Cellulosic coating composition

Abstract

This invention relates to coating compositions and opacifiers, methods for preparing said coating compositions and opacifiers, and methods for coating and forming coatings using the coating compositions. The coating composition comprises an opacifier and a carrier liquid. The opacifier comprises cellulose microparticles and a surfactant, wherein the cellulose microparticles have an average particle length of 0.7 µm to 9 µm; wherein the cellulose microparticles are present in the coating composition in an amount of 1 wt.% to 40 wt.% based on the total mass of the coating composition, and the surfactant is present in the coating composition in an amount of 0.5 wt.% to 6 wt.%; and wherein the composition comprises less than 5% by weight of a metal oxide.

Description

Technical Field

[0001] This invention relates to coating compositions and opacifiers, methods for preparing coating compositions and opacifiers, coatings, and methods for forming coatings using coating compositions. Background Technology

[0002] Organic coatings are widely used as a common, practical, and cost-effective method to provide a barrier between a substrate and its environment (e.g., a metallic substrate and its environment). Ideally, the coating exhibits high resistance to ionic movement and good adhesion to the substrate (e.g., a metal or other surface). 1 Polymer coating systems have been found to have wide applications in automotive, construction, packaging, and marine applications. 2-6 To improve the sustainability and life cycle assessment (LCA) of coatings and manufacturing processes, the use of renewable components is likely highly desirable.

[0003] Traditionally, the industry producing artificial white coating materials has relied on the use of inorganic materials with high refractive indices, such as TiO2 (n ≈ 2.6), ZnS (n ≈ 2.4), and ZnO (n ≈ 2.0). However, TiO2, the most common whitening agent, has recently been banned as a food additive in the EU for health reasons. In 2022, the European Medicines Agency also emphasized the “critical importance” of finding a suitable alternative to TiO2 in medicines (Commission Regulation (EU) 2022 / 63 of 14 January 2022 amended Annex II and III (texts related to the EEA) 1-5 of Regulation (EC) of the European Parliament and the Council on the food additive titanium dioxide (E 171) (European Parliament and Council, 2022)).

[0004] A typical paint composition consists of a pigment (e.g., titanium dioxide as described above), a binder (for forming a viscous film), a solvent (e.g., water) (for adjusting viscosity and facilitating application), and optional additives (for stability, drying control, or specific properties). Pores in the paint film typically form as the solvent or liquid component evaporates during drying. This process leaves voids or micropores in the film, influenced by the packing density of the pigment particles and the binder content. When a metal oxide (e.g., titanium dioxide) is used as an opaque pigment, 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 depends primarily on the pigment's scattering efficiency.

[0005] Porosity is crucial for light scattering because it increases the refractive index contrast between the solid component (e.g., TiO2) and the air-filled voids or pores. Mie scattering theory predicts that the relative intensity of scattered light is a function of particle size, viewing angle, wavelength of the incident beam, and polarization. Therefore, when designing pigments, there exists an ideal particle size for effective 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 finding alternatives to whitening agents is to draw inspiration from nature. Many different biopolymers have been used to produce photonic structures, one such example being cellulose, an abundant and renewable material. Researchers have attempted to use cellulose nanofibers, which are obtained through a homogenization process combined with some enzymatic or chemical pretreatment.

[0007] For example, WO 2019 / 063647 describes the use of cellulose nanofiber materials or fine webs of interwoven cellulose fibrils to produce porous particles that act as fibrous aggregates and scatter white light. WO 2023 / 135261 describes cellulose microparticles produced using chemical processes, and their light-scattering ability is closely related to their physical size. 8 These cellulose microparticles are promising whitening agents.

[0008] WO02100955 discloses an aqueous dispersion latex paint comprising a film-forming polymer binder and milled cellulose particles smaller than 100 micrometers, as measured by weight-volume distribution. The milled cellulose particles are produced by grinding cellulose fibers together with mineral extender, filler, and pigment in a size-reducing grinding operation to produce fairly uniform milled cellulose particles, preferably having a particle size between 10 and 60 micrometers. The weight ratio of milled cellulose particles to milled mineral extender pigment (filler) is between 5 / 95 and 80 / 20. However, milled cellulose in the particle size range described in WO 02 / 100955 A1 does not sufficiently scatter light and cannot form a continuous film when mixed with ionic surfactants 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 co-treated inorganic particulate material as a primary pigment and / or a thickener pigment, wherein the inorganic particulate material is co-treated with a cellulose-containing fibrous substrate during the preparation of the microfibrillated cellulose. The microfibrillated cellulose contributes to the uniform distribution of pigment in the paint, thereby achieving homogeneous coverage and color intensity.

[0010] However, forming a continuous white film using such cellulose-based brighteners is challenging. This is especially true when these cellulose particles are dried directly from a solvent (e.g., water). 9 It is difficult to produce thin, continuous, and homogeneous white films. Cellulose particles are believed to deposit on the substrate and do not assemble homogeneously to form a continuous and homogeneous white film. Films formed by drying these particles directly from a solvent are volatile and of inferior quality compared to films formed with inorganic materials (e.g., TiO2). Therefore, films containing cellulose particles produced by known methods may have poorer light scattering properties, poorer whiteness, and lack of control over these parameters, for example, compared to TiO2 films. Thus, these known white cellulose films may not be ideal alternatives to coatings based on conventional inorganic materials.

[0011] The present invention aims to solve these problems. Summary of the Invention

[0012] In summary, the present invention provides a coating composition comprising a cellulose particle-based opacifier. The opacifier comprises cellulose microparticles and a surfactant. The cellulose microparticles impart opacity to the opacifier, while the surfactant facilitates the distribution of the cellulose microparticles within the coating composition.

[0013] The inventors have discovered that the enhanced distribution and scaffolding effect provided by surfactants enables the effective formation of cellulose microparticle coatings on substrates. This is believed to be because the cellulose microparticles do not prematurely precipitate from the composition during coating solidification (as solvent volume decreases), but are instead homogeneously dispersed in the solvent by the surfactant. This allows for the formation of a homogeneous and continuous cellulose coating, exhibiting uniform and excellent whiteness and opacity. In particular, the average particle length of the cellulose microparticles enables the achievement of very white compositions without the need for TiO2 in the formulation.

[0014] Generally, coating compositions are provided for providing a cellulose microparticle coating on a substrate, the coating composition comprising:

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

[0016] The carrier liquid; and wherein the composition comprises less than 5% by weight of a metal oxide.

[0017] Specifically, the cellulose white pigment contained in the composition according to the invention has an ideal particle size and, in a properly designed paint and coating formulation, can meet the predicted refractive index contrast and optimal scattering efficiency between cellulose particles and pores when forming a continuous and uniform film. Furthermore, the cellulose white pigment can be adjusted to whiteness above and below a critical pigment volume concentration in colloidal suspensions or mixtures.

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

[0019] It has been discovered that the use of surfactants produces uniformly dispersed cellulose microparticle coating compositions that can be formulated with a variety of polar and nonpolar 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, as well as adjustable whiteness and opacity.

[0021] Therefore, in a first aspect of the invention, a coating composition is provided for providing a cellulose microparticle coating on a substrate, the coating composition comprising:

[0022] A light-blocking agent, wherein the light-blocking agent comprises cellulose microparticles having an average particle length of 0.7 µm to 9 µm and a surfactant; and

[0023] Carrier liquid;

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

[0025] In a second aspect of the invention, a light-blocking agent for use in coating compositions is provided, the light-blocking agent comprising:

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

[0027] Surfactants,

[0028] The cellulose microparticles are present in the light-blocking agent at an amount of 50 wt.% to 99.6 wt.% based on the total mass of the light-blocking agent, and the surfactant is present in the light-blocking agent at an amount of 0.4 wt.% to 25 wt.%.

[0029] In some embodiments, the opacifier is a powder. In some embodiments, the opacifier is a powder and has a water content of less than 6% based on the mass of the opacifier.

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

[0031] The cellulose microparticles have an average particle length of 0.7 µm to 9 µm.

[0032] The cellulose microparticles are present in the coating at an amount of 50 wt.% to 99.6 wt.% based on the total mass of the coating, and the surfactant is present in the coating at an amount of 0.4 wt.% to 25 wt.%.

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

[0034] In some embodiments, the surfactant is present in the coating in an amount of 1 wt.% to 20 wt.%, preferably 4 wt.% to 17 wt.%, more preferably 12 wt.% to 15 wt.%, 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, and / 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 less than 25%, preferably less than 20%, and more preferably less than 15%.

[0037] In a preferred embodiment of the invention, the composition is substantially free of metal oxides, particularly TiO2. The term "substantially free" means that no metal oxides, especially TiO2, are added. This composition offers significant advantages in terms of biocompatibility and environmental impact. The absence of metal oxides helps reduce environmental impact. It supports more sustainable production processes and reduces the ecological footprint associated with the mining and processing of metal oxides.

[0038] The compositions according to the invention may additionally contain an antifoaming agent, a suitable polymer (e.g., a latex- or acrylic-based polymer), and water (for water-based coatings or paints) or another suitable solvent (for organic solvent-based coatings or paints).

[0039] In some embodiments, the coating has:

[0040] 65 or higher, preferably 70 or higher, more preferably 80 or higher, and even more preferably 90 or higher, where L*(45° / 0°) is a CEILAB color space coordinate because such a combination reflects a large amount of light and appears very bright or close to white;

[0041] and / or

[0042] 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 in the wavelength range of 400 nm to 700 nm, because such compositions are particularly effective in reflecting visible light, contributing to their brightness and visual appeal; and / or

[0043] The opacity is 60% or more, preferably 70% or more, more preferably 80% or more, and even more preferably 85% or more, wherein the opacity is measured for a coating with a thickness of 10 µm in the wavelength range of 400 nm to 700 nm, because such compositions exhibit excellent coverage and hiding power.

[0044] In some implementations, the coating has the following average reflectivity:

[0045] 30% or more, preferably 35% or more, more preferably 40% or more, wherein the average reflectance is measured in the wavelength range of 100 nm to 400 nm; or

[0046] The average reflectance is 20% or more, preferably 30% or more, and more preferably 35% or more, wherein the average reflectance is measured in the wavelength range of 1000 nm to 2500 nm.

[0047] In some embodiments of the first, second, and third aspects, the cellulose microparticles have an average particle length of 0.7 µm to 9 µm, preferably 1.3 µm to 7 µm, more preferably 1.7 µm to 5 µm, and even more preferably 1.9 µm to 2.8 µm.

[0048] 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.

[0049] In some embodiments of the first, second, and third aspects, the cellulose microparticles have an average width of 0.1 µm to 1 µm, preferably 0.2 µm to 0.8 µm, more preferably 0.3 µm to 0.6 µm, and even more preferably 0.45 µm to 0.55 µm.

[0050] 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, wherein L* (45° / 0°) are CEILAB color space coordinates measured for a 1 wt.% suspension of the cellulose microparticles in water.

[0051] In some embodiments of the first, second, and third aspects, the cellulose microparticles have a reflectance of 50% or more, preferably 55% or more, and more preferably 60% or more, to incident light with wavelengths from 400 nm to 700 nm, wherein the reflectance is measured for a 1 wt.% suspension of the cellulose microparticles in water.

[0052] In some embodiments of the first, second, and third aspects, the surfactant is a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant, preferably a nonionic surfactant. Nonionic surfactants are advantageous because they maintain the stability of the charged cellulose particles without interfering with the intrinsic charge of the charged cellulose particles.

[0053] 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), or alcohol ethoxylate (C9-C 11 Ethoxylated alcohols (ECOSURF SA-9) and secondary alcohol ethoxylates (C 11 -C 15Ethoxylated alcohol (TERGITOL 15-S-9), polyethylene glycol trimethyl nonyl ether (TERGITOL TMN-100X), hexadecyltrimethylammonium bromide (CTAB), 3-(decyldimethylammonium)-propane-sulfonic acid inner salt, or combinations thereof.

[0054] In some embodiments of the first, second, and third aspects, the surfactant is a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant, such as polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100), polyoxyethylene (20) sorbitan monolaurate (Tween 20), or alcohol ethoxylate (C9-C 11 Ethoxylated alcohols (ECOSURF SA-9) and secondary alcohol ethoxylates (C 11 -C 15 Ethoxylated alcohols (TERGITOL 15-S-9), polyethylene glycol trimethyl nonyl ether (TERGITOL TMN-100X), hexadecyltrimethylammonium bromide (CTAB), 3-(decyldimethylammonium)-propane-sulfonic acid inner salt, or combinations thereof; or

[0055] The surfactant is a nonionic surfactant, such as polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100), polyoxyethylene (20) sorbitan monolaurate (Tween 20), and alcohol ethoxylates (C9-C 11 Ethoxylated alcohols (ECOSURF SA-9) and secondary alcohol ethoxylates (C 11 -C 15 Ethoxylated alcohols (TERGITOL 15-S-9), polyethylene glycol trimethyl nonyl ether (TERGITOL TMN-100X), or combinations thereof.

[0056] In a fourth aspect, a method for preparing the light-blocking agent of the second aspect is provided, the method comprising:

[0057] Cellulose microparticles with an average particle length of 0.7 µm to 9 µm and surfactants are added to a carrier liquid to form a suspension;

[0058] Optionally, cellulose microparticles and surfactants are dispersed in a carrier liquid to disperse the suspension; and

[0059] The suspension is dried to provide a light-blocking agent.

[0060] In a fifth aspect of the invention, a method for preparing the coating composition of the first aspect is provided, the method comprising:

[0061] Cellulose microparticles with an average particle length of 0.7 µm to 9 µm and a surfactant, or a light-blocking agent, are added to the carrier liquid.

[0062] Optionally, cellulose microparticles and surfactants or opacifiers are dispersed in a carrier liquid to provide a coating composition.

[0063] In a sixth aspect of the invention, a method for forming a coating on a substrate is provided, the method comprising:

[0064] Apply the coating composition of the first aspect to the substrate, and

[0065] The coating composition is dried to form a coating containing cellulose microparticles.

[0066] Other aspects

[0067] In one aspect of the invention, a light-blocking agent is provided, wherein the light-blocking agent is obtained or is available by a method of a third aspect.

[0068] In one aspect of the invention, a coating composition is provided, wherein the coating composition is obtained or is available by the method of the fifth aspect.

[0069] In one aspect of the invention, a coating applied to a substrate is provided, wherein the coating is obtained or is obtainable by the method of the sixth aspect.

[0070] In one aspect of the invention, use is provided for applying a coating composition according to the first aspect to a substrate to form a coating. Attached Figure Description

[0071] Figure 1 Cellulose microparticles (CMPs) with unique light scattering capabilities were shown. LS Scanning electron microscope (SEM) image of cellulose microparticles (also known as cellulose microparticles). Scale bar: 30 µm.

[0072] Figure 2 The volumetric size distribution (CMP) of cellulose particles in three states obtained from sulfuric acid hydrolysis is shown. z (Right) Has an average particle size >5 µm; 1 µm > CMP LS (Medium) >5 µm; CMP x (Left) <1 µm. Particle size was measured as described in the Examples section.

[0073] Figure 3 shows an image of the comparative composition coated on an opacity chart. After drying, the film broke into heterogeneous fragments, indicating that directly drying an aqueous suspension of CMP does not produce a white film.

[0074] Figure 4 shows the white film of composition 1b on the paper test card. Figure 4a This exemplary coating composition contains 12 wt.% cellulose microparticles (CMP) and 1.75 wt.% nonionic surfactant (Triton-x100) in an aqueous solution, and a white film of composition 2 on paper is shown. Figure 4b The exemplary coating composition contains 12 wt.% CMP and 0.5 wt.% of another nonionic surfactant (Tween 20) in an aqueous solution (right figure). Both films have a thickness of 20 µm.

[0075] Figure 5 A cellulose microparticle coating of composition 1b on wood is shown. This exemplary coating composition contains 12 wt.% cellulose microparticles and 1.75 wt.% nonionic surfactant (Triton-x100).

[0076] Figure 6 shows the remission spectra of composition 1b coatings of different thicknesses (50 µm, 100 µm, and 150 µm) on aluminum, as measured in the Examples section. Figure 6a One of the white films is like... Figure 6b As shown. The whiteness of the membrane, as measured by L*, depends on the membrane thickness.

