WO2017140991A1

WO2017140991A1 - Fluid composition for wood protection

Info

Publication number: WO2017140991A1
Application number: PCT/FR2017/050360
Authority: WO
Inventors: Franck Aurissergues; Antoine DE KERGOMMEAUX
Original assignee: Rhodia Operations
Priority date: 2016-02-17
Filing date: 2017-02-17
Publication date: 2017-08-24
Also published as: FR3047737A1

Abstract

The invention relates to an aqueous suspension of monocrystalline particles of cerium oxide, optionally functionalised with PAA, and a fluid composition formulated in aqueous phase adapted for wood protection and comprising said particles.

Description

FLUID COMPOSITION FOR PROTECTING WOOD

The present invention relates to an aqueous suspension of cerium oxide particles and its use as an additive for aging resistance of wood. It also relates to a fluid composition forming a film on the surface of the wood comprising said particles.

The technical problem

Photooxidation of wood is a phenomenon of degradation of wood exposed to solar radiation in the presence of water and oxygen that can lead to a change in its appearance (color change, cracking, peeling).

The application of a protective film to the surface of the wood to protect it is known. The film then contains an anti-UV additive that can delay or prevent the phenomenon of degradation. The anti-UV additive may be an organic additive of the HALS type. It can also be an inorganic additive in the form of particles. The inorganic additive may for example be based on cerium oxide (Rhodigard ^® W200), titanium oxide (Hombitec ^® RM 400) or iron oxide (produced by Sayerlack).

The Applicant has developed an aqueous suspension of dispersible cerium oxide particles in an aqueous formulation for protecting the wood against UV radiation and against the effects of aging. Cerium oxide particles have such size characteristics that the coating effectively protects the wood without affecting transparency or color.

Brief description of the invention

The invention relates to an aqueous suspension of monocrystalline cerium oxide particles optionally functionalized with polyacrylic acid (PAA) comprising from 15 to 60, preferably from 20 to 30, polymerized acrylic acid units, the average value of the size of the particles determined by the X-ray diffraction technique (doRx) being between 8 and 20 nm, more particularly between 10 and 20 nm, more particularly between 10 and 15 nm. The invention also relates to a fluid composition formulated in aqueous phase adapted to the protection of wood and comprising the aqueous suspension or the above-mentioned monocrystalline cerium oxide particles. The invention also relates to the wood which is protected by the coating formed after application of the fluid composition to the wood and to the use of the suspension or the fluid composition. figure

Fig. 1/3 represents MET images of non-functionalized cerium oxide particles according to the invention. There are individualized particles of homogeneous form.

Fig. 2/3 represents the counting M ET allowing to obtain d MET and SMET for the particles of example 1. abscissa: classes in nm; ordinate: number of particles in each class.

Fig. 3/3 represents the particle size distribution obtained by DLS for the suspension of Example 1. abscissa: diameter in nm; ordinate:% by volume.

The prior art

WO 03/072663 discloses the use of a colloidal dispersion of oxide and / or hydrated oxide of cerium in the stains and varnishes applicable to a support such as wood. The cerium is mainly in the form of cerium IV (Ce '"/ This total of at most 5%) The particles have a size determined by TEM of at most 200 nm, more particularly at most 100 nm. in the form of agglomerates of crystallites whose d ₈ o is at most equal to 5 nm or at most 10 nm according to the embodiment.The dispersion is in the form of a mixture of the particles stabilized with an amphiphilic agent in an organic phase and is usable in an organic and non-aqueous paint.

WO 03/099942 describes a composition that can be used as an aqueous paint, especially as a wood stain. The composition is a colloidal dispersion comprising cerium oxide and / or hydrated oxide particles whose average size determined by M ET is at most 200 nm, more particularly at most 100 nm, more particularly at most 10 nm. The particles are stabilized with an organic acid having at least 3 acid functions, the 3 ^rd pK of which is at most 10. The organic acid can be, for example, citric acid. WO 2005/095505 discloses a colloidal dispersion of cerium oxide particles coated with silica. WO 2006/072743 discloses an aqueous paint comprising a colloidal dispersion of cerium oxide stabilized with a water-soluble or water-dispersible polymer. The particles have a size between 1 and 500 nm. The size measured by dynamic light scattering (DLS) is at most 200 nm, more preferably at most 100 nm, or even at most 10 nm.

WO 2007/068826 discloses a wood treatment method comprising the application of an aqueous composition including a stain, a varnish or a paint may include cerium oxide particles whose size determined by MET is at most 200 nm, more particularly at most 100 nm. This size may be more particularly at most 10 nm. The particles are stabilized by an organic acid or a salt of this acid having at least 3 acid functions, the 3 ^rd pK of which is at most 10. The organic acid may be citric acid. WO 2008/043703 describes a liquid suspension of cerium oxide particles having a size of at most 200 nm, more particularly at most 150 nm, more particularly at most 120 nm, and more particularly at at most 100 nm. These particles are formed of aggregates of primary particles whose size is at most 100 nm, or even at most 80 nm or even more particularly at most 60 nm. The primary particles have an average size of at least 10 nm, especially at least 20 nm, more particularly at least 30 nm. The suspension can be used in paints or cosmetic compositions. In all the examples, the particles have a size close to 100 nm. There is no mention of use in a composition to protect the wood.

WO 2010/020466 discloses a liquid suspension of cerium oxide particles having a size of at most 200 nm, these secondary particles being formed of primary particles whose size is at most 150 nm. The suspension can be used in paints or cosmetic compositions. There is no mention of use in a varnish or stain. In all the examples, the particles have a size close to 100 nm. There is no mention of use in a composition to protect the wood.

