GB2163446A

GB2163446A - Stripping organic coatings

Info

Publication number: GB2163446A
Application number: GB08421329A
Authority: GB
Inventors: David Noel Rees
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-08-22
Filing date: 1984-08-22
Publication date: 1986-02-26
Also published as: GB8421329D0

Abstract

Baked-on organic coatings on steel, are removed by applying a stripping composition, including the following materials Methylene chloride A Glycol together with an acid or alkali activator The composition is applied by brush or spray, left in contact with the coating for a period of time, and then removed with the coating from the steel.

Description

SPECIFICATION Stripping organic coatings The invention relates to compositions and processes for removing organic coatings from metal sheets or other metal objects. The invention is particularly, though not exclusively, applicable to stripping organic finishes such as baked-on coatings from steel sheets as used, for example, in building construction.

These coated steel sheets may need to be guaranteed for a number of years but it can happen that the coating breaks down due, for example, to faulty manufacture or unusually severe atmospheric conditions. Before any rectification can take place the defective coating must be removed.

The usual organic materials used for coating steel sheets for the building industry comprise the various available plastisols, and synthetic organic coating materials such as acrylics, alkyds, polyesters and epoxy resins. The coatings are normally baked onto the steel sheets at high temperature and the usual method of removing the coating has been by means of a paint stripper based on Methylene Chloride, for example. However, the different organic ocatings do not all react in the same way to conventional paint strippers and some are quite unaffected by these strippers depending on the differing elasticity and adhesive properties of the coating.

It is an object of the invention accordingly to provide an improved stripping composition and process which will overcome some of the existing problems and difficulties.

Broadly stated from one aspect the invention consists in a method of removing an organic coating from a metal sheet or other metal object, by applying a stripping composition comprising methylene chloride and glycol, with an acid and/or alkali or activator, allowing the composition to remain on the coating for a period of time, and then removing the coating.

Preferably the glycol and activator are present in proportion by volume between 4:1 and 1:4 and according to a preferred feature of the invention the glycol includes tri- and tetra- ethylene glycol. The activator is preferably cresylic and/or formic acid and the glycol, cresylic and formic acid are present in the appropriate ratio 3:1:1 by volume and in combination represent 3% to 6% by value of the total. The glycols are conveniently obtained as the residues of an esterification process involving fatty acids and alcohols.

From another aspect the invention consists in a stripping composition for removing an organic coating from a metal sheet or object comprising methylene chloride, glycol, and an acid and/or alkali activator.

Preferably the glycol includes tri- and tetra- ethylene glycol, and preferably the glycols are in solution in water. The activator may comprise cresylic and/or formic acid, and preferably the glycols and acid are present in the approximate proportion 3:1:1. The composition may also include methanol and additives or agents such as thixotropic or wetting agents or evaporation retardents.

The invention may be performed in various ways and some specific embodiments will now be described by way of example.

In the first example the stripper composition comprises: 50/50 glycol solution cresylic and/or formic acid methylene chloride The ratio of glycol to acid is preferably between 4:1 and 1:4 and best results are obtained with a ratio of approximately 3:2. The 50/50 glycol preferably includes tri- and tetra- glycols in approximately equal proportions and the cresylic and formic acids are also included in approximately equal proportions. The preferred ratios of tri- and tetra- glycols with acid are approximately 3:2. Generally speaking, the ratio of cresylic/formic acid may be between 5:1 and 1:5.

The glycol constituent may include other glycols such as mono-ethylene glycol, and other acids may be substituted for example acetic acid or hydrofluoric acid. The glycols are preferably included in a 50% water solution, though other solvents may be useful in certain conditions, such as methyl ethyl ketone.

This solution of course is highly flammable but may be of use in special situations.

The preferred formula is as follows: % W/W Max Range.

Methylene chloride 76 60 - 80 Methanol 10 8-15 111Trichloroethane 6 4-10 Trixotropic Agent 1 1 - 21/2 Wetting Agent 3/4 1/2- 2 Paraffin Wax 3/4 50/50 Glycols Formic Acid ) 3:1:1 mix in combination Cresylic Acid ) 4% (VN) 3-6% (VN) One preferred method of preparing the composition is as follows. A paint stripper with a methylene chloride base, as previous defined,with or without activators, is introduced into a mixing tank and to the tank is added the 50/50 glycols with cresylic and formic acids in the proportions specified and the materials are mixed in the tank until a completely uniform colour is obtained. This mixture may be used in this state. Alternatively it may be added on site to a prepared paint stripper.lnitially about one quarter of the paint stripper is added to the composition and thoroughly mixed. The balance of the methylene chloride paint stripper is then added and mixed mechanically until the colour is uniform.

The stripping composition can be applied to the coated steel in various different ways but is normally applied by a low pressure airless spray jet or by brush. If applied by brush the stripping composition should not be given excessive brushing, which would tend to extract the evaporation retardant and cause very rapid flash drying.

Claims

1. A method of removing an organic coating from a metal sheet or other metal object, by applying a stripping composition comprising methylene chloride and glycol, with an acid and/or alkali activator, allowing the composition to remain on the coating for a period of time, and then removing the coating.

2. A method according to Claim 1, in which the glycol and activator are present in proportion by volume between 4:1 and 1:4.

3. A method according to Claim 1 or Claim 2, in which the glycol includes tri- and tetra-ethylene glycol.

4. A method according to any of the preceding claims, in which the activator is a cresylic and/or formic acid.

5. A method according to any of the preceding claims, in which the glycol,cresylic and formic acids are present in the approximate ratio 3:1:1 by volume.

6. A stripping composition for removing organic coatings from metal comprising methylene chloride, glycol, and an acid and/or alkali activator.

7. A composition according to Claim 6, in which the glycol includes tri- and tetra-ethylene glycol.

8. A composition according to Claim 7, in which the glycols are in solution in water.

9. A stripping composition according to any of Claims 6,7 and 8, in which the activator comprises cresylic and/or formic acid.

10. A composition according to Claim 9, in which the glycol and acids are present in the approximately proportion 3:1:1.

11. A stripping composition according to any of the preceding claims, including also methanol and additives or agents such as thixotropic or wetting agents or evaporation retardents.

12. A stripping composition substantially as described in any of the examples.