A cementitious skim coat composition containing cross-linked cellulose ether for mortar having enhanced gel strength.

Abstract

The present invention provides a dry mix for skim coat mortar with improved pot life and workability while reducing the dosage of cellulose ethers, comprising white cement, one or more fillers having a mean sieve particle size of 15 to 60 microns, 0.25 to 0.5 wt. % of one or more gel-like crosslinked cellulose ethers containing polyether groups, preferably mixed cellulose ethers with polyoxypropylenedioxyethylene ether crosslinks, and 1 to 2.5 wt. % of one or more polymeric redispersible powders (RDPs). The at least one gel-like crosslinked cellulose ether has a crossover point, measured by oscillatory rheometry, of 1.0 ω or less, where the storage modulus (G') and loss modulus (G") cross over and are identical. The present invention also provides a method of using the dry mix.

Description

Technical Field

[0001] The present invention relates to a dry mix composition containing cement and a gel-like crosslinked cellulose ether containing a polyether group, having enhanced workability and pot life for use in the production of a cementitious skim coat, and a method of using the composition.

Background Art

[0002] Cellulose ethers are used in mortars for various construction applications to impart water retention properties that limit the loss of moisture from the mortar to the absorption substrate and to improve the rheology of the mortar. For example, cellulose ethers have found use in cement-based tile adhesives by applying a wet adhesive to the back of the tile and adhering it to the substrate. Furthermore, cellulose ethers enable a stable setting rate and high final mechanical strength. However, cellulose ethers having a viscosity level of more than 70,000 mPa·s (measured by a Haake (trademark) Viscotester (trademark) VT550 rheometer by Thermo Fisher Scientific, USA), 2 wt% aqueous solution, 20 °C, 2.55 s

[0003] , ) are difficult to obtain because of the difficulty in procuring and processing the raw material (pulp). When using more readily available cellulose ethers, the addition rate or dosage of the cellulose ether remains high in order to produce sufficient water retention to maintain a useful pot life (e.g., 0.3 to 0.6 wt% based on total solids). For example, there is still a need to reduce the dosage of cellulose ether in skim coat applications.

[0003] The cement-containing skim coat comprises a dry mix composition for mortar, which is formulated with cellulose ether, cement, and finely ground filler. For skim coat application, the dry mortar is mixed with water and then applied thinly in continuous layers over a coating time of, for example, 3 to 4 hours. If, during the coating time, the skim coat mortar does not retain good workability with hand tools and initial wet mortar properties such as tackiness and viscosity, it must be discarded and a new mortar batch must be prepared. However, the desired reduction in the cellulose ether dose level by formulating a skim coat with a higher viscosity cellulose ether may impair the required coating properties of the mortar during the coating time.

[0004] Li's U.S. Patent Publication US2015 / 0315076A1 discloses a skim coat composition having cellulose ether and gluconate, which allows for a reduction in the cellulose ether dose, limited to <18% based on a standard dose of 0.35%, by replacing the cellulose ether with gluconate. However, the substitution of cellulose ether with gluconate slows the setting time, thereby hindering efficient skim coat application by delaying the continuous application of the skim coat and the subsequent application of building coatings on the skim coat.

[0005] The present invention aims to solve the problem of providing a cementitious skim coat dry mix composition containing cellulose ether that forms a mortar with improved pot life and workability while reducing the amount of cellulose ether. [Overview of the Initiative]

[0006] According to the present invention, a dry mix composition for producing a skim coat comprises a cement such as white cement, one or more fillers having a sieve average particle size of 15 to 60 microns, 0.15 to 0.75% by weight, preferably 0.20 to 0.50% by weight, or more preferably 0.23 to 0.45% by weight, one or more gel-like crosslinked cellulose ethers containing polyether groups, preferably mixed cellulose ethers containing hydroxyalkyl groups and alkyl ether groups, and 0.5 to 5% by weight, or preferably 0.5 to 3.5% by weight, or preferably 1 to 2.5% by weight, one or more polymer redispersible powders (RDPs) such as RDPs containing ethylene-vinyl acetate copolymers, acrylate copolymers, or styrene acrylate copolymers, all amounts being weight percent of the total solids in the dry mix composition. Preferably, at least one of the one or more gel-like crosslinked cellulose ethers is a mixed cellulose ether having polyoxypropylene dioxyethylene ether crosslinking. The dry mix composition may contain dry cement, such as white cement, in an amount of 15 to 33% by weight, or preferably 18 to 30% by weight, based on the total weight of the dry mix, and the remainder of the dry mix shall contain one or more fillers, such as white fillers. All weight percentages add up to 100%.

[0007] According to the present invention, a method using a dry mix comprises mixing the dry mix with water to form a mortar, and applying the mortar to a substrate to form a skim coat. The substrate may include, for example, concrete, fiber cement board, cement rendering, reinforcing mortar for exterior insulation finishing systems (EIFS), hardened mortar, or another unfinished substrate.

