically reduce the amount of color developed in the resin. Addition of the formaldehyde later in the process does not have the same effect on color development. As the resins from the reaction of amine derivatives with dialkoxyethanal are known to reduce or scavenge formaldehyde emissions from other resins, it is anticipated that the amount of formaldehyde emissions from this reaction product from the amine derivative, diethoxyethanal and a small amount of formaldehyde will be low. This reaction product can be formulated to act as a formaldehyde scavenger if mixed or reacted with formaldehyde containing resins.
DETAILED DESCRIPTION OF THE INVENTION
DME-melamine resins are typically manufactured by 1) reacting the dimethoxyethanal (DME) and melamine after adjusting to a pH of 9-9.5 at an elevated temperature (e.g. 60° C.) for a couple of hours, 2) adding one or more polyols, 3) then adjusting the pH to below 7 and reacting at an elevated temperature (e.g. 80-100° C.) for an hour or so, and 4) cooling and diluting with water. A problem with the DME-melamine resin is the development of a light to dark amber color in the resin during the final step of reacting at 80-100° C. at a pH below 7. On the Gardner color scale the values can range from about 5 or 6 to about 12 or more in the absence of formaldehyde. These colored resins are aesthetically unpleasing in certain applications where the resin is applied as a surface coating (e.g. wood coatings, overprint varnishes or the like). Bleaching of the amber resins is generally not satisfactory since it degrades the performance and introduces undesirable by-products.
It has unexpectedly been discovered that the addition of a small amount of formaldehyde, relative to the melamine, prior to the step of adjusting the pH to below 7 and heating to 80-100° C. results in dramatically reduced color. Generally the color is not apparent until heat is applied to the reaction mixture at a slightly acidic pH. More color is developed at reflux temperatures (90-99° C.) than at 80° C. It is preferable that the formaldehyde be present initially with the DME under alkaline pH conditions. Adding formaldehyde after the batch has been reacted under acidic conditions has little or no effect on color formation. The optimum amount of formaldehyde to add is a trade-off between adding more formaldehyde to obtain the lightest colored resin (up to 1 or 2 mole based on moles of melamine) and less (0.01, 0.05 or 0.1 moles based on moles of melamine) to reduce the free formaldehyde content.
The exact nature of the dark-colored chromophore is not known. The formation of color under conditions of acidic pH and high heat may be indicative of a dehydration of aldehyde-amino adduct (also known as a Schiff base or Imine) in which the aldehyde has an alpha-carbon containing a proton. Melamine formaldehyde resins are colorless under acidic conditions. The amine-aldehyde adduct in melamine-formaldehyde resin has no hydrogen on an alpha-carbon on the aldehyde portion. Glyoxal is known to cause severe (dark) color formation when reacted with melamine, or reacted up to 3-5% together with DME and melamine. DME is known to contain trace amounts of glyoxal (0.3% or less) and this is known to undergo a Cannnizarro reaction under alkaline conditions.
The exact nature of the compound being made is difficult to specify, and is best described as a reaction product of 1) an amine derivative, 2) dialkoxyethanal (e.g. DME), and 3) formaldehyde which is reacted together to provide a resin composition. Perhaps the resulting resin composition is one with a reduced number of residual primary amino groups on the melamine so as to have less available primary amino groups to react with an undetermined component of the dialkoxyethanal which forms the dark chromophore under dehydrating conditions of high temperature and acidic pH. An aldehyde containing a hydrogen on the alpha carbon reacted with a primary amine would form an imine type of structure (R—N═CH—CHR′R″) when dehydrated. These imines are quite reactive and easily lead to color formation. This reaction product of an amine derivative, dialkoxyethanal and formaldehye is generally formed prior to addition of one or more polyols and the resinification (condensation to build molecular weight) at acidic pH.
Preferably this reaction is initially conducted at a pH above 7 and preferably above 8.0, 8.5 or 9.0 and below 9.5, 10.5 or 11 for a period of time (e.g. at least 5, 10, or 30 minutes) and desirably at an elevated temperature such as above 35° C., above 45° C., and preferably above 55° C. Desirably this reaction is substantially completed before the reaction product is acidified to a pH below 7.
The C
1
-C
8
dialkoxyethanal is reacted with the amine derivative generally at a molar ratio of about 1 to about 6 equivalents of dialkoxyethanal to amine derivative and preferably at a ratio of about 1.5 or 2 to about 4.
The C
1
-C
8
dialkoxyethanal generally has the following formula
wherein R
1
and R
2
are C
1
-C
8
alkyl or R
1
and R
2
are joined to form a 5 or 6 membered cyclic acetal group (i.e. R
1
and R
2
form a single linear or branched alkyl with 2-8 carbon atoms and with the —OCH—O— of the ethanal form a 5 or 6 member ring). Preferably R
1
and R
2
are a C
1
-C
8
alkyl group, preferably the same group and preferably a methyl group as this is the most economical derivative which is commercially available, manufactured by Clariant.
The amine derivative may be any amine derivative reactive with formaldehyde to form amino resins. Preferably the amine derivative is melamine or acetylene diurea.
Desirably formaldehyde is present in amounts from about 0.01 to about 2 moles per mole of the amine derivative. More desirably formaldehyde is present from about 0.01, 0.05 or 0.1 to about 0.5 or moles per mole of the amine derivative.
When the reactants are acidified to a pH below 7, color can be generated. Desirably t
Floyd William C.
North Bernard F.
Hudak Daniel J.
OMNOVA Solutions Inc.
Rywalski Robert F.
Truong Duc
LandOfFree
Color improvement of DME-melamine resins does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color improvement of DME-melamine resins, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color improvement of DME-melamine resins will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2529713