FR2755972A1 - PROCESS FOR THE PREPARATION OF MICROPARTICLES OF MINERAL PIGMENTS COATED WITH A CHAIN LAYER, MICROPARTICLES OBTAINED AND USE OF SUCH MICROPARTICLES - Google Patents

Abstract

The invention concerns mineral pigment microparticles, characterised in that they are covered with a chitin or chitin derivative layer optionally containing one or several organic substances. The invention also concerns the compacted forms of these microparticles, with fast splitting, optionally filled with an active, in particular phytosanitary, substance. The invention finally concerns a method for preparing mineral pigment microparticles covered with a chitin or chitin derivative layer characterised in that a) mineral pigment microparticles in suspense are contacted with a solution of salified chitosan or chitosan derivatives so as to cause the coacervation of the chitosan or the chitosan derivatives around the pigment microparticles, b) the covered microparticles are then subjected to an acetylation reaction.

Description

 The present invention relates to a process for the preparation of microparticles of mineral pigments coated with a layer of chitin or of chitin derivatives.

 It also relates to the microparticles of coated mineral pigments obtained in particular by said process and the use of these microparticles of coated mineral pigments as a film-forming substance or for the granulation of various products.

 Mineral pigments are an important part of the dye industry. Directly derived from oxide chemistry, they provide color and are easy to access. Nevertheless, they sometimes suffer from formulation difficulties and are then replaced by organic pigments having other processing qualities. The deposition of an organic surface film could in some cases overcome the difficulty and be economically or technically a more attractive solution.

 The coating of the pigments can be carried out by various techniques.

For the vast majority of them, it involves depositing on the surface of a pigmentary particle, a polymer in the course of drying, condensation or polycondensation. This mode of action is used in particular to coat the pigments with polysaccharides.

 Numerous studies have already been carried out on the coating with polysaccharides. Techniques of ionic condensations or of crosslinking of chains allow in particular a deposit of organic polymer on a mineral surface.

 However, if a macroscopic vision makes it possible to speak of coating when a condensation is made in the presence of pigments, a microscopic study often suggests a cluster of particles aggregated by the polymer far from being a real film covering the surface of individual particles .

 In particular, it has been observed that, when such methods are applied to the coating of pigment particles with chitin, the reacetylation leads to the formation of a gel in which pigment particles are embedded and not to individual particles coated with chitin .

 Chitin is the structural polymer of arthropods, crustaceans and insects and is part of the membrane of certain fungi. It maintains the endoskeleton of the cephalopods. It is in the animal world the counterpart of what is cellulose in the vegetable kingdom.

 Its particularity lies in its chemical inertness. Not very reactive, insoluble in most known organic solvents, it cannot be thermoformed either. It is only by transforming it into chitosan that it becomes possible to use it.

 To modulate chitin, it is necessary to proceed in two stages. The first consists in transforming chitin into chitosan then the second in transforming chitosan into chitin. It is thus described in patent application EP-A-0 013 181, page 2, a preparation of chitin by acetylation of chitosan with acetic anhydride in a solution of pyridine or a solution of perchloric acid.

 Chitin derivatives have also been prepared. Patent application EP-A-0 013 181 describes the preparation of N-acetyl carboxyalkylchitine by acetylation of deacetylated carboxyalkylchitine with an anhydride of an organic acid. Other chitin derivatives are also mentioned such as hydroxyalkylchitines. The material obtained can be in the form of spherical particles which can be used as ion exchange resins.

 Patent application EP-A-0 021 750 describes a process for the preparation of chitin by acetylation of deacetylated chitin in the presence of an organic acid anhydride and a suspending agent such as a sorbitan monoester.

 Patent application EP-A-0 026 618 describes a material comprising a mixture of two or more derivatives of etherified chitin obtained by the same acetylation process indicated for the two aforementioned documents.

The spherical materials obtained can be used in particular as ion exchange resins.

