Process for the preparation of gypsum fiber boards with separate fiber pre-treatment

Abstract

The present application is concerned with a process for the production of moistened stucco-fiber mat where the fibers are pre-treated with moisture and the thus treated fibers are subsequently mixed with calcium sulfate hemi-hydrate, the resulting mixture is deposited on a substrate, and treated with water from above with suction from below. The present application is further concerned with gypsum fiber boards having a thickness of at least 19 mm, where the boards are prepared by providing a moistened stucco-fiber mat as noted above and subsequently forming the mat to a board and drying. By performing the treatment of the fibers separately (in the absence of calcium sulfate hemi-hydrate), the wettability of a mixture of the fibers with calcium sulfate hemi-hydrate, is favorably influenced, which allows for a stable productions process of respective fiber boards. The present invention is further concerned with an apparatus for the implementation of a respective gypsum board production process and the use of water saturated paper fibers, which have been prepared in the absence of calcium sulfate hemi- hydrate, in the production of stucco-fiber mats and gypsum fiber broads with a thickness of at least 19 mm, for improving the wettability and / or suction behavior of a mixture of calcium sulfate hemi-hydrate and the fibers.

Description

[0001] Knauf Gips KG

[0002] P-KGI-345-WO

[0003] 1

[0004] 5 PROCESS FOR THE PREPARATION OF GYPSUM FIBER BOARDS WITH SEPARATE FIBER PRE-TREATMENT

[0005] The present application is concerned with a process for the production of gypsum fiber boards having a thickness of at least 19 mm, where the fibers to be incorporated into the boards are pre-treated with moisture and the thus treated

[0006] 10 fibers are subsequently mixed with calcium sulfate hemi-hydrate, the resulting mixture is deposited on a substrate, treated with water from above with suction from below and subsequently dried. The present invention is further concerned with an apparatus for the implementation of a respective process and the use of water saturated paper fibers, which have been prepared in the absence of calcium

[0007] 15 sulfate hemi-hydrate, in the production of gypsum fiber broads with a thickness of at least 19 mm, for improving the wettability and / or suction behavior of a mixture of calcium sulfate hemi-hydrate and the fibers.

[0008] State of the art

[0009] Gypsum fiber board panels have been used in the construction industry to form

[0010] 20 the interior and exterior walls of residential and / or commercial structures. Such gypsum fiber boards are usually prepared in continuous processes, which differ mainly in the water content of the starting mixture. Known are e.g. the “wet“- process, the „dry“-process and the “semi-dry” process.

[0011] In the prior art, an important “dry”-process for producing gypsum fiber boards is

[0012] 25 the so-called Siempelkamp process, which is known for example from the publication DE 2 257 827. According to this process, a dry mixture of fibers and the mineral binder calcium sulfate hemi-hydrate is spread uniformly onto a

[0013] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0014] P-KGI-345-WO

[0015] 2 continuously moving conveyor belt. Hydration water is added by wetting the dry mixture before passing it through a continuously working hydraulic press in order to form an endless board, which subsequently may be cut into a plurality of separate pieces. The hydration water is added to the dry mixture before

[0016] 5 compression of the latter and is absorbed by means of vacuum applied to the fiber stucco mixture whereby a large portion of the water, which remains in the endless compressed board, reacts with the stucco. After the setting process is completed, the boards are dried and supplied to further finishing stages, e.g., for grinding, further cutting, stacking, etc.

[0017] 10 At present, for the production of gypsum fiber boards according to the Siempelkamp process, the untreated dry fiber is added to the stucco (calcium sulfate hemi-hydrate) in a continuous mixer during the production of the gypsum fiber board, and the mixture is then pre-treated with approximately 1 .4 % water (based on the total uptake of water of the stucco and paper in the mixture). Thereafter, the mixture is evenly applied to a screen belt and water is continuously added to the running mixture by means of a free-flow box and sucked through the fiber-stucco mixture or the stucco-fiber carpet by vacuum. The wetted fiber mixture is then pressed into a continuous board strand using a continuous press and finish treated as indicated above.

[0018] 20 With the Siempelkamp process, previously, it had only been possible to form gypsum fiber boards having a thickness of up to 19 mm as a maximum. This is because the board thickness is dependent on the mass and the pouring height of the mixture of fibers and calcium sulfate hemi-hydrate applied onto the conveyor belt. At a certain mass and / or pouring height of the dry mixture of fibers and

[0019] 25 calcium sulfate hemi-hydrate, the mass can no longer be wetted sufficiently by the hydration water which is added prior to compression, even if the amount of water is further increased. This has the effect that sometimes dry material remains on the conveyor belt after pressing which is not incorporated into the board to be

[0020] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0021] P-KGI-345-WO

[0022] 3 produced, thereby leading to inadequate process stability and higher cleaning efforts for the processing equipment.

