WO2022002846A1

WO2022002846A1 - Microencapsulated tcmtb

Info

Publication number: WO2022002846A1
Application number: PCT/EP2021/067684
Authority: WO
Inventors: Alexis CASANOVA MORISCO; Angel Fernández González; Roger Segret Pons; Xavier SÁNCHEZ RUIZ; Joan Seguer Bonaventura
Original assignee: Laboratorios Miret, S.A.
Priority date: 2020-07-01
Filing date: 2021-06-28
Publication date: 2022-01-06
Also published as: EP4175473A1; AU2021302520A1; AR122853A1; MX2022016438A; BR112022026167A2

Abstract

The invention relates to a new process for preparing microencapsulated thiocyanomethylthio benzothiazole (TCMTB) by covering TCMTB droplets in an emulsion of an organic phase in an aqueous phase with a melamine-formaldehyde polymer coating to form solid TCMTB microcapsules. The invention further relates to the new TCMTB microcapsules and aqueous suspensions containing the TCMTB microcapsules and the use of microencapsulated TCMTB in tanning or for preserving hides, leather, fibers and polymerized material or for preserving paints, paper products, wood, wood products, or industrial water.

Description

Microencapsulated TCMTB

DESCRIPTION

The invention relates to a new process for preparing microencapsulated thiocyanomethylthio benzothiazole (TCMTB) by covering TCMTB droplets in an emulsion of an organic phase in an aqueous phase with a melamine-formaldehyde polymer coating to form solid TCMTB microcapsules. The invention further relates to the new TCMTB microcapsules and aqueous suspensions containing the TCMTB microcapsules, as well as to compositions comprising the microencapsulated TCMTB. Further, the invention relates to the use thereof in tanning processes or in processes for preserving hides, leather, paints, paper products, wood, wood products, or industrial water.

PRIOR ART AND OBJECT TO BE SOLVED

TCMTB (thiocyanomethylthio benzothiazole or (benzothiazol-2-ylthio)methyl thiocyanate; CAS: 21564-17-0) is used as a wideband microbiocide, in particular as a fungicide in paints, in leather preservation, for the protection of paper products, as wood preservative, and against germs in industrial water. Further, TCMTB is used as a fungicide for seed dressing in cereals, safflower, cotton and sugar beet. Of particular importance is the use of TCMTB for the preservation of hides and leathers in tanning processes.

In its pure state it is a white crystalline solid, although the resultant product from normal synthesis is an amber to dark oil with an active concentration ranging from 80 to 85%. The active in this concentrated oil crystallizes with time at low temperatures so it is required to formulate it to obtain a product that can be handled easily, e.g. by customers, and which is sufficiently stable. The conventional methods to formulate TCMTB are:

• as an emulsifiable concentrate, wherein TCMTB is dissolved in an organic solvent with a package of surfactants which allow to emulsify TCMTB in water, and

• as a concentrated emulsion in water, wherein TCMTB is already formulated in water, which requires a package of solvents and surfactants to maintain the stability of the emulsion and to allow dilution of the mixture in water.

In both cases a high concentration of organic solvents and surfactants is required. When applying such conventional TCMTB formulations, e.g. in tanning processes, the required solvents and surfactants remain in the wastewater or are otherwise released into the environment and the groundwater.

Conventional formulations of TCMTB must be classified as harmful, irritant and as sensitizing in skin contact or upon inhalation and must be labelled accordingly with respective hazard pictograms on the packaging. The prescribed classification and labelling results from the amount of active TCMTB available to interact with the user or workers using the formulations in the industrial sites. Further, as mentioned above, current products in the form of emulsions or concentrates of free TCMTB require high concentrations of surfactants and organic solvents to stabilize the formulations.

Further forms and application fields of TCMTB are described e.g. in EP0425709A1 , JPH04225904A or JPH04270204A.

It was an object of the present invention to provide new TCMTB formulations with reduced hazards and being safer in use. A further object of the invention was to provide new TCMTB formulations with less solvents and surfactants but still high stability and dilution properties to allow easy mixing and application in the use, e.g. in a tanning process. A further object of the invention was to provide new TCMTB formulations with increased stability of the active TCMTB and its reduced degradation, therewith providing increased shelf-life and long-term stability.

A further object of the invention was to provide a new process for encapsulating TCMTB and to provide stronger and more stable encapsulated TCMTB for continuous and prolonged release of the TCMTB after application onto the treated material. A further object of the invention was to provide new TCMTB-containing microcapsules characterized by highly stable and dense polymer film capsules. A further object of the invention was to provide new TCMTB-containing microcapsules with improved safety and reduced environmental impact, allowing to prepare antimicrobial products of improved storage stability and improved performance over time, e.g. providing a longer protection to the hides when used in a tanning process, and allowing to provide formulations with increased activity, reducing the possibility of holes in the microcapsule wall that could release the TCMTB to the media ,in particular long-term activity as well as controlled and prolonged release of the TCMTB in the application. A further object of the invention was to provide new TCMTB-containing microcapsules having a good balance between encapsulation and protection of the active and its release for delivering long-term activity.