WO 2014/005753 discloses surface-modified nanoparticles. The nanoparticles have a size of between 0.1 and 2000 nm, more particularly between 5 and 600 nm. WO 2014/002008 discloses a method for treating wood and / or wood-derived product (s) with at least one drying unsaturated vegetable oil, characterized in that the oil (s) is used in combination with nanoparticles of cerium oxide (CeO ₂ ) of average size MET less than 30 nm, preferably about 10 nm. They may more particularly have an average size ranging from 1 to 20 nm, and preferably about 10 nm.

WO 2010/020466 discloses a suspension of cerium oxide particles having a size of at most 200 nm, these secondary particles being formed of primary particles whose size is at most 150 nm. The suspension can be used in paints. In all the examples, the particles have a size close to 100 nm.

DE 102009040868 discloses compositions which comprise cerium oxide particles but their size is not specified.

WO 2009/077412 discloses surface-modified inorganic particles. It is not specified that the cerium oxide particles are monocrystalline.

Detailed description of the invention

The invention relates to a fluid composition formulated in aqueous phase comprising dispersed cerium oxide particles having certain size characteristics. The particles may be optionally functionalized with polyacrylic acid (PAA). The fluid composition is formulated in aqueous phase which means that at room temperature (20 ° C), water is the major liquid ingredient among the liquid ingredients of the composition. Water is a liquid ingredient of the composition but it is possible that the composition also contains one or more organic solvents. These may be added to enhance certain physicochemical characteristics of the composition or may be provided with the ingredients forming the composition. The proportion of water among the liquid ingredients is greater than 50% by weight. This proportion can be greater than 60%, or even 80%. This proportion can be determined by analysis of the liquid phase forming the composition.

The fluid composition comprises cerium oxide particles according to the invention, having an anti-UV filter function. To protect the wood, the fluid composition also comprises other ingredients usually used in the formulations used to protect the wood. It can thus comprise at least one polymer in solution, in emulsion or in dispersion in water. The polymer may be an acrylic polymer or alkyd urethane. An example of an acrylic polymer may be Mowilith LDM 7714 or 7717 from Celanese. It may also be the Avanse ™ ST-410 acrylic emulsion from Dow Chemicals.

The fluid composition may also comprise at least one thickening agent whose function is to modify the viscosity of the fluid composition. It may also comprise at least one organic solvent. It may also comprise at least one biocidal agent. It may also include at least one surfactant. It may also comprise at least one coloring agent which may be organic or mineral.

For the preparation of a composition according to the invention, it is conceivable to consider fluid compositions in aqueous phase already marketed for the protection of wood and the preparation of a transparent or semi-transparent protective film and to disperse the cerium oxide according to the invention. This may be for example the formulation SC 2321/85 of the Sayerlack Arch Coatings, which is described in particular in Youcef Irmouli's thesis entitled "Study of finishing systems for wood: application of new formulations, aging and improvement of performance ". For compositions already comprising at least one anti-UV additive, it is possible to reconstitute a composition according to the invention by substituting the anti-UV additive (s) with the cerium oxide according to the invention. For example, it will be possible to reconstitute such a composition from Sigmalife DS Acryl Futura or Sigmalife DS Satin grades from Sigma Coatings.

The viscosity at room temperature of the fluid composition may vary depending on the intended application and the manner of applying the composition to the wood. Thus, the composition can be liquid or in the form of a paste. The fluid composition according to the invention is obtained from an aqueous suspension of cerium oxide which is described below. The preparation of the composition consists of mixing together this aqueous suspension and the other ingredients forming the paint composition. According to one embodiment, the aqueous suspension may be mixed with the other ingredients forming the composition which have previously been already mixed together. According to another embodiment, the aqueous suspension may also be mixed with at least one of the other ingredients forming the fluid composition, and then the mixture thus obtained is mixed with the other ingredients. Whatever the embodiment, it is preferable that the cerium oxide particles do not precipitate on contact with one of the ingredients or a mixture of ingredients and remain well dispersed. According to one embodiment, the cerium oxide functionalized by the PAA is brought into contact with one of the ingredients or a mixture of ingredients having a pH> 3. According to one embodiment, the nonfunctionalized cerium oxide is put in contact with one of the ingredients or a mixture of ingredients having a pH <6.

The proportion of cerium oxide that may be functionalized may be between 0.5 and 5.0% by weight, this proportion being calculated relative to the whole of the fluid composition. This proportion can be between 1.0 and 3.0% by weight.

The fluid composition forms a film on the surface of the wood after application to the wood. Depending on the characteristics of the composition, in particular its rheological characteristics, it may be applied by means of a brush or a roller, or may be applied by spraying. The wood may be for example a light wood, for example a wood type pinus sylvestris.

After drying, the film forms a coating that protects the wood. The invention also relates to wood protected by the coating.

Cerium oxide particles do not affect the transmission of light, so it is possible to obtain a transparent coating that leaves the appearance of the wood and its visible structure. It is possible to obtain a coating having a transparency greater than or equal to 90%, this transparency being determined by measuring the total transmission at 550 nm after application of a film of 100 μιτι of the fluid composition on a glass plate and drying of the -this. Similarly, it is possible to obtain a coating having a haze of less than or equal to 20%, the haze being determined after application of a film of 100 μιτι of the fluid composition on a glass plate and drying thereof, and being calculated by the following formula:

haze (%) = [% diffuse transmission /% total transmission] formula in which the total transmission and the diffuse transmission are measured at 550 nm.

For the measurement of the total transmission and diffuse transmission, the film is obtained after application of a glass plate to the fluid composition and its thickness is controlled by means of an automatic applicator. The thickness is measured immediately after application. Then, after drying of the film, the total transmission and diffuse transmission are measured using a UV spectrophotometer equipped with an integration sphere.

