EP2954073B1

EP2954073B1 - Process for treatment of semimanufactured products made of leather, imitation leather and/or fabric/s and items comprising said semimanufactured products resulting thereof

Info

Publication number: EP2954073B1
Application number: EP14710971.4A
Authority: EP
Inventors: Angelo Ramponi; Sandro RECCHIA
Original assignee: Conceria Stefania SpA; Universita degli Studi dell Insubria
Current assignee: Conceria Stefania SpA; Universita degli Studi dell Insubria
Priority date: 2013-02-11
Filing date: 2014-02-04
Publication date: 2016-11-02
Anticipated expiration: 2034-02-04
Also published as: ITMI20130187A1; WO2014122573A1; CN105102640A; CN105102640B; EP2954073A1

Description

The present invention relates to an improved process for the treatment of leather, imitation leather or fabric semimanufactured products as well as to items comprising said semimanufactured products treated with said process.
The applicant had formerly developed a method, covered by international patent application No. PCT/IT/2009/000445 , particularly targeted at the processing of leather or similar materials, such as cowhide and imitation leather (or fabrics resembling leather), to be used in the production of items meant to come at least partially into direct contact with the skin of the end user.
The method covered by the previous patent application provides semimanufactured products made of leather or similar materials with a high degree of comfortableness as well as high transpiration and reduction of the odours caused by the perspiration of the user's skin.
A further advantage achieved with the treatment method envisaged in the previous international patent application is that, by using natural materials, such as proteins, in aqueous solutions for processing leather, so as improve their properties of softness and comfortableness, as well as high water vapour permeability, said use entails a limited environmental impact.
According to the invention of the treatment method covered by the earlier international patent application, antiseptic, deodorant and antibacterial properties are provided to the leather or similar semimanufactured products by the use, in particular, of metal silver particles.
In developing the industrial scale-up of the prior method, the Applicant found that, when using metal silver particles having an average size within a range of some tens of micron, antibacterial properties were indeed preserved at satisfactory levels (at lest 90% of antibacterial activity found on the leather as treated and submitted to protocol ASTM E2149 - 10 "Standard method for determining the antimicrobial activity of immobilized antimicrobial agent under dynamic contact condition") in the semimanufactured products as treated immediately after treatment, but said properties dropped with the passing of time, particularly in semimanufactured products as treated which were later submitted to accelerated wear testing.
In an attempt to achieve leather and/or fabric semimanufactured products having even further improved antibacterial properties, in particular preserving said improved properties in the long term, without losing the other benefits obtained with the former method, such as comfortableness, a high degree of transpiration and high standards of ecological quality of the leather or fabric semimanufactured products after treatment, a new improved process for the treatment of leather, imitation leather or fabric semimanufactured products has been developed and implemented, comprising new materials and application methods.
The purpose of the present invention is therefore a process for the treatment of a leather, imitation leather or fabric semimanufactured product, said process comprising the steps of:

providing the semimanufactured product to be treated;
preparing a treatment solution comprising a binder solution and particles comprising silver ions in the form of insoluble or slightly soluble salts;
applying said treatment solution to at least one surface of said semimanufactured product to be treated,

