EP0549493B1 - Facing panel of fibre reinforced gypsum and method of manufacturing the same - Google Patents

Abstract

Fibre-reinforced gypsum panel made up of at least one layer of fibre-reinforced gypsum in which the cellulose fibres are dispersed and which is optionally used in combination with other layers with identical or different physicochemical characteristics, this layer of fibre-reinforced gypsum being characterised in that its density is moderate, even in the absence of lightening materials and in that the fibres dispersed in the said layer are preferentially oriented in the lengthwise direction of the panel so that the flexural breaking strength of the layer in the lengthwise direction is higher than the flexural breaking strength in the transverse direction of the layer.

Description

The present invention relates to a fiberglass plaster facing plate, a method of manufacturing this plate and the installations for implementing this method.

By fiber-reinforced plaster facing plate is meant a facing plate reinforced by fibers which, unlike traditional plasterboards, is not cardboard on its faces.

To make interior fittings, the most commonly used plaster product on the world market is cardboard plasterboard, in the form of large panels, generally 1.20 meters wide, of length equal to the height of the wall. '' a stage (i.e. 2.40 meters or more), for a thickness of approximately 6 to 25 mm.

One of the main interests of the gypsum plasterboard lies in the fact that it has sufficient mechanical strengths and an elasticity / rigidity balance particularly well suited to the stresses to which it is subjected during its handling, transport, its storage or assembly, mainly due to its own weight. The cardboard plasterboard has mechanical flexural strengths which are greater in the longitudinal direction than those developed in the transverse direction: this adapts well to the dimensions of the board. Indeed, this anisotropy allows it to correctly resist the stresses it undergoes due to its dimensions.

To this it should be added that the good resistance to cracking of the cardboard plasterboard is linked to its low density, which is of the order of 0.7 to 0.95 g / cm ³ . Indeed, the stresses necessary to cause its rupture are much greater than the stresses under its own weight. In addition, the low weight of the plates facilitates their handling.

   dans laquelle :

σ

représente la contrainte à rupture (en Pascal)

P

représente la charge à rupture (en Newton)

b

représente la largeur (en mètre)

L

représente la longueur (en mètre)

h

représente l'épaisseur (en mètre)

• pour une plaque de 12,5 mm d'épaisseur, des résistances à la rupture en flexion d'au moins 6,7 MPa dans le sens long et d'au moins 2,3 MPa dans le sens travers,
• pour une plaque de 9,5 mm d'épaisseur, des résistances à la rupture en flexion d'au moins 7,7 MPa dans le sens long et d'au moins 3,3 MPa dans le sens travers.

The cardboard plasterboard additionally checks the NF P 72-302 standard of June 1985, which requires a cardboard plasterboard that samples of 40 x 30 cm have, for a distance between supports of 35 cm, the resistance to the break in following bending-minima, expressed in stress with the following formula (I), applicable to the homogeneous material: $$\text{σ =}\frac{\text{3}}{\text{2}}\frac{\text{PL}}{{\text{bh}}^{\text{2}}}$$

in which :

σ

represents the breaking stress (in Pascal)

P

represents the breaking load (in Newton)

b

represents the width (in meters)

L

represents the length (in meters)

h

represents the thickness (in meters)

• for a 12.5 mm thick plate, flexural breaking strengths of at least 6.7 MPa in the long direction and at least 2.3 MPa in the cross direction,
• for a 9.5 mm thick plate, flexural breaking strengths of at least 7.7 MPa in the long direction and at least 3.3 MPa in the cross direction.

However, the cardboard plasterboard has some defects, notably the flammability of its cardboard surface. On the other hand, because of its hydrated calcium sulphate core, the cardboard plasterboard is considered a firebreak.

Another drawback of cardboard plasterboard lies in the fact that the cardboard boxes must be of good aesthetic and mechanical quality and adhere perfectly to the core of the plaster. This is why these boxes represent a significant part of the cost of these plates.

Consequently, the abovementioned drawbacks lead to the production of plasterboard without cardboard, reinforced in their thickness, generally by fibers. We therefore sought to prepare a fiber plasterboard which, in addition to the qualities specific to its composition, comply with regulatory requirements in terms of mechanical strength, and in particular in terms of resistance to bending rupture.

In fact, to resist both static and dynamic stresses, the targeted fiber-reinforced plasterboard must have a tensile strength significantly greater than the maximum load resulting from its own weight, when the plate is in a supported horizontal position only at its ends.

   dans laquelle :

σ

représente la contrainte à rupture, (en Pascal)

L

représente la distance libre de la plaque entre les appuis, (en mètre)

h

représente l'épaisseur de la plaque, (en mètre)

ρ

représente la masse volumique de la plaque. (en kg/m³)

For a homogeneous material with which the plastered plasterboard can be assimilated, this corresponds to values of resistance to rupture in bending greater than the fracture line under its own weight given by the following relation (II): $$\text{σ =}\frac{\text{3}}{\text{4}}\frac{{\text{L}}^{\text{2}}}{\text{h}}\text{ρ}$$

in which :

σ

represents the breaking stress, (in Pascal)

L

represents the free distance of the plate between the supports, (in meters)

h

represents the thickness of the plate, (in meters)

ρ

represents the density of the plate. (in kg / m ³ )

This relationship clearly shows the importance of the stress to which the large plates are subjected in the longitudinal direction.

However, this relationship only partially reflects the stress suffered by the plates because the stress envisaged is static, which is rather far from the stresses actually experienced in practice. In reality, the plates are exposed to dynamic stresses. This is why, the resistances to rupture in bending must be clearly higher than those given by the relation (II) to avoid the rupture.

Fiber plasterboard is already known. Unlike cardboard plasterboard, known fiber plasterboard, which is free of cardboard, has its non-combustible surfaces. They are therefore classified in the "M0" category of standard NF P92 501 of October 1975, reviewed on August 28, 1991, provided that their higher calorific value (PCS) is less than or equal to 600 calories per kilogram of material.

However, the known fiber plasterboard is not entirely satisfactory.

