EP2694730B1 - Method for producing gypsum-containing paper - Google Patents

Description

The present invention relates to a process for the production of a gypsum-containing paper, in particular of a gypsum-containing paper designed as a front and / or backside paper of a gypsum board. The invention also relates to a coated paper, in particular designed as a front and / or backside paper of a gypsum board and certain paper. Moreover, the invention relates to a gypsum board, comprising a gypsum core and at least one attached to the gypsum core paper. Likewise, the invention relates to a method for producing a gypsum board.

US 2005/0234174 A1 describes a coating for a wall construction which can be applied to drywall elements prior to installation. US 2009/0297826 A1 describes a gypsum board with a covering paper, which forms the outside of the gypsum board. GB 1 573 871 describes a gypsum wallboard and a method of coating the surface of an adhesive layer. US 4,009,062 describes a gypsum wallboard with a paper layer attached to a core via an adhesive.

A process for the production of paper is described, for example, in US Pat DE 11 2004 001 313 T5 described. A papermaking pulp containing fillers is fed with a predetermined consistency in a molding area of a paper machine, water is removed from the paper pulp by the paper pulp is dewatered through a water-permeable base, such as a long grid, and a paper web thus prepared is dried and rolled up to produce a finished paper product. In particular, it is proposed that the paper pulp is made with certain fillers, including based on calcium hydroxide (Ca (OH) ₂ ). This ensures that certain properties, such. As optical properties and the strength of the paper produced, can be influenced in the desired manner.

Gypsum boards typically consist of a gypsum core located between two paper or board webs. During production, two cardboard or paper rolls are unrolled and the space is filled with a stucco suspension. The Stuckgipssuspension are generally buried various additives, such as starch, surfactants, setting accelerator, etc. A suitable as a coating paper for gypsum board paper z. B. in the EP 0521804 described. There it is proposed that the paper is coated with a pigment layer which is based on at least one mineral filler of light color and has at least one binder. The coating described therein is intended to achieve a particularly bright, white appearance of the front side paper, so that a stud wall planked with such a gypsum board already "aesthetically" works in the bodyshell. In addition, this is to be achieved by the fact that a subsequent application of ink needs to be less opaque than with a gray or brown front paper. Finally, the coating described therein is intended to effect decoupling between the face paper and a subsequently applied layer, such as decoupling a paper wallpaper such that paper wallpapers are applied to the coating paper and can be removed therefrom without tearing the coated paper. Thus, attached to plasterboard paper wallpapers can be easily replaced.

Cardboard is differentiated from paper in different sources: sometimes cardboard is referred to as paper with a greater thickness, other sources speak of cardboard only when there are several (paper) layers. In the following, paper is used as a generic term for paper and board (ie thick and / or multi-ply paper) for better legibility.

In the production of gypsum boards, the raw board, consisting of the two cardboard layers and the gypsum suspension z. B. passed through a forming station and transported on a Abbindeband and finally on a roller conveyor. During this transport, the "setting" takes place, ie the calcium sulfate hemihydrate (CaSO ₄ ½ H ₂ O) is again to calcium sulfate dihydrate (CaSO ₄ 2H ₂ O). The resulting plate is separated with a suitable knife or a pair of scissors and fed into a Mehretagentrockner. The plate dryers typically operate with a strong air flow, which is conducted transversely to the transport direction or longitudinally.

The gypsum boards are still wet when transported in the dryer, so it is a first important requirement of the paper that it has a high wet grip and is not blown off the gypsum core in the drying process when exposed to sometimes strong air currents. The wet grip can z. B. be achieved in that during the manufacturing process, the aqueous gypsum suspension penetrates into the paper and that there crystallize gypsum needles in the cellulosic layer. The gypsum needles represent a mechanical bond between the plate core and the paper. The speed of the setting essentially determines the achievable production speed. To achieve a high production speed, the setting z. B. be accelerated by the addition of finest dihydrate as a seed in the gypsum suspension. In the case of rapid setting, the penetration process of the stucco suspension in the paper must take place just as quickly. Sometimes the paper is heated by burners and the penetrability of the paper is improved as the gypsum slurry is applied during cooling.

