Epoxy resins prepared by co-curing fluorinated epoxy prepolymers and non-fluorinated epoxy prepolymers

Abstract: A non-fluorinated epox prepolymer of known type is mixed with a fluorinated epoxy prepolymer containing perfluoropolyether blocks or perfluoroalkylene blocks of type -(CF₂CF₂) n - and/or of type and the two prepolymers are co-cured by treating the mixture with cross-linking agents of known type suitable for epoxy resins, thereby obtaining a cross-linked epoxy resin having a fluorine content ≦ 30% by weight, preferably ≦ 25% by weight.

Description: The present invention relates to partially fluorinated epoxy resins obtained by co-curing a mixture of non-fluorinated epoxy prepolymers of known type with fluorinated prepolymers containing perfluoroalkylene blocks of type: as described in IT-A-22678 A/86, or containing perfluoropolyether blocks as described in EP-A-212 319 both in the name of the Applicant. The mixture of prepolymers can be cured by means of certain fluorinated or non-fluorinated cross-linking agents to provide cross-linked resins having improved characteristics with respect to the known corresponding resins not containing fluorine. The specific characteristics of the cross-linked resins prepared according to the present invention are: surface properties which impart oil- and -water-repellency as well as a low friction coefficient to the product; stability to hydrolysis and minimum absorption of water; stability to solvents; advantageous dielectric characteristics in particular regarding dielectric constant and volume resistivity; improved flexibility and high impact strength. The present invention is based on the surprising discovery that a prepolymer consisting of a non-fluorinated epoxy resin is fully miscible with a fluorinated prepolymer containing fluoroalkylene chains or perfluoropolyether chains, and that subsequently the co-curing of the two starting prepolymers can be readily obtained by treating the mixture with a certain cross-linking agent for epoxy resins. Furthermore, it has surprisingly been found that the products so obtained possess the typical characteristics of an epoxy resin prepared starting from a fluorinated epoxy polymer having the structure of a fluoroalkane or of a perfluoropolyether. The process according to the invention provides cross-linked products which, although they have a low fluorine content from 1% to 30% by weight and preferably ranging from 1% to 25% by weight, exhibit the same typical surface characteristics of cross-linked epoxy resins having a high fluorine content; from such characteristics derive high oil-repellency and water-repellency, minimum water absorption, high stability to hydrolysis and to solvents. The non-fluorinated epoxy prepolymers used according to the present invention are: (a) non-fluorinated epoxy prepolymers obtainable from (i) epichlorohydrin and (ii) a compound selected from diols containing one or more aromatic, cycloaliphatic, polycyclic or heterocyclic rings, cresol novolak resins and phenolic novolak resins or (b) non-fluorinated epoxy prepolymers derived from 1,2-di(4-hydroxyphenyl)ethane diglycidyl ether, tetraglycidylmethylene dianiline, triglycidyl-isocyanurate or diglycidyl-hydantoin. Specific examples thereof are: Epoxy resins deriving from bisphenol A - epichlorohydrin Epoxy cresol novolak resins Epoxy phenolic novolak resins Resins derived from bisphenol F Polynuclear resins derived from phenol-glycidic ether Resins derived from tetraglycidylmethylenedianiline Resins derived from triglycidyl-isocyanurate Resins derived from diglycidyl-hydantoin Resins deriving from bisphenols or other halogen monomers, for example tetrabromobisphenol A and tetrachlorobisphenol A. It is possible to utilize mixtures of one or more of the above-cited resins. The prepolymers with a high fluorine content to be utilized as masterbatch are comprised in the following general formula (I): where: x is an integer from 0 to 20; y is an integer from 1 to 20; x + y being preferably ≧ 2; B and B', equal or different from each other, are H or A is a radical derived (by removal of the OH-groups) from a fluorinated or non-fluorinated diol containing one or more aromatic or cycloaliphatic or polycyclic rings; R f is a fluoroalkylene radical -(CH₂) q (CF₂CF₂) n -(CH₂) q - or wherein n = 2-8, q = 1 or 2, p = 1-8, m = 1-8, or R f is a perfluoroalkylene radical derived from the corresponding diol, which comprises sequences of an average molecular weight of 500 to 7000 of fluorooxyalkylene units selected from the following classes: I - (C₂F₄O) and (CF₂O), said units being randomly distributed along the fluoropolyoxyalkylene chain; II - (C₃F₆O), (C₂F₄O) and (CFXO), wherein X = F or CF₃, said units being randomly distributed