Their main drawback is their high weight. These fiber plasterboards have a rather high density, which is generally greater than 1.1 g / cm3, and which often reaches 1.3 g / cm3 when they are not combined with lightening materials. When they are in the form of very long panels (generally the height of a storey), their weight therefore reaches values that are sufficiently strong that the panels can break during handling, under the effect of their own weight which is important, when their resistance to breaking in bending is not sufficient. For example, a plasterboard of 1.20 mx 2.50 m, thickness equal to 13 mm and density equal to 1.3 g / cm3 weighs 50.7 kg, while a plate standard cardboard of the same dimension, but which benefits from a lower density, close to 0.9 g / cm3, weighs only 35.1 kg.

In addition, their high weight makes them difficult to handle and expensive to transport.

There are two main ways of manufacturing plasterboard plaster.

• mélanger le plâtre et les fibres de cellulose à sec ou partiellement humidifiées, les fibres pouvant être obtenues elles-mêmes par défibrage selon une voie humide ou sèche,
• ajouter l'eau nécessaire à l'hydratation du plâtre,
• étaler la pâte obtenue, généralement sur une bande continue,
• presser suffisamment le produit déposé pour assurer une bonne répartition de l'eau et éliminer l'eau excédentaire, puis procéder à son séchage après la prise.

A first so-called "dry" or "semi-dry" route mainly consists in:

• mix the plaster and the cellulose fibers dry or partially humidified, the fibers being able to be obtained themselves by defibering according to a wet or dry route,
• add the water necessary for the hydration of the plaster,
• spread the dough obtained, generally on a continuous strip,
• press the product sufficiently to ensure good distribution of water and remove excess water, then dry it after setting.

This route leads to plasterboard fiber bundles characterized by a high density, of the order of 1.2 g / cm3, and a resistance to rupture in bending of the order of 5.5 to 6 MPa. To obtain this level of resistance which is still insufficient, recourse is had to fairly high fiber contents: the majority of the plasterboards sold resulting from these processes often contain at least 15% of fibers relative to the weight of plaster.

In addition to the aforementioned problems caused by their significant weight, these plates are fragile and must be handled with great care. Indeed, according to relation (II), these plates can rupture under the sole action of their weight in the absence of any dynamic effect, as soon as their length exceeds 2.80 m for 12.5 mm plates thick for example. This solution is therefore not satisfactory.

In addition to the additional cost of raw materials, plasterboards with a high fiber content have a greater sensitivity to humidity which leads to dimensional instability in a humid environment, hence, during certain applications, the impossibility of having joints between the plates which do not open over time.

One possible way to reduce density is to incorporate lightening materials. However, this solution is not satisfactory because it leads to lower mechanical strengths and therefore much lower than the minimum values required by standard NF-P-72-302 of June 1985.

There is also known a second, so-called "wet" method of manufacturing plasterboard with fiber. This second route is implemented in an installation of the paper line type, discontinuously or continuously.

• 1- les fibres en suspension aqueuse diluées sont ajoutées au plâtre,
• 2- la pâte obtenue est déposé en couche de fine épaisseur sur une bande sans fin,
• 3- après élimination de l'eau excédentaire, on assemble par pressage sous pression élevée la couche obtenue avec d'autres couches de plâtre fibré, de caractéristiques physico-chimiques, similaires ou différentes,
• 4- ensuite, dès que la prise est réalisée, on effectue une opération de sèchage.

According to the batch process, the preparation of the plates is generally carried out as follows:

• 1- the fibers in dilute aqueous suspension are added to the plaster,
• 2- the paste obtained is deposited in a thin layer on an endless strip,
• 3- after removal of the excess water, the layer obtained is assembled by pressing under high pressure with other layers of fiber plaster, with similar or different physico-chemical characteristics,
• 4- then, as soon as the setting is made, a drying operation is carried out.

An embodiment of this discontinuous process, using Hatschek type installations, is currently widely used.

This embodiment consists, at the end of step (2), in assembling layers of fiber plaster of thin thickness on a rotating cylinder.

Depending on the case, the excess water is removed during step (2), or during the assembly operation, through the rotating cylinder. As soon as the thickness of the assembled layers is sufficient to produce the desired plate, a device cuts the plate in formation so that, by gravity, the plate is released from the cylinder and falls on a conveyor. Then, the plate is subjected to operations (3) and (4) of the batch process.

To assemble the layers on the cylinder, the setting must be slow: to do this, we must therefore incorporate one or more setting retarders in the fiber plaster paste. Consequently, a low flow rate of plates must be maintained on the production line.

These discontinuous processes involve the use of a delayed setting plaster, resulting in low productivity. Furthermore, it is necessary to change the cylinder and the pressing device as soon as it is desired to modify the dimensions of the plates produced, hence the multiplication of equipment.

A plate is obtained with a high density, of the order of 1.1 g / cm3 or greater, when it does not incorporate lightening materials. Also, the flexural strength of these plates is generally high. The major problem posed by these plates comes from their high weight which makes them difficult to handle and expensive to transport.

As a result of their high weight, and their complex and discontinuous method of manufacture, these plastered plasterboards are expensive.

The discontinuous wet process for manufacturing fiber-reinforced plasterboard is described in particular in German patents 1 104 419 and 2 425 276 and French patent 2 346 120. According to the process taught by these patents, plasterboards reinforced with fibers are obtained by the superposition under pressure of several felts approximately 0.2 to 0.3 mm thick, these felts resulting from the deposition in a thin layer, on a conveyor belt permeable to water, of a suspension formed of plaster, fibers and water from which the excess water has been extracted using suction members arranged under the strip.

Due to the method of manufacture of the felts, French patent 2,346,120 specifies that the fibers are preferably oriented in one direction. This could result from the high speed of advance of the conveyor belt combined with the very small thickness of the felts according to the well-known phenomenon of papermakers during the formation of a sheet of paper.

Due to the assembly by pressure, the density of these plates once dried is high and at least equal to 1.2 g / cm3.

Still in the second so-called "wet" path, but this time according to a continuous process, we find, in the scientific documentation, methods allowing access to fiber-reinforced plasterboards of lower density.

