MX2008009810A - Lightweight plasterboard and plaster slurry composition used for its manufacture - Google Patents

Abstract

The subject of the invention is a plaster slurry composition comprising plaster, water and starch, said starch having a Brookfield viscosity of less than 60 cps at a temperature below 600C and a Brookfield viscosity greater than 10,000 cps at a temperature of 700C. Use for manufacturing plasterboards.

Description

CARTON-LIGHTWEIGHT PLASTER AND COMPOSITION OF PLASTER SUSPENSION FOR ITS MANUFACTURE FIELD OF THE INVENTION A subject of the invention is a novel lightweight cardboard or a novel board having improved mechanical compression properties and also a gypsum suspension composition used in its manufacture. The invention also provides a method for manufacturing said board and the use of a specific starch in the manufacture of a plasterboard.

BACKGROUND OF THE INVENTION Gypsum board has been known for many years. These boards generally comprise two sheets or coatings, generally made of paper or cardboard, among which is included, sandwich type, a center of plaster. The coatings have a certain tensile strength while the center has a certain compressive force.

In addition, it seeks to lighten the plasterboard, while still have good mechanical properties. A critical aspect is the compression force of the center of the cardboard. Therefore, a method is sought to prepare a cardboard with a center that has a higher compression force for densities that are identical to the current densities, which would allow cardboard strengths to be obtained for lower densities.

A feature that has been the subject of numerous studies is the adhesion of paper to the plasterboard center. In order to improve the adhesion, the starch is usually added to the gypsum suspension and during the drying of the cardboard the starch migrates to the paper and is concentrated in the center / coating interface. This is obtained by selecting a starch that has a particular rheology as a function of temperature.

FR-A-1 429 406 and EP-A-0 172 773 describe the use of natural or modified starches for the manufacture of paper-coated paperboards, which have improved center / paper adhesion.

EP-A-0 936 201 describes the use of starch blends that are modified with respect to the long-term strength of mixtures of cement-type material, including gypsum. The objective in this document is to control the adjustment value and suspension of the mixed suspension without having any effect on long-term forces.

EP-A-0 807 612 describes the use of a catatonic starch in gypsum suspensions, which has a nitrogen content of less than 0.15% and a solubility greater than 50%. The starch is presented as a thickener for the gypsum suspension.

EP-A-0 172 773 describes the use of a starch having a very precise particle size, such as an adhesive therein for coatings. The advantage presented by the specific particle size is a better migration of the starch towards the center / coating interface.

SU-A-1 100 264 describes the use of sulphates and alkyl fibers to increase the impact strength and impact strength. The presence of starch is optional.

Thus, the starch in gypsum board is very generally used only in the center / coating interface.

US 2004/0 045 481 and US 6 783 587 describe a gypsum suspension for a lightweight board comprising hemihydrate, starch, foam and water, and in which the starch represents from 1.5 to 3% by weight relative to the weight of the hemihydrate and the W / P ratio is between 0.7 and 0.95. It is indicated that the resulting boards have a reduced density. The used starch is any starch, but the example uses an acid-modified starch, available from Staley Manufacturing. The starch in this document is of the type that is modified by acid hydrolysis.

US 2003/0 084 980 discloses a gypsum suspension for a lightweight board comprising hemihydrate, acid-modified starch, a cross-linking agent of starch and water, the pH of the suspension being around 9 to 11. The acid-modified starch is of the same type as that mentioned in US 2004/0 045 481 and US 6 783 587. It is indicated that the starch used has a low gelatinization temperature, which facilitates their migration to the center / coating interface, while cross-linking makes it possible to prevent the starch from migrating completely out of the center. It is further indicated that the starch also has a use as a binder in the center of the carton. It is indicated that the acid modified starches have gelatinization temperatures typically of 70 to 77 ° C, per. example, 72 ° C. In the cooked form, at the moment the cardboard passes through the dryer, it is said that the starch is modified by acid hydrolysis, ie it is fluid, in the form of a syrup, but it becomes a gel when the temperature decreases . In the invention that is the subject of the patent, increasing the pH value of the gypsum suspension reduces the gelatinization temperature to values around 60-66 ° C, typically 61 ° C. In the cooked form, the acid-modified starch thus treated (i.e., thus crosslinked) is solid, i.e. it is more viscous than an unmodified starch and a syneresis effect appears (separation of water and a solid from a gel) . In this document, increasing the pH within a given range is necessary in order to obtain crosslinking and the associated effect.