along the fluoropolyoxyalkylene chain; III - (CH₂CF₂CF₂O), said units being linked in the fluoropolyoxyalkylene chain as follows: -(OCF₂CF₂CH₂) p -O-R' f O-(CH₂CF₂CF₂O) q - wherein R' f is a fluoroalkylene group and p and q are integers, (p + q) being higher than 2; IV - said units being linked in the fluoropolyoxyalkylene chain as follows: wherein R'' f is a fluoroalkylene group, x' is 0 or 1 and a and b are integers, (a + b) being higher than 2; V - (CF₂CF₂CF₂O); VI - (CF₂CF₂O); and D = A or R f . Fluorinated prepolymers of the former type, comprising the fluoroalkylene radicals, are described in IT-A-22678 A/86 while those of the latter type comprising the perfluoropolyether radicals, are described in EP-A-212 319. The epoxy resins (prepolymers) utilizable for the present invention, may be liquid, solid or in solution as a function of the fields of use. The liquid epoxy resins predominantly contain epoxy end groups and free hydroxyl groups inside the chain. The known technology for cross-linking epoxy resins by means of conventional cross-linking agents is fully utilizable in the present invention. Thus, in accordance with the structure, curing is carried out by means of the cross-linking agents which are commonly used for these resins, i.e., anhydrides of polycarboxylic acids, polyfunctional amines, polyamides, polyaminoamides (obtained from polyamines and dimers of fatty acids), polyphenols, polythiols, polycarboxylic acids and polyisocyanates, according to methods well known to those skilled in the art. The utilizable polyamines can be primary or secondary, aliphatic or aromatic; examples thereof are meta-phenylenediamine, diethylenetriamine and xylylenediamine. The diamine is used in such amount as to have an amino hydrogen for each epoxide equivalent, variations of ± 10% being allowable. It is possible also to use anhydrides, such as for example phthalic, hexahydrophthalic, methyltetrahydrophthalic, trimellitic, pyromellitic, 2-dodecyl-succinic, methyl endomethylene-tetrahydrophthalic (methylnadic) anhydride. In order to reduce the reaction times and temperatures, accelerants such as n-butyl imidazoles, tris(dimethylaminomethyl) phenol, benzyldimethylamine, triethanolamine may be added in amounts from 0.5 to 1% by weight referred to the resin. Furthermore, it is possible to use di-, tri- and tetraisocyanates such as e.g. hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), methylene-bis-(4-cyclohexyl-diisocyanate) (H₁₂MDI) and trimers of TDI and HDI. The reaction which gives rise to the urethanic bond can be catalyzed or not catalyzed by the catalysts which are utilized in the technology of the polyurethanes obtained from polyols and polyisocyanates. In any case, the addition of an efficient catalytic system permits to operate at a low temperature (20 to 60°C) in short times. Furthermore, by properly dosing the catalyst it is possible to optimize the pot life, namely the time during which the reaction mixture remains fluid enough. As catalysts it is possible to utilize tin derivatives such as tin butyl dilaurate, tin dibutyl acetate, tin dibutyl oxide, derivatives of iron such as iron acetylacetonate, titanium alcoholates such as titanium tetraisopropylate, tertiary amines such as triethylamine, in amounts ranging from 0.001 to 2% by weight, preferably from 0.01 to 0.5% by weight calculated on the total weight. Furthermore, a class of cross-linking agents which are particularly useful to obtain fluorinated epoxy resins with a high fluorine content is the one of the agents having a perfluoroether chain, which are specified in EP-A-249048 in the name of the Applicant. The cross-linking reaction can be conducted for example at room temperature (with a non-aromatic amine) up to temperatures higher than 200°C (with an anhydride). Mixing of the non-fluorinated epoxy prepolymer of known type with the fluorinated prepolymer can be carried out without or with the addition of a solvent, depending on the composition in question. Generally, the mixing of the fluorinated prepolymer does not rise particular Problems: In some cases, however, mixing can be favoured by addition of proper solvents such as esters, for example butylacetate and amylacetate; ketones, for example acetone, methylethylketone and methylisobutylketone, and aromatic hydrocarbons, for example xylene and toluene, optionally in admixture with characteristic solvents for perfluoropolyethers, such as 1,1,2-trichlorotrifluoroethane (DELIFRENE® LS). At the end of the admixing, it is possible to remove the solvent and to add the curing agent to the mixture or to conduct the cross-linking in solution. The amount of solvent depends on the solution viscosity to be obtained and on the particular application. The formulations