Starch-based tile adhesive

Abstract

The present invention provides a starch-based tile adhesive comprising a substituted starch and a filler, in which a limited amount of cement may be present, but which preferably does not comprise cement. The invention also provides a method for providing the tile adhesive, as well as a method for paving using the adhesive, and a surface of a tile provided by using the adhesive.

Description

Technical Field

[0001] The invention belongs to the field of tile adhesives. Background Art

[0002] The current focus on sustainability and reducing carbon footprints has led the construction industry to research more sustainable alternatives to common building materials. Traditionally, dry-mix tile adhesives used to attach tiles to surfaces such as walls have been based on cement. Cement production is associated with high energy requirements and a high carbon footprint. Cement itself cannot be truly recycled; that is, its adhesive properties cannot generally be reused due to the fact that cement hardening is an irreversible chemical process.

[0003] Cement-based tile adhesives typically contain approximately 25% to 40% by weight of cement as a binder, 60% to 75% by weight of sand as a filler, and approximately 0.15% to 0.50% by weight of a cellulose derivative as a water-retention aid. Cement Types I (normal Portland cement) and II are typically used in tile adhesives.

[0004] To prevent sagging of tiles during application, a small amount (approximately 0.05-0.25 wt%) of starch ether can be added to cement-based tile adhesives. The starch ether binds between cement particles, thereby imparting yield stress to the tile adhesive. This provides the advantage that, during placement of the tile on the surface, the tile remains in place without sagging until the cement hardens. In such applications, the starch ether does not contribute to the adhesion of the tile to the surface. In such applications, the weight ratio of cement to starch ether is typically in the range of at least 100 or higher.

[0005] Cement-based tile adhesives have several disadvantages. The pot life, also known as working time (the length of time the adhesive remains workable after mixing it with water), is limited to one to four hours. After this time, the adhesive begins to set. Cement-based tile adhesives have an even shorter open time. This refers to the time between applying a layer of tile adhesive to a surface and the start of tiling. Therefore, cement-based tile adhesives must be used and applied relatively quickly. Furthermore, excess tile adhesive can remain after application and cannot be reused or stored.

[0006] Furthermore, after the cement-based adhesive has hardened, the equipment used to hold the cement-based adhesive cannot be reused because hardening is an irreversible process; therefore, equipment that has not been cleaned promptly must be discarded.

[0007] However, cleaning equipment also presents its own challenges. Cement particles are hard and heavy, making it very likely that cleaning water will clog sewage systems. In many cases, cleaning waste from cement-based tile adhesive equipment enters the environment directly.

[0008] Generally, the use of cement-based tile adhesives generates a lot of waste due to the rapid and irreversible hardening and non-recyclability of the material and the fact that the installers tend to mix excess material.

[0009] Furthermore, cement-based tile adhesives typically have a pH of approximately 13. Skin contact with cement compositions having a pH of 13 may result in dryness and irritation, and inhalation of such compositions may cause lung problems. This presents a problem for construction workers, as all contact with cement-based tile adhesives is difficult, if not impossible, to avoid.

[0010] Furthermore, cement contains chromium-6, which is suspected of causing various health problems, such as skin allergies, cancer, and reduced fertility. Chromium-6 can be rendered harmless in cement by adding a reducing agent. When mixed with water, the reducing agent converts the chromium-6 into harmless chromium-3. However, current reducing agents have a limited shelf life, which also limits the shelf life of cement.

[0011] Starch is a naturally occurring polymer of glucose. Starch exists in the form of granules, which are particles roughly 1 micron to 100 microns in size. Naturally occurring starch granules are often referred to as native starch.

[0012] Natural starch contains two types of glucose polymers: amylose and amylopectin. Amylose is a linear glucose polymer, and amylopectin is a branched glucose polymer. Conventional natural potato starch contains approximately 20-25% by weight of amylose and 75-80% by weight of amylopectin.

[0013] Starches rich in amylopectin are well known. Such starches (commonly referred to as amylopectin) contain at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of amylopectin. Amylopectin may also be referred to as "waxy starch".

[0014] Starch granules include amylopectin and amylose in crystalline and amorphous regions. Starch granules are insoluble in water at room temperature. Glucose polymers can be released from the granules and dissolved individually by a process called gelatinization. Gelatinized starch is starch that has been subjected to a gelatinization process: sufficient heat is applied, preferably in combination with shearing of the starch granules in water, which results in the dissolution of the starch. The dissolved starch can then be dried to provide a gelatinized starch powder ("pregelatinized starch") that is readily soluble in water at room temperature. Summary of the Invention

[0015] The present invention provides a tile adhesive in which tile to wall adhesion is achieved by gelatinization instead of starch. This overcomes the above problems and even unexpectedly provides better adhesive performance than traditional cement-based tile adhesives.

[0016] The present invention provides a tile adhesive comprising a substituted starch and a filler, wherein the weight ratio of cement to substituted starch is 0-2. Preferably, the present invention provides a cement-free tile adhesive (the weight ratio of cement to substituted starch is 0). The phrases "weight ratio" and "mass ratio" refer to the same concept and are used interchangeably.

