The present invention refers in general to the field of leather tanning, and more precisely refers to a novel process of treatment of pelts that combines optimally the needs of health, ecology and environmental safety, with the aesthetic and functional features required today from leather, thanks to the use of degreasing agents never used until today in this field.
It is known that the process for the manufacture of leather includes different working steps: amongst the first steps of the process is a degreasing step of animal skins, with the purpose of eliminating the natural fat residue usually contained in the dermis' structure of the animal. The presence of fat on the skins to be treated is in fact a "water-repellent" layer that must be necessarily eliminated if a smoother and more uniform penetration is desired of the tanning agents and in general of any water-soluble or water-emulsifiable products to be used in one or more of the manufacture steps.
Currently, for this purpose, so-called "degreasing" agents are used; they are of various types and of different nature, such as chlorinated organic solvents, emulsifiers of various nature, mineral spirits, or natural extracts having a certain solvent power such as the citrus extracts.
Chlorinated organic solvents exhibit a high degreasing capability, but their use has several drawbacks, such as difficulties in the disposal of large amounts of solvents of this type, highly polluting, and even a worse quality of the animal skin degreased by using these solvents. As a matter of fact, animal skin loses its typical fullness and compactness, often resulting too empty and dry, so that even the subsequent tanning treatments are affected in a negative way. Furthermore, current regulations prohibit the use of this type of solvents in open systems.
For these reasons, and in particular for the growing ecological awareness and attention to working conditions also in the tanning industry, degreasing agents such as chlorinated solvents are almost disappeared from this industry, at least in Western countries, where research is now focusing on new degreasing agents that are natural or at least not harmful to people and environment, that produce lower quantities of waste and therefore less pollution. To this advancement the ever-changing industry regulations have also contributed, requiring the development of products and processes that meet increasingly stringent requirements in terms of environmental protection and in terms of health and safety of process workers in manufacturing industry.
These new degreasing agents on the other hand are requested to be at least as efficient in degreasing as the traditional chemical solvents, to have a reasonably low cost and not to weigh too much on the economy of the manufacture process with substances that, as natural and not harmful, however have a prohibitive cost.
Amongst the degreasing agents known and used until today that are not chlorinated organic solvents, it is worth mentioning the mineral spirits used in combination with non-ionic surfactants such as alkylphenol ethoxylates, in particular the nonylphenol ethoxylates, used for their high degreasing efficiency but now considered unsatisfactory because of their toxicity and environmental impact associated with their use.
Other alcohol ethoxylates have been proposed to replace them: they are satisfactory both from the economic point of view and from the ecological point of view, but they are less efficient as broad-spectrum degreasers.
For these reasons up to now, as far as the Applicant is aware, it is still unsolved the technical problem of having available a degreasing process that is ecological, economic but efficient, able to further provide a high quality final product.
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Now the Applicant has found that the products as defined in the following are degreasing agents having high efficiency, for removing the natural fat in the animal skins to be treated as well as for removing fats from the intermediate products in leather manufacture; they are moreover products that are available on the market or that may be anyway manufactured at low costs, and they are not harmful for human health and for the environment.
The leather obtained by using the present degreasing agents is furthermore of high quality, and has valuable aesthetic and functional characteristics, since the compactness and the softness of the starting pelts are advantageously maintained unchanged.
It is therefore subject of the present invention a process for degreasing pelts or intermediate products in leather manufacture, comprising the treatment of said pelts or of said intermediate products with a degreasing agent selected from glycerol diacetate and derivatives thereof, glycerol triacetate, and mixtures thereof according to claim 1.
It is a further subject of the invention a degreasing composition for pelts or for intermediate products in leather manufacture suitable for use in the above said process, which is an aqueous dispersion comprising a degreasing agent selected from glycerol diacetate and derivatives thereof, glycerol triacetate, and mixtures thereof, one or more co-solvents, surfactants and/or co-emulsifying agents.
Further important characteristics of the process and of the composition of the invention are described in the following detailed description.
In the present invention by the term "glycerol diacetate" a structural isomer of glycerol diacetate is meant, i.e. glycerol 1,2-diacetate or glycerol 1,3-diacetate, or mixtures thereof.
By the term "derivatives" of glycerol diacetate, derivatives are meant that are for example selected from esters of glycerol diacetate with aromatic or aliphatic, linear or branched, organic acids, and preferably with organic acids having a number of carbon atoms ranging from 3 to 10; particularly preferred derivatives of glycerol diacetate are esters of glycerol diacetate with benzoic acid, butanoic acid and iso-octanoic acid.
Glycerol diacetate and glycerol triacetate, also known as diacetin or GDA and triacetin or GTA respectively, besides having for their nature practically zero degree of hazard and a much reduced environmental impact, are stable compounds, non-volatile, not inflammable, and easily dispersible in water by addition of a co-solvent or of surfactants.
Furthermore, they are products available on the market at low cost, or they may be easily prepared starting from products available on the market as glycerol and acetic acid, using known procedures, whose optimal experimental conditions may be easily defined by any persons skilled in the field. In both cases, they are products that have been known for decades, but used in completely different fields and for uses that are completely different from that of the invention.
The main use of these products is for instance as plasticizer for cigarette filters, even if other uses are known, triacetin is in fact also used as alimentary additive or as a fungicide agent in cosmetic products.