To better understand the invention and appreciate the advantages thereof, some non-limiting examples of embodiments are described below.
The process according to the present invention is aimed at the treatment of leathers, in particular cowhides of various kinds, but can also be used to treat fabrics similar to leather, such as imitation leather. In the present description, reference will be made by way of example to leather and cowhide.
The process according to the present invention is further aimed at the treatment of fabric(s), meaning both natural fibre fabrics and artificial/synthetic fibre fabrics or fabric(s) deriving from a mixture of said fibres.
The kinds of natural textile fibres of vegetable origin included in the fabric(s) which can be treated with the process covered by the present invention are: cotton, flax, hemp, jute, ramie (or nettle yarn), sisal, coco, broom, hibiscus, manila hemp, straw, bamboo, cork.
The kinds of natural textile fibres of animal origin included in the fabric(s) which can be treated with the process covered by the present invention are: wools such as Merinos, Shetland, Bluefaiced Leicester, Corriedale, Crossed Wools, Lambswool, English, Asian, Mazamet, Regenerated Wools; hairwools such as Angora, Cachemire, Camel, Mohair, Alpaca, Lama, Vicugna or vicuña, Bison, Quivut or Quivuk; Silks, Horsehair or Byssus.
The kinds of natural textile fibres of mineral origin included in the fabric(s) which can be treated with the process covered by the present invention are glass fibres.
The kinds of artificial textile fibres included in the fabric (s) which can be treated with the process covered by the present invention are: cellulose fibres such as Rayon, Modal, Cuprammonium Rayon, Acetate, Triacetate, Lyocell.
The kinds of synthetic textile fibres included in the fabric(s) which can be treated with the process covered by the present invention are: acrylic, polyamide (such as for example Nylon 6, Nylon 6,6), polyester, polypropylene, polyethylene, chlorovinyl, polyurethane, polytetrafluoroethylene, aramid fibres. The process according to the invention firstly comprises a step to provide a semimanufactured product to be treated. Said semimanufactured product can for example comprise a leather pre-tanned with known procedures. Or else, said semimanufactured product may comprise for example a cotton or polyester fabric prepared with known procedures.
The semimanufactured product is treated by applying thereto, according to procedures to be described, a special treatment solution which is prepared according to specific procedures.
The treatment solution is not necessarily applied to the entire semimanufactured product, but preferably only to a surface thereof or only to small spots or an area of the same. In other words, only one side of the leather is treated with the process according to the invention. In this manner the treatment is limited to the portion of the leather destined to come into contact with the user's skin. For example, in the case of footwear, the treated surface is that destined to delimit the seat for the user's foot and which therefore will come into contact therewith. In the case of a watchstrap, the treated surface is the inner surface of the watchstrap, i.e. the surface that will come into contact with the skin of the user's wrist.
While conducting its research and development activity to find a new process for the treatment of leather, imitation leather or fabric semimanufactured products in order to provide said semimanufactured products with improved antibacterial properties both immediately and in the course of time, the applicant unexpectedly implemented and identified new materials which, in the process covered by the present invention, provide treated semimanufactured products with said improved antibacterial properties. In particular, the applicant surprisingly found that particles comprising silver ions in the form of insoluble or slightly soluble salts, whether said particles are:

metal silver particles comprising on the surface said insoluble or slightly soluble silver ion salts, or
particles of insoluble or slightly soluble silver salts,

In particular the applicant, while developing new materials which, in combination with the binder solution used in the process covered by the present invention, were able to provide improved antibacterial properties to the treated semimanufactured product, implemented a process for the preparation of particles comprising said insoluble or slightly soluble silver ion salts starting from metal silver particles on whose surface an insoluble or slightly soluble salt of the same silver is formed.
Checking the feasibility of said process with the formation of particles comprising metal silver whose surface is salified also in an advanced manner until a weight ratio salified surface/mass of metal silver particles is even as high as 90-95%, said particles all having the ability to provide a high antibacterial activity, the applicant, along with the development of this possible embodiment of the present invention, used particles consisting of insoluble or slightly soluble, inorganic or organic silver salts as particles being able to provide an improved antibacterial-activity.
The term "particles comprising silver ions in the form of insoluble or slightly soluble salts according to the present invention" means in particular:

metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts, in particular inorganic salts selected from the group comprising silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite or organic salts selected from the group comprising silver carbonate, silver oxalate, silver thiocyanate,
particles of insoluble or slightly soluble, inorganic or organic silver salts, in particular inorganic salts selected from the group comprising silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite or organic salts selected from the group comprising silver carbonate, silver oxalate, silver thiocyanate.

A preferred embodiment of the present invention envisages the use of metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts, wherein said surface has a minimum thickness of 50 nanometers. More advantageously said particles have a weight ratio between the salified surface and the metal silver mass amounting to at least 1%, preferably amounting to or exceeding 3%, more preferably amounting to or exceeding 20%.
The particles comprising silver ions in the form of insoluble or slightly soluble salts used in the process according to the present invention, both as metal silver particles comprising on the surface said insoluble or slightly soluble silver ion salts and as particles of insoluble or slightly soluble silver salts, are preferably particles having a minimum diameter amounting to or exceeding 0.1 micron, preferably amounting to or exceeding 0.25 micron.
Furthermore, the particles used in the proceeding covered by the present invention can have any shape or morphology: for example, they can be spherical, scaly granular, powders or dispersions/suspensions of fine particulate, although powders of both silver salts and metal silver salified on the surface are the preferred shape and morphology.
In a further, particularly preferred embodiment of the present invention, metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts are achieved through the method comprising the following steps:

a) oxidative aggression in aqueous acid medium of a portion of the surface of the metal silver particles with formation of silver ions;
b) fixation of silver ions on the surface of the metal silver particles treated in step a), in the form of insoluble or slightly soluble, inorganic and organic salts by way of the addition of a precipitating reagent corresponding to the insoluble or slightly soluble, inorganic or organic silver salt of interest;
c) drying of the particles obtained in step b);

In further particularly advantageous embodiments of the method of preparation of the metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts:

step a) of oxidative aggression is preferably performed:
- by using oxidising acids in aqueous phase, namely acids which are soluble in water with sufficient oxidising power to change the surface metal silver into ionic silver, such as for example nitric acid or perchloric acid;
- or else by using mixtures comprising non oxidising acids and oxidising agents, the latter preferably of a kind which can easily be removed from the reaction suspension, mixtures such as sulphuric acid and hydrogen peroxide, wherein any excess of hydrogen peroxide can be decomposed by simply heating the suspension;
in both cases, the oxidative aggression reaction is blocked by adding water, preferably distilled water,
step b) of fixation of silver ions on the surface of metal silver particles, in the form of salts, is preferably performed:
- in the case of slightly soluble, inorganic or organic salts, by gradually, directly adding a precipitating reagent in powder or in aqueous solution corresponding to the slightly soluble silver salt which is meant to be formed, such as for example sodium chloride, sodium carbonate, sodium thiocyanate, or else
- in the case of insoluble, inorganic or organic salts, by firstly forming a slightly soluble salt with the addition of the corresponding precipitating reagent, for example obtaining silver chloride through the addition of sodium chloride, followed by a substitution reaction using a specific precipitating agent to obtain the insoluble salt of interest, for example using a solution of sodium sulphide to obtain the silver sulphide of interest;
step c) of drying the particles obtained in step b) is preferably performed both at ambient temperature and at higher temperatures by using proper drying equipment such as stoves or ventilated dryers.

In a preferred embodiment of step a) of oxidative aggression in aqueous acid medium of a portion of the surface of the metal silver with formation of silver ions, said surface has a minimum thickness of 50 nanometers.

Step b) of fixation of silver ions in the form of slightly soluble organic or inorganic salts on the surface of the metal silver particles is preferably performed by the addition of a precipitating reagent in the form of a soluble salt, preferably a sodium salt, corresponding to the slightly soluble silver salt which is meant to be fixed; preferably said precipitating reagent is sodium carbonate, sodium oxalate, sodium chloride, sodium sulphate, sodium iodate, sodium sulphite.
Step b) of fixation of the silver ions in the form of insoluble, organic or inorganic salts on the surface of the metal silver particles is preferably performed by the addition of a precipitating reagent in the form of a soluble salt, preferably a sodium salt, corresponding to the insoluble silver salt which is meant to be fixed; preferably said precipitating reagent is sodium iodide, sodium bromide, sodium sulphide, sodium thiocyanate, sodium phosphate.
Step b) of fixation of the silver ions in the form of salts on the surface of the metal silver particles preferably entails the formation of salts selected from the group comprising: silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite, silver carbonate, silver oxalate, silver thiocyanate.

The metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts are preferably used in the treatment of products to be used for manufacturing items which require a high degree of thermoregulation, preferably items which come into contact with the end user's foot, because they advantageously preserve a core of metal silver, namely the metal with the highest ever thermal conductivity.
As a further advantageous option, according to the present invention, in specific cases of items or semimanufactured products which do not need exploiting a high degree of thermoregulation but which only require a minimum thermal comfort (by way of example, watchstraps), the metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts advantageously have a weight ratio between the salified surface and the metal silver mass preferably higher than 70%-80%.
Even more preferably, under such conditions it is possible to use advantageously particles comprising only silver ions in the form of insoluble or slightly soluble, organic or inorganic salts, more particularly inorganic salts selected from the group comprising silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite, or organic salts selected from the group comprising silver carbonate, silver oxalate, silver thiocyanate.
The natural proteins used in the binder solution can be of various type. Preferably, they are selected from the group consisting of casein, egg albumin, blood albumin.
The preferred binder used in the solution is in any case casein as this has the capacity to absorb moisture (which can, for example, derive from perspiration of the foot when the semimanufactured product is used to manufacture footwear). Casein is a phosphoprotein which can be obtained from milk through appropriate treatment processes (e.g.: pressure, fermentation, acidification).
Moreover, it is also possible to use a mixture containing one or more of the natural proteins listed to give particular characteristics to the leather treated with the process according to the invention. For example, it is possible for the binder solution to be provided with a combination of casein with albumin. In fact, this combination allows a sufficiently shiny film to be obtained on the leather
The binder solution can also comprise further additives suitable to give the leather specific characteristics. These additives can include one or more of the following additives: linseed mucilage, cellulose derivatives, such as carboxymethyl cellulose, gelatin, lac, soaps.
Their purpose is to make the finish silky and pleasant to touch.
Advantageously, the binder solution contains plasticizers suitable to reduce the stiffness, fragility and elasticity of the film of protein solution once this has been applied to the leather. The plasticizers are preferably selected from the group consisting of: sodium sulphoricinate, higher alcohols, glycols, glycerines, natural oils, natural waxes, both of vegetable and of animal origin.
A particularly advantageous embodiment of the present invention envisages the optional use, in combination with protein products, also of binders based on resins (normally polyurethane, polyamides) in suspension or in aqueous solution, for the preparation of the treatment solution, depending on the kind of semimanufactured product to be treated and the use the latter is meant for. The use of said resins, in combination with the treatment solution according to the present invention, does not bring detriment to the antibacterial capabilities related to the use of the particles comprising silver ions in the form of insoluble or slightly soluble salts according to the present invention.
The application of natural proteins in aqueous solution to the leather has many advantages.
Firstly, the absence of chemical solvents limits the overall environmental impact of the treatment. Moreover, the items produced from semimanufactured products treated with the process according to the invention ensure high ecological quality standards.
A further advantage linked to a binder solution of this type is that the presence of natural proteins ensures that the possibility of causing undesired allergies in the end user is low.
A further advantage linked to the use of an aqueous binder solution is the possibility of producing very thin, transparent and shiny finishes, which allow the leather to retain its natural water vapour permeability , while offering a high degree of comfort. Moreover, the antiseptic properties of particles comprising silver ions in the form of insoluble or slightly soluble salts are increased by the fact that it is immersed in a vapour permeable substance.
Advantageously, the binder solution has anionic charge and, preferably, a pH of 8. The percentage of casein in the binder solution is preferably between 6% and 12%, even more preferably equal to 8% (said percentages are referred to the solution weight, which means % in weight of the binder solution).
Preparation of the treatment solution from the binder solution and from the particles comprising silver ions in the form of insoluble or slightly soluble salts with the aforesaid properties comprises a series of successive steps.
If the particles comprising silver ions in the form of insoluble or slightly soluble salts to be used in the process according to the present invention are particles of insoluble or slightly soluble, inorganic or organic silver salts, preferably silver salts selected from the group comprising silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite, silver carbonate, silver oxalate, silver thiocyanate, said salts can be found on the market; if needed, they can be submitted to granulometric selection. If the particles comprising silver ions in the form of insoluble or slightly soluble salts to be used in the process according to the present invention are metal silver particles comprising on the surface insoluble or slightly soluble, inorganic or organic silver ion salts, said particles are best prepared by a separate process, according to the procedure as described above, before they are mixed with the binder solution.
The binder solution and the particles comprising silver ions in the form of insoluble or slightly soluble salts are mixed, preferably in a ratio of 1:10 (i.e. with one part of powdered particles comprising silver ions in the form of insoluble or slightly soluble salts and ten parts of binder), dispersing the particles comprising silver ions in the form of insoluble or slightly soluble salts in the binder solution. The suspension thus obtained is then mixed until obtaining a substantially homogenous paste.
More generally, the step of preparing the treatment solution comprises the following steps:

providing the binder solution;
providing the particles comprising ionic silver in the form of insoluble or slightly soluble salts;
mixing the binder solution and the particles comprising silver ions in the form of insoluble or slightly soluble salts;
mixing the binder solution and the particles comprising silver ions in the form of insoluble or slightly soluble salts until obtaining a substantially homogeneous paste.

