(19)
(11)EP 3 221 274 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
30.12.2020 Bulletin 2020/53

(21)Application number: 15794947.0

(22)Date of filing:  17.11.2015
(51)International Patent Classification (IPC): 
C04B 28/14(2006.01)
C04B 111/00(2006.01)
C04B 103/56(2006.01)
C04B 111/28(2006.01)
(86)International application number:
PCT/EP2015/076786
(87)International publication number:
WO 2016/079099 (26.05.2016 Gazette  2016/21)

(54)

ADDITIVE FOR SHRINKAGE REDUCTION

ADDITIV FÜR SCHRUMPFREDUZIERUNG

ADDITIF POUR LA RÉDUCTION DU RETRAIT


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 21.11.2014 GB 201420768

(43)Date of publication of application:
27.09.2017 Bulletin 2017/39

(60)Divisional application:
20159919.8 / 3677561

(73)Proprietor: SAINT-GOBAIN PLACO
92400 Courbevoie (FR)

(72)Inventors:
  • BROOKS, Laura
    Loughborough Leicestershire LE12 6JT (GB)
  • FISHER, Robin
    Loughborough Leicestershire LE12 6JT (GB)
  • RIDEOUT, Jan
    Loughborough Leicestershire LE12 6JT (GB)

(74)Representative: Mewburn Ellis LLP 
Aurora Building Counterslip
Bristol BS1 6BX
Bristol BS1 6BX (GB)


(56)References cited: : 
WO-A1-2013/098859
JP-A- 2005 187 278
JP-B2- 2 986 986
JP-A- S55 126 559
JP-A- 2009 263 217
US-A1- 2011 195 241
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] This invention relates to improved high temperature resistant calcium sulphate-based products and, in particular, to calcium sulphate-based products having reduced shrinkage at high temperatures.

    BACKGROUND



    [0002] Calcium sulphate-based products are widely used in the construction of buildings, for example, to form internal partitions (using wallboard, also known as dry wall, gypsum board or plaster board) and ceilings or to encase ducts (e.g. ventilation ducts) within buildings.

    [0003] Calcium sulphate-based products such as wallboard are typically formed by drying an aqueous slurry of the hemihydrate of calcium sulphate (CaSO4.½ H2O), also known as calcined gypsum or stucco, between two sheets of lining paper or fibreglass matting. As the slurry dries and the calcined gypsum is hydrated, a hard, rigid core of gypsum (calcium sulphate dihydrate -(CaSO4.2H2O)) sandwiched between the lining sheets/mats is formed.

    [0004] When wallboard or ceiling tiles are exposed to high temperatures such as those experienced in a building fire or those experienced by wallboards used for encasing ducts carrying high temperature fluids, the water of crystallization contained within the gypsum is driven off to yield the anhydrite of calcium sulphate. Initially, this has the advantage that heat transfer across the wallboard/ceiling tile is reduced thus helping to contain the heat emanating from ducting or generated during a building fire. However, at temperatures around 400-450°C, the initially formed AIII phase anhydrite (also known as γ-CaSO4 or "soluble" anhydrite) converts to the All phase (or "insoluble" anhydrite) and this phase change results in shrinkage of the wallboard/tile i.e. a loss of dimensional stability. This shrinkage often causes the wallboards to pull away from their supporting structures. This is obviously undesirable. It can leave ducts exposed to high temperatures. Furthermore, in situations where wallboard is used for internal partitions and a fire breaks out, shrinkage can leaves gaps exposing rooms adjacent to the fire source to the effects of the heat/fire. Gaps also allow ingress of oxygen into the fire source thus fuelling the fire and negating the effects of any fire doors.

    [0005] At higher temperatures (in excess of 600°C), the insoluble anhydrite goes on to sinter resulting in large reductions in wallboard volume. This results in extreme shrinkage which eventually causes collapse of the internal walls/ceilings/duct casings as they are no longer held by their supporting structures.

    [0006] Efforts have been made to improve the heat resistance of calcium sulphate-based products such as wallboard in an attempt to reduce shrinkage.