Another important requirement for the paper is the adhesion to the gypsum core in the dry state, because in this state, the gypsum boards are ready for use. In order to achieve a high dry adhesion, the gypsum suspension is given a strength. The starch may be pregelatinized and water-soluble. In the stream of evaporating excess water in the plate dryer, the starch enters the boundary layer between the cardboard and the gypsum core, where it acts like a paste or adhesive.

In summary, the adhesion of the paper to the gypsum core, both in the wet and in the dry state, is of great importance for the production and use of gypsum boards.

In the DE 101 39 420 A1 a method for the production of gypsum boards is presented, wherein after applying the Stuckgipsslurry on the lower board web prior to setting at least one of the board webs is acted upon at the side facing away from the gypsum with negative pressure. As a result, gas bubbles generated in the area of the cardboard are to be destroyed, thereby increasing the contact area between cardboard and gypsum and thus improving the bond.

In the DE 197 43 385 A1 a gypsum board with a sub-carton, a top board and a gypsum layer arranged between the two board layers is presented, wherein at least one of the two board layers is provided with a structure embossing produced before setting the gypsum layer. The indentations or elevations which are pronounced by the embossing of the structure on the inner side facing the gypsum compound are completely filled by the still soft gypsum material, so that after the gypsum layer has hardened the structuring of the cardboard layer is reliably preserved. The pronounced on the inside elevations and depressions should have the advantage that, compared to flat board layers a much better connection between gypsum layer and cardboard layer is obtained. In practice, it has been shown that despite the above measures to provide the paper with a good dry and wet adhesion to the gypsum core, continues to be a problem that the paper in the manufacturing process of the gypsum board or even during the life of the gypsum board Gypsum core can replace. In addition, the known measures require costly changes to the production process. In the DE 101 39 420 A1 it is necessary that the production facilities are retrofitted so that they have a means of extraction, for. B. can accommodate a suction box or a suction roll. In the DE 197 43 385 A1 The paper must be provided with a structure embossing, which is also possible only with complex additional process steps. In the EP 0521804 again, the coating of the paper due to the high viscosity can be done only slowly and inefficiently.

In the PCT / EP2011 / 055088 A method of making a paper or paperboard starting from a pulp with cellulosic fibers is presented. The method is characterized in that the slurry is added to the paper or cardboard formation gypsum and the paper or cardboard formed from the slurry a temperature above 110 ° C is dried, so that forms in the paper or cardboard calcium sulfate hemihydrate. Although this already achieves very good adhesion properties of the paper to the gypsum cores, it would often be desirable to achieve an even higher proportion of gypsum in the paper than is possible only by means of the abovementioned admixture in the mash. In addition, it would be desirable to have an alternative method by which a gypsum-containing paper can be obtained. For example, it would be conceivable in principle to "paint" paper with a plaster application. In this case, however, it is problematic in the case of the gypsum particles dispersed in water or in other solvents that the gypsum dispersion has a high viscosity and thus only a very slow application of the gypsum dispersion is possible in terms of process engineering.

It is therefore an object of the present invention to provide a gypsum-containing paper which is intensively bonded to the gypsum core in the production of gypsum boards and is easy and efficient to produce. It is another object of the present invention to provide a paper having advantageous adhesive properties, e.g. B. in the production of a gypsum board in a particularly simple manner stably adheres to the gypsum core. This object is achieved according to a first aspect of the invention by a method of the type mentioned, in which by means of a dispersion with calcium sulfate dihydrate, a gypsum application is applied to one or both surfaces of the paper, wherein the gypsum application in the dried state based on 100 parts gypsum particles additionally comprises the following constituents: at least 20 parts, in particular at least 30 parts of binder in the form of a low-viscosity modified starch and between 0.1 and 0.5 parts of dispersant. According to the invention it is provided that, after the application of the gypsum application, the paper is dried and in this case the calcium sulphate dihydrate is partially converted into calcium sulphate hemihydrate. In particular, it is possible that the heating takes place so that the calcium sulfate dihydrate in stucco, ie a mixture of a large proportion of calcium sulfate hemihydrate and a small amount of calcium sulfate anhydrate, takes place. It is possible that virtually all of the calcium sulfate dihydrate is converted into stucco. According to this embodiment of the invention, it is possible that the paper drying process anyway provided for the process of paper drying is used for the conversion into stucco.

