Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Patent
1985-03-11
1986-08-05
Phynes, Lucille M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
521 88, 521141, 521188, 524598, 525398, 528254, 528256, C08G 1232, C08L 6124, C08L 6128
Patent
active
046044485
DESCRIPTION:
BRIEF SUMMARY
This invention relates to moulding compositions, and is especially concerned with moulding compositions based on melamine-formaldehyde resins. It is more especially concerned with the provision of a novel series of readily handleable and curable resins which lead to the production of stable, durable mouldings which are colour stable, have good water resistance, and in some embodiments are glass-clear and fire-resistant.
Melanine-formaldehyde resins and moulding compositions based thereon are widely known and used. The resins are produced by partially condensing a mixture of melamine and formaldehyde, suitably with the assistance of an acidic or alkali catalyst, to the stage at which a resole resin is formed. This resin is then shaped, e.g. in a mould to produce a molded object or a surface coating or lamination, and its cure is completed by heating and/or by catalytic effect. The manufacture and use of such resins are comprehensively described in the literature.
Melamine-formaldehyde moulding compounds are normally sold at normal temperatures and pressures, i.e. 20.degree. C. and usually at least up to 50.degree. C., and are usually heavily filled with fibrous or non-fibrous materials, for example cellulose-based materials. They are normally moulded at a pressure over 400 p.s.i., and at a temperature in excess of 120.degree. C. The resultant moulded articles are usually opaque and are not weather resistant. Cure of the melamine-formaldehyde moulding compounds may be assisted by the use of acid catalysts. The resins are brittle and prone to shrinkage. Unless heavily reinforced, the mouldings made from them will crack on ageing.
It is an object of the present invention to provide a melamine-formaldehyde moulding composition which does not suffer from the disadvantages of presently known melamine-formaldehyde moulding compositions. It is a further object of the invention to provide a method of forming shaped articles using the novel melamine-formaldehyde moulding compositions.
According to the invention a moulding composition comprises (i) a melamine-formaldehyde resole in which the mole ratio melamine:formaldehyde is in the range 1:1.1 to 1:5.0, and (ii) a glycol or glycol derivative in an amount between 20 and 80%, suitably between 25 and 80%, by weight, based on the weight of solid melamine-formaldehyde resole.
Further according to the invention, a method of forming shaped articles comprises moulding into shape a composition as aforesaid and causing said moulding to cure at a pH of 6.0 or greater, preferably at least 7.5.
The melamine-formaldehyde resoles may be acid-or alkali-catalysed condensates of melamine and formaldehyde, of preferred molar ratio 1:1.2 to 1:4.0, most preferably 1:1.2 to 1:3.0.
It is believed that the glycol component of the moulding composition functions as a reactive solvent, a proportion of the glycol condensing with the methylol groups of the methylol melamine resole whilst curing, to produce unreactive ether side chains. The chemically-bound glycol behaves as an internal plasticiser and retards the rate of polymerisation and cross-linking, thereby controlling the molecular weight and density of cross-linking of the ultimate product. Uncombined glycol dissolves the resin, and functions as an external plasticiser. The overall effect of the use of glycol in the manner proposed by the invention is to improve the clarity, resilience, toughness dimensional stability and weathering performance of the cured resin. Preferably the glycol or glycol derivative is present in the moulding composition of the invention in an amount between 30% and 70% by weight, e.g. between 45 and 70% by weight, based on the melamine-formaldehyde resin.
Suitable glycols include those lower glycols which are liquid at room temperature, and whose molecules contain reactive primary and/or secondary hydroxyl groups. As specific examples there may be mentioned ethylene glycol, triethylene glycol, monopropylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, polyethylene glycols and polypropylene gl
REFERENCES:
patent: 3351615 (1967-11-01), Gordon
patent: 3479247 (1968-11-01), Bonzagni
patent: 4192923 (1980-03-01), Tajkowski
patent: 4303561 (1981-12-01), Piesch et al.
Farkas Robert
Hohmann Lothar M.
Phynes Lucille M.
Polymer Tectonics Limited
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