EP4244196A1 - Phosphate cement based mineral adhesive - Google Patents

Phosphate cement based mineral adhesive

Info

Publication number
EP4244196A1
EP4244196A1 EP20815712.3A EP20815712A EP4244196A1 EP 4244196 A1 EP4244196 A1 EP 4244196A1 EP 20815712 A EP20815712 A EP 20815712A EP 4244196 A1 EP4244196 A1 EP 4244196A1
Authority
EP
European Patent Office
Prior art keywords
adhesive
substrate
mineral
mineral adhesive
phosphate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20815712.3A
Other languages
German (de)
French (fr)
Inventor
Rauno BAESE
Nina KRAWTSCHENKO
Christian ENGERT
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Knauf Gips KG
Original Assignee
Knauf Gips KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Knauf Gips KG filed Critical Knauf Gips KG
Publication of EP4244196A1 publication Critical patent/EP4244196A1/en
Pending legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B12/00—Cements not provided for in groups C04B7/00 - C04B11/00
    • C04B12/02—Phosphate cements
    • C04B12/025—Phosphates of ammonium or of the alkali or alkaline earth metals
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/34—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing cold phosphate binders
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00482—Coating or impregnation materials
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00482—Coating or impregnation materials
    • C04B2111/00517—Coating or impregnation materials for masonry
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00482—Coating or impregnation materials
    • C04B2111/00525—Coating or impregnation materials for metallic surfaces
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00637—Uses not provided for elsewhere in C04B2111/00 as glue or binder for uniting building or structural materials

