High-concentration wax emulsion for wood-based panels and method for production and application

Abstract

The invention relates to a method for producing a high-concentration wax emulsion, comprising mixing a water phase with wax under controlled pressure and temperature to achieve a dry matter content of at least 60%, wherein the wax phase is added in separate parts each dispersed in water at a specific level of shear. The produced wax emulsion show reduced viscosity compared to comparative processes leading to a better applicability. Wax emulsions are used in woodpanels as hydrophobing agents. Furthermor, the inventors show that dilution before use improves the water repellent properties of the dispersed wax, which is particularly advantageous for the high-concentrated wax emulsion produced according to the described production method that is part of the current invention.

Description

[0001] HIGH-CONCENTRATION WAX EMULSION FOR WOOD- BASED PANELS AND METHOD FOR PRODUCTION AND APPLICATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the formulation and application of high-concentration wax emulsions specifically designed for use in wood-based panels such as OSB (Oriented Strand Board), particleboard, and MDF (Medium Density Fiberboard). These wax emulsions comprise a dry matter content of at least 60%. The invention further encompasses a multi-step method for producing these high-concentration wax emulsions using different levels of shear to achieve the desired dry matter content, and a process for diluting the emulsions just before application. The wax emulsions are stabilized using lower quantities of emulsifiers compared to traditional formulations and may include additional components such as electrolytes, alkaline component, preservatives and antifoaming agents. This innovative approach results in improved water repellency, enhanced bonding properties, and reduced production and transportation costs.

[0004] BACKGROUND

[0005] Wax emulsions are extensively utilized in the wood panel industry to provide water-repellent properties to products such as OSB (Oriented Strand Board), particleboard, and MDF (Medium Density Fiberboard). Traditional wax emulsions typically have a lower solid content, around 40-60%, necessitating the use of significant quantities of emulsifiers and stabilizers to maintain homogeneity during production and application. The high concentration of emulsifiers not only increases production costs but can also adversely affect the bonding strength of the wood panels. Furthermore, the transportation and handling of emulsions with higher water content lead to increased logistical costs and complexities. The industry faces challenges in balancing the need for effective water repellency, cost-efficiency, and ease of application, with the current wax emulsions often falling short in one or more of these aspects.

[0006] SUMMARY OF THE INVENTION

[0007] This invention relates to the development of high-concentration wax emulsions with a dry matter content of at least 60%, designed specifically for use in wood-based panels such as OSB, particleboard, and MDF. The wax emulsions are formulated with reduced quantities of emulsifiers, electrolyte, alkaline components for pH control, and preservatives, based on the wax content of the emulsion. The emulsions also contain an antifoaming agent to ensure uniform application. The invention employs a novel production method involving a process that occurs in different steps with different shear levels, to achieve a lower viscosity despite the high solid content.

[0008] The emulsions are diluted just before application, ensuring a consistent and even coating on the wood panels, which enhances water repellency and bonding properties. Key advantages include reduced packaging waste, lower shipment weight, decreased carbon emissions, and enhanced water-repellent properties. The formulation is more eco-friendly due to the higher efficiency of the wax, the reduced use of emulsifiers and contributes to environmental sustainability.

[0009] The invention is based on the finding that a wax emulsion with a deliberately broadened particle size distribution provides a markedly higher wax efficiency in particleboard and OSB. This broadened particle size distribution is obtained by producing the emulsion in a sequence of mixing steps carried out at subsequently decreasing shear rates. In each step a different fraction of the wax phase is dispersed, and by lowering the applied shear rate from one step to the next the emulsion develops a wider range of particle sizes while remaining sufficiently stable for storage, transport and use.

[0010] Preferably, the resulting emulsion has a high dry matter content. The broadened particle size distribution reduces the viscosity and processability of the emulsion, particularly at high dry matter content, which allows it to be stored and transported with a significantly reduced water load without the typical downsides of a very viscous, difficult to process emulsion. This lowers energy consumption, storage volume and transport costs. The emulsion can then be diluted to a lower solids content shortly before its application onto wood particles without requiring any further processing steps. Importantly, the dilution does not narrow the particle size distribution created during the decreasing shear rate sequence, so the characteristic broad distribution is maintained up to the point of use.

[0011] It has been found that this broad particle size distribution leads to an increase in wax efficiency, as reflected by a reduction in water uptake and an improvement in water repellency of the resulting wood articles, for a given total amount of wax introduced into the board. This effect is particularly pronounced in OSB and particleboard applications. Although the same production method can be utilized for hydrophobing all wood articles, particularly including MDF and HDF, the improvement in wax efficiency is particularly pronounced for OSB and particleboards. Importantly, the improved wax efficiency obtained in the present method is achieved without increasing the amount of emulsifiers or surfactants in the formulation. Adjusting the particle size distribution by changing emulsifier or surfactant systems is known, yet such adjustments negatively affect the water repellency of the final wood article. In contrast, the present method creates the desired broad particle size distribution through the controlled use of decreasing shear rates, allowing a stable, high solids emulsion to be produced, transported and applied efficiently, thus maximising the hydrophobic performance of the final wood panel.

[0012] DETAILED DESCRIPTION OF THE INVENTION

[0013] The term "high-concentration wax emulsion" refers in the present invention to a wax emulsion with a dry matter content of at least 60%, which is designed for use in wood-based panels such as OSB, particleboard, and MDF. The dry matter content is measured using the ISO 1625 standard, which specifies the determination of non-volatile matter in wax emulsions. The dry matter content is determined by drying a sample of the emulsion at 105°C until a constant weight is achieved and calculating the percentage of the remaining solid material relative to the initial sample weight.

[0014] The term "wax phases" refers in the present invention to the main wax components of the emulsion, which can include microcrystalline wax, paraffin wax, synthetic waxes and biobased waxes. These waxes are characterized by their melting points and crystalline structures, with typically a melting point range of 30 to 90°C.

[0015] By the term "emulsifier" is meant in the present invention a substance used to stabilize the mixture of wax and water in the emulsion. Emulsifier on wax ratio's can be lower than in traditional wax emulsions due to the high concentration of the present invention. The effectiveness of emulsifiers in a specific application is determined to a great extent by the HLB (Hydrophilic-Lipophilic Balance) system.

[0016] The term "antifoaming agent" refers in the present invention to a substance used to prevent foam formation during the production and application of the wax emulsion. Antifoam SMI is an example of such an agent, which is typically a mineral oil-based compound.

[0017] The term "shear" is a shorter term for "shear rate" and refers to the velocity gradient generated in various emulsifying devices. Velocity gradients create turbulence leading to wax droplet breakup and thus lower particle size and more stable emulsions. Examples of common shear creating devices for emulsification are high pressure homogenisers, rotor-stator mixing devices, sonolators, colloid mills and microfluidisers.

[0018] By the term "homogenizing" is meant in the present invention the operation in which the water phase and the wax components are subjected to high shear to form a fine and uniform emulsion. This step is distinct from the normal mixing operations used earlier in the process for dispersing or pre-blending the components. Homogenizing is typically carried out in a high pressure homogenizer at a pressure between 20 and 500 bar, which generates the high shear rates required to obtain the desired particle size, viscosity and stability. In a homogenizer, the applied shear level is directly related to the homogenization pressure.

[0019] The term "diluting" refers in the present invention to the process of adding water to the high-concentration wax emulsion or adding high-concentration wax emulsion to water, just before its application to a wood panel. This step ensures that the emulsion has the appropriate consistency and properties for effective application and performance.

[0020] In an aspect, the invention pertains to wax emulsions with dry matter content higher than 35%, designed for use in wood-based panels such as OSB, particleboard, and MDF. These emulsions are formulated with a higher percentage of solid wax components, reducing the water content. The significant reduction in water content translates to lower transportation volumes and energy usage, thereby reducing carbon emissions and contributing to more sustainable manufacturing processes.

