Cellulose coating composition

Abstract

The present invention relates to a coating composition and an opacifying agent, a method for preparing the coating composition and the opacifying agent, as well as a coating using the coating composition and a method for forming a coating. The coating composition comprises an opacifying agent — the opacifying agent comprises cellulose microparticles and a surfactant, wherein the cellulose microparticles have an average particle length of 0.7 to 9 μm — and a carrier liquid; wherein, based on the total mass of the coating composition, the cellulose microparticles are present in the coating composition in an amount of 1 to 40 weight% and the surfactant is present in the coating composition in an amount of 0.5 to 6 weight%, and the composition comprises less than 5 weight% of a metal oxide.

Description

Technology Field

[0001] The present invention relates to a coating composition and an opacifying agent, and a method for preparing the coating composition and the opacifying agent, as well as a coating and a method for forming a coating using the coating composition. Background Technology

[0002] Organic coatings are widely used as a general, practical, and cost-effective method to provide a barrier between a substrate and the environment, such as between a metal substrate and the environment. Ideally, the coating possesses high resistance to ion migration and good adhesion to the substrate, such as metal or other surfaces. 1 Polymer coating systems have found a wide range of uses in automotive, construction, packaging, and marine applications. 2-6 The use of renewable components can be highly desirable for improving the sustainability and life cycle assessment (LCA) of coating and production processes.

[0003] Traditionally, to produce artificial white coating materials, the industry uses TiO2 ( n 2.6), ZnS( n 2.4) and ZnO( n It has relied on the use of high-refractive-index inorganic materials such as 2.0. However, due to health concerns, TiO2, the most common whitening agent, was recently banned as a food additive by the European Union. In 2022, the European Medicines Agency also emphasized the 'significant importance' of finding harmless substitutes for TiO2 in medicines ( Commission Regulation ( EU ) 2022 / 63 of 14 January 2022 amending Annexes II and III to Regulation ( EC ) No 1333 / 2008 of the European Parliament and of the Council as regards the food additive titanium dioxide ( E 171 ) ( Text with EEA relevance ) 1-5 (European Parliament and Council, 2022).

[0004] A typical paint composition consists of a pigment (e.g., the aforementioned titanium dioxide), a binder (to form a cohesive film), a solvent, such as water (to control viscosity and facilitate application), and optionally additives (for stability, drying control, or special properties). Porosity in paint films often occurs when the solvent or liquid components evaporate during drying. This process leaves voids or micropores in the film, which are influenced by the packing density of the pigment particles and the binder content. When metal oxides, such as titanium dioxide, are used as opacifying pigments, the pigment volume concentration is closely related to the porosity of the paint mixture. Below the critical pigment volume concentration (CPVC), whiteness is determined by the porosity of the paint. However, above the CPVC, whiteness is driven by the scattering efficiency of the pigment.

[0005] Porosity is important for light scattering because it enhances the refractive index contrast between the solid component (e.g., TiO2) and the air-filled voids or pores. Mie scattering theory predicts the relative intensity of scattered light as a function of particle size, observation angle, and the wavelength and polarization of the incident beam. Therefore, when designing pigments, there is an ideal particle size for efficient scattering based on refractive index contrast. This increased contrast (i) improves the opacity and hiding power of the paint, (ii) maximizes the efficiency of the pigment, and (iii) reduces the amount of paint required for effective coverage.

[0006] A progressive strategy for identifying alternative whitening agents is to seek inspiration from nature. Many different biopolymers have been used to produce optical structures, and one such example is cellulose, an abundant and renewable material. Researchers have attempted to use cellulose nanofibrils obtained using homogenization processes combined with some enzymatic or chemical pretreatment.

[0007] For example, WO 2019 / 063647 describes the production of porous particles that are fibril aggregates and capable of scattering white light using cellulose nanofibril materials or a fine web of interwoven cellulose fibrils. WO 2023 / 135261 describes cellulose microparticles produced using a chemical process, and their light scattering ability is uniquely linked to their physical dimensions. 8 These cellulose microparticles are promising whitening agents.

[0008] WO02100955 discloses an aqueous dispersion latex paint comprising a film-forming polymer binder having milled cellulose particles of less than 100 microns as measured by weight-volume distribution. The milled cellulose particles are produced by milling cellulose fibers together with an inorganic extender filler pigment in a size-reduction milling operation to produce somewhat uniform milled cellulose particles, preferably having a particle size of 10 to 60 microns. The weight ratio of milled cellulose particles to milled inorganic extender pigment (filler) is 5 / 95 to 80 / 20. However, milled cellulose within the particle size range described in WO 02 / 100955 A1 cannot sufficiently scatter light and fails to form a continuous film when mixed with an ionic surfactant in an aqueous suspension.

[0009] EP 2 653 508 discloses a paint composition comprising microfibrillated cellulose, a binder, and a solvent. The microfibrillated cellulose is present in an amount ranging from about 0.1% to about 10% by weight based on the total weight of the paint composition. The composition further comprises an inorganic particulate material co-processed as a primary pigment and / or extender pigment, wherein the inorganic particulate material is co-processed with a fibrous substrate containing cellulose during the preparation of the microfibrillated cellulose. The microfibrillated cellulose helps to evenly distribute the pigment in the paint, resulting in homogeneous coverage and color intensity.

[0010] However, there are difficulties in forming continuous white films using such cellulose-based whitening agents. When these cellulose particles are dried directly from a solvent such as water, 9 It is difficult to produce thin, continuous, and homogeneous white films. It is believed that cellulose particles do not assemble homogeneously to form a continuous and homogeneous white film when deposited on a substrate. Films formed by drying such particles directly from a solvent are variable and of lower quality than films formed from inorganic materials such as TiO2. Consequently, cellulose particle-containing films produced by known methods may have lower light scattering ability and lower whiteness compared to, for example, TiO2 films, and may lack control over these parameters. Therefore, these known white cellulose films may not be desirable substitutes for traditional inorganic material-based coatings.

[0011] The present invention aims to solve these problems.

[0012] Most generally, the present invention provides a coating composition comprising a cellulose particle-based opacifying agent. The opacifying agent comprises cellulose microparticles and a surfactant. The cellulose microparticles impart opacity to the opacifying agent, while the surfactant assists in the distribution of the cellulose microparticles in the coating composition.

[0013] The inventors have discovered that the enhanced distribution and scaffolding effects provided by the surfactant result in the effective formation of a cellulose microparticle coating on a substrate. This is suggested to be because the cellulose microparticles do not prematurely precipitate from the composition during the setting of the coating (as the solvent volume decreases), but rather remain homogeneously dispersed in the solvent by the surfactant. This enables the formation of a homogeneous and continuous cellulose coating, exhibiting uniformly excellent whiteness and opacity. In particular, the average particle length of the cellulose microparticles enables the achievement of a very white composition without the need for TiO2 in the formulation.

[0014] Generally, a coating composition for providing a cellulose microparticle coating on a substrate is provided, and the coating composition is

[0015] An opacifying agent comprising cellulose microparticles and a surfactant, wherein the cellulose microparticles have an average particle length of 0.7 to 9 μm; and

[0016] It comprises a carrier liquid; wherein the composition comprises less than 5 weight percent of metal oxide.

[0017] Specifically, the cellulose white pigment contained in the composition according to the present invention has an ideal particle size and can meet predictions regarding optimal scattering efficiency and refractive index contrast between cellulose particles and pores when forming a continuous, uniform film in appropriately designed paint and coating formulations. Furthermore, the cellulose white pigment can control whiteness above and below the critical pigment volume concentration in a colloidal suspension or mixture.

[0018] In some embodiments, the surfactant is a nonionic, cationic, or amphoteric surfactant. Preferably, the surfactant is a nonionic surfactant. Nonionic surfactants offer distinct advantages due to their compatibility with charged cellulose particles; they do not interfere with the intrinsic charge. This characteristic enhances their versatility, enabling effective formulations in a wide range of products without the risk of destabilization or adverse interactions.

[0019] It has been found that the use of surfactants results in uniformly dispersed cellulose microparticle coating compositions that can be formulated with various polar and non-polar solvents. This enables the formulation of opacifiers and coating compositions for a wide range of commercial applications.

[0020] The coating formed by the coating composition has a controllable thickness, and adjustable whiteness and opacity.

[0021] Accordingly, in the first aspect of the present invention, a coating composition for providing a cellulose microparticle coating on a substrate is provided, and the coating composition is

[0022] An opacifying agent comprising cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant; and

[0023] Includes a carrier liquid,

[0024] Here, cellulose microparticles are present in the coating composition in an amount of 1 to 40 weight percent based on the total mass of the coating composition, a surfactant is present in the coating composition in an amount of 0.5 to 6 weight percent based on the total mass of the coating composition, and the composition contains less than 5 weight percent of metal oxide.

[0025] In a second aspect of the present invention, an opacifying agent for a coating composition is provided, and the opacifying agent is

[0026] Cellulose microparticles having an average particle length of 0.7 to 9 μm, and

[0027] Contains surfactants,

[0028] Here, cellulose microparticles are present in the opacifier in an amount of 50 to 99.6 weight% based on the total mass of the opacifier, and surfactant is present in the opacifier in an amount of 0.4 to 25 weight% based on the total mass of the opacifier.

[0029] In some embodiments, the opacifying agent is a powder. In some embodiments, the opacifying agent is a powder and the opacifying agent has a moisture content of 6% or less based on the mass of the opacifying agent.

[0030] In a third aspect, a coating formed on a substrate is provided, the coating comprises cellulose microparticles and a surfactant, and

[0031] Here, the cellulose microparticles have an average particle length of 0.7 to 9 μm, and

[0032] Here, cellulose microparticles are present in the coating in an amount of 50 to 99.6 weight% based on the total mass of the coating, and surfactants are present in the coating in an amount of 0.4 to 25 weight% based on the total mass of the coating.

[0033] In some embodiments, cellulose microparticles are present in the coating in an amount of 80 to 99 weight%, preferably 85 to 96 weight%, more preferably 86 to 90 weight% based on the total mass of the coating.

[0034] In some embodiments, the surfactant is present in the coating in an amount of 1 to 20 weight%, preferably 4 to 17 weight%, more preferably 12 to 15 weight% based on the total mass of the coating.

[0035] In some embodiments, the coating has an average thickness of 5 μm or more, preferably 10 μm or more, more preferably 15 μm or more, or an average thickness of 500 μm or less, preferably 300 μm or less, more preferably 200 μm or less.

[0036] In some embodiments, the standard deviation of the coating thickness is 25% or less, preferably 20% or less, more preferably 15% or less.

[0037] In a preferred embodiment of the present invention, the composition is essentially free of metal oxides, particularly TiO2. The term "essentially free" means that metal oxides, particularly TiO2, are not added. This composition offers significant advantages in terms of biocompatibility and environmental impact. The absence of metal oxides contributes to a lower environmental impact. This supports more sustainable production processes, thereby reducing the ecological footprint associated with the mining and processing of metal oxides.

[0038] The composition according to the present invention may additionally include an antifoaming agent, for example, a suitable polymer which may be latex or acrylic-based, and water for aqueous coatings or paints, or another suitable solvent for organic solvent-based coatings and paints.

[0039] In some embodiments, the coating is

[0040] 65 or more, preferably 70 or more, more preferably 80 or more, even more preferably 90 or more L*(45° / 0°) — where L*(45° / 0°) is a CIELAB color space coordinate, wherein the composition reflects a significant amount of light and exhibits very bright or nearly white —; and / or

[0041] An average reflectance of 38% or more, preferably 50% or more, more preferably 68% or more, even more preferably 80% or more — wherein the average reflectance is measured over a wavelength range of 400 to 700 nm, and accordingly the composition is particularly effective at reflecting visible light, thereby contributing to its brightness and visual appeal —; and / or

[0042] It has an opacity of 60% or more, preferably 70% or more, more preferably 80% or more, even more preferably 85% or more — where opacity is measured over a wavelength range of 400 to 700 nm for a coating having a thickness of 10 μm, and accordingly, the composition exhibits excellent coverage and hiding power —.

[0043] In some embodiments, the coating is

[0044] An average reflectance of 30% or more, preferably 35% or more, more preferably 40% or more — where average reflectance is measured over a wavelength range of 100 to 400 nm —; or

[0045] It has an average reflectance of 20% or more, preferably 30% or more, more preferably 35% or more — where the average reflectance is measured over a wavelength range of 1000 to 2500 nm —.

[0046] In some embodiments of the first, second, and third aspects, the cellulose microparticles have an average particle length of 0.7 to 9 μm, preferably 1.3 to 7 μm, more preferably 1.7 to 5 μm, and even more preferably 1.9 to 2.8 μm.

[0047] In some embodiments of the first, second, and third aspects, the cellulose microparticles have an average aspect ratio of 2 to 18, preferably 3 to 15, more preferably 4 to 10, and even more preferably 4 to 6.

[0048] In some embodiments of the first, second, and third aspects, the cellulose microparticles have an average width of 0.1 to 1 μm, preferably 0.2 to 0.8 μm, more preferably 0.3 to 0.6 μm, and even more preferably 0.45 to 0.55 μm.

[0049] In some embodiments of the first, second, and third aspects, the cellulose microparticles have an L*(45° / 0°) of 38 or more, preferably 38 to 42, where L*(45° / 0°) is a CIELAB color space coordinate measured for a 1 wt% suspension of cellulose microparticles in water.

[0050] In some embodiments of the first, second, and third aspects, the cellulose microparticles have a reflectance of at least 50%, preferably at least 55%, more preferably at least 60% of incident light at a wavelength of 400 to 700 nm, wherein the reflectance is measured for a 1% by weight suspension of cellulose microparticles in water.

[0051] In some embodiments of the first, second, and third aspects, the surfactant is a nonionic, cationic, or amphoteric surfactant, and preferably, the surfactant is nonionic. A nonionic surfactant is advantageous because it maintains the stability of charged cellulose particles by not interfering with their intrinsic charge.

[0052] In some embodiments of the first, second, and third aspects, the surfactant is polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100), polyoxyethylene (20), sorbitan monolaurate (Tween 20), alcohol ethoxylate (C9-C 11Ethoxylated alcohol (ECOSURF SA-9), secondary alcohol ethoxylate (C 11 -C 15 Ethoxylated alcohol (TERGITOL 15-S-9), trimethyl nonyl ether of polyethylene glycol (TERGITOL TMN-100X), hexadecyltrimethylammonium bromide (CTAB), 3-(decyldimethylammonio)-propane-sulfonate salt, or a combination thereof.

[0053] In some embodiments of the first, second, and third aspects, the surfactant is a nonionic, cationic, or amphoteric surfactant, such as polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100), polyoxyethylene (20), sorbitan monolaurate (Tween 20), alcohol ethoxylate (C9-C 11 Ethoxylated alcohol (ECOSURF SA-9), secondary alcohol ethoxylate (C 11 -C 15 Ethoxylated alcohol (TERGITOL 15-S-9), trimethyl nonyl ether of polyethylene glycol (TERGITOL TMN-100X), hexadecyltrimethylammonium bromide (CTAB), 3-(decyldimethylammonio)-propane-sulfonate salt, or a combination thereof;

[0054] The surfactants are nonionic surfactants, such as polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100), polyoxyethylene (20), sorbitan monolaurate (Tween 20), and alcohol ethoxylate (C9-C 11 Ethoxylated alcohol (ECOSURF SA-9), secondary alcohol ethoxylate (C 11 -C 15 It is an ethoxylated alcohol (TERGITOL 15-S-9), a trimethyl nonyl ether of polyethylene glycol (TERGITOL TMN-100X), or a combination thereof.

[0055] A method for manufacturing an opacifying agent of the second aspect in the fourth aspect is provided, and the method

[0056] A step of forming a suspension by adding cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant to a carrier liquid;

[0057] A step of optionally dispersing cellulose microparticles and a surfactant in a carrier liquid to disperse a suspension; and

[0058] It includes the step of drying the suspension to provide an opacifying agent.

[0059] A method for preparing a coating composition of the first aspect in the fifth aspect of the present invention is provided, and the method

[0060] A step of adding cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant, or an opacifying agent of a second aspect, to a carrier liquid;

[0061] The method includes the step of optionally dispersing cellulose microparticles and a surfactant or an opacifying agent in a carrier liquid to provide a coating composition.

[0062] In a sixth aspect of the present invention, a method for forming a coating on a substrate is provided, and the method

[0063] A step of applying a coating composition of a first aspect to a substrate, and

[0064] It includes the step of drying the coating composition to form a coating containing cellulose microparticles.

[0065] Additional aspects

[0066] In an aspect of the present invention, an opacifying agent is provided, wherein the opacifying agent is obtained or can be obtained by a method of a third aspect.

[0067] In an aspect of the present invention, a coating composition is provided, wherein the coating composition is obtained or can be obtained by the method of the fifth aspect.

[0068] In an aspect of the present invention, a coating applied to a substrate is provided, wherein the coating is obtained or can be obtained by the method of the sixth aspect.

