O/W wax dispersions and gypsum products obtainable from these

Abstract

The invention relates to O/W wax dispersions based on water, an emulsifier and a wax phase containing predominantly aliphatic hydrocarbons and polar compounds having chain lengths of at least 18 carbon atoms, and also plaster compositions comprising the O/W wax dispersion, and the use of the O/W wax dispersion.

Claims

1. A gypsum composition with an O/W wax dispersion added, the O/W wax dispersion comprising: at least 30% by wt. water, at least 20% by wt. wax phase as the disperse phase, wherein the wax phase has a saponification number greater than 0.2 mg KOH/g, at least 0.1% by wt. of an emulsifier or thickening agent as dispersing adjuvant, and wherein the wax phase comprises the following, based on the wax phase: 50 to 98% by wt. aliphatic hydrocarbons (HC) or mixtures thereof, each with a solidification point above 50 C. and below 95 C., 2 to below 50% by wt. of one or more polar, long-chain compounds with at least 18 carbon atoms selected from the group of oxidized Fischer-Tropsch waxes, oxidized paraffins, oxidized polyethylene, and mixtures thereof, wherein the gypsum composition comprises greater than 50% by wt. of calcium sulphate dehydrate and 0.1 to 5% by wt. of the wax phase of the O/W wax dispersion.

2. The gypsum composition according to claim 1, characterized in that the proportion of HCs being linear is greater than 50% by wt.

3. The gypsum composition according to claim 2, wherein the degree of linearity of the HCs is greater than 65% by wt.

4. The gypsum composition according to claim 1, characterized in that the wax dispersion has a pH value of 11 to 13.

5. The gypsum composition according to claim 1, characterized in that the wax phase contains under 0.2% by wt. substituted phenols.

6. The gypsum composition according to claim 1, characterized in that the wax dispersion comprises from 0.5 to 4% by wt. of at least one of polyvinyl alcohols and partially hydrolysed polyvinyl alcohols.

7. The gypsum composition according to claim 1, characterized in that the wax dispersion was added to a gypsum slurry to form the gypsum composition.

8. An O/W wax dispersion comprising: at least 30% by wt. water, at least 20% by wt. wax phase as the disperse phase, wherein the wax phase has a saponification number greater than 0.2 mg KOH/g, at least 0.1% by wt. of an emulsifier or thickening agent as dispersing adjuvant, and wherein the wax phase comprises the following, based on the wax phase: 50 to 98% by wt. aliphatic hydrocarbons (HC) or mixtures thereof, each with a solidification point above 50 C. and below 95 C., 2 to below 50% by wt. of one or more polar, long-chain compounds with at least 18 carbon atoms selected from the group of oxidized Fischer-Tropsch waxes, oxidized paraffins, oxidized polyethylene, and mixtures thereof.

9. The wax dispersion according to claim 8, characterized in that the proportion of HCs being linear is greater than 50% by wt.

10. The wax dispersion according to claim 9, wherein the degree of linearity of the HCs is greater than 65% by wt.

11. The wax dispersion according to claim 8, characterized in that the wax dispersion has a pH value of 11 to 13.

12. The wax dispersion according to claim 8, characterized in that the wax phase contains under 0.2% by wt. substituted phenols.

13. The wax dispersion according to claim 8, characterized in that the wax dispersion comprises from 0.5 to 4% by wt. of at least one of polyvinyl alcohols and partially hydrolysed polyvinyl alcohols.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram showing the production of O/W emulsions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) Advantageous embodiments are the subject of the dependent claims or are described below. Also claimed are gypsum compositions, as described above, containing wax dispersions and the use of wax dispersions in such gypsum compounds or else the gypsum products described above.

(3) Substances that can be used as aliphatic hydrocarbons according to the invention are paraffin, synthetic Fischer-Tropsch waxes and alphaolefins (AO, hydrated and unhydrated) with a solidification point of over 50 C. and below 95 C. and, particularly, with average C chain lengths greater than 25 in each case.

(4) Polar compounds within the meaning of the present invention are compounds displaying hydrocarbon chains with per molecule over 18 C atoms and at least one hydroxyl group, an ether group and/or a carboxyl group (C(O)O), possibly also derivated, i.e. esterified or saponified. The polar compounds display no more than three of the aforementioned groups or a total of three polar groups, particularly one or two groups, per molecule overall.

