WO1994022151A1

WO1994022151A1 - Composition containing iron powder as a magnetically active ingredient plus a binder

Info

Publication number: WO1994022151A1
Application number: PCT/EP1994/000714
Authority: WO
Inventors: Franz-Bernhard Knop; Manfred Leder; Udo Frank WINDHÖVEL; Thomas Tamcke
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1993-03-15
Filing date: 1994-03-09
Publication date: 1994-09-29

Abstract

Described is a non-rusting, powder-form composition, which is stable on storage, for the production of coatings to which overlays fitted with magnets can be affixed. The composition consists of a ferromagnetic substance, in particular iron, a less noble metal than iron, in particular zinc, a dispersable polymer, in particular polyvinyl acetate, as an organic binder and an alkaline substance, in particular calcium hydroxide and cement. In addition, the composition can contain a thickener, e.g. bentonites. After adding a greater or lesser amount of water, a workable compound is obtained which, under normal ambient conditions, hardens within about 24 hours. An overlay fitted with magnets can then be affixed to this substrate.

Description

"Composition with iron powder as a magnetically active component and a binder"

The invention relates to a composition which contains iron powder and a binder as a magnetically active component. It is used for coating walls, ceilings, floors and other substrates on which coverings with magnets are to be attached easily and simply.

Such a composition is known as a filler for fastening decorations by magnetic forces. DE 2620095 describes a method for attaching easily replaceable surface decorations made of stone, ceramic, wood, metal and the like to wall, ceiling and / or floor surfaces made of the same and / or different materials. For this it is necessary to apply one layer of iron powder to one surface and a layer of binder highly filled with magnetic powder to the other surface and to allow it to harden. After magnetization, the decoration can be attached due to the magnetic effect. Putties made of iron powder and inorganic or organic binders are described. The following are mentioned as inorganic binders: gypsum, fine plaster and cement. Liquid plastic compositions, preferably in non-aqueous form, are used as organic binders, for example alkyd resins, epoxy resins, polyurethanes and polymers based on vinyl and / or acrylic compounds. FR 2250394 relates to the use of a tinned metal mesh for the magnetic connection of any materials. For example, the sieve should be glued to a wooden board during its manufacture. The wooden board can serve as an intermediate wall on which a decorative cladding with permanent magnets glued on can be attached. Rubber is mentioned as the adhesive. A pattern made of plaster is also described, which represents a prefabricated intermediate wall into which a magnet with rubber has been integrated.

DE 40 16939 relates to a method for the reversible fastening of floor and wall coverings by magnetic adhesion. A magnetic coating or a magnetic film to be glued or self-adhesive should be applied once to magnetically non-adhesive substrates.

The known compositions for the leveling compounds with reaction resins and in particular epoxy resins as binders have the disadvantage that they can only be processed for a limited time (pot life) and are difficult to elapse due to their great toughness. An addition of solvent would help, but would also give rise to problems with the exhaust air. They are not suitable for the mechanical coating of raised floor elements. In addition, very smooth surfaces are obtained, on which the covering can be moved relatively easily due to the low frictional forces. Finally, there is a risk that the iron powder will rust, especially if the epoxy content is low, so as to save costs. The rusting not only leads to discoloration of the coating, but above all to a reduction in its hardness and magnetic adhesion. The object of the invention is therefore to find an easy-to-process composition which can be applied not only with the spatula, but also, for example, with a roller and which gives a permanent, effective substrate for magnetically active coverings.

The solution according to the invention can be found in the patent claims. It consists essentially in the fact that the ferromagnetic materials, the rust preventives and the binders are stored in the form of a powder mixture and, shortly before use, add water in a few minutes to ready-to-use compositions which, after their application and drying, adhere to many substrates. Initial concerns about working with an aqueous dispersion, since segregation can easily occur during storage due to the relatively high specific weight of iron and, moreover, this particularly easily rusts in an aqueous medium have been overcome. It was possible to produce a coating with relatively little binder, which nevertheless adheres sufficiently well to many substrates.

The solution according to the invention consists of a composition of the following components:

A) as a magnetically active component, a ferromagnetic substance,

B) if appropriate as a rust preventative, a less noble metal than iron,

C) if necessary for pH regulation an alkaline substance and

D) a redispersible polymer as an organic binder, all components A) to D) being in powder form.

