GB2079775A - Cleaning composition and method - Google Patents

Abstract

A cleaning composition for removing metal phosphate coatings, optionally containing lubricant, comprises an alkali metal hydroxide, at least one imino diacetic acid or an alkali metal salt thereof and a larger amount of a polyhydroxy compound sequestering agent.

Description

SPECIFICATION Cleaning composition and method Compositions for cleaning metal surfaces are often based on alkali metal hydroxide and it is known to include sequestering agent in cleaning composition. It is generally desirable for cleaning to be effected at low temperatures.

A particular problem arises when it is necessary to remove metal phosphate, especially at low temperatures. This arises in particular when a metal phosphate and lubricant coating is formed on a metal surface and when the particular metal phosphate is not a satisfactory basis for the subsequent surface treatments.

For instance an iron phosphate and lubricant coating may be very suitable for protecting steel strip during transport, storage and pressing and the iron phosphate may be a suitable basis for some further treatments, but it is often desirable to form a zinc phosphate coating on the clean steel surface, in which event the iron phosphate coating must first be removed. Existing cleaning compositions cannot remove it, except at high temperatures, and this is undesirable.

A composition for removing a metal phosphate coating from a metal surface, preferably at low temperatures, or a concentrate for forming such a composition upon dilution with water, comprises an alkali metal hydroxide and at least 12% of at least one imino diacetic acid or an alkali metal salt thereof and a larger amount, of at least 25%, of a polyhydroxy compound sequestering agent which is a polyhydric alcohol of formula CH20H(CHOH)aCH20H wherein a is at least 2, a starch of the formula (C6H 1o05)x, a polyhydroxymonobasic acid of the formula COOH(CHOH)bCH20H wherein b is at least 4, or a polyhydroxy dibasic acid of the formula COOH(CHOH)CCOOH wherein c is at least 3 or an alkali metal salt thereof.

Throughout this specification percentages of these two classes of sequestering agents are, if the agent is or can be an acid, expressed in terms of the weight of the sodium salt and are all based on the weight of alkali metal hydroxide expressed as sodium hydroxide. The amount of the imino diacetic acid sequestering agent is generally less than 20% and the amount of the other sequestering agent is generally less than 35%.

If the amounts are below the 12% and 25% figures quoted the cleaning action is undesirably slow. Amounts of sequestering agents above the 20% and 35% figures quoted results in an unnecessary increase in cost of the composition.

The precentage of the polyhydroxy compound sequestering agent is more than the percentage of the imino sequestering agent in the composition, generally being in the pro portion 1.2:1 to 2.5:1, preferably 1.3:1 to 1.8:1..

Preferred sequestering agents including an imino diacetic acid group that may be used in the invention include nitrilo triacetic acid (NTA), diethylene triamine pentacetic acid (DPTA) and ethylene diamine tetra acetic acid (EDTA), and their salts.

The other type of sequestering agent which must be present in the composition is preferably sorbitol or a polyhydroxy acid, most preferably gluconic or heptonic acid and their alkali metal salts.

Sequestering agents that include acid groups are generally introduced as alkali metal salts, generally the sodium salts, and if the sequestering agent contains more than one acid group generally all the acid groups are in salt form.

The alkali metal hydroxide in the cleaner composition may be potassium hydroxide or sodium hydroxide or a mixture thereof.

Preferred compositions according to the invention comprise potassium or sodium hydroxide and tetrasodium ethylene diamine tetra acetic acid in an amount of 12% to 25% and sodium gluconate in an amount of 20% to 35%, by weight based on the weight of sodium or potassium hydroxide.

The cleaner compositions generally contain 5 to 70, preferably 8 to 30, grams per litre alkali metal hydroxide, 1 to 15, preferably 2 to 10 grams per litre sodium gluconate or other polyhydroxy compound sequestering agent and a lesser amount, usually in the range 0.5 to 10, preferably 1 to 8 grams per litre tetrasodium EDTA or other imino diacetic acid sequestering agent.

The compositions may additionally contain alkali stable surfactant in an amount generally up to 1% based on the total composition. The preferred surfactants are non-ionic or amphoteric.

The compositions may initially be formulated as concentrates and may be diluted to the quoted concentrations prior to use or may be formed initially with these concentrations.

Compositions containing these two types of sequestrants are already known for other purposes (see British Patent Specification No.