Providing the particles comprising ionic silver in the form of insoluble or slightly soluble salts, when said particles are metal silver particles whose surface comprises insoluble or slightly soluble silver ion salts, means to implement the method, as described above, of preparation of said metal silver particles coated with insoluble or slightly soluble silver ion salts.
Water or the above-mentioned binder products are then added to the paste of casein and particles comprising silver ions in the form of insoluble or slightly soluble salts thus obtained, in order to bring the viscosity of the solution to a suitable value depending on the selected industrial application process.
The step to apply the treatment solution to the semimanufactured product to be treated can be performed in several manners: by way of example, it can be applied by spraying, roller, transfer, screen printing or hand pressing. The choice of the application method depends on the chemical and physical features of the substrate of the semimanufactured product to be treated.

APPLICATION BY SPRAYING

Water is subsequently added to the paste of casein and particles comprising silver ions in the form of insoluble or slightly soluble salts described above, in such a way as to obtain a diluted solution. According to a preferred embodiment, water is added in such a quantity that in the treatment solution the particles comprising silver ions in the form of insoluble or slightly soluble salts reach a concentration of between 7 and 12 g/l, preferably equal to 10 g/l.
Advantageously, the solution thus obtained is then kept under stirring, for example using a blade stirrer. The maintenance speed is preferably between 250 and 350 rpm, even more preferably equal to 300 rpm.
Once the treatment solution has been prepared according to the procedures described, the treatment process includes a step to apply the treatment solution to the semimanufactured product to be treated, in particular to the surface destined to come into contact with the skin of the end user.
In accordance with a possible embodiment, the treatment solution is applied to leather or imitation leather or fabric semimanufactured products by spraying, preferably by means of compressed air guns. The spray pressure is preferably maintained between 0.4 and 0.7 atm.
Preferably, the treatment solution is sprayed through nozzles having a diameter between 0.5 and 1.3 mm, even more preferably equal to 0.8 mm. In other words, the treatment solution is applied at low pressure and high volume, with reference to the pressures and to the volumes which are normally used to treat leathers (for example, when applying dyes).
Advantageously, the step to apply the treatment solution takes place according to a plurality of successive application operations. According to a possible embodiment, the treatment solution is applied in four subsequent application operations, each preferably applying between 40 and 60 grams of treatment solution per square metre of surface of the semimanufactured product. Even more preferably, the quantity of treatment solution applied is equal to 50 grams per square metre of surface of the semimanufactured product. At the end of the four application operations, the treatment solution applied is therefore equal to 200 g per square metre of surface of semimanufactured product, which, according to a preferred embodiment, corresponds to 2 grams of particles comprising silver ions in the form of insoluble or slightly soluble salts per square metre of semimanufactured product to be treated.

APPLICATION BY ROLLER

In accordance with a possible embodiment, the treatment solution can be applied to leather, imitation leather or fabric semimanufactured products by means of a roller, preferably by using engraved cylinder machines of the roller coating kind.
Further organic binder is preferably added to the paste of casein and particles comprising silver ions in the form of insoluble or slightly soluble salts in order to obtain a mixture with optimal viscosity for application by roller.
Advantageously, the solution thus obtained is then kept under stirring, for example using a blade stirrer. The maintenance speed is preferably between 250 and 350 rpm, even more preferably equal to 300 rpm.
Viscosity is measured by an equipment consisting of a Ford viscosity cup with a 4-mm-nozzle. The mixture viscosity must range between 30 and 60 seconds, preferably 50.
The concentration of the particles comprising silver ions in the form of insoluble or slightly soluble salts must range between 10 and 50 gr/litre, preferably 30.
Preferably the solution is applied only to one side of the leather, namely the one which will come into contact with the user's skin.
The treatment solution is applied by using a properly engraved cylinder which can distribute a predetermined amount of mixture on the leather. The depth and the distribution of the engravings on the cylinder determine the amount which can be transferred.
The applied amount can be further increased or decreased also by acting on the leather entrainment speed in the roller coating as well as on the number of rotations of the distributing cylinder.
The treatment solution is distributed on the cylinder through a diaphragm pump which draws the solution from the container where it is kept under stirring. The solution in excess, sent to the cylinder, is reclaimed by a device placed on the apparatus.
The amount of solution applied by the cylinder ranges between 30 and 90 gr/m² and can be obtained with several successive steps depending on the absorption capability of the substrate.
Application by cylinder is followed by drying in conveyor belt ovens where the treated leather is submitted to temperatures of 60 /80 °C for 1 to 5 minutes.

