GB2282607A

GB2282607A - Stripping compositions comprising sulphonic acid and thickener

Info

Publication number: GB2282607A
Application number: GB9320598A
Authority: GB
Inventors: Alan John Walsh
Original assignee: Itac Ltd
Current assignee: Itac Ltd
Priority date: 1993-10-06
Filing date: 1993-10-06
Publication date: 1995-04-12
Also published as: GB9320598D0

Abstract

Composition, which may be used to remove cured silicone, comprises one of: (i) sulphonic acid, dissolved in an organic solvent, thickened with a mixture of polyethylene fibrids and fumed silica; (ii) sulphonic acid, dissolved in a solvent, with thickener (preferably a mixture of polyethylene fibrids and fumed silica) and organo-metallic catalyst.

Description

comPosiXoN This invention relates to a composition which can be used for removing/dissolving cured silicone materials, for example silicone rubbers, silicone sealants and substances of comparable molecular structure.

It is known to use sulphonic acids to dissolve cured silicones.

They react to give relatively unobjectionable by-products which can be relatively easily flushed away or removed. However, it is often difficult to maintain the sulphonic acid in contact with the cured silicone for a sufficient length of time to enable the reaction to take place. On flat or hollow surfaces there is no problem as the liquid containing the sulphonic acid can be allowed to lie on top of the silicone. On vertical surfaces, however, or even on inverted surfaces such as roofs and ceilings it can be extremely difficult to cause the sulphonic acid to stay in contact with the silicone for the requisite length of time.

It is an Object of the present invention to provide an improved composition, for example, for the cleaning/removal of silicone compounds.

The invention provides a compound, for example for removing cured silicones, comprising a sulphonic acid dissolved in an organic solvent and thickened with a mixture of fumed silica and polyethylene fibrids.

The invention also provides a composition, for use for example for removing cured silicones comprising a sulphonic acid dissolved in a solvent, together with a thickener and an organo metallic catalyst.

In either of the above the composition should have a moisture content less than 1% and preferable be completely anhydrous.

The sulphonic acid used can be any organic sulphonic acid, for example benzene sulphonic acid or dodecyl benzene sulphonic acid.

Other sulphonic acids can, of course, be used provided that they can be prepared with minimal water content.

The solvent is desirably a hydrocarbon solvent and is preferably aliphatic rather than aromatic. Although many solvents will operate perfectly well in these circumstances, aliphatic solvents are performed as they are less environmentally damaging when disposed of or incinerated. It is further desirable if the hydrocarbon has a relatively high flash point in order that the composition is not classed as a "flammable" or "highly flammable" material. A preferred solvent is a long chain aliphatic hydrocarbon solvent sold under the name CLAIRSOL 350 and manufactured by Carless Refining and Marketing Limited. This product has a flash point of 790C. The mixture of fumed silica and polyethylene fibrids gives a particularly suitable thickening property to the composition. Fumed silica is the more expensive of the two compounds and therefore it would be desirable to use none at all.However, the fumed silica does have the particular property of very significantly reducing problems of cineresis, that is to say wherein liquid leaches out of the gel and forms a layer on the top during storage. As the re-introduction of such liquid is not easy in this particular composition (it needs slow stirring over a considerable period of time) the elimination of cineresis by the use of fumed silica is most important.

Fumed silica alone is not very efficient as it is reluctant to yield up the sulphonic acid absorbed thereon. On the contrary, the polyethylene fibrids readily give up the acid which makes the mixture of the two thickening agents particular effective.

The use of an organo metallic catalyst greatly increases the rate at which the sulphonic acid attacks the silicone and it can migrate easily out of the polyethylene fibrids in order to be present between the acting paste/gel and the silicone under attack.

Of course, the main point of the thickening compounds is to put the composition into the form of a gel or paste which can easily adhere to vertical or inverted surfaces.

In the following all percentages are by weight.

The organic sulphonic acid is dissolved in the hydrocarbon solvent at a level of between 8 and 20%. The fumed silica is added in a range from 1 - 129, preferably 6%. The polyethylene fibrids are preferably added in a range of from 1 to 10%, preferably 5%.

The invention will be described further, by way of example, with reference to a preferred composition.

A preferred composition of the invention is as set out in the following table.

Ir 1 constituent Percentage Preferred Range Percentage I Solvent / 89 - 60 72.9 I I Sulphonic acid (benzene - or 8 - 20 16 deodeyl benzene) Fumed Silica 1 - 12 6 P.E Fibrids 1 - 10 5 Organo Metallic Catalyst 0.001 - 1 0.1 All percentages by weight.

The preferred composition illustrated above is manufactured by mixing the components together in a slow speed mixer, for example a total batch weighing 200kg is placed in a Z-blade mixer which is operated at 20 - 30 rpm for 15 mins.