1,097,799) but we have surprisingly found that only if the compositions contain the specified ingredients in the specified ratios is it possible to obtain removal of metal phosphate coatings, and especially iron phosphate coat ings, from a metal surface at a satisfactory rate at low temperatures.

To remove such coatings the composition is applied at a temperature of from 20 to 90"C, most preferably 20 to 40"C and contact is maintained for a period of 0.5 to 5 minutes, most preferably 0.5 to 2 minutes. Application may be by, for instance, brushing but generally spraying is sufficient.

The novel cleaner is of particular value for removing metal (generally iron) phosphate coatings and especially such coatings that are under or combined with lubricant coatings, for instance when prepared by the methods described in British Patent Specifications Nos.

1,371,981, 1,508,484, 1,421,386 or 2035383. Preferably the coating is one that has been formed on metal by applying to the strip composition comprising an organic liquid carrier and an acidic reaction product comprising orthophosphate radicals, polyvalent metal cations and lubricant radicals containing 10 to 26 carbon atoms. Suitable compositions and methods are described in our appliction No.

(reference GJE 6080/95) filed even date herewith.

The formation of the reaction product may involve the formation of a phosphate ester of the lubricant radicals, which are therefore generally introduced as alcohols. The reaction product is preferably made by heating the polyvalent metal or a compound thereof with orthophosphoric and/or polyphosphoric acid and either simultaneously or subsequently with a compound, generally an alcohol, providing the lubricant radicals. Instead of using a phosphoric acid a phosphate may be used, but the process then usually needs to include an acidification step.

As polyvalent metal there may be used, for example, zinc, manganese, cobalt, nickel, copper, molybdenum, tungsten, aluminium, lead, magnesium, calcium or iron. The metal preferably is not a metal of group IV A of the Periodic Table, for instance as defined in "General and Inorganic Chemistry" third edition by J.R. Partington. The preferred metal is iron, especially when the metal surface is steel.

The polyvalent metal may be supplied in elemental form provided sufficient time for reaction is provided but preferably is introduced in the form of a compound. The compound is preferably metal phosphate although other salts, but preferably not metal halides, may be used. Iron phosphate may be introduced as ferric or more usually, ferrous phosphate.

The lubricant radicals may be fatty, alkaryl or triterpene radicals. They may be, for example, olefinic radicals, but are preferably alkyl and/or alkaryl radicals. They may be introduced into the reaction mixture by the addition of the corresponding alcohols. The alcohols may be used as pure products or as commercially available impure products. Suitable fatty alcohols have an average carbon content of 1 6 to 18 carbon atoms, oleyl cetyl alcohol being preferred. Aliphatic or triterpene alcohols derived from lanolin are very satisfactory.

The phosphate in the reaction product may be obtained by the use of orthophosphoric acid and/or polyphosphoric acid. Suitable material is commercially available and preferably contains 76 to 88% by weight P205, the remainder being water. It can be prepared by dissolving an excess of solid P20,5 in orthophosphoric acid. The resultant product, known as ''polyphosphoric acid'; or "condensed phosphoric acid" is a mixture of various amounts of orthophosphoric acid in addition to pyro, tri, tetra and higher phosphoric acids.

During the preparation of the acidic reaction product some or all of the polyphosphoric acid is converted to orthophosphoric acid.

A preferred reaction product for use in the invention is prepared by heating iron phosphate with orthophosphoric and/or polyphosphoric acid and then heating the product with an alkyl or alkaryl alcohol having 10 to 36 carbon atoms.

The reaction products are materials that can be put into an organic lubricant carrier to form a single phase system, at least at elevated temperatures. The reaction products are preferably made by reacting the components of the mixture together at elevated temperatures, preferably in the range 60 to 1 50 C, for a reaction time of from 30 to 300 minutes. The reaction product is a mixture of various substances and accurate chemical characterisation is difficult.

The product should be acidic and preferably has a pH of less than 3.

The composition that is applied to the metal surface is preferably substantially non-aqueous, generally containing less than 2%, preferably less than 1.5% water, by weight based on the total composition. The amount of water is usually at least 0.1%. In some instances it is particularly useful to use dilute compositions, as described in more detail below, and it is then desirable that the total amount of water should be below 1.5%, preferably less than 1%, with best results generally being, obtained with a water content of 0.1 to 0.5%.

