GB2058818A

GB2058818A - Spray adhesive compositions

Info

Publication number: GB2058818A
Application number: GB8024980A
Authority: GB
Original assignee: Woellner Werke GmbH and Co
Current assignee: Woellner Werke GmbH and Co
Priority date: 1977-06-28
Filing date: 1978-06-27
Publication date: 1981-04-15
Also published as: GB2001333A; IT1097294B; GB2058818B; NL7806800A; FR2396058B1; AT356785B; NO782157L; DK276678A; ATA467378A; IT7825026A0; GB2001333B; FR2396058A1; NO813673L; SE7807071L

Abstract

Adhesive spray coating compositions comprising alkali metal silicate solution, inorganic powder containing at least 15% kaolinite and finely divided silica have an acceptable balance of properties, particularly excellent storage stability. Preferred embodiments comprise a solution of alkali metal silicate containing a substance which mineralogically contains more than 20% kaolinite and also finely divided silicic acid.

Description

1

GB 2 058 818 A 1

SPECIFICATION

Spray adhesive compositions

This invention is concerned with spray coating adhesive compositions.

In our Application 28043/78, from which this Application is divided, there are disclosed coating or 5 adhesive compositions having a solids content of 35 to 50% comprising (i) a solution of alkali metal 5 silicate (ii) finely divided inorganic powder containing, mineralogically, more than 15% kaolinite and (iii) certain (meth)acrylic acid ester polymer binders. That Application also discloses that the adhesive compositions have especial utility as adhesive spray compositions when more than 20% of the mineral content of the powder component (ii) is kaolinite and the compositions also contain finely divided silicon 10 dioxide, which may be in the hydrated form as silicic acid. 10

In the spray adhesive compositions of the present invention the polymer binder component (iii) is replaced wholly by the silicon dioxide component.

The compositions of the invention are particularly useful as spray adhesivesfor insulation fibres.

The German "Offenlegungsschrift" 24 60 543 discloses a material, which can be used as an 15 adhesive or as a protective coating on metals or other substances and which consists of 60 to 95 parts 1 5 by weight of sodium silicate, 4 to 16 parts by weight of clay mineral substances, 1 to 15 parts by weight of oxides or carbonates or alkali earth metals or of zinc, oxides or hydroxides of aluminium and/or barium sulfate as well as 0 to 5 parts by weight of pigments. As clay mineral substances, china clay, pot clay, talc or mixtures thereof, are employed.

20 The storage capability of such materials is very limited by the presence of the stated oxides, 20

hydroxides and carbonates. The viscosity increases greatly with storage time, whereby such a material will gel after 10 to 15 days, dependent on composition. Furthermore, significant amounts of these materials are inclined to separate, whereby the solid substances deposit in the form of a pasty mass which can only be converted back to the original consistency with great difficulty, if at all.

25 A further disadvantage of these known materials is that in order to avoid cracking at adhesion 25

points or in coatings, very particular drying conditions as well as a very particular degree of drying must be observed.

Spray-insulation of for example power turbines with asbestos has been known for a long time. In this process, finely divided asbestos fibres are blown with air into the part of the apparatus to be 30 insulated and bound by means of water vapour applied at the same time. A particular adhesive has not 30 been required for this purpose. Working with asbestos fibres however results in a large amount of asbestos dust in the working area, which presents a significant hazard to health (Asbestosis).

Thus, attempts have been made for a long time to employ mineral fibres instead of asbestos.

Working for mineral fibres without a binder has however not been possible.

35 An adhesive for spray insulation with application of mineral fibres must satisfy the following 35

requirements:

a) The adhesive must possess a high initial clinging action so that the insulation coating which is sprayed on does not fall off.

b) The adhesive must be able to withstand temperatures up to at least 1000°C.

40 c) The adhesive should not drip or flow out of the insulation coating. 40

d) The adhesive must be able to be stored over a long time.

e) The adhesive may not have a corrosive action on metals. 0

The adhesives known for mineral fibres can not or can only in part meet the criteria.

Attempts have also been made to mix mineral fibres with cement and to blow the mixture onto the 45 article to be insulated and to bind such by spraying on of water. This process has the disadvantage that 45 such a high cement dust concentration is produced in the working area that work is made bery difficult and considerably safety measures are preferable.