Microencapsulated active compounds and methods for microencapsulation of active compounds, such as drugs, insecticides or fungicides, are already known as a possible application form, e.g. from EP2487264A1 , EP0686425A1 , EP0270742A1 and W094/09209A1.

Microencapsulation reduces the availability of the free active compound and allows formulating active compounds with harmful properties as new products with reduced hazards. By microencapsulation, the main part of the active substance is entrapped inside a protective barrier or shell (capsule) which avoids that the encapsulated active compound is available for interacting with the surrounding environment or for harming people using the microencapsulated active. Accordingly, in the calculation of the harmful potential and the hazard classification of the product, the protected (encapsulated) active compound needs not to be considered but only non- encapsulated (free) active. As a result, products containing the microencapsulated TCMTB do not need to be classified with hazard pictograms on the packaging and are much safer in use, both, for workers and environment. A process for microencapsulation of TCMTB has been described e.g. in EP0686425A1 using isocyanates for forming urea resin microcapsules. A process for microencapsulation of TCMTB is described therein in Example 10 with reference to Example 6, said process comprising 20 hours of emulsification at 20 °C followed by precipitation of the microcapsules over one day (24 hours). This very long process time of nearly 2 days results from the very slow polymerization reaction under the applied mild reaction conditions avoiding temperatures above 40 °C needed to control the kinetics of the reaction. The presence of polyvinyl alcohol as a polymeric dispersant is described as necessary. The final product obtained after this long process has around 7% TCMTB and the solids obtained after decantation and filtration give an active content of 48.6% Although this process provides microencapsulated TCMTB the long process time and required mild reaction conditions are disadvantageous and economically inefficient, in particular for large-scale production. A faster and more efficient (higher active concentration) microencapsulation process is desired for industrial scale productions.

EP0270742A1 describes microencapsulation of fungicides, such as e.g. TCMTB, with crosslinked polyurea, crosslinked polyamide and crosslinked polyamide-polyurea with varying crosslinking degrees between 25 to 100 %. The microcapsules described therein are intended for application to foliage and a low phytotoxicity is desired. As described therein, the wall formation and the wall permeability are critical for the desired balance of release and protection of the encapsulated fungicide. The wall permeability is a direct result from the crosslinking degree of the wall material. The crosslinking reaction of the polyamide used in the encapsulation process described therein therefore needs critical control as otherwise with too low crosslinking the permeability is too high, which may deteriorate protection of the encapsulated active, and with too high crosslinking the permeability is too low, which decreases the release of the encapsulated active in the desired use. The process uses a highly flammable solvent (xylene) to solubilise the wall forming materials and the resulting slurry of active capsules suspended in water has a TCMTB concentration below 15% (wt/wt).

An encapsulation process with less critical control of the polymerization degree and which uses less dangerous solvents is desirable to provide encapsulated TCMTB with capsules of high quality, good stability and a suitable balance between sufficient release and protection inside the capsule. This can be achieved with the process of the present invention, wherein the polymerization reaction can be left to proceed until the polymerization reaction is completed but still provides capsules with sufficient release properties in a reasonable process time for industrial scale. With the new process of the invention, it becomes possible to optimize the formation of stable, uniform, continuous and dense polymer films surrounding and enclosing the TCMTB droplets, e.g. by controlling the polymerisation speed in the process, in order to avoid for example holes in the polymer film structure forming the capsule. The new microencapsulated TCMTB of the invention allows applying the TCMTB in the form of a dispersion of the TCMTB- containing melamine-formaldehyde microcapsules in water with slow release of the bioactive compound. W094/09209A1 describes a method of trapping fungicides, such as e.g. TCMTB, in polymethyl methacrylate latex particles. From Example 1 described therein it is apparent that the disadvantages of the process and the kind of polymer coating described therein is on the one hand that the maximum amount of fungicide to be encapsulated is limited by its solubility in the methyl methacrylate monomer and on the other hand the limited release of the fungicide out of the polymer coating. This kind of latex coating holds the fungicide and disables its diffusion into regions adjacent to the latex coated fungicide. As a result, a product to be protected by applying the latex-bound fungicide will only be protected to the extent of with the latex-fungicide-particles covered surface and thus requires a comprehensive and very dense application thereof. The particles suspension obtained with this method has a TCMTB concentration below 1% and it is a slurry to apply directly on the product to protect only as a coating, which limits the final uses. Such coatings are in particular not suitable for the tanning industry. It is desired to provide encapsulated TCMTB with certain release of the TCMTB after application to the treated products to allow a kind of sustained-release protection and for offering the opportunity of reducing the applied amount.