The composition may contain for instance from 1 to 60% of the reaction product, by weight based on the total composition. The amount is normally from 1 to 10%, especially when the reaction product is being used for treating steel strip, but higher amounts can be used. In some instances, especially for the treatment of steel strip, it can be desirable to use very dilute compositions containing from 1 to 4 or 4.5% of the reaction product.

The composition may be formed from 0.02 to 0.05% polyvalent metal phosphate, 0.5 to 20% orthophosphoric and/or polyphosphoric acid and 0.5 to 50% lubricant radicals, all percentages being by weight based on the total composition.

The amount of metal phosphate is prefera bly 0.05 to 0.2% by weight and is preferably iron (generally ferrous) phosphate. The amount of orthophosphoric and/or polyphos phoric acid is often preferably 0.5 to 5% and the amount of the lubricant radicals is often preferably 0.5 to 5%. These values are espe cially useful for the dilute compositions mentioned above and for these the preferred amount of polyphosphoric or phosphoric acid is 1.5 to 3.5% and the preferred amount of Lubricant is from 1 to 3% and the total amount of ingredients other than the liquid carrier is preferably less than 4%, all by weight based on the total composition.

The coating composition preferably includes a corrosion inhibitor which is preferably a salt of a carboxylic acid with an aliphatic amine.

The carboxylic acid is preferably an aliphatic carboxylic acid which preferably contains a long chain, for instance containing 10 to 24 carbon atoms, for instance oleic acid. The aliphatic amine is preferably a tertiary alipha tic amine. It may be a trialkylamine but prefer ably is a trialkanol amine, wherein the alkyl or alkanol groups preferably contain 1 to 4 car bon atoms. The preferred amine is triethanol amine and the preferred inhibitor is triethanol amine oleate. The amount is generally below 1% by weight of the composition, preferably 0.01 to 0.5% by weight.

Preferred compositions according to the in vention contain 0.01 to 1%, preferably 0.05 to 0.5%, of the amine salt and are substan tially non-aqueous (for instance containing less than 1.5% and preferably less than 1% water, by weight based on the total composi tion) and are formed from less than 1% metal phosphate, less than 10% orthosphosphoric acid and/or polyphosphoric acid, and less than 10% lubricant radicals.

The organic liquid carrier is generally se lected so that the coating composition has a viscosity similar to the viscosity of conven zonal mill oil, or oil type press lubricants for instance 10 to 40, preferably 10 to 30, for instance 19.5, centistokes measured by Kine phatic viscometer at 38"C. The carrier is usu ally a vegetable, animal or, more usually, mineral oil. Suitable oils include brightstock oil and solvent neutral oils.

The dilution and the amount of the coating composition that is applied to the metal sur face is preferably such that the weight of the metal phosphate coating (i.e. the weight of the inorganic components of the final coating) is at least 0.05 g/m2 and is preferably at least 0.2 g/m2 but is less than 1.5 g/m2, and preferably less than 1 g/m2. In many in stances it is desirable to have low coating weights, for instance using the dilute compos itions mentioned above. Thus coating weights of from 0.05 to 0.45 g/m2, preferably 0.2 to 0.4 g/m2 may be suitable.

The invention is of particular value when the metal phosphate coating that is being removed is a coating that has been obtained by applying a composition as described above to steel or other metal strip, generally between formation and coiling.

After conventional transport and storage the steel strip is used for the production of articles, such as car bodies, by pressing by conventional press shop methods. The articles are then subjected to cleaning by the method of the invention prior to subsequent treatment, for instance the formation of protective zinc phosphate coatings prior to painting.

It will be appreciated that the compositions may be prepared initially with the desired concentrations for use as cleaning compositions, for instance 5 to 70 and preferably 8 to 30 g/l alkali metal hydroxide, or may initially be prepared in more concentrated form and diluted with water to give the desired concentration for use.

The following are examples of the invention: Example I A cleaning composition consists of 1 3.6 g/l sodium hydroxide, 3.7 g/l sodium gluconate, 2.4 g/l tetrasodium EDTA, 0.2 g/l Triton QS 15 and 0.1 g/l Triton CF 32 (Triton is a trade mark). Triton QS 1 5 and Triton CF32 are surfactants. The composition is made by dissolving the ingredients in the appropriate amount of water.

