IT202200021984A1 - ALGINATE PAINT/VARNISH AND PROCEDURE FOR ITS PREPARATION - Google Patents

Description

ALGINATE-BASED PAINT/VARNISH AND PROCEDURE FOR ITS PREPARATION

DESCRIPTION

FIELD OF INVENTION

The present invention relates to a paint/varnish, in particular it relates to a non-toxic and ecological paint/varnish, based on alginate, capable of being applied on different surfaces (wood, wall, metal, plasterboard, fabrics, leather, etc.). The present invention also relates to a low environmental impact method for the preparation of said paint/varnish.

STATE OF THE PRIOR TECHNOLOGY

Paints are heterogeneous systems, generally made up of the following components: binders (resins), which provide the product with film-forming properties, so as to allow the paint to adhere to the substrate and which give them their particular chemical, physical and mechanical properties. Solvents, which allow the viscosity of the finished product to be manipulated, so as to spread it uniformly. Charges (fillers), which increase the covering power of the product. Pigments/dyes (used to give the paint a colour) and finally additives, such as thickeners, wetting and dispersing agents, preservatives, anti-mold, anti-foam agents, emulsifiers, pH stabilizers and more.

The majority of paints and varnishes on the market are currently products containing petroleum-derived resins or synthetic resins. In both cases, to obtain the starting resins, it is necessary to use industrial processes that are sometimes particularly energy-intensive and that involve the formation of mostly polluting by-products, which are often not easy to dispose of. The binders, which represent approximately 25% of the paint, can be, for example, polymers derived from acrylate, isocyanates or alkyd resins. The paints themselves, after their life cycle, can be polluting and difficult to dispose of, and there can also be substances harmful to the health of those who apply the paints.

Among the other basic components of paints, mentioned above, there are solvents. The solvents normally used in paints often belong to the category of Volatile Organic Compounds (VOCs). VOCs are released from paint not only during the work, but also during drying by evaporation into the ambient air and sometimes, albeit in smaller quantities, even after. Their release into the surrounding environment lasts for weeks or for several months, contributing significantly to the formation of domestic pollution. VOCs can cause a wide range of effects, starting from a general sensory discomfort up to serious alterations in the state of health. Especially in indoor environments, where adequate ventilation is rarely present, it is possible to reach high concentrations of VOCs, causing stress on the central nervous system. Some VOCs are recognized as carcinogenic to humans (benzene, carbon tetrachloride, formaldehyde). Some solvents cause dry mouth and migraines.

For these reasons, the European Directive 2004/42/CE, implemented in Italy through Legislative Decree 161/2006, establishes the permitted quantities of VOCs in products such as paints, varnishes, stuccos, cleaning products and finishing products.

In addition to organic-based paints and varnishes, water-based products are also becoming increasingly important. However, these water-based paints/varnishes/enamels also currently contain both synthetic polymers and VOCs, although in lower quantities than in purely organic-based paints/varnishes/enamels.

Currently, a real transition is underway in this sector, as consumers are increasingly informed about their environmental footprint and the effects of products on their health, so the demand for ecological and non-toxic products, possibly also producible without excessive pollution, is constantly increasing.

However, most of the products on the market do not yet reflect consumer demand and are therefore unable to offer products, in this case paints/varnishes/enamels, that are non-toxic, easy to use in the field and with a preparation process with low or zero environmental impact and without particular disposal difficulties.

Among the non-toxic alternatives to classic resins, alginic acid derivatives have attracted moderate attention in the past and in other sectors, in particular, alginic salts, isolated from a wide range of brown algae. From a chemical point of view, the structure of alginic acid is that of a polysaccharide comprising, roughly, D-mannuronic acid and L-guluronic acid. Alginate is commercially available both as sodium and calcium salts.

An early example of the use of alginate in the construction industry is US 3311 483, which describes a process for treating cellulosic material with calcium and iron salts to obtain a material suitable for the production of concrete. By mixing this material with cement, a concrete coated with alginate was produced, making it fireproof. The intrinsic quality of alginate to be fireproof is also used in WO 2010/135 494 A1, which describes a paint preparation based on alginate.

