Additive for gypsum building materials

Abstract

The present invention relates to additives for the production of gypsum products, as well as to gypsum products containing these additives and methods for producing these gypsum products. The additives include boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts, and cement. (Figure 1)

Description

Additive for gypsum building materials The present invention relates to an additive for gypsum building materials. In particular, the present invention relates to an additive for gypsum building materials that increases the abrasion resistance and fracture resistance of gypsum building materials. Additives which increase the corrosion resistance of gypsum products, in particular gypsum boards, are known from the prior art. The phenomenon of creep in the case of gypsum boards, in particular in humid conditions, e.g. with high humidity in the atmosphere, is already known. For example, DE 17 71 017 B2 describes the use of tartaric acid to reduce the creep of gypsum products. Better results have been achieved with polyphosphates, in particular with STMP (sodium trimetaphosphate), see e.g. WO 99 / 08978. In addition, combinations of various reactions are known from the prior art. For example, US 2006 / 0048680 A1 describes a combination of tartaric acid with boric acid or borate as an additive for improving flood resistance. In addition, alkali metal phosphates or alkali metal phosphates, for example STMP, can also be included. The object of the invention is to provide a further additive for improving the corrosion resistance of gypsum products, wherein the corrosion resistance of the gypsum products is at least as good as that of products made from gypsum containing STMP as an additive for improving the resistance to bending. Furthermore, gypsum products and a method for producing gypsum products of this type will be provided, wherein the gypsum products do not contain any STMP, yet their corrosion resistance is at least as good as that of gypsum products produced with STMP. This object is achieved by using an additive according to claim 1, a gypsum-like material according to claim 7 and a method for producing a gypsum-like material according to claim 8. Features of advantageous embodiments of the invention will be described in the appended claims. The term "additive" is used as an inclusive term for components of a gypsum stone which positively influence the bending resistance of the gypsum-like material. The additive does not necessarily have to be a pre-mixed mixture, and instead, the individual components can also be added separately to the gypsum slurry. Accordingly, an additive for the production of gypsum-based products containing boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts and cement is provided. It can be shown that the known materials due to boric acid, borate, tartaric acid and tartrate (salts of tartaric acid) have improved the strength of cement compared to cement. Boric acid or borates, i.e. boric acid salts, can be present in the additive in amounts of 0.01 to 0.15% by weight, based on the amount of calcined gypsum in which the additive is used. Larger amounts of boric acid or borates are also possible, but are avoided due to the need to declare in accordance with the REACH regulations. Therefore, the additive contains 0.01 to 0.1% by weight of boric acid or borates, respectively, based on the amount of calcined gypsum. According to a particularly preferred embodiment, tartaric acid racemate, i.e. a mixture of D- and L- tartaric acid, is used as tartaric acid. Tartaric acid racemate is a cost-effective form of tartaric acid. Tartaric acid and / or tartaric acid salts are present in the additives in amounts of 0.01 to 0.1% by weight compared to the amount of classical chalk used in them. The additive preferably contains 0.01 to 0.03% by weight of tartaric acid / tartrate or boric acid / borate. For example, Portland cement can be used as the cement. According to one embodiment of the invention, the cement is present in an amount of from 0.05 to 0.5% by weight, preferably from 0.08 to 0.25% by weight, relative to the amount of calcined gypsum in which the additive is used. The invention also relates to gypsum-shaped articles, in particular gypsum-like boards, made from a slurry containing at least calcined gypsum, and an additive for producing gypsum-shaped articles from