TECHNICAL FIELD

[0001] The present invention concerns a process for producing plasterboards formed of a gypsum core sandwiched between two facers. The plasterboards obtained by the process of the present invention have enhanced compressive strength, using state-of-the-art production lines with little modifications thereto, quite simple and inexpensive to implement; The production rates are not affected by the present process.

BACKGROUND OF THE INVENTION

[0002] Plasterboards are plates particularly useful for albeit not restrict to the building industry, comprising a core made of gypsum with various additives in minor amounts, sandwiched between bottom and top facers, generally made of paper and / or glass mat. They can be produced continuously on long production lines and cut to the desired lengths and dried in a drier.

[0003] A slurry of calcined calcium sulphate hemihydrate (or stucco) in water with the desired additives, such as accelerators, fibrous reinforcements, and the like, is continuously dispensed onto a bottom facer moving on a conveyor. The thickness of the layer of slurry on the bottom facer is controlled and a top facer is laid on top of a free surface of the slurry, such as to form a sandwich structure with a core formed by the slurry sandwiched between bottom and top facers. The calcined stucco in the core is allowed to undergo a hydration reaction to form a setting plasterboard with calcium sulphate hemihydrate (CaS0 ₄ .½H ₂ 0) being progressively replaced by calcium sulphate dihydrate (CaSC> ₄ .2H ₂ 0) as the hydration reaction proceeds. Because the hydration reaction is exothermic, it is possible to monitor the kinetics of the hydration reaction by measuring the temperature of the core.

[0004] Once the core has set to a reasonably hard structure, the continuous setting plasterboard is cut to a desired length, prior to being moved into a drier to complete the hydration reaction and remove any excess water present in the core.

[0005] As plasterboards are used mainly in the building industry, where higher mechanical properties are always an advantage, it is desirable to optimize the mechanical properties of plasterboards, so as to remain competitive against alternative materials.

[0006] For example, US8252110 describes plasterboards produced from a slurry comprising calcined gypsum and starch. EP2896605 describes similar compositions specifying the type of starch urea phosphate to be used. In both cases, enhanced mechanical properties were reported.

[0007] US3813312 describes a process of producing gypsum boards of enhanced strength and resistance to humidified bond failure at any particular density through the use of a delayed action accelerator. The delayed action accelerator is the uncalcined product of grinding landplaster with up to about 5% of its weight of sugar. The delayed hydration reaction is monitored by measuring the temperature of the gypsum, and the maximum rate of temperature rise thus measured during set occurs subsequent to the 3 ^rd minute of set and is at least about 1 .5 times the temperature rise occurring during the 3 ^rd minute. This temperature profile indicates that the delayed action accelerator indeed delays the the hydration reaction such that it reaches a maximum kinetics subsequent to the 3 ^rd minute of set only. The plasterboard thus produced exhibit enhanced strength and resistance to humidified bond failure.

[0008] W02015106182 describes a batch process for producing plasterboards, utilizing air along a building board forming line for the purpose of reducing friction between the board and the underlying forming tables. The process employs a series of air nozzles that are formed within the face of the forming tables, delivering pressurized air to the nozzles to create an air cushion between the table and the bottom facer, and thus reduce the friction between the board and the underlying table. This promotes the even distribution of slurry during formation, but the mechanical properties of the thus produced boards are not particularly enhanced.

[0009] EP2910939 describes a method of manufacturing a gypsum-based building board and for detecting online voids in the gypsum-based construction board. The method comprises the steps of cooling a surface of a plasterboard during the exothermic hydration reaction of calcined gypsum by applying a cooling medium to the surface. A temperature distribution of the surface can be visualized by IR imaging, and air gaps within the gypsum core below the top facer appear as cold spots. Defective plasterboards can thus be identified and ejected immediately.

[0010] There remains a need in the art for enhancing the mechanical properties of plasterboards. The present invention proposes a process meeting this need, using conventional materials, and conventional production lines which need simple and inexpensive refurbishing to be configured for running the process of the present invention. These and other advantages of the present invention ar described in detail in the following sections.