According to a further aspect of the invention, the object is achieved by a coated paper, in particular a formed as a front and / or backside paper of a plasterboard and certain paper produced according to one of claims 1 to 7, with a one or both sides of the paper applied Plaster application of 5 g / m ² to 40 g / m ² , in particular from 8 g / m ² to 35 g / m ² , wherein the gypsum application in the dried state based on 100 parts gypsum particles additionally comprises the following components: at least 20 parts, in particular at least 30 parts of binder in the form of a low-viscosity modified starch and between 0.1 and 0.5 parts of dispersant.

According to a further aspect of the invention, this object is achieved by a gypsum board comprising a gypsum core, and at least one paper attached to the gypsum core according to one of claims 8 to 12.

According to yet another aspect of the invention, the object is achieved by a method for producing a plasterboard, comprising the steps of: forming a gypsum core from a stucco plaster, providing a gypsum coated paper according to any one of claims 8 to 12, and producing a gypsum board Gypsum board from the gypsum core and the paper, whereby the paper covering the gypsum slurry absorbs plaster gypsum-saturated water from the gypsum slurry and converts the plaster gypsum grains located on the surface of the paper into calcium sulfate dihydrate, forming "linker crystals". Dihydrate crystallized from the stucco solution and where the forming in paper linker crystals act as crystallization nuclei. Extensive experiments have shown that only by means of the above-mentioned mixing ratios of gypsum particles, low-viscosity modified starch and dispersant on the one hand for the industrial contract sufficiently low viscosity of the dispersion can be achieved and on the other hand with the above mixing ratios a particularly high solids content of the dispersed gypsum particles can be achieved , The binder-modified starch has the task of connecting the gypsum particles with the paper so that even in the typical stress both during production and when attaching the paper to a gypsum core does not come to a detachment of the gypsum, in particular by in that the dispersion penetrates deeper into the paper or the paper layers. In addition, other binders may be provided in the gypsum dispersion, z. For example, latex particles can be used. Likewise, binders with Carboxy-methyl cellulose or polyvinyl alcohol may be provided. The dispersant serves to prevent excessive clustering of the gypsum particles. Thus, the dispersant allows a maximum solids content while maintaining good shelf life of the dispersion. For example, the usual in paper coating customary dispersant sodium polyacrylate can be used. Alternatively or additionally, the dispersant Sokolan may also be added.

With respect to the binder starch used, the experiments have shown that starch modified only in relation to low viscosity results in a sufficiently low viscosity of the entire dispersion. In order to obtain low-viscosity modified starch can, for. For example, dextrination or acid hydrolysis can be used to reduce the viscosity of cooked starch. This starch can then be used in high concentration and processed even when hot.

For the strength come u.a. vegetable starch sources into consideration, for. As corn, wheat, potatoes, as long as this low viscosity is ensured. A Brookfield viscosity at 100 rpm of about 2000 mPas is considered preferred. The solids content should preferably be at most 40%. In general, a Vorverkleisterung the strength, for example, by cooking, appropriate. It goes without saying that in order to increase the adhesion properties or to achieve optical or other purposes, it is also possible according to the invention to additionally add further materials to the dispersion in this case.