[0008] Preferably, in any of the compositions or methods of the present invention, a 1.0 wt% aqueous solution of at least one of one or more gel-like crosslinked cellulose ethers has a crossover point (COV) measured by vibrational rheometry where the storage modulus (G') and loss modulus (G'') intersect and are identical, at a value of 1.5 (ω or rad / s) or less, for example, 0.2 to 1.0 rad / s or 0.45 to 1.0 rad / s, where G' and G'' are measured in Pascals at 20°C using a vibrational rheometer (Anton Paar MCR 302, Anton Paar, Graz, AT) equipped with a plate having a diameter of 50 mm and a cone having a cone angle of 1° and a cone point flattening of 0.05 mm, and the angular frequency (ω) in radians / second is varied in the range of (ω) from 0.1 to 100 rad / s with a strain of 0.5%. More preferably, the ratio of the COV of the gel-like crosslinked cellulose ether to the COV of the same uncrosslinked cellulose ether is in the range of 1:15 to 0.5:1, or preferably 0.1:1 to 0.4:1.

[0009] Preferably, at least one of the one or more gel-like crosslinked cellulose ethers has a hydroxyalkyl substitution MS(HE) degree of 1.5 to 4.5 and a substitution MS(HE) degree of 2.0 to 3.0.

[0010] Preferably, at least one of the one or more gel-like crosslinked cellulose ethers contains, for example, at least 20% by weight, or 20% to 100%, or 20% to 80%, of the crosslinked cellulose ether at least partially derived from wood pulp, based on the weight of the total solids content of the cellulose ether.

[0011] More preferably, at least one of the one or more gel-like crosslinked cellulose ethers is hydroxyethyl methylcellulose containing polyoxypropylene dioxyethylene ether crosslinks, such as a reaction product of hydroxyethyl methylcellulose and polypropylene glycol (PPG) glycidyl ether.

[0012] Preferably, the dry mix composition according to the present invention provides a mortar that, based on the weight of the total solids in the dry mix composition, provides a water retention of at least 94%, preferably at least 95%, more preferably at least 96%, or more preferably at least 97% after 3 hours when tested on a cardboard substrate at 25°C according to the method of DIN EN1015, Part 8, with at least 0.3% by weight of at least one of one or more gel-like crosslinked cellulose ethers used.

[0013] 1. According to the present invention, a dry mix composition for use in the preparation of cementite skim coat mortar comprises 15-33% by weight, preferably 18-30% by weight, of white cement such as aluminate cement or white Portland cement, and 65-83% by weight, preferably 68-80% by weight, of one or more fillers selected from dolomite, kaolinite, calcium carbonate, talc, silica sand, white silica sand, or alkali metal silicates such as calcium silicate or sodium silicate, with a thickness of 15-60 microns, preferably 25 The mixture comprises a filler having a sieve average particle size of ~50 microns, 0.15~0.75% by weight, preferably 0.20~0.5% by weight, or more preferably 0.35~0.45% by weight, of one or more gel-like crosslinked cellulose ethers containing polyether groups, and 0.5~5% by weight, preferably 1~2.5% by weight, or more preferably 1.4~2% by weight, of one or more polymer redispersible powders (RDPs) such as ethylene-vinyl acetate RDP, where all amounts are by weight percentages of the total solids in the dry mix composition, and all proportions total 100%.

[0014] 2. According to the dry mix composition of item 1 above, at least one of the one or more gel-like crosslinked cellulose ethers is present in the absence of crosslinking, at 20°C and a shear rate of 2.55 s. -1It is a cross-linking reaction product of cross-linked cellulose ether, which may have a viscosity of 10,000 to 70,000 mPa·s as measured as a 2 wt% aqueous solution in water using a rotational rheometer (Haake® Viscotester® VT550 by Thermo Fisher Scientific, USA).

[0015] 3. According to the dry mixed composition of item 1 or 2 above, at least one of the one or more gel-like crosslinked cellulose ethers is selected from a mixed cellulose ether containing a hydroxyalkyl group and an alkyl ether group, such as an unmixed cellulose ether containing an alkyl ether group, or an alkylhydroxyethylcellulose, for example, selected from hydroxyalkylmethylcellulose, preferably selected from hydroxyethylmethylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), methylhydroxyethylhydroxypropylcellulose (MHEHPC), methylethylhydroxyethylcellulose (MEHEC), and ethylhydroxyethylcellulose (EHEC), more preferably selected from HEMC.

[0016] 4. According to any one of the dry mix compositions described in item 1, 2, or 3 above, the polyether group in at least one of the one or more gel-like crosslinked cellulose ethers is a polyoxyalkylene having 2 to 100, preferably 2 to 20, or more preferably 3 to 15 oxyalkylene groups.

[0017] 5. According to any one of the dry mixed compositions described in items 1, 2, 3, or 4 above, the polyether group in at least one of the one or more gel-like crosslinked cellulose ethers is a polyoxyalkylene selected from polyoxyethylene, polyoxypropylene, and combinations thereof, preferably polyoxypropylene.

[0018] 6. According to any one of the dry mixed compositions described in items 1, 2, 3, 4, or 5 above, the gel-like crosslinked cellulose ether is polyoxypropylene group-containing hydroxyethyl methylcellulose, or preferably hydroxyethyl methylcellulose containing polyoxypropylene dioxyethylene ether crosslinking.