[0069] In an aspect of the present invention, a use of a coating composition according to a first aspect is provided for forming a coating by applying it to a substrate. Brief explanation of the drawing

[0070] Fig. 1 shows cellulose microparticles, CMP, having unique light scattering ability. LS Shows a scanning electron microscope (SEM) image of (also known as cellulose microparticles). The scale bar is 30 μm. Figure 2 shows the volumetric size distribution for three regions of cellulose particles obtained from the sulfuric acid hydrolysis process, and CMP z (Right) has an average particle size larger than 5 μm; 1 μm > CMP LS (Intermediate) > 5 μm and; CMP x (Left) < 1 μm. Particle size is measured as described in the Examples section. Figure 3 shows an image of a comparative composition coated on an opacity chart. Upon drying, the film decomposes into heterogeneous fragments, which demonstrates that a white film cannot be produced by directly drying an aqueous suspension of CMP. FIG. 4 shows an exemplary coating composition comprising 12 wt% of cellulose microparticles, CMP, and 1.75 wt% of a nonionic surfactant, Triton-x100, in an aqueous solution as a white film of composition 1b on a paper chart (Fig. 4a), and an exemplary coating composition comprising 12 wt% of CMP and 0.5 wt% of another type of nonionic surfactant, Tween 20, in an aqueous solution as a white film of composition 2 on paper (Fig. 4b) (right image). Both films have a thickness of 20 μm. FIG. 5 shows an exemplary coating composition comprising 12 wt% of cellulose microparticles and 1.75 wt% of a nonionic surfactant, Triton-x100, as a cellulose microparticle coating of composition 1b on wood. Figure 6 shows the reflection spectra (Figure 6a) for the coating of composition 1b on aluminum at various thicknesses (50 μm, 100 μm, and 150 μm) measured as described in the Examples section. One of the white films is shown in Figure 6b. The whiteness of the film, measured as L*, appears to depend on the film thickness. FIG. 7 shows the reflection spectra for a cellulose microparticle coating on paper at different coating thicknesses. The coatings are formed on paper using coating composition 1b at thicknesses of 7 μm, 14 μm, and 19 μm. The degree of whiteness, expressed as L*(45 / 0) or backscattering measurements, depends directly on the coating thickness and is measured as described in the Examples section. FIG. 8 shows a piece of cowhide coated with composition 4a (Fig. 8a), illustrating an exemplary coating composition comprising 12 wt% CMP and 2 wt% TERGITOL 15-S-9 (nonionic surfactant) in an aqueous suspension. The CIELAB color values ​​for the white film on the cowhide were measured as L* = 95, a* = -0.1, b* = 2.8, and the whiteness value was 100 - SQRT((100-L*)^2 + a*^2 + b*^2) = 94. It is noteworthy that the coating composition and coating of the present invention provide a flexible white coating suitable for more flexible substrates. FIG. 8b shows an image of a leather sample coated using the same formulation mixed with 10 wt% acrylic paint base in water. The leather sample (Fig. 8b) is bendable and still maintains the white coating after bending without cracking or chipping. Figure 9 shows the exemplary scattering characteristics of cellulose microparticles. Figure 10 shows the opacity trends of compositions based on compositions 1b and 2 at CMP concentration ranges (3 wt%, 6 wt%, 9 wt%, 12 wt%, 15 wt%, 18 wt%, and 20 wt%) for the coatings on the opacity chart. Opacity was measured using a spectrophotometer (sph870, ColorLite GmbH). Figure 11 shows a polynomial plot illustrating the correlation between CIELAB L*(45 / 0) measurements and backscattering for a wide selection of samples coated with cellulose microparticles. The circled areas represent the ranges of white coatings where light scattering measured by any technique is adequately measurable and detectable. The coefficient of determination for this polynomial function, L*(x) = ax b = 0.72 x 0.55 and the coefficient of determination, r 2 = 98.1%. Figure 12 shows a wear test for a CMP coating having a transparent polyurethane film on an aluminum substrate. The test was performed using 600-grit sandpaper loaded with 100 g. Wear is determined based on the water contact angle from the coating measured for both the transparent PU coat alone and the top coat including the transparent layer and the underlying CMP layer. Figure 13 shows the spectra of the coating of Composition 1b (Figure 13a) and the coating of Composition 2 (Figure 13b) for the UV, visible light, and IR regions. The film thickness for the coating in Figure 13a is 15 ± 2 μm, and for the film in Figure 13b, it is 12 ± 3 μm. This demonstrates the ability of these coatings to provide protection / shielding in the UV-visible range. FIGS. 14a to 14f show the appearance of the composition according to the present invention and the comparative example. FIGS. 15a to 15f are coated opacity charts. Specific details for implementing the invention

[0071] Detailed description of the invention

[0072] Generally, the present invention provides a coating composition comprising cellulose microparticles and a surfactant. The surfactant acts to disperse the cellulose microparticles, and the inventors have found that this significantly improves the coating properties of the cellulose microparticle composition. The composition enables the production of a homogeneous and opaque coating on a substrate. The coating can be applied using conventional industrial-scale techniques.

[0073] Cellulose microparticles are typically produced using acid hydrolysis, followed by size classification of the hydrolyzed cellulose particles. Specific sizes and / or shapes of the cellulose microparticles provide characteristic scattering responses in the visible, ultraviolet, and infrared regions. Cellulose microparticles can act as opacifying agents.

[0074] Surfactants are thought to form a scaffold where cellulose microparticles are assembled. The characteristics of the surfactant—namely, critical micelle concentration, solid concentration, and charge—determine the stability and robustness of this scaffold, which assists in the assembly of cellulose microparticles to produce the desired opacity and whiteness at a specific film thickness.

[0075] The shape of the microparticles can be modified to optimize scattering efficiency for the desired application. Surfactants can also be modified to control the scattering and whiteness of the coating by regulating how the cellulose microparticles are assembled. In this way, the resulting cellulose microparticle coating has a refractive index much higher than that of standard cellulose (the average refractive index of cellulose is approximately 1.56).

[0076] Coating composition

[0077] In a general aspect, a coating composition for providing a cellulose microparticle coating on a substrate is provided, and the coating composition

[0078] An opacifying agent comprising cellulose microparticles and a surfactant, wherein the cellulose microparticles have an average particle length of 0.7 to 9 μm; and

[0079] It includes a carrier liquid.

[0080] In the first aspect of the present invention, a coating composition is provided for providing a cellulose microparticle coating on a substrate, and the coating composition is

[0081] An opacifying agent comprising cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant; and

[0082] Includes a carrier liquid,

[0083] Here, cellulose microparticles are present in the coating composition in an amount of 1 to 40 weight percent based on the total mass of the coating composition, a surfactant is present in the coating composition in an amount of 0.5 to 6 weight percent based on the total mass of the coating composition, and the composition contains less than 5 weight percent of metal oxide.

[0084] The coating composition is a composition suitable for coating on a substrate. The coating composition is intended to provide a cellulose microparticle coating on a substrate. The coating composition can be used to coat by any suitable means, such as spraying, curtain coating, knife coating, roll coating, dipping, or draw-down coating. The coating composition typically forms a homogeneous and uniform coating on the substrate.

[0085] The coating composition includes an opacifying agent. The opacifying agent is a component that improves the opacity of the resulting coating. Typically, the opacifying agent is a component that reduces the transmission of light, for example, by scattering. In other words, the opacifying agent has excellent light scattering properties and low light transmittance over a wide wavelength range. The opacifying agent may be a visible light opacifying agent that opacifies in the visible light region (e.g., 400 to 1000 nm). The opacifying agent may be a UV opacifying agent that opacifies in the UV region (e.g., 100 to 400 nm). The opacifying agent may be an IR opacifying agent that opacifies in the IR region (e.g., 1000 to 2500 nm).

[0086] In this case, the opacifying agent comprises cellulose microparticles and a surfactant. The cellulose microparticles and the surfactant are described in detail below. Opacity is typically provided by the cellulose microparticles described herein.

[0087] In some embodiments, cellulose microparticles are present in the coating composition in an amount of 1 to 40 weight percent based on the total mass of the coating composition, and a surfactant is present in the coating composition in an amount of 0.5 to 6 weight percent based on the total mass of the coating composition.

[0088] In some embodiments, cellulose microparticles are present in the coating composition in an amount of 30 weight% or less, preferably 20 weight% or less, more preferably 15 weight% or less, based on the total mass of the coating composition. In some embodiments, cellulose microparticles are present in the coating composition in an amount of 5 weight% or more, preferably 10 weight% or more, more preferably 12 weight% or more, based on the total mass of the coating composition.

[0089] In some embodiments, the coating composition according to the present invention is a particle population CMP having an average particle length of less than 1 μm. X, or a particle population CMP having an average particle length in the range of 1 μm to less than 5 μm LS A particle population CMP comprising, or a mixture thereof, preferably having an average particle length in the range of 1 μm to less than 5 μm LS Includes. In the context of the present invention, the term "particle group" refers to a defined group of individual particles sharing a particle length within the range defined above. The term "particle length of the particle group" refers to the dimensions of each individual particle within the group, rather than the characteristics of an aggregate or bulk material formed by a number of particles. Both particle groups exhibit excellent scattering efficiency, but CMP LS The scattering efficiency of the particle population is exceptional. This outstanding performance enables a reduction in the required particle concentration while still achieving enhanced brightness in the coating composition. Therefore, although both populations offer significant advantages, CMP LS It is clearly outstanding due to its amazing effect.

[0090] In some embodiments, cellulose microparticles are present in the coating composition in an amount of 5 to 20 weight%, preferably 10 to 18 weight%, more preferably 12 to 15 weight% based on the total mass of the coating composition.

[0091] In this way, cellulose microparticles provide opacity to coatings produced using the coating composition. It has been observed that when cellulose microparticles are present in the coating composition at 12 to 15 weight percent, a coating having particularly excellent opacity is provided. Embodiments of the present invention achieve opacity of over 80% for these coating films ( Examples (Refer to Table 3 in the section).

[0092] In some embodiments, the surfactant is present in the coating composition in an amount of 0.05 weight% or more, preferably 0.5 weight% or more, more preferably 1.0 weight% or more, based on the total mass of the coating composition. In some embodiments, the surfactant is present in the coating composition in an amount of 5 weight% or less, preferably 3 weight% or less, more preferably 2.0 weight% or less, based on the total mass of the coating composition.

[0093] In some embodiments, the surfactant is present in the coating composition in an amount of 0.5 to 3 weight%, preferably 1.0 to 2.0 weight%, based on the total mass of the coating composition.

[0094] In some embodiments, the ratio of the amount of cellulose microparticles in weight% to the amount of surfactant in weight% is 2 to 25, where the amount is based on the total mass of the coating composition. Preferably, the ratio is 3 to 15, more preferably 4 to 10, even more preferably 5 to 9, and even more preferably 6 to 8.

[0095] The coating composition comprises a carrier liquid. The carrier liquid may be any suitable liquid capable of dispersing the opacifying agent. The carrier liquid may be a polar or non-polar solvent. The carrier liquid may be a mixture of solvents.

[0096] The carrier liquid is 2-propanol, 1,2-dichloroethane, 1,4-dioxane, 18-crown-6, 2-propanol, 2-ethoxyethanol, acetic acid, acetone, acetonitrile, ammonia, benzene, n-butanol, n-butyl acetate, chloroform, cyclohexane, dichloromethane, diethyl ether, diglyme, dimethylformamide, dimethyl sulfoxide, DME, ethane, ethanol, ethyl acetate, ethylene, ethylene glycol, formic acid, glycerin, heptane, hexane, hexamethylbenzene, HMDSO, HMPA, hydrogen, imidazole, isobutanol, isopropyl alcohol, methane, methanol, n-hexane, nitromethane, n-pentane, propane, propylene, propylene carbonate, pyridine, pyrrole, It may be pyrrolidine, silicone grease, tert-butyl alcohol, tetrahydrofuran, toluene, triethylamine, water, white spirit, xylene, or a combination thereof.

[0097] In some embodiments, the carrier liquid is water, ethanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), or a combination thereof.

[0098] The carrier liquid may also be a mineral oil that is miscible with water, such as glycerin or propylene glycol.

[0099] Preferably, the carrier liquid is mainly water. Preferably, the carrier liquid is water. "Mainly" refers to 95 weight percent or more based on the total mass of the carrier liquid, such as 96 weight percent or more, 97 weight percent or more, 99 weight percent or more, or 99.5 weight percent or more.

[0100] The carrier liquid may also be an emulsion, such as an oil-in-water emulsion, a water-in-oil emulsion, or a double emulsion, such as an oil-in-water emulsion or an oil-in-water emulsion. A surfactant may assist in the formation of the emulsion. In a composition where the carrier liquid is an emulsion, an additional surfactant may be present to stabilize the emulsion. For example, the carrier liquid may be paint.

[0101] Oils suitable for emulsions include algae oil, annatto oil, argan oil, almond oil, apricot kernel oil, avocado oil, babassu oil, Brazil nut butter, butter, cashew butter, castor oil, camellia oil, cherry kernel oil, cocoa butter, coconut oil, corn oil, cottonseed oil, fish oil, grapeseed oil, gardenia oil, ghee, hazelnut oil, jatropha oil, jojoba oil, kokum oil, flaxseed oil, macadamia oil, corn oil, mango seed oil, mango butter, mineral oil, mink oil, olive oil, palm oil, palm kernel oil, peach kernel oil, peanut butter, peanut oil, plum kernel oil, pomegranate oil, rapeseed oil, rice bran oil, rosehip oil, sal oil, sesame oil, shea butter, soybean oil, squalene, sunflower oil, tea seed oil, and walnut oil. For example, oil derivatives obtained from the aforementioned oils, such as esterified oils, fatty acids, fatty alcohols, hydrogenated oils, and triglycerides, can be used as ingredients suitable for the above formulation. Essential oils are also suitable oils.

[0102] Typically, the carrier liquid constitutes the majority of the coating composition. In some embodiments, the carrier liquid is present in the composition in an amount of 70 to 95 weight%, preferably 80 to 92 weight%, more preferably 83 to 90 weight%, and even more preferably 86 to 88 weight% based on the total mass of the composition.

[0103] Opaque

[0104] In a general aspect, an opacifying agent for a coating composition is provided, comprising cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant.

[0105] Opaqueants typically provide a certain degree of opacity when incorporated, for example, into a coating composition or coating. The opacity may be provided primarily by cellulose microparticle components. The opacity may be in the IR, UV, or visible light regions of the spectrum.

[0106] In a second aspect of the present invention, an opacifying agent for a coating composition is provided, and the opacifying agent is

[0107] Cellulose microparticles having an average particle length of 0.7 to 9 μm, and

[0108] Contains surfactants,

[0109] Here, cellulose microparticles are present in the opacifier in an amount of 50 to 99.6 weight% based on the total mass of the opacifier, and surfactant is present in the opacifier in an amount of 0.4 to 25 weight% based on the total mass of the opacifier.

[0110] In some embodiments, cellulose microparticles are present in the opacifier in an amount of 70 weight% or more, preferably 80 weight% or more, more preferably 85 weight% or more, based on the total mass of the opacifier. In some embodiments, cellulose microparticles are present in the opacifier in an amount of 99.6 weight% or less, preferably 98 weight% or less, more preferably 95 weight% or less, and even more preferably 90 weight% or less, based on the total mass of the opacifier.

[0111] In some embodiments, cellulose microparticles are present in the opacifying agent in an amount of 80 to 99 weight%, preferably 85 to 96 weight%, more preferably 86 to 90 weight%, based on the total mass of the opacifying agent.

[0112] In some embodiments, the surfactant is present in the opacifier in an amount of 1 weight% or more, preferably 5 weight% or more, more preferably 10 weight% or more, based on the total mass of the opacifier. In some embodiments, the surfactant is present in the opacifier in an amount of 20 weight% or less, preferably 17 weight% or less, more preferably 15 weight% or less, based on the total mass of the opacifier.

[0113] In some embodiments, the surfactant is present in the opacifier in an amount of 1 to 20 weight%, preferably 4 to 17 weight%, more preferably 12 to 15 weight% based on the total mass of the opacifier.

[0114] An opacifying agent can be used in the coating composition of the first aspect.

[0115] An opacifier is a component that improves the opacity of the resulting coating. Typically, an opacifier is a component that reduces the transmission of light, for example, through scattering. In other words, the opacifier has excellent light scattering properties and low light transmittance over a wide wavelength range. The opacifier may be a visible light opacifier that opacifies in the visible light region (e.g., 400 to 1000 nm). The opacifier may be a UV opacifier that opacifies in the UV region (e.g., 100 to 400 nm). The opacifier may be an IR opacifier that opacifies in the IR region (e.g., 1000 to 2500 nm).

[0116] When an opacifying agent is applied as a coating on a substrate with a thickness of 20 μm, it can provide a transmittance of 20% or less, preferably 18% or less, and more preferably 15% or less with respect to incident light at a wavelength of 400 to 800 nm.

[0117] When an opacifying agent is applied as a coating on a substrate with a thickness of 20 μm, it can provide a reflectance of at least 50%, preferably at least 55%, and more preferably at least 60% of incident light at a wavelength of 400 to 800 nm.

[0118] The opacifying agent may have an L* of 70 or more, such as 75 or more, such as 80 or more, where L* is a CIELAB color space coordinate and is measured for the opacifying agent when applied as a coating on a substrate with a thickness of 20 μm.

[0119] Transmittance, reflectance, and L* are all measured as described in the Examples section.

[0120] Opacity is provided by the cellulose microparticles described in this specification.

[0121] The opacifying agent may be in particulate form. Cellulose microparticles and surfactants may be provided as separate particles or clusters to be mixed together. Alternatively, cellulose microparticles and surfactants may be combined in the same particle or cluster.

[0122] In some of these embodiments, the opacifying agent is a powder. The powder typically comprises a plurality of particles.

[0123] Preferably, the opacifying agent powder is a fluid powder. This fluid powder is useful for commercial applications where the powder is added to a coating composition.

[0124] The opacifying agent powder may have a fluidity of 1 s / g or less, preferably 0.5 s / g or less, more preferably 0.3 s / g or less, wherein the fluidity is measured using a 50 g sample in a Hall flowmeter funnel according to ISO 4490:2018.