SUMMARY OF THE INVENTION

[0011] The present invention is defined in the appended independent claims. Preferred embodiments are defined in the dependent claims. In particular, the present invention concerns a process for producing plasterboards comprising the following steps,

• feeding a gypsum slurry comprising stucco, water, and additives onto a bottom facer laid on a conveyor in motion; the additives can for example comprise one or more of an accelerator, bond protecting agents, fibre reinforcement, consistency reducers, starch and sodium trimetaphosphate (STMP),

• applying a top facer onto a free surface of the gypsum slurry to form a sandwich structure with a core made of the gypsum slurry sandwiched between the top and bottom facers,

• setting by hydration the gypsum slurry forming the core to form a setting plasterboard on the conveyor,

• cutting the setting plasterboard to desired dimensions to yield cut plasterboards,

• drying the cut plasterboards in a drying station (11) to yield the plasterboards.

[0012] The gist of the present invention is to apply a flow of cooling fluid onto the top facer to extract heat therefrom and prevent a temperature of the core from raising by more than 20%, preferably more than 10%, more preferably more than 1% from the moment the gypsum slurry is fed onto the bottom facer until the setting plasterboard is cut. The temperature of the core preferably does not exceed 40°C, more preferably 35°C, most preferably 30°C from the moment the gypsum slurry is fed onto the bottom facer until the setting plasterboard is cut. In a preferred embodiment, the temperature of the core (1c) is higher than 25°C and does not exceed 35°C from the moment the gypsum slurry (1 g) is fed onto the bottom facer (21) until the setting plasterboard is cut. It is even preferred that the temperature of the core does not raise by more than 20%, preferably more than 10%, more preferably more than 1% from the moment the gypsum slurry is fed onto the bottom facer until the cut plasterboards reach the drying station. In a preferred embodiment, a flow of cooling fluid is applied also onto the bottom facer through the conveyor.

[0013] In a preferred embodiment, one or more fans can be used for blowing ambient air to apply the flow of cooling fluid onto the top facer. The one or more fans are preferably coupled to an air conditioning system, cooling an ambient air, prior to blowing the ambient air onto the top facer.

[0014] The conveyor extends over a cutter distance (L) comprised between a position of a slurry feeding unit where the gypsum slurry is fed onto the bottom facer and a position of a cutting station where the setting plasterboard is cut. It is preferred that the flow of cooling fluid be applied onto the top facer at a portion of the conveyor comprised between 25% and 100% of the cutter distance (L) (i.e., between L / 4 and L). The flow of cooling fluid can also be applied onto the top facer of the cut plasterboards at a portion of the conveyor extending beyond the cutter distance (L) by an additional length (DI_) (i.e., between L and (L + DI_)).

[0015] The cooling fluid can have a relative humidity (RH) of not more than 80%, preferably not more than 70%, more preferably of not more than 60%. The cooling fluid can be at a temperature of not more than 25°C, preferably not more than 20°C, more preferably not more than 15°C, more preferably not more than 12°C. A preferred cooling fluid is air.

[0016] The present application also concerns a plasterboard production line for producing plasterboards with a process as defined supra, comprising,

• a conveyor configured for conveying a sandwiched structure with a core made of the gypsum slurry sandwiched between the top and bottom facers, the plasterboard production line comprising the following components along the conveyor, • a roll of bottom facer configured for continuously feeding the conveyor with the bottom facer,

• a slurry dispensing unit is positioned downstream of the roll of bottom facer and configured for pouring a gypsum slurry onto an inner face of the bottom facer as it moves with the conveyor and which faces upwards,

• a levelling blade (5) or roller is arranged downstream of the slurry feeding unit (3) to control the thickness of the layer of slurry deposited on the bottom facer.

• a roll of top facer is positioned above the conveyor, downstream of the levelling blade and is configured for applying the top facer on a free surface of the gypsum slurry to form a sandwich structure with a core made of the gypsum slurry sandwiched between the top and bottom facers.

• a cutting unit is positioned at a cutter distance (L) from the slurry dispensing unit (3) and is configured for cutting the continuous setting plasterboard into panels of specific length referred to as cut plasterboards.

• a drying station is positioned downstream of the cutting unit and is configured for drying the cut plasterboards,

[0017] The plasterboard production line further comprises at least first and second cooling stations positioned above and below the conveyor and configured for blowing a cooling fluid onto the top and bottom facers, respectively, wherein all cooling stations are located downstream of the slurry dispending unit at a distance of at least 25% of the cutter distance (L) therefrom (i.e. > L / 4), and at least one cooling station is positioned upstream from the cutting unit. In a preferred embodiment, the plasterboard production line comprises one or more cooling stations configured for blowing a cooling fluid onto the top facer, wherein the one or more cooling stations are located downstream of the cutting unit at a portion of the conveyor comprised within an additional length (DI_) from the cutting unit (9). The additional length (DI_) is preferably 25 m, more preferably 20 m.