    [0007] It is known e.g. from EP0258064 to use micro silica as an additive in the gypsum core of wallboard to reduce shrinkage. However, this additive only has an effect at temperatures greater than 600°C i.e. it does not resist the shrinkage of the board at lower temperatures and linear shrinkage of more than 10% is still seen as temperatures around 1000°C.

    [0008] It is known from WO99/08979 and WO00/06518 to add sodium trimetaphosphate (STMP), sodium hexametaphosphate (SHMP) or ammonium polyphosphate (APP) to a calcium sulphate wallboard core to improve strength, sag resistance and shrinkage during drying. No effect of these additives on shrinkage during exposure to high temperatures is recorded.

    [0009] US5985013 discloses an ablative type heat protecting material containing calcium sulphate hemihydrate and a hydrated salt. A number of hydrated salts are used including magnesium nitrate hexahydrate (used in an amount of 40wt% based on the weight of dry ingredients). The time taken for heat transfer across the heat ablative material was recorded. No mention is made of any shrinkage resistance properties of the hydrated salts.

    [0010] JP2005-187278 discloses a drying shrinkage reducing agent for a hydraulic material. The drying shrinkage reducing agent comprises at least one compound selected from the group consisting of: a) an inorganic electrolyte containing an alkaline earth metals; b) an inorganic electrolyte containing an N-containing anion; and c) a water soluble organic acid/salt.

    [0011] Calcium sulphate-based products are also used to cast metal or glass objects. Calcium sulphate moulds are heated to 700-900°C prior to being filled with molten metal/glass. It is important to control high temperature shrinkage of such calcium sulphate-based moulds to ensure that the moulds do not leak and to ensure that the cast metal/glass products are not warped.

    [0012] A preferred aim of the present invention is to provide an improved heat resistant calcium sulphate-based product having reduced shrinkage after heat exposure e.g. when in contact with ducting, during a building fire or during casting of metal products. Such an improved heat resistant product may have particular use as a building product e.g. wallboard or panels for forming internal partitions in buildings, ceiling tiles, wallboard or panels for encasing ventilation/smoke extraction ducting, joint filler materials for joining wallboard/panels/tiles or for moulds for use in metal/glass product casting.

    SUMMARY OF THE INVENTION



    [0013] Accordingly, in a first aspect, the present invention provides the use of a metal hydroxide or acetate, or of magnesium, aluminium or zinc sulphate as set out in claim 1. That is, use of a metal hydroxide or acetate, or of magnesium, aluminium or zinc sulphate an additive in a gypsum matrix for reducing shrinkage in a calcium sulphate-based wallboard during heat exposure to temperatures greater than 400°C.

    [0014] Further optional features of the invention are set out in claims 2-5. That is, the additive may be used in an amount greater than or equal to 0.5 wt% (based on the amount of additive and gypsum). The additive may be used in an amount less than 40 wt% (based on the amount of additive and gypsum). The additive may be used in an amount less than 25 wt% (based on the amount of additive and gypsum). The shrinkage resistance additive may be selected from the hydroxide, acetate or sulphate of magnesium, aluminium or zinc, or the hydroxide or acetate of iron.

    [0015] Also disclosed herein is a calcium sulphate-based product comprising gypsum and a shrinkage resistance additive, wherein the shrinkage resistance additive is a metal nitrate, hydroxide, acetate or sulphate.

    [0016] Also disclosed herein is a calcium sulphate-based product comprising gypsum and a shrinkage resistance additive, wherein the product is formed from drying an aqueous slurry containing calcined gypsum and said shrinkage resistance additive, the shrinkage resistance additive being a metal nitrate, hydroxide, acetate or sulphate.

    [0017] Also disclosed herein is a method of forming a calcium sulphate-based product by drying an aqueous slurry comprising calcined gypsum and a shrinkage resistance additive wherein the shrinkage resistance additive is a metal nitrate, hydroxide, acetate or sulphate.