Thus, German Patent No. 2,365,161 describes plasterboard plies which are obtained by intimate kneading of the plaster with a suspension of fibers in water, the paste obtained being spread in a layer on a filter cloth, the excess water being removed before setting the plaster by application of an increasing vacuum in stages. Resulting from this process, when the fiber content increases, the plasterboards of fiber-reinforced plaster are characterized by a decreasing density and consequently by a tensile-flexural strength which decreases in a linear fashion.

According to this patent, due to the progressive suction of excess water, the fibers take a preferential orientation in planes parallel to the faces.

A fiber-reinforced plasterboard, prepared in accordance with this German patent, 10 mm thick containing 12% by weight of cellulosic fibers, with a density equal to 0.81 g / cm 3, has a tensile strength equal to 6 MPa in both directions: in the long direction, this resistance is therefore less than the value required by standard NF P 72-302 of June 1985.

In order to achieve sufficient flexural breaking strengths, the authors recommend using fiber-reinforced plasterboard with densities greater than that mentioned above, which leads them to introduce low amounts of fibers, preferably equal at 2% by weight.

This is why, because of the problems mentioned above, the plasterboard plastered on the market is used in very specific fields as fire or sound protection, or as elements of moderate dimensions such as elements for ceilings or floors.

The main objective of the present invention is to propose a fiber plasterboard which does not have the drawbacks of the prior art.

More specifically, the first objective of the invention is a fiber-reinforced plasterboard which does not require excessively high proportions of fibers, and which also has a low density, mechanical strengths, and in particular resistance to flexural rupture, sufficiently high, and at least equal to those provided by the NF P 72-302 standard for traditional cardboard plasterboard, both in the long direction and in the cross direction.

Another objective of the invention is a method of manufacturing this fiber plasterboard which can be implemented relatively simply, under advantageous economic conditions, and continuously.

Another objective of the invention is an installation for the manufacture of these plasterboard plies which is relatively simple and which can be, for a large part at least, produced from an industrial installation for the production of cardboard plasterboard traditional.

To achieve these objectives, the present invention provides a plasterboard composed of at least one layer of fiber plaster, in which the fibers are dispersed, possibly combined with other layers of identical or different physicochemical characteristics, this layer of fiber plaster being characterized in that its density is less than 1 g / cm ³ in the absence of lightening materials and in that the fibers, dispersed in said layer are preferably oriented in the longitudinal direction of the plate, so that the resistance to bending of the layer in the longitudinal direction is greater than the resistance to bending of the layer in the transverse direction.

In the absence of any lightening materials, the fiber plaster layer according to the invention is characterized by a moderate density, that is to say a density lower than that of the fiber plaster plates sold when the latter are free of allegiant materials. In the absence of a lightening agent, the density of the layer of fiber plaster according to the invention is less than 1 g / cm ³ . Advantageously, the density of the fiber plaster layer according to the invention is close to the density of known cardboard plasterboards, (this is say on the order of 0.7 to 0.95 g / cm ³ ) and more preferably between 0.8 and 0.95 g / cm ³ .

The low density of the fiber plaster layer according to the invention results essentially, on the one hand from the presence of the fibers, and on the other hand from the processes used for its manufacture, which do not require compression under high pressure.

However, thanks to the fibers which are well dispersed in the plaster matrix and despite its low density, the fiber plaster layer according to the invention, once dried, achieves average mechanical strengths (in the long and transverse directions), which are clearly superior to those of plastered plasterboards having an identical composition and thickness and of comparable density and resulting from a manufacturing process known as "semi-dry".

In addition, the average mechanical strengths (in the long and transverse directions) of the layer of fiber-reinforced plaster according to the invention are equivalent to those of the sheets of fiber-reinforced plaster having a comparable composition, thickness and density, and resulting from a so-called "wet" manufacturing track.

• d'une part nettement supérieures à celles des plaques de plâtre précitées, obtenues par une voie dite "humide" de fabrication ;
• et d'autre part, au moins égales voire supérieures à la valeur exigée par la norme NF P 72-302 de Juin 1985.

On the other hand, essentially thanks to the fibers which are preferably oriented in the longitudinal direction, the fiber plaster layer according to the invention achieves mechanical strengths in the long direction which are:

• on the one hand clearly superior to those of the aforementioned plasterboards, obtained by a so-called "wet" manufacturing process;
• and on the other hand, at least equal to or even greater than the value required by standard NF P 72-302 of June 1985.

The fibers suitable for the invention are cellulosic fibers, to which other fibers may optionally be added, on the condition that they do not contain elements harmful to the hydration of the plaster. The fibers provided in addition to the cellulosic fibers are preferably introduced at a rate of 0.2 to 1% relative to the total weight of the dry layer of hydrated and fiberized plaster.

In the following description, the expression "dry layer of hydrated and fiberized plaster" will be used to designate the layer obtained after setting and drying operations, which is composed essentially of calcium sulfate dihydrate and cellulose fibers.

Among the fibers which can be incorporated into the pulp of cellulosic fibers, mention may be made of glass fibers and synthetic fibers.

As cellulosic fibers, use is preferably made of cellulosic fibers from the recovery of old newspapers or other recovered paper. The average length of these fibers, which is generally greater than 500 microns, is indeed sufficient. (Below this value, the fibers tend to take off rather than break when they are stressed in tension and / or bending, resulting in a significantly reduced efficiency.)

The amount of cellulosic fibers in the layer of fiber plaster according to the invention can vary between 5 and 15% relative to the total weight of the dry layer of hydrated and fiber plaster. Unlike the plasterboard plies described in the German patent 2 365 161, one chooses, in accordance with the invention, a higher proportion of cellulosic fibers, preferably between 7 and 13% relative to the total weight of the dry plaster layer. hydrated and fiber, because these conditions, in addition to a low weight, contribute to obtaining satisfactory mechanical strengths and at a competitive cost price.

The thickness of the plaster fiber layers is variable depending on the manufacturing process used. Preferably, it is sufficient for the assembly of at most three layers to be necessary to form planar elements for many applications such as wall elements or elements of floors or ceilings. The thickness of the fiber plaster layer is advantageously between 2 and 15 mm, and preferably between 5 and 10 mm for reasons of productivity.

As semi-hydrated plaster, it is possible to use either the alpha or beta form which has preferably been treated to facilitate the filterability of the plaster.