The stucco gypsum crystallites, which form on the surface of the paper after application and drying of the dispersion, are reactive and rapidly form gypsum with water. It is thus possible in a simple manner to produce a paper with so-called "linkers or anchor crystals" which has particularly advantageous adhesion properties. Even the impinging water in the process of producing the gypsum boards leads to the formation of gypsum in the paper, with the forming needles are anchored particularly well in the paper. They fused in the edge area of paper gypsum core intensively with the forming needles of the gypsum core, resulting in the good wet and dry adhesion. Since, according to the invention, the dispersion can be applied to both surfaces of the paper with calcium sulfate dihydrate, it is also apparent from the above Side of the paper, which does not face the gypsum core, advantageous adhesive properties. If the coated layer is an outer layer, z. Gypsum plasters and gypsum-based leveling compounds in final coatings considerably better. On a primer can be advantageously dispensed with. Also Fugendeckstreifen adhere better to such on the outside coated paper.

In principle, the application of the dispersion can be carried out by any known coating method. For example, the gypsum-containing can be applied in excess to the paper and then the excess with a blade are removed again (so-called Bladestreichen). It would also be possible in principle to spray the dispersion onto the paper by means of spray nozzles or slot nozzles, although it must be ensured that the nozzles are not clogged by the gypsum particles.

In a first embodiment of the invention it is provided that the modified starch is a modified corn starch. Elaborate series of experiments have shown that with modified maize starch particularly high solids content of gypsum particles could be achieved and also has the dispersion during processing particularly advantageous properties. According to a further embodiment of the invention, it is provided that in the preparation of the dispersion, the gypsum particles are dispersed directly into a starch solution. In a further embodiment of the invention, it is provided that the dispersion takes place with interruptions. This is advantageous, since thus clustering of the gypsum particles can be prevented. During the interruption, a uniform dispersion of the gypsum particles is first achieved before further gypsum particles are then added. In particular, it is conceivable that the dispersion is monitored by sensors and the addition of further gypsum particles is only then initiated by an electronic control system, if sufficient dispersion of the agglomerated gypsum particles has been achieved. In a further embodiment of the invention, it is provided that the application takes place by means of a press or an applicator roll. Experiments have shown that these application methods are particularly well suited for the application of the dispersion with calcium sulfate dihydrate.

In a further embodiment of the invention it is provided that the press is a size press. In a size press, the paper is passed through a gap between two rotating rollers. The paper web passes through a so-called open sump between the two rolls. There is thus no pre-metering of the gypsum application, but the paper takes on the passage between the rollers according to the absorption capacity on plaster application. In a size press is thus typically a job on both sides of the paper. According to an alternative embodiment of the invention, it is provided that the gypsum application takes place via a doctor blade application. A doctor job can, for. B. via a roller blade, which predosed the gypsum on the rollers. The gypsum coating on the rolls can then be transferred from the rolls to the paper web. The application of a doctor blade thus enables an exact dosage of the plaster application.

In a particularly advantageous embodiment of the invention, the press is a film press. The paper is thus carried out between two rolls, wherein on the two sides of the paper different dispersions can be applied. For example, it is conceivable that a larger gypsum application is desired on the side of the paper intended to be mounted facing the gypsum core. A film press has the further advantage that you can work at very high speeds. In addition, the paper is less stressed during the application of the plaster dispersion, since the application of the dispersion is not metered on the paper web, but on the applicator roll. It can thus also the number of breaks are reduced.

In a further embodiment, it is also possible that the gypsum application by means of a coating unit or coater, z. B. with a CombiBlade® coating unit and VariBar® from Jagenberg.

Finally, to achieve maximum plaster application, it is also possible that a multiple coat of paper takes place, so z. For example, various of the above paint methods can be carried out in succession. Likewise, it is possible for a paper to be painted on one side with a paint process and on the other with a different paint process. Such different coating methods could z. B. be required if for the gypsum core side facing a Front side paper a much higher gypsum application is desired than for the visible side of the front page paper.

