GB2145447A - A building board, or building component made therefrom provided with a vapour barrier - Google Patents

Abstract

The penetration of water vapour into a wall structure comprising a building board, or building component made therefrom is reduced by coating the said board or component on the surface which faces the warm or humid space with a moisture-impermeable layer of a polyvinylidene halide, especially polyvinylidene chloride.

Description

SPECIFICATION A building board, or building component made therefrom provided with a vapour barrier The present invention relates to building boards, and building components made therefrom, having as a vapour barrier a film which is substantially impermeable to moisture, and to methods for preventing water vapour from penetrating into the wall structure, by fitting on one surface of the interior cladding board of the wall structure a film which is substantially impermeable to moisture.

It is known to provide an exterior wall with a polyethylene film which serves as a vapour barrier between the interior cladding board and the thermal insulation of the exterior wall. By using such films it is not, however, possible to prevent moisture from transferring from the warm and humid space into the interior cladding board itself. This problem could be eliminated by attaching a polyethylene film on that surface of the interior cladding board which face the warm space, but this solution would give rise to insurmountable problems in that paints and wallpaper paste do not adhere to a polyethylene surface.

In practice the taping of polyethylene films to each other is laborious and unreliable, since with present-day tapes the seams often detach, whereupon the vapour barrier is no longer impermeable. Furthermore, a polyethylene film cannot be attached tightly to different structures by current work methods. Also, a polyethylene film is broken at electricity inlets and when nails or fasteners are hammered into the wall. Polyethylene film also turns brittle when it ages, and tears are then easily produced on it. The repairing of such tears is often in practice impossible, since the polyethylene film is hidden behind the interior cladding board.

The present invention eliminates or at least reduces the disadvantages mentioned above and provides a building board or a building component made from building boards, having as a vapour barrier a continuous, seamless film which is substantially impermeable to moisture and which does not turn brittle when it ages but, on the contrary, becomes more impermeable than before. The building board of the present invention, and building components made therefrom has, on that surface of the board or building component which faces the warm or humid space, a substantially moisture-impermeable layer containing a polyvinylidene halide. The said layer is preferably a liquid coating varnish layer containing a polyvinylidene halide, especially polyvinylidene chloride.

The thickness of the coating varnish layer is preferably 30-300 zm, for example about 1 60 ym. The coating varnish can also be spread on the edges of the building component or board, especially of a particle board.

The polyvinylidene halide is preferably applied on a varnish dispersion, in particular an aqueous dispersion, which contains the polyvinylidene halide, and preferably 10-60% of polyvinylidene chloride, in addition to any auxiliary agents and/or pigments.

As auxiliary agents it is possible to use an auxiliary solvent such as a glycol ether, a thickener such as a polyurethane thickener, a wetting agent such as polyethylene oxide, an antifoam agent such as a silicone oil, a pH control agent such as ammonia, and/or a preservative such as 1 ,2-benzisothiazoline-3-one. The pigment used can be, for example, a talc. The binding agent used is preferably an aqueous dispersion of polyvinylidene chloride which contains approximately 60% by weight polyvinylidene chlorde.

The present invention also provides a method of preventing water vapour from penetrating into a wall structure, which comprises providing the interior cladding board of the wall structure with a substantially moisture-impermeable film by spreading a liquid surface coating containing polyvinylidene halide on the surface of the interior cladding board which faces the humid space.

The surface coating is preferably an aqueous dispersion which contains polyvinylidene chloride at 10-60% by weight in addition to any auxiliary agent and pigment. The varnish is preferably spread at 100-500 g of varnish per one m2 of the building component or board.

The varnish dispersion used in the present invention can be used for treating all kinds of surfaces, such as gypsum, stryrox, plastic, wood, and in particular building board surfaces. The coating varnish is especially advantageous for the treatment of particle board, since it not only prevents water vapour from penetrating from the warm space into the particle board so that deformations are not produced in the particle board caused by moisture, but also effectively prevents any emission of formaldehyde from the particle board into the interior space. The edges of particle boards can also be treated with the coating varnish dispersion, in which case no separate treatment of the edges of the particle boards is required.

The invention is described below in greater detail in the following Examples.

Example 1 The vapour permeability of coated and uncoated particle boards was measured in the following manner. Particle board specimens 1 2 mm thick were coated with the coating varnish dispersion specified below, by applying varnish to one side of the particle board specimens twice in such a way that the film thickness estimated on the basis of the amount spread was approximately 1 60 ym.

Substance Amount % Haloflex 202 R.T.M (a mixed polymer containing polyvinylidene chloride, manufacturer ICI) 89.0 Butylethoxol (glycol ether, manufacturer Shell) 2.0 Borchigel L75 (polyurethane, manufacturer Borchers) 1.5 Synperonic PE 39/70 R.T.M (a copolymer of propylene oxide and ethylene oxide, containing 70% by weight ethylene oxide, manufacturer ICI) 1.0 Polymekon 1488 (silicone oil, manufacturer Goldschmidt) 0.1 Proxel HL R.T.M (1 ,2-benzisothiazoline-3-one, manufacturer ICI) 0.1 Ammonia 0.3 Water 6.0 Total 100.0 The coated and the uncoated particle board specimens were attached, with the coated side upwards, as covers on containers in which dry calcium chloride was kept.The containers were stored at a temperature of 20"C and a relative humidity of 70%, and the passage of water vapour through the particle board specimens into the containers was observed by weighing the test containers at approximately one-week intervals.