US 2005/0 126 437 discloses the use, to increase strength, of a modified starch that is insoluble in the gypsum suspension during mixing, but which dissolves when the temperature increases. The starch is modified, for example, by hydroxyalkylation or acetylation.

Nothing in the prior art describes or suggests the invention, which satisfies the requirement to provide a lightweight cardboard having good mechanical characteristics.

SUMMARY OF THE INVENTION The addition of a certain type of starch to the center of the carton makes it possible to increase the compression force up to 30% or even 50%, the starch having a particular rheological profile.

The invention therefore provides a gypsum suspension composition comprising gypsum, water and starch, said starch having a Brookfieid viscosity of less than 60 cps at a temperature below 60 ° C and a Brookfieid viscosity greater than 10,000 cps at a temperature of 70 ° C.

According to one embodiment, the starch has a Brookfieid viscosity of less than 20 cps at a temperature of 60 ° C.

According to one embodiment, the starch has a Brookfieid viscosity of more than 20,000 cps, preferably greater than 30,000 cps, at a temperature of 70 ° C.

According to one embodiment, the starch has a Brookfieid viscosity of more than 60,000 cps at a temperature of 80 ° C.

According to one embodiment, the starch is of the non-retrograde type.

According to one embodiment, the starch has a viscosity at 25 ° C, after cooling following the heating of the starch solution up to 90 ° C, which is greater than the maximum viscosity obtained during the heating of said solution. starch.

According to one embodiment, the starch has a viscosity at 25 ° C, after cooling following the heating of the starch solution up to 90 ° C, of at least 100,000 cps, advantageously at least 300,000 cps.

According to one embodiment, the composition comprises, in relation to the weight of the gypsum, between 0.05 and 1%, preferably between 0.1 and 0.5% by weight of starch.

According to one embodiment, the composition has a pH between 5.5 and 8.5, preferably between 6 and 7.5.

According to one embodiment, in the composition, the W / P ratio varies from 0.55 to 0.95, preferably from 0.65 to 0.80.

According to one embodiment, the composition further comprises a starch modified by acid hydrolysis.

Another subject of the invention is a plasterboard comprising a center obtained by adjusting a gypsum suspension according to the invention.

According to one embodiment, gypsum board has a center density ranging from 540 kg / m3 to 1100 kg / m3, preferably from 750 kg / m3 to 950 kg / m3.

According to one embodiment, the plasterboard has one, preferably two, liner (s).

According to one embodiment, the coating is made of paper, or a mat or nonwoven, preferably a mat of glass fibers and / or synthetic and / or cellulose fibers, said coating being optionally filled with a fine filler and / or a filler that has optionally received a surface treatment.

Another additional subject of the invention is a method for preparing a plasterboard consisting of a gypsum-based center and at least one, advantageously two, coating (s), said method comprising the following steps: - preparing a suspension of the gypsum composition according to the invention by mixing several constituents of the composition with water in a mixer; - depositing the suspension thus prepared in at least one coating, depending on being formed on a batten, with optional covering of the upper face of the suspension using a second coating; - where it is appropriate, to form the ends of the ribbon of the cardboard previously obtained by molding the strip into profiled strips; - Hydraulically adjusting the gypsum in a manufacturing line while the cardboard strip runs along a conveyor belt; -cut the ribbon at the end of the line in predetermined lengths and - dry the obtained cards.

A further subject of the invention is the use, for plasterboard manufacture, of starch having a Brookfield viscosity of less than 60 cps at a temperature below 60 ° C and a Brookfield viscosity greater than 10,000 cps at a temperature of 70 ° C.