[0018] The present application also concerns a flow of cooling fluid (31) to increase the compressive strength of a plasterboard having a top facer (22) and a core, said cooling fluid (31) being applied onto the top facer (22) and extracting heat therefrom and preventing a temperature of the core (1c) from raising by more than 20%, preferably more than 10%, more preferably more than 1% from the moment the gypsum slurry (1g) is fed onto the bottom facer (21) until the setting plasterboard is cut.

[0019] The temperature of the core (1c) is preferably higher than 25°C and does not exceed 35°C from the moment the gypsum slurry (1g) is fed onto the bottom facer (21) until the setting plasterboard is cut. BRIEF DESCRIPTION OF THE FIGURES

[0020] For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

Figure 1 (a) shows a side view of an example of production line configured for carrying out the process of the present invention.

Figure 1(b) shows the degree of hydration of the stucco as a function of the position of the setting plasterboard along the conveyor.

Figure 1(c) shows the temperature profile of the core as a function of the position of the setting plasterboard along the conveyor, wherein the solid line (INV) is with cooling according to the present invention, and the dashed line (P.A.) is according to the prior art, without cooling.

Figure 2: shows a top view of a production line of the type illustrated in Figure 1 (a).

Figure 3: shows a side view of a portion of another example than in Figure 1 (a) of a production line configured for carrying out the process of the present invention.

Figure 4: shows the compressive strength (ffc).as a function of the areal weight (m / A) (or thickness) of the plasterboards, wherein the solid line (INV) is with cooling according to the present invention, and the dashed line (P.A.) is according to the prior art, without cooling.

DETAILED DESCRIPTION OF THE INVENTION

[0021] As illustrated in Figure 1 (a) to 1 (c), the present invention concerns a process for producing plasterboards (1) comprising the following steps,

• feeding a gypsum slurry (1g) comprising stucco, water, and additives onto a bottom facer (21) laid on a conveyor (7) in motion,

• applying a top facer (22) onto a free surface of the gypsum slurry to form a sandwich structure with a core (1c) made of the gypsum slurry sandwiched between the top and bottom facers (21 , 22),

• setting by hydration the gypsum slurry (1g) forming the core (1c) to form a setting plasterboard on the conveyor,

• cutting the setting plasterboard to desired dimensions to yield cut plasterboards (1cp), drying the cut plasterboards in a drying station (11) to yield the plasterboards (1). GYPSUM SLURRY (1g)

[0022] The present invention applies to any composition of gypsum slurry (1g) used to date. This is a major advantage of the present invention, in that the materials used and their contents need not be changed to yield enhanced mechanical properties with the present process. A gypsum slurry (1g) can typically comprise calcined gypsum or stucco or plaster of Paris in the form of calcium sulphate hemihydrate (CaS0 ₄ .½H ₂ 0), water, and additives, including an accelerator, bond protecting agents, fibre reinforcement, consistency reducers, sodium trimetaphosphate (STMP), set adjusting agents, adhesion improvers, and, as mentioned in the “Background of the Invention,” starch (cf. e.g. US8252110 and. EP2896605).

[0023] The present invention is not limited by the presence or absence of additives, nor by the type and nature thereof. Upon bringing water in contact with stucco, an exothermic hydration reaction begins, progressively transforming calcium sulphate hemihydrate (CaS0 ₄ .½H ₂ 0) into calcium sulphate dihydrate (CaSC> ₄ .2H ₂ 0), reducing the amount of water at a rate of 1 .5 mol H2O per mol of stucco.

CONTINUOUS PRODUCTION LINE

[0024] A production line for the continuous production of plasterboards suitable for the present invention is schematically illustrated in Figures 1 (a), 2, and 3. It comprises a roll of bottom facer (21) configured for continuously feeding a conveyor (7) with the bottom facer (21). A slurry dispensing unit (3) is positioned above the bottom facer (21) as it is transported by the conveyor (7) and is configured for pouring a gypsum slurry (1g) onto an inner face of the bottom facer (21), which faces upwards. A levelling blade (5) or roller is arranged downstream of the slurry feeding unit (3) to control the thickness of the layer of slurry deposited on the bottom facer (21). A roll of top facer is positioned above the conveyor, downstream of the levelling blade (5) and is configured for applying the top facer (22) on the free surface of the gypsum slurry (1g) to form a sandwich structure with a core (1c) made of the gypsum slurry sandwiched between the top and bottom facers (21 , 22). At this stage, hydration of the stucco has started but is still incipient. As illustrated in Figure 1 (b), only about 4 to 10% of the stucco has been hydrated. The conveyor (7) transports the thus formed setting plasterboard to allow the setting of the gypsum slurry (1g) forming the core (1c) by hydration to proceed as illustrated in Figure 1 (b).