[0021] The high-concentration wax emulsions are produced using a high-shear mixing process under controlled pressure and temperature conditions. This method results in a lower viscosity of the wax emulsion compared to traditional methods, even with a higher solid content. The emulsions are designed to be diluted just before application, which reduces the need for emulsifiers and stabilizers, further lowering production costs and improving the overall efficiency of the wax.

[0022] Using a lower shear level to disperse a part of the dispersed phase further leads to lower energy use, a more sustainable process and a lower production cost.

[0023] In a further embodiment, the wax emulsions may contain varying amounts of solid content. Preferably, the dry matter content is between 60% and 75%. This flexibility allows for customization based on specific application requirements and manufacturing conditions.

[0024] The composition of the high-concentration wax emulsions includes a wax phase that can consist of more than one wax, which can be microcrystalline wax, paraffin -based, biobased wax or synthetic wax. These waxes are combined with a minimal amount of emulsifier, such ethoxylated fatty alcohol or polyethylene glycol fatty acid esters, a lignin derived product, or long-chain fatty acids such as stearic acid to stabilize the wax during the initial mixing process. An alkaline component such as potassium hydroxide, sodium hydroxide, triethanolamine, diethanolamine, monoethanolamine, morpholine or ammonia or a mixture of bases is included as a pH control agent, ensuring the emulsion maintains optimal properties during storage and application. Additives such as Mergal V615 and Acticide MV are incorporated as preservatives to increase the shelf-life of the emulsions, while Antifoam SMI is used to prevent foam formation during the mixing and application processes. The combination of these components results in a highly efficient wax emulsion that provides superior water-repellent properties and enhances the bonding strength of the wood panels.

[0025] Method for producing wax emulsionsln a second aspect, present invention relates to a method for producing wax emulsions comprising: dividing the wax phase into at least two separate fractions; adding each fraction of the wax phase to the bulk phase in a sequential manner; and mixing each fraction under shear, wherein each shear applied to each subsequent fraction differs from that applied to the preceding one. In a preferred embodiment of the second aspect, the present invention relates to a method for producing wax emulsions comprising dividing the wax phase into at least two separate fractions, adding each fraction of the wax phase to the bulk phase in a sequential manner, and mixing each fraction under a defined shear rate, wherein the shear rate applied to each subsequent fraction differs from the shear rate applied to the preceding one. In a preferred embodiment as an addition to the multi step process, the shear rate applied in each subsequent mixing step is reduced relative to the shear rate applied in the preceding step, thereby ensuring that only a first fraction of the wax phase is dispersed under the highest shear rate. This gradual reduction of shear rate results in a controlled droplet size distribution and a lower overall viscosity of the final emulsion while maintaining stability and homogeneity.

[0026] In a preferred embodiment, the wax and water phase are mixed using a high-shear mixing process. This process ensures that the wax particles are uniformly dispersed within the emulsion, resulting in a stable mixture with reduced viscosity.

[0027] In a preferred embodiment, the reduction of shear rate between steps is achieved by lowering the homogenization pressure in a high pressure homogenizer. In an alternative embodiment, the reduction is achieved by decreasing rotor speed in a rotor stator mixer or by attenuating energy input in a sonolator or microfluidizer. These reduction modes provide flexibility to adapt the decreasing shear principle to different shear generating devices without altering the overall process concept.

[0028] In another embodiment, the emulsion is typically produced using a multi-step process applying different shear levels in different steps of the process. The high-shear process may be a high pressure homogenizer operating at a pressure of 50 to 300 bar, more preferably between 100 and 250 bar, and most preferably between 150 and 200 bar. More preferably, additional dispersed phase is added between at least some of the steps of the multi-step process, i.e. in between applying different shear levels further amounts of wax phase are added to the mixture, which are then dispersed under shear. In a more preferred embodiment, the emulsion is produced in a multi-step high-pressure homogenization process in which the wax phase is dispersed in successive steps carried out at progressively decreasing homogenization pressures. More preferably, between each of these steps, an additional portion of the dispersed phase (wax phase) is introduced into the mixture, after which the mixture is subjected to the next homogenization step at the lower pressure. This sequence of adding further dispersed phase between steps and reducing the applied homogenization pressure between steps results in the controlled application of decreasing shear rates during the formation of the emulsion. Advantageously, this optimizes energy use and broadens the particle size distribution of the resulting emulsion.

[0029] In a preferred embodiment, the process comprises at least one high-pressure homogenisation step performed at a pressure above 100 bar, preferably above 125 bar, more preferably above 150 bar, and most preferably above 175 bar; and at least one later high-pressure homogenisation step performed at a pressure below 100 bar, preferably below 80 bar, more preferably below 65 bar, and most preferably below 55 bar. Preferably, additional wax is added prior to the subsequent step at lower pressure. Such a combination of an initial high-pressure step and at least one subsequent step at a considerably lower pressure provides a controlled decrease in shear during the formation of the emulsion, allowing the wax phase fractions added in the later steps to be dispersed under milder conditions. This approach enables a targeted broadening of the particle size distribution.

[0030] The operating temperature for the preparation of the wax emulsion is preferably between 50 and 100°C, more preferably between 60 and 90°C, more preferably between 70 and 80°C, most preferably around 75°C. These temperature ranges are advantageous as they ensure optimal mixing and stability of the emulsion components, while reducing global energy requirements.

[0031] In one embodiment, a first fraction of the mass of wax is added to the bulk phase and mixed under shear in a first step. In a preferred embodiment, the fraction of the mass of wax added based on mass of the emulsion in the first step is at least 10%. In a more preferred, the fraction of the mass of wax added based on mass of the emulsion in the first step is at least 20%. In an even more preferred, the fraction of the mass of wax added based on mass of the emulsion in the first step is at least 30%. In an even more preferred, the fraction of the mass of wax added based on mass of the emulsion in the first step is at most 60%, more preferably at most 50%, most preferably at most 40%.

[0032] In a preferred embodiment, each fraction of the mass of wax is added to the bulk phase and mixed under shear in subsequent sequential steps. In a further preferred embodiment, the fraction of the mass of the wax added in each step relative to the total mass of the wax in the final emulsion is at least 10%. The mass of each fraction is expressed relative to the total dry wax mass of the final emulsion. In a more preferred embodiment, the fraction of the mass of the wax added in each step relative to the total mass of the wax in the final emulsion is at least 20%. In an even more preferred embodiment, the fraction of the mass of the wax added in each step relative to the total mass of the wax in the final emulsion is at least 30%. In an even more preferred embodiment, the fraction of the mass of the wax added in each step relative to the total mass of the wax in the final emulsion is at least 40%. In another or further embodiment, part of the additives can be added in any subsequent step. In another or further embodiment, part of the additives can be added in every subsequent step.

[0033] In a preferred embodiment, the difference between the highest shear and the lowest shear applied in the different steps is at least 10%, more preferably at least 20%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 100%.

[0034] In another or further preferred embodiment, the shear rate in subsequent steps is reduced, more preferably the shear rate applied in each subsequent step is reduced relative to the shear rate applied in the immediately preceding step, by at least 5%, more preferably at least 8%, more preferably at least 10%, more preferably at least 12%, more preferably at least 15%, more preferably at least 20%, more preferably at least 25%, more preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 100%, more preferably at least 150%. The reduction in shear rate in each subsequent step (n+1) is measured relative to the step preceding it (n).