A further subject of the invention is the use, to increase the compression strength of a gypsum board, preferably by at least 0.5 MPa, of starch having a viscosity of Brookfieid of less than 60 cps at a temperature below 60 ° C and a Brookfieid viscosity greater than 10,000 cps at a temperature of 70 ° C.

According to one embodiment, the uses according to the invention employ the starch described herein.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph depicting viscosity as a function of temperature for a starch according to the invention and for various starches modified by acid hydrolysis. The point at 125 ° C actually represents the point for the temperature of 25 ° C, after heating up to 90 ° C and Figure 2 is a graph depicting viscosity as a function of temperature for three starches according to the invention. The point at 125 ° C actually represents the point for the 25 ° C temperature, after heating up to 90 ° C.

DETAILED DESCRIPTION OF THE INVENTION Starch The starch used in the invention has a fundamentally different rheology as a function of temperature, which allows the starch to be dispersed in the center at low temperatures in order to penetrate the inter-crystalline spaces (without the Applicant is tied to a theory). As soon as the temperature is above 60 ° C, the viscosity of the starch increases rapidly to a very high level to ensure that the starch actually remains in the center and does not migrate to the center / coating interface. In the invention, an effect more or less opposite to the starches modified by acid hydrolysis is sought. Once the starch has thickened, it remains at a high viscosity at the high temperatures of the dryer. As can be seen in Figure 1, for the starches modified by acid hydrolysis of the prior art, the viscosity actually decreases after a peak around 80- 85 ° C. It is said that starch is retrograde. According to one embodiment, the starch according to the invention has a viscosity that remains high and does not have a peak; the starch is preferably a non-retrograde starch.

According to one embodiment, the starch also has the characteristic that the viscosity remains high even when the starch cools, in fact it is higher. The starch used in the invention may be, for example, (i) of the type whose viscosity increases further during cooling or (ii) of the type whose viscosity remains constant during cooling, or even (iii) of the type whose viscosity only decreases by a maximum of 15% during cooling.

Without wanting to be bound by a theory, the Applicant believes that the starch that is viscous in the glass gypsum interfaces contributes to the increase of the compression force.

The starch is chosen by measuring the Brookfield viscosity of a solution obtained by dissolving 100 g of starch in 600 ml of water at a temperature of 20 ° C. The solution is brought to 60 ° C and then heated at a rate of 1 ° C / min to 90 ° C. The solution is stirred during heating. The viscosity is measured at various temperatures (for example: 20, 40, 60, 65, 70, 75, 80, 85, 90 ° C, etc.). The viscometer is a Brookfield viscometer adapted to measure viscosities from 1 to 100,000 cps in particular. The test is done with axis 6 at a speed setting of 10, allowing the maximum result to be read directly from the Brookfield viscometer between 50 and 80% of the range on the scale. Outside that range, another range can be selected.

In contrast to starch modified by acid hydrolysis whose viscosity generally remains less than or equal to 1000 cps up to 90 ° C, the starch used in the invention is of the non-modified type and in accordance with a non-retrograde mode. In general, the starch that can be used in the invention has a Brookfield viscosity of less than 60, preferably less than 20 cps at a temperature below 60 ° C and a Brookfield viscosity greater than 20,000 cps at a temperature of 70 ° C, preferably greater than 30,000 cps at a temperature of 70 ° C, advantageously greater than 60,000 cps at a temperature of 80 ° C. The starch which can be used in the invention also preferably has a high viscosity at high temperatures, for example 90 ° C, whereas the starches modified by acid hydrolysis generally have a drop in viscosity at these high temperatures (these starches modified by hydrolysis acidic are, as already indicated, retrograde). Advantageously, the starch according to the invention will remain at a high viscosity for the entire duration of the heating and cooled. According to one embodiment, the viscosity of the solution at 25 ° C after cooling after heating to 90 ° C will be greater than the viscosity peak during heating. When the starch is of the non-retrograde type, one can not speak of a peak as such and the peak is then considered as the highest value for the temperature of 90 ° C. For example, the Brookfield viscosity of the starch at 25 ° C, after cooling following heating up to 90 ° C, is at least 100,000 cps, advantageously at least 300,000 cps.

