EP0029052A1

EP0029052A1 - A process and a means for cleaning

Info

Publication number: EP0029052A1
Application number: EP19800901010
Authority: EP
Inventors: Ulf Henemo
Original assignee: TEPAB TEKNISK PRODUKTUTVECKLING AB
Current assignee: TEPAB TEKNISK PRODUKTUTVECKLING AB
Priority date: 1979-05-29
Filing date: 1980-12-15
Publication date: 1981-05-27
Also published as: SE7904688L; WO1980002693A1; SE438162B

Abstract

Procede de nettoyage d'une surface, specialement pour l'enlevement de couches de peinture d'une surface, caracterise en ce que ladite surface est traitee par un agent de nettoyage qui comprend de l'acetate d'ethyle, du glycerol, de l'eau et eventuellement un agent tensio-actif.Method for cleaning a surface, especially for removing paint layers from a surface, characterized in that said surface is treated with a cleaning agent which comprises ethyl acetate, glycerol, l and possibly a surfactant.

Description

A process and a means for cleaning.

This invention is related to a process and a means for cleaning, especially for removing surface coating materials of inorganic and organic type from substrates and also for removing superficial impurities, such as fats, waxes, oils, resins, and other hydrophobic or hydrophilic or oleophilic coatings or impurities from solid substrates.

An especially advantageous field of use is the cleaning of printing equipments, especially screen printing equipment, especially screens intended for said printing, in which such screens and other equipment can be freed from stencil material as well as inks used for said printing.

According to a preferred embodiment of the invention a preferably two-phase mixture of ethyl acetate, glycerol, water and preferably also tenside is used as solvent and cleaning agent.

Based on the total weight of ethyl acetate, glycerol and water the solvent according to the invention should comprise 2-50% of ethyl acetate, 2-50% of glycerol and 5-95% of water. The lower content range of ethyl acetate is preferably 5%, especially 10% and particularly 15%. The upper content limit of ethyl acetate is preferably 40%, especially 30% and particularly 25%.

The lower content limit of glycerol is preferably 5% especially 7%. The upper content limit of glycerol is preferably 30%, especially 20% and particularly 15%.

The lower content limit of water is preferably 10%, especia 5 30%, particularly 50% and in some cases 60%. The upper content limit of water is preferably 90% and especially 80%

A preferred composition is 10-30% of ethyl acetate, 5-20% o glycerol and 50-90% of water. An especially preferred 0 composition comprises 15-25% of ethyl acetate, 7-15% of glycerol and 60-80% of water. An example of such an especially preferred composition is about 20% of ethyl acet about 10% of glycerol and about 70% of water.

5 Ethyl acetate and glycerol are preferably used in a mutual weight ratio of 0.1-2 parts by weight of glycerol per part ethyl acetate, especially 0.1-1 part by weight of glycerol per part of ethyl acetate and particularly 0.3-0.7 parts by weight of glycerol per part by weight of ethyl acetate. D

The tenside may consist of any suitable anionic, cationic, nonionic or zwitterionic tenside, preferably in a quantity o 0.0001-5% by weight, based on the total weight of ethyl ace glycerol and water or ethyl acetate, glycerol, water and 5 tenside. The weight quantity of tenside is preferably

0.0005-0.1% by weight and particularly 0.001-0.1% by weight.

A large number of various types of the tensides mentioned ab are well-known to the expert and can be used according to t invention. In this respect reference is made to well-known literature in this field, e.g. "Surface Active Agents", A.M. Schwartz and J. . Perry, and "Surface Active Agents and Detergents", A.M. Schwartz, J.W. Perry and J. Burch, Interscience Publishers, New York, London.

In continued use the cleaning composition is replenished wit spent constituents in a quantity ratio which maintains the desired composition. A common quantity ratio of the /''BU

O , ^•* _/- W Ϊ^' constituents in said replenishing solution or activator is about 50-95% by weight of ethyl acetate, based on the total weight of ethyl acetate and glycerol, preferably about 60-90% by weight of ethyl acetate, especially 70-85% by weight of ethyl acetate and particularly about 80% by weight of ethyl acetate.