 In general, the transformation of chitosan into chitin is a reaction which requires the simultaneous presence of two solvents. Water ensures the solvation of chitosan salts at a pH below 6.5. The chitosan salts are in particular the organic acid salts such as acetic acid or oxalic acid, mineral acid salts such as hydrochloric acid, in sufficient concentration to obtain the chitosan in salified form. The second solvent is a water-soluble organic derivative such as alcohol, tetrahydrofuran, dioxane in an amount sufficient to allow the dissolution of an organic anhydride of acetylated type and whose role is the acetylation of the amine groups of chitosan. Used in the presence of chitosan, this reaction results, if the anhydride is acetic, in chitin.

 All of these techniques are generally well known. Examples can be found in the documents mentioned above.

 Surprisingly, the inventors have observed that under particular conditions, it was possible to obtain the coating of pigment particles with chitosan, while leaving these particles in individualized form and then by re-acetylation, to obtain pigment particles coated with chitin.

 The method according to the invention therefore allows the coating of particles and not the solidification due to the formation of gel.

Other objects and advantages of the present invention will be described during the following description:
Firstly, the invention relates to a process for the preparation of microparticles of mineral pigments coated with a layer of chitin or derivatives of chitin, characterized in that
a) microparticles of mineral pigments in suspension are brought into contact with a solution of salified chitosan or of salified chitosan derivatives so as to cause the deposition of salified chitosan or salified chitosan derivatives around the pigment microparticles,
b) the microparticles of pigments coated with chitosan or derivatives of salified chitosan are then subjected to an acetylation reaction using organic acid anhydride.

 Chitosan is a 4-linked D-glucosamine polymer as shown in the single figure appended to this description.

Among the suitable chitosan derivatives, mention is made in particular of O-etherified or O-esterified derivatives of the type corresponding to formula I below: [C6H803. (NH2) x. (NHCOCH3) y. (OR) a- (OH) b] n in which
R represents at least one group chosen from the carboxyalkyl group of 2 to 4 carbon atoms, a hydroxyethyl group, a hyroxyprnpyl group, a dihydroxypropyl group or an alkyl group of 1 to 3 carbon atoms, x being a number between 0, 1 and 1, v being equal to 1.0 a is a number between 0.1 and 1 and b being equal to 1.0 - a where a salified form of these compounds.

 Chitin or poly N-acetyl-D-glucosamine is a polysaccharide whose units are linked together by ss-1,4 glycosidic bridges.

It is therefore distinguished from chitosan which is an N-deacetylated chitin. When the deacetylation is complete, a singular chitosan is obtained, the polyglucosamine.

 Chitin is naturally deacetylated above 5% and more.

The term chitosan is reserved for derivatives which, having undergone deacetylation, become soluble in an acidic aqueous medium. This requires a degree of deacetylation at least greater than 65%. This rate will influence the physical properties of chitosan, solubility and viscosity, but also on its biochemical behavior.

 The concentration of salified chitosan or salified chitosan derivatives in the solution is such that it is lower than the critical miscellar concentration.

 The value of this concentration, which is necessarily low, depends on the agitation applied of the particles used, on their interaction with chitosan or derivatives of chitosan, and on the concentration of the particles themselves.

 In any event, the concentration of particles in the suspension as well as the concentration of salified chitosan or salified chitosan derivatives in the solution must be such that a deposit of chitosan or chitosan derivatives is produced by adsorption on the surface of the particles. particles unlike the formation of a gel which leads to non-individualized particles.

 The particle size of the mineral pigment particles is generally between 1 and 100 μm although these limits do not limit the part of the present invention and the concentration of the pigments in suspension is generally between 0.4 and 40 g / l.

Among the mineral pigments, there may be mentioned in particular the pearlescent pigments of the Iriodine, FlorapearlX 10 and 12 type and the pigments of the range
Iriodione.

 Among the salified forms of chitosan or derivatives of chitosan, there may be mentioned in particular the organic acid salts such as acetic acid or oxalic acid and the mineral acid salts such as hydrochloric acid. Preferably, mention is made of chitosan acetate or the acetates of chitosan derivatives.

 The invention is now described according to preferred variants which are either taken in combination partially or completely between them, or taken individually in conjunction with the general definition of the invention indicated above.

 - The microparticles of mineral pigments are suspended in a hydroalcoholic solution. The suspension is maintained by stirring. The water: alcohol mixture can vary within wide proportions such that the water: alcohol ratio is between 0.25 and 4 or even 20/80 and 80/20.