The amount of starch used in the invention is variable. In general, the amount of starch, expressed in relation to the amount of hemihydrate involved, may be between 0.05 and 1%, preferably between 0.1 and 0.5% by weight. In general, the amount, for a density board around 8.5 kg / m2, is from 5 to 50 g / m2, in particular from 10 to 30 g / m2.

These starches are commercially available, especially with Carestar under the references RG 03408, PT 20002 and 05903 size C * Figure 1 provides a comparison between a starch modified by acid hydrolysis of the prior art and a non-modified starch according to the invention; as indicated previously.

Finally, it should be noted that the use of the starch according to the invention in no way prevents the use, at the same time, of a starch modified by acid hydrolysis to improve the center / coating interface. Thus, in accordance with one embodiment, the gypsum board also contains a starch modified by acid hydrolysis for adhesion at the center / liner interface.

Carton-veso components The other components of plasterboard are conventional components. First of all they are hydratable calcium sulfate. The term "gypsum suspension" is understood here to mean the conventional gypsum composition, that is composed mostly of gypsum. The pH of said suspension is typically between 5.5 and 8.5, in particular 6 to 7.5. According to a variant, no additive capable of changing the pH towards the basic values during the preparation of the suspension is added.

The term "plaster" is understood, in the present description; which means the product that results from the hydraulic adjustment and hardening of hydratable calcium sulfate, ie anhydrous calcium sulfate (anhydrite II or III) or calcium sulfate hemihydrate (CaS04, ½ H20) in its a or crystalline form. These compounds are well known to a person skilled in the art and are generally obtained from calcination gypsum. It is possible to use natural or synthetic gypsum (type FGD).

The composition may also comprise other hydraulic binders in small amounts.

The density of the center can vary from 540 kg / m3 to 1100 kg / m3, especially from 750 kg / m3 to 950 kg / m3.

The core material may also comprise aggregates and / or fillers, such as, for example, fumed silica, fly ash, blast furnace slag, lime, vermiculite, perlite, microspheres, limestone, recycled components, etc.

The gypsum-based composition according to the invention may further comprise additives which are conventionally used in gypsum-based compositions and are well known to a person skilled in the art. In this regard, mention should be made of: adjustment accelerators, adjustment retarders, bonding agents, adhesive agents, water retention agents, air entraining agents, thickeners, bactericides, fungicides, reinforcing materials, flame retardants and / or fillers. It is also possible to add additives to obtain boards that have water-resistant properties (waxes, silicones, etc.) or fire-resistant properties.

The resins can also be used to further strengthen the board, such as polyacrylic, polystyrene, polyvinyl chloride, polyolefin, polyurethane, cellulose, polyol, polyamide, polyester, polyether, polyphenolic, polysulfide resins, of polysulfone, silicone or fluoropolymer.

Examples of retarder / accelerator pairs are retarder / BMA, sodium polyacrylate / aluminum sulfate and conventional sodium phosphonate / zinc sulfate.

A bubble stabilizing agent can also be used.

Agents that modify the viscosity can also be added. Examples are polymers of variable nature, slurries or additives having a modified surface.

In a very conventional manner, a foam agent is added to the gypsum suspension composition before it settles. In general, alkyl sulfates, sulphates can be used alkyl ether or mixtures thereof. Examples can be found in the following documents: US-P-4 676 335, US-P-5 158 612, US-P-5 240 639, US-P-5 085 929, US-P-5 643 510, WO -A-95 16515, WO-A-97 23337, WO-A-02 70427 and WO-A-02 24595. The amount is standard and can be from 0.01 to 1 g / l of suspension (expressed in dry weight / weight dry solution).

In accordance with one embodiment of the invention, the air is additionally introduced to the gypsum-based composition by adding, for example, a foam. This foam can be produced by the use of any suitable foam agent, for example, the foam agent of formula ROS04M, as defined on page 14, line 20 to page 15, line 16 of the international application WO 99 / 08978.