To quantify the color, colorists have developed different systems from the measurement of tristimulus values using a spectrocolorimère. The CIEL ^* a ^* b ^{* system} is a color representation space in which a point is located in a Cartesian system defined by the luminance L which varies from 0 (black) to 100 (white) and by the coordinates a and b which define the chromaticity plane [a, b] and respectively correspond to the two pairs of complementary colors red-green and blue-yellow. This space is constructed so as to be uniform, which makes it possible to quantify the overall color difference ΔΕ defined by the formula:

ΔΕ = [(L-Linitia,) ² + (a-initial) ² + (b-binital) ² ] ⁷²

in which

respectively designate the colorimetric coordinates L, a, b of the protective film before the start of accelerated aging and L, a, b respectively designate the same coordinates after a given accelerated aging time. The protective coating can lead to a color change limited in time with a ΔΕ <28 after an accelerated aging of 1500 hours performed under the conditions of the AFNOR EN 927-6 standard. Conditions of this standard are in particular given in Example 5.

Accelerated aging according to these standards leads to simulate the aging processes that come into play in natural aging. Apparatus equipped with fluorescent UV lamps and devices for condensation and water spraying are used. The artificial aging of the coatings with fluorescent UV lamps and under the effect of condensation or water spraying is used to produce a certain energy exposure or an agreed total number of hours of loading, so as to obtain a certain degree of modification of one or more properties. The properties of the exposed coatings are compared with those of unexposed coatings having been prepared from the same products under identical conditions. As regards the aqueous suspension of cerium oxide used for the preparation of the fluid composition, the latter comprises monocrystalline particles of cerium oxide. The average value of the particle size determined by the X-ray diffraction technique (d DRx) is between 8 and 20 nm, more particularly between 10 and 20 nm, more particularly between 10 and 15 nm. The term "suspension" refers to a liquid in which solid particles are dispersed.

The average value of the particle size (d DRx) is determined by the X-ray diffraction technique. This measured value corresponds to the size of the coherent domain calculated from the width of the most intense diffraction lines and using the Scherrer model:

k ^■ To

t =;

^ H ² - s ^{2 ■} <: s $

t: size

k: form factor of 0.9

λ (lambda): wavelength of incident beam 1, 540598 Angstrom

H: width at half height of the peak

s: width due to instrument optics defect which depends on the instrument used and angle Θ (theta)

Θ: Bragg angle d _D Rx is the arithmetic mean of the three sizes t1, t2 and t3 determined from Scherrer's formula above on the three peaks at 2Θ (2 theta) = 28.6 °; 47.5 ° and 56.4 °.

This value is close to the mean diameter d _M ET which is calculated from a particle size distribution determined using transmission electron microscopy (TEM). The particles have an _M ET between 8 and 20 nm, more particularly between 10 and 20 nm, more particularly between 10 and 15 nm, and a standard deviation S _M ET less than 35% of said average diameter, d _M AND and S _M ET being calculated from a particle size distribution determined using transmission electron microscopy (TEM). The method consists of measuring the diameter of at least 300 particles on one or more electron microscope slides. The enlargement of the microscope which is retained must make it possible to clearly distinguish the images of the particles on a snapshot. The enlargement can be for example between 50 000 and 500 000. The diameter of a particle which is retained is that of the minimum circle making it possible to circumscribe the entirety of the image of the particle as it is visible on a surface. MET snapshot. The term "minimum circle" (in AAnnggllaaiiss ,, "" mmiinniimmaall eenncclloossiinngg cciirrccllee "")) aa llee sseennss qquuii lluuii eesstt ddoonnnnéé iinn mmaatthhéémmaattiiqquuee rreepprréésseennttee aanndd tthhee cceerrccllee uu uu ddiiaammèèttrree mmiinniimmuumm ppeerrmmeettttaanntt ccoonntteenniirr AANN eennsseemmbbllee uu ppooiinnttss dd''uunn ppllaann .. EAR ssoonntt rreetteennuueess qquuee tthhee ppaarrttiiccuulleess ddoonntt tthhee mmooiinnssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssess lcdcccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc

After determining the diameters of the particles retained by the above method, said diameters are grouped into several size classes ranging from 0 to 500 nm, the width of each class being 1 nm. The number of particles in each class is the basic data to represent the (cumulative) number distribution. The mean diameter of MET is the median diameter such that 50% of the particles (in number) taken into account on the MET plate (s) have a diameter smaller than this value. From this distribution, it is also possible to determine the standard deviation SMET which has the usual meaning used in mathematics and which can be defined as the square root of the variance:

n is the number of (so-called primary) particles taken into account on the SEM image (s);

X, is the diameter of a particle i on the SEM image (s);

is the average diameter of the n particles, calculated according to the formula 1 / nΣ _{= 1} x ,.

The particle size distribution of the aqueous suspension can be obtained using a laser granulometer which is based on the dynamic light scattering technique (also known as dynamic light scattering DLS). This technique is particularly suitable for submicron particles. The average diameter d ₅ o corresponds to the median diameter of a volume distribution of the diameters of the particles obtained using the dynamic light scattering technique. d ₅ o is the value for which on the cumulative volume distribution curve, 50% of the particles have a diameter greater than d ₅ o and 50% of the particles have a diameter less than d ₅ o - An example of a particle size distribution Illustrative is given in FIG. 3/3 for the suspension of Example 1. The Zetasizer Nano ZS from Malvern Instruments can be used to obtain such a distribution. Note that d ₅ o is greater than d _M ET because the particles can agglomerate according to the conditions of preparation of the suspension and according to the pH of the suspension. The dispersion index of the above-mentioned distribution obtained by DLS is defined by the formula:

in which :

- d ₈₄ is the particle diameter for which 84% of particles have a diameter less than d _84;

d-i6 is the particle diameter for which 16% of the particles have a diameter less than di ₆ .

