DK143270B - PROCEDURE FOR THE MANUFACTURING OF CASTLE PLASTICS - Google Patents

Description

143270

The invention relates to a process for making cast gypsum articles with the addition of tartaric or tartaric salts, in particular for the manufacture of a building element, such as a building spade, with a reduced propensity for plastic flow under moist conditions by casting a plastic mixture of gypsum and water.

Items of cast plaster, e.g. plasterboard, in the presence of substantial amounts of free moisture, tends to deform under tension due to a phenomenon known as "plastic flow". A distinction is made between plastic flow which can occur only under the influence of the weight of the object itself and the virtually instantaneous elastic deflection which occurs, e.g. when a load is applied to a beam. The latter phenomenon follows the well-known physical laws, is completely predictable and is insignificant compared to the plastic flow which can occur in adverse circumstances. A plastic flow occurs slowly and increases in size over time, although it eventually tends to reach a limit value. This effect follows unknown physical laws, and the extent to which it will occur is also unpredictable.

It is well known that a number of factors can lead to increases in the size of the recorded plastic flow, especially the absorption of large amounts of moisture, which occur under poor storage conditions at the site in humid or foggy weather, during rainfall or by the formation of condensate on the plates, when the air temperature drops at night, or under unsatisfactory working conditions where the humidity is high and the ventilation is poor. The latter effect can occur both during storage and after construction. Plastic flow is negligible when the plasterboard is dry or substantially dry, or when appropriate measures are taken to avoid the emergence of the above mentioned adverse conditions.

It is known to produce gypsum articles with the addition of relatively large amounts of tartaric or tartaric salts from a mixture of gypsum and water for the purpose of retarding the binding of this mixture or modifying the gypsum crystals.

Surprisingly, it has now been found that by adding relatively small amounts of tartaric acid or tartaric acid salts, gypsum articles can be obtained with an increased resistance to plastic flow.

The process of the invention is characterized in that the gypsum product is prepared from a mixture containing tartaric acid and / or a tartrate in an amount of from 0.005 to 0.2 and preferably from 0.01 to 2% by weight relative to the dry gypsum. .

Examples of usable tartaric salts are alkali metal or alkaline earth metal salts, e.g. dicalcium or calcium tartrate, double alkali metal salts, e.g. sodium potassium tartrate, monosubstituted salts, e.g. potassium hydrogen tartrate or other inorganic and organic tartrates. However, inorganic tartrates are preferred. At a given concentration of tartrate or tartrate, tartaric acid has been found to be the most effective compound for increasing resistance to plastic flow, and the gypsum-water mixture according to the invention is therefore preferably cast under non-basic conditions.

The tartaric acid or tartrate may e.g. is added as a solid to the plaster or dissolved or dispersed in the water to form the plaster mixture.

The total amount of tartaric acid or tartrate, as mentioned, should be between 0.005 and 0.2 and preferably from 0.01 to 0.1% by weight based on the dry gypsum used in the mixture, the preferred range being particularly suitable for the production of gypsum board. A particularly preferred range for tartaric acid in plasterboard is from 0.03 to 0.07% by weight. When a tartrate is used, the tartrate group or the ionic portion of the compound should e.g. from 0.005 to 0.08, preferably from 0.03 to 0.08% by weight of the dry plaster used in the mixture.

The addition of tartaric acid or its salts does not appear to have undesirable side effects, and the effect, as far as the restriction of the plastic flow is maintained, is used when the additive is used in conjunction with known accelerators (eg mineral plaster, ground cured gypsum, potassium sulphate and mixtures). thereof) and other additives (eg, starch and foam) commonly used in plasterboard mills. The mixture can be molded, cast and cured under non-alkaline conditions.

The introduction of tartaric acid or a tartrate is advantageous in the production of molded plaster casts of any shape but is mainly of value in the manufacture of plasterboard and molded sheets and blocks, especially when they will be subjected to stresses which promote deformation by plastic flow.

The following examples illustrate the improvement of resistance to plastic flow produced by the addition of tartaric acid or tartrate. In the examples, the percentages indicated are in percent by weight relative to the weight of the dry plaster used in the mixture, and unless otherwise indicated, the results are the results obtained after a 3 week trial. The sinking is in each case mild as the vertical distance that the area of the beam in the middle between the points supporting the ends of the beam sinks down from the position originally assumed by the midpoint at the laying.

Examples 1-9

A number of experiments were performed to determine the efficacy of tartaric acid as an inhibitor of immersion due to laboratory scale plastic flow. In these experiments, the gypsum water slurry was sometimes aerated, e.g. in the production of plasterboard, while in other cases only simple plaster-water slurries were used. In practice, it is common to add a pre-formed foam to the slurry when making plasterboard. A number of foaming agents were used, two of which are particularly important with the name resin soap and Teepol. Resin soap is based on natural pine resin which is converted to a soap using alkali, while Teepol foaming agents are based on sodium secondary alkyl sulfates and sodium benzene sulfonates. In practice, tartaric acid was found to be as effective in the presence of any of these foaming agents as when no foaming agent was present. Only simple plaster beams were cast, and no attempt was made to make plasterboard, i.e. sheets of cured plaster placed between and adhered to two sheets of paper. The submergence tendency of the beams after drying at 40 ° C was tested by simply supporting them on supports spaced 46 cm apart in an atmosphere having a relative humidity of 90% at 20 ° C. It is now known that this approach yields results which, compared to control rods which do not contain additives, improve to some extent the relative effects compared to the conditions at the construction site by the proper use of plasterboard. However, the method is applicable for comparative and illustrative purposes and, due to its simplicity, is suitable.