[0017] The tile adhesive of the present invention has the advantage of being a fully renewable binder. Due to the reduced energy requirements for adhesive production and the adhesive's biodegradability, its use has a much lower environmental impact. The tile adhesive of the present invention has a longer pot life and working time, which offers several advantages. It allows larger quantities to be prepared at once, which can be stored and applied over extended periods of time. Excess material can be stored and reused. Furthermore, the much longer open time allows tilers to work under fewer time constraints or apply the adhesive to larger surface areas compared to traditional cement-based tile adhesives. Furthermore, the adhesive can be formulated at any desired pH, resulting in a reduced risk of contact exposure. Compared to traditional cement-based tile adhesives, the tile adhesive of the present invention is more user-friendly.

[0018] Equipment used to apply tiles using the adhesive of the present invention does not need to be discarded, but can be cleaned with water. Any discarded adhesive or cleaning waste is non-polluting. Thus, the tile adhesive of the present invention reduces waste compared to conventional cement-based tile adhesives.

[0019] Thus, the pot life and open time of the tile adhesive of the present invention are much longer than for conventional cement-based adhesives, the adhesion strength is higher, and the tile adhesive of the present invention results in less waste and is more user-friendly.

[0020] The tile adhesive of the present invention is an adhesive for attaching ceramic tiles to surfaces. Ceramic tiles are building materials used for aesthetic or practical purposes that can be attached to surfaces such as walls or floors in a process known as tiling. In the context of the present invention, the tile adhesive is preferably an adhesive for indoor tile tiling. Further preferably, the tile adhesive is used in indoor dry rooms, or at least in dry parts of indoor rooms. A dry room is any room in which the amount of water does not exceed that of normal living conditions. A dry room can be, for example, a living room, a hallway, or an office. By definition, a dry room is distinguished from a wet room: a room (or part of it) in which water is present in large quantities. Wet rooms generally include room types such as (part of) a kitchen or (part of) a bathroom.

[0021] Ceramic tiles are a well-known building material. Any type of tile can be laid using the present invention. Generally, tiles are generally flat objects, meaning that the thickness (or, for some tile forms, the maximum thickness) is preferably less than 20% of the longest linear diameter, and more preferably less than 10%. Tiles can have any shape, although in most cases they are square or rectangular. Tiles can be made of any material. However, preferably, the tiles used for laying using the tile adhesive of the present invention are stone, natural stone, or ceramic tiles.

[0022] The ceramic tile may have a porosity, expressed as water absorption, between 0.01% and 25% by weight. In a preferred embodiment, the ceramic tile may have a water absorption between 0.2% and 20% by weight. In an alternative preferred embodiment, the ceramic tile may have a water absorption equal to or less than 0.5% by weight. In another preferred embodiment, the ceramic tile may have a water absorption of 10% to 20% by weight, preferably 12% to 18% by weight. In a further preferred embodiment, the water absorption may exceed 15% by weight.

[0023] Tiling is the process of attaching ceramic tiles to a surface. In the tiling process, which is well known in the art, tile adhesive is applied to the surface on which the tile is to be placed, and / or to the tile to be attached to the surface, preferably in a more or less uniform layer. The tile is then placed on the surface with the adhesive layer between the tile and the surface. The adhesive is then allowed to harden ("dry"). The tile is then firmly attached; if the tile adhesive meets generally accepted adhesion requirements, the tile cannot be removed without considerable force. In the present invention, the term "hardening" is used for this process, which results in a solid-state attachment of the tile to the surface. Hardening of the tile adhesive can be achieved by chemical and / or physical processes.

[0024] The force required to remove a tile and hence the adhesion strength is the subject of various standards. In the European standard EN 12004, for the highest quality (C2) tile adhesives, the adhesion must be at least 1 N / mm 2; For lower quality (C1) tile adhesives, the adhesion strength must be at least 0.5 N / mm 2 This standard is based on a specific type of tile: Winckelmans tiles, which have a water absorption of less than 0.5% by weight. The well-known standard EN 12004 is used throughout this document when referring to "adhesion strength".

[0025] The tile adhesives of the present invention include substituted starches. Substituted starch in the context of the present invention is defined as starch carrying one or more substituents, wherein each substituent is attached to the starch via an ether, ester or carbamate bond via one starch hydroxyl group on one starch glucose group. Thus, a substituted starch is a starch in which a group of atoms (the substituent) is substituted on a starch glucose group via an ester, ether or carbamate bond, wherein the group of atoms is not covalently bonded to a different starch glucose group. A substituted starch is a starch substituted by a group of atoms via an ether, ester or carbamate bond, wherein the group of atoms is attached to the starch via a covalent bond at one starch glucose group. A substituted starch is a starch in which a group of atoms is substituted via an ether, ester or carbamate bond, wherein the group of atoms is attached to the starch via a covalent bond to one starch glucose group.

[0026] In the context of the present invention, starch substitution does not provide crosslinking, although for some applications, the substituted starch may optionally be additionally crosslinked using a crosslinking agent such as defined elsewhere in order to fine-tune the rheology of the tile adhesive. The substituted starch is the product of a reaction between starch and a monofunctional electrophile suitable for use in a nucleophilic substitution or addition reaction.

[0027] Substituted starch can be obtained by reacting activated starch, for example using an alkaline catalyst, with a reagent characterized by the presence of an electrophilic group (suitable for nucleophilic displacement), such as an aldehyde group, an activated carboxylic acid group (such as an anhydride, an acid chloride or a vinyl ester), an epoxy group or a haloalkyl group. The reaction products are starch ethers, starch esters or starch carbamates (urethanes).