To further improve the mechanical properties of the fiber plaster layer according to the invention, suitable agents such as starch can be incorporated into it, preferably at a rate of 0.2 to 3% based on the total weight of the dry layer hydrated and fiberized plaster.

For the same purpose, we can add another 0.5 to 5% by weight of cement, based on the total weight of the dry layer of hydrated and fiberized plaster.

Other agents can also be added, this in order to improve or provide a particular quality, such as in particular one or more water-repellent agents, one or more agents with high fire resistance and all the adjuvants conventionally used in the core. of cardboard plasterboard.

The layer according to the invention is advantageously used alone, if its thickness is sufficient, or in combination with other layers of fiber-reinforced plaster or not to prepare a plasterboard.

• une masse volumique modérée, même en l'absence de matières allégeantes,
• des fibres dispersées dans chaque couche et préférentiellement orientées selon la direction longitudinale de la plaque, de sorte que la résistance à la rupture en flexion de la plaque dans le sens longitudinal soit supérieure à la résistance à la rupture en flexion de la plaque dans le sens transversal et que la plaque remplisse les exigences posées en matière de propriétés mécaniques par la norme française homologuée NF P-72 302 de Juin 1985 pour les plaques de plâtre cartonnées.

In accordance with a preferred embodiment of the invention, a plaster fiber board is prepared by combining at most three layers of fiber plaster according to the invention. As stated previously, a fiber plaster layer according to the invention has the following characteristics:

• a moderate density, even in the absence of lightening materials,
• fibers dispersed in each layer and preferably oriented in the longitudinal direction of the plate, so that the resistance to bending rupture of the plate in the longitudinal direction is greater than the resistance to bending rupture of the plate in the direction transverse and that the plate meets the requirements in terms of mechanical properties by the French standard approved NF P-72 302 of June 1985 for cardboard plasterboard.

More preferably, the fiber plasterboard according to the invention is composed of two layers of fiber plaster according to the invention.

Thanks to the different variants of the fiber-reinforced plasterboard in accordance with the invention, values of resistance to flexural rupture are considerably higher than the stress values undergone by the plate under its weight in accordance with relation (II) and this, surprisingly, despite their moderate density.

The fiber-reinforced plasterboard according to the invention also has the properties of use superior to those of known cardboard plasterboard.

Thus, it meets the installation requirements: as such, it is no more fragile to handling than a traditional plasterboard. It can be machined (cut, screwed, nailed, sanded) without risk of cracking when these operations are carried out normally. A finish, by providing a general flatness, forming edges or coating, can be provided without difficulty.

• bonnes résistances aux chocs,
• bonne protection anti-feu, tant en réaction au feu qu'en résistance au feu,
• bonne cohésion à l'égard des découpes et des perçages ainsi qu'une bonne résistance à l'arrachement des fixations (pointes, vis, agrafes, contreventement ou chevilles devant supporter les charges) grâce à son homogénéité et à sa résistance aussi bonne à coeur qu'en surface,
• bonne résistance à l'humidité et bonne tenue générale dans des conditions humides : dans les conditions de la norme ASTM C 473-84, les phénomènes de fluage sont deux fois plus faibles que ceux constatés avec les plaques de plâtre cartonnées.

Once laid, the fiber plasterboard according to the invention is characterized by the following mechanical properties:

• good impact resistance,
• good fire protection, both in reaction to fire and in fire resistance,
• good cohesion with regard to cutouts and holes as well as good resistance to tearing of fasteners (points, screws, staples, bracing or dowels to support loads) thanks to its homogeneity and its resistance as good at heart that on the surface,
• good resistance to humidity and good general resistance in wet conditions: under the conditions of standard ASTM C 473-84, the phenomena creep are two times lower than those found with cardboard plasterboard.

• possibilité de relier deux plaques contiguës avec des joints assurant une parfaite continuité des surfaces,
• absence de fléchissement différé en plafond,
• possibilité de renouvellement des revêtements de peinture ou de papier peint sans dommage pour la plaque et sans risque de détérioration de la surface comme dans le cas de la plaque de plâtre classique (arrachement de carton).

The fiber-reinforced plasterboard according to the invention perfectly meets the aesthetic requirements, namely:

• possibility of connecting two adjoining plates with joints ensuring perfect continuity of the surfaces,
• absence of deferred deflection in the ceiling,
• possibility of renewing paint or wallpaper coatings without damage to the sheet and without risk of deterioration of the surface as in the case of conventional plasterboard (tearing of cardboard).

• 1) mélanger une suspension diluée dans l'eau de fibres cellulosiques avec du plâtre semi-hydrate et des ajouts éventuels dans un mélangeur, et plus particulièrement celui employé dans les installations de fabrication des plaques de plâtre traditionnelles,
• 2) étendre en couche mince la pâte homogène obtenue sur une toile de coulée mobile, bordée de moyens étanches, (tels que des parois mobiles ou fixes par rapport à la paroi),
• 3) évacuer l'eau en excès par l'application d'un vide,
• 4) puis attendre la prise du plâtre semi-hydrate.

The present invention also relates to a process for the continuous production of said layer of fiber-reinforced plaster, which can be used for the preparation of a plasterboard or of a light and resistant prefabricated element, or of other products incorporating fiber-reinforced plaster. . It consists of :

• 1) mixing a suspension diluted in water of cellulose fibers with semi-hydrated plaster and possible additions in a mixer, and more particularly that used in the installations for manufacturing traditional plasterboards,
• 2) spread in a thin layer the homogeneous paste obtained on a movable casting fabric, bordered by watertight means (such as walls which are movable or fixed relative to the wall),
• 3) remove excess water by applying a vacuum,
• 4) then wait for the semi-hydrated plaster to set.

The method according to the invention is characterized in that, at the end of step (2), as soon as the homogeneous paste is spread on the casting fabric and before the evacuation of the excess water, it is oriented the fibers preferably in the longitudinal direction, thanks to the application of vibrations in the homogeneous paste of fiber plaster during its shearing by passage between fixed or mobile walls, arranged vertically and in planes parallel to the plane containing the direction of movement of the canvas, without creating turbulent movements in the dough.

A variant may consist in the use of vertical walls which are not parallel to each other and which form converging in the direction of movement of the casting fabric.