[0125] The opacifying agent powder may have a Hausner ratio of 1.4 or less, preferably 1.25 or less, more preferably 1 or less, where the Hausner ratio is calculated as the ratio between the tap bulk density of the powder and the free sedimentation bulk density of the powder. The tap density and free sedimentation density may be measured according to ISO 3953:2011.

[0126] In some embodiments, the opacifier is substantially solvent-free. For example, the opacifier has a moisture content of 6% or less based on the mass of the opacifier. This dry powder is useful for commercial applications due to its chemical and biological stability.

[0127] In an alternative embodiment, the opacifying agent is a paste or a slurry. The paste or slurry is typically a plurality of particles suspended in a relatively small amount of carrier liquid. The paste or slurry typically has a higher viscosity than the coating composition. The paste or slurry typically has a higher concentration than the coating composition.

[0128] The carrier liquid may be the same as the carrier liquid described above in the context of the coating composition.

[0129] Pastes are typically viscous and thick. Since pastes are more concentrated than coating compositions, they can be useful for commercial applications. Pastes may be easier to disperse in formulations than powders.

[0130] The opacifying agent paste or slurry may have a viscosity of 20,000 mPa·s or less, preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less. The opacifying agent paste or slurry may have a viscosity of 20 mPa·s or more, preferably 50 mPa·s or more, more preferably 100 mPa·s or more. Viscosity is measured at a temperature of 20°C according to ISO 2555:2018.

[0131] Cellulose microparticles

[0132] Cellulose microparticles have an average particle length of 0.7 to 9 μm.

[0133] Cellulose microparticles can be used in coating compositions and opacifying agents, as well as in other aspects of the present invention.

[0134] Cellulose microparticles of the dimensions disclosed herein provide excellent scattering of IR, UV, and visible light. Color arises from the interaction between electrons of the molecules constituting an object and light waves. On the other hand, structural color is color resulting from reflection from a specific geometric structure and is therefore permanent as long as the geometric structure of the identified material does not change.

[0135] White is obtained through appropriate light scattering from specific particles that depend on the refractive index, and the refractive index is a material-dependent property. For example, titanium dioxide, TiO2, has a refractive index of 2.87 at 632.8 nm. All polymer materials, including cellulose, have a lower refractive index than these metal oxides. Therefore, to produce white using cellulose, cellulose particles of a specific geometric structure that allows for efficient light scattering are used. The cellulose microparticles used in the present invention have the geometric structure and shape necessary to efficiently scatter IR, UV, and / or visible light.

[0136] The length of a particle is generally the longest dimension of the particle. For example, if the particle is rod-shaped, the length is the distance between the ends of the rods. The length of the particle is typically the longitudinal length of the particle.

[0137] The length of a particle is typically the longest lateral dimension. Lateral dimensions are the dimensions observable when viewing the particle in a plan view. In a plan view, the particle appears in two dimensions. For example, if the particle is measured from top to bottom (or planar) from an image, the length is the longest dimension measurable from the image of the particle from top to bottom.

[0138] The length of the particles can be measured using standard techniques. For example, a scanning electron microscope (SEM) may be used. A suitable system includes a Mira3 FEG-SEM system (TESCAN) that operates at 30 kV and has a working distance of 5 mm. The length of the microparticles can then be analyzed by ImageJ.

[0139] Typically, particle length is measured using SEM.

[0140] The number of length measurements is typically 100 to 1,000. Generally, more than 100 measurements of the length are taken. The length is the average value of the measurements taken. The average is a numerical average. By calculating the average value for the length, the influence of outliers is reduced, and the representative length of the particle is represented.

[0141] In some embodiments, the cellulose microparticles are 0.7 to 9 μm, preferably 1 μm to less than 5 μm (i.e., particle group CMP LS ), more preferably 1.3 to 7 μm, even more preferably 1.7 to 5 μm, and particularly preferably 1.9 to 2.8 μm, has an average particle length. This particle length provides appropriate physical dimensions that efficiently scatter light in the visible light range and results in the production of white in the coating. The particle size can also be used to control the flow characteristics of the suspension and thus to control the rheological properties of the coating composition and the coating.

[0142] Typically, the length of a particle provides a particle size distribution that follows a log-normal distribution. Generally, particles have a unimodal particle size distribution, having only one peak or maximum value. The peak or maximum value of a unimodal distribution corresponds to the median average particle diameter based on the number of all particles within the distribution.

[0143] In some embodiments, the particle length provides a multimodal particle size distribution having two or more peaks or maximums in the particle size distribution. In other embodiments, the particle length provides a bimodal particle size distribution having exactly two peaks or maximums in the particle size distribution. In other embodiments, the particle length provides a trimodal particle size distribution having exactly three peaks or maximums in the particle size distribution.

[0144] Percentile values ​​for length can also be calculated as D90, D50, and D10. These values ​​can be calculated based on the length-particle size distribution relative to the number of particles.

[0145] The D90 length is the particle length at which 90% of the particles have a length less than or equal to the D90 particle length.

[0146] In some embodiments, the cellulose particles have a D90 length of 6,000 nm or less, preferably 5,000 nm or less, preferably 4,500 nm or less. In some embodiments, the cellulose particles have a D90 length of 3,000 nm or more, preferably 3,500 nm or more, preferably 3,750 nm or more. In some embodiments, the cellulose particles have a D90 length of 3,000 to 5,000 nm, preferably 3,500 to 4,500 nm.

[0147] In the first embodiment, the D90 length is about 4,500 nm.

[0148] In the second embodiment, the D90 length is about 3,500 nm.

[0149] D50 length is the particle length at which 50% of the particles have a length less than or equal to the D50 particle length.

[0150] In some embodiments, the cellulose particles have a D50 length of 5,000 nm or less, preferably 3,500 nm or less, preferably 3,000 nm or less, more preferably 2,800 nm or less. In some embodiments, the cellulose particles have a D50 length of 1,000 nm or more, preferably 1,300 nm or more, preferably 1,600 nm or more, more preferably 1,900 nm or more. In some embodiments, the cellulose particles have a D50 length of 1,000 to 5,000 nm, preferably 1,300 to 3,500 nm, preferably 1,600 to 3,000 nm, more preferably 1,900 to 2,800 nm.

[0151] In the first embodiment, the D50 length is 1,000 to 5,000 nm, preferably 1,900 to 3,500 nm, more preferably 2,200 to 3,000 nm, even more preferably 2,500 to 2,900 nm, and most preferably 2,600 to 2,800 nm. In the first embodiment, the D50 length is preferably about 2,700 nm.

[0152] In the second embodiment, the D50 length is 1,000 to 4,000 nm, preferably 1,200 to 2,700 nm, preferably 1,500 to 2,500 nm, preferably 1,700 to 2,300 nm, preferably 1,800 to 2,100 nm, more preferably 1,900 to 2,000 nm. In the second embodiment, the D50 length is preferably about 1,950 nm.

[0153] D10 length is the particle length at which 10% of the particles have a length less than or equal to D10 particle length.

[0154] In some embodiments, the cellulose particles have a D10 length of 2,000 nm or less, preferably 1,750 nm or less, preferably 1,500 nm or less. In some embodiments, the cellulose particles have a D10 length of 500 nm or more, preferably 750 nm or more, preferably 1,000 nm or more. In some embodiments, the cellulose particles have a D10 length of 500 to 2,000 nm, preferably 750 to 1,800 nm, preferably 1,000 to 1,700 nm.

[0155] In the first embodiment, the length of D10 is about 1,700 nm.

[0156] In the second embodiment, the length of D10 is about 1,200 nm.

[0157] In some embodiments, the cellulose particles have an average width of 0.1 to 1 μm, preferably 0.2 to 0.8 μm, more preferably 0.3 to 0.6 μm, and even more preferably 0.45 to 0.55 μm.

[0158] The width of a particle is generally the shortest dimension of the particle. For example, if the particle is rod-shaped, the width is the diameter of the rod's cross-section. The width of a particle is typically the lateral diameter of the particle. Width can also be referred to as diameter.

[0159] The width of a particle is typically the shortest lateral dimension of the particle. The lateral dimension is the shortest dimension observable when viewing the particle in a plan view. In a plan view, the particle appears in two dimensions. For example, if the particle is measured from top to bottom (or planar) from an image, the width is the shortest dimension measurable from the image of the particle from top to bottom.

[0160] The width of a particle is generally the shortest dimension of the particle perpendicular to the line defining the particle's length dimension. As explained above, the particle's length is the longest dimension of the particle, and therefore the line defining the particle's length is the line between the particle's farthest extremes. The width can be the shortest dimension of the particle perpendicular to the line defining the particle's length. The shortest dimension can also be defined by the line between the particle's nearest extremes, where the line is perpendicular to the line defining the particle's length. In other words, the shortest dimension can be the narrowest section of the particle that can be connected by a line perpendicular to the line defining the particle's length.

[0161] The width of a particle can be measured similarly to its length.

[0162] Percentile values ​​for width from the particle size distribution can also be calculated as D90, D50, and D10. These values ​​can be calculated based on the width particle size distribution relative to the number of particles.

[0163] D90 width is a particle width in which 90% of the particles have a width of D90 or less.

[0164] In some embodiments, the cellulose particles have a D90 width of 1,000 nm or less, preferably 900 nm or less, preferably 800 nm or less. In some embodiments, the cellulose particles have a D90 width of 250 nm or more, preferably 300 nm or more, preferably 350 nm or more. In some embodiments, the cellulose particles have a D90 width of 300 to 1,000 nm, preferably 350 to 900 nm.

[0165] In the first embodiment, the width of D90 is about 850 nm.

[0166] In the second embodiment, the width of D90 is about 350 nm.

[0167] D50 width is a particle width in which 50% of the particles have a width of D50 or less.

[0168] In some embodiments, the cellulose particles have a D50 width of 800 nm or less, preferably 700 nm or less, preferably 600 nm or less. In some embodiments, the cellulose particles have a D50 width of 100 nm or more, preferably 150 nm or more, preferably 200 nm or more. In some embodiments, the cellulose particles have a D50 width of 200 to 800 nm, preferably 300 to 600 nm, preferably 450 to 550 nm.

[0169] In the first embodiment, the width of D50 is 500 to 540 nm, for example, about 520 nm.

[0170] In the second embodiment, the width of D50 is 200 to 240 nm, for example, about 220 nm.

[0171] D10 width is a particle width in which 10% of the particles have a width less than or equal to D10 particle width.

[0172] In some embodiments, the cellulose particles have a D10 width of 400 nm or less, preferably 300 nm or less, preferably 200 nm or less. In some embodiments, the cellulose particles have a D10 width of 50 nm or more, preferably 100 nm or more, preferably 200 nm or more. In some embodiments, the cellulose particles have a D10 width of 10 to 400 nm, preferably 100 to 300 nm, preferably 110 to 200 nm.

[0173] In the first embodiment, the width of D10 is about 300 nm.

[0174] In the second embodiment, the width of D10 is about 150 nm.

[0175] The aspect ratio may also be a ratio between the length of a particle group and the width of a particle group. In some embodiments, the aspect ratio is the D50 aspect ratio, which is the ratio between the D50 length and the D50 width. In some embodiments, the aspect ratio is the average aspect ratio, which is the ratio between the average length and the average width.

[0176] The particles are not typically spherical because their aspect ratio is greater than 1 (e.g., 2 to 18). The particles may be described as prismatic and / or elongated. Preferably, the particles are rod-shaped.

[0177] In some embodiments, the cellulose microparticles have an average aspect ratio of 2 to 18, preferably 3 to 15, more preferably 4 to 10, and even more preferably 4 to 6.

[0178] In some embodiments, the D50 aspect ratio may be 2 to 18. Preferably, the D50 aspect ratio of the cellulose particles is 2 to 16, more preferably 3 to 14, even more preferably 4 to 10, and most preferably 4 to 6.

[0179] Cellulose particles may have any suitable shape. In some embodiments, the cellulose particles have a rod or rod-like shape, or a flake or flake-like shape. In some embodiments, the cellulose particles have a rod or flake shape.

[0180] Cellulose particles may have a rod or rod-like shape. Thus, the width may be the diameter of the cross-section of the rod. The particles may be elongated, having a length dimension greater than the width dimension.

[0181] Cellulose particles may also have flake or flake-like shapes. Flake or flake-like shapes may be elongated, having a length dimension greater than the width dimension. Flake or flake-like shapes typically have a uniform height over most of the length of the particle.

[0182] Cellulose particles may not be substantially branched. That is, cellulose particles are typically not divided into two or more branches. Preferably, the cellulose particles are not branched cellulose particles and are not over-branched cellulose particles.

[0183] Cellulose particles are typically primary particles. That is, cellulose particles are not aggregates of smaller particles.

[0184] Alternatively, cellulose particles may be secondary particles formed from the aggregation of multiple primary particles. Typically, secondary cellulose particles are held together by non-covalent interactions.

[0185] In this specification, the dimensions of the cellulose particles refer to individually divisible particles. In other words, if the particles are provided as primary particles, the dimensions refer to the primary particles, and if the particles are provided as secondary particles, the dimensions refer to the secondary particles.

[0186] Typically, secondary cellulose particles contain pores or voids. The pores or voids are located between the primary cellulose particles. The clusters can be described as porous.

[0187] Secondary cellulose particles can be manufactured using the methods described herein. For example, secondary cellulose particles can be manufactured by spray-drying or spray-freezing a suspension of cellulose microparticles. The sprayer can be adjusted to control the droplet size of the CMP suspension. The droplet size can be used to control the size of the CMP clusters. Suitable spray-drying equipment is described herein.

[0188] Cellulose particles possess excellent optical properties. Cellulose particles scatter incident light. In particular, cellulose particles can provide high reflectivity and low transmittance. Consequently, cellulose particles offer excellent opacity.

[0189] The optical properties of the particles can be measured using standard techniques, such as combining a light source with a spectrometer and an integrating sphere. The signal can be normalized to the intensity in the absence of a sample. Typically, a white diffuser standard such as the Labsphere SRS-99-010 is used. The background can be recorded when no light is applied, and background noise can be subtracted from the measurement. Optical properties are measured in the visible light range (e.g., 400 nm to 800 nm). Typically, optical properties are measured in air. Transmittance can be measured, and reflectance can be calculated from the transmittance values ​​obtained assuming no absorption by the particles. Typically, five spectra were taken and averaged for each sample.

[0190] In some embodiments, total transmittance and reflectance measurements were performed using an integrating sphere (Labsphere). A light source (Ocean Optics HPX-2000) was coupled to an optical fiber (600 μm Thorlabs FC-UV100-2-SR) via a collimator (Thorlabs), and the signal was collected by a spectrometer (Avantes HS2048) as shown in Fig. 8 (T1 and T2). The signal was normalized to the intensity when no sample was mounted. The background was recorded when no light was applied. The wavelength range was 400 to 700 nm. For each sample, five spectra were taken and averaged to reduce the signal-to-noise ratio. Each spectrum was recorded using an integration time equal to 3 seconds.

[0191] L*(45 / 0) refers to an angle of incidence of 45° with respect to the normal of the surface and an angle of reflection of 0° with respect to the normal of the surface. Measurements are taken for a 0.1 wt% CMP suspension in a 1 cm cuvette.

[0192] In some embodiments, the cellulose microparticles have an L*(45° / 0°) of 38 or more, preferably 38 to 42, where L*(45° / 0°) is a CIELAB color space coordinate measured for a 1 wt% suspension of cellulose microparticles in water.

[0193] In some embodiments, the cellulose microparticles have a reflectance of at least 50%, preferably at least 55%, more preferably at least 60% of incident light at a wavelength of 400 to 700 nm, wherein the reflectance is measured for a 1% by weight suspension of cellulose microparticles in water.

[0194] The surface of cellulose particles can be modified. Typically, hydroxyl groups on the surface of cellulose particles are modified. Cellulose particles can be modified to become hydrophobic or partially hydrophobic.

[0195] In some embodiments, one or more hydroxyl groups on the surface of the cellulose particles are modified. In some embodiments, the hydroxyl groups are converted into different functional groups, such as esters or ethers.

[0196] For example, cellulose particles can be produced by acid hydrolysis. During acid hydrolysis, the cellulose chain backbone of the cellulose particles is modified at the molecular level, which is thought to provide colloidal stability to the cellulose particles. For example, sulfuric acid hydrolysis is thought to modify the cellulose chains into sulfate halfesters.

[0197] Cellulose microparticles typically incorporate 20 to 100 mmol / kg, preferably 40 to 60 mmol / kg of semi-ester sulfate groups on their surface as a result of an acid hydrolysis process. The mass contribution of semi-ester groups (e.g., -SO3H) corresponds to 5% by weight or less, preferably 1% by weight or less, based on the total mass of the cellulose microparticles.

[0198] The density of the semi-ester sulfate group is measured by conductivity titration as in ISO 21400:2018.

[0199] Cellulose particles are preferably anionic. Semi-ester groups can contribute to the anionic charge on the cellulose particles. Thus, in some embodiments, the cellulose microparticles are anionic. In some embodiments, the cellulose microparticles are surface modified with anionic sulfate semi-ester groups.

[0200] Cellulose microparticles have an anionic charge density of 50 mmol / kg or more, preferably 100 mmol / kg or more, more preferably 150 mmol / kg or more.

[0201] Cellulose particles can be further modified to increase their negative charge. For example, cellulose particles can be modified by reaction with sulfamic acid as part of a reactive deep eutectic solvent. Urea can be used to increase the reactivity of sulfamic acid. Highly sulfated cellulose nanoparticles can then be mixed with the surfactant family outlined herein in the manner described in this patent application.