    [0018] Also disclosed herein is a calcium sulphate-based composition for use in forming a calcium sulphate-based product by drying an aqueous slurry of the calcium sulphate-based composition, the calcium sulphate-based composition comprising calcined gypsum and a shrinkage resistance additive, wherein the shrinkage resistance additive is a metal nitrate, hydroxide, acetate or sulphate.

    [0019] The inventors have found that including a metal hydroxide or acetate, or of magnesium, aluminium or zinc sulphate in a calcium sulphate based wallboard e.g. the gypsum core of a wallboard, reduces shrinkage of the wallboard when the board is exposed to high temperatures. Unlike micro silica which only has an effect above 600°C, the metal hydroxide, acetate or sulphate begins to have an effect around 400°C where it undergoes an endothermic decomposition (to yield oxides, oxygen and nitrogen oxides) and thus acts as a heat sink. The metal hydroxide, acetate or sulphate also acts to increase the temperature at which the transition from the soluble to insoluble calcium sulphate anhydrite occurs thus allowing the product to resist the shrinkage arising from the phase change until higher temperatures (greater than 900°C) are reached. The inventors have found that a metal-rich layer forms at the surface of the calcium sulphate based product and it is believed that this metal-rich layer protects the calcium sulphate anhydrite and delays the transition until higher temperatures.

    [0020] Further optional features of the invention will now be set out. These are applicable singly or in any combination with any aspect of the invention.

    [0021] The metal in the metal salt may be an alkaline earth metal e.g. calcium or magnesium. The metal may be a transition metal e.g. copper, iron or zinc. The metal may be aluminium. The metal may be an alkali metal e.g. potassium.

    [0022] The metal hydroxide, acetate or sulphate may be magnesium hydroxide, acetate or sulphate aluminium hydroxide, acetate or sulphate, zinc hydroxide, acetate or sulphate or iron hydroxide or acetate. Preferably, it is magnesium hydroxide (Mg(OH)2), acetate or sulphate. Magnesium acetate is hygroscopic and typically exists as magnesium acetate tetrahydrate, Mg(C2H3O2)2•4H2O. Magnesium sulphate is hygroscopic and typically exists as magnesium sulphate heptahydrate, MgSO4•7H2O.

    [0023] The calcium sulphate-based product is formed from drying an aqueous slurry containing calcined gypsum (or stucco) and the metal nitrate, hydroxide, acetate or sulphate anti-shrinkage additive.

    [0024] Also discussed herein are calcium sulphate-based slurries and compositions suitable for forming a calcium sulphate-based wallboard wherein the metal nitrate, hydroxide, acetate or sulphate is present in the slurry and in the calcium sulphate-based composition in an amount greater than or equal to 1 wt% or greater than or equal to 2 wt% or greater than or equal to 4.5 wt% or greater than or equal to 9 wt% or greater or equal to than 15 wt% or greater than or equal to 20 wt% or greater than or equal to 25 wt% (based on the amount of nitrate, hydroxide, acetate or sulphate /calcined gypsum in the slurry/composition).

    [0025] In some calcium sulphate-based slurries and compositions suitable for forming a calcium sulphate-based wallboard, the metal nitrate, hydroxide, acetate or sulphate is present in the slurry and in the calcium sulphate-based composition in an amount equal to or less than 50 wt% or equal to or less than 40 wt% or equal to or less than 30wt% (based on the amount of nitrate, hydroxide, acetate or sulphate /calcined gypsum in the slurry/composition).

    [0026] In other calcium sulphate-based slurries and compositions suitable for forming a calcium sulphate-based wallboard, the metal nitrate, hydroxide, acetate or sulphate is present in the slurry/composition in an amount between 4.5 wt% and less than 30 wt%.

    [0027] In some embodiments, the metal nitrate, hydroxide, acetate or sulphate is present in the calcium sulphate-based wallboard in an amount greater than or equal to 0.5 wt% or greater than or equal to 2 wt% or greater than or equal to 4 wt% or greater than or equal to 7 wt% or greater or equal to than 12 wt% or greater than or equal to 15 wt% or greater than or equal to 20 wt% (based on the amount of nitrate, hydroxide, acetate or sulphate /gypsum in the product).

