The present invention is related to the area of metal treatment and refers to new degreasing compositions, a method for degreasing hard surfaces and the use of green solvents for degreasing operations.

In ordinary metal processing metal parts are greased to avoid the corrosion process during their manufacture, storage and transport. Since the degreasing agent is incompatible with subsequent metal processing stages, a cleaning step to remove the metal protector is inevitable. Over the past few years, one of the major challenges in the area of metal degreasing has been the transition from fully emissive open-top systems based on the use of chlorinated solvents to closed-loop metal-degreasing systems based on low VOC emission, low toxicity solvents. Alternative chlorinated solvents such as trichloroethanol, chloroform, methyl chloride, CFC-113, HFCs, HCFCs, CO₂ jets, scCO₂ semi-aqueous solvents, alkaline cleaning agents, emulsifying detergent-based cleaners, and aliphatic hydrocarbon based solvents and azeotropic mixtures have been proposed to replace the widely used current industrial standard, namely trichloroethylene. However, none of the proposed alternatives fully satisfy the key industrial needs of the metal finishing sector.

Therefore the object of the present invention has been to develop new compositions allowing to perform metal degreasing operations in highly variable settings, with metal parts of different size and shape, minimizing diffuse emission, release of contaminated air during loading and unloading, and solvent release from cleaned metal parts. The use of these compositions should also avoid the generation of large waste streams, allowing to establish an easy and cost effective process in order to recycle solvent and rinsing water and ultimately delivering parts adequately conditioned for immediate use in subsequent steps of the metal finishing process. More particularly the present invention intends to replace commercial degreasing solvents known from the market by new compositions being more efficient, safer and friendlier to the environment.

The present invention refers to new degreasing compositions comprising at least one glycerol acetal or ketal according to general formula (Ia) or (Ib) in which R¹ stands for hydrogen or an hydroxyl group, and R² and R³ independently from each other mean hydrogen, an hydrocarbon radical having 1 to 22 carbon atoms, and 0 or up to 3 double bonds - optionally substituted by an amine, hydroxyl, phenyl or hydroxyphenyl group.

Surprisingly it has been observed that cyclic acetals or ketals based on glycerol or it partial hydrogenation product propandiol, regardless whether the metal surfaces have been protected by solvent based or cereous metal preservatives containing antioxidants and other additives show a high degreasing efficacy compared with improved eco-toxicological behaviour. In addition, the solvents can be easily rinsed off with water, collected and then recycled without any additional purification. Replacing well known chlorinated organic degreasing solvents (e.g. trichloroethanol trichloroethylene, perchloroethylene) by glycerol acetals and ketals leads to a more environmentally friendly process without losing performance.

Another object of the present invention relates to a method for the degreasing of hard surfaces, characterised in that said surfaces are brought into contact with at least one organic solvent selected from the group consisting of glycerol acetals or ketals according to general formula (Ia) or (Ib) in which R¹ stands for hydrogen or an hydroxyl group, and R² and R³ independently from each other mean hydrogen, an hydrocarbon radical having 1 to 22 carbon atoms, and 0 or up to 3 double bonds - optionally substituted by an amine, hydroxyl, phenyl or hydroxyphenyl group.

In order to avoid ambiguities it is stated that the phrase "glycerol" as used according to the present invention includes also hydrogenation products of glycerol as propandiol-1,2 and propandiol-1,3. This is reflected in general formulae (Ia) and (Ib) for the case R¹ = hydrogen.

Acetals and ketals are obtained by condensation of alcohols and aldehydes or ketones respectively. In case the alcohol is a diol the formation of cyclic, 6-membered or 5-membered structures takes place.

Typical examples for suitable acetals or ketals are those obtained from the condensation of glycerol, 1-2,propandiol or 1,3-propandiol with lower aldehydes like for example formalin, acetaldehyde, propanal, butanal, pentanal, or fatty aldehydes comprising 6 to 22 carbon atoms, like capronal, laurylaldehyde, myristylaldehyde, palmitylaldehyde, stearylaldehyde, oleyl aldehyde, behenyl aldehyde, erucylaldehyde and the like. Suitable ketals are obtained from lower aliphatic ketones like for example acetone or fatty ketones like distearyl ketone. The preferred products are glycerol acetals, in particular those obtained from aliphatic aldehydes having 1 to 6 carbon atoms, more in particular the ones with 3 to 6 carbon atoms like glycerol propanal or glycerol iso-butyral.

