Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1998-10-06
2001-02-13
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S079000, C522S094000, C521S170000
Reexamination Certificate
active
06187893
ABSTRACT:
The invention relates to two-component polyurethane systems which contain reactive diluents.
Two-component polyurethane systems, which are composed of a poyisocyanate component and a polyol component, are known. In the reaction to give the polyurethane, it is of great importance that the polyol component, usually termed the A component, and the isocyanate component, usually termed the B component, are intimately mixed with one another. Only in this way is it possible to prepare polyurethanes which are free from defects.
However, the polyetherols, polyesterols, polyacrylates, etc. usually used as A components are usually markedly more viscous, because of their higher molecular weight, than the associated isocyanate components. This often causes incomplete mixing of the reaction partners unless complicated mixing technology is used, and the polyurethane obtained as end product may contain local defects resulting from defects in mixing.
Ideal mixing of a polyurethane system is generally achieved if both reaction partners have similar, and preferably very low, viscosities. At 23° C., most of the isocyanate components have viscosities in the range from 10 to 500 mPa·s, which can be handled without difficulty by usual mixing apparatus. The viscosities of the polyol components usually start at 1000 mPa·s and their upper limit results only from their handle ability at the temperature of processing. This means that polyols with very high viscosities or very high molecular weights cannot be used even if the desired property spectrum of the polyurethane would require polyols of this type.
A large number of ways are known for lowering the viscosity of the polyol component.
For example, it is possible to lower the viscosity by increasing the processing temperature. However, equipment frequently does not permit a temperature increase of this type, or the increase causes degradation of the polyol component. It is moreover possible for the polyol component used to be polyols with low average molecular weights. However, this possibility cannot realized in every application, since it affects the properties of the end products. When low-molecular-weight polyols are used, the build-up of the molecular weight of the polyurethane takes place more slowly, and, in particular in coating applications, causes lengthening of the time needed for a coating to become physically dry to the touch, as measured by its freedom from tack. Another way of lowering viscosity is to use solvents. Their use is, however, limited, because of their potential to contaminate the environment.
An elegant method for lowering the viscosity of high-molecular-weight products is the addition of reactive diluents. These lower the viscosity in the same way as a solvent, but, since they participate in the reaction, are incorporated into the polyurethane. Use is generally made of low-molecular-weight compounds which contain groups which react with isocyanates.
The use of low-molecular-weight and low-viscosity di- or triols, such as ethylene glycol, propylene glycol, dipropylene glycol, butanediol, glycerol and similar products, is well known and has been described many times. However, these alcohols have the disadvantage of forming hard phases in the polyurethane, and this can adversely affect the properties of foams or coatings. In the reaction with isocyanates, furthermore, a great amount of heat of reaction is generated, due to the high proportion of hydroxyl groups in the molecule, and therefore the polyurethane systems can overheat during the reaction and this may cause safety and processing problems.
The use of oxazolidines as reactive diluents in polyurethane systems is also known. Oxazolidines undergo ring-opening when exposed to moisture and then act as chain extenders or crosslinking agents. They are therefore used as drying agents in polyol components. Such systems are described, for example, in U.S. Pat. No. 3,743,626 and U.S. Pat. No. 5,264,148. A disadvantage of these systems is that oxazolidines are potential water scavengers and the shelf-life of the systems is therefore inadequate. In addition, the ring-opening produces amines, which form ureas with the isocyanates and/or intervene in the polyurethane reaction as catalysts. The resultant effects on the finished polyurethane of these phenomena are difficult to predict and therefore undesirable.
It is an object of the present invention to develop two-component polyurethane systems which contain reactive diluents which are simple to prepare, are incorporated into the polyurethane without difficulty and do not enter into side-reactions with the structural components of the polyurethane.
We have found that this object is achieved by using cyclic acetals and/or ketals as reactive diluents in two-component polyurethane systems.
The invention therefore provides two-component polyurethane systems made from one component which comprises compounds having at least two isocyanate groups, also termed isocyanate component, and one component, which comprises compounds having hydrogen atoms which react with isocyanate, also termed polyol component, wherein cyclic acetals and/or ketals are present as reactive diluents. The invention provides, furthermore, polyol components for two-component polyurethane systems, wherein these comprise hydroxyl-containing cyclic acetals and/or ketals as reactive diluents. The invention moreover provides a process for preparing polyurethanes by reacting polyisocyanates with compounds having at least two reactive hydrogen atoms, wherein the compounds having at least two reactive hydrogen atoms comprise cyclic acetals and/or ketals. The invention also provides for the use of cyclic acetals and/or ketals as reactive diluents in two-component polyurethane systems.
The cyclic acetals and ketals used according to the invention may preferably be prepared by reacting polyhydric alcohols with aldehydes or ketones.
It is advantageous here for the alcohols used as starting materials for the cyclic acetals and ketals used according to the invention to be alcohols usually used as structural components in polyurethane systems, most frequently as chain extenders or crosslinking agents. It is preferable to use alcohols which have at least three hydroxyl groups in the molecule, in particular glycerol and trimethylolpropane (TMP). In the case of the at least trihydric alcohols, two adjacent hydroxyl groups form a ring structure with the aldehyde molecule and/or ketone molecule, and free hydroxyl groups still remain in the molecule. Stepwise reaction of the reactive diluents can therefore occur during polyurethane formation, the free hydroxyl groups reacting initially and, after elimination of the aldehydes and/or ketones, the previously capped hydroxyl groups being able to react with the isocyanate groups.
The elimination of the blocking agents is preferably brought about by compounds which in any case are present in the polyurethane system, for example water, or else by traces of acid from the isocyanate component, or traces of acrylic acid from the acrylate polyols used for coating applications. Due to their volatility, the blocking agents spontaneously diffuse out of the polyurethane after they are eliminated. Because their amounts are usually small, this does not cause any damage to the environment. Aldehydes and ketones used are preferably those having from 1 to 12 carbon atoms, in particular from 3 to 6 carbon atoms, in their main chain.
Particularly suitable compounds are acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde and benzaldehyde.
The cyclic acetals and ketals used according to the invention may be prepared very simply by reacting the corresponding alcohols with the aldehydes and/or ketones. It is can be advantageous here to work in solution. Possible solvents are those which do not react with the starting compounds, and for example are hydrocarbons or ethers. To achieve a good yield, the water produced during the reaction should be
Bruchmann Bernd
Lutter Heinz-Dieter
Mohrhardt Gunter
Renz Hans
Scherzer Dietrich
BASF - Aktiengesellschaft
Borrego Fernando A.
Gorr Rachel
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