The gypsum composition can also comprise fibers, in particular glass fibers, if necessary. - ... ._. . The empty volume in the center may vary within wide limits, depending on the type of aeration in the mixture and the W / P ratio. Typically, the W / P ratio varies from 0.55 to 0.95, preferably from 0.65 to 0.80. The coatings used in the invention are typically made of paper or paperboard, but the coatings can also be used in the form of mats or nonwovens, for example made from a mat of glass fibers and / or synthetic fibers and / or from cellulose. The coatings may also be used comprising blends of different types of fibers, especially glass fibers and organic fibers and / or coatings containing a fine filler dispersed in the fibers forming the mat. Surface treatments are also provided to make the coating hydrophobic or to make it resistant to fire.

The plasterboard thus obtained in the invention has: (1) for equal compression forces, a low density (and therefore a low surface weight) or (2) for equal densities (and therefore both for equal surface weights), an increased compression force, advantageously increased by at least 0.5 MPa.

The paperboard according to the invention is available in conventional dimensions and thicknesses, especially in the form of the so-called standard BA 3 paperboard. Thicknesses other than 12.5 mm are possible, for example 10 mm or smaller, or 15 mm or larger.

Gypsum Cardboard Manufacturing Method The final subject of the invention is a method for continuously manufacturing gypsum board, which essentially comprises the steps of: - preparing a suspension of the gypsum composition according to the invention by mixing several constituents of the composition with water in a mixer; - depositing the suspension thus prepared in at least one coating, followed by forming it on a batten, with optional covering of the upper face of the suspension using a second coating, the formation especially consisting in softening the ends of the cardboard; - where it is appropriate, to form the ends of the ribbon of the cardboard previously obtained by molding the strip into profiled strips; - hydraulically adjust the gypsum in a manufacturing line while the cardboard strip runs along a conveyor belt; -cut the ribbon at the end of the line in predetermined lengths and - dry the obtained cards.

The gypsum suspension composition is conventionally obtained by mixing the hemihydrate with water. The additives can be introduced with the hemihydrate, in particular when they are in powder form or with a portion of the water to be mixed when they are in water-soluble form or available in liquid form. If a foam is injected into the mixer, the additives may optionally be present in that foam.

The drying step is carried out at standard temperatures in the plasterboard manufacturing lines; from this point of view, the use of starch according to the invention does not change the conventional processes. Similarly, the other properties of the board are acceptable in any respect. There is no effect of delayed adjustment or thickening of the suspension that could result in a variation in the size of the cardboard. There is no problem in drying the cardboard under normal conditions in the dryer. The adhesion of the coating to the center in the wet state and in the dry state is good in each case.

EXAMPLES The following examples illustrate the invention without limiting it.

EXAMPLE 1 Minicartons of laboratory were prepared with the following composition. Two different starches, Cerestar PT 20002 and 05903 size C *, A and B respectively, were used. Figure 2 shows the viscosity as a function of temperature. Figure 2 also shows the viscosity of a third starch capable of being used in the invention, RG 03408. The starches presented in the figures are offered by way of illustration only.

The minicartones are obtained from a suspension comprising (in grams): The volume of the foam was 770 ml, the amount of water used to form the foam was 180 g.

The paper was a conventional coating paper, with a base weight of 205 g / m2.

Thus, cartons having a thickness of 12.5 mm and a density of 8.5 kg / m2 were prepared. Then, a starch was added, from which the rheological profile is given in the graph of Figure 2, 10 and 20 g / m2.

The results are provided in the following table.

Example 2 An industrial-scale process was used in the plasterboard manufacturing line. The manufactured cardboard was the standard BA13 cardboard, with a density of 9..15 kg / m2, a W / P ratio of 0.59, a line speed of 68 m / min, using a conventional starch for the adhesion of the paper coating . Starch B was used at 50% dilution in water. The diluted starch solution was added to the mixing water in two doses, 8 and 25 g / m2. The line remained in production for 1 minute. The following results were obtained for the compression force (dry conditions), averaged for 5 values. The variations registered were at 6%.