[0023] In WO 2016 / 101968 A1 , a first solution for increasing the thickness of a board produced on a Siempelkamp production plant above the limit of 19 mm has been

[0024] 5 suggested, which involves the incorporation of quantities of a-calcium sulfate hemi-hydrate of least 10 wt.-% into the regular p-calcium sulfate hemi-hydrate, which is used for the production of the board. On the other hand, as a-calcium sulfate hemi-hydrate is normally produced under high pressure conditions (whereas p-calcium sulfate hemi-hydrate can be produced by simple heating), this

[0025] 10 process faces the economic difficulties.

[0026] Accordingly, there is a need for an easy and economically feasible process for the production of gypsum fiber boards, where in relation to the conventional process, the wettability of the stucco fiber mixture is improved (thereby allowing the production of respective boards with higher thickness) without the necessity for

[0027] 15 the incorporation of larger amounts of a-calcium sulfate hemi-hydrate.

[0028] The present application addresses these needs.

[0029] Detailed description of the invention

[0030] In the investigations, which are underlying the present invention, it has unexpectedly been found that a pre-treatment of the fibers, which are

[0031] 20 subsequently to be incorporated into the gypsum fiber board, with moisture has a positive impact on the wettability of a later mixture of the fibers with calcium sulfate hemi-hydrate. While the applicant does not want to be bound to any particular theory, it is believed that the preliminary treatment of the fibers with moisture saturates the fibers so that in the following they do not longer compete with the

[0032] 25 calcium sulfate hemi-hydrate for water uptake, while the wettability of the mixture is improved. Accordingly, when the water is applied on the stucco fiber mixture in

[0033] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0034] P-KGI-345-WO

[0035] 4 the wetting step, the water uptake is more “homogeneous” over the thickness of the stucco fiber mixture, which in turn provides improved wetting over the entire thickness even if the thickness is 19 mm or larger. In this manner, the risk of dry stucco fiber mixture, which remains on the screen belt after pressing, can

[0036] 5 significantly be reduced in the production of gypsum fiber boards of higher thickness.

[0037] Accordingly, in a first aspect, the present application pertains to a process for the production of a moistened stucco-fiber mat, comprising the steps of

[0038] (i) pretreating paper fibers at a temperature of at least 50 °C in an atmosphere

[0039] 10 with a moisture content of at least 60% to provide pre-saturated paper fibers,

[0040] (ii) preparing a compressible mat of stucco-containing material from a mixture comprising 75 wt.-% to 90 wt.-%, relative to the total dry mix, of calcium sulfate hemi-hydrate and 10 wt.-% to 25 wt.-%, relative to the total dry mix, of paper fibers, which have been pretreated according to step (i);

[0041] 15 (iii) hydrating the dry compressible mat of stucco-containing material with hydration water added from above to the top surface of the mat in excess with suction from below.

[0042] The above process is particularly useful for the preparation of a moistened stuccofiber mat for use in the production of gypsum fiber boards according to the

[0043] 20 Siempelkamp process, where a respective stucco-fiber mat is subjected to subsequent pressing and drying steps. Accordingly, in a second aspect, the present invention pertains to a process for the production of a gypsum fiber board, which comprises the following steps:

[0044] (i) pretreating paper fibers at a temperature of at least 50 °C in an atmosphere

[0045] 25 with a moisture content of at least 60 % to provide pre-saturated paper fibers,

[0046] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0047] P-KGI-345-WO

[0048] 5

[0049] (ii) preparing a compressible mat of stucco-containing material from a mixture comprising 75 wt.-% to 90 wt.-% (relative to the total dry mix) of calcium sulfate hemi-hydrate and 10 wt.-% to 25 wt.-% (relative to the total dry mix) of paper fibers, which have been pretreated according to step (i);

[0050] 5 (iii) moving the dry compressible mat of stucco-containing material on a conveyor belt to a hydration water tank, and

[0051] (iv) hydrating the stucco-containing material with hydration water added from above to the top surface of the mat in excess with suction from below prior to passing the stucco-containing material through a continuous press to form an

[0052] 10 endless gypsum fiber board having a thickness greater than 19 mm.

[0053] In essence, therefore, the process for the production of a gypsum fiber board comprises a process for the production of a moistened stucco-fiber mat as described above where the mat is prepared in a first step and is then subjected to processing in a continuous press to form an endless gypsum fiber board having a

[0054] 15 thickness greater than 19 mm. In addition, the process uses a conveyor belt to transport the stucco-containing material from a position, where the compressible mat is prepared, to a position where the compression is affected, so that the production can be run as a continuous process. By means of the pre-treatment of the papers fibers the process provides for better / more stable and uniform moisture

[0055] 20 penetration even if the compressible mat has a large thickness.

[0056] A preliminary pre-treatment of fibers with water in the production of gypsum fiber boards had previously been described in US 5342566 A, albeit in this case this processing was part of a process, where in a later stage a mixture of the fibers and calcium sulfate hemi-hydrate is mixed with water before the mixture is applied

[0057] 25 on a substrate and pressed to provide a board.

