Polyurethane resins

A process for producing a polyurethane resin having an extended gel time by reacting a polyol component with a polyisocyanate in an NCO:OH ratio of from 10:1 to 1:10 wherein the polyol component contains from 0.1% to 100% by weight of a randomized castor oil prepared by heating castor oil for between about 0.1 and 15 hours at a temperature of between about 100.degree. C. and 280.degree. C. in the presence of a basic lithium salt.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the production of polyurethane materials from 
polyols based on randomized castor oil and isocyanates. The mechanical 
properties of the polyurethane materials according to the invention are 
comparable with those of the materials obtainable from unmodified castor 
oil, although the gel time of the systems is far longer. 
2. Discussion of Related Art 
The use of castor oil and/or other hydroxyfunctional triglycerides for the 
production of polyurethanes has been known for some time. For example, the 
production of elastomers from castor oil and corresponding isocyanates is 
described in Saunders, Frisch: "Polyurethanes: Chemistry and Technology, 
II Technology", Interscience (1964). However, optimal processing of these 
generally two-component systems involves a long gel time, i.e. the time 
during which the mixture of the two components can undergo irreversible 
changes in its external form should be considerable. A long gel time is of 
advantage above all where two-component (2C) systems are used for the 
production of coatings because, on the one hand, better flow is guaranteed 
and, on the other hand, the degassing time available to the system is 
clearly increased which can contribute towards reducing bubble formation. 
Overly short gel times can lead to poor processability of the polyurethane 
systems, for example even in summer or in countries with a generally 
fairly high ambient temperature. 
Whereas the use of catalysts, such as dibutyl tin dilaurate for example, 
has generally been regarded among experts as the easiest solution to the 
problem of shortening the gel time, increasing the gel time is far more 
difficult. An extended gel time was achieved, for example, by 
incorporation of low molecular weight polyols although this resulted in a 
possibly unwanted deviation from the originally planned material 
properties. Accordingly, attempts to extend the short gel time or pot life 
of the mixtures without affecting material quality have hitherto failed. 
Accordingly, the problem addressed by the present invention was to modify 
oleochemical polyols based on castor oil in such a way that, on the one 
hand, the polyol component could be processed to materials, such as 
casting resins or two-component foams for example, having the required 
mechanical properties while, on the other hand, the gel time of the 
polyols could be extended as required for their use in two-component 
systems. 
It has now surprisingly been found that randomized castor oil, which is 
obtainable by heating castor oil at temperatures above 100.degree. C. in 
the presence of lithium as catalyst, leads to a significant increase in 
the gel time without adversely affecting the properties of the 
polyurethane resin. 
DESCRIPTION OF THE INVENTION 
Accordingly, the present invention relates to a process for extending the 
gel time of polyurethane resins of isocyanates and a polyol component with 
an NCO:OH ratio of 10:1 to 1:10, characterized in that castor oil heated 
for about 0.1 to 15 hours to 100-300.degree. C. in the presence of a basic 
lithium salt is used in a quantity of 0.1 to 100% by weight as a 
constituent of the polyol component. 
The modification of the castor oil takes place under conditions which are 
normally used for the transesterification of triglycerides. Thus, the 
reaction is generally carried out in an inert gas atmosphere, the castor 
oil being heated to a temperature of at least 100.degree. C. in the 
presence of the water-free lithium salts. The reaction temperature should 
generally not exceed 300.degree. C. because otherwise product quality 
might suffer. Normally, the reaction is carried out at temperatures below 
that limit, above all for the production of light-colored modified castor 
oils with low viscosities. Accordingly, it has proved to be of advantage 
to carry out the reaction at a temperature in the range from about 150 to 
280.degree. C. and, more particularly, at a temperature of 200 to 
280.degree. C., temperatures in the range from 220 to 260.degree. C. 
leading to particularly good results. 
The reaction time should not be less than 0.1 hour while reaction times 
longer that about 15 hours generally produce no significant improvement in 
the results. The relationship between reaction time and temperature is 
well known to the expert, so that higher temperatures can be compensated 
within wide limits by shorter reaction times and lower temperatures by 
longer reaction times. Reaction times of 0.5 to 10 hours generally lead to 
good results so far as the viscosity of the resulting polyols is 
concerned. Reaction times of 1 to 8 or 2 to 6 hours at temperatures of 220 
to 260.degree. C. normally lead to the desired product. 