US4,100,103 quite generally describes various encapsulation methods with different capsule wall forming polymer components, including among others melamine and formaldehyde. The encapsulated active compounds, i.e. the core material to be encapsulated, are not specifically described but only a broad variety of examples is mentioned, including the general class of biocidal compositions. TCMTB is not mentioned specifically and even less can be found any description of a specific encapsulation method or of particularly suitable coating polymers for encapsulating TCMTB.

Similarly, US4,552,811 and the corresponding EP01333525A2 describe alternative methods for preparing microcapsules using alternative capsule wall forming polymers without mentioning TCMTB as an active compound to be encapsulated and without providing a concrete teaching for a specifically suitable process for encapsulating in particular TCMTB.

EP0041210A1 discloses the preparation of pressure-resistant micro-capsules having an outer polyamide coating and an inner mass structured by polyurethane- polyurea. The micro-capsules may be used for encapsulating biocides for the use in crop protection. However, a method for encapsulating TCMTB is not disclosed.

The above mentioned EP2487264A1 relates to a process for preserving leather and hides by applying a biocide and mentions among others TCMTB as a biocide in a long list. It is further generally mentioned that the biocides may be microencapsulated. However, a concrete teaching of using microencapsulated TCMTB is not given therein.

The inventors of the present invention found that in particular the use of microencapsulated TCMTB provides several advantages in tanning processes.

US2010/099793A1 describes adhesives and sealants, such as silicone rubbers and acrylate sealants, that are antimicrobially furnished with a biocidal active which can be the encapsulated in microparticles of a melamine-formaldehyde resin. The antimicrobial is O!T and it is generally mentioned that OIT can be replaced by a broad variety of other antimicrobials, including inter alia 2-thiocyanomethylthio-benzothiazole (TCMTB). The reaction of encapsulation with OIT is carried out at 20 to 95 °C. The microparticles are prepared from an emulsion with polyacrylate, silicone defoamer and gum arabic, as adjuvant and using water as solvent.

W093/01801A1 relates to lipid vesicles made from N,N-dimethylamides of tall oils (DMATO) or soy bean oils (DMASO), which can be used in the form of a dispersion with TCMTB and organic solvents, such as toluene, as a fungicide for protecting wood, cotton, crop seedlings as well as in leather tanning. The formation of stable microcapsules enclosing TCMTB is not disclosed.

WO2017/095335A1 describes a method of microencapsulation of organic biocides such as DCOIT, which is encapsulated into a polymeric microcapsule with a porous wall enabling a controlled and prolonged release of the biocide. The encapsulation of TCMTB is not disclosed.

The inventors of the present invention further surprisingly found a new microencapsulation process being particularly suitable for microencapsulating TCMTB, thus allowing to provide TCMTB, so far provided in liquid active forms, now in the form of solid particles or capsules which are much safer to handle and use, have a high stability and can be suspended in water easily. The concentration of surfactants and organic solvents can be reduced to a minimum. This allows providing TCMTB as new formulations with high safety for users and environment and in more efficient and economic forms. Apart from improving the hazard classification for the product and reducing the impact on the environment, products formulated with microencapsulated TCMTB are more stable during storage and provide a better performance over time, e.g. providing a longer protection to the hides when used in a tanning process.

In the tanning process TCMTB deposits on the hides. Now, when using the microencapsulated TCMTB instead of the conventional formulations with free TCMTB, the deposited TCMTB is protected from the aggressive environment of tanneries by the capsule wall in the form of a polymeric barrier. Once the tanning process is finished, TCMTB is released from the capsules onto the surface of the hides over time. Tanning factories are usually in warm and wet environments, conditions which promote TCMTB degradation. Using microencapsulated TCMTB allows protecting the deposited TCMTB from the degradation influences, which prevents or remarkably reduces TCMTB degradation and allows maintaining the effective concentration of deposited TCMTB for a longer period. Microencapsulated TCMTB is not in direct contact with the aggressive tanning conditions, therefore its degradation is reduced and its performance extended over time. Hides can be protected for longer time periods with the same TCMTB initial concentration, which allows reducing the amount of TCMTB but still achieve the same preservation effect compared to conventional formulations of free TCMTB. Using the microencapsulated TCMTB in tanning allows extending the shelf life of the hides. DETAILED DESCRIPTION OF THE INVENTION

In a first aspect the invention relates to the use of microencapsulated TCMTB in tanning processes for preserving hides and leather.

In a further aspect the invention relates to a new method of preparing microencapsulated TCMTB by a) preparing an aqueous solution comprising a stabilizer and a melamine- formaldehyde resin, b) mixing TCMTB with an organic solvent, preferably a biodegradable organic solvent, c) adding the mixture b) to the aqueous solution a) and stirring to prepare an emulsion of an organic phase in an aqueous phase containing TCMTB droplets, d) in situ polymerization of the melamine-formaldehyde resin on the TCMTB droplets, e) formation of a suspension of TCMTB microcapsules in the aqueous phase of the reaction medium.