[0035] The improved water repellency imparted by the wax emulsions manufacture by the use of the two step process is advantageous for OSB and other wood-based panels that are exposed to moisture. The enhanced dimensional stability also contributes to the durability and longevity of the final product. Additionally, the reduced need for emulsifiers in the formulation lowers production costs and minimizes any adverse effects on the water uptake and swelling of the wood panels.

[0036] The lower transportation costs, due to the reduced water content during transport, and the improved performance of the emulsions in terms of water repellency and bonding strength make this invention highly competitive in the wood panel industry. Moreover, the reduced carbon emissions contribute to a more sustainable manufacturing process, aligning with global efforts to reduce environmental impact.

[0037] In summary, the high-concentration wax emulsions offer a cost-effective, efficient, and environmentally friendly solution for the wood panel industry. The innovative formulation and production methods ensure that the emulsions maintain stability and performance, providing enhanced water repellency and bonding properties in the final wood products.

[0038] In a preferred embodiment, the wax emulsion formulation also includes additives such as stabilizers, pH control agents, preservatives, and antifoaming agents. These additives are preferably present in small quantities to maintain the overall eco-friendliness of the product. The stabilizers may include electrolytes, preferably in the range of 0.05% to 0.5% by weight, more preferably between 0.1% and 0.4%, more preferably between 0.15% and 0.35%, more preferably between 0.17% and 0.3%, and most preferably around 0.25% by weight.

[0039] In a preferred embodiment, the wax emulsion formulation is prepared using a high-shear mixing process with controlled pressure and temperature. In an even more preferred embodiment, the high shear mixing process involves at least 2 different steps with different levels of high shear. This process results in a lower viscosity of the wax emulsion, making it easier to handle and apply, even with the higher solid content. The wax phase may be subdivided and each part may be added in a different step of the process whereby the level of shear varies between steps.

[0040] In an even more preferred embodiment, the mixing process is performed under high shear. More preferably, the mixing process is performed under high shear by high pressure homogenization. In an even more preferred embodiment, the mixing process is high pressure homogenization and homogenization pressure varies in different steps between 0 and 1000 bar, more preferably between 0 and 500 bar, even more preferably between 0 and 300 bar, most preferably between 0 and 250 bar, whereby the wax phase is subdivided and each part is added in a different step whereby also the homogenization pressure varies between the different steps.

[0041] In another preferred embodiment, the mixing process is high pressure homogenization and homogenization pressure varies in different steps between 25 and 1000 bar, more preferably between 25 and 500 bar, even more preferably between 25 and 300 bar, most preferably between 25 and 250 bar, whereby the wax phase is subdivided and each part is added in a different step whereby also the homogenization pressure varies between the different steps.

[0042] Wax emulsion

[0043] In a further aspect, the invention relates to a wax emulsion as obtainable by the second aspect of the invention. By producing a wax emulsion with a broad particle size distribution, preferably also having a high dry matter content, a high value intermediate product is obtained that is particularly advantageous for the later production of wood panel products.

[0044] The wax emulsion will now be defined in more detail. It is clear that the preferred wax emulsion obtained also is the preferred wax to be made by the process of the previous aspect; and the preferred wax emulsion to be used when producing wood panel items as outlined herein.

[0045] The preferred emulsifiers described above enable the preparation of stable wax emulsions with dry matter contents of 60 to 75 percent. During application, these concentrated emulsions can be diluted to lower solids to achieve improved distribution across wood chips.

[0046] In one embodiment the wax is a paraffin wax. In a more preferred embodiment, the paraffin wax contains between 0 and 40% oil as it is measured using method ASTM D721. In a more preferred embodiment, the paraffin wax contains between 5 and 35% oil as it is measured using method ASTM D721. In an even more preferred embodiment, the paraffin wax contains between 5 and 25% oil as it is measured using method ASTM D721. In a preferred embodiment, the paraffin wax is a petroleum slack wax.

[0047] In a preferred embodiment, the wax emulsion comprises a slack wax originating from solvent refining processes, wherein the slack wax preferably has a normal paraffin content between 30 and 75 percent by weight. Slack waxes of this type are advantageous in wood based applications because the less pronounced paraffin crystallinity promote efficient hydrophobing of wood chips, fibers and strands, enabling consistent water repellency at low dosage.

[0048] In a further embodiment, the wax is a fully refined wax obtained by additional deoiling of slack wax. In another embodiment the wax is a synthetic wax. In a more preferred embodiment the wax is a wax obtained from syngas through the Fisher Tropsch process. Examples of Fisher Tropsch waxes are Sarawax SX50 and Sarawax SX70, produced by Shell. In another more preferred embodiment the wax is a alpha-olefin wax. Examples of alpha olefine waxes are NAO CPChem C24-28 or NAO CPChem C30+, produced by Chevron Phillips Chemical. In jet another embodiment, the wax is a wax obtained from the recycling of plastics using the pyrolysis process. In a more preferred embodiment, the wax is a wax obtained from the recycling of polyethylene using the pyrolysis process. In still another embodiment, the wax is a partly or fully biobased. The wax can be a fully or partially hydrogenated triglyceride or the wax can be an ester based on fatty acid. Triglycerides and fatty acids can be from plant or animal origin.

[0049] The concentration of wax in the emulsion is preferably between 20% and 70%, more preferably between 30% and 65%, more preferably between 40% and 65%, most preferably between 45% and 65%. This range ensures optimal water-repellency while maintaining the stability of the emulsion.

[0050] The wax used in the emulsion preferably has a melting point between 30°C and 70°C, more preferably between 45°C and 65°C, more preferably between 50°C and 65°C, and most preferably around 60°C. This melting point range is preferred to ensure that the wax remains solid at room temperature but melts during the application process, allowing for uniform coverage and penetration into the wood fibers.

[0051] In a preferred embodiment, the dispersed phase may further comprise a paraffinic mineral oil, a naphthenic mineral oil or a triglyceride oil. Suitable triglycerides oils include nonhydrogenated or fully or partially hydrogenated vegetable oils or animal fats. The presence of such co components may improve low temperature flexibility and may contribute to improved penetration of the hydrophobic material into wood fibers, thereby enhancing water repellency under fluctuating humidity.

[0052] In a preferred embodiment, the formulation reduces environmental impact by minimizing the use of chemical emulsifiers or surfactants. In a preferred embodiment, the wax emulsion formulation includes a reduced amount of emulsifiers, which results in a more eco-friendly product, minimizing the environmental footprint. The ratio of the mass of emulsifier on the mass of wax in the formulation is preferably between and 1% and 10 % by weight, more preferably between 1% and 8 by weight, more preferably between 2 and 5 % by weight, and most preferably between 2.5 % and 4 % by weight, relative to the weight of the emulsion. This reduction in emulsifier content is achieved without compromising the stability and performance of the wax emulsion. In a further embodiment, the emulsifier or surfactant system used in the wax emulsion may comprise anionic, non ionic or cationic surfactants or combinations thereof. These surfactants may be used alone or in any mixture to adjust stability, droplet size, viscosity or long term storage characteristics of the emulsion. Typical emulsifiers used are ethoxylated fatty alcohols, polyalkyleneglycol esters of fatty acids, sulphonated surfactants such as sodium dodecyl sulphate, polyalkylene glycol block copolymers, fatty acids such as stearic acid and salts thereof, Kraft lignin or sulfonated lignin, or other natural emulsifiers, which further enhance the eco-friendly nature of the product.

[0053] Preferably, the formulation includes natural or biodegradable emulsifiers, such as fatty acids salts, polysaccharides and proteins, that replace traditional chemical emulsifiers. More preferably, the concentration of these natural emulsifiers ranges between 0.1% and 5.0% by weight of the total formulation, more preferably between 0.5% and 3%, more preferably between 2% and 3%, most preferably around 2.5%. By using these alternative emulsifiers, the formulation not only maintains the stability and performance of the wax emulsion but also significantly reduces the environmental footprint associated with its production and use.