The aqueous suspension is stable, which means that if no agitation is applied to the suspension, the particles remain in suspension and the formation of a settling cake is not observed for several days, for example before at least 8 days. In addition, the settling cake, if it is formed, can be resuspended by gentle stirring.

The cerium oxide particles contemplated in the present application are either functionalized by PAA or non-functionalized, these two terms being now explained:

· Cerium oxide particles functionalized by PAA: when the particles are functionalized by the PAA, the average diameter d ₅ o is between 30 and 70 nm. The term "PAA functionalized particles" is used in this application to describe the fact that PAA is adsorbed on the surface of these particles. This modification is obtained when the PAA interacts via chemical and / or physical bonds with the chemical groups on the surface of the particles. When the cerium oxide is functionalized by PPA, the aqueous suspension is generally stable for a pH> 3, in a pH range generally between 3 and 10, more particularly between 4 and 9. The particles are stabilized by PAA. .

The PAA used comprises from 15 to 60, preferably from 20 to 30, polymerized acrylic acid units. The number of units can be determined by means of size exclusion chromatography which makes it possible to determine the number-average molecular mass M _n . Those skilled in the art know how to determine the molecular weights of PAA using the appropriate conditions for water-soluble polymers of small masses. For example, it may be used a reference chromatography column "aquagel-OH MIXED 8 μιτι" marketed by Agilent. We can use the standards marketed by Agilent under the reference (EasiVial PEG / PEO). Examples of conditions are given below: columns: 2 PL columns aquagel-OH mixed-H 8 μιτι, 300 x 7.5 mm; eluent: aqueous solution 0.2 M NaNO ₃ + 0.01 M NaH ₂ PO ₄ of pH 7; flow rate: 1.0 ml / min; refractometric detector. Once M _{n is known} , the number of motifs is defined by M _n / 72.06. Depending on the pH of the suspension, the PAA is in acidic or basic form or partly in acidic and basic form. The counter anion of the acidic groups of the PAA can be for example K ⁺ , Na ⁺ or NH ₄ ⁺ . non-functionalized cerium oxide particles: the process for preparing the cerium oxide particles from a mixture of Ce '' and Ce ^lv which is described below makes it possible to obtain a stable suspension. In this case, the cerium oxide particles are said to be "non-functionalized" because the suspension thus obtained is stable even in the absence of PAA or any other organic stabilizer in the aqueous suspension, in particular of stabilizer comprising at least one acid function. The stability is likely to be ensured by the residual amounts of inorganic ions present in the suspension, such as nitrate or ammonium ions.The suspension of the non-functionalized cerium oxide particles is generally stable for a period of time. pH <6, in a pH range between 2 and 6, more particularly between 4 and 6. It may have a median diameter d ₅ o of between 20 and 40 nm.

The aqueous suspension may have a dispersion index σ / m <0.6, preferably <0.5.

The cerium oxide particles have a polygonal shape. This shape is regular as can be seen in FIG. 1/3. The distribution of the particle diameters MET can be a monopopulation (see Fig. 2/3), as well as the distribution DLS (see Fig. 3/3).

The proportion by weight of cerium oxide functionalized or non-functionalized with respect to the entire suspension may vary within wide limits and may be at most 30.0%. It can be between 1.0% to 30.0%, preferably between 10.0 and 30.0%.

The liquid phase of the suspension is an aqueous phase. The aqueous phase comprises water and optionally at least one other liquid which is miscible with water in all proportions at a temperature of 20 ° C. A condition in the choice of the nature and the mass proportion of the other liquid in the aqueous phase is however that the suspension remains stable, that is to say that cerium oxide particles do not sediment to form a settling cake in contact with the other liquid miscible with water. The other liquid may be, for example, an aliphatic alcohol or a glycol ether. Water is the majority liquid of the suspension. The mass ratio water / other liquid may vary generally from 100/0 to 75/25. Preferably, the cerium oxide particles are dispersed in water. With regard to the process for preparing the non-functionalized cerium oxide particles, this is described in international application WO 2008/043703 and uses a mixture of Ce '' and Ce ^lv . cerium and the aqueous suspension are capable of being prepared by the process which will now be described.

This process comprises the following steps:

(a) contacting, under an inert atmosphere, a solution of a salt of Ce '' which further comprises ^Cev , with a base, whereby a precipitate is obtained;

- (b) the medium obtained in the preceding step is heated under an inert atmosphere at a temperature between 60 and 95 ° C, at least one of the steps (a) or (b) being conducted in the presence of nitrate ions;

- (c) is carried out successively but in any order acidification and washing of the medium thus obtained, whereby the suspension is obtained. At the first step (a) is prepared from a solution which is a solution of a salt of Ce "further comprising Ce ^lv. As salts of Ce '" can be used in particular nitrate, chloride cerium III sulphate or carbonate as well as mixtures of these salts such as mixed nitrate / chloride. In a known manner this starting solution must have the appropriate acidity so that the cerium is completely present in solution. ^Cev is supplied by a salt which may be, for example, cerium IV nitrate. The amount of Ce ^lv is such that the molar ratio Ce ^lv / Ce _to tai in the starting solution can be between 1/100 and 1/50. It can be between 1/70 and 1/50, more particularly between 1/65 and 1/50. This report ^lv / This is _to re adapted and modified if necessary to reach the desired size of particles DRx.