Definitions

  • the invention concerns a process for the adhesive attachment of planar items on various substrates, which employ a mineral adhesive on the basis of phosphate cement. Such adhesives allow for a fast and stable attachment of the planar items and in particular of tiles to substrates without the necessity of a pretreatment or priming step.
  • the invention is further concerned with corresponding mineral adhesives, composite structures prepared from substrates, the mineral adhesive and tiles and the use of the mineral adhesive for improving the tensile strength of an adhesive joint between a substrate and one or more tiles.
  • Portland cement based adhesives are associated with health risks, mainly because wet Portland cement is highly alkaline and can cause serious burns during handling. It can also cause allergic skin reactions and dermatitis.
  • Phosphate cement as a binder is well known in the art. Especially in dental applications, phosphate cement, mostly as zinc phosphate cement, has long been used for the attachment of tooth crowns or as underfilling with good thermal and chemical insulation or as provisional filling.
  • Phosphate cement has also previously been described as a binder in mortars and concrete and has in particular been used for the repair of runways for planes or the sealing of radioactive waste, where properties such as the compressive strength or the flexural tension are of particular importance.
  • phosphate cements particularly magnesium phosphate cements (MCP), such as magnesium potassium phosphate (MKPC) have a lower carbon footprint compared to e.g. Portland cement.
  • the term “physical mixture” is intended to denote a mixture obtained from mixing individual powders of the phosphate cement in the dry form, so that each solid particle in the mixture is primarily constituted form only one precursor of the phosphate cement. That is, the term “physical mixture” is intended to delimit from mixed particles, such as those obtained by absorbing a solution of one material on another and drying the same.
  • the present invention concerns a process for adhesively attaching one or more planar items to a substrate comprising the steps of: (i) mixing a mineral adhesive on the basis of phosphate cement with water to provide a paste, wherein the mineral adhesive is a physical mixture of precursor constituents of the phosphate cement;
  • the mineral adhesive comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate in a molar ratio of 12:1 to 1.4:1 and wherein the magnesium oxide is a dead-burned magnesium oxide.
  • the phosphate cement can be a phosphate cement on the basis of essentially any phosphate material conventionally used in phosphate cement and can include phosphate salts such as calcium phosphate, potassium phosphate, magnesium phosphate, sodium phosphate, aluminum phosphate, ammonium phosphate, zinc phosphate, and combinations thereof.
  • phosphate comprises the respective phosphates, hydrogen phosphates and dihydrogen phosphates, wherefrom hydrogen phosphates and dihydrogen phosphates are preferred and dihydrogen phosphates are particularly preferred.
  • phosphates also corresponding pyro- and polyphosphates can be used.
  • the phosphate material in the practice of the invention is not phosphoric acid, as phosphoric acid is a highly corrosive liquid, the handling of which requires special precautions.
  • Particularly preferred phosphate materials for use in the inventive method are alkali metal phosphates such as sodium and potassium phosphate, wherefrom potassium phosphate and especially potassium dihydrogen phosphate is preferred.
  • the phosphate cement preferably contains an earth alkaline oxide, such as calcium oxide (CaO) or magnesium oxide (MgO), wherefrom magnesium oxide is most preferred.
  • an earth alkaline oxide such as calcium oxide (CaO) or magnesium oxide (MgO)
  • the curing/setting speed provided by the magnesium oxide depends on the prior treatment of the same, which determines the degree of crystallinity or lattice energy of the magnesium oxide. If magnesium oxide is treated at higher temperatures, the lattice energy thereof increases (due to disappearance of disordered and amorphous structures in the magnesium oxide) and the surface area decreases, which has the effect that the magnesium oxide becomes less active towards reactions with water. This leads to a lower curing/setting time, when the magnesium oxide is mixed with the phosphate material.
  • the “lattice energy” cannot directly be measured, it has become conventional in the art to define the activity of MgO towards reaction with water by means of the treatment conditions, to which the MgO has been subjected.
  • it is distinguished between natural MgO (which is calcined at about 100°C), caustic MgO (which is calcined at about 700°C to 1100°C), dead-burned MgO (which is calcined at about 1300°C to 1800°C), sintered MgO (which is calcined at about 1500°C to 2200°C) and electro-fused MgO (which is calcined at about 2000°C to 3000°C).
  • dead-burned MgO is used because it provides the best workability window provided.
  • the mineral adhesive in the process of the invention comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate, wherein the magnesium oxide is a dead-burned magnesium oxide, preferably the magnesium oxide was calcined at a temperature of at least 1300°C and at most 1800°C.