[0028] The reagent used to obtain the substituted starch can also be a reagent for a nucleophilic addition reaction. Suitable reagents are characterized by an activated double bond. This type of addition reaction is also known as a Michael addition. Suitable reagents include acrylonitrile, (meth) acrylic acid, methyl (meth) acrylate, maleic acid, fumaric acid, etc. The reaction product of this addition reaction is a starch ether.

[0029] When starch in solution or starch granules reacts with a monofunctional electrophilic reagent in a nucleophilic substitution or addition reaction as described above, the resulting starch is called a substituted starch. A monofunctional reagent is one that is capable of reacting once with the hydroxyl groups of starch.

[0030] Well-known examples of substituted starches suitable for use in the present invention are carboxymethylated starch, hydroxypropylated starch, hydroxyethylated starch, acetylated starch, succinate starch, octenylsuccinate starch, cationic starch, starch phosphates, preferably carboxymethylated starch, hydroxypropylated starch, hydroxyethylated starch, acetylated starch, succinate starch, octenylsuccinate starch, cationic starch.

[0031] The substituted starch preferably has a degree of substitution of at least 0.01 mol / mol, preferably at least 0.05 mol / mol. For carboxymethylated starch, hydroxybutylated starch, hydroxypropylated starch, hydroxyethylated starch, succinate starch and octenylsuccinate starch, preferably carboxymethylated starch, hydroxypropylated starch and hydroxyethylated starch, the degree of substitution is preferably at least 0.1 mol / mol.

[0032] For hydroxypropylated starch, the degree of substitution is preferably at least 0.1, more preferably at least 0.2, more preferably at least 0.3, most preferably 0.3-5.0, such as 0.3-4.5 mol / mol.

[0033] For carboxymethylated starch, the degree of substitution is preferably at least 0.1, more preferably at least 0.2, most preferably 0.2-3.0, such as 0.2-2.0 or 0.2-1.0 mol / mol.

[0034] For acetylated starch, the degree of substitution is preferably at least 0.05, such as 0.05-2.0 or 0.05-1.0 mol / mol.

[0035] The degree of substitution ("DS") is the amount of agent bound to starch, expressed as moles of bonding agent per mole of anhydrous glucose units (AGU). The molecular weight of 1 mole of AGU is 162 g / mol. Since each AGU has three available hydroxyl groups, the maximum DS is three. The degree of substitution can be measured by methods known in the art to quantify the degree of substitution.

[0036] The DS defined above can be calculated based on the amount of substituents directly attached to the O atom of AGU; the term DS in the context of the present invention is used interchangeably with the concept of "molecular substitution" ("MS"). MS is calculated based on the amount of substituents covalently bonded to starch, either directly to the O atom of AGU or to any bond to a substituent already bonded to AGU, as is well known in the art.

[0037] Well-known examples of modified starches, the degree of substitution of which is expressed as MS and which may have an MS greater than 3, are hydroxyalkylated starches or starches grafted with ethylenically unsaturated monomers. In the case of such substituted starch types, DS in the context of the present invention should therefore be read as MS.

[0038] The tile adhesive of the present invention further comprises a filler. In the context of the present invention, a filler is a solid, inert particulate material. The filler preferably has a particle size (expressed as D50) of at least 1 μm, preferably at least 5 μm, and more preferably at least 10 μm. The particle size of the filler is at most 600 μm, preferably at most 500 μm, more preferably at most 300 μm, and even more preferably at most 175 μm. The particle size distribution of the filler is typically determined by sieve fractionation. Alternatively, laser diffraction of a suspension or dry powder can be used to determine the particle size distribution. As used herein, particle size refers to the particle size determined by sieve fractionation.

[0039] Suitable fillers for use in the tile adhesives of the present invention are generally known fillers used in cement-based tile adhesives. Examples include sand, clay, and calcium carbonate. An additional advantage of the tile adhesives of the present invention is that, in addition to known filler types, other filler types can also be used, such as, for example, granular starch, ground concrete waste, ground plastic waste, ground organic fibers, ground inorganic fibers, and sawdust.

[0040] In alternative embodiments, tile adhesives without fillers are contemplated and also disclosed herein. The sole presence of the substituted starch as a binder is sufficient to adhere the tile to the surface. In such embodiments, the tile adhesive comprises the substituted starch and further optional components, as defined elsewhere.

[0041] In the tile adhesive of the present invention, the weight ratio of cement to substituted starch is 0-2. Cement is a well-known building material used for support and construction. Cement mixed with fine fillers is called mortar; combined with coarse fillers, the mixture is called concrete. Cement itself is typically an inorganic material that hardens through an irreversible chemical reaction with water or carbon dioxide. Cement is typically a material comprising a mixture of silicates and oxides. In some embodiments, the cement may include calcium oxide.

[0042] The tile adhesives of the present invention preferably contain no cement, in which case the weight ratio of cement to substituted starch is 0. However, cement may be present in the tile adhesives of the present invention. This may be advantageous where the consumer prefers the presence of at least some cement, to provide water or water resistance, or where irreversible hardening is desired.

