The present invention relates to a method of producing an insulating layer having a reinforced surface by combining mineral fibre elements.

DK patent publication No. 131952 discloses a method of producing insulating internal walls of mineral wool blocks wherein the mineral wool blocks are dipped into liquid gypsum plaster so that their surfaces are coated completely with gypsum plaster before they are combined to a wall, and wherein the gypsum is subsequently allowed to harden so as to form a plaster shell on each mineral wool block. It is stated that the insulating wall thus obtained is highly fire-retardant and has a high sound-insulating capacity but the mineral wool blocks as such are not reinforced.

The production of a shell on a wall made from such mineral fibre elements by dipping into gypsum plaster presents a number of practical problems. Firstly, the method requires the setting-up on the construction site of plaster-filled vessels having a sufficient size to allow the mineral fibre blocks to be immersed into the plaster, and secondly the transportation of the elements coated with gypsum plaster from the vessel to the site of use as well as the construction of the wall of the wet elements give rise to a number of handling problems, including spillage of gypsum plaster and soiling of transportation equipment and of the persons constructing the wall .

The object of the present invention is to avoid the problems mentioned above and to provide an insulating layer having an integrated, reinforced surface zone.

According to the invention this object is obtained with a method which is characterized in using mineral fibre elements which contain an activatable binder on at least one surface and in a zone adjoining this surface, and in activating the binder.

By using mineral fibre elements containing an activatable binder

both the production of the mineral fibre elements and the construction of the insulating layer are facilitated.

Thus, the production of the mineral fibre elements can be effected under optimum production conditions, which ordinarily means in a factory, and the elements can be transported to and stored at the site of use without any problems, no matter whether the binder is activated in the factory or in connection with the construction of the insulating layer.

According to a preferred embodiment of the method of the invention the binder is activated at the site of use, i.e. in connection with the construction of the insulating layer.

By effecting the activation of the binder in connection with the construction of the insulating layer, which means that the activation is effected either so shortly before the construction of the insulating layer that the binder is prevented from setting prior to the completion of the insulating layer, during the construction or following the completion of the construction, the very important technical advantage is obtained that during the construction the mineral fibre elements may be compressed to such an extent that no joints or only insignificant joints are formed between the elements. Furthermore, it is easier to form/cut the elements before the binder is activated.

By using mineral fibre element having edge zones which have been subjected to a mechanical treatment in order to make them flexible, cf. DE patent No. 3203622, and by pressing the mineral fibre elements closely together during the construction of the insulating layer, an almost joint-free surface can be obtained following activation of the binder.

According to another preferred embodiment of the method of the invention the activation is effected before the mineral fibre elements are transported to the site of use and preferably in the factory in connection with the production of the mineral fibre elements.

The amount of activatable binder contained in the mineral fibre element may vary within wide ranges and thus it may be adjusted to the desired properties of the final insulating layer.

Thus, a high flexibility is obtained in the production of insulating layers by the method according to the invention.

The activation of the binder can be effected in different ways depending on the nature of the binder. If the mineral fibre elements comprise a hydralic binder, such as cement, gypsum, lime and pozzolanic substances, the binder is activated by supplying an aqueous medium to the elements. When the hydraulic binder is activated in connection with the construction of an insulating layer, it is conveniently effected by applying water to the surface of the combined mineral fibre elements or by treating the surface with a mixture of water and water vapour, thereby accelerating the setting of the hydraulic binder. However, the activation may also be effected immediately before the mineral fibre elements are combined to an insulating layer.

The aqueous medium used for activating the hydraulic binder may suitably contain one or more additives, e.g. one or more setting accelerators, pigments, hydrophobing agents, such as silicone or wax, and catalysts. Furthermore, adhesion improving additives, e.g. polyvinyl acetate or acrylic compounds, may be added.

If the binder is a ther ocuring plastics, the activation may be effected by blowing a stream of hot air towards the surface of the insulating layer or towards the surface of the individual mineral fibre elements or by subjecting the surface to the influence of hot heat waves, e.g. from a heating lamp.

The activation of the binder in a factory may suitably be carried out in the same manner as the activation on the site of use.