  • the molar ratio of magnesium oxide to an alkali metal phosphate is 12:1 to 1.4:1.
  • Struvite is a phosphate mineral with the chemical formula NH4MgPO4-6H2O which crystallizes in an orthorhombic system.
  • the preferred mineral adhesives form struvite structures, wherein the NH4 + -ion is replaced with an alkali metal cation, making it an alkali metal struvite, such as e.g. K-struvite.
  • Suitable retarders for use in the invention comprise e.g. sodium perborate (borax), tartaric acid, and/or buffers. If sodium perborate is used as the retarder, the amount of this agent can be quite small and it is regularly sufficient that the sodium perborate is added in an amount of less than 5 wt. % (based on the dry weight of the mineral adhesive). The effect of tartaric acid as a retarder is less pronounced, so that tartaric acid should be present in an amount of more than 5%, and preferably up to about 10% (based on the dry weight of the mineral adhesive).
  • the mineral adhesive does not comprise a separate retarder.
  • the reaction is retarded by the magnesium oxide itself. This is particularly advantageous, as it reduced the number of components in the formulation of the mineral adhesive.
  • fillers such as sand, in particular as quartz sand, microsilica, fly ash and/or glass fibers. If such fillers are added, it is preferred, however, that their amount is limited to about up to 50 wt.-% (based on the dry weight of the mineral adhesive).
  • the mineral adhesive is devoid of constituents, which can decompose into odorous substances, so that accordingly the mineral adhesive should be substantially devoid of or even fully devoid of ammonium salts.
  • substantially devoid is intended to denote an ammonium salt content of 5 wt.-% or less, preferably 2 wt.-% or less and in even more preferred 1 wt.-% or less.
  • the mineral adhesive is fully devoid of ammonium salts.
  • the phosphate cement is provided as a paste, which is obtained from the mineral adhesive by the addition of water.
  • the amount of water added will regularly be such that a proper paste is formed, where is addition of more water provides a more fluid and the addition of less water a more solid or sticky paste. While the skilled practitioner can thus adjust the amount of water added to his respective needs, it has been found that in most cases pastes with good workability can be obtained with a water/solids ratio of 0.19 to 0.23, and preferably 0.20 to 0.22, wherein the solids encompass all the solid constituents of the mineral adhesive. In some cases, with a water to solids ratio of 0.18, a nice creamy consistence can be obtained which, however, may start to thicken in the mixing container.
  • the substrate, onto which the paste is applied in step (ii) is not particularly limited, even though it has been found the substrates to which advantageous bonding can be provided, include metal substrates (in particular aluminium and/or steel), and substrates from concrete, stone (in particular limestone), wood and plasterboard.
  • a substrate, to which particularly good bonding can be provided even after short curing times is steel, which is therefore a particularly preferred substrate in the process of the invention.
  • Another substrate, to which particularly good bonding can be provided is concrete, which is thus an additional particularly preferred substrate in the inventive process.
  • the mineral adhesive can further contain additives and adjuvants conventional to the art, which include rheological agents, water-retaining agents, airentraining agents, thickening agents, agents for protecting against the growth of algae and fungi, such as biocidal, fungicidal, algicidal or bactericidal agents, dispersing agents, pigments, set-accelerators and/or set- retarders, and also other agents for improving the setting, the curing or the stability of the products after application and in particular for adjusting the color, the workability, the processability or the impermeability.
  • additives and adjuvants conventional to the art, which include rheological agents, water-retaining agents, airentraining agents, thickening agents, agents for protecting against the growth of algae and fungi, such as biocidal, fungicidal, algicidal or bactericidal agents, dispersing agents, pigments, set-accelerators and/or set- retarders, and also other agents for improving the setting, the curing or the
  • planar items to be placed on the paste can be any planar items, but preferably are items to provide an aesthetic of protective benefit to the substrate, to which they are applied.
  • a particular preferred item in this regard is a tile, which can advantageously be a ceramic, stoneware, natural stone or metal tile.
  • Applying of the planar item on the paste involves placing the item on the paste. Preferably, it also involves slightly impressing the item into the paste to increase the contact surface between the two.
  • the amount of paste to be applied onto the substrate will regularly be as small as possible to provide adequate bonding of the item. For most substrates a thickness of about 3 mm will be sufficient to compensate for differences in height thereof, so that preferably the paste is applied in a thickness of ⁇ 3 mm on the substrate.