At the end of the mixing the composition is in a gel or paste form and will adhere readily to vertical and inverted surfaces.

The composition preferably has a viscosity in a range 50 - 2000 poise.

In use the composition is applied to silicone seals and the like which are needed to be removed (perhaps after physically removing the bulk of the seal with a knife or scraper). Because the composition is in the form of a gel or paste the composition adheres to the surface and the sulphonic acid migrates out of the paste to the interface and attacks the silicone.

The solvent CLAIRSOL 350 (RTM) is an aliphatic hydrocarbon solvent, completely free of any water, and of flash point over 79 C. This is important because the finished product does not even need to bear a "flammable" warning let alone a "highly flammable" warning. This is advantageous for sale and use. The use of the organo metallic catalyst greatly enhances the action of the sulphonic acid on the silicone and in combination with the thickening agent acts to migrate out of the thickening agent with the sulphonic acid thus ensuring a steady supply of fresh catalyst as fresh sulphonic acid comes to the surface to attack the silicone.

The fumed silica tends to hold the solvent and suiphonic acid and catalyst (if used) within its structure and to be very reluctant to release these components. However, the polyethylene fibrids release the components quite readily. To use enough fumed silica alone to give the required thickness would result in a composition wherein a large proportion of the sulphonic acid would be bound by the fumed silica and would not be made available for attack on the silicone. If polyethylene fibrids are used without the fumed silica there is a great tendency for the composition to undergo cineresis in storage, that is to say liquid tends to stand on top of the gel body. This is undesirable as it means that the active constituents are leached out of the gel and may be lost, or be a hazard in themselves.

It is not possible to re-introduce such expelled liquid by simple stirring, before use, as prolonged slow stirring is required.

Therefore, cineresis is a severe problem which can be overcome by the use of the minimal quantity of fumed silica with the P.E fibrids The composition adheres readily to vertical and inverted surfaces and is extremely effective in the chemical removal of silicones including silicone rubbers, silicone sealants and materials of comparable molecular structure.

The invention is not limited to the precise details of the foregoing and variations can be made thereto. For example the organo metallic catalyst can be used with any particular thickening agent not only the combination of fumed silica and polyethylene fibrids. The solvent can be any convenient organic solvent, the one chosen being suitable because of its high flash point, relative inoffensiveness, non or low chlorination and being generally easily handled and non-toxic. The sulphonic acid chosen can be any convenient sulphonic acid. For example toluene sulphonic acid can be used, as well as benzene sulphonic acid and dedeyl benzene sulphonic acid.

For the solvent, equivalents of CLARISOL 350 by other makers can be used, or CLAIRSOL 315, white spirita the like can be used, but are not preferred as the CLAIROSO1 315 has a lower flash point and white spirit contains aromatic components.

The organo and metallic catalyst can be tin-based, such as dibutyl tin di-laurate (STANCLERE TL from Akzo Chemicals) or other dibutyl tin catalysts iron octoate or cobalt napthenate.

Many other variations are possible within the scope of the invention.

Claims

1. A composition for example for removing cured silicones, comprising a sulphonic acid dissolved in an organic solvent and thickened with a mixture of fumed silica and polyethylene fibrids.

2. A composition, for use for example for removing cured silicones, comprising a sulphonic acid dissolved in a solvent, together with a thickener and an organo-metallic catalyst.

3. A composition as claimed in claim 2 wherein the thickener is a mixture of fumed silica and polyethylene fibrids.

4. A composition as claimed in claim 1 or 3 and having a moisture content less than 1%.

5. A composition as claimed in any preceding claim, wherein the sulphonic acid is benzene sulphonic acid or dodecyl benzene sulphonic acid.

6. A composition as claimed in any preceding claim wherein the solvent is a hydrocarbon solvent.

7. A composition as claimed in claim 6, wherein the solvent is an aliphatic solvent.

8. A composition as claimed in any preceding claim, wherein the solvent has a flash point above 70or.

9. A composition as claimed in any preceding claim, and exhibiting minimal cineresis.

10. A composition as claimed in any preceding claims wherein the sulphonic acid is present at a percentage of from 8 to 20%.

11. A composition as claimed in claim (10) wherein the percentage is 16.

12. A composition as claimed in any preceding claim wherein the fumed silica is present in the range 1 - 12% preferably 6 to 4%.

13. A composition as claimed in any preceding claim wherein the polyethylene fibrids are present in the range from 1 to 10%, preferably 5%.

14. A composition as claimed in any preceding claim and having a viscosity > 50 poise.

15. A composition as claimed in claim 14 and having a viscosity in the range from 50 to 2000 poise.

16. A composition as claimed in claim 2 or any claim dependent therefrom wherein the organo-metallic catalyst is selected from the group consisting of dibutyl tin di-laurate, iron octoate and cobalt napthenate.

17. A composition substantially as designed with reference to the example.