WO2008122344A1

WO2008122344A1 - Methylhydroxyethylhydroxypropylcellulose (mhehpc) in mineral-bound building material systems

Info

Publication number: WO2008122344A1
Application number: PCT/EP2008/002094
Authority: WO
Inventors: Meinolf Brackhagen; Grit Grote; Martin Kowollik; Hartwig Schlesiger
Original assignee: Dow Wolff Cellulosics Gmbh
Priority date: 2007-04-07
Filing date: 2008-03-15
Publication date: 2008-10-16
Also published as: DE102007016726A1

Abstract

The present invention relates to the preparation of methylhydroxyethylhydroxypropylcellulose (MHEHPC) and the use thereof in mineral-bound building material systems, preferably gypsum-bound building material systems, particularly preferably in gypsum machine plaster.

Description

Methylhydroxyethylhydroxypropylcellulose (MHEHPC) in mineral-bound building material systems

The present invention relates to the preparation of methylhydroxyethylhydroxypropylcellulose (MHEHPC) and the use thereof in mineral-bound building material systems, preferably in gypsum-bound building material systems, particularly preferably in gypsum machine plaster .

The class of substances consisting of the cellulose ethers, in particular the group consisting of the binary alkylhydroxyalkylcelluloses with the commercially utilized members methylhydroxyethyl- cellulose (MHEC) and methylhydroxypropylcellulose

(MHPC) has for several decades been a universal and industrial field of activity and has often been described. An overview of the chemical fundamentals and principles of the production (production processes and process steps) and a material composition and description of the properties and potential uses of the various derivatives appear, for example, in Houben- Weyl , Methoden der Organischen Chemie, Makromolekulare Stoffe [Methods of Organic Chemistry, Macromolecular Substances], 4^th Edition, Volume E20, page 2042 (1987). The commercially utilized methylhydroxyalkylcelluloses form viscous solutions in water at room temperature and are insoluble in hot water at temperatures above the flocculation point.

The preparation of methylhydroxyalkylcellulose may be summarized as follows: The activation of this cellulosic starting material preferably with alkali solution, is effected in an upstream part-step. Subsequently, the alkali metal cellulose formed is reacted with methyl chloride and an alkylene oxide under forced conditions, any alkali used in excess expediently being substantially neutralized with super- stoichiometric amounts of methyl chloride. In a subsequent cleaning step, salt formed and other byproducts are separated off, preferably by washing with hot water.

The preparation of ternary methylhydroxyalkylcelluloses is likewise known and is described, for example, in the patents US 3 873 518 (= DE 24 57 187), EP 0 120 430 Al and EP 1 180 526 Bl.

The alkyl substitution is described in cellulose ether chemistry generally by the DS. The DS is the average number of substituted OH groups per anhydroglucose unit. The methyl substitution is specified, for example, as DS (methyl) or DS (M) .

Usually, the hydroxyalkyl substitution is described by the MS. The MS is the average number of moles of the esterification reagent which are bound in an ether-like manner per mole of anhydroglucose units. The etherification with the etherification reagent ethylene oxide is accordingly stated as MS (hydroxyethyl) or MS

(HE) and the etherification with the propylene oxide as

MS (hydroxypropy1 ) or MS (HP) .

The determination of the DS and MS is effected by the Zeisel method known to the person skilled in the art, described, for example, in P. W. Morgan, Ind. Eng. Chem. Anal. Ed. 18 (1946) 500-504, and R. U. Lemieux, CB. Purves, Can. J. Res. Sect. B 25 (1947) 485-489.

The still water-moist cellulose ether obtained by washing with hot water and freed from byproducts and having a water content of in general > 50% by weight is converted into a saleable form optionally after further pretreatment (conditioning) by subsequent drying and milling. The cellulose ethers are commercially available preferably in powder or granular form having a water content of about 1-10% by weight.

Cellulose ethers are used in building material systems, such as, for example, manual and machine plasters, and filling compounds, as thickeners and water retention agents .

The properties of these building material systems, in particular the consistency and the setting behavior, can be greatly influenced by the choice of the cellulose ether.

Particularly in gypsum-bound building material systems, i.e. gypsum-containing base mixes to which water has been added, clusters, lumps or nodules are often observed, which, in the most unfavorable case, can lead to irregularities and furrows and at least result in delays due to intensive reworking.