[0043] However, the tile adhesives of the present invention are primarily starch-based tile adhesives, and cement, if present, is also considered an additive to aid bonding, even if substituted starch is used as the primary or main binder. The weight ratio of cement to substituted starch is preferably 0-2.0, more preferably 0-1.5, more preferably 0-1.0, even more preferably 0-0.5, more preferably 0-0.19, even more preferably 0-0.15, and most preferably 0-0.1. Most preferably, the tile adhesives of the present invention do not contain cement.

[0044] In some preferred embodiments, the substituted starch is also a cross-linked starch.That is, the starch used in the tile adhesives of the present invention may have been subjected to both a substitution process, as described elsewhere, and a cross-linking process.

[0045] Starch cross-linking is a process in which starch (in granular form or as a solution) is reacted with a difunctional or polyfunctional electrophilic reagent suitable for nucleophilic substitution or addition reactions. Such difunctional or polyfunctional reagents are called cross-linking agents. The cross-linking agent is capable of reacting at least twice with the starch hydroxyl groups, thereby cross-linking the intramolecular or intermolecular amylose or amylopectin chains. In the context of the present invention, cross-linked starch is different from substituted starch. Cross-linking of the starch used in the present invention can be performed before, during or after the substitution reaction. Methods for substituting and / or cross-linking starch are well known to those skilled in the art. Reference is made to OB Wurzburg, CRC Press, 1986, Modified Starches: Properties and Uses.

[0046] Well-known types of cross-linked starch suitable for use in the tile adhesives of the present invention include epichlorohydrin cross-linked starch, trimetaphosphate cross-linked starch, phosphorus oxychloride cross-linked starch, adipic acid cross-linked starch, or starch cross-linked with di- or polyglycidyl ethers, 1,2-dichloropropanol, dichloroacetic acid, di- or polyepoxide cross-linking agents, di- or polyisocyanates, or di- or tricarboxylic acids or mixtures thereof (e.g., mixtures of adipic acid and acetic anhydride). Additionally, well-known cross-linking agents include glyoxal, zirconium carbonate, borax, and compounds containing multiple aldehyde or epoxy groups. The cross-linked starch preferably has a degree of cross-linking ("DC") of at least 0.0001 mol cross-linking agent per mol starch ("mol / mol").

[0047] The substituted starch used in the tile adhesives of the present invention may also be a degraded starch. Degraded starch is one in which the chain length of the glucose polymers is reduced to achieve a molecular weight lower than that of the original starch. That is, the starch used in the tile adhesives of the present invention may have undergone both a substitution process, as described elsewhere, and a degradation process.

[0048] Starch degradation is well known in the art. See OB Wurzburg, CRC Press, 1986, Modified Starches: Properties and Uses. In preferred embodiments, the starch is chemically degraded starch (preferably acid-degraded starch), physically degraded starch, or enzymatically degraded starch. All of these types of degraded starches and methods for obtaining them are well known in the art.

[0049] In some embodiments, the starch may be degraded, cross-linked, or substituted starch.

[0050] In many preferred embodiments, the starch of the present invention is a cold-water soluble starch, i.e., a pregelatinized starch. Pregelatinized starch is starch that has been rendered cold-water soluble by gelatinization. The starch initially exists as granules that are merely dispersed in water but not dissolved in it. To be effective as an adhesive, the starch must be gelatinized, i.e., present in a dissolved form, upon application. Starch gelatinization can be achieved by the well-known method of (jet) cooking or using other methods well known in the art.

[0051] Preferably, the starch of the present invention has been pregelatinized to make it cold water soluble. Pregelatinization is the gelatinization process of a starch suspension followed by drying to a powder. Pregelatinization can be performed before, during, or after substitution and / or cross-linking.

[0052] In the case of pregelatinized starch, the starch is gelatinized and then dried into starch powder or flakes. Pregelatinization can be achieved using techniques well known in the art, including drum drying, spray drying, spray cooking, and extrusion. Of particular interest are drum drying slurries of granular starch in water or pastes or solutions of gelatinized starch. By drum drying the starch slurry, the starch is dissolved and dried simultaneously on heated drums by shear and temperature.

[0053] By applying a gelatinized starch solution or paste onto a rotating heated drum, a thin dry starch film is produced. Another particularly relevant method for preparing cold-water-soluble substituted starches is starch extrusion. Extrusion can be used to convert granular starch into pregelatinized starch as a result of the heat and shear during extrusion. Extrusion also allows for the simultaneous chemical and physical modification of granular starch into gelatinized, cold-water-soluble substituted starch.

[0054] The pregelatinized starch can be ground and sieved into a powder or flakes. The pregelatinized starch preferably has a particle size of less than 5 mm.

[0055] The substituted starch of the present invention is preferably a pregelatinized starch. In a further preferred embodiment, the substituted starch is a drum-dried starch or an extruded starch. Preferably, the substituted starch can be a pregelatinized and drum-dried starch, or a pregelatinized and extruded starch.

[0056] The substituted starch used in the present invention may be of any origin. Preferably, the substituted starch is a substituted tuber starch, a substituted root starch, a substituted nut starch, a substituted cereal starch, or a substituted legume starch. More preferably, the substituted starch may be a substituted potato starch, a substituted sweet potato starch, a substituted tapioca starch, a substituted corn starch, a substituted wheat starch, or a substituted pea starch.