[0058] For the pre-treatment of the paper fibers, it is not of relevant importance if the water is applied to the fibers in a liquid (e. g. via spraying) or gaseous form (as

[0059] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0060] P-KGI-345-WO

[0061] 6 water vapor). In either of the cases, the fact that the fibers are kept in an atmosphere as indicated ensures that the water evenly distributes over the entirety of the fibers and their surfaces (via formation of an equilibrium), thereby providing fibers, which are saturated with water. Such fibers, when bought into contact with

[0062] 5 further water, have a significantly reduced tendency to take up water, so that when mixed with calcined gypsum or calcium sulfate hemi-hydrate they do not change the water uptake characteristics of the stucco. In addition, the pretreated fibers provide increased wettability of a mixture with calcium sulfate hemi-hydrate.

[0063] The skilled practitioner will be aware that the formation of an equilibrium is

[0064] 10 facilitated with increase of the temperature und increase of the moisture content of the respective composition. Accordingly, it is preferred that the step of pretreating the paper fibers is at a temperature of at least 60 °C. The skilled practitioner will also recognize that temperatures of more than 100 °C are less suitable, as this is above the boiling temperature of water. Accordingly, in a particularly preferred embodiment, the treatment in step i) is at a temperature in the range of 70 to 95 °C. Alternatively and preferably in addition thereto, the moisture content for the treatment in step i) is at least 70 % and more particularly in the range of 80 to 95 %.

[0065] A further positive effect on the wettability, which is desired for a stable fabrication

[0066] 20 of gypsum fiber board which higher thickness, may be achieved by the specific selection of the type of wastepaper, which is used in the inventive process. For example, newspapers have a low content of fine particles, whereas journals, magazines and catalogues have a higher content of fine particles. To achieve the best results, wastepaper having a low content of fine particles is a preferred

[0067] 25 source of fibers for use in the inventive process.

[0068] Preferably, the fibers are substantially devoid of fibers having a length of less than 1 pm (i. e. the fibers do not comprise more than 5 % by weight, preferably more than 1 % by weight and more preferably more than 0.1 % by weight of fibers of

[0069] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0070] P-KGI-345-WO

[0071] 7 such length). It is specifically advantageous, if the fibers have a short and thin morphology rather than being long and thick. It is also preferred, that the content of fibers having a length greater than 90 pm is less than 65 wt.-%. In another embodiment, the mean fiber length of the fibers is from 200 pm to 1 mm and

[0072] 5 particularly preferably in the range of 300 to 600 pm. the respective fiber length in the context of this invention is determined according to ISO16065-2:2014, e. g. with a Valmet FS5 fiber analyzer.

[0073] It has further been observed that also the condition of the calcined gypsum, i.e. whether or not the calcined gypsum has been stabilized or not, has an influence

[0074] 10 on the wettability of a mixture of fibers and calcium sulfate hemi-hydrate, as a stabilization treatment slightly reduces then water uptake capabilities of the calcium sulfate hemi-hydrate (in a stabilization, the uppermost surface of calcium sulfate hemi-hydrate particles reacts with water to form calcium sulfate dihydrate, thereby improving the wettability of the calcium sulfate hemi-hydrate particles). Accordingly, it is preferred in the context of this invention that calcium hemi- hydrate, which is to be used for mixing with the paper fibers for the preparation of a compressible mat, is subjected to a stabilization treatment. This stabilization treatment is conventionally performed on the freshly prepared calcined gypsum.

[0075] In the invention, the term “stabilization treatment” designates a processing of the

[0076] 20 stucco, where after calcination the stucco reacts with a small amount of water (which is either added in fluid form or via moisture in the atmosphere, to which the stucco is exposed). This process is also known as "forced aging" of stucco. In “stabilization”, anhydrite III contained in the stucco after calcination is transformed to calcium sulfate hemihydrate, crystal defects in the stucco are healed and fine

[0077] 25 particles are agglomerated. The specific surface area of the stucco is thereby reduced, which in turn reduces the need for water when forming a slurry. In the stabilization treatment, the amount of water relative to the calcined gypsum is usually 6 wt.-% or less and preferably in the range of about 1 to 3 wt.-%.

[0078] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0079] P-KGI-345-WO

[0080] 8

[0081] The way or processing, by which this stabilization treatment is affected, is not subject to any relevant restrictions, as long as the desired stabilization is achieved. Means and methods, by which such stabilization can be provided, are well known to the skilled practitioner and encompass e. g. a stabilization treatment

[0082] 5 as described in EP 1 547 984 A1 . In such treatment, a heated calcium sulfate hemi-hydrate is treated at temperatures over 100 °C, the hot calcium sulfate hemihydrate is then fed in a moistening device having walls heated to at least 100 °C, water is injected into the device such that not yet moistened surfaces of the calcium sulfate hemi-hydrate are exposed to the injected water and / or steam, an

[0083] 10 atmosphere in the moistening device at a level of the dew point in the range 75 to 99 °C is maintained, the moistened blend is fed into a curing device, an atmosphere in the curing device is maintained above 75 °C for at least 3 minutes, the moistened and cured blend are fed into a drying device, and said moistened and cured blend is dried.