    [0028] In some embodiments, the metal nitrate, hydroxide, acetate or sulphate is present in the calcium sulphate-based wallboard in an amount equal to or less than 40 wt% or equal to or less than 35 wt% or equal to or less than 25 wt% (based on the amount of nitrate, hydroxide, acetate or sulphate /gypsum in the product).

    [0029] In preferred embodiments, the metal hydroxide, acetate or sulphate is present in the calcium sulphate-based wallboard in an amount between 4 wt% and less than 25 wt%.

    [0030] The term calcined gypsum (or stucco) is intended to refer predominantly to calcium sulphate hemihydrate (CaSO4.1/2H20) but may also encompass any other calcium sulphate compound having a lower bound water content than calcium sulphate dihydrate (e.g. calcium sulphate anhydrite).

    [0031] The term "gypsum" is intended to refer predominantly to calcium sulphate dihydrate (CaSO4.2H20).

    [0032] In some calcium sulphate-based slurries and compositions suitable for forming a calcium sulphate-based wallboard, the calcined gypsum is present in the slurry and in the calcium-sulphate-based composition in an amount of 99 - 50 wt% (based on the amount of nitrate, hydroxide, acetate or sulphate /calcined gypsum in the slurry/composition). More preferably, it is present in an amount from 98 to 70wt% or 90 to 70 wt%.

    [0033] In some embodiments, the gypsum is present in the calcium sulphate-based wallboard an amount of 99.5 - 60 wt% (based on the amount of nitrate, hydroxide, acetate or sulphate /gypsum in the product). More preferably, it is present in an amount from 98 to 75 wt% or 95 to 75 wt%.

    [0034] Preferably, the wallboard e.g. the gypsum core of the wallboard contains no clinker i.e. no product produced by sintering limestone and alumina-silicate.

    [0035] The term "calcium sulphate-based product" as used herein may include building products such as wallboards (with or without liners) (with or without fibrous reinforcement), tiles (e.g. ceiling tiles), duct encasement panels, joint filler materials (e.g. for joining adjacent wallboards/tiles/panels etc.), plaster compositions and moulds for casting metal products. However the present invention relates to a calcium sulphate-based product which is a calcium sulphate-based wallboard.

    [0036] The term "calcium sulphate-based" will be readily understood as meaning that the product comprises gypsum as a major component i.e. that gypsum is the largest single component in terms of wt% of the product. The term may mean that the product comprises gypsum in 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt% or greater based on the total weight of the product.

    [0037] The calcium sulphate-based product may be a composite product e.g. it may be a wallboard having a gypsum matrix core (containing the shrinkage resistance additive) sandwiched between two liners (e.g. paper liners or fibreglass matting).

    [0038] In some embodiments, the calcium sulphate-based product contains substantially no inorganic fibres e.g. no glass or asbestos fibres. The present inventors have found that the addition of a combination of a clay additive and a metal salt can help maintain strength and structural integrity after heating even in the absence of a fibrous network.

    [0039] However, in some embodiments, the calcium sulphate-based product may contain inorganic fibres (e.g. glass fibres) and/or matting (e.g. glass matting) as this may help improve strength of the product prior to heating.

    [0040] The calcium sulphate-based product may contain additives such as accelerators, retarders, foaming/anti-foaming agents, fluidisers etc.. The accelerators may be, for example, freshly ground gypsum having an additive of sugar or surfactant. Such accelerators may include Ground Mineral NANSA (GMN), heat resistant accelerator (HRA) and ball milled accelerator (BMA). Alternatively, the accelerator may be a chemical additive such as aluminium sulphate, zinc sulphate or potassium sulphate. In certain cases, a mixture of accelerators may be used, e.g. GMN in combination with a sulphate accelerator. As a further alternative, ultrasound may be used to accelerate the setting rate of the slurry, e.g. as described in US2010/0136259.