The suspension comprising the TCMTB microcapsules resulting from step e) can be used as such or used for preparing suitable products containing the TCMTB microcapsules. However, it is also possible to include a further optional step of f) isolating the solid TCMTB microcapsules from the suspension.

Isolation of the TCMTB microcapsules from the suspension of step e) can be achieved by conventional methods, including precipitation of the microcapsules, centrifugal sedimentation, by removing the solvents, e.g. by decantation or filtration, optionally followed by drying of the isolated microcapsules. Drying can be carried out at room temperature (22 °C ± 3 °C) or by heating under normal or reduced pressure. A combination of isolation and/or drying methods is also possible.

The encapsulation method used for TCMTB according to the present invention is based on using melamine-formaldehyde resins as the capsule forming material. The novel process of the invention allows promoting melamine-formaldehyde resin to deposit on the surface of TCMTB droplets which form part of an emulsion of an organic phase in an aqueous phase (oil-in-water emulsion). Apart from the melamine-formaldehyde resin, a stabilizer is used to stabilize the emulsion, which has an important role in supporting the deposition of the resin on the droplet. In principle, different possible options are known to obtain good quality capsules made with melamine-formaldehyde resins, e.g. from US4,552,811. However, the inventors of the present invention surprisingly found that not all conventionally used stabilizers are equally suitable for preparing high quality TCMTB microcapsules. In particular, the very common stabilizer (hydrolysed) polyvinyl alcohol turned out as less suitable. Using polyvinyl alcohol as the stabilizer provided only very weak capsules. Instead the following stabilizers have been found suitable in the process of encapsulating TCMTB with melamine-formaldehyde resins: styrene maleic anhydride copolymer, ethylene maleic anhydride copolymer and functionalized polyacrylic acid.

Among them, styrene maleic anhydride copolymer has been found as a particularly good stabilizer providing very resistant capsules of high quality.

Accordingly, in a preferred embodiment of the method of the invention the stabilizer added to the aqueous solution of step a) is styrene-maleic anhydride copolymer, e.g. commercially available as Xiran 1000P supplied by the company

Polyscope Polymers B.V., or as SMA^®resins from the company Cray Valley USA, LLC.

Among those, SMA^®1000 is preferred.

The inventors of the present invention surprisingly found that the specific selection of melamine-formaldehyde resin allows to provide stable and high quality microencapsulated TCMTB droplets which solve the problems of the prior art.

There are many different types of melamine-formaldehyde resins based on how they are made. In principle, melamine-formaldehyde resins are made by reacting melamine and formaldehyde at alkaline pH. One molecule of melamine has 6 reaction sites so it is able to react with up to 6 molecules of formaldehyde. After melamine reacts with formaldehyde it is possible to modify the chain length attached to the reaction sites by including methylol, ethlylol, and longer chain groups in the reaction site. Depending on the degree of substitution of the 1 to 6 reaction sites and the chain length in each substituted reaction site, the properties of the resulting melamine-formaldehyde resins differ.

For the microencapsulation of TCMTB according to the process of the present invention it turned out as particularly advantageous to use melamine-formaldehyde resins with 3 to 4 substituted reaction sites. Such substitution degree provides enough reaction sites to obtain a bidimensional network for covering the TCMTB oil droplet. More than 4 substituted reaction sites may have the disadvantage of undesired side-reactions as each reaction during the polymerisation will release formaldehyde. Further, the chain length at the substituted reaction sites influences the reactivity of the molecule.

For the microencapsulation of TCMTB according to the process of the present invention it further turned out as advantageous to use melamine-formaldehyde resins, which are substituted with short chain substituents comprising 1 or 2 carbon atoms in the substituent chain. The substituents are preferably selected from alkyl.

This permits carrying out the polymerization reaction under milder conditions.

Accordingly, in the method of the invention the melamine-formaldehyde resin is preferably selected from melamine-formaldehyde resins having 3 to 4 Ci-C2-alkylated reaction sites. More preferred are melamine-formaldehyde resins having 3 to 4 methylated reaction sites.

Particularly preferred are melamine-formaldehyde resins of the imino type.

Most preferred is the use of melamine-formaldehyde resins selected from imino- type melamine-formaldehyde resins having 3 to 4 Ci-C2-alkylated reaction sites, in particular having 3 to 4 methylated reaction sites.

Examples of commercially available melamine-formaldehyde resins being suitable in the process of the present invention include Saduren 163 of the company BASF, MAPRENAL^® MF920w/75WA of the company INEOS Melamines, ASTRO MEL NW-3A of the company H EXION, or CYMEL^® resins of the company Allnex:

such as in particular CYMEL 385.