  • the thickness designates the average thickness of the applied paste i.e. a paste, which is applied with a forked scraper can have a maximum height of the applied paste in excess of 3 mm, as the paste is not applied on the entire surface of the substrate, but the average height of the applied paste can still be less than 3 mm.
  • a particular advantage of the use of the mineral adhesive in the process of the invention is that good bonding can be provided without prior preparative processing of the substrate (e.g. by application of a primer or other preparatory coating thereon).
  • the substrate is not processed or primed prior to application of the mineral adhesive.
  • the present invention concerns a mineral adhesive on the basis of phosphate cement, which comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate, in particular an alkali metal dihydrogen phosphate, in a molar ratio of 12:1 to 1 .4:1 , wherein the magnesium oxide is a dead-burned magnesium oxide.
  • a mineral adhesive on the basis of phosphate cement, which comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate, in particular an alkali metal dihydrogen phosphate, in a molar ratio of 12:1 to 1 .4:1 , wherein the magnesium oxide is a dead-burned magnesium oxide.
  • such mineral adhesives provide short curing times, while avoiding a complex preparation process, as both magnesium oxide and alkali metal phosphates are solid substances, which can simply be physically mixed.
  • the mineral adhesive comprises magnesium oxide and alkali metal phosphate in a molar ratio in the range of 2.5:1 to 1.5:1 and in particular 2.1 :1 to 1 .7:1 .
  • the alkali metal phosphate is an alkali metal dihydrogen phosphate and in particular potassium dihydrogen phosphate.
  • the struvite forming mixture is a potassium struvite forming mixture (K-struvite forming mixture).
  • the mineral adhesive does not comprise a retarder.
  • a yet further aspect of the present invention is a composite structure, which comprises a substrate, a tile layer of one or more tiles and a layer of a cured mineral adhesive as described in detail above, which is disposed between the substrate and the tile layer.
  • a layer is meant to denote material or substance that covers a surface of another (e.g. a mineral adhesive covering a substrate and/or one or more tiles covering a mineral adhesive).
  • a layer has a thickness. It can be distinguished from another layer on account of a different composition and/or texture.
  • the substrate is devoid of a primer.
  • this composite structure exhibits an adhesive tensile strength, when measured according to DIN EN 1348:2007 after 24 h curing at (23 °C and 50 % humidity) of at least 0.5 N/mm 2 , more preferably of least 0.7 N/mm 2 and even more preferably in the range of from 0.9 to 1 ,9 N/mm 2 between substrate and mineral adhesive and/or between mineral adhesive and tile.
  • the inventive mineral adhesive provides for an unexpected improvement of the adhesive tensile strength between substrates and tiles, which are applied thereon.
  • a yet further aspect of the present invention is the use of a mineral adhesive as described above for improving the adhesive tensile strength of an adhesive joint between a substrate and one or more tiles.
  • a mixture of potassium dihydrogen phosphate (KH2PO4) and MgO (dead burned grade) in a molar ratio of 1 :1 ,75 was used as the inventive mineral adhesive.
  • the mineral adhesive was mixed with water in a water/solids ratio of 0.22 (22 parts by weight water on 100 parts by weight of dry adhesive) and applied to a metal, wood or pre-dried concrete substrate in a thickness of 3 mm.
  • testing tiles were bonded to a metal substrate or pre-dried concrete substrate with the inventive mineral adhesive.
  • the testing tiles were pressed onto the surface with a weight of 2000 g for 30 sec.
  • the composite structure was cured/set for 24 hours.
  • Metal test anchors/pull head plates were then adhered to the testing tiles using MC-Quicksolid adhesive.
  • a conventional C2FE adhesive and a C2TES1 adhesive were prepared and tested on a substrate of pre-dried concrete.
  • C2FE and C2TES1 refer to adhesive qualities as specified in DIN EN 12004:2013.
  • the letters C, D and R refer to the general composition, C being cementitious.
  • the numbers 1 and 2 refer to normal or improved adhesive (meets requirements for additional characteristics) and the letters F, T, E and S refer to various characteristics of the adhesive, such as fast setting (E), reduced slip (T), extended open time (E), deformability (S, S1 being deformable and S2 being highly deformable). All test specimens were subjected to tensile testing according to DIN EN 1348:2007.
  • an adhesive tensile strength of 0.75 N/mm 2 on the metal substrate and of 0.75 N/mm 2 on the concrete substrate was determined.
  • the crack of the bond was is both cases primarily between the phosphate cement and tile.
  • the conventional tile adhesive in C2FE and C2TES1 quality in comparison provided adhesive tensile strength values of 1 .0 and 0.4 N/mm 2 on concrete, respectively.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Adhesives Or Adhesive Processes (AREA)
  • Curing Cements, Concrete, And Artificial Stone (AREA)
  • Finishing Walls (AREA)