Usually the cleaning agent comprises at least two phases, in which case it is suitable to use the cleaning agent in the form of an emulsion of one phase in the other phase or optionally as a double emulsion. The emulsion can optionally be stabilized with various stabilizing agents or by powerful comminution but usually it is not an essential inconvenience if the emulsion is unstable and desintegrates within a certain period of time. The emulsion may be prepared with common stirring means or by spraying.

The treated surfaces are suitably brought into contact with the cleaning agent with simultaneous or subsequent mechanical interaction, e.g. by spraying under a certain pressure or brushing or other mechanical interaction on the surfaces, e.g. ultrasonic interaction or interaction of particles dispersed in the solution or by subsequent blasting or other mechanical interaction.

Especially when using a mixture of two or more phases released solid or liquid materials, especially paint flakes or paint particles may be difficult to separate from the cleaning agent and e.g. remain at a phase boundary in the cleaning agent which may optionally be caused by the particles not being wetted or being insuffiently wetted by the underlying heavier phase. In order to facilitate the separation of solid constituents from the cleaning liquid one may add heavy particles which can adhere to solid constituents which shall be separated, e.g. finely comminuted minerals, such as finely comminuted talc. Such added solid particles act as weight increasing agents and add weight on released particles which swim in the treating liquid and precipitate said particles to the bottom of the cleaning liquid so that the particles can be expelled e.g. through a bottom opening in a treatment container or store container for the cleaning agent. Also other methods for separating solid dispersed particles may be used, e.g. filtering, centrifugation, vibration treatment or supersoni treatment for mechanically separating adhering light liquid etc.

When using a weight increasing agent for precipitating disp solid particles the weight increasing agent may be surface treated, e.g. may be made hydrophobic or hydrophilic, for facilitating the adherence to the dispersed particles and wetting of an underlying heavier phase. One example is tal or clay which has been hydrophobated. The particle size of the talc may e.g. vary within the size range up to 1 mm an preferably up to 0.1 mm.

Instead of using an emulsion of two or more phases for clea it is possible to perform the cleaning in two or more steps ^' and to treat the surface in each step with one of the phase in question, e.g. a phase rich in ethyl acetate and prefera also containing glycerol and water, and a phase rich in wat and preferably also containing glycerol and some ethyl acet The treatment with said two phases can be performed e.g. un the particular conditions mentioned above, i.e. mechanical interaction, spraying, etc.

As mentioned above the invention can be used for cleaning printing equipments, e.g. the printing form used for screen printing. Said form consists of a fine mesh screen stretched onto a frame. Said screen is usually made from s or nylon and may comprise about 200 threads per ^'cm. The sc is provided with a pattern (shablon) which consists of a water-soluble material (resin) in the shape of a pattern whi is to be printed. The screen thus will comprise printing as well as non-printing surfaces. A substrate is arranged unde the frame and ink (paint) is spread and pressed through the screen with a so-called doctor, whereafter the screen is lif off and the ink (paint) is allowed to dry on the substrate. The ink used is usually oil-soluble and the shablon is not soluble in the ink. After printing the screen must be cleaned from ink as well as from shablon. According to the invention it is possible to clean very efficiently such screens comprising ink as well as shablon with the cleaning agent mentioned above and preferably under the other conditions mentioned. After cleaning with the cleaning agent it is preferable to subject the screen to an after-wash with an aqueous liquid, especially flushing with high pressure water for removing shablon and remaining ink.

The constituents ethyl acetate and glycerol may each individually be exchanged or substituted with other compounds with similar characteristics.

Thus, the ethyl acetate may completely or partially be substituted with other esters , ethers , aliphatic hydrocarbons , aromatic hydrocarbons, halogenated, preferably chlorinated ^' and/or fluorinated hydrocarbons, ketones , preferably with such solvents which are insoluble in water or exhibit only slight solubility in water, preferably with a solubility of at most 20%, preferably at most 10% and optionally at most 1% in water. Preferably the ethyl acetate is substituted with at most 80% by weight, especially at most 50% by weight and particularly at most 25% by weight, e.g. at most 15 or at most 5% by weight with one or more of said other solvents. As examples the following solvents may be mentioned:

Aliphatic hydrocarbons , preferably with the boiling point range 60-140°C, e.g. 60-95, 80-110 or 100-140°C, terpenic hydro¬ carbons, such as turpentine oil, aromatic hydrocarbons, such as benzene, toluene and xylene, hydroaromatic hydrocarbons, such as cyclohexane, methylcyclohexane, tetrahydronaphthalene decahydronaphthalene, aliphatic and aromatic chlorinated hydrocarbons, such as methylenechloride, carbontetrachloride, dichloroethane , tetrachloroethane, trichloroethylene, mono- chlorobenzene, alcohols, such as methanol, ethanol, n-propanc

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^{■ £}RN & isopropanol, n-butanol, isobutanol, isanol, sec-butanol, am alcohol, methylisobutylcarbinol, hexyl alcohols, heptyl alcohols, ethylhexanol, nonanol, benzyl alcohol, cyclohexan methylchlorohexanol, diacetone alcohol, acetone, acetone oi methylethylketone, methylisobutylketone, mesityloxide, ethy -i-amylketone, diisobutylketone, cyclohexanone, methylcyclo hexanone, di ethylσyclohexanone, cyclohexenone, methylcyclo hexenone, isophoron, methylformate, ethylfor ate, n-butyl- formate, amylformate, methylacetate, n-propylacetate, iso- propylacetate, n-butylacetate, isobutylacetate, sec-butyl- acetate, amylacetate, isohexylacetate, isoheptylacetate, cy hexanolacetate, methylcyclohexanolacetate, benzylacetate, methylpropionate, ethylpropionate, n-propylpropionate, n-bu propionate, ethylbuty ate, propylbutyrate, isobutylbutyrate, n-butylbutyrate, amylbutyrate, ethyllactate, butyllactate, glycolic acid butylester, ethyleneglycolmonomethylether, ethyleneglycolmonoethylether, etyleneglycol onopropylether, ethyleneglycolmonoisopropylether, ethyleneglycolmonobutylet polyethyleneglycolmonoether, propyleneglycolether, 1,3-but l - glycol- (3)-monomethylether (methoxybutanol) , ethyleneglycol- monomethyletheracetate, ethyleneglycolmonoethyletheracetate, ethyleneglycolmonobutyretheracetate, but leneglycol- (3)-mono methylether-1-acetate, ethyleneglycolmonoacetate, glycol- carbonate, propyleneglycolcarbonate, diethylether, tetrahydr furane, dioxane, dimethylacetal, dimethylformamide, dimethyl sulfoxide, tetramethylenesulfon, carbondisulphide, furfurol.

The glycerol may be substituted completely or partly with on or more of the compounds mentioned as substitutes for the ethylacetate, preferably such compounds which are soluble in water or a mixture of glycerol and water in the quantities mentioned above. Preferably ambiphilic substances are used, examples of which are cellosolve, glycolethers, alcohols, ketones. It is preferred to use compositions comprising sai constituents in quantity ratios which give two-phase or poly phase systems or emulsions.

The working temperature may be selected arbitrarily below th

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' Λ boiling point at the pressure used. It is preferred to use a working temperature below 80°C, especially below 60°C and particularly below 40°C. It is suitable to use a temperature above 10°C and especially above 15 or 20°C. 5

The treatment time is selected as needed and may e.g. amount to at least 1 second, preferably at least 10 seconds and especially at least 1 minute. The upper limit is mainly based on economical considerations and may e.g. amount to up to one 0 day, preferably up to 1 hour and especially up to . hour and particularly up to 5 minutes.

The treatment according to the invention may be performed as a cleaning treatment e.g. for removing remaining paint or ink 5 or old paint or ink but also for removing fats and oils, e.g. fat from a lubricant or from surface working or treatment, e.g. prior to a subsequent surface treatment by priming, painting, phosphatizing, chromatizing, etc. In order to protect the surface against rusting it is possible to include rust 0- protecting agents in the solvent, e.g. with the phase which comprises the main part of the water or in the non-aqueous phase or the phase comprising a minor part of the quantity of water. -

_5 Optionally the aqueous phase ^"may also comprise constituents which give a surface treatment, e.g. phosphatizing, chromatizing, etc. of a treated metal surface.