[0202] Through appropriate post-treatment, the total surface charge density can be increased to reach 2000 mmol / kg. This can be useful for highly charged mixtures to ensure stability and maintain the same functionality.

[0203] Cellulose microparticles can have an anionic charge density of 2000 mmol / kg or less.

[0204] The charge density of the particles is measured by conductivity titration, such as according to ISO 21400:2018.

[0205] The charge may depend on the pH of the solution in which the particles are present. The charge of the particles is determined in the present invention by the pH of the coating composition or opacifying agent. This is typically a pH of 7.

[0206] Manufacturing of cellulose microparticles

[0207] The cellulose microparticles used in the present invention can be obtained using the method described in WO2023 / 135261, such as Example 1 of WO2023 / 135261, the details of which are incorporated herein by reference.

[0208] Typically, cellulose microparticles are obtained through the sulfuric acid hydrolysis of biomass using specific acid concentrations, temperatures, and reaction times to control morphology and physical dimensions.

[0209] Generally, cellulose microparticles are manufactured by a method comprising the following:

[0210] (a) A step of adding acid to a cellulose material to hydrolyze cellulose particles;

[0211] (b) a step of removing acid from hydrolyzed cellulose particles; and

[0212] (c) A step of separating hydrolyzed cellulose particles of a specific size.

[0213] Step (a) of “adding acid to cellulose particles” may be referred to as the hydrolysis step. Step (b) of “removing acid from hydrolyzed cellulose particles” may be referred to as the washing step. Step (c) of “separating hydrolyzed cellulose particles of a specific size” may be referred to as the fractionation step.

[0214] The application also provides a method for manufacturing cellulose particles, and the method

[0215] (a) A step of hydrolyzing a cellulose material to provide hydrolyzed cellulose particles;

[0216] (b) a step of washing hydrolyzed cellulose particles; and

[0217] (c) includes the step of fractionating a suspension of hydrolyzed cellulose particles.

[0218] The method is suitable for producing cellulose microparticles for use in the coating composition and opacifying agent of the present invention. However, cellulose microparticles produced by an alternative method may also be used, provided that such particles possess the characteristics required by the opacifying agent.

[0219] The conditions used in the hydrolysis step, the washing step, and the fractionation step can be adjusted to produce cellulose microparticles having the size and shape described herein.

[0220] Any suitable cellulose material may be used. Suitable cellulose materials may be produced from bacterial, plant, or animal sources (e.g., chitin), including subsequent processed products such as paper, filter paper, cotton linters, cellulose powder, and wood pulp, along with plant-based and biomass sources such as cotton and wood.

[0221] Preferably, the cellulose material is a microcrystalline cellulose powder. Suitable microcrystalline cellulose powder is commercially available (e.g., from SERVA Electrophoresis GmbH).

[0222] The cellulose material may be provided in the form of a suspension. Preferably, microcrystalline cellulose powder is dispersed in water to form an aqueous suspension.

[0223] A suspension is a heterogeneous mixture of fluids containing solid particles typically large enough to cause precipitation if the suspension is left undisturbed for an extended period of time. Cellulose particles are suspended in the liquid. To prevent the precipitation of cellulose particles, the suspension can be mixed, for example, by ultrasonic treatment.

[0224] Any suspension medium suitable for holding cellulose materials may be used. Suitable suspension media are typically aqueous solvents such as water. Acidic and basic media may be used. Typically, acids are used, and suitable acids are listed below.

[0225] A method for manufacturing cellulose particles involves hydrolyzing a cellulose material to provide hydrolyzed cellulose particles. This can be known as the hydrolysis step. The hydrolysis step occurs before the washing step.

[0226] Hydrolysis is typically carried out in an aqueous solvent (e.g., water).

[0227] In the hydrolysis step, cellulose materials are typically hydrolyzed with acid. Acid hydrolysis is a hydrolysis process in which protic acids are used to catalyze the cleavage of chemical bonds through substitution reactions involving the addition of water. It is also proposed that during acid hydrolysis, the cellulose chain backbone of cellulose particles is modified at the molecular level, providing colloidal stability to the cellulose particles. For example, sulfuric acid hydrolysis is thought to modify cellulose chains into sulfate halfesters.

[0228] The hydrolysis step may include contacting a cellulose material, such as a suspension of the cellulose material, with an acid.

[0229] The acid may be an organic acid or an inorganic acid. Typically, the acid is an inorganic acid (mineral acid). Suitable inorganic acids include hydrobromide (HBr), hydrochloric acid (HCl), hydrofluoric acid (HF), hydroiodic acid (HI), nitric acid (HNO3), perchloric acid (HClO4), phosphoric acid (H3PO4), sulfuric acid (H2SO4), or combinations thereof. Preferably, the inorganic acid is sulfuric acid or hydrochloric acid. More preferably, the inorganic acid is sulfuric acid.

[0230] Suitable organic acids include formic acid (HCOOH) and acetic acid (CH3COOH). Preferably, the organic acid is formic acid.

[0231] Preferably, the acid is sulfuric acid or hydrochloric acid. More preferably, the acid is sulfuric acid.

[0232] The strength of an (aqueous) acid can be specified using a pH scale. Methods for determining the pH of an aqueous solution are known and include, for example, electrochemical methods (using a pH probe) and titrations using indicator compounds such as universal indicators. Typically, pH refers to the pH of the hydrolysis solution at the end of the hydrolysis step.

[0233] The acid used in the hydrolysis step is highly acidic. Typically, the acid has a pH of 1.0 or less, preferably 0.5 or less, and more preferably 0.0 or less.

[0234] The strength of an acid is proportional to its concentration. The concentration of an aqueous acid can be specified using volume percentage (weight%).

[0235] Typically, the acid concentration is 40 to 60 weight%, preferably 45 to 55 weight%, more preferably 47 to 55 weight%, and even more preferably 49 to 52 weight%. The weight% is typically calculated using water as the solvent.

[0236] The amount of acid is selected to ensure that a desired amount of cellulose material is suspended. The amount of aqueous acid can be specified by specifying the volume of aqueous acid in mL per gram of cellulose material used (ratio of acid to cellulose material).

[0237] Typically, the hydrolysis step uses a mass ratio of acid to cellulose material of 100:1, preferably 80:1, and more preferably 60:1. Additionally or alternatively, the hydrolysis step may use a mass ratio of acid to cellulose material of 4:1, preferably 10:1. For example, the hydrolysis step may use a mass ratio of acid to cellulose material of 100:1 to 4:1, preferably 80:1 to 10:1. A higher ratio of cellulose to acid makes the process more efficient because less acid is required in the hydrolysis step and less solvent is required in the washing step.

[0238] The hydrolysis step can be performed for a sufficient amount of time to allow a desired amount of cellulose material to be hydrolyzed. Typically, hydrolysis is performed for 1 to 10 hours, preferably 2 to 8 hours, more preferably 3 to 7 hours, for example, about 5 hours.

[0239] Hydrolysis occurs from the addition of acid until the reaction is quenched. The reaction can be quenched by any suitable means, such as adding water to dilute the acid, adding a base to neutralize the acid, removing the acid (e.g., by washing such as dialysis), or reducing the temperature.

[0240] The hydrolysis step can be performed at a raised temperature (above ambient temperature; approximately 25°C). Methods for providing heat during the hydrolysis step are known, for example, using a reaction vessel with an external heating jacket or using microwave heating.

[0241] Typically, the hydrolysis step is carried out at a temperature of 40 to 60°C, preferably 45 to 55°C, more preferably 48 to 52°C, for example, about 50°C.

[0242] Preferably, the cellulose material is hydrolyzed with 50% by weight sulfuric acid at a temperature of about 50°C for 3 to 5 hours.

[0243] In some embodiments, in step (b), the cellulose material is hydrolyzed with 50 wt% sulfuric acid at a temperature of 50°C for 5 hours. In some embodiments, in step (b), the cellulose material is hydrolyzed with 55 wt% sulfuric acid at a temperature of 60°C for 5 hours.

[0244] Hydrolysis can be stopped by quenching the acid hydrolysis. Typically, hydrolysis is quenched by the addition of water, such as an excess amount of water. For example, if 60 mL of sulfuric acid is used to hydrolyze cellulose particles, 300 mL of water may be added to quench the acid hydrolysis.

[0245] It is thought that using higher concentrations of acid, higher temperatures, or longer durations increases the rate of acid hydrolysis. Typically, a greater degree of hydrolysis results in smaller cellulose particle sizes.

[0246] Hydrolyzed cellulose particles can be collected by any suitable method. Typically, hydrolyzed cellulose particles are collected by centrifugation. Centrifugation can separate the hydrolyzed cellulose particles from the acid supernatant and, optionally, from water added to quench the acid hydrolysis. The supernatant can then be removed, for example, using a pipette.

[0247] The method for manufacturing cellulose particles

[0248] It includes a step of washing hydrolyzed cellulose particles.

[0249] This can be known as the washing step. The washing step occurs after the hydrolysis step and before the fractionation step.

[0250] Hydrolyzed cellulose particles can be washed by adding water. The water can then be removed. Thus, the washing step may involve bringing the hydrolyzed cellulose particles into contact with water.

[0251] The washing step typically quenches the hydrolysis reaction and thus terminates the hydrolysis step. The washing step can dilute the acid from the cellulose particles, thereby quenching the hydrolysis reaction.

[0252] Typically, the washing step may involve adding enough water to provide a cellulose particle concentration of 1 wt%. For example, for 1 g of hydrolyzed cellulose particles, about 100 mL of water may be added per wash. This may be repeated one or more times, preferably two or more times, more preferably three or more times, to remove acid. The washing water may then be removed by centrifugation.

[0253] Preferably, the washing step may alternatively or additionally include dialyzing the hydrolyzed cellulose particles with water, e.g., distilled water. Dialysis may occur after washing with water as described above. Dialysis involves resuspending the hydrolyzed cellulose particles in distilled water and purifying them from dissolved ions (e.g., acid used in the hydrolysis step) by their uneven diffusion rates through the pores of a semipermeable (dialysis) membrane. Any suitable dialysis membrane may be used. A suitable dialysis membrane has a molecular weight cutoff of 12 kDa or more, e.g., 12 to 40 kDa.

[0254] Distilled water may be replaced during the dialysis process. For example, distilled water may be replaced every 12 hours during dialysis. Distilled water may be replaced at least 5 times, preferably at least 10 times.

[0255] In some embodiments, the hydrolyzed cellulose material is dialyzed against distilled water for 7 days while replacing the distilled water every 12 hours.

[0256] In some embodiments, the hydrolyzed cellulose material is dialyzed until the pH of the hydrolyzed cellulose material stabilizes. The pH may be measured whenever distilled water is replaced during the dialysis process, for example, every 12 hours. Typically, the pH of the hydrolyzed cellulose material is stabilized if the pH remains constant for at least two consecutive measurements, preferably four consecutive measurements, and more preferably six consecutive measurements. Alternatively, the pH may be measured once a day, and the pH is stabilized if it remains constant for at least two consecutive days, preferably three consecutive days, and more preferably four consecutive days.

[0257] A constant pH indicates that an acid or base has been substantially removed from the hydrolyzed cellulose material. The method for determining the pH of an aqueous solution is known as presented above.

[0258] In some embodiments, the washing step may include removing acid from cellulose particles by centrifugation, washing with water and removing water by centrifugation, and dialysis of the hydrolyzed cellulose material.

[0259] The method for manufacturing cellulose particles

[0260] It includes fractionating a suspension of hydrolyzed cellulose particles.

[0261] This can be known as the fractionation step. The fractionation step occurs after the washing step.

[0262] Hydrolyzed cellulose particles can be fractionated by any suitable method. Suitable methods include filtration and centrifugation. Preferably, hydrolyzed cellulose particles are separated from the liquid by differential centrifugation.

[0263] Fractionation takes place in a suspension of hydrolyzed cellulose particles. For the fractionation step, the suspension of hydrolyzed cellulose particles is typically a suspension of individual cellulose particles. That is, the hydrolyzed cellulose particles do not significantly aggregate or do not aggregate in the suspension of hydrolyzed cellulose particles. This is beneficial because the fractionation step avoids removing aggregates of cellulose particles having a desired size and shape. This improves the yield of cellulose particles having a desired size and shape.

[0264] Fractionation (e.g., centrifugation) is performed on a suspension of cellulose particles. Typically, a suspension of cellulose particles is used in water, such as Millipore water. Any suitable concentration may be used. Suitable concentrations include 0.1 wt% to 5.0 wt%, e.g., 0.2 wt% to 2.0 wt%, e.g., 0.2 wt% to 1.0 wt% of cellulose particles. Preferably, the concentration of hydrolyzed cellulose particles is 0.5 wt%.

[0265] A suspension of cellulose particles can be prepared by any suitable method. The hydrolyzed cellulose particles may be mixed or stirred before separation. Typically, the hydrolyzed cellulose particles are sonicated before separation, for example, by tip sonication or sonication.

[0266] In some embodiments, a 30 ml suspension having a particle concentration of 0.5 wt% of hydrolyzed cellulose particles is sonicated at 30% amplitude for 2 minutes with a 2-second on, 2-second off cycle. Sonication can be performed using any suitable device, such as a Fisherbrand sonicator, 20 kHz, with a tip diameter of 12.7 mm.

[0267] Typically, differential centrifugation includes a first centrifugation and a second centrifugation. The first centrifugation is at a different speed from the second centrifugation. The first centrifugation is at a lower speed than the second centrifugation. The second centrifugation is typically performed on the supernatant from the first centrifugation.

[0268] The first centrifugation can be at a speed of 1,000 to 3,000 rpm, preferably 1,500 to 2,500 rpm, more preferably 1,800 to 2,200 rpm, for example, about 2,000 rpm.

[0269] The second centrifugation can be at a speed of 2,000 to 4,000 rpm, preferably 2,500 to 3,500 rpm, more preferably 2,800 to 3,200 rpm, for example, about 3,000 rpm.

[0270] Centrifugation speed can also be quantified using relative centrifugal force (RCF). RCF is a measure of the force acting on particles during centrifugation. RCF is generally expressed as a multiple of the Earth's gravitational field (g). RCF can be calculated by the following equation, where radius (cm) is the distance from the center of the centrifuge to the end of the sample, and rotational speed (revolutions per minute) is the rotational speed of the centrifuge. The radius is typically about 15 cm.

[0271] RCF = 11.2 × radius × (rotational speed / 1000) 2 .

[0272] The RCF of the first centrifugation may differ from that of the second centrifugation. The RCF of the first centrifugation may be less than that of the second centrifugation.

[0273] The first centrifugation may be 50 to 1,500, preferably 150 to 1,500, more preferably 300 to 1,100, even more preferably 500 to 900, and even more preferably 600 to 800 RCF. The first centrifugation may be about 650 RCF.

[0274] The second centrifugation may be 600 to 2,600, preferably 1,000 to 2,000, more preferably 1,300 to 1,700, and even more preferably 1,400 to 1,600 RCF. The second centrifugation may be about 1,500 RCF.

[0275] The first centrifugation may be an RCF of 168 to 1,512, preferably 378 to 1,150, more preferably 544 to 813. The first centrifugation may be an RCF of about 672.

[0276] The second centrifugation may be 671 to 2,688, preferably 1,050 to 3,058, more preferably 1,317 to 1,720 RCF. The second centrifugation may be about 1,512 RCF.

[0277] The first centrifugation can be performed for a time of 1 to 20 minutes, preferably 2 to 15 minutes, preferably 3 to 10 minutes, more preferably 4 to 6 minutes, for example, about 5 minutes.

[0278] The second centrifugation can be performed for 1 to 20 minutes, preferably 2 to 15 minutes, preferably 3 to 10 minutes, more preferably 4 to 6 minutes, for example, about 5 minutes.

[0279] Preferably, the first centrifugation is performed at 2000 rpm for 5 minutes and the second centrifugation is performed at 3000 rpm for 5 minutes, and the second centrifugation is performed on the supernatant from the first centrifugation.

[0280] It is believed that a two-stage differential centrifugation process results in a narrower particle size distribution for cellulose particles. The first centrifugation at a lower speed precipitates larger cellulose particles. Therefore, the supernatant from the first centrifugation still contains particles of the desired size and smaller particles. This supernatant from the first centrifugation is centrifuged again at a high speed to precipitate the desired particles. Smaller particles remain in the supernatant from the second centrifugation. Consequently, the precipitated particles from the second centrifugation do not contain a large proportion of larger or smaller particles, so the particle size distribution is narrower.

[0281] Precipitated cellulose particles can be collected by any suitable method. Typically, cellulose particles are collected by filtration.

[0282] Cellulose particles are typically collected as a slurry or suspension. The slurry or suspension may be with water, ethanol, or acetone. Preferably, the slurry or suspension is with water.

[0283] Larger cellulose particles precipitated from the precipitate fraction of the first centrifugation can be recycled and reprocessed by repeating the sonication and fractionation steps described above. This can improve the yield of the fraction containing a desirable particle size.

[0284] The method for manufacturing cellulose particles also

[0285] It may include a step of drying the fractionated cellulose particles.

[0286] This can be known as the drying step. The drying step typically occurs after the fractionation step. The drying step is typically performed on a slurry or suspension of cellulose particles produced by the fractionation step.

[0287] Typically, the drying step involves removing a solvent from the fractionated cellulose particles. The drying step typically involves removing water, ethanol, or acetone from the fractionated cellulose particles. Preferably, the drying step involves removing water from the fractionated cellulose particles.

[0288] Fractionated cellulose particles can be dried by any suitable method. Suitable methods include evaporation, freeze-drying, spray-drying, or spray-freeze-drying. Preferably, the method is freeze-drying, spray-drying, or spray-freeze-drying. More preferably, the method is freeze-drying.