Abstract

The invention concerns a process for the adhesive attachment of planar items on various substrates, which employ a mineral adhesive on the basis of phosphate cement. Such adhesives allow for a fast and stable attachment of the planar items and in particular of tiles to substrates without the necessity of a pretreatment or priming step. The invention is further concerned with corresponding mineral adhesives, composite structures prepared from substrates, the mineral adhesive and tiles and the use of the mineral adhesive for improving the tensile strength of an adhesive joint between a substrate and one or more tiles.

Description

Phosphate cement based mineral adhesive
The invention concerns a process for the adhesive attachment of planar items on various substrates, which employ a mineral adhesive on the basis of phosphate cement. Such adhesives allow for a fast and stable attachment of the planar items and in particular of tiles to substrates without the necessity of a pretreatment or priming step. The invention is further concerned with corresponding mineral adhesives, composite structures prepared from substrates, the mineral adhesive and tiles and the use of the mineral adhesive for improving the tensile strength of an adhesive joint between a substrate and one or more tiles.
State of the art
Most mineral tile adhesives are based on Portland cement. These Portland cement based adhesives are associated with health risks, mainly because wet Portland cement is highly alkaline and can cause serious burns during handling. It can also cause allergic skin reactions and dermatitis.
Phosphate cement as a binder is well known in the art. Especially in dental applications, phosphate cement, mostly as zinc phosphate cement, has long been used for the attachment of tooth crowns or as underfilling with good thermal and chemical insulation or as provisional filling.
Phosphate cement has also previously been described as a binder in mortars and concrete and has in particular been used for the repair of runways for planes or the sealing of radioactive waste, where properties such as the compressive strength or the flexural tension are of particular importance. In terms of environmental sustainability, phosphate cements, particularly magnesium phosphate cements (MCP), such as magnesium potassium phosphate (MKPC) have a lower carbon footprint compared to e.g. Portland cement.
CONFIRMATION COPY However, many applications of various phosphate cements require retarders that are problematic under the European REACH Directive, such as boric acid. Others have complex preparation processes. Yet others rely on ammonium with the associated odor concerns, once the ammonium degrades and releases ammonia (NH3).
It is the objective of this invention to provide an alternative and simplified mineral adhesive for the attachment of planar items such as tiles to a substrate which preferably can be prepared simply from a physical mixture of solid precursors by addition of water, and which is substantially or even fully devoid for constituents which can decompose into odorous substances. It is a further objective of the invention to reduce the works steps involved in bonding planar items to a substrate and thus provide a more economical type of bonding. This can be accomplished by bypassing the priming step. It is yet a further objective of this invention to provide mineral adhesive, particularly for bonding tiles, that has less health risk potential. In particular, the inventive mineral adhesive does not cause skin burns.
In addition, there is a need for a fast curing mineral adhesive, which provides a secure bond after a comparatively short time. This is particularly important for bonding the increasingly heavy planar items, such as e.g. large stoneware tiles.
The present application addresses these objectives and needs.
Detailed description of the invention
In the investigations underlying the present invention, it has unexpectedly been found that these objectives can be achieved by using a phosphate cement on the basis of a physical mixture of precursor constituents of the phosphate cement. In this connection, the term “physical mixture” is intended to denote a mixture obtained from mixing individual powders of the phosphate cement in the dry form, so that each solid particle in the mixture is primarily constituted form only one precursor of the phosphate cement. That is, the term “physical mixture” is intended to delimit from mixed particles, such as those obtained by absorbing a solution of one material on another and drying the same.
Accordingly, in a first aspect, the present invention concerns a process for adhesively attaching one or more planar items to a substrate comprising the steps of: (i) mixing a mineral adhesive on the basis of phosphate cement with water to provide a paste, wherein the mineral adhesive is a physical mixture of precursor constituents of the phosphate cement;
(ii) applying the paste to the substrate; and
(iii) placing one or more planar items on the paste and curing the composite thus prepared, characterized in that the mineral adhesive comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate in a molar ratio of 12:1 to 1.4:1 and wherein the magnesium oxide is a dead-burned magnesium oxide.
The phosphate cement can be a phosphate cement on the basis of essentially any phosphate material conventionally used in phosphate cement and can include phosphate salts such as calcium phosphate, potassium phosphate, magnesium phosphate, sodium phosphate, aluminum phosphate, ammonium phosphate, zinc phosphate, and combinations thereof. Here, the term “phosphate” comprises the respective phosphates, hydrogen phosphates and dihydrogen phosphates, wherefrom hydrogen phosphates and dihydrogen phosphates are preferred and dihydrogen phosphates are particularly preferred. In addition to phosphates, also corresponding pyro- and polyphosphates can be used. The phosphate material in the practice of the invention is not phosphoric acid, as phosphoric acid is a highly corrosive liquid, the handling of which requires special precautions. Particularly preferred phosphate materials for use in the inventive method are alkali metal phosphates such as sodium and potassium phosphate, wherefrom potassium phosphate and especially potassium dihydrogen phosphate is preferred.