 The alcohol may be a saturated or unsaturated mono or polyalcohol, although it is desirable that the alcohol chosen is among the least reactive with respect to the organic anhydride in order to avoid any parasitic reaction.

 It should also preferably be volatile to facilitate its subsequent elimination.

 Preferably, secondary alcohols of the isopropanol or isobutanol type are chosen.

 Preferably, the suspension is firstly carried out with stirring of pigmentary particles in the hydroalcoholic phase, leaving the suspension in the state sufficient time to allow boiling, then the solution of chitosan or salified chitosan derivatives is added thereto.

 The pH of the solution of salified chitosan or derivatives of salified chitosan is generally between 2 and 6 depending on the salified form chosen.

In the case of chitosan acetate or acetate of chitosan derivatives, the pH is generally between 4 and 4.5.

 Preferably, the concentration of chitosan or salified chitosan derivatives is between 0.005 and 0.5 g / l, advantageously between 0.01 and 0.1 g / l.

 The solution is left under stirring for a sufficient time for the initial adsorption or inking of the chitosan chains or chitosan derivatives on the surface of the pigments and in the case of pigments coated with titanium mica to the fixing of chitosan to titanium either by chelation, or by complexation.

 The acetylation reaction is carried out by adding a solution of an organic acid anhydride in an alcohol.

 As before, the alcohol will preferably be a secondary alcohol such as isopropanol or isobutanol.

 Among the organic acid anhydrides, acetic anhydride is preferably chosen.

 The concentration of organic acid anhydride, in particular acetic anhydride, is between 0.1 and 10 g / l, preferably between 0.5 and 5 g / l.

 According to a preferred variant, the quantity of the different reagents involved is given below, it being understood that this variant is given only for information and cannot in any way limit the method according to the invention.

from to preferably
Water 20 80 50 g
Alcohol (isopropanol) 80 20 50 g
Chitosan acetate 0.005 0.5 0.04 g
Pigments 0.4 40 4 g
Acetic anhydride 0.1 10 1 g
The invention also relates to a preparation process as described above, characterized in that step a) is carried out in the presence of one or more compounds of organic interest such as an active molecule, which will allow a controlled release of this molecule (delay effect) when the microcapsules of mineral pigments obtained have been included in an appropriate medium.

 Among the active molecules, mention may be made of pharmaceutical molecules, various saturated or unsaturated fatty acids, branched or not, such as octylcarboxylic acid. Preferably, these molecules are included in the chitin wall in small quantities so as not to interfere with the cohesion of the chitin film.

 The invention also relates to new microparticles of mineral pigments characterized in that they are coated with a layer of chitin or derivatives of chitin, said layer possibly comprising one or more organic substances and in that said coated microparticles are capable of be obtained by the process according to the invention.

 These coated microparticles have a particle size which of course depends on the particle size of the microparticles of the suspended mineral pigments.

 The coated microparticles according to the invention have surface film-forming properties. Therefore, the particles can form on the one hand dry films without providing viscosity to the processing solution. On the other hand, the pigments can serve as a support skeleton for any formulation and allow it to be molded in the most diverse forms (granulation).

 The microparticles according to the invention therefore have the advantage of being able to be used in an extremely wide manner, in particular as a film-forming substance or for the granulation of products such as toxic products or bacteria.

 They can also be used as a vector for a delay effect when the chitin layer comprises organic molecules, for example pharmaceutical, phytosanitary, cosmetic, etc.

Among the film-forming applications, we cite
the coating of seeds, the coating of pebbles or tablets, for example tablets made effervescent, the use of microparticles in various formulations of printing ink, in particular in the OFFSET process, in heliography or in flexography.

 As another film-forming application, mention is made of the use of these microparticles in paint formulations, in particular vinyl, acrylic, but also glycerophthalic. The addition of such microparticles leads to film deposits with increased covering effect.

 These microparticles can also be used in compaction. The compacting technique consists in hydrating the microparticles of coated pigments with an amount of water less than the amount necessary for their resuspension in liquid. This amount is of the order of twice the weight of the microparticles of dry coated pigments. This system during drying aggregates without significant variations in volume. If other compounds are added to the aqueous phase, these are trapped during drying in the structure of the three-dimensional network of pearlescent pigments.