Attempts have been made to overcome some of these problems by combinations of admixtures. Thus, WO 99/64368 discloses a mixture of additives which mainly comprises cellulose ether, for example methyl- hydroxypropylcellulose (MHPC) and small amounts of a polymerized carboxylic acid and of a methacrylate or acrylate homo- or interpolymer . Unfortunately, the preparation of this mixture of additives is complicated, requires additional mixing units and does not always lead to a reduction of agglomeration. In addition, the use of aqueous carboxylic acid solutions can lead to a pH-induced chain degradation of the cellulose ether. No statement is made about the processability of the plaster.

There is to date therefore an ongoing demand for providing a cellulose ether for improving the processing properties of mineral-bound building material systems, in particular for effectively reducing the agglomeration in gypsum-bound building material systems and at the same time for improving the processing properties.

Methylhydroxyethylhydroxypropylcelluloses (MHEHPC) are well known as thickeners in dispersion-bound coating materials (US 3 873 518 or DE 24 57 187) . According to the teaching of DE 2457187 MHEHPC having a DS (methyl) of from 0.396 to 1.216, an MS (hydroxyethyl) of from 0.335 to 1.087 and an MS (hydroxypropyl) of from 0.381 to 1.286 is used, which MHEHPC has a thermal gel point of > 70⁰C and is preferably both water- and methanol- soluble. Higher degrees of substitution, in particular with regard to the DS (methyl), are not advantageous, so that their suitability for property improvement in dispersion-bound systems, such as emulsion paints, is greatly dependent on the degree of substitution.

Surprisingly, it was found that the processing properties of mineral-bound building material systems, in particular of a gypsum-bound system, can be improved by addition of methylhydroxyethylhydroxypropylcellulose

(MHEHPC) . This effect is further enhanced if a mill drying step is passed through during the preparation for drying and granulation the feed material here having a very specific moisture content.

The invention therefore relates to mineral-bound building material systems containing methylhydroxy- ethylhydroxypropylcellulose (MHEHPC) .

Preferred mineral-bound building material systems are gypsum-bound building material systems, particularly preferably gypsum machine plaster.

The methylhydroxyethylhydroxypropylcelluloses (MHEHPC) to be used according to the invention typically have a DS (methyl) of > 1.30 or > 1.30, preferably > 1.45, particularly preferably of > 1.55, very particularly preferably of > 1.65.

The upper limit of the DS (methyl) is chosen so that the product is soluble in water at room temperature; the DS is preferably < 2.3, particularly preferably < 2.1 and very particularly preferably < 1.95.

The lower limit of the MS (hydroxyethyl) is typically 0.10, preferably 0.20, particularly preferably 0.25 and very particularly preferably 0.30. The upper limit of the MS {hydroxyethyl) is chosen so that the MHEHPC has a thermal flocculation point in water of < 100⁰C. The upper limit of the MS (hydroxyethyl) is therefore typically 0.70, preferably 0.60 and particularly preferably 0.50.

The lower limit of the MS (hydroxypropyl) is typically 0.20, preferably 0.30, particularly preferably 0.35 and very particularly preferably 0.40. The upper limit of the MS (hydroxypropyl) is typically 0.80, preferably 0.70 and particularly preferably 0.60.

The values for MS (hydroxyethyl) and MS (hydroxypropyl) preferably correspond to the above data, the value of the MS (hydroxyethyl) being from 0.3 to 1.3 times, particularly preferably from 0.4 to 1.2 times, particularly preferably from 0.5 to 1.1 times the value of the MS (hydroxypropyl) .

The methylhydroxyethylhydroxypropylcelluloses (MHEHPC) according to the invention are typically prepared by milling and drying the water-moist cellulose ether obtained after the reaction of cellulose with methyl chloride, ethylene oxide and propylene oxide and subsequent purification with hot water. The reaction and purification of the methylhydroxyethylhydroxy- propylcelluloses (MHEHPC) are effected according to the prior art. For example, the purification can be carried out with the use of centrifuges or hydrocyclones with optionally subsequent ultrafiltration as disclosed in EP 0 632 056. In a preferred purification process, a rotary pressure filter is used, as described, for example, in EP-B 1 652 860.

The water-moist filter cake can be conditioned prior to milling by, for example, adding additives, modifiers or further water, cooling the water-moist filter cake or mechanically compacting it.