[0077] Figure 7 The retroreflection spectra of cellulose microparticle coatings with different thicknesses on paper are shown. The coatings were formed on paper using coating composition 1b with thicknesses of 7 µm, 14 µm, and 19 µm. As shown by L*(45 / 0) or backscatter measurements, the degree of whiteness depends directly on the coating thickness and was measured as described in the Examples section.

[0078] Figure 8 shows a piece of cowhide coated with composition 4a ( Figure 8a The exemplary coating composition contains 12 wt.% CMP and 2 wt.% TERGITOL 15-S-9 (a nonionic surfactant) in an aqueous suspension. The CIELAB color values ​​of the white film on cowhide were measured to be L*=95, a*=-0.1, b*=2.8, and the whiteness value = 100 - SQRT((100-L*)^2 + a*^2 + b*^2) = 94. Notably, the coating composition and coating of the present invention provide a flexible white coating to accommodate more flexible substrates. Figure 8b Images are shown of leather samples coated using the same formulation mixed with 10 wt.% acrylic paint base in water. (Leather sample) Figure 8b It can be bent and retains its white coating even after bending, without cracking or breaking.

[0079] Figure 9 An exemplary scattering characteristic of cellulose microparticles is shown.

[0080] Figure 10 The opacity trends for coatings on an opacity test card, based on the compositions of compositions 1b and 2, are shown within the CMP concentration range (3 wt.%, 6 wt.%, 9 wt.%, 12 wt.%, 15 wt.%, 18 wt.%, and 20 wt.%). Opacity was measured using a spectrophotometer (sph870, ColorLite GmbH).

[0081] Figure 11 A polynomial plot is shown 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 range of white coatings that can be correctly measured and detected by either technique. The coefficients of determination for this polynomial function are L*(x) = ax b = 0.72 x 0.55 Coefficient of determination r 2 = 98.1%.

[0082] Figure 12 Abrasion testing of a CMP coating with a transparent polyurethane film on an aluminum substrate is shown. The test was conducted using 600-grit sandpaper with a 100 g load. Abrasion was determined based on the water contact angle on the coating, which was measured against both the standalone transparent PU coating and the topcoat containing the transparent layer and the underlying CMP layer.

[0083] Figure 13 shows the coating of composition 1b in the UV, visible, and IR regions. Figure 13a The spectral response of composition 2 and the coating of composition 2 Figure 13b The spectrum of ). Figure 13a The coating thickness is 15 ± 2 µm. Figure 13b The film thickness is 12 ± 3 µm. This demonstrates the ability of these coatings to provide protection / shielding in the UV-visible light range.

[0084] Figures 14A to 14F The appearance of the compositions according to the present invention and the compositions of comparative examples is shown.

[0085] Figures 15A to 15F Opacity test card with coating. Detailed Implementation

[0086] Generally, this invention provides a coating composition comprising cellulose microparticles and a surfactant. The surfactant is used to disperse the cellulose microparticles, which the inventors have found to significantly improve the coating properties of the cellulose microparticle composition. This composition enables the preparation of homogeneous, opaque coatings on substrates. The coating can be applied using conventional industrial-scale techniques.

[0087] Cellulose microparticles are typically produced using acid hydrolysis, followed by size sorting of the hydrolyzed cellulose particles. The specific size and / or morphology of cellulose microparticles exhibit characteristic scattering responses in the visible, ultraviolet, and infrared regions. Cellulose microparticles can function as light-blocking agents.

[0088] It is believed that surfactants form a scaffold around which cellulose microparticles assemble. The properties of the surfactant (i.e., critical micelle concentration, solids concentration, and charge) determine the stability and robustness of this scaffold, which facilitates the assembly of cellulose microparticles to produce the desired opacity and whiteness at a given film thickness.

[0089] The morphology of the microparticles can be altered to optimize their scattering efficiency for desired applications. The surfactant can also be modified to adjust the assembly of the cellulose microparticles, thereby regulating the scattering and whiteness of the coating. In this way, the resulting cellulose microparticle coating has a refractive index significantly higher than that of standard cellulose (the average refractive index of cellulose is approximately 1.56).

[0090] Coating composition

[0091] In a general aspect, a coating composition is provided for providing a cellulose microparticle coating on a substrate, the coating composition comprising:

[0092] A light-blocking agent comprising cellulose microparticles and a surfactant, wherein the cellulose microparticles have an average particle length of 0.7 µm to 9 µm; and

[0093] Carrier liquid.

[0094] In a first aspect of the invention, a coating composition is provided for providing a cellulose microparticle coating on a substrate, the coating composition comprising:

[0095] A light-blocking agent, wherein the light-blocking agent comprises cellulose microparticles having an average particle length of 0.7 µm to 9 µm and a surfactant; and

[0096] Carrier liquid;

[0097] The cellulose microparticles are present in the coating composition in an amount of 1 wt.% to 40 wt.% based on the total mass of the coating composition, and the surfactant is present in the coating composition in an amount of 0.5 wt.% to 6 wt.% based on the total mass of the coating composition, and the composition contains less than 5% by weight of metal oxide.

[0098] This coating composition is suitable for application onto a substrate. It is used to provide a cellulose microparticle coating on a substrate. The composition can be applied by any suitable method (e.g., spraying, curtain coating, blade coating, roller coating, dip coating, or draw-down coating). The composition typically forms a homogeneous, uniform coating on the substrate.

[0099] This coating composition contains a light-blocking agent. A light-blocking agent is a component that enhances the opacity of the resulting coating. Typically, a light-blocking agent is a component that reduces light transmittance (e.g., through scattering). In other words, a light-blocking agent has good light scattering properties and poor light transmittance over a wide wavelength range. The light-blocking agent can be a visible light-blocking agent, which blocks light in the visible light region (e.g., 400 nm to 1000 nm). The light-blocking agent can be a UV light-blocking agent, which blocks light in the UV region (e.g., 100 nm to 400 nm). The light-blocking agent can be an IR light-blocking agent, which blocks light in the IR region (e.g., 1000 nm to 2500 nm).

[0100] In this case, the opacifier comprises cellulose microparticles and a surfactant. The cellulose microparticles and surfactant are described in detail below. Opacity is typically provided by the cellulose microparticles described herein.

[0101] In some embodiments, based on the total mass of the coating composition, cellulose microparticles are present in the coating composition in an amount of 1 wt.% to 40 wt.%, and surfactants are present in the coating composition in an amount of 0.5 wt.% to 6 wt.%.

[0102] In some embodiments, based on the total mass of the coating composition, cellulose microparticles are present in the coating composition in an amount of 30 wt.% or less, preferably 20 wt.% or less, more preferably 15 wt.% or less. In some embodiments, based on the total mass of the coating composition, cellulose microparticles are present in the coating composition in an amount of 5 wt.% or more, preferably 10 wt.% or more, more preferably 12 wt.% or more.

[0103] In some embodiments, the coating composition according to the invention comprises a particle group CMP having an average particle length of less than 1 µm. X or a group of particles, CMP, having an average particle length in the range of 1 µm to less than 5 µm.LS or mixtures thereof, preferably CMPs with an average particle length in the range of 1 µm to less than 5 µm. LS In the context of this invention, the term "particle swarm" refers to a group of defined, independent particles that share a particle length within the range defined above. The term "particle length of a particle swarm" relates to the size of each individual particle in the swarm, rather than the properties of an aggregate or bulk material formed by multiple particles. Both particle swarms exhibit good scattering efficiency; however, CMP... LS The scattering efficiency of the particle group is outstanding. This excellent performance allows for enhanced brightness in the coating composition while reducing the required particle concentration. Therefore, although both groups offer significant benefits, CMP... LS It clearly outperforms others due to its significant effectiveness.

[0104] In some embodiments, based on the total mass of the coating composition, cellulose microparticles are present in the coating composition in an amount of 5 wt.% to 20 wt.%, preferably 10 wt.% to 18 wt.%, more preferably 12 wt.% to 15 wt.%.

[0105] In this way, cellulose microparticles provide opacity for coatings produced using the coating composition. It has been observed that coatings provided with particularly excellent opacity are those where cellulose microparticles are present in the coating composition at 12 wt.% to 15 wt.%. Embodiments of the present invention achieve opacity exceeding 80% for these coated films (see Table 3 in the Examples section).

[0106] In some embodiments, the surfactant is present in the coating composition in an amount of 0.05 wt.% or more, preferably 0.5 wt.% or more, and more preferably 1.0 wt.% 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 wt.% or less, preferably 3 wt.% or less, and more preferably 2.0 wt.% or less, based on the total mass of the coating composition.

[0107] In some embodiments, the surfactant is present in the coating composition in an amount of 0.5 wt.% to 3 wt.%, preferably 1.0 wt.% to 2.0 wt.%, based on the total mass of the coating composition.

[0108] In some embodiments, the ratio of the amount of cellulose microparticles (wt.%) to the amount of surfactant (wt.%) is 2 to 25, wherein 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 still more preferably 6 to 8.

[0109] This coating composition comprises a carrier liquid. The carrier liquid can be any suitable liquid capable of dispersing the opacifier. The carrier liquid can be a polar or non-polar solvent. The carrier liquid can be a mixture of solvents.

[0110] The carrier liquid may be 2-propanol, 1,2-dichloroethane, 1,4-dioxane, 18-crown ether-6, 2-propanol, 2-ethoxyethanol, acetic acid, acetone, acetonitrile, ammonia, benzene, n-butanol, n-butyl acetate, chloroform, cyclohexane, dichloromethane, diethyl ether, diethylene glycol dimethyl ether, dimethylformamide, dimethyl sulfoxide, DME, ethane, ethanol, ethyl acetate, ethylene, ethylene glycol, formic acid, glycerol, heptane, hexane, hexamethylbenzene, HMDSO, HMPA, hydrogen, imidazole, isobutanol, isopropanol, methane, methanol, n-hexane, nitromethane, n-pentane, propane, propylene, propylene carbonate, pyridine, pyrrole, tetrahydropyrrole, silicone grease, tert-butanol, tetrahydrofuran, toluene, triethylamine, water, petroleum solvent (white spirit), xylene, or combinations thereof.

[0111] In some embodiments, the carrier liquid is water, ethanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), or a combination thereof.

[0112] The carrier liquid can also be a water-miscible mineral oil, such as glycerol or propylene glycol.

[0113] Preferably, the carrier liquid is primarily water. "Primarily" means 95 wt.% or more of the total mass of the carrier liquid, for example, 96 wt.% or more, 97 wt.% or more, 99 wt.% or more, or 99.5 wt.% or more.

[0114] The carrier liquid can also be an emulsion, such as a water-in-oil emulsion, an oil-in-water emulsion, or a dual emulsion (such as a water-in-oil-in-water emulsion or an oil-in-water-in-oil emulsion). Surfactants can facilitate emulsion formation. In compositions where the carrier liquid is an emulsion, additional surfactants can be present to stabilize the emulsion. For example, the carrier liquid can be a paint.

[0115] Oils suitable for use in 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. Oil derivatives obtained from the above oils (e.g., esterified oils, fatty acids, fatty alcohols, hydrogenated oils, and triglycerides) can be used as suitable ingredients in the aforementioned formulations. Essential oils are also suitable.

[0116] 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 wt.% to 95 wt.%, preferably 80 wt.% to 92 wt.%, more preferably 83 wt.% to 90 wt.%, and even more preferably 86 wt.% to 88 wt.%, based on the total mass of the composition.

[0117] sunblock

[0118] In general, a light-blocking agent for coating compositions is provided, the light-blocking agent comprising cellulose microparticles having an average particle length of 0.7 µm to 9 µm, and a surfactant.

[0119] Opacities typically provide a degree of opacity, for example, when incorporated into coating compositions or coatings. Opacity can be primarily provided by the cellulose microparticle component. Opacity can be present in the IR, UV, or visible light regions of the spectrum.

[0120] In a second aspect of the invention, a light-blocking agent for use in coating compositions is provided, the light-blocking agent comprising:

[0121] Cellulose microparticles, said cellulose microparticles having an average particle length of 0.7 µm to 9 µm, and

[0122] Surfactants,

[0123] The cellulose microparticles are present in the light-blocking agent at an amount of 50 wt.% to 99.6 wt.% based on the total mass of the light-blocking agent, and the surfactant is present in the light-blocking agent at an amount of 0.4 wt.% to 25 wt.%.

[0124] In some embodiments, based on the total mass of the opaque agent, cellulose microparticles are present in the opaque agent in an amount of 70 wt.% or more, preferably 80 wt.% or more, more preferably 85 wt.% or more. In some embodiments, based on the total mass of the opaque agent, cellulose microparticles are present in the opaque agent in an amount of 99.6 wt.% or less, preferably 98 wt.% or less, more preferably 95 wt.% or less, and even more preferably 90 wt.% or less.

[0125] In some embodiments, based on the total mass of the opaque agent, cellulose microparticles are present in the opaque agent in an amount of 80 wt.% to 99 wt.%, preferably 85 wt.% to 96 wt.%, more preferably 86 wt.% to 90 wt.%.

[0126] In some embodiments, the surfactant is present in the light-blocking agent in an amount of 1 wt.% or more, preferably 5 wt.% or more, more preferably 10 wt.% or more, based on the total mass of the light-blocking agent. In some embodiments, the surfactant is present in the light-blocking agent in an amount of 20 wt.% or less, preferably 17 wt.% or less, more preferably 15 wt.% or less, based on the total mass of the light-blocking agent.

[0127] In some embodiments, the surfactant is present in the opaque agent in an amount of 1 wt.% to 20 wt.%, preferably 4 wt.% to 17 wt.%, more preferably 12 wt.% to 15 wt.%, based on the total mass of the opaque agent.

[0128] Opacifiers can be used in the coating compositions of the first aspect.

[0129] A light-blocking agent is a component that enhances the opacity of the resulting coating. Typically, a light-blocking agent is a component that reduces light transmittance (e.g., through scattering). In other words, a light-blocking agent exhibits good light scattering properties and poor light transmittance over a wide wavelength range. A light-blocking agent can be a visible light-blocking agent, blocking light in the visible light region (e.g., 400 nm to 1000 nm). A light-blocking agent can be a UV light-blocking agent, blocking light in the UV region (e.g., 100 nm to 400 nm). A light-blocking agent can be an IR light-blocking agent, blocking light in the IR region (e.g., 1000 nm to 2500 nm).

[0130] When applied as a coating to a substrate with a thickness of 20 µm, the opacifier can provide a transmittance of less than 20%, preferably less than 18%, and more preferably less than 15% for incident light with wavelengths from 400 nm to 800 nm.

[0131] When applied as a coating to a substrate with a thickness of 20 µm, the opacifier can provide more than 50%, preferably more than 55%, and more preferably more than 60% reflectance for incident light with wavelengths from 400 nm to 800 nm.

[0132] The opacifier can have an L* of 70 or higher (e.g., 75 or higher, 80 or higher). Wherein, L* is a CEILAB color space coordinate and is measured for the opacifier when applied as a coating on a substrate with a thickness of 20 µm.

[0133] Transmittance, reflectance, and L* were measured as described in the Examples section.

[0134] The opacity is provided by the cellulose microparticles described herein.

[0135] The opacifier may be in particulate form. Cellulose microparticles and surfactants may be provided as separate particles or clusters mixed together. Alternatively, cellulose microparticles and surfactants may be combined in the same particles or clusters.

[0136] In some of these implementations, the opacifier is a powder. The powder typically contains multiple particles.

[0137] Preferably, the opacifier powder is a flowable powder. Such a flowable powder can be used in commercial applications where the powder is incorporated into a coating composition.

[0138] The opacifier powder may have a flowability of less than 1 s / g, preferably less than 0.5 s / g, more preferably less than 0.3 s / g, wherein the flowability is measured according to ISO 4490:2018 using a 50 g sample in a Hall flowmeter funnel.

[0139] The opacifier powder may have a Hausner ratio of 1.4 or less, preferably 1.25 or less, and more preferably 1 or less, wherein the Hausner ratio is calculated as the ratio between the tapped bulk density and the free settling bulk density of the powder. The tapped density and the free settling density may be measured according to ISO 3953:2011.

[0140] In some embodiments, the opacifier is essentially solvent-free. For example, based on the mass of the opacifier, it has a water content of less than 6%. Due to its chemical and biological stability, this dry powder can be used in commercial applications.

[0141] In alternative embodiments, the opacifier is a paste or slurry. A paste or slurry typically consists of multiple particles suspended in a relatively small amount of carrier liquid. A paste or slurry typically has a higher viscosity than a coating composition. A paste or slurry typically has a higher concentration than a coating composition.

