Foamed Liquefiers in Gypsum Boards

Abstract

The invention concerns a method for producing gypsum boards, wherein a liquefier for the gypsum slurry is foamed with gas to provide a foam having a water content of less than 85 wt.-%, then incorporated into a gypsum/water mixture and the mixture thus obtained is applied on a two dimensional substrate. The incorporation of the liquefier in foamed form allows for a significant reduction of the amount of liquefier required to provide a desired flowability of the gypsum/water mixture, thus allowing the production of gypsum boards with similar characteristics with less liquefier. The invention further concerns gypsum board prepared using this process, apparatuses for producing gypsum boards using this process and the use of a corresponding liquefier foam to minimize the amount of liquefier required to establish a desired flowability of a gypsum/water mixture.

Claims

1. A method for producing a gypsum board, wherein a liquefier for the gypsum slurry is foamed with a gas to provide a foam, the liquefier having a water content of less than 85 wt.-%, then incorporated into a gypsum/water mixture and the mixture thus obtained is applied on a two dimensional substrate.

2. The method of claim 1, wherein the liquefier is foamed with the gas such that it has a density of 30 to 80%, preferably 40 to 65 wt.-%, relative to the density of the non-foamed liquefier.

3. The method of claim 1, wherein the foamed liquefier is incorporated into the gypsum/water mixture by addition to the solid constituents thereof prior to mixing with water or to the gypsum/water mixture after it is formed in the mixer, in particular via a feed line in front of the dispensing device for application to the two dimensional substrate.

4. The method of claim 1, wherein the foamed liquefier is added to the water to prepare the gypsum/water mixture.

5. The method of claim 1, wherein at least 60 wt.-% and preferably at least 80 wt.-% of the liquefier is incorporated into the gypsum/water mixture as a foam.

6. The method of claim 1, wherein a further soap based foam is incorporated into the gypsum/water mixture.

7. The method of claim 6, wherein the soap based foam and the foamed liquefier are generated independently from each other.

8. The method of claim 1, wherein the two dimensional substrate to which the mixture is applied comprises cardboard or a nonwoven, and wherein the mixture is optionally covered after the application with a further substrate, which may be constituted from the same material which forms the two dimensional substrate or a different material.

9. The method of claim 1, wherein the liquefier is selected from the group comprising lignosulfonate salts, in particular with alkali or alkaline earth metal ions, naphthalenesulfonates, melamine resins, polycarboxylates, polycarboxylate esters and mixtures thereof.

10. The method of claim 1, wherein the liquefier is included in a proportion of 0.1 to 2.5 wt.-% and in particular 1 to 2 wt.-%, based on the weight of the stucco, in the gypsum/water mixture.

11. The method of claim 1, further comprising incorporating one or more of accelerators, fibers, preferably in the form of glass fibers, and additives into the gypsum/water mixture.

12. The method of claim 1, wherein the liquefier is foamed in a device which is spatially separated from the device in which the foamed liquefier is introduced into the gypsum/water mixture.

13. A gypsum/water mixture or gypsum board obtainable according to a method as described in claim 1.

14. An apparatus for producing a gypsum board, preferably for implementing a method as described in claim 1, said apparatus comprising a foaming device, a mixer for producing a gypsum/water mixture, and an output device for dispensing the gypsum/water mixture prepared in the mixer on a two dimensional substrate, wherein the foaming device is fluidly coupled to a supply line of water to the mixer, a supply line for solid constituents of the gypsum board to be formed or with a discharge device of the mixed material from the mixer in front of the output device.

15. Use of a liquefier foam having a water content of less than 85 wt.-% to minimize the amount of liquefier required to establish a desired flowability of a gypsum/water mixture, wherein the foamed liquefier is mixed into the gypsum/water mixture either as constituent used to prepare the mixture or after the mixture has formed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] To further illustrate the invention, reference is made to the attached FIGS. 1 and 2. FIG. 1 illustrates an embodiment of a standard process to prepare gypsum boards with a forming station and molding channel 9, a setting belt 10 and a roller conveyor 11. In this process, all constituents of the gypsum board including the liquefier, which may have been mixed into the process water, are mixed in the mixer 1 and applied to a substrate 2 such as cardboard via the discharge device 3. Soap/surfactant foam can be added separately (not shown).

[0043] Subsequently, the applied mixture forms a flat core and a further layer of substrate (e.g. cardboard) 4 is applied thereon. Finally, the sandwich construct 5 is cut and is conveyed further to a dryer 6.

[0044] FIG. 2 illustrates an embodiment of an inventive process. In this process, the liquefier is pre-processed to a foam in a foaming device 7 and then introduced to the gypsum board preparation device between the gypsum/water mixer 1 and the discharge device 3 via line 8. Alternatively, the foamed liquefier can also be applied into the feed line for water into the mixer 1 or into the feed line for solid constituents of the gypsum board into the mixer 1. In FIGS. 1 and 2 gypsum, water, accelerator and optional additives are mixed in the mixer 1.

