All-purpose adhesive material and process for its production

Field of the invention

The present invention relates to an all-purpose two-component adhesive material that can be used both for fastening together flexible and porous material, such as for example wood, plastics, fabric, as well as for joining stiff material such as metal, stone.

Furthermore, the invention relates to a process for its production. In particular, but not exclusively, the process can also be carried out by using compounds resulting from processes of neutralization of sulphuric exhausted acid as reagents.

In large amount, the adhesive material can be used to make coating material, such as tiles.

In different concentration, the adhesive material can be used as fire-retardant varnish.

Description of the prior art

Two-component cements and adhesives are known that are very strong, which however have the drawback that they are based on noxious organic compounds, that in particular contain noxious volatile solvents.

For many applications, instead, the need is felt of having adhesive material the least noxious possible and with very low impact on the environment.

Another aspect for cements and other adhesive material is their different efficacy depending on whether they are used for joining either porous surfaces such as wood and rough surfaced stone, or smooth surfaces, such as metal and glossy stone. Normally, an adhesive for smooth material is not suitable for wood and other porous material such as tiles and vice versa.

It is also appealing on the market a cheap adhesive material that in large quantities can be used to make coating material such as tiles.

It is furthermore felt the problem of disposing of and/or regenerating baths of sulphuric acid used in the industry in known processes, such as for example for the production of titanium dioxide and in many other. In this sense recovery methods are known that are expensive and then not preferable, wherein the exhausted baths are normally delivered to companies that carry out the neutralisation, which is an expensive process and generates not recyclable residues. Neutralisation processes of baths of exhausted sulphuric acid are also known with final production of calcium sulphate.

Summary of the invention

It is an object of the present invention to provide an adhesive material that does not require organic solvents and has high resistance for applications both to porous surfaces and to compact surfaces.

It is a particular object of the invention to provide an adhesive material that in large amount is used to provide tiles or similar coating material.

It is another particular object of the invention to provide an adhesive material that is used also as fire-retardant varnish.

It is a further object of the present invention to provide a process to make such a material that can be made at a very low cost, in particular through exploitation of exhausted sulphuric acid.

According to a first aspect of the invention, an adhesive material formed by a first and a second component suitable for being mixed before being applied on surfaces to be joined, wherein:

• the first component is an aqueous solution, having concentration higher than 5% in weight, of a magnesium or zinc salt or a mixture thereof, said salt being chosen among a sulphate, chloride, nitrate, acetate of magnesium or zinc;
• the second component is a mixture of magnesium oxide MgO, metal hydroxides, calcium sulphate hemi-hydrated.

Preferably, in the first component the magnesium or zinc salt are chosen among:

• magnesium sulphate MgSO₄, magnesium chloride MgCl₂; magnesium nitrate MgNO₃; magnesium acetate Mg(CH₃COO)₂, zinc sulphate ZnSO₄, zinc chloride ZnCl₂; zinc nitrate ZnNO₃; zinc acetate Zn(CH₃COO)₂.

Advantageously, in the second component the metal hydroxides are chosen among or are a mixture of:

   Mg(OH)₂; Al(OH)₃; Fe(OH)₃; Ti(OH)₄.

Preferably, in the second component the following weight proportion can be provided:

• MgO 5% - 40%
• Metal hydroxides 10% - 40%
• Calcium sulphate hemi-hydrated CASO₄.0.5 10% - 80% H₂O

In the second component a charge can be added, in a weight proportion from 0,1 to 2,5%, chosen among:

• Cellulose fibres;
• Glass fibres.

The adhesive material according to the invention operates according to two principles, one of physical nature and the other of physical/chemical nature, according to the material to be joined.