Basically, any catalysts which are known to be suitable for the catalysis 
of esterification reactions may be used for the modification 
(randomization) reaction. In general, however, the expert will resort to 
basic esterification catalysts, more particularly to the salts of the 
alkali and/or alkaline earth metals showing a basic reaction in aqueous 
solution, such as for example lithium, sodium, potassium, calcium and/or 
magnesium. Depending on their effectiveness, these catalysts may be used 
in concentrations ranging from a few ppm (parts per million) to a few 
percent, for example in concentrations of 0.1 ppm to about 2%. However, 
residual contents of catalyst can be problematical to the subsequent use 
of the polyols. If the residual contents of alkali metals are too high, 
the polyurethanes obtained are generally of inferior quality with 
properties that do not meet normal requirements, particularly in regard to 
hydrolysis stability. In general, therefore, the catalysts have to be 
removed from the polyol by one or more different purification steps. The 
residual alkali metal contents can thus be reduced to sufficiently low 
levels for the required subsequent processing to the polyurethane. 
Modified castor oils produced in this way should have a residual alkali 
metal or alkaline earth metal content of no more than about 10 ppm, lower 
residual contents, such as 5, 2 or 1 ppm down to the detection limit of 
the particular determination method applied being advantageous. 
An exception is the lithium ion. On the one hand, even small quantities 
enable the transesterification to be carried out; on the other hand, it 
has little or no influence on the properties of the resulting 
polyurethanes, so that there is generally no need for the polyol component 
to be purified where lithium catalysts are used. Accordingly, the use of 
basic lithium compounds, such as lithium hydroxide, lithium carbonate, 
lithium acetate, lithium alkoxylates or the lithium salts of higher fatty 
acids, has proved successful for the purposes of the invention. The 
transesterification catalyst is normally added to the reaction mixture in 
a concentration of 0.1 to 500 ppm and preferably in a concentration of 0.1 
to 300 ppm. Accordingly, polyol mixtures with a lithium content of at most 
about 200 ppm are advantageous for the purposes of the invention. Lithium 
contents with an upper limit of at most 100, preferably below 70 and more 
preferably below 50 ppm have a particularly positive effect on the color 
and hydrolysis stability of the resulting polyurethanes by comparison with 
higher or identical contents of other alkali metals. The most suitable 
polyols for the purposes of the invention have negligible contents, if any 
(advantageously less than 10 ppm), of alkali metals apart from lithium, 
the lithium content advantageously being below 40 ppm. 
The polyols obtainable in this way generally have substantially the same 
characteristic data as the castor oil originally used. Thus, their OH 
value normally falls by no more than 2 to 7 mg KOH/g while the Hoppler 
viscosity (25.degree. C.) of the modified oil compared with the castor oil 
used, which has a Hoppler viscosity of 970 mPas (25.degree. C.), is 
generally increased by only about 50 to 150 mPas and preferably by only 50 
to 120 mPas. 
The castor oil used for the randomization may be both pure castor oil and 
the technical triglyceride which may contain other fatty acid esters 
besides the esters of ricinoleic acid. Thus, besides ricinoleic acid, 
palmitic acid, stearic acid, oleic acid and/or linoleic acid, for example, 
may occur in small quantities of up to about 5% and, in individual cases, 
even higher. In general, however, the castor oil used should contain at 
least 80% of ricinoleic acid units. 
The randomized castor oil will generally be the only constituent of the 
polyol mixture, although it may be necessary or at least advantageous for 
modifying the properties of the resulting polyurethane to add other 
components to the polyol mixture. Such polyol mixtures contain 2, 3 or 
more polyol components. Accordingly, the percentage content of the 
modified castor oil in the polyol mixture as a whole may fall to 90, 80 or 
70% by weight. The modified castor oil may even make up only about half 
the polyol mixture as a whole, a margin of 1% by weight existing in this 
case. However, even smaller quantities of castor oil can still make a 
contribution towards increasing the gel time of the polyurethane resins. 
Quantities of only about 1 to 49% by weight may be sufficient for this 
purpose. 
However, both low molecular weight polyols and relatively high molecular 
weight, hydroxyfunctional molecules up to correspondingly functionalized 
polymers are suitable as further constituents of the polyol mixture. For 
example, other hydroxyfunctional triglycerides may be present in the 
polyol mixture. The hydroxyfunctional triglycerides may be of both natural 
and synthetic origin. For example, unsaturated triglycerides can be 
epoxidized by per acids and the oxiranes obtainable in this way may be 
reacted in acid- or alkali-catalyzed ring opening reactions with 
monohydric or polyhydric alcohols to form hydroxyfunctional triglycerides. 
Suitable unsaturated triglycerides are those of synthetic and/or natural 
origin with iodine values of 30 to 150 and preferably in the range from 85 
to 125. Typical examples of the group of unsaturated triglycerides are 
linseed oil, palm oil, palm kernel oil, coconut oil, peanut oil, tea oil, 
olive oil, olive kernel oil, babassu oil, meadowfoam oil, chaulmoogra oil, 
coriander oil, soybean oil, lard oil, been tallow, lard, fish oil and 
sunflower oil and rapeseed oil from old and new plants. 
