WO1993015177A1

WO1993015177A1 - Cleaning of equipment with respect to amino resins

Info

Publication number: WO1993015177A1
Application number: PCT/SE1993/000056
Authority: WO
Inventors: Peter Herder; Håkan NORLING; Yngve WÅHLSTEDT; Ingvar Lind
Original assignee: Casco Nobel Ab
Priority date: 1992-01-30
Filing date: 1993-01-27
Publication date: 1993-08-05
Also published as: SE500522C2; FI943378A7; FI943378A0; EP0624187A1; NO304837B1; SE9200255L; NO942821D0; NO942821L; SE9200255D0; FI943378L

Abstract

Use of polyethylene imine or imines for cleaning equipment of amino resins. The polyethylene imine or imines are preferably utilised in the form of an aqueous solution. The amount of polyethylene imine or imines used lies within a range of from about 0.005 % by weight to about 10 % by weight of pure polyethylene imine, based on the amount of resin to be washed away. The polyethylene imine or imines may be used for cleaning different sorts of glue spreading equipment of glue.

Description

CLEANING OF EQUIPMENT WITH RESPECT TO AMINO RESINS

The present invention relates to the cleaning of equipment of amino resins. More precisely, the invention concerns the use of polyethylene imine or imines for Ξ cleaning equipment of amino resins.

In the woodworking industry, large amounts cf a ino- resin-based glues are used for making e.g. furniture, parquet floors, laminates and particle boards. These glues are based on formaldehyde and amino-containing compounds, 0 such as urea, melamine and benzoguanamine. The urea-formal¬ dehyde resins (commonly referred to as urea glues) are the most common. The glues are applied by means cf different; sorts of glue spreading equipment, such as roller spreaders and ribbon spreaders, or by spraying. Further, amino resms 5 are used also in other fields, e.g. in lacquers and paper additives.

Cleaning equipment of amino resins may pose serious problems. The situation has been aggravated in recent years, since the formaldehyde content of the amino resins 0 has been significantly reduced. The synthesis of amino resins having a high molar ratio of formaldehyde to amino compound yields a product with a high concentration cf hydrophilic methylolic compounds. These compounds are relatively easy to disperse and dilute in water, which 5 facilitates the cleaning of the resins. However, the dilution of amino resins having a low molar ratio may result in a rubber- or latex-like sticky mass which iε difficult to wash away. The structure of this mass is not known, but may consist of a mixture of oligomers or other C small molecules and crystalline compounds of amino-resir: type which, when diluted, form floes or gel-like states.

The cleaning problems are also linked with the waste disposal of amino-resin residues. Basically, there are three feasible ways of taking care of the amino-re-sin- 5 containing wash water. Thus, one may resort to acid curing, ^'combustion or simply discharge into the municipal sewage syεtem. Acid curing yields a hard, essentially insoluble ammo elastic which has to be treated as solid waste wmcr- releases formaldehyde. The combustion of wash water essen¬ tially requires that the resin residues are readily dis¬ persed in water to obtain a manageable dispersion. Normal¬ ly, it is not allowed to dump the resin residues directly in the municipal sewage system. Dumping requires that the resin concentration be brought to an acceptably low level by dilution.

DE 39 01 328 discloses a washing solution for clean¬ ing containers and glue spreading equipment of amino-resin glue. The washing solution is made up of five different components, inter alia two different polymer ingredients. To achieve satisfactory washability, a fairly complex solution is required.

One object of the present invention is, therefore, to solve the cleaning problems with regard to amino resins in a simple and rational manner. Another object of the inven¬ tion is to ensure acceptable handling of the waste resul¬ ting from the cleaning.

As appears from the appended claims, the objects of the present invention are achieved by the use of polyethy¬ lene imine or imines for cleaning equipment of amino resins. It has surprisingly been found that, when the polyethylene imine or imines are applied to the amino- resin-smeared equipment, the resin will be effectively washed away and dispersed in the aqueous phase. The resul¬ ting dispersion may then without problems be diluted with large amounts of water.

Polyethylene imines make up a family of water-sol¬ uble, hydrophilic polyamines of varying molecular weight. They act as weak bases and have a cationic nature (at pH <10.5) . Generally, polyethylene imines are heavily branch¬ ed and contain primary, secondary as well as tertiary amine groups. Polyethylene imines are commercially avail¬ able at molecular weights ranging from about 300 g/mole to more than 6 x 10 g/mole. It is common to use polymers of comparatively high molecular weight (MW >10,000 g/mole). For instance, polyethylene imines are widely used for improving the retention in papermaking (i.e. as retention agents). Polyethylene imines may then be used for binding fibres (fines) and colloidal particles, so that these become effective in the paper by improved dewatering. Otherwise, the fines have a tendency to circulate in the system.