It has proven particularly advantageous if the methyl- hydroxyethylhydroxypropylcelluloses (MHEHPC) used in the mill drying have a special moisture content of the material to be milled with respect to the water content .

The present invention therefore also relates to a process for the preparation of milled/dried methyl- hydroxyethylhydroxypropylcellulose (MHEHPC) , in which, as feed material, water- and optionally alcohol-moist methylhydroxyethylhydroxypropylcellulose having a DS (methyl) of > 1.30, an MS (hydroxyethyl) of > 0.10, an MS (hydroxypropyl) of > 0.20 and a water content of from 35 to 63% by weight is subjected to mill drying.

The water content is preferably not more than 61% by weight, particularly preferably not more than 57% by weight, very particularly preferably not more than 53% by weight and most preferably not more than 50% by weight .

The water content is, however, preferably at least 38% by weight, particularly preferably at least 40% by weight, very particularly preferably at least 42% by weight and most preferably at least 44% by weight. Lower water contents in the filter cake are achievable only by disproportionately long filtration times or predrying of the filter cake.

For establishing abovementioned moisture contents, water or filter cake having a higher moisture content can be added in the case of values which are too low. For reducing the moisture content of a filter cake, it is preferable to admix already dried and milled cellulose ether powder or granules .

The addition of dried and milled cellulose ether powder or granules to the optionally conditioned water-moist filter cake can be effected continuously or batchwise at various points after the filtration. The addition is preferably effected outside the milling chamber. The mixing can be carried out, for example, in a commercially available mixer or in a conveying screw. A mixing member and/or a conveying screw which ensures adequate thorough mixing is preferably present between the location of the addition and the mill.

The dried and already milled cellulose ether powder or granules used for adjusting the moisture content is preferably added by means of a metering device which permits the targeted adjustment of the desired range of the total moisture content of the composition. The cellulose ether powder may completely or partly comprise the oversize occurring during the milling, which is metered continuously or batchwise to the optionally conditioned water-moist filter cake.

The flowability of the optionally conditioned water- moist filter cake is generally substantially improved by the addition of the dried and milled cellulose ether powder or granules and hence blockages and caking in the plant can be reduced.

By mixing the water-moist filter cake with dried cellulose ether powder or granules, it is possible to establish moisture contents of the material to be milled which cannot be achieved by economical filtration methods.

The material to be milled, consisting either of an optionally conditioned water-moist filter cake of an MHEHPC or of a composition which additionally contains dried and milled cellulose ether powder or granules is then comminuted and dried by known methods.

Preferably no (pre) drying is effected before the milling; particularly preferably, drying is effected simultaneously with the milling.

Particularly preferably, a reduction of the water content is effected simultaneously with the comminution so that the difference between the water contents in % by weight, based on the total mass, between mill entrance and exit is more than 10% by weight, preferably more than 20% by weight, particularly preferably more than 35% by weight.

Methods for the simultaneous comminution and drying of cellulose ethers are known, for example, from the teaching of GB 2 262 527, DE 38 39 831, EP 1 127 910 and EP 1 127 895. Various mill types may be used, for example pinned-disk mills, bowl mills, hammer mills, screen mills, hammer bar mills and impact mills. The effective drying is preferably supported by the use of gas or gas mixtures heated to temperatures of > 80⁰C, preferably > 100⁰C, in the comminution apparatus. The mill drying can be followed by further milling and/or drying steps. However, the milling is preferably effected in one stage and a screenless high-speed impact mill is used as the mill.

After the milling and drying stage, the product stream can be classified and the oversize completely or partly recycled batchwise or continuously to the process.

After the milling and drying, which are preferably carried out simultaneously in the form of mill drying, the methylhydroxyethylhydroxypropylcelluloses (MHEHPC) have a residual moisture content, based on the proportion of water in the solid, of from 0.1 to 15% by weight, preferably from 1 to 10% by weight, particularly preferably from 1.5 to 7% by weight.

The invention furthermore relates to the methylhydroxy- ethylhydroxypropylcelluloses (MHEHPC) obtainable by the process according to the invention.