gypsum (improvement of bending strength). The additive comprises the above-mentioned ingredients, in particular boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts and cement. The invention further relates to a method for producing a gypsum board, in particular a gypsum board, comprising the steps of mixing calcined gypsum with water and an additive, forming a gypsum material and optionally drying the gypsum board in order to produce gypsum articles of the set gypsum (improved bending resistance). The additive comprises the above-described components, in particular boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts and cement. The present invention will be explained in more detail below based on exemplary embodiments. Carrier line tests were carried out with different additives designed to improve the corrosion resistance of gypsum boards. The gypsum board produced is made from a foam gypsum core, which is wrapped by a cardboard sheet. The gypsum board is produced according to the conventional method, for example, first gelatin is produced from beta hemihydrate, water, the corresponding additive and further additives, in particular an accelerator and a sodium foam solution. Since both tartaric acid and boric acid have a delaying effect on regulating the drying speed of the gypsum, the amount of accelerator added is adjusted so that an approximately constant time is achieved for the different slurries. Fine-grained, i.e. potassium sulfate dihydrate powder was used as the accelerator. The choice of accelerator is not critical within the scope of the invention, and therefore other accelerators known to those skilled in the art can also be used. In addition to the gypsum core, a thin layer of compressed gypsum was also added to the back of the paper web. Some of the liquid produced as described above was conveyed by a pump before the compressor, where the foam was destroyed in a controlled manner. The right-hand paper sheet was applied directly to the slurry of the core layer. Both the thin gypsum layer and the core layer had the same composition but different densities. In order to determine the size of the manufactured gypsum boards, samples measuring 10 cm and 67 cm were taken from the gypsum boards at predefined points, see Figure 1, Gypsum board. Three longitudinal samples (RL = right side length, ML = middle side length and LL = left side length) and three transverse samples (RQ = right side width, MQ = middle side width and LQ = left side width) were examined per board. The longitudinal samples were taken from the boards under examination, such that their length ran in the direction of production of the boards. The transverse samples were taken from the boards under examination, such that their length was set perpendicular to the direction of the boards. One sample in each case (ML, MQ) was taken from the middle of the gypsum board, i.e. equidistant from the two longitudinal edges of the gypsum board, and one sample in each case (LL, LQ and RL, RQ) was taken from an area of ​​the gypsum board to the left or right, respectively. The samples were then dried, on their longitudinal edge, in a drying cabinet until constant weight was achieved, and the zero value for determining the curvature (the beginning of curvature) was determined using a precision depth gauge in the middle of the sample. The specimens were stored on edge (distance between the backs: 60 cm) in a climate chamber at a temperature of 20 ± 1 °C and a relative humidity of 90 ± 1% for 7 days. After that, the curvature was determined again in the manner described above and the absolute value was determined by subtracting the onset of curvature. The values ​​of the three longitudinal specimens and the values ​​of the three transverse specimens per board were approximately the average. In the first experiment, the curvature of gypsum boards containing exclusively STMP as an additive (standard STMP, L1) was compared with gypsum boards containing a mixture of STMP, boric acid and cement (internal standard L0), since this mixture is commonly used in conveyor belts. The line used for the test showed that the curvature of the internal standard boards (addition mixture consisting of 0.022 wt% of STMP, 0.05 wt% of boric acid and 0.1 wt% of cement in relation to the amount of calcined gypsum used) was slightly weaker than that of the standard STMP, but still within the range