The pressure difference of water vapour between the exterior and the interior surfaces of the test specimens was 1600 Pa. The surface area of the coated and the uncoated particle boards used as test specimens was 78.5 cm2 and the test period was 28 days.

When the particle boards treated with the coating varnish according to the invention and the uncoated particle boards were measured with respect to their permeability and resistance to water vapour, it was found that the mean water vapour permeability of the particel boards treated with the coating varnish according to the invention was 0.022 g/m2h (0.0037 X 10-9 kg/m2 s Pa) and their water vapour resistance was 270 x 10-9 m2 s Pa/kg, whereas the mean water vapour permeability of the uncoated particle boards was 3.35 g/m2 h (0.582 x 10-9 kg/m2 s Pa) and their water vapour resistance 1.7 X 10-9 m2 s Pa/kg. The water vapour permeability of the particle boards treated with the coatng varnish according to the invention was thus considerably decreased as compared with the uncoated particle boards, and their resistance to water vapour was respectively elevated.

Example 2 The emission of formaldehyde from particle boards treated with coating varnish in accordance with Example 1 was determined, and the results were compared with the formaldehyde emission obtained from uncoated particle boards. Eight specimens of 400 x 600 X 1 2 mm3 were sawn from particle board, and four of them were coated with the coating varnish according to the invention on both sides twice, the amount spread being in total 300 + 10g/m2. The boards were allowed to dry for a couple of weeks, and their edges were then protected with paraffin wax. The test boards were placed in metal boxes having a volume of 0.12 m3 and an air replacement coefficient of approximately 0.5 h-l. The air temperature was 20"C and the relative humidity was 85%.The concentration of formaldehyde in the air in the box was determined after 7 days; the load in the boxes was 1 6 m2/m3. The boards were stored in a storage room for 6 months, during which time the determination was repeated twice. The formaldehyde emission measured from test boards treated with the coating varnish according to the invention was 0.11 mg/m3, and the result obtained at a repeat determination after 3 months was 0.09 mg/m3, and 3 months after the previous repeat determination the result was 0.05 mg/m3. The result obtained from untreated boards was respectively 1.04 mg/m3, after repeat measurement 0.91 mg/m3, and after 3 months from the previous repeat measurement 1.11 mg/m3.

The above examples thus clearly show that the coating varnish according to the invention can be used as an interior diffusion barrier instead of the conventional polyethylene film used in wall structures.

Example 3 The relative humidity of room air varies from season to season, but in practice it normally remains between 30 and 70%. For this reason, deformations occur in conventional wood boards without surface treatment as the boards contract and expand.

By treating particle boards or other wooden building materials with the coating varnish of the invention described in Example 1, it is possible to slow down and reduce the deformation, caused by annual changes in the conditions, of a materal which is.subject to changes in relative humidity and temperature, and thereby to improve the usable properties of the material.

When the coating varnish according to the invention was applied twice to the surface of the particle boards, allowing the surface to dry between the applications, the deformation due to shrinkage in the direction of the plane of the board decreased to about 25% as compared with the deformation of untreated particle board at two months, the temperature being 20"C and the conditions varying from 95% and 70% to 45% relative humidity. These deformations can be decreased even more by treating the edges of the board with the coating varnish according to the invention. The results are presented graphically in the accompanying drawing, which depicts the deformation of the particle boards treated in the manner described above (swelling in per mill.) as a function of relative humidity (RH). It is seen that the deformation tendency of the particle board according to the invention decreases substantially in comparison with the uncoated particle board. In a building component made from particle boards thus coated the contracting and expanding of the seams is thereby prevented, and in consequence, the seams can be sealed by taping or by some other method in order to produce a continuous surface, for example on connection with the installation of the interior boards of the exterior wall.

The surface of a particle board treated with the coating varnish according to the invention is highly water-repellant, in which case the weight increase of the board in a water spray decreases, being only approximately 7-15% of the weight increase of the reference board.

Claims (11)

1. A building, or a building component made therefrom having on that surface of the board or building component which faces the warm space, a substantially moisture-impermeable layer containing a polyvinylidene halide.

2. A board or component according to Claim 1, in which the layer is spread also on the edges of the board or component.

3. A board or component according to Claim 1 or 2, in which the said layer contains polyvinylidene chloride.

4. A board or component according to any of the preceding claims, in which the thickness of the said layer is 50-300,um.

5. A board or component according to Claim 4 in which the thickness of the said layer is approximately 1 60 Jum

6. A board or component according to Claim 1, substantially as hereinbefore described.

7. A method of preventing water vapour from penetrating into a wall structure, which comprises providing the interior cladding board of the wall structure with a substantially moisture-impermeable film by spreading a liquid surface coating containing polyvinylidene halide on the surface of the interior cladding board which faces the humid space.

8. A method according to Claim 7, in which a coating layer containing polyvinylidene chloride is spread on the surface of the interior cladding board which faces the humid space.

9. A method of according to Claim 8, in which an aqueous dispersion which contains 10-60% by weight polyvinylidene chloride and optionally auxiliary agents and/or pigments is spread on the surface of the interior cladding board which faces the humid space.

10. A method according to Claim 7, 8 or 9, in which the coating is spread at 100-500 g/m2 on the surface of the interior cladding board which faces the humid space.

11. A method according to any one of Claims 7 to 10, in which the coating is spread also on the edges of the interior cladding board.

1 2. A method according to Claim 7 substantially as hereinbefore described.