[0025] A cutting unit (9) is positioned at a cutter distance (L) from the slurry dispensing unit (3) and is configured for cutting the continuous setting plasterboard into panels of specific length referred to as cut plasterboards (1cp). Taking account of the speed of the conveyor (7), the cutter distance (L) separating the cutting unit (9) from the slurry dispensing unit (3) corresponds to a level of hydration (or conversion from hemi- to di-hydrate) of about 70 to 85%, preferably of about 78% ± 5%, more preferably of about 75% (cf. Figure 1 (b)). The cut plasterboards (1cp) are then driven into a drying station (11). After the cutting unit (9) the conveyor ceases to necessarily be linear as illustrated in Figure 1 (a) but can comprise changes of directions as illustrated in the top view of Figure 2. The cut plasterboards (1 cp) can be turned over, realigned, and the like, prior to entering into the drying station (11).

[0026] The drying station (11) is positioned downstream of the cutting unit (9). It is configured for drying the cut plasterboards (1cp) during a drying period sufficient for gently evaporating any excess water, which was required to form the initial slurry. After the plasterboards (1) have dried, they are trimmed and stacked to form pallets ready for use (not shown).

[0027] The foregoing elements define the essential components of a state-of-the-art plasterboard continuous production line. To implement the process of the present invention, it suffices to install on such state-of-the-art production lines one or more cooling stations (30) configured for applying a flow of cooling fluid (31) onto the top facer (22) to extract heat therefrom and prevent a temperature of the core (1c) from raising by more than 20%, preferably more than 10%, more preferably more than 1% over the cutter distance (L) comprised between the position of the slurry feeding unit (3) where the gypsum slurry (1g) is fed onto the bottom facer (21) and the position of the cutting station (9) where the setting plasterboard is cut.

COOLING STATION (30)

[0028] Each of the one or more cooling stations (30) preferably comprise a fan (30f) used for blowing ambient air to apply the flow of cooling fluid (31) onto the top facer (22). The fans can blow ambient air at ambient temperature onto the top facer (22). In a preferred embodiment, each cooling station (30) is coupled to an air conditioning system, cooling the ambient air to a predefined temperature, prior to blowing the ambient air onto the top facer (21). The cooling fluid (31) is at a temperature of preferably not more than 25°C, preferably not more than 20°C, more preferably not more than 15°C, more preferably not more than 12°C.

[0029] A relative humidity of the air is preferably controlled. Drier air is advantageous as it removes more excess water from the setting plasterboards which needs not be evacuated in the drying station (11), and the evaporation of more water also removes more heat from the core of the setting plasterboards. For example, the cooling fluid (31) is air having a relative humidity (RH) of not more than 80%, preferably not more than 70%, more preferably of not more than 60%.

[0030] As illustrated in Figures 1 (a) and 2, it is preferred to apply the flow of cooling fluid (31) onto the top facer (22) at a portion of the conveyor (7) comprised between 25% and 100% of the cutter distance (L) comprised between the position of the slurry feeding unit (3) and the cutting station (9) (i.e., between L / 4 and L).

[0031] It is also preferred that the flow of cooling fluid (31) be also applied onto the top facer of the cut plasterboards (1 c) at a portion of the conveyor extending beyond the cutter distance (L) by an additional length (DI_) (i.e., between L and (L + DI_)). Since the conveying speed (V) of the conveyor (7) after the cutting station (9) ceases to be constant and can vary or even be nil (i.e., stopped as the cut plasterboards (1cp) change direction or are flipped, contrary to the constant speed along the cutting distance (L) prior to the cutting station, it is difficult to assign a specific value to the additional length (AL). The additional length (DI_) can be expressed in terms of the conveyor speed (V) after the cutting station (9), and the time (Dί) required for moving of the additional distance (DI_) at the conveyor speed (V) as AL = V x At. The time (At) corresponds to the time required for reaching a hydration level either of about 90% ± 5% or exceeding the level of hydration at the cutting station (9) by an additional 15% ± 5%; preferably the former condition of a hydration level either of about 90% ± 5%.