(5) The further polar compounds may be oxidised and possibly also partially saponified Fisher-Tropsch waxes, oxidised paraffin, oxidised polyethylene, so-called PE wax esters (jointly referred to as oxidised hydrocarbons (HC) or partially saponified oxidised HC's) and modified natural and/or synthetic resins, as well as natural waxes. Furthermore, fats (triglycerides), e.g. of vegetable origin, such as palm, soya and rapeseed fats, are suitable. The acid groups contained in the polar additives may be saponified during the course of the wax dispersion production with the aid of alkaline substances (e.g. potassium or caustic soda). These lyes are overdosed in this case, so that pH values of over 11 are obtained. This also has a favourable effect on the resistance of the wax dispersions to biological decomposition and mildew. The Wax dispersion comprises esterified colophonium resins such as glycerine and/or pentaerythrite maleic acid colophonium resins, beeswax and/or carnauba wax, wherein the colophonium-resins preferably are used in combination, particularly with oxidised HC's and/or partially saponified oxidised HC's.

(6) It is particularly preferable for the wax dispersion to contain carnauba wax as a constituent part of the polar compounds, particularly at 1 to 20% by wt., particularly 1 to 15% by wt., relative to the wax phase.

(7) Particularly advantageous are mixtures of polar compounds, which contain as polar compounds the above oxidised hydrocarbons (HC) or partially saponified, oxidised HC's (greater than 1% by wt.) and carnauba wax (greater than 1% by wt.) or the above oxidised hydrocarbons (HC) or partially saponified, oxidised HC's (greater than 1% by wt.) and the above synthetically modified colophonium resins. The percentages by weight each relate to the wax phase (=100% by wt.).

(8) The water-repellent effect is reinforced if the polar compounds contain as the predominant constituent part oxidised and possibly also partially saponified Fischer-Tropsch waxes, oxidised paraffin, oxidised polyethylene, so-called PE waxes and, as the lesser component, fats (e.g. palm fats or soya oils) and/or fatty alcohols (e.g. Nafol 20+). This produces synergistic effects. In other words, the reduction in water absorption when additives are combined increases even more than can be expected from the sum of the individual effects.

(9) In this case, the wax phase is preferably added to the gypsum slurry in the form of an aqueous wax dispersion, as gypsum board production is water-based and the dosing of the wax phase can therefore be significantly more accurate. Furthermore, the preferably small particle size of the disperse wax phase (average particle size less than 2 m and particularly roughly 1 m) ensures a particularly uniform distribution of the active substance in the gypsum slurry.

(10) In principle, all types used for the production of wax dispersions, i.e. non-ionic, anionic and cationic emulsifier types, but also combinations of these (non-ionic with anionic and non-ionic with cationic) are suitable as emulsifiers. Non-ionic and anionic emulsifiers are particularly suitable. Furthermore, emulsifiers that achieve stabilisation by concentrating the water phase are also suitable. These may be natural resins, for example, (Gum Ghatti, derivated cellulose) or xanthane polymers or else polysaccharide, but also inorganic substances of the bentonite type. Particularly suitable as emulsifiers are sulphonates such as naphthaline sulphonate and/or lignin sulphonate, preferably along with a thickening agent such as Gum Ghatti, in particular.

(11) Furthermore, polyvinyl alcohols may be added to the wax dispersion, particularly up to 0.5 to 4% by wt. relative to the wax dispersion, which are available, for example, as partially hydrolised ethylene vinyl acetate polymers, but also produced from acrylates and other polyvinyl esters. Degrees of hydrolysis of over 70%, particularly over 85%, are desirable, but not a requirement.

(12) The compositions according to the invention are advantageously wax dispersions, which can be produced with the aid of homogenisers. In this case, at least two phases are combined with one another (pre-emulsion).

(13) At least the wax-containing phase is heated above the solidification point for this, in order to melt the wax. The other phase is the aqueous phase. This is preferably mixed with the emulsifier and is advantageously heated likewise.

(14) The pre-emulsion is then passed through the circuit e.g. via splitting homogenisers, until the desired particle size of the wax phase is achieved. The emulsion is then cooled to temperatures below the solidification point of the wax phase. The individual wax particles of the disperse phase are evenly distributed in the aqueous, continuous phase by the process and a wax dispersion with prolonged stability is thereby obtained. The wax dispersion is thereby created. This is an oil in water (O/W) wax suspension with an average particle diameter of particularly 0.1 to 10 m, advantageously 0.5 to 2 m. The wax dispersion according to the invention is particularly suitable for the production of the water-repellent gypsum compositions described above, particularly those containing or comprising foamed gypsum or aerated gypsum and, in particular, coated gypsum plasterboard, preferably using the aforementioned gypsum.