The starting solution may be degassed beforehand by contact with an inert gas. By "inert gas" or "inert atmosphere" is meant for the present description an oxygen-free atmosphere or gas, the gas being, for example, nitrogen or argon. The contacting may be a bubbling of the inert gas in the solution. The starting solution is reacted with a base. As a base, the products of the hydroxide type can be used in particular. There may be mentioned alkali or alkaline earth hydroxides and ammonia. It is also possible to use secondary, tertiary or quaternary amines. However, amines and ammonia are preferred insofar as this makes it possible to reduce the risks of pollution by alkaline or alkaline-earth cations. The base may also be degassed beforehand by contact with an inert gas. The amount of base used is in excess of the cations present in the starting solution, so as to precipitate all the cerium present. It is possible to use a base amount which may be such that the base / cation molar ratio present in the starting solution is greater than 1.30.

To conduct the reaction, the contacting can be done in any order of introduction of the reagents. However, it is preferable to introduce the starting solution in a medium containing the base. This step (a) must be conducted under an inert atmosphere. It can be conducted either in a closed reactor or in a semi-closed reactor with inert gas scavenging. The contacting is generally carried out in a stirred reactor. This step is generally carried out at room temperature (20-25 ° C) or at a temperature of at most 50 ° C.

The ^2nd step (b) of the process is a heat treatment of the reaction mixture obtained at the end of the previous step. This treatment consists in heating the mixture and maintaining it at a temperature which is generally at most 95 ° C. and more particularly between 60 ° C. and 95 ° C. The duration of this treatment can be between a few minutes and a few hours. This treatment is also carried out under an inert atmosphere, which has been described with respect to this atmosphere for step (a) applying likewise here.

According to a characteristic of the process, at least one of the steps (a) or (b) must be conducted in the presence of nitrate ions. Generally, the nitrate ions are provided by the addition of nitric acid, more particularly in step (a), during the preparation of the Ce '' solution. The amount of nitrate ions, expressed by the molar ratio NO ₃ ^" / Ce '" is generally between 1/6 and 5/1, rather between 1/3 and 5/1. Step (c) actually comprises two successive operations that can be performed in any order. These operations are on the one hand an acidification and on the other hand a washing. These operations will be described below more precisely in the case of a sequence of acidification and then washing. Acidification generally takes place after cooling of the medium obtained at the end of step (b) by addition of an acid. Any mineral or organic acid can be used. Nitric acid is more particularly used. The amount of acid added is such that the pH of the medium after acidification is between 1 and 5. This operation can be conducted in air, it is no longer necessary to operate under an inert atmosphere at this stage of the process.

The acidification is followed by a washing which aims to remove from the suspension the soluble species, mainly salts. The washing can be done in different ways with or without solid / liquid separation. It can thus be carried out by separating the solid particles from the liquid phase, for example by frontal filtration, decantation or centrifugation. The solid obtained is then resuspended in an aqueous phase. One can also proceed by tangential filtration. This washing may be optionally renewed if necessary, for example until a given conductivity of the suspension is obtained, the conductivity measuring the level of impurities present in this suspension. As indicated above, the order of operations can be reversed with respect to what has just been described. Thus, at the end of step (c) and, again, generally after cooling the medium obtained, it is then possible to carry out a washing as described above. At the end of the washing, the acidification of the medium obtained is then carried out. The advantage of this process is to obtain a suspension of cerium oxide without calcination step at high temperature.

At the end of step (c), the suspension of nonfunctionalized cerium oxide is thus obtained. The cerium oxide can be described here as non-functionalized because it is not necessary that the suspension comprises an organic stabilizer, including a stabilizer comprising at least one carboxylic acid or carboxylate function. The suspension nevertheless remains stable, the stability being able to be ensured by the residual amounts of inorganic ions present in the suspension, such as nitrate or ammonium ions.

A variant of the process will now be described. This differs only in the fact that a solution of a salt of Ce '"further comprising hydrogen peroxide is used as starting solution, which has been described above on the nature of the salt of Ce '"likewise applies here. The amount of H ₂ O _{2 solution} is such that the molar ratio H2O2 / Ce '' in the cerium salt solution is between 1 / 10,000 and 1 / 100. The remainder of the process according to this variant proceeds as described above.

Steps (a), (b) and (c) may be more particularly the following:

(a) an acidic solution formed from nitrate of Ce '', nitrate of Ce ^IV , is contacted with an ammonia solution under an inert atmosphere, whereby a precipitate is obtained;

(b) the medium obtained in the preceding step is heated under an inert atmosphere at a temperature of between 60 and 95 ° C .;

- (c) is carried out successively but in any order acidification and washing of the medium thus obtained, whereby the suspension according to the invention is obtained.

The solutions used in step (a) are preferably degassed with a neutral gas, such as, for example, nitrogen. The acidic solution can be a nitrate solution of Ce "and Ce ^lv and nitric acid. The amount of ammonia used is in excess of the cations present in the starting solution and to precipitate the throughout this cerium. One can use an amount of ammonia being such that the molar ratio NH ₄ OH / cations present in the starting solution is greater than 1, 30. the ratio Ce ^lv / This is adapted _to tai, and modified if necessary, to achieve the desired particle size Ô DRX.It may be between 1/100 and 1/50, more particularly between 1/70 and 1/50, even more particularly between 1/65 and 1/50. According to one embodiment, the solution of Ce '' and Ce ^lv is added to the ammonia solution. The duration of the addition can be between 20 minutes and 1 hour.

In step (c), one carries out successively but in any order an acidification and a washing of the medium thus obtained, whereby one obtains the suspension according to the invention.