of the epoxy resins prepared in accordance with the present invention can include other compounds such as pigments or fillers of a different nature, in relation to the requirements of the various fields of use, which are suited to reduce the costs of the article, to increase the consistency thereof, to favour the levelling of the pigment inside the resin, or to help in reinforcing the structure of the resin from a mechanical point of view. The pigments and other fillers, of pigmentary nature or not, can be added to coat and/or protect the surface on which the resin is spread, for example by reflecting the destructive sunlight rays which otherwise could pass through the resin and cause the decay of the underlying material. The resins of the invention, in spite of their low fluorine content, are compatible with particular fillers such as, for example, polytetrafluoroethylene (PTFE) and C₂F₄/C₃F₆ copolymers (FEP), which may be added to improve certain mechanical characteristics, such as impact strength and resistance to abrasion. The use, according to the present invention, of cross-linking agents with perfluoropolyether chain imparts to the conventional epoxy resins highly improved chemico-physical and mechanical characteristics with respect to the hydrogenated epoxy resins of the prior art, so allowing the obtainable materials to be suitable for a plurality of applications. In particular, the resins obtainable in accordance with the present invention are characterized by: high stability to hydrolysis, chemical agents and atmospherical agents, high thermal stability, low refractive index, considerable dimensional stability, low wettability, self-lubricating properties, excellent mechanical properties, water-repellency, oil-repellency, flame-retardant properties, low dielectric constant. In consideration of such exceptional characteristics, examples of fields of application for the products of the invention are those of adhesives, of structural materials and of high-performance composite materials to be used, for example, in the aeronautical sector or in the sector of electronics, as supporting resins for printed circuits, encapsulating materials for chips, resins for electric cables. Furthermore, a very broad field of use is that of coatings and paints in general, and in particular for printed circuits, magnetic tapes and discs, optical readout discs, optical fibres and optical systems in general, paints for aeronautical and aerospace uses, barrier paints for marine environments, hydrophobic coatings for submarine systems, coatings of mechanical parts immersed in solvents and in general coatings of metal systems subjected to corrosion. In particular, the perfluoropolyether component forms a rubber-like phase, which, in interpenetration with the rigid epoxy matrix, imparts to the final product improved properties of tenacity, flexural strength and impact strength. The following examples are given for a merely illustrative purpose, without being, however, a limitation of any possible embodiments of the invention. Example 1 10.3 of a liquid epoxy resin prepared from bisphenol A and epichlorohydrin, having an equivalent weight of 190, were mixed with 14.7 g of a fluorinated resin (prepared according to the procedure illustrated in Example 2 of IT-A-22 678 A/85 in the name of the Applicant) having an epoxy equivalent weight of 900. 22.5 g of methylnadic anhydride and 0.25 g of 1-butyl-imidazole were added to the mixture obtained. The epoxy polymer (fluorine content = 10%) was cross-linked in an oven at 100°C for 1 hour and was post-crosslinked at 165°C for 30 minutes. The resulting glass-like transparent material exhibited the following properties: glass transition temperature = 154°C, water absorption (96 h immersion at 25°C, ASTM D570) = 0.2% by weight, contact angle (H₂O) = 90°, friction coefficient = 0.13. Comparative Example 1 The same liquid epoxy resin prepared from bisphenol A and epichlorohydrin and cross-linked with methylnadic anhydride and 1-butylimidazole in the same proportions and according to the same procedure as described in Example 1, exhibited the following characteristics: glass transition temperature = 154°C, water absorption = 0.3% by weight, contact angle (H₂O) = 62°, friction coefficient = 0.35. Example 2 21.4 g of a fluorinated resin prepared as described in Example 6 of EP-A-212 319, having an epoxy equivalent weight of 2140, were mixed with 15.0 g of a liquid epoxy resin based on bisphenol A and epichlorohydrin having an epoxy equivalent weight of 190. To the resulting mixture there were added 32.75 g of methylnadic anhydride and 0.36 g of 1-butylimidazole. The epoxy polymer (fluorine content = 18%) was cross-linked in an oven at 100°C for 1 hour and post-cross-linked at 165°C for 1 hour. The resulting material exhibited the following properties: water absorption (96 hours, 25°C) = 0.2% by weight contact angle (H₂O) = 95° friction coefficient = 0.12 improved impact strength characteristics with respect to the resin of Comparative Example 1. Example 3 90 g of a liquid epoxy resin prepared from bisphenol A and epichlorohydrin, having an equivalent weight of 190, were mixed with 10 g of a fluorinated epoxy resin (prepared according to the procedure illustrated in Example 4 of IT-A-22678 A/86) having an epoxy equivalent weight of 800. 