[0032] In a preferred embodiment illustrated in Figure 3, a flow of cooling fluid (31) is applied also onto the bottom facer (21) through the conveyor (7). For example, the conveyor can comprise rollers arranged side by side and spaced apart from one another allowing the cooling fluid to flow between rollers. Alternatively, the conveyor may comprise a foraminous belt, permeable to the flow of cooling fluid. Both foregoing examples allow the cooling fluid (31) to be blown from a bottom side of the conveyor through the conveyor (7) and onto the bottom facer (21) to withdraw more heat from the core of the setting plasterboards as well as from the cut plasterboards (1cp) depending on whether the one or more cooling stations are arranged below the conveyor within the cutter distance (L) or beyond the cutting station, within a comprised between L and (L + DI_) from the slurry dispensing unit (3). The additional distance (DI_) can be of the order of 20 m ± 5 m.

PROCESS FOR PRODUCING PLASTERBOARDS

[0033] As described supra, the process for producing plasterboards of the present invention Is very similar to state-of-the-art processes, with the sole difference that the core (1c) of the sandwiched structure is prevented from freely heating up during the exothermic hydration reaction transforming stucco into plaster according to,

CaS0 ₄ .½H ₂ 0 + 1½ H2O CaS0 ₄ .2H ₂ 0 (1)

[0034] Figure 1 (c) shows the temperature evolution in the core (1 c) of the setting plasterboard during setting. The dashed line illustrates the temperature evolution according to a state-of-the-art process without active cooling of the setting plasterboard. It can be seen that the temperature increases monotonously by about 7°C between the slurry dispensing unit (3) and the cutting unit (9). By contrast, the solid line illustrating the temperature evolution of the core (1c) of the setting plasterboard in a process according to the present invention with air being blown onto the top facer (22) as illustrated in Figure 1 (a). In this embodiment, the temperature does not rise between the slurry dispensing unit (3) and the cutting unit (9). According to the present invention the temperature is allowed to rise by up to 20%, but it is preferred that the temperature does not rise by more than 10%, more preferably by more than 1% from the moment the gypsum slurry (1g) is fed onto the bottom facer (21) until the setting plasterboard is cut. It is preferred that the temperature of the core (1c) does not exceed 40°C, preferably 35°C, more preferably 30°C from the moment the gypsum slurry (1g) is fed onto the bottom facer (21) until the setting plasterboard is cut.

[0035] As mentioned supra and illustrated in Figure 1 (b), the level of hydration of the core of the setting plasterboard at the level of the cutting unit (9) is about 70 to 85%, preferably of about 78% ± 5%, more preferably of about 75%. It follows that hydration is still going to proceed by about 20 to 25% until it reaches around 97% hydration at the level of the drying station (11). It is preferred to prevent the core temperature of the cut plasterboards (1cp) from freely rising as the exothermic hydration reaction proceeds. For this reason, it is preferred that the temperature of the core (1c) does not raise by more than 20%, preferably more than 10%, more preferably more than 1% from the moment the gypsum slurry (1g) is fed onto the bottom facer (21) until the cut plasterboards (1cp) reach the drying station (11). This can be achieved by positioning an additional cooling station (30) between the cutting unit (9) and the drying station (11) as illustrated in Figures 1 (a) and 2. The additional cooling station (30) allows maintaining substantially constant the core temperature of the cut plasterboards (1cp) until they reach the drying station (11) as shown in Figure 1 (c).

[0036] Contrary to the delay in the hydration reaction observed in US3813312 with the use of a delayed action accelerator, the hydration reaction kinetics is not significantly altered by the application of the flow of cooling fluid onto the top facer. The temperature drop in the core (1 c) provoked by the cooling fluid compared with no cooling during the hydration reaction is insufficient to yield substantial kinetics reduction according to the Arrhenius law.

COMPRESSIVE STRENGTH AND HUMID BOND

[0037] Plasterboards (1) were produced with different thicknesses with an inventive process according to the present invention, with application of a cooling fluid (31) onto the top facer (22) and according to a prior art process, differing from the inventive process solely in that no cooling fluid was applied onto the top facer (22).

[0038] Humid bond was measured after conditioning the plasterboards for 2 h at 30°C ± 2°C and at and 90 % RH ± 5 % RH in a climate room. Six samples 150 x 300 mm are collected from each plasterboard, at corners and central positions. After conditioning the samples in the climate room for two hours, taking the samples, the paper on one side of the board is scored with a knife and the sample broken. In a bending movement the two faces of the sample are brought together plying the paper. One of the faceis pulled so as to try separating the plaster core from the paper on both halves of the sample. Both pieces of board are then separated by pulling off the paper along all the sample. The area over which the facer was pulled off is measured and a rating in % is defined as the relative area of facer which still adhered to the core (i.e., perfect bond, no delamination yields a rating of 100%, and complete delamination of the facer yields a rating of 0%). The humid bond for the plasterboards produced with the inventive process was 90%, against only 50% for the plasterboards produced by the prior art process.

