IMPROVEMENT OF THE MECHANICAL PROPERTIES OF WATERPROOF GYPSUM PANELS WITH POLYDIMETHYLSILOXANES

Abstract

The invention relates to the use of a mixture of magnesium oxide and a gypsum crystal modifier to improve the buckling resistance of waterproof gypsum panels, particularly in hot and humid climatic conditions.

Description

IMPROVEMENT OF THE MECHANICAL PROPERTIES OF GYPSUM PANELS nj / bnn / Lznz / E / Yi WATERPROOF WITH POLYDIMETHYLSILOXANES FIELD OF INVENTION The invention relates to waterproof gypsum boards and a method for producing such gypsum boards. In particular, the invention relates to gypsum boards that are waterproofed with the aid of siloxanes and that contain magnesium oxide as a catalyst for the polymerization of the siloxane. BACKGROUND OF THE INVENTION Waterproof gypsum boards are prior art. These boards are made water-repellent by means of a hydrophobic agent. Several hydrophobic agents are known from prior art. One group of hydrophobic agents frequently used for this purpose includes silicone oils, or those known as siloxanes. Siloxanes are added to the gypsum slurry during gypsum board production, resulting in a waterproof gypsum board. During this hardening process, the siloxanes polymerize and, generally speaking, form a polysiloxane network within the gypsum board. WO 2006 / 020369 A2 describes how this polymerization can be catalyzed by magnesium oxide. Consequently, the amount of siloxane used to produce a given waterproof product can be reduced. The use of magnesium oxide as a catalyst for siloxane polymerization, however, has a serious drawback. Waterproof panels made in this way are particularly susceptible to gypsum slippage. A significant quality characteristic in the production of gypsum panels, particularly drywall, is the mechanical stability or resistance of the panels to sagging due to gypsum slippage, especially when mounted horizontally. When panels are mounted horizontally, for example, on ceiling profiles running parallel to each other and spaced apart, gravity eventually causes the gypsum to recrystallize within the panels. Panel sagging occurs in the areas not attached to the profiles. This phenomenon is particularly pronounced in warm, humid weather. It is known in the production of gypsum boards that adding additives to the gypsum slurry improves the sagging resistance of the boards. A well-known example of such an additive is trisodium metaphosphate (STMP = sodium trimetaphosphate), see, for example, WO 99 / 08979 A2. It is known from EP 1 910 243 B1, however, that STMP should be used with caution and that STMP with certain conventional additives, such as pH enhancers, can lead to a significant delay in the hardening of the slurry. In such cases, STMP also loses its ability to protect the gypsum board against sagging. The invention further relates to providing waterproof gypsum panels that are less susceptible to gypsum slippage, particularly under hot and humid weather conditions. A method for producing such waterproof gypsum panels is also provided. The object is achieved by means of plasterboard panels having the characteristics according to claim 1 and a method for producing plasterboard panels according to claim 12. The advantageous developments of the inventions are represented in the dependent claims. nj y^nn / L^n^ / e / Yii A gypsum board according to the invention is waterproofed by means of at least one polysiloxane and contains magnesium oxide as a catalyst for the polymerization of the siloxane. Furthermore, the gypsum board comprises a gypsum crystal modifier that is effective during the production of the gypsum board during the rehydration of hemihydrate to dihydrate. Magnesium oxide can preferably be caustic MgO. However, MgO that has been calcined to death can also be used. It has been surprisingly found that gypsum crystal modifiers that are effective during the recrystallization of gypsum hemihydrate to gypsum are able to compensate for the negative consequences of adding magnesium oxide as a catalyst to the siloxane. The buckling resistance of gypsum panels can, in some cases, not only be recovered but even increased. The crystal modifier improves the buckling resistance of gypsum panels by using MgO as a catalyst. Polysiloxane is preferably polymethylsiloxane. The preferred gypsum crystal modifier is selected from divalent heavy metal salts, metal silicates, borates, and mixtures thereof. In particular, transition metal or heavy metal salts that are readily soluble in aqueous media (solubility at 20°C > 200 g / L of water, preferably > 300 g / L), for example, sulfates, chlorides, and hydroxides as salts or oxides, are suitable as modifiers for gypsum crystals. Particularly preferred substances are copper sulfate (solubility of the anhydrous variant in water at 20°C: 203 g / L, solubility of the pentahydrate in water at 20°C: 317 g / L) and zinc sulfate (solubility of the monohydrate in water at 20°C: 350 g / L, solubility of the heptahydrate in water at 20°C: 965 g / L) or hydrates thereof. Therefore, iron salts and / or tin salts are preferred. Metallic silicates that are effective as gypsum crystal modifiers can have the general formula SiO2:Me2O. These are preferably alkali silicates, particularly potassium or sodium silicates or mixtures thereof. The preferred metal silicate has a SiO2:Me2O ratio between 1.0 and 4.0. According to a development of the invention, the metallic silicate may belong to the class of condensed silicates, in particular metasilicates. If borates are used as a modifier of the gypsum crystal, these can preferably be selected from metaborates, in particular Me2B4O?, MeBsOs, Me2BwOi6, Me2BsOi3Con Me= alkali metals or mixtures thereof. The content of the gypsum crystal modifier may be between 0.001 and 0.3% by weight relative to the mass of the hardening calcium sulfate phases used in the production process, i.e., the mass of the stucco used. The preferred ranges are between 0.01% and 0.2% by weight (inclusive limits). The preferred concentration is greater than or equal to 0.01%, particularly preferably greater than or equal to 0.05% by weight. The preferred amount applied is less than or equal to 0.2% by weight, more preferably less than or equal