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
1999-06-14
2001-07-24
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...
C525S132000, C525S134000, C525S480000, C525S504000, C525S505000, C525S509000, C525S523000, C525S534000, C525S535000, C525S537000
Reexamination Certificate
active
06265491
ABSTRACT:
The present invention relates to improvements relating to resin compositions, in particular relating to curable thermoset resin compositions, such as epoxy resin compositions, by the provision of a suitable curing means, to the process for the preparation of such curable resin compositions and to the cured products thereof.
Thermoset resins, or thermosets, are characterised by their temperature stability, induced in the curing stage by the onset of cross-linking. The resistance of this product to further application of heat (up to charring point) makes it eminently suitable for a wide number of applications, typically as structural plastics, laminates, surface coatings and adhesives. Additionally, the structural nature of these resins render them with excellent properties of mechanical and electrical strength and chemical resistance. The resins are additionally characterised by a low shrinkage on polymerisation.
It is common practice to incorporate a certain amount of a thermoplastic component in curable thermoset resins to induce additional properties of toughness and ductility and solvent resistance which extends the useful range of these products.
Conventional thermosets include the phenolics, aminoplastics, epoxys and some polyurethanes. Despite their wide range of usefulness, these resins are all characterised by a high processing cost, induced by the requirement for a high curing temperature in order to initiate the cross-linking stage of the curing process, commonly known as the post-curing stage. In European patent application no. EP-A-0 311 349 in the name of ICI Composites Inc are described epoxy resins requiring a curing temperature of the order of 180° C. or more, with the inclusion of a catalyst, in particular, curable resin compositions comprising a thermoset resin component, together with a thermoplastic resin component for property modification, and a poly aryl sulphone curing agent. The curable resins typically pass through a glass transition temperature at 120° C. but require elevated temperatures of 180° C. or more for post-curing, to raise the glass transition temperature (Tg). Typically curing is carried out at elevated pressure in the region of 3 to 7 bar, requiring the use of an autoclave or the like, increasing further both equipment and operation costs.
Whilst it is true that a lower than optimum temperature may be employed, this requires increase in cure time and the possibility that cross-linking may nevertheless not be absolute or that properties may be otherwise compromised, and nevertheless delivers little or no economic saving due to maintaining the selected temperature for a prolonged period. In industrial application, this is moreover significant since the productivity would be significantly reduced were it necessary to cure thermoset products for up to 18 hours, moreover taking up valuable autoclave time.
In certain applications thermoset resins are employed for the preparation of products which are to be produced in limited number as “designer” products, or intended for a small specialist market, or for the preparation of products which have a limited life cycle, not by virtue of their physical or mechanical integrity, but rather by virtue of changes in market demands and renewal of appearance or design. This is a severe limitation of the commercial potential of such products, since the high processing temperatures employed for their preparation necessitate the use of high temperature resistant moulds or tools where such products are made by means of moulding processes. It would be readily apparent that the most temperature resilient tools which are able to maintain their moulding integrity at the required temperatures in excess of 180° C., are typically constructed of metals and as such are expensive to commission and will be required to pay back over a relatively long period of time. This is particularly the case for example, for the manufacture of panels such as for use in the specialist aerospace industry or in the construction of vehicle, caravan, mobile home or motorbike body shells or the like which are typically subject to fluctuating demands of fashion induced by severe competition, and of technology demanding changes in body shell shape for improved stream-lining, road holding, compatibility with other technical components, weight reduction and the like. Application to other products, for example for use in the construction of composite furniture such as household, office or garden items is also envisaged, for the above reasons.
Accordingly, there is need for a curable thermoset resin which may be cured at a temperature which is less than that corresponding to the maximum temperature resistance of a suitable composite material which may be employed as a mould and which mould is required to serve for only a limited number of products and/or a limited lifetime. Moreover there is a need for such curable thermoset resin for the preparation of composite objects or products at low industrial processing cost. Moreover there is a need in some applications for such curable thermoset resin for the preparation of composite objects or products which are unmodified in respect of their mechanical and physical properties by virtue of the modified curable resin and accordingly are able to meet the demands to which the products will be subjected, for example for application in the manufacture of panels as hereinbefore described and in particular aerospace product, racing car, motor car and motorbike panels which must be able to perform to a high level of reliability in terms of mechanical and physical properties.
We have now surprisingly found a resin composition and a process for the preparation thereof which meet the above mentioned requirements in admirable manner, specifically by means of incorporation of a certain class of compounds within a curable thermoset resin composition, which compounds enable the curing at reduced temperature.
REFERENCES:
patent: 3776978 (1973-12-01), Markovitz
patent: 5231150 (1993-07-01), McGrail
patent: 5741879 (1998-04-01), McCormick
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Carter Jeffrey T.
McGrail Patrick Terence
Cytec Technology Corp.
Fitzpatrick ,Cella, Harper & Scinto
Short Patricia A.
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