The microparticles of mineral pigments according to the invention can also be used in the granulation of different products
the toxic products mixed with the microparticles according to the invention, after drying, form a pebble which limits the toxic effect of the pulverulent treatment product. This roller can then be used by simple mixing with water or it disintegrates without viscosing the medium.

 The granulation of bacteria in microparticles according to the invention is also an easy solution to the difficulties which are generally encountered in the use of bacterial systems in biotechnological applications. We know indeed the difficulties of conservation of the strains in their transport and in their implementation.

 The microparticles according to the invention in which the chitin layer comprises one or more active substances can be released in a controlled manner. The release factors are generally the humidity of the medium, the pH, the biodegradation of the system.

 Other uses can also be envisaged such as the compacting of dyes, pigments or even perfumes. In particular, the pleasant touch of the microparticles according to the invention allows their use in the dry formulation of the cosmetic industries (foundation).

 The examples below illustrate the invention without implied limitation.

Example 1
Coating of Iriodine 221 Pearlescent Pigments Initial Preparation
In a 30 liter reactor, successively poured
-1 kg of Iriodine 221 pigments with a particle size between 5 and 25 Fm
- 8 liters of isopropanol
-12 liters of water
The mixture is stirred for two hours in order to boil the solutions.

Chitosan fixation phase
On the previous stirring solution, we pour
a previously filtered solution of 5 liters of water containing 30 g of chitosan (0.6%, 0.18 moles) and 15 g of acetic acid.

 The mixture is stirred for two hours for maximum adsorption of the chitosan on the pigments.

Reacetylation phase
On the previous stirring solution, we pour
500 ml of a freshly prepared but homogeneous solution of propylene glycol (monopropylene glycol) containing 100 g (one mole) of acetic anhydride.

 Under these conditions, the acetylation is carried out for temperatures between 15 and 25 "C., the coated pigments phase shift with loss of flux within 5 to 45 min following the addition of the reacetylation solution. Stirring is maintained during 2 hours, then, after decanting and draining by any suitable method, the pigments are dried and conditioned.

Example 2
Coating of Iriodine 111 pearlescent pigments (particle size 1 to 15 zm)
The operating conditions of Example 1 are reproduced and lead to the corresponding pigments.

Application example
A - Film-forming applications
seed coating
A corn film-coating solution is produced by mixing 30 parts by weight of pigments from Example 1 previously coated with 1% chitin, 60 parts of conventional phytosanitary products and 90 parts of water in order to ensure wetting. This solution commonly called porridge is stirred in the presence of corn or sprayed on it at the rate of 2 kg per 100 kg of corn. The absorption of water by corn seeds causes the deposition of porridge which is deposited on the surface of the seed. The film-forming maintenance of the formula is ensured by the coated pigments.

Bath pebbles
A part of coated pigments, hydrated beforehand, at 20% is sprinkled on 100 parts of a composition having the form of pebbles or tablets made effervescent in water by their CO2 emission. The coated pigments are deposited to form a protective film on the surface of the tablets.

Printing ink
A composition of 10 to 60 parts per 100 g of coated pigments, preferably 30 parts, is added in various formulations of printing ink. These formulas can be used in OFFSET processes, heliography and flexography.

Painting
A preparation with 30 parts of pigments in a paint formulation leads in vinyl solvent, acrylic but also in glycerophatic medium to film deposits with increased covering effect.

. Compaction
The compacting technique consists in hydrating the coated pigments with an amount of water less than the amount necessary for their resuspension in liquid. This amount is of the order of twice the weight of the microparticles of dry coated pigments. This system during drying aggregates without significant variations in volume. If other compounds are added to the aqueous phase, these are trapped during drying in the structure of the three-dimensional network of pearlescent pigments.

B - Granulation
Toxic products
50 g of coated florapearl 128 are mixed with 50 of phytosanitary product. The dried whole forms a pebble which limits the powdery toxic effect of the treatment product. This roller can then be used by simple mixing with water where it disintegrates without viscosing the medium.