[0142] The carrier liquid may be the same as the carrier liquid described above in the context of the coating composition.

[0143] Pastes are typically viscous and thick. They are used in commercial applications because they are more concentrated than coating compositions. Pastes can be dispersed into formulations more easily than powders.

[0144] The opacifier paste or slurry may have a viscosity of 20,000 mPa·s or less, preferably 5,000 mPa·s or less, and more preferably 1,000 mPa·s or less. The opacifier paste or slurry may have a viscosity of 20 mPa·s or more, preferably 50 mPa·s or more, and more preferably 100 mPa·s or more. Viscosity is measured at 20°C according to ISO 2555:2018.

[0145] Cellulose microparticles

[0146] Cellulose microparticles have an average particle length of 0.7 µm to 9 µm.

[0147] Cellulose microparticles can be used in coating compositions and opacifiers, as well as other aspects of the present invention.

[0148] The cellulose microparticles of the size disclosed herein provide excellent scattering of IR, UV, and visible light. Color is emitted by the interaction of light waves with electrons in the molecules that make up a substance. On the other hand, structural color is the color reflected by a specific geometry, and therefore structural color is permanent as long as the geometry of the material being identified remains unchanged.

[0149] White color is achieved through appropriate light scattering by specific particles, which depends on the refractive index, a material-dependent property. For example, titanium dioxide (TiO2) has a refractive index of 2.87 at 632.8 nm. All polymeric materials, including cellulose, have lower refractive indices compared to such metal oxides. Therefore, to produce white color using cellulose, cellulose particles with specific geometries that allow for effective light scattering are used. The cellulose microparticles used in this invention have the desired geometry and morphology to effectively scatter IR, UV, and / or visible light.

[0150] The length of a particle is typically its longest dimension. For example, if the particle is rod-shaped, the length is the distance between the two ends of the rod. The length of a particle is typically its longitudinal length.

[0151] The length of a particle is typically its longest lateral dimension. Lateral dimensions are the dimensions that are observable when viewing a particle in a two-dimensional view. Particles appear two-dimensional in a two-dimensional view. For example, if a particle is measured from a top-down (or planar) image, then the length is the longest dimension of the particle measured from the top-down image.

[0152] The length of the particles can be measured using standard techniques. For example, scanning electron microscopy (SEM) can be used. A suitable system includes the Mira3 FEG SEM system (TESCAN) operating at 30 kV and a working distance of 5 mm. The length of the particles can then be analyzed using ImageJ.

[0153] Typically, SEM is used to measure the length of particles.

[0154] The number of length measurements is typically between 100 and 1,000. Generally, more than 100 measurements are taken. The length is the average of the measurements. The average is a numerical average. By calculating the average length, the influence of outliers is reduced, and the representative length of the particle is indicated.

[0155] In some embodiments, the cellulose microparticles have a particle size of 0.7 µm to 9 µm, preferably 1 µm to less than 5 µm (i.e., particle size distribution CMP). LS The average particle length is preferably 1.3 µm to 7 µm, even more preferably 1.7 µm to 5 µm, and particularly preferably 1.9 µm to 2.8 µm. This particle length provides suitable physical dimensions to effectively scatter light in the visible light range and produce a white color in the coating. Particle size can also be used to control the flow characteristics of the suspension, and therefore can be used to adjust the rheological properties of the coating composition and the coating.

[0156] Typically, particle length gives rise to a particle size distribution that follows a log-normal distribution. Generally, particles exhibit a unimodal particle size distribution, which has only one peak or maximum value. The peak or maximum value of the unimodal distribution corresponds to the number-order median mean particle diameter of all particles in the distribution.

[0157] In some embodiments, the particle length gives a multimodal particle size distribution with two or more peaks or maximum values. In other embodiments, the particle length gives a bimodal particle size distribution with exactly two peaks or maximum values. In yet another embodiment, the particle length gives a trimodal particle size distribution with exactly three peaks or maximum values.

[0158] It is also possible to calculate the percentiles of length, such as D90, D50, and D10. These values ​​can be calculated based on the length-particle size distribution based on the number of particles.

[0159] D90 length refers to a particle length at which 90% of particles have a length less than or equal to the D90 particle length.

[0160] In some embodiments, the cellulose particles have a D90 length of 6,000 nm or less, preferably 5,000 nm or less, and more 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, and more preferably 3,750 nm or more. In some embodiments, the cellulose particles have a D90 length of 3,000 nm to 5,000 nm, preferably 3,500 nm to 4,500 nm.

[0161] In the first embodiment, the D90 length is approximately 4,500 nm.

[0162] In the second embodiment, the D90 length is approximately 3,500 nm.

[0163] D50 length refers to a particle length at which 50% of the particles have a length less than or equal to the D50 particle length.

[0164] In some embodiments, the cellulose particles have a D50 length of 5,000 nm or less, preferably 3,500 nm or less, more preferably 3,000 nm or less, and 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, more preferably 1,600 nm or more, and more preferably 1,900 nm or more. In some embodiments, the cellulose particles have a D50 length of 1,000 nm to 5,000 nm, preferably 1,300 nm to 3,500 nm, more preferably 1,600 nm to 3,000 nm, and more preferably 1,900 nm to 2,800 nm.

[0165] In the first embodiment, the D50 length is 1,000 nm to 5,000 nm, preferably 1,900 nm to 3,500 nm, more preferably 2,200 nm to 3,000 nm, even more preferably 2,500 nm to 2,900 nm, and most preferably 2,600 nm to 2,800 nm. In the first embodiment, the D50 length is preferably about 2,700 nm.

[0166] In the second embodiment, the D50 length is 1,000 nm to 4,000 nm, preferably 1,200 nm to 2,700 nm, preferably 1,500 nm to 2,500 nm, preferably 1,700 nm to 2,300 nm, preferably 1,800 nm to 2,100 nm, and more preferably 1,900 nm to 2,000 nm. In the second embodiment, the D50 length is preferably about 1,950 nm.

[0167] D10 length refers to a particle length at which 10% of the particles have a length less than or equal to the D10 particle length.

[0168] In some embodiments, the cellulose particles have a D10 length of 2,000 nm or less, preferably 1,750 nm or less, and more 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, and more preferably 1,000 nm or more. In some embodiments, the cellulose particles have a D10 length of 500 nm to 2,000 nm, preferably 750 nm to 1,800 nm, and more preferably 1,000 nm to 1,700 nm.

[0169] In the first embodiment, the D10 length is approximately 1,700 nm.

[0170] In the second embodiment, the D10 length is approximately 1,200 nm.

[0171] In some embodiments, the cellulose particles have an average width of 0.1 µm to 1 µm, preferably 0.2 µm to 0.8 µm, more preferably 0.3 µm to 0.6 µm, and even more preferably 0.45 µm to 0.55 µm.

[0172] The width of a particle is generally its shortest dimension. 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 its transverse diameter. It can also be referred to as its diameter.

[0173] The width of a particle is typically its shortest lateral dimension. The lateral dimension is the shortest dimension observable when viewing a particle in a planar view. A particle appears two-dimensional in a planar view. For example, if the particle is measured from a top-down (or planar) image, the width is the shortest dimension measured from that top-down image.

[0174] The width of a particle is generally its shortest dimension, perpendicular to the line defining its length. As explained above, the length of a particle is its longest dimension, therefore the line defining the length is the line between its two farthest endpoints. The width can be the shortest dimension of the particle, perpendicular to the line defining its length. The shortest dimension can also be defined by the line between the two nearest endpoints of the particle, where this line is perpendicular to the line defining the length. In other words, the shortest dimension can be the narrowest part of the particle, which can be connected by a line perpendicular to the line defining the length.

[0175] The width of a particle can be measured similarly to its length.

[0176] Percentile values ​​for width, such as D90, D50, and D10, can also be calculated from the particle size distribution. These values ​​can be calculated based on the width particle size distribution based on the number of particles.

[0177] D90 width refers to a particle width at which 90% of the particles have a width less than or equal to the D90 particle width.

[0178] In some embodiments, the cellulose particles have a D90 width of 1,000 nm or less, preferably 900 nm or less, and more 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, and more preferably 350 nm or more. In some embodiments, the cellulose particles have a D90 width of 300 nm to 1,000 nm, preferably 350 nm to 900 nm.

[0179] In the first embodiment, the D90 width is approximately 850 nm.

[0180] In the second embodiment, the D90 width is approximately 350 nm.

[0181] D50 width refers to a particle width at which 50% of the particles have a width less than or equal to the D50 particle width.

[0182] In some embodiments, the cellulose particles have a D50 width of 800 nm or less, preferably 700 nm or less, and more 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, and more preferably 200 nm or more. In some embodiments, the cellulose particles have a D50 width of 200 nm to 800 nm, preferably 300 nm to 600 nm, and more preferably 450 nm to 550 nm.

[0183] In the first embodiment, the D50 width is 500 nm to 540 nm, for example, about 520 nm.

[0184] In the second embodiment, the D50 width is 200 nm to 240 nm, for example, about 220 nm.

[0185] D10 width refers to a particle width at which 10% of the particles have a width less than or equal to the D10 particle width.

[0186] In some embodiments, the cellulose particles have a D10 width of 400 nm or less, preferably 300 nm or less, and more 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, and more preferably 200 nm or more. In some embodiments, the cellulose particles have a D10 width of 50 nm to 400 nm, preferably 100 nm to 300 nm, and more preferably 150 nm to 200 nm.

[0187] In the first embodiment, the width of D10 is approximately 300 nm.

[0188] In the second embodiment, the width of D10 is approximately 150 nm.

[0189] Aspect ratio can also be the ratio between the length and 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.

[0190] The particles are typically not spherical because their aspect ratio is greater than 1 (e.g., 2 to 18). The particles can be described as prismatic and / or elongated. Preferably, the particles are rod-shaped.

[0191] 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.

[0192] In some embodiments, the D50 aspect ratio can be from 2 to 18. Preferably, the D50 aspect ratio of the cellulose particles is from 2 to 16, more preferably from 3 to 14, even more preferably from 4 to 10, and most preferably from 4 to 6.

[0193] Cellulose particles can have any suitable shape. In some embodiments, the cellulose particles are rod-shaped or similar to rods, or sheet-shaped or similar to sheet. In some embodiments, the cellulose particles are rod-shaped or sheet-shaped.

[0194] Cellulose granules can have a rod-like or rod-like shape. Therefore, the width can be the diameter of the cross-section of a rod. The granules can be elongated, with the length dimension being greater than the width dimension.

[0195] Cellulose granules can also have a sheet-like or sheet-like shape. A sheet-like or sheet-like shape can be elongated, with its length dimension greater than its width dimension. A sheet-like or sheet-like shape typically has a uniform height over most of the granule's length.

[0196] Cellulose particles can be largely unbranched. That is, cellulose particles typically do not divide into more than two branches. Cellulose particles are preferably neither branched nor hyperbranched.

[0197] Cellulose particles are typically primary particles. That is, cellulose particles are not aggregates of smaller particles.

[0198] Alternatively, cellulose particles can be secondary particles formed by the aggregation of multiple primary particles. Typically, secondary cellulose particles are held together by non-covalent interactions.

[0199] In this article, the size of cellulose particles refers to particles that can be separated individually. In other words, when particles are provided as primary particles, the size refers to the primary particles, and when particles are provided as secondary particles, the size refers to the secondary particles.

[0200] Typically, secondary cellulose particles contain pores or voids. These pores or voids are located between primary cellulose particles. Clusters can be considered porous.

[0201] Secondary cellulose particles can be prepared using the methods described herein. For example, secondary cellulose particles can be prepared by spray-drying or spray-freezing a suspension of cellulose microparticles. The sprayer can be adjusted to regulate 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.

[0202] Cellulose particles possess excellent optical properties. They scatter incident light. In particular, cellulose particles can provide high reflectivity and low transmittance. Therefore, cellulose particles offer good opacity.

[0203] The optical properties of the particles can be measured using standard techniques, such as a light source coupled to a spectrometer and an integrating sphere. The signal can be normalized to its 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 measurements. 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 obtained transmittance values ​​assuming no absorption by the particles. Typically, five spectra are taken for each sample and averaged.

[0204] In some implementations, total transmittance and reflectance are measured using an integrating sphere (Labsphere). A light source (Ocean Optics HPX-2000) is coupled to an optical fiber (600 μm Thorlabs FC-UV100-2-SR) via a collimator (Thorlabs), and signals are collected using a spectrometer (Avantes HS2048), as shown in Figure 8 (T1 and T2). The signals are normalized to their intensity without a sample mounted. The background is recorded without applied light. Wavelengths range from 400 nm to 700 nm. Five spectra are taken for each sample, and the average is used to reduce the signal-to-noise ratio. Each spectrum is recorded using an integration time equal to 3 seconds.

[0205] L*(45 / 0) refers to the angle of incidence at 45° to the surface normal and the angle of reflection at 0° to the surface normal. Measurements were performed in a 1 cm cuvette for a 0.1 wt.% CMP suspension.

[0206] In some embodiments, the cellulose microparticles have an L* (45° / 0°) of 38 or more, preferably 38 to 42, wherein L* (45° / 0°) are CEILAB color space coordinates, measured for a 1 wt.% suspension of the cellulose microparticles in water.

[0207] In some embodiments, the cellulose microparticles have a reflectance of 50% or more, preferably 55% or more, and more preferably 60% or more for incident light with wavelengths from 400 nm to 700 nm, wherein the reflectance is measured for a 1 wt.% suspension of the cellulose microparticles in water.

[0208] The surface of cellulose particles can be modified. Typically, the hydroxyl groups on the surface of cellulose particles are modified. Cellulose particles can be modified to be hydrophobic or partially hydrophobic.

[0209] 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 (e.g., ester or ether groups).

[0210] For example, cellulose particles can be prepared by acid hydrolysis. During acid hydrolysis, it is believed that the cellulose chain backbone of the cellulose particles is modified at the molecular level to provide colloidal stability to the cellulose particles. For example, sulfuric acid hydrolysis is believed to modify the cellulose chains with sulfate half-ester groups.

[0211] As a result of the acid hydrolysis process, cellulose microparticles are typically incorporating 20 mmol / kg to 100 mmol / kg, preferably 40 mmol / kg to 60 mmol / kg, sulfate half-ester groups on their surface. Based on the total mass of the cellulose microparticles, the mass contribution of the half-ester groups (e.g., -SO3H) is less than 5 wt.%, preferably less than 1 wt.%.

[0212] The density of the sulfate half-ester groups was measured by conductivity titration (e.g., according to ISO 21400:2018).

[0213] The cellulose particles are preferably anionic. The hemiester groups can contribute to the anionic charge on the cellulose particles. Therefore, in some embodiments, the cellulose microparticles are anionic. In some embodiments, the cellulose microparticles are surface-modified with anionic sulfate hemiester groups.

[0214] Cellulose microparticles have an anionic charge density of 50 mmol / kg or more, preferably 100 mmol / kg or more, and more preferably 150 mmol / kg or more.

[0215] Cellulose particles can be further modified to increase their negative charge. For example, cellulose particles can be modified by reacting with aminosulfonic acid, which is part of a reactive eutectic solvent. Urea can be used to enhance the reactivity of aminosulfonic acid. The highly sulfated cellulose nanoparticles can then be mixed with the family of surfactants outlined herein, as described in this patent application.

[0216] We can increase the total surface charge density to 2000 mmol / kg through appropriate post-processing. This can be used for high-charge mixtures to ensure stability and maintain the same functionality.

[0217] Cellulose microparticles can have anionic charge densities below 2000 mmol / kg.

[0218] The charge density of the particles is measured by conductivity titration (e.g., according to ISO 21400:2018).

[0219] The charge can depend on the pH of the solution in which the particles are contained. In this invention, the charge of the particles is determined at the pH of the coating composition or opacifier. The pH is typically 7.

[0220] Preparation of cellulose microparticles

[0221] The cellulose microparticles used in this invention can be obtained using the methods described in WO2023 / 135261, such as Example 1 of WO2023 / 135261, the contents of which are incorporated herein by reference.

[0222] Typically, cellulose microparticles are obtained by controlling the morphology and physical size of biomass through sulfuric acid hydrolysis using specific acid concentrations, temperatures, and reaction times.