    DESCRIPTION OF THE DRAWING



    [0041] Figure 1 shows a graph of linear shrinkage for various samples during heating to 1000°C.

    EXPERIMENTAL



    [0042] The following examples are given by way of illustration only. Only samples including use of a metal hydroxide or acetate, or of magnesium, aluminium or zinc sulphate (i.e. samples 18, 19 and 20) are according to the present invention.

    Control sample 1



    [0043] 200g of calcined gypsum was added to 140g of water at 40°C. This was mixed by hand for 30 seconds and the resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm). The sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 1 -magnesium nitrate - 1% wt:wt calcined gypsum



    [0044] 2g of magnesium nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 1.0 wt% nitrate based on weight of calcined gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 2 - magnesium nitrate - 2.5% wt:wt calcined gypsum



    [0045] 5g of magnesium nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 2.4 wt% nitrate based on weight of dry ingredients/containing 2.5 wt% based on weight of calcined gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 3 - magnesium nitrate - 5% wt:wt calcined gypsum



    [0046] 10g of magnesium nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 4.8 wt% nitrate based on weight of dry ingredients/containing 5 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 4 - magnesium nitrate - 10% wt:wt calcined gypsum



    [0047] 20g of magnesium nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1 wt% nitrate based on weight of dry ingredients/containing 10 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 5 - magnesium nitrate - 30% wt:wt calcined gypsum



    [0048] 60g of magnesium nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 23.1 wt% nitrate based on weight of dry ingredients/containing 30 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 6 - aluminium nitrate - 2.5% wt:wt calcined gypsum



    [0049] 5g of aluminium nitrate nonahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 2.4 wt% nitrate based on weight of dry ingredients/containing 2.5 wt% based on weight of calcined gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 7 - aluminium nitrate - 5% wt:wt calcined gypsum



    [0050] 10g of aluminium nitrate nonahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 4.8 wt% nitrate based on weight of dry ingredients/containing 5 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 8 - aluminium nitrate - 10% wt:wt calcined gypsum



    [0051] 20g of aluminium nitrate nonahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1 wt% nitrate based on weight of dry ingredients/containing 10 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 9 - zinc nitrate - 2.5% wt:wt calcined gypsum



    [0052] 5g of zinc nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 2.4 wt% nitrate based on weight of dry ingredients/containing 2.5 wt% based on weight of calcined gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 10 - zinc nitrate - 5% wt:wt calcined gypsum



    [0053] 10g of zinc nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 4.8 wt% nitrate based on weight of dry ingredients/containing 5 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 11 - zinc nitrate - 10% wt:wt calcined gypsum



    [0054] 20g of zinc nitrate hexahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1 wt% nitrate based on weight of dry ingredients/containing 10 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 12 - iron nitrate - 2.5% wt:wt calcined gypsum



    [0055] 5g of iron (III) nitrate nonahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 2.4 wt% nitrate based on weight of dry ingredients/containing 2.5 wt% based on weight of calcined gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 13 - iron nitrate - 5% wt:wt calcined gypsum



    [0056] 10g of iron (III) nitrate nonahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 4.8 wt% nitrate based on weight of dry ingredients/containing 5 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 14 - iron nitrate - 10% wt:wt calcined gypsum



    [0057] 20g of iron (III) nitrate nonahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1 wt% nitrate based on weight of dry ingredients/containing 10 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 15 - potassium nitrate - 10% wt:wt calcined gypsum



    [0058] 20g of potassium nitrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1 wt% nitrate based on weight of dry ingredients/containing 10 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 16 - copper nitrate - 8% wt:wt calcined gypsum



    [0059] 16g of copper nitrate tetrahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 7.4 wt% nitrate based on weight of dry ingredients/containing 5 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 17 - calcium nitrate - 9% wt:wt calcined gypsum



    [0060] 18g of calcium nitrate tetrahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 8.3 wt% nitrate based on weight of dry ingredients/containing 9 wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 18 - magnesium hydroxide - 10% wt:wt calcined gypsum