 Florapearl 128 is Iriodine, micatitane reference Iriodine 120, called Florapearl for its application in seeds.

Bacteria
A culture of Rhizobium is carried out beforehand. It is directly mixed in equal proportion with coated pigments previously sterilized by irradiation. After drying by an appropriate method, in molds, the rollers obtained are kept in a sterile environment and then tested for their ability to cause nodulations after 1, 2, 6, 9, 12 months and successfully compared with controls fixed on various other media.

 A culture of Azospirillium and a culture of Speudomonas could be preserved by the same methods to promote biological control.

Their application is made in granules at the direct periphery of the treated plants.

Vector for delay and fixation effect
The pigment microparticles can be coated with a more or less high content of chitin. A number of parameters will depend on this quantity. In particular, if during coating or during compaction, an active molecule comprising binding sites sensitive to hydrogen bonds such as most conventional organic molecules is trapped in the nascent chitin or in the granules in formation, their release in time can be mastered. The release factors will then be the humidity of the medium, the pH, the biodegradation of the system.

 This technique has been used on various saturated or unsaturated fatty acids, branched or not. Among other examples, octylcarboxylic acid trapped at 1% in a pebble 5 cm in diameter and 1 cm thick and kept under running water, completely releases (loss of spectrographic signal) in three weeks.

 Other examples can be given. Compaction can be used to maintain dyes, pigments or even perfumes. Its pleasant touch allows it to be used in the dry formulation of the cosmetic industries (foundation, etc.).

Claims (18)

 1. Process for the preparation of microparticles of mineral pigments coated with a layer of chitin or of chitin derivatives.  b) the coated microparticles are then subjected to an acetylation reaction using organic acid anhydride.  a) microparticles of inorganic pigments in suspension are brought into contact with a solution of chitosan or derivatives of chitosan salified so as to cause the coacervation of chitosan or derivatives of chitosan around the microparticles of pigments, characterized in that:  2. Preparation process according to claim 1, characterized in that the microparticles of mineral pigments are suspended in an aqueous-alcoholic solution.  3. Preparation process according to claim 1, characterized in that the solution of chitosan or salified chitosan derivatives is an acetic solution.  4. Preparation process according to claim 1, characterized in that the acetylation is carried out by means of an organic solution of acetic anhydride.  5. Preparation process according to claim 4, characterized in that the acetylation is carried out by means of an alcoholic solution of acetic anhydride.  6. Preparation process according to one of claims 2 or 5, characterized in that the alcohol is chosen from the group consisting of volatile alcohols which are not reactive with respect to the organic acid anhydride.  7. Preparation process according to claim 6, characterized in that the alcohol is chosen from the group consisting of a secondary alcohol, in particular isopropanol, isobutanol alone or as a mixture.  8. Preparation process according to claim 1 or 3, characterized in that the concentration of chitosan or salified chitosan derivatives is between 0.005 and 0.5 g / l.  9. Preparation process according to claim 8, characterized in that the concentration of chitosan or salified chitosan derivatives is between 0.01 and 0.1 g / l.  10. Preparation process according to claim 1 or 2, characterized in that the concentration of pigments in the suspension is between 0.4 and 40 g / l.  11. Preparation process according to claim 10, characterized in that the concentration of pigments in the suspension is between 1 and 20 g / l.  12. Preparation process according to one of claims 1, 4, 5, characterized in that the concentration of organic acid anhydride is between 0.1 and 10 g / l.  13. Preparation process according to one of the preceding claims, characterized in that the microparticles of mineral pigments have an average particle size between 1 and 100 Fm.  14. Preparation process according to one of the preceding claims, characterized in that step a) is carried out in the presence of one or more compounds of interest, organic.  15. Microparticles of mineral pigments, characterized in that they are coated with a layer of chitin or chitin derivatives optionally comprising one or more organic substances and in that they are capable of being obtained by the process according to one of claims 1 to 14.  16. Use of the microparticles according to claim 15 as a film-forming substance.  17. Use according to claim 16, characterized in that the microparticles are used for coating seeds, bath rollers, in printing inks, paints, compacting.  18. Use of the microparticles according to claim 15, for the granulation of toxic products, bacteria.