[0223] Generally, cellulose microparticles are prepared by a method comprising the following steps:

[0224] (a) Adding acid to cellulose material to hydrolyze cellulose particles;

[0225] (b) Removal of acid from hydrolyzed cellulose particles; and

[0226] (c) Separate hydrolyzed cellulose particles of a specific size.

[0227] The step (a) of “adding acid to cellulose particles” can be called the hydrolysis step. The step (b) of “removing acid from the hydrolyzed cellulose particles” can be called the washing step. The step (c) of “separating hydrolyzed cellulose particles of a specific size” can be called the grading step.

[0228] This application also provides a method for preparing cellulose particles, the method comprising:

[0229] (a) Hydrolyzing cellulose material to provide hydrolyzed cellulose particles;

[0230] (b) Washing hydrolyzed cellulose particles; and

[0231] (c) Fractionation of the suspension of hydrolyzed cellulose particles.

[0232] This method is suitable for preparing cellulose microparticles for use in coating compositions and opacifiers of the present invention. However, cellulose microparticles prepared by alternative methods may also be used, provided that these particles possess the properties required for opacifiers.

[0233] The conditions used for the hydrolysis, washing, and grading steps can be adjusted to prepare cellulose microparticles with the size and shape described herein.

[0234] Any suitable cellulose material can be used. Suitable cellulose materials can be prepared from bacterial, plant or animal sources (e.g., chitin), including plant-based and biomass-based sources (e.g., cotton and wood) and subsequent processed products (e.g., paper, filter paper lint, cellulose powder and wood pulp).

[0235] Preferably, the cellulose material is microcrystalline cellulose powder. Suitable microcrystalline cellulose powder is commercially available (e.g., from SERVA Electrophoresis GmbH).

[0236] Cellulose materials can be provided in the form of suspensions. Preferably, microcrystalline cellulose powder is dispersed in water to form an aqueous suspension.

[0237] A suspension is a heterogeneous mixture of fluids containing solid particles. If the suspension is undisturbed for an extended period, these solid particles are typically large enough to precipitate. Cellulose particles are suspended in a liquid. Suspensions can be mixed (e.g., by ultrasonication) to prevent the precipitation of cellulose particles.

[0238] Any suitable suspending medium for maintaining cellulose materials can be used. A suitable suspending medium is typically an aqueous solvent (e.g., water). Both acidic and alkaline media can be used. Acids are commonly used, and suitable acids are listed below.

[0239] Methods for preparing cellulose granules include hydrolyzing cellulose material to provide hydrolyzed cellulose granules. This can be referred to as the hydrolysis step. The hydrolysis step is performed prior to the washing step.

[0240] Hydrolysis is typically carried out in an aqueous solvent (e.g., water).

[0241] In the hydrolysis step, cellulose materials are typically hydrolyzed using acids. Acid hydrolysis is a hydrolysis process in which the breaking of chemical bonds is catalyzed by a substitution reaction involving the addition of water using a protic acid. During acid hydrolysis, it has also been proposed to modify the cellulose chain backbone of the cellulose particles at the molecular level to provide colloidal stability. For example, sulfuric acid hydrolysis is thought to modify the cellulose chains using sulfate hemiester groups.

[0242] The hydrolysis step may include contacting the cellulose material (e.g., a suspension of the cellulose material) with an acid.

[0243] The acid can be an organic acid or an inorganic acid. Typically, the acid is an inorganic acid (mineral acid). Suitable inorganic acids include hydrobromic acid (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.

[0244] Suitable organic acids include formic acid (HCOOH) and acetic acid (CH3COOH). Preferably, the organic acid is formic acid.

[0245] Preferably, the acid is sulfuric acid or hydrochloric acid. More preferably, the acid is sulfuric acid.

[0246] The strength of (aqueous) acids can be expressed using a pH scale. Methods for determining the pH of aqueous solutions are known and include, for example, electrochemical methods (using pH probes) and titrations with indicator compounds (e.g., universal indicators). Typically, pH refers to the pH of the hydrolyzed solution at the end of the hydrolysis step.

[0247] 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.

[0248] The strength of an acid is directly proportional to its concentration. The concentration of aqueous acids can be expressed as a volume percentage (wt.%).

[0249] Typically, the concentration of acid is 40 wt.% to 60 wt.%, preferably 45 wt.% to 55 wt.%, more preferably 47 wt.% to 55 wt.%, and even more preferably 49 wt.% to 52 wt.%. wt.% is usually calculated with water as the solvent.

[0250] The amount of acid is selected to suspend the desired amount of cellulose material. The amount of aqueous acid can be expressed by stating the volume of aqueous acid (in mL) per gram of cellulose material used (the ratio of acid to cellulose material).

[0251] Typically, the hydrolysis step uses an acid-to-cellulose material mass ratio of 100:1, preferably 80:1, and more preferably 60:1. Alternatively, the hydrolysis step can use an acid-to-cellulose material mass ratio of 4:1, preferably 10:1. For example, the hydrolysis step can use an acid-to-cellulose material mass ratio of 100:1 to 4:1, preferably 80:1 to 10:1. The higher the ratio of cellulose to acid, the more efficient the process, because less acid is needed for the hydrolysis step and less solvent is needed for the washing step.

[0252] The hydrolysis step can be carried out for a sufficient time to hydrolyze the desired amount of cellulose material. Typically, hydrolysis is carried out for 1 to 10 hours, preferably 2 to 8 hours, more preferably 3 to 7 hours, for example, about 5 hours.

[0253] Hydrolysis begins with the addition of acid and continues until the reaction is quenched. The reaction can be quenched by any suitable means, such as by adding water to dilute the acid, adding a base to neutralize the acid, removing the acid (e.g., by washing (e.g., by dialysis)), or lowering the temperature.

[0254] The hydrolysis step can be carried out at a high temperature (above ambient temperature; about 25°C). Methods for providing heat during the hydrolysis step are known and include, for example, the use of a reaction vessel with an external heating jacket or the use of microwave heating.

[0255] Typically, the hydrolysis step is carried out at a temperature of 40°C to 60°C, preferably 45°C to 55°C, more preferably 48°C to 52°C, for example, about 50°C.

[0256] Preferably, the cellulose material is hydrolyzed with 50 wt.% sulfuric acid at a temperature of about 50°C for 3 to 5 hours.

[0257] 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.

[0258] Hydrolysis can be stopped by quenching it with acid. Typically, hydrolysis is quenched by adding water (e.g., excess water). For example, if 60 mL of sulfuric acid is used to hydrolyze cellulose particles, 300 mL of water can be added to quench the acid hydrolysis.

[0259] It is believed that using higher concentrations of acid, higher temperatures, or longer time periods increases the rate of acid hydrolysis. Generally, the higher the degree of hydrolysis, the smaller the size of the resulting cellulose particles.

[0260] Hydrolyzed cellulose particles can be collected by any suitable method. Typically, hydrolyzed cellulose particles are collected by centrifugation. Centrifugation separates the hydrolyzed cellulose particles from the acid supernatant, and water may be added to quench the acid hydrolysis. The supernatant can then be removed (e.g., using a pipette).

[0261] Methods for preparing cellulose particles include:

[0262] The hydrolyzed cellulose particles are washed.

[0263] This can be called the washing step. The washing step takes place after the hydrolysis step and before the grading step.

[0264] Hydrolyzed cellulose particles can be washed with water. The water can then be removed. Therefore, the washing step may include contacting the hydrolyzed cellulose particles with water.

[0265] The washing step typically quenches the hydrolysis reaction, thus ending the hydrolysis process. The washing step dilutes the acid in the cellulose particles, thereby quenching the hydrolysis reaction.

[0266] Typically, the washing step involves adding enough water to provide a cellulose particle concentration of 1 wt.%. For example, for 1 g of hydrolyzed cellulose particles, approximately 100 mL of water can be added per wash. This can be repeated once or more, preferably twice or more, more preferably three times or more, to remove the acid. The wash water can then be removed by centrifugation.

[0267] Preferably, the washing step may alternatively or additionally include dialysis of the hydrolyzed cellulose particles with water (e.g., distilled water). Dialysis can be performed 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., the acid used in the hydrolysis step) by utilizing their different diffusion rates through the pores of a semipermeable membrane (dialysis). Any suitable dialysis membrane can be used. Suitable dialysis membranes have a molecular weight cutoff of 12 kDa or higher (e.g., 12 kDa to 40 kDa).

[0268] The distilled water can be changed during the dialysis process. For example, during dialysis, the distilled water can be changed every 12 hours. The distilled water can be changed more than 5 times, preferably more than 10 times.

[0269] In some implementations, the hydrolyzed cellulose material is dialyzed against distilled water for 7 days, with the distilled water being replaced every 12 hours.

[0270] In some embodiments, the hydrolyzed cellulose material is dialyzed until its pH stabilizes. The pH can be measured each time (e.g., every 12 hours) the distilled water is changed during the dialysis process. Typically, the pH of the hydrolyzed cellulose material is considered stable once it has remained constant for at least two consecutive measurements, preferably four, and more preferably six. Alternatively, the pH can be measured daily, and it is considered stable once it has remained constant for at least two consecutive days, preferably three, and more preferably four.

[0271] A constant pH indicates that the acid or base has been substantially removed from the hydrolyzed cellulose material. As mentioned above, methods for determining the pH of aqueous solutions are known.

[0272] 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.

[0273] Methods for preparing cellulose particles include:

[0274] The suspension of hydrolyzed cellulose particles was fractionated.

[0275] This can be called the grading step. The grading step is performed after the washing step.

[0276] Hydrolyzed cellulose particles can be fractionated by any suitable method. Suitable methods include filtration and centrifugation. Preferably, the hydrolyzed cellulose particles are separated from the liquid by differential centrifugation.

[0277] Fractionation is performed on 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 aggregate in the suspension. This is advantageous because it avoids the fractionation step of removing aggregates of cellulose particles with the desired size and shape. This improves the yield of cellulose particles with the desired size and shape.

[0278] The suspension of cellulose particles is fractionated (e.g., by centrifugation). Typically, a suspension of cellulose particles in water (e.g., Millipore water) is used. Any suitable concentration can be used. Suitable concentrations include 0.1 wt.% to 5.0 wt.% of cellulose particles, for example, 0.2 wt.% to 2.0 wt.%, or, for example, 0.2 wt.% to 1.0 wt.%. Preferably, the concentration of hydrolyzed cellulose particles is 0.5 wt.%.

[0279] Suspensions of cellulose particles can be prepared by any suitable method. Hydrolyzed cellulose particles can be mixed or stirred prior to separation. Typically, hydrolyzed cellulose particles are sonicated prior to separation (e.g., by tipsonication or ultrasonification).

[0280] In some embodiments, a 30 mL suspension of hydrolyzed cellulose particles with a particle concentration of 0.5 wt.% is ultrasonicated for 2 min at 30% amplitude with a 2-second on-off cycle. Ultrasonication can be performed using any suitable equipment (e.g., a Fisherbrand ultrasonic disruptor, 20 kHz, probe diameter 12.7 mm).

[0281] Typically, differential centrifugation consists of a first centrifugation and a second centrifugation. The first centrifugation is performed at a different speed than the second centrifugation. The first centrifugation is performed at a lower speed than the second centrifugation. The second centrifugation is usually performed on the supernatant from the first centrifugation.

[0282] The first centrifugation can be performed at a speed of 1,000 rpm to 3,000 rpm, preferably 1,500 rpm to 2,500 rpm, more preferably 1,800 rpm to 2,200 rpm, for example, about 2,000 rpm.

[0283] The second centrifugation can be performed at a speed of 2,000 rpm to 4,000 rpm, preferably 2,500 rpm to 3,500 rpm, more preferably 2,800 rpm to 3,200 rpm, for example about 3,000 rpm.

[0284] Centrifugation speed can also be quantified using relative centrifugal force (RCF). RCF is a measure of the force acting on the particles during centrifugation. RCF is usually expressed as a multiple of the Earth's gravitational field (g). RCF can be calculated using the following equation, where the radius (cm) is the distance from the center of the centrifuge to the end of the sample, and the rotational speed (revolutions per minute) is the rotational speed of the centrifuge. The radius is typically about 15 cm.

[0285] RCF = 11.2 × radius × (rotation speed / 1000) 2 .

[0286] The RCF of the first centrifugation can differ from that of the second centrifugation. The RCF of the first centrifugation can also be smaller than that of the second centrifugation.

[0287] The first centrifugation can be performed at an RCF of 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. The first centrifugation can also be performed at an RCF of about 650.

[0288] The second centrifugation can be performed at an RCF of 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. The second centrifugation can also be performed at an RCF of about 1,500.

[0289] The first centrifugation can be performed at an RCF of 168 to 1,512, preferably 378 to 1,150, more preferably 544 to 813. Alternatively, the first centrifugation can be performed at an RCF of approximately 672.

[0290] The second centrifugation can be performed at an RCF of 671 to 2,688, preferably 1,050 to 3,058, more preferably 1,317 to 1,720. The second centrifugation can also be performed at an RCF of approximately 1,512.

[0291] The first centrifugation can be carried out for 1 to 20 minutes, preferably 2 to 15 minutes, more preferably 3 to 10 minutes, and even more preferably 4 to 6 minutes, for example, about 5 minutes.

[0292] The second centrifugation can be carried out for 1 to 20 minutes, preferably 2 to 15 minutes, more preferably 3 to 10 minutes, and even more preferably 4 to 6 minutes, for example, about 5 minutes.

[0293] Preferably, the first centrifugation is performed at 2000 rpm for five minutes, the second centrifugation is performed at 3000 rpm for five minutes, and the supernatant from the first centrifugation is separated a second time.

[0294] It is believed that a two-step differential centrifugation process produces a narrower particle size distribution of cellulose particles. The first centrifugation, performed at a lower speed, causes larger cellulose particles to precipitate. Therefore, the supernatant from the first centrifugation still contains particles of the desired size and smaller particles. Then, the supernatant from the first centrifugation is centrifuged again at a higher speed to cause the desired particles to precipitate. Smaller particles remain in the supernatant from the second centrifugation. Therefore, the precipitate from the second centrifugation does not include most of the larger or smaller particles, resulting in a narrower particle size distribution.

[0295] The precipitated cellulose particles can be collected by any suitable method. Typically, cellulose particles are collected by filtration.

[0296] Cellulose particles are typically collected in the form of a slurry or suspension. The slurry or suspension may be mixed with water, ethanol, or acetone. Preferably, the slurry or suspension contains water.

[0297] Larger cellulose particles 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 fractions containing the desired particle size.

[0298] Methods for preparing cellulose particles may also include:

[0299] The graded cellulose particles are dried.

[0300] This can be called the drying step. The drying step usually takes place after the classification step. The drying step is typically performed on the slurry or suspension of cellulose particles prepared by the classification step.

[0301] Typically, the drying step includes removing the solvent from the graded cellulose particles. The drying step typically includes removing water, ethanol, or acetone from the graded cellulose particles. Preferably, the drying step includes removing water from the graded cellulose particles.

[0302] Graded 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.

[0303] Any suitable freeze-drying equipment can be used. Suitable freeze-drying equipment includes LaboGene A / S's Scanvac and Coolsafe freeze dryers, or SP Scientific's VirTis freeze dryers.

[0304] Any suitable spray drying equipment can be used. Suitable spray drying equipment includes the PrecisionCoat spray coater from SpecialtyCoating Systems (SCS).

[0305] Any suitable spray freeze-drying equipment can be used. Suitable spray freeze-drying equipment includes SCS's PrecisionCoat spray coater and LaboGene A / S's Scanvac and Coolsafe freeze dryers.

[0306] Typically, a drying step provides a dry powder of cellulose particles. Freeze-drying or spray-drying can provide a dry powder of cellulose particles. Preferably, freeze-drying provides a dry powder of cellulose particles.

[0307] The drying step can provide cellulose particle clusters. Preferably, spray drying or spray freeze drying provides cellulose particle clusters.

[0308] The shape and size of dried cellulose granules are usually the same as those before drying.

[0309] Dry cellulose granules can be used in many applications. Some applications require cellulose granules to be supplied in dry powder form so that they can be redispersed in different media.