It is also possible simultaneously during step (2), the orientation of the fibers and the flow in thin layer on the casting fabric.

The method according to the invention is advantageous in that it also allows the formation of fibrous layers of thin thickness of the order of 2 mm or of greater thickness which can reach 15 mm and this without hindering the orientation of the fibers.

Another advantage of the process according to the invention is linked to its effectiveness in orienting the cellulosic fibers both in plaster-based pastes and in pastes containing other compounds with hydraulic properties such as cements.

The desired orientation of the fibers, which results in a significant increase in the mechanical properties of the plate in the longitudinal direction compared to those in the transverse direction, was obtained with the fiber alignment devices combining one (or more) system (s) s) generating laminar flows in the dough associated with one (or more) system (s) simultaneously creating vibrations in the mass of the dough.

It is said that, in the case of suspensions of very dilute fibers, of the order of 0.1% by weight, the fibers can orient themselves in flows in the absence of vibration: this is the case during paper making. At this concentration, there are few interactions between the fibers which are therefore sufficiently distant from each other.

On the other hand, at higher fiber rates, of the order of 0.5% and more, the fibers are tangled together and form flocs. These flocs are not destroyed and the fibers are not dispersed during the shearing of the suspension in flows.

We have surprisingly demonstrated that the combination of shear and vibration makes it possible to separate and orient the fibers. However, it is in this concentration domain that this process according to the invention is interesting (reduced filtration time, hence a higher line speed, and significantly lower quantities of recycled water).

According to a first embodiment of the method according to the invention, the vibrations applied in the homogeneous paste of fiber plaster are brought by the walls which are made to vibrate: to do this, one can vibrate all the walls or only a part walls provided that each fixed wall is surrounded by at least two vibrated walls.

According to a second embodiment of the method according to the invention, the vibrations applied in the homogeneous paste of fiber-reinforced plaster are provided by means of a vibrated planar device, such as a vibrating sheet, placed horizontally under the casting fabric, at the right of the vertical walls.

According to a third embodiment of the method according to the invention, the vibrations applied in the homogeneous paste of fiber plaster are provided by a combination of the means constituting the first and second embodiments mentioned above.

• Un premier dispositif d'alignement longitudinal est composé d'un ensemble vibré de plaquettes solidaires. Celles-ci sont montées verticalement et parallèlement à la direction du mouvement de la toile de coulée, et situées en aval de la tête d'alimentation et des moyens assurant le réglage de l'épaisseur de la couche fibrée.
• Un deuxième dispositif d'alignement des fibres est composé d'un ensemble vibré de disques solidaires, en rotation, de préférence dans le sens de déplacement de la toile de coulée ; en outre, ces disques sont montés verticalement et parallèlement à la direction du déplacement de la toile de coulée et sont situés en aval de la tête d'alimentation et des moyens assurant le réglage de l'épaisseur de la couche fibrée. Avantageusement, on peut modifier l'intensité du cisaillement de la pâte fibrée en faisant varier la vitesse de rotation de ces disques.
• Un troisième dispositif d'alignement des fibres est composé :
  • . d'un ensemble vibré de disques solidaires, en rotation, de préférence dans le sens de déplacement de la toile de coulée, montés verticalement et parallèlement à la direction de déplacement de la toile de coulée, ces disques étant situés en aval de la tête d'alimentation et des moyens assurant le réglage de l'épaisseur de la couche fibrée,
  • . et intercalé entre chaque disque, d'un ensemble vibré de plaquettes solidaires, qui sont montées verticalement et parallèlement à la direction du mouvement de la toile de coulée, et situées en aval de la tête d'alimentation et des moyens assurant le réglage de l'épaisseur de la couche fibrée.

Advantageously, the first embodiment of the method is implemented by means of the following alignment devices:

• A first longitudinal alignment device is composed of a vibrated set of integral plates. These are mounted vertically and parallel to the direction of movement of the casting fabric, and located in downstream of the feed head and of means ensuring the adjustment of the thickness of the fiber layer.
• A second fiber alignment device is composed of a vibrated assembly of integral discs, in rotation, preferably in the direction of movement of the casting fabric; in addition, these discs are mounted vertically and parallel to the direction of movement of the casting fabric and are located downstream from the feed head and means ensuring the adjustment of the thickness of the fiber layer. Advantageously, the intensity of the shearing of the fiber-reinforced dough can be modified by varying the speed of rotation of these discs.
• A third fiber alignment device is made up of:
  • . of a vibrated set of discs integral, in rotation, preferably in the direction of movement of the casting fabric, mounted vertically and parallel to the direction of movement of the casting fabric, these discs being located downstream of the head d 'feed and means ensuring the adjustment of the thickness of the fiber layer,
  • . and inserted between each disc, a vibrated set of integral plates, which are mounted vertically and parallel to the direction of movement of the casting fabric, and located downstream of the feed head and means ensuring the adjustment of the thickness of the fiber layer.

The best fiber orientation results have been obtained with the third device on condition of avoiding going into a turbulent flow regime.

• pâte homogène comprenant du plâtre, des fibres, de l'eau et éventuellement des adjuvants traditionnels et/ou du ciment tel que du ciment Portland,
• variation de la proportion de fibres contenues dans la pâte homogène coulée sur la toile qui est avantageusement comprise entre 5 et 15 % en poids rapporté au poids total de la couche sèche de plâtre hydraté et fibré.

The preferred orientation of the fibers in the longitudinal direction of the plates, and the increase in the mechanical characteristics in the longitudinal direction which results therefrom have been confirmed under the following varied operating conditions:

• homogeneous paste comprising plaster, fibers, water and optionally traditional additives and / or cement such as Portland cement,
• variation in the proportion of fibers contained in the homogeneous paste poured onto the canvas which is advantageously between 5 and 15% by weight relative to the total weight of the dry layer of hydrated and fiberized plaster.

On the other hand, it has been found that certain operating conditions can have a harmful effect on the longitudinal orientation of the fibers, and therefore lead to plates having equivalent mechanical characteristics in the transverse and longitudinal directions.

In this respect, the amplitude of the vibrations imposed on the homogeneous pulp must be controlled because too strong vibrations are not able to orient the fibers longitudinally.