In a further embodiment of the invention it is provided that the dispersant is sodium polyacrylate and the calcium sulfate dihydrate is dispersed while adjusting the pH. The pH generally plays a major role in papermaking, in particular there is a strong influence on most polymer additives as well as on the viscosity of the dispersion. It has been shown that by suitable adaptation of the pH, the viscosity can be reduced and thus a more efficient handling is made possible. In a further embodiment of the invention, it is provided that the gypsum is ground or unground REA gypsum or ground natural gypsum or a mixture thereof. In principle, at least the following options with regard to the addition of calcium sulfate dihydrate into the dispersion before the application of the dispersion are conceivable: exclusively unground REA gypsum is used; only ground REA gypsum is used; only ground natural gypsum is used; a mixture of ground and unground REA gypsum is used; a mixture of ground natural gypsum and unground REA gypsum is used; a mix of ground natural gypsum and ground REA gypsum is used. In the case of REA gypsum, it may be particularly advantageous to use the REA gypsum undried in the seizure state. The use of natural gypsum is particularly advantageous when the gypsum boards (and thus also the boundary layer gypsum core / paper) should be lower to some extent. Since the arrangement of gypsum crystals is more chaotic in natural gypsum than in REA gypsum, natural gypsum can be more stable here.

In one embodiment of the invention, it is provided that the paper has a plurality of layers, of which at least one layer is gypsum-containing. Thus, it is thus possible that even before the application of the dispersion (eg by means of a press or an applicator roll) the tube paper already contains gypsum in at least one layer. Thus, a particularly high gypsum density of the finished paper can be achieved because gypsum is incorporated in both the paper layers and gypsum is applied to one or both surfaces of the paper. It may be provided here that a layer which is located on a surface of the paper has a highest proportion of gypsum. Here lies the thought on the basis that the adhesive properties of the gypsum 'come into effect, especially within the surface of the paper.

In an advantageous embodiment of the invention it is provided that the paper has at least three layers, wherein the two surface layers of the paper have a higher proportion of gypsum than non-surface layers of the paper.

The invention will be further illustrated below with regard to further features and advantages with reference to the description of several embodiments. According to a first embodiment of a paper according to the invention, a yellow cardboard is provided, which is intended to be arranged on the visible side of a gypsum core. This yellow board has three layers of paper, of which only one layer, which is located on the underside of the board, was mixed with gypsum in the manufacture of cellulose pulp. The paper layers in the middle and on the side facing away from the gypsum core, however, have no gypsum. However, the yellow board is coated by means of a film press on the visible side (ie the side facing away from the gypsum core) with an application with gypsum and yellow dye as well as on the plasterboard side facing an application with gypsum without dye. The cardboard has a grammage of 160 g / m ² to 190 g / m ² .

It has been found that the yellow cardboard filled with gypsum as described above could be very well connected to the gypsum core and a significantly increased adhesion to the gypsum core resulted both in the still wet state of the gypsum core and in the ready-to-use gypsum board. In particular, experiments have shown that gypsum application could greatly improve the adhesion properties of wallpapers to the yellow board. Plasterboard provided with the yellow cardboard can thus either be used as a plasterboard without additional wallpaper or optionally also be provided with a well-adhering wallpaper.

According to a second embodiment of a carton according to the invention, a gray cardboard is produced which has three paper layers. Here, all paper layers have been prepared in the same way, with each of the cellulose pulp gypsum was added. In addition, plaster is applied on both sides of the gray box by means of a size press. hereby Overall, a particularly high gypsum content of the entire carton results. The cardboard has a grammage of 170 g / m ² , no dyes are used.

The gray cardboard described above is placed on the back of the plasterboard. The gypsum filling in all three layers and the surface application results in a particularly intensive adhesion with the plaster of the gypsum core, in particular it is possible that gypsum needles fused through several layers with gypsum needles grown out of the gypsum core and thus a particularly stable intergrowth form. According to a further embodiment, a gypsum application is applied to a base paper having a grammage of about 155 g / m ² by means of a Combi Blade Varibar at a speed of 250 meters per minute and a pressure of 0.9 bar. The weight is 12 g / m ² . The dryer uses temperatures between 100 ° C and 160 ° C.

According to another embodiment, a conventional paper with a grammage of 100 g / m ² , which is not originally intended for coating plasterboard, provided on both sides by means of a film press with a gypsum. Experiments have shown that the paper thus coated adheres well to gypsum boards and thus can be used as a cost effective variant to thicker papers or boxes.