Oxiranes of the type in question are normally ring-opened with monohydric 
or polyhydric alcohols. According to the invention, monohydric alcohols 
are preferably used. Monohydric alcohols include both aliphatic and 
aromatic alcohols, aliphatic alcohols preferably being used. The alcohols 
used may be branched or unbranched, saturated or unsaturated, although 
aliphatic saturated alcohols are preferably used. Methanol, ethanol, 
n-propanol, isopropanol, n-butanol, isobutanol, tert.butanol, pentanol, 
hexanol, heptanol and the higher homologs are preferably used for the ring 
opening reaction. 
Fatty alcohols containing 8 to 22 carbon atoms may also be used for the 
ring opening reaction. Fatty alcohols in the present context are primary 
aliphatic alcohols corresponding to formula (I): 
EQU R.sup.1 OH (I) 
in which R.sup.1 is an aliphatic, linear or branched hydrocarbon radical 
containing 6 to 22 carbon atoms and 0 and/or 1, 2 or 3 double bonds. 
Typical examples are caproic alcohol, caprylic alcohol, 2-ethylhexyl 
alcohol, capric alcohol, lauryl alcohol, isotridecyl alcohol, myristyl 
alcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl 
alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, linolyl 
alcohol, linolenyl alcohol, elaeostearyl alcohol, arachyl alcohol, 
gadoleyl alcohol, behenyl alcohol, erucyl alcohol and brassidyl alcohol 
and the technical mixtures thereof obtained, for example, in the 
high-pressure hydrogenation of technical methyl esters based on fats and 
oils or aldehydes from Roelen's oxosynthesis and as monomer fraction in 
the dimerization of unsaturated fatty alcohols. 
The hydroxyfunctional triglycerides may optionally be subjected to 
transesterification with polyhydric alcohols. The alcohols used for this 
purpose generally have functionalities of 2 to 10 and preferably 2 to 6. 
They include, in particular, diols such as, for example, ethane-1,2-diol, 
propane-1,2-diol, propane-1,3-diol, butane-1,4-diol, hexane-1,6-diol or 
neopentyl glycol; and polyols such as, for example, trimethylol propane, 
glycerol, trimethylol ethane, pentaerythritol, sorbitol and/or oligomeric 
glycerols. Besides the unmodified alcohols, however, derivatives thereof, 
for example reaction products with ethylene oxide and/or propylene oxide, 
may also be used for the transesterification reaction. For example, 
alkoxylated alcohols containing 2 or 3 OH groups, such as ethane diol, 
propane diol, glycerol, pentaerythritol, trimethylol propane and/or 
trimethylol ethane, may be used. Parameters such as, for example, 
hydrolysis stability, hydrophilicity or even the gel time can be further 
influenced by the incorporation of such alcohols. 
Besides their use as alcohols in the transesterification reaction, the low 
molecular weight polyhydric alcohols mentioned above may be added both in 
unmodified form and in alkoxylated form to the polyol mixture containing 
the modified castor oil. 
Suitably functionalized macromolecules, for example hydroxy-terminated 
polyesters or polyurethanes and suitably functionalized polyacrylates, may 
optionally be used as a further constituent of the polyol mixture. 
Besides the polyol mixtures, the polyisocyanates are the second important 
building block for the polyurethane materials according to the invention. 
Isocyanates react with free hydroxy groups to form a urethane group in an 
addition reaction well-known to the expert. In general, suitable 
isocyanate components according to the invention are any of the usual 
polyfunctional aromatic and aliphatic isocyanates and, for example, any of 
the oligomeric and polymeric isocyanate compounds obtainable by the 
oligomerization or cyclization of polyisocyanates in the presence of 
moisture or by reaction of polyhydric alcohols with polyisocyanates. The 
polyisocyanates may be used in more or less than the stoichiometrically 
necessary quantities. Examples include hexamethylene diisocyanate, HDI 
trimer (tris(6-isocyanatohexyl)isocyanurate (Tolonate.RTM. HDT, 
Rhone-Poulenc), 4,4-diphenylmethane diisocyanate (MDI) (Desmodur.RTM. 
Bayer AG), HDI biuret (1,3,5-tris(6isoisocyanatohexyl)biuret, 
hexamethylenediisocyanate (Desmodur.RTM. N75, Bayer AG) and an aromatic 
polyisocyanate based on toluene diisocyanate (Desmodur.RTM. L67, Bayer 
AG). The isocyanates may be used both in pure form and in the form of 
technical mixtures with or without solvent. 