(15) FIG. 1 shows how the O/W emulsions are typically produced. In a wax boiler (1) fitted with a temperature sensor and temperature monitoring system, the wax emulsifier (2), water and hot steam (3) are produced, agitated and moved into the pre-emulsion boiler (4) by means of a pump (5), where the water-emulsifier mixture (6) is added. Delivery and transfer into the homogeniser (8) takes place using the pump (7). By means of a cooling medium (9), the temperature of the emulsion is lowered in the cooling system (10), e.g. to 30 C., in order to obtain the finished wax dispersion (11).

(16) Experiments

(17) The degree of water repellence can be determined by subjecting the gypsum body to an immersion test. This involves the water absorption being determined in % by wt. after a 120 minute immersion period (H.sub.2O 120 mins column in the following table). Suitable threshold values in this case are <10% by wt. and, particularly, <5% by wt. water absorption.

(18) Table 1 shows the data for the finished wax phases (% stands for % by wt. in each case). It emerges that predominantly hard wax phases (needle penetration at 25 C.<20 [0.1 mm] in accordance with ASTM D1321) with solidification points of between 60 and 80 C. and also acid numbers (DIN 51558) of between 0 and 10 (mg KOH/g) and also saponification numbers from 0 to 20 mg KOH/g have a beneficial effect on water repellence. This produces the values required by DIN 18180 of <10% by wt. water absorption. The water absorption is therefore significantly reduced compared with the blind value (31%) of the natural gypsum used in this case, which demonstrates the effect of the wax mixtures used as wax dispersions. The wax dispersions (WD) were made according to the following suggested formulation:

(19) 60% by wt. water; 3% by wt. Marlophen NP 10 (non-ionic surfactant from Sasol Olefins and Surfactants GmbH on an ethoxylate base); 1% by wt. KOH (45% by wt.) and 36% wax phase.

(20) Laboratory Production of the Wax Dispersion:

(21) The water was heated to approx. 80 C. along with the surfactant and the KOH and agitated for roughly 20 mins. The molten (80-100 C.) wax phase was then added and agitated for a further 5 minutes. The pre-emulsion was added to the homogeniser and passed through the circuit for 1 minute, after which it was homogenised for 1 minute at a pressure of roughly 200 bar. The wax emulsion was then cooled to room temperature during which the wax particles solidified and the wax dispersion was produced.

(22) TABLE-US-00002 TABLE 2 Substances used Name Type Manufacturer Paraffin Sasolwax 6403 (Fully Sasol Wax GmbH Paraffin) EP 64/66 Carnauba wax Natural palm wax Kahl & Co Resin Escorez 1102 F, aliphatic Exxon Mobil hydrocarbon resin

(23) TABLE-US-00003 TABLE 1 Properties of different wax dispersions PenN2 5 Paper Start of End of Flow Data (1) AN SN Foam H.sub.2O adhesion hard- hard- measure Composition EP (0.1 (2) (3) reduc- 120 min (6) ening (6) ening (6) (6) No. Dispersion/unit ( C.) mm) (mgKOH/g) tion (4) (5) (% by wt.) Min (*) * Gypsum blind value 31 = 6 9 = VI* Montan wax/ 70.5 10 3 8.7 = 2.4 + +2 +4 Higher ** paraffin V2 Montan wax/ 64.5 11 3.1 9 = 2.5 + +2 +4 Higher ** paraffin 1 Carnauba wax/ 66 16 0.3 1.4 = 2.3 + = +4 Higher paraffin (2.5% carnauba) 2 Carnauba wax/ 65 11 0.5 4.1 Smaller 4.6 + +2 +2 = paraffin (5% carnauba) 3 Carnauba wax/ 67 11 1 8.2 = 3.6 + = +4 Thicker resin/paraffin (10% carnauba, 5% escorez) 4 Carnauba wax/ 66 19 1 8.2 6 paraffin (10% carnauba wax) Key to Table 1 (*) Blind value of the untreated natural gypsum 31% (**) These two dispersions serve for comparison purposes with the state of the art (1) Solidification point ASTM D 938 (2) Needle penetration ASTM D 1321 at 25 C. (3) Acid number according to DIN 51558 (4) Saponification number according to DIN 51559 (5) Water absorption according to DIN 81180 (6) Internal house methods + better than blind value (possibly better than gypsum value by how much) = equal to blind value not measured