[0054] In a particularly preferred embodiment, the emulsifier comprises a fatty acid soap consisting of a fatty acid and a counterion. The fatty acid is preferably a CIO to C24 fatty acid, more preferably a saturated fatty acid with a chain length above C16. Most preferred are technical stearic acid mixtures. Further more preferably, the stearic acid has an having an iodine value below 3 grams iodine per 100 grams, preferably below 2 grams iodine per 100 grams, and even more preferably below 1 gram iodine per 100 grams. These fatty acids provide excellent cost to performance ratios and form stable soaps that promote fine particle sizes under high shear conditions. In a preferred embodiment, the counterion is selected from potassium, sodium or water soluble amines. In a more preferred embodiment, the counterion is an amine selected from monoethanolamine, diethanolamine or triethanolamine. Triethanolamine may further improve storage stability and robustness of the emulsion by forming stronger soap structures. These emulsifiers are particularly suitable for wood panel applications because they generate stable emulsions at the high solid contents required for economical transport.

[0055] In another embodiment, the emulsifier comprises a non ionic surfactant selected from ethoxylated fatty alcohols, fatty acid esters, polyalkylene glycol block copolymers, esters of fatty acid with polyalkyleneglycol or esters of saturated C12 to C24 alcohols with polyethylene glycol having a molecular weight between 100 and 3000. These emulsifiers may be used alone or in combination with fatty acid soaps to tailor the stability of the emulsion and may contribute to narrower particle size distribution, which is beneficial for achieving uniform water repellency in wood based panels.

[0056] In another embodiment, suitable anionic surfactants include, without limitation: fatty acid soaps of CIO to C24 fatty acids, lignin sulphonate, alkyl naphthalene sulphonate, petroleum sulphonate, Turkey red oil, alpha olefin sulphonate, secondary alkane sulphonate, linear alkyl sulphonates, linear alkyl benzene sulphonates, sodium alkyl sulphates, ammonium alkyl sulphates, sodium alkyl ether sulphates, ammonium alkyl ether sulphates and phosphate ester surfactants. These anionic surfactants may be selected depending on the required balance between cost efficiency, droplet stability and processing robustness. In another embodiment, the emulsifier comprises non ionic surfactants, preferably selected from ethoxylated fatty alcohols, fatty acid esters, esters of fatty acids with polyalkyleneglycol and esters of saturated C12 to C24 alcohols with polyethylene glycol having a molecular weight between 100 and 3000, polyalkylene glycol block copolymers. These non ionic emulsifiers are compatible with both slack waxes and synthetic waxes and can be used to achieve narrow particle size distributions or to fine tune viscosity after homogenisation. In aother embodiment, the surfactant system may comprise one or more cationic surfactants. Suitable examples include quaternary ammonium compounds and cationically modified starch, such as starch carrying quaternary ammonium groups. These cationic emulsifiers may be used to adjust emulsion stability under acidic or neutral conditions or to improve adhesion of the wax to certain wood species. In another embodiment, lignin derived surfactants or emulsifiers may be used, including lignin sulphonates or sulfonated lignin. These materials may be used alone or in combination with other surfactants and provide an advantageous route toward partially biobased emulsifier systems suitable for wood panel applications. In a further embodiment, any of the above anionic, non ionic or cationic surfactants may be used in combination. In a particular preferred embodiment, a fatty acid soap, preferably those described herein, may be used together with an ethoxylated fatty alcohol or with a fatty acid esterified with a polyalkylene glycol copolymer. This combinations may offer improved stability of the concentrated emulsion, enhanced robustness during dilution or improved spreading in the wood blend during pressing.

[0057] Moreover, in another preferred embodiment, the wax emulsion may optionally be formulated to have a pH range that is favorable for the stability of the natural emulsifiers and additional stabilizing agents. Preferably, the pH of the formulation is between 5 and 10, more preferably between 7 and 9, more preferably between 8 and 9, most preferably around 8,5. This pH range ensures optimal performance and stability of the wax emulsion while minimizing any potential environmental impact.

[0058] Overall, these preferred embodiments of the formulation not only reduce the environmental impact by minimizing the use of chemical emulsifiers but also maintain or enhance the performance and stability of the wax emulsion. The use of natural or biodegradable components ensures that the formulation is more sustainable and environmentally friendly, aligning with current trends and regulations aimed at reducing the environmental footprint of industrial products.

[0059] In a preferred embodiment, the high-concentration wax emulsion with dry matter content of at least 60% is designed for use in wood-based panels. The formulation preferably includes a lower water content, which results in a lighter shipment weight and reduced container volume. This reduction in weight and volume is advantageous as it contributes to decreased carbon emissions during transportation, aligning with sustainability goals in the industry.

[0060] The wax emulsion is optionally prepared using a high-shear mixing process, which is preferably conducted under controlled pressure and temperature conditions. This process more preferably results in a lower viscosity of the wax emulsion, even with the higher solid content. The lower viscosity is beneficial as it makes the emulsion easier to handle and apply, thus improving the efficiency of the application process.

[0061] In a further preferred embodiment, the wax emulsion is diluted just before application to the wood panel. This dilution step is optional but preferable as it improves the efficiency of the wax in reducing the water uptake of board, especially in OSB and particleboard, which can impact both the cost. Lower wax concentration can have a positive effect on the bonding strength of the wood panel; Withous being bound to theory, we assume that the wax efficiency is improved by a better blending, wetting and distribution of the wax in the final blend. Thus the diluted emulsion demonstrates enhanced water-repellent properties and improved bonding with adhesives, leading to a higher quality final wood product. This effect is particularly pronounced in OSB and particleboard. In summary, the preferred embodiments of the high-concentration wax emulsion provide significant advantages in terms of cost reduction, improved performance, and sustainability. The lower water content, reduced need for emulsifiers, and enhanced application efficiency make this invention a highly competitive solution for the wood panel industry.

[0062] In a preferred embodiment, the wax emulsion includes an electrolyte as a stabilizer, preferably to increase the long-term stability of the wax emulsion and to maintain the homogeneity of the wax emulsion over extended storage periods. This stabilization is more preferably achieved by mitigating issues related to separation and aggregation of the wax particles within the emulsion. This is particularly beneficial when the emulsion is subjected to varying temperature conditions during storage and transport. By preventing the separation of the wax phase from the aqueous phase, the electrolyte more preferably ensures that the emulsion remains in a usable state even after prolonged periods of inactivity. In a further preferred embodiment, the addition of the electrolyte may also enhance the compatibility of the wax emulsion with other additives, such as biocides, antifoams, and pH control agents. This compatibility is preferably crucial in maintaining the overall performance characteristics of the emulsion. More preferably, the electrolyte does not interfere with the efficacy of these additives, thereby preserving the intended properties of the final wood-based product.

[0063] The electrolyte is a water soluble salt such as the combination of an ammonium derivative or an alkali or earth-alkali metal ion with a halogen anion, a carbonate, a carbonic acid derivative or the anion of an oxidated sulphur or nitrogen atom containing molecule. Typical examples are NaCI or KCL The concentration of electrolyte is preferably between 0.1% and 0.01% by weight of the total emulsion composition, more preferably between 0.05% and 0.01%. This range ensures optimal stabilization without negatively impacting other properties of the emulsion.

[0064] The preferred method of incorporating the electrolyte into the wax emulsion involves its addition during the initial mixing stage. This stage preferably includes the combination of the water phase and wax components under controlled pressure and temperature conditions. The electrolyte powder is more preferably dissolved in the water phase before the addition of the wax components. This approach ensures that the electrolyte stabilizer is uniformly distributed throughout the emulsion, thereby maximizing its stabilizing effect.