[0019] 7. Preferably, according to any one of the dry mix compositions of the present invention described in item 1, 2, 3, 4, 5, or 6 above, a 1.0 wt% aqueous solution of at least one of one or more gel-like crosslinked ethers has a crossover point, measured by vibrational rheometry, where the storage modulus (G') and loss modulus (G'') intersect and are identical, and G' and G'' are measured in Pascals at 20°C using an Anton Paar MCR 302 (Anton Paar, Graz, AT) equipped with a plate having a diameter of 50 mm and a cone having a cone angle of 1° and a cone point flattening of 0.05 mm, with the angular frequency (ω) in radians / second varying in the range of 0.1 to 100 (ω) with a 0.5% strain.

[0020] 8. According to any one of the dry mix compositions of the present invention described in item 1, 2, 3, 4, 5, 6, or 7 above, a dry mix is ​​provided when, based on the weight of the total solids in the dry mix composition, a 0.3 wt% use of at least one of one or more gel-like crosslinked cellulose ethers in the dry mix is ​​mixed with water to a viscosity of 380,000 to 450,000 cPs (mPa·s) at 25°C, as measured at 5 rpm using a Brookfield rheometer RVDV II Pro (DV II) with Helipath spindle number T96, and provides a workable mortar exhibiting a water retention of at least 94%, preferably at least 95%, more preferably at least 96%, or even more preferably at least 97%, when tested on a cardboard substrate at 25°C after 3 hours according to the method of DIN EN1015, Part 8.

[0021] 9. In another aspect of the present invention, the present invention provides a method for using any one of the dry mix compositions described in items 1 to 8 above, comprising: preparing a mortar by combining the dry mix composition with water or an aqueous liquid; and applying the mortar to an unfinished cement substrate such as concrete or cement rendering to form a smooth surface.

[0022] 10. The method of the present invention described in item 9 above further comprises drying a smooth surface and applying an architectural coating such as paint to the thus dried smooth surface.

[0023] 11. According to the method of the present invention described in either item 9 or 10 above, at least one of the one or more gel-like crosslinked cellulose ethers of the dry mix is ​​subjected to the absence of crosslinking at 20°C and a shear rate of 2.55 s. -1 It is a crosslinked product of cellulose ether, which may have a viscosity of 10,000 to 70,000 mPa·s as measured as a 2 wt% aqueous solution in water using Haake® Viscotester® VT550.

[0024] Preferably, according to the method of the present invention, the dry mix comprises at least one gel-like crosslinked cellulose ether having polyether groups which are polyoxyalkylene having 2 to 100, preferably 2 to 20, more preferably 3 to 15 oxyalkylene groups. More preferably, the polyether groups in the at least one gel-like crosslinked cellulose ether are polyoxypropylene. More preferably, the at least one gel-like crosslinked cellulose ether is hydroxyethyl methylcellulose containing polyoxypropylene dioxyethylene ether crosslinks.

[0025] Preferably, according to the method of the present invention, the dry mix comprises at least one gel-like crosslinked cellulose ether that exhibits a crossover point (COV) of storage modulus (G') and loss modulus (G") of 1.5ω or less, measured by oscillatory rheometry. More preferably, the ratio of the COV of the gel-like crosslinked cellulose ether to the COV of the same cellulose ether without crosslinking is in the range of 1:15 to 0.5:1, or preferably 0.2:1 to 0.4:1.

[0026] Preferably, according to the method of the present invention, in the dry mix, based on the weight of the total solids in the dry mix composition, a usage amount of at least 0.3% by weight of at least one of the one or more gel-like crosslinked cellulose ethers in the dry mix, when measured at 5 rpm using a Brookfield rheometer RVDV II Pro (DV II) equipped with a Helipath spindle number T96 and mixed with water to a viscosity of 380,000 to 450,000 cPs (mPa·s) at 25°C, provides a dry mix that, when tested at 25°C after 3 hours on a cardboard substrate according to the method of DIN EN 1015, part 8, exhibits a water retention of at least 94%, or preferably at least 95%, or more preferably at least 96%, or even more preferably at least 97%, to provide a workable mortar.

Embodiments for Carrying out the Invention

[0027] According to the present invention, the gel-like crosslinked cellulose ether enables the provision of a dry mix and mortar for use in the production of a skim coat having the same or improved workability and open time even with a reduced cellulose ether dosage. The gel-like cellulose ether is irreversibly crosslinked and exhibits gel-like behavior characterized by an increase in storage modulus at low angular frequencies in response to oscillatory rheometry. The gel-like behavior leads to, for example, an improvement in water retention in use as a mortar.

[0028] It has been found that the behavior of cementitious skim coat compositions is significantly improved when crosslinked cellulose ethers containing polyether groups in the crosslinking agent, preferably cellulose ethers containing alkyl ethers and hydroxyalkyl groups. For example, the skim coat mortar exhibits enhanced gel strength properties, such as greater concentration or viscosity and greater elasticity, compared to the same uncrosslinked cellulose ether at a given concentration. In addition, the present invention allows for a reduction in the amount of cellulose ether to more than 30% without impairing skim coat performance. For example, the gel-like crosslinked cellulose ether of the present invention enables the provision of skim coat compositions that exhibit improved workability at lower doses than gel-like CE under harsh high-temperature (45°C) application conditions. The gel-like crosslinked cellulose ether of the present invention can be used at significantly lower addition rates than conventional crosslinked cellulose ethers, enabling the production of economical cementitious skim coats.