of the curvature error of the boards with the standard STMP (0.022 wt% of STMP), so the internal standard can be used similarly to the standard STMP. In addition, a gypsum board without additives to improve corrosion resistance (without L2 additives) was tested for comparison. The gypsum board without additives showed a deflection up to five times higher than that using the STMP standard or the internal standard. The test results are given in Table 1. Table 1 Sample Bending direction (mm) Bending ø (mm) L0 (Internal standard: STMP, boric acid, cement) Length RL 2.25 2.34 ML 2.34 LL 2.44 Width RQ 3.083 2.97 MQ 3.11 LQ 2.71 L1 (STMP standard) Length RL 2.17 2.23 ML 2.14 LL 2.37 Width RQ 3.43 3.32 MQ 3.46 LQ 3.06 L2 (without additive) Length RL 8.93 8.67 ML 8.72 LL 8.35 Width RQ 14.61 14.83 MQ 15.31 LQ 14.56 Table 2 shows the results of bending tests on different boards containing known additives, individually and in combinations of the two methods. Here, 0.022 wt% tartaric acid (L3), or 0.022 wt% tartaric acid and 0.1 wt% cement (L4), or 0.05 wt% boric acid and 0.1 wt% cement (L5) were used as additives. The results show that none of these combinations achieve the STMP or internal standard results. In particular, the combination of boric acid and cement does not provide acceptable values ​​with respect to the curvature of the gypsum board samples after storage in the climatic chamber. Table 2 Sample Bending direction (mm) Bending ø (mm) L3(Tartaric acid) Length RL 3.9 3.93 ML 3.94 LL 3.96 Width RQ 6.25 5.98 MQ 6.08 LQ 5.61 L4(Cement, Tartaric acid) Length RL 3.79 3.76 ML 3.81 LL 3.67 Width RQ 5.68 5.53 MQ 5.45 LQ 5.46 L5 (Cement, Boric acid) Length RL 6.21 6.26 ML 6.24 LL 6.33 Width RQ 9.57 9.39 MQ 9.58 LQ 9.03 The compositions according to the present invention of boric acid, tartaric acid and cement as well as the specific curvature values ​​for these compositions can be found in Table 3. Since this test was carried out on different days compared to the tests considered above, the described boards were re-measured with standard additives. In tests L10 to L12 the amount of tartaric acid was varied with fixed amounts of boric acid and cement. In all three tests, 0.05 wt% boric acid and 0.1 wt% cement were used, in each case corresponding to the amount of calcined gypsum used. The amount of tartaric acid ranged from 0.011 to 0.033 wt%. The lowest curvature was observed in both the longitudinal and transverse directions with 0.022 wt% tartaric acid (L11). These specimens represented the lowest measured values ​​of the series of tests. In tests L14 and L15 the tartaric acid content (0.022 wt%) and cement content (0.1 wt%) were kept constant. The boric acid content was 0.025 wt% in L14 and 0.075 wt% in L15. In this series of tests, sample L11 was also determined in this series of test samples and contained the same tartaric acid and cement content as L14 and L15, but 0.05 wt% boric acid. The lowest curvature of the samples containing different levels of boric acid, in both the longitudinal and transverse directions, was presented by sample L15. In sample L16, the cement content was increased from 0.1 (sample L11) to 0.2 wt%, and in sample L17, the cement content was increased to 0.3 wt%, while the tartaric acid and boric acid contents were as high as in sample L11. All samples L11, L16 and L17 had similar and low grain sizes. The best results, in both longitudinal and transverse directions, were provided by sample L17. In addition to the three-way combination of additives according to the invention, two-way combinations were also investigated. Sample L13 was compared to sample L12 in terms of its content of cement and tartaric acid; however, the addition of 0.05% by weight of boric acid was omitted. The values ​​of sample L13 for the measured curvature after treatment in the climatic chamber are much weaker than those of sample L12, which has a similar composition. The curvature is more than 1.5 times greater than that of L12. In the L19 test, a mixture of 0.022 wt% tartaric acid and 0.05 wt% boric acid was used. If this mixture is compared with the internal standard (L18), it can be seen that the curvature of the L19 samples is slightly higher than the standard. However, it should be noted that the curvature value was much lower than that of the L17 samples, which additionally contained 0.3 wt% cement. Table 3 STMP sample (wt%) Tartaric acid (wt%) Boric