GB2149689A - Applying insulating coatings - Google Patents

Abstract

Problems experienced in the application of sprayed cellulose fibre coatings for insulation purposes are at least alleviated by the use of a binder having enhanced short term binding power through having either (i) reduced water content by virtue of its being used in the form of a foam, or (ii) inclusion of a thermosetting resin to develop tack rapidly without need of drying i

Description

SPECIFICATION Improvements in and relating to insulation This invention relates to sprayable compositions of the kind intended to build up a coating on a substrate.

Such compositions are well-known; fibrous compositions containing mineral wool and a cementitious binder are commonly used to create thick coatings for thermal/acoustic insulation. More recently it has been proposed to use cellulose fibres obtained by shredding/grinding/pulping waste paper as the fibrous component, in combination with a film-forming binder such as polyvinyl acetate in aqueous solution. This combination is effective but limited as to the coating thickness which can be developed in a single pass. Furthermore the drying time is so very great that an additional coating or coatings cannot be applied economically, because additional weight applied to a wet or even to a notyet-fully dried coating will cause the latter to delaminate or to fall off the substrate and it is simply not practicable to wait for the coating to attain the necessary degree of integrity/adhesion.

According to the present invention this problem is at least alleviated by using a binder having enhanced short term binding power through having either: (i) reduced water content by virtue of its being used in the form of a foam and/or, (ii) included therein a thermosetting resin to develop cohesive strength rapidly without need of drying.

The water content can be reduced when the binder is used as a foam because the air in the foam can effectively replace some of the water and enable a binder of much higher solids content to be used without loss of uniformity of mixing of fibres and binder. In the case of a conventional polyvinyl acetate binder used with cellulose fibres this means that solids contents of over 25% can be used instead of the 15% which is usual. The foam will wet out the fibres as effectively as unfoamed liquid binder but results in a product which is less wet and therefore has a tackier film, and a lower wet bulk density.

Inclusion of a thermosetting resin is a particularly effective means of rapidly developing cohesion in the sprayed product Amino-formaldehyde resins are preferred, and may be used with advantage in combination with a conventional film forming binder polymer. The amino-formaldehyde resin may be a urea-formaldehyde resin, or a melamine formaldehyde resin and it includes for example melamine-modified urea-formaldehyde resins. Polyvinyl acetate is a particularly preferred film forming binder polymer, and may be used, if desired, in modified form e.g. methylolated, for improved moisture resistance when dry.

The use of a reactive binder which cures in situ results in rapid development of cohesive strength, both between the fibres themselves and between the coating and the substrate to which it is applied.

The additional use of a film-forming material pro vides greater initial tackiness than does the amino plast alone; it therefore contributes to the cohesion of the whole.

The fibre may be treated with a fire retardant, such as borax. A fire retardant may also be in cluded in the binder system.

The proportion of reactive binder to film-forming binder employed will depend on the cure time re quired and the dilution use amongst other factors, and some experimentation may be necessary to obtain optimum performance.

When a mixed amino-formaldehyde/film forming binder system is used, a total solids content in the binder solution in the range 5 to 50% by weight, may be used. In the case of urea-formaldehyde resin and polyvinyl acetate as the binder system, roughly equal amounts of each have yielded a sat isfactory mixture. The exact proportions and amounts of binder used are capable of variation to suit circumstances. For example, the nature of the surface of the substrate to be coated is important and also the absorbency of the fibres used in the coating. It is to be noted that the higher end of the range of binder solids contents mentioned above is best utilised in a foamed binder system as mentioned below.

It is also important to remember that the binder system may be further diluted by the hardener for the resin.

Dilute phosphoric acid is commonly used as a hardener for amino-formaldehyde resin and the weight of diluent (water) will add to the total weight of the sprayed coating on the substrate. It is essential to try to reduce this weight in order to maximise the coating thickness and at the same time minimise the risk of it peeling off under its own weight.

It is particularly preferred that solutions of the binder system comprises a mixture of amino-formaldehyde resin and film-forming polymer supplied in the form of a foam. This is most conveniently accomplished by causing an airborne stream of the fibres to meet/intermingle with a foamed pre-mixed binder, to form a single stream at or before reaching the substrate to be coated.

