Aqueous amino resin blends

Details Aqueous amino resin blends Aqueous amino resin blends

2002-05-06

2004-04-13

Short, Patricia A. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S509000, C427S385500, C427S391000, C524S598000, C528S258000, C528S262000, C528S263000

Reexamination Certificate

active

06720392

ABSTRACT:

The present invention relates to aqueous amino resin blends comprising as additives aliphatic amines containing at least one amino group and at least one hydroxyl group, the use thereof as impregnating resins, and a process for the reduction of the formaldehyde emission from impregnates by adding such amines to amino resins.
The faces and edges of woodbase materials are coated using coated foils (finished foils) and impregnated cardboards (edgings), respectively (Kunststoff-Handbuch vol. 10, Duroplaste [Thermosets], Hanser-Verlag, 2
nd
ed. 1988, p. 464 f., pp. 477 to 479). These finished foils and edgings are produced by impregnating absorbent papers with amino resins (thermosets) such as urea-formaldehyde and/or melamine-formaldehyde resins, for example, in combination where appropriate with aqueous dispersions of thermoplastic resins such as acrylic dispersions or styrene-acrylic dispersions, drying the coated papers in a stream of hot air and at the same time curing the resins, and then coating the impregnated or resinated papers.
Adequate penetration of the impregnation liquors into the paper is achieved if the resin solution is processed from aqueous or alcoholic dilution. Owing to the high level of cellulose swelling in aqueous systems, the foils and edgings produced from high aqueous dilution are brittle, exhibit a high level of water absorption, and even in the coated state have a surface whose aesthetic appeal is low. The procedure described in DE-A 23 09 334, which uses impregnating liquors diluted with C
1
to C
4
alcohols, does give foils and edgings having good performance properties but requires cumbersome measures for reprocessing the waste air. The route to a solution that is described in DE-A 44 39 156, modifying melamine resins with guanamines, does make it possible to carry out impregnation from purely aqueous liquors. A disadvantage, however, is the significantly higher cost of the amino resin, resulting from the use of the guanamines. In patent application DE-A 198 35 114, there are claimed methyl-etherified aqueous melamine-formaldehyde resins for producing microcapsules to which ammonia or primary, secondary or tertiary amines are added. There is no reporting of the advantageous effect of (hydroxyalkyl)amines on the reduction of formaldehyde emissions from finished foils and edgings.
In EP-A 0 913 412, non-etherified urea-formaldehyde resins are described which have a mass fraction of melamine in the finished resin of from 1 to 5%, the reaction mixture being neutralized, following complete condensation, by the addition of specific tertiary hydroxyalkylamines (preferably triethanolamine, methyldiethanolamine, and dimethylethanolamine). These resins are used as impregnating resins. There is no reporting of the advantageous effect of (hydroxyalkyl)amines on the reduction of formaldehyde emissions from finished foils and edgings.
Formaldehyde emissions of ready-produced finished foils and edgings are determined following storage under standard climatic conditions (23° C., 50% relative humidity) in accordance with the standard EN 717-2 (FESYP method, gas analysis). Foils and edgings with formaldehyde emission values of less than 3.6 mg/(h·m
2
) by the FESYP method comply with the limit (“E 1”) and are referred to below as E1 edgings. The rates of emission found remain more or less constant even after several weeks of storage under standard conditions. Emissions of formaldehyde are due to the use of urea-formaldehyde and/or melamine-formaldehyde resins in the liquors for impregnating the paper or cardboard sheets and/or in the formulations for coating the foils and edgings. By using particularly low-formaldehyde urea-formaldehyde and/or melamine-formaldehyde resins it is possible to reduce the formaldehyde emissions as measured by the FESYP method (standard conditions) to levels of around 2 mg/(h·m
2
).
It has surprisingly now been found that when E1 edgings produced in accordance with the prior art with initial formaldehyde emission levels of from 1.0 to 3.5 mg/(h·m
2
) are stored, especially under nonstandardized climatic conditions at customary summer temperatures and atmospheric humidities, the formaldehyde emissions rise in the course of a few weeks to levels of in some cases much higher than 3.5 mg/(h·m
2
), and so no longer satisfy the E1 criterion. This unexpectedly high increase in formaldehyde emissions was confirmed by storage under defined conditions in a tropical climate (35° C., 90% relative humidity), with measurement being carried out only after three-day reconditioning under standard conditions following storage under the tropical climate conditions.
From the prior art it is known that the amount of free formaldehyde and also formaldehyde emissions may be reduced by adding formaldehyde scavengers such as urea and urea derivatives, for example. For example, according to DE-A 38 37 965, finished foils and edgings with formaldehyde emissions that are negligible as determined in accordance with DIN 52368 may be produced by adding urea to the melamine-formaldehyde condensation product. No information is given, however, regarding storage behavior, in particular under tropical conditions.
According to DE-A 34 03 136, mixtures of organic hydroxy compounds and an amide are suitable for use as formaldehyde-binding agents in boards made from wood cellulose materials. The use of these mixtures as formaldehyde scavengers in finished foils and edgings is not described. Addition of the mixtures described in DE-A 34 03 136 to amino resins that are used to produce finished foils and edgings leads to a marked deterioration in the flexibility of the finished foils and edgings produced with them. The use of formaldehyde scavengers known from the literature, such as urea, ethyleneurea, and propyleneurea, resulted in finished foils and edgings which did meet the E1 criterion under standard conditions but which greatly exceeded the E1 limit of 3.5 mg/(h·m
2
) under tropical climate conditions.
It is an object of the present invention to provide modified amino resins for producing films and edgings that can be used to produce finished foils and furniture edgings which have formaldehyde emissions reduced significantly in relation to the prior art when stored, particularly also under tropical conditions, but which retain the required performance properties.
This object is achieved by means of aqueous amino resin blends which comprise as additives, aliphatic linear, branched or cyclic amines containing hydroxyl groups.
This invention therefore relates to a process of reducing the formaldehyde emission from finished foils and edgings, wherein aqueous amino resin blends are used for impregnation which comprise aliphatic linear, branched or cyclic amines A having at least one amino group which may be primary, secondary or tertiary, at least one hydroxyl group and from 2 to 20 carbon atoms, and non-etherified or at least partly etherified amino resins B.
Addition of these amines A brings about a reduction of up to 90% in the formaldehyde emissions from the finished foils or edgings (impregnates) as compared with the same resin without added amine.
The present invention also relates to a method of use of amines A having at least one amino group that may be primary, secondary or tertiary, one hydroxyl group and 2 to 20 carbon atoms, comprising adding these amines A to amino resins, and impregnating paper or cardboard with such modified amino resins to reduce formaldehyde emissions from the impregnates.
The invention also relates to an aqueous amino resin blend comprising aliphatic linear, branched or cyclic amines A having at least one amino group which may be primary, secondary or tertiary, at least one hydroxyl group, and 2 to 20 carbon atoms, and non-etherified or at least partly etherified amino resins B, wherein the amino resins have a mass fraction of melamine of less than 1% or more than 5%, in the case where the amines A comprise tertiary hydroxyalkylamines. It is preferred in this case, that the mass fraction of melamine in the amino resins is at least 7

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