IE900804L

IE900804L - Impregnation of pressed cement products with a plastics¹dispersion and a wax disperion

Info

Publication number: IE900804L
Application number: IE900804A
Authority: IE
Inventors: Hansjurgen Miko; Karl Kirchmayr; Gunter Ernecker
Original assignee: Redco Sa
Priority date: 1989-03-08
Filing date: 1990-03-07
Publication date: 1990-09-08
Also published as: YU1190A; CS8906954A2; HU213449B; DD300825A5; HUT55269A; PT93365B; AT390608B; EP0388391B1; DE59003919D1; PL163290B1; ATA52289A; EP0388391A1; ATE98946T1; SK279234B6; IE65259B1; CZ282949B6; RU1802810C; HU896017D0; ES2048484T3; PT93365A

Abstract

A process is proposed for the impregnation of cement products, preferably pressed after forming, especially under the action of heat, in particular fibre-reinforced cement products, before the setting thereof, in which a preferably aqueous plastics dispersion and, subsequently thereto, a preferably aqueous wax dispersion, especially a paraffin dispersion, is applied to the products wet from the mould. Advantageously, the wax dispersion is here applied within about 2 minutes after the application of the plastics dispersion; advantageously, above all the plastics dispersion, and preferably both the plastics dispersion and the wax dispersion, are rolled on.

Description

65259 €£)<■//so The invention relates to a process for the impregnation of cement products, especially fibre cement products, before they set, and to products manufactured according to this process. These products have preferably 5 been pressed after moulding, in particular under the effect of heat.

In hydraulically set products, herein referred to as cement products, especially fibre cement products, efflorescence occurs under certain conditions. 10 Essentially, efflorescence consists of deposits of salts on brick masonry and stone masonry, on concrete, mortar, xylolith or moulded bodies of fibre cement. It is produced by the migration of water-soluble salts contained in the building material to the surface there-15 of, and subsequent evaporation of the transport water. In most cases a chemical reaction also occurs, as a result of which the efflorescent material becomes insoluble in water. Its chemical composition depends on the nature of the building material. With brickwork, deposits of gypsum 20 may occur, arising from sodium sulphate in the brick and lime in the pointing mortar. In the case of building materials which are exposed to the elements, and which consist wholly or only partly of hydrated alkaline earth metal silicates, soluble calcium hydroxide can reach the 25 surface together with water, where it is converted by the carbon dioxide in the air to white calcium carbonate of very low solubility.

In a large majority of cases, efflorescence does not detract from the quality of the building materials, 30 but does noticeably detract from their appearance. Especially with coloured building materials the appearance of efflorescence is particularly displeasing, because even small amounts of salt mask the colour of the building material and form ugly white patches. The low 35 solubility of the efflorescence in water and its good adhesion to the substrate may seriously detract from the appearance of buildings for a long period of time.

Several methods are already known for preventing the occurence of efflorescence on fibre cement products / roro 6 b £ 0 i having an approximately 0.1 - 1.5 mm thick, cement-bound coloured layer on their outer surface (visible surface). In order to avoid efflorescence of this sort aluminate cement, for example, was used for the thin coloured layer 5 instead of Portland cement, which is the binding agent of the untinted base slab. In this manner improvements were achieved with respect to the appearance of efflorescence.

Another manner of preventing efflorescence consists in applying a surface layer of pigmented Port-10 land cement to fibre cement slabs. In this case, however, an additional coating of the surface is necessary to achieve efflorescence-free products. This additional coat cannot, however, be applied during the production process, but only when the cement in the surface layer has 15 achieved a certain hardness, so that subsequent, expensive, additional processing.is required.

The Applicant has already suggested the application of a paraffin dispersion to cement products, especially fibre cement products, before they set, and 20 more particularly before they are pressed, in order to seal their surface.

It has become apparent that, even with this paraffin seal, a complete suppression of efflorescence is difficult to achieve, particularly as this necessitates 25 the mutual adjustment of various manufacturing parameters, e.g maintaining a constant setting temperature and/or varying the composition of the mineral surfacing, if present, as well as varying the wax concentration or type.

Cases have occurred where, as a result of the heat of setting of the cement, fibre cement slabs thus treated have soaked up the paraffin so much that the desired continuous surface coating is not formed on the sheets, and efflorescence occurred, albeit in small 35 amounts.

On the other hand, however, the application of large amounts of paraffin causes some of the wax to be lost by leakage during the production, so that, firstly, the effluent water is polluted and, secondly, the press plates too are heavily soiled, and have then to be specially cleaned. This is particularly noticeable when the wax has been sprayed on.

