WO2012025899A1

WO2012025899A1 - Fragrance slow-release silica-based layer, ceramic tile and production process thereof

Info

Publication number: WO2012025899A1
Application number: PCT/IB2011/053734
Authority: WO
Inventors: Bruno Miguel MAGALHÃES JARRAIS; José Fernando OLIVEIRA DA SILVA; Cosme Neves Resende De Moura
Original assignee: Dominó - Indústrias Cerâmicas Sa
Priority date: 2010-08-26
Filing date: 2011-08-25
Publication date: 2012-03-01
Also published as: PT105270A; PT105270B

Abstract

Fragrance slow-release layer comprising porous silica matrix (2A) and hollow silica shells (2B) covalently linked to the porous silica matrix (2A), also respective production process comprising coating with a sol-gel formulation and firing, wherein said formulation comprises silicium alkoxide, water soluble polymer, hollow silica shells, a basic catalyst. Also, a fragrance slow-release ceramic tile comprising said layer, composed of a ceramic body (1A) and a glaze layer (1 B), covalently linked with the fragrance slow-release layer. The fragrance slow-release layer comprises adsorbed fragrance and therefore, is useful for delivering perfumes or scents.

Description

D E S C R I P T I O N

"FRAGRANCE SLOW-RELEASE SILICA-BASED LAYER, CERAMIC TILE

AND PRODUCTION PROCESS THEREOF"

Technical field

The present invention relates to a fragrance slow-release silica-based layer, ceramic tile and production process thereof.

Summary

The present invention describes a fragrance slow-release layer (2) comprising a porous silica matrix (2A) and hollow silica shells (2B) covalently linked to the porous silica matrix (2A).

In a preferred embodiment the hollow silica shells (2B) have a diameter between 0,65 - 2,0 μιη and a specific surface area between 300 - 500 m2/g.

In a preferred embodiment the porous silica matrix (2A) has porosity between 30 - 70 %.

In a preferred embodiment the layer (2) thickness is between 10 - 50 μιη. The present invention also describes a production process of a fragrance slow- release layer (2) comprising coating with a sol-gel formulation and firing said coating, wherein said formulation comprises silicium alkoxide, water soluble polymer, hollow silica shells, a basic catalyst.

In a preferred embodiment the formulation further comprises ethylene glycol.

In a preferred embodiment the silicium alkoxide is selected from tetraethylortosilicate (TEOS), or tetramethylortosilicate (TMOS), or mixtures thereof.

In a preferred embodiment the basic catalyst is selected from ammonium hydroxide, or triethanolamine, or mixtures thereof.

In a preferred embodiment the water soluble polymer is selected from polyvinyl alcohol (PVA), polyacrylamide, or polyacrylic acid, or mixtures thereof.

In a preferred embodiment the formulation is obtained by a first part, which is obtained by: using 25 mL of an aqueous solution of PVA with a concentration of 5 - 15% wt, preferably M ~ 30000-70000, mixing with 50 - 150 mg of hollow silica shells, stirring, preferably sonically for 1 hour, 3 times within each 7 hours of stirring, up to 21 hours; and by a second part, which is obtained by: using 30 - 40 mL of an aqueous solution of silicium alkoxide, preferably 3 - 6 mL of silicium alkoxide in 18 - 36 mL of water, mixing 1 - 4 mL of basic catalyst, stirring for a period of time; and by mixing and stirring the first and second parts, wherein all said amounts are scalable to the final quantity of formulation needed.

In a preferred embodiment the firing of the coating is at 480-650 °C and up to three hours.

The present invention also describes a fragrance slow-release ceramic tile (1 ) comprising, as an outer layer, any fragrance slow-release layer (2) of the above described, wherein the fragrance slow-release layer (2) is covalently linked to the ceramic tile (1 ).

In a preferred embodiment the ceramic tile (1 ) comprises a ceramic body (1A) and a glaze layer (1 B), and wherein the fragrance slow-release layer (2) is covalently linked to the glaze layer (1 B).

In a preferred embodiment the fragrance slow-release ceramic tile (1 ) further comprises adsorbed fragrance in said fragrance slow-release layer (2).

Background Art

One of objectives is generically to provide fragrance, or aroma, slow-release ceramic tiles enabling them to release fragrances over large periods of time. In the field of slow release technologies, one must first distinguish between the technologies that use solutions inside an equipment or system, generally a diffuser, that promotes the evaporation of the fragrance containing solution through heating, and all the other technologies that do not use heating, but rather physical entrapment.