The composition, preferably the aqueous phase, may also 0 comprise pH adjusting constituents, e.g. ammonium and alkali metal salts, e.g. hydroxides, carbonates, silicates, organic bases, preferably for adjusting to a basic pH e.g. up to 14, preferably up to 12, usually above 8 and especially above 9.

5 The composition may also comprise viscosity adjusting and/or emulsion stabilizing agents, such as viscosity increasing agents, e.g. polymers, such as cellulose based substances.

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O PI -_, ^Wiρo ^" Z£Rx;.τ\ Example .

A screen printing fabric made from nylon stretch mo.unted on frames which had been used for conventional screen printin was cleaned with the cleaning agent according to the invent The cleaning agent consisted of a mixture of 70% of water, 20% of ethylacetate and 10% of glycerol and 1% of tenside, based on the other constituents. As tensides nonionic, anionic, cationic and zwitterionic tensides were tested. T cleaning agent was maintained in a container into which the screen printing frames could be submerged. Prior to submer the frame the mixture was subjected to vigorous stirring wi a propeller stirrer so that a fine dispersion or emulsion of phase with a high content of ethylacetate in a phase with a high content of water was obtained. The screen printing fr were submerged in the emulsion and hereby rapid release and peeling of the printing ink from. the frames was obtained. Furthermore, spraying of the emulsion against the frames and mechanical working with a brush combined with the interactio of the emulsion was tested and hereby the speed of the relea - of the printing ink from the frames was increased further. frames treated in said way were completely free from printin ink within a period of time of a few minutes up to 10 minute For removing the water-soluble stencil from the frames completely the frames were thereafter treated by being spray with water under high pressure.

The composition of the cleaning agent was also varied from t composition stated above within the limits -10% of the conte figures stated above, and by said treatments efficient clean was also obtained.

Furthermore, cleaning agents of the composition stated above were tested for cleaning metal articles provided with organi surface coatings of various types. Said coatings consisted of epoxy paints, linseed oil paints, alkyd paints, aerylate paints, cellulose lacquer.

The objects provided with an organic surface coating were

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Sλ, \ cleaned by dipping in the cleaning agent after emulgating said agent and by spraying the emulsion of the cleaning agent. In all cases efficient release of paint from the substrate was obtained so that the paint was peeled off but without dissolving the paint to a liquid state. In order to improve removal of the paint mechanical interaction by brushing and by spraying the cleaning agent under high pressure was also tested. Said measures speeded up the release and removal of the paint.

Furthermore, also in this case a variation of the composition of the cleaning agent with -10% as mentioned above was tested and also in this case efficient cleaning was obtained.

In order to improve removal of the released paint from the treatment liquid an addition of a weight increasing agent consisting of talcum powder was tested. The added talcum powder was aggregated to the released paint flakes whereby the volume weight of said flakes was increased to such an extent that the paint flakes sedimented rapidly and could be drained - off from the bottom of the treatment vessel.

As mentioned above a surface active agent or wetting agent is a desired constituent of compositions according to the invention. Such surface active agents may be used in varying quantities depending on the activity of the agents. The lower limit is in many cases 0.0001, in certain cases 0.01 or 0.1% by weight, but also higher concentrations may be suitable, such as at least 0.5 or at least 1% by weight. Usually there is no upper limit of the content which is mainly decided by. economical considerations and the need to include other constituents in the compositions. Suitable upper limits may be 10% by weight or 5% by weight but also lower contents such as 2 or 1% by weight may be desired as well as in other cases also 0.1% or lower.

As examples of suitable anionic surface active agents may be mentioned alkylarylsulfonates , preferably with 8-18 carbon atoms in the alkyl group, and the alkyl group may

consist of phenyl or naphthyl, e.g. dodecylbenzene sodium sulfonate, alkalialkylsulfates , preferably with 8-18 carbon atoms in the alkyl group, e.g. sodiumlaurylsulf te, alkyl- sulfonates , preferably with 8-18 carbon atoms in the alkyl group, e.g. sodiumdecylsulfonate, arylsulfonates , in which the aryl preferably is phenyl or naphthyl, preferably sodiu tetrahydronaphthalene sulfonate, alkali metal salts of fatt acids with preferably 8-18 carbon atoms, e.g. sodiumstearat alkali metal lignosulfonates. Sodiumalkylarylsulfonate is suitable surface active agent and in the experiments mentio above also anionic tensides in a quantity of 0.1-1% active tenside and preferably 0.2% active tenside based on the cleaning agent were also used.

