AU641977B2 - Process for removing paint coatings from surfaces - Google Patents

Description

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Process for Removing Paint Coatings from Surfaces Subject matter of the present invention is a process for removing paint coatings from surfaces by high pressure waterblasting.

In order to clean surfaces, processes operating with water jets compressed to high pressures are widely used. In this fashion, building exteriors, ships and bridges, for example, are cleaned. Similarly, the sandblasting process is widely used. A precondition for employing the described processes is a certain firmness of the surfaces to be treated.

Therefore, these processes could not be used for cleaning or treating surfaces made up essentially by modern material such as synthetics reinforced by glass fiber and carbon fiber, or material on the basis of epoxy resin.

Removal of paints from sensitive surfaces for lightweight emonctrcutij especially in the construction of aeroplanes, is effected according to prior art by treating the surfaces with scouring agents such as organic chlorocarbons, and then removing the pretreated paint mechanically.

Here, however, in addition to the paint to be actually removed, other, deeper layers are also affected and scaled.

Thus, in the construction of aeroplanes, for instance, polyester-based fillers are coated onto the epoxy resin base body onto which in turn a so-called primer layer on the basis of polyurethane, for example, is coated. Eventually, this primer layer then is provided with the surface lacquer. Depending on -2type of aircraft, three or four layers are coated prior to surface-lacquering.

Using the above-mentioned scouring agent, these layers are similarly affected, however. Moreover, the use of chlorocarbons gives rise to reservations with respect to health; furthermore, this use is not environmentally compatible.

It is object of the invention to provide a process that permits exclusive removal of the surface lacquer layer of a surface build-up consisting of several layers of plastics, optionally removal of the layer underneath the surface lacquer layer, and which is environmentally compatible and non-hazardous to health.

SAccording to the invention, this problem is solved by a process for removing :o 6* paint coatings from sensitive surfaces by high pressure waterblasting wherein.aaof the following characteristics is used individually-@i in combination: 15 the surface is treated with an aqueous solution containing an organic noncorrosive swelling agent; the organic non-corrosive swelling agent, depending on the nature of the surface, acts upon the surface to be treated for a period of time sufficient to cause swelling of the paint coating to be removedanc.

20 the surface is treated with a water jet at a temperature of 20 °C and a pressure of from 100 to 600 bars.

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in the spirit of the process according to the invention, the term water is meant to represent water in the broadest sense. Thus, it may be pure water in the chemical sense as well as normal tap water or recycled process water. Where organic noncorrosive swelling agents are used, the water jet is also understood to be a jet of an aqueous solution thereof.

In a preferred embodiment of the process according to the invention, a water jet at a higher temperature, preferably of 930212,q:\oper\ee,70432deu.res2 3 from 30 0 C to 100 0 C, is used. Depending on the nature of the surfaces, the water jet temperature is adjusted; with easily removable lacquer layers, the temperature of the water jet may be kept lower, whereas higher temperatures must be employed to remove other lacquer layers.

It has proven advantageous to use an aqueous solution containing benzyl alcohol as the organic non-corrosive swelling agent. Preferably, benzyl alcohol is employed as an aqueous solution of from 40 to 80% by volume. Optionally, the aqueous solution of the organic non-corrosive swelling agent may further contain auxiliary agents such as emulsifiers, surfactants, detergents, stabilizers, etc..

In the removal of aged paints, it was found advantageous to keep the duration of exposure to the organic non-corrosive swelling agent in the range of from 120 to 240 minutes. Where relatively new surface paints are to be removed, longer exposure periods, preferably of from 180 to 300 minutes at a defined temperature, must be kept. In case the surface laquer layer has already become largely brittle, use of swelling agent may be abandoned.

The higher the temperature of the high pressure water jet, the less organic non-corrosive swelling agent must be applied in advance. The ideal temperature in relation to used amount of organic non-corrosive swelling agent may be determined by the artisan using appropriate preliminary experiments. Here, also aspects of business management may play a central role, minimizing of expenses which, depending on expense situation of swelling agent and heated water, are to be coordinated.

When operating without using an organic non-corrosive swelling agent, it can be generally stated that the higher the temperature of the water jet, the lower the pressure of the water jet can be kept. In particular, this becomes apparent 4 when comparing the treatment of aluminum surfaces to surfaces being made up of composite material. While aluminum surfaces may quite well be processed in regions of higher pressure of up to 600 bars where, preferred in particular, the temperature can be maintained in the range of 80 0 C, composite material, on the contrary, is preferably processed in a pressure range of from 200 to 400 bars, where the temperature of the water jet, however, is preferably kept at about 100 0

C.