• a) in case of material that have a porosity, such as for example wood, tiles, ceramic material, baked Tuscan tiles, gypsum, the adhesive material is adsorbed by the surfaces to join at the moment of the contact, whereby a branched crystal lattice is formed that allows to obtain a high adhesivity and resistance. More precisely, the crystal lattice is obtained by the overlapping of main crystals of the lattice with a secondary lattice of calcium sulphate. The main lattice can be made of crystals of oxy-chloride of magnesium or of zinc, oxy-sulphate of magnesium or of zinc, oxy-nitrate or oxyphosphate of magnesium or of zinc. In the examples given hereinafter oxy-sulphate of magnesium is obtained as main lattice intersected with the calcium sulphate lattice.
• b) In the case of smooth surfaced material such as for example metals, in particular aluminium, glossy marble, etc., the main lattice has ions charged with electrically opposite signs at the vertices; for this reason in the composition of the adhesive material the hydroxides of not noxious cations are provided that according to different applications can have the pH adjusted between 5,5 and 11. Therefore, the metal ions of the metal surface integrate the main lattice and the same do the ions that belong to the hydroxides of the composition, thus obtaining an improved adhesivity.

According to another aspect of the invention, a material that can be used in the building industry comprises a first and a second component suitable for being mixed and cast into moulds and has the characteristic that:

• The first component is an aqueous solution, having concentration higher than 5% in weight, of a magnesium or zinc salt or a mixture thereof, said salt being chosen among a sulphate, chloride, nitrate, acetate of magnesium or zinc;
• The second component is a mixture of magnesium oxide MgO, calcium sulphate hemi-hydrated and a filling charge.

The filling charge can be chosen among or is a mixture of one of the following substances:

• Mg(OH)_2; Al(OH)₃; Fe(OH)_3; Ti(OH)₄ or other metal hydroxides;
• feldspath,
• silicon dioxide,
• kaolin,
• metal powder,
• quartz powder,
• calcium carbonate.

The material thus obtained has a high resistance to wear and to shocks and can be used for production of many types of floors, in particular tile floors.

According to a further aspect of the invention, a process for the production of a material for the building industry such as an adhesive material or a material suitable for being cast into moulds for the production of tiles and the like, starting from a bath of sulphuric exhausted acid in presence of metal ions in solution, comprises the steps of:

• reaction of the sulphuric exhausted acid having metal sulphates as impurity with an aqueous solution of a soluble calcium salt chosen among calcium chloride, calcium nitrate, calcium perchlorate, with the precipitation of calcium sulphate bi-hydrated;
• separation of the calcium sulphate bi-hydrated from the remainder of the solution, the latter containing metal salts deriving from a reaction of double exchange with the metal sulphates;
• addition of calcium carbonate to the remainder of the solution deprived of the calcium sulphate for forming again a solution containing the calcium salt;
• precipitation from the solution containing the calcium salt by means of addition of calcium hydroxide, obtaining insoluble metal hydroxides, after the precipitation remaining only the soluble calcium salt;
• filtration of the metal hydroxides from the calcium salt in solution;
• formation together with the filtered metal hydroxides of a mixture containing also magnesium oxide and calcium sulphate hemi-hydrated;
• preparing an aqueous solution, having concentration higher than 5% in weight, of a magnesium or zinc salt or a mixture thereof, said salt being chosen among a sulphate, chloride, nitrate, acetate of magnesium or zinc;
• addition of the mixture to the solution with the magnesium or zinc salt and making a mixture that can be used as adhesive material or as material for the building industry.
  
  

  MgO can be also used for preparation of MgSO₄, according to the reaction: $${\text{MgO+ H}}_{\text{2}}{\text{SO}}_{\text{4}}{\text{→ MgSO}}_{\text{4}}{\text{+ H}}_{\text{2}}\text{O,}$$   whereas the calcium sulphate hemi-hydrated can be obtained by the reaction of calcination of the calcium sulphate bi-hydrated $${\text{CaSO}}_{\text{4}}{\text{.2H}}_{\text{2}}{\text{O → CaSO}}_{\text{4}}{\text{.0,5H}}_{\text{2}}{\text{O + H}}_{\text{2}}\text{O↑.}$$

The reaction H₂SO₄ is the sulphuric exhausted acid and the reagent MgO is present in a mixture of metal oxides obtained by calcination of the metal hydroxides Mg(OH)₂; Al(OH)₃; Fe(OH)_3; Ti(OH)₄.