65 g of methylnadic anhydride and 1 g of 1-butylimidazole were added to the mixture so obtained. The epoxy polymer (fluorine content = 2%) was cross-linked in an oven at 100°C for 1 hour and was post-crosslinked at 165°C for 1 hour. The resulting glass-like, transparent material exhibited the following properties: glass transition temperature: 129°C; water absorption: 0.25% by weight; dielectric constant (22°C): 3.1; dissipation factor: 2.5 x 10³. Comparative Example 2 The same liquid epoxy resin prepared from bisphenol A and epichlorohydrin and cross-linked with methylnadic anhydride and 1-butylimidazole in the same proportions and according to the same procedure as described in Example 3, exhibited the following characteristics: glass transition temperature: 131°C; water absorption: 0.35% by weight; dielectric constant (22°C): 3.4; dissipation factor: 2.5 x 10⁻³. Example 4 90 g of a liquid epoxy resin prepared front bisphenol A and epichlorohydrin, having an equivalent weight of 190, were mixed with 10 g of the fluorinated epoxy resin of Example 2. 65 g of methylnadic anhydride and 1 g of 1-butylimidazole were added to the mixture so obtained. The epoxy polymer (fluorine content = 2.5%) was cross-linked in an oven at 100°C for 1 hour and was post-cross-linked at 165°C for 1 hour. The resulting glass-like, transparent material exhibited the following properties: glass transition temperature: 146°C; water absorption: 0.25% by weight; dielectric constant (22°C): 2.4; dissipation factor: 1.5 x 10⁻³.

Claims: A cross-linked fluorinated epoxy resin containing from 1 to 30% by weight of fluorine, prepared by co-curing with cross-linking agents selected from anhydrides of polycarboxylic acids, polyfunctional amines, polyamides, polyaminoamides obtained from polyamines and dimers of fatty acids, polyphenols, polythiols, polycarboxylic acids and polyisocyanates, a mixture of a prepolymer containing fluoroalkylene or perfluoropolyether blocks and being of general formula (I): wherein: x is an integer from 0 to 20; y is an integer from 1 to 20; B and B', equal to or different from each other, are H or A is a radical derived from a fluorinated or non-fluorinated diol containing one or more aromatic or cycloaliphatic or polycyclic rings; R f is a fluoroalkylene radical -(CH₂) q (CF₂CF₂) n -(CH₂) q - or wherein n = 2-8, q = 1 or 2, p = 1-8, m = 1-8, or R f is a perfluoroalkylene radical derived from the corresponding diol, which comprises sequences of an average molecular weight of 500 to 7000 of fluorooxyalkylene units selected from the following classes: I - (C₂F₄O) and (CF₂O), said units being randomly distributed along the fluoropolyoxyalkylene chain; II - (C₃F₆O), (C₂F₄O) and (CFXO), wherein X = F or CF₃, said units being randomly distributed along the fluoropolyoxyalkylene chain; III - (CH₂CF₂CF₂O), said units being linked in the fluoropolyoxyalkylene chain as follows: -(OCF₂CF₂CH₂) p -O-R' f O-(CH₂CF₂CF₂O) q - wherein R' f is a fluoroalkylene group and p and q are integers, (p + q) being greater than 2; IV - said units being linked in the fluoropolyoxyalkylene chain as follows: wherein R'' f is a fluoroalkylene group, x' is 0 or 1 and a and b are integers, (a + b) being greater than 2; V - (CF₂CF₂CF₂O); VI - (CF₂CF₂O); D = A or R f ; with (a) a non-fluorinated epoxy prepolymer obtainable from (i) epichlorohydrin and (ii) a compound selected from diols containing one or more aromatic, cycloaliphatic, polycyclic or heterocyclic rings, cresol novolak resins and phenolic novolak resins or (b) a non-fluorinated epoxy prepolymer derived from 1,2-di(4-hydroxyphenyl)ethane diglycidyl ether, tetraglycidylmethylene dianiline, triglycidyl-isocyanurate or diglycidyl-hydantoin. The resin according to claim 1, containing from 1 to 25% by weight of fluorine. The resin according to claim 1 or 2, prepared by using cross-linking agents selected from the following classes: anhydrides of polycarboxylic acids, polyfunctional amines, polyphenols, polyisocyanates.

Inventors: DE GIORGI MARCO, RE ALBERTO, DE GIORGI, MARCO, RE, ALBERTO
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1987
Main classification: C08G59
IPC codes: C08G59, C08L63