[0029] Unless otherwise specified, all temperature and pressure units are room temperature (19–23°C) and standard pressure (1 atm). Unless otherwise specified, all conditions include 50% relative humidity (RH).

[0030] Unless otherwise explicitly indicated by the context, the singular forms "a," "an," and "the" refer to multiple objects.

[0031] Unless otherwise defined, technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art.

[0032] All phrases containing parentheses indicate one or both of the items enclosed in the parentheses, or their absence. For example, the phrase "(poly)oxyalkylene" alternatively includes polyoxyalkylene and oxyalkylene.

[0033] All cited ranges are comprehensive and combinable. For example, the disclosure of 0.25 to 0.5 wt%, or preferably 0.35 to 0.45 wt%, includes all of the following: 0.25 to 0.5 wt%, or preferably 0.35 to 0.45 wt%, or 0.25 to 0.35 wt%, or 0.25 to 0.45 wt%, or 0.35 to 0.5 wt%, or 0.45 to 0.5 wt%.

[0034] As used herein, the term “anhydrous glucose unit” or “AGU” refers to a monosaccharide in its (co)polymerized form.

[0035] As used herein, the term “aqueous” means that the continuous phase or continuous medium is water and contains 0 to 10% by weight of a water-miscible compound based on the weight of the medium. Preferably, “aqueous” means water.

[0036] As used herein, the phrase "based on total solids" refers to the total weight of non-volatile components in a given composition, including synthetic polymers, cellulose ethers, acids, defoamers, hydraulic cements, fillers, other inorganic materials, and other non-volatile additives. Water, ammonia, and volatile solvents are not considered solids.

[0037] As used herein, the term “crossover point” means the angular frequency (ω) measured by vibrational rheometry at which the storage modulus (G') and the loss modulus (G”) intersect and are identical, where G' and G'' are measured in Pascals by vibrational rheometry at 20°C as a function of angular frequency (ω) using an Anton Paar MCR 302 vibrational rheometer (Anton Paar, Graz, AT) having a plate with a diameter of 50 mm and a cone with a cone angle of 1° and a cone point flattening of 0.05 mm, with the angular frequency (ω) in radians / second varied in the range of 0.1 to 100 (ω) with a 0.5% strain. In rheometry, the analyte cellulose ether or cross-linked cellulose ether is dissolved in 99.0% by weight water by dispersing 1.0% by weight of cellulose ether in dry, sheared water for 1 minute at room temperature with stirring, followed by stirring at 1000 rpm for 10 minutes, and then storing the solution in a tightly sealed round glass container for 24 hours, rotating it slowly around its longitudinal (horizontal) axis throughout the 24 hours to dissolve it in water.

[0038] As used herein, the term "DIN EN" refers to the European standard edition of the German material specifications published by Beuth Verlag GmbH, Berlin, DE. Similarly, as used herein, the term "DIN" refers to the German edition of the same material specifications.

[0039] As used herein, the term “dry mix” means a storage-stable powder containing cement, cellulose ether, any other polymer additives, and any fillers and drying additives. The dry mix is ​​storage-stable because it does not contain water.

[0040] As used herein, the term "DS" refers to the average number of alkyl-substituted OH groups per anhydrous glucose unit in cellulose ether, as determined by the Zeisel method, and the term "MS" refers to the average number of hydroxyalkyl-substituted OH groups per anhydrous glucose unit. The term "Zeisel method" refers to the Zeisel cleavage procedure for determining MS and DS; see G. Bartelmus and R. Ketterer, Fresenius Zeitschrift fuer Analytische Chemie, Vol. 286 (1977, Springer, Berlin, DE), pages 161 to 190.

[0041] As used herein, the term "low-viscosity or medium-viscosity crosslinked cellulose ether" refers to the case where crosslinking is absent, at 20°C, and at a shear rate of 2.55 s. -1 This refers to cross-linked cellulose ether that may have a viscosity of 10,000 to 40,000 mPas as measured as a 2 wt% aqueous solution in water using a Haake Rotovisko (trademark) RV100 rheometer (Thermo Fisher Scientific, Karlsruhe, DE).

[0042] As used herein, the term "high viscosity crosslinked cellulose ether" refers to the ether obtained in the absence of crosslinking, at 20°C and a shear rate of 2.55 s. -1 This refers to cross-linked cellulose ether that may have a viscosity exceeding 40,000 mPas, as measured as a 2 wt% aqueous solution in water using a Haake Rotovisko (trademark) RV100 rheometer (Thermo Fisher Scientific, Karlsruhe, DE).

[0043] As used herein, the term "setting" refers to the hardening of mortar that occurs under ambient conditions in the presence of water and continues as the mortar dries.

[0044] As used herein, the term “average particle size of sieve” means the average particle size determined by the Malvern Panalytical Mastersizer 2000 (Malvern, UK).

[0045] As used herein, the term “weight percent of total solids” means the weight of all non-volatile components of a given composition, as determined by their volatility at temperatures below 40°C and atmospheric pressure. Examples of volatile substances include water and solvents that evaporate under ambient temperature and pressure conditions, such as methyl chloride.