[0065] Overall, the inclusion of electrolyte powder as a stabilizer in the wax emulsion preferably results in a more stable, homogeneous product that is less prone to separation and aggregation. This stabilization is more preferably achieved without compromising the performance characteristics of the emulsion, ultimately leading to improved efficiency and cost-effectiveness in wood panel applications.

[0066] In a preferred embodiment, the wax emulsion includes a alkaline component as a pH control agent. The amount of pH control agent is preferably between 0.5% and 1.5% by weight, more preferably between 0.6% and 1.4%, more preferably between 0.7% and 1.3%, more preferably between 0.8% and 1.2%, and most preferably between 0.9% and 1.1% by weight. The inclusion of the alkaline component is especially beneficial for stabilizing the pH level within the wax emulsion, which ensures consistent performance and extends the shelf life of the product. The pH stabilization provided by the alkaline component is crucial for maintaining the emulsion's stability during storage and application, thereby preventing pH fluctuations that could lead to destabilization. By maintaining a stable pH, the wax emulsion remains homogenous and effective over extended periods, reducing the need for additional stabilizers and preservatives.

[0067] In another preferred embodiment, the use of the alkaline component not only stabilizes the pH but also interacts synergistically with other components of the emulsion, such as emulsifiers, to enhance the overall stability and performance of the product. This interaction can lead to improved water repellency and bonding properties when the emulsion is applied to wood-based products. The enhanced performance is particularly noticeable in OSB, particleboard, MDF and HDF applications, where consistent quality and durability are critical. The combination of these stabilizers ensures that the emulsion remains effective under varying storage conditions and during the dilution process prior to application. This dual-stabilizer approach provides a robust solution for maintaining the integrity of high-concentration wax emulsions, making them more reliable and cost-effective for industrial use.

[0068] The pH control agent is referred to as alkaline component and is preferably a strong base such as potassium hydroxide or sodium hydroxide, a water-soluble amine or a combination of different water-soluble amines. In a more preferred embodiment the alkaline component is a amine. In an even more preferred embodiment the alkaline component is an ethoxylated amine such as ethanolamine, diethanolamine, triethanolamine or ammonia.

[0069] Preferably, the alkaline component is added in a quantity able to neutralize 30 to 200% of all acidic groups present in the wax emulsion. More preferably, the alkaline component is added in a quantity able to neutralize 40 to 150% of all acidic groups present in the emulsion. Even more preferable the alkaline component is added in a quantity able to neutralize 50 to 100 % of all acidic groups present in the wax emulsion. Most preferably the alkaline component is added in a quantity able to neutralize 50 to 85% of all acidic groups present in the emulsion.

[0070] In a preferred embodiment, the wax emulsion composition includes biocides. The inclusion of these biocides prevent microbial growth which could otherwise degrade the emulsion, and ensures that the wax emulsion maintains its effectiveness over a prolonged duration. Preferably, the biocide contains a formaldehyde releasing component. More preferably the biocide contains both a formaldehyde releasing components and isothiazolines. Even more preferably the biocide contains a formaldehyde releasing component and a combination of chloromethyl- and methyl-isothiazolines. Preferably, the concentration of biocides in the wax emulsion ranges from 0.05% to 0.3% by weight. More preferably, the concentration is between 0.07% and 0.15%, even more preferably between 0.08% and 0.12%, and most preferably around 0.1% by weight.

[0071] The combined use of formaldehyde releasing components and isothiazolines in these preferred concentrations ensures that the wax emulsion remains stable and effective for a longer period, which is particularly beneficial for industrial applications where prolonged storage may be required. The extended shelf life provided by these preservatives reduces the need for frequent production batches, thereby lowering overall production costs and improving operational efficiency. Overall, the inclusion of a combination of a formaldehyde releasing component and isothiazolines in the wax emulsion composition not only extends its shelf life but also ensures that the emulsion retains its water-repellent properties and effectiveness over time. This makes the wax emulsion highly suitable for use in the production of OSB and other woodbased panels, where long-term stability and performance are critical.

[0072] An example of a isothiazoline compound is Mergal V615, which is a broad -spectrum biocide effective against bacteria, yeasts, and fungi. An example of a formaldehyde releasing biocide is Bodoxin AE.

[0073] In a preferred embodiment, the wax emulsion comprises an antifoaming agent. The inclusion of the antifoaming agent is optionally aimed at ensuring a uniform application of the wax emulsion to the wood panel surfaces. The antifoaming agent may preferably relate to substances that reduce or prevent the formation of foam during the mixing and application processes. More preferably, the antifoaming agent can be a silicone-based antifoams or a non-silicone-based organic antifoams such as a mineral oil-based antifoams. In one embodiment, the antifoaming agent used is a silicone-based antifoam due to its high efficiency in foam suppression and stability under a wide range of temperatures.

[0074] In another embodiment, the antifoaming agent is a mineral oil based antifoam due to its high cost efficiency.

[0075] The antifoaming agent is preferably included in the wax emulsion in an amount ranging from 0.05% to 2% by weight of the total emulsion. More preferably, the amount ranges from 0.1% to 0.8% by weight, even more preferably from 0.1% to 0.5% by weight, and even more preferably from 0.1% to 0.3% by weight and most preferably around 0.2%, by weight. The precise amount of the antifoaming agent may be adjusted based on the specific formulation of the wax emulsion and the intended application process, ensuring optimal performance and cost-efficiency.

[0076] In a further preferred embodiment, the use of the antifoaming agent enhances the water-repellent properties of the wood panels. This enhancement is optionally achieved by promoting a more uniform distribution of the wax emulsion across the wood surface, thereby ensuring consistent coverage and penetration. The antifoaming agent may also contribute to the overall quality of the wood panels by minimizing defects such as bubbles or voids that could compromise the structural integrity and aesthetic appearance of the final product.

[0077] Additionally, in another preferred embodiment, the antifoaming agent may facilitate the handling and application of the wax emulsion. This facilitation is optionally achieved by reducing the viscosity of the emulsion, making it easier to pump, spray, or otherwise apply to the wood panels. The reduced viscosity may also enable more precise control over the application process, leading to more efficient use of the wax emulsion and potentially reducing waste.

[0078] In the most preferred embodiment of the wax emulsion, it comprises, more preferably essentially consists of:

[0079] a) a slack wax having a normal paraffin content between 30 and 75 wt.%, preferably 45 and 75 wt.%;;

[0080] b) an emulsifier, preferably said emulsifier chosen from a fatty acid soap, a non-ionic emulsifier or a mixture thereof, wherein said fatty acid soap consists of a fatty acid and a counterion, wherein said fatty acid is selected from CIO to C24 fatty acids, and wherein said counterion is selected from: potassium, sodium or amines, most preferably mono, di or triethanolamine; and

[0081] c) water.

[0082] Such waxes are particularly well suited for present process and use for the production of wood panels, especially OSB and particleboard, providing great water repellency. The wax emulsion preferably has a dry matter content of at least 60 wt.%, more preferably at least 65 wt.%, more preferably at least 70 wt.% when produced, transported and stored. However, it is preferably diluted to 30-50 wt.% (immediately) prior to the production of the wood panel particularly for OSB and particleboard. Dilution is neither necessary nor as advantageous for MDF and HDF applications.

