Building Board

Abstract

A building board for interior construction selected from the group consisting of mineral fiber boards, gypsum fiber boards and cement boards and containing from 1 to 25% by weight of zeolites.

Description

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to building boards.

2. Discussion of the Background Art

Building boards are employed to a large extent in the construction field for the preparation of floors, walls and ceilings or ceiling and wall linings.

For different intended uses, there are different optimized plates, for example, plates with increased moisture stability, plates with increased refractoriness or with reduced sound transmission properties.

For cement boards, there are different preparation methods. A common feature of all these methods is the fact that the binder is premixed with various aggregates. This mixture is admixed with water and applied two-dimensionally to a curing tape, which may be segmented, for example. For reinforcement, a glass fiber cloth or fabric may be required as a sheath. The glass fiber cloth or fabric is then applied to the curing tape immediately before the binder-aggregate mixture is applied. After the binder-aggregate mixture has been applied, a second glass fiber cloth or fabric is optionally placed on top as a final layer. The thus formed sandwich element can pass through an extruding or smoothing unit, which causes a densification and smoothing of the boards. The thus produced raw boards can be separated while still wet by on-line saws or separated after the curing is complete. Typically, cement boards have a cement content of about 30% by weight, the balance being mineral fillers, such as sand or limestone granules.

Mineral fiber boards consist of mineral fibers composed of, for example, rock and/or glass wool fibers, cellulose fibers, clay aggregates, light-weight aggregates, such as perlites, other mineral aggregates and fillers as well as starch as a binder. Mineral fiber boards are mostly used for the preparation of ceiling boards. The production of mineral fiber boards proceeds by analogy with the production of paper or cardboard on screening machines, for example, slot screening machines. Boards of sufficient thickness are produced by combining several thin layers and pass through various densification and drying units. The string-shaped web is separated by cutting or sawing means. The thus formed individual boards can be finally coated, dyed and texturized.

Gypsum fiber boards predominantly consist of plaster of Paris, CaSO₄.½H₂O, as a binder and 10 to 20% cellulose fibers. The preparation of the gypsum fiber boards is effected either according to the semidry method, known under the designation of Siempelkamp-Fermacell method or Schenck method, and by wet technology, embodied as a flow-on, lap roller or Hatscheck technology. All these methods have the common feature that intimate mixtures of the binder with the fiber pulp, which is produced dry by milling or in wet digestion by pulping, are prepared. These are coated two-dimensionally on a moving curing tape by scattering technology in a dry state or wet as a slurry. In the case of semidry methods, the “cake” applied to the tape is subsequently soaked with moisture and compressed, whereby the main part of the mixing water is pressed out.

SUMMARY OF THE DISCLOSURE

It is the object of the present disclosure to provide building boards with improved properties. Surprisingly, it has been found that building boards containing from 1 to 25% by weight of zeolites can result in a reduction of air pollutants in interior rooms. Preferred zeolite contents are at least 5% by weight, more preferably at least 10% by weight, the ranges of from 5 to 20% by weight or from 10 to 15% by weight being particularly preferred.

Particularly high contents of zeolites (>30% by weight) render the plate mechanically unstable, because they do not undergo any binding interactions with the rest of the board matrix.

The contents are based on the proportion of zeolite in the total board after drying (atro).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

When cement boards are prepared, the zeolites employed according to the disclosure can be premixed together with the binder and the aggregates.

In mineral fiber boards, the zeolites may also be mixed with the further auxiliaries, such as light-weight aggregates, and employed in the preparation.

In gypsum fiber boards, the zeolites can be added to the plaster of Paris, for example, and the gypsum fiber board can be prepared in the usual way.

WO 2004/033385 discloses an artificial stone board. It contains zeolites within a range of from 40 to 50% by weight, which are mixed with white cement and an acrylate emulsion in order to achieve a bonding between the white cement, the zeolite and the aggregate. The zeolites support the bonding between the cement and aggregates. The critical point is that the artificial stone is particularly light-weight because it is applied to a wall for decoration. In contrast, the cement boards according to the disclosure are the building material for the wall itself and can bear static loads.

The building boards according to the disclosure preferably contain less than 5% or organic admixtures, more preferably less than 3%, and are most preferably essentially free from organic ingredients, especially film-forming organic binders, such as latex, acrylates, styrene acrylates. Surprisingly, the zeolites are inserted into the board matrix relatively loosely in the building boards according to the disclosure, which can be observed by scanning electron microscopy. This accounts for the activity of the zeolites.

The cement board according to the disclosure preferably has a density of from 800 to 1200 kg/m³.

It is particularly preferred according to the disclosure to employ natural zeolites, i.e., zeolites which are not prepared synthetically (e.g., synthetic preparation by reacting SiO₂-containing and Al₂O₃-containing substances with alkali hydroxides at temperatures of more than 50° C. in an aqueous phase). Thus, naturally occurring zeolites are those exploited from deposits.

Suitable zeolites include, in particular, those having a mineral phase composition selected from the group consisting of clinoptilolite, heulandite, chabasite, phillipsite, morderite and mixtures thereof. The zeolites can be used not only in a thermally activated, i.e., thermally dehydrated, form, but astonishingly also in a native form.