[0046] Suitable cellulose ethers for use in the method for producing the crosslinked polyether group-containing cellulose ether of the present invention include, for example, hydroxyalkylcellulose or alkylcellulose, or mixtures of such cellulose ethers. Examples of cellulose ether compounds suitable for use in the present invention include, for example, methylcellulose (MC), ethylcellulose, propylcellulose, butylcellulose, hydroxyethylmethylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), hydroxyethylcellulose ("HEC"), ethylhydroxyethylcellulose (EHEC), methylethylhydroxyethylcellulose (MEHEC), hydrophobic modified ethylhydroxyethylcellulose (hmEHEC), hydrophobic modified hydroxyethylcellulose (hmHEC), sulfoethylmethylhydroxyethylcellulose (SEMHEC), sulfoethylmethylhydroxypropylcellulose (SEMHPC), and sulfoethylhydroxyethylcellulose (SEHEC). Preferably, the cellulose ether is a mixed cellulose ether containing a hydroxyalkyl group and an alkyl ether group, such as alkylhydroxyethylcellulose, such as hydroxyalkylmethylcellulose, such as hydroxyethylmethylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), methylhydroxyethylhydroxypropylcellulose (MHEHPC), methylhydroxyethylcellulose (MEHEC), and ethylhydroxyethylcellulose (EHEC).

[0047] In the gel-like crosslinked cellulose ether of the present invention, alkyl substitutions are described in cellulose ether chemistry by the term "DS". DS is the average number of substituted OH groups per anhydrous glucose unit. Methyl substitutions may be reported, for example, as DS(methyl) or DS(M). Hydroxyalkyl substitutions are described by the term "MS". MS is the average number of moles of etherifying agent bound as ether per mole of anhydrous glucose unit. Etherification with the etherifying agent ethylene oxide is reported, for example, as MS(hydroxyethyl) or MS(HE). Etherification with the etherifying agent propylene oxide is reported correspondingly as MS(hydroxypropyl) or MS(HP). Side groups are determined using the Zeisel method (see: G. Bartelmus and R. Ketterer, Fresenius Zeitschrift fuer Analytische Chemie 286(1977), 161-190).

[0048] The crosslinked hydroxyalkyl group-containing cellulose ether preferably has a hydroxyalkyl substitution MS(HE) degree of 1.5 to 4.5, or more preferably a substitution MS(HE) degree of 2.0 to 3.0.

[0049] Preferably, a mixed ether of methylcellulose is used for crosslinking. In the case of HEMC, the preferred methyl-substituted DS(M) value is in the range of 1.2 to 2.1, more preferably 1.3 to 1.7, or even more preferably 1.35 to 1.65, and the hydroxyalkyl-substituted MS(HE) value is in the range of 0.05 to 0.75, more preferably 0.10 to 0.45, or even more preferably 0.15 to 0.40. In the case of HPMC, the preferred DS(M) value is in the range of 1.2 to 2.1, or more preferably 1.3 to 2.0, and the MS(HP) value is in the range of 0.1 to 1.5, or even more preferably 0.15 to 1.2.

[0050] Suitable crosslinking agents for use in the present invention include, for example, compounds having two or more crosslinking groups, preferably two, such as polyoxyalkylene or polyalkylene glycol groups and glycidyl or epoxy groups, that form an ether bond with the cellulose ether when crosslinking the cellulose ether, or ethylenically unsaturated groups, such as vinyl groups. Suitable bifunctional compounds can be selected from, for example, diglycidyl polyalkoxy ethers, diglycidyl phosphonates, and divinyl polyoxyalkylenes containing sulfone groups. Examples of these are diglycidyl polyoxypropylene and glycidyl(poly)oxyalkyl methacrylates, preferably diglycidyl polyalkoxy ethers, such as diglycidyl polyoxypropylene, glycidyl(poly)oxyalkyl methacrylates, diglycidyl phosphonates, or divinyl polyoxyalkylenes containing sulfone groups.

[0051] The amount of crosslinking agent used may be in the range of 0.0001 to 0.05 equivalents, where "equivalent" represents the molar ratio of each crosslinking agent to the number of moles of anhydrous glucose units (AGU) in the cellulose ether. A preferred amount of crosslinking agent used is 0.0005 to 0.01 equivalents, or more preferably, 0.001 to 0.005 equivalents. As used herein, the unit "eq" represents the molar ratio of moles of each crosslinking agent to the number of moles of anhydrous glucose units (AGU) in the cellulose ether, and the resulting crosslinked polyether group-containing cellulose ether is granulated and dried.

[0052] The dry mix composition according to the present invention further comprises finely divided cement, such as hydraulic cement powder, preferably white cement. Suitable examples of white cement include aluminate cement and white Portland cement containing white inorganic materials. The dry cement may be used in an amount of 15 to 33% by weight, or preferably 18 to 30% by weight, based on the total weight of the dry mix.

[0053] The dry mix composition according to the present invention further comprises 65 to 83% by weight, or preferably 68 to 80% by weight, of a filler, preferably a white filler. Suitable fillers can be selected from alkali carbonates and silicates, and their calcined, sintered, or ceramic forms, such as dolomite, kaolinite, calcium carbonate, magnesium carbonate, talc, silica sand, white silica sand, or alkali metal silicates, such as calcium silicate, sodium silicate, or mixtures thereof.