    [0061] 20g of magnesium hydroxide was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1wt% hydroxide based on weight of dry ingredients/containing 7.8wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 19 - magnesium acetate - 10% wt:wt calcined gypsum



    [0062] 20g of magnesium acetate tetrahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1wt% acetate based on weight of dry ingredients/containing 7.8wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    Sample 20 - magnesium sulphate - 10% wt:wt calcined gypsum



    [0063] 20g of magnesium sulphate heptahydrate was added to 140g of water at 40°C. 200g of calcined gypsum was added to the solution and the resulting slurry (containing 9.1wt% sulphate based on weight of dry ingredients/containing 7.8wt% based on weight of gypsum) was blended by hand for 30 seconds to form a slurry. The resulting slurry was poured into a cylindrical silicone mould (of height 25mm and diameter 12mm) and the sample was transferred to an oven at 40°C and left to dry overnight (at least 12 hours).

    [0064] A summary of all sample formulations is shown in Table 1 below.
     % wt:wt stuccoWt% in slurryWt% in product
    Mg Nitrate 1 1 1.0 0.8
    2 2.5 2.4 2.0
    3 5 4.8 4.0
    4 10 9.1 7.8
    5 30 23.1 20.2
    Al Nitrate 6 2.5 2.4 2.0
    7 5 4.8 4.1
    8 10 9.1 7.8
    Zn Nitrate 9 2.5 2.4 2.0
    10 5 4.8 4.1
    11 10 9.1 7.8
    Fe Nitrate 12 2.5 2.4 2.0
    13 5 4.8 4.0
    14 10 9.1 7.8
    K Nitrate 15 10 9.1 7.8
    Cu Nitrate 16 8 7.4 6.3
    Ca Nitrate 17 9 8.3 7.1
    Mg(OH)2 18 10 9.1 7.8
    Mg(C2H3O2)2 19 10 9.1 7.8
    MgSO4 20 10 9.1 7.8

    Linear Shrinkage



    [0065] The linear shrinkage of the samples was measured using a Netzsch dilatometer with a ceramic rod attached to a linear displacement transducer having a resolution of 8nm. The samples were supported by other ceramic rods and the heated in a furnace to 1000°C at a rate of 5°C/min. The results are shown in Figures 1 and 2 and Table 2 below.
    FormulationLinear Shrinkage (%)
    500°C750 °C900 °C950°C1000°C
    Control -1.8 -3.6 -7.1 -18.0 Off scale
    Mg nitrate 1 -0.8 -0.7 -1.3 -10.6 -12.3
    2 -0.3 -0.1 0.0 -4.4 -12.1
    3 -0.3 -0.3 -0.5 -7.0 -12.1
    4 -0.0 -0.1 0.2 -2.8 -6.5
    5 -0.5 0.1 0.2 -0.5 -1.9
    Al nitrate 6 -0.7 -2.0 -5.6 -11.7 -16.7
    7 -0.8 -1.4 -5.3 -10.4 -15.7
    8 -0.7 -0.4 -0.4 -0.9 -3.5
    Zn nitrate 9 -0.9 -1.1 -7.4 -17.8 Off-scale
    10 -0.4 -0.8 -7.6 -17.3 Off-scale
    11 -0.2 -0.3 -1.8 -6.5 -9.7
    Fe nitrate 12 -0.9 -1.6 -4.7 -15.9 -17.0
    13 -0.3 -0.7 -2.9 -9.0 -15.9
    14 -0.6 -0.7 -3.6 -7.7 -12.3
    K nitrate 15 -0.9 -2.8 -16.4 -17.4 Off-scale
    Cu nitrate 16 -0.2 -1.5 -12.9 Off-scale Off-scale
    Ca nitrate 17 -0.3 -2.8 -9.1 -9.1 Off-scale
    Mg hydroxide 18 -1.4 -3.2 -5.8 -8.0 -9.9
    Mg acetate 19 -0.7 -3.5 -5.3 -9.7 -12.7
    Mg sulphate 20 -1.4 -3.2 -5.1 -7.4 -11.1


    [0066] It can be seen that:
    1. a) linear shrinkage is reduced at 500°C and 750°C for all samples;
    2. b) linear shrinkage is reduced at all temperatures for all magnesium and aluminium salt samples;
    3. c) linear shrinkage at 900°C is reduced to less than around 1% for all samples containing magnesium nitrate; and
    4. d) linear shrinkage reduction is greater at addition levels greater than 4 wt% (based on amount of additive/gypsum in product) and especially at addition levels greater than 7 wt%.