In a particularly preferred embodiment, the zeolites are employed in a native form, i.e., without thermal activation or dehydration. A thermal pretreatment of the zeolites is not necessary. Surprisingly, it has been found that the drying of the building boards according to the disclosure at least results in a partial dehydration of the zeolites, which is sufficient for a catalytic pollutant degradation. The open plate structure enables the air-borne pollutants to interact with the incorporated zeolite particles. Film-forming organic binders, as employed in WO 2004/033385, would preclude this or interfere with it.

Astonishingly, it seems that an activation of the zeolites occurs during the preparation/drying of the products. The dehydration of zeolites can be measured, for example, by thermogravimetric analysis (TGA).

Nevertheless, such a zeolite in the building board according to the disclosure shows the activity for the reduction of air pollutants as required according to the disclosure.

The building boards preferably contain zeolites having a grain size of≦200 μm, preferably smaller than 150 μm. This can be achieved in the simplest way by fine milling.

Particularly suitable zeolites have d50 values of from about 30 to about 90 μm, more preferably from 40 to 70 μm.

The zeolites preferably have an oil number (determination according to DIN 53199) of at most 25 g/100 g of zeolite, preferably at most 10 g/100 g of zeolite.

The materials employed according to the disclosure preferably contain less than 3% of diatomaceous earth, and the zeolites are not doped with “antibacterial cations”.

The present disclosure also relates to the use of the building boards according to the disclosure for reducing air pollutants in interior rooms. Air pollutants that can be successfully removed from the indoor air include, for example, formaldehyde, benzene, ammonia and tobacco smoke. Smells, such as fish smell, can also be reduced, as could be proven experimentally by the degradation of triethylamine. Thus, the boards are also suitable for reducing offensive smells from food and hygienic areas (liquid manure, toilet zones etc.).

Surprisingly, the air pollutants are not bound to the materials, but degraded/decomposed, so that there is no saturation of the materials.

For formaldehyde, the maximum admissible working place concentration (MAK value) is 600 μg/m³. In a smoker room, the average formaldehyde content is 220 μg/m³ for an air-exchange rate of 0.5 changes/hour. The WHO assumes a benchmark of 100 μg/m³ for protecting health. A value to be sought in apartments is about 60 μg/m³.

An average benzene content in a smoker room is about 45 μg/m³ for an air-exchange rate of 0.5 changes/hour. The value to be sought in apartments is<10 μg/m³.

By using the building boards according to the disclosure, correspondingly reduced values can be obtained.

EXAMPLE

Gypsum fiber boards with 10% natural zeolites (native, i.e., not dehydrated) having a grain size of at most 200 μm and a d₅₀ value of 40 μm were laid in a room with a normal climate, wherein 1.23 m² of gypsum fiber board area was present per 1 m³ of room volume. In this room, a respective pollutant gas concentration was adjusted by continuously supplying a defined mixture of pollutant gases with the pollutant gases formaldehyde and benzene as well as with a mixture of pollutant gases from cigarette smoke. The air exchange rate of the respective mixture was 0.5 changes/hour, i.e., the mixture of pollutants was renewed completely within two hours. In the outflowing mixture, the remaining pollutant value was measured as a gas concentration.

By the contact with the building boards, the major part of the pollutant gases were degraded, and a pollutant gas concentration from a starting value (inflowing mixture) to the equilibrium value (outflowing mixture)

for formaldehyde from 600 μg/m3 to <100 μg/m3
                      220 μg/m3 to <50 μg/m3
for benzene from      45 μg/m3 to <10 μg/m3

became established.

For cigarette smoke, in addition, a substantial reduction of offensive smells (cold smoke smell) by the contact of the smoke with the gypsum building boards according to the disclosure was proven by olfactometry.

In the experimental series, it was additionally established that the pollutants are not incorporated into the building board, but reactively converted to harmless compounds.

Experiments with modified zeolite proportions in the boards and cement boards or mineral fiber boards yielded similar results.

Claims

1. A building board for interior construction selected from the group consisting of: mineral fiber boards, gypsum fiber boards and cement boards, and comprising from 1 to 25% by weight of naturally occurring zeolites.

2. The building board according to claim 1, wherein said zeolites have a grain size of≦200 μm.

3. The building board according to claim 1, wherein said zeolites have d50 values of from 30 to 90 μm.

4. The building board according to claim 1, wherein said zeolites have a mineral phase composition selected from the group consisting of clinoptilolite, heulandite, chabasite, phillipsite, morderite and mixtures thereof.

5. The building board according to claim 1, wherein said zeolite is employed in a native form.

6. The building board according to claim 1, wherein said building board is a mineral fiber board.

7. The building board according to claim 1, wherein said building board is a gypsum fiber board.

8. The building board according to claim 1, wherein said building board is a cement board.

9. The building board according to claim 1, wherein less than 3% by weight of organic substances are contained in said building board.

10. A method for reducing air pollutants comprising: using a building board selected from the group consisting of: mineral fiber boards, gypsum fiber boards and cement boards, and comprising from 1 to 25% by weight of naturally occurring zeolites in interior rooms.

11. The method according to claim 10, wherein said air pollutants are selected from the group consisting of: formaldehyde, benzene, ammonia, tobacco smoke and mixtures thereof.

12. A method for reducing offensive smell in interior rooms, said method comprises: using a building board selected from the group consisting of: mineral fiber boards, gypsum fiber boards, and cement boards and comprising from 1 to 25% by weight of naturally occurring zeolites.

13. The method according to claim 12, wherein said smells are derived from food and hygienic areas.