[0054] The dry mix composition according to the present invention may further contain water-redispersible polymer powder (RDP). The RDP can be formed in the conventional manner by spray-drying an emulsion polymer binder formed by conventional aqueous emulsion polymerization. The aqueous emulsion polymer can be selected from a variety of compositional classifications, such as vinyl acetate polymer, vinyl acetate-acrylic copolymer, vinyl acetate-ethylene copolymer, acrylic polymer, styrene-acrylic polymer, styrene-butadiene copolymer, and blends thereof. The RDP composition may further contain a solidification inhibitor such as clay and a colloidal stabilizer such as poly(vinyl alcohol), which enable the formation of a finely divided powder by spray-drying. The RDP can improve the adhesion and durability of skim coat mortar.

[0055] Other components in dry form, such as accelerators like calcium formate, additional organic or inorganic thickeners and / or secondary water-retaining agents like non-crosslinked cellulose ethers, anti-sagging agents, wetting agents, defoaming agents, dispersants, water-repellent agents, biopolymers, and fibers, may be included in the dry mix composition of the present invention. All of these other components are known in the art and are available from commercial sources.

[0056] The method for producing the polyether group-containing cellulose ether of the present invention by crosslinking cellulose ether may include crosslinking the cellulose ether in the presence of a corrosive agent or alkali in the reactor in which the cellulose ether itself is produced. Therefore, the crosslinking reaction is generally carried out in the step of producing cellulose ether. Since the step of producing cellulose ether involves the stepwise addition of reactants for forming alkyl or hydroxyalkyl groups on cellulose, preferably, the crosslinking of the cellulose ether is preceded by (i) one or more additions of an alkyl halide, such as methyl chloride, in the presence of an alkali for forming an alkyl ether of cellulose, or (ii) an alkylene oxide in the presence of an alkali for forming a hydroxyalkyl group on cellulose, or (iii) both of (i) and (ii).

[0057] Any step in the stepwise addition for forming alkyl, hydroxyalkyl, or ether groups on cellulose may be carried out at a temperature of 40 to 90°C, preferably 70°C or lower, or more preferably 65°C or lower, whether it occurs before, during, or after the crosslinking of the cellulose ether.

[0058] To prevent the cellulose ether from degrading or decomposing during processing, the crosslinking reaction is carried out in an inert atmosphere at a temperature of room temperature to 90°C or lower, or preferably at the lowest possible temperature. For example, this method is preferably carried out at 60°C to 90°C, or preferably at 70°C or higher.

[0059] After the polyether group-containing cellulose ethers of the present invention are prepared, they are granulated and dried. Granulation may be followed, if necessary, by dehydration or filtration to remove excess water.

[0060] The skim coat dry mix composition is formed by mixing all the materials of the present invention in their dry form. The cementitious skim coat composition is generally used as a dry mix powder.

[0061] According to the present invention, a method of using a dry mix includes mixing the dry mix with water to form a skim coat mortar and applying the mortar to a substrate. The skim coat mortar may be applied to a rougher substrate, such as concrete or cement rendering, to form a very smooth final coat. The final coat may be a smooth and homogeneous substrate for subsequent application of a building coating.

[0062] The mortar may be applied in multiple thin layers, for example, three layers, within a 3-4 hour application time frame. During this time, the skim coat mortar maintains good workability with hand tools and wet mortar properties, particularly freshness / tackiness and viscosity.

[0063] The composition of the present invention is used as a cementitious skim coat for concrete such as walls, fiber cement boards, and cement renderings. [Examples]

[0064] The present invention is illustrated by the following examples. Unless otherwise specified, all parts and percentages are by weight, and all temperatures are in °C. The following abbreviations are used in the following examples and in Tables 1, 2, and 3: RDP: redispersible polymer powder, DGE: diglycidyl ether, COV: crossover value. The following materials were used.

[0065] Cement: White Portland cement containing oxides of CaO2, SiO2, and Al2O3, meeting Indian standard IS:8042-1989 (Birla White® cement Ultra Tech Cement Ltd., Jodhpur, Rajasthan, IN).

[0066] Crosslinked Cellulose Ether 1: DGE crosslinked cellulose ether prepared from hydroxyethyl methylcellulose, DS (methyl) = 1.57, MS (hydroxyethyl) = 0.28, viscosity of product: 12690 mPa·s, 1% wt aqueous solution, shear rate: 2.55 s⁻¹, 20°C (Haake® Viscotester® VT550), COV = 0.65 rad / s (Anton Paar MCR302, Anton Paar). Crosslinked Cellulose Ether 1 has the viscosity of a 1% wt aqueous solution, measured using a Haake® Viscotester® VT550 viscometer at 20°C and a shear rate of 2.55 s⁻¹. -1 It was prepared from uncrosslinked cellulose ether with a pressure of 9960 mPa·s and a COV of 3.3 rad / s. The COV ratio of the crosslinked cellulose ether to the same uncrosslinked cellulose ether is approximately 1:5.