[0289] Any suitable freeze-drying device may be used. Suitable freeze-drying devices include Scanvac and Coolsafe freeze dryers by LaboGene A / S, or VirTis freeze dryers by SP Scientific.

[0290] Any suitable spray-drying device may be used. Suitable spray-drying devices include the PrecisionCoat spray coater by Specialty Coating Systems (SCS).

[0291] Any suitable spray-freeze drying device may be used. Suitable spray-freeze drying devices include PrecisionCoat spray coaters by SCS and Scanvac and Coolsafe freeze dryers by LaboGene A / S.

[0292] Typically, the drying step provides a dry powder of cellulose particles. Freeze-drying or spray-drying may provide a dry powder of cellulose particles. Preferably, freeze-drying provides a dry powder of cellulose particles.

[0293] The drying step can provide clusters of cellulose particles. Preferably, spray drying or spray-freeze drying provides clusters of cellulose particles.

[0294] The shape and size of dried cellulose particles are generally the same as those of cellulose particles before drying.

[0295] Dry powder of cellulose particles is useful for many applications. Several applications require that cellulose particles be provided as a dry powder so that they can be redispersed in different media.

[0296] Dry powder also minimizes storage and transportation costs due to the reduced mass of the solvent. Dry powder also inhibits fungal and bacterial growth on cellulose particles. Dry powder also enables the redispersion of cellulose particles in a polar solvent different from that used in their manufacture. For example, if cellulose particles are manufactured in a polar solvent (e.g., water), the dry powder can be redispersed in a non-polar solvent (e.g., an organic solvent). Dry powder can also undergo further chemical modification. The dry powder can be redispersed in an organic solvent prior to further chemical modification.

[0297] Optionally, a method for manufacturing cellulose particles

[0298] It may further include a step of modifying the surface of the cellulose particles.

[0299] This can be known as the surface modification step. Typically, the surface modification step is performed after the fractionation of cellulose particles.

[0300] Surface modification can be performed on any cellulose particles. Typically, surface modification is performed on cellulose particles obtained from the fractionation or drying step described above.

[0301] The surface modification step typically involves converting hydroxyl groups on the surface of cellulose particles into different functional groups. The hydroxyl groups are preferably converted into esters (esterification) or ethers (etherification). For example, the hydroxyl groups can be converted into ether groups, such as silyl ether groups.

[0302] In some embodiments, the surface modification step comprises contacting the cellulose particles with an esterifying agent or an etherifying agent. Preferably, the surface modification step comprises contacting the cellulose particles with a hydrophobic agent.

[0303] Any suitable reagent may be used to perform surface modification. Preferably, the reagent is an esterification reagent or an etherification reagent. Preferably, the surface modification step involves treating the cellulose particles with an anhydride, an acyl chloride, or an epoxy-retaining reagent. The hydrophobic agent includes any suitable hydrophobic agent, such as trimethylchlorosilane (TCMS) and chlorotrimethoxysilane. Preferably, the hydrophobic agent is TCMS.

[0304] Reagents can be liquids or vapors (gases). Typically, the reagent is a vapor.

[0305] Surface modification can be performed in solution or in a gas phase reaction. The solution may be an aqueous or non-aqueous solution. Surface modification can be performed under an inert atmosphere, such as a nitrogen or argon atmosphere.

[0306] Hydroxyl groups on the surface of cellulose particles can be activated prior to the surface modification reaction. Any suitable activator may be used. Preferably, the activator is a basic solution, preferably a sodium hydroxide solution.

[0307] Surface modification can be performed in the presence of a catalyst. Any suitable catalyst may be used. Preferably, the catalyst is a basic catalyst. Preferably, the catalyst is pyridine, 4-dimethylaminopyridine, or trimethylamine.

[0308] The surface deformation step can be performed for any suitable time length. Typically, the surface deformation step is performed for 5 minutes or less, e.g., 3 minutes or less, e.g., 2 minutes or less, e.g., 1 minute or less.

[0309] The surface modification step provides surface-modified cellulose particles. Although we do not wish to be bound by theory, it is thought that modifying the hydroxyl groups on the surface of cellulose particles—for example, modifying them to esters or ethers—alters the hydrogen bonds between the surfaces of the cellulose particles. The modification can increase or decrease the hydrogen bonds. Preferably, the modification reduces the hydrogen bonds between the hydroxyl groups so that the pores or voids between the cellulose particles are not prone to collapsing under capillary pressure, for example, during solvent evaporation.

[0310] Surface modification to a hydrophobic agent provides hydrophobic cellulose particles. It is thought that replacing some of the hydroxyl groups on the surface of cellulose particles with hydrophobic groups (e.g., -OTMS) reduces hydrogen bonding between the hydroxyl groups, thereby making the pores or voids between the cellulose particles less likely to collapse under capillary pressure, for example, during solvent evaporation. The dispersibility of the particles in solution can also be customized, for example, to increase dispersibility in non-polar solvents.

[0311] surfactants

[0312] Surfactants are present in the coating composition and opacifying agent, as well as in other aspects of the present invention.

[0313] Surfactants assist in the dispersion of cellulose microparticles. Cellulose microparticles are hydrophilic and cannot be easily dispersed in non-polar solvents. Due to their relatively large size, cellulose particles may settle under gravity after a certain period if no external mechanical action is applied.

[0314] Surfactants, such as nonionic surfactants, are physically mixed with weakly charged cellulose microparticles to form a stereostable combination that can be well dispersed in both polar and nonpolar solvents and can efficiently interact with both hydrophobic and hydrophilic systems. Therefore, nonionic surfactants are preferred when the solvent is relatively nonpolar (e.g., acetone).

[0315] For highly or variably charged systems or suspensions, amphoteric surfactants and CMPs can create an ideal combination for incorporation into polar solvents. Therefore, amphoteric surfactants are preferred when the solvent is relatively polar (e.g., water, ethanol).

[0316] Surfactants can also improve stability in emulsions, such as oil and water emulsions. This ensures a stable, homogeneous, and well-dispersed colloidal suspension over a long period of time (e.g., exceeding several days).

[0317] Surfactants are organic compounds that typically have a relatively hydrophilic portion and a relatively hydrophobic portion. Surfactants may include a 'head' group and a 'tail' group, where the head and tail are hydrophilic or hydrophobic.

[0318] Typically, the head group is hydrophilic. The head group is polar and can be an optionally charged group. For example, the head group can be a carboxylate, sugar, phosphate, or ammonium group.

[0319] Typically, the tail group is hydrophobic. The tail group can be a hydrocarbon chain, such as a branched, linear, or aromatic carbon chain. The tail group can be a hydrophilic chain, such as a fluorocarbon chain, a polyether chain, or a polyether-modified siloxane chain. The tail group can be modified to change the degree of hydrophobicity or hydrophilicity.

[0320] A surfactant may have one or more head groups and one or more tail groups.

[0321] Surfactants can be classified according to the charge of the head group or hydrophilic group. Surfactants can be classified as nonionic, anionic, cationic, or amphoteric. Amphoteric surfactants can also be known as positive surfactants.

[0322] Nonionic surfactants have a net zero charge on the head / hydrophilic group.

[0323] Anionic surfactants have a net negative charge (at the head / hydrophilic group).

[0324] Cationic surfactants have a net positive charge on their head / hydrophilic group.

[0325] Amphoteric surfactants have a net zero charge with positive and negative charge centers within the head / hydrophilic group.

[0326] The charge may depend on the pH of the solution in which the surfactant is present. The charge of the head / hydrophilic group is determined in the present invention by the pH of the coating composition or opacifier. This is typically a pH of about 7.

[0327] Preferably, the surfactant is a nonionic, cationic, or amphoteric surfactant at, for example, about 7. The surfactant is particularly preferably a nonionic surfactant at, for example, about 7.

[0328] Suitable nonionic surfactants may include ethoxylate surfactants, polyethylene glycol monododecyl ether surfactants, alkylphenol ethoxylates, nonoxynol, polyethoxylated tallow amines, cocamide monoethanolamine, cocamide diethanolamine, terminal blocking ethoxylates, poloxamers, fatty acid esters of polyhydroxy compounds, fatty acid esters of glycerol, glycerol monostearate, glycerol monolaurate, fatty acid esters of sorbitol, fatty acid esters of sucrose, alkyl polyglucosides, and alkyl polyglycosides.

[0329] Suitable cationic surfactants may include alkyl ammonium surfactants, cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT), dimethyldioctadecylammonium chloride, and dioctadecyldimethylammonium bromide (DODAB).

[0330] Suitable amphoteric surfactants may comprise a combination of a cationic portion based on a primary, secondary, or tertiary amine or quaternary ammonium cation and an anionic portion based on a sulfonate, carboxylate, or phosphate. For example, amphoteric surfactants may comprise phospholipids such as phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelin; betaines such as cocamidopropyl betaine; sulfanes such as CHAPS (3-[(3-colamidopropyl)dimethylammonio]-1-propanesulfonate) and cocamidopropyl hydroxysulfane; lauryl dimethylamine oxide and myristamine oxide.

[0331] Surfactants can be characterized by their critical micelle concentration (CMC). The CMC refers to the concentration of a surfactant at which micelle formation is first observed in solution. Surfactants present above this concentration, as well as any additional surfactants added, will form micelles. Micelles are self-assembled aggregates of surfactants.

[0332] CMC is provided for a given dispersant (solvent) at a specific temperature and pressure. In this specification, CMC values ​​are provided for water as the solvent at a temperature of 20°C and a pressure of 1 atm. Deviations from these conditions are noted if present. Typically, the critical micelle concentration is measured according to ISO 4311:1979.

[0333] In some embodiments, the surfactant has a critical micelle concentration of 0.03 mM or more, preferably 0.04 mM or more, more preferably 0.06 mM or more. In some embodiments, the surfactant has a critical micelle concentration of 30 mM or less, preferably 25 mM or less, more preferably 20 mM or less, even more preferably 1 mM or less, even more preferably 1.5 mM or less, and most preferably 0.9 mM or less.

[0334] In some embodiments, the surfactant has a critical micelle concentration of 0.03 to 30 mM, preferably 0.04 to 25 mM, more preferably 0.05 to 10 mM, even more preferably 0.05 to 1.5 mM, and even more preferably 0.06 to 0.9 mM.

[0335] For nonionic surfactants, the critical micelle concentration of the surfactant is preferably 0.06 to 0.9 mM (measured in water as the solvent at 25°C and 1 atm). For cationic or amphoteric surfactants, the critical micelle concentration of the surfactant is typically higher, e.g., 0.9 to 25 mM (measured in water as the solvent at 25°C and 1 atm).

[0336] The critical micelle concentration (CMC) is typically defined as the concentration of surfactant at which micelles are formed and all additional surfactants added to the system will form micelles. The critical micelle concentration can be measured using ISO 4311:1979.

[0337] The inventors surprisingly discovered that the use of surfactants having these specific CMC values ​​results in particularly excellent dispersion of cellulose microparticles, and thus provides a coating composition and coating having excellent homogeneity. Consequently, the coating has reliable and consistent optical properties such as whiteness (L*) and opacity.

[0338] In some embodiments, the surfactant is Triton X-100, Tween 20, ECOSURF SA-9, TERGITOL 15-S-9, TERGITOL TMN-100X, hexadecyltrimethylammonium bromide (CTAB), 3-(decyldimethylammonio)-propane-sulfonate salt, or a combination thereof.

[0339] In some embodiments, the surfactant is a nonionic surfactant selected from Triton X-100, Tween 20, ECOSURF SA-9, TERGITOL 15-S-9, TERGITOL TMN-100X, or a combination thereof.

[0340] In some embodiments, the surfactant is a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB).

[0341] In some embodiments, the surfactant is an amphoteric surfactant that is 3-(decyldimethylammonio)-propane-sulfonate salt.

[0342] Triton X-100 has the structure given by chemical formula (1). Triton X-100 is also known as polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether. The average number of polyethylene glycol repeating units is 9.5 (n=9.5). The CMC is 0.22 mM.

[0343]

[0344] Tween 20 has a structure given by chemical formula (2). Tween 20 is also known as polyoxyethylene (20) sorbitan monolaurate. The average total number of polyethylene glycol repeating units is 20 (therefore, the sum of w+x+y+z is 20). The CMC is 0.08 mM.

[0345]

[0346] ECOSURF SA-9 has CAS number 68937-66-6. The CMC is 22 ppm (25°C, 1 atm, water solvent).

[0347] TERGITOL 15-S-9 has the structure given by the chemical formula (3). The value of n + m is 2 to 6. TERGITOL 15-S-9 has CAS number 84133-50-6. The CMC is 52 ppm. The molecular weight is 596 g / mol, which gives the CMC of 0.037 mM.

[0348]

[0349] TERGITOL TMN-100X has CAS number 60828-78-6. The CMC is 830 ppm. The molecular weight is 570 g / mol, which provides a CMC of 1.46 mM.

[0350] Hexadecyltrimethylammonium bromide (CTAB) has the structure given by the chemical formula (4). CTAB has a CMC of 0.9 mM.

[0351]

[0352] 3-(decyldimethylammonio)-propane-sulfonate endochloride has the structure given by chemical formula (5). The CMC of 3-(decyldimethylammonio)-propane-sulfonate endochloride is 25-40 mM (20 to 25°C).

[0353]

[0354] additives

[0355] The opacifying agent and / or coating composition may further include additives. These additives are not particularly limited. The additives may be included in the opacifying agent component (e.g., in combination with cellulose microparticles and surfactants in a powder or paste). Alternatively, the additives may be included in the coating composition (e.g., incorporated into a liquid carrier).

[0356] Additives may include colorants, softeners, oils, polymers, waxes, and gelling agents. Additives are typically suitable for the intended application and use. The opacifying agent and / or coating composition may include one or more additives, such as two or more additives, or three or more additives.

[0357] The additives may include colorants. When a specific colorant is added to the initial CMP suspension, a film of a controlled color can be produced. It is appropriate to note that while individual cellulose microparticles retain their ability to scatter light and form a colloidal white suspension, these particles can only be assembled into a continuous white film with the assistance of a scaffold.

[0358] The coloring agent may include any suitable dye or pigment. The coloring agent may be an organic or inorganic coloring agent, preferably an organic coloring agent. The coloring agent may absorb a narrow light band (light of a specific wavelength) to impart color to the coating. This differs from the opacifying function of cellulose microparticles, which reflect light over a wide range of wavelengths.

[0359] The coloring agent may be beta-naphthol, BON arylamide, benzimidazolone, diazo condensation, quinacridone, perylene, anthraquinone, dibromantron, pyranthrone, diketopyrrolo-pyrrole pigment (DPP), copper phthalocyanine, indantron, phthalocyanine green, dioxazine violet, perinone orange, pyrazolone orange, carbon black, graphite, aniline black, anthraquinone black, benzimidazolone, diazo condensation, or a combination thereof.

[0360] The cellulose microparticle coating formulation may also be mixed with any colorant to control a specific shade of color. The colorant is preferably provided in the carrier liquid. For example, the carrier liquid may be paint.

[0361] Additives may include emollients. Suitable emollients include ammonium lactate, petrolatum, salicylic acid, and urea.

[0362] Additives may contain oil.

[0363] Suitable oils include algae oil, annatto oil, argan oil, almond oil, apricot kernel oil, avocado oil, babassu oil, Brazil nut butter, butter, cashew butter, castor oil, camellia oil, cherry kernel oil, cocoa butter, coconut oil, corn oil, cottonseed oil, fish oil, grapeseed oil, gardenia oil, ghee, hazelnut oil, jatropha oil, jojoba oil, kokum oil, flaxseed oil, macadamia oil, corn oil, mango seed oil, mango butter, mineral oil, mink oil, olive oil, palm oil, palm kernel oil, peach kernel oil, peanut butter, peanut oil, plum kernel oil, pomegranate oil, rapeseed oil, rice bran oil, rosehip oil, sal oil, sesame oil, shea butter, soybean oil, squalene, sunflower oil, tea seed oil, and walnut oil. Oil derivatives obtained from the aforementioned oils, such as esterified oils, fatty acids, fatty alcohols, hydrogenated oils, and triglycerides, can be used as ingredients suitable for the above formulation. Essential oils are also suitable oils.

[0364] The additive may include a polymer. Suitable polymers may include stabilizers, plasticizers, and flame retardants.

[0365] Polymer stabilizers refer to any polymer suitable for inhibiting or delaying the degradation of opacifiers, coating compositions, or coatings. Polymer stabilizers may be UV absorbers, antioxidants, and biocides.

[0366] Plasticizers refer to polymers that increase the plasticity of a coating. These may include phthalate-based plasticizers, DMP, DEP, DIBP, DBP, DINP, terephthalates, trimellitates, and organic phosphates.

[0367] Flame-retardant polymers refer to polymers that inhibit or delay combustion. These may include organic halogen or organic phosphorus compounds.

[0368] Preferably, the polymer additive is a poly(meth)acrylate polymer, such as polyacrylate. The polymer additive may be in monomer form, preferably (meth)acrylate. The monomer may be a monofunctional monomer (e.g., (meth)acrylate) or a difunctional monomer (e.g., di(meth)acrylate). In this way, the monomer may act as a binder or a crosslinking agent. The polymer additive may be cured, such as during the drying of the coating. The polymer additive can improve the adhesion of the coating to the substrate, increase wear resistance, and improve the flexibility of the coating.

[0369] Additives may include wax.

[0370] Suitable waxes include beeswax, candelilla wax, carnauba wax, Japanese wax, lanolin, palm wax, and paraffin.