[0083] In summary, the inclusion of an antifoaming agent in the wax emulsion is preferably aimed at improving the uniformity of application, enhancing the water-repellent properties, and overall quality of the wood panels, while also facilitating the handling and application process. Wood panel productin an aspect, the invention relates to a wood-based panel such as OSB, particleboard, HDF or MDF, most preferably OSB or particleboard, comprising a wax from a wax emulsion produced according to one of the previous aspects; or comprising a wax emulsion produced by the method of the second aspect. In a preferred embodiment, the wood panel comprises the wax emulsion obtained by the process described above or the wax emulsion defined herein as a preferred composition. The controlled droplet size distribution, high dry matter content and low emulsifier levels of this wax emulsion contribute directly to the lower water repellency and the better dimensional stability of the finished wood panel. Further more preferably, the invention relates to a wood panel, selected from the group oriented strand board (OSB), particleboard, high density fiberboard (HDF) or medium density fiberboard (MDF) comprising:

[0084] 50 - 95 wt.% wood chips, fibers, flakes or strands

[0085] 3 - 20 wt.% glue

[0086] 0.1 to 5 wt%, more preferably 0.5 to 3.0 wt. % wax emulsion as described herein.

[0087] In an preferred embodiment, the invention pertains to a high-concentration wax emulsion with at least 60 % dry matter content, designed for use in wood -based panels such as OSB, particleboard, HDF and MDF, most preferably OSB and I or particleboard. The high-concentration wax emulsion is characterized by its ability to be diluted just before application, which significantly enhances its utility and efficiency in industrial applications, without the need for further processing steps and allowing concentrated transport and storage. This innovative approach involves a unique formulation and production method that reduces the need for emulsifiers, thereby lowering production costs and improving the environmental footprint of the manufacturing process.

[0088] In a preferred embodiment, the wood material comprises wood chips, fibers, flakes or strands derived from softwood or hardwood species. Suitable softwoods include pine, spruce and cedar, and suitable hardwoods include oak, beech, birch and poplar. The use of the preferred wax emulsion in panels containing either softwood or hardwood offers consistent hydrophobing performance. For MDF or HDF panels which preferably use softwood fibers, the emulsions described herein promote uniform penetration into shorter fibers and contribute to reduced edge swell. In another embodiment, the wood panel comprises a mixture of fresh wood and recycled wood. In particleboard, the recycled content may be up to 100 percent. The preferred wax emulsion provides reliable hydrophobic performance even in panels containing recycled fractions which may have variable surface chemistry and porosity.

[0089] In a preferred embodiment, the wood panel comprises urea formaldehyde glue or a mixture of urea formaldehyde with melamine. These glues typically require higher concentrations in woodpaneles, such as 5.0 to 15.0%, most preferably about 10.0% urea formaldehyde by weight. In another embodiment, the wood panel comprises MDI glue. MDI glues are typically used in lower quantities, such as 3.0 to 7.0%, most preferably 3.0 to 5.0% by weight; relative to the weight of the wood panel. The wax emulsion described herein is compatible with both systems because the particle size and melting behavior promote spreading of the wax during pressing without interfering with adhesive cure.

[0090] In a preferred embodiment, the wood panel comprises between 0.1 and 5.0 wt.%, more preferably 0.2 and 3.0 percent by weight of the wax emulsion. This concentration is effective to impart water repellency while avoiding excess wax that may interfere with internal bond strength. In a more preferred embodiment, the wood panel comprises between 0.3 and 1.5 percent by weight of wax emulsion. These ranges provide a practical balance between hydrophobing efficiency, cost and mechanical performance.

[0091] Method for wood panel production

[0092] In a further aspect, the invention relates to a process for producing a wood panel using a concentrated wax emulsion. This process uses the wax emulsions described herein, including the wax emulsions produced by the multi step method and the preferred wax emulsions defined by their composition. The process enables efficient distribution of the wax across the wood material after a controlled dilution step and before hot pressing. This approach results in improved water repellency, dimensional stability and overall panel quality.

[0093] In this aspect, the invention provides a wood panel production process comprising the steps of producing or providing a concentrated wax emulsion having a dry matter content greater than 60 percent by weight, diluting the concentrated wax emulsion with water to form a diluted wax emulsion, bringing into contact through mixing, blending, coating, or other methods the diluted wax emulsion with wood chips, fibers, flakes or strands and glue to form a wood blend, and forming the wood blend into a wood panel. The concentrated wax emulsion is preferably a wax emulsion obtained according to the processes described above, or a wax emulsion defined herein as a preferred composition. In a preferred embodiment, the method comprises the steps of:

[0094] producing a concentrated wax emulsion in accordance with any one of claims 1 to 7, thereby forming a concentrated wax emulsion;

[0095] diluting said concentrated wax emulsion, thereby forming a diluted wax emulsion; bringing into contact said diluted wax emulsion in an amount of 0.1 to 5.0 wt.%, preferably in an amount of 0.1 to 3.0 wt.%; with 50-95 wt.% of woodchips, fibers, flakes or strands and 3 to 20 wt.% of glue, thereby forming a wood blend; and forming said wood blend to a wood panel.

[0096] The core of this invention lies in its ability to maintain a high dry matter content, specifically at least 60 %, which is a significant improvement over traditional wax emulsions that typically contain around 50-60% dry matter content. The reduction in water content not only decreases transportation costs but also minimizes packaging waste, contributing to environmental sustainability. The high dry matter content ensures that the wax emulsion is more concentrated, leading to better water repellency and enhanced bonding properties when applied to wood-based panels; yet upon use is still diluted to maximize wax efficiency. Additionally, the production process results in a broad and targeted particle size distribution, which enhances wax efficiency (in terms of the water-repellency of wood panels made thereof), lowers the wax emulsion viscosity improving its handing through devices such as pumps, filters and spraying nozzles, and stabilizes the concentrated emulsion.

[0097] The production method of the high-concentration wax emulsion involves a multi-step high-shear mixing process, typically using a high pressure homogenizer. This method where the emulsion is subjected to different levels of shear results in a wax emulsion with lower viscosity despite its higher solid content. In a preferred embodiment, only part of the wax is sheared at the highest shear level. This method ensures that the emulsion is easier to handle and apply, which is particularly beneficial for industrial applications where efficiency and ease of use are critical.

[0098] The high-concentration wax emulsion can be diluted just before application, which further reduces the need for emulsifiers. This aspect of the invention is particularly advantageous as it lowers production costs and enhances the overall performance of the wax emulsion. The diluted emulsions demonstrate improved water repellency and bonding properties, thereby increasing the efficiency of both the wax and adhesives used in the final wood product.

[0099] In summary, the preferred embodiments of the wax emulsion formulation and production method offer significant advantages, including improved durability, enhanced water-repellent properties, reduced production costs, and better handling characteristics. These benefits make the wax emulsion particularly suitable for use in Oriented Strand Board (OSB), particleboard, High Density Fiberboard (HDF) and Medium Density Fiberboard (MDF) and other wood-based products, where water repellency and bonding strength are critical performance factors.

[0100] Overall, the controlled homogenization and pumping pressures, combined with the optimized use of emulsifiers and stabilizers, preferably result in a wax emulsion that is more efficient, cost-effective, and stable. This improved emulsion is optionally easier to handle and apply, leading to enhanced performance in wood-based products.

[0101] In a preferred embodiment, the concentrated wax emulsion used in the process has a dry matter content between 60 and 75 percent by weight. The concentrated emulsion may be produced on site or provided from an external production unit and may be stored or transported before dilution. The concentrated emulsion is stable during storage due to its controlled droplet size distribution, emulsifier system and wax composition.