[0084] A particular preferred stabilization treatment for use in the practice of the invention is a stabilization treatment, which involves the addition of water to the freshly prepared calcium sulfate hemi-hydrate to provide a moistened calcium sulfate hemi-hydrate and subjecting the moistened calcium sulfate hemi-hydrate to a treatment at a temperature of at least 30 °C for a time of at least 30 Min to obtain

[0085] 20 the stabilized calcium sulfate hemi-hydrate. For respective details on such stabilization treatment and preferred embodiments thereof, reference is made to the disclosure of WO 20191010968 A1 , the relevant contents are herewith incorporated into this application by reference in their entirety.

[0086] The terms “calcium sulfate hemi-hydrate”, “calcined gypsum”, “stucco” and

[0087] 25 “gypsum hemi-hydrate” are used with interchangeable meaning herein and refer to a material with the general formula CaSO4 x1 / 2 H2O. This includes both calcium sulfate hemi-hydrate in the alpha and beta form. The terms “gypsum” and “calcium sulfate dihydrate” likewise are used interchangeably herein and refer to a material

[0088] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0089] P-KGI-345-WO

[0090] 9 with the general formula CaSCU x 2 H2O. Besides these two hydrates, gypsum can also exist in a dehydrated form with the formula CaSC (“anhydrous gypsum”), the presence of which is not excluded in the product of the invention. It is noted though, that the formation or presence of significant quantities of anhydrous

[0091] 5 gypsum is usually not observed. For the calcium sulfate hemi-hydrate product of the invention, it is also not excluded that it may contain minor quantities of calcium sulfate dihydrate, whereas the amounts of respective hemi-hydrate and dihydrate, that were determined in the examples by means of XRD are the amounts of the respective calcium sulfate dihydrate and hemi-hydrate only. However, the skilled

[0092] 10 person knows that in natural calcium sulfate containing material some content of other minerals, e. g. calcium carbonate can occur. In some cases, up to 25 wt. -% of other minerals can be comprised. In general, the term “calcium sulfate containing material” means in the present invention inorganic compounds with the formula CaSCU and all related hydrates. The stabilization of the calcium sulfate hemi-hydrate can be carried out in the in absence of presence of the fibers, which have undergone pretreatment. In a preferred embodiment, the stabilization is carried out in the presence of respective fibers.

[0093] The processing according to the invention described herein has good compatibility with the invention as described on WO 2016 / 101968 A1 . Accordingly, in one

[0094] 20 embodiment the calcium sulfate hemi-hydrate for use in the inventive process is a mixture of a-calcium sulfate hemi-hydrate and [3-calcium sulfate hemi-hydrate, wherein the content of a-calcium sulfate hemi-hydrate in the mixture is at least 10 wt.-% (relative to the total calcium sulfate hemi-hydrate). The combination of the solutions of this invention and the one described in WO 2016 / 101968 A1 can

[0095] 25 e. g. provide favorable wettability of the fiber / calcium sulfate hemi-hydrate mixture even for the production of gypsum fiber boards with a very high thickness of 31 mm or more. To this end, in a preferred embodiment, the calcium sulfate hemi-hydrate comprises at least 20 wt.-% (relative to the total calcium sulfate hemi-hydrate), in particular, about 30 wt.-% (relative to the total calcium sulfate hemi-hydrate) of a-

[0096] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0097] P-KGI-345-WO

[0098] 10 calcium sulfate hemi-hydrate, and at least 50 wt.-% (relative to the total calcium sulfate hemi-hydrate), in particular, about 60 wt.-% (relative to the total calcium sulfate hemi-hydrate) of [3-calcium sulfate hemi-hydrate.

[0099] On the other hand, since as noted above the use of a-calcium sulfate hemi-hydrate

[0100] 5 is associated with economical disadvantages, in another embodiment it is preferred that the content of a-calcium sulfate hemi-hydrate in the preparation of the mixture of fibers and calcium sulfate hemi-hydrate is preferably less than 5 % (based on the total amount of calcium sulfate hemi-hydrate therein), more preferably less than 2 % and even more preferably less than 1 %.

[0101] 10 Next to the possible presence of a-calcium sulfate hemi-hydrate, also the particle size of the calcium sulfate hemi-hydrate has an influence of the wettability of the compressible mat, which is prepared in the course of the inventive process. In this regard, to provide particularly suitable processing characteristics, it is preferred that the granulation of a portion of less than 90 %, in particular less than 70 % of

[0102] 15 the stucco fiber composition is above 1 pm.

[0103] The mixture, which is prepared in step (ii) of the inventive process, can be constituted predominantly (i. e. with contents of other constituents of less than 5 wt.-% and preferably less than 1 wt.-%) or even exclusively from water, calcium sulfate hemi-hydrate and the fibers. Alternatively, it is possible to optimize

[0104] 20 processing parameters and stability of the inventive process by incorporating additives into the mixture of fibers and calcium sulfate hemi-hydrate. Such additives can either be added directly into the mixer, where the mixture is prepared, or can be added previously to either the dry calcium sulfate hemi- hydrate or the pretreated fibers.