to 0.1% by weight. The magnesium oxide used for catalysis of siloxane formation preferably amounts to between 0.01 and 1% by weight, in relation to the mass of the hardening calcium sulfate phases used in the production process. The method according to the invention for producing a waterproof gypsum board comprises at least the following steps: a) producing a suspension by mixing one or more hardening phases of calcium sulfate, water, siloxane, magnesium oxide and a gypsum crystal modifier, b) form of the mixture. Apart from the constituents mentioned above, the suspension may contain additional additives known to a person skilled in the art of the particular fields of application. These additives may include specific surfactants or foaming agents in general, hardening accelerators, hardening retarders, starches, starch ethers, plasticizers, or water retention enhancers, among others. The gypsum crystal modifier can be selected from divalent heavy metal salts, metal silicates, borates, and mixtures thereof. In addition, the use of a mixture of magnesium oxide and a gypsum crystal modifier selected from divalent heavy metal salts, metal silicates, borates, and mixtures thereof to improve the buckling resistance of gypsum panels, particularly in hot and humid weather conditions, is for protection. Gypsum panels within the scope of this invention are understood to be: gypsum board, gypsum fiberboard, gypsum panels covered with fiberglass mat, partition wall panels made of gypsum, and panels in which the panel material consists of at least 50% by weight of gypsum. DETAILED DESCRIPTION OF THE INVENTION The invention will be explained in greater detail from here onward on the basis of an exemplary embodiment. The example is in no way considered to limit the invention. The plasterboard panels were produced on an experimental conveyor line. The stucco (calcined gypsum, primarily β-hemihydrate) was processed with water, siloxane, magnesium oxide, and copper sulfate pentahydrate, the gypsum crystal modifier, to form a suspension. In the example presented, 0.28 wt% H-siloxane (polydimethylsiloxane), 0.15 wt% MgO, and 0.05 wt% copper sulfate pentahydrate were used, in each case relative to the amount of stucco employed (see Test 3, Table 1). The suspension was processed conventionally to form plasterboard panels. For comparative testing, the gypsum panels were produced on the condition that they had essentially the same composition as the panel according to the invention. However, in test 1 (see Table 1), neither MgO nor copper sulfate pentahydrate was added. In test 2, MgO was added, but copper sulfate pentahydrate was not. The gypsum panels differed only by the aforementioned differences. The copper sulfate pentahydrate was dosed in liquid form, i.e., dissolved in water, and continuously fed as a solution from a storage container into the water and stucco mixing process. This can be done, for example, by means of a pump that mixes the solution indirectly into one of the liquid feed streams to the mixer or that doses the solution directly into the mixer. The metal sulfates can also be dosed as a solid material in powder form into one of the solid material streams within the mixer, for example, by means of a typical solid material dosing station. To determine the sag of the produced gypsum board panels, samples measuring 10 cm x 67 cm were cut from the gypsum board panels at predefined points (see Figure 1) on the construction panel. Three longitudinal samples (RL = right longitudinal, ML = middle longitudinal, and LL = left longitudinal) and three transverse samples (RQ = right transverse, MQ = middle transverse, and LQ = left transverse) were taken per panel examined. The samples were duplicated on a second panel. The longitudinal samples were cut from the examined panels so that their longitudinal extent ran in the direction of panel production. The transverse samples were cut from the examined panels so that their longitudinal extent was perpendicular to the direction of panel production.In each case, a sample (ML, MQ) was taken from the middle of the panel, that is, at an equal distance from the two longitudinal edges of the panel, and in each case, a sample (LL, LQ or RL, RQ) was taken from a region of the panel located closer to the left and closer to the right of the edge of the panel respectively. The removed samples were then dried in a drying cabinet to constant weight, remaining on their longitudinal edge. The zero value for determining buckling (initial buckling) was then determined using a precision depth gauge at the midpoint of the sample. The samples were stored, supported on their edges (support spacing: 60 cm) in a climate chamber at 20 ± 1°C and 90 ± 1% relative humidity for 7 days. The buckling, as described above, was then re-determined, and the absolute value was calculated by subtracting the initial buckling. The values ​​for the three longitudinal samples and the values ​​for the three transverse samples per panel were averaged in each case. nj / ^ηη / ίζηζ / Ε / γι Table 1 Additive Test 1 Test 2 Test 3 A H-Siloxane (polymethyl hydrogen siloxane) 0.28% 0.28% 0.28% B Magnesium oxide - 0.15% 0.15% C Copper sulfate - - 0.05% 2.72 4.17 2.94 Sample 1 2.72 3.97 2.99 Sample 2 2.65 4.19 2.8 Sample 3 2.59 4.33 3.03 Sample 4 2.75 4.19 2.92 Sample 5 2.81 4.08 2.95 Sample 6 2.81 4.27 2.95 4.50 6.95 4.86 Sample 1 4.22 6.94 4.88 Sample 2 4.34 6.91 4.71 Sample 3 4.36 7.24 4.79 Sample 4 4.12 6.78 5.01 Sample 5 4.24 6.89 4.83 Sample 6 5.69 6.95 4.91 The comparison between the sample according to the invention (test 3) and the comparative samples (tests 1 and 2) revealed the following: In test 1, H-siloxane was added to the waterproofing product; however, the polymerization was not catalyzed. In this test, the gypsum crystal modifier was also not added. In the longitudinal direction, the samples had an average buckling of 2.72 mm after treatment in the climate chamber. This value deteriorated to 4.17 mm if the siloxane polymerization was catalyzed by MgO (test 2). If a very small amount of copper sulfate pentahydrate was added, the buckling improved considerably again to 2.94 mm. The same is true for the buckling in the longitudinal direction.

