Aqueous binder solutions and dispersions

Details Aqueous binder solutions and dispersions Aqueous binder solutions and dispersions

2001-06-11

2002-03-12

Yoon, Tae H. (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...

C524S599000, C524S600000, C523S401000, C523S402000, C528S298000, C528S300000, C528S50200C

Reexamination Certificate

active

06355722

ABSTRACT:

The present invention relates to aqueous solutions and dispersions of binders for preparing aqueous coating materials, and to processes for their preparation.
The condensation of alcohols with carboxylic acids produces per crosslinked hydroxyl or carbonyl—group one molecule of water, H2O:
R
1
—OH+HOOC—R
2
→R
1—O—CO—R
2
+H
2
O
alcohol+carboxylic acid→ester+water
Since the ester is the reaction product which is of interest, in the prior-art preparation processes the water produced is removed from the reaction mixture as so-called “water of reaction”. This water of reaction is generally contaminated with other components of the reaction and must therefore be disposed of. A procedure of this kind is necessary, for example, in the coatings industry in connection with the preparation of coating binders.
In the coatings industry, the preparation of polyesters and alkyd resins from polycarboxylic acids and/or polycarboxylic anhydrides and polyalcohols and, if desired, monocarboxylic acids by condensation reactions gives rise to a quantity of about 5 to 11%, based on the polymer produced, of water of reaction. The water of reaction is normally removed effectively from the reaction mixture with the assistance of entrainers (for example xylene).
The vapor mixture comprising water of reaction and entrainer is—especially where saturated polyesters are being prepared—passed through a column whose function is to separate volatile polymer building blocks (especially lower polyalcohols) from the vapor mixture by liquid/vapor exchange and thereby to avoid losses of these building blocks from the reaction mixture. For polyesters and alkyd resins, which contain no constituents which are volatile—under the reaction conditions in the reactor or with steam—an overflow pipe is employed.
In each case, however, the vapor mixture is subsequently liquefied in a condenser and is collected in a separation receiver. In the separation receiver, an aqueous phase of relatively high specific gravity separates from the organic phase of lower specific gravity. The organic phase consists almost entirely of the entrainer employed; it is separated from the aqueous phase by means of an overflow and is passed into the reactor at the head of the column (circulation technique) possibly under control and by means of the use of a pump (possibly a metering pump).
Another possibility is to operate without entrainer. In this case there is no need for a separation receiver but only for a single receiver into which aqueous phase is collected.
Although the aqueous phase contains high proportions of water, it is always contaminated with relatively small amounts of volatile or steam-volatile building blocks (mostly lower polyols) and/or with water-soluble degradation products from the building blocks of the polyester as well. Degradation products which may be produced and may be present in the aqueous phase of the water of reaction are monoalcohols, partial aldehydes of polyols, acetals, and in special cases cyclic, oxygen-containing compounds as well.
Separation of the secondary constituents from the aqueous phase during the preparation of polyesters and alkyd resins, by distillation or extraction, is complex and does not lead to reusable materials. Simple disposal of the distillate, for example by way of settling basins, is a risk. Usually, therefore, despite its small content of organic constituents the water of reaction is incinerated, usually together with other residues which are richer in organic substances. This requires separation and storage of the waters of reaction and special control as they are fed to the incinerator.
Because of their ecological advantages, water-dilutable coating materials have increasingly been used in the coatings industry in recent years. With these coating materials it is possible largely or completely to dispense with organic solvents whose evaporation as the coating material dries leads to emissions and to the known, associated environmental problems. In the course of preparing such aqueous coating systems, the binders of the coating material must be brought into the form of an aqueous solution or dispersion. Dispersions of this kind are highly unstable. Even small quantities of impurities may destroy or severely hinder the dispersibility of the binders. For example, a solution of this kind cannot be prepared using tap water (drinking water, mains water), which contains inorganic constituents. It is therefore necessary to employ deionized or distilled water. This implies more complex preparation and therefore increased preparation costs as well.
The object which the present invention has set itself is to avoid the disadvantages of the prior art, described above, which occur in particular during the disposal of water of reaction and during the preparation of binder dispersions.
This object is achieved in accordance with the invention by an aqueous solution or dispersion of a binder for preparing aqueous coating materials, which solution or dispersion includes as at least one aqueous component the water which can be prepared by condensation of alcohols with carboxylic acids and can be separated off from the condensation mixture.
It has surprisingly been found that during the preparation of polyesters or alkyd resins (which are then preferably employed for water-dilutable coating PAT 95445 systems, the water of reaction is able to replace a portion of the distilled or deionized water which is otherwise used to prepare the aqueous colloidal solution or dispersion of the polyester or alkyd resin. Unlike tap water (drinking water, mains water), which contains certain proportions of inorganic constituents which impair the usefulness for preparing aqueous colloidal solutions or dispersions of coating binders, it is possible with fractions of the waters of reaction to prepare stable aqueous colloidal solutions. The use of these aqueous polyester-resin or alkyd-resin solutions or dispersions in aqueous coating systems has only an insignificant influence on their properties. This effect was completely surprising in view of the sensitivity of the binder dispersions to impurities. On the basis of conventional experience, the opposite was to be expected. However, it is found that in most cases the secondary constituents act as cosolvents. If aqueous coating systems are employed on application lines with stoving furnaces—which is generally the case with the industrial use of aqueous coating systems—the abovementioned substances accompanying the water of reaction do not become volatile until they are in the stoving furnace, although some of them also participate in film forming (for example reaction with amine resins). Environmental pollution as a result of the constituents, therefore, is largely ruled out, and in any case the waste air from stoving furnaces includes organic cleavage products and is therefore cleaned by means of catalytically processes or filters.
In the text below, the term water of reaction is intended always to denote the water which is eliminated during the condensation of alcohols with carboxylic acids and which is or can be separated off from the condensation mixture.
In accordance with the invention, the water of reaction is preferably taken from reactions in which the alcohols are present as polyalcohols, the term polyol referring to an organic compound which bears at least 2 hydroxyl groups. Examples of suitable polyols are ethylene glycol, propanediols, butanediols, pentanediols, neopentylglycol, hexanediols, diethylene glycol, glycerol, trimethylolethane, trimethylol-propane, pentaerythritol, dipentaerythritol, neopentylglycol hydroxypivalate, 2-methyl-2-propyl-1,3-propanediol, 2,2,4-trimethyl-l,3-pentanediol and 2,2,5-trimethyl-1,6-hexanediol It is preferred to employ neopentylglycol, 1,6-hexanediol and neopentylglycol hydroxypivalate. The polyols can of course be employed in pure form or as mixtures.
In the case of the novel preparation of the water of reaction, polycarboxylic acids are preferably employed. These may comprise a polycarboxylic acid

Affiliated with

Also associated with

Rating

Aqueous binder solutions and dispersions does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Aqueous binder solutions and dispersions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous binder solutions and dispersions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2839712