It is on the later technology that the background art here described here after will focus, as the present invention is also based on the same phenomenon. Products having the ability of releasing substances progressively in time have gained huge importance in the last few years, in the fields of medicine, agriculture and fragrance delivery. With the boost on research focused on materials having micro and nanostructures, much new products have been created. Patents WO 2010/053337, WO 2009/077732, WO 2008/149320, WO2002/066010, WO 2001/010414, and the like, relate to particle systems that can deliver drugs or bioactive molecules progressively. Patents WO 2008/076538, WO 2007/025462, WO 2007/024753, WO 2007/022732, WO 2004/004453, and the like, relate to fertilizer delivery systems, mainly constituted by polymeric materials with an entrapped component to be delivered to the soil. As for fragrance delivery, patents WO 2007/022168, WO 2005/018795, WO 2004/067584, WO 2004/034819, WO 2001/06231 1 , WO 1999/008721 , WO 1998/023149, WO 2009/108051 , WO 2003/076175, WO 2004/098555, and the like, describe different sorts of delivery systems, namely particle systems, like organic microspheres with fragrances encapsulated, multilayered polymeric films, polymeric bottles, porous agglomerations, and the like. The basis on the uptake and slow release on these systems are the capillarity forces between the porous matrices that constitute these systems and the liquid/solution containing the fragrance.

The present invention addresses the issues in these documents, providing a longer-lasting and/or alternative means for providing the slow-release of fragrance.

Disclosure of the Invention

The present invention relates to a fragrance slow-release ceramic tile and production process thereof.

This invention relates to multi-fired ceramic tiles having fragrance slow release properties and their production method thereof. The aroma slow release multi- fired ceramic tiles here described have a specific layer composition on their outer surface that enables them to release fragrances over large periods of time. As such, what is described in the present invention is a multi-fired ceramic tile having on its outer surface, a porous silica matrix, which on its turn, has incorporated micro-sized hollow silica shells and the method for the continuous production of these ceramic tiles comprising the entire production cycle, starting with the raw materials preparation, followed by wet milling and spray drying, pressing and drying of the green body, firing with glazing (single or double), and additional heat treatment.

The present invention describes a multi-fired ceramic tiles having fragrance slow release properties, which are to be used indoors, providing a pleasant odor atmosphere during long periods of time. The fragrance itself is incorporated onto the ceramic tiles, by simply spraying and/cleaning their outer surface with any perfumed solution, which can be a specific fragrance solution or a commercially available perfumed cleaning product.

The present invention also relates to the continuous manufacturing of double or triple fired ceramic tiles having these fragrance slow release properties, namely the specific layer composition on their outer surface that enables them to release fragrances over large periods of time. The ceramic tile product described in this invention is a double or triple fired ceramic tile having fragrance slow release properties. The ceramic tile is composed of the body, the glazing, and an outer composite layer. In Figure 1 , it is depicted the body and glazing (1 ) and the composite layer (2).

Figure 2 depicts the fragrance slow release multi-fired ceramic tile cross-section scheme with the following elements: (1A) ceramic body, (1 B) glaze, (2A) silica matrix and (2B) hollow silica shell. The ceramic body is composed of mainly clays, feldspars, sands, carbonates and kaolins. The nature of the glaze coating is essentially vitreous, although in many cases the glaze structure contains crystalline elements. The glaze, just like the ceramic body, is made up of a series of inorganic raw materials. The major glaze component is silica (glass former), as well as other elements that act as fluxes (alkalis, alkaline earths, boron, zinc, etc.), opacifiers (zirconium, titanium, etc.), and as coloring agents (iron, chromium, cobalt, manganese, etc.). A wide variety of glazes are formulated depending on the type of product, firing temperature, and the desired effects and properties of the finished product. The hollow silica shells are available commercially from a number of suppliers and its existence is known of the skilled person. The shape may vary such that the circular or spherical representation in the drawings is merely for illustrative purposes. The skilled person will recognize that a full enclosure of the shell is not necessary, as long as a significantly void portion of space is preserved during manufacture of the silica-based layer.