Thus the object was to fundamentally improve the wax impregnation process already proposed, so that the careful optimisation of the treatment parameters which was hitherto necessary no longer has its previous importance and the difficulties mentioned no longer occur.

This is achieved in accordance with the invention by pre-impregnation (priming) of the products with plastics before the wax is applied.

Accordingly the process according to the invention for the impregnation of cement products, especially fibre cement products, before they set, is characterised mainly in that an aqueous plastics dispersion and an aqueous wax dispersion, especiallv a oaraffin dispersion, are successively applied to the products without any further surface treatment, while said products are fresh from moulding.

Surprisingly it was found to be possible to apply the wax dispersion immediately after the application of the plastics dispersion, without mixing of the coats occurring, so that the surface layer still consists solely of wax.

This is probably as a result of the fact, also surprising, that plastics dispersions penetrate the outer layer of cement products much faster than wax dispersions .

In practice, good results are achieved if the wax dispersion is applied within about 2 minutes of applying the plastics dispersion.

It is advantageous to apply at least the plastics dispersion by means of rollers; preferably both the plastics dispersion and the wax dispersion are applied by rollers. Plastics used are principally film-forming plastics, especially thermoplastic materials, which preferably have low temperature plasticity.

In practice, plastics from the group containing acrylic resins, polyurethane resins and epoxy resins are preferred.

The amount of plastics dispersion applied is advantageously such that 5 to 60 g of plastics per m2 of surface is present. For this purpose plastics dispersions with a plastics content up to about 60 % by weight are 5 used.

Plastics dispersions containing pigments may be used, especially those which contain up to about 5 % by weight of pigment/ e.g FeO, based on the plastics proportion.

The wax dispersions used are particularly those with a wax content having a softening point around 65 to 100°C/ especially one which is at least 80°C. Particular use is made of paraffin dispersions, but other waxes may also be used.

Wax dispersions are advantageously used, which have a wax content which is substantially unsaponifiable.

The wax dispersions are chiefly used in amounts of from 10 to 60 g, preferably 12 to 40 g, more particularly 15 to 35 g, wax per m2 of surface, wax 20 dispersions advantageously being used which have a wax content of from *25 to 65 % by weight, preferably 30 to 55 % by weight, more particularly 35 to 50 % by weight.

Non-ionogenic wax dispersions, moreover, are preferably used.

Wax dispersions are used which have, in particular, a viscosity at 25°C between 40 and 100 cP, preferably at or around 50 cP.

Wax dispersions are of advantage, which have a density, i.e the wax content of which has a density at 30 15°C between 0.8 and 0.95 g/cm3, especially of about 0.88 g/cm3.

The pH of the wax dispersion used is not particularly critical, but is preferably about 5 to 8.

The wax dispersions may also be pigmented, and in 35 particular the pigment proportion may be present in amounts up to 5 % by weight, based on the wax proportion.

Preferably, however, only the plastics dispersion is pigmented, the colours appearing particularly well through the unpigmented wax layer.

The invention is now described in more detail with reference to an exemplary embodiment.

The solid ingredients of a fibre cement suspension are removed as a felt via a revolving-screen drum and are passed by a sieve conveyor onto a rotating formatting roller. When the required layer thickness has been reached, the felt is slit open along a generatrix of the roller and the rectangular felt sheet thus obtained is fed into a stamping machine where the individual roofing tiles are stamped from the sheet. The unfinished roofing tiles are placed one beside the other and conveyed onto a presser plate by means of a suction device, and are carried to the first coating point, where a plastics, dispersion is applied to them by rollers. Subsequently, in a second coating point which immediately follows the first coating point, a wax dispersion is applied to them by rollers. The individual presser plates are then stacked, so that the upper side of each of the roofing tiles, which is coated with wax, lies against the underside of the presser plate above it. The stack of tiles is passed into a press and pressed therein, the hydraulic setting process being so far advanced that the roofing tiles are dimensionally stable. The stack of tiles is subsequently separated, the wax coating allowing clean separation of the roofing tiles. The roofing tiles are taken from the presser plates (plated) and go to storage. The presser plates are cleaned, optionally preheated and return for renewed reception of unfinished roofing tiles.

The pressing is preferably carried out at a temperature between 40 and 90°C.

The charged presser plates are preferably each simply advanced under a rise-and-fall coating roller. The dosing of the plastics dispersion or the wax dispersion onto the respective coating roller may be carried out in the conventional manner, e.g via a slot nozzle or via an auxiliary roller which dips into a dispersion of this sort and which lies against the coating roller. The coating rollers may have rigid or flexible surfaces, e.g a rubber envelope.