Per better disclosing the invention, the following examples, not limitative, are given.

EXAMPLE 1

A composition used as adhesive material having the following weight proportion:

First component

• 13% Solution of magnesium sulphate   MgSO₄ 54,05%

Second component

• MgO   11,5%
• Metal hydroxides   19,1%
• Calcium sulphate hemi-hydrated CASO₄.0.5 H₂O   15,3%
• Cellulose fibres   0,05%
  
  

  Total   100%

EXAMPLE 2

A composition used as material for the building industry having the following weight proportion:

• Solution 20% magnesium sulphate MgSO₄   48%
• MgO   13%
• Metal hydroxides to pH 10   13%
• Calcium sulphate hemi-hydrated CASO₄.0.5   25,5%
  
  

  H₂O

• Ferrite (dye)   0,5%
  
  

  Total   100%

A product with high resistance to wear and to shocks red coloured that can be used for making floors is obtained.

EXAMPLE 3

In a possible exemplifying application of the process, the sulphuric exhausted acid and the soluble calcium salt, for example CaCl₂, are mixed in a precipitator, with the consequent precipitation of calcium sulphate bi-hydrated, which is filtered in a decantation apparatus and washed: $${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}{\text{+ M}}_{\text{x}}{\text{(SO}}_{\text{4}}{\text{)}}_{\text{X+1}}{\text{+ CaCl}}_{\text{2}}{\text{+ H}}_{\text{2}}{\text{O→CaSO}}_{\text{4}}{\text{.2H}}_{\text{2}}{\text{O↓ + HCl + M}}_{\text{X}}{\text{Cl}}_{\text{X+1}}$$   wherein M_x is a metal ion present as impurity in the sulphuric acid, whereas M_XCl_X+1 is a soluble metal chloride obtained for reaction of ion exchange with said metal ion. The metal ions M^x+ are for example Mg²⁺, Fe³⁺, Ti⁴⁺, Al³⁺.

In the precipitator hydrochloric acid and metal salts in solution remain in liquid phase, as resulting from the reaction of ion exchange respectively between the ions H⁺ and other metal cations of the bath of sulphuric acid with the anions of the calcium chloride.

The starting calcium chloride can be obtained by a reaction of ion exchange between added calcium carbonate and the hydrochloric acid as coming out from the precipitator, wherein the calcium sulphate is already precipitated, as liquid part split from the calcium sulphate: $${\text{HCl +MCl}}_{\text{2}}{\text{+MCl}}_{\text{3}}{\text{+MCl}}_{\text{4}}{\text{+CaCO}}_{\text{3}}{\text{→ CaCl}}_{\text{2}}{\text{+ H}}_{\text{2}}{\text{O + MCl}}_{\text{2}}{\text{+MCl}}_{\text{3}}{\text{+MCl}}_{\text{4}}\text{.}$$

In particular the metal chlorides MCl_x in solution are MgCl₂ + AlCl₃+ FeCl₃ + TiCl₄ + H₂O.

Carbon dioxide is formed also that is stored apart.

To separate the calcium chloride lime is added, whereby by adjusting the pH metal hydroxides precipitate that are decanted apart, according to the reaction: $${\text{CaCl}}_{\text{2}}{\text{+H}}_{\text{2}}{\text{O+MCl}}_{\text{2}}{\text{+MCl}}_{\text{3}}{\text{+MCl}}_{\text{4}}{\text{+Ca(OH)}}_{\text{2}}{\text{→ CaCl}}_{\text{2}}{\text{+M(OH)}}_{\text{2}}{\text{+M(OH)}}_{\text{3}}{\text{+M(OH)}}_{\text{4}}$$

The calcium chloride in solution is then used again for reaction with other exhausted acid.

The metal hydroxides precipitated and filtered Mg(OH)₂ + Al(OH)₃+ Fe(OH)₃ + Ti(OH)₄ are then used in the mixture for making adhesive material or for making material for the building industry as above described.

