Method of producing polyurethanes with increased resistance to abrasion

Abrasion resistant polyurethane elastomers using a combination of a waxing agent, a powdered mineral type lubricant and a polyhalogenated polyalkylene powder are disclosed. Although all three types are known to impart abrasion resistance to polyurethane elastomers, a synergistic effect has been found in the use of these additives such that better abrasion resistance is found with smaller quantities of additives.

The present invention generally relates to polyurethane elastomers with 
additives which impart abrasion resistance and low friction factors. 
BACKGROUND OF THE INVENTION 
It is well known to use various release aids, slip agents, internal and 
external lubricants, and various polymers as blends or on the surface of 
polyurethanes for reducing surface friction and increasing abrasion 
resistance. 
For example, in Mobay Chemical Co., Technical Bulletin TIB 37-V13, 
"Semi-Self Lubricating Multrathane Types from Graphite," the advantages of 
using graphite as an additive are discussed. Also in U.S. Pat. No. 
2,951,053 the use of molybdenum disulfide is disclosed. The use of these 
additives enables polyurethane elastomers to be used in applications 
requiring low friction. The elastomers become essentially self-lubricating 
and more abrasion resistant. 
DESCRIPTION OF THE INVENTION 
It has been found that combinations of certain additives in small amounts 
are more useful and produce polyurethanes with better abrasion resistance 
than are obtainable with only one of the additives. It has also been found 
that less of the combination of additives is required than would be 
expected on the basis of the observed results from each alone. 
Accordingly, the present invention relates to the use of a combination of a 
waxing agent, a powdered mineral type lubricant and powdered 
polyhalogenated polyalkylenes in conjunction with the making of 
polyurethane elastomers. It is possible to use a smaller amount of a 
combination of additives than would be necessary to impart a similar 
resistance given a similar amount of only one additive. 
Suitable starting materials for the production of elastomeric polyurethanes 
according to the invention include those organic compounds which contain 
at least two hydroxyl groups and have a molecular weight of from about 800 
to about 5000, preferably a molecular weight of from about 1000 to about 
3000. 
Any suitable hydroxyl polyester may be used such as linear or slightly 
branched polyesters obtained, for example, from oxycarboxylic or 
carboxylic acids and mono- or polyhydric alcohols optionally with amino 
alcohols, diamines, oxyamines and diamino alcohols. Any suitable 
polycarboxylic acid may be used such as, for example, oxalic acid, malonic 
acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic 
acid, azelaic acid, brassylic acid, sebacic acid, thapsic acid, maleic 
acid, fumaric acid, glutaconic acid, diethylsuccinic acid, isophthalic 
acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, and the like as 
well as hydroxy carboxylic acids. Any suitable primary hydroxylic 
polyhydric alcohol may be used such as, for example, ethylene glycol, 
diethylene glycol 1,5-pentane diol, 1,6-hexane diol, 1,7-heptane diol and 
the like. The polyesters may contain double or triple bonds in unsaturated 
fatty acid moieties. 
Any suitable linear or slightly branched polyether, such as, a polyhydric 
polyalkylene ether may be used such as, for example, the condensation 
product of an alkylene oxide optionally with any suitable initiator. The 
initiator may be difunctional compounds including water so that the 
resulting polyether is essentially a chain of repeating alkylene oxy 
groups as in polyethylene ether glycol, poly 1,4-butylene ether glycol and 
the like; of the initiator may be any suitable active hydrogen containing 
compound which may be a monomer or even a compound having a relatively 
high molecular weight including other active hydrogen containing compounds 
as disclosed above. It is preferred that the initiator has 2 active sites 
to which the alkylene oxides may add including, for example, amines, 
polyfunctional alcohols, amino alcohols and the like. Any suitable 
alkylene oxide may be used such as, for example, ethylene oxide, 
tetrahydrofuran and epihalohydrins. Copolymers of this type may also be 
used. Any suitable initiator may be used including, for example, water, 
polyhydric alcohols, preferably having 2 hydroxyl groups, amino alcohols, 
amines preferably having 2 replaceable hydrogen atoms bonded to nitrogen 
atoms. 