Spray application may be carried out if required. This is not preferred, however, as it is associated with soiling of the edges of the presser plates.

With the process according to the invention, it was found not only that excellent long-term impregnation was achieved, which effectively prevented efflorescence, it was also found that no adhesion at all occurs in separating the stack of tiles,, even when very little wax is applied, as the wax remains practically completely on the surface which has previously been sealed with plastics.

The process according to the invention can advantageously be used in general with freshly moulded "green" cement products. It is particularly suited to the production of roofing tiles and facade cladding sheets, which may also be provided with mineral surfacing in a known manner.

The invention thus also relates to cement products manufactured by the process according to the invention, especially fibre cement products, with a surface impregnation of wax, below which a plastics impregnation has been applied.

Claims

- 7 -Patent claims:

1. Process for the impregnation of cement products, especially fibre cement products, before they set, characterised in that an aqueous plastics dispersion and 5 an aqueous wax dispersion, especially a paraffin dispersion, are successively applied to the products without any further surface treatment, while said products are fresh from moulding.

2. Process according to Claim 1, characterised in 10 that the wax dispersion is applied within about 2 minutes of applying the plastics dispersion.

3. Process according to one of Claims 1 or 2, characterised in that the plastics dispersion is applied by rollers. 15

4. Process according to one of Claims 1 to 3, characterised in that the wax dispersion is applied by rollers.

5. Process according to one of Claims 1 to 4, characterised in that a dispersion of a film-forming 20 plastics material is applied.

6. Process according to one of Claims 1 to 5, characterised in that a dispersion of at least one thermoplastic material is applied.

7. Process according to Claim 6, characterised in 25 that a dispersion of at least one plastics material with low temperature plasticity is applied.

8. Process according to one of Claims 1 to 7, characterised in that a dispersion of at least one plastics substance chosen from the group containing 30 acrylic resins, polyurethane resins and epoxy resins is applied.

9. Process according to one of Claims 1 to 8, characterised in that the plastics dispersion is applied in an amount between 20 and 60 g of plastics per m2 of 35 surface.

10. Process according to one of Claims 1 to 8, characterised in that a plastics dispersion with a plastics content of up to approximately 60 % by weight is applied. - 8 -

11. Process according to one of Claims 1 to 10, characterised in that a plastics dispersion containing a pigment is applied.

12. Process according to Claim 11, characterised in | 5 that a plastics dispersion with a pigment content of up to 5 % by weight, based on the plastics proportion, is ^ applied.

13. Process according to one of Claims 1 to 12, characterised in that a wax dispersion with a wax 10 proportion having a softening point between 65 and 100°C, especially one of at least 80°C, is applied.

14. Process according to one of Claims 1 to 13, characterised in that a wax dispersion with a wax component which is substantially unsaponifiable is 15 applied.

15. Process according to one of Claims 1 to 14, characterised in that the wax dispersion is applied in an amount of from 10 to 60 g, preferably 12 to 40 g, more particularly 15 to 35 g of wax per m2 of surface. 20

16. Process according to one of Claims 1 to 15, characterised in that a wax dispersion is applied which has a wax proportion of from 25 to 65 % by weight, preferably 30 to 55 % by weight, more particularly 35 to 50 % by weight. 25

17. Process according to one of Claims 1 to 16, characterised in that a non-ionogenic wax dispersion is applied.

18. Process according to one of Claims 1 to 17, characterised in that a wax dispersion is applied which 30 has a viscosity at 25°C between 40 and 100 cP, preferably at or about 50 cP.

19. Process according to one of Claims 1 to 18, characterised in that a wax dispersion is applied which has a density, i.e the wax content of which has a density 35 at 15"C between 0.8 and 0.95 g/cm3, especially of about ^ 0.88 g/cm3.

20. Process according to one of Claims 1 to 19, characterised in that a wax dispersion is applied which has a pH value between 5 and 8.

21. Process according to one of Claims 1 to 20, characterised in that a wax dispersion containing a pigment is applied.

22. Process according to Claim 21, characterised in that a wax dispersion with a pigment content of up to 5 % by weight, based on the proportion of wax, is applied.

23. Cement product, especially fibre cement product, with a surface impregnation of wax, below which a plastics impregnation has been applied, produced by the process according to one of Claims 1 to 22.

24. A process according to one of claims 1 to 22, substantially as described herein by way of Example.