More precisely, WO 2010/135 494 A1 describes the preparation of an aqueous alginate suspension. More precisely, in a preferred embodiment, sodium alginate is suspended in water and beta-carotene and cochineal are subsequently added as colorants. Finally, the suspension is deposited on the wall to be painted and the deposited layer is sprayed with an aqueous calcium chloride solution, preferably 23%. Although this solution provides a paint with a high level of fire resistance, it has limitations, such as the requirement to carry out the calcium solution spraying process every time the alginate preparation is used, thus extending the working hours on site and requiring more complex equipment for complete painting. Furthermore, it is possible that the work may end up being inhomogeneous and unsuitably finished if the sprayer malfunctions.

It is necessary, as taught by WO 2010/135 494 A1, once the suspension has been deposited on the wall, to introduce a source of calcium in order to prepare calcium alginate in situ, a polymer which, normally, being neither hydrophilic nor lipophilic, is problematic to use.

Although calcium alginate is, as mentioned, generally difficult to solubilize, it has also found applications in clinical research, where it is used for the programmed delivery of drugs, or drug delivery.

Another intrinsic characteristic of alginate is its compatibility with humans. Being non-toxic, it has also been studied in the field of tissue engineering. In Biomaterials 22 (2001) 511-521 Ma et al. investigate the possible use of alginate-based gels as scaffold tissues, i.e. tissues suitable for grafting cells to provide adequate structural support during their growth. Ma et al. disclose - in a completely different field from that of paints and varnishes - a new method of controlled gelation, more precisely the preparation of a suspension of calcium carbonate is taught, to which another suspension containing sodium alginate is added. Finally, the gelation is started by adding a freshly prepared aqueous solution of glucono-?-lactone (GDL). Subsequently, the gelation is carried out in a room with high humidity levels for 48 hours. Following this preparation, the gelation is carried out in a room with high humidity levels for 48 hours. It is possible to produce and subsequently cut different solid forms of alginate-based gels. Ma et al. disclose a gelation, a type of complete cross-linking, achieving the formation of a large polymer network, which translates, from the macroscopic point of view, into a solid and hard final state.

FR 2998 576 B1 discloses paints based on algae extracts, where casein is introduced into the final product as a preservative.

FR 3106 593 B1 discloses a paint based on algae extracts and St. James's shell powder.

PROBLEM AND SOLUTION

The problem underlying the invention is to propose a water-based, non-toxic paint that can be applied to different substrates such as, for example, wood, walls, metal, plasterboard, fabrics, leather, which overcomes the aforementioned drawbacks and allows for long-term conservation, with convenient storage and transport methods compared to the prior art, by replacing traditional binders with a natural binder. Another purpose of the present invention is to propose a low environmental impact method for the preparation of the paint. These purposes are achieved, according to a first aspect, through an ecological paint, having a composition containing alginate, characterized by what said alginate is present in a gel, where the alginate is partially cross-linked and coupled to a cation and by what also contains one or more alcohols and/or lecithin, a lactone and an aqueous or oily solvent.

According to a second aspect, the present invention refers to a process for the preparation of an ecological paint, characterized by which it provides the following steps:

suspending an alkaline alginate in an aqueous solvent, heating to a temperature between 50?C and 80?C, adding alcohol and/or lecithin, adding dropwise a freshly prepared solution of a metal salt and a lactone; stirring the mixture; removing the heat source.

The subordinate claims describe preferential features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention are however more clearly evident from the following detailed description of a preferred embodiment, given purely by way of example and not of limitation and illustrated in the attached drawings, in which:

fig. 1 represents an embodiment of the present invention, where the paint is ready for use;

Figs. 2-3 represent an embodiment of the present invention, where the paint has a degree of hydration useful for short/medium term conservation; and

Figs. 4-5 represent an embodiment of the present invention, in which the paint has a degree of hydration useful for medium/long-term conservation.

DETAILED DESCRIPTION OF THE PREFERRED FORM OF IMPLEMENTATION

As set forth above, the present invention relates to an ecological and non-toxic paint, having a composition containing a partially cross-linked alginate gel, coupled to a cation; one or more alditols and/or lecithin; a lactone and an aqueous or oily solvent.

