Rapidly crosslinking fluoropolymer

Details Rapidly crosslinking fluoropolymer Rapidly crosslinking fluoropolymer

2003-02-19

2004-06-01

Lipman, Bernard (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S222000, C526S250000

Reexamination Certificate

active

06743874

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a rapidly crosslinking liquid fluoropolymer containing the essential components tetrafluoroethylene and at least one compound from the group diiodomethane, 1,2-diiodo-1,1-difluoroethane, 1-iodo-2-bromo-1,1-difluoroethane, 1-bromo-2-iodo-1,1-difluoroethane and/or 1,2-dibromo-1,1-difluoroethane, which has certain portions on the terminal group of the formula —CH
2
—X where X=Br and/or iodine and iodine/bromine contents in the range 0.05 to 1 wt. % and a certain molecular weight and viscosity, a process for producing it and its use.
BACKGROUND OF THE INVENTION
There is a general wish in the rubber industry for better processability of the rubbers used. This relates in particular to flow properties. The lower the viscosity of the rubber, the easier the processing technology and thus the greater the productivity and the smaller the amount of waste. These aspects are particularly relevant to fluororubbers, as they are expensive rubbers which cannot all be processed in the injection moulding machinery of the rubber industry.
Most fluororubbers with Mooney viscosities (ML
1+10
at 120° C.) >60 can be processed only by compression- or transfer moulding methods. Fluororubbers with Mooney viscosities of ≦60 can be processed in special injection moulding machines for solid rubbers, but this requires long cycle times and also produces a considerable amount of waste (flash-out).
Rubbers with Mooney viscosities (ML
1+10
at 120° C.) of 20-60 Mooney units are known, which can be processed into compression mouldings by this principle. The mechanical properties of these rubbers are not noticeably impaired [P. Ferrandez, St. Bowers, Gummi Fasem Kunstst. 48 (1995) 626-633].
A greater reduction of the molecular weight of rubbers, particularly fluororubbers, in order to reduce their viscosity still further impairs the properties of the vulcanised material, in particular the strength. Liquid fluororubbers are known from U.S. Pat. No. 5,852,125. However, the fluororubbers described here have a lower molar mass and a higher iodine content than those disclosed in this application. They are also slower to crosslink.
Furthermore, storage stability is still a problem today with many mixtures. The low-molecular fluororubbers with iodine contents of 1 to 30 wt. % described in U.S. Pat. No. 4361678, for example, which contain a molecular weight regulator of the type Rf/I
x
, wherein Rf is a perfluorocarbon-, chloroperfluorocarbon- or chlorofluorocarbon group, are not stable during storage. The lack of storage stability is probably due to the fact that the iodine atom in the regulator is bonded to a carbon atom containing at least one fluorine atom, preferably to a chloroperfluorocarbon group, and thus at least half of the resulting terminal groups have the structure —Rf—I, e.g. —CF
2
—I. The iodine-carbon bond in such groups is particularly labile and iodine can very easily be split off thermally or under the influence of light. This makes the handling of fluoropolymers with high iodine contents very difficult. The reactive groups intended for crosslinking may also react prematurely and the resulting polymeric radicals may recombine. Crosslinked mouldings produced from this material also have poor ageing properties, see V. Arcella et al., Kautsch., Gummi, Kunstst., 44 (1991) 833-837.
According to WO 94/07929, regulators, which contain at least one iodine or bromine atom on a CH
2
group, as described e.g. in JP-A 60 221 409 and EP-A 101 930, have the disadvantage that they severely retard polymerisation. Hitherto, they have been used only to produce fluororubbers with high molecular weights or low iodine contents.
Of the non-aqueous processes, polymerisations in the pure liquefied fluoromonomer have proved disadvantageous, as most of the resulting polymers are not soluble in it and also swell only a little. A reproducible polymerisation with good heat and mass transfer and thus acceptable space-time yields is equally impossible by this means.
However, fluoromonomers can be polymerised well in the presence of certain fluorine-containing solvents, see e.g. U.S. Pat. No. 4,243,770, DE-A 196 40 972.1. U.S. Pat. No. 5,182,342 describes the use of fluorocarbons in the presence of up to 20% water as polymerising medium, which fulfill certain criteria with regard to the F/H ratio and the position of the hydrogens. With all compounds of this type, which contain hydrogen and optionally also chlorine, there is always the problem that they may enter into these transfer and/or termination reactions.
In WO-98/15583, 1,1,2-trichlorotrifluoroethane is used as the polymerising medium. However, compounds of this type (chlorofluorocarbons) have considerable ozone-damaging potential and for this reason, their use in industry is prohibited in many industrialised countries. The fluororubbers described in this patent contain 0.5-2.5 wt. % iodine terminal groups.
In the application DE 197 40 633, liquid fluororubbers are produced in inert solvents of the type RF-SO2F or perfluoroalkylsulfone in the presence of a molar mass regulator. The fluororubbers described here also have iodine or bromine terminal groups, but the combination of features in this application and their surprising influence on the crosslinking speed is not mentioned.
Application WO-A-98/15583 describes a liquid fluororubber and a process for producing it. However the combination of features in this application and their surprising influence on the crosslinking speed is not mentioned and the molar masses are too small.
There was thus still a need for liquid fluororubbers, which are pumpable at least at slightly raised temperatures (60-120° C.) and can be processed in conventional thermoplastic processing machines. These liquid fluororubbers should also remain stable during storage and crosslink rapidly and the resulting rubber pieces should have good mechanical and ageing properties, which are very close to those of conventional solid fluororubbers.
SUMMARY OF THE INVENTION
The object of the present invention was therefore to provide fluororubbers which have these properties.
A further object of the invention was to remove, at least partially, the disadvantages of the fluororubbers known from the prior art.
It was found, that fluororubber consisting of the essential components tetrafluoroethylene and at least one compound from the group diiodomethane, 1,2-diiodo-1,1-difluoroethane, 1-iodo-2-bromo-1,1-difluoroethane, 1-bromo-2-iodo-1,1-difluoroethane and/or 1,2-dibromo-1,1-difluoroethane,
which has certain portions on the terminal group of the formula —CH
2
—X where X=Br and/or iodine and iodine and/or bromine contents in the range 0.05 to 1 wt. % and a certain molecular weight and viscosity, solves this problem.
DETAILED DESCRIPTION OF THE INVENTION
The present invention therefore relates to a liquid fluoropolymer which can be produced from tetrafluoroethylene and optionally other fluorine-containing and/or non-fluorine containing monomers and at least one co-compound from the group diiodomethane, 1,2-diiodo-1,1-difluoroethane, 1-iodo-2-bromo-1,1-difluoroethane, 1-bromo-2-iodo-1,1-difluoroethane and/or 1,2-dibromo-1,1-difluoroethane, in which at least 80% of the terminal groups has the formula —CH
2
—I and/or —CH
2
—Br and which has a complex viscosity at 100° C. and &ohgr;=6.3 s
−1
of 0.01-30 kpas and a temperature index, calculated as the quotients of the viscosities at 40 and 100° C. of 3-250, characterised in that, the fluoropolymer
a) has more than 10 mol % repeated units derived from tetrafluoroethylene,
b) contains in the range of 0.05 to 1 wt. % iodine and/or bromine and
c) has an average molecular weight (number average Mn) of over 25,000 g/mol.
Fluorine-containing monomers according to the invention are preferably fluorinated, optionally substituted ethylenes, which may contain, besides fluorine, hydrogen and/or chlorine, such as e.g. vinylidene fluoride and chlorotrifluoroethylene, fluorinated 1-alkenes with 2-8 carbon atoms, such as e.g. hexafl

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