IES62633B2 - Process for the manufacture of urea formaldehyde foams - Google Patents

Abstract

The invention relates to a process for the manufacture of urea formaldehyde foams of the type used in mining or tunnel construction. The process comprises: (a) mixing a solution of urea formaldehyde resin with a foaming agent; and (b) curing the mixture; characterized in that, from 3 to 12% by weight of the total composition of urea is added to the urea formaldehyde resin or the foaming agent or both immediately prior to the mixing of the components in step (a).

Description

PROCESS FOR TE< MANUFACTURE OF UREA FORMALDEHYDE FOAMS The present invention relates to a process for the manufacture of urea formaldehyde foams. In particular it relates to a process for producing such foams for use in mining or tunnel construction.

It is known to manufacture urea formaldehyde foams by mixing an air foam of a diluted tenside solution, such as butylnaphtalinesulfonate, with an aqueous solution of urea formaldehyde condensation resin and then cold curing the mixture using acid. Urea formaldehyde foams are used for thermal and gas insulation in the mining industry and in tunnel construction. The foams may be formed by the mixture of solutions of urea formaldehyde and a tenside followed by the foaming of the mixture in situ. The cure time of these foams is of the order of from 2 to 5 minutes.

The urea formaldehyde resin solutions contain a certain amount of free formaldehyde which increases their storage stability and storage lifetime. For example the shelf-life of a 42% by weight solution of urea formaldehyde resin containing 0.1% by weight free formaldehyde is four weeks; while the same solution with 0.8% by weight free formaldehyde has a shelf-life of two to three months. During : hardening of the urea formaldehyde resin and the drying of the final foam, formaldehyde is released. Obviously this may have serious consequences if the material is used in a poorly ventilated area such - 1 v as a mine shaft or tunnel. As a result, the amount of free formaldehyde in the resin must not exceed 0.5% by weight if it is to be used in mining or tunnel construction.

It is an object of the present invention to provide a process for the manufacture of urea formaldehyde foams in which formaldehyde emission during the curing and drying processes is reduced.

It has surprisingly been found that this object may be achieved by 10 the addition of pure urea to the foaming composition immediately prior to the foaming process.

Accordingly, the present invention provides a process for the manufacture of urea formaldehyde foams comprising the steps of: (a) mixing a solution of urea formaldehyde resin with a foaming agent; and (b) curing the mixture; characterized in that, from 3 to 12% by weight of the total composition of urea is added to the urea formaldehyde resin or the foaming agent or both immediately prior to the mixing of the components in step (a).

It has been found that using the process of the present invention resin solutions with a free formaldehyde content of up to 1% produce a foam with a formaldehyde concentration below the limit required for use in confined areas such as mines. As a result resin solutions with a shelf-life in excess of two months may be used.

Preferably, the amount of urea added is from 4 to 9% by weight of the total composition.

Preferably, the foaming agent is a tenside solution such as the Ί4_ν1δ -^^sulphonates, C^-C^y sodium salts of C^-C. alkanesulphonates, cocosalkyldiglvcol ether sulphonates and butvlnaphthalinesufonate, or lauryldimethylaminoxide. The preferred foaming agent is the sodium salt of butylnaphthalinesulphonate. - 2 Preferably, an anti-shrinking agent such as sorbitol, sugar or sacarride or a combination thereof is added to the resin solution before mixing.

In a preferred embodiment, a 70% sorbitol solution with a urea content of from 4 to 8% by weight of the total composition is added to the resin solution immediately prior to mixing.

The invention shall be described in further detail with regard to the following examples. All percentages are by weight of total composition unless otherwise stated.

EXAMPLE 1 (Comparative example) A foam composition comprising a resin solution with a solid matter content of 42% having a free formaldehyde content of 0.3% by weight (determined using the sulphite procedure according to DIN16476-A) and a 2% tenside solution containing diluted phosphoric acid was foamed using 3 a SINSCHMATIK foam generator. A quantity of 0.23m of the foam was filled into a container which was closed immediately after filling.

The volume above the foam was 48 litres. After closing the box the residual air volume was extracted and pumped through a tube containing activated charcoal by means of a reciprocating pump. In total 150 piston strokes which are equal to 15 litres of air were pumped through the tube. Formaldehyde was extracted from the charcoal with n-hexane and the amount of formaldehyde was determined by gas chromatography. Over a period of one hour after filling the container the formaldehyde content of the residual air removed was determined to be 1350 mg/m .

EXAMPLES 2 -5 The procedure outlined in Example 1 was followed using a series of foam compositions in which urea and/or sorbitol were added, in the amounts indicated, to the urea formaldehyde resin immediately prior to foaming.

Example Urea (%) Sorbitol (%) Formaldehyde measured (mg/m3) 2 4 - 1150 3* 6 10 870 4 9 - 620 5 12 - 635 * In Example 3 a solution comprising 6% urea and 10% sorbitol by weight of the total composition was made up 20 minutes prior to addition to the resin. A 70% sorbitol solution was used.

EXAMPLE 6 (comparative example) The procedure of Example 1 was followed using a resin solution with solid matter and free formaldehyde contents of 42% and 0.9% respectively. The formaldehyde extracted from the extracted residual air as before was measured at 3580 mg/m .

EXAMPLE 7 9% urea was added to the foam composition of Example 5. The 25 formaldehyde content of the extracted residual air was found to be 630 mg/m3.

EXAMPLES 8 and 9 The procedure of Example 1 was followed, but, in these cases the urea was added to the tenside solution as opposed to the urea formaldehyde resin.

Example Urea Formaldehyde 35 (%) measured (mg/m3) 8 6 1165 9 9 650

Claims (5)

1. A process for the manufacture of urea formaldehyde foams comprising the steps of: (a) mixing a solution of urea formaldehyde resin with a foaming agent· and (b) curing the mixture; characterized in that, 10 from 3 to 12% by weight of the total composition of urea is added to the urea formaldehyde resin or the foaming agent or both immediately prior to the mixing of the components in step (a).

2. A process according to Claim 1 wherein from 4 to 9% by weight of 15 the total composition of urea is added.

3. A process according to either of Claims 1 or 2 wherein the foaming agent is a tenside solution. 20

4. A process according to any of the previous claims wherein the urea is added in the form of a 70% sorbitol solution with a urea content of from 4 to 8% by weight of the total composition.

5. A process for the manufacture of urea formaldehyde foams 25 substantially as hereinbefore described with reference to Examples 2 to 5 or 7 to 9.