Among nonionic surface active agents may be mentioned alkyl phenylethyleneoxide condensates in which the alkyl group preferably comprises 8-18 carbon atoms and the number of mo of condensated ethyleneoxide units varies from 1 to 100 per alkyl group, e.g. isooctylphenyl polyethoxyethanol, dodecyl ' phenyl polyethyleneglycol, and generally condensation produ of ethyleneoxide and hydrophobic compounds derived from aci alcohols, alk lphenols , amines, amides, etc., e.g. oxyethyl alkylphenols with hydrophobic hydrocarbon chain with prefer 8-18 or 8-12 carbon atoms and a hydrophilic oxyethylene chai with a varying average of oxyethylene groups, e.g. 3-6 oxy¬ ethylene groups. Other nonionics are polyoxyethylene thio- ethers , propyleneoxide-ethyleneoxide condensates, fatty aci alkanol amides with preferably 8-18 carbon atoms in the fat acid, e.g. lauric acid alkanol amide, alkylpol (ethyleneo ethanols, preferably with 8-18 carbon atoms in the alkyl gro and from 1 to 100 molecules condensed ethyleneoxide per alky group, such as tridecyloxypol (ethyleneoxy) ethanol or ethyleneoxide condensates of stearyl alcohol comprising abo 10 ethyleneoxide groups per stearyl group, and polyhydroxy- alkyl fatty acid esters, such as glycerolmonooleate or sorbitan stearate.

Common exam-oles of nonionic surface active agents which cax

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O used are thus polyethyleneoxy ethers of alkyl phenols, e.g. with 6-20 or more moles of ethyleneoxide and preferably with from 5 to 18 carbon atoms in the alkyl group or alkyl group . The aromatic nucleus may e.g. consist of benzene, naphthalene or diphenyl. Polyethyleneoxy ethers of alcohols and mercaptanes , preferably aliphatic alcohols and mercaptanes with more than 8 carbon atoms are suitable. Difunctional or polyfunctional polyethyleneoxy ethers, polyethyleneoxy esters, e.g. based on fatty acids of oxidized paraffin wax, polyethyleneoxy compounds with amide bonds and with other bonds are also suitable.

As examples of cationic surface active agents reference can be made to non-quaternary nitrogen bases , such as nitriles , amines without intermediary bonds , amines with intermediary bonds, such as ester and ether bonds, amide-bonded amines, other nitrogen bases, such as imidazolinederivatives prepared by condensing^* a fatty acid with ethylenediamine, quatemized imidazolines , quaternized nitrogen bases . Examples are straight chain alkyl fat amines with 8-18 carbon atoms in the alkyl - group, e.g. di-cocoamine, N-alkyltrimethylenediamines with 8-18 carbon atoms in the alkyl group, e.g. N-lauryltrimethyl- diamine, higher alk lpyridinium halogenides with 8-18 carbon atoms in the alkyl group, e.g. cetylpyridinium bromide, mono- alkyl and dialkylmethyl quaternary ammonium salts with 8-18 carbon atoms in the alkyl group, e.g. mono-cocotrimethyl quaternary ammoni^*umchloride and didodecyldimethyl quaternary ammoniumchloride, quaternary salts with phosphorus based cation, e.g. stearamidepropyldimethyl-?-hydroxyethylammoniαm dihydrogen phosphate, fat-acyl derivative of hydroxylated diamines , e.g. N- (aminoethyl) ethanolamine, alkylpyridins with 8-18 carbon atoms in the alkyl group, alkylsubstituted 2 ,3-dihydroindols with 8-18 carbon atoms in the alkyl group, 2-alkylbenzimidazoles with 8-18 carbon atoms in the alkyl group and quaternary salts thereof, 2-alkylquinolines with 8-18 carbon atoms in the alkyl group and quartary salts thereof.

