HK1175162A - Lightweight gypsum products having enhanced water resistance - Google Patents

Description

Lightweight gypsum product with enhanced water resistance

The present invention relates to gypsum (gypsum) products having an exposed surface and provides such products with enhanced water resistance.

Gypsum products, including gypsum blocks, paperless gypsum (paperless gypsum) boards, and also gypsum veneers (facing), can suffer from moisture absorption problems, especially when the product is intended for use in a wet or humid environment, because such products have exposed surfaces that are susceptible to water ingress.

The standard method of testing "moisture resistant" wallboard requires that it have a water absorption of, for example, no more than 5% — expressed, for example, as the weight percent of water absorbed by a 300mm x 300mm board sample immersed in water at 20 ℃ for 2 hours. Such moisture resistant panels may be used in situations where there is a limited risk of exposure of the panel to moisture.

To achieve moisture resistance, it has been proposed that hydrophobic additives can be incorporated into the plaster of paris (plaster) slurry used to form the board.

For example, as described in our european patent 957070, the hydrophobic additive may be a silicone; the use of such hydrophobic additives requires thermal curing, and it would be advantageous to avoid the energy input requirements involved in such thermal curing. Latex copolymers have also been proposed in WO2008/152519, but it is not clear whether the resulting plaster of paris has long-term water resistance.

It remains desirable to improve the mechanical properties of set (set) gypsum products under wet conditions and to produce such products with reduced open porosity, as this property enables improved water resistance.

In particular, there is a need for water-resistant gypsum products that have improved strength properties after prolonged contact with water, and that can be prepared under a mild drying regime (regime).

According to the present invention, there is provided a method of producing a water-resistant gypsum product, wherein the gypsum product is prepared from: a settable aqueous calcium sulfate dispersion having a water to solids ratio of less than 0.4 to 1, said dispersion having distributed throughout it a lightweight hollow body having a water-impervious (water-impervious) surface; a hydratable cement (e.g., calcium sulfoaluminate) capable of hydrating in the presence of the calcium sulfate dispersion, the hydratable cement being reactive with excess water in the dispersion. Thus, the hydratable cement reacts with water, preferably without significant heat input, to fill pores that may otherwise result from the presence of excess water during curing.

The hydratable cement is typically a calcium sulfoaluminate cement, which is such that: which reacts with the water in the dispersion to form ettringite.

The hydratable binder is present in an amount sufficient to react with excess water resulting from the reaction of the calcium sulfate with water, such as 5-15% by weight based on the weight of the hydraulic powder (i.e., based on the weight of settable solids in the calcium sulfate dispersion comprising the hydratable binder). More preferred amounts are about 10%, e.g., 8-12%, on the same basis.

The calcium sulfate in the dispersion is typically calcium sulfate known to be suitable for low water demand plaster; examples include alpha-plaster of paris, anhydrite II or anhydrite III. The dispersion may further comprise other materials to minimise its water demand, for example one or more superplasticisers (superplasticisers). The calcium sulfate is optionally beta-plaster of paris with a high performance superplasticizer.

The lightweight hollow bodies can be, for example, expanded polystyrene beads, granulated cork, hollow spheres or spheres made from polymer foam which polymerises after solidification (so that the spheres are impermeable to water). The hollow bodies each have one or more cavities (void) or closed cavities (cavity), the cavities or cavities in each hollow body having the property of being closed pores (which do not allow gaseous and/or liquid communication with the surface of the respective hollow body). In each such hollow body, the cavity or void is surrounded by the water impermeable surface of the hollow body. The hollow bodies are typically present in an amount of 0.5 to 2% by weight, based on the weight of the hydraulic powder.

In some embodiments of the invention, it is particularly preferred that the dispersion comprises at least one additive having a pronounced hydrophobicity; such additives are typically at least one amphiphilic compound, such as soap (soap). Preferred examples of such soaps are long chain fatty acid salts, such as calcium, zinc, magnesium and/or aluminium stearates. Such soaps contain hydrocarbon chains (which contribute to hydrophobicity) and also carboxylate groups (which contribute to hydrophilicity) -this is why they can be characterised as amphiphiles. The preferred amount is 1 to 15% based on the weight of the hydraulic powder.