[0057] The amount of substituted starch used as a binder and filler in the tile adhesive of the present invention is not particularly limited. Generally, the tile adhesive comprises substituted starch in an amount of 2% to 99% by weight, preferably 2.5% to 75% by weight, and more preferably 5% to 50% by weight, relative to the dry weight of the tile adhesive.

[0058] Further generally, the tile adhesive comprises the filler in an amount of 1 wt.-98 wt.-%, preferably 25 wt.-97.5 wt.-%, more preferably 50 wt.-95 wt.-%, expressed relative to the dry weight of the tile adhesive.

[0059] In the tile adhesive of the present invention, the filler / substituted starch mass ratio is preferably 0.25-40, more preferably 0.3-25, even more preferably 1.0-20.

[0060] The filler / total binder mass ratio is greater than 0.5, preferably greater than 1.0. The "total binder" amount refers to the total amount of substituted starch and any further binding material (if present). Further binding materials in this context can be, for example, cement, redispersible powders, synthetic polymers or gums.

[0061] The weight ratio of cement / substituted starch is equal to or less than 2, preferably equal to or less than 1.8, more preferably equal to or less than 1.5, and most preferably in the range of 0 to 1. In another preferred embodiment, the tile adhesive of the present invention does not contain any cement.

[0062] The tile adhesive according to the invention can be provided in the form of a dry mix suitable for mixing with water or in the form of an aqueous tile adhesive composition in which the substituted starch is present in gelatinized form, the aqueous tile adhesive composition having a viscosity of 300 Pa.s to 700 Pa.s as measured using a Brookfield Helipath using spindle TE measured at 4 rpm and 23°C.

[0063] A dry mix is the preferred form for marketing the tile adhesive of the present invention. When the tile adhesive is a dry mix, the substituted starch is preferably pregelatinized. This facilitates mixing the dry mix with water under end-use conditions to obtain a tile adhesive containing dissolved substituted starch. The dry ingredients are as defined above and include at least the substituted starch and a filler.

[0064] Alternatively, the tile adhesive of the present invention can be provided as an aqueous mixture. In the case of an aqueous mixture, the substituted starch can also be in granular form. Before the granular substituted starch is mixed with the other ingredients and ultimately used in the tiling composition, the substituted starch must undergo a gelatinization step. After gelatinization, the gelatinized starch solution is added to the other ingredients, or vice versa. The added ingredients include at least fillers.

[0065] The aqueous tile adhesive composition is the form in which the tile adhesive of the present invention is used for installation. It can be prepared immediately prior to installation by mixing with water, but it can also be prepared industrially on a large scale for sale to the end consumer in suitable containers. In the aqueous tile adhesive composition, the substituted starch is present as gelatinized substituted starch. Preferably, the viscosity of the aqueous tile adhesive composition is 300 Pa·s to 700 Pa·s, as measured using a Brookfield Helipath using Spindle TE at 4 rpm and 23°C. This viscosity is advantageous because at this viscosity, dripping and sagging of the adhesive are minimized, while still making application relatively easy.

[0066] Tile adhesives may further optionally contain various additional ingredients. Suitable ingredients include, by way of non-limiting example, redispersible polymer powder, hydrated lime, gypsum, and water-retaining agents such as cellulose ethers ((HP / HE)-methylcellulose) or guar gum and its derivatives. Other optional ingredients include calcium formate, glass spheres, cellulose fibers, polypropylene fibers, polyethylene terephthalate fibers, polyvinyl alcohol, thickeners, accelerators, retarders, high-range water reducers, water-repellents, hydrophobic agents, air-entraining agents, defoamers, pigments, gelatin, proteins, urea-formaldehyde resins, melamine-formaldehyde resins, and synthetic polymer dispersions.

[0067] Optionally, the tile adhesive may contain additives to increase the water resistance of the finished tile adhesive. Such additives may be hydrophobic agents, network builders or hardeners.

[0068] Hydrophobing agents impart hydrophobicity to tile adhesives. They can be based on additives or emulsions containing fatty acids, or a type of oil, paraffin, or wax. Other suitable hydrophobing agents are aqueous silanes, siloxanes, and silicone resin additives. Similarly, other types are based on synthetic polymer dispersions.

[0069] Network building agents can improve the water resistance of tile adhesives by creating a starch network during or after application of the tile adhesive. Suitable network building agents effect a crosslinking reaction of the starch hydroxyl groups during or after laying using the adhesive of the present invention. Suitable network building agents in the context of the present invention can be crosslinking agents known for their starch crosslinking as discussed elsewhere, which allow the crosslinking reaction to occur under the conditions of tile adhesive application (i.e., at ambient temperature in an aqueous environment). One suitable network building agent is glyoxal. Other suitable starch network building agents are zirconium carbonate, borax, and compounds containing multiple aldehyde or epoxy groups.

[0070] Alternatively, a hardener may be added to induce network formation during or after laying. For this purpose, proteins such as gelatin or network-forming resins such as urea-formaldehyde resin or melamine-formaldehyde resin may be added. A further suitable hardener is water glass.

[0071] Tile adhesives may include synthetic binders such as acrylic resins. Preferably, the tile adhesives of the present invention do not contain more than 15% by weight (relative to the dry matter of the total composition) of synthetic binders. In a very preferred embodiment, the adhesives of the present invention do not contain synthetic binders.

