EP3489370A1

EP3489370A1 - Leather with antimicrobial and self-cleaning properties and process for obtaining thereof

Info

Publication number: EP3489370A1
Application number: EP17464014.4A
Authority: EP
Inventors: Carmen Cornelia Gaidau; Manuela Calin; Cristina Ana Constantinescu; Daniela Rebleanu; Stoica Tonea
Original assignee: Institutul National De Cercetare-Dezvoltare Pentru Textile Si Pielarie (incdtp) Sucursala Institul De Cercetare Pielarie Incaltaminte (icpi)
Current assignee: Institutul National De Cercetare-Dezvoltare Pentru Textile Si Pielarie (incdtp) Sucursala Institul De Cercetare Pielarie Incaltaminte (icpi)
Priority date: 2017-11-22
Filing date: 2017-11-23
Publication date: 2019-05-29
Also published as: RO133342B1; RO133342A2

Abstract

The invention relates to leather with antimicrobial and self-cleaning properties in the visible domain, surface-finished with nitrogen-doped titanium dioxide nanoparticles and 1.6% nano silver deposits with a mean particle size of 30 nm. The process for obtaining antimicrobial and self-cleaning leather consists of the application of a base coat containing 0.01-8 g/L nitrogen-doped titanium dioxide nanoparticles and 1.6% nano silver deposits dispersed with 0.001-8 g/L of sodium polyacrylate by mechanical stirring for 10 minutes followed by 5 minutes of ultrasonic stirring with pigment paste, water and acrylic binder. This basic composition is applied by spraying in successive layers with intermediate drying and ironing at 110°C and 100 kg/cm² followed by fixing with nitrocellulose lacquer in successive layers with intermediate drying and final ironing at 110°C and 120 kg/cm². Antimicrobial and self-cleaning properties are ensured by photocatalytic degradation of organic dirt under the influence of visible light.

Description

The invention relates to antimicrobial and self-cleaning leather, properties of interest for leather intended for shoe linings, furniture upholstery, car or aircraft upholstery, and leather garments, and the process for obtaining thereof.
There are organic chemicals that may be used in the treatment of natural leather in order to limit the attack of bacteria and fungi in intermediate stages of their processing, but which have potential for effluent pollution and are volatile. The final treatments of natural leather to provide dirt-resistant properties make use of film-forming polymers, silicone additives or fluorinated copolymers [ US 20130184400 A1 ] which allow the surface of the skin to be rendered hydrophobic or oleophobic. Although fluorinated compounds are highly effective, they have a number of limitations due to their high cost and negative impact on the environment.
Procedures are known for making decorative leather using a SiO ₂ powder of micrometric sizes and silver nanoparticles integrated into coating pigments [ US 20130078451 A1 ]. The decorative leather according to the invention has resistance to wearing, water and antibacterial properties.
Natural furs with antimicrobial properties were obtained through aqueous treatments with chemically synthesized silver nanoparticles dispersed in polyurethanes in aqueous solution [ RO 127655 B1 ]. Another patent [ RO127959 B1 ] presents the self-cleaning and fungi resistance properties of the surface of leather or sheep fur treated with base and fixation film-forming composites with silver nanoparticles deposited on titanium dioxide and exposed to UV radiation.
Other patents show combinations of materials and nanomaterials with self-cleaning properties based on silanol, carbinol, metals and nanoparticles of silicon dioxide, titanium dioxide, nano silver or silver nanodioxide applied to the last layer of finishing of metal or polymer surfaces for components used in the automotive industry or for household purposes [ US 20090263586 A1 ]. The application of the composition is done by a combination of roller or knife deposition, or spraying techniques and has self-cleaning properties even in the dark.
According to the patent [ CN 102199396 A ], the presence of silver nano in concentrations of 0.1-0.3% provides antimicrobial and self-cleaning properties to tetraethoxysilane-based compositions and hydrophobizing polymers applied to decorative, sanitary and construction articles.
Patent [ CN 104017398 A ] describes an aqueous coating composition with self-cleaning properties for paints, made by modifying titanium nanodioxide by dispersing it in vinyl monomer, obtaining a core-shell polymer/TiO₂-latex structure which is then mixed with modified silicon dioxide, wetting agents and polymerization accelerators. Self-cleaning properties are attributed to the superhydrophilic surface generated by photocatalytic reactions under the influence of UV radiation and were evaluated by measuring the contact angle in dynamic conditions and decomposition of the methylene blue dye. The patent [ CN 103666246 A ] describes a composition for paints containing 0.1 to 0.2% titanium nano dioxide by means of which transparent, super-hydrophilic photocatalytic layers under the action of natural light are obtained, exhibiting self-cleaning properties for fatty stains.
The technical problem solved by the invention relates to natural leather having antimicrobial (antibacterial and antifungal) and self-cleaning properties (decomposition of Orange II dye, methylene blue, ball point pen stains) under the influence of visible light and a process for obtaining thereof using titanium dioxide nanoparticles doped with nitrogen and having electrochemical nano silver deposits on the surface.
Antimicrobial and self-cleaning leather has the following advantages:

It is multifunctional because it exhibits resistance to action of bacteria, fungi and self-cleaning under the influence of visible light;
Antimicrobial properties are required for footwear intended for persons with foot disorders, healthy persons, athletes; they provide antimicrobial properties for protective footwear, furniture upholstery, furniture upholstery, automotive or aircraft upholstery and for leather garments in direct contact with human skin, etc.;
Self-cleaning properties are necessary for white and light coloured leather articles which require more frequent maintenance treatments (chemical cleaning, refinishing) than for medium- and dark-colored items;
Self-cleaning properties increase the durability of leather goods and consumer comfort, reduce pollution by cleaning and reconditioning solvents;
Nanomaterials and quantities used for leather processing do not show cytotoxicity, according to human skin and lung cell tests (HaCaT keratinocyte line and A549 lung epithelial cell line);
It has been established that the nanoparticles used do not produce cytotoxicity for skin cells for concentrations up to 800 µg/ml and for lung cells up to 1000 µg/ml, which ensures a wide range of safe applications;
Leather tests regarding dry and wet rubbing as well as perspiration resistance, and SEM-EDX microscopy indicated good nanoparticle anchorage and a leachate of up to 40% and in concentrations below the cytotoxicity limit;
Leather processing ensures the immersion of nanoparticles into polymeric composites which are then fixed with nitrocellulose lacquers and thus do not come in direct contact with the human skin;

The antimicrobial and self-cleaning leather is made using titanium dioxide nanoparticles doped with nitrogen and having electrochemical deposits of 1.6% nanosilver on the surface. Nanosilver electrodeposition on the surface of nitrogen-doped titanium dioxide provides an increase in absorbance by 240% and a shift of nitrogen-doped titanium dioxide adsorption in the visible field with superior antimicrobial and self-cleaning effects compared to non-doped titanium dioxide nanoparticles, or doped with smaller quantities of nanoasilver. The size of nitrogen-doped titanium dioxide nanoparticles with 1,6% silver nanoparticle electrodeposition is 30 nm (according to TEM measurements), they have spherical shape (according to SEM-EDX analyzes) and form stable aqueous dispersions (Zeta potential of - 47.4 mV), with an average size of 50 nm.
The antimicrobial and self-cleaning leather is made by covering the leather surface by conventional spray-coating with flm-forming composites containing nitrogen-doped titanium dioxide nanoparticles with 1.6% nano silver electrodeposition in a concentration of 0.01-8 g/L of the base finishing composite volume. Titanium dioxide nano particles doped with nitrogen and 1,6% nano silver electrodeposition are obtained using the electrochemical method [ RO 125498 B1 ], by the anodic solubilization of some Ag electrodes dispersed in nitrogen-doped titanium dioxide nanoparticles, with particle size of 20 nm. The photocatalytic properties of nitrogen-doped titanium dioxide nanoparticles with nano silver deposits were verified by interacting with Orange II (C₁₆H₁₁N₂NaO₄S) dye solutions and visible light exposure for 30 minutes and recording UV-Vis spectra (λ max = 483 nm).

The self-cleaning properties were evaluated by staining the surface of leather finished with nitrogen-doped titanium dioxide nanoparticles and nano silver deposits with organic stains represented by methylene blue (C₁₆H₁₈ClN₃S·3H₂O), Orange II (C₁₆H₁₁N₂NaO₄S) and ball point pen and by exposure to visible light with a 500W halogen lamp, according to the literature procedures. As a reference, surfaces of finished leather without nano particles were exposed in identical conditions. The results are shown in Table 1 and show that in visible light self-cleaning occurs under the influence of visible light compared to control samples without nanoparticles, which is an important advantage for consumers.

Table 1 - Self-cleaning surface of leather treated with titanium dioxide nanoparticles doped with nitrogen and electroplating of 1.6% nano silver and exposed to visible light, compared to untreated leather

Initially stained with ball point pen, methylene blue and Orange II dye	After 70 hours of exposure to visible light
Leather surfaces finished with titanium dioxide nano particles doped with nitrogen and depositions of 1.6% nano silver