Typical results obtained by a series of experiments over the stated periods in connection with various gypsum products manufactured in a laboratory are given in Table 1 below: 143270 4

Table 1

Example% tartaric acid% control beam immersion nothing 100 after 1 week after 3 weeks 1 0.001 84 83 2 0.002 71 68 3 0.005 53 51 4 0.01 45 20-45 5 0.020 33 29 6 0.03 15-35 6a 0.04 23-50 7 0.05 9-26 8 0.06 17-35 9 0.09 24-31 9a 0.10 16

The marked improvement in the resistance to immersion at all levels of tartaric acid is evident from these results. Although the invention relates to the addition of tartaric acid over a range of 0.005 to 0.2% by weight relative to the dry plaster, these results indicate that an amount of from 0.01 to 0.10% by weight relative to the gypsum will normally be preferred. The different improvement from example to example and within some of the individual examples is due to the fact that each example covers a series of experiments performed with different types of plaster and plaster mixtures.

Examples 10-14

Factory tests were performed in two ways. The tartaric acid was added either to the gypsum starting material as a solid or as a solution to the main volume of water, and the two methods proved to be equally effective.

Subsequent results were obtained by comparing the tendency to plastic flow by producing plates containing tartaric acid and control plates which did not contain additives. Pieces of each type of plasterboard were simply placed between supports spaced 46 cm apart in a 90% relative humidity atmosphere at 20 ° C for a period of 3 weeks.

Table 2

Example Tartaric acid% immersion relative to control plates none 100 10 0.01 69 11 0.02 45 12 0.04 35 13 0.06 36 14 0.09 27

The plate produced was a plate of normal production quality with the exception of the addition of tartaric acid. The weight of the dry plate was approx. 8.5 kg / m, and this weight was adjusted in the normal way by the addition of pre-made foam. The foaming agent used was of the Teepol type. Commonly used amounts of starch binder were also added to the slurry to prepare the plasterboard.

Examples 15-16

The above examples relate to all studies in humid air. Experiments have also been conducted showing that although the plaster objects are wetted with water, the improvement of the immersion resistance is not impaired. Whole plates were fixed e.g. for floor joists at a distance of 40.6 cm and some of them were sprayed with water for a period of 5 days, the total amount of water 2 applied to the boards during that period corresponding to 32 kg / m. The plates were kept in an atmosphere with a relative humidity of at least 90% at 20 ° C between the spraying operations.

The following results were obtained:

Table 3 143270

Example Tartaric acid Amount of plate to% immersion in plate (%) relative to control plates 15 0.06 wetted 41 16 0.06 not wetted 48

Example 17

Small plate pieces with dimensions of 50 x 5 cm were cut from whole plates mentioned in Examples 15 and 16 and these pieces were saturated with water in the laboratory. Freely supported with a distance of 46 cm between the support points, there was also an immersion, which averaged approx. 35-40% of the immersion exhibited by pieces of the control plate. This is comparable to the 36% immersion obtained for non-soaked sheets in an atmosphere having a relative humidity of 90% at 20 ° C.

Examples 18-31

Other tartrates have also been found to be beneficial in increasing the resistance to immersion for simple cured plaster beams, examples of which are given in Table 4. The beams were supported on supports spaced 46 cm apart, as in the above examples.

143270 7

Table 4

Example Additive Amount of 1% immersion for control beam holders

None - 100 18 Calcium 0.05 (0.029) 23 Tartrate 0.10 (0.057) 29 19 Potassium Hydro 0.05 (0.039) 33 Gentartrate 0.10 (0.079) 41 20 Sodium Potassium 0.05 (0.026) 51 Umtartrate 0.10 (0.052) 47 21 Dicalium tar 0.05 (0.032) 39 treat 0.10 (0.063) 47 22 Antimony bar 0.144 (0.06) 26 Umtartrate 23 Antimony potassium 0.132 (0.06) 29 Umtartrate 24 Antimony sodium 0.125 (0.06) 34 Umtartrate 25 Ammonium (D +) 0.075 (0.06) 47 Tartrate 26 Cupritartrate 0.108 (0.06) 32 27 Sodium Hydro- 0.077 (0.06) 46 Gentartrate 28 Bismuth Sodium-0.160 (0.06) 29 umtartrate 29 Sodium (D +) 0.094 (0.06) 46 tartrate 30 Lead tartrate 0.144 (0.06) 34 31 Ethylenedia- 0.085 (0.06) 46 mintartrate

The numbers in parentheses indicate the weight percent based on the dry gypsum of the tartrate radical or ion used in the respective tartrate additive.