[0072] The present invention also provides a method for preparing a tile adhesive as defined above, comprising the following steps, in any order: providing a solution of a substituted starch in water, and homogenizing the dry ingredients in water at a water / total dry ingredients mass ratio of 0.1 to 5. The end use of the tile adhesive according to the invention is based on an aqueous tile adhesive composition in which the substituted starch is present in dissolved form as gelatinized substituted starch.

[0073] In either option, the dry ingredients are mixed with water at a water / total dry ingredients mass ratio of 0.1-5, preferably 0.2-4, more preferably 0.3-3. This mass ratio ensures that the mixture obtained after homogenization has an appropriate viscosity. The dry ingredients are as defined above and include at least the substituted starch and the filler.

[0074] The preferred viscosity for the end use of the tile adhesive of the invention is 300 Pa.s to 700 Pa.s as measured with a Brookfield Helipath using spindle TE measured at 4 rpm and 23°C.

[0075] In some embodiments, tile adhesives can be entirely starch-based. In such embodiments, the tile adhesive comprises gelatinized substituted starch as a binder and granular starch as a filler, preferably pregelatinized substituted starch as a binder and granular starch as a filler. The entirely starch-based tile adhesive can be mixed with cold water to provide an aqueous tile adhesive composition, which can be used as described in detail elsewhere. Using granular potato starch as a filler offers the advantage of being a completely renewable and 100% starch-based tile adhesive.

[0076] The present invention also provides a method for providing one or more tiles to a surface, comprising the steps of

[0077] a) providing an aqueous tile adhesive composition comprising a gelatinized substituted starch as defined elsewhere, the aqueous adhesive composition having a viscosity of 300 Pa.s to 700 Pa.s, and the aqueous tile adhesive composition optionally being provided by mixing a dry mix for a tile adhesive as defined elsewhere with water;

[0078] b) providing a surface to which one or more tiles are to be provided or at least one tile to be laid onto a surface using an aqueous tile adhesive composition;

[0079] c) attaching one or more tiles to the surface;

[0080] d) allowing the aqueous tile adhesive composition to dry.

[0081] In the method of the invention for providing one or more tiles to a surface, steps b) to d) represent steps that are in accordance with common general knowledge in the field of tile laying. Step a) represents providing an aqueous tile adhesive composition for use in laying, which can be provided as is (such as an aqueous composition from a suitable container) or can be provided by homogenizing a dry mix with water.

[0082] The present invention also provides a surface comprising one or more tiles, wherein the tiles are attached to the surface using a tile adhesive as defined above. The surface comprising one or more tiles comprises three layers: a basic surface layer, an intermediate layer and a tile layer, wherein the basic layer is a surface capable of being provided with tiles, the intermediate layer comprises dry tile adhesive, and the tile layer comprises tiles, as defined elsewhere.

[0083] The base surface is the surface to which the tiles are attached using tile adhesive. The base surface can be made of different types of materials, such as concrete, brick, wood, mortar, or plaster. Tile adhesive is suitable for attaching tiles to any base surface, but is particularly well-suited for adhering tiles to concrete or wood base surfaces.

[0084] The intermediate surface comprises the dry tile adhesive and therefore the gelatinised substituted starch and filler, and any optional further ingredients as defined elsewhere. DETAILED DESCRIPTION

[0085] Examples

[0086] The tile adhesives described below were prepared by dry mixing of the solid ingredients. Cold water soluble starch has been used to prepare the waterborne tile adhesive. Tap water (20° C.) has been used. All solid materials have been used commercially dry.

[0087] Preparation of tile adhesive

[0088] The mixing process is based on EN-120004. In short:

[0089] • Dry blend all compounds in a plastic bag, close the bag, and shake well.

[0090] Fill the mixing bowl with the required amount of water.

[0091] • Attach the paddle to the mixer.

[0092] • Add the dry blend to the water and place the bowl into the mixer and start the mixer after 30 seconds (t=0)

[0093] The mixer follows the following mixing protocol:

[0094] a. Minutes 0 to 1 / 2: Mix the mortar with the mixer at 140 rpm.

[0095] b. Minutes 1 1 / 2 to 1 1 / 2: Rest; lower the bowl in the mixer and scrape the paddle; remove the bowl from the mixer and scrape the inside of the bowl.

[0096] c. Minute 1 1 / 2 to 2 1 / 2: The mortar is mixed again at 140 rpm

[0097] d. Minute 2 1 / 2 to 5: Rest; when viscosity is high, scrape down the paddle and bowl again.

[0098] e. minutes 5 to 5 1 / 4: Final mixing with the mixer at 140 rpm.

[0099] Remove the bowl from the mixer and scrape down the paddle and bowl.

[0100] If necessary, carefully cut through the mortar with the silicone trowel to remove air cavities in the mortar and use the top of the silicone trowel to level the surface of the mortar.

[0101] Viscosity measurement

[0102] The viscosity is determined by a Brookfield Helipath using a spindle TE at 4 rpm and 23°C. The viscosity measurement begins 7 minutes after the start of adhesive preparation. The data are taken at 1 second intervals. After 18 seconds of stabilization, the average viscosity of 10 data points (10 seconds) is reported. The water / powder ratio (w / p ratio) is selected in such a way that the Brookfield viscosity of the tile adhesive is between 300 Pa.s and 700 Pa.s.