As an alkaline component, the phosphate cement preferably contains an earth alkaline oxide, such as calcium oxide (CaO) or magnesium oxide (MgO), wherefrom magnesium oxide is most preferred. In connection with magnesium oxide, it has been observed during the investigations leading to this invention, that the curing/setting speed provided by the magnesium oxide depends on the prior treatment of the same, which determines the degree of crystallinity or lattice energy of the magnesium oxide. If magnesium oxide is treated at higher temperatures, the lattice energy thereof increases (due to disappearance of disordered and amorphous structures in the magnesium oxide) and the surface area decreases, which has the effect that the magnesium oxide becomes less active towards reactions with water. This leads to a lower curing/setting time, when the magnesium oxide is mixed with the phosphate material.
As the “lattice energy” cannot directly be measured, it has become conventional in the art to define the activity of MgO towards reaction with water by means of the treatment conditions, to which the MgO has been subjected. In this regard, it is distinguished between natural MgO (which is calcined at about 100°C), caustic MgO (which is calcined at about 700°C to 1100°C), dead-burned MgO (which is calcined at about 1300°C to 1800°C), sintered MgO (which is calcined at about 1500°C to 2200°C) and electro-fused MgO (which is calcined at about 2000°C to 3000°C). In the practice of the inventive process, dead-burned MgO is used because it provides the best workability window provided.
The mineral adhesive in the process of the invention comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate, wherein the magnesium oxide is a dead-burned magnesium oxide, preferably the magnesium oxide was calcined at a temperature of at least 1300°C and at most 1800°C. In addition, the molar ratio of magnesium oxide to an alkali metal phosphate is 12:1 to 1.4:1. Struvite is a phosphate mineral with the chemical formula NH4MgPO4-6H2O which crystallizes in an orthorhombic system. The preferred mineral adhesives form struvite structures, wherein the NH4+-ion is replaced with an alkali metal cation, making it an alkali metal struvite, such as e.g. K-struvite.
To adjust and fine-tune the reactivity and curing/setting speed of the mineral adhesive, the same can be modified with a retarder. Suitable retarders for use in the invention comprise e.g. sodium perborate (borax), tartaric acid, and/or buffers. If sodium perborate is used as the retarder, the amount of this agent can be quite small and it is regularly sufficient that the sodium perborate is added in an amount of less than 5 wt. % (based on the dry weight of the mineral adhesive). The effect of tartaric acid as a retarder is less pronounced, so that tartaric acid should be present in an amount of more than 5%, and preferably up to about 10% (based on the dry weight of the mineral adhesive).
In a further embodiment, the mineral adhesive does not comprise a separate retarder. In this case, the reaction is retarded by the magnesium oxide itself. This is particularly advantageous, as it reduced the number of components in the formulation of the mineral adhesive.
In addition, it is also possible to incorporate fillers such as sand, in particular as quartz sand, microsilica, fly ash and/or glass fibers. If such fillers are added, it is preferred, however, that their amount is limited to about up to 50 wt.-% (based on the dry weight of the mineral adhesive).
As noted above, it is preferred that the mineral adhesive is devoid of constituents, which can decompose into odorous substances, so that accordingly the mineral adhesive should be substantially devoid of or even fully devoid of ammonium salts. Here, “substantially devoid” is intended to denote an ammonium salt content of 5 wt.-% or less, preferably 2 wt.-% or less and in even more preferred 1 wt.-% or less. Most preferably, the mineral adhesive is fully devoid of ammonium salts.
As noted above, the phosphate cement is provided as a paste, which is obtained from the mineral adhesive by the addition of water. As the skilled practitioner will understand, the amount of water added will regularly be such that a proper paste is formed, where is addition of more water provides a more fluid and the addition of less water a more solid or sticky paste. While the skilled practitioner can thus adjust the amount of water added to his respective needs, it has been found that in most cases pastes with good workability can be obtained with a water/solids ratio of 0.19 to 0.23, and preferably 0.20 to 0.22, wherein the solids encompass all the solid constituents of the mineral adhesive. In some cases, with a water to solids ratio of 0.18, a nice creamy consistence can be obtained which, however, may start to thicken in the mixing container.
The substrate, onto which the paste is applied in step (ii) is not particularly limited, even though it has been found the substrates to which advantageous bonding can be provided, include metal substrates (in particular aluminium and/or steel), and substrates from concrete, stone (in particular limestone), wood and plasterboard. A substrate, to which particularly good bonding can be provided even after short curing times is steel, which is therefore a particularly preferred substrate in the process of the invention. Another substrate, to which particularly good bonding can be provided is concrete, which is thus an additional particularly preferred substrate in the inventive process. In addition, the mineral adhesive can further contain additives and adjuvants conventional to the art, which include rheological agents, water-retaining agents, airentraining agents, thickening agents, agents for protecting against the growth of algae and fungi, such as biocidal, fungicidal, algicidal or bactericidal agents, dispersing agents, pigments, set-accelerators and/or set- retarders, and also other agents for improving the setting, the curing or the stability of the products after application and in particular for adjusting the color, the workability, the processability or the impermeability.
The planar items to be placed on the paste, can be any planar items, but preferably are items to provide an aesthetic of protective benefit to the substrate, to which they are applied. A particular preferred item in this regard is a tile, which can advantageously be a ceramic, stoneware, natural stone or metal tile.
Applying of the planar item on the paste involves placing the item on the paste. Preferably, it also involves slightly impressing the item into the paste to increase the contact surface between the two.
