GB1584442A - Bonding foamed plastics boards with an adhesive containing finely divided inorganic powders and based on alkali metal silicate solutions - Google Patents

Abstract

The invention relates to adhesives for plastic foam panels, especially polystyrene foam panels, based on a solution of one or more alkali metal silicates containing one or more materials which mineralogically contain more than 15 % of kaolinite. These adhesives are inexpensive to manufacture and absolutely flame-resistant, and do not cause any environmental problems either in use or on exposure to fire or heat radiation.

Description

(54) BONDING FOAMED PLASTICS BO ARDS WITH AN ADHESIVE CONTAINING FINELY DIVIDED INORGANIC POWDERS AND BASED ON ALKALI METAL SILICATE SOLUTIO NS (71) We, WoELLNER-WERKB, a body Corp orate organised under the laws of Federal Republic of Germany of Woellnerstrasse, 67 Ludwigshafen/Rh., Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: For the thermal insulation of buildings or parts of buildings the materials used include foamed plastics boards, particularly foamed polystyrene boards. In addition, facing surfaces, for example, ceilings of rooms, are made with the aid of boards of this kind.

These boards are almost exclusively attached by adhesive bonding, utilising adhesives based on synthetic resin dispersions, although these have considerable disadvantages. These adhesives based on synthetic resin dispersions are not only expensive, but in addition are combustible. In the usual commercial grades they can only be classified as "difficulty inflammable". When the adhesive is applied at the normal rate of from 500 to 600 grams per square metre, the fireproofing of buildings or parts of buildings is considerably affected. Another disadvantage of the use of these known adhesives consists in that environmental pollution through organic polymers or flame proofing agents or their combustion products must be accepted.

The problem underlying the invention is therefore that of providing an adhesive for the adhesive bonding of foamed plastics boards which can be produced inexpensively, is completely flame-proof, causes no environmental pollution, and provides a good adhesive action.

According to the invention this problem is solved by the adhesive bonding of foamed plastics boards, comprising treating the foamed plastics boards with an alkali metal silicate adhesive comprising a solution of one or more alkali metal silicates having incorporated therein one or more material or materials in the form of a finely divided inorganic powder containing mineralogically (as hereinafter defined) more than 15% by weight of kaolinite.

Not only is the adhesive of the invention flame-proof, but it will also serve as fire protection agent because it offers not inconsiderable insulating resistance to a fire or to the radiation of heat caused by a fire. It has an excellent adhesive action and gives rise to no environment protection problems either during its use or when subjected to the action of fire or heat radiation, since it contains only components such as also occur in nature.

DT AS 1,092,586 describes a waterglass adhesive, containing finely divided inorganic powders, for the continuous bonding of webs of cardboard in corrugated cardboard machines, which adhesive is characterized in that it consists essentially of a waterglass solution and so-called Neuburg chalk. The bonding of webs of cardboard imposes different requirements on an adhesive from those imposed by the adhesive bonding of foamed plastics boards, if only because of the fact that in the former case the material is hydrophilic while in the latter case it is hydrophobic. In addition, in this known case the adhesion mechanism is based on a structural variation, specific to the components, in the colloidal system, since it is emphasised that when kaolin is used instead of Neuburg chalk the reverse effect is achieved under the same conditions.The suitability of Neuburg chalk for the adhesive bonding of webs of carboard is based on the specific physical structure of this material, as is clearly stated in the German Patent Specification previously mentioned.

It was therefore surprising that not only Neuburg chalk, which comes within the definition "material containing mineralogically more than 15% of kaolinite", but also kaolin, which is likewise covered by this definition, are suitable for producing an adhesive which is suitable for the adhesive bonding of foamed plastics boards, that is to say of material which differ fundamentally from webs of cardboard in respect of their chemical and physical structure.

According to the invention both naturally occurring materials containing mineralogically more than 15% by weight of kaolinite and synthetically produced materials containing mineralogically more than 15% by weight of kaolinite, and therefore also indude pure kaolinite, can be used. Since however, these materials occur frequently in nature, naturally occurring materials are preferably used. It is essential that these materials should contain mineralogically more than 15% of kaolinite. "Mineralogically" means that the specified amount of kaolinite is incorporated in the lattice of the inorganic material used according to the present invention, The lattice structure of kaolinite is given for example in "Remy, Lehrbuch der anorganischen Chemie", 12th Edition, page 624.