acid (wt%) Cement (wt%) Bending direction (mm) Bending ø (mm) L9 0.022 - 0.05 0.1 Longitudinal RL 3.32 3.39 ML 3.40 LL 3.46 Transverse RQ 3.08 3.15 MQ 2.82 LQ 3.55 L10 - 0.011 0.05 0.1 Longitudinal RL 3.15 3.12 ML 3.20 LL 3.00 Transverse RQ 2.81 2.67 MQ 2.71 LQ 2.48 STMP sample (wt%) Tartaric acid (wt%) Boric acid (wt%) Cement (wt%) Bending direction (mm) Bending ø (mm) L11 - 0.022 0.05 0.1 Longitudinal RL 2.62 2.61 ML 2.63 LL 2.58 Transverse RQ 1.78 2.04 MQ 2.04 LQ 2.31 L12 - 0.033 0.05 0.1 Longitudinal RL 3.24 3.15 ML 3.17 LL 3.05 Transverse RQ 2.55 2.37 MQ 2.45 LQ 2.11 L13 - 0.033 - 0.1 Longitudinal RL 5.55 5.51 ML 5.69 LL 5.29 Transverse RQ 3.63 3.95 MQ 4.03 LQ 4.18 L14 - 0.022 0.025 0.1 Longitudinal RL 3.93 3.69 ML 3.78 LL 3.37 Transverse RQ 2.76 2.78 MQ 2.73 LQ 2.85 L15 - 0.022 0.075 0.1 Longitudinal RL 2.33 2.44 ML 2.56 LL 2.42 Transverse RQ 1.64 1.93 MQ 1.81 LQ 2.34 L16 - 0.022 0.05 0.2 Longitudinal RL 2.73 2.73 ML 2.52 LL 2.66 Transverse RQ 1.86 2.02 MQ 2.18 LQ 2.02 L17 - 0.022 0.05 0.3 Longitudinal RL 2.37 2.34 ML 2.37 LL 2.28 Transverse RQ 1.93 1.91 MQ 1.92 LQ 1.87 L18 0.022 - 0.05 0.1 Longitudinal RL 3.11 3.08 ML 3.07 LL 3.05 Transverse RQ 2.66 2.77 MQ 2.73 LQ 2.92. STMP sample (wt%) Tartaric acid (wt%) Boric acid (wt%) Cement (wt%) Bending direction (mm) Bending ø (mm) L19 - 0.022 0.05 - Longitudinal RL 3.06 3.09 ML 3.12 LL 3.10 Transverse RQ 2.81 2.83 MQ 2.90 LQ 2.78 Table 4 shows tests in which unique additive components were substituted for replacement, namely L-tartaric acid, borates and tartrates. Again, a mixture of 0.222 wt% STMP, 0.05 wt% boric acid, and 0.1 wt% cement was used as the internal standard (L24). In all other samples (L21 to L23) a different additive was used. In L21, L-tartaric acid was used in the amount of 0.022 wt% instead of STMP. The amount of boric acid (0.05 wt%) and the amount of cement (0.1 wt%) were in accordance with the internal standard. In D / L-tartaric acid L22, 0.022 wt% was used instead of STMP, while the amount of boric acid and cement was in accordance with the internal standard (i.e., 0.05 wt% boric acid and 0.1 wt% cement). In L23, D / L-tartaric acid was used in the permitted amount of 0.022% by weight. In addition, instead of boric acid, a borate, specifically disodium borate, was used in an amount of 0.05% by weight of boric acid. The results show that replacing STMP with L-tartaric acid (L21) or D / L-tartaric acid (L22) is possible without loss of quality, and even better results than the internal standard are obtained in the bending test with these compounds. Replacing boric acid with pentasodium borate (L23) is also possible, but results will be slightly lower than the internal standard or L22. L22 differs slightly from L23 only by using boric acid instead of the borate used in L23. In Table 5, the replacement of STMP with tartrate, a salt of tartaric acid, was tested. The internal standard (L25) contained 0.022 wt% STMP, 0.05 wt% boric acid, and 0.1 wt% cement. In sample L26, STMP was replaced with the same amount of D / L-tartaric acid. In sample L27, STMP was replaced with the same amount of Na / K tartrate. The results show that the samples with tartrate in combination with boric acid and cement (L27) are slightly lower even in the test sample with bending test compared to the sample with internal standard (L25). However, the lowest amount of curvature was obtained by sample L26, which contained D / L-tartaric acid instead of STPM (L25). The boric acid and cement content were similar in both samples. Table 4 Sample L-Tartaric Acid (wt%) DL / -Tartaric Acid (wt%) Borate (wt%) Bending Direction (mm) Bending ø (mm) L21 0.022 Longitudinal RL 2.76 2.79 ML 2.71 LL 2.90 Transverse RQ 2.68 3.00 MQ 3.15 LQ 3.17 L22 0.022 Longitudinal RL 2.33 2.34 ML 2.31 LL 2.39 Transverse RQ 2.52 2.65 MQ 2.72 LQ 2.72 L23 0.022 0.05 Longitudinal RL 4.35 3.91 ML 3.76 LL 3.63 Transverse RQ 3.82 3.69 MQ 3.75 LQ 3.51 L24 Internal standard, see text Longitudinal RL 3.52 3.46 ML 3.46 LL 3.39 Transverse RQ 3.14 3.74 MQ 4.00 LQ 4.08 Table 5 STMP sample DL / -tartaric acid (wt%) Na / K- tartrate (wt%) Bend direction (mm) Bend ø (mm) L25 0.022 Longitudinal RL 3.09 3.19 ML 3.59 LL 2.89 Transverse RQ 3.15 3.69 MQ 4.05 LQ 3.88 L26 0.022 Longitudinal RL 2.61 2.57 ML 2.63 LL 2.48 Transverse RQ 2.63 2.67 MQ 2.83 LQ 2.56 L27 0.022 Longitudinal RL 3.16 2.93 ML 2.76 LL 2.88 Transverse RQ 2.99 3.29 MQ 3.52 LQ 3.36