[0310] Due to the reduced solvent mass, the dry powder also minimizes storage and transportation costs. It also inhibits the growth of fungi and bacteria in the cellulose particles. Furthermore, the dry powder allows for the redispersibility of the cellulose particles in solvents of a different polarity than the solvent used to prepare the cellulose particles. For example, if the cellulose particles are prepared in a polar solvent (e.g., water), the dry powder can be redispersed in a non-polar solvent (e.g., an organic solvent). The dry powder can also undergo further chemical modification. Prior to further chemical modification, the dry powder can be redispersed in an organic solvent.

[0311] Optionally, the method for preparing cellulose particles may further include:

[0312] The surface of cellulose particles is modified.

[0313] This can be called the surface modification step. Typically, the surface modification step is carried out after the cellulose particles are graded.

[0314] Surface modification can be performed on any cellulose particles. Typically, surface modification is performed on cellulose particles obtained from the grading or drying steps described above.

[0315] Surface modification steps typically involve 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, hydroxyl groups can be converted into ether groups (e.g., silyl ether groups).

[0316] In some embodiments, the surface modification step includes contacting the cellulose particles with an esterifying agent or an etherifying agent. Preferably, the surface modification step includes contacting the cellulose particles with a hydrophobic agent.

[0317] Surface modification can be performed using any suitable reagent. Preferably, the reagent is an esterifying or etherifying reagent. Preferably, the surface modification step includes treating the cellulose particles with a reagent containing anhydrite, acyl chloride, or epoxy. The hydrophobic agent includes any suitable hydrophobic agent, such as trimethylchlorosilane (TCMS) and trimethoxychlorosilane. Preferably, the hydrophobic agent is TCMS.

[0318] The reagent can be a liquid or a vapor (gas). Typically, the reagent is a vapor.

[0319] Surface modification can be carried out in solution or gas phase reactions. The solution can be aqueous or non-aqueous. Surface modification can be carried out under an inert atmosphere (e.g., nitrogen or argon atmosphere).

[0320] The hydroxyl groups on the surface of cellulose particles can be activated prior to the surface modification reaction. Any suitable activator can be used. Preferably, the activator is an alkaline solution, preferably a sodium hydroxide solution.

[0321] Surface modification can be carried out in the presence of a catalyst. Any suitable catalyst can be used. Preferably, the catalyst is a basic catalyst. Preferably, the catalyst is pyridine, 4-dimethylaminopyridine, or trimethylamine.

[0322] The surface modification step can be performed for any suitable duration. Typically, the surface modification step is performed for less than 5 minutes, for example, less than 3 minutes, for example, less than 2 minutes, for example, less than 1 minute.

[0323] The surface modification step provides surface-modified cellulose particles. It is not desirable to be bound by theory that modifying the hydroxyl groups on the surface of the cellulose particles (e.g., with esters or ethers) alters the hydrogen bonds between the cellulose particle surfaces. Modification can increase or decrease hydrogen bonds. Preferably, modification reduces hydrogen bonds between hydroxyl groups, thus the pores or voids between the cellulose particles are less likely to collapse under capillary pressure, such as during solvent evaporation.

[0324] Surface modification with hydrophobic agents provides hydrophobic cellulose particles. It is believed that replacing some of the hydroxyl groups on the surface of cellulose particles with hydrophobic groups (e.g., -OTMS) reduces the hydrogen bonds between the hydroxyl groups, thus making the pores or voids between the cellulose particles less prone to collapse under capillary pressure, such as during solvent evaporation. The dispersion of the particles in solution can also be customized, for example, to increase the dispersion in nonpolar solvents.

[0325] surfactants

[0326] Surfactants are present in coating compositions and opacifiers, as well as in other aspects of this invention.

[0327] Surfactants facilitate the dispersion of cellulose microparticles. Cellulose microparticles are hydrophilic and not easily dispersed in nonpolar solvents. Due to their relatively large size, cellulose particles can settle under gravity if no external mechanical action is applied after a period of time.

[0328] Surfactants (e.g., nonionic surfactants) are physically mixed with mildly charged cellulose microparticles to form a sterically stable combination that is well dispersed in both polar and nonpolar solvents and interacts effectively in both hydrophobic and hydrophilic systems. Therefore, nonionic surfactants are preferred when the solvent is relatively nonpolar (e.g., acetone).

[0329] For systems or suspensions with high or dissimilar charges, zwitterionic surfactants and CMPs can form an ideal combination for incorporation into polar solvents. Therefore, zwitterionic surfactants are preferred when the solvent is relatively polar (e.g., water, ethanol).

[0330] Surfactants can also improve the stability of emulsions (e.g., oil-water emulsions). This ensures that homogeneous and well-dispersed colloidal suspensions remain stable over long periods of time (e.g., more than a few days).

[0331] Surfactants are typically organic compounds having a relatively hydrophilic portion and a relatively hydrophobic portion. Surfactants can contain a "head" group and a "tail" group, wherein the head and tail are either hydrophilic or hydrophobic.

[0332] Typically, the head group is hydrophilic. The head group can be polar and optionally charged. For example, the head group can be a carboxyl group, a sugar group, a phosphate group, or an ammonium group.

[0333] Typically, the tail group is hydrophobic. The tail group can be a hydrocarbon chain, such as a branched, straight, or aromatic carbon chain. Alternatively, it 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 alter the degree of hydrophobicity or hydrophilicity.

[0334] Surfactants can have one or more head groups and one or more tail groups.

[0335] Surfactants can be classified according to the charge of their head group or hydrophilic group. Surfactants can be classified as nonionic, anionic, cationic, or amphoteric. Amphoteric surfactants are also called amphoteric surfactants.

[0336] Nonionic surfactants have a net zero charge at the head / hydrophilic group.

[0337] Anionic surfactants have a net negative charge at the head / hydrophilic group.

[0338] Cationic surfactants have a net positive charge at the head / hydrophilic group.

[0339] Amphoteric surfactants have a net zero charge and positive and negative charge centers within the head / hydrophilic group.

[0340] The charge can depend on the pH of the solution in which the surfactant is located. In this invention, the charge of the head / hydrophilic group is determined at the pH of the coating composition or opacifier. This is typically a pH of about 7.

[0341] Preferably, the surfactant is a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant, for example at a pH of about 7. The surfactant is particularly preferred to be a nonionic surfactant, for example at a pH of about 7.

[0342] Suitable nonionic surfactants may include ethoxylated surfactants, polyethylene glycol monododecyl ether surfactants, alkylphenol polyoxyethylene ethers, nonoxynol ethers, polyethoxylated tallow amine, cocoyl monoethanolamine, cocamide diethanolamine, end-capped ethoxylated surfactants, poloxamer, polyhydroxy fatty acid esters, glycerol fatty acid esters, glycerol monostearate, glycerol monolaurate, sorbitol fatty acid esters, sucrose fatty acid esters, alkyl polyglucosides, and alkyl polyglycosides.

[0343] Suitable cationic surfactants may include alkylammonium surfactants, cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzyl chloride (BZT), dimethyl dioctadecyl ammonium chloride, and dioctadecyl dimethyl ammonium bromide (DODAB).

[0344] Suitable zwitterionic surfactants may comprise a combination of a cationic moiety based on a primary, secondary, or tertiary amine or quaternary ammonium cation and an anionic moiety based on a sulfonate, carboxylate, or phosphate. For example, zwitterionic surfactants may comprise phospholipids (e.g., phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, and sphingomyelin), betaines (e.g., cocamidopropyl betaine), sulfobetaines (e.g., CHAPS (3-[3-(cholamidopropyl)dimethylamino]-1-propanesulfonic acid inner salt) and cocamidopropyl hydroxysulfobetaine), lauryl dimethylamine oxide, and myristamine oxide.

[0345] Surfactants can be characterized by their critical micelle concentration (CMC). The CMC is the concentration of the surfactant at which micelle formation is first observed in solution. Above this concentration, existing surfactants and any additional surfactants added will form micelles. Micelles are self-assembled aggregates of surfactants.

[0346] CMC is provided for a given dispersant (solvent) at specified temperature and pressure. Here, the CMC value is given for water as the solvent at a temperature of 20°C and a pressure of 1 atm. Any deviations from these conditions are noted. Typically, the critical micelle concentration is measured according to ISO 4311:1979.

[0347] In some embodiments, the surfactant has a critical micelle concentration of 0.03 mM or more, preferably 0.04 mM or more, and 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, and even more preferably 1.5 mM or less, and most preferably 0.9 mM or less.

[0348] In some embodiments, the surfactant has a critical micelle concentration of 0.03 mM to 30 mM, preferably 0.04 mM to 25 mM, more preferably 0.05 mM to 10 mM, even more preferably 0.05 mM to 1.5 mM, and even more preferably 0.06 mM to 0.9 mM.

[0349] For nonionic surfactants, the critical micelle concentration is preferably 0.06 mM–0.9 mM (measured at 25°C and 1 atm using water as the solvent). For cationic or amphoteric surfactants, the critical micelle concentration is typically higher, such as 0.9 mM to 25 mM (measured at 25°C and 1 atm using water as the solvent).

[0350] Critical micelle concentration (CMC) is generally defined as the concentration of a surfactant above which micelles will form, and any additional surfactant added to the system will also form micelles. CMC can be measured using ISO 4311:1979.

[0351] The inventors have surprisingly discovered that using surfactants with these specific CMC values ​​produces particularly excellent dispersion of cellulose microparticles, and thus provides coating compositions and coatings with excellent homogeneity. Consequently, the coatings exhibit reliable and consistent optical properties, such as whiteness (L*) and opacity.

[0352] In some embodiments, the surfactant is Triton X-100, Tween 20, ECOSURF SA-9, TERGITOL 15-S-9, TERGITOL TMN-100X, cetyltrimethylammonium bromide (CTAB), 3-(decyldimethylammonium)-propane-sulfonic acid inner salt, or a combination thereof.

[0353] 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 combinations thereof.

[0354] In some embodiments, the surfactant is a cationic surfactant, such as hexadecyltrimethylammonium bromide (CTAB).

[0355] In some embodiments, the surfactant is an amphoteric surfactant, which is a 3-(decyldimethylammonium)-propane-sulfonic acid inner salt.

[0356] Triton X-100 has the structure given by formula (1). Triton X-100 is also known as polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether. The average number of repeating units in polyethylene glycol is 9.5 (n=9.5). The CMC is 0.22 mM.

[0357] (1)

[0358] Tween 20 has the structure given by equation (2). Tween 20 is also known as polyoxyethylene (20) sorbitan monolaurate. The average total number of repeating polyethylene glycol units is 20 (therefore the sum of w+x+y+z is 20). The CMC is 0.08 mM.

[0359] (2)

[0361] ECOSURF SA-9 has CAS number 68937-66-6. CMC is 22 ppm (25°C, 1 atm, water-based).

[0362] TERGITOL 15-S-9 has the structure given by equation (3). The values ​​of n+m are 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, and its given CMC is 0.037 mM.

[0363] (3)

[0364] TERGITOL TMN-100X has CAS number 60828-78-6. Its CMC is 830 ppm. Its molecular weight is 570 g / mol, with a given CMC of 1.46 mM.

[0365] Hexadecyltrimethylammonium bromide (CTAB) has the structure given by formula (4). CTAB has a CMC of 0.9 mM.

[0366] (4)

[0367] The 3-(decyldimethylammonium)-propane-sulfonic acid inner salt has the structure given by formula (5). The CMC of the 3-(decyldimethylammonium)-propane-sulfonic acid inner salt is 25 mM-40 mM (20℃-25℃).

[0368] (5)

[0369] additive

[0370] The opacifier and / or coating composition may further include additives. There are no particular limitations on these additives. Additives may be included in the opacifier component (e.g., in powder or paste form combined with cellulose microparticles and surfactants). Alternatively, additives may be included in the coating composition (e.g., incorporated into a liquid carrier).

[0371] Additives may include colorants, softeners, oils, polymers, waxes, and gelling agents. Additives are generally suited to the intended application and use. Opacifiers and / or coating compositions may contain one or more additives, such as two or more additives, or three or more additives.

[0372] Additives may include colorants. By adding specific colorants to the initial CMP suspension, films with modulated colors can be produced. It is worth noting that individual cellulose microparticles retain their ability to scatter light and form colloidal white suspensions, but these particles can only assemble into continuous white films with the aid of a scaffold.

[0373] Colorants can include any suitable dyes or pigments. Colorants can be organic or inorganic, with organic colorants being preferred. Colorants can absorb narrow-band light (light of a specific wavelength), thereby imparting color to the coating. This differs from the opaque function of cellulose microparticles, which reflect light across a wide range of wavelengths.

[0374] The colorant may be β-naphthol, BON arylamide, benzimidazole, azo condensate, quinacridone, perylene, anthraquinone, dibromoanthrone, pinanthrone, diketopyrrolopyrrole pigment (DPP), copper phthalocyanine, indanone, phthalocyanine green, dioxazine violet, pyrene orange, pyrazolone orange, carbon black, graphite, aniline black, anthraquinone black, benzimidazole, azo condensate, or a combination thereof.

[0375] Cellulose microparticle coating formulations can also be mixed with any colorant to adjust the hue of a specific color. The colorant is preferably provided in a carrier liquid. For example, the carrier liquid can be a paint.

[0376] Additives may include plasticizers. Suitable plasticizers include ammonium lactate, petrolatum, salicylic acid, and urea.

[0377] Additives may include oils.

[0378] 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 above oils (e.g., esterified oils, fatty acids, fatty alcohols, hydrogenated oils, and triglycerides) can be used as suitable ingredients in the aforementioned formulations. Essential oils are also suitable oils.

[0379] Additives may include polymers. Suitable polymers may include stabilizers, plasticizers, and flame retardants.

[0380] Polymer stabilizers are any polymers suitable for inhibiting or delaying the degradation of opacifiers, coating compositions, or coatings. Polymer stabilizers can be UV absorbers, antioxidants, and bactericides.

[0381] Plasticizers are polymers that increase the plasticity of a coating. This can include phthalate-based plasticizers, DMP, DEP, DIBP, DBP, DINP, terephthalates, trimellitic esters, and organophosphates.

[0382] Flame-retardant polymers are polymers that inhibit or delay combustion. This can include organohalogens or organophosphorus compounds.

[0383] Preferably, the polymer additive is a poly(meth)acrylate polymer (e.g., polyacrylate). The polymer additive can be in monomer form, preferably (meth)acrylate. The monomer can be a monofunctional monomer (e.g., (meth)acrylate) or a difunctional monomer (e.g., di(meth)acrylate). In this way, the monomer can function as a binder or crosslinking agent. For example, the polymer additive can cure during the drying process of the coating. The polymer additive can enhance the adhesion of the coating to the substrate, improve abrasion resistance, and enhance the flexibility of the coating.

[0384] Additives may include waxes.

[0385] Suitable waxes include beeswax, candelilla wax, carnauba wax, Japanese wax, lanolin, palm wax, and paraffin wax.

[0386] Additives may include gelling agents.

[0387] Suitable gelling agents include cellulose-derived thickeners (e.g., hydroxyethyl cellulose), as well as gum arabic, agar, aloe vera 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 (e.g., hydroxyethyl cellulose).

[0388] When an additive is present in a coating composition, the additive can be provided as part of a carrier liquid. The carrier liquid can be a composition containing such an additive.

[0389] The carrier liquid can be a food composition (e.g., a pet food composition), a cosmetic composition, a personal care composition, a pharmaceutical composition, an ink, a paint, a laminating composition, a laundry detergent composition, or a building material composition. These compositions contain typical components necessary for them to function.

[0390] For example, the carrier liquid can be a paint base that comprises a binder and water. Specifically, the carrier liquid can be an acrylic paint base that comprises an acrylic binder and water.

[0391] Methods for preparing opaque agents

[0392] In a fourth aspect, a method for preparing the light-blocking agent of the second aspect is provided, the method comprising:

[0393] Cellulose microparticles with an average particle length of 0.7 µm to 9 µm and a surfactant are added to a carrier liquid to form a suspension.

[0394] Optionally, cellulose microparticles and surfactants are dispersed in a carrier liquid to disperse the suspension; and

[0395] The suspension is dried to provide a light-blocking agent.

[0396] The method for preparing a light-blocking agent may also include:

[0397] Provides cellulose microparticles and surfactants.

[0398] This can be referred to as the "preparation step," which involves preparing suitable cellulose microparticles and a suitable, available surfactant. The preparation step typically takes place before the addition step.