A substance is considered to be "ferromagnetic" if it acts magnetically under the influence of an external magnetic field. Iron powder is preferred. Magnetic iron (Fe3Ü4) is also an option. It has the advantage of not rusting. It is therefore not necessary to add components B) and C).

The grain size depends on the processing conditions and the intended use and can be determined with a few routine tests. Essentially the same standards are to be applied as for the fillers.

Metals are less noble than iron if their normal potential in volts, measured against the normal hydrogen electrode at 25 ° C, is less than that of Fe / Fe ⁺⁺ , i.e. less than -0.44 volts. Of the theoretically possible metals, in addition to aluminum, zinc with a normal potential of -0.76 volts is of particular interest. The less noble metals cause a surface passivation of the iron through element formation.

The alkaline substances should have a pH of more than 9, in particular 10 to 12. In addition to alkali metal hydroxides, calcium hydroxide and cement are particularly suitable, especially Portland cement or metallurgical cements (Eisenportland cement, blast furnace cement). At the same time, they also act as inorganic binders.

The "redispersible polymers" are powders which are usually obtained from dispersions by spray drying and in aqueous media at room temperature, optionally with stirring, in a few minutes, preferably within 3 minutes, again in a dispersion. Suitable redispersible polymers are, for example, homopolymers and copolymers of acrylates or methacrylates with, for example, styrene. The alcohol component of the esters should contain 1 to 4 carbon atoms. However, preferred redispersible polymers are homopolymers and copolymers of vinyl esters, the carboxylic acid containing 2 to 4, in particular 2, carbon atoms, with the copolymers ethylene and maleinates, the Alcohol component contains 1 to 4 carbon atoms. Casein is also used. It is insoluble in water, but in alkaline solution. The casein powder is preferably broken down with alkali hydroxides, borax and especially with lime milk or cement. Good water resistance can be obtained with casein. Bone glues are also possible.

Commercially available redispersible polymers are those based on vinyl acetate, vinyl acetate / ethylene, vinyl acetate / ethylene / vinyl acid and styrene / acrylate. Manufacturers are Wacker (Vinnapas), Höchst (Mowilith), Ebnöther (Elotex), Rohm & Haas, Rhone-Poulenc and BASF.

The ferromagnetic substance, the base metal, the alkaline agent and the redispersible polymer are in powder form. Their grain size is therefore less than 0.5 mm, preferably between 0.05 and 0.3 mm. Powders with particle sizes outside this range are also possible if one accepts disadvantages, e.g. Dust or a very rough surface. In principle, the components can also be scale-like or fibrous if the resulting disadvantages are acceptable, e.g. poor spreadability.

A thickener can also be added to regulate the viscosity, preferably in an amount of 0.2 to 2, in particular 0.4 to 1.0% by weight, based on the iron powder. In addition to organic high molecular weight substances such as polyacrylates, polycarboxylic acids, alginates and cellulose ethers such as carboxymethyl cellulose, inorganic thickeners such as, for example, polysilicic acid, clay minerals, zeolites and in particular bentonites are suitable as thickeners. Well-known trademarks are: Bentone (Rheox), Thixogel (Südchemie). In addition, other additives can be added, such as dyes.

For the composition by weight, specific rules can only be given with regard to the base metal and the organic binder: for example, at least 5, in particular 10 to 50 g of base metal and 5 to 12, in particular 6 to 10 g, should be added to 100 g of iron powder come on organic binder. The amount of alkaline agents should be sufficiently high to ensure a pH of more than 9 over a longer period, even in the presence of acids. Since the preferred alkaline agents calcium hydroxide and cement act simultaneously as inorganic binders, a generous dimensioning is appropriate. It can be of the same order of magnitude as that of the organic binders. However, it is also possible not to add any alkaline substance at all if one only looks at rusting and there are no major requirements to be met here. Under certain circumstances, they can be met simply by adding base metal. The same applies vice versa: if necessary, there is also no need to add zinc if only enough alkaline substances are present. This applies in particular to hydrated lime. The best rust protection effect is achieved when base metal and alkaline substances are used together, especially hydrated lime.