Preferably, the alginate contained in the paint according to the invention is calcium alginate and acts as a binder. The one or more alditols contained in the paint act as mechanical property enhancers of said paint and, preferably, the added alditol is glycerol, which is readily available at a low price as a by-product in the production of soaps. In this context, the definition of mechanical property enhancer also includes the function of wetting and dispersing agent. The mechanical enhancer allows for better distribution of the particles in the dispersion and also acts as a modulator in the evaporation of the solvent, reducing the possibility of any cracks in the deposited paint, due to excessively rapid drying. Other embodiments of the present invention may, for example, have as an alditol instead of glycerol or in combination with it, sorbitol, mannitol, erythritol, or even easily available natural substances. As an alternative to the alditol or in addition to it, glycerol may be added to the alditol. it is possible to use a lecithin, such as soy lecithin.

As regards lactone, the paint preferably contains glucono-?-lactone (GDL). GDL is commonly used by various food industries as a food additive (with E number E575) as a seasoning, leavening and marinating agent. In the present invention, it plays the role of a cross-linking modulator and is the key ingredient, which allows the desired results to be achieved. The cross-linking process will be explained in detail later. Preferably, the cross-linking solvent is an aqueous solvent, preferably water is used as an aqueous solvent, preferably distilled water, but rainwater, sea water, drinking water, a water-ethanol mixture, a water-acetic acid mixture, etc. can also be used. The solvent not dedicated to cross-linking can be aqueous or oily; If drying oils are used as an oily solvent, preferably selected between boiled linseed oil and uncooked linseed oil, these drying oils also act as a co-binder (secondary binder).

As previously mentioned, the varnish preferably has a calcium alginate gel as a binder. The most important step in the process presented in this invention is a sol-gel transition. In general, a ''sol'' is defined as a colloidal dispersion of particles, which constitutes a liquid system having some properties close to those of a solid; said dispersions can generally be destabilized by the action of heat, by pH variations, by the addition of electrolytes, thus giving rise to a gel, a gelatinous system rich in liquid, but which has some properties of a solid. The sol-gel transition of the present invention occurs through a partial cross-linking reaction. In this document, an alginate gel is in fact described, where said alginate gel is defined as 'partially cross-linked' because, thanks to the process which will be explained in detail later, it is It is possible to modulate the degree of cross-linking, preventing total gelation of the paint and thus avoiding the formation of a dry, hard, solid or almost solid preparation, which would have little applicability in the field of paints. The phenomenon of total cross-linking and hardening of the alginate gel is evident in WO 2010/135 494 A1 and in Biomaterials 22 (2001) 511-521.

From the present invention, however, it is possible to obtain a paint ready for use or to package and rehydrate before application.

The paint according to the present invention may also include fillers, mostly natural inorganic substances, such as calcium carbonate. It may possibly contain pigments, also mostly inorganic and natural, such as titanium dioxide, zinc oxide. Any additives are also preferably of natural origin.

Another object of the present invention, as set forth above, is the process for preparing the varnish just described. The key step in the preparation is the synthesis of the binder for said varnish, namely a divalent cation alginate gel, preferably a partially cross-linked calcium alginate gel. Cross-linking generally induces the formation of ionic bonds between the different polymer chains, promoting a sol-gel transition. In the case of the present application, the divalent cations brought into solution interact with the polymer, coordinating the oxygen-containing functional groups (ethers, hydroxyls, carboxylic acids) on different alginate polymer chains, thereby promoting the formation of a three-dimensional network. In the inventive synthesis of the gel, unlike the prior art, an aqueous solution comprising GDL and calcium carbonate is added to a suspension containing sodium alginate. Ma et al., on the other hand, added a sodium alginate solution to a suspension containing calcium carbonate. 2+> ion.

The preparation of the paint, as anticipated in the preamble, has a low environmental impact, since the raw materials are obtained through non-energy-intensive processes that do not produce toxic or difficult-to-dispose by-products. For example, a typical industrial process for obtaining sodium alginate from the phylum Phaeophyceae includes steps such as drying, grinding, washing, acid/base treatment and precipitation. Other processes, easily scalable and even less energy-intensive, exploit the biosynthesis of two genera of bacteria: Pseudomonas and Azotobacter; alginic acid is in fact among the major components of the biofilms produced by these bacteria.