[0105] 25 Additives, which are particularly suitable for combination with the fibers and calcium sulfate hemi-hydrate in the inventive process, include e. g. an accelerator, in particular, in the form of calcium sulfate dihydrate, which might originate from

[0106] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0107] P-KGI-345-WO

[0108] 11 sawing or grinding of gypsum boards or other gypsum articles. By means of specific additives, as for example, retardants or accelerators, the calcium sulfate hemi-hydrate may be modified so as to fulfill specific requirements of the intended application areas. Retarders, which can be used in the practice of the invention

[0109] 5 include e. g. citric acid. Further additives, which may be incorporated into the inventive process, are wetting agents, which are compounds, which influence the surface tension of the hydration water. By the addition of such agents the wettability can be even further increased.

[0110] In a particularly preferred embodiment, the inventive processes involve the

[0111] 10 addition of a retardant, in particular, citric acid, and / or the addition of an accelerator, in particular in the form of coated calcium sulfate dihydrate, for the preparation of a mixture of calcium sulfate hemi-hydrate and the fibers in step (ii) (i. e. prior to the processing of the mixture to a compressible mat).

[0112] In the inventive processes, it is furthermore preferred that the compressible mat,

[0113] 15 which is prepared in step ii) of the inventive process prior to the application of water thereon for hydration in step iii) or iv) has a thickness in the range of 70 mm to 250 mm, and more preferably in the range of 80 to 200 mm.

[0114] As noted above, the endless gypsum fiber board, which is prepared by the inventive process, has a thickness of at least 19 mm. In a preferred embodiment,

[0115] 20 the thickness of endless gypsum fiber board is greater than 23 mm, in particular greater than 26 mm, and even more preferably in the range of 28 to 40 mm. If the thickness is above 40 mm, even with the inventive processing, it is very difficult to provide sufficient process stability. In addition, a thickness of more than 40 mm provides very heavy boards, which only have limited uses and benefits.

[0116] 25 The invention in addition to the processes as described above, also pertains to a gypsum fiber board, which is prepared according to the above process. Preferably,

[0117] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0118] P-KGI-345-WO

[0119] 12 the board has a thickness of more than 26 mm and even more preferably equal to or more than 30 mm.

[0120] In the above processes, the “suction from below” is usually provided by a pump, which generates a reduced pressure of vacuum in a space below the compressible

[0121] 5 mat of stucco-containing material in step (ii) of the process. In one embodiment, the vacuum pump is arranged at a glass container provided with a funnel and a sieve (and paper filter) at its upper open end.

[0122] The invention also pertains to an apparatus, which is adapted for the implementation of a process for the production of gypsum fiber boards as described above. Accordingly, in a further aspect the present application is directed to an apparatus for the production of a gypsum fiber board, wherein the apparatus comprises a device adapted for the treatment of paper fibers with a water containing gas, wherein the device is fluidly connected to a mixer positioned downstream of the device, the mixer having an outlet which is adapted for

[0123] 15 deposition of a material, which has been mixed in the mixer, on a substrate, a conveyor belt, on which the substrate is conveyed, a hydration water tank, which is adapted for the application of water onto material on the conveyor belt, wherein the hydration tank is positioned downstream in moving direction of the conveyor belt relative to the mixer, and a continuous press, which is adapted for compression of material conveyed in the conveyor belt, which is positioned downstream in moving direction of the conveyor belt relative to the hydration water tank.

[0124] In this regard, the term “downstream” is intended to denote a position of the apparatus, which under regular operation conditions is at a later stage of the

[0125] 25 production of the gypsum fiber board, than the position which is in reference thereto. E.g., when the continuous press is downstream to the hydration tank, during the production of the gypsum fiber board the material first passes the water

[0126] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0127] P-KGI-345-WO

[0128] 13 tank and is subsequently supplied to the continuous press for compression. This “supplying” in the inventive apparatus is effected by the conveyor belt.

[0129] The conveyor belt, which is used in the context of the inventive apparatus, is preferably a sieve belt.

[0130] 5 In the inventive apparatus, the device, which is used in the pre-treatment of the fibers with water is not subject to any relevant limitations, and any device, in which the fibers can be treated at the indicated temperature and moisture is suitable as such device. However, as a particularly preferred device, in which such treatment can be performed, a continuous mixer or continuous reactor can be mentioned.

[0131] 10 Likewise, the hydration water tank is preferably a free flow box. In the apparatus of the invention, it is in addition preferred if the apparatus comprises a water suction device, which is positioned below the hydration water tank and the conveyor belt, wherein in operation of the apparatus a mat of paper fibers and calcium sulfate hemi-hydrate is conveyed from the point, where the mixture of

[0132] 15 papers fibers and calcium sulfate hemi-hydrate is deposited of the conveyor belt, to the continuous press. In operation of the apparatus, in this manner water can be applied onto the mat of fibers and calcium sulfate hemi-hydrate and excess water can be removed from the mat via suction from below, thereby minimizing later drying effort.