As mentioned above the amount of binder may vary within wide ranges and depends i.a. on the type of binder used and the desired reinforcement.

When using quick-setting Portland cement the binder is preferably used in an amount of 2-15 kg/m ² .

Preferably the mineral fibre element has a density of from 50 to 180 kg/m ³ and it may consist of a conventional mineral fibre boards, i.e. boards of mineral fibres which are bonded together by means of a binder, such as phenol formaldehyde binder.

The mineral fibres are preferably rock wool fibres but glass fibres, slag fibres and similar fibres may also be used.

In a conventional mineral fibre board the fibres are ordinarily positioned in such a manner that they have a predominant fibre orientation which runs parallel with the board surface.

However, a mineral fibre board may also be composed of adjacent interconnected rod-shaped fibre elements (lamella), the fibres having a predominant fibre orientation which runs substantially perpendicularly to the board surface.

Mineral fibre elements of this type are particularly suitable for use in the method according to the invention as a particularly high penetration depth is obtained with such mineral fibre layers. Consequently it is possible to obtain a particularly satisfactory surface reinforcement. Furthermore, the fibre orientation mentioned above results in a considerable increase in the compression strength of mineral fibre elements of the same density.

The hydraulic binder is preferably Portland cement as this binder has a higher strength than a number of other prior art hydraulic binders. The reinforced surface zone preferably has a thickness of at least 5 mm, and particularly preferred between 7 and 15 mm.

The reinforcement layer formed may optionally be post-treated, e.g. by water scouring or sack scouring, and/or by application of a surface coating, such as coat of paint or a further cement layer (of the type Cempexo ^® ), or a thin coat of plaster, e.g. in an amount of 1-3 kg/m ² .

In the production of a building front insulation the mineral fibre elements may conveniently be secured to the front by means of an adhesive, e.g. a cement adhesive, an asphalt adhesive or an acrylic adhesive. The adhesive is preferably of the kind which is capable of bonding immediately after application and sets quickly.

The invention also relates to a mineral fibre element for use in the method described above, which element is characterized in that it contains an activatable binder on primarily one surface and in a zone adjoining this surface.

Furthermore the invention relates to a method of producing a mineral fibre element for use in the construction of an insulating layer of combined mineral fibre elements. This method is characterized in that a gas stream containing a particulate, activatable dry binder is caused to pass through a mineral fibre element in such a manner that a binder-containing surface zone is formed on at least one surface of the mineral fibre element and in a zone adjoining this surface and that the activatable binder optionally is activated.

The production method set forth above ensures that a satisfactory and uniform penetration of the particulate binder into the mineral fibre element is obtained.

The method according to the invention is particularly suitable for the production of mineral fibre elements having a surface zone comprising a hydraulic binder, such as cement.

Investigations of mineral fibre elements produced by the method according to the invention have shown that it is possible to obtain a binder penetration depth of up to aprox. 25 mm by using cement as binder.

A further advantage of the method according to the invention is that it allows considerably larger amounts of binder to be introduced into a mineral fibre element than by a prior art wet method.

Thus, tests with a board of rock wool fibres made from lamella and having a density of 140 kg/m ³ have shown that the wet method allows

no more than about 2.9 kg binder per m ² to be introduced without use of additives and by using additives in the form of e.g. a plasticizer and/or anti-flocculant and/or flotation agent no more than 5.5 kg/m ² , whereas the method according to the invention allows binder without additives to be introduced in an amount of up to 10 kg/m ² .

As a result thereof the point loading strength of the board thus produced (determined with a 0 25 mm mandrel having aαimpression velocity of 7 mm/min.) could be increased from about 400 for a board produced by the wet method to more than 2000 N for a board produced by the method according to the invention.

In a preferred embodiment of the method according to the invention an air stream is generated through the mineral fibre element by generating a sub-atmospheric pressure on the down-stream side of the element, thereby avoiding contamination of the environment with the solid binder.

However, it should be noted that it will also be possible to introduce the particulate binder by generating a superatmospheric pressure on the up-stream side of the mineral fibre element and atmospheric pressure on the down-stream side.