    Claims

    1. Use of a metal hydroxide or acetate, or of magnesium, aluminium or zinc sulphate as an additive in a gypsum matrix for reducing shrinkage in a calcium sulphate-based wallboard during heat exposure to temperatures greater than 400°C.
     
    2. Use according to claim 1 wherein the additive is used in an amount greater than or equal to 0.5 wt% based on the amount of additive and gypsum
     
    3. Use according to claim 1 or claim 2 wherein the additive is used in an amount less than 40 wt% based on the amount of additive and gypsum
     
    4. Use according to claim 3 wherein the additive is used in an amount less than 25 wt% based on the amount of additive and gypsum.
     
    5. Use according to any one of claims 1 to 4 wherein the shrinkage resistance additive is selected from the hydroxide, acetate or sulphate of magnesium, aluminium or zinc, or the hydroxide or acetate of iron.
     


    Ansprüche

    1. Verwendung eines Metallhydroxids oder -acetats oder von Magnesium-, Aluminium- oder Zinksulfat als Additiv in einer Gipsmatrix zur Verringerung der Schrumpfung einer Wandplatte auf Calciumsulfat-Basis, wenn diese Hitze bei Temperaturen von mehr als 400°C ausgesetzt ist.
     
    2. Verwendung nach Anspruch 1, wobei das Additiv in einer Menge größer oder gleich 0,5 Gew.-%, bezogen auf die Menge an Additiv und Gips, eingesetzt wird.
     
    3. Verwendung nach Anspruch 1 oder 2, wobei das Additiv in einer Menge von weniger als 40 Gew.-%, bezogen auf die Menge an Additiv und Gips, eingesetzt wird.
     
    4. Verwendung nach Anspruch 3, wobei das Additiv in einer Menge von weniger als 25 Gew.-%, bezogen auf die Menge von Additiv und Gips, eingesetzt wird.
     
    5. Verwendung nach einem der Ansprüche 1 bis 4, wobei das Schrumpfbeständigkeitsadditiv aus dem Hydroxid, dem Acetat und dem Sulfat von Magnesium, Aluminium oder Zink oder aus dem Hydroxid und dem Acetat von Eisen ausgewählt wird.
     


    Revendications

    1. Utilisation d'un hydroxyde ou d'un acétate de métal, ou de sulfate de magnésium, d'aluminium ou de zinc comme additif dans une matrice de gypse pour réduire un retrait dans un panneau mural à base de sulfate de calcium lors d'une exposition à de la chaleur à des températures supérieures à 400°C.
     
    2. Utilisation selon la revendication 1, dans laquelle l'additif est utilisé en une quantité supérieure ou égale à 0,5% en poids sur la base de la quantité d'additif et de gypse.
     
    3. Utilisation selon la revendication 1 ou la revendication 2, dans laquelle l'additif est utilisé en une quantité inférieure à 40 % en poids sur la base de la quantité d'additif et de gypse.
     
    4. Utilisation selon la revendication 3, dans laquelle l'additif est utilisé en une quantité inférieure à 25 % en poids sur la base de la quantité d'additif et de gypse.
     
    5. Utilisation selon l'une quelconque des revendications 1 à 4 dans laquelle l'additif de résistance au retrait est choisi parmi l'hydroxyde, l'acétate ou le sulfate de magnésium, d'aluminium ou de zinc, ou l'hydroxyde ou l'acétate de fer.
     




    Drawing








    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description