Preferred adhesives of the invention can be made which not only satisfy all the stated requirements for an adhesive for spray insulation employing mineral fibres, but may even exceed them 50 by additionally providing protection against corrosion of metal substrates. 50

Preferred adhesives of the invention also possess very good storage stability. In closed containers they may be stored indefinitely.

According to this invention there is provided an aqueous spray coating adhesive composition comprising (i) a solution of alkali metal silicate (ii) 1 to 10% by weight of finely divided inorganic powder 55 containing, mineralogically more than 15% kaolinite and (iii) finely divided silica. 55

In a preferred form, the spray coating adhesive comprises as the silica component up to 5% by weight of finely divided hydrated silicon dioxide (silicic acid).

Advantageously, the preparations of the invention additionally contain one or more water-soluble silicone materials, particularly alkali metal salt of methyl silicic acid and/or one or more aluminium salts 60 of straight chain aliphatic carboxylic acid having 16 to 26 carbon atoms, to increase the hydophobic 60 : properties and hence the water stability.

The compositions further preferably contain one or more alkali metal aluminates in particular sodium and/or potassium aluminate, since in the compositions alkali metal aluminates will in time form water-soluble alkali metal silicates, which are available in divided form and assist the water stability.

2

GB 2 058 818 A 2

Alkali metal aluminates furthermore increase the viscosity, which assists separation of pigments. Also, a thixotropic effect is obtained by this additive.

Advantageously, the added alkali silicate solution comprises sodium silicate solution, potassium silicate solution or a mixture of these solutions. In the latter case, a particularly flexible coating or 5 adhesive (binder) point is obtained.

Preferably the sodium silicate solution possesses a poroportion by weight of Si02: Na20 of 2.5 to 3.8:1 and the potassium silicate solution a proportion by weight of Si02: K20 of 1.6 to 2.7:1.The solids content of the sodium silicate solution is preferably 28 to 42, particularly 34 to 38% by weight and the solids content of the potassium silicate solution 24 to 44 and in particular 35 to 41% by weight. The 10 preparations preferably contain a mixture of 98 to 50% by weight, particularly 96 to 90% by weight of such sodium silicate solution and 2 to 50% by weight, particularly 4 to 10% by weight of such potassium silicate solution based on the weight of the combined silicate solutions.

The content of the powder material, of whose mineral content more than 15%, preferably more than 20%, by weight is kaolinite, is preferably 1 to 10% by weight, in particular 2 to 6% by weight. In 15 this specification the % by weight figures of the total mixture refer to the mixture of alkali metal silicate, kaolinite-containing material and silicon dioxde, on a solid basis wherever appropriate. The alkali metal aluminate content is preferably up to 10% by weight, particularly 1 to 5% by weight.

The silicone product is preferably present in an amount of from 0.1 to 10% by weight and in particular in an amount of 0.5 to 3% by weight. An alkali metal salt of methyl silicic acid is particularly 20 preferred. The content of the aluminium salt of a straight-chain aliphatic carboxylic acid with 12 to 26 carbon atoms is preferably from 0.05 to 5% by weight and in particular 0.01 to 1% by weight.

The preparations of the invention can furthermore contain up to 1%, for example 0.1 to 1% by weight of polymeric ammonium or sodium polyacrylate as pigment distributor, fn particular for distribution of iron oxide pigments as well as the aluminium salts of the mentioned straight-chain 25 aliphatic carboxylic acids.

Additionally, the preparations can advantageously contain up to 3% by weight, for example 0.1 to 3% by weight of lithium hydroxide to increase water resistance.

Furthermore, up to 4% by weight of alkali-resistant, usually alkali metal-containing, pigment may be added.

30 For the purpose of increasing flexibility of points of adhesion, up to 5% by weight, particularly 0.5 to 2% by weight, of polyhydric alcohols can be added.

The addition of a micro-crystalline polyethylene on polypropylene wax, in particular in an amount of 0.1 to 4% by weight, in a very particularly preferred manner in an amount of from 0.3 to 1.5% by weight, has also been shown to be useful for increasing hydrophobic properties.