As explained above, typically the hard surfaces represent metal surfaces, such as those used in the manufacture of automotive and building components. The glycerol acetals or ketals, which are used as so-called "green solvents" serve as degreasing agents in order to remove all greases and stains, in particular the preservatives from the surfaces. This can be done either by tipping the parts into the solvent or - more convenient - by spraying. Once degreasing has taken place, the acetals or ketals are collected and reused several times without purification.

As outlined above, glycerol acetals and ketals show excellent performance in removing stains, grease and especially preservatives from hard surfaces. Another object of the present invention is therefore directed to the use of glycerol acetals or ketals according to general formula (Ia) or (Ib) in which R¹ stands for hydrogen or an hydroxyl group, and R² and R³ independently from each other mean hydrogen, an hydrocarbon radical having 1 to 22 carbon atoms, and 0 or up to 3 double bonds - optionally substituted by an amine, hydroxyl, phenyl or hydroxyphenyl group, as degreasing agents for hard surfaces.

The degreasing process consists of the following phases:

1. (i) Immersion or spraying of the metal parts coated with the preservative at room temperature;
2. (ii) Drain off the excess solvent in the metal part;
3. (iii) Rinsing with water by immersion or spray; and
4. (iv) Recovery of the solvent and water for further use in subsequent cycles.

The solvent can be reused several times without loss of efficacy. At the end of its useful life, the solvent can be recycled by distillation with yields higher than 80%. Figure 1 shows the fundamental aspects of the degreasing process.

For our evaluation, a comparative method was used, in which removal efficacy (RE) of several alternative solvents are compared with RE value obtained for the industrial standard degreaser, trichloroethylene.

Removal Efficacy (RE) measures the degree of removal of organic materials (grease and/or solvent) from the surface of metal parts. Removal efficacy screening test, remove the grease of ten metallic greased pieces by degreasing process. The standard procedure was done by bringing the solvent into contact with the metal surface, more particular by immersion without agitation during 10 minutes in one volume of fresh solvent followed by three consecutive washing cycles by immersion in clean water. The amount of organic material (grease and/or solvent) that was not eliminated by the assayed procedure was determined by direct weight after removal of organic residues from the metallic parts by standard cleaning procedure with trichloroethylene.

The removal efficacy (RE) for a standard degreasing solvent in industry CHCl=CCl₂ is between 94-98 % depending on the nature of the preservative (Table 1). These RE values were used to compare with the results obtained by assayed solvents and to determine their effectiveness compared with trichloroethylene. Removal Efficacy (%) value for trichloroethylene Preservative A (solvent-based) B (cereous-based) RE (%) 94.2 98.1

The removal efficacy of the glycerol acetal and ketal solvent family was studied. These experiments remove the grease of ten greased pieces according to the procedure described before. This experiment was carried out for two different greases and the obtained results are described in table 2. RE (%) value normalized to trichloroethylene for acetals and ketals solvents Solvent Solvent-based preservative Cereous preservative Trichloroethylene 100 100 Glycerol propanal 34 72 Glycerol isobutyral 57 78 Glycerol formal 21 53

In order to have an economically viable process, the degreasing solvent must be able to be used several times without any prior purification. For this reason reusability of the solvent glycerol formal has been studied in both preservatives. The results are outlined in Table 3. Reusability of glycerol formal. Figures indicate percentage reduction of maximum efficacy. Number of cycles Solvent based preservative Cereous preservative 1 99.21 99.01 2 98.05 98.70 5 96,11 98,13 9 89.97 97.49

After 5 cycles with the solvent-based preservative the loss in efficiency was less than 4% for both solvent based and cereous preservatives.