APPLICATION BY TRANSFER

In order to provide the antibacterial properties using the transfer technique, the treatment solution comprising a binder solution and particles comprising silver ions in the form of insoluble or slightly soluble salts can be applied to a sheet, for example a polyester or silicone paper sheet, and then transferred on the leather, imitation leather or fabric(s) by hot-pressing. For transfer procedures, machines developing temperatures above 90°C, even up to 150°C, pressures ranging between 2 and 3 bar and contact times from 0.5-2 sec up to even 15-30 sec must be used.

APPLICATION BY SCREEN PRINTING AND HAND PRESSING

The treatment solution according to the present invention can also be applied to any semimanufactured product also using techniques similar to printing by a screen-print frame and hand pressing, without any change of procedure compared to said techniques, applicable according to the relevant well-known procedures from the state of the art.
The step to apply the solution to the semimanufactured product by any of the above techniques can in its turn be followed by the successive steps to fix and/or to dry and/or to buff, which are described below.

FIXING

Advantageously, the treatment process according to the invention also comprises a step to fix the treatment solution to the surface of the semimanufactured product. The fixing step has the purpose of insolubilizing the natural proteins of the binder solution, so as to make them swell less in water and thus obtain stability to wet treatments.
Preferably, the fixing step takes place according to a plurality of successive fixing operations. In particular, each application operation is followed by a fixing operation suitable to fix the treatment solution applied in the specific application operation to the surface of the semimanufactured product.
According to a possible embodiment, each of the fixing operations comprises the application of a fixing substance to the surface of the semimanufactured product (to which the treatment solution has been previously applied).
Preferably, the fixing substance contains aldehydes suitable for crosslinking the natural proteins of the binder solution (and of the treatment solution). In particular, according to a preferred embodiment, the fixing substance contains glyoxal, which is suitable for crosslinking casein. Glyoxal is preferably included in the fixing substance in a percentage between 3% and 5%.

DRYING

In accordance with an embodiment, the process according to the invention comprises a step to dry the semimanufactured product on which the treatment solution has been applied, which can be performed with a plurality of successive operations.
The single drying operations can be implemented by placing the semimanufactured product in an environment which has a predetermined drying temperature, for example in a drying oven. The drying temperature is preferably between 30°C and 90°C, even more preferably equal to 60 °C. The time of the drying operations preferably varies from 20 to 120 seconds.