DESCRIPTION OF THE INVENTION

[0045] In the following, the invention will be further illustrated by means the examples, which should however not be construed as in any way limiting to the invention.

EXAMPLES

Example 1

[0046] Naphthalenesulfonate (density 1.2 kg/L) was used as the liquefier. A foam of the liquefier was produced by subjecting the naphthalenesulfonate to mixing at 4200 U/min to provide a foam having a stability of between 5 and 30 min (i.e. in this time at most 10% of the liquid initially used may separate). The thus generated foam had a density of about 610 g/L.

[0047] The foamed naphthalenesulfonate was subsequently used for the preparation of gypsum boards prepared from 400 g stucco, 276 g water, 1 g accelerator (calcium sulfate dihydrate) and 2 g/1 g liquefier (0.50/0.25 wt.-% on stucco) as follows:

[0048] Water, stucco, accelerator and liquefier were mixed in a KitchenAid mixer by introducing the stucco/accelerator premix into the water for 10 sec and mixing for 7 sec at full throttle. In samples 1 and 2, the foamed liquefier was added to the water prior to introduction of the stucco/accelerator premix. In samples 3 and 4 the foamed liquefier was added to the stucco/accelerator premix prior to introduction thereof into the water. In sample 5 and 6 half the amount of liquefier (1.0 g, 0.25 wt.-%) compared to samples 3 and 4 was used. For comparison, a further sample without liquefier (comp. 1) was tested.

[0049] The samples were subjected to slump flow testing as follows: A stucco slurry was prepared as indicated above. After the mixing at full throttle, the slurry was transferred into a testing cone (with a 5 cm height and 10 cm width ring) within 13 sec, and excess slurry was removed with a spatula. Then, after a total time of 30 sec, the ring was lifted from the surface, and the slump flow was determined as the largest dimension of the stucco mixture spread on the surface after the flowing of the mixture has stopped. The results of these tests are provided in the below table 1:

TABLE-US-00001 TABLE 1 Liquefier Liquefier (non-foamed, (foamed, Slump flow Sample 1200 g/L) 610 g/L) added [mm] comp. 1 0 0 — 197 1 2.0 To the water 240 2 2.0 To the water 249 3 2.0 To the gypsum mass 235 4 2.0 To the gypsum mass 255 5 1.0 To the gypsum mass 213 6 1.0 To the gypsum mass 222

[0050] As is apparent from the above, a strong effect on the slump flow can be seen when the foamed liquefier is added to the gypsum mass prior to mixing (samples 3 to 6). However, also when the liquefier was added to the water, the slump flow is improved relative to the sample, which was prepared using a non-foamed liquefier.

Example 2

[0051] To determine the quantity for the effect of slump flow two samples using a non-foamed liquefier (samples 7 and 8) and two samples using a foamed liquefier (samples 9 and 10) were measured. The tests were performed as indicated above with a composition of 400 g stucco, 276 g water, 5.2 g calcium sulfate dihydrate (accelerator), 0.044 g retarder and 1.88 g liquefier. For samples 9 and 10 the foamed liquefier was added to the dry gypsum mixture. For sample 11, the amount of liquefier was reduced by about 10% to 1.68 g. The results of these tests is indicated in the below table 2:

TABLE-US-00002 TABLE 2 Sample Addition of liquefier Density [g/L] Slump flow [mm] 7 Pure, non-foamed 1200 242 8 Pure, non-foamed 1200 240 9 foamed 650 260 10 foamed 675 259 11 foamed 720 245

[0052] As is apparent from the above, the effectivity of the foamed liquefier is increased by about 8 to 9% relative to the non-foamed liquefier. In addition, sample 11 shows that about the same slump flow can be obtained with a foamed liquefier, whose content has been reduced by about 10%.

Example 3

[0053] To determine whether the improved effectivity of the liquefier is an effect resulting from better homogenization of the liquefier, a comparison of a foamed liquefier (sample 13) and a liquefier, which was mixed/homogenized with water, but not foamed (sample 14), was made (for comparison, also sample 12 is provided, which uses a non-foamed liquefier). The compositions of the test samples were the same as in example 2 (i.e. 1.88 g liquefier on 400 g stucco). The results of this test are provided in the below table 3.

TABLE-US-00003 TABLE 3 Sample Addition of liquefier Density [g/L] Slump flow [mm] 12 Pure, non-foamed 1200 237 13 foamed 630 253 14 mixed/homogenized 1200 233 with water

[0054] Table 3 shows that mixing/homogenizing the liquefier with water has no significant impact on the slump flow, relative to the non-foamed sample. In contrast, if the liquefier is foamed, the slump flow is significantly increased.

LIST OF REFERENCE SIGNS

[0055] 1 mixer [0056] 2 substrate [0057] 3 discharge device [0058] 4 second substrate [0059] 5 sandwich construct (gypsum board) [0060] 6 dryer [0061] 7 foaming device [0062] 8 line for feeding liquefier foam [0063] 9 forming station and molding cannel [0064] 10 setting belt [0065] 11 roller conveyor