As regards the process for preparing the suspension of the cerium oxide particles functionalized with PAA, it consists in first bringing into contact a suspension in water of the non-functionalized cerium oxide particles obtained. from the method using the mixture of Ce '"and Ce ^lv as just described, with a solution of PAA in water, the pH of the suspension comprising the non-functionalized cerium oxide and the PAA is generally between 3 and 4. Then, the pH of this suspension is raised using a base to a pH of between 5 and 9.5 It can be used as NaOH, KOH or NH _{4 base} The contact time may vary between 10 minutes and 2 hours, for example it may be between 20 and 40 minutes. The suspension in water of the non-functionalized cerium oxide particles obtained from a solution of Ce '' and Ce ^lv according to the method already described has a pH <7, in a pH range from 2 to 6 (so-called acid suspension) It is possible to directly use this acid suspension for the preparation of the functionalized particles It is also possible in a step prior to contact with the PAA, to add a base to the acid suspension until precipitating the cerium oxide particles and then separating the solid particles from the liquid medium Precipitation occurs around a pH close to 7. The separation step may be optionally followed by a step washing the particles with water The re-dispersal of the particles after filtration and the possible washing leads to a suspension which can have a pH> 7. The pH of this suspension can be between 7 and 8. It is also possible to use this suspension for the preparation of functionalized particles. According to one embodiment, the suspension of cerium oxide is added with stirring to the PAA solution. According to another embodiment, the PAA solution is added with stirring to the cerium oxide suspension.

According to one embodiment, the suspension obtained after contacting the suspension of cerium oxide and PAA and raising the pH can be subjected to shear in order to disaggregate the particles. This step makes it possible to disaggregate the particles which would have agglomerated at one of the preceding stages. At this stage, it is possible to use for example a wet jet mill (in English: "wet jet mill").

The added PAA does not bind fully to the surface of the particles. Indeed, only a part of the PAA is adsorbed on the surface of the cerium oxide particles and the other part remains in solution. The amount fixed depends on the surface area and the surface state of the cerium oxide. Tests have shown that for a better stability of the suspension, the amount of PAA (expressed in mg of PAA per g of nonfunctionalized cerium oxide) to be added is preferably at least 0.87 × S BET OÙ SBET designates the specific surface area in m ² / g of cerium oxide before modification. For example, it is possible to add an amount of between 0.87XS BET and XSBET-BET is determined by nitrogen adsorption using the Brunauer-Emmet-Teller method which has been described in J. Am. Chem. Soc. 1938, 60, p.309. The principle of this method is also described in ASTM D3663-03. The Shimadzu Flowsorb II 2300 can be used to determine the BET specific surface area. This one is determined automatically using a Tristar II 3020 Micromeritics device on samples in accordance with the indications recommended by the manufacturer The samples are previously treated under vacuum for 15 min at 300 ° C. The measurement is made on 5 points in the range of relative pressures p / p ₀ ranging from 0 to 0.3 inclusive. Equilibrium time for each point: 5 seconds.

Use of the cerium oxide suspension. The cerium oxide suspension as well as the cerium oxide particles can be used in the preparation of the fluid composition. They can also be used as an anti-UV additive in a fluid composition to protect the wood.

Examples

EXAMPLE 1 Preparation of a Colloidal Suspension of CeOg with dgo = 25 nm (according to the invention)

A solution of cerium nitrate is prepared by adding 271.5 g of a solution of trivalent cerium nitrate (concentration 2.88 M, density d = 1.714), 42.5 g of HNO ₃ solution. at 68% and 8.34 g of tetravalent cerium nitrate solution (concentration 1.33M, density d = 1.440). This solution, the molar ratio Ce ^lv / Ce _to tai is equal to 1/60, is loaded into a semi-closed tank, then degassed with vigorous stirring and bubbling with nitrogen for 2 hours.

A dilute ammonia solution is prepared by adding 171.5 g of 28% ammonia and 1614.1 g of water. This solution is placed in a semi-closed 2.5 l reactor, then stirred at 400 rpm under nitrogen bubbling for 2 h.

The solution of cerium nitrate prepared above is then added over 30 min to the ammonia solution with the same agitation and under a nitrogen sweep. The reaction mixture is then heated to 83 ° C in 45 min, then maintained at this temperature for 4 h under the same agitation and under nitrogen sweep.

At the end of this heat treatment, the mixture is cooled and then acidified to a pH = 2 by adding 68% nitric acid. The nitrogen sweep is stopped then the suspension and washed by a series of centrifugation and repulping with deionized water until a suspension adjusted to 25% by weight having a pH of 5.3 and a conductivity 0.5 mS / cm.

Part of the suspension is oven dried at 200 ° C to obtain a powder for X-ray analysis (XRD). The diffractogram X of this powder has the signature crystallized CeO ₂ (ASTM sheet 34-394). The average size of the coherence zone calculated from the width at half height of the diffraction peaks at 2Θ = 28.6 °; 47.5 ° and 56.4 ° according to the Scherrer formula gives 1 1 nm (apparatus used: PANalytical diffractometer, model X'Pert PRO MPD). The instrumental correction values s are at these angles:

28.6 ° s = 0.070

47.5 ° s = 0.066

56.4 ° s = 0.066

The BET surface area determined by nitrogen adsorption is 93.1 m ² / g which gives an average particle size of 9 nm. MET and SMET values were also determined on MET images: dMET = 8.9 nm; SMET = 2.9 nm (32.6%).

The size of the secondary particles is measured from a Zetasizer Nano ZS laser granulometer from Malvern using an optical index of 2.2 for CeO ₂ in water as reference. The d ₅ o of the suspension is 25.0 nm. The dispersion index σ / m was fixed at 0.37 (di ₆ 18.4 nm; d ₅ o 25.0 nm d ₈₄ 36.9 nm).