[0133] 20 In a further preferred embodiment, the inventive apparatus comprises a device, which is adapted for applying a stabilization treatment of calcium sulfate hemi- hydrate. Whereas this treatment, as noted above, can be any treatment which stabilizes the calcium sulfate hemi-hydrate, in a particularly preferred embodiment the device adapted for this purpose is adapted for the application of water onto

[0134] 25 calcium sulfate hemi-hydrate (e. g. in the form of a spraying system) and for maintaining the thus treated calcium sulfate hemi-hydrate at a temperature of at least 30 °C for a time of at least 30 Min, preferred of at least 15 Min. The device can be a device, which operated in batch wise mode, or the device can be a

[0135] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0136] P-KGI-345-WO

[0137] 14 continuous device, where e. g. the calcium sulfate hemi-hydrate is transported continuously over an extended length, where the calcium sulfate hemi-hydrate is exposed to the conditions as indicated.

[0138] With regard to the stabilization treatment, as noted above, this can in principle

[0139] 5 also be carried out in the presence of the fibers, which have been pretreated, i. e. the pretreated fibers can be mixed with freshly prepared calcium sulfate hemi- hydrate, and the mixture can be subjected to conditions, where the calcium sulfate hemi-hydrate is stabilized. Here, as the fibers have already been pretreated with water, they do not affect the stabilization reaction as they do not compete with the

[0140] 10 calcium sulfate hemi-hydrate for water absorption. In addition, having the fiber already pre-treated with water has the advantage that the amount of water required in the stabilization step can be reduced, which leads to greater process reliability and stability and significantly reduces the risk of dihydrate formatio n in the bunker or baking formation. In this embodiment, the stabilization treatment can e. g. be carried out in the mixer, where the calcium sulfate hemi-hydrate is mixed with the fibers. To this end, the mixer can be fitted with respective water application means.

[0141] In a further preferred embodiment, the inventive apparatus further comprises a cutting device, by which compressed continuous material from the continuous

[0142] 20 press can be cut in the traverse direction relative to the moving direction of the conveyor belt to thereby produce individual boards of the compressed material. Yet in addition, it is preferred if the inventive apparatus further comprises a drying oven or furnace for drying the compressed material, which is positioned after the sawing device.

[0143] 25 In the following the inventive apparatus and process will be further illustrated by means of figure 1 , which depict an inventive apparatus in schematic form.

[0144] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0145] P-KGI-345-WO

[0146] 15

[0147] In particular, Fig. 1 is a depiction of a Siempelkamp production plant 1 for producing gypsum fiber boards in a dry Siempelkamp process. The production plant 1 comprises a paper processing device 2 and a paper fiber bunker 19 for processing wastepaper 16. The inventive apparatus further has a fiber pre¬

[0148] 5 treatment device 17, where the pre-treatment of the paper fibers with moisture is carried out, which is positioned between the paper processing device and the paper fiber bunker.

[0149] Further, the production plant 1 comprises a sequence of processing stations 3a to 3d for preparing the calcium sulfate hemi-hydrate with 3a indicating a station comprising a recycling device, 3b indicating a station for processing (e.g., milling) the recycled material, 3c indicating a gypsum reservoir for storing gypsum to be added from the reservoir 3c to a calcination device 3d in which the mixture of recycled and processed material is subjected to a calcination procedure together with the gypsum added from the reservoir 3c in order to dehydrate the material.

[0150] 15 The accordingly processed paper fibers from the paper processing device 2 and the calcined material from the calcination device 3d are supplied to a mixing and spreading device 4 which then spreads the mixed stucco fiber composition uniformly onto a continuously moving conveyor belt 5. The spread stucco fiber composition now forms a mat 6 on the conveyor belt 5. Then, as the mat 6 is carried further on the conveyor belt 5, prior to being passed through a continuous hydraulic press 8, it is hydrated by supplying hydration water from a tank 7 from above onto the top surface 9 of the mat 6 whereby the water is applied in excess with suction from below. Then the mat 6 travels through the hydraulic press 8 such that the stucco fiber composition is compressed to a board.

[0151] 25 The bulk thickness of such board can e. g. be about 25 mm with a density in the range of 1220 to 1390 kg / m3. After leaving the hydraulic press 8 as an endless board, the latter is being grinded, whereby a thickness of about 23 mm can be provided and cut to single pieces having a predetermined length by means of a

[0152] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0153] P-KGI-345-WO

[0154] 16 sawing device 9. The cut pieces or boards 10 are then supplied to a drying furnace 1 1 followed by a grinding device 12 and a primer device 13. The finished gypsum fiber boards 10 are then stacked on pallets 14 on which they may be loaded into a vehicle 15. The velocity of the conveyor belt 5 for a board 10 thus produced can

[0155] 5 e. g. be 120 mm / s. As shown in figure 1 , the apparatus can have a separate device 18, where the calcined gypsum can be stabilized, or the mixer 4 can be adapted for the implementation of such stabilization treatment, in which case there is no separate device 18.

[0156] In an alternative embodiment of the inventive apparatus, the fiber pre-treatment

[0157] 10 device 17 can be positioned directly before the device, where the calcined gypsum is stabilized, which is at a position in the apparatus where the calcined gypsum and the fibers have been mixed (e. g. in the spreading device 4).

[0158] In an alternative embodiment of the inventive apparatus, the fiber pre-treatment device 17 and the device, where the calcined gypsum is stabilized can be in the same device, which is positioned in the apparatus at a stage after the calcined gypsum and the fibers have been mixed (e. g. in the spreading device 4).