35 The adhesive may also comprise additives such as are conventionally added to adhesives based on an alkali metal silicate, in particular alkali metal phosphates, advantageously sodium phosphate, or one or more sugars.

The following Example describes a preferred embodiment of the invention, is given for illustration only and illustrates an adhesive for a spray coating insulation.

40 EXAMPLE 1

93.5% by weight sodium silicate solution

(solids: 36.5%yatio by weight Si02:Na20 = 3.30:1)

6.0% by weight "Neuburger" chalk

0.5% by weight finely divided hydrated silicon dioxide (silicic acid)

45 100.0% by weight.

Claims

1. An aqueous spray coating adhesive composition comprising (i) a solution of alkali metal silicate (ii) 1 to 10% by weight of finely divided inorganic powder containing, mineralogically, more than 15% kaolinite and (iii) finely divided silica.

50

2. A composition as claimed in Claim 1 wherein the silica is included in the form of silicic acid.

3. A composition as claimed in Claim 1 or 2 wherein the amount of component (iii) is up to 5% by weight.

4. A composition as claimed in any preceding claim wherein the amounts of component (ii) is 2 to 6% by weight.

55

5. A composition as claimed in any preceding claim wherein the amount of component (iii) is 0.5

to 3.5% by weight.

6. A composition as claimed in any preceding claim wherein the kaolinite content of component (ii) is more than 20% by weight of the minerals in that component.

7. An adhesive composition as claimed in any preceding claim which further contains a water-60 soluble silicone product or an aluminium salt of a straight chain aliphatic carboxylic acid having 16 to

26 carbon atoms to increase its hydrophobic properties.

8. An adhesive composition as claimed in Claim 7 wherein the silicone product comprises an alkali

5

10

15

20

25

30

35

40

45

50

55

60

3

GB 2 058 818 A 3

metal salt of methyl silicic acid.

9. An adhesive composition as claimed in any preceding claim which contains alkali metal aluminate.

10. An adhesive composition as claimed in any preceding claim in which the alkali metal silicate

5 solution consists of a sodium silicate solution, a potassium silicate solution or a mixture of these 5

solutions.

11. An adhesive composition as claimed in claim 10, in which the sodium silicate possesses a ratio by weight of Si02: Na20 = 2.5 — 3.8:1 and the potassium silicate a ratio by weight of Si02:K20= 1.6-2.7.

10

12. An adhesive composition as claimed in Claim 10 or Claim 11, in which the solids content of 10 the sodium silicate solution is 28 to 42% by weight and the solids content of the potassium silicate solution is 24 to 44 by weight.

13. An adhesive composition as claimed in any of the preceding claims which contain a mixture of 98 to 50% by weight of sodium silicate solution and 2 to 50% by weight of potassium silicate solution

15 the percentage being based on the weight of the combined silicate solutions. 15

14. An adhesive composition as claimed in any preceding claim which contains up to 10% by weight of alkali metal aluminate.

15. An adhesive composition as claimed in any preceding claim which contains 0.1 to 10% by weight of alkali metal salt of methyl silicic acid, and/or 0.05 to 5% by weight, of aluminium salt of

20 straight chain aliphatic carboxylic acid having 12 to 26 carbon atoms. 20

16. An adhesive composition as claimed in any preceding claim which contains up to 1% by weight of polymeric ammonium or sodium polyacrylate pigment distributor.

17. An adhesive composition as claimed in any preceding claim which contains up to 3% by weight of lithium hydroxide.

25

18. An adhesive composition as claimed in any preceding claim which contains up to 4% by 25

weight of alkali-resistant colour pigment.

19. An adhesive composition as claimed in any preceding claim which contains up to 5% by weight of polyhydric alcohol.

20. An adhesive composition as claimed in any preceding claim which contains micro crystalline

30 polyethylene or polypropylene wax in an amount of from 0.1 to 4% by weight. 30

21. An adhesive composition as claimed in any preceding claim which additionally contains alkali metal phosphate, preferably sodium phosphate, or sugar additive such as is conventionally added to adhesives based on alkali metal silicate.

■

22. An adhesive composition as claimed in Claim 1 substantially as described in the foregoing

35 example. 35

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.