Hence, the process according to the invention preferably is suited for treating thin-walled aluminum sheets as well as surfaces of composite material such as FRP (fibrous-glass reinforced plastics) and fibrous-carbon reinforced material that are used in aircraft and ship construction.

Using common procedures, the swelling agent is applied by spraying or brushing to the surfaces to be delaquered.

According to the previously determined duration of exposure to the swelling agent selected as described above depending on lacquer condition, the surface lacquer affected by the organic non-corrosive swelling agent then is removed using a water jet. Here, the water jet effuses from a so-called flat nozzle or rotational nozzle. The water to be used here is, for instance, normal tap water, optionally at elevated temperature, which in advance has been brought to appropriate pressures of from 100 to 600 bars, preferably from 200 to 500 bars Here, the water jet may develop a recoil force of about 15 kp.

Furthermore, in a preferred embodiment of the process according to the invention, push-type nozzles may be used.

In another particularly preferred embodiment of the process according to the invention, rotational nozzles are used where the water discharges at a pressure of from 200 to 500 bars, a nozzle size of 1 mm having proven useful. Preferably, the water jet is held to the surface to be delacquered under a flat angle at a distance of from 50 to 150 mm. Preferably, the nozzle is moved further on at a velocity of about 50 mm/s.

Here, the angle of impact should be kept flat and, preferably, should be from to 60 0. It has proven advantageous to direct the water jet such that impact occurs at a positive angle to the surface when viewed from the direction of impact i.e. it is preferred that the angle of impact is not too flat but also that the water jet is not directed perpendicularly to the surface to be treated.

Likewise, the water jet may be generated by a multiplicity of nozzles.

Thereby, a larger area is covered by the water jet.

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By using an aqueous solution containing an organic non-corrosive swelling 15 agent, paints may be removed from surfaces for lightweight construction by a high doe pressure waterblasting process. In particular, use of an aqueous solution containing benzyl alcohol, preferably in concentrations of from 40 to 80%, is recommended.

Such solutions are commercially available and are sold by the company Turco (Turco 9064, 6088).

Thus, the process according to the invention permits environmentally S: compatible and non-polluting removal of paints from surfaces, especially from aluminum and composite material surfaces. It operates avoiding environmentally impairing scouring agents such as methylene chloride. In cases where merely a water jet at elevated temperatures is used, it is completely sufficient to remove the lacquer residues from the waste water and to recycle this process water into the process.

Moreover, when applying the process according to the invention using the organic non-corrosive swelling agent, considerable advantages result as compared to known prior art processes. These swelling agents are environmentally compatible and non-hazardous to health. By filtering the peeled-off 930212,q:\oper\ee,70432deu.res5 6 lacquer residues it is possible to refeed the water to the high pressure pump. Thus, it is possible to use the water several times and to further increase economic efficacy. Re-using the water is also advantageous for environmental reasons. The amount of non-corrosive organic swelling agent may be optimized by appropriately selecting the temperature of the water jet so as to be fitting each cleaning problem.

Claims (10)

1. A process for removing paint coatings from sensitive surfaces by high pressure waterblasting wherein o~neof the following characteristics is used i4nidua lly in combination: the surface is treated with an aqueous solution containing an organic non- corrosive swelling agent; the organic non-corrosive swelling agent, depending on the nature of the surface, acts upon the surface to be treated for a period of time sufficient to cause swelling of the paint coating to be removed and the surface is treated with a water jet at a temperature of 20 °C and a pressure of from 100 to 600 bars. S. 2. The process according to claim 1, wherein said surface is a thin-walled 15 aluminum surface or a surface consisting of fibrous-glass reinforced or fibrous-carbon reinforced plastics.

4. The process according to at least one of the claims 1 to 3, wherein the aqueous solution of the organic non-corrosive swelling agent contains from 40 to 80% by volume benzyl alcohol. 930212,q:\oper\ee,70432deu.res7 8 The process according to at least one of the claims 1 to 4, wherein the aqueous solution of the organic non-cor- rosive swelling agent contains auxiliary agents such as emulsifiers, surfactants, detergents, etc..

6. The process according to at least one of the claims 1 to 5, wherein the duration of exposure to the organic non- corrosive swelling agent is from 120 to 240 minutes in the case of aged paints, and in other cases from 180 to 300 minutes.

7. The process according to at least one of the claims 1 to 6, wherein the temperature of the high pressure water jet is from 30 0 C to 100 0 C.

8. The process according to at least one of the claims 1 to 7, wherein the water jet discharges from so-called flat nozzles or rotational nozzles.