Leather surfaces finished without nanoparticles

Leather surface resistance to bacteria and fungi was assessed by sensitivity testing (EN ISO 20645) of Escherichia coli ATCC 2592, Escherichia coli ATCC and by the method of absorption (ISO 20743) by direct inoculation with Candida albicans ATCC 26790 and Candida albicans 1760. Reduction of the viable colonies of fungi was 100%, indicating a sterilization effect, while the surface area of bacteria medium in contact with the nanoparticle-treated leather was clear, showing sensitivity to the tested bacteria.
The process for making bovine leather with antimicrobial and self-cleaning properties consists in the integration of nitrogen-doped titanium dioxide nanoparticles with nano silver deposition in the base finishing composite containing acrylic binders, pigment paste and water by dispersing them through mechanical stirring and ultrasounds in the presence of sodium polyacrylate. The application of the coating layers is done in a classical manner, by hand, by spraying, or in the automatic finishing cabin, in successive layers, with intermediate drying, ironing at temperature and pressure, forming the base film and final coating prior to fixing the base coat, with layers of nitrocellulose lacquer, which finally polymerize by ironing.
The advantages of the antimicrobial and self-cleaning leather-making process are as follows:

It is a simple and efficient process that does not require extra operations compared to the classic process and does not require the use of organic biocides or special film-forming polymers;
Small amounts of nano material are used, providing multifunctionality and durability to the leather surface properties;
The method used does not rigidize the surface and does not limit the use for various types of leather, from rigid to soft ones;
The antimicrobial and self-cleaning properties by photocatalytic effects under the action of visible light increase the functionality of leather items and further protect the users of leather items.

Following is an example of making leather with antimicrobial and self-cleaning properties under the influence of visible light and 1 example of making control leather.

Example 1

Bovine or sheep leather tanned with basic chromium salts or ecologically tanned (with glutaric aldehyde tanning agents and syntans) and retanned using the classic method (with chromium salts and synthetic tanning agents) is finished with polymeric composites based on compact acrylic binders and pigment pastes additivated with antimicrobial and photocatalytic nanoparticles, which constitute the base coat and then fixed with nitrocellulose lacquers, according to the procedure described below. The preparation of the base coat containing nitrogen-doped titanium dioxide nanoparticles with 1.6% nano silver deposits, with an average particle size of 30 nm, is achieved by mixing a quantity of 0.01-8 g/L nanoparticles with 0.001-8 g/L sodium polyacrylate, 110 g/L pigment paste, 250 g/L acrylic binder and water up to 1 L followed by 30 minutes of mechanical stirring and 5 minutes of ultrasonic stirring at 50 Hz. The base finishing consists in applying the basic composite by spraying and intermediate drying of 2 layers, followed by ironing at 100°C and pressure of 120 kgf/cm². Then 2 layers of base finish are applied with intermediate and final free drying. Two final sealing layers are made by spraying a nitrocellulose lacquer in a concentration of 850 g/L with intermediate drying between layers and ironing at 110°C and 120 kgf/cm².

Example 2

Bovine or sheep leather tanned with basic chromium salts or ecologically tanned (with glutaric aldehyde tanning agents and syntans) and retanned using the classic method (with chromium salts and synthetic tanning agents) is finished with polymeric composites based on compact acrylic binders and pigment pastes, which constitute the base coat and then fixed with nitrocellulose lacquers, according to the procedure described below. The base coat is made by mixing the same amount of sodium polyacrylate as in Example 1, 110 g/L pigment paste, water to 1L and 250 g/L acrylic binder. The base finishing consists in applying the basic composite by spraying and intermediate drying of 2 layers, followed by ironing at 100°C and pressure of 120 kgf/cm². Then 2 layers of base finish are applied with intermediate and final free drying. Two final sealing layers are made by spraying a nitrocellulose lacquer in a concentration of 850 g/L with intermediate drying between layers and ironing at 110°C and 120 kgf/cm².

Claims

Bovine or sheep leather with antimicrobial and self-cleaning properties, characterized by the fact that the leather surface is coated with 0.01-8 g/L of nitrogen-doped titanium dioxide nanoparticles with 1.6% nano silver deposits with the average particle size of 30 nm, with low cytotoxicity, and exhibiting properties of photocatalytic decomposition of organic dirt under the influence of visible light, and is resistant to bacteria and fungi, compared to leather finished without nanoparticles.
Process for the manufacture of natural leather with antimicrobial and self-cleaning properties characterized by the fact that leather surface finishing consists of introducing 0.01-8 g/L nitrogen-doped titanium dioxide nanoparticles and 1.6% nano silver deposits with a mean particle size of 30 nm in the base coat by mechanical stirring for 10 minutes followed by 5 minutes of ultrasonication with 0.001-8 g/L sodium polyacrylate, 110 g/L pigment paste, 250 g/L acrylic binder and water up to 1 L, which is applied in 2 layers by spraying with intermediate drying and final ironing at 100°C and 120 kgf/cm², followed by 2 layers of base finish with intermediate and final free drying and fixing with 2 layers of nitrocellulose lacquer emulsion with a concentration of 850 g/L and final ironing at 110°C and 120 kgf/cm².