Examples of amphoteric surface active agents are such agents comprising carboxy or phosphate ester as acid group quaternary nitrogen as basic group, products produced by addition of fat a ine to acrylester, methacrylester or crotonester and hydrolysis of the product obtained, -N-highe alkylasparatic acid, compounds comprising sulpho groups as well as non-quaternary amino groups, N-alkyltaurines, mono- acyl derivatives of diamine condensed with lower aliphatic halogenated sulphonic acids , condensation products of alkan sulphonamide with formaldehyde and e hyl aurine, a ino- sulphonic acid compounds in which the sulphonic acid group bonded to an aromatic ring, the reaction product of aromati aminosulphonic acids with higher alkylhalides and aralkyl- halides. Examples are alkali metal salts of N-cocoamino- butyric acid, cetylpalmitin alkanolamides with 8-18 carbon atoms in the alkyl group, natural lecithins, N-coco- ?-amino propionic acid, polyethox amino' acid salts with 1-100 conde ethoxy groups.

The tenside should have the ability to emulgate the ethyl acetate phase or corresponding phase in the aqueous phase an - may preferably also have an anti-redepositing effect which contributes to keep the released paint or ink residues or other dirt suspended so that redeposition on the cleaned surface is prevented.

The stability of the emulsion can be improved by vigorous stirring with supersonics and similar, stirrers with vigorou shear effect, ho ogenizers or similar, preferably to a dropl size which to 90 and preferably 99% is below 5 microns, preferably 1 micron or 0.5 microns or also below 0.1 micron.

The invention is not restricted to any specific theoretical explanation but it is probable that the activity is based on a combined effect of a vigorous spreading effect, on the fir hand of ethyl acetate or of components included as substitut thereof, and a surface swelling or surface coating effect, o the first hand on the material which shall be removed, such as a paint layer, dirt or similar. Said surface swelling or surface coating effect may be caused on the first hand by th glycerol or components included as substitutes thereof.

Experiments, e.g. when removing screen printing ink and screen printing pattern (shablon) from nylon screen, have also shown that the phase with high ethyl acetate concentration spreads rapidly on the nylon screen surface and gives a very low contact angle on the nylon surface which in practice makes measurements on the contact angle impossible.

Experiments , on the first hand with ethyl acetate , glycerol and water/surface active agent (YES & registered trademark) in a quantity ratio of 99:1 show that mixtures of said three components at room temperature exhibit a mixing gap with a homogenous, clear single phase area, which is also obvious from the ternary graph on the enclosed drawing. The edges of the triangle correspond to the pure components . The concentrations of tested compositions are also noted on the figure. From said graph it is obvious that there is a single phase area within a range of a quantity ratio of water:glycerol. Similar ^" single phase areas surrounded by two-phase areas can be obtained if glycerol and ethyl acetate resp. are substituted completely or partly with, like glycerol, comparatively high solubility in water, preferably complete miscibility with water and/or when substituting ethyl acetate completely or partly with compounds with low solubility in water, preferably below 10% solubility, which preferably have a good dissolving effect on the material which shall be removed and/or have a low surface tension on the substrate material. This refers on the first hand to the compounds which are stated as substitutes for the glycerol and the ethyl acetate resp. above.^"

Usually it is suitable to use a composition within the single phase area, preferably with the highest possible content of water or with a composition within the two-phase area at higher water contents , in which case it is for economical reasons suitable to use a water content which is as high as possible. Alternatively, it is also possible to use the two-phase area within which the water content is lower. As tenside use the tenside components stated as alternatives above in concentrations within the stated ranges.