[0039] Compressive strength of the plasterboards thus produced were measured on a compression testing device equipped with parallel platens of diameter of 70 mm moving at constant speed. Three samples of 60 mm diameter are collected on each board, one at a left side, at a centre, and at a right side. Three boards are thus tested for each areal weight (m / A) or thickness (t), thus summing up to nine samples per board thickness (t). The samples are dried, cooled and their weight (m), thicknesses (t) and diameters measured prior to testing. A sample is positioned between the platens which are moved towards one another at a constant rate of 4 mm / min. The force is measured as a function of displacement of the platens. The beginning of collapse of the plasterboard core corresponds to the point where the first linear part of the curve ends (= end of elastic deformation). The result for a plasterboard of given thickness is the minimum of all nine compression tests.

[0040] Figure 4 plots the compressive strength of plasterboards produced with the inventive process (solid line) and with the prior art process (dashed line) as a function of the areal weight (m / A) of the plasterboards. The areal weight (m / A) is related to the thickness (t) of the plasterboards through the density (p) of the plasterboard by t = (m / A) / p. Since the density (p) is substantially constant, it can be concluded that the plasterboard thickness (t) is substantially proportional to the areal weight (m / A) (i.e. , t o (m / A)).

[0041] It can be seen in Figure 4 that for low areal weights (m / A) or thicknesses (t), the compressive strength of the plasterboards produced by the inventive process is substantially higher than the one of the plasterboards produced with the prior art process. At an areal weight (m/ A) value of about 8.6 kg / m ² , the plasterboards produced by the inventive and prior art processes have similar compressive strength. Without wishing to be bound by any theory, it is believed that this is explained by the fact that the same production line was used for producing the plasterboards of all thicknesses (t) and that the cooling stations (30) of the experimental set up were sub-dimensioned for extracting enough heat from thicker cores (of areal weight m / A > 8.6 kg / m ² ). By adapting the cooling capacity of the cooling stations (30) to the thickness of the plasterboard, such that the temperature profile is the same for all thicknesses, it is strongly believed that the solid line (= INV) and the dashed line (= P.A.) of Figure 4 would be substantially parallel to one another. At an areal weight m / A = 8.2 kg / m ² , the compressive strength increases from 2.8 MPa for the plasterboards produced with the prior art process, to 3.2 MPa for the plasterboards produced with the inventive process, i.e., an enhancement of about 14% over the prior art process. Considering the little investment required to adapt the plasterboard production line to be configured for carrying out the inventive process, with the mere addition of one or more cooling stations (30), an enhancement of the compressive properties of 14% is exceptional. CONCLUDING REMARKS

[0042] The present invention concerns a process for producing plasterboards having enhanced mechanical properties, the process differing from state of the art processes solely in that a flow of cooling fluid (31) is applied onto the top facer (22) to extract heat therefrom and prevent a temperature of the core (1c) from raising by more than 20%, preferably more than 10%, more preferably more than 1% from the moment the gypsum slurry (1g) is fed onto the bottom facer (21) until the setting plasterboard is cut. By this simple operation, humid bond is increased from 50% to 90%, and compressive strength can be increased by about 14%. The application of the flow of cooling fluid requires one or more cooling stations (30) each being preferably provided with a fan (30f). [0043] The present invention also concerns a plasterboard production line distinguished from prior art production lines in that it comprises first and second cooling stations (30) configured for applying a flow of cooling fluid onto the top facer (22) and onto the bottom facer (21) through the conveyor (7), respectively.

[0044] The present invention yields plasterboards with enhanced properties regardless of the slurry composition and regardless of the existing continuous production line on which cooling stations (30) have been added. The kinetics of the hydration does not seem to be substantially affected by the application of a flow of cooling fluid.

REF DESCRIPTION

1 Plasterboard

1c Core

1cp Cut plasterboard ig Gypsum slurry

1cp Cut plasterboards

3 Slurry dispensing unit

5 Levelling blade

7 Conveyor

9 Cutting unit

11 Drying station

21 Bottom facer

22 Top facer

30 Cooling station 30f Fan

31 Cooling fluid