The preparation of the varnish of the present invention begins with an aqueous suspension of alkali metal alginate, preferably 0.1 to 2% by weight of sodium alginate in water is added, heating to a temperature of 50?C to 80?C, preferably about 65?C. An alkali metal alginate is used because it has excellent solubility, when compared to alginates of other cations and to alginic acid. Subsequently, one or more alcohols are added, preferably the amount added is about 0.1 to 1% by weight. Preferably, 0.3% by weight of alcohol is added, selected from glycerol, sorbitol and erythritol, more preferably glycerol is added which, as already stated, is easily available at low cost. The alcohol, as previously stated, enhances the properties of the varnish. mechanical properties of the finished product and in the preparation of the present invention is preferably added before the cross-linking process, in order to incorporate it into the partially cross-linked calcium alginate, in this way it can take on the role of plasticizer, decreasing the stiffness of the polymer film of the paint once dried. Subsequently, a freshly prepared solution of a metal salt and a lactone is added to the alginate hydrogel, drop by drop, while maintaining a constant temperature; preferably, the solution contains an amount of between 0.001 and 0.5% by weight of metal salt, where said salt is, preferably, calcium carbonate and said lactone is, preferably, glucono-?-lactone, a compound readily available in nature and which leaves no harmful by-products; said glucono-?-lactone is added at between 0.01 and 0.5% by weight; more preferably, approximately 0.09% by weight of GDL is added. GDL is the lactone that best allows for regulation of cross-linking. The addition of the solution containing the metal salt and lactone preferably occurs according to the method described above in order to maintain a constant concentration of said metal salt and lactone in the alkali metal alginate hydrogel, further regulating the cross-linking.

During the addition of said metal salt solution and a lactone, the alginate hydrogel is kept under constant stirring. Once the heat source has been removed and the compound has cooled, the secondary components of the preparation are added, i.e., rheology modifiers and thickeners, selected from cellulose, cellulose waste and clays, xanthan gum, polyurethanes and polyacrylates; mechanical enhancers, selected from glycerol, sorbitol and/or soy lecithin; fillers, selected from calcium carbonate, talc, micas and quartz powder; and a water repellency enhancer, a drying oil selected from cooked linseed oil and uncooked linseed oil and colorants/pigments selected from titanium dioxide, zinc oxide, chlorophylls, carotenoids, flavonoids, tannins, anthocyanins. Adding further volumes of an aqueous or oily solvent, chosen from water, distilled water, rainwater, a water-ethanol mixture, a water-acetic acid mixture, or even a drying oil, chosen from cooked linseed oil or uncooked linseed oil, allows for correct mixing in the finished product.

Some of the above-mentioned aqueous mixtures (e.g. water-ethanol or water-acetic acid) are particularly preferred in embodiments with high concentrations of colorants/pigments to achieve a low-viscosity paint embodiment.

The oil solvent is used in certain embodiments that provide an environmentally friendly paint that is particularly water resistant, for example, making the paint desirable on external substrates, in continuous contact with atmospheric agents.

Preferably, once all mixing has stopped, the degree of cross-linking achieved in this step of the process increases the viscosity of the formulation to the point that, if the degree of cross-linking is suitably high, the formulation is partially solid. By initially preparing aqueous solutions with smaller volumes of water and adding smaller quantities of water during the addition of the secondary components of the paint, it is in fact possible to obtain a paint similar to that shown in Figs.

4-5. The smaller amount of water in the "preservation" mode has some benefits, including a lower weight in shipping, the possible preservation in laminated or multi-layered cardboard and above all a lower or zero proliferation of bacteria, fungi, mold.