[0102] In a preferred embodiment, the dilution method ensures a consistent and even coating across the wood panel, enhancing the overall quality and reliability of water repellency performance. This method preferably involves diluting the high-concentration wax emulsion just before application to achieve an optimal balance between viscosity and coverage. The emulsio water dilution ratio is preferably between 1:0.2 and 1:5, more preferably between 1:0.2 and 1:4, even more preferably between 1:0.2 and 1:3, even more preferably between 1:0.2 and 1:2, even more preferably between 1:0.5 and 1:1.5 and most preferably between 1:0.5 and 1:1. This ensures that the wax emulsion maintains its stability while providing a uniform coating on the wood surface.

[0103] In a preferred embodiment, the diluted wax emulsion is not further processed after dilution. In particular, the diluted emulsion is not passed through a homogenizer, sonolator, microfluidizer, rotor stator mixer or any high shear device. In a further embodiment, no emulsifier, no surfactant and no additive is added to the diluted emulsion after dilution. The diluted emulsion is therefore used in the wood blend in the form in which it is obtained by simple mixing with water.

[0104] In a preferred embodiment, the diluted wax emulsion is not further processed after dilution. In particular, the diluted emulsion is not passed through a homogenizer, sonolator, microfluidizer, rotor stator mixer or any other device that generates high shear. No emulsifier, surfactant or additive is added after dilution. The diluted emulsion is therefore used in the wood blend in the form in which it is obtained by simple mixing with water. Further high shear treatment after dilution is generally not desirable, since for OSB and particleboard it usually does not provide a meaningful benefit and may even reduce wax efficiency. This reduction can occur because additional high shear narrows the particle size distribution and removes the larger droplets that contribute positively to water repellency in these products.

[0105] In an alternative embodiment, the diluted wax emulsion is subjected to an additional processing step after dilution. In this embodiment, the diluted emulsion may be exposed to a high shear treatment, for example by passing it through a homogenizer, sonolator, microfluidizer or rotor stator mixer. In a more preferrable embodiment, the diluted wax emulsion is subjected to a high-shear homogenisation step, more preferably with a high pressure homogeniser. This post-dilution treatment is a trade-off between a reduction in the particle size of the dispersed wax phase, and narrowing of the particle size distribution and higher energy costs. This trade-off generally favours no homogenisation for OSB and particleboard; but can be favourable for homogenisation for MDF and HDF applications.

[0106] In a preferred embodiment, the glue added to the wood blend comprises urea formaldehyde glue, optionally in combination with melamine. In another embodiment, the glue comprises MDI glue, typically used in OSB and particleboard. The wax emulsions described herein are compatible with both systems and do not interfere with adhesive distribution or adhesive cure.

[0107] In a preferred embodiment, the diluted wax emulsion is added to the wood material before the glue addition. In another embodiment, the diluted wax emulsion and glue are added simultaneously. In a further embodiment, the diluted wax emulsion is added after the glue addition if required by the equipment layout or processing constraints. All orders of addition remain compatible with the preferred characteristics of the diluted emulsion.

[0108] In a further preferred embodiment, the wood blend comprising wood material, glue and diluted wax emulsion is formed into a mat and pressed under heat and pressure to form the wood panel. Press temperatures are typically between 150 and 250 degrees Celsius. Press time and pressure depend on the board thickness, glue system and desired final density. During pressing, the wax droplets melt and spread across the surfaces of the wood particles or fibers, creating a hydrophobic layer that contributes to reduced water uptake and swelling.

[0109] In a preferred embodiment, the use of a concentrated wax emulsion that is diluted before blending results in improved hydrophobing efficiency compared to conventional emulsions having solids contents around 40 to 50 percent. Panels produced with diluted concentrated emulsions exhibit lower thickness swell and lower water uptake under standardized testing conditions such as EN317. Without wishing to be bound by theory, this improvement is believed to arise from enhanced distribution and spreading of wax droplets during hot pressing and the lower emulsifier on wax ratio.

[0110] In a further embodiment, the process is used for the production of particleboard, oriented strand board, medium density fiberboard or high density fiberboard. The wax emulsions described herein deliver improved performance across these panel types due to their controlled droplet size and viscosity characteristics. Most preferably, the wood panel is chosen from particleboard or oriented strand board (OSB). It was surprisingly found that the increase in wax efficiency, achieved by the broadening of the particle size distribution by the method of present application was most pronounced for these applications. Without wishing to be bound by theory, it is expected to be the result of the production and forming method of these types of wood panels.

[0111] In a further preferred embodiment, the dilution process may involve the use of hard water, which is preferred for its ability to maintain the emulsion's stability and performance characteristics. The water temperature during dilution is preferably between 5°C and 40°C, more preferably between 10°C and 35°C, even more preferably between 15°C and 30°C, and most preferably around 20°C. This temperature range ensures that the wax emulsion remains in a liquid state, facilitating easy application and penetration into the wood fibers.

[0112] Additionally, in another preferred embodiment, the method of application may involve first a mixing process of the concentrated emulsion and water to make sure that the diluted emulsion is homogeneous, resulting in a uniform and consistent coating of the wood particles in the wood panel. In an even more preferred embodiment, this mixing process of the concentrated emulsion in water is done using an in-line static mixer. EXAMPLES

[0113] The present invention will now be further exemplified with reference to the following examples. The present invention is in no way limited to the given examples or to the embodiments presented in the figures.

[0114] Two water-based emulsions of a paraffin slack wax, Prowax 1385 from Exxon, were produced according to the composition in table 1. The emulsifier was composed of a combination of a biobased emulsifier, a fatty acid named Radiacid 0444 and an ethoxylated fatty alcohol, Lutensol TO8 of BASF. The Lutensol TO8 was first diluted to 80% in water before use. 25% ammonia solution in water was used as an alkaline component. In both formulations, a biocide, Preventol D9 produced by Lanxess, was added for preservation against microbial growth and an antifoaming agent, Antifoam SMI produced by GOVI, was added to prevent application problems due to excessive foaming.

[0115] Table 1. composition of paraffin wax emulsions

[0116]

[0117] Further, 2 different methods were used to produce the paraffin wax emulsions with the composition shown in table 1.

[0118] In the first production method, first, the soft water, Lutensol TO8 solution, Radiacid 0444 and 25 % ammonia were mixed together in the softened water at a temperature between 70 and 80 °C to produce an aqueous phase. In a second step, Prowax 1385 at a temperature between 70 and 80 °C was added. Both fractions of Prowax 1385 indicated in Table 1 were added at the same time in the first production method. Both aqueous and wax phase were mixed together to produce a homogeneous emulsion with coarse particle size. This coarse emulsion was then homogenized using a APV1000 lab-scale high pressure homogenizer (produced by APV) at 180 bar first in a closed circuit for a time sufficient to have the emulsion volume passed once on average over the homogenizer and then homogenized once more whereby the emulsion was now directed towards the tube-in-shell cooler. The temperature during homogenization was always kept between 70 and 80 °C. In the tube-in-shell cooler the emulsion is cooled down to a temperature between 20 and 30 °C, before the Antifoam SMI and the Preventol D9+ are added under gentle mixing. In the second production method, 33,33% of the Prowax 1385 was added before the start of the homogenization in closed loop at 180 bar and the remaining 66.67% was only added just before the second homogenization step towards the tube-in-shell cooler. This second homogenization step was performed at 50 bar in the second production method. Except for the above mentioned differences, the second production method follows the procedure described for the first production method. Emulsion properties are shown in Table 2. The "viscosity" is measured using a Brookfield viscometer DV / E using a spindle 3 at 5 rpm. The pH is measured using a glass electrode.

[0119] Table 2. properties of paraffin wax emulsions

[0120]

[0121] Table 2 shows the properties of the different emulsions produced. Production method 2 gave larger particles, a broader particle size distribution and a lower viscosity than an emulsion made according to the same formulation with method 1.

