Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
1998-04-21
2001-01-23
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S172000
Reexamination Certificate
active
06177378
ABSTRACT:
This invention relates to peroxide-containing catalyst compositions and to the use thereof as starter peroxide compositions in the pultrusion process.
Fibre-reinforced continuous plastics sections can be produced by the pultrusion process. In the course of this process, pre-dried fibre rovings are impregnated in a resin bath and are subsequently brought into the desired sectional shape by means of a heated extrusion die tool. The resin crosslinks due to the heat supplied. On the one hand the die used in this process should be as short as possible due to the high frictional forces which occur, and on the other hand the resin has to crosslink to an extent such that the emerging section remains stable in the following pull-off device (Michaeli, W.: “Einfuhrung in die Kunststoff Verarbeitung”, Carl Hansen Verlag 1992, page 150). In other words, it has to be ensured that the gel formation time in the front part of the die is as short as possible, in order thus to prolong the curing phase until the product leaves the die. The latter requirement imposes stringent demands on the temperature-sensitive peroxides or peroxide mixtures, which are dissolved in the resin bath and which determine the course of the crosslinking process, and which thus also determine the quality of the fibre-reinforced final products.
A review of peroxides which have hitherto been used in the pultrusion process is given in the Akzo Nobel publication entitled “The Pultrusion Process, selection criteria for the cure system” (presented to the Conference of the European Pultusion Technology Association, London, 1996). A distinction is made in this publication between highly reactive starter peroxides (which act in the front die region) and into peroxides of lesser reactivity, which are responsible for the final curing.
The present invention relates to the former, i.e. to starter peroxide compositions. The prior art which is relevant thereto is therefore acknowledged below.
The Akzo Nobel publication describes the starter peroxides which determine the prior art, namely bis(4-tert.-butyl-cyclohexyl)-peroxydicarbonate and a methyl isobutyl ketone formulation. Bis(4-tert.-butyl-cyclohexyl)-peroxydicarbonate is normally used in the pultrusion process. This has a peroxide content of 95% by weight, but is only obtainable in solid form and is scarcely soluble in unsaturated polyester resins such as those which are used in the pultrusion process. The peroxydicarbonate therefore has to be dissolved in styrene if unwanted bubble formation in the resin is to be prevented; this comprises an additional operation. If bis(4-tert.-butyl-cyclohexyl)-peroxydicarbonate is stored in styrene, its stability on storage decreases due to thermal polymerisation. Moreover, bis(4-tert.-butyl-cyclohexyl)-peroxydicarbonate is only stable up to 20° C. during storage and transport, i.e. sufficient cooling must be ensured, particularly in hotter regions or in the hotter months of the year. The average pot life of resin compositions which contain bis(4-tert.-butyl-cyclohexyl)-peroxydicarbonate is two days, wherein the average pot life constitutes the period from stirring in the peroxide until the time at which the batch is still capable of being processed.
The second starter peroxide described in the Akzo Nobel publication is commercially available in the form of a methyl isobutyl ketone peroxide formulation with a peroxide content of 45% by weight. Compared with bis(4-tert.-butyl-cyclohexyl)-peroxydicarbonate, this has the advantage of existing in liquid form and is also stable on storage at 25° C. Despite this, the relevance of this formulation to production technology is slight, since the pot lives only range from 6 to 9 hours, due to which the processability of the resin-peroxide composition is severely limited with respect to time and the amount thereof
The object of the present invention was to provide a peroxide composition which eliminates the aforementioned disadvantages of the products which have been used hitherto as a starter peroxide, and which in particular is soluble as a liquid formulation in unsaturated polyester resins, has a higher stability during storage and transport, and ensures long pot lives, without the quality of the final products thereby being impaired.
Surprisingly, this object is achieved by a peroxide-containing catalyst composition which comprises
60 to 80% by weight of a ketone peroxide component (A),
10 to 20% by weight of a ketone ester component (B) and
10 to 20% by weight of an inhibitor component (C),
wherein component (A) behaves in an inert maimer in relation to component (B) and the sum of the proportions by weight of components (A), (B) and (C) is 100% by weight.
The proportion by weight of component (A) is preferably 65 to 75% by weight, the proportion of component (B) is preferably 12.5 to 17.5% by weight and the proportion of component (C) is preferably 12.5 to 17.5% by weight, wherein the sum of the proportions by weight of components (A), (B) and (C) is 100% by weight
Ketone peroxide component (A) in turn consists of 40 to 60% by weight of one or more monomeric ketone peroxides or of a mixture of monomeric and dimeric ketone peroxides, 15 to 40% by weight of a plasticizer, 1 to 10% by weight of a &bgr;-hydroxyketone, 1 to 5% by weight of hydrogen peroxide, 1 to 10% by weight of water and 5 to 15% by weight of a ketone, wherein the sum of these components is 100% by weight.
Methyl isobutyl ketone peroxide, methyl ethyl ketone peroxide, acetylacetone peroxide or cyclohexanone peroxide can be used as ketone peroxides, for example, wherein methyl isobutyl ketone peroxide is preferred. The peroxides generally exist in their monomeric form, but contain subsidiary proportions of dimers. Methyl isobutyl ketone peroxide, which is preferred, can even be used in the pultrusion process at 60° C. without the addition of accelerators in the polyester resin, whilst methyl ethyl ketone peroxide, acetylacetone peroxide and cyclohexanone peroxide can normally only be used above 80° C. However, under the same conditions as those for the use of methyl isobutyl ketone, new applications are opened up where extremely long pot lives are desirable. In some cases the pot life can be prolonged 10-fold (see Table 2 also).
All commercially available plasticizers can be used as plasticizers. In this respect, phthalic acid esters are preferred and dimethyl phthalate is particularly preferred.
Ketoester component (B) primarily serves as a solvent for the ketone peroxides and inhibitors. There are in fact diverse solvents for inhibitors, but these are often unsuitable for dissolving ketone peroxides. Ketoesters have proved suitable. The choice thereof is critical, however, since some ketoesters tend to react with ketone peroxides. Thus, for example, acetoacetic ester is only of limited suitability for the dissolution of acetylacetone peroxide, but has a high reactivity towards the other ketone peroxides according to the invention, i.e. a considerable decrease in active oxygen results (see Table 2). A reactivity of this kind is unacceptable for safety reasons alone. A preliminary choice of ketoester component can be made by means of the “iron(III) chloride test”, for example. If an iron(III) enolate is formed, the tested ketoester component is generally unsuitable in the composition according to the invention. Therefore, the only ketoesters which can be used as ketoester component (B) are those which do not react with ketone peroxide component (A). The use of levulinic acid n-butyl ester, which exhibits inert behaviour towards all the ketone peroxides tested, is preferred in this respect.
The function of inhibitor component (C) is to prolong the pot life of the resin composition by capturing peroxide radicals which are formed. The concentration of the inhibitor component is critical in this respect. If the concentration of the inhibitor is too low, this leads to a significant shortening of the pot life. If it is too high, clear solutions are not formed. It is therefore essential to select the inhibitor concentration so that it amounts
Bell Mark L.
Elf Atochem Deutschland GmbH
Merchant & Gould P.C.
Pasterczyk J.
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