[0371] The additive may include a gelling agent.

[0372] Suitable gelling agents include cellulose-derived thickeners such as hydroxyethyl cellulose, as well as acacia gum, agar, aloe gel, gelatin, guar gum, gum arabic, tragacanth gum, pectin, alginate, starch, carrageenan, and xanthan gum. Preferably, the gelling agent is a cellulose-derived gelling agent such as hydroxyethyl cellulose.

[0373] If an additive is present in the coating composition, the additive may be provided as part of the carrier liquid. The carrier liquid may be a composition containing such an additive.

[0374] The carrier liquid may be a food composition (e.g., pet food composition), a cosmetic composition, a personal care composition, a pharmaceutical composition, an ink, a paint, a laminate composition, a laundry powder composition, or a building material composition. These compositions contain typical ingredients necessary to perform their functions.

[0375] For example, the carrier liquid may be a paint base containing a binder and water. In particular, the carrier liquid may be an acrylic paint base containing an acrylate binder and water.

[0376] Method for manufacturing an opacifying agent

[0377] A method for manufacturing an opacifying agent of the second aspect in the fourth aspect is provided, and the method

[0378] A step of forming a suspension by adding cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant to a carrier liquid;

[0379] A step of optionally dispersing cellulose microparticles and a surfactant in a carrier liquid to disperse a suspension; and

[0380] It includes the step of drying the suspension to provide an opacifying agent.

[0381] The method for manufacturing an opacifying agent also

[0382] It may include a step of providing cellulose microparticles and a surfactant.

[0383] This may be known as the "manufacturing step" and refers to making suitable cellulose microparticles and suitable surfactants available. The manufacturing step typically occurs before the addition step.

[0384] As described herein, any suitable cellulose microparticles and surfactants may be used. The cellulose microparticles and / or surfactants may be provided as a suspension or solution in a solvent. The suspension may also take the form of a slurry. Alternatively, the cellulose microparticles and / or surfactants may be provided as a dry powder or paste.

[0385] The step of adding cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant to a carrier liquid to form a suspension may be referred to as the "addition step."

[0386] Cellulose microparticles and surfactants may be added separately or together. The carrier liquid used may be the same as described above in the context of the coating composition. Preferably, the carrier liquid is water.

[0387] Where cellulose microparticles and / or a surfactant are provided as a suspension or solution, the addition step simply refers to a combination of suspensions to form a suspension of both cellulose microparticles and a surfactant.

[0388] A suspension is a heterogeneous mixture of fluids containing solid particles typically large enough to cause precipitation if the suspension is left undisturbed for an extended period of time. Cellulose microparticles are suspended in a liquid. Surfactants can be dissolved in the carrier liquid. The suspension can also take the form of a slurry.

[0389] The step of dispersing the suspension by optionally dispersing cellulose microparticles and a surfactant in a carrier liquid may be referred to as the "dispersion step."

[0390] The dispersion step may include sonicating the suspension. The sonication may be tip sonication or ultra-sonication. The sonication may be at an energy of 400 to 1,000 J / g, preferably 500 to 900 J / g, more preferably 600 to 800 J / g. Preferably, the sonication is at an energy of about 700 J / g.

[0391] Ultrasonic treatment can be performed by any suitable device, such as a Fisherbrand ultrasonic disintegrator.

[0392] The step of drying the suspension to provide an opacifying agent may be referred to as the "drying step." The drying step typically occurs after the addition step or, if present, after the dispersion step. The drying step is typically performed in a slurry or suspension of cellulose microparticles and a surfactant.

[0393] Typically, the drying step involves removing a carrier liquid (solvent) from the suspension. The drying step typically involves removing water, ethanol, or acetone from the suspension. Preferably, the drying step involves removing water from the suspension.

[0394] The suspension may be dried by any suitable method. For example, the suspension may be dried by evaporation, freeze-drying, spray-drying, or spray-freeze-drying. The apparatus for the production of cellulose microparticles may be as described above.

[0395] The drying step can remove substantially all of the carrier liquid (solvent). For example, freeze-drying, spray-drying, or spray-freeze-drying can remove substantially all of the carrier liquid. This typically produces an opacifying powder, wherein the powder comprises clusters of cellulose microparticles and surfactants.

[0396] Typically, the drying step provides a dry powder of cellulose microparticles and a surfactant. Freeze-drying or spray-drying may provide the dry powder. Preferably, spray-drying provides a dry powder of cellulose microparticles and a surfactant.

[0397] The opacifying agent powder may be as described in this specification.

[0398] Alternatively, the drying step can remove only a portion of the carrier liquid (solvent). In this way, the suspension is dried only partially.

[0399] For example, evaporation, freeze-drying, spray-drying, or spray-freeze-drying can remove only a portion of the carrier liquid. This typically produces an opacifier powder, paste, or slurry that retains some solvent. Partial drying preferably produces an opacifier paste or slurry.

[0400] An opacifying agent paste or slurry is typically a relatively concentrated mixture of cellulose microparticles and a surfactant partially suspended in a carrier liquid. The opacifying agent paste or slurry is as described herein.

[0401] The method for manufacturing an opacifying agent also

[0402] It may include a step of adding one or more additives to the opacifying agent.

[0403] The step of adding one or more additives may be performed sequentially with the addition step. The step of adding one or more additives may be performed after the dispersion step, if present. Preferably, the step of adding one or more additives is performed after the addition step and before the dispersion step. Thus, the additives may also be dispersed in the dispersion step.

[0404] When multiple additives are added, the additives may be added separately or together.

[0405] The additives are as described in this specification.

[0406] The opacifying agent produced by the method described in this specification may be used in the coating composition of the present invention or in the method for preparing the coating composition of the present invention.

[0407] Accordingly, in an aspect of the present invention, an opacifying agent is provided, wherein the opacifying agent is obtained or can be obtained by a method of a third aspect.

[0408] Method for preparing a coating composition

[0409] A method for preparing a coating composition of the first aspect in the fifth aspect of the present invention is provided, and the method

[0410] A step of adding cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant, or an opacifying agent of a second aspect, to a carrier liquid;

[0411] The method includes the step of optionally dispersing cellulose microparticles and a surfactant or an opacifying agent in a carrier liquid to provide a coating composition.

[0412] A method for manufacturing a coating composition also

[0413] It may include a step of providing cellulose microparticles and a surfactant, or a step of providing an opacifying agent.

[0414] This may be known as the "manufacturing step" and refers to making suitable cellulose microparticles and suitable surfactants available, or making suitable opacifying agents available. The manufacturing step typically occurs before the addition step.

[0415] As described herein, any suitable cellulose microparticles and surfactants may be used. The cellulose microparticles and / or surfactants may be provided as a suspension or solution in a solvent. The suspension may also take the form of a slurry. Alternatively, the cellulose microparticles and / or surfactants may be provided as a dry powder or paste.

[0416] Any suitable opacifying agent according to the second aspect may be used. The opacifying agent typically comprises microparticles and a surfactant as described herein. The opacifying agent may be provided as a suspension in a solvent. The suspension may also take the form of a slurry. Alternatively, the opacifying agent may be provided as a dry powder or paste.

[0417] The step of adding cellulose microparticles having an average particle length of 0.2 to 20 μm and a surfactant, or an opacifying agent of the second aspect, to a carrier liquid may be referred to as the “addition step.”

[0418] The components may be added separately or together. The carrier liquid used may be the same as that described above in the context of the coating composition. Preferably, the carrier liquid is water.

[0419] Where cellulose microparticles and / or a surfactant are provided as a suspension or solution, the addition step simply refers to a combination of suspensions to form a suspension of both cellulose microparticles and a surfactant.

[0420] A suspension is a heterogeneous mixture of fluids containing solid particles typically large enough to cause precipitation if the suspension is left undisturbed for an extended period of time. Cellulose microparticles are suspended in a liquid. Surfactants can be dissolved in the carrier liquid. The suspension can also take the form of a slurry.

[0421] The step of optionally dispersing cellulose microparticles and a surfactant or opacifying agent in a carrier liquid to form a suspension may be referred to as a "dispersion step."

[0422] A dispersion step may be necessary if the cellulose microparticles or opacifying agent are not sufficiently dispersed as a result of the addition step. The cellulose microparticles or opacifying agent are preferably homogeneously dispersed in the carrier liquid.

[0423] The dispersion step may include sonicating the suspension. The sonication may be tip sonication or ultra-sonication. The sonication may be at an energy of 400 to 1,000 J / g, preferably 500 to 900 J / g, more preferably 600 to 800 J / g. Preferably, the sonication is at an energy of about 700 J / g. Sonication energy refers to the energy per total mass of the suspension being sonicated.

[0424] Ultrasonic treatment can be performed by any suitable device, such as a Fisherbrand ultrasonic disintegrator.

[0425] A method for manufacturing a coating composition also

[0426] The method may include the step of adding one or more additives to the coating composition.

[0427] The step of adding one or more additives may be performed sequentially with the addition step. The step of adding one or more additives may be performed after the dispersion step, if present. Preferably, the step of adding one or more additives is performed after the addition step and before the dispersion step. Thus, the additives may also be dispersed in the dispersion step.

[0428] When multiple additives are added, the additives may be added separately or together.

[0429] The additives are as described in this specification.

[0430] A coating composition produced by the method described in this specification may be used as a coating composition of the present invention or in a method for coating a substrate.

[0431] Accordingly, a coating composition is provided in an aspect of the present invention, wherein the coating composition is obtained or can be obtained by the method of the fourth aspect.

[0432] coating

[0433] In a third aspect of the present invention, a coating applied to a substrate is provided, and the coating is

[0434] Cellulose microparticles having an average particle length of 0.7 to 9 μm, and

[0435] Contains surfactants,

[0436] Here, cellulose microparticles are present in the coating in an amount of 50 to 99.6 weight% based on the total mass of the coating, and surfactants are present in the coating in an amount of 0.4 to 25 weight% based on the total mass of the coating.

[0437] The coating composition of the present invention can be used to produce homogeneous films of controllable thickness. Although not wishing to be bound by theory, it is believed that the surfactant acts as a scaffold for the uniform assembly of cellulose microparticles. Layer-by-layer assembly of these films is also possible without interfering with the organization of these microparticles or the desired opacity.

[0438] The coating may be formed using typical coating techniques as described herein. The coating has the ability to scatter light in the infrared and ultraviolet wavelength ranges as well as visible light.

[0439] Cellulose microparticles are as described in this specification.

[0440] Cellulose microparticles may be present in the coating in an amount of 50 weight% or more, preferably 80 weight% or more, more preferably 85 weight% or more, based on the total mass of the coating. In some embodiments, cellulose microparticles are present in the coating in an amount of 99.6 weight% or less, preferably 98 weight% or less, more preferably 95 weight% or less, and even more preferably 90 weight% or less, based on the total mass of the coating.

[0441] Cellulose microparticles are present in the coating in an amount of 50 to 99.6 weight percent based on the total mass of the coating. In some embodiments, cellulose microparticles are present in the coating in an amount of 80 to 99 weight percent, preferably 85 to 96 weight percent, and more preferably 86 to 90 weight percent based on the total mass of the coating.

[0442] The surfactant is as described in this specification.

[0443] In some embodiments, the surfactant is present in the coating in an amount of 1 weight percent or more, preferably 5 weight percent or more, more preferably 10 weight percent or more, based on the total mass of the coating. In some embodiments, the surfactant is present in the coating in an amount of 20 weight percent or less, preferably 17 weight percent or less, more preferably 15 weight percent or less, based on the total mass of the coating.

[0444] The surfactant is present in the coating in an amount of 0.4 to 25 weight percent based on the total mass of the coating. In some embodiments, the surfactant is present in the coating in an amount of 1 to 20 weight percent, preferably 4 to 17 weight percent, more preferably 12 to 15 weight percent based on the total mass of the coating.

[0445] The coating is substantially free of a carrier liquid (e.g., solvent). Typically, the coating contains less than 5 weight percent, preferably less than 1 weight percent, more preferably less than 0.5 weight percent, and even more preferably less than 0.1 weight percent of a carrier liquid based on the total mass of the coating.

[0446] The coating typically has a thickness greater than the shortest dimension of the cellulose particles. For example, the coating typically has a thickness greater than the width of the cellulose microparticles. The width of the cellulose microparticles is as specified herein. Cellulose microparticles As described in the section.

[0447] The coating preferably has a thickness greater than the longest dimension of the cellulose particles. For example, the coating typically has a thickness greater than the length of the cellulose microparticles. The length of the cellulose microparticles is as specified herein. Cellulose microparticles As described in the section.

[0448] Coating thickness can be measured using any suitable method, such as a micrometer screw head, an ultrasonic thickness gauge, a surface profilometer, an SEM, or an AFM (atomic force microscope). Coating thickness can be measured by taking multiple readings distributed across the coated area, such as 10 readings, and calculating the average of such readings. Thickness can be measured using the method described in ISO 2808:2019.

[0449] In some embodiments, the coating has an average thickness of 5 μm or more, preferably 10 μm or more, more preferably 15 μm or more. In some embodiments, the coating has an average thickness of 500 μm or less, preferably 300 μm or less, more preferably 200 μm or less.

[0450] In some embodiments, the coating has an average thickness of 5 to 500 μm, preferably 10 to 300 μm, more preferably 15 μm to 200 μm.

[0451] The coating thickness may be substantially uniform across the coated area. For example, the coating thickness may have a standard deviation of 25% or less, preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less. The coating thickness may have a standard deviation of 10 μm or less, preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0452] The coating also has excellent optical properties such as whiteness and reflectance.

[0453] In some embodiments, the coating has an L*(45° / 0°) of 65 or more, preferably 70 or more, more preferably 80 or more, and even more preferably 90 or more, where L*(45° / 0°) is a CIELAB color space coordinate. L* is measured as described herein.

[0454] In some embodiments, the coating has an average reflectance of 38% or more, preferably 50% or more, more preferably 68% or more, and even more preferably 80% or more, wherein the average reflectance is measured over a wavelength range of 400 to 700 nm.

[0455] The coating may also reflect in the UV region. In some embodiments, the coating has an average reflectance of 30% or more, preferably 35% or more, more preferably 40% or more, where the average reflectance is measured over a wavelength range of 100 to 400 nm.

[0456] The coating may also reflect in the IR region. In some embodiments, the coating has an average reflectance of 20% or more, preferably 30% or more, more preferably 35% or more, where the average reflectance is measured over a wavelength range of 1000 to 2500 nm.

[0457] In some embodiments, the coating has an opacity of 60% or more, preferably 70% or more, more preferably 80% or more, and even more preferably 85% or more. Opacity is typically measured over a wavelength range of 400 to 700 nm for a coating having a thickness of 10 μm. Opacity can be measured for a coating formed from a coating composition comprising 12 weight percent cellulose microparticles. Opacity is measured as described in the Examples section.

[0458] The coating applied to the substrate may comprise two or more layers. The two or more layers may comprise two or more layers containing cellulose microparticles and surfactants of the present invention. The two or more layers may be identical or different. Preferably, the two or more layers are identical. In this way, a coating having a desired thickness can be produced by constructing a plurality of layers containing cellulose microparticles and surfactants of the present invention.

[0459] Two or more layers may be applied sequentially. Alternatively, two or more layers may be interposed by different layers, such as additional layers described below. The use of multiple separate layers may be used to achieve a film having a more uniform thickness than a single layer of equivalent thickness.

[0460] The coating applied to the substrate may include an additional layer. The additional layer is different from the cellulose microparticle and surfactant-containing layer of the present invention.

[0461] An additional layer may include a primer layer. The primer layer is typically disposed between the substrate and the layer(s) containing cellulose microparticles and a surfactant. Preferably, the primer layer improves the adhesion of the cellulose microparticle-containing layer to the substrate.

[0462] Any suitable primer layer may be used. The suitable primer layer may include an oil-based primer, a latex-based primer, or a shellac primer.

[0463] Adhesion can be further improved to the desired degree by applying a primary layer or a primer. Primers are particularly suitable when the substrate is metal, wood, or leather, and close structural pores within the substrate or smooth the surface roughness of the substrate.

[0464] An additional layer may include a top-coat layer. The top-coat layer is typically positioned opposite the cellulose microparticle and surfactant-containing layer from the substrate. Preferably, the top-coat layer encapsulates the cellulose microparticle-containing layer. The top-coat layer may provide the coating with improved wear resistance, scratch resistance, antimicrobial resistance, and / or stain resistance properties.

[0465] The coating of the present invention maintains whiteness when a primer or top coat layer is applied. The top coating layer is preferably transparent, for example, transparent to visible light. Transparency typically refers to a transmittance of 80% or more of incident light, for example, 90% or more, or 95% or more.

[0466] Any suitable top-coat layer may be used. A suitable top-coat layer may include a polyurethane layer, an epoxide layer, or a shellac-based layer.

[0467] Coating method

[0468] In a sixth aspect of the present invention, a method for forming a coating on a substrate is provided, and the method

[0469] A step of applying a coating composition of a first aspect to a substrate, and

[0470] It includes the step of drying the coating composition to form a coating containing cellulose microparticles.

[0471] A coating containing cellulose microparticles can be referred to as a layer containing cellulose microparticles.

[0472] The method of forming a coating also

[0473] It may include the step of providing a coating composition and a substrate.

[0474] This may be known as the "coating manufacturing step" and refers to making a suitable coating composition and substrate available. The manufacturing step typically takes place before the application step.

[0475] As described in this specification, any suitable coating composition and substrate may be used.

[0476] The step of applying the coating composition of the first aspect to a substrate may be referred to as the "application step."