Now the Applicant has surprisingly found that these products are also excellent degreasing agents for animal skins and solve the technical problem illustrated above. As a matter of fact, they have shown a high solvent power towards natural triglycerides present in animal skins, which are therefore more easily extracted from the derma fibrous structure thus facilitating an in-depth degreasing, otherwise not practicable or anyway difficult if carried out with the other degreasing agents until now used in an aqueous environment.
A particularly preferred degreasing agent according to the invention is triacetin.
The present degreasing agents may be for instance used in aqueous solution and in amount comprised between 0.1 and 5% by weight with respect to the total weight of the pelts treated, and preferably in amount comprised between 2 and 3%. Depending on the kind of starting pelt to be treated, on the seasonality and of the type of final desired product, the amount of degreasing agent may be varied accordingly, and the optimal amounts of the product to be used may be found from time to time.
According to the invention, the present degreasing agents may be also used "under dry conditions", i.e. in the absence of water or other solvents, according to the procedures and with the equipment commonly used for this kind of application.
The present degreasing agents may be moreover used alone or in combination with other degreasing agents, natural or not, and/or with surfactants of various nature. During degreasing in aqueous environment, one or more co-solvents may be furthermore added to water in order to increase solubility of possible additional components of the formulation besides the degreasing agent.
Surfactants of possible use in the present compositions are selected from the group consisting of:
Co-emulsifying agents of possible use in the present compositions are selected from the group consisting of:
Co-solvents of possible use in the present compositions are selected in the group consisting of:
Possible colouring agents and/or perfumes may be added to the present degreasing composition, as well as possible further excipients or diluents commonly used in this kind of compositions, for example in order to modify their organoleptic characteristics and/or make the present composition more easily recognised on the market.
The leather obtained with the process of the invention is resistant, but also soft and in general of highly satisfactory quality. Furthermore, the characteristics of the starting pelts are not altered, even minimally, by this degreasing process, if not for the removal of the fat layer. In addition, no trace of substances harmful to people or to the environment is present in the leather degreased which, if subsequently tanned with the various known techniques, may be used for the manufacture of any finished product.
The present process has therefore proved to be an effective solution to the technical problem highlighted above of not being able to get an efficient degreasing with non-toxic or non bioaccumulative agents, but to get a satisfactory degreasing only with chemicals, with a strong impact on the environment and on safety. The use of the present compositions in the conditions of the present process allows instead to strongly reducing the use of chemical products that are highly bioaccumulative and dangerous to work environments, but still obtaining a finished leather product having the aesthetic and functional characteristics of softness and strength required by the market.
More specifically, the analyses carried out on leather products degreased by using the present process showed a residual amount of fat, which is less than or equal to that present in the leather products treated with traditional organic solvents, while maintaining a high quality of the finished leather.
The present process, besides for removing the layer of fat from the dermis of animal skins used as starting product in leather manufacture, may be used for degreasing any intermediate products in this type of manufacture, that needs a degreasing, for instance in the so-called phase of soaking to facilitate the operations of washing; in the re-tanning to ensure adequate removal of triglycerides on those pelts that have high quantities of fat and to act as "detergent" of the surface of the pelts themselves; in the fattening step to favour an uniform distribution of softeners provided during the application process; in the recovery of leather products having problems caused by a wrong greasing or other similar defects caused by too much fat on the surface.
An example of composition according to the present invention has been prepared with the following components:
The preparation of the composition was carried out in a reactor of suitable size containing the glycerol triacetate, to which were added under slow stirring in the following order: iso-C10 alcohol ethoxylate 3 mEO, castor oil ethoxylate 25 mEO, iso-C10 alcohol ethoxylate 5 mEO, castor oil ethoxylate 40 mEO, and finally sorbitan monooleate and hexylene glycol. Each component was added only after complete dispersion of the previous components. Finally, once the composition was homogeneous, water has been added.
In a drum of suitable size containing skins of New Zealand sheep to be degreased, water and the composition prepared as described in example 1 are added, in amount of about 4.5% by weight with respect to the total weight of animal skins, at temperature of approximately 30°C for about 1 hour.
At the end of this treatment the pelt is washed with water and sent to the subsequent phases to finally obtain a Chrome-tanned semi-finished product and commonly indicated as "Wet Blue".
The product obtained as described in Example 2 was compared with the same type of leather, but degreased with commercial formulations based on mineral solvents and non-ionic surfactants: the excellence of the product degreased with the process of the invention was emphasized both in terms of greater efficiency of degreasing and cleaning and in terms of better distribution of natural fats present in the leather itself.
On this product analyses were performed, in particular to evaluate the amount of fat residue remaining on the leather, and therefore to assess the efficiency of the executed degreasing. More specifically, it is carried out the determination of substances extractable with methylene chloride according to the method IUC/4 by taking different samples of material in as many different points of the treated pelts. The result of this analysis has showed that the residual fat was in amount of about 2.7-3% by weight with respect to the weight of the leather itself, a value well below the average amount of residual fat detectable for pelts degreased with the degreasers known and used until today. The result is even more significant for the fact that it was obtained starting from a pelt such as that of the New Zealand sheep, which has a high content of natural fat, approximately equal to 25% by weight.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.