Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-12-04
2001-02-13
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C092S047000
Reexamination Certificate
active
06187876
ABSTRACT:
The invention relates to a product obtained from copolyether ester elastomers and to the copolyether ester composition required therefor.
Copolyether ester compositions are used for example there where the product made from them is exposed to frequent deformation. Very well-known applications are in this context bellows for protecting drive and transmission shafts, steering columns and suspension assemblies and sealing rings. In such applications the material also frequently or continuously comes into contact with lubricants, such as oils or greases. The resistance of the copolyether ester compositions to the effects of oils and greases is one of the reasons, alongside their simple processability in relatively complex shapes, for their wide use. The continuing miniaturisation of, among other things, the so-called CV (constant velocity) joints in automobiles has led to a demand for an improved lubricant to meet the higher requirements relating to friction and tribology. New lubricants have been developed to this end, which function well even at the higher ambient temperatures associated with the continuing development of automobiles.
However, it has now been found that, at the elevated operating temperatures, these newly developed lubricants cause much faster aging of sealing bellows made from the currently common thermoplastic elastomer compositions, as a result of which tear initiation soon occurs, followed by rapid tear propagation at bending points and premature leakage of lubricant.
The aim of the invention, then, is to provide a thermoplastic elastomer composition which, under the more severe conditions with the new lubricants, prevents premature leakage of lubricant from the products obtained therewith.
It has now been found that this aim is achieved with a copolyether ester composition comprising a mixture of at least 2 copolyether esters A and B, composed of hard segments derived from at least one alkylene glycol and at least one aromatic dicarboxylic acid and soft segments derived from at least one polyalkylene oxide glycol and at least one aromatic dicarboxylic acid, in which the concentration of soft segments X in A and the concentration of soft segments Y in B lie between 30 and 65 wt. %, relative to the copolyether ester and the molecular weight M of X and Y lies between 500 and 3000 and |Mx−My|≧400.
Mixtures of copolyether esters are known from U.S. Pat. No. 4,751,132, JP-A-5905851 and JP-A-61203165. The mixture of U.S. Pat. No. 4,751,132 contains as one component a copolyether ester containing at least 75 wt. % soft segments and exhibits too low a melting point and poor mechanical properties. The copolyether ester mixture of JP-A-5905851 consists of 2 copolyether esters A and B in a weight ratio of 40-90:60-10, in which A and B contain 45-70 and 60-85 wt. % identical soft segments, respectively. This composition, too, shows the drawbacks of the composition of U.S. Pat. No. 4,751,132, though to a lesser extent.
JP-A-61203165 discloses a mixture of 2 copolyether esters A and B, of which A and B contain 10-60 wt. % soft segments and the concentration of soft segments in A is 2-20 wt. % higher than the concentration of soft segments in B. In the examples the molecular weights of the soft segments in A and B are the same. The flow properties are improved relative to those of the individual copolyether esters and the flexural fatigue behaviour lies between that of the individual copolyether esters.
It is very surprising that a greatly improved flexural fatigue behaviour is obtained with the copolyether ester composition according to the invention.
The copolyether esters of the composition according to the invention are state of the art and are described in for example “Encyclopedia of Polymer Service and Engineering”, Vol. 12, pp.75-117 (1988).
Alkylene diols with 2-12 C atoms, preferably with 2-4 C atoms, can be mentioned as examples of alkylene diols. Examples of aromatic dicarboxylic acids are phthalic acids, preferably terephthalic acid, naphthalene dicarboxylic acids and diphenyldicarboxylic acids. Preferably the dicarboxylic acid is terephthalic acid or a mixture of tere- and isophthalic acid in a molar ratio of at least 80:20, naphthalene dicarboxylic acid or 4,4′-diphenyldicarboxylic acid or a mixture of 4,4′-diphenyldicarboxylic acid and terephthalic acid. The molecular weight of the hard segments may vary within a wide range, for example between 400 and 4000, preferably between 600 and 2500.
The poly(alkylene oxide) glycol is for example poly(propylene oxide) glycol. Poly(butylene oxide) glycol is preferable. The molecular weight of the poly(alkylene oxide) glycol segments lies between 500 and 3000, preferably between 600 and 2500. The molecular weights of the poly(alkylene oxide) glycol segments of copolyether esters A and B differ by at least 400, preferably by at least 500, even more preferably by at least 750.
The concentrations of soft segments in A and B generally lie between 30 and 65 wt. %, preferably between 35 and 60 wt. %, even more preferably between 40 and 60 wt. %. Preferably the concentrations of soft segments X and Y in A and B, respectively, are chosen so that the number average molecular weights of the hard segments in A and B differ by not more than a factor of 5, preferably by not more than a factor of 3. Even more preferably the number average molecular weights of the hard segments in A and B are almost the same.
The A:B weight ratio may vary within a wide range, for example between 0.1 and 10, preferably between 0.25 and 4, even more preferably between 0.5 and 2.
In aging processes it has most surprisingly been found that delamination took place in the aged samples of the invention. This effect is indicative of the presence of two unmixed phases. According to the inventors this explains the superior behaviour of the composition according to the invention.
For this reason the present invention also covers a copolyether ester composition comprising at least 2 copolyether esters A and B that are at least partly unmixed. The partly unmixed condition may be caused by A and B being incompatible even under very intensive stirring conditions. On the other hand, complete mixing may be deliberately prevented, for example by choosing copolyether esters A and B with viscosities that differ only little from one another or by choosing very mild stirring conditions, or by choosing both.
It is incidentally also possible to control the viscosities of A and B by incorporating a multifunctional compound; a well-known example of such a multifunctional compound that ensures a controlled degree of crosslinking is trismethylolpropane (TMP), which is used in a concentration of between 0.05 and 5.0 wt. %, preferably 0.05 and 3.0 wt. %, relative to the polyether ester, or by incorporating a diisocyanate, which causes chain lengthening.
In the last case the copolyether esters concerned may in principle be completely miscible, but A and B are deliberately mixed in co-continuous phases in the composition.
In addition, the invention also covers products obtained with a composition according to the invention.
The invention also covers the use of this product under conditions of dynamic deformation in flexure.
Particularly advantageous is the use under dynamic deformation in the case of contact with oils and greases at elevated temperatures. The greatest advantage over the products according to the state of the art is obtained at temperatures of at least 125° C.
The composition according to the invention preferably also contains 0.05-2 wt. %, preferably 0.1-1.5 wt. %, of an oxidation stabiliser, for example sterically hindered phenolic or secondary amines. Very suitable are polyphenols containing amide.
The composition according to the invention may also contain the usual fillers, preferably in minor amounts, i.e. less than 50 wt. %, even more preferably less than 35 wt. %, most preferably less than 25 wt. %, of the composition including the fillers. Examples of fillers are carbon black, talcum, clay, colorants. If so desired, other
Berendse Henk W.
Fudala Béla B.
Vulic Ivan
DSM N.V.
Pillsbury Madison & Sutro LLP
Short Patricia A.
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