[0067] Cellulose ether 2: Very high viscosity methylhydroxyethylcellulose powder (TYLOSE MHS ​​300000 P6, non-crosslinked, viscosity 8000-11000 mPa·s Brookfield RV, 20 UpM, 1.0 wt% aqueous solution, 20℃, 20°dH, SE Tylose GmbH & Co. KG, Wiesbaden, DE).

[0068] Cellulose ether 3: (WALOCEL (trademark) MW 60000 PFV hydroxyethyl methylcellulose (HEMC, DS (methyl) = 1.38, MS (hydroxyethyl) = 0.21, viscosity 7830 mPa·s, 1 wt% aqueous solution, Haake (trademark) Viscotester (trademark) VT550, shear rate 2.55 s⁻¹, 20℃ (Dow)).

[0069] Crosslinking agent 1: Epilox® M985 poly(propylene glycol) diglycidyl ether crosslinking agent (Leuna-Harze GmbH, Leuna, DE) is made from polypropylene glycol (PPG), has a molecular weight of 850-1000 g / mol, and is formulated as follows: [ka] It is a linear poly(propylene glycol) diglycidyl ether having the formula (wherein n is 7 to 12).

[0070] RDP1:DLP2025 redispersible latex powder (Dow, Midland MI) is a readily flowing white powder obtained by spray-drying an aqueous vinyl acetate ethylene copolymer dispersion in the presence of an anti-caking agent and a colloidal stabilizer.

[0071] Packing material: Dolomite, average particle size on a 37 micron (400 mesh) sieve.

[0072] Example of cross-linked cellulose ether synthesis: Cross-linked HEMC cellulose ether was synthesized in the same manner as synthesis example 1A of Hild et al.'s U.S. Patent No. 10,150,704B2 (Hild reference), in the absence of cross-linking, at 20°C and a shear rate of 2.55 s at 9960 mPa·s. -1 Using a Haake® Viscotester® VT550 rheometer, the cellulose ether was prepared from a blend of approximately 75 wt% wood pulp and 25 wt% cotton linter, and further treated at 40°C with 1 0.003 mol crosslinking agent / mol AGU (anhydrous glucose units) in the manner disclosed in Synthesis Example 3 of the Hild reference. The resulting gel-like crosslinked cellulose ether had a viscosity of 12690 mPa·s (1 wt%, Haake® Viscotester® VT550, D=2.55s). -1 (20℃).

[0073] Cellulose ether was tested and characterized in aqueous solution form and in skim coat mortar having the compositions shown in Tables 1 and 2 below, as discussed below. [Table 1] *If the formulation contains less than 0.4% by weight of cellulose ether, the amount of dolomite is adjusted so that the total proportions add up to 100%. [Table 2] *Comparative examples are shown.

[0074] The dried mix was formed by carefully weighing the components shown in Tables 1, 2, and 3 above as individual raw materials on an electronic scale, drying and blending them as powders, and allowing them to stand for 24 hours. The dried mix material was then tested as follows.

[0075] Water Demand for Determining the Water-to-Powder Ratio: Water demand indicates viscosity, measured by the viscosity of the mortar paste. 500 gm of the indicated dry mix was mixed at a constant speed in a Hobart mixer at 25°C with a pre-measured amount of water (ranging from 35-40% of the dry mix) (approximately <40% less than required to make the mortar) to ensure a desired viscosity of 380,000-450,000 cPs or MPa·s. Mixing was continued for 1 minute, then the material was allowed to stand for 3 minutes, and then the material was mixed again for 1 minute to form a paste. The paste was filled into a 500 ml container, and the viscosity was measured at 5 rpm using a Brookfield rheometer (DVII) with a Helipath spindle no. T96 to determine if the target viscosity was achieved. If the paste achieved the desired viscosity of 380,000-450,000 cPs (mPa·s) at 25°C, the water level was reported as the water demand of the formulation. Otherwise, water was added as needed to achieve the target viscosity.

[0076] Workability: Visual testing methods were used to determine ease of application, feel, and leveling. Workability was determined from the paste after determining water requirements. Workability was measured by applying skim coat paste onto a fiber cement board (30.72 cm × 30.72 cm) using a flat-edge steel trowel (20.48 cm long) at 25°C. A rating of 9 to 1 was determined by an experienced experimental technician. A higher rating indicates better workability. The ratings are as follows:

[0077] 9: Excellent, has a creamy viscosity, is non-sticky, and is easy to level. 7: Good, has a creamy viscosity, and is easy to level. 5: Acceptable, has a buttery viscosity, is not very easy to level, and is slightly sticky. 3: Difficult, has a buttery viscosity, is not easy to level, dries very quickly, and is easily peeled off. 1: Poor viscosity, poor workability.

[0078] Pot Life: To determine the pot life, a 1 kg sample of the indicated skim coat paste was held in a pot at 25°C, and its workability was checked after 1, 2, and 3 hours as described above. Based on the workability evaluation, the pot life of the sample was recorded after the indicated period.

[0079] Water retention (%): The water retention of the indicated mortar was tested on a cardboard substrate at 25°C according to the method of DIN EN 1015, Part 8, and indicated the amount of water (expressed as a percentage) retained in the indicated paste after capillary water removal via the absorbent substrate. Thus, water retention indicates the effectiveness of cellulose ether as a water-retaining agent in inorganic mortar systems. The amount of absorbed water was measured after the indicated period (e.g., 60 minutes or 180 minutes). A water retention of >95% after 3 hours is considered acceptable.