Part of the metal hydroxides, further to reaction of calcination form metal oxides according to the reaction: $${\text{M(OH)}}_{\text{2}}{\text{+ M(OH)}}_{\text{3}}{\text{+ M(OH)}}_{\text{4}}{\text{→ MO + MO}}_{\text{2}}{\text{+ MO}}_{\text{3}}{\text{+ H}}_{\text{2}}\text{O↑}$$

These metal oxides may be TiO₂, Al₂O₃, MgO. In particular MgO is used as component of the mixture according to the present invention above described, whereas Fe₂O₃ can be used as dye for applications like example 2,

EXAMPLE 4

Sulphuric acid is provided by a chemical plant at a concentration of 98 g/l and temperature 50°C.

In a reactor for precipitation the acid is mixed with a solution of CaCl₂ at 10% p/v and kept at a temperature of 50°.

Starting from a flow rate of 2,4 t/h of sulphuric acid and 2,7 t/h of calcium chloride 4,2 t/h of calcium sulphate are stoichiometrically obtained. Since an is necessary excess of 15% of calcium chloride, its flow rate must be of 2,7*1,15= 3,15 t/h.

For recovering metal oxides from the reaction $${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}{\text{+ Mg}}^{\text{2+}}{\text{+ Fe}}^{\text{3+}}{\text{+ Ti}}^{\text{4+}}{\text{+ Al}}^{\text{3+}}{\text{+ CaCl}}_{\text{2}}{\text{+ H}}_{\text{2}}{\text{O → CaSO}}_{\text{4}}{\text{.2H}}_{\text{2}}{\text{O↓ + HCl + MgCl}}_{\text{2}}{\text{+ AlCl}}_{\text{3}}{\text{+ FeCl}}_{\text{3}}{\text{+ TiCl}}_{\text{4}}{\text{+ H}}_{\text{2}}\text{O,}$$

Once separated the calcium sulphate, calcium carbonate is added for the preparation of calcium chloride. Then the metal chlorides precipitate after the addition of calcium hydroxide. Bringing the pH to 5.6 precipitates at first Fe(OH)₃ + Ti(OH)₄. Then, bringing the pH to 11,5 Mg(OH)₂ + Al(OH)₃ precipitate.

The metal hydroxides precipitated are calcined at 1000°C obtaining a solid mixture (A) containing both ferric oxide at high resistance to wear and corundum artificial of high hardness and resistance. With 25000 l/h of effluent containing sulphuric exhausted acid 1.3 t/h of solid mixture (A) of metal oxides are obtained.

Parallel, red calcium sulphate bi-hydrated is calcined at 1000° C to obtain calcium sulphate hemi-hydrated (B) (plaster of Paris).

Part of the solid mixture (A) reacts with the sulphuric exhausted acid up to neutralization so that the magnesium oxide MgO forms magnesium oxy-sulphate MgSO₄ in solution (C). The other metal oxy-sulphates are used as charge.

By making a solid mixture (A) + (B) with 75% of (A) and 25% of (B) and by adding the liquid (C) further diluted in water at 12%, a mixture is obtained that is warmed up to 75° and then cast into tiles that are baked in oven, obtaining "baked red Tuscan tiles".

EXAMPLE 5

With reference to example 4, at first Fe(OH)₃ + Ti(OH)₄ + Al(OH)₃ can be precipitated with pH less than 11, then Mg(OH)₂ can be obtained bringing the pH to 11.5. Then, after calcination MgO is obtained.

Then, building material can be made from the mixture

CaSO₄.0.5H₂O white

25%

MgO

20%

SiO₂

30%

MgSO₄ (12% solution)

25%

That is warmed up to 75° and then moulded into tiles that are baked in oven.

EXAMPLE 6

A composition according to example 5 used as fire-retardant varnish, with dilution by addition of water to obtain a consistency suitable for application onto wood or plastics surfaces for insulating them from fire.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.