There are many desirable processes for the preparation of polyhydric 
polyalkylene ethers including U.S. Pat. Nos. 1,922,459, 3,009,939 and 
3,061,625 or by the process disclosed by Wurtz in 1859 and in Encyclopedia 
of Chemical Technology, Volume 7, pages 257 to 262, published by 
Interscience Publishers, Inc. (1951). 
Specific examples of difunctional initiators (i.e., those having two active 
hydrogen atoms) are water, ethylene glycol, aniline, diethylene glycol, 
hexane-1,6-diol, N-methyl diethanolamine and the like. 
The hydroxyl polyester may also be a polyester amide such as is obtained, 
for example, by including some amine or amino alcohol in the reactants for 
the preparation of the polyesters. Thus, polyester amides may be obtained 
by condensing an amino alcohol such as ethanolamine with the 
polycarboxylic acids set forth above or they may be made using the same 
components that make up the hydroxyl polyester with only a portion of the 
components being a diamine such as ethylene diamine and the like. 
Any suitable polyacetal may be used such as, for example, the reaction 
product of formaldehyde or other suitable aldehyde with a polyhydric 
alcohol such as those disclosed above for use in the preparation of the 
hydroxyl polyesters. Also, any suitable polycarbonates may be employed if 
desired. It is also possible to employ mixtures of various organic 
compounds having at least two hydroxyl groups and a molecular weight of 
from about 800 to about 5,000. 
Any suitable organic diisocyanate may be used in the process of the present 
invention including aromatic, aliphatic and hetrocyclic diisocyanates. In 
other words, two isocyanate radicals may be bonded to any suitable 
divalent organic radical to produce the organic diisocyanates which are 
useful in accordance with the present invention including acyclic, 
alicyclic, aromatic and hetrocyclic radicals. Suitable organic 
polyisocyanates are, therefore, ethylene diisocyanate, ethylidene 
diisocyanate, propylene-1,2-diisocyanate, 1,4-butane diisocyanate, 
1,6-hexane diisocyanate, 1,8-octamethylene diisocyanate, 
cyclohexylene-1,2-diisocyanate, m-phenylene diisocyanate, 2,4-toluene 
diisocyanate, 2,6-toluene diisocyanate, 3,3'-dimethyl-4, 4'-biphenylene 
diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 
3,3'-dichloro-4,4-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 
furfurylidene diisocyanate and the like. 
Examples of preferred diisocyanates include aliphatic diisocyanates, having 
the general formula: 
EQU OCH--(CH.sub.2).sub.n NCO 
wherein n represents a number from 2 to 8; cycloaliphatic diisocyanates, 
such as hexahydrotolylene-2,4- and 2,6-diisocyanate and mixtures of these 
isomers, 4,4'-dicyclohexyl methane diisocyanate, 1,4-diisocyanato 
cyclohexane, 1,3-diisocyanato cyclohexane, araliphatic diisocyanates such 
as tolylene-2,4 or 2,6-diisocyanate and mixtures of these isomers such as 
a mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene 
diisocyanate, phenylene-1,4-diisocyanate, phenylene-1,3-diisocyanate, 
diphenylmethane-4,4'-diisocyanate, diphenyl ether 4,4'-diisocyanate, 
naphthylene-1,5-diisocyanate and the like. Isophorone diisocyanate and 
ester diisocyanates of carboxylic acid of the kind described, for example, 
in British Patent Specifications No. 965,474 and 1,072,956 may also be 
used as diisocyanates in accordance with the invention. Proportions of 
triisocyanates such as, benzene-1,3,5-triisocyanate or p,p',p"-triphenyl 
methane triisocyanate and the like may be used. Most preferred isocyanates 
are p-phenylene diisocyanate, diphenylmethane-4,4'-diisocyanate and 
naphthalene-1,5-diisocyanate. 