The use of a foamed system is extremely effective in reducing water content; the foam is "broken" by the fibres; this is helpful in a achieving uniformity of distribution of binder. The foaming of the binder in this way is particularly readily achieved if the composition is sprayed using a spray-head as described in our co-pending patent application (our ref JKA/23/83) of even date herewith. The invention will now be particularly described by means of the following examples.

Example I One part (by volume) of a polyvinyl acetate latex of about 50% solids content was mixed with one part of urea-formaldehyde resin solution (of about 65% solids content and 1:1:6 U/F ratio) and two parts by volume of water. The binder system thus formed was pre-mixed with a foamed solution of phosphoric acid hardener and sprayed so as to intermingle with a simultaneously sprayed stream of cellulose fibres obtained from waste paper so that the streams of sprayed material converged together onto the substrate to be coated. The resultant layer could be built up to well in excess of the 2 to 2.5 cm thickness usuaily obtained with the use of polyvinyl acetate alone, at the conventional solids content of 10-20% by weight of binder polymer in the coating, calculated as add-on to the cellulose, as before.

Example 2 One part by volume of the polyvinyl acetate latex (as used in Ex.1.) was diluted with one part by volume of water. The binder system thus formed was sprayed as a foam, by using a spray jet fed with a mixture of compressed air and the liquid, so as to intermingle with a simultaneously sprayed stream of cellulose fibres (as used in Ex.1.) before impinging on a substance to be coated.

A coating on the substrate of over 2.5cm thickness could be built up using a mix which resulted in an add-on of 20% by weight of binder solids (based on weight of fibre) in the coating.

Example 3 One part by weight of urea-formaldehyde resin solution (as in Ex.1.) was mixed with one part by weight of water and 0.01 parts by weight of sodium dodecyl benyene sulphate. The binder system thus formed was pre-mixed with an equal weight of aqueous solution of hardener (ammonium chloride) which had been foamed.

The resulting foamed binder was sprayed so as to intermingle with a simultaneously sprayed stream of glass fibres ('E' glass) of 2cm fibre length. A satisfactory coating was obtained using a mix which produced a coating with an add-on weight of binder of 10% based on the weight of the glass fibres.

Example 4 One part by weight of polyvinyl acetate latex (as used in Ex.1.) was mixed with one part by weight of urea-formaldehyde resin solution (as used in Ex.1.) 0.1 parts by weight of Ammonium Chloride and 4 parts by weight of water.

The binder solution thus formed was sprayed as a fine spray of liquid so as to intermingle with a simultaneously sprayed stream of cellulose fibres (as used in Ex.1.). A satisfactory coating was obtained with an add-on solids binder content of 20% by weight based on the weight of cellulose fibres in the coating.

Claims (1)

1. A process for forming a bound coating of fibres on a substrate by spraying said fibres and an organic binder wherein the development of the binding strength in the coating upon spraying is accelerated by virtue of the binder having either: (i) reduced water content by virtue of its being used in the form of a foam and/or (ii) included therein a thermosetting resin to develop cohesive strength rapidly without need of drying.

2. A process according to claim 1 wherein the binder comprises a mixture of a curable amino-formaldehyde resin and a film-forming material.

3. A process according to claim 1 or claim 2 wherein the binder is formed prior to spraying.

4. A process according to claims 1 and 3 wherein the fibres and the binder are sprayed separately as two streams which thereafter intermingle to form an essentially-single stream at or before reaching the surface of a substrate to be coated.

5. A process according to any preceding claim wherein the aminoplast resin in the urea-formaldehyde, melamine formaldehyde or a melamindmodified urea-formaldehyde.

6. A process according to any of claims 2 and 5 wherein the film-forming material is polyvinyl acetate.

7. A process according to claim 1 in which the binder comprises a foamed polyvinyl acetate solution of solids content greater than 25 per cent.

8. A process according to any preceding claim wherein the binder incorporates a fire-retardant material.

9. A process according to any preceding claim in which the fibres comprise cellulose fibres.

10. A process for forming a bound coatig formed by a process as claimed in claim 1 comprising organic fibres, polyvinyl acetate and an amino-formaldehyde resin.

12. A coating according to claim 11 in which the fibres are cellulose fibres.

13. A coating substantially as described in any one of the foregoing examples.