Claims (15)

1. A method for producing gypsum-containing paper, especially a gypsum-containing paper formed and determined as a front-side and/or rear-side paper of a gypsum plasterboard, characterized in that a gypsum application is applied to one or both surfaces of the paper by means of a dispersion with calcium sulphate dihydrate, wherein the gypsum application additionally comprises the following components in the dried state relating to 100 parts of gypsum particles:

   - at least 20 parts, especially at least 30 parts, of binding agent in form of a low-viscosity modified starch, and

   - between 0.1 and 0.5 parts of a dispersing agent,

   characterized in that the paper is dried after the application of the gypsum application and thereby the calcium sulphate dihydrate is converted at least partly into calcium sulphate hemihydrate.
2. A method according to claim 1, characterized in that the modified starch is a modified maize starch.
3. A method according to claim 1 or 2, characterized in that in the preparation of the dispersion the gypsum particles are dispersed directly in a starch solution, wherein the dispersion preferably occurs with interruptions.
4. A method according to one of the preceding claims, characterized in that the application occurs by means of a press, especially a size press or an application roller, wherein the gypsum application preferably occurs via a doctor blade application.
5. A method according to claim 4, characterized in that the press is a film press.
6. A method according to one of the preceding claims, characterized in that the dispersing agent is sodium polyacrylate and the calcium sulphate dihydrate is dispersed under adjustment of the pH value.
7. A method according to one of the preceding claims, characterized in that the gypsum is ground or non-ground FGD gypsum or ground natural gypsum or a mixture thereof.
8. A coated paper, especially a paper formed and determined as a front-side and/or rear-side paper of a gypsum plasterboard, produced according to one of the preceding claims, comprising a gypsum application of 5 to 40 g/m², especially 8 to 35 g/m², applied to one or both sides of the paper, wherein the gypsum application comprises the following components in the dry state relating to 100 parts of gypsum particles: at least 20 parts, especially at least 30 parts, of binding agent in form of a low-viscosity modified starch and between 0.1 and 0.5 parts of a dispersing agent.
9. A paper according to claim 8, characterized in that the gypsum application is only applied to one side of the paper, especially to the side of the paper formed as the front or rear paper of a gypsum plasterboard, which paper is fastened to the gypsum core.
10. A paper according to claim 8 or 9, characterized in that a gypsum application is applied to both sides of the paper, wherein preferably the gypsum applications of the two sides are made of different gypsum dispersions, and the gypsum application especially contains a dye admixture on one side.
11. A paper according to one of the claims 8 to 10, characterized in that the paper comprises several layers, of which at least one layer contains gypsum, wherein preferably one layer which is located on a surface of the paper has a highest proportion of gypsum.
12. A paper according to one of the claims 10 or 11, characterized in that the paper comprises at least three layers, wherein the two surface layers of the paper have a higher proportion of gypsum than layers of the paper which are not disposed at the surface.
13. A gypsum plasterboard, comprising a gypsum core, and at least one paper according to one of the claims 8 to 12 which is attached to the gypsum core, wherein preferably the paper attached to the gypsum core has a gypsum-containing coat on the side facing the gypsum core.
14. A gypsum plasterboard according to claim 13, characterized in that the paper attached to the gypsum core comprises a gypsum-containing coat on the side facing away from the gypsum core.
15. A method producing a gypsum plasterboard, comprising the following steps:

    - forming a gypsum core from a plaster of Paris slurry;

    - providing a paper according to one of the claims 8 to 12 which is coated with a gypsum application;

    - producing a gypsum plasterboard from the gypsum core and the paper, wherein the paper surrounding the gypsum slurry absorbs water saturated with plaster of Paris from the gypsum slurry, and the plaster of Paris grains disposed on the surface of the paper convert into calcium sulphate dihydrate under formation of "linker crystals", wherein calcium sulphate dihydrate crystallises in parallel thereto from the solution saturated with plaster of Paris, and wherein the linker crystals that are formed in the paper act as crystallisation seeds.