In Fig. 1 a paint is illustrated with a level of hydration such that it can be directly applied to different substrates such as, for example, wood, wall, metal, plasterboard, fabrics, leather and others. In Fig. 1 an embodiment of the present invention is depicted which can be defined, in this document, as "ready to use". The paint illustrated in Fig. 1 also comprises: cellulose, as a rheological modulator of the paint. Other embodiments could preferably contain, instead of cellulose, or cellulose waste, clays, xanthan gum polyurethanes and polyacrylates. The paint illustrated in Fig. 1 also comprises talc and calcium carbonate which, in this embodiment, is both the initial donor of metal ion with oxidation state <2+>, i.e. what starts the cross-linking process of the alginate, and a filler of the paint. There are other metal ion donors that allow the alginate to cross-link, for example, other alkaline earth metals, such as strontium, barium, or metals with the same oxidation state, but belonging to different groups, such as copper, zinc, cobalt and manganese. Instead of talc and an additional amount of calcium carbonate, other embodiments may contain micas, quartz powder and other minerals. As a colorant, in this particular embodiment, betanin was used, a natural glycoside extracted from beetroot that is used as a colorant in the food industry with the European coding code E162, making the paint pink; other natural pigments, organic and non-organic, can be used to modulate the color in order to achieve a wide range of colors. Some colorants/pigments include, for example, titanium dioxide, zinc oxide, chlorophylls, carotenoids, flavonoids, tannins, anthocyanins and others. The present invention uses natural dyes/pigments mainly for two reasons: the first is the environmental compatibility of said dyes/pigments, the second is the possibility of obtaining some of the above-mentioned dyes/pigments as waste from other processes in the food industry. The embodiment shown in Fig. 1 also comprises a water repellency enhancer, preferably comprising boiled linseed oil. A particular embodiment of the present invention, not shown, but included in Table I (sample 4) does not include any dyes/pigments and is therefore transparent.

Other embodiments of the present invention may contain other secondary additives, such as anti-molds, such as essential oils. Optionally, said essential oils may be chelated or encapsulated in specific supramolecular systems, for example, a guest/host system having an essential oil chelated or encapsulated in a cyclodextrin may be used. Other host systems may be metalorganic structures (MOF) or zeolites. Other embodiments may contain anti-foaming agents such as, for example, vegetable oils or glycols (silicone oils, paraffins, stearates), pH stabilizers such as sodium hydroxide, ammonium hydroxide and ammonia and finally emulsifiers.

Figs. 2-3 illustrate another embodiment of the present invention, in which the hydration level, intermediate, is that of a short/medium term preservation mode.

Figs.4-5 illustrate another embodiment of the present invention, in which the hydration level, low, is that of a medium/long-term conservation method.

None of the illustrated embodiments contain any preservatives; however, some embodiments may contain some preservatives, although alginate naturally prevents the growth of mold and bacteria.

The “preservative” execution forms illustrated in Figs. 2-5, in order to be used in the field, require that the operator rehydrates the paint with water, distilled or not, and mixes vigorously to obtain the “ready-to-use” paint mode, illustrated, as mentioned, in Fig. 1. At this point, unlike WO 2010/135 494 A1, where sodium alginate-based paint was used, it is not necessary to spray an aqueous solution containing Ca<2+> ions on the surfaces just painted with the paint. Instead, it is sufficient to spread the paint on a substrate in a known way and wait for it to dry, just like with a traditional paint. This is possible thanks to the only partial cross-linking of the alginate and the reactions with Ca<2+> ions in the preparation process.

The paint/varnish according to the present invention can be used on the most common substrates, such as wood, masonry, plasterboard, metal or fabrics. However, the use of a composition of this type allows its application without damage also on skin and mucous membranes.

In the following, for the sake of clarity, an example of preparation is described, which has a purely illustrative and non-limiting function.

PREPARATION EXAMPLE I

This example describes a preparation to obtain a white paint in the "ready-to-use" mode. 100 ml of distilled water are heated until it reaches a temperature of about 65?C; subsequently, 1.5 g of sodium alginate are added. The suspension is left under stirring until a homogeneous and transparent hydrogel is obtained. Subsequently, still under mechanical stirring, 0.5 g of glycerol are added.

Separately, an aqueous solution is prepared. 0.05 g of calcium carbonate and approximately 0.25 g of GDL are added to approximately 10 ml of water. The freshly prepared solution is vigorously stirred for 5 minutes. Subsequently, the GDL and calcium carbonate solution is added ?dropwise? to the initial hydrogel via a dropping funnel or similar apparatus.