In the process of the invention the styrene-maleic anhydride copolymer stabilizer acts as a polymeric surfactant, which helps to stabilize the emulsion of step c). In the chemical polymerization reaction which takes place in step d) two different melamine- formaldehyde entities react under formation of a bond between two substituted reaction sites and release of formaldehyde into the reaction medium. In the beginning of the polymerization reaction, the low molecular weight chains of the preferred melamine- formaldehydes are soluble in water, but with increasing chain length the molecular weight increases and the water solubility decreases until precipitation in the reaction medium. Very tiny precipitates (in the nanoscale) are hydrophobic and are directed to the interface of the TCMTB droplets in the emulsion by the surface-active stabilizer, where they deposit. With advancing reaction, the deposition of the tiny particles increases and they react with themselves forming a continuous polymer covering around the TCMTB oil droplet, resulting in the microcapsule of the invention.

A further aspect of the invention relates to the control of the reaction conditions in the process of the invention. The control of the temperature and of the pH in the process steps and reaction media helps to promote optimized deposition of the melamine-formaldehyde resin on the surface of the TCMTB droplets of the emulsion.

By controlling the polymerisation speed in the process of the invention it is possible to optimize the formation of stable and dense polymer films around the TCMTB droplets. A dense polymer film is desired to avoid holes in the polymer film structure forming the capsule.

If the polymerization speed is too high, polymers of melamine-formaldehyde with high molecular weight are formed, which precipitate in the reaction media without sufficient time to deposit on the interface surface of the droplets. In contrast, a high polymerization speed leads to continued polymerization reaction with the formation of longer polymer chains. As a result, the aqueous phase of the reaction medium thickens and the formation of microcapsules is prevented.

A too high polymerization speed may result from too high reaction temperatures and/or too low pH values in the reaction media.

Otherwise, if the polymerisation speed is too low, the formation of the polymer films around the TCMTB droplets is too slow and the reaction becomes inefficient and incomplete. A delayed polymerization further bears the risk of changes in the emulsion.

A too low polymerization speed may result from too low reaction temperatures and/or too high pH values in the reaction media.

The inventors of the present invention found that very good polymerization properties and capsule formation of high quality, density and stability with a good balance between encapsulation and release of the TCMTB can be achieved by controlling the reaction temperature within a range of 40 to 90 °C, preferably in a range of 45 to 85 °C, more preferably in a range of 50 to 80 °C; each with a possible variance of ± 20 °C, preferably ± 1.0 °C.

TCMTB may degrade at high temperatures so it is preferred that the reaction temperature in the process of the invention does not exceed 90 °C, preferably the reaction temperature is < 85 °C, more preferably < 80 °C, more preferably < 75 °C, each with a possible variance of ± 2.0 °C, preferably ± 1.0 °C.

It is preferred that the reaction temperature in the process of the invention is higher than 40 °C, preferably > 45 °C, more preferably > 50 °C, even more preferably > 55 °C; each with a possible variance of ± 2 0 °C, preferably ± 1.0 °C.

The inventors of the present invention further found that very good polymerization properties and capsule formation of high quality, density and stability can be achieved by controlling the pH in the reaction media of the process of the invention within a range of pH 3.0 to 7.0, preferably in a range of pH 3.5 to pH 6.5, preferably in a range of pH 4.0 to 6.0, more preferably in a range of pH 5.0 to 6.0, each with a possible variance of ± 0.3 or preferably ± 0.2.

It is preferred that the pH in the reaction media of the process of the invention is controlled to be < pH 7.0, preferably < pH 6.5, more preferably < pH 6.0, even more preferably < pH 5.8, each with a possible variance of ± 0.3 or preferably ± 0.2.

It is preferred that the pH in the reaction media of the process of the invention is controlled to be> pH 3.0, preferably > pH 3.5, more preferably > pH 4.0, even more preferably > pH 4.5, even more preferably > pH 5.0, each with a possible variance of ± 0.3 or preferably ± 0.2.

It is particularly preferred that in the process of the invention the aqueous solution of step a) is controlled to have a pH in the range of pH 5.0 to 6.0, preferably of pH 5.5, each with a possible variance of ± 0.3 or preferably ± 0.2.

It is particularly preferred that in the process of the invention the aqueous solution of step a) is controlled to have a temperature of 50 to 60 °C with a possible variance of ± 2.0 °C or preferably ± 1.0 °C.

In a particularly preferred aspect, the aqueous solution of step a) is controlled to have a pH in the range of pH 5.0 to 6.0, preferably of pH 5.5, each with a possible variance of ± 0.3 or preferably ± 0.2, and a temperature of 50 to 60 °C, with a possible variance of ± 2.0 °C, preferably ± 1.0 °C

It is particularly preferred that in the process of the invention after formation of the emulsion in step c) the pH is adjusted to pH 5.5 ± 0.3 or preferably ± 0.2.

It is particularly preferred that in the process of the invention after formation of the emulsion in step c) the temperature is raised to 70 °C ± 2.0 °C or preferably ± 1.0 °C.