The outer layer is composed of a porous silica matrix [Figure 2], preferably having a thickness range of 10 - 50 μιη, and an independently preferable porosity of 30 - 70 %. Within this porous matrix, there are hollow silica shells having a preferable diameter range of 0,65 - 2,0 μιη and a independently preferable specific surface area of 300 - 500 m²/g. These parameters are preferred ranges and the skilled person will be easily able to find other values that still represent the invention inasmuch as the thickness and porosity of the layer allow for sufficient fragrance to pass it, and as the number and dimension of the shells allow for sufficient fragrance to be accumulated.

These silica shells are covalently linked to the porous silica matrix , which on its turn, is preferably covalently linked to its substrate, preferably a ceramic tile, preferably a glazed ceramic tile, both through Si-O-Si bonds. The resulting high specific area matrix, together with the inherent hollow silica shells' porosity, will be responsible for the great adsorption capacity of the fragrance molecules, and consequently, for its slow release in time. The manufacturing process of the preferred embodiment of a slow release multi-fired ceramic tile consists of a series of successive stages, which can be summarized as follows: raw materials preparation, wet milling and spray drying, pressing and drying of the green body, firing with glazing (single or double), and additional heat treatment. The product to be made is glazed, whether single fire, double fire or third fire is involved, before an additional heat treatment stage, where the outer composite layer is produced and applied. As will be easily understood by the skilled person, this layer may be applied onto different substrates, other than a glazed ceramic tile, such that of the following steps , the additional heat treatment stage, where the outer composite layer is produced and applied, can in fact be used independently of the other previous stages.

The process starts by selecting the raw materials required for the body composition, which are mainly clays, feldspars, sands, carbonates and kaolins. The raw materials are generally used as-mined or after some minor treatment. As natural raw materials are involved, preliminary homogenisation is required in most cases to ensure consistent characteristics.

After a first mixing of the body components, the mixture is wet milled (continuous or batch ball mills). In the resulting milled material all particles are smaller than 200 microns. The raw materials can be wholly or partially fed into the ball mills. Part of the water contained in the resulting suspension is removed by spray drying to obtain a product with the required moisture for next process stage. In this drying process, the fine drops of sprayed suspension come into contact with hot air to yield a solid with low water content. The spray drying process reduces the water content to 0,045-0,080 kg water/kg dry solid. The spray-drying operation is as follows (Figure 4). The slip from the milling facility storage tanks, with a 60-70 % solids content and appropriate viscosity (around 1000 cp), is fed into the spray dryer by reciprocating pumps. The slip is sprayed as a fine mist, which dries on coming into contact with the hot gas stream. The gases come from a conventional air-natural gas burner or are exhaust gases from a cogeneration turbine. The granulate, with a moisture content of between 5,0% and 8,0%, is discharged onto a conveyor belt and conveyed to the silos for subsequent pressing. The stream of gases used to dry the slip and produce the powder is exhausted through the top of the spray dryer.