Example 2: Preparation of a colloidal suspension of CeO 2 particles 10 nm functionalized with PAA (according to the invention)

200 g of the suspension containing 25% by weight of ex. 1 and 300 g of water are added to give 500 g of a suspension of 10% by weight. 500 g of an aqueous solution containing 4.0 g of polyacrylic acid (or PAA) having a molecular weight of 1800 g / mol (Aldrich) are prepared in parallel. The suspension of CeO ₂ is added to the aqueous PAA solution with vigorous stirring, and then stirred for an additional 15 minutes. This suspension is then centrifuged and the supernatant is removed. The centrifugation cake obtained is then redispersed in deionized water and adjusted to pH = 8 with ammonia 28% so that a 25% suspension is obtained at pH = 8. The particle size of the suspension is determined from a Zetasizer Nano ZS laser granulometer from Malvern by taking an optical index of 2.2 for CeO ₂ in water. The suspension has a d ₅ o = 50 nm and a dispersion index σ / m 0.34 (di ₆ 35.7 nm; d ₅ o 50.0 nm d ₈₄ 70.0 nm).

Example 3: Preparation of a colloidal suspension of CeO? with dgn = 112 nm (comparative)

The same method as in Example 1 was used to prepare a cerium oxide suspension having a higher d ₅ O. The crystallite size as determined by X-ray diffraction is 99 nm. Example 4 Preparation of a Fluid Composition According to the Invention

An acrylic formulation comprising cerium oxide particles is prepared. 20.0 g of the aqueous suspension of Example 1 (proportion by weight of 25% CeO ₂ ) are added slowly dropwise over a period of 30 minutes in 480.0 g of a colorless acrylic formulation. The addition is carried out with stirring using a stirring machine with 4 inclined blades, at a speed of 100 rpm.

This acrylic formulation has a solids content of 23% (after evaporation of the liquids at 110 ° C. to constant weight). At the end of the addition, a fluid (liquid) composition containing 1% by weight of cerium oxide is recovered from the total composition (1 part by weight of cerium oxide functionalized per 100 parts by weight of liquid composition). A few grams of this composition are placed on a contrast card itself fixed on an automatic film applicator (Elcometer brand) equipped with an application bar allowing the production of a film of 120 μιτι thick. The film obtained is dried on the 24 h chart and its colorimetric characteristics are measured using a Minolta colorimeter according to the CIE 1976 method (L, a, b). The colorimetric characteristics of a composition without an anti-UV additive and a composition with cerium oxide particles marketed under the name Rhodiguard W200 are measured for comparison. The Lab values are given in Table I, as is the Ab variation. Table I

Table II identically describes the colorimetric characteristics of other compositions with the suspensions of Examples 1 and 2 and comparative compositions.

Table II

acrylic liquid composition% additive L a b Àb

acrylic formulation without

0 98.91 0.33 1, 39

additive (reference) reference with the suspension

1% Ce0 ₂ 98.40 0.21 2.03 +0.64 of Example 1 (invention)

reference with the suspension

1% Ce0 ₂ -PAA 98.10 0.14 2.37 + 0.98 of Example 2 (invention)

reference with the suspension

of Rhodigard W200 1% of Ce0 ₂ 96.78 -0.65 8.67 +7.28

(comparative)

1% of Tinuvin

reference with Tinuvin 1 130 98.79 0.35 1, 28 -0.09

1,130

It is found that Ab is lower with the suspension according to the invention than with the other suspension of cerium oxide (Rhodiguard). It can be seen that on the contrast cards, the acrylic formulation obtained from Rhodiguard® W200 leaves a yellow mark, visible to the naked eye. The same yellow trace is not observed after application of the suspensions of Example 1 or Example 2.

Example 5: Formulation of additives

Each additive of Table II is added dropwise with stirring into 480 g of a colorless acrylic paint having a solids content of 23% (after drying at 110 ° C. to constant weight).

Table III: tested additives

* commercial product based on cerium oxide

** marketed by CIBA

Example 5 Application of Wood Formulations and Aging Tests

The liquid compositions obtained in Example 4 are applied to wood (with a brush). Specifically, in accordance with the AFNOR EN 927-6 standard, the formulations are applied to Scots pine test pieces (dimensions 150x79x1 8), then the test pieces are subjected to an accelerated artificial aging test. Each liquid composition is applied to four test pieces. Three test pieces are subjected to accelerated aging and the fourth serves as a control. mode of application on the wooden test-tube

1 ^st application (1 00 to 1 20 g / m ^2), drying for 3 h at 20 ° C. light peeling

^2nd application (100 to 1 20 g / m ² ), drying for 3 hours at 20 ° C. light peeling

^3rd application (100-1 20 g / m ^2), drying for 3 h at 20 ° C. light peeling After the 3 ^rd application, it is then allowed to dry for 10 days at room temperature before accelerated aging. QUV test (EN 927-6 standard)

An exposure cycle lasts one week and includes a period of condensation, followed by a sub-cycle of water spray and exposure to UV-A 340, according to Table IV.

Table IV

The cycle lasts 168 h (= 1 s). The cycle must be repeated 12 times, giving a total exposure of 2,016 h (= 12 s). During accelerated aging, samples are taken at different times: tO +1 week; tO +2 weeks; tO + 3 weeks; tO +6 weeks; t0 + 9 weeks; tO +12 wk (tO: early aging). At each sampling, both quantitative and qualitative measurements are made, namely: a colorimetric measurement E

^■ colorimetric measurement ΔΕ: the variation of ΔΕ as defined above is determined;

^■ gloss measurement (or qloss in English): this measurement is made using a glossmeter (or glossmeter) at an incident angle of 60 ° to the surface (always according to the same standard);

^■ qualitative measurement (according to ISO 4628): the general appearance of the test piece is noted in order to note the possible presence of blistering, cracking, peeling or chalking (ISO 4628 standard).