Example 2 0.86 grams ferrous phosphate (Fe3 (P04)2.8H20), 24.31 grams of 88% orthophosphoric acid and 1 6.7 grams oleyl cetyl alcohol are combined by heating at 80"C for 90 minutes and then mixed with 48.76 grams brightstock oil, and 1. 1 4 grams triethanolamine oleate. The resultant mixture is diluted with sufficient 100 solvent neutral oil to give 1000 grams. During the preparation of the composition the water content of the components is controlled so that the total amount of water introduced into the composition is between 2.5 and 3.3 grams.

This composition is applied by spray or squeegee to both surfaces of steel strip as it comes from the strip mill and the strip is then immediately tightly wound. After transport and storage articles, such as car bodies, can be pressed from the steel strip by conventional press shop methods.

After pressing the metal is sprayed at 35"C for 1.5 minutes with the cleaner composition of Example 1 to reveal a clean steel surface. A zinc phosphate coating can then be applied on this by conventional methods.

Claims (11)

1. A composition for removing a metal phosphate coating from a metal surface, or a concentrate for forming such a composition upon dilution with water, and that comprises an alkali metal hydroxide and at least 12% of at least one imino diacetic acid or an alkali metal salt thereof and a larger amount, of at least 25%, of a polyhydroxy compound sequestering agent which is a polyhydric alcohol of the formula CH20H(CHOH)aCH20H wherein a is at least 2, a starch of the formula (C6H1oo5)X a polyhydroxymonobasic acid of the formula COOH(CHOH)bCH20H wherein b is at least 4, or a polyhydroxy dibasic acid of the formula COOH(CHOH)CCOOH wherein c is at least 3 or an alkali metal salt thereof, in which the percentages of the sequestering agents are, if the agent is or can be an acid, expressed in terms of the weight of the sodium salt, and all percentages are based on the weight of alkali metal hydroxide expressed as sodium hydroxide.

2. A composition according to claim 1 in which the amount of the imino sequestering agent is 1 2 to 20% and the amount of the polyhydroxy sequestering agent is 25 to 35%.

3. A composition according to claim 1 or claim 2 in which the percentages of the polyhydroxy sequestering agent:imino sequestering agent are in the proportion 1.2:1 to 2.5:1.

4. A composition according to claim 3 in which the precentages are in the proportion 1.3:1 to 1.8:1.

5. A composition according to any preceding claim in which the imino sequestering agent is nitrilo triacetic acid (NTA), diethylene triamine pentacetic acid (DTPA) or ethylene diamine tetra acetic acid (EDTA), or a salt thereof.

6. A composition according to any preceding claim in which the polyhydroxy sequestering agent is sorbitol or a polyhydroxy acid or a salt thereof.

7. A composition according to any preceding claim in which the imino sequestering agent is ethylene diamine tetra acetic acid or a salt thereof and the polyhydroxy sequestering agent is gluconic or heptonic acid or a salt thereof.

8. A composition according to any preceding claim in which the alkali metal hydroxide is sodium hydroxide and the sequestering agents are present as sodium salts.

9. A composition according to any preceding claim containing surfactant.

10. A composition according to any preceding claim for removing metal phosphate coating from a metal surface and comprising 5 to 70 g/l alkali metal hydroxide, 1 to 1 5 g/l polyhydroxy sequestering agent and a lesser amount of 0.5 to 10 g/l imino sequestering agent.

11. A composition according to claim 10 containing 8 to 30 g/l alkali metal hydroxide, 2 to 10 g/l polyhydroxy sequestering agent and a lesser amount of 1 to 8 g/l imino sequestering agent.

1 2. A composition according to claim A substantially as herein described.

1 3. A method of removing a metal phosphate coating by applying a composition according to claim 10 or claim 11 to the coating at a temperature of 20 to 90"C for 0.5 to 5 minutes by brushing or spraying.

1 4. A method according to claim 1 3 in which contact is at 20 to 40"C for 0.5 to 2 minutes by spraying.

1 5. A method according to claim 1 3 or claim 14 in which the coating also includes lubricant.

1 6. A method according to claim 1 5 in which the coating is a coating that was formed by applying to a metal surface a composition comprising organic liquid carrier and an acidic reaction product comprising orthophosphate radicals, polyvalent metal cations and lubricant radicals.