In addition to polyols which contain primary hydroxyl groups, it is also 
possible to use polyols which contain secondary hydroxyl groups, provided 
they are used in the form of prepolymers. Some examples of compounds 
containing secondary hydroxyl groups are 1,2-propylene glycol, 
1,3-butylene glycol, 1,3-pentane diol, 1,4-pentane diol and the like. The 
most preferred prepolymers of secondary hydroxyl group containing 
compounds are those prepared from propylene glycol and diphenyl methane 
diisocyanate and polyesters containing secondary hydroxyl groups with 
diphenyl methane diisocyanate. 
The elastomers may be prepared by the known one-shot or prepolymer methods 
and the formulations may include, in addition to these components 
mentioned above, various catalysts, fillers and the like which are known. 
Extensive details concerning the formulations and processing parameters 
for making polyurethane elastomers may be found in e.g. Saunders and 
Frisch, Polyurethanes: Chemistry and Technology, Part II, 1974, pages 
299-451 and Wright and Cumming, Solid Polyurethane Elastomers, Maclaren 
and Sons Ltd., London, (1969). 
In general the invention is preferably directed to harder polyurethane 
elastomers such as one-shot and prepolymer type cast elastomers but is 
applicable to all types of elastomers. The abrasion resistant additives 
may be mixed in with the prereacted polyurethane formulation or one of its 
components in an extruder or some other known mixing device. The 
preferable mixing means is in a Banbury mixer. 
Among the powdered mineral type lubricants are graphite, molybdenum 
disulfide, tungsten disulfide, mica, talc, sternbergite, tetradymite, and 
the like. Certain of these compounds such as molybdenum disulfide are 
suitable although not preferred due to their degrading effect on the final 
product when exposed to humid ageing. Graphite is particularly preferred. 
Among the polyhalogenated, polyalkylene powders which are useful as 
components in the present invention are various polyhalogenated 
polyethylenes and polypropylenes known in the art. Particularly preferred 
are Teflon and Teflon-related compounds e.g., tetrafluoroethylene 
fluorocarbon polymers and fluorinated polyethylene and polypropylene. 
Suitable waxing agents include those which are well known, such as 
vegetable waxes. Hoechst waxes S, L, E, OP, S and C; polyethylenes 
polypropylenes, chlorinated paraffins polyoxyethylenes, carbowax, certain 
high molecular weight hydrocarbons, certain carboxylic acids and salts, 
esters, hydroxyl compounds, carbonyl compounds, amides, amines and 
polymeric lubricants etc., may also be used. Details concerning these 
types of waxing agents may be found in Encyclopedia of Polymer Science and 
Technology, Vol. 8, pp. 325-338, Vol. 14, pp. 768-778 and in Encyclopedia 
of Chemical Technology (2 nd ed.), Vol. 22, pp. 156-173, the disclosures 
of which are herein incorporated by reference. 
The abrasion resistance of a given polyurethane will greatly vary with its 
formulation. The effect of any particular additive and any given amount 
thereof on a particular polyurethane cannot be uniformly predicted with 
general rules. However, according to the invention the additives may be 
used in combined amounts of from about 0.1 to about 10% by weight based on 
the weight of the polyurethane. It is preferred that 0.5 to 5% be used. 
The relative amounts of each of the three types of abrasion resistant 
additives used may vary within wide limits. It is preferred that each 
additive be used in a weight ratio of between 1:5 and 5:1 with respect to 
any other additive. 
The polyurethane elastomers of the present invention are particularly 
useful in applications requiring that the product possess high abrasion 
resistance and a low friction factor. The elastomers may be used, for 
example, as impression rolls, auto panels, press brake forming dies, solid 
tires, pallet rollers, liners, gears, gravure rolls, top lift cleats etc.