[0399] As described herein, any suitable cellulose microparticles and surfactants can be used. Cellulose microparticles and / or surfactants can be provided in the form of solutions or suspensions in solvents. Suspensions can also be provided in the form of slurries. Alternatively, cellulose microparticles and / or surfactants can be provided as dry powders or pastes.

[0400] The step of adding cellulose microparticles with an average particle length of 0.7 µm to 9 µm and a surfactant to a carrier liquid to form a suspension can be referred to as the “addition step”.

[0401] Cellulose microparticles and surfactants may be added individually or together. The carrier liquid used may be the same as described above in the sections on coating compositions. Preferably, the carrier liquid is water.

[0402] When cellulose microparticles and / or surfactants are provided in the form of suspensions or solutions, the addition step simply refers to combining the suspensions together to form a suspension of cellulose microparticles and surfactants.

[0403] A suspension is a heterogeneous mixture of fluids containing solid particles. If the suspension remains undisturbed for an extended period, these solid particles are typically large enough to precipitate. Cellulose microparticles are suspended in a liquid. Surfactants can dissolve in a carrier liquid. Suspensions can also take the form of slurries.

[0404] Optionally, the step of dispersing cellulose microparticles and surfactants in a carrier liquid to disperse the suspension can be referred to as the "dispersion step".

[0405] The dispersion step may include sonicating the suspension. The sonication may be probe sonication or ultrasonic sonication. The sonication may be performed at an energy of 400 J / g to 1,000 J / g, preferably 500 J / g to 900 J / g, more preferably 600 J / g to 800 J / g. Preferably, the sonication is performed at an energy of about 700 J / g.

[0406] Ultrasonic processing can be performed using any suitable equipment, such as the Fisherbrand ultrasonic pulverizer.

[0407] The step of drying a suspension to provide an opacifier can be referred to as the "drying step." The drying step typically occurs after the addition or dispersion step (if applicable). The drying step is generally performed on slurries or suspensions of cellulose microparticles and surfactants.

[0408] Typically, the drying step includes removing the carrier liquid (solvent) from the suspension. The drying step typically includes removing water, ethanol, or acetone from the suspension. Preferably, the drying step includes removing water from the suspension.

[0409] The suspension can be dried by any suitable method. For example, the suspension can be dried by evaporation, freeze-drying, spray drying, or spray freeze-drying. The equipment can be as described above for the preparation of cellulose microparticles.

[0410] The drying step can essentially remove all of the carrier liquid (solvent). For example, freeze-drying, spray drying, or spray freeze-drying can remove virtually all of the carrier liquid. This typically produces an opacifier powder, in which the powder contains clusters of surfactants and cellulose microparticles.

[0411] Typically, the drying step provides a dry powder of surfactant and cellulose microparticles. Freeze-drying or spray drying can provide this dry powder. Preferably, spray drying provides a dry powder of surfactant and cellulose microparticles.

[0412] Opacifier powder can be as described in this article.

[0413] Alternatively, the drying step can remove only a portion of the carrier liquid (solvent). In this way, the suspension is only partially dried.

[0414] For example, evaporation, freeze-drying, spray drying, or spray freeze-drying can remove only a portion of the carrier liquid. This typically produces opacifier powder, paste, or slurry, in which some solvent is retained. Partial drying preferably produces an opacifier paste or slurry.

[0415] Opacifier pastes or slurries are typically relatively concentrated mixtures of surfactants and cellulose microparticles, partially suspended in a carrier liquid. Opacifier pastes for slurries are as described herein.

[0416] The method for preparing a light-blocking agent may also include:

[0417] One or more additives are added to the opacifier.

[0418] The step of adding one or more additives can be performed sequentially with the addition step. The step of adding one or more additives can 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. Therefore, the additives can also be dispersed in the dispersion step.

[0419] When multiple additives are added, the additives can be added individually or together.

[0420] Additives are as described in this article.

[0421] The light-blocking agent produced by the method described herein can be used in the coating compositions of the present invention, or in the method for preparing the coating compositions of the present invention.

[0422] Therefore, in one aspect of the invention, a light-blocking agent is provided, wherein the light-blocking agent is obtained or available by a method of a third aspect.

[0423] Method for preparing coating compositions

[0424] In a fifth aspect of the invention, a method for preparing the coating composition of the first aspect is provided, the method comprising:

[0425] Cellulose microparticles with an average particle length of 0.7 µm to 9 µm and a surfactant, or a light-blocking agent, are added to the carrier liquid.

[0426] Optionally, cellulose microparticles and surfactants or opacifiers are dispersed in a carrier liquid to provide a coating composition.

[0427] The method for preparing the coating composition may also include:

[0428] Provide cellulose microparticles and surfactants, or provide light-blocking agents.

[0429] This can be referred to as the "preparation step," which involves preparing suitable cellulose microparticles and suitable, available surfactants or suitable, available opacifiers. The preparation step is typically performed before the addition step.

[0430] As described herein, any suitable cellulose microparticles and surfactants can be used. Cellulose microparticles and / or surfactants can be provided in the form of solutions or suspensions in solvents. Suspensions can also be provided in the form of slurries. Alternatively, cellulose microparticles and / or surfactants can be provided as dry powders or pastes.

[0431] Any suitable opacifier according to the second aspect can be used. As described herein, opacifiers typically comprise microparticles and surfactants. Opacifiers can be provided as suspensions in a solvent. Suspensions can also be in the form of slurries. Alternatively, opacifiers can be provided as dry powders or pastes.

[0432] The step of adding cellulose microparticles with an average particle length of 0.2 µm to 20 µm and a surfactant, or a light-blocking agent, to a carrier liquid may be referred to as the “addition step”.

[0433] These components may be added individually or together. The carrier liquid used may be the same as described above in the context of coating compositions. Preferably, the carrier liquid is water.

[0434] When cellulose microparticles and / or surfactants are provided in the form of suspensions or solutions, the addition step simply refers to combining the suspensions together to form a suspension of surfactants and cellulose microparticles.

[0435] A suspension is a heterogeneous mixture of fluids containing solid particles. If the suspension remains undisturbed for an extended period, these solid particles are typically large enough to precipitate. Cellulose microparticles are suspended in a liquid. Surfactants can dissolve in a carrier liquid. Suspensions can also take the form of slurries.

[0436] Optionally, the step of dispersing cellulose microparticles and surfactants or opacifiers in a carrier liquid to form a suspension may be referred to as a "dispersion step".

[0437] If the cellulose microparticles or opacifier are not sufficiently dispersed as a result of the addition step, a dispersion step may be required. The cellulose microparticles or opacifier are preferably homogeneously dispersed in the carrier liquid.

[0438] The dispersion step may include sonicating the suspension. Sonication may be probe sonication or ultrasonic sonication. Sonication may be performed at an energy level of 400 J / g to 1,000 J / g, preferably 500 J / g to 900 J / g, more preferably 600 J / g to 800 J / g. Preferably, sonication is performed at an energy level of about 700 J / g. The sonication energy refers to the energy per unit total mass of the sonicated suspension.

[0439] Ultrasonic processing can be performed using any suitable equipment, such as the Fisherbrand ultrasonic pulverizer.

[0440] The method for preparing the coating composition may also include:

[0441] One or more additives are added to the coating composition.

[0442] The step of adding one or more additives can be performed sequentially with the addition step. The step of adding one or more additives can 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. Therefore, the additives can also be dispersed in the dispersion step.

[0443] When multiple additives are added, the additives can be added individually or together.

[0444] Additives are as described in this article.

[0445] The coating compositions produced by the methods described herein can be used as coating compositions of the present invention, or as methods for coating substrates.

[0446] Therefore, in one aspect of the invention, a coating composition is provided, wherein the coating composition is obtained or is available by the method of the fourth aspect.

[0447] coating

[0448] In a third aspect of the invention, a coating applied to a substrate is provided, the coating comprising:

[0449] Cellulose microparticles, said cellulose microparticles having an average particle length of 0.7 µm to 9 µm, and

[0450] Surfactants,

[0451] The cellulose microparticles are present in the coating at an amount of 50 wt.% to 99.6 wt.% based on the total mass of the coating, and the surfactant is present in the coating at an amount of 0.4 wt.% to 25 wt.%.

[0452] The coating compositions of the present invention can be used to produce homogeneous films with controllable thickness. It is not desirable to be bound by theory, but rather to consider the surfactant as a scaffold on which cellulose microparticles are uniformly assembled. Layer-by-layer assembly of these films is also possible without disrupting the microparticle structure or the desired opacity.

[0453] The coating can be formed using the typical coating techniques described herein. The coating has the ability to scatter visible light as well as light in the infrared and ultraviolet wavelength range.

[0454] Cellulose microparticles are as described in this article.

[0455] Based on the total mass of the coating, cellulose microparticles are present in the coating in an amount of 50 wt.% or more, preferably 80 wt.% or more, more preferably 85 wt.% or more. In some embodiments, based on the total mass of the coating, cellulose microparticles are present in the coating in an amount of 99.6 wt.% or less, preferably 98 wt.% or less, more preferably 95 wt.% or less, and even more preferably 90 wt.% or less.

[0456] Based on the total mass of the coating, cellulose microparticles are present in the coating in an amount of 50 wt.% to 99.6 wt.%. In some embodiments, based on the total mass of the coating, cellulose microparticles are present in the coating in an amount of 80 wt.% to 99 wt.%, preferably 85 wt.% to 96 wt.%, more preferably 86 wt.% to 90 wt.%.

[0457] Surfactants are as described in this article.

[0458] In some embodiments, the surfactant is present in the coating at an amount of 1 wt.% or more, preferably 5 wt.% or more, and more preferably 10 wt.% or more, based on the total mass of the coating. In some embodiments, the surfactant is present in the coating at an amount of 20 wt.% or less, preferably 17 wt.% or less, and more preferably 15 wt.% or less, based on the total mass of the coating.

[0459] The surfactant is present in the coating at an amount of 0.4 wt.% to 25 wt.% based on the total mass of the coating. In some embodiments, the surfactant is present in the coating at an amount of 1 wt.% to 20 wt.%, preferably 4 wt.% to 17 wt.%, more preferably 12 wt.% to 15 wt.% based on the total mass of the coating.

[0460] The coating is substantially free of carrier liquid (e.g., solvent). Typically, based on the total mass of the coating, the coating contains less than 5 wt.%, preferably less than 1 wt.%, more preferably less than 0.5 wt.%, and even more preferably less than 0.1 wt.% of carrier liquid.

[0461] 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, as described in the cellulose microparticle section of this document.

[0462] 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 described in the cellulose microparticle section of this document.

[0463] Coating thickness can be measured using any suitable method, such as a micron screw head, ultrasonic thickness gauge, surface profilometer, SEM, or AFM (atomic force microscopy). Coating thickness can be measured by taking multiple readings (e.g., 10 readings) over the coated area and calculating the average of these readings. Thickness can be measured using the method described in ISO 2808:2019.

[0464] In some embodiments, the coating has an average thickness of 5 µm or more, preferably 10 µm or more, and 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, and more preferably 200 µm or less.

[0465] In some embodiments, the coating has an average thickness of 5 µm to 500 µm, preferably 10 µm to 300 µm, and more preferably 15 µm to 200 µm.

[0466] The coating thickness can be substantially uniform across the entire coated area. For example, the coating thickness can have a standard deviation of less than 25%, preferably less than 20%, more preferably less than 15%, and even more preferably less than 10%. The coating thickness can have a standard deviation of less than 10 µm, preferably less than 8 µm, more preferably less than 5 µm, and even more preferably less than 3 µm.

[0467] The coating also exhibits excellent optical properties, such as whiteness and reflectivity.

[0468] 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, wherein L* (45° / 0°) are CEILAB color space coordinates. L* is measured as described herein.

[0469] 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 in the wavelength range of 400 nm to 700 nm.

[0470] The coating can also reflect light 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, wherein the average reflectance is measured in the wavelength range of 100 nm to 400 nm.

[0471] The coating can also reflect light 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, wherein the average reflectance is measured in the wavelength range of 1000 nm to 2500 nm.

[0472] 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 for a coating with a thickness of 10 µm in the wavelength range of 400 nm to 700 nm. The opacity of a coating formed from a paint composition containing 12 wt.% cellulose microparticles can be measured. Opacity measurement is as described in the Examples section.

[0473] The coating applied to the substrate may comprise two or more layers. These two or more layers may comprise two or more layers of the present invention comprising cellulose microparticles and a surfactant. The two or more layers may be identical or different. Preferably, the two or more layers are identical. In this way, multiple layers comprising cellulose microparticles and a surfactant of the present invention can be constructed to produce a coating with a desired thickness.

[0474] Two or more layers can be applied sequentially. Alternatively, two or more layers can be interspersed with different layers, such as the additional layers described below. The use of multiple individual layers can be used to achieve a more uniform thickness in the membrane than a single layer of equivalent thickness.

[0475] The coating applied to the substrate may include an additional layer. This additional layer differs from the layer of the present invention, which contains cellulose microparticles and a surfactant.

[0476] The additional layer may include a primer layer. The primer layer is typically disposed between the substrate and the layer containing cellulose microparticles and a surfactant. Preferably, the primer layer improves the adhesion of the layer containing cellulose microparticles to the substrate.

[0477] Any suitable primer can be used. Suitable primers may include oil-based primers, latex-based primers, or shellac primers.

[0478] Adhesion can be further improved to the desired level by applying a primer layer or base coat. Primers are particularly suitable for substrates such as metal, wood, or leather, to seal structural pores or smooth the surface roughness of the substrate.

[0479] Additional layers may include a topcoat layer. The topcoat layer is typically disposed on the opposite side of the layer containing cellulose microparticles and a surfactant. Preferably, the topcoat layer encapsulates the layer containing cellulose microparticles. The topcoat layer can provide the coating with improved abrasion resistance, scratch resistance, antimicrobial properties, and / or stain resistance.

[0480] When a primer or topcoat layer is applied, the whiteness of the coating of the present invention is maintained. The topcoat layer is preferably transparent, for example, transparent to visible light. Transparency generally refers to a transmittance of 80% or more, such as 90% or more, or 95% or more of the incident light.

[0481] Any suitable topcoat layer can be used. Suitable topcoat layers may include polyurethane layers, epoxy layers, or shellac-based layers.

[0482] Coating method

[0483] In a sixth aspect of the invention, a method for forming a coating on a substrate is provided, the method comprising:

[0484] Apply the coating composition of the first aspect to the substrate, and

[0485] The coating composition is dried to form a coating containing cellulose microparticles.

[0486] A coating containing cellulose microparticles can be referred to as a layer containing cellulose microparticles.

[0487] Methods for forming a coating may also include:

[0488] Provide coating compositions and substrates.

[0489] This can be referred to as the "coating preparation step," which refers to making a suitable coating composition and substrate available. The preparation step is usually carried out before the application step.

[0490] As described herein, any suitable coating composition and substrate can be used.

[0491] The step of applying the coating composition of the first aspect to the substrate can be referred to as the "application step".

[0492] The coating can be applied to the substrate using any suitable method. Suitable methods of applying the coating may include spraying, curtain coating, blade coating, roller coating, dip coating, or draw-down coating. Preferably, the coating is applied by spraying or draw-down coating, more preferably by spraying.

[0493] Pull-down coating can include pulling down with a stainless steel rod, which is made of stainless steel wire tightly wound around a stainless steel bar. These rods may also be called grooved metering rods. Pull-down coating can also be performed using a bird film applicator. Typically, an appropriate volume of paint suspension is placed in front of the pull-down rod or bird film applicator, the rod or applicator is held from the end and moved at the same speed while applying the same pressure to the top of the surface to be coated.

[0494] Spraying is typically performed by applying a suspension using a suitable reservoir connected to a nozzle. For example, the suspension is placed in a reservoir, and the pressure on the nozzle is adjusted to minimize dissipation outside the intended coating area. When the volume is <50 mL, the pressure within the nozzle typically does not exceed 1 bar.

[0495] The method of coating application can vary depending on the intended substrate and the intended use of the coating. For example, coatings on walls or roofs, which serve as substrates, can preferably be applied by spraying. However, coatings on paper or wood can preferably be applied by applying the coating by slick.

[0496] In some embodiments, the method further includes the step of applying a primer layer to a substrate prior to applying the coating composition, wherein the coating composition is applied to the primer layer. The primer layer is as described above.

[0497] In some embodiments, the method further includes the step of applying a topcoat layer onto the layer containing cellulose microparticles after the coating composition has dried, preferably wherein the topcoat layer encapsulates the layer containing cellulose microparticles. The topcoat layer is as described above.