A substantial increase was therefore observed in adding the starch according to the invention.

Claims (19)

1. CLAIMS 1. A gypsum suspension composition comprising gypsum, water and starch, said starch having a Brookfieid viscosity of less than 60 cps at a temperature below 60 ° C and a Brookfieid viscosity greater than 10,000 cps at a temperature of 70 ° C.
2. 2. The composition according to claim 1, wherein the starch has a Brookfieid viscosity of less than 20 cps at a temperature of 60 ° C.
3. 3. The composition according to claim 1 or 2, wherein the starch has a Brookfieid viscosity greater than 20,000 cps, preferably greater than 30,000 cps, at a temperature of 70 ° C.
4. 4. The composition according to one of claims 1 to 3, wherein the starch has a Brookfieid viscosity of more than 60,000 cps at a temperature of 80 ° C.
5. 5. The composition according to one of claims 1 to 4, wherein the starch is of the non-retrograde type.
6. 6. The composition according to one of claims 1 to 5, wherein the starch has a viscosity at 25 ° C, after cooling following the heating of the starch solution to 90 ° C, which is greater than the maximum viscosity obtained during the heating of said starch solution.
7. 7. The composition according to one of claims 1 to 6, wherein the starch has a viscosity at 25 ° C, after cooling following the heating of the starch solution up to 90 ° C, of at least 100,000 cps, advantageously of at least 300,000 cps.
8. 8. The composition according to one of claims 1 to 7, comprising, in relation to the weight of the gypsum, between 0.05 and 1%, preferably between 0.1 and 0.5% by weight of starch.
9. 9. The composition according to one of claims 1 to 8, which has a pH between 5.5 and 8.5, preferably between 6 and 7.5.
10. 10. The composition according to one of claims 1 to 9, wherein the W / P ratio varies from 0.55 to 0.95, preferably from 0.65 to 0.80.
11. 11. The composition according to one of claims 1 to 10, further comprising starch modified by acid hydrolysis.
12. 12. The plasterboard comprising a center that can be obtained by adjusting a plaster suspension according to one of claims 1 to 11.
13. 13. The gypsum board according to claim 12, having a center density ranging from 540 kg / m3 to 1100 kg / m3, preferably from 750 kg / m3 to 950 kg / m3. '
14. 14. The plasterboard according to one of claims 12 or 13, which has one, preferably two, coating (s).
15. 15. The plasterboard according to claim 14, wherein the coating is paper, or a mat or non-woven, preferably a mat of glass fibers and / or synthetic fibers and / or cellulose, said coating being optionally filling with a fine filler and / or a filler that has optionally received a surface treatment.
16. 16. A method for preparing a gypsum board consisting of a gypsum-based center and at least one, advantageously two, lining (s), said method comprises the following steps: - preparing a suspension of the gypsum composition according to one of claims 1 to 11 by mixing several constituents of the composition with water in a mixer; - depositing the suspension thus prepared in at least one coating, followed by forming it on a batten, with optional covering of the upper face of the suspension using a second coating; - where it is appropriate, to form the ends of the ribbon of the cardboard previously obtained by molding the strip into profiled strips; - Hydraulically adjusting the gypsum in a manufacturing line while the cardboard strip runs along a conveyor belt; -cut the ribbon at the end of the line in predetermined lengths and - dry the obtained cards.
17. 17. The use of starch having a Brookfieid viscosity of less than 60 cps at a temperature below 60 ° C and a Brookfieid viscosity greater than 10,000 cps at a temperature of 70 ° C, to manufacture a plasterboard.
18. 18. The use of starch having a Brookfieid viscosity of less than 60 cps at a temperature below 60 ° C and a Brookfieid viscosity greater than 10,000 cps at a temperature of 70 ° C, to increase the compression strength of a plasterboard, preferably by at least 0.5 MPa.
19. 19. The use according to claim 17 or 18, wherein the starch is according to one of claims 2 to 7.