The methylhydroxyethylhydroxypropylcelluloses according to the invention preferably have the following grading curve :

The viscosity of the products at 23°C, measured as a 2% by weight solution in water using a Haake Rotovisko at 2.55 s^'1, is preferably from 10 to 200 000 mPa-s, particularly preferably from 100 to 150 000 mPa-s, very particularly preferably from about 1000 to 100 000 mPa-s and most preferably from 10 000 to 80 000 mPa-s.

The bulk density of the products, measured on a loose bed, is preferably from 200 to 700 g/1, particularly preferably from 250 to 650 g/1 and very particularly preferably from about 300 to 600 g/1.

The cellulose ethers essential to the invention permit the production of mineral-bound building material systems, preferably gypsum-bound building material systems having particularly advantageous properties. In particular, such gypsum-bound building material systems exhibit reduced agglomeration and improved processability compared with the prior art on mixing with water for the production of gypsum-bound building material systems .

The methylhydroxyethylhydroxypropylcellulose (MHEHPC) is used in amounts of from 0.01 to 5% by weight, preferably from 0.1 to 0.8% by weight and particularly preferably from 0.2 to 0.4% by weight, based in each case on the dry mass of the mineral-bound building material system.

In addition to the cellulose ether, the mineral binder and water, for example, but not only, the following ingredients may be present in such mineral-bound building material systems:

• Slaked lime 0-30% by weight

• Mineral aggregates 0-30% by weight

(e.g. quartz sand, limestone sand, limestone gravel, limestone powder, mica)

• Lightweight aggregate 0-20% by weight (e.g. Perlite)

• Plastic dispersion powder 0-20% by weight

• Fibers 0-2% by weight (e.g. cellulose fibers)

• Accelerator 0-0.8% by weight

• Added thickener 0-0.5% by weight

(e.g. starch derivatives and guar derivatives, synthetic thickeners, polyacrylamide, polyvinyl alcohol )

• Retardant 0-0.5% by weight

• Air-entraining agent 0-0.1% by weight

The water/solids ratio in the mineral-bound building material systems according to the invention is preferably from 0.3 to 0.9, particularly preferably from 0.4 to 0.8.

It is known to a person skilled in the art that cellulose ethers cannot usually be used alone but with a number of additives and/or modifiers in the base mixes. Thus, for example in basic building material mixes, methylhydroxypropylcelluloses can be used as a mixture with small amounts of auxiliaries and additives, e.g. antifoams, swelling agents, fillers, lightweight aggregates, polyacrylates, polyacrylamides , air-entraining agents, dispersants, water repellents, plasticizers , superabsorbers , stabilizers and synthetic, semisynthetic and natural thickeners.

Examples

A water-moist filter cake of a methylhydroxyethyl- hydroxylpropylcellulose having a DS (methyl) = 1.69, an MS (hydroxyethyl) = 0.43 and an MS (hydroxypropyl) = 0.54 is divided into two portions after washing with hot water. One portion each is adjusted to a water content of 48% by weight and 63% by weight, respectively .

Each portion is then comminuted and dried separately in a screenless high-speed gas jet rotary mill having a vertically arranged driveshaft and seven grinding tracks which are equipped with impact plates which operate against a profiled opposite grinding track. The drying and transport gas used is nitrogen, which is fed to the gas circulation at various points. Downstream of the mill is a cyclone where the main proportion of the finely milled product is deposited. The gas stream is then freed from residual dust in a downstream bag filter.

Arranged on the pure gas side is a radial fan which transports the dust-free gas stream into a heat exchanger where the transport gas is heated to the required drying temperature and finally passed back into the mill. The proportion of water vapor in the circulation gas is removed from the circulation gas before the mill in a gas scrubber arranged after the cyclone, so that a nitrogen-rich carrier gas composition is maintained.

Excess circulation gas is discharged from the gas circulation via a valve.

Various MHPC (MHPC 1 and 2) are prepared by the same process .

Use in a gypsum machine plaster

The products MHEHPC 1 and 2 and MHPC 1 and 2 were used in a base mix for a light gypsum machine plaster (0.24% by weight of cellulose ether, based on the total base mix) and applied to a wall by means of a plastering machine. The processability, the agglomeration and the surface appearance were rated according to school grades, 1 (very good) being the best grade and 5 (poor) being the poorest grade. The following symbols are used: very good: ++, good +, satisfactory o, adequate -, poor --.