[0498] Any substrate suitable for receiving the coating composition can be used. The substrate is preferably flat, although it may be curved or complex in shape (e.g., applied by spraying or dripping).

[0499] In some embodiments, the substrate is paper, wood, plastic, leather, or metal. The substrate can be any suitable type of paper, wood, plastic, leather, or metal.

[0500] Suitable papers include copy paper, bond paper, card stock, glossy paper, matte paper, newsprint, tissue paper, construction paper, watercolor paper, kraft paper, tracing paper, and parchment.

[0501] Suitable timber includes natural timber (including air-dried and undried timber) and engineered timber (e.g., plywood, MDF, particleboard, cardboard, and veneer).

[0502] 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).

[0503] Suitable leathers include reconstituted leather, bridle leather, deerskin leather, full-grain leather, and cowhide leather.

[0504] Suitable metals include aluminum, cadmium, chromium, copper, iron, lead, nickel, tin, zinc, and combinations or alloys thereof.

[0505] In embodiments where cellulose microparticles provide good IR scattering, the substrate can be the walls or roof of a building. In this way, the coating can reduce radiation through light reflection from these coated surfaces. Therefore, this cellulose white coating could be a viable solution for heat management in buildings and elsewhere, and ultimately contribute to mitigating global warming through the sustainable use of renewable materials.

[0506] In embodiments where the cellulose microparticles have good UV scattering, the substrate can be the subject's skin. In this way, the coating can provide UV protection to the subject.

[0507] The step of drying the coating composition to form a layer containing cellulose microparticles can be referred to as the "curing step".

[0508] The curing step can be achieved by any suitable method. The curing step involves removing the carrier liquid (solvent) from the suspension. The curing step occurs after the coating is applied to the substrate to cure the coating in the appropriate location on the substrate.

[0509] The coating can be dried at ambient temperature or high temperature. The coating can be passively dried (e.g., by relying on air convection to remove evaporated solvent) or actively dried (e.g., by allowing airflow to pass over the coating surface).

[0510] Either a conductive dryer or a convection dryer can be used in the curing step. Examples of suitable conductive dryers include paddle dryers, disc dryers, or thin-layer dryers. Examples of suitable convection dryers include vacuum dryers or fluidized bed dryers.

[0511] The curing step produces a coating that is substantially free of carrier liquid (e.g., solvent). This allows the coating to be "cured". Typically, based on the total mass of the coating, the coating produced by the drying step has less than 5 wt.%, preferably less than 1 wt.%, more preferably less than 0.5 wt.%, and even more preferably less than 0.1 wt.% of carrier liquid.

[0512] In the drying step, it is assumed that cellulose microparticles assemble on a surfactant scaffold to form a continuous white film. Due to the use of the surfactant, the cellulose microparticles do not prematurely precipitate from the coating composition during curing (as the solvent volume decreases), but are instead homogeneously dispersed in the solvent by the surfactant. The cellulose microparticles then assemble into a coating having a homogeneously distributed distribution of cellulose particles, thus providing uniform and continuous whiteness and opacity.

[0513] The coatings / paints produced by the methods described herein can be used as coating compositions of the present invention.

[0514] Therefore, in one aspect of the invention, a coating is provided, wherein the coating is obtained or is obtainable by the method of the sixth aspect.

[0515] use

[0516] In one aspect of the invention, use is provided for applying a coating composition according to the first aspect to a substrate to form a coating.

[0517] The coatings of this invention can be used to improve the whiteness of a substrate or to provide opacity to the substrate. These coatings are particularly suitable as whiteness enhancers for substrates because they have a high level of reflectivity and reflect light at a similar level across the entire visible light spectrum.

[0518] This can be applied in food additives (e.g., pet food additives), cosmetics, personal care products, pharmaceuticals, inks, paints, laminates, laundry detergents, light-harvesting devices (e.g., photovoltaic cells), light-distributing devices (e.g., LEDs), household goods (e.g., furniture), and building materials.

[0519] Other preferred options

[0520] This document explicitly discloses each or every compatible combination of the above embodiments, as if each or every one has been individually and explicitly listed.

[0521] In view of this disclosure, those skilled in the art will understand various other aspects and embodiments of the invention.

[0522] As used herein, “and / or” should be considered as a specific disclosure of each of two particular features or components, whether or not accompanied by the other. For example, “A and / or B” should be considered as a specific disclosure of (i) A, (ii) B, and (iii) A and B, as if each were listed separately herein.

[0523] Unless the context otherwise indicates, the description and definition of the features listed above are not limited to any particular aspect or implementation of the invention, and are equally applicable to all aspects and implementations described.

[0524] Some aspects and implementations of the invention will now be described by way of examples and with reference to the accompanying drawings.

[0525] Example

[0526] The following embodiments are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

[0527] Material

[0528] Microcrystalline cellulose powder (MCC) was purchased from SERVA Electrophoresis.

[0529] Sulfuric acid (concentration > 95%) was purchased from Fisher Chemical.

[0530] The acrylic paint base is obtained from Galaxus and includes binder (acrylic acid) and water as its main components.

[0531] The Triton X-100 is sourced from Sigma-Aldrich.

[0532] Twain 20 was obtained from Sigma-Aldrich.

[0533] ECOSURF SA-9 was obtained from Dow.

[0534] TERGITOL 15-S-9 was obtained from Dow.

[0535] The TERGITOL TMN-100X was obtained from Dow.

[0536] Hexaalkyldimethylammonium bromide (CTAB) was obtained from Sigma-Aldrich.

[0537] 3-(decyldimethylammonium)-propane-sulfonic acid inner salt was obtained from Sigma-Aldrich.

[0538] The opacity test chart (also known as the contrast test chart) is obtained from Leneta. The opacity test chart has a simple combination of white and black areas, large enough to be used for wide-aperture reflectance measurements. The black and white areas are sealed with a clear, waterproof topcoat to prevent the applied paint from seeping into the paper.

[0539] Measurement methods

[0540] SEM images were obtained using a FEI Nanolab 650 FIB-SEM operating at 5.0 kV and a working distance of 6.9 mm.

[0541] Whiteness can be quantified by converting the reflectance (measured as described below) to CEILAB (L*a*b*) color space coordinates. Here, a* represents the position between red (positive) and green (negative), and b* represents the position between blue (negative) and yellow (positive). L* represents the perceived brightness or luminance of the reflected light. A brightness of 0 is black, and a brightness of 100 is diffuse white. Brightness close to 100 indicates excellent whiteness of the material.

[0542] Whiteness can be measured at different incident angles (the angle of incident light). L*(45 / 0) refers to the incident angle at 45° to the surface normal and the reflection angle at 0° to the surface normal.

[0543] Total reflectance was measured using an integrating sphere (Labsphere). A light source (OceanOptics HPX-2000) was coupled to an optical fiber (600 μm Thorlabs FC-UV100-2-SR) via a collimator (Thorlabs), and the signal was collected using an Avantes HS2048 spectrometer. The signal intensity was normalized relative to the intensity without a sample. Background was typically recorded without applied light. Wavelengths ranged from 400 nm to 700 nm. Five spectra were taken for each sample, and the average was used to reduce the signal-to-noise ratio. Each spectrum was recorded using an integration time of 3 seconds.

[0544] To quantify whiteness, we can assume that perfect white has color space coordinates (100, 0, 0). Whiteness can be defined and calculated as listed in WO2023 / 135261.

[0545] The thickness of the coating is measured using a micron screw head. The coating thickness is measured by taking multiple readings (e.g., 10 readings) over the coated area and calculating the average of these readings.

[0546] When cellulose microparticles are applied as a paint, the solvent begins to evaporate, a process that causes pores to form in the dried film. As the solvent evaporates, the liquid phase decreases, allowing the cellulose microparticles to come into closer contact with each other. This results in small voids or pores within the matrix of the applied paint. Ideally, the pore size should be on the order of half a wavelength of light, preferably in the range of 50 nm to 900 nm, and particularly preferably in the range of 100 nm to 500 nm. Small pores are more suitable for UV protection, while large pores are more suitable for IR scattering.

[0547] Considering the uniformity of the pore size distribution is also crucial. The narrower the pore size distribution, the more effective the scattering ability of the material or structure. The presence of these pores and the uniformity of their size distribution enable increased light scattering, which not only enhances the aesthetic qualities of the paint or coating but also makes the appearance more uniform. Therefore, the size and distribution of the pores can contribute to achieving optimal light scattering, thereby increasing the brightness and opacity of the applied white paint. Thanks to these microporous properties, paints can not only produce high-gloss surfaces but also improve the breathability of the coated material. As mentioned above, below the critical pigment volume concentration (CPVC), designing the pore size and pore size distribution can significantly improve the scattering performance of coatings and paints.

[0548] Preparation of CMPs

[0549] Three different CMPs were prepared: CMP-LS, CMP-X and CMP-Z.

[0550] 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 quenching with 300 mL of milli-Q water. The acidic 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 (MWCO 12-14 kDa) for one week, with the water changed twice daily. The dialysate suspension of hydrolyzed cellulose particles (0.5% wt, 30 mL) was subjected to probe sonication in an ice bath (Fisher brand ultrasonic disruptor 500 W, 20 kHz, probe diameter 12.7 mm, amplitude 30%, 2 seconds on, 2 seconds off). The suspension was centrifuged at 2000 rpm for 5 minutes, and then the supernatant was collected and centrifuged at 3000 rpm for 5 minutes to obtain cellulose nanoparticles CMP-LS.

[0551] CMP-X was obtained using the same method as CMP-LS, except that cellulose filter paper (Whatman No. 1) was used instead of cellulose microcrystalline powder. The cellulose filter paper (Whatman No. 1) was hydrolyzed with sulfuric acid (55 wt.%, 60 mL) at 50 °C for 0.5 hours.

[0552] CMP-Z was prepared from cellulose filter paper (Whatman No. 1), which was first ground into small pieces using a coffee grinder and then oxidized with TEMPO. 1 g of cellulose was suspended in 150 mL of milli-Q water, and 0.123 g of TEMPO, 1.23 g of NaBr, and 1.23 g of NaClO were added. The mixture was stirred at room temperature for 4.5 h, 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. The oxidized cellulose fibers were then washed by filtration and dialyzed relative to milli-Q water to provide cellulose fiber CMP-Z.

[0553] Characterization of CMPs

[0554] CMP-LS was characterized by scanning electron microscopy (SEM). Figure 1 SEM images of cellulose microparticles with unique light scattering capabilities are shown. Scale bar: 30 µm.

[0555] The size distributions of CMP-LS, CMP-X, and CMP-Z were measured using scanning electron microscopy (SEM). A diluted suspension of CMPs (0.001 wt.%) was dropped onto a carbon-coated copper grid (300 mesh) for 2 minutes and removed through a filter paper. Then, a drop of uranyl acetate solution (2%) was applied as a dye for 1 minute, followed by removal through a filter paper. Particle length was analyzed using ImageJ. Length refers to the maximum diameter of the particle visible in the SEM image. The number of measurements performed to determine the size distribution typically ranges from 100 to 1,000. Generally, more than 100 measurements are performed for length.

[0556] The particle length distributions of CMP-LS, CMP-X, and CMP-Z are as follows: Figure 2 As shown, the size distribution is quantified by the particle volume.

[0557] Preparation of the composition

[0558] The coating compositions of the present invention (compositions 1a to 7) are prepared by mechanically mixing a surfactant solution (water as a solvent) with CMP-LS powder and then subjecting it to ultrasonic treatment.

[0559] A comparative coating composition (comp. 1) was prepared by mechanically mixing water with CMP-LS powder and then subjecting it to ultrasonic treatment. No surfactant was present.

[0560] A surfactant-containing solution was prepared by mixing the surfactant with water at the concentrations shown in Table 1. The amount of CMP added is shown in Table 1. The mixture was ultrasonicated at 700 J / g to prepare the coating composition.

[0561] For example, composition 1a was prepared by mixing 2 wt.% of an aqueous solution of Triton-X-100 and CMP powder in a w:w ratio of 3:17, and then sonicating it at 700 J / g to produce a suitable coating composition for coating various surfaces.

[0562] Table 1. Formulations of cellulose microparticles (CMP) containing different surfactant families

[0563]

[0564] coating of substrate

[0565] Down-coating is performed using a stainless steel rod made of stainless steel wire tightly wound around a stainless steel bar. This rod can also be called a grooved metering rod. In certain cases, a bird-type applicator is also used for down-coating. The coating thickness is determined by the depth of the down-coat / rod.

[0566] Place the substrate on a flat surface. Place an appropriate volume of the coating composition in front of the pull rod or bird-shaped applicator. Hold the rod or applicator from the end and move it at the same speed while applying the same pressure to the top of the surface to be coated.

[0567] Apply the coating using a suitable reservoir connected to the nozzle. Place the composition into the reservoir and adjust the pressure on the nozzle to minimize dissipation outside the intended coating area. When the volume is <50 mL, the pressure within the nozzle should generally be controlled to not exceed 1 bar.

[0568] Depending on the volume of the coating composition used, air dry the composition for 1-60 minutes.

[0569] Comparative composition 1 was applied to an opacity test card. 5–10 mL of the comparative coating composition was placed in front of the pull rod, which was then pulled across the opacity test card to form a film. The film was dried for 45 minutes. After drying, the film broke into heterogeneous fragments.

[0570] The resulting coating is shown in Figure 3. Visual inspection of the coating reveals that it is discontinuous, containing large pores. The coating is also heterogeneous throughout the coated area and has inconsistent thickness. Therefore, the visual appearance is uneven, exhibiting varying whiteness and opacity across the entire coated area. The coating is also non-uniform.

[0571] To avoid being bound by theory, it is assumed that when the solvent evaporates from this comparative CMP composition, the cellulose particles deposit on the surface and fail to form a continuous white film (Figure 3). This indicates that directly drying an aqueous suspension of CMP does not produce a white film.

[0572] Composition 1b was coated onto paper by a downward application. The coating was air-dried for 45 minutes. The resulting film had a thickness of 20 µm. The resulting white film appeared as shown. Figure 4a As shown.

[0573] The composition 1b was further coated with thicknesses of 7 µm, 14 µm, and 19 µm.

[0574] Composition 2 was coated onto paper by applying it downwards. The coating was air-dried for 45 minutes. The resulting film had a thickness of 20 µm. The resulting white film appeared as shown. Figure 4b As shown.

[0575] Composition 1b was applied to the wood using a pull-down technique. The coating was air-dried for 30 minutes. The resulting film had a thickness of 20 µm. The resulting white film appeared as shown. Figure 5 As shown.

[0576] Composition 1b was coated onto aluminum at thicknesses of 50 µm, 100 µm, and 150 µm by a drag coating. The coatings were air-dried for 20 minutes. The resulting 10 µm white film... Figure 6b As shown.

[0577] Composition 4a was applied to cow leather with a coating thickness of ~20 µm by a downward application. The coating was air-dried for 45 minutes. The resulting white film on the leather was as shown. Figure 8a As shown.

[0578] Composition 4b (comprising 10 wt.% acrylic paint base in water) was applied to cow leather using a downward coating technique to a thickness of 20 µm. The coating was then air-dried for 45 minutes. The resulting white film on the leather appeared as shown in the image. Figure 8b As shown.

[0579] Figure 8b The leather sample shown can be bent, and the white coating remains intact after bending without cracking or crumbling. The resulting white film maintains a good degree of dimensional stability even under deformation.

[0580] Regarding Figure 4, Figure 5The coatings of compositions 1b, 2, 4a, and 4b shown in Figures 6 and 8 were visually inspected. The formed coatings were continuous, without voids or gaps. It was also found that the coatings were homogeneous and had a consistent thickness throughout the coated area. Therefore, the visual appearance was highly uniform and flat, with excellent whiteness and opacity throughout the coated area. The film thickness was highly controllable through the coating process.

[0581] To avoid being bound by theory, it is proposed that surfactants form a scaffold, and CMPs assemble on the scaffold by maintaining a uniform periodic distance between particles to form a continuous lattice structure. This periodic structure amplifies the light scattering contrast between cellulose particles and adjacent spaces (occupied by air), thus forming a clear, continuous white film.

[0582] It is also believed that surfactants reduce the surface tension or interfacial tension between cellulose microparticles and solvents. However, surfactants do not interfere with the light scattering ability of CMPs.