9. The process according to at least one of the claims 1 to 8, wherein push-type nozzles are utilized. The process according to at least one of the claims 1 to 9, wherein the water jet has a recoil force of 15 kp.

11. The process according to at least one of the claims 1 to 10, wherein impact of the water jet on the surface oc- curs at an angle of 900.

12. The process according to claim 11, wherein the angle is from 300 to Tho prococG according t a wt east on cuf the plaiiut to 10, wherein impact o-ne water jet occurs at a posi- I tive angle viw Incutting diecti. -9-

13. The process according to at least one of the claims 1 to 10, wherein impact of the water jet occurs at a positive angle to the surface when viewed from the direction of impact.

14. The process according to at least one of the claims 1 to 13, wherein the water jet is generated by a multiplicity of nozzles. 1 3--t I(lle.nnSI snlntinn containing an organic non-Gerrosive swlling agnt- for removing paint means of a high pressure waterblasting process. S16.- Use oQf an aqueons solition 9ccOajt -i-nj--t-g 0 .DATED this 12th day of February, 1993. DEUTSCHE LUFTHANSA AG 000 By Its Patent Attorneys DAVIES COLLISON C VE 00a 0 0 QO ,I 930212,q:\oper\ee,7432detres9 W .ff 10 ABSTRACT A process is described for removing paint coatings from surfaces by high pressure waterblasting wherein one of the following characteristics is used individually or in combina- tion: the surface is treated with an aqueous solution co taining an organic non-corrosive swelling agent; the organic non-corrosive swelling agent, depending on the nature of the surface, acts upon the surface to be treated for a certain period of time and/or the surface is treated with a water jet at a temper- ature of 20"C and a pressure of from 100 to 600 bars. INTERNATIONAL SEARCH REPORT International Application No PCT/EP90/01877 I. CLASSIFICATION OF SUBJ.CT MATTER (if several classification symbols apply, indicate all) Accurding to International Patent Classification (IPC) or to both National Classificatlon and IPC Int.Cl 5 B44D 3/16, B08B 3/02 II. FIELDS SEARCHED Minimum Documentation Searched 7 Classiflcatlon System Classification Symbols Int.C 5 B44D, BOBB C09D Documentation Searched other than Minimum Documentation to the Extent that such Documents are Included In the Fields Searched Ill. DOCUMENTS CONSIDERED TO BE RELEVANT' Category Citation of Document, 1 with indication, where appropriate, of the relevant passages 1 2 A 1 EP, A, 0194242 (AKTIEBOLAGET ELECTROLUX) September 1986 see page 3, lines 19-36 A US, A, 3470023 JOHNSTON) September 1969 see column 1, line 39 column 2, line 58 A DE, A, 2952391 (GRENSING GmbH) 24 September 1981 see claims 1-3; page 6, lines 6-17 I Relevant to Claim No. 13 1,7,8,15 1,5,12 1,8 SSpecial categories of cited documents: to document defining the general state of the art which Is not considered to be of particular relevance earlier document but published on or after the -ternational filing date document which may throw doubts on priority claim(s) or which is cited to establish the publication date of another citation or other special reason (as specified) document referring to an oral disclosure, use, exhibition or other means document published prior to the international filing date but later than the priority date claimed lat e document published after the international filing date o, priority date and not in conflict with the application but cited to understand the principle or theory underlying the invention document of particular relevance: the claimed invention cannot be considered novel or cannot be considered to Involve an inventive step document of particular relevance;'the claimed Invention cannot be considered to involve an inventive step when the document is combined with one or more other such docu- ments, such combination being obvious to a person skilled in the art. document member of the same patent family IV. CERTIFICATION Date of the Actual Completion of the International Search Date of Mailing of this International Search Report' April 1991 (05.04.91) 24 May 1991 (24.05.91) International Searching Authority SignatL:u .i Authorized Officer European Patent Office Form PCT/ISA/210 (second sheet) (January 1985) I ANNEX TO THE INTE RNATIONAL SEARCH RE PORT ON INTERNATIONAL PATENT APPLICATION NO. EP 9001877 SA 41555 This annex lists the patent family members relating to the patent documents cited in the above-mentioned international search report. The members are as contained in the European Patent Offce EDP file on 29/04/91 The European Po~tent Office is in no way liable for these particulars which are merely given for the purpose of info mnation. Patent docuiment Publication IPatent family Publication ci'ted in search report date member(s) date EP-A- 0194242 10-09-86 JP-A- 61222581 03-10-86 US-A- 3470023 30-09-69 None OE-A- 2952391 24-09-81 None M For more details about this annex see Official Journal of the Ethropean Patent Office, No. 12/82