BUFFING

In accordance with an embodiment, the process according to the invention also comprises a final buffing step. This buffing step can, for example, be obtained through hot stretching using heated rollers that press the semimanufactured product on the treated side. This process allows a leather with a high level of smoothness and shine to be obtained.
The semimanufactured product treated according to the procedures described can advantageously be used to manufacture a particular item, such as an article of clothing, footwear, a watchstrap, a small leather article (wallet, purse), a covering for objects (for eyewear, for seats), or the like.
For example, with reference to footwear, it is possible to treat the surface of the semimanufactured product destined to come into contact with the foot of the user with the process according to the -invention.
Due to the treatment to which the semimanufactured product is subjected, based on an aqueous binder solution, the leather of the shoe is soft and elastic, as well as sufficiently breathable. Moreover, the presence of the particles comprising silver ions in the form of insoluble or slightly soluble salts limits the production of unpleasant odours linked to perspiration of the foot due to the antiseptic, antibacterial and odour-preventing action of the particles comprising silver ions in the form of insoluble or slightly soluble salts dispersed on the internal surface of the shoe.
Analogous effects are naturally obtained also in other types of items destined to come into contact with the skin and possibly with the perspiration of the user.
From the above description those skilled in the art can appreciate how with the process according to the invention it is possible to obtain leathers, imitation leathers or fabrics and therefore items that ensure a high degree of well-being, both in terms of softness and comfort, and in terms of reducing unpleasant odours.
Moreover, those skilled in the art may appreciate how the use of natural proteins in the binder solution ensures a low environmental impact of the process and reduces the risk of allergic reactions of the user.
Finally, those skilled in the art may appreciate how the combination of aqueous binder solution and the particles comprising silver ions in the form of insoluble or slightly soluble salts, especially when applied to leather, provides products with a high level of permeability to perspiration and the capacity to limit the occurrence of unpleasant odours.
For the purpose of satisfying specific contingent requirements, those skilled in the art will be able to make numerous modifications or additions to the embodiments described above of the process for the treatment of a semimanufactured product made of leather or similar material and of the item produced with the semimanufactured product treated according to this process, or to substitute elements with other functionally equivalent elements, without however departing from the scope of the appended claims.
In order to check for the advantages related to the process covered by the present invention, a series of experimental tests have been performed.
Under the same conditions, identical samples or specimens of the same kinds of leather or hide meant to be used as footwear lining were tested: one was submitted to the treatment method as described in international patent application No. PCT/IT/2009/000445 , characterised by the use of metal silver particles, two were submitted to the treatment method according to the present invention, in one case using particles of a silver salt in the treatment solution and applying said solution by roller, in the other case using particles of metal silver whose surface was coated by the same type of salt as the one used for the former sample in the treatment solution and applying said solution by roller.
The three solutions for application by roller were prepared by keeping the same concentrations in weight of the products which make up the solution, namely: natural proteins (including casein), plasticizers, organic binders and water in order to have solutions at 30 g/l of metal silver particles (No. PCT/IT/2009/000445 ), silver salt particles and metal silver particles coated by silver salt, respectively. Each of the three solutions was kept under stirring during application (250 - 350 rpm using a blade stirrer), after checking viscosity with a Ford viscosity cup -with a 4-mm-nozzle. The roller coating machine was set to apply 35 g/m² of binder solution for each of the different samples.
The antibacterial activity of all the three specimens obtained at the end of the respective treatments was tested using the method/protocol ASTM E2149 - 10 "Standard method for determining the antimicrobial activity of immobilized antimicrobial agent under dynamic contact condition" wherein the antibacterial activity is tested by putting the leather samples into contact with known amounts of bacterial strains of Escherichia coli and counting progressively in time the residual bacterial charge.
In the case of the leather specimen treated with the method comprising metal silver granules, the sampled antibacterial activity remained at satisfactory levels of least 90%. In the case of the other two leather specimens, the sampled antibacterial activity ranged between 98 and 100%.
The same specimens whose the antibacterial activity had been tested immediately after being treated were then submitted to an accelerated wear test, in compliance with norm UNI EN 13520, consisting of rubbing a leather or imitation leather specimen with abrasive fabric on a Martindale abrasion testing machine, in order to test the residual antibacterial activity after the maximum envisaged wear, with reference to the quality standards of the leather industry; the antibacterial activity was tested according to the above-mentioned method (method/protocol ASTM E2149 - 10).
The abrasion testing equipment is a machine named "Martindale" ensuring the formation of the Lissajous figure during movement between the sample holders, on which a leather specimen is mounted, and the abrading plane coated with wool fabric, submitted to a constant pressure of (12 ± 0,2) kPa. The device is provided with a revolution counter: each revolution corresponds to an ellipse of the Lissajous figure.
It was found that in the leather specimen/sample treated with the method comprising metal silver granules, the sampled antibacterial activity dropped to 63% after a wear period of only 6,400 revolutions, whereas in both the other leather specimens/samples, the one treated with the method comprising silver salt particles and the one treated with the method comprising metal silver particles whose surface was coated by the same salt as the one used with the former sample, the antibacterial activity remained at the highest levels of 98-100%, not only after a wear period of 6,400 revolutions, but also per a far longer wear period, namely after 51,200 revolutions.