The reaction between polyols and isocyanates normally takes place at a 
temperature in the range from 0 to 100.degree. C. and preferably at a 
temperature in the range from 5 to 50.degree. C. For processing, the 
components are normally first intensively mixed and then processed during 
the remaining pot life. The components may be mixed either by the user 
himself by stirring, whisking or other measures suitable for mixing, 
although mixing may also be carried out by an automatic mechanism, as for 
example during removal from a pressurized container with separate 
compartments for polyol and isocyanate. The mixture thus formed may be 
further processed to coatings, casting resins, foams or composite 
materials. Accordingly, the ratio of NCO to OH groups can vary according 
to the intended application. In general, an NCO:OH ratio of 8:1 to 1:8 or 
4:1 to 1:4 is sufficient for all applications. However, it is well known 
to the expert that a narrower NCO:OH ratio, for example from 1.5:1 to 
1:1.5, generally leads to products of relatively high molecular weight. 
Where particularly durable and rigid materials are required, an NCO:OH 
ratio of about 1:1 is recommended. 
Accordingly, the present invention also relates to a process for extending 
the gel time of polyurethane resins of isocyanates and a polyol component 
with an NCO:OH ratio of 10:1 to 1:10, characterized in that castor oil 
heated for about 0.5 to 15 hours to 100-300.degree. C. in the presence of 
a basic lithium salt is used in a quantity of 0.1 to 100% by weight as a 
constituent of the polyol component. 
The production of polyurethane foams generally requires at least one 
blowing agent and, optionally, one stabilizer. In addition, other 
additives, for example solvents, flameproofing agents, plasticizers, cell 
regulators, emulsifiers, fungicides, fillers, pigments and antiagers, may 
be incorporated. 
Preferred blowing agents are 1,1,1,2-tetrafluoroethane, 1,1-difluoro ethane 
and dimethyl ether. However, carbon dioxide, dinitrogen oxide, n-propane, 
n-butane and isobutane may also be used. Chlorine-free fluorocarbons with 
boiling points of -40 to +60.degree. C., propane/butane mixtures and 
dimethyl ethers or mixtures thereof are preferably used as blowing agents 
and solvents. 
The foam-forming composition may additionally contain stabilizers. 
"Stabilizers" in the context of the invention are, on the one hand, 
stabilizers which stabilize the viscosity of the composition during 
production, storage and application. Monofunctional carboxylic acid 
chlorides, monofunctional highly reactive isocyanates and non-corrosive 
inorganic acids, for example, are suitable for this purpose. Benzoyl 
chloride, toluene sulfonyl isocyanate, phosphoric acid or phosphorous acid 
are mentioned by way of example. 
Stabilizers in the context of the invention are also antioxidants, UV 
stabilizers or hydrolysis stabilizers. The choice of these stabilizers is 
determined on the one hand by the principal components of the composition 
and, on the other hand, by the application conditions and by the loads the 
foam plastic is expected to withstand. Normally, antioxidants, optionally 
in combination with UV stabilizers, are mainly required. Examples of 
suitable UV stabilizers are the commercially available sterically hindered 
phenols and/or thioethers and/or substituted benzotriazoles or sterically 
hindered amines of the HALS (hindered amine light stabilizer) type. 
Hydrolysis stabilizers, for example of the carbodiimide type, may 
optionally be used to stabilize the ester bonds. 
The present invention also relates to the use of the polyurethanes 
according to the invention in composite materials and/or blends, blends in 
the context of the invention being homogeneous micro- or macro-separated 
mixtures with other polymers. To this end, the polyurethanes may be 
processed in various mixing ratios with one or more additional components 
to form a material having improved and/or new properties. In contrast to 
fillers, which mainly have a cost-reducing function, the additives 
discussed in the following perform a functional task in the material 
mainly associated with an improvement in its physical properties. 
To produce composite materials, the polyurethanes according to the 
invention are processed, for example, with natural or synthetic fibers, 
chopped strands, cloths or the like. Suitable materials are, for example, 
natural fibers, such as silk, cotton, wool, jute, hemp, flax, sisal, straw 
or the like. However, secondary products of these fibers in their 
processed form, for example as woven cloths, are also suitable. The fibers 
may be incorporated in the polyurethanes according to the invention both 
in untreated form and in treated form. Suitable surface treatment 
formulations are, for example, the siloxane-based or polyester-based sizes 
known to the expert for such surface treatments. Many of the composite 
materials thus formed have excellent stability, tear strength, abrasion 
resistance and toughness, as required for many applications. Besides 
natural fibers, synthetic fibers, for example polyamide, polyester, 
polyether or carbon fibers or even inorganic fibers, for example glass 
fibers and glass fiber mats, may also be incorporated. 
Accordingly the polyurethanes according to the invention are suitable in 
principle for the production of foams, casting resins, coatings and/or 
composite materials.