The above components are in the form of a mixture, ie they are intimately mixed with one another. The mixture is preferably dry or powdery. However, it can also be in a highly viscous form, the viscosity should be so high that virtually no segregation occurs. Before use, 20 to 40 g of water - based on 100 g of powdery composition - are added and, with stirring, the mixture changes into an aqueous dispersion in a few minutes at room temperature. The amount of water depends on how viscous the dispersion should be or in other words how you want to process it, for example with a roller or with a spatula. In general, the viscosity should be 20,000 to 30,000 mPas at 21 ^β C, measured in the rotary viscometer Haake viscosity ester VT 181.

The low-viscosity to pasty mass, which preferably has a smooth to honey-like consistency, is applied to the surface to be prepared, that is, above all to walls, ceilings and floors or other surfaces, such as plates, to which a covering is magnetically attached shall be. The mass hardens there. Depending on the drying conditions, this usually takes at least a few hours. After 24 hours the coating is so hard that the coverings can be attached to it. The amount of iron to be applied depends on the requirements with which force the coverings should adhere to the surface. In general, 1.5 to 2.0 kg of powdery composition per m ^{2 of} covering are sufficient.

The advantages of the composition according to the invention lie in its storage stability and simple handling, depending on the desired mode of operation (machine or manual), and in its good resistance to corrosion and economy. The coatings obtained are flat and rough. Relatively large frictional forces are therefore necessary in order to shift the covering parallel to the plane, compared to a coating made of epoxy resin and the same amount of iron. Even with a small amount of iron per m ^2, the adhesion perpendicular to the surface is sufficient so that the covering cannot be lifted up with a vacuum cleaner. Because of the good adhesive properties of the composition according to the invention, it is suitable for coating substrates made of different materials such as mineral screeds, cement, ceramic, plastic, wood or chipboard. The substrates which are to be coated with a ferromagnetic layer are walls, ceilings and floors, in particular double floor panels made of screed or wood for the production of raised floors. Other substrates are plastic-bonded chipboard.

The coverings to be applied to the substrates can be formed from stone, ceramic, wood, metal, PVC, linoleum or from textile surfaces, for example textile fabrics. The coverings can be provided with the magnetically active material either directly during their manufacture or afterwards, which can be based on both a metallic and an oxide basis. Ferrites are particularly useful.

The invention is explained in detail by the following composition (I):

500 g iron powder,

50 g zinc powder,

20 g polyvinyl acetate redispersion powder,

25 g calcium hydroxide and 2.5 g Bentone LT.

This composition was processed with 180 ml of water in 2 min at room temperature by stirring with a mechanical stirrer to a pulpy mass. This could be applied very well to both wood and screed with a spatula. The mass was hard after 24 hours under ambient conditions. It adhered well to both substrates. Formation of rust was not noted among conventional Raum¬ humidity, even after 14 days at 20 ^β C and 95% relative humidity: The hardness of the coating was the same, as the adhesion of the magnetic surfaces.

The leakage resistance, measured according to DIN 53276, was approximately 10 ^ to 10 ⁷ ohms.

Another composition (II) consists of: 600 g magnetite,

20 g polyvinyl acetate redispersing powder and 2.5 g Bentone LT. 100 g of this composition (II) with 30 g of water in a few minutes at room temperature with stirring, an aqueous dispersion which is suitable for coating.

Claims

1. Composition for coating walls, ceilings, floors and other substrates containing

A) as a magnetically active component, a ferromagnetic substance,

B) if appropriate as a rust preventative, a less noble metal than iron,

C) if necessary for pH regulation an alkaline substance and

2. Composition according to claim 1, characterized by Eisen¬ powder as a ferromagnetic substance.

3. Composition according to claim 1 or 2, characterized by zinc as a base metal.

4. Composition according to claims 1, 2 or 3, characterized by calcium hydroxide and / or cement as an alkaline substance.

5. Composition according to at least one of claims 1 to 4, characterized by polyvinyl acetate and casein as an organic binder.

6. The composition according to at least one of claims 1 to 5, characterized by at least 5, in particular 10 to 50% by weight of zinc powder and 5 to 12, in particular 6 to 10% by weight of binder, based on the iron powder.

7. composition according to at least one of claims 1 to 6, characterized by the additional use of a thickening agent, in particular a bentonite in an amount of 0.2 to 2, preferably 0.5 to 1 wt .-%, based on the Iron powder.

8. The composition according to at least one of claims 1 to 7, characterized by the additional use of water and other additives for the production of coating compositions in a liquid, mushy or pasty state.