Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-05-18
2003-10-07
Sellers, Robert E. L. (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C523S466000, C523S468000, C524S507000, C524S513000, C524S514000, C524S517000, C524S521000, C524S522000, C524S529000, C524S533000, C524S534000, C524S535000, C524S555000, C524S558000, C524S572000, C427S386000
Reexamination Certificate
active
06630204
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to hard-rubber coatings for protection against corrosion.
BACKGROUND OF THE INVENTION
Hard-rubber coatings or rubberlinings have been used for decades as protection against corrosion for steel surfaces and concrete surfaces. For this purpose, unvulcanised or pre-vulcanised rubber sheets are traditionally glued on to the surface to be protected and subsequently, so far as required, vulcanised at an elevated temperature. With so-called factory rubberlinings, this last step takes place, as a rule, in an autoclave under excess pressure. A decisive cost factor in the case of this method is the high expenditure on time and work that is required for the lining of the often geometrically demanding structural components.
It is therefore desirable to find a system which can be applied by simple methods (such as spraying or rolling, for example) and, apart from this, does not have to rely on the additional use of adhesives.
For some years, so-called “liquid hard rubbers” with a content of low-molecular polybutadienes have been known, which, in contrast to conventional rubber mixtures, are viscous liquids. After vulcanisation, the coatings produced therewith have the properties of a hard rubber.
A system described in DE-A 37 40 181 is based on a low molecular 1,4-cis-polybutadiene, to which, in addition to fillers and vulcanisation chemicals, is also added a highly aromatized polybutadiene, partly in combination with a copolymer of isobutylene and isoprene, in order to improve resistance to chemicals and mechanical properties. A similar system, likewise based on linear 1,4-cis-polybutadiene, was described by O. Figovsky et al. (Proceedings of International Conference: Corrosion in Natural and Industrial Environments: Problems and Solutions, Grado, 1995).
The use of epoxidized low-molecular polybutadienes as a base for liquid hard rubbers is suggested in WO-A 98/22225. In this case, in addition to the vulcanisation process by means of sulphur, a cross-linking as a result of reaction of the epoxide groups with amines is also to take place. An improvement in the mechanical properties is achieved by the addition of a high-molecular butadiene-nitrile rubber.
The flow processes which occur during heating are a fundamental problem in the use of liquid rubbers. Above all in the case of comparatively thick layers, they lead to not yet cross-linked or vulcanised mixture running off non-horizontal surfaces. Mixtures described hitherto, which are adjusted by admixtures or other mixing ratios in such a way that this problem is slightly less pronounced, can be processed only with difficulty because of their high viscosity.
It is therefore the object of the present invention to make available a liquid hard-rubber coating agent which has a low viscosity suitable for spray application and which displays no run-off from non-horizontal walls, or as little run-off as possible, in the case of the subsequent heating required for vulcanisation.
SUMMARY OF THE INVENTION
Surprisingly, it has been discovered that this requirement can be fulfilled if a coating agent based on liquid rubbers, optionally in combination with a reactive diluent of low viscosity, is, immediately after application, solidified to such an extent as a result of a prepolymerization or pre-cross-linking preceding the vulcanisation that a run-off is substantially or completely prevented. In order to do this, functionalised rubbers are used having those reactive groups that react with an added chain extension agent or cross-linking agent, forming preferably covalent bonds, and thereby forming lengthened or branched molecules.
Therefore, mixtures containing the indicated mass fractions of the following constituents are the subject-matter of the invention:
10 to 90%
of at least one functionalised low-
molecular rubber A,
1 to 50%
of at least one cross-linking agent B for
the functionalised rubber A, and
optionally
0.01 to 10%
accelerators/catalysts C for the pre-
cross-linking reaction,
0 to 60%
reactive diluents D,
1 to 50%
vulcanisation chemicals E,
5 to 50%
fillers F and optionally auxiliary
substance G,
wherein the sum of the mass fractions in the mixture must always be 100%, and at least one of the average functionalities of the constituents A or B is at least 2. “Mass fraction” denotes the ratio of the mass of an individual component to the total mass.
Preferably, the mass fraction of A amounts to 15 to 60%, in particular 20 to 50%; that of the cross-linking agent B amounts to 1.5 to 45%, in particular 2 to 40%; that of the accelerators C amounts to 0.02 to 7%, in particular 0.05 to 5%; that of the reactive diluents D amounts to 2 to 55%, in particular 5 to 50%; that of the vulcanisation chemicals E amounts to 2 to 45%, in particular 5 to 40%, and finally the sum of the mass fractions of fillers and auxiliary substances F and G amounts to 7 to 45%, in particular 10 to 40%.
The presence of the cross-linking agent B is required for the pre-cross-linking or pre-polymerization (=chain lengthening) of the low-molecular rubber. The expression cross-linking agent is used in the following for reasons of simplification; in this connection, however, it can also be, in principle, a compound (chain-lengthening agent) which in combination with a rubber A leads only to the formation of a linear polymer.
The functionalised low-molecular rubber A and the cross-linking agent B for this rubber are contained separately from each other in different components of a two-component system, while the other constituents C to G can be distributed between the two components in any desired way. The accelerator C for the pre-cross-linking or the pre-polymerization is advantageously also separated from the cross-linking agent B if its stability is impaired thereby.
The functionalised low-molecular rubber A is preferably one or more of (co)polymerizates of monomers selected from doubly saturated or multiply unsaturated hydrocarbons, in which case singly olefinically unsaturated monomers, such as styrene, acrylic ester and acrylonitrile, for example, can additionally be present in the monomer mixture if appropriate. The rubbers A have olefinic double bonds along the main chain and/or in side chains, which double bonds are accessible to the usual vulcanisation with sulphur. Additionally, these functionalised low-molecular rubbers A also have reactive groups at the chain ends (terminal) and/or in side chains (lateral), which groups react with the cross-linker B forming oligomers or partially cross-linked systems. In this connection, the reactive groups of the cross-linking agent B are such that they react with the reactive groups of the rubber A, preferably forming covalent bonds. The functional groups of the low-molecular rubber A and those of the cross-linking agents B are therefore selected in each case from the group consisting of hydroxyl groups, epoxide groups, carboxylic acid anhydride groups, carboxyl groups, amine groups and isocyanate groups, and A and B are combined in such a way that upon the reaction of A and B, their functional groups react, forming a urethane bond —NR—CO—O—, an ester bond —CO—O—, a urea bond —NR—CO—NR—, a &bgr;-hydroxyamine bond —CR(OH)—NR—, or an acid amide bond —CO—NR—. The radical R in these formulae can be the same or different and signify hydrogen, linear, branched or cyclic aliphatic radicals with preferably 1 to 20 carbon atoms or aromatic radicals with preferably 5 to 16 carbon atoms.
In this connection, those mixtures in which the rubber A is hydroxy-functional and the cross-linking agents B have functional groups selected from isocyanate groups, acid anhydride groups and epoxide groups are preferred.
It is advantageous that the average functionality of the rubbers A is 1.5 to 5.5 and that the average functionality of the cross-linking agents B is 5.0 to 1.9. In particular, those combinations in which the average functionality of A is 1.8 to 2.3 and that of the cross-linking agents B is 4 to 2.0 are advantageous. B
Burkhart Thomas
Hessel Gerd
Hoelter Dirk
Connolly Bove & Lodge & Hutz LLP
Sellers Robert E. L.
SGL Acotec GmbH
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