The amount of paste to be applied onto the substrate will regularly be as small as possible to provide adequate bonding of the item. For most substrates a thickness of about 3 mm will be sufficient to compensate for differences in height thereof, so that preferably the paste is applied in a thickness of < 3 mm on the substrate. In this regard, the thickness designates the average thickness of the applied paste i.e. a paste, which is applied with a forked scraper can have a maximum height of the applied paste in excess of 3 mm, as the paste is not applied on the entire surface of the substrate, but the average height of the applied paste can still be less than 3 mm.
As noted above, a particular advantage of the use of the mineral adhesive in the process of the invention is that good bonding can be provided without prior preparative processing of the substrate (e.g. by application of a primer or other preparatory coating thereon). Thus, in a preferred embodiment of the inventive process the substrate is not processed or primed prior to application of the mineral adhesive.
In a second aspect-, the present invention concerns a mineral adhesive on the basis of phosphate cement, which comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate, in particular an alkali metal dihydrogen phosphate, in a molar ratio of 12:1 to 1 .4:1 , wherein the magnesium oxide is a dead-burned magnesium oxide. As noted above, such mineral adhesives provide short curing times, while avoiding a complex preparation process, as both magnesium oxide and alkali metal phosphates are solid substances, which can simply be physically mixed.
In a preferred embodiment, the mineral adhesive comprises magnesium oxide and alkali metal phosphate in a molar ratio in the range of 2.5:1 to 1.5:1 and in particular 2.1 :1 to 1 .7:1 . Alternatively, or in addition thereto, it is preferred that the alkali metal phosphate is an alkali metal dihydrogen phosphate and in particular potassium dihydrogen phosphate. Preferably, the struvite forming mixture is a potassium struvite forming mixture (K-struvite forming mixture).
In another preferred embodiment, the mineral adhesive does not comprise a retarder.
A yet further aspect of the present invention is a composite structure, which comprises a substrate, a tile layer of one or more tiles and a layer of a cured mineral adhesive as described in detail above, which is disposed between the substrate and the tile layer. A layer is meant to denote material or substance that covers a surface of another (e.g. a mineral adhesive covering a substrate and/or one or more tiles covering a mineral adhesive). A layer has a thickness. It can be distinguished from another layer on account of a different composition and/or texture.
In a preferred embodiment the composite structure presented above, the substrate is devoid of a primer.
In another preferred embodiment, this composite structure exhibits an adhesive tensile strength, when measured according to DIN EN 1348:2007 after 24 h curing at (23 °C and 50 % humidity) of at least 0.5 N/mm2, more preferably of least 0.7 N/mm2 and even more preferably in the range of from 0.9 to 1 ,9 N/mm2 between substrate and mineral adhesive and/or between mineral adhesive and tile.
As noted above, it has unexpectedly been found by the present inventors that the inventive mineral adhesive provides for an unexpected improvement of the adhesive tensile strength between substrates and tiles, which are applied thereon. Thus, a yet further aspect of the present invention is the use of a mineral adhesive as described above for improving the adhesive tensile strength of an adhesive joint between a substrate and one or more tiles. With regard to the above, it is noted that any combination of features is deemed to be encompassed by the present disclosure even if this combination is not explicitly described, except where the combination of features leads to obvious contradictions.
In the following, the present invention will further be illustrated by means of examples, which should however not be construed as limiting in any way to the scope of this application.
Examples
Example 1
To test the adhesion of the mineral adhesive to the substrate, a mixture of potassium dihydrogen phosphate (KH2PO4) and MgO (dead burned grade) in a molar ratio of 1 :1 ,75 was used as the inventive mineral adhesive. The mineral adhesive was mixed with water in a water/solids ratio of 0.22 (22 parts by weight water on 100 parts by weight of dry adhesive) and applied to a metal, wood or pre-dried concrete substrate in a thickness of 3 mm. After 24 hours, test anchors/pull head plates were glued to the set mineral adhesive (using MC-Quicksolid = a bonding adhesive for pull-off tests, MC- Bauchemie Muller GmbH & Co. KG) and the test specimens were subjected to tensile testing according to DIN EN 12004:2013.
The results of these tests as well as the type of crack formation is provided in the Table 1.
Table 1 The letters A and C differentiate the type of failure or crack: A = adhesive failure between the mineral adhesive and pull-head plate C = cohesive failure (within the mineral adhesive). * = highest and lowest values were excluded.
Example 2
To test the adhesion capabilities of the mineral adhesive to both the substrate and testing tiles, testing tiles were bonded to a metal substrate or pre-dried concrete substrate with the inventive mineral adhesive. After application of the mineral adhesive (which was applied in a thickness of about 3 mm), the testing tiles were pressed onto the surface with a weight of 2000 g for 30 sec. The composite structure was cured/set for 24 hours. Metal test anchors/pull head plates were then adhered to the testing tiles using MC-Quicksolid adhesive. For comparison, a conventional C2FE adhesive and a C2TES1 adhesive were prepared and tested on a substrate of pre-dried concrete. C2FE and C2TES1 refer to adhesive qualities as specified in DIN EN 12004:2013. The letters C, D and R refer to the general composition, C being cementitious. The numbers 1 and 2 refer to normal or improved adhesive (meets requirements for additional characteristics) and the letters F, T, E and S refer to various characteristics of the adhesive, such as fast setting (E), reduced slip (T), extended open time (E), deformability (S, S1 being deformable and S2 being highly deformable). All test specimens were subjected to tensile testing according to DIN EN 1348:2007.
For the inventive mineral adhesive an adhesive tensile strength of 0.75 N/mm2 on the metal substrate and of 0.75 N/mm2 on the concrete substrate was determined. The crack of the bond was is both cases primarily between the phosphate cement and tile. The conventional tile adhesive in C2FE and C2TES1 quality in comparison provided adhesive tensile strength values of 1 .0 and 0.4 N/mm2 on concrete, respectively.