• la partie servant à la distribution de la pâte homogène sur la toile de coulée en la complétant avec l'un des dispositifs d'alignement précédemment décrits.
• la partie servant à l'évacuation de l'eau en excès. L'eau recueillie peut être recyclée et réutilisée pour le pulpage des fibres.

One of the major advantages of the process according to the invention resides in the fact that it makes it possible to manufacture continuously and at high speed (which may be greater than 60 m / min.) Plasterboard panels in existing industrial chains. of manufacturing traditional plates in which it will be necessary to modify only:

• the part used for the distribution of the homogeneous dough on the casting fabric by completing it with one of the alignment devices previously described.
• the part used for the evacuation of excess water. The collected water can be recycled and reused for pulping the fibers.

An installation which is very suitable for the manufacture of plastered plasterboard is shown diagrammatically in FIG.

• un bac de mélange (1) pour le défibrage et la mise en suspension de papiers dans l'eau, généralement des vieux journaux, jusqu'à l'obtention d'une pulpe. Dans ce bac, on prépare des pulpes comprenant de préférence de 1 à 2,75 % en poids de fibres.
• une quantité déterminée de cette pulpe est ensuite conduite grâce à une pompe (2) adaptée au transfert des fluides chargés en solide dans un mélangeur (3), simultanément avec une quantité dosée de plâtre provenant du bac de stockage (4) et les ajouts habituels tels que les agents de correction de prise.

This installation includes:

• a mixing tank (1) for defibering and suspending papers in water, generally old newspapers, until a pulp is obtained. In this tank, pulps are preferably prepared comprising from 1 to 2.75% by weight of fibers.
• a determined quantity of this pulp is then carried out using a pump (2) suitable for transferring the fluids loaded with solid into a mixer (3), simultaneously with a metered quantity of plaster coming from the storage tank (4) and the usual additions such as catch correction officers.

When the intimate mixture of plaster, fibers and water is produced, the homogeneous paste obtained is poured onto a moving canvas (6), through the feed head (5). The feed head (5) is designed to maintain the homogeneity of the fiber dough and allow spreading at regular rate over the width of the casting fabric.

The feed head (5) is equipped with a vibrated plate (7) which regulates the thickness of the fiber layer. The fiber alignment device comprises vibrated plates (8) and vibrated rotating discs (9), mounted vertically and parallel to the direction of movement of the casting fabric indicated by the arrows (10).

As can be seen more easily in FIG. 2, the vibrations of the plate (7) are generated by a vibrator (11), for example a pneumatic or electric unbalance vibrator, in a direction almost vertical to the casting fabric ( 6). The main role of the plate (7) is to adjust the thickness of the fiber plaster layer. The small-scale vibration applied to it ensures its self-cleaning.

The plates (8) and the discs (9) are connected to a chassis (12) which is itself subject to a vibrator (13). For example, two similar imbalance vibrators, but rotating in opposite directions at equal speed, can be used, which are mounted on the chassis (12) supporting the pads (8) and the discs (9), the chassis (12) itself resting on springs.

The rotation of the discs is obtained by a motor, for example at variable speed, not shown, which drives the hub (14) on which the discs are mounted and secured.

A material is chosen for the plates (8) and the discs (9) which is not liable to deteriorate on contact with the fiber plaster paste. As material, one can choose stainless steel.

According to the structure of the fiber orientation device (for example, the dimensions of the plates (8) and / or discs (9), etc.), according to the mode of operation of the orientation device (for example, the amplitude and frequency of vibrations, the speed of rotation of the discs (9), the speed of movement of the casting fabric (6), etc.) the element is adapted between two vertical walls, made up of two plates ( 8), either of two discs (9), or of a succession of plates and discs, in order to obtain the desired orientation of the fibers.

The casting fabric (6) has movable rubber walls, fixed relative to the canvas, to delimit the edges of the plate. The suction of excess water is carried out through the casting fabric (6) using the vacuum boxes (15) and an endless vacuum belt filter (16). The geometry of the band filter is taken care of in order to have good dimensional characteristics of the plates.

Downstream, the fiber-reinforced plasterboard being formed is subjected to a calendering operation by means of the device (17) with pressure cylinder provided to give a good condition to the upper surface of the plates. This calendering is therefore light and does not allow the plates to be densified significantly.

After calendering, the gripping of the plastered plasterboards continues on the conveyor belt.

To do this, the casting fabric (6) is connected downstream to a production line for cardboard plasterboard, not shown in FIG. 1.

The edges of the plate can be formed by various means such as trowelling, knurl systems, forming strips, etc.

The quality of the surface of the plate can be improved by light coating and even by means of a trowel, for example vibrating and / or sliding, with if necessary addition of a little water on the surface before the action of the trowel. The plates are then placed in a dryer and treated according to the methods usually used for cardboard plasterboard.

Other advantages and characteristics will appear in the examples which follow, given by way of illustration and without limitation of the invention.

The physical characteristics of the plates exemplified were obtained by the measurement methods described in the French standard approved NF P-72 302 of October 1981, modified in June 1985.

EXAMPLES 1 TO 4

These tests were carried out in an industrial installation of the type shown in FIG. 1, which, as the case may be, includes an alignment device shown schematically, in one of its configurations, in FIG. 2.

In the case of alignment devices 2 to 4, the vibration of the pads and / or discs is obtained by means of two similar unbalance vibrators, rotating in opposite directions at an equal speed of 2700 rpm. at 50 Hz. The two vibrators are mounted on a steel frame supporting the pads and / or the discs, this frame itself resting on four compression springs with the close ends flat, free length equal to 80 mm and stiffness equal to 1.210 daN / mm.