At this point, as previously stated, the alginate begins to cross-link and the compound is homogenized using an electric mixer for a period of between 2 and 5 minutes, until said homogenization is complete. Once the heat source has been removed, the preparation is allowed to cool naturally, under mechanical stirring, to room temperature. At this point, all the secondary components are added consecutively and at the same temperature. According to this example, 20 g of cellulose and 38 g of calcium carbonate are added. 32 g of titanium dioxide and 10 g of cooked linseed oil are added. During said final additions, additional volumes of water are constantly added, until a total of 200 ml is added. It is clear that the present invention is able to overcome the problems encountered with respect to the prior art, allowing for easier transport and packaging. The present invention surpasses the known art of alginate-based paints also in terms of ease of use, allowing the operator - thanks to the particular preparation methods - to work using traditional and reliable techniques, having the opportunity to manage a non-toxic, low environmental impact, odorless product with excellent covering ability, which is washable and resistant to abrasion. In particular, the use of GDL does not allow the paint to be excessively hard to be used, either directly or after rehydration if it has been stored. The storage methods are also very simple and effective, not requiring the use of additives such as antioxidants and anti-mold. The alginate hydrogel according to the present invention is biodegradable, compostable and even edible, so that its disposal at the end of its life is not at all problematic. Furthermore, these characteristics make the paint/varnish suitable for children too.

It is understood, however, that the invention is not to be considered limited to the particular arrangement illustrated above, which constitutes only an exemplary form of execution of the same, but that various variants are possible, all within the reach of a technician in the field, without thereby departing from the scope of protection of the invention itself, as defined by the claims that follow.

Table I ? examples of paint composition

Claims (11)

1) Ecological paint, having a composition containing alginate, characterised by what is called alginate being present in a gel, where the alginate is partially cross-linked and coupled to a cation and by what also contains one or more alditols and/or lecithin, a lactone and an aqueous or oily solvent. 2) Painting as in 1), characterized in that the partially cross-linked alginate present in a gel is coupled to Ca<2+>. 3) Painting as in 1) or 2), characterized in that the one or more alcohols are chosen from glycerol, sorbitol, mannitol and erythritol. 4) Paint as in any of the preceding claims, characterised in that the lactone is glucono-?-lactone (GDL). 5) Paint as in any of the preceding claims, characterised in that the aqueous or oily solvent is selected from one or more of water, distilled water, rain water, a water-ethanol mixture, a water-acetic acid mixture or even drying oil, selected from boiled linseed oil and uncooked linseed oil. 6) Paint as in any of claims 1) to 5), characterised by comprising further secondary components, where the secondary components are: rheology modifiers and thickeners, selected from cellulose, cellulose waste, clays, xanthan gum, polyurethanes and polyacrylates; mechanical enhancers, selected from glycerol, sorbitol and/or soy lecithin; fillers, selected from calcium carbonate, talc, micas and quartz powder; and a water-repellent enhancer, a drying oil selected from boiled linseed oil and uncooked linseed oil; colourants and pigments, selected from titanium dioxide, zinc oxide, chlorophylls, carotenoids, flavonoids, tannins, anthocyanins. 7) Procedure for the preparation of an ecological paint, characterized by the following steps: suspending an alkaline alginate in an aqueous solvent, heating to a temperature between 50?C and 80?C; adding alcohol; adding dropwise a freshly prepared solution containing a metal salt and a lactone; stirring the mixture; removing the heat source. 8) Procedure as in 7) characterised in that the alkali metal alginate is sodium alginate. 9) Procedure as in 7) and 8), characterized in that the solution just prepared contains a metal salt and a lactone; where the metal salt is calcium carbonate and the lactone is glucono-?-lactone. 10) Process as claimed in any of claims 7)-9) characterised in that, after the removal of the heat source, secondary components and an aqueous or oily solvent are added, selected from one or more of water, distilled water, rain water, a water-ethanol mixture, a water-acetic acid mixture or drying oil, selected from cooked linseed oil and uncooked linseed oil and in that the secondary components are rheology modifiers and thickeners, selected from cellulose, cellulosic waste, clays, xanthan gum, polyurethanes and polyacrylates; mechanical enhancers, selected from glycerol and sorbitol; fillers, selected from calcium carbonate, talc, micas and quartz powder; and colorants selected from titanium dioxide, zinc oxide, chlorophylls, carotenoids, flavonoids, tannins, anthocyanins, betanin, red onion extracts. 11) Process as in any of claims 7) -10) characterised in that the sodium alginate is added in a percentage of between 0.1 and 2% by weight of the total paint, the alcohol is added in a percentage of between 0.1 and 1%, the calcium carbonate necessary for cross-linking in a percentage of between 0.001 and 0.5% by weight of the total paint and the glucono-?-lactone is added in a percentage of between 0.01 and 0.5% by weight of the total paint.