As additives, which substitute glycerol and/or water, also lower alkanols are suitable, especially lower alkanols with 1-6 carbon atoms, such as methanol and ethanol. A suitable quantity ratio of glycerol:ethanol is e.g. 1:10-1:0.5, preferably 1:5-1:1. Suitable quantity ratios of glycerol:e acetate:ethanol are e.g. 0.5-2:2:1-10, based on the weight. Said composition can be mixed^' with water in a quantity rati ethyl acetate:water of 2:5-50. The quantity of tenside is preferably the quantity stated above, e.g. up to 5%, prefer up to 1% or 0.5% of the quantity of water, based on the wei and preferably at least 0.001 and especially 0.01 and particularly 0.1% by weight of the quantity of water. In agents comprising lower alkanols, especially methanol, etha and propanol, the alkanol may completely or partly substitu the water component, in which case the other components preferably are used in concentrations within the ranges sta - above. The water concentration stated above may thus to up 25%, up to 50%, up to 75% or up to 100%, inclusive 100%, be substituted with said lower alkanols.

Suitable areas of use in addition to printing screens are e. cleaning .of surfaces, especially of steel, iron, zinc, alumi plastics, glass, ceramics and similar, from fat, oil, water soluble dirt, paints, lacquers, etc., e.g. prior to a surfac treatment by phosphatizing, chromatizing, anodizing, painti etc., cleaning of oil tanks, e.g. in ships, as substitutes defatting agents for metal articles, such as tri, etc.

Experiments were performed with cleaning of screen printing frames after printing. The frames consisted of pre-preparat

Adressett frames, size 10x25 cm, screen designation 110 T. Ink: Grafisk Farg 55-44500 and 55-44500, pattern (shablon) :

Adressettramen direct shablon or Autotype Alpa Star. After printing the ink was left to dry 1 day and 1 week resp. whereafter the frame was dipped into an open container witl

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O ₇fJ? ^•T5 the cleaning agent and optionally was brushed for mechanical working of the screen during the cleaning treatment. Further¬ more, stirring with a propeller was tested. After the treatment in the cleaning agent washing by spraying water of high pressure was tested in some cases. The cleaning agent used was an emulsion according to the invention comprising, in % by weight:

20% of ethyl acetate

10% of glycerol 1% of tenside (YES® , active material about 30%)

69% of water

In said experiments efficient removal of ink and pattern (shablon) was obtained. Similar experiments were performed also with the addition of lower alkanols, such as ethanol, in a quantity ratio of up to 5 parts of ethanol per part of glycerol and a quantity ratio glycerol:ethyl acetate = 1:2, and in said experiments good results were obtained.

- Furthermore, cleaning of phosphatized and painted cylindrical steel articles was tested. The paint consisted of oil paint, alkyd paint and two-component paint of epoxy type. The cleaning agent of the composition stated above was used. In all cases efficient removal of paint was obtained and the articles could thereafter be painted again with good adherence.

Furthermore, cleaning of surfaces of galvanized material and aluminum sheet with and without anodizing layer was tested. Efficient cleaning and removal of dirt, e.g. fat and oil, and paints of the types mentioned above was obtained with the cleaning solution stated above with interaction times at room temperature from a couple of minutes up to a couple of hours.

Claims

1. A process for cleaning a surface, especially for removing coating layers and paint layers from a surface, characterized by treating said surface with a cleaning agen comprising ethyl acetate, glycerol, water and optionally tenside.

2. A process according to claim 1, characterized in tha the cleaning agent comprises, based on the combined weight of ethyl acetate, glycerol and water, 2-50% of ethyl acetat 2-50% of glycerol and 5-95% of water.

3. A process according to claim 2, characterized in tha the cleaning agent comprises 10-30% of ethyl acetate, 5-20% of glycerol and 50-90% of water.

4. A cleaning agent according to claim 3, characterized by comprising 15-25% of ethyl acetate, 7-15% of glycerol an 60-80% of water.

5. A process according to claim 4, characterized in tha the cleaning agent comprises about 20% of ethyl acetate, ab 10% of glycerol and about 70% of water.

6. A process according to any of the preceding claims, characterized in that the cleaning agent comprises 0.0001-5 by weight of tenside,. preferably anionic, cationic, nonioni or zwitterionic surface active agent.

7. A process according to any of the preceding claims, characterized in that up to 100%, preferably up to 50%, of the glycerol is substituted with one or more other ampholyt agents which are suitable in the cleaning -agent.

8. A process according to any of the preceding claims, characterized in that up to 50% of the quantity of ethyl acetate is substituted with one agents for the surface coatings