The different alignment devices tested are specified and referenced in the following Table I: Reference Description of the alignment device Example 1 (Witness) This test was carried out without a fiber orientation device. Example 2 The orientation device is composed of a vibrated set of discs (9), rotating at a relative speed of 39 m / min. relative to the casting fabric (6), in the same direction as the canvas. The discs (9) have a diameter of 240 mm. They are spaced 1 cm apart. Example 3 The orientation device is composed of a vibrated set of integral plates (8). The dimensions of the inserts are as follows:
- a length of 40 cm
- And a height greater than the thickness of the dough poured in a thin layer. The plates are spaced 1 cm apart. Example 4 The alignment device is composed of:
- a vibrated set of integral plates (8), identical to those used in Example 3, mounted downstream of the plate (7),
- And inserted between each plate, a vibrated set of integral discs (9), identical to those used in Example 2. These discs are mounted downstream of the plate (7) and rotate at a relative speed of 39 m / min . with respect to the casting fabric, in the same direction as the canvas.
The spacing between a disc (9) and a plate (8) is 4.65 mm.

From a pulp of the order of 1.7% by weight of cellulose fibers, semi-hydrated plaster and water, a paste is prepared with a W / P ratio (weight of water to weight of plaster ) equal to 0.9 and a percentage of fibers of 15% by weight relative to the weight of plaster, or 11.5% relative to the total weight of the hydrated and fiberized dry layer, in an installation of the type presented on the figure 1. This paste is then transformed into plasterboards of fiber plaster whose thickness is, according to the example, between 4.5 mm and 8 mm. The excess water is gradually sucked through the casting fabric. You can adjust the density of the dry fiber board according to the amount of water remaining in the fiber paste.

The physical characteristics of the fiber plasterboard obtained are given in Table II below: TABLE II Example No. Density (g / cm ³ ) Breaking strength in Flexion (MPa) Ratio of breaking strengths long / cross direction SL / ST 1 0.83 SL = 7.06 1.06 (Witness) ST = 6.72 2 0.85 SL = 8.09 1.32 ST = 6.08 3 0.82 SL = 7.22 1.55 ST = 4.63 4 0.85 SL = 9.35 1.58 ST = 5.92 SL = longitudinal direction ST = cross direction

The devices of Examples 2, 3 and 4 with which the SL / ST ratios reach values greater than 1, make it possible to orient the cellulosic fibers preferentially in the long direction of the plates.

Industrially, the fiber orientation devices leading to SL / ST ratios greater than or equal to 1.5 will preferably be selected, and more preferably those leading to SL / ST ratios greater than or equal to 1.75.

If the vibrations imposed on the wafers in Example 4 are of high amplitude and generate turbulence in the dough, for example when the unbalance rotation speed of the two vibrators mounted on the chassis is 3100 rpm, we observes a very clear decrease in the longitudinal orientation of the fibers (SL / ST is then equal to 1.1) which is accompanied by a notable decrease in the resistance to breaking in bending in the long direction (ie 6.5 MPa ).

EXAMPLES 5 to 7

Examples 5 to 7 were carried out under the operating conditions of Example 4 with the differences given in Table m below: TABLE III Example No. Modified operating conditions compared to Example 4 5 Speed of rotation of vibrated discs and direction of rotation identical to the speed and direction of movement of the casting fabric. 6 Relative speed of rotation of vibrated discs equal to 51 m / min. and rotation in the opposite direction to the direction of movement of the fabric. 7 Relative speed of rotation of vibrated discs equal to 84 m / min. and rotation in the direction of movement of the fabric. The results of Examples 5, 6 and 7 are given in the following Table IV: Example No. Volumic mass Flexural strength (MPa) Ratio of breaking strengths in long bending to cross bending direction SL / ST 5 0.86 SL = 8.00 1.83 ST = 4.88 6 0.84 SL = 8.43 1.73 ST = 4.86 7 0.83 SL = 8.08 1.88 ST = 4.30

The average orientation of the fibers in the long direction of the plates is little modified, under the conditions of these tests, when the relative rotation speed of the discs is modified relative to the casting fabric or when the direction of rotation is reversed. some discs.

All other conditions being equal, if in Examples 5, 6 and 7, the rotating discs are not vibrated, there is a decrease in the preferential orientation of the fibers in the longitudinal direction. This results in SL / ST ratios of less than 1.4 and generally between 1 and 1.2.

EXAMPLES 8 to 10

• le pourcentage de fibres est de 9,42 % en poids par rapport au poids de plâtre, soit 7,5 % exprimé en pourcentage du poids total de la couche sèche hydratée et fibrée,
• la vitesse de rotation des disques vibrés et le sens de leur rotation imposés des exemples 8, 9, et 10, correspondent rigoureusement et respectivement aux conditions imposées aux disques vibrés et tournants dans les exemples 4, 5 et 6.

The tests were carried out under the operating conditions of Example 4, with the following differences:

• the percentage of fibers is 9.42% by weight relative to the weight of plaster, that is 7.5% expressed as a percentage of the total weight of the hydrated and fiberized dry layer,
• the speed of rotation of the vibrated discs and the direction of their rotation imposed in Examples 8, 9, and 10, correspond strictly and respectively to the conditions imposed on the vibrated and rotating discs in Examples 4, 5 and 6.

The results of Examples 8 to 10 are given in the following Table V: TABLE V Example No. Volumic mass Flexural strength (MPa) Ratio of breaking strengths in long bending to cross bending direction SL / ST 8 0.91 SL = 7.81 1.95 ST = 4.00 9 0.90 SL = 7.68 1.72 ST = 4.60 10 0.88 SL = 7.58 1.97 ST = 4.08 If in Example 8, all other conditions being equal, it is raised to 3100 rpm. the speed of rotation of the unbalances of the two vibrators mounted on the chassis, one obtains a fiber-reinforced plasterboard with a density equal to 0.75, of resistance to rupture in bending equal to 3.6 MPa in the long direction and to 3 MPa in the cross direction corresponding to SL / ST equal to 1.21.

