US-12617753-B2 - Urea derivatives and their use as curatives and curative accelerators for resin systems

Abstract

Bisorthohydroxy aromatic urones and their use as curatives and cure accelerators in resin systems particularly epoxy resin systems provide formulations with good outlife, low curing temperatures and desirable glass transition temperatures after curing, they are particularly useful in prepregs used in the production of components for the aerospace and wind turbine industries.

Inventors

• Christopher Mason

Assignees

• HEXCEL COMPOSITES LIMITED

Dates

Publication Date

20260505

Application Date

20210812

Priority Date

20200813

Claims (2)

1. 1 . A process for the production of an article comprising curing a prepreg by an externally applied temperature of 60° C. to 190° C.; wherein said prepreg comprises: (a) bisorthohydroxy aromatic urone of formulae: wherein R 1 is selected from S, SO2, SO, P, PX, N, NH, or NX, P═O(—OH), P═O(—OX), C═O, a substituted or unsubstituted linear or branched aliphatic radical, or an unsubstituted, halo substituted and/or alkyl substituted aromatic radical and n is a number from 2 to 20; wherein X is a substituted or unsubstituted linear or branched aliphatic radical, or an unsubstituted, halo substituted and/or alkyl substituted aromatic radical; wherein R 2 and R 3 is at each occurrence, independently of one another, selected from an alkyl, cycloalkyl, alkenyl, cycloalkenyl, or aralkyl group, which may be substituted by a halogen atom or by a hydroxyl or cyano group; and and wherein R 4 is at each occurrence, independently of one or another, selected from H, NH 2 , NO 2 , nitrile, a halogen, linear or ranched aliphatic radical, or an unsubstituted, halo substituted and/or alkyl substituted aromatic radical, and Y=1 to 3; and wherein wherein the bisorthohydroxy aromatic urone comprises 0.1 to 20 wt % of said prepreg; further comprising a fibrous reinforcement material selected from a woven fabric, a multi-axial fabric, individual fibre tows, and mixtures thereof.
2. 2 . The process according to claim 1 wherein the curing is performed in a press.

Description

The present invention relates to novel derivatives of urea, their use as curatives or curative accelerators for resin systems particularly epoxy resins, epoxy resin formulations containing the derivatives of urea and prepregs and moulded articles employing such epoxy resin formulations. Accordingly the invention provides novel urea based compounds, a curative system, a resin formulation, a cured resin, a use, a composite and a moulding material. Adipic acid dihydrazide and isophthalic acid dihydrazide are known as curatives for epoxy resin formulations. It has been suggested that they may be used together with accelerators such as urea based materials as is disclosed in U.S. Pat. Nos. 4,404,356 and 4,507,445. However there remains a need for curatives, which enable the combination of storage stability of the resin formulation prior to cure, low temperature cure, fast cure to produce a cured resin having a high glass transition temperature (Tg) and which also retains the Tg over a period of time particularly when subjected to moisture particularly at elevated temperatures. One object of the present invention is therefore to provide a curable epoxy resin composition having excellent storage stability, enhanced curing characteristics including low temperature and faster cure and which provides a cured product having excellent mechanical properties. A curative is a compound which is adapted to initiate or advance a polymerisation reaction of a polymerisable resin. An accelerator is a compound which enhances the polymerisation reaction (or “curing”) caused by a curative. The curing of epoxy resins is usually an exothermic reaction and it is important that the reaction is controlled to avoid excess temperatures that can degrade the epoxy material and can cause stress and deformation such as cracking in articles and components created from the epoxy containing formulation. There is however an ongoing need to increase the Tg of cured epoxy resins particularly to provide sufficient strength to the articles and components particularly when the resins are being used in resin impregnated fibre reinforcements sometimes known as prepregs that are used to produce larger and larger articles and particularly thicker articles made from stacks of prepregs such as stacks of more than 40, sometimes more than 60 up to 80 prepregs especially in the production of components for the aerospace and wind turbine industries. A prepreg comprises a fibrous reinforcement impregnated with a curable resin ready for curing within a mould or vacuum bag. To date a higher Tg has been obtained using higher curing temperatures and/or longer curing cycles and employing hardeners such as dicyandiamide which require higher curing temperatures; however, this increases the risk of high temperature degradation of the resin. It has been proposed that the use of urones as curatives can enable higher Tgs to be obtained using lower cure temperatures and shorter cure cycles. Derivatives of urea are known as is their use as curatives for epoxy resins and such derivatives are sometimes known as urones. U.S. Pat. No. 4,404,356 relates to hydroxy phenyl ureas of formula and to their use as accelerators for heat curing of epoxy resins and also to their use as primary curing agents for epoxy resins. U.S. Pat. No. 9,663,609 relates to the use of bis or multifunctional N,N′-(Dimethyl) urones and a method for curing epoxy resin compositions using such urones. The use of these materials is said to provide a method for the controlled curing of epoxy resins particularly for solid components having large layer thickness of epoxy resins to avoid internal stresses or other thermal damage in mouldings or components that are produced therefrom. The bis- or multi-functional N,N′-(dimethyl) urones are of the general formula where R is a linear or branched aliphatic radical or an unsubstituted, halo substituted and/or alkyl substituted aromatic radical and n is a number from 2 to 20. However, U.S. Pat. No. 9,663,609 does not envisage that when R is an aromatic radical it can be hydroxy substituted. The use of the bis- or multifunctional orthohydroxy aromatic urones according to this invention as curatives or curative accelerators provides a further improvement in the control of the curing of epoxy resins particularly in prepregs. We have now produced bisfunctional orthohydroxy aromatic urones and we have found that when used as curatives for epoxy resins, the resin can be cured at lower temperatures, such as an externally applied temperature from 80° C. to 150° C. to produce a cured epoxy resin having a higher Tg at complete cure than is produced from the non-hydroxy substituted aromatic bisfunctional urones such as those described in U.S. Pat. No. 9,663,609 and the hydroxyl phenyl ureas of U.S. Pat. No. 4,404,356. The urones of this invention may also be used as accelerators for other epoxy curatives when the curing temperature may be higher for example up to 180  C. In one e