[0103] Adhesion strength and open time

[0104] Adhesion strength and open time were determined according to EN 12004 (using Winckelmans tiles, but also MOSA tiles). For adhesion strength, Winckelmans tiles were used. Winckelmans tiles have (very) low porosity (water absorption <0.5% by mass), while MOSA tiles, used for open time, have high porosity (water absorption approximately 15 ± 3%). The use of both high- and low-porosity tiles supports the general applicability of the tile adhesives of the present invention. Unless otherwise stated, adhesion was determined on concrete surfaces. In short:

[0105] 10 minutes after the start of preparation, apply a layer of tile adhesive to the surface

[0106] · Winckelmans tiles were placed into the adhesive layer 5 minutes after application. These tiles were used for adhesion strength.

[0107] • MOSA tiles were placed into the adhesive layer 5, 30 or 60 minutes after the adhesive layer was applied. These tiles were used for open time.

[0108] The starches used in the examples of this aspect include the following.

[0109]

[0110]

[0111] The amounts of DS and DC as reagents added to starch during the reaction are expressed as moles of reagent per mole of AGU.

[0112] A conventional reference cement-based tile adhesive was prepared according to the following recipe:

[0113]

[0114] 1 Quartz sand; D50 of 144 μm

[0115] 2 HPMC defined by the following viscosity (2% solution, 20°C): 25,000 mPa·s - 35,000 mPa·s Example 1: Types of starch for use as tile adhesives

[0116] A starch-based tile adhesive was prepared using the following formulation:

[0117]

[0118] 1 Quartz sand; D50 of 144 μm

[0119] Starch was added as commercial dry material. The moisture content depended on the starch type: dextrin (11 wt% moisture), maltodextrin (7 wt%), extruded starch (13 wt%), drum dried starch (6 wt%).

[0120] For all types of starch, the adhesion strength was determined following EN 12004. The results are provided in Table 1:

[0121]

[0122] 1 w / p = water / powder ratio.

[0123] In Table 1, it is shown that starches 1-7 showed insufficient adhesion to Winckelmans. Starches 8-18 showed the required adhesion to Winckelmans, easily meeting the C2 requirement.

[0124] From this it can be inferred that substituted starches can provide adequate adhesion under EN 12004. It can also be inferred that many starch types perform even better than the reference (cement-based) tile adhesive, even in the absence of cement.

[0125] Further modification of the starch, such as cross-linking, does not hinder the adhesion of the substituted starch. Therefore, cross-linked starches can be used where this may result in optimized rheology.

[0126] Example 2: Fillers to be combined with starch in tile adhesives

[0127] Using Starch 9, the formulation of Example 1 was used to evaluate the tile adhesive's tolerance to the presence of various fillers. The alternative fillers used were Durcal 40 (calcium carbonate with a D50 of 40 μm) or native potato starch. It should be noted that native potato starch is present in the tile adhesive in granular form. Therefore, the tile adhesive used in the adhesion testing in Experiment 2-2 contained gelatinized substituted starch as a binder and granular starch as a filler.

[0128] The results are shown in Table 2:

[0129]

[0130] The results show that alternative fillers can be used while still meeting C2 requirements under EN 12004.

[0131] Example 3: Tolerance of the ratio of substituted starch to filler

[0132] Using starches 9 and 13 as exemplary starches and quartz sand as filler, different ratios between the substituted starch and the filler were evaluated. The results are shown in Table 3.

[0133] The results show that at 1% starch 9, adhesion becomes insufficient, while at 2.5% and up to 100% starch 9, adhesion meets requirement C2. Similar behavior is observed for starch 13. Increasing starch content (and therefore decreasing sand content) results in the need for a higher w / p ratio. It is noteworthy that fillers are not strictly required to meet adhesion requirements.

[0134] Table 3:

[0135]

[0136]

[0137] Example 4: Opening hours

[0138] The starch-based tile adhesive based on Starch 9 in the formulation of Example 1 was compared with a cement-based reference adhesive using MOSA tiles. The filler in both adhesives was sand ( 12A).

[0139] The results are shown in Table 4:

[0140]

[0141] Table 4 shows that the reference (Experiment 4-2) and the Starch 9 formulation (Experiment 4-5) meet the requirements of at least 0.5 N / mm after 30 minutes of open time. 2 The requirement for adhesion strength of 100 μg / cm2 was met. However, even after 60 minutes, the Starch 9 formulation (Experiment 4-6) easily met this requirement, while the cement reference did not (Experiment 4-3). Thus, the open time of the inventive (starch-based) tile adhesive was longer than that of the cement-based reference, which allowed the tile to be applied with fewer time constraints and to be applied to a larger surface area than with conventional cement-based tile adhesives, thereby avoiding waste generation to a significant extent.

[0142] Example 5: Adhesion to alternative surface materials

[0143] Various starch-based tile adhesives according to the formulation of Example 1 were tested for their bond strength (multiplicity) to wood and compared to a cement-based reference using the procedure set out in EN 12004.

[0144] The results are shown in Table 5:

[0145]

[0146]

[0147] Table 5 and the previous examples show that starch-based tile adhesives can be used on different surfaces including wood and concrete. In addition, this experiment shows that since unsubstituted starch 7 (drum-dried potato starch) does not provide any adhesive strength, a substituted starch is needed to adhere tiles to wooden surfaces.