Forming takes place by mechanically compressing the paste (at 5,0-8,0% moisture content) in the die with hydraulic presses. In pressing, the oil-hydraulic press system drives the rams into the powder bed in the die. After forming, the tile body is dried to reduce the moisture content (< 0,5 %) to appropriately low levels for the glazing stage. In the dryers, heat is transferred by convection from hot gases to the tile surface, and also slightly by radiation from these gases and from the dryer walls to the tile surface. Therefore, during the drying of ceramic bodies, a simultaneous and consecutive displacement of the water takes place through the wet solid and the gas. The air used must be sufficiently dry and hot, because it not only serves to remove the water from the solid but also to provide energy in the form of heat to evaporate the water. The bodies are dried in vertical or horizontal dryers. After shaping, the bodies are placed in the dryer where they face a hot gas countercurrent. The hot gases come from an air- natural gas burner or from the kiln cooling stack. The main heat transfer mechanism between the air and the bodies is convection. In the vertical dryers, the pieces are fed into baskets consisting of several decks of rollers. The groups of baskets move upward through the dryer, where they come into contact with the hot gases. The temperature in this type of dryer is normally less than 200 °C and the drying cycles range from 35-50 minutes. The horizontal dryers are designed like the rollers kilns. The items are fed onto different decks inside the dryer, and conveyed horizontally on the rollers. Burners located on the sides of the kiln produce the hot drying air countercurrent. The maximum temperature in these types of facilities is usually higher than in the vertical dryers (around 350 °C) and the drying cycles are shorter, between 15 and 25 minutes. Glazing involves applying one or more coats of glaze with a total thickness of 75-500 microns onto the tile proper surface by different methods. Glazing is done to provide the fired product with a series of technical and esthetical properties such as impermeability, cleanability, gloss, colour, surface texture, and chemical and mechanical resistance. The nature of the resulting glaze coating is essentially vitreous, although in many cases the glaze structure contains crystalline elements. The glaze, just like the ceramic body, is made up of a series of inorganic raw materials. The major glaze component is silica (glass former), as well as other elements that act as fluxes (alkalis, alkaline earths, boron, zinc, etc.), opacifiers (zirconium, titanium, etc.), and as coloring agents (iron, chromium, cobalt, manganese, etc.). A wide variety of glazes are formulated depending on the type of product, firing temperature, and the desired effects and properties of the finished product. In this process, raw materials of a glassy nature (frits) are used. These are prepared from the same crystalline materials that have previously undergone heat treatment at high temperature. In the glaze preparation process, the frit and additives are ground in alumina ball mills until a preset reject is obtained. The conditions of the aqueous suspension are then adjusted. Suspension characteristics will depend on the application method to be used. Ceramic tile glazing is done continuously, by waterfall glazing or spraying, screen or roller printing and inkjet printing technology. In the firing operation, the tiles are subjected to a thermal cycle during which a series of reactions take place in the piece, generating changes in the microstructure and providing the desired final properties. Ceramic materials can undergo one, two or more firings and is done in single-deck roller kilns. An additional drying stage after glazing occurs just before the material is placed in the kiln, to reduce tile water moisture content to less than 0,1 %. In the single- deck roller kilns, the tiles travel over rollers and the heat required for firing is provided by natural gas-air burners fitted at the sides of the kiln. The thermal cycle must be adapted according to the tile to be made. Schedules can be less than 40 minutes, but for large sizes it can be used at least 80 minutes cycles. The temperatures can rise up to 1200 °C.

The additional heat treatment stage, where the outer composite layer is produced and applied, comprises a spray coating of a sol-gel formulation containing at least one silicium alkoxide, such as tetraethylortosilicate (TEOS), tetramethylortosilicate (TMOS) and the like, one water soluble polymer, such as polyvinyl alcohol (PVA), polyacrylamide, polyacrylic acid and the like, optionally ethylene glycol, and hollow silica shells and one basic catalyst, such as ammonium hydroxide, triethanolamine and the like, on the outer surface of the tiles. The mixture is prepared as described hereafter (quantities are scalable and will be used here as an example).

Onto 25 mL of an aqueous solution of PVA (M ~ 30000-70000) with a concentration of 5 - 15% wt, is added 50 - 150 mg of hollow silica shells, and preferably this mixture is allowed to stir for up to 21 hours, being sonicated with an ultrasonic bath (50/60 Hz, 200 W) for 1 hour 3 times within each 7 hours of stirring.

Afterwards, onto 30 - 40 mL of an aqueous solution of the silicium alkoxide (preferably 3 - 6 mL of the silicium alkoxide in 18 - 36 mL of water) is added 1 - 4 mL of basic catalyst, and this mixture is allowed to stir for preferably up to 30 minutes.

Then, the first mixture is added to the second and the final mixture is allowed to stir for preferably up to 1 hour.

The glazed ceramic tiles are conducted trough rolls [Figure 6, (3)] and coated, preferably sprayed, with preferably ethanol through a compressed air nozzle (4) and are cleaned with a cleaning apparatus (5) and dried with compressed air (6). The previous described mixture is then applied preferably through a series of compressed air nozzles (7), at a distance of preferably at least 50 centimeters and at a preferably maximum air pressure of 8 bar. The ceramic tiles then enter a kiln (8) and undergo a second firing stage at a temperature range of preferably 480-650 °C, preferably for up to three hours. The skilled person will easily appreciate too high a temperature will glaze the layer and will impede the required porous structure, while too low a temperature will not cure the formulation into the desired layer. Otherwise, firing temperatures and times are linked (inversely) as known in the art, as longer times are needed for lower temperatures in order to reach the desired result.

The resulting products consist of double or triple fired ceramic tile having fragrance slow release properties.