The dispersion may further comprise a water repellent (water repellent) that cures in an alkaline environment to form a hydrophobic silicone resin. Examples of such are alkyl/vinyl alkoxysilanes, alkyl/vinyl siloxanes, alkyl/vinyl silanols, alkyl silicates (siliconates) and mixtures thereof. Suitable examples of commercially available are Wacker Silres BS16 and BS 1260. In some embodiments, the water repellent or precursor thereof may be in powder form.

The dispersion may further comprise fibrous reinforcement, such as, in particular, glass fiber reinforcement; when glass fiber reinforcement is present, it is particularly preferred that the dispersion further comprises a water repellent such as described in the preceding paragraph.

The solids used to make up the dispersion may be provided in the form of dry components to be combined with water in situ to form the dispersion. Such dry blending may be provided for casting the lightweight block in situ.

In use, the dispersion is allowed to set to form a plaster of ripen stone, such as a block or panel, or a veneer layer for application to a wall surface or the like.

When gypsum board is produced according to the present invention, the board may or may not have a surface reinforcement or liner sheet; when surface enhancements are used, the latter may for example be a fibre scrim (fibre scrims), a fibre mesh (fibre mesh) or paper.

It is particularly preferred that the gypsum body is produced without externally applied heating to cause drying thereof, due to the high energy costs in conventional gypsum board production (in terms of direct purchase of energy and in terms of CO)₂Make-up aspects of emissions-off), which can be a further advantage; thus, the product according to the invention may have a reduced energy consumption for compounding (embodified energy).

Other non-toxic materials, adjuvants and components may be present in the dispersion as appropriate. Such non-toxic materials may include optional other components such as starches, set accelerators and retarders, deformation inhibitors (e.g., anti-sagging agents), anti-shrinkage additives, re-calcination inhibitors (recalcination inhibitors), foam stabilizers, bactericides, fungicides, pH adjusters, colorants, flame retardants, and fillers (e.g., particulate inorganic materials or plastics, which may be in expanded form in some embodiments).

The pH of the dispersion used according to the invention is typically 10-13.

The invention extends to gypsum building products such as blocks, wall panels, facings etc. when produced by a method according to the invention, particularly such products for use in outdoor environments and such products that are subject to rain or other contact with water, for example with a body of water.

Certain advantageous features of the invention and methods of operating the invention are now explained in the following illustrative examples of operation.

Example 1

Laboratory samples were produced using a planetary mixing action using a Kenwood KM300 Chef Mixer. The hydraulic material was either pure alpha plaster (Saint-Gobain Formula, 'crystal Base') or a 9:1 blend of alpha plaster: Belitex CSA cement. The density was reduced using 1mm diameter expanded polystyrene beads dry blended to 1.2% w: w of the hydraulic material in a plastic bag. Calcium stearate powder (i.e. SM-Microfine "grade obtained from faci (uk)) was also blended at this stage in subsets 1.3 and 1.4. Tap water was preheated to 40 ℃ to replicate the typical mill slurry temperature when mixing with the powder. Water was weighed at 0.35:1 water to solid powder and added first to the mixing tank followed by the liquid hydrophobic additive in subsets 1.5 and 1.6.

The hydraulic material with EPS beads was poured on the liquid over 30 seconds, left for 30 seconds and mixed for 1 minute (starting at setting 1 and progressively increasing the speed of mixing every 10 seconds until ending at setting 6). The slurry was deposited in a silicone rubber mold to cast 6 cuboids of dimensions 20mm x 100 mm. After hydration of the plaster of paris is complete (which is typically 1 hour and is determined by temperature measurement), the sample is demolded and then sealed in a plastic bag for 48 hours to allow further hydration of the CSA. The samples were then dried at 40 ℃ for 12 hours or more. Preparation included cutting 5mm of the edge with a band saw to expose the core and allowing it to settle in the chamber at 23 ℃/50% RH for 12 hours or more. The weight and size at this point were obtained to give the initial weight and density.