[0080] Crossover point or crossover value (COV): This gel strength test was performed via vibrational rheology as defined above, using cellulose ether as a 1 wt% aqueous solution. The indicated cellulose ether or crosslinked cellulose ether was dissolved in water in an amount of 1.0 part by weight of cellulose ether and 99.0 parts by weight of water on a dry basis. To prepare the aqueous solution, the cellulose ether was dispersed in water at room temperature for 1 minute with stirring to avoid clump formation. The mixture was then stirred at 1000 rpm for 10 minutes. The solution was then stored in a round glass container tightly sealed with a lid and slowly rotated around its longitudinal (horizontal) axis for 24 hours.

[0081] The properties of the various cellulose ether materials and skim coat mortars tested in the examples are shown in Table 3 below. [Table 3] *-Comparative examples are shown. 1. The reduction value represents the reduction in the percentage amount of cellulose ether used compared to Example 5 (0.4% by weight).

[0082] As shown in Table 3 above, the dry mix compositions of the present invention in Examples 1 and 2 allow for the use of lower proportions of crosslinked cellulose ether while maintaining excellent water demand and workability / pot life. The compositions of the present invention exhibit dramatically improved water retention compared to all comparative examples (compared to Examples 1 to Comparative Examples 3 and 5, and Examples 2 to Comparative Example 4). Surprisingly, the compositions of the present invention enable such properties, including improved workability at lower doses for gel-like CE under harsh high-temperature application conditions.

Claims

1. A dry mix composition for use in the preparation of cementitious skim coat mortar, 15-33% by weight of white cement, A sieve containing 65-83% by weight, with an average particle size of 15-60 microns, and containing one or more fillers selected from dolomite, kaolinite, calcium carbonate, talc, silica sand, white silica sand, or alkali metal silicates, 0.15 to 0.75% by weight of one or more gel-like crosslinked cellulose ethers containing polyether groups, It comprises 0.5 to 5% by weight of one or more polymer redispersible powders (RDPs), All amounts are weight percent of the total solids in the dry mix composition, and all proportions add up to 100%. A dry mix composition comprising a 1.0 wt% aqueous solution of at least one of the one or more gel-like crosslinked cellulose ethers having a crossover point (COV) measured by vibrational rheometry, where the storage modulus (G') and loss modulus (G'') intersect and are identical, and G' and G'' are 1.0 (ω) or less, wherein the angular frequency (ω) in radians / second, measured in Pascals at 20°C using a Universal Dynamic Spectrometer™ UDS200 vibrational rheometer comprising a plate having a diameter of 50 mm and a cone having a conical angle of 1° and a conical point flattening of 0.05 mm, varies in the range of 0.1 to 100 (ω) with a 0.5% strain.

2. At least one of the one or more gel-like crosslinked cellulose ethers is present in the absence of crosslinking, at 20°C and a shear rate of 2.55 s. －１ The dry mix composition according to claim 1, which is a crosslinked cellulose ether having a viscosity of 10,000 to 70,000 mPa·s as measured as a 2% by weight aqueous solution in water using a Haake® Viscotester® VT550 rheometer.

3. The dry mix composition according to claim 1, wherein the RDP comprises vinyl acetate polymer, vinyl acetate-acrylic copolymer, vinyl acetate-ethylene copolymer, acrylic polymer, styrene-acrylic polymer, styrene-butadiene copolymer, or a blend thereof.

4. The dried mix composition according to claim 1, wherein the polyether group in at least one of the one or more gel-like crosslinked cellulose ethers is a polyoxyalkylene selected from polyoxyethylene, polyoxypropylene, and combinations thereof.

5. The dried mix composition according to claim 1, wherein at least one of the one or more gel-like crosslinked cellulose ethers is a mixed cellulose ether containing a hydroxyalkyl group and an alkyl ether group.

6. The dried mix composition according to claim 5, wherein at least one of the one or more gel-like crosslinked cellulose ethers is a non-mixed cellulose ether containing an alkyl ether group.

7. The dried mix composition according to claim 1, wherein at least one of the one or more gel-like crosslinked cellulose ethers is polyoxypropylene group-containing hydroxyethyl methylcellulose.

8. The dried mix composition according to claim 1, wherein at least one of the one or more gel-like crosslinked cellulose ethers is a mixed cellulose ether having polyoxypropylene dioxyethylene ether crosslinking.

9. The dried mix composition according to claim 1, wherein at least one of the one or more gel-like crosslinked cellulose ethers is a reaction product of hydroxyethyl methylcellulose and polypropylene glycol (PPG) glycidyl ether.

10. The dry mix composition according to claim 1, wherein the ratio of the COV of the gel-like crosslinked cellulose ether to the COV of the same cellulose ether without crosslinking is 1:15 to 0.5:

1.

11. A method for using the dry mix composition described in claim 1, comprising: preparing a mortar by combining the dry mix composition with water or an aqueous liquid; and applying the mortar to a substrate to form a skim coat.

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