As will be clear to the skilled person, alternatively non-glazed ceramic tiles may be used, or even alternatively other substrates. The addition of ethylene glycol is beneficial in the stability of the mixture in handling and application.

The provision of the hollow silica shells is not only useful for containing fragrances, but they also provide resilience and facilitate the uniform formation of the porous film. Brief Description of Drawings

The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of invention.

Figure 1 : Schematic representation of a preferred embodiment of a slow release multi-fired ceramic tile where:

(1 ) represents the body and glazing of the ceramic tile, and

(2) represents the outer composite layer.

Figure 2: Schematic representation of a preferred embodiment, with a cross- section view of a fragrance slow release multi-fired ceramic tile where:

(1 A) represents the body of the ceramic tile,

(1 B) represents the glaze of the ceramic tile,

(2A) represents a silica matrix, and

(2B) represents a hollow silica shell.

Figure 3: Schematic representation of firing cycle temperatures, showing preheating and cooling phases.

Figure 4: Schematic representation of a preferred setup for additional heat treatment and outer composite layer application, where: (3) represents rolls,

(4) represents a compressed air nozzle,

(5) represents cleaning apparatus,

(6) represents compressed air,

(7) represents compressed air nozzles for mixture application, and

(8) represents a kiln.

The following claims set out particular embodiments of the invention.

Claims

C L A I M S

1. Fragrance slow-release layer (2) comprising a porous silica matrix (2A) and hollow silica shells (2B) covalently linked to the porous silica matrix (2A).

2. Layer according to claim 1 wherein the hollow silica shells (2B) have a diameter between 0,65 - 2,0 μιη and a specific surface area between 300 - 500 m2/g.

3. Layer according to claim any previous claim wherein the porous silica matrix (2A) has porosity between 30 - 70 %.

4. Layer according to claim any previous claim wherein the layer (2) thickness is between 10 - 50 μιη.

5. Production process of fragrance slow-release layer (2) comprising coating with a sol-gel formulation and firing said coating, wherein said formulation comprises:

- silicium alkoxide,

- water soluble polymer,

hollow silica shells,

- a basic catalyst.

6. Process according to claim 5 wherein the formulation further comprises ethylene glycol.

7. Process according to any claim 5 - 6 wherein the silicium alkoxide is selected from tetraethylortosilicate (TEOS), or tetramethylortosilicate (TMOS), or mixtures thereof.

8. Process according to any claim 5 - 7 wherein the basic catalyst is selected from ammonium hydroxide, or triethanolamine, or mixtures thereof.

9. Process according to any claim 5 - 8 wherein the water soluble polymer is selected from polyvinyl alcohol (PVA), polyacrylamide, or polyacrylic acid, or mixtures thereof.

10. Process according to any claim 5 - 9 wherein the formulation is obtained by a first part, which is obtained by:

- using 25 mL of an aqueous solution of PVA with a concentration of 5 - 15% wt, preferably M ~ 30000-70000,

- mixing with 50 - 150 mg of hollow silica shells,

- stirring, preferably sonically for 1 hour, 3 times within each 7 hours of stirring, up to 21 hours;

and by a second part, which is obtained by: - using 30 - 40 mL of an aqueous solution of silicium alkoxide, preferably 3 - 6 mL of silicium alkoxide in 18 - 36 mL of water,

- mixing 1 - 4 mL of basic catalyst,

- stirring for a period of time;

and by mixing and stirring the first and second parts, wherein all said amounts are scalable to the final quantity of formulation needed.

1 1. Process according to any claim 5 - 10 wherein the firing of the coating is at 480-650 °C and up to three hours.

12. Fragrance slow-release layer (2) obtainable by the process according to any claim 5 - 1 1.

13. Fragrance slow-release ceramic tile (1 ) comprising, as an outer layer, the fragrance slow-release layer (2) according to any claim 1 - 4, 12, wherein the fragrance slow-release layer (2) is covalently linked to the ceramic tile (1 )-

14. Fragrance slow-release ceramic tile (1 ) according to the previous claim, wherein the ceramic tile (1 ) comprises a ceramic body (1A) and a glaze layer (1 B), and wherein the fragrance slow-release layer (2) is covalently linked to the glaze layer (1 B).

15. Fragrance slow-release ceramic tile (1 ) according to the previous claim further comprising adsorbed fragrance in said fragrance slow-release layer (2).