In a particularly preferred aspect, after formation of the emulsion in step c) the pH is adjusted to pH 5.5 ± 0.3 or preferably ± 0.2 and the temperature is raised to 70 °C ± 2.0 °C or preferably ± 1.0 °C. It is even more preferred, that after formation of the emulsion in step c) the reaction mixture is left to stand for sufficient time to complete the polymerization reaction. Preferably, within this time period the reaction conditions are controlled to have a temperature of 70 °C ± 2.0 °C or preferably ± 1.0 °C, and a pH of 5.0 to 6.0, preferably a pH of 5.5, ± 0.3 or preferably ± 0.2.

The reaction mixture is left to stand until the completion of the polymerization reaction. Therewith, the encapsulation process finishes once there is no more resin available for reaction. If the process is stopped by discharging from the reactor before the polymerization is completed, i.e. if unreacted resin remains, these unreacted resin residues will continue to react during storage, even if at low speed, which negatively affects and changes the physical properties of the product. For example, the viscosity may increase and aggregates can form. Preferably, the polymerization reaction is carried out for at least 4 hours, preferably for at least 5 hours.

It is possible, to add one or more formaldehyde scavengers to the reaction medium in the process of the invention. If used, they will be added once the microcapsules are formed, in step e), and they should be left to react for enough time (preferably about 20 to 30min).

In principle, all suitable and conventional formaldehyde scavengers can be used. Preferred formaldehyde scavengers are selected from the group consisting of urea, acetoacetamide, and imidazolidone, a particularly preferred formaldehyde scavenger is urea or acetoacetamide.

It is also possible, to add one or more thickeners to the reaction medium in the process of the invention. If used, the thickeners will be added after microcapsules are formed and the scavengers have reacted, in step e).

Thickeners help to stabilize the formed microcapsules and support their suspension in the reaction medium. This also allows reducing the overall concentration of surfactants and organic solvents to a minimum.

In principle, all suitable and conventional thickener can be used. Preferred thickeners are selected from the group of polysaccharides, such as starches, vegetable gums, sugar polymers, or proteins. Preferably the thickeners are selected from microbial and vegetable gums, such as alginate, guar gum, locust bean gum, and xanthan gum, among which xanthan gum is particularly preferred. Proteins used as thickeners include collagen and gelatine. Sugar polymers include agar, carboxymethyl cellulose, pectin and carrageenan. Further suitable thickeners are selected from thickeners for alkali swellable emulsions (ASE), hydrophobically modified alkali swellable emulsions (HASE), and hydrophobically modified polyurethanes (HEUR). In a most preferred embodiment the thickener is xanthan gum.

The organic solvent used in step b) for mixing with the TCMTB can be any suitable organic solvent known in the art. Preferred organic solvents are biodegradable ones selected from methyl esters or saturated and un saturated C16-C18 fatty acids, e.g. such as known from Thomas et al. “Natural attenuation of fatty acid methyl esters (FAME) in soil and groundwater”; Quarterly Journal of Engineering Geology and Hydrogeology, 2016. In a most preferred embodiment the organic solvent of step b) is rapeseed oil methyl ester (RME). Using biodegradable organic solvents is advantageous with respect to providing a process and product which is less hazardous, less harmful for the environment and safer. Rapeseed methyl esters preferably used in the present invention are usually used and well-known as biodiesel.

A further aspect of the invention relates to the microencapsulated TCMTB (TCMTB microcapsules) obtainable by the process of the invention as described herein.

Such novel TCMTB microcapsules comprise TCMTB as the core material, which is encapsulated by a melamine-formaldehyde polymer microcapsule. Therein, the melamine-formaldehyde polymer microcapsule forms a continuous polymer film covering a TCMTB oil droplet. Such TCMTB microcapsules are in the form of solid microcapsules.

Such TCMTB microcapsules preferably have an average particle size distribution d50 of < 40 microns. Therein, the d50 value (the mass-median-diameter MMD) is represented by the log-normal distribution mass median diameter. The MMD is considered to be the average particle diameter by mass. The d50 value is measured by laser diffraction determination, e.g. by a method as described in the Examples below.

The particle size can be controlled by the mixing and stirring process when preparing the emulsion with the formation of the TCMTB droplets. By controlling the stirring rate larger or smaller droplets are achieved, which determines the final particle size of the microcapsules.

A further aspect of the invention relates to an aqueous suspension containing the solid TCMTB microcapsules as described above.

Such aqueous suspension preferably contains< 1.0 % not encapsulated (free) TCMTB, more preferably <0.9 %, preferably <0.8 %, preferably <0.7 %, preferably <0.6 %, more preferably <0.5 % not encapsulated (free) TCMTB.

The TCMTB microcapsules and the aqueous suspension containing the solid TCMTB microcapsules are particularly suitable for the use as preservative or fungicide.

Accordingly, in a further aspect of the invention the TCMTB microcapsules or the aqueous suspension containing the solid TCMTB microcapsules are further formulated in a preservative composition, in particular a fungicidal composition.

The microencapsulated TCMTB or the aqueous suspension as well as the preservative or fungicidal composition as described above are in particular suitable for the use in tanning processes, for preserving hides or leather, for protection of fibers, leather and polymerized material, or for preserving paints, paper products, wood and wood products, and to combat germs in industrial water.