[0477] The coating may be applied to the substrate using any suitable means. Suitable means for applying the coating may include spraying, curtain coating, knife coating, roll coating, immersion, or draw-down coating. Preferably, the coating is applied by spraying or draw-down coating, and more preferably by spraying.

[0478] Draw-down coating may involve a draw-down using a stainless steel bar formed from a stainless steel rod tightly wound with stainless steel wire. These rods may also be referred to as groove metering rods. Draw-down coating may also be performed using a Bird Film Applicator. Typically, an appropriate volume of the coating suspension is placed in front of the draw-down rod or bird applicator, and the rod or applicator is held at both ends and moved at a constant speed while applying equal pressure to the surface to be coated.

[0479] Spray coating is typically performed by spraying a suspension using a suitable reservoir connected to a nozzle. For example, the suspension is placed in the reservoir, and the nozzle pressure is adjusted to minimize dissipation outside the intended coating area. The nozzle pressure typically does not exceed 1 bar for a volume of <50 ml.

[0480] The method of applying the coating may depend on the intended substrate and the intended use of the coating. For example, coating a wall or roof as a substrate can preferably be achieved by spraying. However, coating a paper or wood can preferably be achieved by draw-down coating.

[0481] In some embodiments, the method further comprises the step of applying a primer layer to a substrate before applying a coating composition, wherein the coating composition is applied on the primer layer. The primer layer is as described above.

[0482] In some embodiments, the method further comprises the step of applying a top coating layer to a cellulose microparticle-containing layer after drying the coating composition, preferably wherein the top coating layer encapsulates the cellulose microparticle-containing layer. The top coating layer is as described above.

[0483] Any substrate suitable for receiving the coating composition may be used. The substrate is preferably flat, but the substrate may be curved or have a complex shape (e.g., when applied by spray or drip coating).

[0484] In some embodiments, the substrate is paper, wood, plastic, leather, or metal. The substrate may be any suitable type of paper, wood, plastic, leather, or metal.

[0485] Suitable papers include copy paper, bond paper, cardstock, glossy paper, matte paper, newspaper, tissue paper, construction paper, watercolor paper, vellum, tracing paper, and parchment.

[0486] Suitable wood includes natural wood, including dried and undried wood, and manufactured wood such as plywood, MDF, chipboard, hardboard, and veneer.

[0487] Suitable plastics include acrylic or polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PETE or PET), polyvinyl chloride (PVC), or acrylonitrile-butadiene-styrene (ABS).

[0488] Suitable leathers include bonded leather, bridle leather, deerskin, full-grain leather, and cowhide.

[0489] Suitable metals include aluminum, cadmium, chromium, copper, iron, lead, nickel, tin, zinc, and combinations or alloys thereof.

[0490] In an embodiment where cellulose microparticles provide excellent IR scattering, the substrate may be a wall or roof of a building. In this way, the coating can reduce radiation through light reflection from these coated surfaces. Such a white cellulose coating can therefore be a viable solution for thermal management in buildings and elsewhere, and ultimately contribute to reducing global warming by using renewable materials in a sustainable manner.

[0491] In an embodiment where cellulose microparticles provide excellent UV scattering, the substrate may be the skin of an object. In this way, the coating can provide UV protection to the object.

[0492] The step of drying the coating composition to form a layer containing cellulose microparticles may be referred to as a "setting step."

[0493] The setting step can be achieved by any suitable means. The setting step includes removing the carrier liquid (solvent) from the suspension. The setting step occurs after the coating is applied to the substrate and sets the coating at a location on the substrate.

[0494] The coating can be dried at ambient temperature or at elevated temperature. The coating can be air-dried passively (e.g., by relying on air convection to remove evaporated solvent) or air-dried actively (e.g., by passing air over the coating surface).

[0495] A conduction dryer or a convection dryer may be used during the setting stage. Examples of suitable conduction dryers include paddle dryers, disc dryers, or thin film dryers. Examples of suitable convection dryers include vacuum dryers or fluidized bed dryers.

[0496] The setting step results in a coating that is substantially free of a carrier liquid (e.g., solvent). This 'sets' the coating. Typically, the drying step produces a coating having less than 5% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, and even more preferably less than 0.1% by weight, based on the total mass of the coating.

[0497] During the drying step, it is believed that cellulose microparticles are assembled onto a surfactant scaffold to form a continuous white film. As a result of the surfactant used, the cellulose microparticles do not prematurely precipitate from the coating composition during the setting process (as the solvent volume decreases), but rather remain homogeneously dispersed in the solvent by the surfactant. The cellulose microparticles are then assembled into a coating layer, which has a homogeneous distribution of cellulose particles and thus provides uniform and continuous whiteness and opacity.

[0498] A coating produced by the method described in this specification can be used as a coating composition of the present invention.

[0499] Accordingly, in an aspect of the present invention, a coating is provided, wherein the coating is obtained or can be obtained by the method of the sixth aspect.

[0500] use

[0501] In an aspect of the present invention, a use of a coating composition according to a first aspect is provided for forming a coating by applying it to a substrate.

[0502] The coating of the present invention can be used to improve the whiteness of a substrate or to provide opacity. Since the coating has a high level of reflectance and reflects light at similar levels across the entire spectrum of visible light, it is particularly suitable as a whiteness enhancer for a substrate.

[0503] Applications can be found in food additives (e.g., pet food additives), cosmetics, personal care products, pharmaceuticals, inks, paints, laminates, laundry powders, light harvesting devices (e.g., photovoltaics), light distribution devices (e.g., LEDs), household goods (e.g., furniture), and building materials.

[0504] Other preferences

[0505] Each and every compatible combination of the embodiments described above is explicitly disclosed in this specification as each and every combination is individually and explicitly cited.

[0506] Various additional aspects and embodiments of the present invention will be apparent to those skilled in the art in light of the present disclosure.

[0507] As used herein, “and / or” shall be taken as specific disclosures of each of two specified features or components, with or without other. For example, “A and / or B” shall be taken as specific disclosures of (i) A, (ii) B, and (iii) A and B, respectively, as if each were presented individually in this specification.

[0508] Unless otherwise indicated by the context, the description and definition of the features presented above are not limited to any specific aspect or embodiment of the invention and apply equally to all described aspects and embodiments.

[0509] Specific aspects and embodiments of the present invention will now be described by way of example and with reference to the drawings described above.

[0510] Examples

[0511] The following examples are provided to further illustrate the invention and are not intended to limit the scope of the invention.

[0512] ingredient

[0513] Microcrystalline cellulose powder (MCC) was purchased from SERVA Electrophoresis.

[0514] Sulfuric acid (concentration > 95%) was purchased from Fisher Chemical.

[0515] The acrylic paint base is obtained from Galaxus and contains a binder (acrylic) and water as its main components.

[0516] Triton X-100 was obtained from Sigma-Aldrich.

[0517] Tween 20 was obtained from Sigma-Aldrich.

[0518] ECOSURF SA-9 was obtained from Dow.

[0519] TERGITOL 15-S-9 was obtained from Dow.

[0520] TERGITOL TMN-100X was obtained from Dow.

[0521] Hexadimethylammonium bromide (CTAB) was obtained from Sigma-Aldrich.

[0522] 3-(decyldimethylammonio)-propane-sulfonate endochlorine was obtained from Sigma-Aldrich.

[0523] The opacity chart, also known as a contrast ratio chart, was obtained from Leneta. The opacity chart features a simple combination of white and black areas large enough for wide aperture reflectance measurements. The black and white areas are sealed with a transparent, impermeable topcoat that prevents the applied coating from penetrating the paper.

[0524] measurement method

[0525] SEM images are obtained using an FEI Nanolab 650 FIB-SEM operating at 5.0 kV and having a working distance of 6.9 mm.

[0526] Whiteness can be quantified by converting reflectance (measured as described below) into CIELAB(L*a*b*) color-space coordinates. Here, a* represents a position between red (positive value) and green (negative value), and b* represents a position between blue (negative value) and yellow (positive value). L* represents the perceptual brightness or luminous intensity of the reflection. A brightness of 0 is black, and a brightness of 100 is diffuse white. Brightness close to 100 indicates excellent whiteness of the material.

[0527] Whiteness can be measured at different angles of incidence, which refer to the angle of the incident light. L*(45 / 0) refers to an angle of incidence of 45° with respect to the normal of the surface and an angle of reflection of 0° with respect to the normal of the surface.

[0528] Total reflectance measurements were performed using an integrating sphere (Labsphere). A light source (Ocean Optics HPX-2000) was coupled to an optical fiber (600 μm Thorlabs FC-UV100-2-SR) via a collimator (Thorlabs), and the signal was collected by a spectrometer (Avantes HS2048). The signal can be normalized to the intensity when no sample is mounted. The background is typically recorded when no light is applied. The wavelength range can be 400 to 700 nm. Five spectra are taken for each sample and can be averaged to reduce the signal-to-noise ratio. Each spectrum can be recorded using an integration time equal to 3 seconds.

[0529] For the quantification of whiteness, it can be assumed that perfect white has color space coordinates (100, 0, 0). Whiteness can be defined and calculated as set forth in WO2023 / 135261.

[0530] The thickness of the coating was measured using a micrometer screw head. The coating thickness was measured by taking multiple readings distributed across the coated area, such as 10 readings, and calculating the average of those readings.

[0531] When microcellulose particles are applied as paint, the solvent begins to evaporate, a process that leads to the formation of porosity in the dried film. As the solvent evaporates, the liquid phase decreases, causing the microcellulose particles to come into closer contact with each other. This results in the creation of small voids or pores within the matrix of the applied paint. The ideal pore size should be approximately half the wavelength of light, preferably in the range of 50 to 900 nm, and particularly preferably in the range of 100 to 500 nm. Smaller pores may be more suitable for UV protection, while larger pores may be suitable for IR scattering.

[0532] It is also important to consider the uniformity of the pore size distribution. The narrower the pore size distribution, the more effective the scattering power of the material or structure. The presence of these pores and the uniformity of their size distribution enable increased light scattering, which not only improves the aesthetic quality of the paint or coating but also results in a more uniform appearance. Therefore, pore size and distribution can contribute to optimal light scattering, which increases the brightness and opacity of the applied white paint. Thanks to these microporous characteristics, the paint can not only produce a high-gloss surface but also improve the air permeability of the coated material. As mentioned above, manipulating pore size and pore size distribution can significantly contribute to the scattering performance of coatings and paints below the critical pigment volume concentration of CPVC.

[0533] CMP manufacturing

[0534] Three different CMPs were manufactured: CMP-LS, CMP-X, and CMP-Z.

[0535] For CMP-LS, cellulose microcrystalline powder (1 g) was hydrolyzed with sulfuric acid (50 wt%, 60 mL) at 50°C for 5 hours, followed by the addition of 300 mL of milli-Q water and rapid cooling. The acid supernatant was removed by centrifugation. The hydrolyzed cellulose particles were dispersed by adding 100 mL of milli-Q water and then centrifuged. This process was repeated three times to remove most of the acid, and the suspension of hydrolyzed cellulose particles was dialyzed against milli-Q water for one week with water replacement twice a day (MWCO 12-14 kDa). The dialyzed suspension of hydrolyzed cellulose particles (0.5 wt%, 30 mL) was tip-sonicated in an ice bath (Fisher brand sonicator 500 W, 20 kHz, tip diameter 12.7 mm, amplitude 30%, 2 seconds on and 2 seconds off). The suspension was centrifuged at 2000 rpm for 5 minutes, the supernatant was collected, and the supernatant was centrifuged at 3000 rpm for 5 minutes to obtain cellulose nanoparticles CMP-LS.

[0536] CMP-X was obtained using the same method as CMP-LS, except that the cellulose microcrystalline powder was replaced with cellulose filter paper (Whatman No. 1). The cellulose filter paper (Whatman No. 1) was hydrolyzed with sulfuric acid (55 wt%, 60 mL) at 50°C for 0.5 hours.

[0537] CMP-Z was prepared from cellulose filter paper (Whatman No. 1), which was first ground into small pieces using a coffee grinder, followed by TEMPO oxidation. 1 g of cellulose was suspended in 150 mL of milli-Q water, 0.123 g of TEMPO, 1.23 g of NaBr, and 1.23 g of NaClO were added, and the mixture was stirred at room temperature for 4.5 hours while maintaining the pH at 10 by adding 1 M NaOH solution. The reaction was stopped by adjusting the pH to 6 with 5 M HCl, after which the oxidized cellulose fibers were washed by filtration and dialyzed against milli-Q water to yield cellulose fibers CMP-Z.

[0538] Characterization of CMP

[0539] CMP-LS was characterized by scanning electron microscopy (SEM). Figure 1 shows an SEM image of cellulose microparticles with unique light scattering ability. The scale bar is 30 μm.

[0540] The size distributions of CMP-LS, CMP-X, and CMP-Z were measured by scanning electron microscopy (SEM). A diluted suspension of CMP (0.001 wt%) was dropped onto a carbon-coated copper grid (300 mesh) for 2 minutes and removed by a piece of filter paper, after which a drop of uranyl acetate solution (2%) was applied as a stain for 1 minute before being removed by a piece of filter paper. The particle lengths were analyzed by ImageJ. Length refers to the largest diameter of the particle visible in the SEM image. The number of measurements taken to provide the size distribution is typically 100 to 1,000. Generally, more than 100 measurements of length are taken.

[0541] The particle length size distribution of CMP-LS, CMP-X, and CMP-Z is shown in Fig. 2. The size distribution is quantified by the volume of the particles.

[0542] Preparation of a composition

[0543] The coating compositions of the present invention (compositions 1a to 7) were prepared by mechanically mixing a surfactant solution (water as a solvent) with CMP-LS powder and then ultrasonically treating it.

[0544] The comparative coating composition (comp. 1) was prepared by mechanically mixing water with CMP-LS powder and then ultrasonically treating it. No surfactant was present.

[0545] A surfactant-containing solution was prepared by combining a surfactant with water at the concentrations specified in Table 1. The amount of added CMP was as specified in Table 1. The mixture was ultrasonically treated at 700 J / g to produce a coating composition.

[0546] For example, composition 1a was prepared by combining a 2 wt% Triton-X-100 aqueous solution and CMP powder in a 3:17 w:w ratio, and then ultrasonically treating at 700 J / g to produce a suitable coating composition for coating various surfaces.

[0547] Table 1. Includes different surfactant families

[0548] Cellulose Microparticle (CMP) Formulation

[0549]

[0550] coating of the substrate

[0551] Drawdown coating was performed using a stainless steel bar formed from a stainless steel rod tightly wound with stainless steel wire. The bar may also be referred to as a groove metering rod. Drawdown coating was also performed using a Bird Film Applicator where specified. The depth of the drawdown bar / rod is used to determine the coating thickness.

[0552] The substrate was secured to a flat surface with tape. An appropriate volume of the coating composition was placed in front of a drawdown rod or bird applicator. The rod or applicator was held from both ends and moved at a constant speed while applying equal pressure to the surface to be coated.

[0553] Spray coating was performed using a suitable reservoir connected to a nozzle. The composition was placed in the reservoir, and the nozzle pressure was adjusted to minimize dissipation outside the intended coating area. The nozzle pressure is controlled so as not to exceed 1 bar for a volume <50 mL.

[0554] The composition was air-dried for 1 to 60 minutes depending on the volume of the coating composition used.

[0555] Comparative composition 1 It was coated onto an opacity chart. 5 to 10 mL of the comparative coating composition was placed in front of the drawdown load, which was then pulled onto the opacity chart to form a film. The film was allowed to dry for 45 minutes. Upon drying, the film decomposes into heterogeneous pieces.

[0556] The formed coating is illustrated in Fig. 3. The coating was inspected visually. The coating is discontinuous, and large holes were formed in the coating. The coating is also non-uniform and has an inconsistent thickness across the coated area. Consequently, the visual appearance is non-uniform, having varying whiteness and opacity across the coated area. The coating is also uneven.

[0557] Although I do not wish to be bound by theory, it is thought that when the solvent evaporates from these comparative CMP compositions, cellulose particles are deposited on the surface without the ability to form a continuous white film (Fig. 3). This demonstrates that a white film cannot be produced by directly drying the aqueous suspension of CMP.

[0558] Composition 1bIt was coated onto paper by drawdown. The coating was air-dried for 45 minutes. The resulting film has a thickness of 20 μm. The resulting white film is shown in Fig. 4a.

[0559] Additional coatings of composition 1b were formed at thicknesses of 7 μm, 14 μm, and 19 μm.

[0560] Composition 2 It was coated onto paper by drawdown. The coating was air-dried for 45 minutes. The resulting film has a thickness of 20 μm. The resulting white film is shown in Fig. 4b.

[0561] Composition 1b It was coated onto wood by drawdown. The coating was allowed to air dry for 30 minutes. The resulting film has a thickness of 20 μm. The resulting white film is shown in Fig. 5.

[0562] Composition 1b It was coated on aluminum by drawdown at coating thicknesses of 50 μm, 100 μm, and 150 μm. The coating was air-dried for 20 minutes. The resulting 10 μm white film is shown in Fig. 6b.

[0563] Composition 4a It was coated onto cowhide by drawdown at a coating thickness of approximately 20 μm. The coating was allowed to air dry for 45 minutes. The resulting white film on the leather is shown in Fig. 8a.

[0564] Composition 4b (containing 10 wt% acrylic paint base in water) was coated onto cowhide by drawdown at a coating thickness of 20 μm. The coating was allowed to air dry for 45 minutes. The resulting white film on the leather is shown in Fig. 8b.

[0565] The leather sample shown in Fig. 8b can be bent and maintains the white coating even after bending without cracking or chipping. The white film produced in this way maintains excellent dimensional stability even under deformation.