The results are given in Table V. Table V

It can be seen that the cerium oxides of Examples 1 and 2 make it possible to effectively protect the wood and are more effective than the organic additive Tinuvin, since cracks appear as early as 500 hours with the Tinuvin 1 1 30 which is nevertheless suitable for wood protection as described in the commercial brochure of this UV additive. Example 6 Measurements of the Transparency of the Protective Coating

The transparency of a film of the liquid composition is measured using a spectrophotometer. For this purpose, a film of the liquid composition is formed on the surface of a microscope glass slide with the aid of an automatic applicator. The film is dried in ambient air for 24 hours and a spectrum of total transmission and diffuse transmission is then carried out using a Perkin Elmer lambda 900 spectrophotometer, equipped with an integration sphere. The measurement is between 280 and 600 nm with a step of 1 nm.

The percentage of total transmission (TT) at the wavelength of 550 nm is recorded for a film of 50 μm in thickness and for a film of 100 μm in thickness.

Table VI

^* thickness of the film after application of the formulation

We can thus calculate the haze in%. Table IV

^* TT: total transmission; TD: diffuse transmission

Claims

1. A wood protected by a transparent coating which comprises monocrystalline cerium oxide particles optionally functionalized with polyacrylic acid (PAA) comprising from 15 to 60, preferably from 20 to 30, polymerized acrylic acid units, the average value of the particle size determined by the X-ray diffraction technique (d DRx) being between 8 and 20 nm, more particularly between 10 and 20 nm, more particularly between 10 and 15 nm

Protected wood according to claim 1 wherein the particles are obtainable by the process comprising the following steps:

(a) contacting a solution of a salt of Ce '"which further comprises ^Cev , with a base, whereby a precipitate is obtained;

- (c) is carried out successively but in any order acidification and washing of the medium thus obtained.

3. Protected wood according to claim 1 or 2 wherein the particles are obtainable by the process comprising the following steps:

4. Protected wood according to one of claims 1 to 3 characterized in that the volume distribution of the diameters of the particles obtained using the dynamic light scattering technique has a median diameter d ₅ o including:

o between 20 and 40 nm in the absence of any organic stabilizer in the aqueous suspension;

o between 30 and 70 nm when the particles are functionalized by the PAA.

Protected wood according to one of the preceding claims, characterized in that the volume distribution of the diameters of the particles obtained by means of the dynamic light scattering technique has a dispersion index σ / m <0.6, preferably <0.5, σ / m being defined by the formula:

in which :

6. Protected wood according to one of the preceding claims wherein the cerium oxide particles have a mean diameter d MET of between 8 and 20 nm, more particularly between 10 and 20 nm, more particularly between 10 and 15 nm, and a SMET standard deviation of less than 35% of said average diameter, d MET and SMET being calculated from a particle size distribution determined using transmission electron microscopy (TEM).

7. Protected wood according to one of the preceding claims wherein the PAA is in acid or basic form or partly in acid and basic form.

8. An aqueous suspension of monocrystalline cerium oxide particles optionally functionalized with polyacrylic acid (PAA) comprising from 15 to 60, preferably from 20 to 30, polymerized acrylic acid units, the average value of the particle size determined by the X-ray diffraction technique (DR DRX) being between 8 and 20 nm, more particularly between 10 and 20 nm, more particularly between 10 and 15 nm.

The aqueous suspension of claim 8 wherein the particles are obtainable by the process comprising the steps of:

10. An aqueous suspension according to claim 8 or 9 wherein the particles are obtainable by the process comprising the following steps:

1 1. Aqueous suspension according to one of Claims 8 to 10, characterized in that the volume distribution of the diameters of the particles obtained by means of the dynamic light scattering technique has a median diameter d ₅ inclusive of:

o between 30 and 70 nm when the particles are functionalized by the PAA.

12. An aqueous suspension according to one of claims 8 to 11, characterized in that the volume distribution of the diameters of the particles obtained using the dynamic light scattering technique has a dispersion index σ / m <0 , 6, preferably <0.5, σ / m being defined by the formula:

σ / m = (d ₈ - d ₁₆ ) / 2 d ₅₀

in which :

13. Aqueous suspension according to one of claims 8 to 12 wherein the cerium oxide particles have an average diameter d _M AND between 8 and 20 nm, more particularly between 10 and 20 nm, even more particularly between 10 and 15 nm, and a standard deviation S _M ET less than 35% of said average diameter, d _M ET and S _M ET being calculated from a particle size distribution determined using transmission electron microscopy ( TEM).

14. aqueous suspension according to one of claims 8 to 13 wherein the PAA is in acid or basic form or partly in acid and basic form.

15. A fluid composition formulated in aqueous phase adapted to the protection of wood and comprising the aqueous suspension according to one of claims 8 to 14 or cerium oxide particles as defined in one of claims 8 to 14.

16. Wood protected by a transparent coating obtained from a fluid composition as defined in claim 15.

17. Wood according to one of claims 1 to 7 or according to claim 16 characterized in that the protective coating has a variation ΔΕ <28 after an accelerated aging of 1500 hours according to AFNOR EN 927-6.

18. Wood according to one of claims 1 to 7 or according to claim 16 or 17 characterized in that the protective coating has a transparency greater than or equal to 90%, this transparency being determined by measuring the total transmission at 550 nm after applying a film of 100 μιτι of the fluid composition as defined in claim 8 to a glass plate and drying thereof.

19. Wood according to one of claims 1 to 7 or according to claim 16 to 18 having a haze less than or equal to 20%, the haze being determined after applying a film of 100 μιτι of the fluid composition as defined in claim 8 on a glass plate and drying thereof, and being calculated by the following formula:

haze (%) = [% diffuse transmission /% total transmission] in which the total transmission and the diffuse transmission are measured at 550 nm.

20. Wood protection method of applying to the wood the fluid composition as defined in claim 15.

21. Use of the aqueous suspension according to one of claims 8 to 14 in the preparation of a fluid composition formulated in aqueous phase suitable for the protection of wood.

22. Use of the fluid composition as defined in claim 21 to protect the wood.