In a further aspect the invention also relates to a method of tanning hides or leather comprising the treatment of the hides or leather with TCMTB microcapsules, an aqueous suspension containing TCMTB microcapsules or a preservative / fungicide composition containing TCMTB microcapsules, preferably in each case the new TCMTB microcapsules described in the present invention.

Further aspects of the invention relate to a method of preserving paints, paper products, wood, wood products, or industrial water comprising the treatment of the paints, paper products, wood, wood products, or industrial water with the TCMTB microcapsules, the aqueous suspension containing the TCMTB microcapsules or the preservative / fungicide composition containing the TCMTB microcapsules, each as described above.

The invention is further illustrated by the following Examples, without being limited thereto.

EXAMPLES

1. Manufacturing Process

The TCMTB microencapsulation has been carried out as follows:

Step a)

284 g deionised water are placed in a three-neck reactor and heated to 80°C.

10 g styrene-maleic anhydride copolymer as the stabilizer (surfactant) and 6 g NaOH 50% are added and the mixture is left to dissolve at 80°C while stirring.

Once the solution is clear, the mixture is cooled down to 55°C and the pH is adjusted to pH 5.5 with 30% HCI.

15 g melamine-formaldehyde resin are added to the aqueous phase and mixed well for 10 minutes.

Step b)

In the meantime, in a different vessel, 150 g TCMTB 80 and 25 g of rapeseed oil methyl esters as the solvent are mixed with the help of a magnetic stirrer.

Step c)

The organic phase mixture of step b) is added to the aqueous phase mixture of step a) and mixed well for 10 minutes to prepare an oil-in-water emulsion by stirring at high speed for another 20 minutes. The temperature is controlled to be kept at 55°C.

Step d)

Once the emulsion of step c) is formed, the polymerization reaction is initiated by adjusting the pH to 5.6 with HCI and by slowly starting to heat the mixture to 70°C.

The reaction mixture is controlled to be kept at 70°C for 5 hours and the pH is monitored every hour.

Step e) The TCMTB microcapsules are formed as solid particles in a suspension of the reaction medium.

If a formaldehyde scavenger is added, then the reaction mixture is left to react for 20 to 30 minutes at 70°C.

By adding a thickener, keeping the formed TCMTB microcapsule particles in suspension can be supported.

The resulting product is a suspension of TCMTB microcapsules in an aqueous reaction phase with a concentration of the active compound of around 24 wt.%, related to the whole aqueous suspension.

Optional step f)

If isolation of the solid TCMTB microcapsules is desired, the suspension is cooled down after completion of the 5h polymerization reaction, followed by removing the water by decantation or filtration to obtain the solid TCMTB microcapsule particles. The isolated solid particles can be dried further at room temperature.

Measurement of the particle size d50 bv laser diffraction determination

The particle size of the TCMTB microcapsules is determined using a conventional automated process, comprising the following steps:

The measurement cel! is prepared, cleaned, filled with water and placed in the measurement chamber. The instrument is configured by choosing the solvent used (and selecting its refractive index) and selecting the measurement time (usually 1 min) and the number of measurements (usually 3). Once the set-up is ready the measurement starts. First, an alignment is made and a background is recorded. Then the sample is placed in the measurement cell until the desired obscuration is reached (usually 3-4 drops of a previously 1/10 diluted sample). The measurement starts and the data are obtained.

2. Reaction Components

The raw materials used in the above described microencapsulation process are:

• deionised water

• styrene-maleic anhydride copolymer; Xiran 1000P supplier Polyscope.

• NaOH 50 wt.%.

• HCI 30 wt.%.

• TCMTB 80 (80% active content, supplier Lamirsa)

• rapeseed oil methyl esters (methylated C16-C18 fatty esters) • melamine-formaldehyde resin; high imino methylated melamine-formaldehyde resin; supplier BASF (Saduren 163) or A!lnex (Cyme! 385)

• if desired, urea or acetoacetamide as formaldehyde scavenger

• if desired, xantham gum as thickener

3. Product Characteristics

The resulting product is an aqueous suspension of TCMTB microcapsules with the following characteristics:

• TCMTB concentration: 24%, related to the aqueous suspension

• not encapsulated (free) TCMTB: <0.5%

• viscosity: 1000 to 1500cP (if thickener is added)

• pH: 5.0 to 7.0

• colour: beige

• particle size: d50<40 microns

• VOC FREE (free of volatile organic compounds)

4. Use in a tanning process

The microencapsulated TCMTB are used in a tanning process, therein having the following advantages during application:

• The formulation is VOC FREE, reducing the solvents use in the factory and the spills to the environment.

• The concentration of not encapsulated (free) TCMTB is very low and the product thus constitutes no hazard for workers during use.

• The encapsulated TCMTB turned out to have increased activity, in particular long-term activity, compared to conventional formulations containing free TCMTB.