[0122] The emulsions were then tested as hydrophobing agent in the production of wood panels. First about 387g of wood chips were mixed during 4 minutes in an LGB100 lab blender (IMAL Pal) with a paraffin emulsion with composition according to one of both formulas in Table 1 and produced according to one of both production methods described above. In the examples 'Ex.

[0123] 1 diluted' and 'Ex. 2 diluted', the paraffin wax emulsion was first diluted to 33 %(m / m) solid content before application whereas in the examples 'Ex. 1' and 'Ex. 2' comparative example 'C. Ex. l'the emulsion was applied undiluted. The final wax concentration in the particleboard was 0,7 weight percent on dry wood. Then, the treated wood chips were mixed during 4 minutes in the LGB100 lab blender with a 65% aqueous solution of an El ureum formaldehyde glue. The final concentration is 9 mass % dry glue on dry wood.

[0124] The codes used in Table 2, Table 3, Fig. 1 and Fig. 2 consist of 3 parts separated by underscores. In the first part, the use of formula 1 (high wax concentration) is indicated by 'Forml' whereas the use of the formula 2 (standard wax concentration) is indicated by 'Form2'. In the second part, the first production method is indicated by 'PM1', whereas the second production method is indicated by 'PM2'. In the third part 'UNDIL' means we did not dilute before use whereas 'DIL' means we diluted the emulsion to 33% (m / m) dry matter content just application to the glued wood chips.

[0125] The wood chip mass containing the glue and the wax emulsion is then formed into a 26 x 22 cm mat with a thickness as even as possible. This mat is then pressed for 150 seconds using a lab press (Model GEM40T produced by JBT Engineering). The final board thickness was determined by 12 mm metal spacers and the press plate temperatures were both 200 °C. Boards were equilibrated for 1 week in ambient conditions. Four 5 x 5 cm pieces were cut out or each board and subjected to water uptake and swelling test according to NBN EN317:1993. A linear regression of both swelling and wateruptake versus board density was performed in order to correct for variation introduced by varying board densities. The calculated values on the linear regression curve at 575 kg / m3are reported in table 3. In Fig. 1 and Fig. 2 the reference value of the board made with the undiluted 65% wax emulsion produced with the first production method was always substracted. So the Fig. 1 and Fig. 2 rather indicate the change in swelling and water uptake respectively compared a the reference emulsion.

[0126] Table 3. Water uptake and swelling results at 0,63% dry matter from emulsion in the board.

[0127]

[0128] The data in Table 3 and Fig. 1 & 2 show that emulsion added at a lower wax concentration in the emulsion gives a lower water uptake. This is surprising since the amount of dry matter from emulsion and thus the composition of the boards are basically the same.

[0129] Comparing the emulsions produced according to formula 1, the sample produced with production method 2 gave clearly a lower viscosity than the one produced with production method 1, as indicated in Table 2. This resulted in a better applicability of the emulsion in the wood panel production process and ultimately also a lower water uptake and swelling result (Table 3 and Figs. 1 & 2).

[0130] Fig. 1 displays the swelling result after substraction of reference swelling result at 0,63 %(m / m) dry matter from emulsion in the board. Reference = Forml_PMl_UNDIL.

[0131] Fig. 2 displays the water uptake result after substraction of reference water uptake result at a dry matter from emulsion concentration of 0,63 %(m / m) in the board. Reference = FORM1_PM1_UNDIL. It is clear that the wax emulsions produced by the method of the invention result in a greater water repellency in the final wood panel. This effect is obtained by dilution prior to use, while advantageously allowing transport and storage of the concentrated formulation.

[0132] It is supposed that the present invention is not restricted to any form of realization described previously and that some modifications can be added to the presented example of fabrication without reappraisal of the appended claims. For example, the present invention has been described referring to OSB, particleboard, MDF and HDF, but it is clear that the invention can be applied to other wood-based products requiring water repellency, for instance or to other industrial applications requiring high-concentration emulsions.

[0133] It is clear that the method according to the invention, and its applications, are not limited to the presented examples.

[0134] The present invention is in no way limited to the embodiments described in the examples and / or shown in the figures. On the contrary, methods according to the present invention may be realized in many different ways without departing from the scope of the invention.

Claims

CLAIMS1. A method for producing a wax emulsion comprising a dispersed phase comprising a wax within an aqueous bulk phase, the method comprising: providing an aqueous bulk phase and a wax phase to be dispersed; dividing the wax phase into at least two separate fractions; sequentially adding each fraction of the wax phase to the bulk phase; and mixing each fraction under a shear rate, wherein the shear rate applied to subsequent steps is reduced by at least 10%.

2. A wax emulsion production process according to any of the preceding claims, wherein the shear rate applied to subsequent steps is reduced by at least 50%.

3. A wax emulsion production process according to any of the preceding claims, wherein the mass of at least one fraction is at least 10% of the mass of the total wax content in the wax emulsion.

4. A wax emulsion production process according to any of the preceding claims, wherein the mass of each fraction is at least 10% of the mass of the total wax content in the wax emulsion.

5. A wax emulsion production process according to any of the preceding claims, wherein the mixing each fraction under shear rate is achieved by a high pressure homogenizer, a sonolator or a microfluidizer, preferably a high pressure homogenizer.

6. A wax emulsion obtained by a process according to any of claims 1-5, said wax emulsion having a dry matter content of between 60 and 75 % by weight.

7. A wax emulsion according to claim 6, said wax emulsion having an emulsifier content less than 8 wt.%, more preferably less than 6 wt.% of the wax content by weight.

8. A wax emulsion according to claim 6 or 7, said wax emulsion comprising, preferably essentially consisting of:a) a slack wax having a normal paraffin content between 30 and 75 wt.%, preferably 45 and 75 wt.%;b) an emulsifier, preferably said emulsifier chosen from a fatty acid soap, a nonionic emulsifier or a mixture thereof, wherein said fatty acid soap consists of a fatty acid and a counterion, wherein said fatty acid is selected from CIO to C24 fatty acids, and wherein said counterion is selected from: potassium, sodium or amines, most preferably mono, di or triethanolamine; andc) water.

9. A wood panel, selected from the group oriented strand board (OSB), particleboard, high density fiberboard (HDF) or medium density fiberboard (MDF) comprising:50 - 95 % wood chips, fibers, flakes or strands3 - 20 % glue0.1 to 5.0wt. %, preferably 0.1 to 3.0 wt.% wax emulsion according to any of claims 6-8, or a wax emulsion obtained by a process according to any of claims 1-5.

10. A wood panel production process, comprising the steps of:producing a concentrated wax emulsion in accordance with any one of claims 1 to 5, thereby forming a concentrated wax emulsion;diluting said concentrated wax emulsion, thereby forming a diluted wax emulsion;bringing into contact said diluted wax emulsion in an amount of 0.1 to 5.0 wt.%; with 50-95 wt.% of woodchips, fibers, flakes or strands and 3 to 20 wt.% of glue, thereby forming a wood blend; andforming said wood blend to a wood panel.

11. A wood panel production process according to claim 9, wherein said concentrated wax emulsion has a dry matter content greater than 60%.

12. A wood panel production process according to any of claims 9-10, wherein said diluted wax emulsion has a dry matter content between 25 and 55 wt.%, preferably 33 to 45 wt.%.

13. A wood panel production process according to any one of claims 10 to 12, wherein the emulsion is mixed before use with a quantity of water between 50 and 150% of the original weight of the emulsion.

14. A wood panel production process, wherein said concentrated wax emulsion is stored and I or transported prior to diluting said concentrated wax emulsion.

15. A wood panel production process, wherein said wood panel is chosen from:particleboard, oriented strand board (OSB), medium density fiberboard (MDF), high density fiberboard (HDF), preferably particleboard or oriented strand board (OSB).

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