[0583] The white cellulose film was found to provide good adhesion to paper, wood, aluminum and leather substrates.

[0584] Optical characterization of coatings

[0585] Table 2 shows the whiteness of various coating compositions as measured by L*.

[0586] For the whiteness measurements provided in Table 2, a 10 µm coating was formed on the opacity test card using a pull-down coating method.

[0587] The exemplary compositions provide excellent L* values, typically having an L* of 77 or higher, and in some cases having an L* of 85 or higher.

[0588] Table 2: Whiteness of the coating

[0589]

[0590] Figure 6a The remission spectra of the coating formed on aluminum by composition 1b are shown. As measured by L*, the whiteness of the film depends on the film thickness.

[0591] Figure 7 The retroreflection spectra of coatings (7 µm, 14 µm, and 19 µm thick) formed on paper by composition 1b are shown. L* is 66 (7 µm), 77 (14 µm), and 80 (19 µm). It was found that the degree of whiteness, represented by L* (45 / 0), depends directly on the coating thickness.

[0592] The spectrum of the coating formed by composition 4a on cow leather gives CIELAB color values: L*=95, a*=-0.1, b*=2.8. The whiteness value is 94 [calculated as 100 - SQRT((100-L*)^2 + a*^2 + b*^2)].

[0593] In this color space, the numerical differences between values ​​roughly correspond to the amount of variation perceived by humans between colors. When cellulose microparticles are used with nonionic or cationic surfactants, the whiteness value of the cellulose-based film, characterized by L* (45° / 0°), is >85, while when using amphoteric surfactants, the whiteness value is >75. This indicates that CMPs possess excellent whiteness and excellent scattering properties.

[0594] Opacity test

[0595] The opacity dependence of CMP concentration was tested.

[0596] 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). The compositions comprised CMPs 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.

[0597] Various coating compositions were applied to an opacity test card (as described above). The coating was applied to a thickness of 10 µm by a pull-down coating method.

[0598] The opacity of the coating is measured using the same method as L* described above. Opacity is the percentage of the "y" value (according to the CIE Y-value system) measured on the opacity test card relative to the white portion of the card.

[0599] The opacity value of the coating is provided in Figure 10 middle.

[0600] Figure 10 The results showed that coatings containing CMPs and nonionic surfactants increased as the CMP concentration increased from 3 wt.% to 12 wt.% or 15 wt.%. Opacity increased from approximately 60% with 3 wt.% CMP to over 80% with 12 wt.% CMP.

[0601] At concentrations of 12 wt.% to 15 wt.%, the opacity tends to plateau or decrease. In some embodiments, the opacity remains at approximately 85% at CMP concentrations of 12 wt.% to 20 wt.%.

[0602] Table 3 provides the accurate opacity measured at 12 wt.% CMP.

[0603] Table 3. Opacity of cellulose microparticle coatings with different formulations

[0604]

[0605] L* and backscattering

[0606] The reflectivity of the coatings produced in the above embodiments was tested. The reflectivity was measured as described above, and L* (45° / 0°) and backscattering of different coatings were determined. All exemplary compositions were applied to an opacity test card.

[0607] Backscattering was measured using diffuse wave spectroscopy (DWS), a light scattering technique used to measure the Brownian motion of particles in suspension. DWS analyzed the temporal intensity fluctuations of light scattered by the particles.

[0608] When measuring L* (45° / 0°), the measurements were calibrated using a 1 wt.% cellulose microparticle suspension and a 1 cm thick cuvette. Alternatively, other optical techniques for measuring backscattering can be used, such as the DWSRheolab instrument or a similar instrument.

[0609] For the same 1 wt.% aqueous suspension calibrated using 1 cm thick glass cuvettes, the L* (45° / 0°) of the cellulose microparticles has a value between 38 and 42, or a backscatter response >1300 au (see [reference]). Figure 11 ).

[0610] Figure 11 The diagram shows L* and backscatter, presented as a polynomial plot illustrating the correlation between CIELAB L* (45° / 0°) measurements and backscatter for a wide selection of samples coated with cellulose microparticles, and how we quantify whiteness. The circled areas represent the range of whiteness measured by any technique where light scattering represents a suitable measurable and detectable value. The fitted curve of the experimental data can be described as a polynomial function, L*(x) = ax b = 0.72 x 0.55 Coefficient of determination r 2 =98.1%.

[0611] This shows the correlation between CIELAB L* measurements and DWS backscatter. Acceptable whiteness levels fall within the circle range: L* in the range of 37 to 41, and backscatter between 1300 au and 1400 au. L* above the circle area is also acceptable, as the whiteness is even greater. L* below the circle area is generally unacceptable.

[0612] The tests also showed that these compositions are tunable to provide coatings with higher L* (or backscatter) values ​​as needed. Whiteness and backscatter exhibited a good correlation across all levels of whiteness.

[0613] UV-Visible Light and IR Reflection

[0614] Composition 1b was coated onto an opacity test card by pull-down coating to produce a film with a thickness of 15 ± 2 µm.

[0615] Composition 2 was coated onto paper by pull coating to produce a film with a thickness of 12 ± 3 µm.

[0616] The UV and IR reflectance of the film were tested using the method described above. The UV-visible spectrum was measured at wavelengths from 150 nm to 900 nm, and the IR spectrum was measured at wavelengths from 1000 nm to 2500 nm. Figure 13a The spectrum of the coating of composition 1b is shown. Figure 13b The spectrum of the coating of composition 2 is shown.

[0617] The cellulose white film exhibits excellent spectral response in the ultraviolet (UV) and infrared (IR) ranges, displaying 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.

[0618] Additional coating

[0619] As described above, composition 1b is coated onto an aluminum substrate using a pull-down coating method. A transparent polyurethane film is applied over a white cellulose coating using pull-down coating. This results in an aluminum substrate with a white cellulose coating (CMP+PU) covered by a PU coating.

[0620] As a control, a transparent polyurethane film was applied directly to an aluminum substrate. The polyurethane film was applied using a pull-coating method. This resulted in an aluminum substrate with a PU coating. The PU coating thickness was approximately 10 µm.

[0621] It was found that the PU coating had no effect on the whiteness or opacity of the CMP coating.

[0622] abrasion resistance

[0623] The abrasion resistance of CMP+PU coated aluminum and PU coated aluminum was tested. Abrasion tests were performed using 600-grit sandpaper with a 100 g load at a rate of 2 passes (back and forth) per cycle. The coatings underwent 10 cycles of abrasion.

[0624] Wear was determined based on the water contact angle of the coating. The water contact angle (CA, θ) was measured using a droplet shape analyzer (FirstTen Angstroms, USA) at ambient temperature. 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.

[0625] The results are shown in Figure 12 Before wear (cycle 0), the water contact angles of both CMP+PU and PU were approximately 85°. After one cycle (cycle 1), the water contact angle of the PU coating remained at approximately 85°, while that of the CMP+PU coating decreased to 65°. For cycles 2-10, the water contact angle remained constant between 75° and 85°. CMP+PU generally exhibited a lower water contact angle than PU. This is considered to be a result of the hydrophilicity of the cellulose particles and the surfactant.

[0626] Clearly, as measured by the water contact angle, the scratch resistance of the multilayer (cellulose microparticles and polyurethane) remained almost stable across a wide range of cycles.

[0627] This indicates that a top transparent layer can be applied without affecting the whiteness of the underlying layer, while simultaneously enabling the white coating to have improved scratch and abrasion resistance.

[0628] Comparative example

[0629] Milled cellulose particles with a particle size of 40 µm were prepared using a blade mill (e.g., a Retsch SM300 or similar system) and mixed with different additives disclosed in WO02 / 100955A1.

[0630] Comparative Example 1:

[0631] A mixture comprising 12 w% of milled cellulose particles (40 μm) and 2 w% of the nonionic surfactant EcoSurf SA-9 was prepared from an aqueous suspension. This combination did not form any film; only randomly aggregated particles were observed (see CE_01 in the table below).

[0632] Comparative Example 2:

[0633] When milled cellulose was combined with calcium carbonate and ionic surfactants, the results showed only minimal aggregation and no formation of a continuous film (see CE_02 in the table below).

[0634] Comparative Example 3:

[0635] The combination of milled cellulose with calcium carbonate and titanium dioxide—regardless of the presence of nonionic surfactants (CE_05 or CE_06)—produces only faint traces in the attempt to form a film, indicating insufficient film formation.

[0636] Comparative Example 4:

[0637] When titanium dioxide is used alone with a nonionic surfactant (CE_04), the resulting product is a heterogeneous film. This indicates that nonionic surfactants are not conducive to the assembly of TiO2 particles into a uniform film, and in fact, they disrupt this process.

[0638] The composition according to the present invention:

[0639] In contrast, a composition from an aqueous suspension containing 12 w% CMP-X and 2 w% EcoSurf SA-9 successfully produced a continuous and homogeneous white film (see CE03_001_01 in the table below).

[0640]

[0641] Therefore, milled cellulose particles within the size range specified in WO 02 / 100955 A1 do not exhibit the same light scattering properties as the cellulose microparticles contained in the compositions according to the invention. Furthermore, when these milled cellulose particles are mixed with ionic surfactants from aqueous suspensions, they fail to form a continuous film. Instead, they tend to simply aggregate, which further inhibits the formation of homogeneous films with other light scattering agents (e.g., calcium carbonate or titanium dioxide). Moreover, when mixed with metal oxide particles (e.g., titanium dioxide), the nonionic surfactant does not function as a scaffold. The scaffold-like function of the surfactant appears to be characteristic of the cellulose microparticles contained in the compositions according to the invention, thus the cellulose particles are designed to have specific physical dimensions.

[0642] References

[0643] Numerous publications have been cited above to more fully describe and disclose the invention and the prior art to which it pertains. Full citations of these references are provided below. The entire contents of each of these references are incorporated herein by reference.

[0644]

Claims

1. A coating composition for providing a cellulose microparticle coating on a substrate, the coating composition comprising: The light-blocking agent comprises cellulose microparticles and a surfactant, wherein, The cellulose microparticles have an average particle length of 0.7 µm to 9 µm as measured by scanning electron microscopy; as well as Carrier liquid; The cellulose microparticles are present in the coating composition in an amount of 1 wt.% to 40 wt.% based on the total mass of the coating composition, and the surfactant is present in the coating composition in an amount of 0.5 wt.% to 6 wt.% based on the total mass of the coating composition, and the composition contains less than 5% by weight of metal oxide.

2. The coating composition, wherein, The composition is substantially free of metal oxides, and preferably substantially free of TiO2.

3. The coating composition according to claim 1 or 2, wherein, Based on the total mass of the coating composition, the cellulose microparticles are present in the coating composition in an amount of 5 wt.% to 20 wt.%, preferably 10 wt.% to 18 wt.%, more preferably 12 wt.% to 15 wt.%.

4. The coating composition according to any one of the preceding claims, wherein, Based on the total mass of the coating composition, the surfactant is present in the coating composition in an amount of 0.5 wt.% to 3 wt.%, preferably 1.0 wt.% to 2.0 wt.%.

5. The coating composition according to any one of the preceding claims, 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 based on the total mass of the coating composition in wt.%.

6. The coating composition according to any one of the preceding claims, comprising a particle group CMP having an average particle length of less than 1 µm. X or a group of particles (CMP) with an average particle length in the range of 1 µm to less than 5 µm. LS or mixtures thereof, preferably CMP particles having an average particle length in the range of 1 µm to less than 5 µm. LS .

7. The coating composition according to any one of the preceding claims, wherein, The carrier liquid is water, ethanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), or a combination thereof, preferably, wherein the carrier liquid is water.

8. A light-blocking agent for use in a coating composition, said light-blocking agent comprising: Cellulose microparticles, said cellulose microparticles having an average particle length of 0.7 µm to 9 µm, and Surfactants, in, Based on the total mass of the light-blocking agent, the cellulose microparticles are present in the light-blocking agent in an amount of 50 wt.% to 99.6 wt.%, and the surfactant is present in the light-blocking agent in an amount of 0.4 wt.% to 25 wt.%. Optionally, the light-blocking agent is a powder.

9. A cellulose microparticle coating formed on a substrate, the coating comprising cellulose microparticles and a surfactant. in, The cellulose microparticles have an average particle length of 0.7 µm to 9 µm as measured by scanning electron microscopy. The cellulose microparticles are present in the coating in an amount of 50 wt.% to 99.6 wt.% based on the total mass of the coating, and the surfactant is present in the coating in an amount of 0.4 wt.% to 25 wt.% based on the total mass of the coating, and the coating contains less than 5% by weight of metal oxide.

10. The cellulose microparticle coating according to claim 9, wherein, The coating has the following characteristics: L*(45° / 0°) is 65 or higher, preferably 70 or higher, more preferably 80 or higher, and even more preferably 90 or higher, wherein L*(45° / 0°) is the CEILAB color space coordinate measured for a coating with a thickness of 10 µm.

11. The coating composition according to any one of claims 1-7, the opacifier according to claim 8, or the cellulose microparticle coating according to claim 9 or 10, wherein, The cellulose microparticles have: An average particle length of 1.3 µm to 7 µm, more preferably 1.7 µm to 5 µm, and even more preferably 1.9 µm to 2.8 µm, wherein the average particle length is measured by scanning electron microscopy; and / or The average aspect ratio is 2 to 18, preferably 3 to 15, more preferably 4 to 10, and even more preferably 4 to 6, wherein the average particle length and average particle width used for the aspect ratio are measured by scanning electron microscopy; and / or The average width is 0.1 µm to 1 µm, preferably 0.2 µm to 0.8 µm, more preferably 0.3 µm to 0.6 µm, and even more preferably 0.45 µm to 0.55 µm, wherein the average particle width is measured by scanning electron microscopy.

12. The coating composition according to any one of claims 1-7 or 11, the opacifier according to any one of claims 8 or 11, or the cellulose microparticle coating according to any one of claims 9-11, wherein, The cellulose microparticles are anionic, optionally, wherein: The cellulose microparticles are surface-modified with anionic sulfate half-ester groups; and / or The cellulose microparticles have an anionic charge density of 50 mmol / kg or more, preferably 100 mmol / kg or more, and more preferably 150 mmol / kg or more, wherein the anionic charge density is determined according to ISO 21400:2018.

13. The coating composition according to any one of claims 1-7 or 11-12, the opacifier according to any one of claims 7, 8 or 11-12, or the cellulose microparticle coating according to any one of claims 9-12, wherein, The surfactant is a nonionic surfactant, a cationic surfactant, or an amphoteric surfactant, preferably selected from polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, polyoxyethylene (20) sorbitan monolaurate, and alcohol ethoxylates (C9- ... 11 Ethoxylated alcohols), secondary alcohol ethoxylated compounds (C 11 -C 15 The group consisting of ethoxylated alcohols, polyethylene glycol trimethyl nonyl ether, hexadecyltrimethylammonium bromide (CTAB), and 3-(decyldimethylammonium)-propane-sulfonic acid inner salt, or combinations thereof; or The surfactant is a nonionic surfactant, preferably selected from polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, polyoxyethylene (20) sorbitan monolaurate, and alcohol ethoxylates (C9-C 11 Ethoxylated alcohols), secondary alcohol ethoxylated compounds (C 11 -C 15 The group consisting of ethoxylated alcohols and polyethylene glycol trimethyl nonyl ether, or combinations thereof.

14. The coating composition according to any one of claims 1-7 or 11-13, the opacifier according to any one of claims 6 or 9-13, or the cellulose microparticle coating according to any one of claims 9-13, wherein, The surfactant has a critical micelle concentration of 0.03 mM to 30 mM, preferably 0.04 mM to 25 mM, more preferably 0.05 mM to 10 mM, and even more preferably 0.05 mM 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.

15. A method for preparing a coating composition according to any one of claims 1-7 or 11-14, the method comprising: Cellulose microparticles having an average particle length of 0.2 µm to 20 µm and a surfactant, or a light-blocking agent according to any one of claims 6 or 9-12, are added to the carrier liquid; Optionally, the cellulose microparticles and surfactant, or the opacifier, are dispersed in the carrier liquid to provide the coating composition.

16. A method for forming a coating on a substrate, the method comprising: Apply the coating composition according to any one of claims 1-7 or 11-14 to the substrate, and The coating composition is dried to form a cellulose microparticle coating.

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