The introduction of the solid particulate binder into the mineral fibre element can be effected under such conditions that the binder layer is deposited a distance below the surface, e.g. in a depth of more than 1-2 mm. In this manner it is prevented that the surface of the mineral fibre element is sealed by a subsequent activation of the binder and thus comprises a large number of protruding fibre ends. The presence of the latter is of great importance in obtaining a satisfactory anchoring of a surface coating which may subsequently be applied, e.g. in the form of a coat of paint or an asphalt coating.

It is also possible to adjust the introduction of the binder in such a manner that the surface zone obtains a desired porosity or a density which varies with the depth. For instance it has been possible to produce mineral fibre boards having the following

density variation:

Surface layer 1500-1600 kg/m ³

10 mm from the surface 800-900

20 mm from the surface 300-400 - .

The method according to the invention allows the production of mineral fibre elements having a surface zone of set binder on both sides but ordinarily it will suffice to reinforce one surface.

The reinforced surface zone can be dyed, e.g. by use of a coulored binder. A dust retaining agent, e.g. polyglycol , glycerin, oil, wall paper paste and small amounts of water (20-100 g per m ² ), may be applied on the non-activated surface.

To illustrate the increase in strength which is obtained with the insulating board elements produced by the method according to the invention, point loading strenght measurements have been performed on three different rock wool boards weighing 80 kg/m ³ .

Thus, the rock wool boards were lamella boards, i.e. composed of adjacent lamella and having a predominant fibre orientation perpendicularly to the board surface.

The following boards were used: (1) an uncoated lamella board, (2) a lamella board which comprised a pressure distributing plate attached thereto by glueing and having a density of 180 kg/m ³ , a thickness of 20 mm and a binder content of 3.5 percent by weight, and (3) a lamella board having a 7 mm thick surface zone reinforced with set cement.

The following results were obtained:

Board Measured point loading strength kPa/cm ² *

1 25 2 154 3 350.

* Heel strength measured with a 50 mm mandrel having an impression velocity of 7 mm/min.

As will appear from the above test results, the point loading strenght obtained with the element produced by the method according to the invention is surprisingly high compared to that of the lamella board comprising a pressure distributing plate having a considerably larger thickness than the thickness of the cement layer.

The production of the binder-containing mineral fibre element may e.g. be carried out in an apparatus comprising a container having means for securing the mineral fibre element in the container in such a manner that said element forms a separating wall between the two chambers, said apparatus being provided with means for generating a gas stream through the mineral fibre element and means for supplying particulate, activatable binder to the container on the up-stream side of the mineral fibre element.

The means for producing a gas stream through the mineral fibre element preferably consist of an air pump, such as a centrifugal pump, the suction side of which is connected with the one chamber and the delivery side of which is connected with the other chamber. Preferably the pump has a capacity which permits a pressure difference of 700-5000 mms to be established across the mineral fibre element. The pressure difference is preferably adjusted so that a binder-containing surface zone having a thickness of from 5 to 15 mm is formed.

The invention will now be described in further detail with reference to the drawing which shows a schematic view of an apparatus for carrying out the method described above.

In the drawing 1 designates a container which is divided into two chambers 2 and 3 by a mineral fibre element 4 which is maintained in the container 1 by securing means (not shown). The chamber 3 is connected with the suction side of an air pump 6 through a pipe 5 and the delivery side of said pump is connected with the chamber 2 through a pipe 7. In the chamber 2 an air distribution grid 8 is

provided which serves to distribute the air uniformly over the cross section of the chamber 2.

The apparatus 1 further comprises a supply pipe 10 provided with a cell wheel 9 for particulate, activatable binder. Finally an air vent 11 is connected with the pipe 7.

When starting the pump 6 and the cell wheel 9 an air stream is generated within the pipe 7 and this air stream carries the particulate binder supplied through the cell wheel 9 and the pipe 10. The binder supplied is conveyed to the chamber 2 wherein the air passes through the mineral fibre element after having passed the grid 8, thereby depositing the binder in surface of the element on its up-stream side to form a binder-containing surface zone.