The results obtained are shown in table 1 below.

TABLE 1

Example 2 (comparative)

For comparison purposes, a commercially available Glasroc block (piece) was obtained from Saint-Gobain Gyproxroc. Polymethylhydrosiloxane is added to the glass reinforced product at the mixer stage and coated with a polymer to further prevent surface water ingress. It was cut into 125mm × 125mm blocks to conduct the water absorption test. The results are shown in Table 2 in comparison with example 3.

Example 3

The same procedure as detailed in example 2 was employed, except for the following differences.

The hydraulic powder was a 9:1 blend of alpha plaster of Paris and CSA cement. The water metering (dosing) was slightly higher for 40 ℃ than in example 1, at a water to solids ratio of 0.4. The excess slurry was deposited in two molds with a glass mat (glass tissue) facing material from Johns Manville in the lower portion. The mold was made of brass squares (internal dimensions) of dimensions 152mm x 12.5 mm. A top block of glass mat is then placed on top of the slurry and the slurry is forced through by sliding a metal rod across the two ends, thereby impregnating the mat. The mold was depressed between two Perspex sheets.

After hydration, the samples were demolded and mounted onDrying was carried out in a climate chamber at 60 ℃ and 20% RH for 12 hours. Preparation included cutting the edges with a band saw to expose the core and producing samples of length and width 114 and 122 mm.

The results of the water absorption test are shown in Table 2. The wet strength test results are shown in table 3.

TABLE 2

TABLE 3

Water absorption test

The water uptake test was performed by submerging the sample in tap water at 23 ℃ so that a water head difference of 30mm between the top of the sample and the water level was maintained. After a given time, the sample was removed and the excess water was blotted dry before being reweighed. The method used is the same as given in section 5.9.2 of EN520:2004, but the sample size is smaller and an immersion time longer than 2 hours is used to demonstrate the improved water resistance of the invention. The results of example 1 are the average of three measurements, whereas examples 2 and 3 were obtained from two measurements.

Wet strength test

The wet strength of the samples soaked for 240 hours (i.e., saturated samples) was determined using a method similar to ASTM-C473, section 12, for the hardness measurements of the center and edges of gypsum boards. The maximum force required to drive a 2mm diameter steel punch (ASTM-C473 Specification 2.5mm) through a 13mm sample was measured using a Mecmesin dynamometer at a crosshead speed of 30 mm/min. This test was repeated 16 times around the edge of the sample to determine the average.

Claims (10)

1. A method of producing a water resistant gypsum product, wherein the gypsum product is prepared from: a settable aqueous calcium sulfate dispersion having a water to solids ratio of less than 0.4 to 1, the dispersion having distributed throughout it a lightweight hollow body having a water impervious surface; a hydratable cement capable of hydrating in the presence of the calcium sulfate dispersion, the hydratable cement being reactive with excess water in the dispersion, wherein the hydratable cement is present in an amount of 5-15% based on the weight of hydraulic powder.

2. The method according to claim 1, wherein the hydratable cement comprises calcium sulphoaluminate.

3. A method according to claim 1 or 2, wherein the hollow body is expanded polystyrene.

4. Process according to any one of claims 1 to 3, wherein the hollow body is present in an amount of 0.5 to 2% by weight, based on the weight of the hydraulic powder.

5. A method according to any one of claims 1 to 4, wherein the dispersion comprises an amphiphilic compound.

6. A method according to claim 5 wherein the amphiphilic compound is a soap.

7. A method according to any one of claims 1 to 6 wherein the dispersion comprises a water repellent which cures in an alkaline environment to form a hydrophobic silicone resin.

8. The method according to the invention, wherein the dispersion further comprises glass fiber reinforcement.

9. The method of any one of claims 1 to 8, wherein the gypsum product has a surface enhancement.

10. The method of any one of claims 1-9, wherein the gypsum product is produced without externally applied heating.