Claims

Claims of the invention:

1. A shaped slurry of calcined gypsum, water and an additive for producing shaped gypsum materials, comprising boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts and cement, wherein boric acid and / or boric acid salts are present in an amount of 0.01 to 0.15% by weight relative to an amount of calcined gypsum, tartaric acid and / or tartaric acid salts are present in an amount of 0.001 to 0.1% by weight relative to an amount of calcined gypsum, and cement is present in an amount of 0.05 to 0.5% by weight relative to an amount of calcined gypsum.

2. A slurry according to claim 1, characterized in that boric acid and / or boric acid salts are present in an amount of from 0.01 to 0.1% by weight relative to an amount of calcined gypsum.

3. A slurry according to any one of the preceding claims, characterized in that the tartaric acid is tartaric acid racemate or L-tartaric acid.

4. A slurry according to any one of the preceding claims, characterized in that tartaric acid and / or tartaric acid salts are present in an amount of from 0.005 to 0.03% by weight relative to the amount of calcined gypsum.

5. A grout according to any one of the preceding claims, characterized in that the cement is a Portland cement.

6. Grout according to any one of the preceding claims, characterized in that the cement is present in an amount of from 0.08 to 0.25% by weight relative to the amount of calcined gypsum.

7. A shaped gypsum material, in particular gypsum board, produced from at least one slurry as defined in claims 1 to 6.

8. A method for producing gypsum shaped materials, in particular a gypsum board, comprising the steps of mixing calcined gypsum with water and an additive, wherein the additive comprises boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts and cement, forming a gypsum shaped material and drying the gypsum shaped material, wherein boric acid and / or boric acid salts are present in an amount of 0.01 to 0.15% by weight relative to an amount of calcined gypsum, tartaric acid and / or tartaric acid salts are present in an amount of 0.001 to 0.1% by weight relative to the amount of calcined gypsum, and cement is present in an amount of 0.05 to 0.5% by weight relative to the amount of calcined gypsum.

9. A method for increasing the sag resistance of gypsum building materials comprising the step of adding an additive for producing shaped gypsum materials, comprising boric acid and / or boric acid salts, tartaric acid and / or tartaric acid salts, and cement to a slurry containing calcined gypsum and water.

10. The method according to claim 9, wherein the tartaric acid is L-tartaric acid.