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
2000-02-02
2002-03-19
Niland, Patrick D. (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...
C427S372200, C427S385500, C428S423100, C428S425800, C524S589000, C524S590000
Reexamination Certificate
active
06359060
ABSTRACT:
RELATED APPLICATIONS
This application claims priority to Austrian application No. A 143/99, filed Feb. 4, 1999, herein incorporated by reference.
1. Field of the Invention
In the coating of wood it is common to use moisture curing systems. In many cases such systems contain solvent and also residues of free aromatic isocyanates. This should be avoided for reasons of industrial hygiene.
2. Object of the Invention
An object was, therefore, to develop new wood coating binders which are not cured by means of isocyanates and in which the presence of solvents can be extensively avoided or even done away with altogether.
SUMMARY OF THE INVENTION
A known property of alkyd resins is that they dry oxidatively in air through crosslinking of the double bonds originating from the unsaturated fatty acids. If groups of this kind derived from unsaturated fatty acids are incorporated into polyurethanes, then those polyurethanes can be used to prepare aqueous dispersions which give air-drying coatings.
It has been found that the polyurethane dispersions of this kind are particularly suitable for coating wood.
The invention therefore provides oxidatively drying aqueous polyurethane dispersions obtainable by reacting drying and/or semidrying oils A with low molar mass hydroxy compounds B having two or more hydroxyl groups to give compounds AB, which contains on average at least one hydroxyl group and at least one radical of a fatty acid having at least one olefinic double bond, then reacting the compounds AB together with high molar mass polyols C, compounds D, which have at least two isocyanate-reactive groups and at least one acid group or at least one group which, after neutralisation, forms a cationic group, like, for example, an ammonium group, with polyfunctional isocyanates E to give prepolymers ABCDE having a mass fraction of unreacted isocyanate groups of from about 0.1 to about 4%, based on the mass of the prepolymer. If desired, the prepolymer is then reacted with a compound F, which has an isocyanate-reactive group, followed by neutralizing the product formed with tertiary amines or monofunctional acids G and transferring the utilized product to the aqueous phase, and subsequently, if desired, reacting any excess isocyanate groups still present by adding chain extenders H, which have at least two primary or secondary amino groups or hydrazine groups per molecule.
The invention additionally provides a process for preparing oxidatively drying of aqueous polyurethane dispersions, which comprises, in a first stage a), reacting drying or semidrying oils A having an iodine number of preferably more than about 100 g/(100 g) with low molar mass hydroxy compounds B having two or more hydroxyl groups per molecule. This reaction (trans-esterification) is preferably conducted with alkaline catalysis; particular preference is given to the addition of alkali metal hydroxides in a fraction of from about 5 to about 200 mg, preferably from about 15 to about 100 mg, per 100 g of the mixture of components A and B. The transesterification is preferably conducted at a temperature from about 150 to about 250° C., with particular preference at from about 200 to about 240° C. In the second stage b), this transesterification product AB is introduced as the initial charge; the high molar mass polyol C and, if desired, a further catalyst are added and heated to an elevated temperature of from about 30 to about 100° C., preferably from about 50 to about 80° C. Component D is added subsequently, preferably as a solution in an aprotic solvent such as, for example, N-methylpyrrolidone, and is mixed with the components in the initial charge. Thereafter, the isocyanate component E is added. The mixture is held at the stated reaction temperature until there is no longer any marked change in the isocyanate concentration. Following this step, if desired, a compound F, which is monofunctional with respect to isocyanate, can then be added, preferably in an amount such that the isocyanate groups still present are fully consumed by this reaction. In stage c), this mixture is stirred for from about 10 to about 20 minutes into a solution of the tertiary amine or monofunctional acid G in deionized water (mass fraction of the amine or acid in the water from about 10 to about 40%, preferably from about 20 to about 35%). The solution is at a temperature of from about 50 to about 90° C., preferably from about 70 to about 80° C. If free isocyanate groups are still present in the reaction product, a chain extender H can be added. H preferably contains either two or more primary or secondary amino groups or hydrazine groups and is preferably in the form of an aqueous solution. A chain extension reaction of this kind usually requires an additional reaction time of from about 10 to about 15 minutes. In step d), a dispersion is prepared by the addition of additional water. The dispersion which has a mass fraction of solids of preferably from about 20 to about 40%, with particular preference from about 25 to about 35%.
Finally, the invention also provides for the use of the oxidatively drying aqueous polyurethane dispersions for the preparation of binders to be used for coating wood, plastics, metals and flexible substrates such as leather, paper and card. For the latter utilities, in particular, the combination of high flexibility and high surface hardness, obtainable by using the oxidatively drying aqueous polyurethane dispersions of the invention, is essential.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable compounds A are the compounds known as drying and semidrying oils, preferably having an iodine number of about 100 g/(100 g) or more. (The iodine number indicates the ratio of the mass of iodine m(I) to the mass of the sample m
B
of the unsaturated compound which is able to undergo addition with said mass of iodine, accompanied by decoloring of the iodine solution and consumption of the double bonds; the customary unit of measurement is “g/(100 g)”.) Examples of suitable oils are soya oil (120 to 136), safflower oil (140 to 150), linseed oil (155 to 205), sunflower oil (125 to 144), rapeseed oil (105 to 115), castor oil, wood oil, cottonseed oil (109 to 116), and animal oils (the numbers in brackets are in each case the iodine number in g/100 g).
Compounds which can be used as polyols B include dihydric and polyhydric aliphatic hydroxy compounds having, for example, 2 to 12 carbon atoms. Particular preference is given to dihydroxy compounds, such as glycol, 1,2- and 1,3-propylene glycol and 1,4-butanediol, and trihydroxy compounds, such as glycerol and trimethylolpropane and -ethane. Here, polyols having a molar mass of less than about 400 g/mol are referred to as low molar mass polyols. However, it is also possible to use higher alcohols having 4 or more hydroxyl groups, such as ditrimethylolpropane, erythritol and pentaerythritol, sorbitol, mannitol, dipentaerythritol, and sugars such as glucose as well. However, care should be taken to ensure that the functionality of the compounds AB is not too high; it should preferably remain below about 3, with particular preference below about 2.5. This parameter can also be controlled, for example, by using the higher-functional hydroxy compounds in a mixture with diols such as glycol, 1,2- and 1,3-propylene glycol, and oligomeric oxyalkylene glycols, especially oxyethylene glycols having degrees of polymerization of from 2 to 10.
Suitable polyols C are high molar mass polyether polyols, polyester polyols, polycarbonate polyols and polyurethane polyols having a number-average molar mass of about 400 to about 20,000 g/mol, preferably from about 600 to about 15,000 g/mol and, with particular preference, from about 800 to about 10,000 g/mol. They preferably have two hydroxyl groups per molecule. The polyether polyols are derived, for example, from ethylene oxide (oxirane), 1,2-propylene oxide (methyloxirane) and oxacyclopentane (tetrahydrofuran). It is also possible to use mixed polyethers, such as those having blocks of successive oxyethylene units and oxypropylene units. Particular pre
Anner Birgit
Arzt Anton
Awad Rami-Raimund
Glettler Martina
Gsoell Hannelore
Niland Patrick D.
Solutia Austria GmbH
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