It is in addition extremely surprising that when the structurally very similar silicates, bentonite (montmorillonite), talcum, and mica are used, it is not possible to produce the adhesive for the process of the invention although in respect of thixotropy, for example, and other physical properties regarded as essential to an adhesive action, these materials are almost identical with the materials defined according to the invention.

It must also be surprising that not only are bentonite (montmorillonite), talcum, and mica unsuitable for producing the adhesives of the invention, but that in addition they cancel the action of, for example, kaolinite when these materials are used mixed with kaolinite, even if a large proportion of kaolinite is used.

The adhesive of the invention preferably contains, referred to the total mixture, from 15 to 50% by weight, particularly from 25 to 45% by weight of the material containing mineralogically more than 15% of kaolinite.

The alkali metal silicate solution preferably consists of sodium silicate solution or of a potassium silicate solution or a mixture of these two solutions. The sodium silicate solution preferably has a weight ratio of SiO2 : NaO2 of from 2.9 to 3.7:1 and the potassium silicate solution a weight ratio of SiO2:K2O of from 2.2 to 2.7:1. The solids content of the sodium silicate solution preferably amounts to from 25 to 40% by weight, more preferably from 32 to 37% by weight, and that of the potassium silicate solution to from 20 to 32% by weight and more preferably from 25 to 30% by weight.

In addition, the adhesives of the invention may contain additives such as are added conventionally to adhesives based on alkali metal silicate solutions, particularly starch, starch degradation products, sugar, and alkali metal phosphates.

The adhesives of the invention are in the form of spreadable preparations which can be applied without difficulty to vertical surfaces or ceiling surfaces, for example with the aid of a spatula. The foamed plastics boards, particularly foamed polystyrene boards, which are to be adhesively bonded are normally coated at the rate of from 500 to 600 grams per square metre and lightly pressed against the support to which they are to be bonded. An adhesive action occurs immediately and holds the boards in place.

Drying at room temperature for a period of about 15 hours then preferably follows.

Thereafter the adhesive action is so strong that in an attempt to separate the plastics boards from the support the boards will tear above the band before the separation is achieved.

The supports on which foamed plastics boards can be adhesively bonded with the aid of the adhesive of the invention are preferably supports of wood or of mineral materials.

The following examples explain the invention.

Example I 32% of kaolin consisting mineralogically of 95% of kaolinite is incorporated in 68% of sodium waterglass solution having a solids content of 35.8% and a weight ratio of SiO2: Na2O of 3.3:1. The adhesive prepared in this manner can be applied with the aid of a spatula to a foamed plastics board which is to be bonded in position. After a board of this kind has been pressed onto a wooden support or mineral support, adhesion takes place immediately and holds the board firmly in place. After drying for a period of about 15 hours the board cannot be detached without tearing above the adhesive bond.

Example 2 38% of Neuburg chalk consisting mineralogically of 35% kaolinite and 65% silicic acid modification, is incorporated in 62% of sodium waterglass solution having a solids content of 34.2-0/, and a weight ratio of siO2 Na2O of 3.15:1. When this adhesive is applied at the rate of from 500 to 600 grams per square metre to a'foamed plastics board which is to be bonded in position, there is obtained immediately after drying a bond which is so firm that in an attempt to detach the board the latter likewise tears above the adhesive bond.

Example 3 38%, of Neuburg chalk, which consists mineralogically of 25 % of kaolinite and 75% of a silicic acid modification, is incorporated in 62% of sodium waterglass solution having a solids content of 32.5% and a weight ratio of SiO2 : Na2O of 3.42:1. In this case also the same adhesive action as in the preceding examples is obtained when the adhesive is applied at the rate of from 500 to 600 grams per square metre.

Example 4 30% of kaolin consisting mineralogically of 92% kaolinite and 8% feldspar, is incorporated in 70% of sodium waterglass solution having a solids content of 35% and a weight ratio of SiO2 : Na2O of 3.45:1.

When applied in the same way as in the preceding examples an adhesive prepared in this manner gives results comparable with those of the preceding examples.

WHAT WE CLAIM IS:- 1. A process for the adhesive bonding of foamed plastics boards, comprising treating the foamed plastic boards with an alkali metal silicate adhesive comprising a solution of one or more alkali metal silicates having incorporated therein one or more material or materials in the form of finely divided inorganic powder containing mineralogically (as hereinbefore defined) more than 15% by weight of kaolinite.