In addition, the encapsulated TCMTB is protected from the tanning conditions against degradation and shows a better performance once applied onto the hides. Pieces of leather without treatment have been tanned following a standard tanning process for wet blue and for wet white (two different standard types of tanning), in which the encapsulated TCMTB versus conventional TCMTB formulations containing free TCMTB are added as a protective treatment.

The protective effect of the new encapsulated TCMTB versus the conventional product with free TCMTB (not encapsulated) is compared.

Once the leathers are tanned, TCMTB residuals have been measured initially and after one month ageing at 40°C.

In addition, a comparative fungicide test has been performed, which comprises placing a piece of leather on a petri dish with a selected standard growth medium, inoculation of a fungi (Aspergillus niger) and measurement of the inhibition halo formed after one week at 25°C.

The following results have been found:

The results show that in the wet blue tanning process the performance of the encapsulated product is clearly better than of the not encapsulated one even when using half the amount of active.

In the wet white tanning process the degradation of the active is reduced, when encapsulated, and the performance of the encapsulated product is also better than the performance of the not encapsulated one. The halo formation clearly shows that the encapsulated TCMTB applied to the leather pieces is also released from the capsules in a long-term release to the adjacent growth medium, which supports the surprising finding of good balance between encapsulation and protection of the active and release for delivering long-term activity.

Claims

1. A method of preparing microencapsulated TCMTB (thiocyanomethylthio benzothiazole) by a) preparing an aqueous solution comprising a stabilizer and a melamine- formaldehyde resin, b) mixing TCMTB with an organic solvent, c) adding the mixture b) to the aqueous solution a) and stirring to prepare an emulsion of an organic phase in an aqueous phase containing TCMTB droplets, d) in situ polymerization of the melamine-formaldehyde resin on the TCMTB droplets, e) formation of a suspension of TCMTB microcapsules in the aqueous phase of the reaction medium, and f) optionally isolating the solid TCMTB microcapsules.

2. The method according to claim 1 , wherein the stabilizer added to the aqueous solution of step a) is styrene-ma!eic anhydride copolymer.

3. The method according to claim 1 or 2, wherein the melamine-formaldehyde resin is selected from melamine-formaldehyde resins having 3 to 4 Ci-C₂-alkylated reaction sites.

4. The method according to any one of the preceding claims, wherein the melamine- formaldehyde resin is selected from methylated imino melamine-formaldehyde resins.

5. The method according to any one of the preceding claims further comprising a step of adding a formaldehyde scavenger and/or a thickener to the emulsion of step c).

6. The method according to claim 5, wherein the formaldehyde scavenger is selected from the group consisting of urea, acetoacetamide, and imidazolidone, and the thickener is selected from the group consisting of gums such as xanthan gum, alkali swellable emulsions (ASE), hydrophobically modified alkali swellable emulsions (HASE), and hydrophobically modified polyurethanes (HEUR).

7. The method according to any one of the preceding claims, wherein the organic solvent of step b) is selected from biodegradable organic solvents such as methyl esters or saturated and un saturated C₁₆-C₁₈ fatty acids.

8. The method according to any one of the preceding claims, wherein the reaction temperature is controlled to be within a range of 40 to 90 °C.

9. The method according to claim 8, wherein the reaction temperature is controlled to be within a range of 45 to 85 °C.

10. The method according to claim 8 or 9, wherein the reaction temperature is controlled to be within a range of 50 to 80 °C.

11. The method according to any one of the preceding claims, wherein the pH in the reaction media is controlled to be within a range of pH 3.0 to 7.0.

12. The method according to claim 11, wherein the pH in the reaction media is controlled to be within a range of pH 3.5 to pH 6.5.

13. The method according to claim 11 or 12, wherein the pH in the reaction media is controlled to be within a range of pH 4.0 to 6.0.

14. The method according to claim 11, 12 or 13, wherein the pH in the reaction media is controlled to be within a range of pH 5.0 to 6.0.

15. The method according to any one of the preceding claims, wherein after formation of the emulsion in step c) the reaction mixture is maintained at 70 °C and pH 5.5 ± 0.3 for at least 4 hours.

16. The method according to claim 15, wherein the reaction mixture is maintained at 70 °C and pH 5.5 ± 0.3 for at least 5 hours.

17. Microencapsulated TCMTB obtainable by a process according to any one of the preceding claims.

18. Microencapsulated TCMTB comprising TCMTB as the core material, which is encapsulated by a melamine-formaldehyde polymer microcapsule.

19. Aqueous suspension comprising the TCMTB microcapsuies according to claim 17 or 18, suspension according to claim 19 in a tanning process or for preserving hides or leather, paints, paper products, wood, wood products, or industrial water. 21. A method of tanning hides or leather or a method of preserving hides, leather, fibers or polymerized material, comprising the treatment of the hides, leather, fibers or polymerized material with TCMTB microcapsules or with an aqueous suspension containing TCMTB microcapsules.