Claims (19)

1. Fibre-reinforced gypsum board, composed of at least one gypsum layer, in which cellulose fibres are dispersed, optionally combined with other layers of identical or different physicochemical characteristics, this fibre-reinforced gypsum layer being characterized in that its density is less than 1 g/cm³ in the absence of lightening materials and in that the fibres, dispersed in the said layer, are preferentially oriented along the lengthwise direction of the board, so that the flexural ultimate strength of the layer in the lengthwise direction is greater than the flexural ultimate strength of the layer in the transverse direction.
2. Gypsum board according to Claim 1, characterized in that the density of the fibre-reinforced gypsum layer is between 0.7 and 0.95 g/cm³.
3. Gypsum board according to Claim 2, characterized in that the density of the fibre-reinforced gypsum layer is between 0.8 and 0.95 g/cm³.
4. Gypsum board according to any one of Claims 1 to 3, characterized in that the amount of cellulose fibres in the fibre-reinforced gypsum layer varies between 5 and 15%, with respect to the total weight of the dry layer of fibre-reinforced hydrated gypsum.
5. Gypsum board according to Claim 4, characterized in that the amount of cellulose fibres in the fibre-reinforced gypsum layer varies between 7 and 13%, with respect to the total weight of the dry layer of fibre-reinforced hydrated gypsum.
6. Gypsum board according to any one of claims 1 to 5, characterized in that the thickness of the fibre-reinforced gypsum layer is between 2 and 15 mm and preferably between 5 and 10 mm.
7. Gypsum board according to any one of Claims 1 to 6, characterized in that the dry fibre-reinforced gypsum layer additionally comprises other fibres, provided that these fibres do not contain a component which is harmful to the setting of the gypsum.
8. Gypsum board according to any one of Claims 1 to 7, characterized in that the fibre-reinforced gypsum layer additionally comprises starch, preferably in the proportion of 0.2 to 3% with respect to the total weight of the dry layer of fibre-reinforced hydrated gypsum.
9. Gypsum board according to any one of Claims 1 to 8, characterized in that the fibre-reinforced gypsum layer additionally comprises cement in the proportion of 0.5 to 5% with respect to the total weight of the dry layer of fibre-reinforced hydrated gypsum.
10. Gypsum board according to any one of Claims 1 to 9, characterized in that it comprises at most three layers of fibre-reinforced gypsum.
11. Method for the continuous manufacture of the fibre-reinforced gypsum layer, employed for manufacturing the gypsum board in accordance with Claims 1 to 10, which comprises:

    1) mixing a dilute suspension in water of cellulose fibres with hemihydrate gypsum and optional additives in a mixer (3);

    2) spreading, as a thin layer, the homogeneous slurry obtained over a moving casting belt (6), bordered by walls which are moving or stationary with respect to the belt (6);

    3) discharging the excess water by application of a vacuum;

    4) and then waiting for the hemihydrate gypsum to set; this method being characterized in that, on conclusion of the stage (2), as soon as the homogeneous slurry is spread over the casting belt (6) and before discharging the excess water, the fibres are preferentially oriented along the lengthwise direction, by virtue of the application of vibrations in the homogeneous fibre-reinforced gypsum slurry during its shearing by passage between stationary or moving walls (8, 9) arranged vertically and in parallel planes containing the direction of progression of the casting belt, without creating turbulent movements in the slurry.
12. Method according to Claim 11, characterized in that the vibrations applied in the homogeneous fibrereinforced gypsum slurry are contributed by the combined vertical walls or a portion of the vertical walls, which are made to vibrate.
13. Method according to Claim 11, characterized in that the vibrations applied in the homogeneous fibre-reinforced gypsum slurry are contributed by means of a planar vibrated device arranged horizontally under the casting belt (6), to the right of the vertical walls.
14. Method according to Claim 11, characterized in that the vibrations applied in the homogeneous fibre-reinforced gypsum slurry are contributed, on the one hand, by means of the combined vertical walls or of a portion of the vertical walls, which are made to vibrate, and, on the other hand, by means of a planar, vibrated device arranged horizontally under the casting belt, to the right of the vertical walls.
15. Method according to claim 12, characterized in that the fibres are preferentially oriented along the lengthwise direction by virtue of an alignment device composed of a vibrated assembly of immovably-attached plates (8), which are mounted vertically and parallel to the direction of movement of the casting belt and which are situated downstream of the feed head and of the means providing for adjustment of the thickness of the fibre-reinforced layer.
16. Method according to Claim 12, characterized in that the fibres are preferentially oriented along the lengthwise direction by virtue of an alignment device composed of a vibrated assembly of immovably-attached rotating discs (9), preferably rotating in the direction of movement of the casting belt, these discs being mounted vertically and parallel to the direction of movement of the casting belt and being situated downstream of the feed head and of the means providing for adjustment of the thickness of the fibre-reinforced layer.
17. Method according to Claim 12, characterized in that the fibres are preferentially oriented along the lengthwise direction by virtue of an alignment device composed:

    - of a vibrated assembly of immovably-attached rotating discs (9), which are mounted vertically and parallel to the direction of movement of the casting belt, these discs being situated downstream of the feed head and of the means providing for adjustment of the thickness of the fibre-reinforced layer and rotating in a direction parallel to the movement of the casting belt,

    - and, inserted between each disc, of a vibrated assembly of immovably-attached plates (8), which are mounted vertically and parallel to the direction of movement of the casting belt and which are situated downstream of the feed head and of the means providing for adjustment of the thickness of the fibre-reinforced layer.
18. Method for the continuous manufacture of the fibre-reinforced gypsum layer, employed for manufacturing the gypsum board in accordance with Claims 1 to 10, which comprises:

    1) mixing a dilute suspension in water of cellulose fibres with hemihydrate gypsum and optional additives in a mixer (3);

    2) spreading, as a thin layer, the homogeneous slurry obtained over a moving casting belt (6), bordered by walls which are moving or stationary with respect to the belt (6);

    3) discharging the excess water by application of a vacuum;

    4) and then waiting for the hemihydrate gypsum to set; this method being characterized in that, on conclusion of the stage (2), as soon as the homogeneous slurry is spread over the casting belt and before discharging the excess water, the fibres are preferentially oriented along the lengthwise direction, by virtue of the application of vibrations in the homogeneous fibre-reinforced gypsum slurry during its shearing by passage between vertical walls (8, 9), which converge towards one another in the direction of movement of the casting belt.
19. Application of the method according to any one of Claims 11 to 18 for the orientation of the fibres of a fibre-reinforced layer, preferentially along a lengthwise direction, it being possible for this layer to be used alone or in combination with other layers of identical or different physicochemical characteristics in the preparation of a fibre-reinforced gypsum board or of a prefabricated component or of other products incorporating a fibre-reinforced gypsum layer.

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