2. A process according to Claim 1, in which the adhesive contains, referred to the total weight of the mixture, from 15 to 50% by weight, of the inorganic powder material.

3. A process according to Claim 2, in which the adhesive contains, referred to the total weight of the mixture, from 25 to 45% by weight of the inorganic powder material.

4. A process according to any of the foregoing claims in which the alkali metal silicate solution consists of a solution of sodium silicate or potassium silicate or of a mixture of these solutions.

5. A process according to Claim 4, in which the sodium silicate solution has a weight ratio of SiO2 : Na2O of from 2.9 to 3.7:1 and the potassium silicate solution has a weight ratio of SiO2 : K2O of from 2.2 to 2.7:1.

6. A process according to Claim 4 or 5, in which the solids content of the sodium silicate solution amounts to from 25 to 40% by weight and the solids content of the potassium silicate solution amounts to from 20 to 32% by weight.

7. A process according to Claim 6 in which the solids content of the sodium silicate solution amounts to from 32 to 37% by weight and the solids content of the potassium silicate solution amounts to from 25 to 30% by weight.

8. A process according to any of the foregoing claims in which the kaolinite containing material(s) is or are naturally occurring material(s).

9. A process according to Claim 8 in which the kaolinite containing materials(s) is or are kaolin and/or Neuberg chalk.

10. A process according to any of the foregoing claims also containing an additive such as is added conventionally to an alkali metal silicate adhesive.

11. A process according to Claim 1, substantially as hereinbefore described in any one of the Examples.

12. A foamed plastics board when adhesively bonded by the process of any one of the foregoing claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. Example 3 38%, of Neuburg chalk, which consists mineralogically of 25 % of kaolinite and 75% of a silicic acid modification, is incorporated in 62% of sodium waterglass solution having a solids content of 32.5% and a weight ratio of SiO2 : Na2O of 3.42:1. In this case also the same adhesive action as in the preceding examples is obtained when the adhesive is applied at the rate of from 500 to 600 grams per square metre. Example 4 30% of kaolin consisting mineralogically of 92% kaolinite and 8% feldspar, is incorporated in 70% of sodium waterglass solution having a solids content of 35% and a weight ratio of SiO2 : Na2O of 3.45:1. When applied in the same way as in the preceding examples an adhesive prepared in this manner gives results comparable with those of the preceding examples. WHAT WE CLAIM IS:-

1. A process for the adhesive bonding of foamed plastics boards, comprising treating the foamed plastic boards with an alkali metal silicate adhesive comprising a solution of one or more alkali metal silicates having incorporated therein one or more material or materials in the form of finely divided inorganic powder containing mineralogically (as hereinbefore defined) more than 15% by weight of kaolinite.

2. A process according to Claim 1, in which the adhesive contains, referred to the total weight of the mixture, from 15 to 50% by weight, of the inorganic powder material.

3. A process according to Claim 2, in which the adhesive contains, referred to the total weight of the mixture, from 25 to 45% by weight of the inorganic powder material.

4. A process according to any of the foregoing claims in which the alkali metal silicate solution consists of a solution of sodium silicate or potassium silicate or of a mixture of these solutions.

5. A process according to Claim 4, in which the sodium silicate solution has a weight ratio of SiO2 : Na2O of from 2.9 to 3.7:1 and the potassium silicate solution has a weight ratio of SiO2 : K2O of from 2.2 to 2.7:1.

6. A process according to Claim 4 or 5, in which the solids content of the sodium silicate solution amounts to from 25 to 40% by weight and the solids content of the potassium silicate solution amounts to from 20 to 32% by weight.

7. A process according to Claim 6 in which the solids content of the sodium silicate solution amounts to from 32 to 37% by weight and the solids content of the potassium silicate solution amounts to from 25 to 30% by weight.

8. A process according to any of the foregoing claims in which the kaolinite containing material(s) is or are naturally occurring material(s).

9. A process according to Claim 8 in which the kaolinite containing materials(s) is or are kaolin and/or Neuberg chalk.

10. A process according to any of the foregoing claims also containing an additive such as is added conventionally to an alkali metal silicate adhesive.

11. A process according to Claim 1, substantially as hereinbefore described in any one of the Examples.

12. A foamed plastics board when adhesively bonded by the process of any one of the foregoing claims.