Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1996-07-19
1998-10-20
Berman, Susan W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522 34, 522 39, 522 42, 522 50, 522 53, 522 46, 522 84, 522 85, 522 86, 522153, 522152, 522150, 522 79, 523160, 524804, 524815, 524833, 524831, C08J 328, C08F 250, C08F22018
Patent
active
058247165
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to acrylic latices which are capable of forming photocrosslinkable films.
Traditional latex paints readily employ aqueous emulsions of acrylic polymers or copolymers which, by progressive drying, form a coalesced film. When they are applied in building, especially in exterior applications, these paints are expected to show rapid dust-free drying and then curing, affecting essentially the surface, while it is appreciated that the underlying layers retain a certain flexibility in order to accommodate any imperfections of the substrate (microfissures in a wall, for example), and if appropriate to exhibit good resistance to soiling.
BACKGROUND OF THE INVENTION
Prior Art
The interest of specialists has turned towards latices obtained from the emulsion copolymerization of .alpha.,.beta.-unsaturated monomers which are preferably chosen such that the copolymer formed has a glass transition temperature Tg which should be lower than the temperature of use in order that a polymer film may form by coalescence at this temperature. The material of the films thus formed is a thermoplastic substance, and it is obviously highly advantageous to be able to implement its post-curing by crosslinking after coalescence. This post-crosslinking can, moreover, also affect the properties of the copolymer by crosslinking of the polymer chains as well as participating in the cohesion of the film by crosslinking between the particles of latex deposited. Various modes of crosslinking are possible. It seemed appropriate to make use of photocrosslinking, especially since the coatings at issue in this case are exterior coatings and are therefore subject to natural UV irradiation. This photocrosslinking, which is a mechanism of photopolymerization, consists in causing luminous or electromagnetic radiation to act in order to induce the polymerization of functional monomers, oligomers or polymers. The energy absorbed by the system is used to create new bonds between the molecules. Photocrosslinking can be initiated by using photoinitiators, crosslinking agents and polymers which are intrinsically photocrosslinkable. In formulations which are already complex, such as those of paints, the latter solution is adopted for reasons of convenience. Since the latices which it is proposed to improve are latices of acrylic type, the choice is made to incorporate other monomers in the chain which carry a methacrylate function and which also possess a reactive function which will permit the formation of bridges when the coalesced latex film is irradiated, as is already known from the prior art: dicyclopentenyloxyethyl acrylate, and preferably dicyclopentenyloxyethyl methacrylate or DCPOEMA (FIG. 1).
DCPOEMA possesses two double bonds having a priori different reactivities. One of them is acrylic, and behaves in practice like that of traditional acrylic monomers. The other is cyclic and is known to be markedly less reactive but capable of giving rise to post-crosslinking by virtue of appropriate treatment.
DCPOEMA has been used as an additive in latices for coatings as a reactive coalescence agent (U.S. Pat. No. 4,097,677), as a plasticizer of the latex particles, as an agent for lowering the minimum film-forming temperature and as a siccative in the presence of metal salts. It therefore takes part in the formation of films of high hardness. It is also mentioned in the European publication EP 20125, where it is employed as optional comonomer in latices obtained by emulsion polymerization, in combination with isobornyl (meth)acrylate in promoting adhesion to polypropylene, where it acts as a crosslinking agent by autoxidation. Similar products, dicyclopentenyl acrylate and methacrylate (DCPA and DCPMA), also appear in U.S. Pat. No. 4,144,212 as functional comonomer in latices, leading to coatings which can be dried in the presence of metal salts and which also have good solvent resistance. Finally, DCPOEMA appeared recently (EP 478193) as a comonomer which can be used in core-shell latices which are resistant to bas
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patent: 4144212 (1979-03-01), Linder et al.
patent: 4948819 (1990-08-01), Green et al.
patent: 5168087 (1992-12-01), Li Bassi et al.
patent: 5230984 (1993-07-01), Tachiki et al.
Patent Abstracts of Japan, vol. 7, No. 290 (P-245), Sep. 1983.
Coqueret Xavier
Rousseau Pierre
Verge Christophe
Berman Susan W.
Elf Atochem S.A.
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