[0159] For completeness, it is noted that any embodiments which have been described above as preferred or suitable for the inventive process are likewise preferred in the context of the inventive apparatus, even if this is not specifically indicated, and

[0160] 20 vice versa.

[0161] The process according to the invention as well as the apparatus as described above specifically provide the advantage of an improvement of the process with regard to wettability and dewatering of the stucco fiber mixture, which makes it possible to produce thicker boards using the Siempelkamp process.

[0162] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0163] P-KGI-345-WO

[0164] 17

[0165] In the following, the invention will be further described by means of examples, which should however not be construed as having any limiting effect to the scope of the invention.

[0166] 5 For the following tests wastepaper fibers were either treated at 80°C in an atmosphere with 90 % humidity to pre-saturate the paper fibers or were used directly (not treated).

[0167] In addition, stucco, which was used in the following test, was either subjected to stabilization treatment as described in WO 20191010968 A1 or was used as

[0168] 10 obtained from the calcination directly.

[0169] 500g of stucco fiber mixture was mixed with 10 % of wastepaper fibers and placed on a suction apparatus. The mixture was evenly distributed with a spatula and compacted with a 5 kg tamper. A vacuum of 0.4 bar was then applied to the stucco fiber mixture. Then 750 g of water was added to the mixture using a sprayer. The water was sucked through the stucco fiber mixture by the negative pressure and collected in an Erlenmeyer flask. This flask was placed on a balance to weigh th e collected water and determine how quickly and how much water entered the flask.

[0170] The curves from the respective suction experiments are provided in figure 2. Here, it is apparent that the untreated fiber and stucco samples had the slowest water

[0171] 20 uptake and did take up more water (absolute) than the other samples. A pretreatment of the fibers did not affect the amount of water, that was taken up by the mixture, but more water is sucked though the mixture more quickly, which is indicated by the higher slope of the water curve after t = 0.

[0172] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0173] P-KGI-345-WO

[0174] 18

[0175] The stabilization of stucco similarly leads to a faster water uptake, which is even faster when the fibers have also been pretreated. In this case, the absolute water uptake by the mixture is less than in the case of the use of non-stabilized stucco.

[0176] Accordingly, these experiments show that the fiber pre-treatment to provide moisture 5 saturation of the fibers prior to combination of the fibers with the stucco provides improved suction behavior.

[0177] As the fibers have a high absorbency, the stucco fiber carpet on the system shows an increasing deterioration in water penetration, depending on the height. A reduction in the absorption behavior could significantly increase the performance and product variety of io the system.

[0178] Received at EPO via Web-Form on Aug 19, 2024 Knauf Gips KG

[0179] P-KGI-345-WO

[0180] 19

[0181] List of reference signs

[0182] 1 gypsum fiber board production apparatus

[0183] 2 paper processing device

[0184] 3a recycling device

[0185] 5 3b milling station

[0186] 3c reservoir for storing gypsum

[0187] 3d calcination device

[0188] 4 spreading device

[0189] 5 conveyor belt

[0190] 10 6 mat

[0191] 7 hydration water tank

[0192] 8 continuous hydraulic press

[0193] 9 sawing device

[0194] 10 cut pieces or boards

[0195] 11 drying furnace

[0196] 12 grinding device

[0197] 13 primer device

[0198] 14 stacking pallets

[0199] 15 vehicle

[0200] 20 16 wastepaper

[0201] 17 fiber pre-treatment device

[0202] 18 stabilization device of calcium sulfate hemi-hydrate

[0203] 19 paper fiber bunker

[0204] Received at EPO via Web-Form on Aug 19, 2024

Claims

Knauf Gips KGP-KGI-345-WO205 Claims1 . Process for the production of a moistened stucco -fiber mat, comprising the steps of(i) pretreating paper fibers at a temperature of at least 50 °C in an10 atmosphere with a moisture content of at least 60% to provide presaturated paper fibers,(ii) preparing a compressible mat of stucco-containing material from a mixture comprising 75 wt.-% to 90 wt.-%, relative to the total dry mix, of calcium sulfate hemi-hydrate and 10 wt.-% to 25 wt.-%, relative to the15 total dry mix, of paper fibers, which have been pretreated according to step (i);(iii) hydrating the dry compressible mat of stucco-containing material with hydration water added from above to the top surface of the mat in excess with suction from below.20 2. Process for the production of a gypsum fiber board, comprising the steps of(i) pretreating paper fibers at a temperature of at least 50 °C in an atmosphere with a moisture content of at least 60% to provide presaturated paper fibers,(ii) preparing a compressible mat of stucco-containing material from a25 mixture comprising 75 wt.-% to 90 wt.-%, relative to the total dry mix, of calcium sulfate hemi-hydrate and 10 wt.-% to 25 wt.-%, relative to the ceived at EPO via Web-Form on Aug 19, 2024Knauf Gips KGP-KGI-345-WO21 total dry mix, of paper fibers, which have been pretreated according to step (i);(iii) moving the dry compressible mat (6) of stucco-containing material on a conveyor belt (5) to a hydration water tank (7), and5 (iv) hydrating the stucco-containing material with hydration water added from above to the top surface (9) of the mat (6) in excess with suction from below prior to passing the stucco-containing material through a continuous press (8) to form an endless gypsum fiber board (10) having a thickness greater than 19 mm.10 3. Process according to claim 1 or 2, wherein the calcium sulfate hemi-hydrate prior to the preparation of the compressible mat in step (ii) is subjected to a stabilization step, where the water is added to the freshly prepared calcium sulfate hemi-hydrate to provide a moistened calcium sulfate hemi-hydrate and the moistened calcium sulfate hemi-hydrate is maintained at a15 temperature of at least 30 °C for a time of at least 30 Min to obtain the stabilized calcium sulfate hemi-hydrate.