Claims

Claims
1 . Process for adhesively attaching one or more planar items to a substrate comprising the steps of:
(i) Mixing a mineral adhesive on the basis of phosphate cement with water to provide a paste, wherein the mineral adhesive is a physical mixture of precursor constituents of the phosphate cement;
(ii) Applying the paste to the substrate; and
(iii) Placing one or more planar items on the paste and curing the composite thus prepared, characterized in that the mineral adhesive comprises a struvite forming mixture of magnesium oxide and an alkali metal phosphate in a molar ratio of 12:1 to 1 .4:1 and wherein the magnesium oxide is a dead-burned magnesium oxide.
2. Process according to claim 1 wherein the substrate is not primed prior to application of the mineral adhesive.
3. Process according to claim 1 or 2, wherein water is added in a water/solids ratio of 0.19 to 0.23, preferably from 0.20 to 0.22, based on the solid constituents of the mineral adhesive.
4. Process according to any one of claims 1 to 3, wherein the substrate is selected from metal, concrete, stone, wood, plasterboard, preferably steel and/or aluminium.
5. Process according to any one of the preceding claims, wherein the one or more planar items are tiles, preferably ceramic tiles, stoneware tiles, natural stone tiles, or metal tiles.
6. Process according to any one of the preceding claims, wherein the paste is applied in a thickness of < 3 mm on the substrate.
7. Process according to any one of the preceding claims, wherein the mineral adhesive does not comprise a separate retarder.
8. Mineral adhesive on the basis of phosphate cement, comprising a struvite forming mixture of magnesium oxide and an alkali metal phosphate, in particular an alkali metal dihydrogen phosphate, in a molar ratio of 12:1 to 1.4:1 , wherein the magnesium oxide is a dead-burned magnesium oxide.
9. Mineral adhesive according to claim 8, wherein the magnesium oxide to alkali metal phosphate ratio is in the range of from 2.5:1 to 1 .5:1 and preferably 2.1 :1 to 1 .7:1 .
10. Mineral adhesive according to claim 8 or 9, wherein the alkali metal dihydrogen phosphate is potassium dihydrogen phosphate and/or the struvite forming mixture is a potassium struvite forming mixture.
11. Mineral adhesive according to any one of the claims 8 to 10, wherein the mineral adhesive does not comprise a retarder.
12. Composite structure comprising a substrate, a tile layer of one or more tiles and a layer of a cured mineral adhesive according to any one of claims 8 to 11 , which is disposed between the substrate and the tile layer.
13. Composite structure according to claim 12 characterized in that the substrate is devoid of a primer.
14. Composite structure according to claim 12 or 13, which exhibits an adhesive tensile strength, when measured according to DIN EN 1348:2007 of at least 0.5 N/mm2, preferably of least 0.7 N/mm2 and in particular in the range of from 0.9 to 1 .9 N/mm2.
15. Use of a mineral adhesive according to any one of claims 8 to 11 for improving the adhesive tensile strength of an adhesive joint between a substrate and one or more tiles.
EP20815712.3A 2020-11-12 2020-11-12 Phosphate cement based mineral adhesive Pending EP4244196A1 (en)

Applications Claiming Priority (1)

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PCT/EP2020/000191 WO2022100808A1 (en) 2020-11-12 2020-11-12 Phosphate cement based mineral adhesive

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA2927337C (en) * 2013-10-14 2022-06-14 Certain Teed Gypsum, Inc. Struvite-k and syngenite composition for use in building materials
CN105837159A (en) * 2016-03-18 2016-08-10 派丽(上海)管理有限公司 High-performance neutral tile bonding material

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