[0148] Example 6: Mixing Tile Adhesive

[0149] The starch-based tile adhesives of the present invention were evaluated for their resistance to the presence of cement. This was done by evaluating mixtures of a reference tile adhesive and a formulation of the present invention. The compositions evaluated are shown below:

[0150] experiment 6-1 6-2 6-3 6-4 Cement tile adhesive [unit] 1 1 1 1 35% starch + 65% sand [parts] 2 2 10% starch + 90% sand [parts] 1 2 starch 9 13 9 9

[0151] This translated into adhesion testing of the following compositions, with the results shown in Table 6 (amounts as received in wt. %):

[0152]

[0153]

[0154] The results in Table 6 show that mixtures containing substituted starch, fillers, and cement do not always provide sufficient adhesion strength. However, the presence of cement can be tolerated, albeit at the expense of adhesion strength. It can be seen that cement can be present, but preferably in relatively low amounts, compared to substituted starch.

[0155] Example 7: Tolerance to other ingredients

[0156] The starch-based tile adhesives of the present invention were evaluated for their tolerance to the presence of other components. This was done by adding additives commonly found in cement-based tile adhesives, as well as another additive. The component types and results are shown in Table 7:

[0157]

[0158] Table 7 shows that the addition of typical cement tile adhesive ingredients such as redispersible powder ("RDP", Vinnapas 5010N) or nanoclay (Cloisite 116) did not negatively impact adhesion. Neither did non-typical cement tile adhesive ingredients such as gelatin 250 Bloom.

Claims

1. A tile adhesive comprising substituted starch and a filler, wherein the weight ratio of cement to substituted starch is 0-2.

2. The tile adhesive of claim 1, wherein the filler comprises sand, clay, calcium carbonate, granular starch, ground waste concrete, ground waste plastic, ground organic material, ground inorganic material and / or sawdust.

3. Tile adhesive according to claim 1 or 2, wherein the filler has a particle size expressed as D50 of at least 1, preferably at least 5 μm, and wherein the particle size is preferably at most 500 μm, preferably at most 300 μm, more preferably at most 175 μm.

4. The tile adhesive according to any one of claims 1 to 3, wherein the substituted starch is carboxymethylated starch, hydroxybutylated starch, hydroxypropylated starch, hydroxyethylated starch, acetylated starch, octenylsuccinate starch, cationic starch or any combination thereof, and wherein preferably the degree of substitution of the starch is at least 0.01 mol / mol.

5. The tile adhesive according to claim 4, wherein the substituted starch is also a cross-linked starch, preferably an epichlorohydrin cross-linked starch, a trimetaphosphate cross-linked starch, a phosphorus oxychloride cross-linked starch, adipic acid cross-linked starch, and / or wherein the substituted starch is also a degraded starch, preferably an acid-degraded starch, a physically degraded starch or an enzymatically degraded starch.

6. The tile adhesive according to any one of claims 1 to 5, wherein the substituted starch is pregelatinized starch.

7. The tile adhesive according to any one of claims 1 to 6, wherein the substituted starch is a substituted tuber starch, a substituted root starch, a substituted nut starch, a substituted grain starch or a substituted legume starch, and wherein the substituted starch is preferably a substituted potato starch, a substituted sweet potato starch, a substituted tapioca starch, a substituted corn starch, a substituted wheat starch or a substituted pea starch.

8. The tile adhesive according to any one of claims 1 to 7, wherein the amount of substituted starch is 2% to 99.9% by weight, and wherein the amount of filler is 0.1% to 98% by weight, said amounts being expressed relative to the dry weight of the tile adhesive.

9. The tile adhesive according to any one of claims 1 to 8, wherein the filler / substituted starch mass ratio is 0.25-40, preferably 0.3-25, more preferably 1.0-20.

10. The tile adhesive according to any one of claims 1 to 9, wherein the filler / total binder mass ratio is greater than 0.5, preferably greater than 1.

0.

11. The tile adhesive according to any one of claims 1 to 10, wherein the tile adhesive does not contain cement.

12. The tile adhesive according to any one of claims 1 to 11, wherein the tile adhesive is a dry mix suitable for mixing with water, wherein the substituted starch is a pregelatinized starch, or wherein the tile adhesive is an aqueous tile adhesive composition, wherein the substituted starch is a gelatinized substituted starch, the aqueous tile adhesive composition having a viscosity of 300 Pa.s to 700 Pa.s measured with a Brookfield Helipath using spindle TE measured at 4 rpm and 23°C.

13. A method for preparing a tile adhesive according to any one of claims 1 to 12, comprising the steps, in any order, of providing a solution of substituted starch in water, and homogenizing at least one dry ingredient in water at a water / total dry ingredient mass ratio of 0.1 to 5.

14. A method for providing one or more tiles to a surface comprising the steps of a) providing an aqueous tile adhesive composition comprising gelatinized substituted starch as defined in claim 12, the aqueous tile adhesive composition optionally being provided by homogenizing a dry mixture for a tile adhesive as defined in claim 12 with water; b) providing a surface to be provided with one or more tiles or at least one tile to be laid onto a surface at least partially utilizing said aqueous tile adhesive composition; c) applying the one or more tiles to the surface; d) drying the aqueous tile adhesive composition.

15. A surface comprising one or more tiles, wherein the tiles are affixed to the surface using a tile adhesive as defined in any one of claims 1 to 12.

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