[0566] The coatings of compositions 1b, 2, 4a, and 4b shown in Figures 4, 5, 6, and 8 were visually inspected. The formed coatings were continuous without voids or gaps. The coatings were also found to be homogeneous and have a consistent thickness across the coated area. Consequently, the visual appearance is highly uniform and flat, with excellent whiteness and opacity across the entire coated area. The thickness of the film was highly controllable by the coating process.

[0567] Although I do not wish to be bound by theory, it is thought that the surfactant forms a scaffold that is assembled to allow the CMP to form a continuous lattice structure by maintaining uniformly periodic distances between the microparticles. This periodic structure amplifies the light scattering contrast between the cellulose microparticles and the adjacent space (occupied by air), resulting in the formation of a distinct, continuous white film.

[0568] It is also thought that surfactants reduce the surface tension or interfacial tension between cellulose microparticles and the solvent. However, surfactants do not interfere with the light scattering ability of CMP.

[0569] Cellulose white film was found to provide excellent adhesion to paper, wood, aluminum, and leather substrates.

[0570] Optical characterization of coatings

[0571] The whiteness of various coating compositions measured in L* is provided in Table 2.

[0572] For the whiteness measurements provided in Table 2, a 10 μm coating was formed on the opacity chart using drawdown coating.

[0573] The example composition provides an excellent L* value, typically having an L* of 77 or more, and in many cases having an L* of 85 or more.

[0574] Table 2: Whiteness of the coating

[0575]

[0576] The reflection spectrum for a coating formed from composition 1b on aluminum is shown in Fig. 6a. The whiteness of the film, as measured by L*, depends on the film thickness.

[0577] Reflection spectra for coatings formed from composition 1b on paper at thicknesses of 7 μm, 14 μm, and 19 μm are shown in Fig. 7. L* is 66 (7 μm), 77 (14 μm), and 80 (19 μm). It was found that the degree of whiteness, as indicated by L* (45 / 0), depends directly on the coating thickness.

[0578] The spectrum for the coating formed from composition 4a on cowhide yields CIELAB color values ​​of L* = 95, a* = -0.1, and b* = 2.8. The whiteness value is 94 [calculated as 100 - SQRT((100-L*)^2 + a*^2 + b*^2)].

[0579] In this color space, the numerical difference between values ​​roughly corresponds to the amount of variation humans perceive between colors. L*(45 o / 0 o The whiteness of the cellulose-based film characterized by ) shows a value of > 85 when cellulose microparticles are used with nonionic or cationic surfactants and > 75 when amphoteric surfactants are used. This indicates the excellent whiteness and excellent scattering characteristics of the CMP.

[0580] Opacity test

[0581] The dependence of CMP concentration on opacity was tested.

[0582] A series of coating compositions were prepared based on Composition 1b (1.75 wt% Triton X-100) and Composition 2 (0.5 wt% Tween 20) described above. The compositions contained CMP at concentrations of 3 wt%, 6 wt%, 9 wt%, 12 wt%, 15 wt%, 18 wt%, and 20 wt%. The coating compositions were prepared as described above.

[0583] Various coating compositions were coated on the opacity chart (described above). The coatings were applied by drawdown coating at a thickness of 10 μm.

[0584] The opacity of the coating was measured using the same method as described above for L*. Opacity is the percentage ratio of the "y" value (according to the CIE Y value system) measured in black to the white part of the opacity chart paper.

[0585] The opacity values ​​of the coating are provided in Fig. 10.

[0586] Figure 10 shows that a coating containing a CMP with a nonionic surfactant increases with increasing CMP concentration from 3 wt% to 12 or 15 wt%. The opacity increases from about 60% at 3 wt% CMP to over 80% at 12 wt% CMP.

[0587] At concentrations of 12 to 15 wt% or more, opacity is flattened or reduced. In some examples, the volume remains at about 85% from 12 wt% to 20 wt% CMP.

[0588] The exact opacity measured at 12 wt% CMP is provided in Table 3.

[0589] Table 3. Opacity of cellulose microparticle coatings with different formulations

[0590]

[0591] L* and backscattering

[0592] The reflectance of the coating produced in the example described above was tested. The reflectance was measured as described above and L*(45 for different coatings o / 0 o ) and backscattering were determined. All example compositions were applied to an opacity chart.

[0593] Backscattering was measured using diffuse wave spectroscopy (DWS), a light scattering technique used to measure the Brownian motion of particles in a suspension. DWS analyzes the temporal intensity-variation of light scattered by particles.

[0594] L*(45 o / 0 o When measuring ), the measurement was calibrated using a 1 wt% suspension of cellulose microparticles and a 1 cm thick cuvette. Alternatively, other optical techniques for measuring backscattering can be used, for example, using a DWS Rheolab instrument or a similar one.

[0595] L*(45 for cellulose microparticles o / 0 o ) has a value of 38 to 42, or has a backscattering response of >1300 au for the same 1 wt% aqueous suspension corrected using a 1 cm-thick glass cuvette (see FIG. 11).

[0596] L* and backscattering are shown in FIG. 11, which is CIELAB L*(45 for a wide selection of samples coated with cellulose microparticles o / 0 o This is a polynomial plot illustrating the correlation between measurement and backscattering and a method for quantifying whiteness. The area marked with circles represents the range indicating a whiteness at which light scattering measured by a specific technique is appropriately measurable and detectable. The curve fitted to the experimental data is a polynomial function, L*(x) = ax b = 0.72 x 0.55 It can be described as the coefficient of determination, r 2= 98.1%.

[0597] This shows the correlation between CIELAB L* measurements and backscattering by DWS. Acceptable whiteness levels correspond to the range indicated by the circles: L* in the range of 37 to 41 and backscattering between 1300 and 1400 au. L* levels higher than the circled area are also acceptable because the whiteness is much greater. L* levels lower than the circled area are typically not acceptable.

[0598] This test also demonstrates that the composition is adjustable to provide coatings with higher L* (or backscattering) values ​​as needed. Whiteness and backscattering are highly correlated at all degrees of whiteness.

[0599] UV-Visible and IR Reflection

[0600] Composition 1b was coated onto an opacity chart by drawdown coating to produce a film having a thickness of 15 ± 2 μm.

[0601] Composition 2 was coated onto paper by drawdown coating to produce a film having a thickness of 12 ± 3 μm.

[0602] The UV and IR reflections of the film were tested using the method described above. The UV-visible spectrum was measured at wavelengths from 150 to 900 nm, and the IR spectrum was measured at wavelengths from 1000 to 2,500 nm. The spectrum for the coating of Composition 1b is shown in Fig. 13a, and the spectrum for the coating of Composition 2 is shown in Fig. 13b.

[0603] The spectral response of white cellulose films is excellent in the ultraviolet (UV) and infrared (IR) ranges, and they exhibit high reflectivity in the UV-visible range (for very thin films). This demonstrates the ability of these coatings to provide protection / shielding in the UV-visible range.

[0604] additional coating layer

[0605] Composition 1b was coated onto an aluminum substrate by drawdown as described above. A transparent polyurethane film was applied over a white cellulose coating using drawdown coating. This resulted in an aluminum substrate (CMP+PU) having a white cellulose coating covered by a PU coating.

[0606] As a control, a transparent polyurethane film was applied directly to an aluminum substrate. The polyurethane film was applied using a drawdown coating. This resulted in an aluminum substrate (PU) with a PU coating. The PU coating thickness was approximately 10 μm.

[0607] It was found that the PU coating does not affect the whiteness or opacity of the CMP coating.

[0608] Wear resistance

[0609] The wear resistance of CMP+PU and PU-coated aluminum was tested. The wear test was performed using 600-grit sandpaper loaded with 100 g at a rate of 2 passes (back and forth) per cycle. The coatings underwent 10 cycles of wear.

[0610] Wear is determined based on the water contact angle of the coating. The water contact angle (CA, θ) was measured at ambient temperature using a droplet shape analyzer (First Ten Angstroms, USA). A 5 μL water droplet was placed on the surface of the sample, and the contact angle was the average of six measurements taken at different locations on the surface.

[0611] The results are shown in Fig. 12. Before wear (cycle 0), the water contact angle for both CMP+PU and PU is approximately 85°. After one cycle (cycle 1), the water contact angle for the PU coating remains approximately 85°, while the CMP+PU coating decreases to 65°. For cycles 2 through 10, the water contact angle consistently remains between 75° and 85°. CMP+PU generally exhibits a lower water contact angle than PU. This is thought to be a result of the hydrophilicity of the cellulose particles and the surfactant.

[0612] It is evident that the scratch resistance of multilayer cellulose microparticles and polyurethane maintains nearly constant wear resistance, as measured by the water contact angle over a wide range of cycles.

[0613] This demonstrates that the upper transparent layer can be applied without affecting the whiteness of the lower layer, while simultaneously enabling the white coating to have improved scratch or wear resistance.

[0614] Comparative example

[0615] Milled cellulose particles having a particle size of 40 μm were prepared using a knife mill, for example, a Retsch SM300 or a similar system, and mixed with different additives as disclosed in WO02 / 100955A1.

[0616] Comparative Example 1:

[0617] A mixture comprising 12 wt% of milled cellulose particles (40 μm) and 2 wt% of the nonionic surfactant EcoSurf SA-9 was prepared from an aqueous suspension. This combination resulted in no film formation; only randomly aggregated particles were observed (see CE_01 in the table below).

[0618] Comparative Example 2:

[0619] When milled cellulose was combined with calcium carbonate and an ionic surfactant, the result showed only minimal aggregation without the formation of a continuous film (see CE_02 in the table below).

[0620] Comparative Example 3:

[0621] The combination of milled cellulose, calcium carbonate, and titanium dioxide—regardless of whether a nonionic surfactant was present (CE_05 or CE_06)—produced only faint marks during attempts to form a film, indicating poor film formation.

[0622] Comparative Example 4:

[0623] When titanium dioxide was used independently with a nonionic surfactant (CE_04), the resulting product was a heterogeneous film. This demonstrates that the nonionic surfactant does not facilitate the assembly of TiO2 particles into a uniform film and actually hinders the process.

[0624] Composition according to the present invention:

[0625] In contrast, a composition containing 12 wt% CMP-X and 2 wt% EcoSurf SA-9 from an aqueous suspension resulted in the successful production of a continuous and homogeneous white film (see CE03_001_01 in the table below).

[0626]

[0627] Therefore, milled cellulose particles within the size range specified in WO 02 / 100955 A1 do not exhibit the same light-scattering characteristics as the cellulose microparticles contained in the composition according to the present invention. Furthermore, when these milled cellulose particles are mixed with an ionic surfactant from an aqueous suspension, they cannot form a continuous film. Instead, they simply tend to aggregate, which can further inhibit the formation of a homogeneous film when combined with other light-scattering agents such as calcium carbonate or titanium dioxide. Additionally, non-ionic surfactants do not act as a scaffold when mixed with metal oxide particles such as titanium dioxide. The scaffold-like function of the surfactant appears to be exclusive to the cellulose microparticles contained in the composition according to the present invention, i.e., cellulose particles designed with specific physical dimensions.

[0628] References

[0629] Numerous publications have been cited above to more fully describe and disclose the invention and the technical field to which the invention belongs. Full citations of these references are provided below. The entirety of each of these references is incorporated herein.

[0630]

Claims

Claim 1 A coating composition for providing a cellulose microparticle coating on a substrate, wherein the coating composition comprises cellulose microparticles having an average particle length of 0.7 to 9 μm as measured by a scanning electron microscope and an opacifying agent comprising a surfactant; and a carrier liquid. Herein, the cellulose microparticles are present in the coating composition in an amount of 1 to 40 weight percent based on the total mass of the coating composition, the surfactant is present in the coating composition in an amount of 0.5 to 6 weight percent based on the total mass of the coating composition, and the composition comprises less than 5 weight percent of metal oxide. Claim 2 A coating composition, wherein the composition is essentially free of metal oxides, preferably TiO2. Claim 3 A coating composition according to claim 1 or 2, wherein cellulose microparticles are present in the coating composition in an amount of 5 to 20 weight%, preferably 10 to 18 weight%, more preferably 12 to 15 weight% based on the total mass of the coating composition. Claim 4 A coating composition according to any one of claims 1 to 3, wherein the surfactant is present in the coating composition in an amount of 0.5 to 3 weight%, preferably 1.0 to 2.0 weight%, based on the total mass of the coating composition. Claim 5 A coating composition according to any one of claims 1 to 4, wherein the ratio of the amount of cellulose microparticles to the amount of surfactant is 2 to 25, preferably 5 to 9, more preferably 6 to 8, wherein the amount is a weight% based on the total mass of the coating composition. Claim 6 In any one of claims 1 to 5, a particle group CMP having an average particle length of less than 1 μm X , or a particle population CMP having an average particle length in the range of 1 μm to less than 5 μm LS A particle population CMP comprising, or a mixture thereof, preferably having an average particle length in the range of 1 μm to less than 5 μm LS A coating composition comprising Claim 7 A coating composition according to any one of claims 1 to 6, wherein the carrier liquid is water, ethanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), or a combination thereof, and preferably the carrier liquid is water. Claim 8 An opacifying agent for a coating composition, wherein the opacifying agent comprises cellulose microparticles having an average particle length of 0.7 to 9 μm and a surfactant, wherein the cellulose microparticles are present in the opacifying agent in an amount of 50 to 99.6 weight% based on the total mass of the opacifying agent and the surfactant is present in the opacifying agent in an amount of 0.4 to 25 weight% based on the total mass of the opacifying agent; optionally, the opacifying agent is a powder. Claim 9 A cellulose microparticle coating formed on a substrate, wherein the coating comprises cellulose microparticles and a surfactant, wherein the cellulose microparticles have an average particle length of 0.7 to 9 μm as measured by a scanning electron microscope, wherein the cellulose microparticles are present in the coating in an amount of 50 to 99.6 weight% based on the total mass of the coating, and the surfactant is present in the coating in an amount of 0.4 to 25 weight% based on the total mass of the coating, and the coating comprises less than 5 weight% of a metal oxide. Claim 10 A cellulose microparticle coating according to claim 9, wherein the coating has an L*(45° / 0°) of 65 or more, preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, where L*(45° / 0°) is a CIELAB color space coordinate measured for a coating having a thickness of 10 μm. Claim 11 A coating composition, an opacifying agent, or a cellulose microparticle coating according to any one of claims 1 to 7, claim 8, or claim 9 or 10, wherein the cellulose microparticles have an average particle length of 1.3 to 7 μm, more preferably 1.7 to 5 μm, even more preferably 1.9 to 2.8 μm as measured by a scanning electron microscope; and / or an average aspect ratio of 2 to 18, preferably 3 to 15, more preferably 4 to 10, even more preferably 4 to 6 with respect to the average particle length and average particle width as measured by a scanning electron microscope; and / or an average width of 0.1 to 1 μm, preferably 0.2 to 0.8 μm, more preferably 0.3 to 0.6 μm, even more preferably 0.45 to 0.55 μm as measured by a scanning electron microscope. Claim 12 A coating composition, an opacifier, or a cellulose microparticle coating according to any one of claims 1 to 7 or 11, any one of claim 8 or 11, or any one of claims 9 to 11, wherein the cellulose microparticles are anionic, optionally the cellulose microparticles are surface modified with anionic sulfate half-esters and / or; said cellulose microparticles have an anionic charge density of 50 mmol / kg or more, preferably 100 mmol / kg or more, more preferably 150 mmol / kg or more, wherein said anionic charge density is determined according to ISO 21400:2018. Claim 13 In any one of claims 1 to 7 or claims 11 to 12, any one of claims 7, 8 or claims 11 to 12, or any one of claims 9 to 12, the surfactant is preferably polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, polyoxyethylene (20) sorbitan monolaurate, alcohol ethoxylate (C9-C 11 Ethoxylated alcohol), secondary alcohol ethoxylate (C 11 -C 15 A nonionic, cationic, or amphoteric surfactant selected from the group consisting of ethoxylated alcohols, trimethyl nonyl ethers of polyethylene glycol, hexadecyltrimethylammonium bromide (CTAB), and 3-(decyldimethylammonio)-propane-sulfonate salts or combinations thereof; the surfactant is preferably polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, polyoxyethylene (20) sorbitan monolaurate, alcohol ethoxylate (C9-C 11 Ethoxylated alcohol), secondary alcohol ethoxylate (C 11 -C 15 A coating composition, an opacifier, or a cellulose microparticle coating, which is a nonionic surfactant selected from the group consisting of ethoxylated alcohols and trimethyl nonyl ethers of polyethylene glycol or combinations thereof. Claim 14 A coating composition, an opacifying agent, or a cellulose microparticle coating, wherein the surfactant has a critical micelle concentration of 0.03 to 30 mM, preferably 0.04 to 25 mM, more preferably 0.05 to 10 mM, and even more preferably 0.05 to 1.5 mM, wherein the critical micelle concentration is measured according to ISO 4311:1979 at a temperature of 25°C, a pressure of 1 atm, and water as a solvent. Claim 15 A method for preparing a coating composition according to any one of claims 1 to 7 or 11 to 14, the method comprising the step of adding cellulose microparticles having an average particle length of 0.2 to 20 μm and a surfactant, or an opacifying agent according to any one of claims 6 or 9 to 12, to a carrier liquid; optionally, the step of dispersing the cellulose microparticles and surfactant, or the opacifying agent, in the carrier liquid to provide the coating composition. Claim 16 A method for forming a coating on a substrate, the method comprising the steps of applying a coating composition of any one of claims 1 to 7 or claims 11 to 14 to the substrate, and drying the coating composition to form a cellulose microparticle coating.

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