4. Process according to claim 2 or 3, wherein the endless gypsum fiber board(10) has a thickness of greater than 23 mm, preferably of greater than 26 mm and more preferably in the range of 28 to 40 mm.20 5. Process according to any one of claims 1 to 4, wherein the pretreating of the paper fibers is at a temperature of at least 60 °C, preferably in the range of 70 to 95 °C, and / or at a moisture content of at least 70 % and preferably in the range of 80 to 95 %.

6. Process according to any one of the preceding claims, wherein the calcium25 sulfate hemi-hydrate is a mixture of a-calcium sulfate hemi-hydrate and [3- calcium sulfate hemi-hydrate, wherein the content of a-calcium sulfate hemi- ceived at EPO via Web-Form on Aug 19, 2024Knauf Gips KGP-KGI-345-WO22 hydrate in the mixture is at least 10 wt.-%, relative to the total calcium sulfate hemi-hydrate.

7. Process according to claim 6, wherein the calcium sulfate hemi-hydrate comprises at least 20 wt.-%, relative to the total calcium sulfate hemi-5 hydrate, in particular, about 30 wt.-%, relative to the total calcium sulfate hemi-hydrate, of a-calcium sulfate hemi-hydrate, and at least 50 wt.-%, relative to the total calcium sulfate hemi-hydrate, in particular, about 60 wt.- %, relative to the total calcium sulfate hemi-hydrate, of [3-calcium sulfate hemi-hydrate.10 8. Process according to any one of the preceding claims, further comprising a step of adding a retardant, in particular, citric acid, and / or a step of adding an accelerator, in particular, coated dihydrate.

9. Process according to any one of the preceding claims, wherein the granulation of a portion of less than 90 %, in particular less than 70 % of the15 stucco fiber composition is above 1 pm.

10. Process according to any one of the preceding claims, wherein the thickness of the dry compressible mat (6) prior to adding water is within the range of 80 mm to 100 mm, in particular 85 mm to 95 mm.1 1 . A gypsum product, in particular a gypsum fiber board, which is prepared by20 a process according to any one of claims 1 to 9.

12. An apparatus (1 ) for the production of a gypsum fiber board, wherein the apparatus is preferably adapted for the implementation of a process according to any one of claims 2 to 10, the apparatus (1 ) comprising a device (17) adapted for the treatment of paper fibers with a water containing25 gas, which is fluidly connected to a mixer (2) positioned downstream of the device (17), the mixer having an outlet which is adapted for deposition of a material, which has been mixed in the mixer (2) on a substrate, a conveyor ceived at EPO via Web-Form on Aug 19, 2024Knauf Gips KGP-KGI-345-WO23 belt (5), on which the substrate is conveyed, a hydration water tank (7), which is adapted for the application of water onto material on the conveyor belt, which is positioned downstream in moving direction of the conveyor belt (5) relative to the mixer, and a continuous press (8), which is adapted5 for compression of material conveyed in the conveyor belt, which is positioned downstream in moving direction of the conveyor belt relative to the hydration water tank (7), preferably wherein the conveyor belt is a sieve belt.

13. The apparatus according to claim 12, wherein the device (4) is a continuous10 mixer / reactor and / or wherein the hydration water tank (7) is a free flow box.

14. The apparatus according to claim 12 or 13, further comprising a device (18) which is adapted for the application of water onto calcium sulfate hemihydrate and for maintaining the thus treated calcium sulfate hemi-hydrate at a temperature of least 30 °C for a time of at least 30 Min.15 15. The apparatus according any one of claims 12 to 14, further comprising a cutting device (9), by which compressed continuous material from the continuous press can be cut in the traverse direction relative to the moving direction of the conveyor belt (5) to thereby produce individual boards of the compressed material.20 16. The apparatus according to any one of claims 12 to 15, further comprising a drying furnace (1 1 ) for drying the compressed material, which is positioned after or before the cutting device (9).

17. Use of water saturated paper fibers, which have been prepared in the absence of calcium sulfate hemi-hydrate, in the production of a stucco fiber25 mat or gypsum fiber broads with a thickness of at least 19 mm for improving the wettability and / or suction behavior of a mixture of calcium sulfate hemi- hydrate and the fibers. ceived at EPO via Web-Form on Aug 19, 2024

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