The best surface appearance is achieved with MHEHPC 1. The lumps formed are destroyed again during processing. In the case of MHEHPC 2, which was prepared with a higher moisture content of the material to be milled, some lumps remain hidden below the plaster surface and lead to irregularities in the surface. The comparative samples show pronounced agglomeration which cannot be compensated again in the course of the further processing.

Use in a synthetic resin plaster I (comparative experiment)

For the production of a synthetic resin plaster according to DE-A 24 23 618, a solution of 2% by weight of the cellulose ethers MHEHPC 1 and 2 and MHPC 1 and 2 is prepared. For this purpose, an amount of 7 g of cellulose ether is added to 343 g of water with stirring. The stirrer used was an RW20 DZ from Jahnke & Kunkel, which was operated at 2000 rpm and was equipped with a propeller stirrer tool. In the case of all cellulose ethers used, intensive agglomeration was likewise found on sprinkling in.

Use in a synthetic resin plaster II (comparative experiment)

In a further experiment, the procedure was effected according to DE-A 102 38 242 and a binder premix comprising 2% by weight of cellulose ether and 4% by weight of a redispersible powder based on a vinyl acetate homopolymer was prepared. The cellulose ether used is in each case the MHEHPC 1 and MHEHPC 2 according to the invention or MHPC 1 or 2 as a comparison. For this purpose, 329 g of water was stirred at 2000 rpm with a propeller stirrer and 7 g of cellulose ether and 14 g of a redispersible powder based on a vinyl acetate homopolymer were added. After stirring for 15 minutes at this speed, lumps were still detectable regardless of the cellulose ether used.

Claims

Patent claims

1. A mineral-bound building material system containing methylhydroxyethylhydroxypropylcellulose (MHEHPC) .

2. The mineral-bound building material system as claimed in claim 1, characterized in that it is a gypsum-bound system.

3. The mineral-bound building material system as claimed in claim 1 or 2, characterized in that the methylhydroxyethylhydroxypropylcellulose is present in amounts of from 0.01 to 5% by weight, based on the dry mass of the mineral-bound building material system.

4. A process for the preparation of mill dried methylhydroxyethylhydroxypropylcellulose (MHEHPC) , in which water- and optionally alcohol-moist methyl- hydroxyethylhydroxypropylcellulose having a DS (methyl) of > 1.30, an MS (hydroxyethyl) of > 0.10, an MS (hydroxypropyl) of > 0.20 and a water content of from 35 to 63% by weight, as feed material, is subjected to mill drying.

5. The process as claimed in claim 4, characterized in that the mill dried methylhydroxyethylhydroxy- propylcellulose is prepared by milling and drying the water-moist cellulose ether obtained after the reaction of cellulose with methyl chloride, ethylene oxide and propylene oxide and subsequent purification with hot water .

6. The process as claimed in claim 5, characterized in that the methylhydroxyethylhydroxypropylcellulose has a

DS (methyl) in the range of more than 1.30 to less than 2.3, an MS (hydroxyethyl) in the range of at least 0.10 to not greater than 0.70, and an MS (hydroxypropyl) in the range of at least 0.20 to not greater than 0.80.

7. The process as claimed in claim 4 or 5, characterized in that the value of the MS (hydroxyethyl) being from 0.3 to 1.3 times the value of the MS (hydroxypropyl) .

8. The process as claimed in any of claims 4 to 7 , characterized in that the water content of the feed material is adjusted by mixing at least two methylhydroxyethylhydroxypropylcelluloses of different moisture contents.

9. The process as claimed in claim 8, characterized in that at least one methylhydroxyethylhydroxypropyl- cellulose having a moisture content of from 0.1 to 15% by weight is used for moisture adjustment.

10. The process as claimed in any of claims 4 to 9 , characterized in that at least one methylhydroxyethyl- hydroxypropylcellulose having a water content of less than < 62% by weight but more than 44% by weight is used for providing the feed material .

11. The process as claimed in any of claims 4 to 10, characterized in that the process is operated so that the mill dried methylhydroxyethylhydroxypropylcellulose has a residual moisture content, based on water, of from 1.5 to 7% by weight.

12. A mill dried methylhydroxyethylhydroxypropyl- cellulose obtainable by a process as claimed in any of claims 4 to 11.

13. The mineral-bound building material system as claimed in any of claims 1 to 3 , characterized in that a mill dried methylhydroxyethylhydroxypropylcellulose as claimed in claim 12 is used.