Stock material or miscellaneous articles – Composite – Of aldehyde or ketone condensation product
Patent
1999-01-12
2000-06-20
Acquah, Samuel A.
Stock material or miscellaneous articles
Composite
Of aldehyde or ketone condensation product
528248, 528252, 528254, 528256, 528257, 528266, 528269, 428526, 428528, 428530, B32B 2742, C08G 1202
Patent
active
060776145
DESCRIPTION:
BRIEF SUMMARY
Melamine resin laminates based on impregnated papers have a wide field of use as decorative and protective surfaces because of their good fastness to light, abrasion resistance, resistance to chemicals, resistance to glowing heat and surface hardness.
Such laminates which are obtained by impregnation of carrier webs of textiles, paper or glass nonwovens with aqueous solutions of melamine-formaldehyde precondensates and subsequent drying and curing at temperatures above 100.degree. C. are described, for example, in EP-A-0 077 067. EP-B1-0 268 809 describes melamine resin films which are obtained by coating papers with an at least 70% strength by weight aqueous solution of a melamine resin etherified by methyl.
The disadvantage of these known melamine resins and melamine resin laminates is, in particular, that they show a relatively high shrinkage during curing, that their mechanical properties, such as, for example, resistance to boiling water, are inadequate in many cases, and that above all they are very brittle and show no postforming properties.
It is known from U.S. Pat. No. 4,424,261 that the use of hydroxyalkylmelamines as modifying agents for melamine-formaldehyde resins leads to an improvement in the postforming properties. However, the disadvantage of these modifying agents is their instability, which means they are not easily available and furthermore can be handled only with difficulty, since they have a marked tendency to undergo self-crosslinking.
Other modifying agents, such as, for example, guanamines, which lead to postforming properties of the resins, are described in EP-A1-0 561 432. However, guanamines, especially those with aromatic nuclei, such as benzoguanamine, do not have an adequate resistance to light, which means that the modified resins yellow easily. Furthermore, the low solubility of the guanamines in the reaction medium has an adverse effect on the preparation process for the resins.
WO-A-9620 230 furthermore discloses resins consisting of the components formaldehyde melamine, dicyandiamide in an amount of 5 to 25% by weight based on the melamine and a polyalcohol such as trimethylolpropane in an amount of 8 to 30% by weight based on the melamine. Although these resins also show postforming properties and resistance to boiling water, the possibility of converting these resins into powder form by spray drying is not described.
EP-A-0 007 705 discloses resins which comprise melamine, formaldehyde and a hydroxymonoamine, part of the melamine being replaced by urea. Properties such as postforming, resistance to boiling water and suitability for spray drying are not described.
It was therefore necessary to discover a modifying agent for melamine resins which does not have the disadvantages of the modifying agents known to date and greatly improves the postforming properties of the melamine resins without reducing their resistance to boiling water and which leads to resins which can-be spray-dried. It has now been found, unexpectedly, that such melamine resins are obtained by using special modifying agents comprising a combination of certain polyalcohols and dicyandiamide or certain amines, and addition of urea.
The present invention accordingly relates to modified melamine-formaldehyde resins which comprise a condensate of formaldehyde, melamine, urea and modifying agent comprising dicyandiamide and 8 to 30% by weight, based on the melamine, of polyalcohol of the formula ##STR1## where n is 0 to 3, IIa or a radical of the formula ##STR2## R.sub.2 is a linear or branched (C.sub.1 to C.sub.4)alkylene radical and, in the formula Ib, R.sub.3 is a cycloalkylene radical having 6 C atoms or R.sub.3, like R.sub.4 and R.sub.5 is a linear or branched (C.sub.1 to C.sub.6)alkylene radical, which can optionally be substituted by a further hydroxyl group, where R.sub.3, R.sub.4 and R.sub.5 can be identical or different and/or on the meaning of X, are a linear or branched or cyclic C.sub.1 to C.sub.12 -alkyl or alkylene radical and R.sub.2 is a linear or branched or cyclic C.sub.1 to C.sub.12 -a
REFERENCES:
patent: 3488310 (1970-01-01), McCombs
patent: 3496131 (1970-02-01), Bornmann et al.
patent: 4145371 (1979-03-01), Tohyama et al.
Conti Natale
Heger Friedl
Acquah Samuel A.
Agrolinz Melamin GmbH
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