Claims

A process for the treatment of a semimanufactured leather, imitation leather or fabric product, said process comprising the steps of:
- providing the semimanufactured product to be treated;

- preparing a treatment solution comprising a binder solution and particles comprising silver ions in the form of insoluble or slightly soluble salts;

- applying said treatment solution to at least one surface of said semimanufactured product to be treated,
wherein said binder solution comprises natural proteins in aqueous solution.
The process according to claim 1, wherein said natural proteins comprise casein and/or egg albumin and/or blood albumin.
The process according to claim 1 or 2, wherein said binder solution comprises natural protein plasticizers, said plasticizers being selected from the group comprising: sodium sulphoricinate, higher alcohols, glycols, glycerines, natural oils, natural waxes either of vegetable or animal origin.
The process according to any one of the preceding claims, wherein said binder solution comprises further additives selected from the group comprising: linseed mucilages, cellulose derivatives, gelatin, shellac, soaps.
The process according to any one of the preceding claims, wherein said natural proteins are present in the binder solution with a percentage of 8% by weight of the binder solution.
The process according to any one of the preceding claims, wherein said binder solution has anionic charge and has a pH value equal to 8.
The process according to claim 1 wherein the particles comprising silver ions in the form of insoluble or slightly soluble salts are particles of insoluble or slightly soluble silver salts, either of inorganic or organic type.
The process according to claim 7 wherein the particles of insoluble or slightly soluble silver salts are particles of inorganic salts selected from the group comprising silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite or organic salts selected from the group comprising silver carbonate, silver oxalate.
The process according to claim 1 wherein the particles comprising silver ions in the form of insoluble or slightly soluble salts are metal silver particles comprising on the surface insoluble or slightly soluble silver ion salts either of inorganic or organic type.
The process according to claim 9 wherein the salts on the surface of the metal silver particles are inorganic salts selected from the group comprising silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodate, silver phosphate, silver sulphite or organic salts selected from the group comprising silver carbonate, silver oxalate.
The process according to claim 9 wherein the metal silver particles comprising on the surface insoluble or slightly soluble silver ion salts are obtained by a process comprising the following steps:
a) oxidative aggression in aqueous acid medium of a portion of the surface of the metal silver with formation of silver ions;

b) fixation of silver ions on the surface of the metal silver particles treated in step a), in the form of insoluble or slightly soluble inorganic and organic salts by way of the addition of a precipitating reagent corresponding to the insoluble or slightly soluble inorganic or organic silver salt of interest;

c) drying of the particles obtained in step b).
The process according to claim 11 wherein in step a) of oxidative aggression in aqueous acid medium of a portion of the surface of the metal silver with formation of silver ions, said surface has a minimum thickness of 50 nanometers.
The process according to claim 11 wherein step b) of fixation of silver ions in the form of salts on the surface of the metal silver particles involves the formation of salts selected from the group comprising: silver chloride, silver iodide, silver bromide, silver sulphate, silver sulphide, silver iodide, silver phosphate, silver sulphite, silver carbonate, silver oxalate.
The process according to any one of the preceding claims, wherein said step of preparing the treatment solution comprises the steps of:
- providing the binder solution;

- providing the particles comprising ionic silver in the form of insoluble or slightly soluble salts;

- mixing the binder solution and the particles comprising silver ions in the form of insoluble or slightly soluble salts;

- mixing the binder solution and the particles comprising silver ions in the form of insoluble or slightly soluble salts until obtaining a substantially homogeneous paste.
The process according to any one of the preceding claims, wherein said step to apply the treatment solution to the semimanufactured product to be treated comprises:
- a spraying step, or

- a roller application step, or

- a transfer application step or

- a screen printing application step or

- a hand pressing application step
of said treatment solution on the surface of the semimanufactured product.
The process according to any one of the preceding claims, further comprising a step of fixing the treatment solution applied to said at least one surface of the semimanufactured product to be treated.
The process according to any one of the preceding claims, further comprising a step of drying the semimanufactured product.
The process according to any one of the preceding claims, comprising a buffing step, preferably by hot stretching.
An item made from a semimanufactured leather, imitation leather or fabric product treated with the process according to any one of the preceding claims.