Claims

1. A waterproof gypsum board wherein the gypsum board is waterproofed by means of at least one polysiloxane and contains magnesium oxide as a catalyst for the polymerization of the siloxane, characterized in that the gypsum board comprises a gypsum crystal modifier, wherein the gypsum crystal modifier is effective during the production of the gypsum board in the rehydration of hemihydrate to dihydrate, wherein the crystal modifier improves the buckling resistance of the gypsum board.

2. The waterproof plasterboard according to claim 1, characterized in that the polysiloxane comprises a polydimethylsiloxane.

3. The waterproof gypsum panel according to any one of the preceding claims, characterized in that the gypsum crystal modifier is selected from divalent heavy metal salts, metal silicates, borates and mixtures thereof.

4. The waterproof plasterboard according to claim 3, characterized in that the divalent heavy metal salts are sulfates, chlorides, hydroxides, oxides and combinations thereof.

5. The waterproof gypsum board according to claim 3, characterized in that the divalent heavy metal salts are selected from a group consisting of copper salts, zinc salts, iron salts, tin salts, and mixtures thereof. nj / bnn / Lznz / B / Yi 6. The waterproof gypsum board according to claim 3, characterized in that the metallic silicates have the general formula SiOziMezO, wherein they are preferably alkali silicates, in particular sodium silicates or potassium silicates or mixtures thereof.

7. The waterproof gypsum board according to claim 5, characterized in that the metal silicate has a SiOziMezO ratio between 1.0 and 4.

0.

8. The waterproof plasterboard according to any one of claims 3, 5 or 6, characterized in that the silicate belongs to the class of condensed silicates, in particular metasilicates.

9. The waterproof plasterboard according to claim 3, characterized in that the borates are selected from metaborates, in particular MθζΒαO?, MeBsOs, Me?BioOi6, MesBsOis with Me= alkali metals.

10. The waterproof gypsum panel according to any one of claims 1 to 10, characterized in that the content of the gypsum crystal modifier is between 0.001 and 0.3% by weight, relative to the mass of the hardening-capable calcium sulfate phases used in the production process.

11. The waterproof gypsum board according to any one of the preceding claims, characterized in that the magnesium oxide content is between 0.01 and 1% by weight, relative to the mass of the hardening calcium sulfate phases used in the production process. nj / nnn / i 7n7 / E / Yl· 12. A method for producing a waterproof gypsum panel comprising the following steps: a) producing a suspension by mixing one or more hardening-capable phases of calcium sulfate, water, siloxane, magnesium oxide and a gypsum crystal modifier, wherein the crystal modifier improves the buckling resistance of the gypsum panel; b) forming the mixture.

13. The method according to claim 12, characterized in that the suspension further contains additives, in particular surfactants, foam formers, hardening accelerators, hardening retarders, starches, starch ethers, plasticizers, or means for improving water retention.

14. The method according to any one of claims 12 or 13, characterized in that the gypsum crystal modifier is selected from divalent heavy metal salts, metal silicates, borates and mixtures thereof.

15. Use of a mixture of magnesium oxide and a gypsum crystal modifier selected from divalent heavy metal salts, metal silicates, borates and mixtures thereof to improve the buckling resistance of gypsum panels, particularly in hot and humid weather conditions.