Also, polyethylene imine may be used in washing compositions for cleaning metal surfaces of metal oxides and the like, as disclosed e.g. in US 3,627,687 and US 3,754,990. The excellent dispersing and washing effect of poly¬ ethylene imine or imines on amino resins can be explained by the fact that the cationic groups electrostatically bind to anionic or polar groups on amino-resin oligomers and/or amino-resin crystals in the resin or .the glue. The high density of cationic groups on the branched polymer imparts a hydrophilic nature to the formed aggregates, which thus become readily dispersible. This is combined with an osmotic effect (steric stabilisation), keeping the aggregates apart in the solution. The washing method of the invention also results in improved waste disposal, which constitutes a preferred embodiment of the invention. A method has been developed, in which the dispersed resin, after the cleaning, is further diluted with water under agitation in a separate tank until the concentration of amino resin has reached an acceptably low level. By 'an acceptably low level' is here meant such a low concentration of amino resin in the wash water that the latter may be discharged into the public sewage system. If this method is to work, the wash water has to be a readily diluted dispersion, which is achieved by the proposed washing method.

Many years of experience of polyethylene imines in papermaking have shown that the use thereof does not involve any health hazards. Also, polyethylene imines only have a marginal effect on the environment when discharged in diluted form.

The polyethylene imines that can be used for cleaning are water-soluble polyethylene imines having a molecular weight ranging from about 200 g/mole to about 10⁷ g/mole, preferably from about 10⁴ g/mole to about 5 x 10⁶ g/mole, and most preferred from about 10⁵ g/mole to about 1.5 x 10° g/mole. Such polyethylene imines are well-known as well as commercially available.

The amount of polyethylene imine to be added to give a satisfactory washing effect may vary within comparative¬ ly wide limits. However, should the amount of polyethylene imine added be too small, the amino resin may be insuffi- ciently dispersed, which would involve the risk of gel formation. An excessive amount of polyethylene imine may, on the other hand, result in considerable foaming. Gener¬ ally, the amount of polyethylene imine added should suitab¬ ly lie within a range of from about 0.005% by weight to about 10% by weight of pure polyethylene amine, based on the amount of resin to be washed away, preferably within a range of from about 0.1% by weight to about 3% by weight, and most preferred within a range of from about 0.2% by weight to about 0.6% by weight. The polyethylene imine or imines may be used un¬ diluted in the cleaning operation.^' The polyethylene imines are, however, preferably used in the form of a water-based washing solution. The concentration of the water-based washing solution is not critical. A suitable concentration may range from about 10% by weight to about 30% by weight of polyethylene imine. However, use may very well be made of solutions having much higher concentrations. Solutions having low concentrations (<5% by weight) are less suit¬ able, since they involve considerable amounts of water for obtaining an effective amount of polyethylene imine. The solution employed is prepared by dissolving the polyethy¬ lene imine in water. It can be prepared at room tempera¬ ture, but the temperature is not critical, since polyethy¬ lene imines are soluble within a broad temperature range. The polyethylene imine solution can be used for cleaning all sorts of equipment that has come into contact with amino resins. .Preferably, the washing solution is used for cleaning different sorts of glue spreading equip- ment with respect to amino-resin glues. These glues are, for instance, made up of reaction products of formaldehyde and urea, melamine and bezoguanamine or mixtures thereof.

The washing of the equipment is performed in conven- tional manner.

The invention will now be described in more detail by means of a non-restricting Example. The figures in parts and per cent relate to parts by weight and per cent by weight, unless otherwise stated. Example:

The washing solution consisted of polyethylene imine SK (BASF) (20% active content; molecular weight: 1.3 x 10⁶ g/mole (M_m) ) .

In the cleaning of a glue roller spreader, the solution was poured out along the entire width of the roller in a thin strand, and the glue (urea-formaldehyde resin glue) and the washing solution were mixed for 0.5-1 min by rotating the rollers. The concentration of the washing solution corresponded to an amount of added poly- ethylene imine of about 1-3% by weight of the amount of glue. This yielded a fine milky white dispersion readily diluted with large amounts of water.

Corresponding tests involving clean water, surfactant solutions (non-ionic and cationic), polyethylene glycol solutions or polyacrylates did not yield a dilutable dispersion, but instead resulted in the formation of gels or coagulates which in some cases underwent phase separa¬ tion.

Claims

1. Use of polyethylene imine or imines for cleaning equipment of amino resins.

2. Use as claimed in claim 1, wherein the polyethy- lene imine or imines are in the form of an aqueous solu¬ tion.

3. Use as claimed in claim 1, wherein the amount of polyethylene imine or imines lies within a range of from about 0.005% by weight to about 10% by weight of pure polyethylene imine, based on the amount of resin to be washed away.

4. Use as claimed in claim 1, wherein the amino resins consist of glue.

5. Use as claimed in claim 4, wherein the glue is made up of reaction products of formaldehyde and urea, melamine and benzoguanamine or mixtures thereof.

6. Use as claimed in claim 1, wherein the equipment is made up of different sorts of glue spreading appliances.

7 . Use as claimed in claim 1, wherein the amino resins after the cleaning are further diluted with water under agitation until the concentration of amino resin has reached an acceptably low level.